US20140272636A1

US20140272636A1 - Hybrid Autothermal Steam Reformer for Fuel Cell Systems

Info

Publication number: US20140272636A1
Application number: US14/210,213
Authority: US
Inventors: Donald Frank Rohr; John Anthony Vogel
Original assignee: Combined Energies LLC
Current assignee: Combined Energies LLC
Priority date: 2013-03-14
Filing date: 2014-03-13
Publication date: 2014-09-18
Also published as: US10320018B2; US20140272656A1; US20140260964A1; US10644338B2; US20140278709A1; US20190260052A1

Abstract

A reactant processing module with a hybrid autothermal reformer (HASR) can allow for control of both the amount of cathode recirculation and the amount of water sent to the HASR. At the beginning of life of the fuel cell, reactant processing module can operate on full cathode recirculation. As the fuel cell begins to age and become less efficient, the amount of nitrogen-heavy, vitiated air from the fuel cell cathode can be monitored by a control system and restricted using a valve. In order to compensate for the aforementioned restriction, the rate of input of the external air supply is increased to the HASR and the deficit in water is supplied in liquid form from a water reservoir and turned to steam within the HASR. The amount of liquid water input from the water reservoir that meets the need for continued efficient operation is relatively small.

Description

RELATED APPLICATION DATA

This application claims the benefit of priority of U.S. Provisional Patent Application No. 61/788,532 filed Mar. 15, 2013, and titled Dynamically Responsive High Efficiency CCHP System, U.S. Provisional Patent Application No. 61/788,300 filed Mar. 15, 2013, and titled System and Method of Regenerating Desulfurization Beds in a Fuel Cell System, U.S. Provisional Patent Application No. 61/781,965 and filed Mar. 14, 2013, and titled Power Conversion System with a DC to DC Boost Converter, and U.S. Provisional Patent Application No. 61/784,894 filed Mar. 14, 2013, and titled Hybrid Autothermal Steam Reformer for Fuel Cell Systems, each of which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of hydrogen generation. In particular, the present invention is directed to a hybrid autothermal steam reformer for fuel cell systems.

BACKGROUND

A fuel cell is an electrochemical device which reacts hydrogen with oxygen to produce electricity and water. The basic process is highly efficient and fuel cells fueled directly by hydrogen are substantially pollution free. Moreover, as fuel cells can be assembled into stacks of various sizes, fuel cell systems have been developed to produce a wide range of electrical power output levels and thus can be employed in numerous applications.
Although the fundamental electrochemical processes involved in all fuel cells are well understood, engineering solutions have proved elusive for making efficient use of fuel cells, especially in residential and light commercial applications, where the power output demands of a fuel cell are not as significant. The prior art approach of sophisticated balance-of-plant systems are unsuitable for optimizing and maintaining relatively low power capacity applications and often result in wasted energy and systems that are not cost-effective.
For example, the use of steam reforming (SR), and consequently, steam generation, in a residential or light commercial CCHP appliance is problematic because of the processes and waste involved with providing water to the SR system. For example, available water from tap or well must be de-ionized—removing minerals, additives, and ions by passing it through a reverse osmosis (RO) filter—in order to prevent mineral build up in the fuel cell system's boiler and reformer. Commercially available filters are about 7:1 efficient; that is, for every gallon of de-ionized water generated, seven gallons are separated as waste. In many parts of the world, such as Europe, this level of water consumption is unacceptable. Moreover, tap pressure is often insufficient to push the water through an RO filter to the boiler, so a pump is added to the fuel cell system, further adding cost, complexity, and parasitic loads to the CCHP appliance.
Moreover, after de-ionization, the water is sent to a boiler to be converted into steam, which is then injected into the reformer. The boiler typically uses a hydrocarbon fuel, such as natural gas, decreasing the system efficiency of the appliance and requiring exhaust management to vent the combustion products. The SR also requires an external heat source for startup and operation since the SR reactions are endothermic. This often comes in the form of a separate natural gas burner, further debiting system efficiency.

SUMMARY

In a first exemplary aspect a hybrid autothermal steam reformer (HASR) included within a reactant processing module having a variable cathode air recirculation system and a water delivery system, the reactant processing module providing a reformate stream to a power generation module, the HASR comprises: an enclosure including: an autothermal reformer; a water inlet fluidly coupled to the water delivery system; an air inlet in fluidly coupled to the variable cathode air recirculation system; and a reformate stream exit fluidly coupled to the power generation module, wherein the autothermal reformer receives a refined fuel and a quantity of air, the quantity of air received from the power generation module via the variable cathode air recirculation system when the autothermal reformer is operated in full cathode recirculation, and wherein the autothermal reformer receives the refined fuel, a quantity of external air via the variable cathode air recirculation system, and a quantity of water received from the water delivery system when the quantity of air received from the power generation module becomes nitrogen-heavy.
In another exemplary aspect, a power generation system comprises: a FAWD module capable of producing a refined fuel stream; a reactant processing module capable of receiving the refined fuel stream and producing a reformate stream; a power generation module capable of receiving the reformate stream and providing to the reactant processing module a quantity of air; and a control system in communication with the reactant processing module and the power generation module, wherein the control system monitors the quantity of air and determines whether the reactant processing module can operate in a full cathode recirculation mode or if an external air and/or water supply is necessary for efficient operation of the power generation module.
In yet another exemplary aspect, a method of improving the efficiency of a fuel cell system comprises: monitoring an air stream from a fuel cell cathode; determining the degree of vitiation of the air stream; increasing a rate of input of an external air supply to a reactant processing module based upon the determining; and increasing a rate of input of an external water supply to the reactant processing module based upon the determining.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 is a block diagram of a combined cooling, heating, and power system according to an embodiment of the present invention;

