Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Plant    Application of GREEN Ice Thermal St...
Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Planttemperature on the electric output of t...
Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Plantattributed to minimizing the on-peak “p...
Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantPlant Annual Hourly Operation DataThe e...
Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Plantthe TIC required cooling load. Consider...
Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantThe manufacturer of the LM6000 confirme...
Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Plantcompatible capacity. With space limitat...
Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantDuring the TES discharge cycle, chilled...
Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantProposed Operation CycleThe proposed op...
Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantCharge/Discharge schedule will minimize...
Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantAccording to the simulation results and...
Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Plantoff-peak). Considering the chiller’s sp...
Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantAppendixTable of FiguresFigure 1: Years...
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Ice Slurry TES for TIC

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Application of GREEN Ice Thermal Storage System for
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Ice Slurry TES for TIC

  1. 1. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Plant Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Plant. Mr. Stan (Shlomi) Rott, IDE Technologies; Dr. Ishai Oliker, P.E., Joseph Technology Corporation, Inc.AbstractThe latest developments in Thermal Energy Storage (TES) technology have played anincreasingly important role in its use in peaking power plants for Gas Turbine (GT) inletcooling applications. The chiller system design utilizes TES to increase hot weather GTpower output and improved performance, while shifting chiller parasitic powerconsumption to off-peak periods. Additional benefits can be achieved if Vacuum IceMaking (VIM) technology producing Ice Slurry (as the TES medium) is utilized,resulting in low GT compressor inlet temperatures of about 42°F.The presented study is based on an actual peaking load power station with a single 47MW (ISO conditions) Stewart & Stevenson LM6000 HP SPRINTTM GT, equipped with achiller for inlet cooling. The study was prepared while extensively utilizing analyticaltools for modeling GT performance and economics. VIM TES and cycle simulationswere based on the actual hourly GT compressor inlet temperatures, atmospheric pressure,gross MW output power and net MW power measurements that were recorded at thepower plant over a one year period. Additionally, the VIM TES charge/dischargeschedule was optimized based on LM6000 HP SPRINTTM compressor mass flowrequirements to reduce chiller parasitic power consumption to the maximum extentpossible.Use of the VIM TES has been found advantageous in terms of parasitic load shift to off-peak hours, as well as an increase in net MW power output. The results were based on theturbine manufacturer’s proposed modifications to the SPRINTTM system, in conjunctionwith the low compressor inlet temperatures achievable with VIM TES technology. Thisapproach resulted in a 25% decrease in chiller parasitic power consumption and a 12%increase in net MW power output of the turbine.Key words • Ice Slurry • Static Ice • Vacuum Ice Maker (VIM) • Dynamic Ice • Thermal Energy Storage (TES) • TES Systems • “On demand” Chillers • Turbine Inlet Cooling (TIC)IntroductionThis paper presents the specialized application of TES for the Combustion Turbine (CT)inlet cooling of an LM6000 gas turbine equipped with the SPRINTTM system. The mainobjective of the study was to evaluate the effects of the lowest allowable compressor inletMarch 3, 2011 Page | 1
  2. 2. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Planttemperature on the electric output of the turbine, as well as to quantify annual addedMW-hours.A variety of cooling approaches are typically considered for turbine cooling applications.One characteristic common to all approaches is the ability to push closer to (or evenbelow) the compressor air inlet temperature at ISO conditions, namely 59°F and 14.7psig.Additional factors that need to be considered during the selection process are theelectrical rate structure or time-variable value of power, the capital cost of the TICsystem, operation and maintenance costs, efficiency of the equipment and modularity andexpandability of the system to accommodate future expansions.One of the most popular approaches to GT inlet cooling is the use of standard mechanicalchillers. These chillers are brought online simultaneously with the GT, at the time whenload is demanded. Therefore, they are sometimes referred to as “on demand” chillers.When “on demand” chillers are applied to a variable load, they should be able to respondby increasing or decreasing their compressor capacity in the most efficient and rapid way.When an “on