System And Method For Increasing The Efficiency For A Solid Oxide Fuel Cell System (Cummins Power Generation)

System And Method For Increasing The Efficiency For A Solid Oxide Fuel Cell System (Cummins Power Generation)
United States Patent Application 20160028096
Vesely; Charles J. ;   et al.   January 28, 2016
Applicant: Cummins Power Generation IP, Inc.
Abstract
System and method for increasing efficiency of a solid oxide fuel cell (SOFC) system by recapturing water via a condensate extraction system that extracts water from a hot cathode exhaust flow of the SOFC stack. Further, the SOFC system can include a radiant heater which has a fuel inlet, an air intake, and an exhaust outlet independent and separate from the power generating components in the SOFC system. The radiant heater can bring the SOFC stack up to operating temperature quickly and/or maintain near operational mode temperatures of the SOFC stack during a hibernation mode.
FIELD
[0001] This disclosure relates to increasing the efficiency of solid oxide fuel cell (SOFC) system.
BACKGROUND OF THE INVENTION
[0002] Under normal operation, a typical SOFC system maintains a system operating temperature of approximately 700.degree. C. For the high temperature fuel cell system to become operational, the system typically requires significant startup time ranging anywhere between 1 to 4 hours to reach the operating temperature from near ambient environmental conditions.
[0003] Generally, in a portable SOFC system, a stack (or hot box) is heated up from the environment using the following two methods. One method burns fuel in a combustor and uses the exhaust from the combustor as a heat source for heating an incoming cold cathode air. Then, the heated cathode air is used to heat up the stack. Another method requires a separate combustor or an electric heater in the stack. The method uses the hot exhaust from the combustor to heat up the stack by convection with the external stack surface.
[0004] Further, conventional SOFC system generally uses a reformer to generate usable fuel from a hydrocarbon based (HC) feed stock fuel. The reformer can be operated as an Auto Thermal Reactor (ATR) or a steam reformer, both of which require a source of water for proper operation. A water source independent system is generally required for a portable or remote power system, especially for RV or remote site telecom gensets. In the water source independent system, water can be acquired by condensing water vapors from the exhaust anode fuel of the SOFC stack. At the SOFC stack, an electrochemical conversion process occurs which produces electricity directly from oxidizing the fuel. SOFC stack has a solid oxide or ceramic, electrolyte which requires high operating temperature which results in longer start-up times and mechanical and chemical compatibility issues.
[0005] A conventional method for condensing water vapor is to use ambient air with a heat exchanger to cool down the anode exhaust gas and then extract liquid water from that anode exhaust. This method is limited to moderate ambient temperatures, which tend to limit its usefulness in high environmental temperature conditions (e.g., summer).
[0006] Conventional methods for heating up a fuel cell stack in a SOFC system from the environment typically have low efficiencies. For example, using the exhaust from the combustor as the heat source for heating up the incoming cold cathode air, a substantial portion of the heat from the exhaust is directly released to environment and not utilized for heating the fuel cell stack. Conventional methods can also suffer from high parasitic loss of power, which can increase the fuel burn rate of the combustor.
[0007] In portable SOFC systems, conventional methods for heating up the stack can present a challenge for a battery bank capacity because portable SOFC systems are generally operated without an external power source. Additionally, high condensation rates are required to supply the system needs and achieve a water balance for increasing the efficiency of the SOFC system. The increased level of condensate production cannot be achieved by conventional methods described above at high ambient air temperatures. Thus, there can be a risk of running out of water in conventional SOFC systems absent an external water supply.
SUMMARY OF THE INVENTION
[0008] Embodiments disclosed herein increase the efficiency of SOFC system by recapturing water via a condensate extraction system that extracts water from a hot cathode exhaust flow of the SOFC stack. Further, the SOFC system can include a radiant heater which has a fuel inlet, an air intake, and an exhaust outlet independent and separate from the power generating components in the SOFC system. The radiant heater can bring the SOFC stack up to operating temperature quickly and/or maintain near operational mode temperatures of the SOFC stack during a hibernation mode.
[0009] Embodiments disclosed herein are directed to achieving the water balance for increasing efficiency of SOFC systems. Embodiments can include a condensate extraction system that cools the hot cathode exhaust flow (about 400.degree. C. typically) using an intake of ambient air through a heat exchanger to extract water as a condensate. The remaining exhaust is then rejoined to the cathode exhaust flow entering the makeup burner. The heat from the heat exchanger is also used to flash the water condensate back to vapor in the incoming air stream, which is then routed into the ATR reformer for use. The cooler of an embodiment is placed in the cathode exhaust stream exiting the heat exchanger to further cool the exhaust and condense water out of the exhaust stream.
