Large Frame Gas Turbines, The Leading Technology …

1 Mitsubishi Heavy Industries, Review Vol. 41 No. 5 (Oct. 2004)1 Large Frame Gas Turbines, The Leading Technology ofPower generation IndustriesIn developing Large -capacity gas turbines for use in power generation as the main machines in combined cycle powerplants, MHI has made every effort to increase thermal efficiency. Since the 1980s when the commercial operation of powergeneration plants with a combustion temperature of 1 100 began, the combustion temperatures have been increasingat a rate of approximately 20 per year. The maximum combustion temperature currently reaches about 1 500 , temperature increases beyond that temperature come up against a number of technical problems including reduc-ing NOx emissions and the need to increase the strength of materials and, accordingly, the gradient of temperature risetends to decrease.

2 On the other hand, the period of high growth in which a specified increase in demand for power could beexpected has come to an end for gas turbines, which have been increasing in capacity with a rise in temperature, and now itis a time in which new products must be created that are capable of coping with dramatically varying social and economicconditions. In addition, global environmental problems are becoming greater, and from the viewpoint of the utilization oflimited fossil fuels and reducing the amount of CO2 emissions, it is indispensable to develop more highly efficient powergeneration plants.

3 This paper takes a brief look at future directions in the development of Large -capacity gas Introduction1. Introduction1. Introduction1. Introduction1. IntroductionSince their adoption as the main power generatingmachines of Japanese thermal power plants at the be-ginning of the 1980s, Large commercial gas turbinesoperating on natural gas as a main fuel have contrib-uted significantly to an increase in thermal efficiencyand reducing contamination by exhaust emissions. Themaximum turbine inlet temperature (combustor outlettemperature) at present is 1 500 , and the overallthermal efficiency has reached almost 60% on a lowercalorific value basis (LHV).

4 The past twenty years werean era in which the efficiency of combined power gener-ating plants had been increased through increases in thetemperature and efficiency of gas the amount of air required for a lean-premixedcombustion at 1 500 nears the amount of air thatis usable for combustion, any increases in efficiency byfurther rises in temperature tends to be slowed down atpresent due to an increase in the amount of cooling airnecessary to maintain safe operation, even if the mostadvanced material with high thermal strength are this paper, the future direction in the Large -capac-ity gas turbines is described from the four viewpoints ofan increase in cycle maximum temperature, diversifica-tion of fuels, intermediate capacity peak powergeneration, and challenges to new Increase in maximum cycle temperature2.

5 Increase in maximum cycle temperature2. Increase in maximum cycle temperature2. Increase in maximum cycle temperature2. Increase in maximum cycle temperatureAccording to the second law of thermodynamics,when the maximum temperature of a thermal cycle israised, the efficiency of recovery energy conversion isincreased. It is an ideal combination in which the powerof high temperature heat energy at 1100 or higheris recovered by the gas turbine, while the power fromlow temperature heat energy at 600 or less is re-covered by the steam turbine. By using what arecommonly referred to as heat cascades in the combina-tion of two temperature ranges, thermal efficiency canbe increased more in combined cycles than in Steam cooling Steam cooling Steam cooling Steam cooling Steam cooling technologyMitsubishi Heavy Industries, Ltd.

6 (MHI) has devel-oped a variety of advanced technologies aimed atincreasing peak temperatures of cycle. One of these tech-nologies consists of cooling the high temperature partsof a gas turbine by using steam cycle. As shown in ,the gas temperature at the outlet of a combustor (inletof 1st vane) and the temperature on the downstream sideof the outlet can be increased by adopting this systemfor cooling the 1 Steam cooled combustor systemSupplySupplySupplyTemperatureTempe ratureFlow of flue gasFlow of flue gasCombustorCombustorSteamSteamReturnRet urnReturn1st stage vanes1st stage blades1st stage vanes1st stage bladesYASUSHI FUKUIZUMI*1 SHIGEHIRO SHIOZAKI*1 AKIMASA MUYAMA*2 SUMIU UCHIDA*3*1 power Systems Headquarters*2 Takasago Machinery Works*3 Takasago Research & Development Center.

7 Technical Headquarters2 Mitsubishi Heavy Industries, Review Vol. 41 No. 5 (Oct. 2004)In addition, by cooling steam at the 1st vane, the in-let gas temperature of the 1st blade can be furtherincreased for recovering power . By using the cooling ef-fect of steam having a Large specific heat, the mixing ofcooling air into the main gas flow can be reduced andthe maximum cycle temperature can be increasedthrough the use of conventional shown in , since 1997 eighteen G-seriesgas turbines started operation in the verificationpower plant of MHI Takasago Machinery Works inwhich cooling steam is adopted in the then, these turbines have been commerciallyoperated in the world.

8 Their cumulative operatingtime currently exceeds 190000 hours. Their operationhas continued satisfactorily with high reliabilitythrough an improved design that makes use of MHI'sextensive experience in the verification power genera-tion the adoption of steam cooling, the tip clear-ance of the turbine blades can be controlled by the activeuse of the steam heat transfer, as shown in Inthis Technology , the tip clearance is increased at the timeof start up of the gas turbine by allowing steam to flowinto the turbine blade ring cooling passage Leading tothe combustor to heat the turbine casing.

9 The tip clear-ance is minimized by cooling the casing at the time ofrated load operation. This Technology has been adoptedin the G-series gas turbines.'94 '95 '96 '97 '98 '99 '00 '01 '02 '03 '04 '05 '06 '071 500oCTurbine inlet temperature1 450oC 1 500oCACC (Active Clearance Control)Operating hours: 197 000 hoursReliability: %Commercial operation: 18 unitsUnder construction: 17 unitsSeries G1500500oCIIijan (The Philippines,) 4 GT (2 on1)Mystic (USA) 4 GT (2 on1)Fore River (USA) 2 GT (2 on1)USA 2 GT(2 on1)Covert (USA) 3 GT(1 on1)Fig.

10 2 Operating experience of G-series gas turbinesM501G initial design1st M501G machine ("T" Point: 60 Hz)1st M701G machine (Tohoku Electric power : 50Hz)M701G2 shop testTokyo Electric PowerTohoku Electric power ( # 3, 4)1 500oCAir flow +10 %120100806040200120100806040200 Rotational speed,load (%)Rotational speed,load (%)-300 30 60 90 120 150 180-30 0 30 60 90 120 150180 Fig. 3 Blade tip active clearance control (ACC)From combustor cooling outletTo combustor cooling inletFrom HRSG1st stage 1st stage blade ringblade ring1st stage blade ring2nd stage 2nd stage blade ringblade ring2nd stage blade ring1ststage vanes1ststage blades2ndstage vanes2ndstage bladesClearanceClearanceNormal blade ringRotational speedRotational speedLoadLoadRadial clearanceRadial clearanceACC blade ringTime (m)Mitsubishi Heavy Industries, Review Vol.