demand” chiller is coupled with a turbine GT that operates during peakdemand hours only, the plant owner will realize a significant loss of net power andrevenue due to the chiller’s parasitic power consumption. Most standard chillers are ratedat a 45°F supply water temperature and can experience as much as 30% reduction ofcapacity if and when operating at substantially lower than rated temperatures.Ice-based systems are frequently found to be used in industrial cooling applications. Ice-based TES systems function independently of the cooling load. During its operation, anice-based TES system charges while building ice for use during a subsequent dischargecycle. Such ice-based systems, in which the ice is formed and later melted in one place(on a heat transfer surface), are known as “static ice” systems. The ice formation occurswhile a low temperature refrigerant is circulated through the heat exchange surface toextract the heat of the surrounding water. In order to address the required load, the ice ismelted by circulating a secondary refrigerant through the tank or through the heatexchange surface. In the former case, the secondary refrigerant melts the external layer ofice, hence “external melt”; in the latter case, the secondary refrigerant melts the internallayer of ice, hence “internal melt”.Ice slurry makers are often referred to as “dynamic ice” systems. Such systems are able toproduce ice with the consistency of slush or snow. In other words, the ice particle is verysmall. An additional characteristic of ice slurry is improved heat transfer capability due tothe vastly increased available heat transfer surface. In addition, VIM ice slurry does notrequire a defrost cycle in the traditional sense, which allows for a rapid and highlyvariable discharge rate to address load fluctuations when required. Finally, with VIM iceslurry production, there are no adverse insulating effects associated with the thickness ofan ice layer formed on a heat transfer plate, coil or tube.In general, the benefits of applying any type of TES to the industrial processes include,but are not limited to, the following: smaller capacity and footprint attributed to therefrigeration equipment, increased level of redundancy, load shifting, revenue recoveryMarch 3, 2011 Page | 2
  3. 3. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Plantattributed to minimizing the on-peak “parasitic” power consumption and (especially forice slurry TES) lower water supply temperatures even during rapid TES discharge.Feasibility AnalysisThe plant under consideration is equipped with one (1) LM6000 SPRINTTM Gas Turbine,manufactured by GEs Stewart & Stevenson. The GT combustor temperature is 1,600 °F,and the heat rate of the GT is 8,900 Btu/kWh. The plant efficiency is estimated at 38%.The GT is equipped with an HP SPRINTTM, which injects an atomized spray ofdemineralized water into the inlet of the high-pressure stage of the compressor in order toincrease the GT’s electric power output and improve its heat rate.Existing TICThe plant is located in the humid, continental climate of the North East coast of theUnited States and is equipped with a McQuay 2,000 Ton chiller with two compressors.The chiller uses 134a refrigerant and circulates a water-glycol solution through the GTcompressor air inlet coil. Typical inlet air temperature at the compressor inlet is between50 and 55 °F; glycol supply temperature is 47 °F with a return temperature of 54 °F. Theestimated parasitic power consumption due to the operation of the “on demand” chiller isin access of 2 MW. The specific power consumption of the chiller system (chiller, pumpsand condenser fans) is 0.755 kW/Ton.Plant Operation ModeThe plant operates for 7 to 8 hours a day during peak load demand hours, includingweekends, for the most of spring, summer and early- to mid-fall months.Operating Hour StatisticsThe plant’s operating history is presented below in Figure 1; the data was collectedbetween the years 2005 and 2010. The total time that the plant was operational during theyear 2009 was 395 hours. This small amount of operational hours is attributed to thescheduled maintenance that the turbine underwent during that period. Figure 1: Years 2005 - 2010March 3, 2011 Page | 3
  4. 4. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantPlant Annual Hourly Operation DataThe evaluation of the turbine operation in general, and TIC functionality in particular,was based on the annual hourly data that was recorded starting from August 1, 2009 toJuly 31, 2010. The recorded data included the following parameters: Gross Power Output[MW], Net Power Output [MW], Compressor Inlet Temperature [°F], Ambient Dry BulbAir Temperature, DB [°F], Compressor Inlet Pressure [psia], and Relative Humidity [%].The analysis of the aforementioned data included filtering out all the operating valuesattributed to the turbine operation without inlet cooling. Accordingly, values that wererecorded while the ambient air temperature was below 46 °F were not included in theanalysis. Also, the turbine is equipped with a boiler, which supplies hot water to the inletcoil when ambient air temperature drops below 42 °F.Superimposing Gross Power Output