FIG. 2 is a block diagram of a fuel cell system according to an embodiment of the present invention;

FIG. 3 is a block diagram of a reactant processing module including a hybrid autothermal steam reformer according to an embodiment of the present invention;

FIG. 4 is a block diagram of a process of operating a steam reformer according to an embodiment of the present invention;

FIG. 5 is a schematic of a high temperature polymer electrolyte membrane fuel cell according to an embodiment of the present invention;

FIG. 6 is a block diagram of a waste heat recovery system according to an embodiment of the present invention;

FIG. 7 is a block diagram of a combined cooling, heating, and power system according to another embodiment of the present invention; and

FIG. 8 is a block diagram of a computing environment that may be used to implement a combined cooling, heating, and power system including a hybrid autothermal steam reformer according to an embodiment of the present invention.

DESCRIPTION OF THE DISCLOSURE

Low hydrogen concentration in the supply reformate sent to a fuel cell causes a high stress, low efficiency regime within the fuel cell. The lack of sufficient hydrogen results in a fuel cell system operation that consumes more reactants for equivalent power production and produces a less humidified exhaust (lower water content), thus returning less water to the reformer. Less water returning to the reformer operating in cathode recirculation mode translates into further reductions in hydrogen production in the reformer, exacerbating the problem and creating a “death spiral” for the fuel cell. Fuel cell system integrators have found the linkage between low hydrogen concentration and water production as barriers to the development of the most compact, cost-effective alternative for hydrocarbon conversion in a fuel-cell-based CCHP system.
A combined cooling, heating, and power (CCHP) system including a hybrid autothermal steam reformer according to the present disclosure generates high-efficiency power, heating, and/or cooling on demand, while improving CCHP operation, reducing maintenance costs, and preserving the investment in the fuel cell system. The CCHP system of the present disclosure can be operated so as to produce high utilization of a fuel cell or group of fuel cells (often referred to as a “fuel cell stack”), using both the electric and thermal energy generated by the fuel cell for use within a structure throughout the year. In this way, the CCHP system provides near complete energy recovery. Operationally, a CCHP system according to one or more embodiments of the present disclosure allows for the use of readily available hydrocarbon fuels, such as natural gas, near atmospheric pressure operation, close-coupled heating and cooling systems, optimized power electronics, drop-in replacement for existing heating, cooling, and hot water systems, and grid integration. The hybrid autothermal steam reformer, an example of which is described herein, overcomes many of the limitations of the prior art by providing increased hydrogen and oxygen to the fuel cell, as needed, without the need for significant additional equipment, thus increasing CCHP system efficiency.
FIG. 1 shows an exemplary CCHP system 100 according to an embodiment of the present invention. At a high level, CCHP system 100 includes a fuel cell system 104, a waste heat recovery system 108, and a control system 112. In operation, and as explained in more detail below, fuel cell system 104 uses a refined mixture of water, air, and hydrogen to produce electrical energy and thermal energy. As with most fuel cells, fuel cell system 104 must be kept within a predetermined temperature range in order to promote efficient operation of the cell. Thus, at least a portion of the thermal energy produced by fuel cell system 104 is removed by waste heat recovery system 108, which, as described more fully below, is designed and configured to make the fuel cell system's thermal energy available for both reuse within the fuel cell system as well as heating and cooling of the structure, e.g., residence, commercial building, etc., where CCHP system 100 resides.
FIG. 2 shows the primary components of an exemplary fuel cell system 104. As shown, fuel cell system 104 includes a fuel-air-water delivery (FAWD) module 116, a reactant processing module 120, a power generation module 124, and a power conditioning module 128.
At a high level, FAWD module 116 receives fuel, air, water, and heat as inputs, and produces a desulfurized, humidified fuel stream, i.e., a refined fuel stream 132, as an output. The fuel used in fuel cell system 104 generally varies by the type of fuel cell employed. For example, hydrogen, carbon monoxide, methanol, and dilute light hydrocarbons like methane (by itself or in the form of natural gas) are used by common fuel cell types. As discussed in more detail below, the type of fuel cell used effectively in fuel cell system 104 produces both electrical and thermal energy in sufficient amounts for use in the structure in which it is deployed. In an exemplary embodiment, a high temperature polymer electrolyte membrane (PEM) fuel cell is used in fuel cell system 104 and the input into FAWD module 116 is natural gas, which is generally readily commercially available, although other fuels could be used.
In an exemplary embodiment, FAWD module 116 can desulfurize the fuel (if necessary) by contacting the fuel with an adsorbent that preferentially adsorbs hydrogen sulfide, carbonyl sulfide, sulfur odorants, or combinations thereof, at a selected temperature and pressure. In another exemplary embodiment, FAWD module 116 can also include a hydrocarbon desulfurization bed, such as the hydrocarbon desulfurization bed described in Applicants' co-pending patent application entitled “Regeneration System and Method of Desulfurization in a Fuel Cell System,” U.S. application Ser. No. 14/194,786, filed on Mar. 2, 2014, which is incorporated by reference for its discussion of the same.
FAWD module 116 may also further condition the fuel by altering the water content of the fuel to an appropriate level for fuel cell system 104. The humidity of refined fuel stream 132 may be increased by increasing the water input to FAWD module 116.
The input rate, temperature, pressure, and output of FAWD module 116, and any regeneration process, are regulated via control system 112, described in more detail below, so as to be responsive to the needs of the structure (e.g., thermal and electrical loads) and to optimize the utilization and efficiency of CCHP system 100.
