A Study of Advanced Hydrogen/Oxygen Combustion Turbines

Transcription

1 A Study of Advanced ydrogen/oxygen Combustion urbines. SUGISIA and. MORI akasago R& D Center, Mitsubishi eavy Industries, Ltd -- Shinhama Arai-cho, akasago, yogo Pref. 66 Japan K. UEMASU akasago Machinery Works Mitsubishi eavy Industries, Ltd -- Shinhama Arai-cho, akasago, yogo Pref. 66 Japan ABSRAC Mitsubishi eavy Industries Ltd. have proposed the advanced hydrogen/oxygen combustion turbine system which is an inter-cooled topping recuperation cycle as part of a Japanese government sponsored program WE-NE (ÒWorld Energy NetworkÓ). he efficiency of this cycle reaches more than 6% (V), not (LV), with a power capacity of 5MW. his cycle is formed by a compressor, turbines, a combustor and heat exchangers. he combustor burns hydrogen/oxygen to make high temperature ( C) steam. As a result of MI research in 99 [], the topping extraction cycle (A) designed by Jericha et al. [] was found to be the best cycle. MI also designed the inter-cooled topping recuperation cycle (BI) in 995 which modified cycle (A) to be suitable for a high combustion temperature ( C). his paper presents the details of the comparison between the above mentioned cycles. he investigation shows that cycle (BI) is considered to be better than cycle (A) from the point of view of both the thermal efficiency and the feasibility of manufacture. INRODUCION WE-NE, a part of ÒNew Sunshine ProjectÓ, is a Japanese government program aimed at solving energy and environmental problems in the world. WE-NE, which began in 993 and is expected to last for 3 years, has the aim of constructing a clean energy network throughout the world; firstly by producing ydrogen by electric dissolution of water using hydro-electric-power, solar energy, geothermal energy, wind energy, etc. and then transporting, storing and generating electricity using this produced ydrogen. In this paper some evaluation of Òydrogen/Oxygen Combustion urbine CyclesÓ, which is a sub-task of ÒWorld Energy NetworkÓ, is presented. In 99, three di ferent closed hydrogen combustion turbine cycles, were evaluated []. hese are the Bottoming Reheat Cycle, the opping Extraction Cycle (A) designed by Jericha et al. [] and the Rankine Cycle. Results of this study showed the opping Extraction Cycle (A) to be the best cycle. Subsequent to this research, further work was undertaken to design a highly efficient and highly feasible cycle adapted to high combustion temperature ( C) - the opping Recuperation Cycle (B). Cycles with an inter-cooler between low pressure and high pressure compressors in cycles (A) and (B) have also been investigated which are the Inter-cooled opping Extraction Cycle (AI) and the Intercooled opping Recuperation Cycle (BI).

