kane ramsey and david young v3 pdf - enscope limited - the layout of compressor stations and optimum...

DEVELOPMENT | ENGINEERING | MANAGEMENT | COMPLETIONS

• Observations from our personal experience as both Turnkey EPC Contractors and Owner Representatives

• Each of us have direct experience working in a variety of roles on around 40 compressor stations projects over the past 20 years

• David will touch on some of the engineering and design aspects, particularly modularisation

• Kane will focus more on the commercial side and the consequent affect on the schedule

• What has gone well and what hasn’t gone well

2

Introduction


• Like all resources projects the key objectives in the delivery of compressor stations are;

- lowest cost

- best quality

- shortest timeframe

(safety is a given)

• These objectives are generally not aligned

• We believe that the focus should be on a “lowest cost per TJ compressed” basis

3

Key Objectives


• Decision on Contracting Strategy should be taken early –ideally in the concept development stage

• Factors to be considered include;

- Owner’s appetite for risk

- Schedule objectives

- Capacity of the owner’s team to self-perform

- Bankability requirements

- Company procurement policies

- Existing relationships

- Resource availability

4

Contracting Strategy


• Options available for the owner to consider include;

- tendered engagement of consulting engineers and contractors on a Lump Sum basis

- tendered engagement on a Schedule of Rates orIncentivised basis (risk/reward)

- engagement of a head contractor on a Design and Construct basis – either tendered or sole-sourced

- engagement of a head contractor on a Turnkey EPC basis

- engagement on an EPCM basis

- use of a full project Alliance model

5

Contracting Options


• There are many pro’s and con’s to the contracting model adopted

• Compressor stations are generally not technically complex

• Success factors include;

- don’t reinvent the wheel – standardisation in concept from one project to the next has merit

- early engagement of the contractor

- use contractors that have previously performed

- for contractors the carrot usually works better than the stick

- flexibility in contract model to allow pre-commissioning to start before the construction is finished

6

Contracting Options

(cont.)


• Neither the owner nor the contractor wants to take risk –without suitable compensation

• Risk apportionment workshops prior to contract award are a key success factor

• Establishing possible scenarios and role play can help inform these workshops

• Risk should lay with the party best placed to manage (or mitigate)

• Residual risks should lay with the owner

• Drafting the contract should then follow

7

Balance / Risk

Apportionment


• To the extent possible contracts should be balanced

• AS4900 suite provide a good basis, for example AS4902 (Design and Construct) includes;

- Principal Project Requirements

- Requirement for a “functional” design

- Flexibility allowing a variety of contract models

- Indemnity provisions for both parties

- “Good faith” superintendant

- No payment for unfixed plant

• Ultimately, it is the owner that sets the terms…

8

AS4900 Suite of

Contracts


• Outside cost, time is usually the key project driver

• The contract model selected has a direct bearing on the total time for delivery

• The 3 slides that follow are reasonable for typical midline boost compression with a single GT driven compressor

• NB: civils and earthworks disciplines removed for clarity

9

Typical Delivery

Timeframes


• Total delivery period of ~24 months

10

Traditional Sequential /

Tendered approach

FID

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 MONTHS

FEED

Detailed Design

Place Order for Compressor(s)

Compressor Manufacture and Delivery

Other Long Lead Equipment Procurement

Compile Construction ITT

Completion of Detailed Design

Tender Period

Negotiate and Award to Successful Contractor

Construction Contractor Project Team Establishment

Offsite Piping Fabrication

Arrival of Compressors on site

Arrival of Remaining Long Lead Equipment on Site

Mechanical and Piping Installation

Electrical / Instrument Installation

Construction Contractor Practical Completion

Precommissioning

Gas Commissioning

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nTRADITIONAL SEQUENTIAL DELIVERY WITH COMPETITIVE TENDER APPROACH



11

FID

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 MONTHS

FEED

Detailed Design




Compile Construction Scope of Work / Engagement terms


Contractor Pricing and Finalisation of Target Price

Construction Contractor Project Team Establishment







Precommissioning

Gas Commissioning

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onSOLE SOURCE TARGET PRICE / INCENTIVE APPROACH