FAWD module 116 supplies refined fuel stream 132 to reactant processing module 120. Reactant processing module 120 provides the conditions necessary to deliver a reformate stream 136 to power generation module 124 that contains primarily H₂, CO, CO₂, CH₄, N₂and H₂O. The two reactions, which generally take place within reactant processing module 120 and convert the refined fuel stream into hydrogen, are shown in equations (1) and (2).
½O₂+CH₄→2H₂+CO Equation (1):
H₂O+CH₄→3H₂+CO Equation (2):
The reaction shown in equation (1) is sometimes referred to as catalytic partial oxidation (CPO). The reaction shown in equation (2) is generally referred to as steam reforming. Both reactions may be conducted at a temperature of about 100° C. in the presence of a catalyst, such as platinum. Reactant processing module 120 may use either of these reactions separately or in combination. While the CPO reaction is exothermic, the steam reforming reaction is endothermic. Reactors utilizing both reactions to maintain a relative heat balance are sometimes referred to as autothermal (ATR) reactors.
As evident from equations (1) and (2), both reactions produce carbon monoxide (CO). Such CO is generally present in amounts greater than 10,000 parts per million (ppm). In certain embodiments, because of the high temperature at which reactant processing module 120 is operated, this CO generally does not affect the catalysts in the reactant processing module.
Notably, the use of a high-temperature PEM fuel cell (as opposed to a low temperature PEM fuel cell system (e.g., less than 100° C.) substantially avoids the problem of removing most of the CO from the reformate stream 136. Should additional CO removal be desired, however, reactant processing module 120 may employ additional reactions and processes to reduce the CO that is produced. For example, two additional reactions that may be used are shown in equations (3) and (4). The reaction shown in equation (3) is generally referred to as the shift reaction, and the reaction shown in equation (4) is generally referred to as preferential oxidation (PROX).
CO+H₂O→H₂+CO₂ Equation (3):
CO+½O₂→CO₂ Equation (4):
Various catalysts and operating conditions are known for accomplishing the shift reaction. For example, the reaction may be conducted at a temperature from about 300-600° C. in the presence of supported platinum. Other catalysts and operating conditions are also known. Such systems operating in this temperature range are typically referred to as high temperature shift (HTS) systems. The shift reaction may also be conducted at lower temperatures, such as 100-300° C., in the presence of other catalysts such as, but not limited to, copper supported on transition metal oxides. Such systems operating in this temperature range are typically referred to as low temperature shift (LTS) systems.
The PROX reaction may also be used to further reduce CO. The PROX reaction is generally conducted at lower temperatures than the shift reaction, such as between about 100-200° C. Like the CPO reaction, the PROX reaction can also be conducted in the presence of an oxidation catalyst such as platinum. The PROX reaction can typically achieve CO levels less than about 100 ppm (e.g., less than 50 ppm). Reactant processing module 120 can include additional or alternatives steps than those listed above to remove CO as is known in the art, and it is known that other processes to remove CO may be used.
In addition to converting the refined fuel stream 132 for use within power generation module 124 and removing undesirable components, reactant processing module 120 also removes heat from refined fuel stream 132. In an exemplary embodiment, heat removal is provided by a thermal fluid loop (not shown), which acts as a heat exchanger to remove heat from refined fuel stream 132 before the stream exits as reformate stream 136. Additional exemplary reactant processing modules are described in U.S. Pat. Nos. 6,207,122, 6,190,623, and 6,132,689, which are hereby incorporated by reference for their description of the same.
An exemplary embodiment of reactant processing module 120, reactant processing module 300, is shown in FIG. 3. Reactant processing module 300 includes a hybrid autothermal steam reformer (HASR) 304, a cathode air recirculation system 308, and a water delivery system 312. HASR 304 typically includes an enclosure, a catalyst monolith or bed, a water gas shift (either medium temperature shift or high temperature shift) catalyst monolith or bed, one or more heat exchangers to adjust the temperature of the reactants and to remove the heat of the catalytic reactions, temperature sensors. The hydrocarbon, e.g., refined fuel stream 132, and air input into HASR 304 are facilitated by blowers, mass flow sensors, and shut off valves (not shown). Variable cathode air recirculation system 308, which in the embodiment shown in FIG. 3 includes a control valve or three-way valve 316, regulates the wet, recirculated cathode exhaust air from power generation module 124 (shown as waste output in FIG. 2). Water delivery system 312 includes a water reservoir 320 that may be periodically filled from a resupply tank or other water source, such as, but not limited to, a potable water line 324 and a condensate line 328 that includes water recovered from power generation module 124. Water delivery system 320 can also include a particulate filter 332 and a pump (not shown) for injecting the water into HASR 304.
Reactant processing module 300 can allow for control of both the amount of cathode recirculation and the amount of water sent to HASR 304. At the beginning of life of the fuel cell, HASR 304 can operate on full cathode recirculation as the fuel cell is operating efficiently and is producing enough water for efficient reforming of refined fuel stream 132. As the fuel cell begins to age and become less efficient, the amount of nitrogen-heavy, vitiated air from the fuel cell cathode can be monitored, by for example, control system 112, and restricted using valve 316. In order to compensate for the aforementioned restriction, the rate of input of the external air supply is increased to HASR 304 and the deficit in water is supplied in liquid form from water reservoir 320 and turned to steam within the HASR. The amount of liquid water input from water reservoir 320 that meets the need for continued efficient operation is relatively small (for example, a 3 kW fuel cell running at peak power output would require about 2 liters of water per day and under certain conditions may be 1 liter of water per day or less). Because the amount of liquid is small, any minerals or impurities entering reactant processing module 300 should not affect the operation of HASR 304 or down-stream CCHP system 100 components. The amount of heat required to turn the liquid water into steam is also relatively small and can be provided by thermal management module 144 (described in more detail below). Notably, the increase in outside air and water from water reservoir 320 can be controlled by control system 112 based on the operating characteristics of the fuel cell.
