wÄrtsilÄ technical journal -...

012015Tw

enty

four

7.

WÄRTSILÄ TECHNICAL JOURNAL

ENERGY

Defining true flexibility A comparison of gas-fired power generating technologies

INTERNAL COMBUSTION

ENGINEGAS TURBINEVS.

10

52

28 Achieving energy security The role of fuel flexibility and low water use

More power with less money Fuel efficiency in key role

MARINE

New LNG Tug opens a market First LNG Tug to operate in the Middle East

34

COVER STORY

pages4–33

IN DETAIL

ENERGY THEME

Comparing ICEs with GTs

issue no. 01.2015in detail

ENERGY

MARINE

FUTURE

Contents

iPad

Web

Gas-fired power generation

– a technology overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Defining true flexibility – a comparison

of gas-fired power generating technologies . . . . . . . . 10

Gas-fired efficiency in part-load

and pulse operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Power plant performance under

extreme ambient conditions . . . . . . . . . . . . . . . . . . . . .22

Achieving energy security:

the role of fuel flexibility and low water use . . . . . . .28

New LNG Tug opens a market . . . . . . . . . . . . . . . . . . . 34

The new Wärtsilä Steerable Thruster family . . . . . . 40

The new Wärtsilä LNGPac™

– a step towards greener shipping . . . . . . . . . . . . . . 44

Increasing market share for

Wärtsilä Controllable Pitch Propellers . . . . . . . . . . . . 48

More power with less money . . . . . . . . . . . . . . . . . . . . . .52

Smart monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Publisher: Wärtsilä Corporation, John Stenbergin ranta 2, P.O. Box 196, FIN-00531 Helsinki, Finland | Editor-in-Chief: Ilari Kallio | Managing editor and editorial office: Virva Äimälä | English editing: Tom Crockford, Crockford Communications | Editorial team: Tomas Aminoff, Marit Holmlund-Sund, Christian Hultholm, Dan Pettersson, Dinesh Subramaniam, Minna Timo, Susanne Ödahl | Layout and production: Spoon | Printed: April 2015 by PunaMusta, Joensuu, Finland ISSN 1797-0032 | Copyright © 2015 Wärtsilä Corporation | Paper: cover Lumiart Silk 250 g/m², inside pages UPM Fine 120 g/m²

E-mail and feedback: [email protected]

THIS ISSUE OF IN DETAIL is also available on iPad as a Wärtsilä iPublication app from Apple's Appstore, as well as in a browsable web version at http://indetailmagazine.com/.

Internal combustion engines (ICEs) have been around since the 19th century . These days, they are more relevant than ever when it comes to power generation and transportation .

Today’s energy markets, characterized by an increasing amount of renewable power, call for fast start up and high ramp rate capa-bilities . Superior efficiency also in part load makes ICE the most suitable option for this kind of operation, far better than other technologies currently on the market like combined cycle gas turbines (CCGTs) and coal-fired plants . ICE also offers superior performance in extreme ambient conditions like high altitudes and high temperatures .

According to the United Nations, by 2025 1 .8 billion people will be living in countries or regions with absolute water scarcity, and two-thirds of the world population could live under water stress conditions . If you consider the map of where energy demand is expected to increase the most and compare it to a map of what parts of the world will suffer from the biggest water shortage, you’ll quickly come to the conclusion that these maps are identical in many places around the world . At Wärtsilä we have the ideal offering for covering the needs these maps present: our Dry Flexicycle power plants consume nearly 96% less water than a CCGT plant of similar size .

Flexibility is not just about fast start up and other operational capabilities . The current oil price fluctuations are a reminder to us all that fuel flexibility is also very important . The capability to switch between various liquid and gaseous fuels is not only economical but comes with a lower risk too . Having said that, in the long run the world is increasingly turning towards gas: we see more gas solutions everywhere, on different kind of vessels . One of the latest is an LNG tug we will deliver to the Middle East .

Our solutions go beyond engines – our broad offering covers all related gas equipment . Please acquaint yourselves with our latest LNGPac solution that not only has improved interfaces for installation and lower costs of operation, but also offers even more reliability, making it attractive to both shipyards and ship operators . All this neatly packed for better space utilisation .

We are constantly scouting out new things to enhance our custom-ers’ life . In this process, we trust open innovation and team up with startups for a very agile way of trying out new things . In this issue you can get a sneak preview on how one might monitor engines in the future .

Enjoy your reading!

Ilari Kallio Vice President of R & D, Ship Power Engines Editor-in-Chief of In Detail

3in detail

WÄRTSILÄ TECHNICAL JOURNAL | WWW.WARTSILA.COM

MORE ON PAGE 40 MORE ON PAGE 56MORE ON PAGE 22

Power plant performance under extreme ambient conditions.

The new Wärtsilä Steerable Thruster family.

With a glance.A new take on engine monitoring.

Wärtsilä has power plants operating in the harshest climates around the world.

First field applications include the propulsion units for an offshore vessel and a harbour tug.

Together with Korulab, Wärtsilä built a prototype for monitoring engines from your wrist.

STATING THE CASE: ICE VERSUS GT

The world’s power systems need flexibility

– internal combustion engines can provide it

In this issue of In Detail, the Energy section features a theme topic: internal combustion engines (ICE) vs. gas turbines (GT). The differences between these two technologies, as well as their pros and cons, will be thoroughly reviewed from various angles.

Dawn Santoianni, Managing Director of a technical communications firm and an accomplished writer on energy and environmental issues, will dive deeply into this topic. Ms. Santoianni is a combustion engineer by degree and has an impressive resumé. For instance, she was appointed by the U.S. Secretary of Energy to the National Coal Council, a federal advisory committee that provides guidance and recommendations on general policy matters related to coal. She is also a faculty member of The Oxford Princeton Programme, writing and teaching

courses on coal production, its utilization and regulations. In her position as a Topic Director and subject matter expert for the Our Energy Policy Foundation, Ms Santoianni helps facilitate substantive dialogue on energy policy issues for policymakers, the media and the public.

With more than 20 years experience in the energy industry matters, she has worked collaboratively with utilities, municipalities, industry groups, research organizations, and engineering consultants. Her regulatory and policy experience includes testifying before a congressional subcommittee on the impacts of a proposed environmental regulation, producing an executive report for members of Congress, providing commentary on energy policy, regulatory impact analysis, and the editing of regulatory compliance documents.

4 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]

[ ENERGY / IN DETAIL ]

Gas-fired power generation – a technology overviewAUTHOR: Dawn Santoianni

5in detail

WÄRTSILÄ TECHNICAL JOURNAL 01.2015

International policies to reduce carbon emissions and increase the deployment of renewable energy have posed challenges for maintaining a reliable, efficient electric supply. As a result, flexible gas-fired generation has taken a central role in power systems around the world.

With natural gas producing only half the carbon emissions as coal per kilowatt-hour, displacing coal-fired power with natural gas-based power can help achieve emissions reductions goals. But perhaps more important, as variable renewable energy production from wind and solar are added to electric grids, the need for responsive, dispatchable power is increasing. Gas turbines and internal combustion engines (ICEs) are flexible generating assets that are filling this crucial role.

The use of gas turbines for generating electricity dates back to 1939 [1]. Today, gas turbines are one of the most widely-used power generating technologies in part because of their load-following capabilities. ICE power plants are based on the well-known reciprocating engine technology

used in automobiles, trucks, construction equipment, marine propulsion, and backup power applications. ICE technology is being deployed for a wide range of service, from baseload operation to distributed energy installations where reliable, fast-ramping power is needed.

Combustion occurs continuously in gas turbines, as opposed to ICEs in which combustion occurs intermittently. The differences in how the technologies produce electricity from fuel affect key performance characteristics. This article presents an overview of gas turbines, ICEs and combined cycles, highlighting the fundamental differences between the technologies. Subsequent articles in this issue explore the performance of gas turbine and ICE technologies from

6 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


flexibility, efficiency and derating perspectives.

How do gas turbines work?

In gas turbines, an air-fuel mixture is burned, creating hot gases that spin a turbine to produce power. It is the production of hot gas during fuel combustion, not the fuel itself that gives gas turbines their name. Although gas turbines can be designed to burn alternative fuels, the vast majority gas turbines worldwide operate on natural gas. The thermodynamic process used in gas turbines is the Brayton cycle.

Gas turbines are comprised of three primary sections: the compressor, the combustion chamber (or combustor) and the turbine. The compressor can be either axial flow or centrifugal flow. Axial flow compressors are more common in power generation because they have higher flow rates and efficiencies. These types of compressors are comprised of multiple stages of rotating and stationary blades (or stators) through which air is drawn in parallel to the axis of rotation and incrementally compressed as it passes through each stage. The acceleration of the air through the rotating blades and diffusion by the stators increases the pressure and reduces the volume of the air. Although no heat is added, the compression of the air also causes the temperature to increase. (Figure 1)

The compressed air is mixed with fuel injected through nozzles. The fuel and compressed air can be pre-mixed or the compressed air can be introduced directly into the combustor. The fuel-air mixture ignites under constant pressure conditions and the hot combustion products (gases) are directed through the turbine where it expands rapidly and imparts rotation to the shaft. The turbine is also comprised of stages, each with a row of stationary blades (or nozzles) to direct the expanding gases followed by a row of moving blades. The rotation of the shaft drives the compressor to draw in and compress more air to sustain continuous combustion. The remaining shaft power is used to drive a generator which produces electricity. Approximately 55 to 65 percent of the power produced by the turbine is used to drive the compressor. To optimize the transfer of kinetic energy from the combustion gases to shaft rotation, gas turbines can have multiple compressor and turbine stages.

Because the compressor must reach a certain speed before the combustion process is continuous – or self-sustaining – initial momentum is imparted to the turbine rotor from an external motor, static frequency converter, or the generator itself. The compressor must be smoothly accelerated and reach firing speed before fuel can be introduced and ignition can occur. Turbine speeds vary widely by manufacturer and design, ranging from 2000 revolutions

per minute (rpm) to 10,000 rpm. Initial ignition occurs from one or more spark plugs (depending on combustor design). Once the turbine reaches self-sustaining speed – above 50% of full speed – the power output is enough to drive the compressor, combustion is continuous, and the starter system can be disengaged.

Enhancing gas turbine performance

The fuel-to-power efficiency of a gas turbine is optimized by increasing the difference (or ratio) between the compressor discharge pressure and inlet air pressure. This compression ratio is dependent on the design. Gas turbines for power generation can be either industrial (heavy frame) or aeroderivative designs. Industrial gas turbines are designed for stationary applications and have lower pressure ratios – typically up to 18:1. Aeroderivative gas turbines are lighter weight compact engines adapted from aircraft jet engine design which operate at higher compression ratios – up to 30:1 [2]. They offer higher fuel efficiency and lower emissions, but are smaller and have higher initial (capital) costs. Aeroderivative gas turbines are also more sensitive to the compressor inlet temperature.

The temperature at which the turbine operates (firing temperature) also impacts efficiency, with higher temperatures leading to higher efficiency. However, turbine inlet temperature is limited by the thermal

Fig. 2 – Spark-ignited ICE during compression stroke. Fig. 1 – Three primary sections of gas turbines are the compressor, the combustion chamber and the turbine.

7in detail


conditions that can be tolerated by the turbine blade metal alloys. Gas temperatures at the turbine inlet can be 1200ºC to 1400ºC, but some manufacturers have boosted inlet temperatures as high as 1600ºC by engineering blade coatings and cooling systems to protect metallurgical components from thermal damage.

Because of the power required to drive a gas turbine compressor, energy conversion efficiency for a simple cycle gas turbine power plant is typically about 30 percent, with even the most efficient designs limited to 40 percent. A large amount of heat remains in the exhaust gas, which is around 600ºC as it leaves the turbine.

How do internal combustion engines work?

In ICEs, the expansion of hot gases pushes a piston within a cylinder, converting the linear movement of the piston into the rotating movement of a crankshaft to generate power. ICEs are characterized

by the type of combustion: spark-ignited (SG) or compression-ignited, also known as diesel. The SG engine is based on the Otto cycle, and uses a spark plug to ignite an air-fuel mixture injected at the top of a cylinder. In the Otto cycle, the fuel mixture does not get hot enough to burn without a spark, which differentiates it from the Diesel cycle. In diesel engines, air is compressed until the temperature rises to the auto-ignition temperature of the fuel. As the fuel is injected into the cylinder, it immediately combusts with the hot compressed air and expanding combustion gases push the piston to the bottom of the cylinder.

Each movement of the piston within a cylinder is called a stroke. ICEs are described by the number of strokes to complete one power cycle and the speed of crankshaft (expressed in revolutions per minute, rpm). For electric power generation, four-stroke engines are predominately used. During the intake stroke, the premixed

air and fuel (SG engines) or air (diesel engines) is drawn into the cylinder as the piston moves down to “bottom dead center” position. During the compression stroke in SG engines, the air-fuel mixture is compressed by the piston and ignited by a spark from a plug. Auto-ignition in SG engines is prevented with proper limits on the compression ratio. (Figure 2)

In diesel engines, the fuel is injected into the cylinder near the end of the compression stroke when the air has been compressed enough to reach the auto-ignition temperature. Combustion of the air-fuel mixture causes an accelerated expansion of high pressure gases, which push the piston to the bottom of the cylinder during the power stroke, imparting rotation to the crankshaft. Combustion occurs intermittently – only during the power stroke – whereas in gas turbines combustion occurs continuously. As the piston is returned to the top of the cylinder

Fig. 3 – Engine hall at Goodman Energy Center in Kansas, USA showing Wärtsilä ICEs.

8 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


during the exhaust stroke, the products of combustion (exhaust gases) are pushed out an exhaust valve. Multiple cylinders are connected to the crankshaft, oriented so that while some pistons are imparting rotation to the crankshaft during their power strokes, other pistons are being pushed back to the top of the cylinders during their exhaust strokes.

Optimizing ICE performance

The size and power of an ICE is a function of the volume of fuel and air combusted. Thus, the size of the cylinder, the number of cylinders and the engine speed determine the amount of power the engine generates. By boosting the engine’s intake of air using a blower or compressor – called supercharging – the power output of the ICE can be increased. A commonly used supercharger is a turbocharger, which uses a small turbine in the exhaust gas path to extract energy for driving a centrifugal compressor.

Diesel engines are generally more efficient than SG engines, but also produce more nitrogen oxides (NOx), sulfur dioxide (SO2), and particulate matter (PM). SO2 and PM formation is a function of the fuel, with natural gas producing low emissions. The formation of NOx is coupled with combustion temperature. In SG engines, premixing of air with the fuel to produce “lean” conditions (more air than is needed for combustion) has the effect of lowering the combustion temperature and impeding NOx formation.

In a power plant, many SG or diesel ICEs are grouped into blocks called generating sets: every engine is connected to a shaft which is connected to its electric generator. These generating sets provide modular electric generating capacity and come in standardized sizes, ranging from four (4) to 20 MW. Wärtsilä ICE power plants are highly efficient with simple cycle efficiencies of 46 to 49 percent, surpassing the performance of steam electric or simple cycle gas turbine power plants. (Figure 3)

Increasing efficiency with combined cycle

To increase the overall efficiency of electric power plants, multiple processes can be combined to recover and utilize the residual heat energy in hot exhaust gases. The term “combined cycle” refers to the combining of multiple thermodynamic cycles to generate

power. Combined cycle operation employs a heat recovery steam generator (HRSG) that captures heat from high temperature exhaust gases to produce steam, which is then supplied to a steam turbine to generate additional electric power. The process for creating steam to produce work using a steam turbine is based on the Rankine cycle. After exiting the steam turbine, the steam is sent to a condenser which routes the condensed water back to the HRSG.

The HRSG is basically a heat exchanger, or rather a series of heat exchangers. It is also called a boiler, as it creates steam for the steam turbine by passing the hot exhaust gas flow from a gas turbine or ICE through banks of heat exchanger tubes. The HRSG can rely on natural circulation or utilize forced circulation using pumps. As the hot exhaust gases flow past the heat exchanger tubes in which hot water circulates, heat is absorbed causing the creation of steam in the tubes. The tubes are arranged in sections, or modules, each serving a different function in the production of dry superheated steam. These modules are referred to as economizers, evaporators, superheaters/reheaters and preheaters.

