START UP ANALYSIS OF A H2-O2 FIRED GAS TURBINE CYCLE

Transcription

1 START UP ANALYSIS OF A HO FIRED GAS TURBINE CYCLE T. Funatsu Toshiba Corporation Heavy Apparatus Engineering Laboratory, Suehirochou, Tsurumiku, Yokohama, Japan M. Fukuda, Y. Dohzono Toshiba Corporation Thermal Power Plant Engineering Department 6, Tsurumichuou, Tsurumiku, Yokohama, Japan ABSTRACT The new thermodynamic cycle using hydrogen energy is now under investigation by many engineers. The Japanese World Energy Network research program is also hydrogen technology development program. One of the target of the program is to develop the high thermal efficiency power plant without emissions. The HO fired gas turbine is the key technology of the project and the new RANKINE cycle is suggested as one of the most effective cycle. The new RANKINE cycle is based on the direct steam expansion cycle and the performance calculation has been examined to find the optimal operating point. For the cycle development, further investigations of the component development, the operational ability, and the cost competitiveness are important. Among these investigations, this paper reports the operational ability, especially the start up performance. In this analysis, the algorithm and flow line for start up is developed. And the investigation finds that the new RANKINE cycle has the good possibility for the practical use. NOMENCLATURE A heat transfer area Cp specific heat under constant pressure D diameter F mol flow per second G weight H enthalpy per unit mass HHV higher heating value per unit mass I momentum of inertia K coefficient of heat transfer M heat capacity N revolution per minute Q heat transfer quantity T torque W mass flow per second dtm logarithmic mean temperature difference efb combustion efficiency eff isentropic efficiency g gravitation mtl metal section rotational speed per second subscripts b combustion c cold side d driving g gas h hot side I inlet l load o outlet sat saturated steam stm superheated steam tb turbine w water superscript th theoretical INTRODUCTION Hydrogen energy is the clean energy if it is produced by the renewable water electrolysis energy or solar energy. It can also contribute to an emission free thermal cycle if it is combusted with pure oxygen. In this point of view, HO fired gas turbine combined cycle is paid much attention ( Jericha et al., 99). In Japan, the cycle is also investigating in World Energy Network (WENET) research program proposed by Japanese government. In the program, the hydrogen production

2 technology, the hydrogen storage and transportation technology, and hydrogen utilization technology is now under investigation. (Katayama, 99) To compare the HO combustion thermal cycle with the conventional combined cycle or proposed high efficiency fossil fuel cycles (Briesch, 99 ; Nakhamkin, 996), the exact estimation of the energy which is consumed by the H and O production, storage, and transportation. With respect to this matter, some researches and estimations are reported (Hassman et al., 99; Jericha et al., 99). On the other hand, the scope of hydrogen utilization is to develop the best thermodynamic cycles which can change the hydrogen energy to the electric power in high efficiency (Yamashita, 99). Among some proposed thermodynamic cycles, one of the direct steam expansion cycle called the new RANKINE cycle is investigated. And the performance calculations has been has been carried out. As the next step of the cycle investigation, the partial load performance calculation or the operation ability analysis is important. This paper deals with the operation ability analysis which investigate the algorithm and process flow lines for start up by dynamic simulations. Results shows that the new RANKINE cycle has the good possibility for the practical use. CONFIGURATION O H O H Figure Schematic diagram of the new RANKINE cycle Figure shows the new RANKINE cycle configuration. The feed water from the condenser () is pressurized by the boiler feed water pump () to the super critical pressure, and heated in the heat recovery boiler (). The steam which is generated in, is expanded in the high pressure turbine (HT), reheated in the HO fired high pressure combustor (), and expanded in the high pressure gas turbine (IHT) again. The reheat and expansion is repeated in the HO fired low pressure combustor () and the low pressure gas turbine (ILT). The steam from ILT heat the feed water in and condensed in after through the low pressure steam turbine (LT). In the cycle, because of the hydrogen and the oxygen is burned equivalently, the combustion gas is consist of pure steam and no emission is generated. As the development target, HT inlet condition is set to. MPa ( ata) and 7, which is the advanced technology from that of Ultra Super Critical achievement. And also IHT inlet temperature is set to 7. MPa (7 ata) and 7, which is more advanced technology than that of the former Japanese moonlight program. Figure shows the new RANKINE cycle performance. The calculation includes the turbine blade cooling. The results indicate over 6 percent HHV thermal efficiency. (NEDO, 99; NEDO, 996) O H O H Location Pressure Flow Temp. Enthalpy MPa Generating Power Thermal efficiency. kg/s MW 6.7 % (HHV) 7.89 % (LHV) 7.9kJ/kg Figure The new RANKINE cycle performance START UP ALGORITHM The following two approaches are considered for the start up procedure. () Turbines start up and heat up is operated independently () Turbines start up and heat up is operated cooperatively The approach () needs to add some start up flow lines. Figure shows the process flow configuration which include

