Hybrid Solar Thermal Integration at Existing Fossil Generation Facilities

August 2013Manager of Engineering, Black & Veatch, South AfricaKevin MillerHybrid Solar Thermal Integration at Existing Fossil Generation FacilitiesAGENDA Solar Thermal Integration at Existing Rankine Cycle Generating Facilities [HYBRID CSP]Solar Integration with Coal / Oil Steam Plants2Integrated Solar Combined Cycle adds steam to the Rankine CycleConcepts of combined Brayton / Rankine Cycle Generation3

Rankine CycleBrayton Cycle3As a brief and probably unnecessary review of thermal electric power generation, most thermal power plants use a condensing, or Rankine thermodynamic cycle. This includes conventional concentrating solar power (CSP facilities that use solar energy to generate steam.

A variation on the Rankine cycle is the combined cycle power plant that uses both gas turbines (Brayton thermal cycle) and use exhaust heat recovered from the Brayton cycle to generate steam for use in the Rankine cycle; the (2) cycles are combined. The Hybrid concept takes the concept a step farther and adds steam generated from solar energy to the Rankine cycle. Is sometimes called an Integrated Solar cycle, or in the Martin Station case, ISCC, Integrated solar-combined cycle. [You get the point] Steam produced from renewable source Reduces use of natural gas or light oilNo additional capacity (MW) will result from the operation of the solar thermal facilityHybrid Concepts of Integrated Solar Thermal (ICSS)44The Hybrid concept takes the concept a step farther and adds steam generated from solar energy to the Rankine cycle. Is sometimes called an Integrated Solar cycle, or in the Martin Station case, ISCC, Integrated solar-combined cycle. [You get the point] More efficient with lower capitol costSolar energy can be converted to electric energy at a higher efficiency.Capital costs are lower than for a CSP-only facility of similar size.Minimal additional plant staff is requiredA hybrid plant does not suffer from the thermal inefficiencies associated with the daily startup and shutdown of the CSP facilityPotential reduction in fuel costs (fossil fuel input / MWh will decrease)Significant reduction in carbon emissions / MWh

Why consider Hybrid CSP?August 2013Eskom CSP Workshop55In comparison to conventional Rankine cycle power plants using parabolic trough or power tower collection fields, hybrid CSP plants offer the following advantages:

Typically CSP-generated steam can be introduced into the steam cycle at a point where energy is incremental energy input is efficiently used. Incremental Rankine cycle efficiencies are essentially the same or better (95 to 120) percent those of a conventional CSP plant fossil plant

Capital costs are lowerSteam generators, steam turbine, heat rejection systems, electrical interconnect, BOP are shared

Conventional CSP plants have to be started and shut down on a daily basis, using significant energy from the field that is lost for power generation. Hybrid facilities avoid these startup/shutdown energy losses.

POTENTIAL REDUCTION:The NEXT GENERATION hybrid concept was installed at a combined cycle (CC) facility that had provisions for additional energy input from duct firing during peak periods. The CSP field displaced the need for 75MW of natural gas fuel when the duct firing would have otherwise been used; thus there is a fuel saving. Alternatively, if duct firing would not have been used, the system didnt REALLY need the power that badly) the gas turbines would be base loaded but the overall amount of energy generated by the hybrid facility is 75MW more than would be generated by the fuel supplied to the GTs alone. (This may be splitting hairs and confusing the issue. The point here is that the plant can be run as a 4X1 cc plant w/o duct firing. With the CSP addition, it can produce 75MW more with the same amount of fossil fuel. In this case, there is no fuel saving, but the fossil fuel cost/carbon emissions / MWh is significantly lower. Located in area of high Direct Normal Solar Irradiation (DNI)Adequate space availableAllocation of approximately 2.75 Hectares / Mw

Key Characteristics of Candidate Facilities for addition of hybrid CSPAugust 2013Eskom CSP Workshop66

Direct Normal Irradiation (DNI)August 2013Eskom CSP Workshop7Black & Veatch was Owners Engineer on the addition of 75 MW of CSP steam generation at Martin StationArea with high Direct Normal Solar Irradiation (DNI)Available adjacent land area (202 hectare)Available steam turbine capacityReduction in associated fuel cost & carbon emissionsIntegration of CSP at an existing Gas Turbine Combined Cycle facility in Florida, USAAugust 2013Eskom CSP Workshop8

Martin Next Generation Solar Energy Center is the solar parabolic-trough component of an integrated solar combined cycle, or ISCC 1150 MW plant, in western Martin County, Florida,

The Unit is a natural gas fired 4-on-1 combined cycle unit with a nominal capacity of 1150 MW. Light oil is used as backup. Placed into commercial operation in May of 2005, is integrated with the solar plant.

