US20140260964A1

US20140260964A1 - System and method of regenerating desulfurization beds in a fuel cell system

Info

Publication number: US20140260964A1
Application number: US14/194,786
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: 2014-03-02
Publication date: 2014-09-18
Also published as: US20190260052A1; US10644338B2; US20140272656A1; US20140278709A1; US20140272636A1; US10320018B2

Abstract

A desulfurization system is disclosed that facilitates in situ or ex situ regeneration of hydrocarbon desulfurization beds. The desulfurization system can use a bed characterization limit, a predetermined sulfur threshold or other metric to determine when the hydrocarbon desulfurization bed should be regenerated. The desulfurization system can include heat and air intakes and an air/sulfur purge outlet to allow for the removal of sulfur from the hydrocarbon desulfurization bed. Alternatively, the regeneration of hydrocarbon desulfurization bed may be performed in situ by a service technician by using a prebuilt appliance that is connected to the inlet and outlets of the desulfurization appliance. The prebuilt appliance heats and purges hydrocarbon desulfurization bed, in substantially the same manner as described just above, and captures the sulfur outside of the desulfurization system.

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 fuel desulfurization. In particular, the present invention is directed to a System and Method of Regenerating Desulfurization Beds in a Fuel Cell System.

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.
Moreover, there are significant costs associated with the onsite change-out, transportation, and remote disposal of desulfurization adsorbents used to remove sulfur from natural gas and propane in residential and light commercial fuel cell systems. These sulfur compounds occur naturally and in some instances are added to natural gas as an odorant for safety reasons. The sulfur compounds include, but are not limited to: Tetrahydrothiophene (THT), Tertiary Butyl Mercaptan (TBM), Dimethyl Sulfide (DMS), and Hydrogen Sulfide (H₂S). Since these sulfides are strong catalyst poisons, even in trace amounts, the sulfides must be removed from fuel streams prior to encountering reforming catalysts or other electrochemical catalysts in the fuel cell system.
To remove the compounds, typically, sulfur adsorbent beds are placed at the hydrocarbon inlet of the desulfurization appliance. Sulfites are highly reactive; thus, a variety of adsorbents are effective removers of sulfites. As is known, small beds of adsorbents tailored to the major groups of different sulfur species can provide protection, but only until the beds become saturated. Upon saturation, sulfur breakthrough occurs, causing irreparable damage to the catalysts downstream. To prevent breakthrough, active sulfur detection steps are taken or the adsorbent beds are designed for periodic change-out. Active sulfur detection can occur through sensors or other detection devices, but is expensive and poses significant reliability hazards. Thus, desulfurization appliances typically have the bed characterized and undergo regular adsorbent replacement.
Adsorbent bed replacement requires a customer visit by a service technician who may require special training and certifications depending on the service location and the compounds involved. Direct adsorbent media change-out onsite is normally impossible due to the impact of exposed, concentrated odorants; therefore, cartridge change-outs are the current, preferred method of adsorbent replacement. Used adsorbent cartridges are removed from the appliance, sealed, and sent for disposal. Again, depending upon the location and the compounds involved, the cartridges may require hazardous waste handling. This is also a consideration during a desulfurization appliance's decommissioning; used desulfurization adsorbents contained in systems being removed from residential or light commercial applications may require hazardous waste handling.
Adsorbent beds can reasonably be sized for about a year of operation, which translates into 10 to 15 onsite customer visits and the replacement of hundreds of pounds of spent media during the average lifetime of a fuel cell system. The expense of this activity severely impacts the economic viability of fuel cell based systems.