Overall, reactant processing module 300 improves hydrogen concentration and boosts the efficiency of a fuel-cell-based power generation module 124 and concomitantly, CCHP system 100. For example, as the fuel cell approaches end of life, reactant processing module 300 can discontinue cathode recirculation and use more external air and more liquid water. This operation achieves hybrid steam reforming that maximizes hydrogen concentration by using slightly more water, but benefiting from the increases in power generation efficiencies. One of the many benefits of this technique is in greatly increasing the useful life of the fuel cell and the amount of useable power extracted from it. Upon fuel cell replacement, reactant processing module 300 should be reset to take advantage of full cathode recirculation.
Water reservoir 320 can be maintained in several ways. For example, periodic resupply may be completed by a service technician, who can fill water reservoir 320 with de-ionized water—high purity water for use in the process. As another example, water can also be reclaimed from the exhaust of burner module 148 (described below), especially when cathode recirculation is not employed. In yet another example, local water from any potable source can resupply the small amount of water necessary to maintain the reaction. Given the small amount of water necessary, gravity or local water pressure can provide enough motive force to feed the required water through into HASR 304. In the event this is inadequate, a small pump may be employed.
Reformate stream 136, exiting reactant processing module 124 or reactant processing module 300 is provided as an input to power generation module 124. Power generation module 124 is a device capable of producing electric power and concomitantly generating thermal energy. In an exemplary embodiment, power generation module 124, when operating, is capable of producing thermal energy at a temperature of between about 120° C. and about 190° C. In another exemplary embodiment, power generation module 124, when operating, is capable of producing thermal energy to sufficiently meet the loads required of the structure, for example, the peak heating and hot water demands of an average residential home. In another exemplary embodiment, power generation module 124, when operating, is capable of producing thermal energy at about 1.5 kW of thermal energy per 1 kW of electrical energy. In another exemplary embodiment, power generation module 124 is a high temperature polymer electrolyte membrane (PEM) fuel cell (sometimes referred to as proton exchange membrane fuel cell), such as the PEM fuel cell 500 shown in FIG. 5 (below).
Turning now to an exemplary method 400 of operation of a reactant processing module, such as reactant processing module 124 or 300, and with reference to FIGS. 1-3 and with further reference to FIG. 4, at step 404 a recirculated air stream, typically received from a power generation module and specifically a fuel cell cathode of a fuel cell, is monitored for its quality, e.g., nitrogen content.
At step 408, a determination is made as to whether the recirculated air stream has become vitiated such that it is affecting the performance of the fuel cell. If the recirculated air quality is good, the process proceeds to step 412 and thus full cathode recirculation is continued. If the recirculated air quality is poor, the process proceeds to step 416 where the amount of recirculated air is restricted. In an exemplary embodiment, recirculated air quality can be considered poor when the oxygen level drops to a point where nitrogen content begins to exceed about 20% over ambient conditions, or approximately 48%.
So as to compensate for the restriction in step 416, the process continues to steps 420 and/or 424 where external air and/or external water supplies, respectively, are used to make-up for the restriction and thus to provide appropriate amounts of air and water to the fuel cell for continued efficient power production. Whether or not external air or external water are supplied to the fuel cell to make up for the restriction of recirculated air in step 416 depends upon the conditions of the fuel cell. For example, as the fuel cell ages and the operating voltage decreases, low oxygen/hydrogen concentrations are stressors on the fuel cell further driving down voltage. At beginning of life or under light power load conditions, the system can run at full cathode recirculation with no water added. Over time, as voltage decreases under full cathode recirculation, voltage can be regained by increasing hydrogen content which can be accomplished by adding water to the system (step 424). As stress on the fuel cell further increases (e.g., nitrogen content increases) there will be a need to increase the oxygen content by limiting recirculation and increasing the external air supplied (step 420) and, depending on the moisture content of the external air, adding water, from, for example, a water delivery system, so as to increase the moisture content to desired levels. The process then returns to step 404 for continued monitoring of the air stream that now includes external air and/or water.
As the fuel cell ages, the amount of external air and/or water can be gradually increased so as to maintain the efficient operation of the fuel cell until the fuel cell needs to be replaced.
In PEM fuel cell 500, a membrane 504, such as, but not limited to, a phosphoric acid-doped cross-linked porous polybenzimidazole membrane, permits only protons 516 to pass between an anode 508 and a cathode 512. At anode 508, reformate stream 136 from reactant processing module 120 is reacted to produce protons 516 that pass through membrane 504. The electrons 520 produced by this reaction travel through circuitry 524 that is external to PEM fuel cell 500 to form an electrical current. At cathode 512, oxygen is reduced and reacts with protons 516 to form water. The anodic and cathodic reactions are described by the following equations (1) and (2), respectively:
H₂→2H⁺+2e⁻ Equation (1):
O₂+4H⁺+4e⁻→2H₂O Equation (2):
A typical single fuel cell has a terminal voltage of up to approximately one volt DC. For purposes of producing much larger voltages, several fuel cells may be assembled together to form an arrangement called a fuel cell stack—an arrangement in which the fuel cells are electrically coupled together in series to form a larger DC voltage (a voltage near 100 volts DC, for example) and thus to provide more power and more thermal energy. An exemplary description of a fuel cell stack is found in U.S. Pat. No. 6,534,210, titled “Auxiliary Convective Fuel Cell Stacks for Fuel Cell Power Generation Systems”, which is incorporated by reference for its discussion of the same. Typically, the fuel cell stack may include flow plates (graphite, composite, or metal plates, as examples) that are stacked one on top of the other. The flow plates may include various surface flow channels and orifices to, as examples, route the reactants and products through the fuel cell stack. In the instance of use of a fuel cell stack, several membranes 504 (each one being associated with a particular fuel cell) may be dispersed throughout the fuel cell stack between anodes 508 and cathodes 512 of different fuel cells. Electrically conductive gas diffusion layers (GDLs) 532 may be located on each side of each membrane 504 to act as a gas diffusion medium and in some cases to provide a support for fuel cell catalysts 528. In this manner, reactant gases from each side of the membrane 504 may pass along the flow channels and diffuse through the GDLs 532 to reach the membrane 504.
Returning to FIG. 2, power conditioning module 128 receives variable DC electrical energy produced by power generation module 124 and outputs conditioned DC or AC power, depending on the desired application of the output power. In an embodiment, power conditioning module 128 converts variable, low-voltage DC power from the power generation module 124 using a highly efficient, high boost ratio (e.g., >5:1), variable low voltage input, bi-directional DC-DC converter connected to a highly efficient bidirectional inverter connected to the electrical grid. An example of a highly efficient, high boost ratio, bi-directional DC-DC converter is found in Applicants' co-pending application entitled, “Power Conversion System with a Dc to Dc Boost Converter”, U.S. Provisional Application Ser. No. 61/781,965 filed on Mar. 14, 2013, which is incorporated by reference for its discussion of the same. Power conditioning module 128 may also be designed and configured to provide conditioned power to the structure, for example, for residential uses. In another embodiment, power conditioning module 128 conditions power for both local loads, e.g., battery-powered cars, battery strings, other residential or light commercial loads, and for the electric grid. In this embodiment, if local loads are not high enough to use all of the power produced by the power generation module 124, the excess electrical power is conditioned for input to the electric grid.
As discussed previously, CCHP system 100 includes a waste heat recovery system 108, an exemplary embodiment of which is shown in FIG. 6. Waste heat recovery system 108 includes a thermal management module 144, a burner module 148, a cooling system 152, and a distribution system 156.
Thermal management module (TMM) 144 assists in controlling the operating temperatures of FAWD 108, reactant processing module 120, and power generation module 124, and directs thermal energy, as needed by the structure, to cooling system 152, and distribution system 156. TMM 144 manages the heat distribution throughout CCHP system 100 primarily via a heat transfer loop 140. Heat transfer loop 140 includes valves and pumps (not shown) that are controlled by control system 112 so as to provide the proper rate of fluid flow in the heat transfer loop. Metrics that are considered in determining the rate of fluid flow include, but are not limited to, a pump speed, a fuel cell stack inlet temperature, a fuel cell stack outlet temperature, a valve setting, and a return temperature from heat transfer loop 140, so as to provide efficient heat generation and distribution.
In an exemplary embodiment, the rate of fluid flow is determined by receiving a command for heating or cooling to a load in need thereof and providing stored heat or cooling to the load. If stored capacity is unable to satisfy the load demand from storage, burner module 148 (discussed further below) provides heat to heat transfer loop 140. Heat transfer loop 140 is used to heat the power generation module, reactant processing module 120, and heating and/or cooling system. In this embodiment, control system 112 can receive signals indicative of, for example, temperature inside the structure, the temperature outside the structure, and can use algorithms based on these signals to determine whether to start the fuel cell and export power. If the fuel cell needs to be operated, fuel flows to FAWD module 116 and reactant processing module 120. Once reformate stream 132 is of sufficient quality, it is delivered to the fuel cell, which begins to generate power and send heat to heat transfer loop 140. Control system 112 monitors temperature in heat transfer loop 140 and if necessary for heating or cooling, turning burner module 148 down or off as appropriate. In an exemplary embodiment, peak heating or cooling demands are met by controlling burner module 148 rather than oversizing the rest of CCHP system 100.
Burner module 148 generates on-demand heat for use in the structure, provides auxiliary heat for subsystems during the startup of reactant processing module 120 and power generation module 124, provides auxiliary heat for special operations, provides peak heat for application heating and cooling loads, and assists in completing the combustion of unburned hydrocarbons, volatile organic compounds or carbon monoxide in the exhaust stream coming from FAWD module 116 as well as the reactant processing and power generation modules. Burner module 148 is monitored for burn temperatures to ensure substantially complete combustion of exhaust gases.