Features four 170 MW gas turbines, one 470 MW steam turbine, and a single condenser and cooling tower[1]

170 x 4 = 880 Steam to produce 1075 MW leaving 75 mw to make up with additional steam from Duct Burners 8Martin Next Generation Solar Energy CenterAugust 2013Eskom CSP Workshop

Source; John Van Beekum for The New York Times 99REVIEW and REREAD /

Per Wikipedia, Martin Station has a total installed capacity of ~3675 MW: 2X800MW gas fired steam units (the big stacks), 2 2X1 gas/oil fired combined cycle (the (4) stacks in the middle),and the 4X1 gas/oil fired combined cycle, over on the far right.

The single solar field circuit heats 4 steam generators, after each gas turbine. The Martin solar thermal facility is designed to provide steam for FPL's existing Martin Unit 8 combined cycle unit, thus reducing FPL's use of natural gas. No additional capacity (MW) will result from the operation of the solar thermal facility. The Solar Energy Center has an array of approximately 190,000-mirror parabolic troughs on about 500 acres (202ha) of the Martin County plant.[3] The solar collectors feed heat to the existing steam plant, generating electricity at a rate of 155,000MWh per year

Parabolic trough concentrating solar power systems use trough shaped mirrors to focus sunlight on to an absorber tube/ receiver located at the mirrors focal line. The troughs are designed to track the sun along a north/ south axis. The receiver tubes contain a heat transfer fluid, typically synthetic oil or molten salt, which is super heated by the sun. This superheated thermal fluid is circulated through the receivers and pumped through a heat exchanger to produce steam for the steam turbine genset. Parabolic trough technology is proven and widely used, although the live steam generation temperatures are lower than central tower receiver solar CSP plants.

Martin Next Generation Solar Energy Center was, until recently, the second largest solar-thermal facility in the world and the largest solar plant of any kind outside of California Facility may be the first hybrid facility in the world to connect a solar facility to an existing combined-cycle power plantProvides 75 megawatts of solar thermal capacity Designed to produce an average of 155,000 MWh of electricity annuallyThe expected reduction of system-wide green-house gas emissions is projected to be approximately 2.75 million tons over a 30-year period

Martin Next Generation Solar Energy CenterAugust 2013Eskom CSP Workshop1010(The cost, according to the filings made to the Florida public utilities commission, was $475 million. This would include land costs and all permitting/development costs, IDC, etc. That is, of course, $5000/kW, a VERY big number when compared to the cost of other generation]. 155,000MWh/year is a capacity factor of ~25%.Combined Cycle Generic LayoutAugust 2013Eskom CSP WorkshopHPSHRH HPECHPECIPSHIPECLPSHLPECSteam TurbineGas TurbineAirFuelHeat Recovery Steam GeneratorAir-Cooled CondenserLPEVIPEVHPEVHPECHPIP / LPLP SteamHot ReheatCold ReheatMain SteamIP SteamHP SteamBFPDuctFiring1111Admit Steam In LP CircuitAdmit Steam Into Cold ReheatAdmit Steam Into Hot ReheatAdmit Steam Into HRSG HP Circuit Between Evaporator and SuperheaterAdmit Main SteamPotential Solar Steam Injection PointsAugust 2013Eskom CSP WorkshopThe most efficient use of solar energy is displacing saturated steam production at the highest pressure.

The least efficient use of solar energy is feedwater preheating and steam superheating1212Parabolic Trough Technology was selected by the ClientTYPICAL ACHIEVABLE STEAM TEMPERATURESParabolic TroughFluid: Synthetic oil; HTF Temperature: 748F (398C)Steam Temperature - ~715 FCentral ReceiverFluid: Steam, molten salt, airSteam Temperature: 1025F (550C)Compact Linear Fresnel ReflectorFluid: SteamSteam Temperature: 520F (270C)Steam Admission Locations Driven By Solar TechnologyAugust 2013Eskom CSP Workshop1313Because parabolic trough systems are more mature commercially and technically.

