Study on Advanced Micro disk Gas Turbine Using Hydrogen Fuel Produced by Very High Temperature Nuclear Reactor

Transcription

1 Study on Advanced Micro disk Gas Turbine Using Hydrogen Fuel Produced by Very High Temperature Nuclear Reactor Sri Sudadiyo 1 * 1 PTRKN BATAN, Tangerang, Indonesia * sudadiyo@batan.go.id Abstract STUDY ON ADVANCED MICRO DISK GAS TURBINE USING HYDROGEN FUEL PRODUCED BY VERY HIGH TEMPERATURE NUCLEAR REACTOR. On the present work, it has been selected a model of advanced micro disk gas turbine or micro ceramic Shinla gas turbine as part of very high temperature nuclear reactor (VHTNR) system project being investigated by the Reactor Development Group of National Nuclear Energy Agency which has good potential for the application to electricity generation device. Study is carried out using hydrogen as fuel which produced by the VHTNR system. Within the micro combustion chamber, this hydrogen will be burned by preheated air to maintain the high thermal performance. After leaving micro combustor, those hot gases were flowed through the micro disk gas turbine that be mounted by micro compressor on the same shaft. Furthermore, the exhaust gases were transferred to a ceramic heat exchanger to preheat compressed air before entering the micro combustor. The model configuration was investigated on operating conditions at a compression pressure ratio of 2.5 and a micro disk gas turbine inlet temperature of approximately 1150 K, it would result in a CER as high as about 65 percent and it had achieved a significant reduction in the hydrogen consumption up to approximately 38 percent. In closing, this advanced micro disk gas turbine system could be coupled to Shinla turbine system with solar collector which offer good potential for higher thermal CER, and will be very promising for the future facilities. Keywords: Micro disk gas turbine, Hydrogen, Very high temperature nuclear reactor 1. Introduction From the viewpoint of energy systems and environment, an advanced micro disk gas turbine or a micro ceramic Shinla gas turbine within combined cycles has been selected for the project of very high temperature nuclear reactor system investigated by Reactor Development Group of National Nuclear Energy Agency, as described based on reference [1]. A schematic diagram of topping Brayton cycle, bottoming Rankine cycle, and nuclear reactor system is essentially shown in the Figure 1 as an ideal representation of thermal energy utilization system for a plant with the aim to stimulate on the design of future facilities. In this model of topping cycle, the exhaust heat is recovered through a high effectiveness heat exchanger and transported back to a micro disk gas turbine combustor to enhance the thermal Carnot efficiency ratio (CER) of the cycle. The present paper addresses to investigate a model of a 3 kw micro disk gas turbine system using hydrogen fuel that produced by nuclear reactor and it is burned within its micro combustor. The thermodynamic cycle analyses are described to yield in a higher temperature for the heat addition process in the micro combustion chamber. 2. Potential Applications of 2.1. Nuclear Reactor System The investigated nuclear reactor system in this study is the type of very high temperature nuclear reactor (VHTNR) namely a gas cooled graphite moderated nuclear reactor that developed by Generation IV International Forum as a primary option for the concept of hydrogen production plant [2]. The detailed design of this nuclear reactor system is not still decided yet. The VHTNR has a reference concept of nuclear thermal power with a coolant outlet temperature of higher than 1273 K. The main components of VHTNR system are shown in the Figure 2 that has the potential applications of heat transfer technology for hydrogen production plant which offers increasing in thermal CER and reductions in pollution. Many countries are developing this nuclear reactor system namely France, Japan, South Africa, South Korea, and United Kingdom. This paper considers industrial production of thermal energy by using nuclear heat source for the utilization of hydrogen as the fuel that will be burned within micro combustion chamber. 385