with the Compressor Inlet Temperatures in Figure 2allowed the reconstruction of the turbine performance signature, and, further, gave theopportunity to extrapolate this to compressor inlet temperatures lower than 46 °F, downto 42 °F, which is considered the lower value for a safe operating range for the LM6000(to avoid the chance of icing in the inlet to the compressor). Figure 2: Turbine SignatureNext, unavoidable parasitic power consumption has to be isolated in order to evaluate themagnitude of the shifted load that would be acquired due to the use of the TES.Comparing ambient air temperatures with the delta between the turbine’s Gross and NetPower Output in Figure 3 allowed estimating avoidable parasitic power consumption.The average monthly DB temperatures are shown in Figure 4.LM6000 Cooling Load RequirementsAccording to ASHRAE guidelines for Turbine Inlet Cooling, the site conditions of TDB =91 °F, TWB = 74 °F, and optimal inlet air TWB = 46 °F should be used in order to estimateMarch 3, 2011 Page | 4
  5. 5. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Plantthe TIC required cooling load. Considering GT Inlet Compressor nominal mass flow of291 lb/s, the required calculated cooling load is: . lbs sec Btu Btu 1Q = m(h1 − h2 ) = 291 ] * 3,600[ [ ] * (37.8[ ] − 18.2[ ]) * = 1,711TR sec hour lbs lbs Btu 12,000[ ] tonRFor good engineering practices, the TES sizing and operation schedule was based on acooling load requirement of 1,750 tonR. Figure 3: Avoidable Parasitic Power Consumption 90 AVERAGE MONTHLY DRY BULB 80 70 TEMPERATURE, F 60 50 40 30 20 10 0 0 2 4 6 8 10 12 14 Figure 4: Average Monthly DB TemperaturesHowever, the reduction of the compressor inlet temperature to below 46 °F would requiremodification of the SPRINTTM system, as well as turbine control system adjustments.March 3, 2011 Page | 5
  6. 6. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantThe manufacturer of the LM6000 confirmed that keeping the compressor inlet airtemperature at 45°F would result in a turbine electric output increase from about 47 MW(today) to 51.3 MW provided the generator operates at, or above, a Power Factor (PF) of0.85 (Figure 5). Figure 5: Generator CurveEquipment Selection ConsiderationsSeveral types of TES systems were considered for this particular application. It is alsoimportant to note that TES offers a better redundancy in comparison to the “on demand”chiller alone. If the chiller was brought down for maintenance, the TES would havesupplied the necessary cooling load to support turbine operation. Conversely, if the TESis taken off line, the chiller would have been able to supply the cooling load to supportthe turbine operation.Chilled Water TESThe chilled water storage is the most common and tested approach for inlet cooling. Itoffers the desired redundancy at low initial cost and ease of integration into any existinginlet cooling system. However, when operating at lower discharge temperature, thechiller power consumption increases and its performance is de-rated. In addition, therequired chilled water TES volume is several times larger than that of an Ice TES ofMarch 3, 2011 Page | 6
  7. 7. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Plantcompatible capacity. With space limitation at the power plant, chilled water TES sizebecomes an issue for the implementation. Finally, stratified chilled water TES is limitedto a minimum supply temperature of approximately 39 °F (4 °C), which is thetemperature at which water exhibits its maximum density.Static Ice TESStatic ice TES is a frequently used solution for shifting load in commercial and industrialapplications. It also offers the desired redundancy; however, it does so at a higher initialcost in comparison to chilled water TES, when applied to large scale applications.Additionally, most often, static ice TES requires dedicated chillers and rathercomplicated tanks filled with internals and/or moving parts, resulting in extensivemaintenance. Also, due to the adverse insulating effects of the static ice layers, therefrigerant during the freeze cycle has to be at a very low temperature, typically at 14 to22 °F. Such low temperatures require, or prefer, the application of ammonia, the use ofwhich becomes an issue, especially in urban surroundings. Finally, static ice TESsystems, with their inherently limited heat transfer surface area, are incapable ofmaintaining a cold supply temperature during the rapid TES discharge periods that arecommonly desired for TIC applications.Dynamic Ice TESDynamic or ice slurry TES systems are commonly used when rapid refrigeration isrequired. As with the two previously discussed TES systems, dynamic ice TES offers thedesired redundancy, and does so at a cost comparable to static ice. Due to its dynamicstate, ice slurry can be pumped; and therefore the ice slurry generator can be locatedseparately from the TES tank. This advantage allows for the construction of simple, lowcost and low maintenance TES tanks, without any internal heat transfer surfaces ormoving parts. Finally, VIM ice slurry is produced using water vapor as the onlyrefrigerant, making it environmentally friendly.Operation of the Vacuum Ice Maker (VIM)In order