The economizer is a heat exchanger that preheats the water to approach the saturation temperature (boiling point), which is typically supplied to a thick-walled steam drum. The drum is located adjacent to finned evaporator tubes that circulate heated water. As the hot exhaust gases flow past the evaporator tubes, heat is absorbed causing the creation of steam in the tubes. The steam-water mixture in the tubes enters the steam drum where steam is separated from the hot water using moisture separators and cyclones. The separated water is recirculated to the evaporator tubes. Steam drums also serve storage and water treatment functions. An alternative design to steam drums is a once-through HRSG, which replaces the steam drum with thin-walled components that are better suited to handle changes in exhaust gas temperatures and steam pressures during frequent starts and stops. In some designs, duct burners are used to add heat to the exhaust gas stream and boost steam production; they can be used to produce steam even if there is insufficient exhaust gas flow.

Saturated steam from the steam drums or once-through system is sent to the superheater to produce dry steam which

is required for the steam turbine. Steam conditions acceptable for the steam turbine are dictated by thermal limits of the rotor, blade, and casing design. Preheaters are located at the coolest end of the HRSG gas path and absorb energy to preheat heat exchanger liquids, such as water/glycol mixtures, thus extracting the most economically viable amount of heat from exhaust gases.

Combined cycle gas turbines – operational limitations

The overall efficiency of fuel-to-electric power conversion for gas turbines can be as low as 30 percent. This means that two-thirds of the latent energy of the fuel ends up wasted, much of it as thermal energy in the hot exhaust gases from the combustion process. By recovering that waste heat to produce more useful work in a combined cycle configuration, gas turbine power plant efficiency can reach 55 to 60 percent. In combined cycle gas turbine (CCGT) plants, the output produced by the steam turbine accounts for about half of the CCGT plant output.

There are many different configurations for CCGT power plants, but typically each GT has its own associated HRSG, and multiple HRSGs supply steam to one or more steam turbines. For example, at a plant in a 2x1 configuration, two GT/HRSG trains supply to one steam turbine; likewise there can be 1x1, 3x1 or 4x1 arrangements. The steam turbine is sized to the number and capacity of supplying GTs/HRSGs.

Designs and configurations for HRSGs and steam turbines depend on the exhaust gas characteristics, steam requirements, and expected power plant operations. Because the exhaust gases from a gas turbine can reach 600ºC, HRSGs for GTs may produce steam at multiple pressure levels to optimize energy recovery; thus they often have three sets of heat exchanger modules – one for high pressure (HP) steam, one for intermediate pressure (IP) steam, and one for low pressure (LP) steam. The high pressure steam in a large CCGT plant can reach 40 – 110 bar. With a multiple-pressure HRSG, the steam turbine will have multiple steam admission points. In a three-stage steam turbine, HP, IP and LP steam produced by the HRSG is fed into the turbine at different points.

There are operational limitations

Fig. 4 – Wärtsilä Flexicycle power plant based on ICEs.

9in detail


associated with operating gas turbines in combined cycle mode, including longer startup time, purge requirements to prevent fires or explosions, and ramp rate to full load. As the HRSGs are located directly downstream of the gas turbines, changes in temperature and pressure of the exhaust gases cause thermal and mechanical stress. When CCGT power plants are used for load-following operation, characterized by frequent starts and stops or operating at part-load to meet fluctuating electric demand, this cycling can cause thermal stress and eventual damage in some components of the HRSG [3]. The HP steam drum and superheater headers are more prone to reduced mechanical life because they are subjected to the highest exhaust gas temperatures.

Important design and operating considerations are the gas and steam temperatures that the module materials can withstand; mechanical stability for turbulent exhaust flow; corrosion of HRSG tubes; and steam pressures that may necessitate thicker-walled drums. To control the rate of pressure and temperature increase in HRSG components, bypass systems can be used to divert some of the GT exhaust gases from entering the HRSG during startup.

The HRSG takes longer to warm up from cold conditions than from hot conditions. As a result, the amount of time elapsed since last shutdown influences startup time. When

gas turbines are ramped to load quickly, the temperature and flow in the HRSG may not yet have achieved conditions to produce steam, which causes metal overheating since there is no cooling steam flow. In 1x1 configurations, the operation of the steam turbine is directly coupled to the GT/HRSG operation, limiting the rate at which the power plant can be ramped to load.

Flexicycle: combined cycle efficiency with responsiveness

The FlexicycleTM power plant is a combined cycle power plant with unique characteristics based on Wärtsilä gas or dual-fuel ICEs. Because ICEs convert more of the fuel energy into mechanical work, they have higher simple cycle efficiencies, averaging near 50 percent. The exhaust gases from ICEs are around 360ºC, much lower temperature than GT exhaust. Due to the lower exhaust gas temperatures, HRSGs designed for ICE power plants are much simpler in design, creating steam at one pressure level – approximately 15 bar. The steam turbine process adds approximately 20% to the efficiency of the Flexicycle power plant. (Figure 4)

In a Flexicycle power plant, each ICE generator set has an associated HRSG. Bypass valves are used to control the admission of steam to the steam turbine when an engine set is not operating. One engine can be used to preheat all the HRSG

exhaust gas boilers with steam to keep the HRSGs hot and enable fast starting. Flexicycle power plants combine the advantages of high efficiency in simple cycle and the modularity of multiple engines supplying the steam turbine. The steam turbine can be run with only 25 percent of the engines at full load, or 50 percent of the engines at half load. For a 12-engine power plant of around 200 megawatts (MW), this means only three of the engines need to be operating to produce enough steam to run the steam turbine. The result is a very efficient power plant that retains the operational agility of a power plant based on simple-cycle engines.

References

[1] “Neuchâtel Gas Turbine.” ASME. The American

Society of Mechanical Engineers, n.d. Web. 27 Jan.

2015. <https://www.asme.org/about-asme/who-we-

are/engineering-history/landmarks/135-neuchatel-

gas-turbine>.

[2] Almasi, Amin. “Large Aero-Derivative Gas

Turbines for Power Generation.” Power Engineering.

PennWell Corporation, 01 Jan. 2012. Web. 27 Jan.

2015. <http://www.power-eng.com/articles/print/

volume-116/issue-1/features/large-aero-derivative-

gas-turbines-for-power-generation.html>.

[3] Aurand, Jonathan D. “HRSG Cycling

Assessment.” CCJ Online Combined Cycle

Journal. CCJ Online Inc., n.d. Web. 27 Jan. 2015.

<http://www.ccj-online.com/2q_2012-outage-

handbook/hrsg-cycling-assessment/

10 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


Defining true flexibility – a comparison of gas-fired power generating technologiesAUTHOR: Dawn Santoianni

Power plant flexibility – the ability to rapidly adjust output up or down as demand and system loads fluctuate – is recognized as a vital tool to manage variable renewable energy production and provide grid support services. Wärtsilä power plants set the standard for true flexibility due to their rapid startup time, fast ramping capability and modular design.

Increasing penetration of variable renewable energy sources presents challenges for transmission grid operators to maintain electric reliability. The intermittency in wind and solar loads is managed with redundant generating capacity that can quickly respond to these fluctuations, and has predominately been served by coal and gas-fired units that are synchronized to the grid but operating at part load. Flexible power generation that can be rapidly brought online reduces the inefficiency of

relying on part load operation. Two primary measures of flexibility are startup time and ramp rate. Transmission system operators define such “quick-start” or “non-spinning” reserve as generation capacity that can be synchronized to the grid and ramped to capacity within 10 minutes [1].

Whereas conventional steam cycle generators (based on the Rankine cycle) can take more than 12 hours to reach full load, gas turbines and internal combustion engines (ICEs) can be dispatched in

Wärtsilä modular power plant comprised of multiple ICE generating units provides output flexibility.

11in detail


minutes. Startup time is a significant metric for flexibility, but comparison of different technologies and designs is complicated by the way startup time is measured by different manufacturers. The startup time quoted can be from push of the start command or from ignition. In the case of gas turbines, this difference in “start” definition can be as much as 20 minutes. Further, it is important to differentiate between the ramp time to full load versus partial load.

Gas turbine startup

During startup, a gas turbine undergoes a sequence of increasing compressor spin to reach firing speed, ignition, turbine acceleration to self-sustaining speed, synchronization, and loading. There are numerous thermo-mechanical constraints during startup of the gas turbine, including limits on airflow velocity through the compressor blades to prevent stall, vibrational limits, and combustion temperature limits to prevent turbine blade

fatigue, with the significant parameter being the turbine inlet temperature.

In combined cycle operation, the heat recovery steam generator (HRSG) imposes additional thermal limitations, as the high temperature environment subjects HRSG components to thermal stress [2]. The HRSG is directly coupled to the gas turbine, so changes in turbine exhaust gases induce flow, temperature, and pressure gradients within the HRSG. These gradients must be carefully controlled to prevent adverse impacts such as material fatigue, creep (damage caused by high temperatures) and corrosion [3]. In addition, the steam turbine can restrict the gas turbine loading rate if the steam temperature leaving the HRSG exceeds steam turbine limits. To avoid this, the gas turbine is ramped to hold points (held at steady load) to allow steam temperatures and pressures to rise slowly within allowable material limits.

It takes longer to start the HRSG and steam turbine from cold conditions than from hot conditions. The definition of

“hot” conditions varies by manufacturer, but is generally defined as within eight (8) to 16 hours of HRSG shutdown. As a result, the amount of time elapsed since last shutdown greatly influences startup time. Once-through HRSGs are used by some manufacturers to overcome the startup thermal and pressure limitations that exist with steam drums.

Combined cycle gas turbines (CCGTs) are also subject to purge requirements to prevent auto-ignition from possible accumulation of combustible gases in the gas turbine, HRSG and exhaust systems. The purge is required before the unit is restarted. Purge times depend on the boiler volume and air flow through the HRSG, and are typically set to about 15 minutes. This purge time adds to the overall start time.

In order to enable faster startup and ramping, CCGT manufacturers have attempted to decouple the gas turbine startup from the HRSG and steam turbine warm-up. Bypass systems are used to isolate the steam turbine, ultra-low nitrogen

Fig. 1 – Loading and unloading of a Wärtsilä 34 gas power plant.

Wärtsilä 34 gas power plant

1 12 23 / 0 3 5 5 6 7 8 mins

80 80

100 100

Load %

Cycle #1 Cycle #2

Load %

70 70

90 90

60 60

10 10

20 20

30 30

40 40

50 50

2 min to full load

0.5 min to full syncronisation

Min. down-time: 5 min

Spinning reserves• Ramp rate > 100%/min• Frequency balancing

Non-spinning reserves• Available in 30 sec & full output in 2 min

• No fuel consuption & no emissions• No wear

Min. load per genset: 30% (*)

Min. up-time: 0 min

1 min full unloading

(*) A power plant with e.g. 10 gensets can correspondlingly operate at 3% of its total nominal output.

12 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


oxides (NOx) combustion systems are used to reduce emissions while ramping, and attemperators maintain steam temperatures within appropriate limits [4]. A “purge credit” allows the system purge to be completed at shutdown, eliminating the requirement for a redundant purge at next startup [5]. The purge credit can only be used in some HRSGs that have no duct burners and where the gas turbine is fired on natural gas only. These improvements have resulted in higher CCGT ramp rates and startup times of about 30-35 minutes, about half the time for conventional hot start that would require purge and gas turbine holds. However, rapid cycling imposes increased CCGT maintenance costs [6]. In simple cycle, published start times for gas turbines are about 10 to 15 minutes.

ICE startup

An ICE power plant can start and ramp to full load very quickly due to rapid ignition of fuel within the cylinders and the coordinated starting of multiple generating sets. Wärtsilä ICE power plants employ high efficiency lean-burn technology that can reach full load in as little as two (2) minutes under “hot start” conditions. To meet “hot start” conditions, cooling water is preheated and maintained above 70°C, engine bearings are continuously prelubricated, a jack up pump supplies prelubrication to the generator bearings, and the engine is slow turning (cycling).

The Wärtsilä 34SG power plant requires only 30 seconds to complete startup preparations, speed acceleration, and synchronization to the grid. Loading to full power occurs rapidly in just 90 seconds. Startup time is not affected by the amount of time the unit had been previously shut down. The Wärtsilä 50SG power plant takes seven (7) minutes to reach full load. Under cold startup conditions, the Wärtsilä 34SG power plant can reach full load in 10 minutes and the Wärtsilä 50SG in 12

minutes. FlexicycleTM power plants offer advantages over CCGTs as sufficient steam pressure can be generated with only a subset of the engines operating.

Rapid startup for flexible power generation

Figure 2 shows a startup time comparison of the Wärtsilä 34SG and Wärtsilä 50SG power plants with simple cycle and combined cycle gas turbine plants from manufacturers GE, Alstom, and Siemens. All startup times are measured from operator initiation of the start sequence. As can be seen from the graph, Wärtsilä power plants provide quick start ability under 10 minutes, which meets system operator requirements. Unlike CCGTs, hot start conditions in a Wärtsilä power plant can be maintained regardless of how long the engines had previously been inactive. Ramp rate: how fast is fast?

Because solar and wind generation can change within minutes, electric grid operators rely on dispatchable units that can provide additional load (or curtail load) on the same timescale as variations in renewable output. The increase or reduction in output per minute is called the ramp rate and is usually expressed as megawatts per minute (MW/min). Ramp rates of most industrial frame gas turbine models are advertised as 10 MW/min up to 100 MW/min, with an average of about 25 MW/min. Ramp rate depends on generating unit capacity, operating conditions (whether unit is just starting up or operating at a minimum load hold point) and optional technologies for reducing startup time and increasing ramp rate.

The ramp rate of a gas-fired power plant also depends on the number of units and configuration. For example, a ramp rate of 100 MW/min is based on multi-turbine plant designs, such as a 2x1 CCGT (net power output of 750 MW) where each gas turbine is rated to ramp

at 50 MW/min. While ramp rate in MW/minute is a valuable metric, it is important to understand the operating conditions under which advertised ramp rates can be achieved.

Starting loading capability versus ramp rate

The starting loading capability is often quite different than the advertised ramp rate for gas turbines. Gas turbine ramp rates of 35–50 MW/min are achievable only after the unit has reached self-sustaining speed. The fastest loading gas turbine models produce 30 percent load delivery after 7 minutes and take nearly 30 minutes to reach full output under hot start conditions [7]. Wärtsilä 34SG engines have true quick start capability – an effective ramp rate of 50 percent per minute, reaching full load within 2 minutes. For a 200 MW plant, this equates to 100 MW/min.

The starting load delivery of Wärtsilä power plants and gas turbines is compared in Figure 3, showing the percentage of load delivered 7 minutes after startup. This assumes optional gas turbine technology for enabling fast loading and is based on manufacturer-published ramp rates. The fast startup time of Wärtsilä ICE provides a significant operational advantage over gas turbines. As gas turbines are just producing output, both the Wärtsilä 34SG and Wärtsilä 50SG engines have already reached full load.

Operational ramp rates of Wärtsilä engines and the most popular industrial frame gas turbine models of similar size (200 MW) are compared in Figure 4, with ramp rate expressed in two metrics – MW/minute and percent of full load per minute. Once running and at nominal operating temperatures, Wärtsilä power plants can adjust output up or down rapidly. Wärtsilä power plants can ramp from 10 percent to 100 percent load (or down) in just 42 seconds. This means that a power plant comprised of 12 Wärtsilä 50SG engines has an effective operational ramp rate of 288

Fig. 2 - While combined cycle gas turbines can take over 30 minutes to start, Wärtsilä ICE power plants can start and reach full load in less than 10 minutes.

Fig. 3 - Wärtsilä power plants have a rapid starting capability, delivering full load in 7 minutes or less. The effective starting ramp rate of gas turbines is much lower, delivering only partial load in that time.

13in detail


90

60

50

80

40

70

30

20

10

0 10 20 302 12 22 324 14 24 346 16 26 368 18 28 38 40

Wärtsilä 34SG power plant under hot start conditions: 70°C cooling water temp, prelubrication of the engine and gen bearings

Wärtsilä 50SG power plant under hot start conditions: 70°C cooling water temp, prelubrication of the engine and gen bearings

Simple cycle industrial (heavy duty) gas turbine under hot start conditions: GE, Alstom

GE FlexEffiency CCGT under hot start conditions: purge credit, Rapid Reaponse, startup within 8 hours of shutdown

Siemens F-class CCGT under hot start conditions: auxiliary steam, stack dampers maintain HRSG temperature and pressure

80

60

100

40

20

0

Time (minutes)

Perc

ent (

%) o

f ful

l loa

d

Starting loading rate

Perc

ent (

%) o

f ful

l loa

d at

7 m

inut

es

Wär

tsilä

20

V34

SG

Wär

tsilä

32x

18V

50S

G

GE

7F-5

CC

GT

GE

7F-5

Sim

ple

Cyc

le

Sie

men

s F-

Ser

ies

CC

GT

Sie

men

s F-

Ser

ies

Sim

ple

Cyc

le

Fig. 4- Wärtsilä engines have a significantly higher operational ramp rate than gas turbines of similar size.

