Gas Turbine Combined Cycle Plant Repowering.pdf

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  Aeroderivative Gas Turbines LM2500 ® to LM2500+DLEGas Turbine Combined CyclePlant Repowering Authors: Michael T. McCarrick GE Energy Kenneth MacKenzie P.Eng. City of Medicine Hat  Abstract The province of Alberta, Canada developed annual emission intensity limits for the power generation sector in order to preserve air quality by reducing emissions of sulfur dioxide (SO x ),nitrogen dioxide (NO x ), and primary particulate matter. EffectiveJanuary 1, 2006, all new gas-fired power plants were required tomeet Annual Emission Intensity Limits for NO x . In the Spring of 2006, the City of Medicine Hat (COMH) LM2500 gas turbine unitswere due for their 50,000-hour major overhaul cycle, and COMHwas faced with this new NO x emission requirement, along withan increasing power load demand for the city. Working closelywith GE Energy’s Aero Services group, COMH decided to upgradethe two LM2500 gas turbines to two LM2500+DLE gas turbines tomeet the new emissions requirements and boost power outputto support the growing needs of the city.This paper will describe the engineering design challenges tomodify the existing LM2500 gas turbine package to accept thelonger and more powerful LM2500+DLE gas turbine, and the results of the evaluations of the additional mass flow impact onsteam production and combined cycle plant performance. This paper will also detail the upgrade execution outages andcommissioning experience of the LM2500+DLE gas turbines atthe COMH plant. The actual operational performance results willbe outlined to show the approximately 30% increase in gas turbine power output, 5% decrease in gas turbine heat rate, andthe annual reduction in NO x emissions of up to 900 tons per year. Background and Description of Original Plant Configuration The City of Medicine Hat (COMH) Electric Utility is a municipallyowned utility in Alberta, Canada that operates a natural gas-firedcombined cycle power plant with a 209 MW ISO capacity. The plant began in 1910 with a single-cylinder natural gas-fired 2 engine driving a generator. Over the intervening years, the plantgrew into a strictly Rankine-cycle steam plant and finally intotoday’s configuration, a fully combined cycle plant. The present configuration of the plant is shown in Figure 1. Units10 and 11, the subject of this paper, were srcinally installed in1990 as refurbished General Electric (GE) Frame 5M gas turbinesoperating in simple cycle with a heat rate of 13,900 BTU/kWe-Hr(LHV). A summary of past and present unit configurations isshown in Table 1. In 1993, single-pressure HRSGs were constructed for both units toimprove plant efficiency and increase plant capacity, achieving a combined cycleheat rate of 8,880 BTU/kWe-Hr (LHV) with a corresponding steam turbine power production of 10.1 MWe. Figure 2 shows the heat balance for the 1993 configuration. In 1998 the Frame 5M units were replaced with GE’s LM2500-PEmodel aeroderivative gas turbines in an attempt to improve reliability and further improve efficiency. The LM2500 is derivedfrom the CF6 family of aircraft engines used on a variety of commercial aircraft and is a hot-end drive, two-shaft gas generator with a free power turbine. The LM2500-PE features a Single Annular Combustor (SAC) and a 6-stage power turbine. The ISO exhaust flow of the LM2500-PE engines, at 499,000 lb/hrwas significantly lower than the previous Frame 5 ISO engine exhaust rate of 716,000 lbs/hr. Thus, the steam production from the respective Unit 10 and 11 HRSGs decreased to 6.1 MWe asmeasured in steam turbine electric power output. However, thecombined cycle heat rate improved to 7,500 BTU/kWe-Hr (LHV) as a result of the turbine replacements. Figure 3 shows the heatbalance for the 1998 configuration with the LM2500-PE. Table 1 – Units 10 and 11 Performance Summaries (at 15C 60%RH 666m el.) Simple CycleHeat Rate LHV BTU/MWe-Hr)Gas Turbine Generator Power (MWe) HRSG HP Steam(lb/hr) Steam Turbine(MWe) Combined Power (MWe) Combined CycleHeat Rate LHV BTU/MWe-Hr) Frame 5M 13.90 17.9 91,00010.128.08.9 LM2500PE 9.74 20.4 55,000 6.1 26.5 7.50 LM2500PR 8.88 27.0 62,0006.9 33.9 7.08 LM2500 to LM2500+DLE Gas Turbine Combined Cycle Plant Repowering Michael T. McCarrick GE Energy Kenneth MacKenzie P.Eng. City of Medicine Hat  3Figure 2Figure 1  4 LM2500 Gas Turbine History and Evolution to the LM2500+/+G4 In the early 1970s, the LM2500 gas turbine was derived from the CF6-6 flight engine, which to date has accumulated over300,000,000 flight hours on a variety of commercial aircraft. The LM2500 utilized a 16-stage compressor section with inlet guidevanes and 6-stages of variable stator vanes with a 2-stage high-pressure turbine (HPT) section exhausting into a 6-stage freepower turbine. The srcinal design had twin-shank HPT blades andan ISO power rating of 17.9 MW with 35.8% simple cycle thermal efficiency. In 1992 a single-shank HPT blade was introduced that allowed for a higher firing temperature while maintaining the expected 25,000-hour hot section life on natural gas. The ISO powerrating was correspondingly increased to 23.8 MW with a 37.5% simple cycle thermal efficiency.In 1997, the LM2500 was upgraded to the LM2500+ when a zerostage blisk was added to the front end of the compressor sectionto provide a total of 17 stages of compression and boost thecompression ratio from 20:1 to 23:1. Some material changes inthe HP turbine section and enlarging of the free power turbineflow function raised the ISO power rating to 31.3 MW with 39.5%simple cycle efficiency. The major differences between theLM2500 and the LM2500+ gas turbines are shown in Figure 4.The LM2500+G4 gas turbine, the most recent uprate to theLM2500 family, was introduced in 2005. The LM2500+G4 provides approximately a 10% power increase over the LM2500+model and was considered for this use in this project, however,the electric generator could not handle the LM2500+G4 outputacross the full range of ambient conditions, and the LM2500+was selected for the COMH Repowering Project.As of this writing, the LM2500/+/+G4 models have over51,000,000 operating hours in power generation, marine, cogeneration, and mechanical drive applications. Figure 3
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