[0010] In other embodiments, to limit the power draw of the cooler, the temperature of the exhaust stream exiting the heat exchanger is monitored and the cooling is controlled and/or regulated to cool sufficiently enough for condensing the water vapor out. In another embodiment where an absorption chiller is included and used, heat from the main exhaust is used to drive the chilling cycle and cools the exhaust exiting the heat exchanger.
[0011] An embodiment of a SOFC system for heating a solid oxide fuel cell comprises a hot box containing a fuel cell; a reformer which provides a reformed fuel to the fuel cell; and a condensate chiller mechanism, wherein the condensate chiller mechanism receives anode exhaust from the fuel cell and condenses liquid water from the anode exhaust, vaporizes the liquid water to water vapor, and directs the water vapor to the reformer to increase the amount of water vapor received by the reformer for producing the reformed fuel. In another embodiment the condensate chiller mechanism comprises a Peltier cooler for separating the liquid water from the anode exhaust. In another embodiment, the condensate chiller mechanism comprises a phase change cooler for separating the liquid water from the anode exhaust.
[0012] An embodiment of the system further comprises a fuel-based radiant heater, wherein the fuel-based radiant heater for heating the fuel cell, wherein the fuel-based radiant heater directs radiation to the fuel cell to bring the fuel cell to operating temperature at startup and/or maintain a temperature of the fuel cell to near operating temperature during hibernation mode. In an embodiment of the system, the fuel-based radiant heater is a diesel fuel-based radiant heater. In another embodiment of the system, the fuel-based radiant heater is a directed fuel-based radiant heater.
[0013] An embodiment of the system further comprises a fuel inlet for generating electricity from the fuel cell, wherein the fuel-based radiant heater has a radiant heater fuel inlet that is independent and separate from the fuel inlet. Another embodiment of the system further comprises an exhaust outlet for generating electricity from the fuel cell, wherein the fuel-based radiant heater has a radiant heater exhaust outlet that is independent and separate from the exhaust outlet. In another embodiment of the system, the radiant heater exhaust outlet is directed to provide heat to the fuel cell.
[0014] An embodiment of the system for heating a solid oxide fuel cell comprises a hot box containing a fuel cell, and a fuel-based radiant heater, wherein the fuel-based radiant heater for heating the fuel cell, wherein the fuel-based radiant heater directs radiation to the fuel cell to bring the fuel cell to operating temperature at startup and/or maintain a temperature of the fuel cell to near operating temperature during hibernation mode.
[0015] An embodiment of a method for increasing an efficiency of a SOFC system comprises the steps of directing an anode exhaust from a fuel cell to a condensate chiller; extracting water vapor from the anode exhaust and directing the water vapor to an air intake of a reformer for producing a reformed fuel with an increased water balance; producing the reformed fuel with the increased water balance; and supplying the reformed fuel with the increased water balance to the SOFC fuel cell.
[0016] Another embodiment of the method further comprises the step of generating radiation by supplying a fuel to a fuel-based radiant heater, wherein the fuel-based radiant heater directs the radiation to the fuel cell to bring the fuel cell to operating temperature at startup and/or maintain a temperature of the fuel cell to near operating temperature during hibernation mode.
[0017] Another embodiment of the method further comprises the step of bringing the fuel cell to operating temperature at startup by generating radiation from a fuel-based radiant heater, wherein the fuel-based radiant heater directs the radiation to the fuel cell.
[0018] Another embodiment of the method further comprises the step of maintaining a temperature of the fuel cell at near operating temperature of the fuel cell in hibernation mode by generating radiation from a fuel-based radiant heater, wherein the fuel-based radiant heater generates the radiation and directs the radiation to the fuel cell.
[0019] Another embodiment of the method further comprises the step of maintaining a temperature of the fuel cell at near operating temperature of the fuel cell in hibernation mode by generating radiation from a fuel-based radiant heater, wherein the fuel-based radiant heater directs the radiation to the fuel cell.
[0020] Another embodiment of the method further comprises the step of bringing the fuel cell to operating temperature at startup by generating radiation from a fuel-based radiant heater, and directing the radiation to the fuel cell.
[0021] Another embodiment of the method further comprises the step of maintaining a temperature of the fuel cell at near operating temperature of the fuel cell in hibernation mode by directing heat from radiant heater exhaust from a fuel-based radiant heater to the fuel cell.
[0022] Another embodiment of the method further comprises the step of bringing the fuel cell to operating temperature at startup by directing heat from radiant heater exhaust from a fuel-based radiant heater to the fuel cell.
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