14 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


MW/minute – significantly faster than a comparably sized gas turbine.

Economies of numbers provides greater flexibility

Over the course of a century, the trend in the electric power industry had been toward ever increasing generating unit sizes and plant capacities. Centralized power plants were built using custom-engineered technology of massive size. Conventional wisdom was that “bigger is better” as the capital costs per unit of capacity and production costs declined with increasing unit size, delivering economies of scale driven in part by improved steam turbine efficiencies.

The push for higher outputs and efficiencies directly led to the development of combined cycle, necessitating larger gas turbines with higher firing temperatures that enabled exhaust gas heat recovery to drive a steam turbine. While in the 1950s the firing temperature of gas turbines was about 800°C and average turbine size was around 10 MW, by the 1990s advanced gas turbines averaged over 100 MW and had firing temperatures exceeding 1300°C.

However, large gas turbines required considerable on-site construction and assembly, and could not easily adjust load to meet fluctuating demand. Modularized smaller-scale generating units operated in parallel and deployed as needed to match the

changing power requirements began to serve an important function for the stability of electric transmission grids. This shift toward “economies of numbers” provides reliability, construction, and efficiency benefits.

ICEs are ideally suited to modular use, as sets of 4 – 30 MW engine units can provide a range of incremental part load power without sacrificing efficiency. For example, a Wärtsilä power plant that has 28 modular Wärtsilä 34SG engine units, each sized at approximately 10 MW, can deliver a range of output from just a few MW to over 270 MW. Due to the modular design of Wärtsilä power plants and rapid startup, the engines can be loaded and unloaded individually. By operating only a subset of the engines at full load to produce the desired output, high efficiency is maintained.

Modularity offers simplified maintenance features and quality benefits, as components are prefabricated in a factory-controlled environment and tested. Prefabricated power generation modules are self-contained components of the system that are designed to interface with auxiliary power plant systems. As a result, the timeframe to plan, engineer and construct a power plant is shortened.

Because generating units are incrementally sized, a wide range of plant capacities and fuel options – including multi-fuel use – can be designed.

Expanding power needs in the future can be met with the addition of more engine units and ancillary modules, rather than the construction of a new power plant. Wärtsilä ICE modularity provides built-in redundancy in case of unit outages or maintenance without significantly affecting overall full plant output.

Limitations to gas turbine flexibility

Gas turbine power plants, which have traditionally required significant on-site assembly, have begun to be designed in a modular fashion to shorten construction time. Modularity in architecture provides limited operational flexibility for gas turbines, however. This is due to the size of units, small number of units, and efficiency tradeoffs for simple cycle versus combined cycle.

Industrial gas turbines for power generation may be 100 – 350 MW apiece and have limits on the lower range of output at which they can operate. This minimal load, or “turndown” percentage, is bounded by emissions limits. When the gas turbine operates at low load, the compressor airflow may not be enough to support conversion of carbon monoxide (CO) into carbon dioxide (CO2) in the combustion chamber. Gas turbines are generally constrained to a turndown of 30 to 40 percent of full load to meet emissions regulations [8]. A simple cycle power plant with two gas turbines can

80

00

20

20

60

140

Wärtsilä 22x20V34SG

GE 7F-5

Wärtsilä 12x18V50SG

Siemens SGT6-5000F40

20

0 100 200 300 400

Ramp rateNominal 200 MW power plant

Loading rate (MW/minute)

Ope

rati

onal

ram

p ra

te(%

per

min

ute)

Fig. 5 - Screen shot from a dispatch center shows the drop off in wind generation (green line) and rapid ramp up of Plains End power plant to compensate. Compared to the fast ramping of the Wärtsilä plant, gas turbine output (purple line) increases more slowly (Source: Colorado Dispatch Center, Xcel Energy, USA).

15in detail


adjust plant output down to about 15 to 20 percent of full load by operating only one turbine, but efficiency is limited to about 30 percent.

Combined cycle operation introduces more complexity into the operating parameters of the gas turbine plant. Modular architecture for CCGT power plants consists of one to four gas turbines, HRSGs for each gas turbine, and a common proportionally-sized steam turbine. The lower load limit is affected by the turbine exhaust temperature, which must be high enough to generate sufficient steam pressure in the HRSG to power the steam turbine. Emissions-compliant turndown for CCGT plants is usually 40 to 50 percent of full load. For example, a combined cycle power plant design based on 200 MW gas turbines (in a 2x1 configuration) has a rated output of over 600 MW, limiting turndown ability to about 300 MW. In comparison, a Flexicycle power plant based on Wärtsilä ICEs does not have similar restrictions on load turndown because sufficient steam pressure can be developed by operating only 25 percent of the engines.

Actual performance demonstrates true flexibility

Wärtsilä ICEs are perfectly suited to cycling, as the ability to quickly startup and ramp up or down in load does not affect the

maintenance schedule. In addition to a fast startup time, Wärtsilä engines can stop within one minute and have lower emissions due to lean-burn technology. The difference in performance between gas turbines and Wärtsilä power plants is evident in Figure 5, which presents a screen shot from an actual dispatch center in Colorado, U.S. The Plains End power plant units (red and white load curves) were used to compensate for a sudden drop off in wind output, rapidly starting and ramping to full load within minutes. By contrast, gas turbines (purple load curve) ramped up at a much slower rate from a low load. This underscores that advertised ramp rates and startup times do not always reflect operational capability, and illustrates the true flexibility provided by Wärtsilä power plants.

References

[1] Ellison, James F., Leigh S. Tesfatsion, Verne W.

Loose, and Raymond H. Byrne. Project Report: A

Survey of Operating Reserve Markets in U.S. ISO/

RTO-managed Electric Energy Regions. Rep. no.

SAND2012-1000. Sandia National Laboratories,

Albuquerque NM.

[2] Pasha, Akber, and Darryl Taylor. “HRSGs for

Next Generation Combined Cycle Plants.” Power

Engineering. PennWell Corporation, 01 July 2010.

Web. 27 Jan. 2015. <http://www.power-eng.com/

articles/print/volume-114/issue-7/Features/hrsgs-

for-next-generation-combined-cycle-plants.html>.

[3] Taylor, Darryl, and Akber Pasha. “Economic

Operation of Fast-Starting HRSGs.” POWER

Magazine. Access Intelligence, 01 June 2010.

Web. 27 Jan. 2015. <http://www.powermag.com/

economic-operation-of-fast-starting-hrsgs>.

[4] Strebe, Martin-Jan, and Arvo Eilau. “The

Evolution of Steam Attemperation.” POWER

Magazine. Access Intelligence, 01 Nov. 2012. Web.

27 Jan. 2015. <http://www.powermag.com/the-

evolution-of-steam-attemperation/>.

[5] Moelling, David S., and Peter S. Jackson.

“Startup Puge Credit Benefits Combined

Cycle Operations.” POWER Magazine. Access

Intelligence, 01 June 2012. Web. 27 Jan. 2015.

<http://www.powermag.com/startup-purge-credit-

benefits-combined-cycle-operations/>.

[6] Lefton, Steven, Nikhil Kumar, Doug Hilleman,

and Dwight Agan. The Increased Cost of Cycling

Operations at Combined Cycle Power Plants. Tech.

no. TP203. Sunnyvale, CA: Intertek, 2012.

[7] “7HA Gas Turbine (60 Hz).” GE Power

Generation. General Electric, n.d. Web. 27 Jan.

2015. <https://powergen.gepower.com/plan-build/

products/gas-turbines/7ha-gas-turbine.html>.

[8] Probert, Tim. “Fast Starts and Flexibility:

Let the Gas Turbine Battle Commence.” Power

Engineering International. PennWell Corporation,

06 Jan. 2011. Web. 27 Jan. 2015. <http://www.

powerengineeringint.com/articles/print/volume-19/

issue-6/features/fast-starts-and-flexibility-let-the-

gas-turbine-battle-commence.html

Load

Gas generation

Plains End 1 & 2 power plants Flexible generation

Wind generation

Coal power plants

16 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


Gas-fired efficiency in part-load and pulse operationAUTHOR: Dawn Santoianni

Gas-fired power plants are the most responsive and flexible generating assets in electricity markets, adjusting output to balance system demand and loads. But technology choice matters for efficiency in part-load and pulse operation. The efficiency and economic performance of Wärtsilä power plants during cycling operation is far superior to gas turbines.

Preferential access for renewables and feed-in tariffs often result in fossil-fueled generation curtailing output to allow for wind and solar loads. This periodic adjustment of output is called cycling. A recent assessment by the California Independent System Operator (CAISO) in the U.S. demonstrated the need for significant cycling over two hours during the morning peak (8000 MW) and the end of the work day (13,500 MW) to meet demand when solar and wind are not producing (Figure 1) [1]. This challenge is not unique to California, as many

countries are adopting energy policies to achieve 20 percent or more from renewable sources. Surges in wind and solar output in Germany recently peaked at 59 percent of electric generation during a single day, causing conventional power plants to ramp down significantly.

Simple cycle gas turbines have traditionally served as peaking units because they can be started within minutes and ramped up and down quickly to meet spikes in demand or sudden changes in electric system loads. They also have lower efficiencies – less than 40 percent – so they

Fig. 1 - CAISO load profile demonstrates need for rapid, short duration (pulse) generation to accommodateload fluctuations from wind and solar sources. Image credit: Combined Cycle Journal.

17in detail


operate during when electric demand peaks and the price of electricity is high. With the expanding need for more flexible power, capacity that was designed for continuous, baseload operation is often being used to provide load-following and even peaking electric service. This is particularly true for combined cycle gas turbines (CCGTs) which can respond to changes in load much faster than conventional steam power plants.

The cycling of CCGT plants presents other issues however, including increased thermal and mechanical stress on plant components and load turndown limitations. The performance of cycling power plants at part load and for short duration pulsed output is an important consideration for minimizing power system emissions,

maintaining high efficiency, and maximizing operational flexibility. This article explores the partial load limitations and efficiency performance of internal combustion engines (ICEs) compared with gas turbines.

Minimum environmental load

A technical constraint for partial load operation of gas turbine power plants is the minimum environmental load, also called the minimum emissions-compliant load. This is the lowest output at which the generating unit can operate and still meet environmental limits for nitrous oxides (NOx) and carbon monoxide (CO) emissions. The minimum environmental load for most CCGTs is about 50 percent of full output.

To facilitate a wider range of gas turbine

output, manufacturers have introduced control systems designed to extend emissions-compliant turndown while minimizing efficiency impacts at part load. While the exact methods for turndown optimization vary from manufacturer to manufacturer, the control systems use variable guide vanes to decrease compressor mass flow and sequential firing (reheat) to produce higher combustion temperatures at low loads. Higher combustion temperatures not only enhance the conversion of CO to carbon dioxide (CO2) but also boost steam production and thus output from the steam turbine, improving overall part-load plant efficiency. As a result, some gas turbine models can achieve emissions-compliant turndown to about 40 percent of baseload power.

40,000

6,00036,000

5,00032,000

4,000

44,000

8,000

8,000

8,000

28,0003,000

24,000 2,000

20,000 1,000

21:0018:0015:0012:009:006:003:00 0:000:00

Load Net Load Wind Solar

Load, Wind Solar Profiles – High Load CaseJanuary 2020

Load

& N

et L

oad

(MW

)

Win

d &

Sol

ar (M

W)

Fig. 2 - Part load efficiency of Wärtsilä engines compared with gas turbines.

18 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


For all practical purposes, ICE power plants do not have minimum load limitations and can maintain high efficiency at partial load due to modularity of design – operating of a subset of the engines at full load.

Impacts of cycling: part load efficiency

Gas turbine manufacturers boast efficiencies of 55 percent or greater, but this is the efficiency at full output. Cycling and operation at partial load negatively affects CCGT efficiency. To compare the performance of CCGTs, simple cycle gas turbines, and Wärtsilä ICEs at varying load, efficiency data was produced using GT PRO [2]. The gas turbines chosen for comparison were based on popular heavy frame industrial models well-suited for combined cycle operation that could also be used in simple cycle operation as peaking units.

Similar sized units are compared, with

capacities of approximately 180 – 275 MW in simple cycle, and 235 – 310 MW when running in combined cycle mode (depending on ambient conditions). This assumes a 1x1 CCGT configuration (one gas turbine and heat recovery steam generator supplying one steam turbine), air-cooled condensers and a bypass stack to isolate the steam generating portion of the plant from the gas turbine.

Figure 2 shows efficiency curves for plants operating at summer ambient conditions of 25°C (77°F). The efficiencies of CCGTs drop below 50 percent between 55 to 65 percent of full load. In simple cycle mode, the degradation of gas turbine efficiency is more pronounced, with gas turbines dropping to less than 30 percent efficiency at half load. The minimum environmental load of 50 percent for typical GT turndown and 40 percent for extended turndown is

noted in Figure 2. For a 300 MW combined cycle plant, this means that the minimum emissions-compliant output is between 120 to 150 MW.

Unlike gas turbines, Wärtsilä ICE power plants have near full range capability of emissions-compliant turndown. As load is decreased, individual engines within the generating set are shut down to reduce output. The engines that remain operating can generate at full load, retaining high efficiency of the generating set. Flexicycle efficiency is above 48 percent all the way down to 23 percent of full load (69 MW). Beyond the minimum load for the Flexicycle steam turbine, the engines will operate in simple cycle mode. Thus, the output of a 300 MW Flexicycle plant can be turned down to only 18 MW. As a result, Flexicycle power plants provide a much wider range of output flexibility than gas turbines without

60

30

25

40

45

50

55

20

35

15

10

5

0 6020 7030 804010 50 90 100

Percent of full load

Effien

cy (%

)

Typical minimum GT load destriction due to emissions

Extended gas turbine turndown

Flexicycle running in simple cycle mode

Minimum load for Wärtsilä reciprocating engines due to emissions

Minimum load for Flexicycle steam turbine

GE 7FA.05 Combined cycle, 25°C GE 7FA.05 Simple cycle, 25°C

Siemens SGT6-5000F Combined cycle, 25°C Siemens SGT6-5000F Simple cycle, 25°C

Wärtsilä Flexicycle, 25°C Wärtsilä Simple cycle, 25°C

Fig. 3 - Two-shifting (4–2–4 pulse production) for Wärtsilä Flexicycle plant compared with CCGT. The fast startup and shutdown of the Flexicycle plant reduces fuel consumption and minimizes non-productive operating hours.

19in detail


Time from full load (minutes)

the constraints of turndown limitations or efficiency impacts.

Impacts of cycling: pulsed operation

A key characteristic of flexibility is cycling to produce short-duration or pulse load. Pulsed loads are produced in response to the sudden loss of a power generator, reduced output from wind and solar sources, or spikes in demand. Pulse generation improves system reliability and power quality by stabilizing the electric grid. Power plant owners want to optimize operation to minimize fuel consumption and maximize revenue. The startup time, time to ramp up output to full load, minimum load restrictions, and the efficiency at part load determine the amount of fuel consumed (energy input) and the length of time the plant operates each day. By producing output during peak demand times, the power plant earns revenue from high electric tariffs. Ramping up and down should be as fast as possible without risking damage to the power plant equipment.

As explored deeper in other articles in this issue, CCGTs have technical constraints

that affect their startup time, ramp rate, and minimum load for maintaining hot conditions. Cycling raises concerns about increased air emissions and thermo-mechanical stress on CCGT plant equipment [3]. Wärtsilä engines have lower exhaust gas temperatures (360°C) compared with a gas turbine (600°C) and thus lower steam temperatures, enabling quicker startup and ramping to full load.

Typically, a load following CCGT ramps up slowly during early morning hours, operates at full load during morning peak demand, curtails output during midday hours to a minimum operating load at which hot conditions are maintained (40 to 50 percent of full load), then ramps back up again to full load for the evening peak. The plant is shut down at night and then ramped up again in the early morning hours the next day. This double pulse load profile, also called “two-shifting” or “two-cycling” for a typical CCGT compared with a Wärtsilä Flexicycle™ power plant is shown in Figure 3. The duration of each pulse is 4 hours, with a curtailment in between pulses of 2 hours (4–2–4 pulse production). The shaded area

in Figure 3 shows when the power plant would be receiving revenue from pulse production.

As can be seen in Figure 3, the slower startup time and the minimum load limit increase the total time the CCGT plant is operating – and thus its overall energy (fuel) consumption and operating expenses. While a typical CCGT requires about 60 minutes to reach full load in the morning, a Wärtsilä power plant starts within a few minutes.