Cooling system 152 is used to deliver conditioned air to the structure. In an exemplary embodiment, cooling system 152 includes a reactor 160 and an evaporator 164. Reactor 160 contains an active substance, such as salt, and evaporator 164 contains a volatile, absorbable liquid, such as water. At a high level, the operation of this exemplary cooling system 152 is as follows: (1) heat from TMM 144 is delivered to reactor and hence absorbed water is expelled from the reactor to the condenser; (2) when cooling is desired, a vacuum is applied to the evaporator 164, the water begins to rapidly be removed from the evaporator, and the remaining water gets colder. By coupling a coiled tube proximate to the evaporator, a liquid can be cooled and subsequently used for cooling within the structure.
Distribution system 156 manages the heat provided by TMM 144 to the application (e.g., residence, light industrial). In an exemplary embodiment, distribution system 156 includes appropriate fan/pump and connected ducting/piping to provide heat to the structure.
Control system 112 is designed and configured to manage the components of CCHP system 100 by collecting information from inputs that are internal and external to the system. Those inputs that are internal to the system include, but are not limited to, a reactant processing temperature, a FAWD blower/pump speed, a TMM temperature, a TMM pump speed, a stack inlet temp, a stack outlet temp, a valve setting, a stack voltage, a stack DC power output, an inverter power output, an air mass flow rate, and a fuel mass flow rate. Those inputs that are external to the system include, but are not limited to, a heat demand, a cooling demand (e.g., thermostat information), a hot water demand, and a load demand. Information collected by control system 112 is input into programmed algorithms, set points, or lookup tables so as to determine operating parameters for CCHP system 100 components, control signals, and/or to generate external data for use in evaluating the efficiency, lifespan, or diagnosing problems with the CCHP system. Although control system 112 is presently described as a separate component of CCHP system 100, it is understood that control system 112 can be dispersed among the various components described herein without affecting the function of the CCHP system.
In general, for fuel cell system 104, power generation is increased by raising fuel and air flow to the fuel cell in proportion to the stoichiometric ratios dictated by the equations listed above. Thus, control system 112 may monitor, among other things, the output power of power generation module 124 and/or the thermal energy output, and based on the monitored output power and voltage of the fuel cell, estimate the fuel and air flows required to satisfy the power demand by the thermal or electrical load of the structure.
As briefly discussed above, CCHP system 100 may provide power to a load, such as a load that is formed from residential appliances and electrical devices that may be selectively turned on and off to vary the power that is demanded. Thus, in some applications the electric load required of CCHP system 100 may not be constant, but rather the power that is consumed by the load may vary over time and/or change abruptly. Moreover, thermal loads required by the structure, such as heating requirements in the fall and winter months or cooling requirements in the summer, with or without electric load demands, may place different demands on the CCHP system 100. The availability of power and thermal capacity from CCHP system 100 is controlled by control system 112.
Another embodiment of a CCHP system, CCHP system 600, is shown in FIG. 7. In this embodiment, CCHP 600 includes the primary components of CCHP 100 (not labeled for clarity) in a single structure or enclosure 604, which can be sized and configured to drop in as a replacement for a traditional heating, cooling, and water heating unit. Auxiliary components, such as auxiliary heating equipment 608, auxiliary power equipment 612, and auxiliary cooling equipment 616, while including items such as duct work for distributing heated air throughout a structure, are each also typically designed and configured such that the CCHP 600 is not “over-designed”. For example, CCHP 600 may be designed to heat the structure in which it resides on all but the 5% of coldest days and to rely on the auxiliary heating equipment 608 to provide the additional heat on those days. In this way, CCHP 600 is not overdesigned by being sized to handle all possible heating loads. Similarly, CCHP 600 need not be designed to meet all possible cooling or power loads, as auxiliary cooling equipment 616 and auxiliary power equipment 612 can assist during peak demand times.
Among the advantages of one or more of the exemplary CCHP systems as described herein are:
1. The CCHP system can allow for high utilization (approaching, and at times including, 100%) of the fuel cell, allowing for substantial use of the electric and thermal power during varying electric and thermal load conditions. In an exemplary embodiment, the CCHP system can allow utilization of the fuel cell approaching 100%.
2. Substantial energy recovery is achieved by storing thermal energy produced by the fuel cell system.
3. The CCHP system is capable of using readily available hydrocarbon fuels such as natural gas and propane instead of expensive, difficult-to-obtain fuels such as hydrogen or methanol. Moreover, the use of high-temperature PEM fuel cells, as proposed herein, lessens the need for expensive steam or low efficiency, low temperature shift reformers.
4. The CCHP system can operate near atmospheric pressure, thereby increasing the system efficiency of the appliance by reducing parasitic losses from compressors and blowers (sometimes used to increase power density by pressurizing feed streams to manage liquid water in the system). For example, the CCHP system is about 20% more efficient than similar systems that use compressors. The CCHP system does not require liquid water management, and power density is traded off for system efficiency.
5. The CCHP system uses close-coupled heating and cooling systems, which share plumbing and heat transfer media, thereby creating a simple, integrated appliance.
6. The CCHP system can include optimized power electronics, such as power conditioning system 120, which assists in maximizing power generation, extending fuel cell stack life, and providing high system efficiency.
7. The CCHP system is designed and configured as a drop-in replacement for existing heating, cooling, and hot water systems, thereby reducing the expense of using the CCHP system as a replacement. Moreover, by using the grid to supplement the CCHP system during peak load, the most expensive component in the system, the fuel cell system can be right-sized for maximum utilization, rather than sizing the fuel cell system for peak load power usage (ensuring an over-capacity component that is challenged to return its capital cost) or under-sizing the fuel cell system such that it runs beneath the power usage profile of the application.
