Abstract
A theoretical solid oxide fuel cell–gas turbine hybrid system has been designed using a Capstone 60 kW micro-gas turbine. Through simulation it is demonstrated that the hybrid system can be controlled to achieve transient capability greater than the Capstone 60 kW recuperated gas turbine alone. The Capstone 60 kW gas turbine transient capability is limited because in order to maintain combustor, turbine and heat exchangers temperatures within operating requirements, the Capstone combustor fuel-to-air ratio must be maintained. Potentially fast fuel flow rate changes, must be limited to the slower, inertia limited, turbo machinery air response. This limits a 60 kW recuperated gas turbine to transient response rates of approximately 1 kW s −1. However, in the SOFC/GT hybrid system, the combustor temperature can be controlled, by manipulating the fuel cell current, to regulate the amount of fuel sent to the combustor. By using such control pairing, the fuel flow rate does not have to be constrained by the air flow in SOFC/GT hybrid systems. This makes it possible to use the rotational inertia of the gas turbine, to buffer the fuel cell power response, during fuel cell fuel flow transients that otherwise limit fuel cell system transient capability. Such synergistic integration improves the transient response capability of the integrated SOFC gas turbine hybrid system. Through simulation it has been demonstrated that SOFC/GT hybrid system can be developed to have excellent transient capability.
Highlights
Introduction and backgroundSolid oxide fuel cell gas turbine hybrid technology is being considered as a power alternative that achieves the goal of generating electric power at high thermal efficiency
As the technology develops, it is important to quantify the transient capability of fuel cell gas turbine hybrid systems and understand the dynamics, controls, performance, and risks of hybrid transient capability
The transient capability of fuel cells and turbines are each limited by the balance of plant that is required to maintain the system within operating requirements
Summary
Solid oxide fuel cell gas turbine hybrid technology is being considered as a power alternative that achieves the goal of generating electric power at high thermal efficiency. In hybrid systems the high temperature exhaust of the fuel cell is used to drive a gas turbine which provides the fuel cell air flow and supplementary power Solid oxide fuel cell gas turbine hybrid systems are often believed to have poor transient load following capability in part because the few demonstrated hybrid systems have been very conservative and limited research has been conducted to realize and develop fuel cell hybrid transient capability. To investigate and demonstrate the load following capability of both systems, a model of a Capstone 60 kW recuperated gas turbine has been developed and compared against experimental transient performance data. With a Capstone 60 kW gas turbine was developed and modeled Both gas turbine and hybrid systems are designed, controlled, and simulated such that all system components are maintained within operating requirements. The modeling platform provides the ability to investigate aggressive fuel cell operation without damaging expensive prototype systems
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