to reduce the LM6000 compressor inlet air temperature to below 46 °F and avoidthe chiller parasitic losses during daily plant operation, it is proposed to install the VIMTES system described below in Figure 6.Inside the VIM freezer, water is at its “triple point” where all three phases (vapor, liquid,and solid) are in equilibrium, exposed to a deep vacuum at 32 °F. The vacuum forces asmall part of the water to evaporate while another part of the remaining water freezes,forming a water-ice mixture. The mixture is pumped out of the freezer as ice slurry into aTES tank until the ice concentration in the tank reaches 50%.In order to maintain the deep vacuum in the freezer, the water vapor is continuouslyevacuated from the freezer, compressed and fed into a condenser by a unique centrifugalcompressor. Condensing the water vapor requires cooling water at 5.5 °C (42 °F), whichis supplied from a conventional new or (in this instance) existing water chiller.March 3, 2011 Page | 7
  8. 8. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantDuring the TES discharge cycle, chilled water at 32 °F from the bottom of the TES tankis circulated through a heat exchanger in order to meet the required cooling load demand. Figure 6: VIM TES Flow DiagramProposed ConfigurationThe integrated approach for the retrofit of the existing TIC system at the LM6000 seemsto be most appropriate. In addition to the immediate capital investment savings,integrating VIM TES into the existing TIC offers a greater degree of redundancy and,therefore, ensures continued operation of the Power Plant overall (Figure 7). Figure 7: Proposed Configuration - Flow DiagramMarch 3, 2011 Page | 8
  9. 9. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantProposed Operation CycleThe proposed operation cycle is based on a weekly cycle charge period that takes placeduring off-peak hours on weekdays, as well as during extended hours over the weekend.The off-peak period is Monday through Friday between 10:00 pm and 8:00 am; therefore,the proposed daily off-peak charge period is 10 hours. A VIM with a nominal capacity of1,000 Tons will be able to accumulate 10,000 ton-hrs during each weekday chargeperiod. In addition, the VIM will continue charging TES during the extended weekendhours in order to make up for the mismatch of cooling charge and discharge capacitiesduring weekdays.8-Hours Daily Discharge PeriodThe average duration of the LM6000 operation is 8 hours per day, including weekends.Therefore, the required daily cooling load is: DailyDemand = 8hours *1,750Ton = 14,000TR − hIn order to optimize the TES tank capacity and minimize capital investment, the weekenddaily discharge period is reduced to 5 hours per day. Therefore, the weekend cooling loaddemand for the inlet cooling is: WeekendDem and = 5hours * 1,750Ton = 8,750TR − hThe estimated minimal TES Tank capacity required to support the operation of theweekly cycle is 30,000 Ton-hrs. The optimized Charge/Discharge TES cycle, with 8hrs/day of discharge on weekdays and 5 hrs/day of discharge on Saturday and Sunday,and 10 hrs/night of charge on weeknights and 18.8 hrs/night of charge on Saturday andSunday, is illustrated in Table 1: [TR-h] Mon Tue Wed Thu Fri Sat Sun TES Cap 30,000 26,000 22,000 18,000 14,000 10,000 20,000 Discharge 14,000 14,000 14,000 14,000 14,000 8,800 8,800 Residual 16,000 12,000 8,000 4,000 0 1,200 11,200 Charge 10,000 10,000 10,000 10,000 10,000 18,800 18,800 Final Cap 26,000 22,000 18,000 14,000 10,000 20,000 30,000 Table 1: TES Discharge Cycle - 8-HoursConsidering 3 ft3 per Ton-hr of TES, the estimated volume of the ice slurry TES Tank is90,000 ft3 or about 0.67 million gallons (e.g. a vertical cylindrical tank of 53.5 ft diameterand 40 ft high).Power Consumption EstimationThe power consumption of the VIM TES has to be looked at separately during theCharge and Discharge cycles. During the off-peak Charge cycle, the biggest powerconsumers, in descending order, will be the supporting (existing) chiller, the VIM, andthe coolant pump. It is important to note that the use of TES and the optimizedMarch 3, 2011 Page | 9
  10. 10. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantCharge/Discharge schedule will minimize existing chiller power consumption duringpeak (high power value) periods. The heat load that the existing chiller is required toreject includes VIM and its auxiliaries, estimated to be about 1,120 Tons. With a specificpower consumption of 0.755 kW/Ton, the 2,000 Ton-rated chiller will reject at least 25%more cooling load. However, the system will operate during the night hours at coolerambient condensing temperatures in comparison to the day time. This factor willcontribute to an improvement in the chiller’s seasonal efficiency. Table 2 summarizes thepower consumption data during the off-peak TES Charge cycle: Power Item Qty Consumption (kW) VIM System 1 382 Supporting Chiller 1 868 Coolant Pump 1 55 Total: 1,305 Table 2: Power Consumption – Off-Peak TES Charge CycleDuring the peak TES Discharge cycle the power consumption of the system is limited totwo pumps only, namely the circulation and coolant pumps. Table 3 summarizes thepower consumption data during the peak TES