2 2.2. High Temperature Air Combustion The technology of high temperature air combustion (HiTAC) could be applied in almost all kinds of combustion, power generation, and propulsion systems and has significant potential for utilizing various kinds of gas, liquid, solid, and waste fuels, and can also provide reduction in the physical size. The potential applications of HiTAC have been successfully demonstrated in a number of publications, and in this paper will be discussed for application to a micro disk gas turbine system as shown in Figure 1, including the development of its micro combustion chamber. The temperature of combustion air was preheated to higher 500 K. It is well known that the enthalpy of the exhaust gases will effectively increase the temperature in the region of combustor for micro gas turbine, if the heat from the exhaust gas is used to preheat the combustion air Hydrogen Fuel The opportunity to enable micro disk gas turbines to operate on gaseous fuel like hydrogen with a low heating value (LHV) of approximately 120 MJ/kg are presently being undertaken. From the study on the published book by Tsuji et al. [3] and many the published papers as described in [4] and [5], the high temperature air is advantageous for stability limit and good combustibility of hydrogen air flame compared to normal air combustion case. An illustration of the phenomena for the oxidation of hydrogen at high pressure and temperature had also been studied on reference [6]. This information can provide useful insights for practical application to the micro combustor. 3. Micro Gas Turbine System 3.1. State of The Art An advanced micro disk gas turbine or micro ceramic Shinla gas turbine is selected as the topping cycle in the present study. The main reason for this selection is that it is able to operate at a high CER or a high thermal efficiency based on state of the art component technology when utilizing HiTAC technology, and this necessitating the use of ceramic in the hot components including micro combustion chamber, heat exchanger, and micro turbine. An expression for the thermal efficiency of the cycle can be written as follows : cpa ( T2 T1 ) ηtcpg ( T4 T5 ) ηc ηth = (1) c T η T + c T 1 + η pg ( ) ( ) 4 he 5 pa 2,act where subscripts of 1, 2, 3, are thermodynamics states identified in Figure 1, whereas the definition of he CER is a ratio of the cycle thermal efficiency to the Carnot efficiency. The heat exchanger effectiveness can be obtained by the following relationship : η T T 3 2 he = (2) T5 T2 All calculations further were based on the study on references [7] and [8]. As demonstrated in the Figure 3 that the HiTAC cycle gives the benefit of improved the thermal efficiency or the CER over simple cycle for any inlet temperature of micro gas turbine. It can be stated that for a selected point at operating conditions of pressure ratio of 2.5 and micro gas turbine inlet temperature of 1150 K, the CER of cycle could achieve 65 percent when employed the HiTAC technology. The next discussions are main components of the advanced micro disk gas turbine system Micro Air Compressor A micro radial compressor of single stage is adopted since it can generate the required the pressure ratio. By assuming an ideal flow, air enters this micro compressor in the axial direction and leaves in the radial direction. The micro radial compressor and micro gas turbine are mounted on the same shaft in which the power developed by micro gas turbine is utilized to drive micro compressor with power of about 55 percent of power output of micro gas turbine. The operating conditions of this micro compressor are listed in the Table 1. The correlation between pressure ratio and CER under gas turbine inlet temperature (TIT) of about 1150 K is plotted in the Figure 4. Table 1. Operating Conditions of Micro Compressor Discharge temperature 389 K Pressure ratio 2.5 Required work 3.7 kw Adiabatic efficiency 85 percent 3.3. Micro Can Combustor The combustion chamber that is modeled in the present paper is a typical can combustor as had been developed and investigated in the past studies because it is the more widely used in most of the micro gas turbines. Its configuration was shown on references [8] and [9]. Operating conditions of this micro combustor are listed in the Table 2. The optimal cross sectional area of the casing is determined as discussed in the published book by 386

3 Lefebvre on reference [10], and it may be calculated from the following expression : R m3 T 3 ΔP3 4 ΔP 3 4 A ref = 2 P3 q ref P 3 Table 2. Operating Conditions of Micro Can Combustor Combustion loading parameter kg/s/atm 1.8 /m 3 Inlet temperature 650 K Outlet temperature 1150 K Maximum temperature 1178 K Fuel air ratio Combustion efficiency 95 percent (3) The variation between the burning efficiency ratio (BER) and the combustion loading parameter (CLP) with certain operating condition is illustrated in the Figure 5. In the real micro combustor, the combustion efficiencies can be correlated as a function of the θ parameter is defined as follows : T3 P3 A ref Dref exp 300 θ = (4). ma Then by reading off θ value at point along a horizontal line within the hatched area in Figure 6, the combustion efficiency could be obtained to be 95 percent. From cycle analysis, it could be achieved approximately 38 percent reduction of fuel mass flow rate, whereas physical dimensions could be reduced approximately 15 percent Micro disk Gas Turbine A schematic of the rotor of a micro disk gas turbine or micro ceramic Shinla gas turbine is shown on the reference [9]. It was assembled by the disks of the ceramic that had the same shape and dimensions. Exhaust gases from micro combustor expands through nozzle and rushes out at supersonic speed to impinge on rotor to perform shaft working. The power produced by this micro disk gas turbine is partially consumed by a micro compressor is proportional to absolute temperature of gas passing through those devices. After leaving this micro disk gas turbine, the exhaust gases were flowed through a ceramic heat exchanger to preheat compressed air before entering micro combustor. The operating conditions of this micro disk gas turbine are listed in the Table 3 below. Table 3. Operating Conditions of Advanced Micro Disk Gas Turbine Outlet temperature Outlet pressure Gas flow rate Resulted work Net work Adiabatic efficiency 963 K 0.1 MPa kg/s 6.7 kw 3 kw 85 percent 4. Promising Facilities In the current work, the performance of model is made by comparison between the present model and other micro gas turbine manufacturers to emphasize the thermal CER of systems, as shown in Figure 7. It may be noted that the present model predicted the results quite well. Furthermore, the Shinla turbine cycle had been developed and investigated by Saitoh et al. is employed as bottoming cycle, and it may be added solar collector as a heat source for working fluid. Rotor of this Shinla turbine was installed from disks, which arranged innumerably with the order spacing of micro meter, as illustrated on references [8] and [11]. Based on the use of micro systems technology, a projection of the combined cycles between topping cycle and bottoming cycle within the VHTNR system will enable to be developed into engineering field to improve the overall thermal CER of system. 5. Conclusion The performance of a 3 kw micro disk gas turbine model, which will be applied to topping cycle within a VHTNR system, has been investigated. For range of operating parameters, the performance of that with HiTAC cycles always indicate in cycle CER superior to that of a simple cycle. And also, the bottoming cycle of solar Shinla turbine system had been discussed on the present paper. Additional work was focused at preliminary development processing of hydrogen production plant using nuclear heat source (in this case is a VHTNR) that will be utilized for a micro disk gas turbine system that could be operated over the cycle CER of about 65 percent, so that it would provide useful information in considering development of the future facilities. 387