3 the start up flow line for the approach (). The start up steam (auxiliary steam) line is added for providing the start up steam. The turbine bypass lines, the turbine bypass valves, and the turbine inlet valves are also added to each turbine. The start up algorithm is the following procedure. The auxiliary steam is introduced to the combustors and through the turbine bypass valves while turbines are isolated by turbine inlet valves. is heated up after the ignition of the combustors. When heat up is completed, main steam generated in is introduced to HP, and the turbines are started by opening inlet valves. The details of this algorithm is described in figure. Using this algorithm, turbines are started by the main steam, the stable start up response like the conventional combined cycle is expected. On the other hand, the process flow line is complicated. O H O H O H O H Process flow line for start up Figure The start up flow line using approach () Process flow line for start up Figure The start up flow line using approach () Start Spinning Reserve Hold Minimum Introduce Start Turbines Rated Ignition Stop End Heat Up Introduce Main Figure The start up algorithm using approach () The approach () needs the less additional line than the approach (). Figure shows the process flow configuration which include the start up flow line for the approach (). The only additional line is the auxiliary steam line, and the IHT bypass line and valve. This bypass line and valve is necessary to control IHT rotational speed. The start up algorithm is the following procedure. Turbines are started up by the auxiliary steam. After the turbine rotational speed reaches the rated speed, heat up starts and the initial load is maintained during the heat up. The details of this algorithm is described in figure 6. Using this algorithm, the start up process flow line is more simple than that of approach (). However, it is difficult to introduce the sufficient auxiliary steam because the big capacity of auxiliary steam supply system is required to maintain the initial load. Start Stop Rated Start up &Turbines Minimum End Ignition Introduce Main Spinning Reserve Hold Heat Up Figure 6 The start up algorithm using approach () As mentioned above, these two algorithms have merit and demerit with each other. However, using algorithm (), high temperature combustion gas flows through the turbine bypass line to. Therefore the high temperature piping area much increases, and the additional material development is required. On the other hand, using algorithm (), despite the requirement of the big capacity of the

4 auxiliary steam supply system, there is no additional development. Considering above, algorithm () is adopted to the new RANKINE cycle start up procedure. COMPUTATIONAL MODEL The simple dynamic simulation model is developed using Advanced Continuous Simulation Language (ACSL). The main components models are outlined as follows. Turbine Model In turbine model, outlet enthalpy and rotational speed is calculated. The turbine flow and turbine adiabatic efficiency is approximated from the appropriate turbine map. Turbine outlet specific enthalpy: H tbo = H tbi eff (H tbi H tbo th ) () Turbine rotational speed: dn = Td Tl dt Iw GD where, I =, w = p N g 6 Combustor Model The hydrogen and the oxygen is controlled to combust stoichiometrically. So the exhaust gas enthalpy is described in the following equations. dq = efb HHV F dq Hb = Fb 8 Fbrn = F H H H Where, the enthalpy of hydrogen and oxygen before combustion is ignored. Boiler Model The boiler model is separated into the three sections which are the steam section, the steamwater section, the water section. Cold Side: Water Section Qw = Aw Kw dtmw = Wc (Hw Hci) (6) Water Section Qsat = Asat Ksat dtmsat = Wc (Hsat Hw) (7) Section Qstm = Astm Kstm dtmstm = Wc (Hco Hsat) (8) () () () () Hot Side: Qg = Ag Kg dtmg = Wh Cpg(Thi Tho) (9) Metal Section: dtmtl Mmtl * = Qg Qw Qsat Qstm () dt RESULTS AND DISCUSSIONS Dynamic simulation is carried out for the new RANKINE cycle. The auxiliary steam condition used in the simulation is.96 MPa and. Hence, to get the sufficient flow, the auxiliary steam flow is introduced to the HT, IHT and ILT inlet, respectively. Figure 7 shows the configuration of the system. P O H O H P: pressure ; T: temperature ; F: mass flow RPM: revolution ; MW: requirement power Figure 7 The new RANKINE cycle configuration (CASE ) ITEMS (Control Conditions) HT start up rate IHT start up rate Main steam pressure Initial load Minimum load transient rate (Boundary Conditions) temp. press. Fuel flow range Table Simulation conditions F ITIONS min / ( to rated speed) min / ( to rated speed) 8.MPa (Initial pressure) % of rated power 8 % of rated power % / min..96 MPa % to % of rated flow Figures 8(ae) gives the dynamic simulation results. The control and boundary condition using the start up analysis is shown in table. The cold start is assumed in this analysis, so that the turbine heat soak must be considered. Therefore, turbines start up rate are set to min / ( to rated speed). T