Energy use

The cumulative energy input of a 200 MW Wärtsilä power plant compared with a similarly sized CCGT for two-shifting operation (4–2–4 pulse production) is shown in Figure 4. The amount of energy input is a function of the efficiency of the power plant and the total operating time. The rapid Wärtsilä start eliminates the need for a load hold point to maintain hot conditions, reducing the overall operating time. This in turn reduces the amount of energy (fuel) input to generate revenue-producing load. As a result, the cumulative energy input of a Flexicycle plant is five

Wärtsilä Flexicycle CCGT

100

80

60

0

40

20

–60 60 180 2400 300 600540480420360120

Pla

nt L

oad

(% o

f Ful

l Loa

d)

Fig. 4 - Two-shifting (4–2–4 pulse production) cumulative energy input for Wärtsilä Flexicycle plant compared with CCGT. The fast start of a Wärtsilä power plant reduces total fuel consumption.

Fig. 5 - Two-shifting (4–2–4 pulse production) cash flow for Wärtsilä Flexicycle plant compared with CCGT based on startup costs, fuel costs and O&M costs in Table 1.

20 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


percent less than a CCGT over the same operating period.

Profitability

The cash flow for 4–2–4 pulse production is shown in Figure 5 for a 200 MW plant. The cash flow projection takes into account startup costs, fuel costs, and O&M costs (see Table 1). The shaded area indicates negative cash flow – the power plant is costing more money to operate than revenue earned. As can be seen in Figure 5, a CCGT does

not become profitable until the end of the second four-hour pulse. The decline in cash flow after the first pulse is because the gas turbine continues to run at the minimum hold point and burns fuel less efficiently until it ramps back up again for the second pulse during the evening peak.

There may be several types of pulse load output that a power plant produces over the course of a year including one-hour, two-hour, four-hour, and eight-hour single pulses, as well as 2–2–2 pulse operation.

Shorter pulses and more cycling decrease the efficiency of CCGTs and increase the amount of energy input (fuel) per MWh of electricity produced. This impacts the plant’s profitability by increasing operating and fuel costs. Figure 6 illustrates the disparity in income per pulse for a 200 MW Flexicycle power plant compared with a CCGT of similar size for the most common pulse outputs. While the Wärtsilä power plant is profitable for any pulse duration or cycling, a CCGT plant is not profitable for short duration pulse operation.

Pulse efficiency

Pulse efficiency is the net efficiency for the duration of the operating period, including startup, shutdown and part load operation. As discussed above, the efficiency of a plant at part load can be dramatically different than the baseload efficiency. ICEs can reach full load and curtail output to zero within minutes. Based on modular architecture, Wärtsilä power plants maintain full load efficiency at part load by running only a subset of the engines.

The impact of pulsed operation (cycling) on efficiency is seen in Figure 7. While the CCGT has higher efficiency during baseload operation at full output, the Flexicycle plant achieves higher overall efficiency for all pulses less than 8 hours long. Impacts of pulse operation on CCGT efficiency is most pronounced for pulse duration of two hours or less. Wärtsilä power plants are efficient and economic over a wide range of pulsed loads, providing ultra-flexible capacity for meeting the challenges of renewables integration and changing demand.

References[1] “Integrating Renewables May Call for Some

Combined Cycles to Start Twice Daily, Increasing

Emissions.” CCJ Online Combined Cycle Journal.

CCJ Online Inc., 21 Oct. 2012. Web. 27 Jan.

2015. <http://www.ccj-online.com/integrating-

renewables-may-call-for-some-combined-cycles-

to-start-twice-daily-increasing-emissions/>.

[2] “GT PRO.” Thermoflow Products - Combined

Cycle. Thermoflow Inc., n.d. Web. 27 Jan. 2015. <http://

www.thermoflow.com/combinedcycle_GTP.html>.

[3] Kumar, N., P. Besuner, S. Lefton, D. Agan, and

D. Hilleman. Power Plant Cycling Costs. Rep. no.

NREL/SR-5500-55433. Golden, CO: National

Renewable Energy Laboratory, 2012.



Wärtsilä Flexicycle


CCGT

CCGT

0 120 360 600240 480

4000

6000

2000

8000

–8000

–6000

–2000

–4000

0

–10000

Cas

h flo

w (E

UR

)

0–60

–60

120 360 600240 480

1400

1600

1800

1200

2000

200

400

800

600

1000

0

Cum

ulat

ive

ener

gy in

put (

MW

h)

21in detail


Fig. 6 - Income per pulsed operation for a 200 MW power plant. The Wärtsilä Flexicycle plant is profitable for a wide range of pulse operation while the CCGT plant is not profitable.

Fig. 7 - Net efficiency over pulse duration for Wärtsilä Flexicycle plant compared with CCGT. Wärtsilä plants are more efficient than CCGTs for short duration pulse operation.

Table 1 - Cost inputs for calculation of pulse cash flow and income, based on nominal 200 MW power plant.

500

50

0

1000

55

–2500

–2000

30

–1000

40

–1500

35

–500

45

–3000

25

Pulse income

Pulse effiency

EUR

Effien

cy (%

)



CCGT

CCGT

Base values for technologies Wärtsilä plant CCGT Electricity and fuel prices

Full load efficiencies (%) 45.7 simple cycle

55.0 1 hour pulse 75 EUR/MWh el 49.7 Flexicycle

Startup time (minutes) 6 60 2 hour pulse 70 EUR/MWh el

Shut-down time (minutes) 2 30 4 hour pulse 65 EUR/MWh el

O&M costs (EUR/MWh) 5 3 8 hour pulse 60 EUR/MWh el

Startup costs (EUR/MW) 0 50 Non-pulse hours 0 EUR/MWh el

Baseload generating cost 59.7 simple cycle(EUR/MWh el) 55.3 Flexicycle

48.5 Fuel price 25 EUR/MWh

8-hr

Baseload

4-hr

4-hr8-hr

1-hr

1-hr

2-2-2

2-2-2

2-hr

2-hr

4-2-4

4-2-4

22 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


Power plant performance under extreme ambient conditionsAUTHOR: Dawn Santoianni

23in detail


Delivering reliable power in the world’s most demanding climates requires technology that provides stable output despite ambient conditions. Wärtsilä power plants outperform gas turbines in areas where heat, humidity and altitude pose operational challenges.

Harsh climatic conditions can pose a significant barrier to electrification plans and economic growth in developing countries. Hot climates, high elevations and excessive humidity put huge demands on power generating technology. Depending on the site conditions, a power plant’s actual electrical output, efficiency, and fuel consumption can be quite different than its performance at design conditions. Ambient conditions (temperature, humidity and pressure) can

vary dramatically with geographic location and by season. Summer temperatures in the Middle East and northern Africa frequently exceed 40°C (104°F) and some areas around the world experience large seasonal temperature swings of over 38°C (100°F), as shown in Figure 2.

Ambient temperature, humidity and altitude affect the density of air, which can negatively impact power plant output and performance. As surging temperatures

Fig. 1 – Wärtsilä technology selected for the Antelope Station in Texas, U.S. was based on the need to deliver full power to the electric grid in less than five minutes in ambient conditions that ranged from -23°C to 46°C.

Fig. 2 - In some regions of the world, average temperatures exceed 30°C. Image credit: Maps on the Web.

24 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


Hot and humid air is less dense than dry, cooler air. As the density of air decreases, more power is required to compress the same mass of air. This reduces the output of the gas turbine and decreases efficiency. Studies have found that gas turbine efficiency deteriorates by one percent for every 10 degree rise in temperature above ISO conditions [1]. This translates into a power output reduction of 5 to 10 percent, depending on the type of gas turbine. Gas turbine manufacturers use various techniques to cool inlet air and boost turbine output, including evaporative coolers and mechanical chillers. However, inlet air cooling requires additional power consumption, and the efficacy of cooling systems is highly dependent on the ambient humidity. Wärtsilä ICEs are less sensitive to temperature and humidity, retaining their rated efficiency and power output over a broader range of ambient conditions.

Performance in hot conditions

The performance of simple cycle gas turbines, combined cycle gas turbines (CCGT) and Wärtsilä ICEs at varying ambient conditions was assessed using data from GT PRO [2]. Popular model heavy frame industrial gas turbines were compared with similarly sized Wärtsilä engines, for capacities of 200 – 275 MW in simple cycle, and approximately 300 MW in combined cycle (see Table 1 for full load output of the specific models compared). For combined cycle operation, a 1x1 CCGT configuration was assumed with air-cooled condensers and a bypass stack to isolate the steam generating portion of the plant from the gas turbine. Figure 3 presents the net power plant output at varying ambient temperatures ranging from 10°C to 40°C (50°F to 104°F) for gas turbines and Wärtsilä ICEs operating in combined cycle (Flexicycle). CCGT output decreases by 15 to 18 percent at 40°C compared to ISO reference conditions, while the Wärtsilä Flexicycle™ plant output decreases by only 8 percent compared to reference conditions.

The impact on plant efficiency is shown in Figure 4 for both combined cycle and simple cycle operation. At an ambient temperature of 40°C, CCGT efficiency decreases by 3.5

usually correspond to peak electrical demand, a reduction in power output with high ambient temperatures and humidity can be problematic. High altitudes present engineering challenges. Air pressure decreases at higher altitudes, so the amount of air available for combustion is decreased. The air pressure at 1500 meters above sea level (masl) is 85 kPa (12.3 psi), significantly lower than standard gas turbine ISO reference conditions of 101 kPa (14.7 psi)*. At high temperatures, humidity or

elevations, gas turbine output and efficiency can significantly degrade compared to standard reference performance. Wärtsilä internal combustion engines (ICEs) are designed to operate in even the most adverse conditions, setting the standard for efficiency and economic performance.

How do temperature and humidity affect power plant output and efficiency?

In gas turbines, power output is dependent on the mass flow through the compressor.

* The standard reference conditions (prescribed by the International Organization for Standardization,

or ISO) are the temperature and pressure conditions under which manufacturers evaluate generating

capacity and efficiency. These ISO reference conditions differ depending on the technology. Standard

reference conditions for gas turbines (ISO 3977) are 15°C (59°F) and 101.3 kPa (14.7 psia) while for

combustion engines (ISO 3046) reference conditions are 25°C (77°F) and 99 kPa (14.4 psia).

25in detail


percent compared to ISO conditions. In a Flexicycle power plant, efficiency only drops by 1.1 percent at 40°C. All values represent net efficiency at the high-voltage grid side at sea level pressure. In simple cycle operation, Wärtsilä power plants demonstrate significant efficiency advantages over gas turbines. While simple cycle efficiency of a gas turbine is approximately 35 percent at 40°C, Wärtsilä efficiency is over 45 percent.

The impact of ambient temperature on efficiency becomes even more pronounced

when the plant is operating at part load. Operation at part load is becoming more and more common for gas-fired power plants due to cycling to follow renewable loads (see article Defining true flexibility, page 10). At 25°C, the efficiency of a CCGT drops from 55 percent at full load to 49 percent at half-load. The efficiency of a similarly-sized Flexicycle plant only drops 0.1 percent (49.1 percent efficiency at half-load). Although CCGTs are sometimes perceived as having unmatched high

efficiency, in real-world situations including high heat and humidity, Wärtsilä engines offer equal efficiency and greater flexibility than gas turbines without the limitations of minimum turndown load.

Performance at high altitudes

Although high elevations are often associated with remote mountainous terrain, 140 million people worldwide live at altitudes above 2500 meters (8200 feet), including cities and densely populated

Fig. 3 – Wärtsilä Flexicycle plants experience less derating at high ambient temperatures than CCGTs.

Ambient temperature

GE 7FA.05 Combined cycle


Siemens SGT6-5000F Combined cycle

Table 1 - Plant net output at varying ambient temperatures.

GE 7FA.05 Siemens SGT6-5000F Wärtsilä

Combined cycle Simple cycle Combined cycle Simple cycle Flexicycle Simple cycle

10˚C (50˚F) 312 214 296 204 305 276

15˚C (59˚F) 306 209 289 198 304 276

20˚C (68˚F) 300 205 280 191 303 276

25˚C (77˚F) 292 200 270 185 301 276

30˚C (86˚F) 282 194 259 178 300 276

35˚C (95˚F) 271 188 248 172 292 269

40˚C (104˚F) 260 182 235 164 278 257

10°C (50°F) 40°C (104°F)30°C (85)20°C (58°F)

300

310

290

320

240

250

270

260

280

230

Pla

nt n

et o

utpu

t (M

W)

26 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


areas in South America, Africa and Asia. In addition, it is not unusual for mining and other industrial operations to be located above 2000 masl. At these high altitudes, air density is lower than at sea level. Lower air density means less air is available for combustion and can create problems with startup and cooling. In gas turbines, the main impact of high altitude is the effect on the compressor inlet pressure and thus mass flow. (Figure 5)

Gas turbine power output decreases proportionately with altitude, reducing by approximately 12 percent for every 1000 meters above sea level [3]. At 1500 masl, gas turbine output would be 18 percent less than its rated full capacity. While boosting inlet airflow with air injection (supercharging) can be used to prevent derating, it requires additional energy input, negatively impacts the overall economics of the plant and is seldom used in practice. Employing radiator cooling and turbocharging to achieve better performance at high altitudes, Wärtsilä 34SG engines can maintain full output to 2000 masl. The severe derating impact of altitude on gas turbines is evident in Figure 6, which shows the superior performance of Wärtsilä engines at high altitudes.

Economic implications

Gas turbine performance derating has direct economic investment implications. Oversizing a gas turbine to compensate for derating results in additional capital investment costs, with an estimated cost increase of 18 percent for a gas turbine at 1500 masl compared one at sea level [4]. Efficiency degrading under challenging ambient conditions also increases fuel costs and emissions. Life-cycle cost analysis has shown that ambient conditions of 35°C and an altitude of 500 masl would increase the cost of a 200 MW CCGT unit by € 2.0 million, and would have to run an additional 1000 hours to produce the same output as a similarly-sized Wärtsilä power plant [5].

Wärtsilä has power plants operating in the harshest climates around the world. The recently inaugurated Sasol gas engine power plant located south of Johannesburg, South Africa is powered by 18 Wärtsilä 34SG generating sets operating at an elevation of 1500 masl [6]. Wärtsilä’s highest elevation power plant serves the Mina Pirquitas mining project in Argentina, operating at an altitude of 4100 masl [7]. The ability to efficiently deliver load despite ambient conditions along with the operational

flexibility advantages of rapid startup and quick ramping makes Wärtsilä power plants ideally suited for integrating renewable energy sources. Technology selected for the Antelope Station in Texas, U.S. (20 Wärtsilä 34SG engines) was based on the need to deliver full power to the electric grid in less than five minutes in ambient conditions that ranged from -23°C (-10°F) to 46°C (115°F) at 1020 masl [8].

As global energy needs expand into areas with challenging climatic conditions, Wärtsilä technology provides the most cost-effective solution for reliable power.

References

[1]Farouk, N., L. Sheng, and Q. Hayat. “Effect of

Ambient Temperature on the Performance of Gas

Turbines Power Plant.” International Journal of

Computer Science Issues, 10:1. 3 January 2013.

Web. 28 January 2015. <http://www.ijcsi.org/papers/

IJCSI-10-1-3-439-442.pdf >.

[2]“GT PRO.” Thermoflow Products - Combined

Cycle. Thermoflow Inc., n.d. Web. 27 Jan. 2015. <http://

www.thermoflow.com/combinedcycle_GTP.html>.

[3]Meher-Homji, Cyrus B., Mustapha A. Chaker,

and Hatim M. Motiwala. “Gas Turbine Performance

Deterioration.” Proceedings of the 30th

Turbomachinery Symposium. 2001. Web. 27 Jan.

2015.

Fig. 4 - Efficiency of Wärtsilä engines compared with gas turbines at varying ambient temperatures.

Ambient temperature

GE 7FA.05 Combined cycle GE 7FA.05 Simple cycle

Wärtsilä Flexicycle Wärtsilä Simple cycle

Siemens SGT6-5000F Combined cycle Siemens SGT6-5000F Simple cycle

10°C (50°F) 40°C (104°F)30°C (85)20°C (58°F)

55

50

60

35

40

45

30

Effien

cy (%

)

27in detail


[4]“Recips give gas turbines a run for their money.”

Modern Power Systems. Global Trade Media, 5

February 2002. Web. 27 January 2015. <http://

www.modernpowersystems.com/features/

featurerecips-give-gas-turbines-a-run-for-their-

money/ >.