FIG. 8 shows a diagrammatic representation of one implementation of a machine/computing device 700 that can be used to implement a set of instructions for causing one or more components of CCHP system 100, for example, control system 112, HASR 304, etc., to perform any one or more of the aspects and/or methodologies of the present disclosure. Device 700 includes a processor 705 and a memory 710 that communicate with each other, and with other components, such as control system 112, fuel cell system 104, and waste heat recovery system 108, via a bus 714. Bus 714 may include any of several types of communication structures including, but not limited to, a memory bus, a memory controller, a peripheral bus, a local bus, and any combinations thereof, using any of a variety of architectures.
Memory 710 may include various components (e.g., machine-readable media) including, but not limited to, a random access memory component (e.g, a static RAM “SRAM”, a dynamic RAM “DRAM”, etc.), a read-only component, and any combinations thereof. In one example, a basic input/output system 720 (BIOS), including basic routines that help to transfer information between elements within device 700, such as during start-up, may be stored in memory 710. Memory 710 may also include (e.g., stored on one or more machine-readable media) instructions (e.g., software) 725 embodying any one or more of the aspects and/or methodologies of the present disclosure. In another example, memory 710 may further include any number of program modules including, but not limited to, an operating system, one or more application programs, other program modules, program data, and any combinations thereof.
Device 700 may also include a storage device 730. Examples of a storage device (e.g., storage device 730) include, but are not limited to, a hard disk drive for reading from and/or writing to a hard disk, a magnetic disk drive for reading from and/or writing to a removable magnetic disk, an optical disk drive for reading from and/or writing to an optical media (e.g., a CD, a DVD, etc.), a solid-state memory device, and any combinations thereof. Storage device 730 may be connected to bus 714 by an appropriate interface (not shown). Example interfaces include, but are not limited to, SCSI, advanced technology attachment (ATA), serial ATA, universal serial bus (USB), IEEE 1395 (FIREWIRE), and any combinations thereof. In one example, storage device 730 may be removably interfaced with device 700 (e.g., via an external port connector (not shown)). Particularly, storage device 730 and an associated machine-readable medium 735 may provide nonvolatile and/or volatile storage of machine-readable instructions, data structures, program modules, and/or other data for device 700. In one example, instructions 725 may reside, completely or partially, within machine-readable medium 735. In another example, instructions 725 may reside, completely or partially, within processor 705.
Device 700 may also include a connection to one or more systems or modules included with CCHP system 100. Any system or device may be interfaced to bus 714 via any of a variety of interfaces (not shown) including, but not limited to, a serial interface, a parallel interface, a game port, a USB interface, a FIREWIRE interface, a direct connection to bus 714, and any combinations thereof. Alternatively, in one example, a user of device 700 may enter commands and/or other information into device 700 via an input device (not shown). Examples of an input device include, but are not limited to, an alpha-numeric input device (e.g., a keyboard), a pointing device, a joystick, a gamepad, an audio input device (e.g., a microphone, a voice response system, etc.), a cursor control device (e.g., a mouse), a touchpad, an optical scanner, a video capture device (e.g., a still camera, a video camera), a touchscreen, and any combinations thereof.
A user may also input commands and/or other information to device 700 via storage device 730 (e.g., a removable disk drive, a flash drive, etc.) and/or a network interface device 745. A network interface device, such as network interface device 745, may be utilized for connecting device 700 to one or more of a variety of networks, such as network 750, and one or more remote devices 755 connected thereto. Examples of a network interface device include, but are not limited to, a network interface card, a modem, and any combination thereof. Examples of a network include, but are not limited to, a wide area network (e.g., the Internet, an enterprise network), a local area network (e.g., a network associated with an office, a building, a campus, or other relatively small geographic space), a telephone network, a direct connection between two computing devices, and any combinations thereof. A network, such as network 750, may employ a wired and/or a wireless mode of communication. In general, any network topology may be used. Information (e.g., data, instructions 725, etc.) may be communicated to and/or from device 700 via network interface device 755.
Device 700 may further include a video display adapter 760 for communicating a displayable image to a display device 765. Examples of a display device 765 include, but are not limited to, a liquid crystal display (LCD), a cathode ray tube (CRT), a plasma display, and any combinations thereof.
In addition to display device 765, device 700 may include a connection to one or more other peripheral output devices including, but not limited to, an audio speaker, a printer, and any combinations thereof. Peripheral output devices may be connected to bus 714 via a peripheral interface 770. Examples of a peripheral interface include, but are not limited to, a serial port, a USB connection, a FIREWIRE connection, a parallel connection, a wireless connection, and any combinations thereof.
A digitizer (not shown) and an accompanying pen/stylus, if needed, may be included in order to digitally capture freehand input. A pen digitizer may be separately configured or coextensive with a display area of display device 765. Accordingly, a digitizer may be integrated with display device 765, or may exist as a separate device overlaying or otherwise appended to display device 765.
Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions, and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.