Trough Steam Admission Points:LP, Cold Reheat, HP Steam Between Evap and SuperheaterPower Tower Steam Admission Points:Could be same as trough, but also allows higher temperature admissions to Hot Reheat or Main SteamCompact Linear Fresnel ReflectorLP, Cold Reheat Steam Admission Locations Driven By Solar TechnologyAugust 2013Eskom CSP Workshop1414 but when it is being integrated into an existing facility, by the characteristics / capabilities of the existing steam cycle and equipment can become overriding considerationsSteam Admission Locations Driven By Solar TechnologyAugust 2013Eskom CSP Workshop1515Extraction point can impact the feedwater temperature further influencing the size of the solar fieldBoiler Feed Pump (BFP) DischargeHP Economizer Exit with Booster Pump (A unique booster pump may be needed to overcome the additional pressure drop on the HTF water / steam side) Typical Feedwater Extraction LocationsAugust 2013Eskom CSP Workshop1616Feedwater extraction location affects supply water temperature to solar steam generation train, the amount of feedwater preheating required in the SSG train, the size of the solar field and the heat balance / steam production within the HRSG

The electrical output can be greater for the BFP discharge option but the solar usage efficiency is poorerFeedwater From BFP Discharge + HP Steam Admission used in this caseAugust 2013Eskom CSP WorkshopHPSHRH HPECHPECIPSHIPECLPSHLPECSteam TurbineGas TurbineAirFuelHeat Recovery Steam GeneratorAir-Cooled CondenserLPEVIPEVHPEVHPECHPIP / LPMain SteamHP SteamBFPDuctFiringSolar Field / Solar Power BlockBFP Discharge1717Other configurations are available, including vertical orientationsRepresentative Solar Steam Generator OutlineAugust 2013Eskom CSP Workshop

HTF inHTF outThe vessel shown is ~ 15 meters long, 3 meters in diameterIn this design there were (3) vessels for each GT / HRSG grouping; Preheater Steam generator (this vessel)SuperheaterSteam OutSteam Out182 steam outlets on top of vessel. HTF in-and-out are on the end cap. There are steam separators a the top of the vessel (drum). There are (4) of these 3-vessel steam generation sets; 1 for each GT/HRSG train!! Each one generates enough steam for ~19 MW; 75 MW total.18Thermal lag time in solar fields is large, 30 minutes or more, due to the large volume of Heat transfer fluid (HTF) and variable HTF flowCloud cover events result in changing HTF flow as the solar field responds to control HTF outlet temperaturesAs areas of the solar field see varying levels of cloud cover and the duration of the cloud passage is a variable, the degree the power plant output is impacted is dependant on the magnitude of these eventsPlants operating in regions with frequent cloud cover should consider these impacts into the design to mitigate operational impacts and to maximize daily solar utilizationSolar Resource IntermittencyAugust 2013Eskom CSP Workshop1919By controlling the flow of the HTF, the exit temperature can be controlled to a certain degree. It may be possible to maintain HTF exit temperature by reducing the flow (and allowing more residence time in the field). This would allow generation of steam at the required conditions. However, the AMOUNT of steam may be reduced.These events can lead to a shut-off of the solar steam generator train(s) (SSGs) if the HTF temperature falls near or below the saturation temperature of the steam supply generator (SSG) evaporatorsUnlike stand-alone solar plants, the steam pressure of the SSG is driven by the operating load of the CC plant CTGs, not the amount of steam that could be produced if the evaporator was free to slide in pressureImpact of Cloud Cover on Solar Steam Generation (SSG) OperationAugust 2013Eskom CSP Workshop2020For the case of a straight Rankine cycle, additional fuel could be added to maintain a given steam generation in the event of an extended cloud event.Martin Next Generation Solar Energy CenterAugust 2013Eskom CSP WorkshopArray includes 6,864 Units192,000 MirrorsCovers approximately 202 ha21

21The solar collectors feed heat to the existing steam plant, generating electricity at a rate of 155,000MWh per year.[4] The 2012 solar derived production was about 89,000 MWh of power,

There has been a steady stream of new hybrid natural gas + solar CSP power plants developed and built since the completion of the Martin Next Generation Solar Energy Center in 2010. Among the completed and commissioned facilities are 30 MW solar CSP in Morocco, 25 MW Solar CSP in Algeria, and 20 MW Solar CSP in Egypt.