2 CYCLE CONFIGURAIONS he Inter-cooled opping Extraction Cycle (AI) shown in Figure is a kind of gas turbine combined cycle whose working fluid is steam. he topping cycle is a Brayton cycle comprising of low pressure compressor, high pressure compressor, turbine,heat exchanger 5,6, and combustor 3. he bottoming cycle of cycle (AI) is a Rankine cycle. Steam is extracted from between heat exchanger 5 and 6, is expanded by turbine 6, and condensed by condenser. he same flow rates as the hydrogen fuel and stoichiometric oxygen are discharged, the rest of the steam is pumped up by pump and 3. he steam is economized by feed water heaters and, recuperated by heat exchanger 5 and 6, expanded by turbine 9 and mixed with the topping steam in the outlet of compressor. he water to be intercooled is extracted after being condensed in condenser 3, and pumped up in pump. It is mixed with the the topping steam in the outlet of compressor. he opping Extraction Cycle (A) is same as non-inter-cooled one of cycle (AI). he Inter-cooled opping Recuperation Cycle (BI) shown in Figure is also a kind of gas turbine combined cycle like cycle (AI). Cycle (BI) has added heat exchangers and 5 compared with cycle (AI). he heat exchanger recuperates the heat from the exhaust of turbine to the exit of compressor. 3 ASSUMPIONS CONDIIONS he investigations are carried out preliminarily in the operating conditions in able and the component efficiencies in able. able shows the operating pressures and temperatures of each component (such as turbines, compressors, and heat exchangers) which are assumed to be the almost the same values in cycle (A), (AI), (B) and (BI). he values in able and are expected in the near future. Because of these assumptions, the thermal di ferences of the cycles can be clarified. he total output of all cycles is a constant 5MW. Combustor outlet temperatures are assumed to be both C and 5 C, because the firing temperatures of current high efficiency industrial gas turbines have already reached 5 C. Cooling steam flow rate ratio is %, and 5%. he outlet pressure downstream of the condensers is fixed at.5bar( 5 Pa). As the componentsõ assumptions and conditions above are almost the same, the manufacturing realization of the components (turbines,heat exchangers, compressors, combustors and so on) should be nearly equivalent. he paramatric studies based on the above investigations are carried out to assess the characteristics of pressure ratio and the inlet temperature of turbine. he pressure ratio should be selected carefully if the operating temperature is decided because a lot of factors are affected by the pressure ratio. he merits and demerits of increasing the pressure ratio are displayed in able 3. From able 3, it would be beneficial to achieve a high cycle thermal efficiency at the lowest possible pressure ratio. PERFORMANCES AND FEASIBILIY OF COMPONEN Cycle calculations for cycle (A), (AI), (B) and (BI) were carried out to estimate the performance of the cycles. he typical results of cycle calculations, assuming that combustor outlet temperature is C and cooling steam flow rate ratio is % are shown in able. Comparison of cycle (A) and (BI) shows the thermal efficiency of cycle (BI) to have a relative change of.% higher than cycle (A). he first vane height of the high pressure, high temperature turbine of cycle (BI) has a relative change of % higher than cycle (A). he exhaust temperature of the turbine and the maximum operating temperature of the heat exchanger in each cycle are almost the same at C. he compressor outlet temperature is about C in cycles (A) and (B) and 55 C in cycles (AI) and (BI). herefore, cycle (BI) is judged to be the best cycle from the point of view of the feasibility of the components. he results of other cases are shown in able 5. he results of the parametric studies are shown in Figure 3 and. he results show that the pressure ratio for the maximum thermal efficiency is about 3 in cycle (A) and 5 in cycle (BI). he thermal

3 efficiency of cycle (BI) is higher than cycle (A) for a pressure ratio of less than. If the pressure ratio becomes higher, a lot of problems shown in able 3 are anticipated. Cycle (BI), therefore, has an advantage in terms of thermal efficiency at a more feasible pressure ratio. he pressure ratio should,therefore, be set to 5. he thermal efficiency of cycle (BI) is higher than cycle (A) when the turbine inlet temperature is more than 5 C. Cycle (BI) is, therefore, suitable for the high operational temperature cycle of more than 5 C. he features of the Inter-cooled opping Recuperation Cycle are shown in able 6. 5 CONCLUSIONS ) he thermal efficiency of cycle (BI) is 6.%(V), which is a relative change of.% higher than cycle(a). ) he cycle (BI) has a relative change of % larger first stage turbine vane height than cycle (A), and the advantage from the point of view of both the manufacturing of the complex cooling passage inside the vane and the turbine aerodynamic efficiency. It is especially important to have high aerodynamic efficiency of the high temperature turbines in each cycle to achieve higher overall thermal efficiency. 3) he pressure ratio for the maximum thermal efficiency is about 5 in cycle (BI), which is lower than that of cycle (A) at 3. Cycle (BI), therefore, has an advantage of high thermal efficiency at a more feasible pressure ratio. ) Cycle (BI) is suitable for a high operational temperature cycle of more than 5 C. 5) he inter-cooled topping recuperation cycle (BI) in Figure is considered to be the best cycle from the view point of the thermal efficiency and the feasibility of manufacturing. References [].Sugishita,.Mori and K.Uematsu ÒA Study of hermodynamic Cycle and System Configurations of ydrogen Combustion urbinesó, th World ydrogen Energy Conference, Stuttgart Germany, June 3-6,996, pp5-6. []. Jericha, R.Ratzesberger, ÒA Novel hermal Peak Power PlantÓ, ASME Cogen-urbo Nice France August 3 - September,99.