Claims

What is claimed is:

1. A hybrid autothermal steam reformer (HASR) included within a reactant processing module having a variable cathode air recirculation system and a water delivery system, the reactant processing module providing a reformate stream to a power generation module, the HASR comprising:

an enclosure including:

an autothermal reformer;

a water inlet fluidly coupled to the water delivery system;

an air inlet in fluidly coupled to the variable cathode air recirculation system; and

a reformate stream exit fluidly coupled to the power generation module,

wherein said autothermal reformer receives a refined fuel and a quantity of air, said quantity of air received from the power generation module via the variable cathode air recirculation system when said autothermal reformer is operated in full cathode recirculation, and wherein said autothermal reformer receives said refined fuel, a quantity of external air via the variable cathode air recirculation system, and a quantity of water received from the water delivery system when said quantity of air received from the power generation module becomes nitrogen-heavy.

2. An HASR according to claim 1, wherein said autothermal reformer monitors the quality of said quantity of air received from the power generation module via the variable cathode air recirculation system.

3. An HASR according to claim 2, wherein said autothermal reformer includes a control system for monitoring the quality of said quantity of air received from the power generation module via the variable cathode air recirculation system.

4. An HASR according to claim 2, wherein said control system restricts said quantity of air when said quantity of air has a nitrogen content greater than about 48%.

5. An HASR according to claim 1, wherein said air inlet is fluidly coupled to a controllable valve, said controllable valve being adjustable to allow for decreases in said quantity of air received from the power generation module via the variable cathode air recirculation system and increases in said quantity of external air.

6. An HASR according to claim 5, wherein said controllable valve is a three-way valve.

7. A power generation system comprising:

a FAWD module capable of producing a refined fuel stream;

a reactant processing module capable of receiving said refined fuel stream and producing a reformate stream;

a power generation module capable of receiving said reformate stream and providing to said reactant processing module a quantity of air; and

a control system in communication with said reactant processing module and said power generation module,

wherein said control system monitors said quantity of air and determines whether said reactant processing module can operate in a full cathode recirculation mode or if an external air and/or water supply is necessary for efficient operation of said power generation module.

8. A power generation system according to claim 7, wherein said reactant processing module includes a variable cathode recirculation system.

9. A power generation system according to claim 8, wherein said variable cathode recirculation system is fluidly coupled to said power generation module and receives said quantity of air and is fluidly coupled to an external air source.

10. A power generation system according to claim 8, wherein said variable cathode recirculation system includes a multi-port valve.

11. A power generation system according to claim 10, wherein said multi-port valve is a three-way valve.

12. A power generation system according to claim 8, wherein said reactant processing module includes a water delivery system.

13. A power generation system according to claim 12, wherein said water delivery system includes at least one of a water reservoir, a potable water input line, and a condensate input line in fluid communication with power generation module.

14. A power generation system according to claim 13, further including a burner module and wherein said water delivery system recovers water from said burner module.

15. A power generation system according to claim 7, wherein said power generation module is a fuel cell.

16. A power generation system according to claim 15, wherein said fuel cell is a high temperature polymer electrolyte membrane fuel cell.

17. A method of improving the efficiency of a fuel cell system comprising:

monitoring an air stream from a fuel cell cathode;

determining the degree of vitiation of the air stream;

increasing a rate of input of an external air supply to a reactant processing module based upon said determining; and

increasing a rate of input of an external water supply to the reactant processing module based upon said determining.

18. A method according to claim 17, wherein the external water supply is a water reservoir in fluid communication a hybrid autothermal steam reformer included within the reactant processing module.

19. A method according to claim 17, wherein the fuel cell system includes a variable cathode recirculation system and wherein said variable cathode recirculation system performs said monitoring and said increasing a rate of input of an external air supply.

20. A method according to claim 17, wherein said increasing a rate of input of an external water supply reaches a maximum of about 0.66 liters per day per kilowatt.