Sole Source Target

Price approach



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FID

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 MONTHS

Design and Construct Contractor Selected Prior to FID

FEED

Detailed Design











Precommissioning

Gas Commissioning

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nDESIGN AND CONSTRUCT APPROACH, CONTRACTOR SELECTED PRIOR TO FID

Design and Construct

approach


A few selected observations;

• Project success comes down to the people not the logo

• There is a propensity to under-resource project teams

• Engineering leading into procurement tends to drive the schedule more than any other single factor

• Compressor delivery is rarely the critical path

• The receipt date of vendor data can be overlooked

• Valve delivery is nearly always a problem

… and lastly – projects tend to go well when the contractor makes a reasonable profit.

13

Other Observations


• Modularisation of compressor stations can be done in many ways and to varying degrees generally with the goal of reducing the overall project cost and delivery time.

• Typically the mechanism by which the savings are generated is by reducing the number of the high cost and lower efficiency site hours and transferring a large proportion of these hours to a low cost, highly efficient workshop (locally or overseas).

• In our experience the success of this modularisation process to meet the reduction in cost and time goals varies depending on the characteristic of the individual project and the manner in which the modularisation is executed.

• We will look at 3 different types of Modularisation and assess there benefits for use in the delivery of Compressor Station Projects.

14

Modularisation


• Large Module for LNG Storage Facility Boil Off Gas (BOG) compressor. Made Overseas and barged in. Weighs ~ 1,500 tons

• Structural fabrication and Piping fabrication, PWHT, NDT, hydro testing surface treatment, final assembly and Instrumentation hook-up is completed offsite.

15

Large Modules

BOG COMPRESSOR BUILDING

BOG COMPRESSOR MODULE


16

Large Modules


• “Skids” are generally designed and manufactured to fit on a road transportable truck (say 2.4m -4.5m wide) and weight between 5-50 tons (single lift). Some do go up to 150T.

• Structural fabrication and Piping fabrication, PWHT, NDT, hydro testing surface treatment, final assembly and E&I hook-up (to on-skid JB) is completed offsite to maximise work shop hours and reduce site hours.

17

Skids

TYPICAL METERING SKID


18

TYPICAL FUEL GAS SKID

Skids


Piping and Support fabrication, PWHT, NDT, hydro testing and surface treatment is completed of site with support installation, final bolt-up and electrical hook up completed at site. Reduces or removes the requirement for site fit and weld, PWHT, NDT, Hyro-testing and painting. 19

Complete Offsite Fabrication


20

Can be used very effectively for brownfields work, especially when used in conjunction with laser scanning for tie-ins.



21



Modularisation

Experiences

• Our experience of modularisation for compressor stations has seen mixed results. Projects these days seem to have tighter schedules and limited budgets (as a result of higher costs).

• Orders are often placed late, vendor data comes in late, designs then run late, equipment arrives late, so modules often get shipped late or in an incomplete state.

• This results in an erosion of the potential savings from modularisation.

• Often the additional cost in added design and increase in structural steel is greater that the savings in marginal labour cost between the workshop and site.

• To many COW’s in the BOG!!

22


Modularisation

Summary

• We do not believe that large scale modularisation provides a cost effective or timely solution for compressor station design and construction.

• Small to medium sized “skids” can provide a cost effective solution for compressors station particularly if there is a standardised design with known vendor information to allow early commencement of fabrication.

• The use of complete offsite fabrication with the majority of all the Welding, PWHT, NDT, Hydro and Surface treatment being completed in the workshop, can provide a very cost effective solution for compressor station construction especially for brown fields work when combined with laser scanning to provide accurate fabrication dimensions.

23


• Consider a 500km free flow pipeline

• Front end compression to 14 MPag

• Delivery at 8 MPag Assume Free flow capacity of 250 TJ/d

• Simple pipeline pressure profile

24

Parallel vs Series

• Selecting Parallel or Series configuration for your midline compressor station is an important decision to be made early in a projects life to ensure the design best meets the facilities functional requirements.