[5]Back, Andreas. “Lifecycle cost knowledge will

impact power plant investment decisions.” In detail

Wärtsilä Technical Journal, 2010: 9-13.

[6]Overton, T. “Top Plant: Sasol Gas Engine Power

Plant, Sasolburg, South Africa.” POWER Magazine.

Access Intelligence, 01 September 2013. Web.

27 January 2015. <http://www.powermag.com/

sasol-gas-engine-power-plant-sasolburg-south-

africa/?printmode=1 >.

[7]Voyles, Bennett. “On Top of the World.”

Twentyfour7. Wärtsilä. 1/2010: 55-58.

[8]Finn, Dennis, Anna Jarowicz, and Chauncet

Thomas. “Providing fast wind following response.” In

detail Wärtsilä Technical Journal, 2012: 26-30.

Fig. 5 - 140 million people worldwide live at altitudes above 2500 meters. Photo: “El Alto” by Danielle Pereira, licensed under Creative Commons.

Fig. 6 - Wärtsilä engines maintain output even at high altitudes while gas turbine output degrades significantly above 1000 masl.

Altitude (meters above sea level)

Wärtsilä 34SG SC

Industrial gas turbine

Wärtsilä 34SG Flexicycle

0 3,0002,5002,0001,5001,000500

95

100

90

65

70

80

75

85

60

Perc

ent o

f ful

l out

put

28 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


Achieving energy security: the role of fuel flexibility and low water use AUTHOR: Dawn Santoianni

Fig. 1 – The IPP3, world’s largest tri-fuel power plant in Jordan, maximizes national grid’s fuel flexibility by being able to run on natural gas, heavy fuel oil and light fuel oil.

29in detail


Energy security has become a significant concern for many countries around the world. Fuel shortages, supply interruptions and price constraints – even if only temporary – pose considerable economic and electric reliability risks. At the same time, water scarcity is already threatening power supply in many regions of the world. With multi-fuel capability and minimal water requirements, Wärtsilä power plant technology ensures a reliable energy supply.

Today, many nations are facing energy security threats from geopolitical instability, fuel supply disruptions, surging fuel costs and low water supplies for power generation. In the Middle East for example, where natural gas accounts for 60 percent of power generation, disruptions to the Arab Gas Pipeline jeopardize electric reliability. Droughts and diminishing reservoir levels are stressing power systems globally, cutting hydropower output and derating steam-electric capacity due to reduced cooling water availability. Europe’s coal and nuclear electric capacity is projected to decrease by 6 – 19 percent in the coming decades because of insufficient cooling water [1]. To mitigate these risks, some countries are now specifying multi-fuel capability and low water use for new power plants as important criteria in technology selection.

What is fuel flexibility?

Fuel flexibility is the ability to burn a variety of fuels and immediately switch fuels during operation without reducing load or sacrificing power plant availability. Liquid fuels that can be used for electric power generation include crude oil, residual fuel oils (RFO), and distillate fuels including light fuel oils (LFO), naphtha and diesel.

However, not all power plants are designed to run on liquid fuels for extended periods of time. When natural gas shortages cause gas turbines to burn fuel oil as backup, additional inspection and maintenance is required, resulting in more frequent outages. Wärtsilä internal combustion engines (ICEs) are designed to burn a variety of gaseous and liquid fuels without incurring increased maintenance or reducing availability, providing an efficient reliable power supply

30 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


24/7/365 and agilely responding to evolving dispatch needs.

While gas turbines are often advertised as having fuel flexibility, about 90 percent of gas turbines worldwide operate on natural gas or liquefied natural gas (LNG) because of its purity and ease of combustion. The fleet of Wärtsilä plants with fuel oil capability includes over 4000 plants encompassing 8900 engines in 165 countries, as shown in Figure 2. A number of Wärtsilä power plants were designed to operate on liquid fuels while natural gas infrastructure was built or expanded, leveraging multi-fuel capability to meet both short-term and long-term power needs.

Maintenance issues for gas turbines operating on fuel oils

Liquid fuels present many challenges for gas turbines because they can contain water-soluble salts, high concentrations of heavy metals and other impurities. Crude and residual oils are more viscous and contain higher concentrations of trace metals than distillates. Metals and salts are abrasive to turbine blades and can create ash deposits which lead to fouling and corrosion in hot gas path components. Because combustion occurs continuously in gas turbines, the unit must be taken offline for inspection and maintenance. A combination of fuel conditioning (cleaning, blending, heating and pressurization) and more frequent maintenance cycles are required for gas turbines running on fuel oil. Catalysts may

be added to improve combustion, and in some cases, heavy fuel oils (HFO) or crude may be blended with higher purity liquid fuels to achieve permissible sulfur, ash and metals content. Fuels containing vanadium or lead, which are oil-soluble and cannot be removed by washing or centrifuging, require corrosion inhibitors for use in gas turbines. Generally distillate fuels are considered to be relatively free of contaminants, but contamination during fuel transportation and delivery has led to occurrences of corrosion in gas turbines [2].

Overhauling a gas turbine that was designed for natural gas to burn liquid fuels is costly and requires adjustment of the firing temperature control, revised startup and shutdown procedures, and offline cleaning cycles to remove ash deposits. As a result, the availability of the gas turbine power plant is decreased. Because certain fuel oils contain volatile components with low flash points (such as naphtha), explosion protection is also often required for gas turbines.

Thus, the ability of most gas turbines to operate on liquid fuels is very limited, in terms of the characteristics of fuels oils that can be used and the amount of time the turbine can operate on such fuels. Liquid fuel options for gas turbines vary by manufacturer and model, with some gas turbines only able to use No. 2 distillate. Multiple fuel delivery systems and combustors are employed to accommodate different fuels.

Fig. 2 - Extensive global fleet of Wärtsilä power plants operating on fuel oils.

Wärtsilä multi-fuel capability

Wärtsilä engine maintenance is not affected by fuel type as the ICEs are not sensitive to metals or salts in fuel oils. No corrosion inhibitors are needed and only minimal fuel conditioning (centrifugal separators and filters) is required to burn lower quality fuels including HFO/RFO and crude. Because combustion occurs intermittently in ICEs with the expulsion of combustion products during the exhaust stroke, the buildup of ash deposits is prevented.

While the use of ash-forming fuels (such as HFO) reduces gas turbine output by 4 to 5 percent compared to natural gas operation, Wärtsilä multi-fuel engines retain the same output and high efficiency whether running on natural gas, LFO or HFO. If the natural gas supply is interrupted, a Wärtsilä multi-fuel power plant instantaneously switches to a backup fuel oil and maintains load without incurring any maintenance penalty. When routine maintenance is required, the modular architecture of Wärtsilä power plants allows an engine to be taken offline while maintaining the bulk of plant output.

Wärtsilä offers two different types of multi-fuel engines: dual-fuel (DF) engines and gas-diesel (GD) engines. Wärtsilä 34DF and Wärtsilä 50DF engines use lean-burn combustion technology when operating on gas and a normal diesel process when operating on fuel oil. Wärtsilä DF engines have three fuel delivery systems that work in parallel: a pilot fuel injection system, a liquid fuel supply, and a gas admission system. The liquid backup fuel system allows the engine to transfer automatically and instantaneously from gas operation to liquid fuel operation at any load. The tri-fuel delivery system allows instantaneous switching from LFO to HFO as well.

Wärtsilä 32GD and Wärtsilä 46GD engines employ a diesel process whether operating on either gas or liquid fuels, and can burn natural gas, associated gas, LFO, HFO and crude oil. Ignition of liquid pilot fuel prior to gas injection makes Wärtsilä

31in detail


GD engines very tolerant of low gas quality and insensitive to methane number, which is a measure of the fuel’s resistance to engine knock. In addition to being able to switch instantly to fuel oil operation, Wärtsilä GD engines are also able to operate in fuel sharing mode burning varying percentages of gaseous and liquid fuels simultaneously. Wärtsilä GD engines can operate in fuel sharing mode at loads of 30 – 100 percent.

While gas turbines require about 10 minutes to switchover from baseload gas to fuel oil, Wärtsilä multi-fuel engines can switch from natural gas to fuel oil instantaneously. Switching back to gas from liquid fuel takes approximately 90 seconds for both Wärtsilä DF and GD engines with no load reduction. As shown in Table 1, Wärtsilä multi-fuel engines offer numerous advantages over gas turbines for flexible fuel solutions including the ability to operate

on a wide range of fuels without sacrificing power plant availability or incurring additional maintenance costs. This fuel flexibility provides cost savings because a Wärtsilä power plant can ensure a secure power supply as fuel supplies change over time.

Fuel flexibility was big consideration in the selection of Wärtsilä 50DF technology instead of gas turbines in the Quisqueya I and II project. Under two separate engineering, procurement and construction contracts, Wärtsilä supplied and installed two almost identical tri-fuel power plants with total capacity of 430 MW for two separate clients in the Dominican Republic. Both Quisqueya plants feature Wärtsilä Flexicycle combined cycle technology and operate on 12 Wärtsilä 50DF dual-fuel engines each. The prime fuel is natural gas with liquid fuels as back-up.

Water use and reliable power

Electric power represents one of the largest uses of water globally. In 2010, water use for energy production accounted for 583 billion cubic meters – 15 percent of the world’s water withdrawals [3]. In some countries the energy sector accounts for even high percentage of water withdrawals. In the U.S. for example, over 40 percent of freshwater withdrawals are for thermoelectric power. Water is used during the extraction and processing of fossil fuels, to power hydroelectric generation and for thermal power plant cooling and emissions control systems.

The World Bank estimates that 90 percent of global power production is water intensive [4]. With global electric demand expected to grow 35 percent by 2035, water withdrawals will increase 20 percent and consumptive water use will rise 85 percent.

Fig. 3 - Water demand for power generation will increase significantly in developing countries.

Table 1 - Fuel flexibility of Wärtsilä engines compared to gas turbines.

Fuel flexibility characteristic Wärtsilä DF engines Wärtsilä GD engines Gas turbines

Ability to run on crude, HFO, LFO and gaseous fuels

Insensitive to metals and salts in fuel oils

No increased maintenance needs when running on fuel oil

Instantaneous switchover from gas to fuel oil

Switch fuels while maintaining full load

Fuel sharing operation

32 in detail

[ EN

ER

GY

/ I

N D

ET

AIL

]


Withdrawal refers to the amount of water used that can be returned to its source while consumptive water use reduces the amount of water that can be used for other purposes because it is lost to evaporation or incorporated into byproducts or waste streams. The growing competition for water use by people, energy, agriculture, and industries is particularly pronounced in developing countries. The interdependence of energy needs and water resources in developing countries is captured in the World Bank’s infographic (Figure 3).

Power plant cooling needs dominate water use

Thermal power plants – which include coal, nuclear, oil, biomass and natural gas fueled generation – currently account for 80 percent of global electricity production. Most of these power plants utilize steam-electric technology, in which water is used to produce steam which spins turbines to produce electricity. This steam is passed through a condenser and cooled before being used again. Cooling is accomplished through one of three main methods:

Once-through cooling systems require very high water withdrawals from adjacent waterbodies such as rivers, lakes or oceans. In these cooling systems, a large volume of water is passed through the condenser, and a portion of the water is returned to the source at a higher temperature. Although once-through systems are highly effective, large water intake structures and excess heat from discharged water can be detrimental to aquatic organisms. Environmental regulations have sought to limit such impacts and as a result many new power plants employ recirculating cooling systems.

Recirculating cooling systems cool water by exposure to ambient air in either cooling towers or (less frequently) cooling ponds. Heat transfer with air occurs primarily through evaporation. As water evaporates, minerals and other impurities in the remaining coolant water become increasingly concentrated and must be removed by periodic “blowdown” cycles. Recirculating systems only withdraw make up water to replace evaporative losses and maintain water quality. Recirculating cooling

systems withdraw 20 – 80 times less water than once-through systems, but the percentage of water consumed is much greater. Once-through cooling systems consume about 4 percent of the water withdrawn, while recirculating systems consume 80 percent of the water withdrawn. There are several different designs for cooling towers to facilitate air to water contact, depending on the ambient conditions and heat load from the condenser.

Dry cooling systems use mechanical forced air systems to condense steam and have no water requirements. While well-suited to arid climates, dry cooling systems are less efficient, particularly at high ambient temperatures. Dry cooling is not suitable for power plants that have significant steam production and thus large cooling needs.

Although power plants use water for various processes including pollutant scrubbing to control air emissions, sanitary systems, plant cleaning and fuel processing, the vast majority of water use is for cooling. Lifecycle analysis of water use from extraction through operation found that water for cooling purposes dominates water use in natural gas-fueled power plants [5].

How much water do power plants use?

The amount of cooling required by a steam-electric power plant correlates with its efficiency, irrespective of the fuel used. More efficient power plants have less heat loss and therefore lower cooling needs. Reviews of water consumption rates at power plants have shown that while a nuclear power plant with cooling towers will consume about 2500 liters/MWh, a CCGT power plant with recirculating cooling will consume approximately 780 liters/MWh [6]. In comparison, a Wärtsilä ICE power plant operating in simple cycle on natural gas will consume mere 3 liters/MWh. This is due to the high efficiency and low cooling needs of Wärtsilä engines.

In combined cycle plants, the output from the steam portion of the plant affects water consumption. About half of the output in a CCGT power plant is generated from through steam cycle, and one-quarter of the energy is lost through evaporation. In a Wärtsilä Flexicycle power plant the

steam cycle only contributes 10 percent of the load. Thus, because of lower steam cycle temperatures, a Flexicycle plant with cooling towers uses about 50 percent less water than a comparably-sized CCGT with cooling towers. In combined cycle, a Flexicycle plant with a cooling tower will consume only 409 liters/MWh. Water use at a Wärtsilä Flexicycle plant is compared with other technologies using cooling towers in Figure 4.

Flexicycle plants typically utilize a water-cooled condenser and induced draft cooling tower. In water-stressed regions, Wärtsilä’s Dry Flexicycle™ plants utilize air-cooled condensers (dry cooling) to reduce water use to near zero. The cooling system uses a radiator closed-loop circuit and fans to help dissipate heat. Dry cooling is seldom used at CCGT plants as it imposes increased costs and reduction in plant efficiency.

Analysis of derating due to dry cooling compared with cooling towers found that on hot days, CCGT output would degrade by 3 to 9 percent [7]. Water consumption at a 12 x Wärtsilä 18V50SG power plant (gas engines) in simple cycle and Flexicycle operation is compared with a CCGT plant in Figure 5. All plants are nominally sized at 220 MW. Dry Flexicycle plants use 96 percent less water than a CCGT with cooling towers. Wärtsilä power plants offer efficient electric generation with the lowest water use of any thermoelectric technology. (Figure 5)

With low water requirements and fuel flexibility, Wärtsilä simple cycle and Flexicycle power plants are able to ensure reliable electric supply even in regions of the world with potential fuel supply disruptions or water scarcity. Fuel flexibility was a major factor in the selection of Wärtsilä multi-fuel engine technology to help solve energy supply challenges in Jordan, where chronic water shortages are also a problem. The 573 MW IPP3 plant, comprised of 38 Wärtsilä 50DF engines that can utilize natural gas, LFO and HFO is the largest tri-fuel power plant in the world, providing Jordan with dependable power.

The growing energy needs of developing countries and protecting water supplies are often viewed as competing priorities, but Wärtsilä power plant technology can meet both objectives.

33in detail


References

[1] “US and European Energy Supplies Vulnerable to

Climate Change – Nature Climate Change Study.”

International Institute for Applied Systems Analysis.

IIASA, 03 June 2012. Web. 27 Jan. 2015. <http://

www.iiasa.ac.at/web/Resources/MediaCenter/

NewsForJournalists/Archive/2012/US-and-

European-energy-supplies-vulnerable.en.html >.

[2] Kurz, Rainer, Klaus Brun, Cyrus Meher-Homji,

and Jeff Moore. “Gas Turbine Performance and

Maintenance.” Proceedings of the Forty-First

Turbomachinery Symposium. Houston, TX.

Turbomachinery Laboratory, Texas A&M University

and Solar Turbines Inc., 2012.

[3] International Energy Agency. Water for Energy:

Is Energy Becoming a Thirstier Resource? Paris,

France: OECD/IEA, 2012. <http://www.iea.org/media/

weowebsite/2012/WEO_2012_Water_Excerpt.pdf>.

[4] “Thirsty Energy: Securing Energy in a Water-

Constrained World.” Sustainable Development.

The World Bank Group, 29 Aug. 2013. Web. 27

Jan. 2015. <http://www.worldbank.org/en/topic/

sustainabledevelopment/brief/water-energy-nexus>.