Discharge cycle. Power Item Qty Consumption (kW) Circulation Pump 1 75 Coolant Pump 1 75 Total: 150 Table 3: Power Consumption – Peak TES Discharge CycleResultsThe analysis of the original annual data and the performance simulation yielded thefollowing observations and results. The average electric gross power output of theLM6000 SPRINTTM with the existing TIC chiller running is about 47 MW (Figure 2).The average parasitic power consumption of the turbine support systems is about 3.5MW, with an estimated total unavoidable parasitic power consumption attributed to theauxiliaries and natural gas supply pump of 1.5 MW. The estimated avoidable parasiticpower consumption attributed to the existing chiller is about 2 MW. Therefore, the outputof the turbine, including unavoidable power consumption, is estimated at 45 MW.March 3, 2011 Page | 10
  11. 11. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantAccording to the simulation results and manufacturer’s data, executing the compressorinlet temperatures below 46 °F, control adjustments, and HP SPRINTTM conversion tofull SPRINTTM will increase electric power output to 51.3 MW, resulting in a net increaseof about 4.3 MW.Summarizing the above, the retrofit for the existing turbine inlet cooling systems, inconjunction with the required modification, will result in shifting 2 MW from peak to off-peak hours as well as increasing turbine electric output by an additional 4.3 MW. Theresults of the simulation are summarized in Table 4: Operation Data Summary Discharge Period (weekdays) 8-hours Annual estimated recharge hours (VIM Operation hours) 2,628 Charge cycle power consumption, off-peak (MW) 1.305 Annual power consumption to recharge TES, off-peak (MW-h) 3,430 Annual estimated discharge hours 1,680 Discharge cycle power consumption, on-peak (MW) 0.15 Annual power consumption to discharge TES, on-peak (MW-h) 252 Avoided parasitic power consumption, on-peak (MW) 2 Annual avoided parasitic power consumption, on-peak (MW-h) 3,360 Estimated added power capacity, on-peak (MW) 4.3 Annual added electric power output (MW-h) 7,224 Total annual increase in net off-peak consumption (MW-h) 3,430 Total annual increase in net on-peak production (MW-h) 10,584 Table 4: Summary of Simulation ResultsConclusionsThe study of the VIM TES retrofit for the existing mechanical chiller inlet cooling systemof the LM6000 SPRINTTM has been found plausible and attractive in terms of parasiticload shift to off-peak hours, as well as in terms of an increase in net MW peak poweroutput.When considering the turbine power electric output, the addition of 4.3 MW results in a9.1% increase in terms of turbine gross electric output. When considering the parasiticpower consumption, the load shift of 2 MW to off-peak hours results in a 3.0% increasein terms of turbine gross electric output. The total increase of turbine net electric output isabout 12% or 5.7 MW.The TIC configuration currently installed at the turbine uses an “on-demand” chiller toaddress the required cooling load. After the VIM TES retrofit, the required cooling loadis reduced from 1,750 Tons (occurring during peak) to only about 1,100 Tons (occurringMarch 3, 2011 Page | 11
  12. 12. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power Plantoff-peak). Considering the chiller’s specific power consumption of 0.755 kW/Ton, thetotal parasitic power consumption was reduced by more than 25% and moved fromcritical, high-value peak periods to less critical, low cost off-peak periods. In addition,the use of TES adds valuable redundant capacity to the TIC system.March 3, 2011 Page | 12
  13. 13. Application of GREEN Ice Thermal Storage System for Peaking Gas Turbine Power PlantAppendixTable of FiguresFigure 1: Years 2005 - 2010 ......................................................................................................... 3Figure 2: Turbine Signature ......................................................................................................... 4Figure 3: Avoidable Parasitic Power Consumption ....................................................................... 5Figure 4: Average Monthly DB Temperatures .............................................................................. 5Figure 5: Generator Curve ........................................................................................................... 6Figure 6: VIM TES Flow Diagram .................................................................................................. 8Figure 7: Proposed Configuration - Flow Diagram ........................................................................ 8List of TablesTable 1: TES Discharge Cycle - 8-Hours......................................................................................... 9Table 2: Power Consumption – Off-Peak TES Charge Cycle ......................................................... 10Table 3: Power Consumption – Peak TES Discharge Cycle........................................................... 10Table 4: Summary of Simulation Results .................................................................................... 11March 3, 2011 Page | 13

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