500250


• Expansion required from ~250 TJ/d to ~300 TJ/d

• Install mid-line compressor station with a single compressor unit or 2 units operating in duty and standby.

• Pipeline pressure profile shows a typical ‘sawtooth’.

• Compressor station suction pressure being drawn down, discharge pressure increases above free flow pressure

25

500250

Parallel vs Series


• Single unit operation

• The compressor wheeling or staging is selected to optimise efficiency at normal Operating Condition

• Suitable surge margin is achieved

26

Single Unit

78%

80%76%

74%

Surge control line

Area of choke flow or stonewall

Surge

500250

Parallel vs Series


• Simplified midline centrifugal compressor station configuration (valves removed).

• Pig Launcher and Receiver

• Suction scrubber/ filter/coalescer

• Compressor

• Aftercooler

• Anti surge and cooled recycle

27

Parallel vs Series


• If further expansion is required from ~300 TJ/d to ~350 TJ/d

• Most cost effective option maybe to install a second compressor at the existing midline compressor station

• Pipeline ‘sawtooth’ shows compressor station suction pressure being FURTHER drawn down, discharge pressure increases above SINGLE UNIT pressure

28

500250

Parallel vs Series


• Should the second unit be installed in SERIES with the existing unit or in PARALLEL?

• SINGLE unit typical configuration

29

Parallel vs Series


• TWO units in PARALLEL-typical configuration

• Common Suction Header and a common Discharge Header.

• Units see the same suction and discharge pressure

30

Parallel vs Series


• TWO units in SERIES-typical configuration

• Discharge of the upstream compressor delivers into the suction of the down stream compressor

• Let’s consider the compressor wheelmaps for parallel vs series operation

31

Parallel vs Series


• Initial configuration (single unit operation) operating point is located at optimal efficiency point on wheelmap

• Two units in PARALLEL means less flow per unit but higher head

• If the original wheeling is used for the new PARALLEL configuration, each unit will likely end up operating near surge and may require continuous recycle

• This would result in inefficient operation as power is consumed to recycle gas and we are no longer operating in the highest efficiency envelope on the wheelmap.

32

Original Single Unit

Actual Point

Recycle required

Required Point

Surge

Parallel


• Continuous recycle is a poor outcome so the existing unit would likely need to be rewheeledor restaged.

• The new units wheeling or staging would be selected for optimum efficiency for 2 units operating in PARALLEL (lower flow, higher head)

• The issue now is that if the lower flow rate of 300TJ is required, the new unit or the existing re-wheeled unit are operating at a lower efficiency close to choke flow.

33


No re wheel recycle

2 unit parallel operating point

New Wheel map

Parallel


• Two units in SERIES means less head across and more mass flow through each of the units.

• In SERIES configuration, the existing wheelmap may provide a suitable compressor selection for the upgraded operating conditions.

• Avoids the need to rewheel the existing unit as both units operate at close to there highest efficiency envelope

• Both units can be operated efficiently as a single unit if a lower flow rate is required.

• It is recommended that the original unit should be the installed as the down stream unit as this is likely to see less change in the operating point.

• So where is the downside? Stopping a Unit!

34


Upstream Unit

Down Stream Unit

Series


• Let’s consider what happens when both compressors are operating in PARALELL with our new optimised wheel map

• What happens to the operating unit when the other unit has a FAST STOP/trip or is taken off load?

• Initially the operating unit still sees the same suction pressure and delivers the same head. The flow through the station will effectively be halved.

• Over time, the discharge pressure will reduce as the second unit is no longer assisting and the single operating unit will deliver more flow but at a reduced head.

• No upset conditions created due to a single unit tripping or being taken off load

35

2 Units in Parallel


Single operating unit after trip

Parallel vs Series


• Compressors operating in SERIES

• What happens to the operating unit when the other unit has a FAST STOP or is taken off load?

