Power and temperature control of fluctuating biomass gas fueled solid oxide fuel cell and micro gas turbine hybrid system

Abstract

Power and temperature control of fluctuating biomass gas fueled solid oxide fuel cell and micro gas turbine hybrid system AbstractThis paper addresses how the power and temperature are controlled in a biomass gas fueled solid oxide fuel cell (SOFC) and micro gas turbine (MGT) hybrid system. A SOFC and MGT dynamic model are developed and used to simulate the hybrid system performance operating on biomass gas. The transient behavior of both the SOFC and MGT are discussed in detail.An unstable power output is observed when the system is fed biomass gas. This instability is due to the fluctuation of gas composition in the fuel. A specially designed fuel controller succeeded not only in allowing the hybrid system to follow a step change of power demand from 32 to 35 kW, but also stably maintained the system power output at 35 kW. In addition to power control, fuel cell temperature is controlled by introduction and use of a bypass valve around the recuperator. By releasing excess heat to the exhaust, the bypass valve provided the control means to avoid the self-exciting behavior of system temperature and stabilized the temperature of SOFC at 850• C.

Novel solid oxide fuel cell system controller for rapid load following

“…The model is nonlinear based on transport and conservation principles. The modeling methodology used has been verified experimentally and utilized for controls development in previous work [2][3][4][5][6][7][8][9]. Since the focus of the paper is controls, the physical dynamic model is only briefly presented in Appendix A.…”

“…Most research groups have investigated overall system controls [4,6,8,10,11,13] while some have investigated specific operating requirements in more detail [5,7,14,19]. While the control strategies developed vary to some extent, a seemingly effective control strategy to meet system power demand and maintain the fuel cell operating requirements suggested by the literature includes the following features:…”

Experimental and theoretical evidence for control requirements in solid oxide fuel cell gas turbine hybrid systems

“…In the SOFC/GT hybrid system, the fuel cell high temperature SOFC exhaust drives a gas turbine, providing air flow and pressurizing the SOFC while driving an electric generator that produces additional electrical power. As a result, SOFC/GT hybrid systems have demonstrated efficiencies above 50% [5,18] and studies have shown the possibility for electrical conversion above 70% [4,19] when operating on natural gas and above 60% in an integrated coal gasification plant [6,19]. Higher efficiency reduces CO 2 emissions while separated fuel and air flows in the SOFC allow system designs for CO 2 sequestration with minimal performance cost [16,20,21].…”

“…At the system design level both prototypes and mathematical modeling have developed multiple system designs and control strategies [8,19,[24][25][26][27]. The current work seeks to illustrate the fidelity of the hybrid system modeling methodology developed at the National Fuel Cell Research Center [10,18,24,28,29] and draw attention to critical system sensitivities caused by fluctuations in temperature, electrochemical current, and fuel composition variations.…”

“…Kaneko et al also developed a dynamic SOFC/GT hybrid system model [18]. They studied the performance characteristics of the SOFC/GT hybrid system operating on biomass gas with fluctuating species concentrations, and developed a power and temperature control strategy to cope with such transients.…”