Solar Integration with Coal / Oil Steam Plants2222Typical Steam Plant Generic SchematicAugust 2013Eskom CSP WorkshopCondenserHPIP/LPCold ReheatSteam TurbineLP FW HeatersHP FW HeatersBFPDeaeratorFinal FeedwaterMain SteamHot ReheatCondensatePumpSteam Generator(BOILER)Generator2323CONFIGURATIONS CAN INCLUDE THE FOLLOWING, ALONE OR IN COMBINATIONFeedwater heating - External heatingFeedwater heating Provide heating steamGeneration of Cold Reheat SteamGeneration of Hot Reheat SteamGeneration of HP steam Generation of Main Steam

Potential Injection Points for Solar-Sourced Thermal EnergyAugust 2013Eskom CSP Workshop2424External Heating of FW means running the FW through a dedicated trough system where thermal energy is directed directly into the FWno HTF or additional heat exchanger required. Provide Heating Steam means using solar generated steam for FW heating.

Note: the difference between Main Steam and HP steam is that Main Steam is ready to go to the HP ST. HP Steam is essentially the same PRESSURE, but requires more superheat to conform to the required HP ST inlet steam conditions..MAXIMUM ACHIEVABLE STEAM TEMPERATUREParabolic TroughFluid: Synthetic oil; HTF Temperature: 748F (398C)Steam Temperature - ~715 F (379C)Central ReceiverFluid: Steam, molten salt, airSteam Temperature: 1025F (550C)Compact Linear Fresnel ReflectorFluid: SteamSteam Temperature: 520F (270C)Steam Admission Locations Driven By Solar Technology, and are the same as shown previously for the Martin case study (temperatures shown are typical; representative)August 2013Eskom CSP Workshop2525I added the Temperatures shown are Typical/Representative because there may be suppliers in the audience that will claim that their system is different/can do better than that.Criteria used in the selection of the solar technology used in a specific plant should include not only the capabilities of the candidate technology, but the steam cycle and characteristics of the existing steam cycleCandidate Trough Steam Admission Points:Feedwater Heating, LP, Cold Reheat, HP Steam Between Evap and SuperheaterCandidate Power Tower Steam Admission Points:Could be same as trough, but also allows higher temperature admissions to Hot Reheat or Main SteamCandidate Compact Linear Fresnel ReflectorFeedwater Heating, LP, Cold ReheatSteam Admission Locations Driven By Solar TechnologyAugust 2013Eskom CSP Workshop2626This slide assumes that most hybrid solar projects would be installed at existing facilities, rather than incorporated in an initial, greenfield design. If you were starting with a clean sheet of paper, then there would be opportunities to optimize the cycle and costs/benefits.External Feedwater HeatingAugust 2013Eskom CSP WorkshopAir-Cooled CondenserHPIP / LPCold ReheatSteam TurbineLP FW HeatersHP FW HeatersBFPSolar Field / Solar Feedwater HeatersDeaeratorSteam GeneratorFinal FeedwaterMain SteamHot ReheatCondensatePump2727If you are heating feedwater, you could use an arrangement where the BFW is circulated directly through the field, or you could use an HTF and heat the feedwater in a conventional heat exchanger.Generation of HP SteamAugust 2013Eskom CSP WorkshopAir-Cooled CondenserHPIP / LPCold ReheatSteam TurbineLP FW HeatersHP FW HeatersBFPSolar Field / Solar Steam GeneratorsDeaeratorSteam GeneratorFinal FeedwaterMain SteamHot ReheatCondensatePumpHP Steam to HP Superheater2828This could be done with a direct steam generation technology, or a trough or power tower that heats salt or another HTF for generation of steam in a steam generator.Boiler Feed Pump (BFP) DischargeFinal Feedwater exiting Top Feedwater Heater Feedwater extraction location affects supply water temperature to solar steam generation train, the amount of feedwater preheating required in the SSG train, the size of the solar field and the heat balance within the thermal plant steam cycle

Typical Feedwater Extraction LocationsAugust 2013Eskom CSP Workshop2929Hybrid Solar thermal has been applied on large scale basis at an existing combined cycle facilityThe concept has proven to be operationally acceptableApplication at existing coal or oil-fired facilities is technically feasibleDesigns must consider the steam cycle, where addition of solar generated energy is physically possible, as well as the required temperature and pressure requirements of the cycleSummaryAugust 2013Eskom CSP Workshop30Operationally Acceptable means, Hey, it works! It does add additional considerations to the plant operations, and it will be better suited to some applications and facilities than others. But it IS technically and operationally functional.30www.bv.com