4 Acknowledgment The author would like to thanks to Prof. T.S. Saitoh at Tohoku University for his supervision throughout period of research on systems of micro gas turbine and organic Shinla turbines. The author would also like grateful to peoples who have supported this work for presenting in ICANSE Nomenclature A = Area of the combustor, [m 2 ] BER = Burning efficiency ratio, [percent] CER = Carnot efficiency ratio, [percent] CLP = Combustion loading parameter, [kg/s/atm 1.8 /m 3 ] c p = Specific heat at constant pressure, [J/kg/K] D = Diameter of the combustor, [m] HiTAC = High temperature air combustion k = Specific heat ratio LHV = Low heating value of the fuel. = Mass flow rate, [kg/s] m P = Working fluid pressure, [kpa] P 2 /P 1 = Pressure ratio of compression q = Dynamic pressure, [kpa] R = Gas constant, [= J/kg/K] T = Working fluid temperature, [K] TIT = Inlet temperature of micro gas turbine, [K] VHTNR = Very high temperature nuclear reactor Greek η C = Adiabatic efficiency of compressor, [percent] η he = Heat exchanger effectiveness η T = Adiabatic efficiency of turbine, [percent] η th = Thermal efficiency of cycle, [percent] θ = Reaction controlled parameter Subscripts 3 = Combustor inlet plane 4 = Combustor outlet plane a = Air act = Actual value g = Gas ref = Reference value References 1. Sudadiyo, S. (2007), Proposal of Research, Submitted to Ministry of Research and Technology of Indonesia. 2. Abrams, B. (2002), A Technology Roadmap for Generation IV Nuclear Energy Systems, U.S. DOE Nuclear Energy Research Advisory Committee and Generation IV International Forum. 3. Tsuji, H. et al. (2003), High Temperature Air Combustion, CRC Press. 4. Gupta, A.K. (2004), Journal of Engineering for Gas Turbines and Power, ASME, 126, Sudadiyo, S. (2007), Proceeding of Industrial Technology, ITS Surabaya, Sudadiyo, S. (2000), Lab. Report, Course in MSc. Program, Leeds University, England. 7. Kuniyoshi, I. (2002), Micro Gas Turbine System (In Japanese), Ohmsha, Japan. 8. Sudadiyo, S. and Saitoh, T.S. (2005), Proceeding of WRERC. 9. Sudadiyo, S. (2006), A Study of High Efficient Distributed Power Generation System Using Micro Gas Turbine and Organic Shinla Turbines, Doctoral Thesis, Tohoku University, Japan. 10. Lefebvre, A.H. (1999), Gas Turbine Combustion, 2 nd Edition, Taylor and Francis, London. 11. Saitoh, T.S. (2004), Shinla Turbine System, the Innovative Next Generation Thermal Electric System Superior to Photovoltaic Cell / Fuel Cell, Press Information, Tohoku University Group. 12. Peterson, R.B. (2004), Micro Technology, Energy Applications of, Encyclopedia of Energy, Elsevier Academic Press, 4, Dellenback, P.A. (2002), Journal of Engineering for Gas Turbines and Power, ASME, 124,

5 Hydrogen Production Processes (i.e. Nuclear Reactor) Figure 1. A simplified process diagram for integration of a micro disk gas turbine and solar Shinla turbine into the very high temperature nuclear reactor [1, 8, and 9] control rods pump graphite reflector hydrogen production plant water blower oxygen reactor coolant HX hydrogen (to micro disk gas turbine systems) Figure 2. The very high temperature nuclear reactor system for hydrogen production plant [2] 389

6 CER [percent] HiTAC cycle TIT [K] Simple cycle Figure 3. Influence of TIT on the thermal CER for selected cycles with the effectiveness of heat exchanger of 97 percent CER [percent] Pressure Ratio Figure 4. Effect of pressure ratio on the thermal CER under TIT condition of 1150 K 96 BER [percent] CLP Figure 5. Trend line of burning efficiency ratio versus combustor loading parameter for the design efficiency of 99.9 percent Figure 6. Chart of combustion efficiency for the present micro can combustor CER [percent] Power Output [kw] Advanced Micro-Disk Gas Turbine Other Micro Gas Turbines Figure 7. Performance diagram between the present model and other micro gas turbines 390