5 POWER [MW] REVOLUTION(RPM) TEMPERATURE [ ] 8 6 REQUIREMENT POWER GENERATING POWER Figure 8(a) The start up transient results (CASE ) 8 6 IHT REVOLUTION HT,ILT,LT REVOLUTION TIME (HOURS) Figure 8(b) The start up transient results (CASE ) 6 8 HT INLET TEMPETATURE IHT INLET TEMPERATURE ILT INLET TEMPERATURE Figure 8(c) The start up transient results (CASE ) The results (CASE ) show the plant start up time to the rated load is about.7 hours. This is close to the conventional combined cycle. heat up time is about. hours, where the auxiliary steam flow is about kg/s. The IHT inlet temperature, which is controlled to maintain the output power, shows about. Where the ILT inlet temperature is set to 8. Under these conditions, Mw initial load is maintained. and maximum fuel flow is about 7 percent and percent of the rated fuel flow, respectively. 7 AUX. STEAM FLOW MAIN STEAM FLOW Figure 8(d) The start up transient results (CASE ) FUEL FLOW FUEL FLOW Figure 8(e) The start up transient results (CASE ) In this case, about kg/s auxiliary steam flow is required to maintain the initial load. To get the flow sufficiently, the big capacity of auxiliary steam supply system is necessary. To reduce the auxiliary steam flow, the configuration shown in figure 9 is proposed. In this configuration, the feed water is sprayed to and during the initial load, instead of the auxiliary steam. These sprays will also activate to control the turbine inlet temperatures during the load operation. Figures (ae) show the dynamic simulation results using the configuration depicted in figure 9. The control set for the analysis is the same as CASE. The results (CASE ) show that this method gives almost the same start up time and heat up time as CASE. The maximum auxiliary steam flow is about kg/s which is indicated just before the initial load transient.

6 P O H O H TEMPERATURE [ ] 6 8 HT INLET TEMPERATURE IHT INLET TEMPERATURE ILT INLET TEMPERATURE P: pressure ; T: temperature ; F: mass flow RPM: revolution ; MW: requirement power Figure 9 The new RANKINE cycle configuration (CASE ) POWER [MW] 8 6 REQUIREMENT POWER GENERATING POWER Figure (c) The start up transient results (CASE ) 7 AUX. STEAM FLOW SPRAY FLOW SPRAY FLOW MAIN STEAM FLOW Figure (d) The start up transient results (CASE ) REVOLUTION [RPM] Figure (a) The start up transient results (CASE ) 8 6 HT,ILT,LT REVOLUTION IHT REVOLUTION Figure (b) The start up transient results (CASE ) FUEL FLOW FULE FLOW Figure (e) The start up transient results (CASE ) During the initial load, the auxiliary steam flow, the spray flow and the spray flow indicates kg/s, 9kg/s, and kg/s respectively. The ILT inlet temperature is set to the same temperature as CASE. The and LPCONB maximum fuel flow are twice as 6

7 much as CASE. But there are only percent and percent of the rated fuel flow, respectively. Therefore, no significant problem is shown in CASE. Consequently CASE is confirmed to be the good method for the new RANKINE cycle start up.. CONCLUSION For the new thermodynamic cycle study, the operation ability analysis is important as well as the performance analysis. This paper develops the algorithm and process flow line for start up of the new RANKINE cycle. In the start up analysis, the same operational condition of the cold start as the conventional gas turbine combined cycle is used. That is () The start up rate of turbines are set to min / ( to rated speed) which is considered the heat soak. () The load transient rate is set to % / min. which is also considered the reduction of the turbine thermal stress. For getting the same start up performance under these conditions, heat up procedure is investigated. To reduce the heat up time in spinning reserve hold, the sufficient turbine steam flow is necessary. The feed water spray to and is useful to avoid the increase of the auxiliary steam flow and the combustion temperature. Through the operational analysis, the new RANKINE cycle shows the good possibility for the practical use. Conference, 9CTP79 Yamashita, I.,99, Background and Possibility of the H O Fired Gas Turbine Development, Journal of the Gas Turbine Society of Japan, Vol., No. 86, pp. 96. (in Japanese) New Energy and Industrial technology Development Organization, 99, International Clean Energy System Technology using Hydrogen (WENET), The Development of H O Fired Gas Turbine (), NEDO 99 Annual Report, NEDOWENET98, (in Japanese) New Energy and Industrial technology Development Organization, 996, International Clean Energy System Technology using Hydrogen (WENET), The Development of H O Fired Gas Turbine (), NEDO 99 Annual Report, NEDOWENET98, (in Japanese) ACKNOWLEDGEMENT The authors are grateful to New Energy and Industrial technology Development Organization, and Central Research Institute of Electric Power Industry. They gave useful suggestions. REFERENCES Jericha, H. et al., 99, " Cooled Hydrogen / Oxygen Combustion Chamber for the Hightemperature cycle", 9th International Congress on Combustion Engines Katayama, S., 99, International Clean Energy System Technology using Hydrogen (WENET), Journal of the Gas Turbine Society of Japan, Vol., No. 86, pp. 8. (in Japanese) Briesch, M. S. et al., 99, "A Combined Cycle Designed to Achieve Greater Than 6 Percent Efficiency", ASME J. Engineering for Gas Turbine and Power, Vol. 7, pp. 7 7 Nakhamkin, M. et al., 996, "The Cascaded Humidified Advanced Turbine (CHAT)", ASME J. Engineering for Gas Turbine and Power, Vol. 8, pp. 6 7 Hassman, K. et al., 99, "Primary Energy Sources for Hydrogen Production", Int. J. Hydrog. Energy, Vol. 8, No. 8, pp. 66 Jericha, H. et al., 99, "The GRAZ Cycle Max Temperature Potential HO Fired CO Capture With CHO Firing", 99 ASME Cogen Turbo Power 7