4 Inlet of urbine = C Cooling Steam Flow Rate Ratio = IC C C KJ/kg kg/s bar P GEN CD 3 P F C: : : P: P Combustor urbine Pump : F: CD: IC: eat Exchager Feed Water eater Condenser Inter Cooler F Component Power(MW) C 5.9 C Mech Loss 5. Gen Loss.6 otal 5 hermal Efficiency 59.% Fig. A ypical Calculation Result of Intercooled opping Extraction Cycle(AI) Inlet of urbine = C Cooling Steam Flow Rate Ratio = IC C C KJ/Kg kg/s bar P GEN CD 3 P C: : : P: P Combustor urbine Pump : F: CD: IC: F eat Exchanger Feed Water eater Condenser Inter Cooler F Component Power(MW) C. C Mech Loss 5. Gen Loss.6 otal 5. hermal Efficiency 6.% Fig. A ypical Calculation Result of Intercooled opping Recuperation Cycle (BI)

5 hermal Efficiency (%) (V) 6 =. C opping Recuperation Cycle (Cycle B) = 6. C =. C = 65. C =. C = 65. C Outlet of igh Pressure =.3 C = 3. C = 65 C = 35 C Intercooled opping Recuperation Cycle (Cycle BI) : Outlet ( C) : Outlet of igh Pressure ( C) opping Extraction Cycle (Cycle A) Intercooled opping Extraction Cycle(Cycle AI) = 55 C = 55 C = 5 C hermal Efficiency (%) A : opping Extraction Cycle AI: Intercooled opping Extraction Cycle B : opping Recuperation Cycle BI: Intercooled opping Recuperation Cycle Cycle A =.3 C Cycle BI = 55 C Cycle AI = 55 C Cycle B =.3 C : Outlet Inlet of urbine = C Cooling Steam flow rate ratio =.5 opping Pressure Ratio = 5 = 6. C 6 Pressure Ratio Fig.3 Effects of opping Pressure Ratio 53 5 Inlet of urbine ( C) Fig. Effects of Inlet of urbine able Operating Conditions able Components Efficiency Inlet Pressure Inlet Outlet Pressure Outlet urbine Inlet Cooling Air Flow Rate Ratio of urbine urbine Outlet urbine 9 Inlet urbine 9 Inlet Pressure Maximum Operating of eat Exchanger Efficiency of eat Exchanger otal Output. bar +5 C of a Saturated 5. bar 55 C (With inter-cooled), 5 C,.5 Less than C 593 C 35 bar Less than 9 C Less than.5 5 MW Efficiency urbine Efficiency Combustion Efficiency Combustor Pressure Loss eat Exchanger Pressure Loss Pump Loading Mechanical Efficiency Generater Efficiency % of inlet pressure 5% of inlet pressure.99.95

6 able 3 Merits and Demerits by increasing Pressure Ratio Merits igher hermal Efficiency Demerits Increase the number of stages of turbines and compressors Increase the leakage flow rate igher compressor exhaust temperature hicker casing of compressor outlet and combustor chamber igher heat transfer coefficient on the surface of blades igher energy to pump up a fuel Lower height of first stage turbine vanes Cycle A Cycle AI Cycle B CycleBI hermal Efficiency (%) able Comparison of Results Relative Change of hermal Efficiency Relative Change of First Stage urbine Vane eight of urbine.9.9. Outlet ( C) Exhaust of urbine ( C) 3 3 Maximum Operating of eat Exchanger ( C) 3 3 Inlet of urbine = C Cooling Steam flow Rate Ratio= able 5 Results of Cycle Calculations opping Extraction Cycle opping Recuperation Cycle Cycle (A) (AI) (B) (BI) Pressure ratio Inlet temperature of turbine Cooling Flow rateratio Outlet Low igh Inlet temperature of urbine Flow rate of urbine hermal Efficiency (%) (5=53 C) (5=566 C) able 6 Features of Cycles. System Configurations. Recuperation from urbine Outlet to Combustor Inlet 3. Characteristic of Pressure Ratio. Characteristic of of urbine Inlet 5. Steam Flow Rate of urbine Inlet Inter-cooled opping Extraction Cycle (AI) Combined Cycle Optimized Pressure Ratio is about 3 igher Efficiency in less than 5 C Small Inter-cooled opping Recuperation Cycle (BI) Optimized Pressure Ratio is about 5 igher Efficiency in more than 5 C Large (Easier to construct complicated cooling passages)