SUMMARY

In a first exemplary aspect a desulfurization appliance for producing a substantially desulfurized fuel comprises a hydrocarbon desulfurization bed having a fuel inlet, a refined fuel outlet, and an air/sulfur outlet and wherein said hydrocarbon desulfurization bed has a bed characterization limit; a heat stream in thermal communication with said hydrocarbon desulfurization bed; and a purge valve in fluid communication with said hydrocarbon desulfurization bed and said air/sulfur outlet, said purge valve configured to open when said bed characterization is exceeded.
In another exemplary aspect a desulfurization appliance for a fuel cell system is disclosed, the desulfurization appliance being capable of self-regeneration of a hydrocarbon desulfurization bed contained therein, the desulfurization appliance comprising: a fuel inlet valve in fluid communication with the hydrocarbon desulfurization bed; a refined fuel outlet valve in fluid communication with the hydrocarbon desulfurization bed and the fuel cell system; a heat stream in thermal communication with the hydrocarbon desulfurization bed; a purge valve in fluid communication with the hydrocarbon desulfurization bed and an air/sulfur outlet; an air stream in fluid communication with the hydrocarbon desulfurization bed; and a control system configured to: determine a sulfur content proximate said refined fuel outlet; compare said sulfur content to a first predetermined sulfur amount and/or a bed characterization limit; direct said fuel inlet valve to close, said refined fuel outlet valve to close, said purge valve to open, said heat stream to provide thermal energy, and said air stream to provide air, when said sulfur content exceeds said first predetermined sulfur amount and/or said bed characterization limit is reached.
In yet another aspect a method of operating a fuel cell system comprises providing a desulfurization appliance having a hydrocarbon desulfurization bed; determining a sulfur content in a refined fuel exiting the hydrocarbon desulfurization bed; comparing the sulfur content to a predetermined sulfur limit; self-regenerating the hydrocarbon desulfurization bed when the sulfur content exceeds the predetermined sulfur limit.

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 fuel-air-water delivery (FAWD) module including a desulfurization appliance according to an embodiment of the present invention;

FIG. 4 is a block diagram of a process of regenerating a desulfurization appliance 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 according to an embodiment of the present invention.