[5] Meldrum, J., S. Nettles-Anderson, G. Heath, and

J. Macknick. “Life cycle water use for electricity

generation: a review and harmonization of literature

estimates.” Environmental Research Letters, 8:1. 12

March 2013.

[6] Macknick, J., R. Newmark, G. Heath, and K.C.

Hallett. “Operational water consumption and

withdrawal factors for electricity generating

technologies: a review of existing literature.”

Environmental Research Letters, 7:4. 20 December

2012.

[7] Maulbetsch, John S., and Michael N. DiFilippo.

Cost and Value of Water Use at Combined-cycle

Power Plants. Rep. no. CEC-500-2006-034.

Berkeley, California: California Energy Commission,

2006. Web. 27 Jan. 2015. <http://www.energy.

ca.gov/2006publications/CEC-500-2006-034/

CEC-500-2006-034.PDF

Fig. 4 - Wärtsilä Flexicycle power plants consume nearly 50 percent less water than a similarly-sized CCGT power plant and 75 – 85 percent less water than a coal or nuclear plant with cooling towers.

Fig. 5 - Wärtsilä Dry Flexicycle™ power plants consume 96 percent less water than a CCGT plant.

0.70

2,000

0.80

3,000

2,500

0.20

500

0.10

0.30

0.50

0.40

1,000

0.60

1,500

0.00

0

Water consumption: Wärtsilä engines vs. CCGT

Water consumption at power plants with cooling towers

Wat

er c

onsu

mpt

ion

(m3 /M

Wh)

Wat

er c

onsu

mpt

ion

(Lit

ers/

MW

h)

Wärtsilä Simple cycle

Flexicycle

Flexicycle (cooling towers)

Nuclear

DryFlexicycle

CCGT

CCGT(cooling towers)

Coal

34 in detail

[ MARINE / IN DETAIL ]

[ MA

RIN

E /

IN

DE

TA

IL ]

New LNG Tug opens a marketAUTHOR: Giulio Tirell i , Dire c tor, Eng ine s Por t fo l io & A pplic at ions , Wär t si lä S hip Power

Wärtsilä recently signed a contract related to the first LNG Tug to operate in the Middle East. This represents a milestone for two major reasons: the very demanding performance requirements of this vessel, and the opening of a new geographical area for the utilization of liquefied natural gas (LNG) as fuel.

LNG as a marine fuel is not a new topic and neither are tugs. However, the combination of these two elements makes the recently signed contract between Drydocks World (DDW) and Wärtsilä a remarkable milestone in the marine industry.

The background of this development lays in the ‘green’ initiative launched by the Dubai government. This is intended to set an example for promoting environmental sustainability throughout the region.

Consequently, and in alignment with the same initiative, in May 2014 Drydocks World announced the signing of a Memorandum of Understanding (MOU) with Wärtsilä. The target was to put into practice the Dubai Government’s wish and

develop the marine market in the United Arabs Emirates (UAE) accordingly. The vessels identified as the most promising for being the first capable of operating with a drastically reduced environmental footprint were tugs.

In November 2014, the technical and economic details between the two parties were settled and the contract for the first in a series of nine harbour tugs was signed and announced to the market.

When delivered later in 2015, this vessel will be the first to be fuelled by LNG in the Middle East region. LNG was already present and available in the market, but had always been used as a commodity and, up to now, never as marine fuel. The


35in detail

milestone represents, therefore, not only a technical and environmental achievement, but it opens new opportunities for different applications to be developed in the area. The vicious circle commonly related to the lack of an available LNG fuel supply slowing developments in LNG-powered vessels, and vice versa, has thus been dissolved by this first contract signed. It is now more likely that other vessel types will be designed to operate on LNG in the Persian Gulf. Hypothetically, even bigger liners calling at ports in the area could possibly bunker LNG for use on longer routes, or for when operating in Emission Controlled Areas (ECA).

The technical challenge

Tugs are vessels specifically intended to be capable of the highest performance in assisting, towing or re-positioning a vessel. The commonly accepted measure for characterising the effectiveness of such vessels is the “tons of bollard pull” (TBP),

the force that the vessel is able to exert on the towing line at zero speed. This is, in fact, tested on a shore-mounted bollard.

This force is achieved from the effective performances of the propulsion components and their integration. For the specific project presented in this article, a level of 55 TBP was specified. Two Wärtsilä 9L20DF (nine cylinders in-line 20DF dual-fuel) engines, combined with WST-18 Wärtsilä Steerable Thrusters (WST) were selected as being the best choice for achieving the required performance.

A typical characteristic of the operational profile of tugs is their very low utilization rate. Tugs often have an extremely low number of running hours during a year. In indicative terms, a harbour tug could be running for some 2000 hours a year, which is very little, especially if compared to liners or Ro-Pax vessels that usually operate on a 24/7 basis.

While assisting a vessel, the majority of the time is spent waiting on stand-by with

the engines idling or operating at extremely low power. This new tug has been designed to be capable of handling all operational requirements while continuously running on gas. The selected Wärtsilä 20DF dual-fuel engines match perfectly this requirement, since they are capable of being started, running without load, and operating continuously at any engine load constantly in gas mode.

If it is true that engines installed on a tug will be operated for the majority of their lifetime at extremely low loads, the transition time needed to reach their maximum output is usually extremely short. The operator commonly demands full power almost instantly from the tug’s thrusters. This requirement stems from the need to reduce the operational time to a minimum, and to be able to handle possible emergency situations with the most time-efficient response. Again, Wärtsilä dual-fuel technology was selected as the most suited for achieving maximum vessel

36 in detail


[ MA

RIN

E /

IN

DE

TA

IL ]

performance. The engines themselves have outstanding load taking capabilities, being able to adjust to the tug operators’ requirements. In addition, the dual-fuel technology ensures that, even in a possible combined situation of high load demand and a failure in the gas supply system, the engine will be able to continue increasing its load by simply switching to diesel. The operator would, therefore, not even notice the difference in vessel response to his operational requirements and could complete the manoeuvre in the most safe and reliable way. Once the possible failure in the gas supply system is fixed, the engines could again be switched back to gas operation without any loss in power or speed. (Figure 2)

Performance is not the only criterion. Tugs are commonly extremely compact and agile vessels, where the equipment installed onboard should occupy the minimum space required without compromising the reliability and safety of the vessel.

The challenge for the utilization of LNG as marine fuel comes, consequently, from the usually considerable space needed for the LNG storage tank(s) vs. the restricted onboard space availability. The answer to

that is twofold: Wärtsilä dual-fuel engines are intrinsically redundant products, thanks to their capabilities to instantaneously and seamlessly switch from gas to diesel in whichever operative condition. Since this redundancy is already inherently built into the engines, no additional redundancy is required from the fuel gas system, thus the Wärtsilä LNGPacTM fuel storage and supply system was designed with the smallest onboard footprint. A single Wärtsilä LNGPac (having a capacity of approximately 25 m3) and a single tank connection space (commonly referred as the “cold-box”, the space where the majority of the LNG process equipment and safety devices are installed) matched the project requirements with high levels of redundancy and safety and were, consequently, selected. (Figure 3)

The economic impacts

As outlined earlier, the annual running hours for a tug vessel are often fairly low. This aspect clearly has a direct impact on the cost structure for a tug owner or operator. Where in other shipping applications fuel costs are almost always among the two highest factors influencing economic performance, tug owners and operators

typically see costs related to Investment and Depreciation having a greater effect than the cost of fuel.

Fuel consumption is, nevertheless, a very high priority because of both cost consciousness and environmental impact. However, the initial investment cost of a tug is one of the most important criteria for owners when choosing a new vessel. From this perspective, the LNG-as-fuel alternative could appear to be quite challenging, due to the implied increase in the initial vessel Capital Expenditures (CAPEX).

DDW and Wärtsilä were able to meet the requirements of the owner and operator (consequently making this project economically sound) also from this perspective, thanks mainly to two items: again the specificity of the dual-fuel solution, meaning that a single LNG tank combined with a single “cold-box” could be selected, thereby keeping the CAPEX level to a minimum, and the strong integration work done between the different elements included in the project.

By integrating the ship design, engines, propulsion equipment, LNG storage and onboard process system(extended to include also bunkering stations), and the

Fig. 1 - An artistic impression of the 55 TBP LNG-powered tug scheduled to become operational in 2015.


37in detail

Fig. 2 - Tug operating profile and operational time distribution.

20

30

100

100

25

80

80

5

20

20

10

40

40

15

60

60

0

0

0

Ope

rati

ng ti

me

(%)

Engi

ne lo

ad (%

)

Loite

ring/

Stan

dby

Ass

ist,

10%

MC

R

Ass

ist,

15%

MC

R

Ass

ist,

25%

MC

R

Ass

ist,

60%

MC

R

Ass

ist,

100

% M

CR

Ass

ist,

30%

MC

R

Operating time (%)

Operating profile Average engine load

38 in detail


[ MA

RIN

E /

IN

DE

TA

IL ]

automation, the overall CAPEX of the vessel was within market standards, making this project also a good base for possible further fleet expansions. (Figure 4)

The tug market has other peculiarities as well. Vessels are often intended as flexible assets, capable of being utilized in different ports or conditions despite having been originally intended to operate in a specific location. This makes the second hand market for tugs particularly active and transparent. The dual-fuel solution ensures that the second hand value of the

owner’s asset will remain high throughout the entire lifetime of the vessel. In fact, the tug will not be limited to operating only in harbours where gas is available, but could be utilized wherever its technical specifications are suited to the requirements of the job. Therefore, during its lifetime, the dual-fuel-powered tug could be used for different periods of operation in different fuel modes (gas or diesel, independently) without the need to change or modify the installed equipment, thus avoiding possible related expenditures.

The same consideration applies to another fairly frequent activity in the tug market, which is the need to re-locate the vessels to different harbours for certain operational periods. During the voyage between harbours the dual-fuel technology allows the owner or operator to sail the vessel in complete autonomy, regardless of the transfer distance, voyage duration or fuel availability.

The tug could easily utilize diesel as an alternative fuel while re-locating, and switch back to gas when reaching the port

Fig. 3 - Indicative general arrangement drawings for the LNG Tug. A single LNGPac, a single “cold-box” and two dual-fuel engines mechanically driving the thrusters are at the core of the advantages of such a vessel, combining the lowest CapEx with the lowest OpEx and the highest level of safety.


39in detail

Investment & Depreciation 33%

Crewing and Management 42%

Fuel and other consumables 15%

Regular maintenance 7%

Cyclical maintenance 3%

Vessels not operating in ECA 25%Vessels operating in ECA 75%

Fig. 4 -Indicative total cost of ownership structure.Source - ITS 2014 Damen Shipyards Gorinchem (Dirk Degroote/Robert van Koperen).

Fig. 5 - Proportion of the total tug fleet operating in or passing through ECAs.

of destination. The same applies to delivery of the tug from the shipyard to the point of operation, or when going to and coming from a repair yard.

The dual-fuel capability also enables the use of a smaller LNG tank, since missions requiring longer sailing time can be made partly in diesel mode. LNG storage is often cited as being one of the most costly items related to LNG powered vessels.

The DDW-Wärtsilä LNG Tug project is a breakthrough thanks to its technical performance, equipment optimization

and integration, and its sound economics. With about 75% of the total worldwide fleet of tugs currently operating in or passing through ECAs, the LNG solution seems to have gained market acceptance. This project, therefore, opens the path to new market expansions towards operational flexibility combined with environmental sustainability. (Figure 5)

40 in detail


[ MA

RIN

E /

IN

DE

TA

IL ]

The new Wärtsilä Steerable Thruster family AUTHORS: El ias Boletis , Dire c tor, Re se arch & D evelopment

Norber t Bulten, G eneral Mana ger, Hydro dynamic sAlber t Drost , Prog ram Mana ger

To provide the optimal solution for vessel applications where the steerable thruster requirements vary according to the vessel type, Wärtsilä has developed a new series of steerable thrusters with a power rating from 800 kW to 3 MW.

When it comes to steerable thrusters with a power rating of 3000 kW, applications vary and include vessels such as tugboats, OSV (Offshore Support Vessels), PSV (Platform Supply Vessels) and AHTS (Anchor Handling Tug Supply Vessels). As the application varies so do the requirements set towards the propulsion unit, in this case the steerable thruster. To provide the

optimal solution for this market Wärtsilä has developed a new series of steerable thrusters, which is highly versatile and can be configured to comply with the specific vessel requirements. This is done without compromising on cost, simplicity, reliability or efficiency. On the contrary, as compared to available existing thrusters, the new Wärtsilä steerable thruster (WST)

Fig. 1 - The new WST-18 thruster (for the Nam Cheong offshore vessel).


41in detail

is more efficient, stronger and can comply as standard with ice-classes up to ice-1B. At the same time, the thruster can deal with various input speeds ranging from 750 to 1800 rpm, which means that it can be connected to more or less any diesel engine. The WST-18 is the first in this series to be introduced onto the market. The first field applications include the propulsion units for an offshore vessel (Nam Cheong Shipyard) and a harbour tug (Drydocks World Dubai).

Systems integration

By updating the systems and through extensive integrating, the physical dimensions of the thruster have remained small, thereby reducing the need for additional space in the machine room. This also allows the thrusters to be installed from either below, above, or split mounting. This was achieved by building-up all the hydraulics onto the top-plate and, where possible, integrating the oil conduits and the lubrication pump into the castings. Another feature contributing to the reduced space requirements is the integration of the clutch into the upper gearbox housing, which in addition serves as the support for the power take-off. The clutch itself was specifically developed for the WST thrusters in cooperation with one of the main clutch

suppliers, and is available in either on/off or slipping execution, thus enabling optimal operation of the engine and thruster under all conditions. The clutch suits either a CPP (Controllable Pitch Propeller) or FPP (Fixed Pitch Propeller) thruster application.

Drive-train and supporting structure

The drive-train of the thrusters has been designed based upon the experience gathered from the field and the latest insights in gear and bearing design. The latest design tools allow any operational conditions caused by gear misalignments resulting from the accumulated effect of geometric tolerances, loads and temperature expansion, to be taken into account. This data is then used when calculating the gear-teeth flank topology.

Propulsion controls

Together with the next generation of thrusters, a new machinery controls automation platform has been developed. The Local Machinery Control System (LMCS) contains redundant embedded controllers and has a full colour Human Machine Interface (HMI) 7” touch screen at the door of the cabinet. The HMI’s user friendly Graphical User Interface (GUI) supports local control of the steering and

thrust, calibration and test modes, as well as trending and logging, since the thruster’s sensors and transmitters are all connected to the LMCS. By standardizing the instrumentation and with the use of fieldbus technology, engineering, assembly, test, installation and commissioning times are all reduced. The LMCS can interface with an external remote control system by means of fieldbus, as well as with the Wärtsilä ProTouch system to enable remote control of the thruster from the bridge and engine control room.

The state-of-the-art ProTouch system with its levers, touch screen displays and indicators, can easily be fitted into even the most compact bridge designs, while providing the user with full manual control under all circumstances. Other sailing modes, such as dynamic positioning, joystick and auto pilot, are supported by means of standardized interfaces to those systems and with clear visual information of the selected mode for the operator on the bridge.

Optimized hydrodynamic unit design

The propeller is obviously the most important and complex part in the design process, since it has to transfer all the engine power into the water and to convert it as

42 in detail


[ MA

RIN

E /

IN

DE

TA

IL ]

efficiently as possible into a thrust force. Based on years of hydrodynamic research, it has been established that the cross-sectional shape of the nozzle, which is placed around the propeller, has an important impact on the occurring flow phenomena. The pressure distribution around the nozzle can easily produce about half of the total unit thrust in the so-called bollard pull condition. Therefore, the design of the nozzle and propeller need to be aligned in order to achieve optimum performance.

In the hydrodynamic design process of the lower gearbox housing and the vertical shank, the main focus is on reducing the drag of these components as much as possible. The main dimensions of these components are to a large extent, however,

dictated by the interior mechanical parts. Wärtsilä’s hydrodynamic experts make

use of a variety of design tools to develop the optimum design of the units. This includes, to a large extent, the use of computational fluid dynamics.

Propeller variants

The WST-18 thruster units can be equipped with either FPP or CPP propellers, according to the need of the application. Based on the physics, the hydrodynamic efficiency of an FPP will be the highest. Nevertheless, the CPP can be a good alternative should multiple operational conditions need to be covered.

With an FPP there is a direct relationship between power and the RPM for any given

ship speed. This might be a limiting factor where both bollard pull and free sailing performance are important.

Two diameter options are available with the WST-18 type (2200 mm and 2400 mm) covering most of the needs of ship installations in this market section.