• Immediately, the operating unit sees a large increase in head across the compressor

• A unit stopping has created a potential surge event on the operating unit

• The station will go into recycle (and flow may completely stop) until the head washes out and the single compressor can generate enough head to create station flow.

36

Unit in Series

Compressor instantly moves towards surge

Single operating unit after trip

Required point after trip

Parallel vs Series

• Operating units in Series should include design measures to actively protect the units from these trips and the resultant potential surge events.

• Surge margin equalisation and load sharing is recommended for both series and parallel operation.


37

• In most application including upstream or front of line Compressor Stations Parallel configuration is likely to be the best option.

• For midline compressor stations which experience very little variance in pipeline flow and where the fully compressed pipeline design only has one operating unit (ie duty/standby) parallel configuration will likely be the best option.

• However, for midline compressor station with variable pipeline demand and where the fully compressed pipeline design has multiple units operating at each compressor station configuring your compressors in series should be considered.

Parallel vs Series

Summary


• Unit Aftercoolers- has a single set of coolers per compressor train.

• Unit Anti Surge

• Unit Cooled Recycle

• Station Aftercoolers- a single set of coolers for the entire station

• Unit Anti Surge

• Station Cooled Recycle

38

Unit vs Station

Aftercoolers


39

Unit vs Station

Aftercoolers


UNIT AFTERCOOLERS

What are the benefits?

• Simple to operate and maintain

• Each set of coolers are designed for the individual compressor making selection easier.

• No start up or cool down issues

What are the downsides?

• Lower utilisation of installed capacity resulting in reduced station capacity for the given capital cost (where the equivalent amount of coolers are installed).

• Lower availability- If a cooler fan from one train fails and the compressor from the other train fails the station may not be operable at full capacity.

40

Unit vs Station

Aftercoolers


41

STATION AFTERCOOLERS

Unit vs Station

Aftercoolers


STATION AFTERCOOLERS


• Lower capital cost (if only one cooler per compressor is provided) or,

• If cooler bays for both units are installed you get better utilisation of the asset and more station cooling with one unit operating.

• Availability is greater (i.e. Compressors do not rely on an individual aftercooler)


• Issues with cool down and start up due to temperature build up in anti surge line (particularly with parallel configuration).

• Maintenance is more complex as process isolation of the cooler units will take out the entire station (unless additional valving is provided). 42

Unit vs Station

Aftercoolers


ON-SKID CLOSE FIT ENCLOSURES


• Low cost option

• Medium level of acoustic attenuation

• Good for ventilation


• Poor access for maintenance

• Noise maybe a problem

43

Compressor

Enclosures


OFF-SKID CLOSE FIT ENCLOSURES


• Good acoustic noise attenuation

• Medium for ventilation

• Moderate level of access for maintenance


• Middle range cost option

44

Compressor

Enclosures


COMPRESSOR HALL

What are the benefits? • Good access for maintenance• Good acoustic attenuation

What are the downsides?• Highest cost option• Potentially higher insurance costs due to multiple

compressors operating in close proximity (escalation)• Maintenance issues if the other unit/s are running• Large amounts of ventilation maybe required

45

Compressor

Enclosures


COMPRESSOR SHEDS


• Good ventilation (natural ventilation – i.e. mechanical ventilation system not required)

• Low cost option

• Good access for maintenance


• Low acoustic noise attenuation

46

Compressor

Enclosures


47

Conclusion

• Key decisions such as contracting strategy, degree of modularisation, compressor and aftercooler configuration and the types of enclosures to be used are critical to the overall success of a compressor station project.

• We would recommend careful consideration and selection of these options be made very early in the project life cycle (iebefore commencement of the FEED) so as to increase the chances of overall project success.

• All of the various options discussed in this presentation have there respective advantages and disadvantages and we would not promote any particular option.

• In our experience the biggest factor in a projects success is ensuring it is suitably resources with experienced personnel from the outset, the key decisions are made early and these plans are executed in a timely manner.

kane ramsey and david young v3 pdf - enscope limited - the layout of compressor stations and optimum...

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