Nozzle variants

The fact that steerable thrusters are being used for different operational profiles (bollard pull or free sailing) has resulted in the development of two different nozzles. The bollard pull nozzle has a length that is 0.5 of the propeller diameter (L/D=0.5) and a specifically designed nozzle exit area. The effectiveness of this nozzle is best at low ship speeds. At ship speeds in the range of 12 to

Fig. 2 - Calculated velocities of the jet stream of the thruster in bollard pull condition.


43in detail

16 knots, the contribution to the total thrust is limited.

For free sailing applications, a dedicated nozzle design has been developed, which has improved performance in the free sailing speed range. The length of the nozzle has been reduced to 40% of the propeller diameter. This reduces the wetted area on the outside significantly, which is beneficial for drag reduction at transit speed.

Design tools & methods

The design of the propeller geometry has been carried out using various in-house developed propeller design software modules. In order to properly determine the impact of the thruster housing geometry on the performance, and to analyze the occurring flow phenomena,

the commercial CFD (Computational Fluid Dynamics) software Star-CCM+ has been used. The viscous CFD calculation method has been validated extensively within the Hydrodynamics department. Nowadays, accurate predictions can be made not only for thruster performance, but also on the detailed transient blade loading fluctuations. These blade load fluctuations can be a result of the flow obstruction of the shank or, alternatively, due to oblique inflow at a given steering angle.

The thruster validation process

Wärtsilä follows a systematic approach to thruster validation. This includes the production of a prototype unit for the series (a WST-14 in this case), which is used for the validation of the manufacturing process

and the design structural integrity. Testing of the latter is carried out at our full load test facility in Tuusula, Finland. The test facility allows the simulation of field loads as applicable in high ice classes.

Fig. 3 - Calculated streamlines and pressure distribution on the thruster unit in free sailing condition.

44 in detail


[ MA

RIN

E /

IN

DE

TA

IL ]

The new Wärtsilä LNGPac™ – a step towards greener shipping AUTHORS: Vik tor Bergman, D evelopment Eng ine er, Fuel G a s Handling , Wär t si lä S hip Power Mathias Jansson, S enior Mana ger, Fuel G a s Handling , Wär t si lä S hip Power


45in detail

The shipping industry is facing new challenges. With fluctuating fuel prices and more stringent environmental regulations, ship owners have been forced to look for alternative fuels to power their ships. Liquefied natural gas (LNG) is the solution to most of the problems and with LNG becoming increasingly viable and popular as a marine fuel, Wärtsilä continues to develop technical solutions that facilitate this trend. Wärtsilä’s latest developments in this field include an upgraded version of the Wärtsilä LNGPac, an integrated fuel gas handling system, and the Wärtsilä Gas Valve Unit (GVU).

Wärtsilä introduced its first LNGPac in 2010 and the first LNG project, the conversion of the chemical tanker Bit Viking from conventional heavy fuel oil (HFO) to LNG, was completed already in 2011.The LNGPac comprises a complete LNG fuel gas handling system, including the bunkering station, the LNG tank and tank connection space with the necessary process equipment, the heating media skid, and the control and monitoring system. This unique system has proven to be a valuable enabler of LNG fuel for marine applications with more than 50 LNGPac systems in operation or on order.

Since the system’s introduction in 2010, there has been a strong focus on further developing the system so as to provide a simple LNG system that is also the most efficient on the market. Wärtsilä’s vast knowledge base and product offering has made it possible to look beyond just the fuel system, and instead combine and integrate other components of the ship into the LNGPac.

Modularisation and integration is the key to success

An effective way of reducing uncertainty, while also making the installation time faster, is by modularising the larger components. In this way separate

components can be built simultaneously and remotely from each other. The components can be pre-tested and transported to the yard for quick and simple installation.

The new LNGPac introduces many significant improvements, all of which have one thing in common; they make the fuel system more compact with fewer interfaces. The development work included an emphasis on removing unnecessary interfaces and equipment, thus making the complete package as compact and simple as possible. Besides reducing the capital expenditure (CAPEX) and physical dimensions, a significant reduction in operational expenditure (OPEX) has also been achieved. This continuous development has resulted in a much improved LNGPac.

Wärtsilä has taken every stakeholder into consideration when designing the new LNGPac. Not only is the end customer, the ship owner, gaining a huge economic benefit from the optimised operational performance and interface integration, but the shipyard also profits from the fact that the installation can be made easier and faster.

Significant improvements

The airlock had previously been kept as a separate room allowing passage into the

Fig. 1 – The New Wärtsilä LNGPacTM features many new benefits for all stakeholders.

46 in detail


[ MA

RIN

E /

IN

DE

TA

IL ]

tank hold space. This setup has taken up unnecessary floor space, while also causing the entire tank hold space (the space containing the LNG storage tank) to become a hazardous area when access to the tank connection space has been needed. In the new LNGPac, the airlock is integrated with the tank connection space which reduces the footprint, increases safety, and makes the installation for the yard much easier.

In addition to the airlock, the control cabinet has also been integrated with the tank connection space. This innovation dramatically reduces the amount of electrical cabling required to connect the LNGPac to the external switchboards, while also minimising the number of interfaces. Furthermore, all electrical wiring can be pre tested before shipping the LNGPac to the yard. By integrating the control cabinet, Wärtsilä has been able to reduce the installation time even more and eliminate almost all risk and uncertainty associated

with the electrical cabling work.The Wärtsilä GVU is a module located

between the LNG tank and the dual-fuel (DF) engine. It is used to ensure a safe and reliable gas feed to the engines, as well as a safe disconnect of the gas system should that be necessary. The GVUs have previously been placed in a completely separate, gas tight room onboard the ship. The GVU room needed to fulfil several requirements: it housed all the electrical equipment necessary for ATEX (Atmosphères Eplosibles – Explosive Atmospheres in English) hazardous area compliance, it required an airlock to be installed to allow access to the room, and needed redundant ATEX ventilation fans, etc.

The new LNGPac offers innovative alternatives for the GVU solution; it can now be either enclosed or integrated. In the enclosed design all process components of the GVU are placed within a compact gas tight enclosure, enabling the GVU

to be placed inside the engine room. The enclosure functions as a secondary barrier in case a of a gas leakage and eliminates the need for a separate room solely for the GVUs.

Further development of the GVU has enabled its functional components to be installed inside the tank connection space. By combining the LNGPac and the GVU into a single, fully integrated system, considerable space can be saved and a simple ‘plug and play’ solution saves installation time and costs for the yard.

Previously, a separate heating media skid containing the pumps, located separately from the LNGPac, has been used to provide heat for evaporating the LNG. In the new LNGPac the heating media skid is replaced by natural circulation of an intermediate heating media inside the tank connection space. The new heating media circuit requires no pumps and directly utilizes the engine’s cooling water, resulting in fewer

Conventional LNGPac (before).


47in detail

New LNGPac™ (after)

Efficient space utilisation Fewer interfaces Reduced installation

and operating costs Increased reliability Maximised LNG

storage volume Improved cold recovery

New LNGPac (after).

interfaces and less installation work. By enabling fewer electrical consumers Wärtsilä is making ships even more environmentally friendly.

A similar modification has been made to Wärtsilä’s Cold Recovery solution, which enables the cold energy of the LNG to be utilised by the ship’s HVAC-system (Heating, Ventilating, and Air Conditioning). In the new Cold Recovery system, Wärtsilä has been able to directly connect the ship’s HVAC (or other refrigeration systems) to the tank connection space, thereby removing a complete circuit consisting of heat exchangers, valves and pumps.

Leading the way

Today, Wärtsilä is recognized as the leader in propulsion solutions for gas fuelled vessels, and has led the way in developing a complete value chain of systems, solutions and bunkering arrangements – both

onboard and shore-based – to accelerate the use of environmentally sustainable and economically competitive LNG fuel. These latest developments are fully in line with Wärtsilä’s commitment to ensuring better economic and environmental performance for the marine sector.

48 in detail


[ MA

RIN

E /

IN

DE

TA

IL ]

The global market for Wärtsilä Controllable Pitch Propellers (CPP) has shifted during recent years. From a situation where commercial and contracted vessels constituted a large part of the market, we have seen a temporary decline in ship building and a change in the operational conditions. The current market is dominated by offshore vessels, such as anchor handling tug supply vessels (AHTS), production

supply vessels (PSV), and special vessels. Offshore sector vessels are today operating more heavily in dynamic positioning (DP) mode, which imposes different demands on the CPP installation. We also expect to see a shift towards high ice class vessels capable of operating in the Northwest Passage when this becomes more easily accessible. The market decline due to the financial crisis, plus the shift in the ready market, has increased the

As the market for Wärtsilä Controllable Pitch Propellers increasingly focuses on offshore applications, the company seeks to increase its position with its new Wärtsilä CPP product.

Increasing market share for Wärtsilä Controllable Pitch PropellersAUTHORS: El ias Boletis , Dire c tor, Re se arch & D evelopment

Monica Grimstad, G eneral Mana ger, Me chanic al & S te er ing S ys temsNorber t Bulten, G eneral Mana ger, Hydro dynamic s

Fig. 1 - Numerical flow simulation of twin screw vessel with controllable pitch propeller.


49in detail

Fig. 2 - The new Wärtsilä Controllable Pitch Propeller with main design features.

competition to win contracts. In addition to high quality, Wärtsilä CPPs have to be cost competitive to win market share.

Wärtsilä Controllable Pitch Propeller project

This has led Wärtsilä to address the situation through its WCP (Wärtsilä CPP Project) initiative. This project seeks to increase market share by refining and updating the current CPP E-hub, the oil distribution boxes, the hydraulic power pack, and the controls system. The Wärtsilä CPP hub is a high power density hub, built for high vessel speed, low noise, and good hydrodynamic properties. The updating objectives of the hub have been to strengthen it so as to make it more suitable for both DP demands and ice operation, to reduce the total weight, to optimize it for environmental acceptable lubricants (EALs), and to reduce the overall cost. The oil distribution box transfers the hydraulic power from the static to the rotating parts of the propeller shaft assembly. The transfer needs to be reliable, and with a low pressure drop. The oil distribution box also includes valves to lock the blade pitch angle in case the hydraulic power of the system is lost. The refined version optimizes the pressure drop to the flow needed for each hub, and increases the resolution of the pitch position feedback. The incorporation of the new Wärtsilä Controls and updated Controls Software provides advanced system reliability.

The new Wärtsilä CPP hub design

The new Wärtsilä CPP hub covers high power density installations in the mid to upper range. Several components like the moving yoke are made of a stronger material, resulting in a stronger structure and smaller hub size in many cases. The blade bearing geometry has been optimized to lower the peak surface pressure and the blade foot has been made symmetrical for ease of manufacturing. The hub flange cover has been redesigned to reduce the overhang of the propeller. This will reduce the inclination at the aft sterntube bearing of the propeller shaft. With the new cover it is also possible to disassemble the hub from the propeller shaft without pulling the propeller shaft from the sterntube, thereby easing service activities.

With the new VGP (Vessel General Permit) rules and the demand that EALs be used as the hydraulic oil to control the blade pitch, there is a need to be able to flush the hydraulic oil out of the hub for monitoring purposes. The new Wärtsilä CPP hub has a flushing system whereby all the oil in the hub (both the hydraulic and the lubrication oil) is shifted within hours. In this way the oil can be thoroughly monitored and checked. Note that the flushing system is unique for the Wärtsilä hubs and a patent application is in process.

The weight of the hub has been reduced by 7% (size 1190) and the load capacity increased by 8%. With these

improved features and the cost reductions implemented, the Wärtsilä CPP hubs are stronger, lighter and compatible with EALs.

The new Wärtsilä CPP hydraulics

The hydraulic system is, to a large extent, the brainpower of any CPP installation. Controlled by the vessel control system or the DP system, the hydraulic system has to deliver the hydraulic power to move the blade pitch position as commanded and feed back the pitch position signal continuously. The updated oil distribution box portfolio has been optimized to provide the flow needed for the total Wärtsilä CPP portfolio in order to minimize the pressure drop. Variations in the design of the different sizes have been limited in order to ease manufacturing requirements and service activities. There will also be a poka yoke (‘mistake-proofing’) system on the oil connections. The interface with the marine gear box is unchanged from that of the current portfolio enabling the use of the new oil distribution box on existing installations. The size is based upon the selected hub’s total stroke and needed flow. The new oil distribution box will be EAL compatible as standard, and all sizes have a high resolution, contact free, pitch position sensor. For each size, there is a weight reduction of 10% with the new design and the number of unique parts has been reduced by 20%, providing benefits during

Easy hub disassemly

EAL compatibleFlushed system

Steel yoke Gilding Wipers

50 in detail


[ MA

RIN

E /

IN

DE

TA

IL ]

the manufacturing process and the logistic handling.

For the hydraulic system power there are two main designs. The hydraulic power can be integrated into the marine gear box, or can be a standalone unit known as the hydraulic power pack. For the new Wärtsilä Hydraulic Power Pack (HPP), the main aim has been to have total Wärtsilä ownership and control of the design. During the last 10 years, there has been an increase in the number of variations of installed HPPs, and the portfolio needed to be streamlined. The new portfolio will reduce the number of variants from more than 104 to less than 28 standards. There will be no class variants, which makes it easier to engineer with fewer risks.

The use of current Wärtsilä logistic and documentation systems safeguard the integrity of the technical information and quick response to customer inquiries. All electrical signals from the HPP will

be available for the Wärtsilä CPP-CBMS (Condition Based Monitoring System) and the connections (both electrical and hydraulic) have been standardized and optimized for ease of installation and commissioning. The HPP will be compatible with EAL installations and prepared for options, such as extra flushing of the hub, water separation, and oil monitoring.

The new Wärtsilä CPP propulsion controls

As part of the WCPP project, the next generation platform for the machinery controls’ automation for CP propellers has been developed. This platform interfaces with the recently introduced Wärtsilä ProTouch remote control system of levers and displays, or to any external remote control system.

The core part of this machinery control is the Local Machinery Control System (LMCS), which contains redundant embedded controllers and has a full colour

Human Machine Interface (HMI) 7” touch screen at the door of the cabinet. The new LMCS will replace the current Lipstronic7000 PCU cabinet and the so called Hydraulic Control Unit (HCU) for applications having a separate HPP. The new control system design is modular thus enabling cost effective solutions and, since it fits the complete range of the new hub and its related marine markets, it also supports more complex configurations. The HMI’s user friendly Graphical User Interface (GUI) supports local control, calibration, and test modes, as well as trending and logging as all the sensors and transmitters are connected to the LMCS.

The standardization and further improvement of the HPP’s instrumentation and the OD box/shaft, together with the use of fieldbus technology, reduces the engineering, assembly, test, installation and commissioning times and, therefore, also the costs. The new system provides optimal

Fig. 3 - The complete WCP Propeller system including: Wärtsilä propeller design, propeller hub, shaftline, Wärtsilä Marine Gearbox, Oil Distribution Box, Hydraulic Power Pack, Controls with the Wärtsilä ProTouch.


51in detail

performance for all supported modes, from maneuvering to transit, as well as dynamic positioning.

The Hydrodynamics for WCP systems

In the hydrodynamic design process of WCP propulsion systems, optimal use is made of (a) the use of Wärtsilä’s extensive data base (b) the company’s calculation procedures, and (c) the use of state-of-the-art tools, based on recent developments in numerical flow simulations.

The design of a controllable pitch propeller always involves the challenge of fulfilling the various requirements, including efficiency, cavitation behaviour and blade strength. These requirements need to be met not only in the design pitch, but in all the other possible pitch settings as well so that the propeller works as it should. Bollard pull, dynamic positioning, and astern operation are a few examples of these operating conditions. Since they will be

needed frequently, these conditions must be fully taken into consideration in the design process.

With the numerical simulation tools (CFD), detailed performance predictions can be made for each propeller design. Nowadays these open water performance curves can be calculated overnight on Wärtsilä’s advanced computer cluster. The performance estimates can be made for both model scale and actual full scale. In this way. knowledge can be obtained on the occurring Reynolds scaling effects.

In addition to the open water propeller performance, the overall propulsive efficiency can also be calculated with CFD (Computational Fluid Dynamics). In such simulations the complete configuration of the ship with both propeller and rudder is taken into account. This provides information on the actual efficiency of the propeller in the non-uniform wake field and on the transient blade load

fluctuations during a revolution. This kind of data is difficult to derive from model tests, and therefore it is expected that this sophisticated interpretation of the CFD results will open a new era of understanding of the occurring flow phenomena. This next step in the optimization of propellers is captured with the OPTI-Design process, which has been developed within Wärtsilä.

The WCP Product summary

The new updates to Wärtsilä’s Controllable Pitch Propeller installations strengthen the company’s position in an increasingly challenging market. The importance of environmental solutions to comply with new regulations is clearly visible and the competition is strong. With its new products and solutions, Wärtsilä is assured of being competitive and of having the best technical solutions.

Fig. 4 - Calculated streamlines along vessel with CPP and EnergoPac rudder.

52 in detail


[ MA

RIN

E /

IN

DE

TA

IL ]

The fuel efficiency of an installation is determined at the design stage. All systems should be optimized for their purpose and synchronized with each other. An installation can be compared to an orchestra – for good performance, all musicians must play the same piece of music.

Attention must also be paid to the liquid input such as fuel quality – the water content, heat value, sulphur and ash content of the fuel – and lubrication oil and cooling water quality, as well as measured parameters such as the load of the equipment, ambient conditions and air intake temperature.

Regular maintenance, optimization of the engine and propulsion performance create

Fuel efficiency means the efficiency of the process that converts the chemical potential energy of the fuel into kinetic energy or work. Improving fuel efficiency is the most effective way of reducing operating costs.

The fuel efficiency of an engine is commonly expressed as the amount of fuel consumed per unit of energy produced.

In the marine industry the choice of fuel is largely determined by the engine type, fuel prices and the environmental demands set by the International Maritime Organization (IMO) and international and national authorities in the vessel’s operating areas. At present natural gas offers the easiest way to reduce emissions and in many cases also to lower the OPEX.

Despite recent changes in oil prices, fuel efficiency still has a crucial effect on the operating costs of vessels and power plants, as a majority of the operating expenses consist of fuel costs. With volatile fuel prices and increasingly strict environmental demands, fuel efficiency is a focal point when it comes to deciding on power solutions.

More power with less moneyAUTHORS: Rober t Niemotko, G eneral Mana ger, Innovat ion & Pro duc t D evelopment , Propulsion Por t fo l io , Wär t si lä S er vic e s

Andreas Vestergren, Mana ger, Pro duc t L ine - S mall and Me dium B ore , Wär t si lä S er vic e s


53in detail

the basis for reliable and economically-viable operation.

Improving the engine Specific Fuel Oil Consumption (SFOC)

Correctly-timed service ensures optimum engine performance and fuel consumption. Condition Based Maintenance provides an efficient tool for scheduling the overhauls.

Instead of operating hours, the service intervals in Condition Based Maintenance are determined on the basis of up-to-date information received through communication with the equipment. The constant monitoring and analysis of the engine enables access to premature information on impending failures. Timely maintenance may reduce the number of overhauls and both operating and fuel costs.

The condition of the equipment has a significant effect on fuel consumption. Calculations made by Wärtsilä show that for example on a poorly maintained engine with 5000 kW output, the causes and subsequent increases in fuel consumption listed below could occur within a period of 6000 operating hours.

Partly blocked or dirty nozzle ring of a turbine or a compressor in a turbocharger: loss of 90 tons

Dirty intake air filters: loss of 60 tons Partly-blocked charged air coolers: loss

of 60 tons Worn injection pump elements: loss of

150 tons Worn injection nozzles: loss of 60 tons Increased exhaust gas back pressure: loss

of 9 tons

Furthermore the calculations show that a water content of 1% in the fuel increases the fuel consumption by 60,000 kg. Low fuel heat value causes a fuel loss of 75,000 kg. For every 1% increase of sulphur in the fuel the net heat value will decrease by 0.8%, causing a fuel loss of 45,000 kg, and for every 0.10% of ash content in the fuel the drop of net heat value will lead to a loss of 6000 kg of fuel.

Focus on propulsion

In improving the comprehensive fuel efficiency of a vessel, the propulsion system

comes into focus. The measures available fall into three categories – maintenance of the equipment, tuning the propulsion installation to the operating profile of the vessel and harnessing physical phenomena related to the hydrodynamic properties of the propulsion installation.

Propeller maintenance is a cost-effective way of cutting fuel costs. Both in ports and during operation, propeller blades are subject to marine growth. The higher the water temperature, the stronger the marine growth. Impurities on the propeller blades and cracked or fractured blade edges cause resistance that can lead to a drop ’of up to 5% in the vessel’s performance. They also increase vibration of the vessel, producing negative impacts on the machinery.

A current trend to minimize the operating cost of a vessel is reducing speed, for example from 25 knots to around 20 knots. Modified operational profile also demands tuning of the propeller accordingly. The gained savings in fuel cost can be substantial and may pay off the design and manufacturing costs of a new propeller and the changes to the engine.

In current propeller design, the most sophisticated tool is Computational Fluid Dynamic (CFD) analyses of 3D geometrics. In addition to propeller performance, the software is used to analyze the entire interaction between the propeller and the hull. With this state-of-the-art design protocol, the vessel’s overall propulsive efficiency can be optimized.

In vessels sailing below 15 knots, such as trawlers, dredgers and coasters, conversions from open to ducted propeller can increase bollard pull by up to 25% and sailing efficiency by up to 15%.

Based on its knowledge of hydrodynamics, Wärtsilä has developed energy-saving solutions, i.e. hydrodynamic appendages in the propeller area for additional measures to optimize propeller efficiency and reduce fuel costs. Such solutions include Wärtsilä EnergoProFin and Wärtsilä EnergoPac.

Wärtsilä EnergoProFin is a propeller cap provided with fins which rotates together with the propeller. The Wärtsilä

EnergoProFin increases propulsive efficiency by weakening the hub vortex. The decreased propeller resistance appears in the form of increased propulsion thrust. The overall propulsion efficiency increases by up to 5%. The Wärtsilä EnergoProFin is applicable only with fixed pitch propellers.

Wärtsilä EnergoPac is designed to reduce a vessel’s fuel consumption by fully integrating the design of both the propeller and rudder for optimum energy efficiency without compromising the vessel’s manoeuvrability or comfort level. It reduces flow separation behind the propeller hub. For the same course-keeping capabilities, Wärtsilä EnergoPac creates less drag than conventional rudder systems. The high-lift performance of Wärtsilä EnergoPac requires smaller angles, thus reducing rudder resistance. The potential fuel savings are largest for vessels with highly-loaded controllable pitch propeller systems, such as RoRo vessels, ferries, container and multipurpose vessels, and ships with an ice notation.

Improved operational efficiency through fuel conversions

The need to reduce operational expenditure and the new emission regulations are key issues for the marine and power industries. While the reciprocating engine will maintain its strong position in the foreseeable future, gas is increasingly gaining ground as a fuel choice due to its properties and competitive price. At the same time, multi-fuel solutions are interesting for their greater fuel flexibility.

On the marine side, Wärtsilä currently offers conversions for the Wärtsilä 32 and 46 engines. In the future conversions will also be available for other engine types. In many cases a conversion may be economically a more feasible solution than buying a brand-new engine. After a conversion, the engine is granted the same warranty as a new engine, and the maintenance schedule is reset. In other words, by choosing the right time for a conversion, the engine operator can avoid the costs of a major overhaul of the original engine.

54 in detail


[ MA

RIN

E /

IN

DE

TA

IL ]

Power plant gas conversions are available for the following engine types:

Vasa 32 > 32DG, 32DF and 34SG Wärtsilä 32 > W32GD, W34DF and

W34SG Wärtsilä 46 > W46GD, W50DF and

W50SG Wärtsilä 34DF > Wärtsilä 34SG Wärtsilä 50DF > Wärtsilä 50SG

A reset maintenance schedule is granted for the DF and SG conversions.

Three gas conversion technologies Wärtsilä offers three gas conversion technologies:

SG (spark-ignited) gas-only engines DF (dual-fuel) engines, an engine

optimized for running on gas with the possibility of running on HFO (heavy fuel oil) or LFO (light fuel oil) in back-up mode

GD (gas-diesel) engines that run on HFO, LFO, crude, natural gas and associated gas

The SG engines are lean-burn Otto cycle gas engines. In the process, gas is mixed with air before the inlet valves. During the intake period, gas is also fed into a prechamber, where the gas mixture is rich compared to the gas mixture in the cylinder. At the end of the compression phase the mixture of air and gas in the prechamber is ignited by a

spark plug. The flames from the nozzle of the prechamber ignite the gas/air mixture in the main combustion chamber. After the working phase, the cylinder is emptied of exhaust gas and the process is repeated.

In the gas mode the dual-fuel engine utilizes the lean-burn Otto combustion process. The gas is mixed with air before the intake valves during the air intake period. After the compression phase, the gas/air mixture is ignited by a small amount of liquid pilot fuel (LFO). After the working phase, the exhaust gas valves open and the cylinder is emptied of exhaust gases. The inlet air valves open when the exhaust gas valves close.

In the event of gas flow interruption, the engine switches automatically to the backup fuel system (LFO, HFO) without load reduction, utilising the conventional diesel process.

The gas-diesel engine utilises the diesel combustion process in all operational modes. In gas mode the gas is injected at high pressure after the pilot fuel and ignited by flame from the pilot fuel injection.

The GD engine can instantly be switched to liquid fuel mode during operation. The liquid fuel can be LFO, HFO or crude oil. In this case, the process is the same as the conventional diesel process.

The GD process tolerates variations in the gas quality allowing the utilization

of associated gases that have earlier been simply flared at oil fields. The GD concept requires very few engine modifications and allows true fuel flexibility.

Environmental drivers urge marine conversions

Environmental demands force ship operators to make fast decisions concerning the emission levels of their fleet. The most pressing regulations are for those operating within Emission Control Areas (ECA). The regulation concerning the ECAs came into force in the beginning of 2015.

For operating in the ECAs, LNG is the most viable solution for its low emissions and attractive price. Other solutions for low emissions include methanol, low sulphur fuel (MDF) and SOx scrubbers.

Whichever route the customer chooses to reduce emissions, Wärtsilä aims to provide the optimal solution.

The rising interest in LNG has encouraged the construction of LNG infrastructure and the building of bunkering facilities in major ports. Wärtsilä is playing an instrumental role in this development.

Fuel conversion of a vessel must always be based on a comprehensive feasibility study providing information on the scope of the required changes, risk analysis, costs, payback time and the time required for the

Running hours

SFOC over 16000 hour overhaul interval

Cumulative SFOC increase

Fouling of the air cooler

Fouling of turbo charger

Fouling of air intake filter

Nozzle wear

Injection pump wear

20000 16000140001200080004000 100006000

6

5

7

2

3

4

1

0

SFO

C in

crea

se (%

)

The graph shows the increase in specific fuel consumption taking into account normal scheduled overhauls.


55in detail

conversion. Each case is unique.Of vessel types, good candidates for gas

conversions include tankers, RoRo vessels, RoPax vessels and smaller ferries. One of the biggest challenges with gas conversions is finding space for the LNG storage and processing equipment.

A lot is involved with converting a vessel to operate on LNG. The question is not only of getting the engine to run on gas. The best option may be to look at it as a process, as illustrated below.

Power plant operators look for greater efficiency and lower emissions

The trend towards gas conversions of power plants derives mainly from the demand for greater fuel efficiency and lower emissions, as well as the growing availability of gas and its low price compared to HFO. Power companies are either replacing HFO engines with gas or DF engines or converting their HFO engines to gas or DF mode.

The site-specific objectives may, however, vary. For example, power plants located in the vicinity of oil and gas fields are increasingly converted to utilise associated gas, which would otherwise be flared. Energy companies in need of peaking power look for gas power plants with fast starting and stopping capabilities that require a minimum amount of fuel for stand-by energy. For these cases Wärtsilä has developed its Smart Power concept.

Since 2000 Wärtsilä has carried out conversions on more than 20 power plants, totalling 914 MW.

In addition to engine conversion, Wärtsilä’s power plant conversion concept may include all the aspects from safety to reliability of operation. After the conversion, the power plant is upgraded according to the latest Wärtsilä design.

The evaluation of a new case typically starts with a desktop study which reveals the technical history of the power plant, the best solution for the customer’s needs, the scope of the conversion, risks, the time span required for the conversion, costs and the expected payback time.

In addition to the installation of the gas delivery and pressure control system and changes to the engine, a conversion may also include modifying or upgrading such critical components and systems as the engine cooling system, fuel system, automation and exhaust gas system.

A standars propeller-rudder design compared with th improved design using Energopac. The reduction in pressure pulses, due to a more homogenous water inflow into the propeller, results in lower vibration and increased comfort onboard the vessel.

Energopac reduces flow separation behind the propeller hub and creates less drag than conventional rudder systems.

Process of converting a vessel to operate on LNG.

Vibration frequency (nth harmonic of blade passage)

Rudder steering force (% of prop. thrust)

–100 10040 60 80

3rd

20

2nd

0–40 –20–60

1st

–80

20

6

25

5

1

5

3

10

2

4

15

0

Preliminaryfeasibilitystudy

Request for proposal

Cleaning,painting,finishing

Feasibility study

Basic design

Buildingspecification

Hullmodification

Tankinstallation

Piping ondeck

Piping and cabling

Automation system upgrades

Propulsion control upgrades

Class approval

Sea trials andcommissioning

Crewtraining

Conversioncompleted

Engineconversion

Detailed design

Docking arrangements

Equipment delivery

Start of conversion

Conversion contract with shipyard

Risk analysis

Budgeting

0

Des

ign

confi

gura

tion

Perc

ent o

f Ful

l Out

put Stamdard semi-spade rudder

Wärtsilä Energopac

Full scale Energopac

Model scale Energopac

Improved propeller design

Reference design

56 in detail

[ FU

TU

RE

/ I

N D

ET

AIL

]

[ FUTURE / IN DETAIL ]

Smart monitoringAUTHOR: Lena Barner-Rasmussen PHOTO: Karl Vilhjalmsson

Wärtsilä teamed up with software developer Korulab for making a prototype for a wearable monitoring device.

Terho Niemi and Christian Lindholm, co-founders at Korulab, worked with Wärtsilä’s Mikael Leppä (in the middle) on the wearable monitoring device.

57


in detail

As in most emergency cases, saving a few seconds can be the difference between catastrophe and just a scare. That certainly goes for engines, whether you are on a vessel or in a power plant. If essential parameters change for some reason, you want to know about it instantly.

A vessel or a power plant is dotted with screens all over to make sure that the crew or operators are notified immediately if something is awry. But even though the captain is working around the clock, there are certain moments when the screens don’t reach him. That might change in the near future. Wärtsilä teamed up with Finnish software developer Korulab to make a proof of concept for a wearable device that the crew or operators can carry with them at all times, making sure that they are notified instantly if something isn’t right.

Prototype first

The idea was born inside Mikael Leppä’s head as he visited the engine room of one of the vessels sailing out of Helsinki. Then he bumped in to Christian Lindholm, who for several years has been busy developing software for wearables, those tech gadgets that are projected to take over from the smartphone as the one thing we cannot live without.

Part of Wärtsilä’s innovation team is situated in the Open Innovation House in Otaniemi, just outside Helsinki. The place is an innovation hub that has drawn researchers, startups like Korulab and even big corporations such as Wärtsilä to interact and come up with completely new concepts.

Korulab has the best know-how when it comes to wearable software, so thoughts

quickly turned into actions as Leppä and Lindholm got started on a prototype. They received helping hands from Jonatan Rösgren and the whole Engine Automation team in Vaasa.

“The cost for the actual hardware – the watch – is relatively low, making it possible to build a proof of concept and take it from there,” says Lindholm.

Vital info

So the engines were given IP addresses making it possible to monitor the values on an individual cylinder level. Leppä chose what parameters to include and designed the user interface and Lindholm got busy with the software. All this in less than one month.

While you can insert all sorts of features into a wearable, Leppä opted for just a few crucial parameters to make navigation simple. Lindholm adds that the info needs to be ‘glanceable’, in other words, easy to grasp with just a glance.

“But still, all vital info like engine RPM, oil pressure, water temperature and exhaust gas temperatures can fit in,” says Leppä.

These are all parameters that will behave unusually if something unexpected happens. Think of a vessel trying to dock at an oil platform in rough sea. If something is askew, every second counts.

So far, the prototype has received lots of positive comments.

“A wearable monitoring device can give the crew peace of mind,” says Leppä.

So far, all there is to this project is this one prototype. But both Leppä and Lindholm are convinced that in the near future, all engines – both on vessels and in power plants – can be monitored from the wrist.

“Even though the captain is working around the clock, there are certain moments when the screens don’t reach him.”

A wearable device makes it possible to monitor engine on the go.

wÄrtsilÄ technical journal -...

Documents