DESCRIPTION OF THE DISCLOSURE

A combined cooling, heating, and power (CCHP) system including a system of regenerating desulfurization beds 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. Moreover, the system and method of regenerating desulfurization beds in a fuel cell system disclosed herein facilitates in situ regeneration of the beds by the CCHP appliance. While the system and method of regenerating desulfurization beds disclosed herein are described in the context of a CCHP appliance or system, the system and method can be readily adapted to any hydrocarbon fuel using appliance that requires sulfur removal prior to the fuel's use.
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 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.
An exemplary embodiment of a portion of FAWD module 116 having a desulfurization appliance 200 is shown in FIG. 3. In this embodiment, one or more desulfurization adsorbent beds 204 are regenerated onsite or remotely by desorbing the sulfur compounds from the media after a predetermined condition is met. As shown in FIG. 3, desulfurization appliance 200 includes hydrocarbon desulfurization bed 204, a heat source stream 208, an air source stream 212, an air/sulfur compound exhaust stream 216, and a sulfur capture system 220. Hydrocarbon desulfurization bed 204 includes a quantity of desulfurization media (zeolites) in a container, through which is passed gaseous hydrocarbon fuel via hydrocarbon inlet 224 for sulfur compound removal. The hydrocarbon fuel can enter hydrocarbon desulfurization bed 204 at line pressure from the fuel source or can be pressurized via a blower (not shown).
Heat source 222 and air source 226, producing heat source stream 208 and air source stream 212, respectively, can originate either internally from or externally to FAWD module 116. In an exemplary embodiment, during regeneration, FAWD module 116 provides heat and air to hydrocarbon desulfurization bed 204 via connection with a heat transfer fluid and outside air, respectively. In another exemplary embodiment, a service technician connects a portable apparatus to the inlet and outlet of the container that would supply sufficient regenerative heat and/or air to hydrocarbon desulfurization bed 204.
Air/sulfur compound exhaust stream 216 provides a safe path for the catalyst poisons, i.e., sulfur compounds, to leave hydrocarbon desulfurization bed 204. After leaving hydrocarbon desulfurization bed 204, air/sulfur compound exhaust stream 216 is delivered to sulfur capture system 220, where the exhaust stream is scrubbed, removing concentrated compounds from the exhaust stream and capturing the compounds for disposal. In an exemplary embodiment, air/sulfur compound exhaust stream 216 is bubbled through water, creating sulfuric acid and removing the compounds from the exhaust.
Advantageously, hydrocarbon desulfurization bed 204 can be regenerated in situ by FAWD 116. In this embodiment, and as discussed previously, hydrocarbon fuel, typically natural gas or propane, enters FAWD 116 either at line pressure or is pressurized via a blower. The hydrocarbon fuel enters hydrocarbon desulfurization bed 204 and is passed over a desulfurization bed where the sulfur compounds are adsorbed onto the bed media. Desulfurized fuel, i.e., refined fuel stream 132, is then sent to reactant processing module 120 for further processing. Hydrocarbon desulfurization bed 204 continues to adsorb sulfur compounds until a predefined desulfurization bed characterization limit is reached. As discussed previously, the adsorption limit of the desulfurization beds can be determined by using a sulfur compound sensor, such as sensor 244, to monitor air and sulfur compound exhaust stream 216 and/or until a performance profile of the desulfurization bed indicates breakthrough.
When breakthrough is determined or expected, hydrocarbon desulfurization bed 204 is directed to follow a regeneration process. In this process, heat from thermal management module 144 (discussed below) is delivered to hydrocarbon desulfurization bed 204 to elevate the temperature of the hydrocarbon desulfurization bed to over 100° C. Once this temperature is reached, the CCHP system begins to shed electrical load, as fuel flow block valves 228A-B close, an air purge valve 232 and an air intake valve 236 open, and air begins to flow over the heated, saturated hydrocarbon desulfurization bed 204 and through sulfur capture system 220. Thermal energy from heat source 222, e.g., heat from thermal management module 144 or an auxiliary burner, is delivered via heat transfer loop 140 to hydrocarbon desulfurization bed 204, increasing the temperature of the adsorbents in the hydrocarbon desulfurization bed, which increases the rate of desorption. After a predetermined period of time or after sensors determine that the rate of desorption has fallen below a certain threshold, heat transfer to hydrocarbon desulfurization bed 204 is ended and the air purge stops. FAWD 116 then restarts itself and the sulfur compound system 220 is drained and reset during the next service outage.
In another exemplary embodiment, regeneration may follow process 300, shown in FIG. 4. At step 304, the content of sulfur in the desulfurized fuel, i.e., refined fuel stream 132 is monitored. As mentioned previously, refined fuel stream 132 may be monitored using sensors, such as sensor 244.
At step 308, a determination is made as to whether an absorption threshold has been reached. This may be accomplished by comparing the sensed sulfur amount with a predetermined limit or by an evaluation of bed characterization limits based upon the sensed output. In an embodiment, control system 112 receives a signal from sensor 244 indicative of an amount of sulfur in refined fuel stream 132 and determines whether or not the hydrocarbon desulfurization beds, such as beds 204, are in need of regeneration. If the beds are not in need of regeneration, the process continues to step 312 where absorption of sulfur continues and the beds continued to be monitored.
If the beds are in need of regeneration as determined at step 308, process 300 begins the regeneration at step 316. In an exemplary embodiment, step 316 includes step 320 which stops the flow of fuel to the hydrocarbon desulfurization beds, step 324 which raises the temperature of the desulfurization beds, step 328 which increases air flow through the desulfurization beds, and step 332 which collects the entrained sulfur from the exhausted gases, such as by the use of sulfur capture system 220 (FIG. 3).
Step 316 can continue for a predetermined amount of time, or, in an exemplary embodiment, and as shown in FIG. 4, can continue until a sufficient amount of sulfur has been removed from the desulfurization beds. At step 336, while regeneration is taking place the desorption rate of sulfur is monitored. This measurement may be accomplished by included a sensor proximate the exhaust gas output that detects the amount of sulfur leaving the hydrocarbon desulfurized beds over a period of time.
At step 340, a comparison of the desorption rate and a predetermined rate or characterization is conducted so as to determine whether more regeneration needs to occur. If the threshold has not been reached, process 300 returns to step 336 and monitoring is resumed. If the threshold has been reached, process 300 continues to step 344.
At step 344, the heat supply and air input to the hydrocarbon desulfurization beds is removed and, once cooled, fuel flow is resumed and the fuel cell system is returned to operation.
Alternatively, the regeneration of hydrocarbon desulfurization bed 204 may be performed in situ by a service technician. In this embodiment, a service technician has a prebuilt appliance that is connected to the inlet and outlets of FAWD 116. The prebuilt appliance heats and purges hydrocarbon desulfurization bed 204, in substantially the same manner as described just above, and captures the sulfur outside of FAWD 116.
In yet another embodiment, hydrocarbon desulfurization bed 204 can be regenerated ex situ. In this embodiment, a service technician removes hydrocarbon desulfurization bed 204, transports them to a convenient location, and regenerates them using the technique and prebuilt appliance described above. After regeneration, hydrocarbon desulfurization bed 204 is then ready for redeployment.
Advantageously, FAWD 116 can have the ability to effectively and efficiently regenerate hydrocarbon desulfurization bed 204, thereby providing an efficient CCHP system without sulfur compound (SOx) emissions.
FAWD module 116 may also further condition the fuel by altering the water content of the fuel to an appropriate level for the fuel cell system 104. The humidity of the refined fuel stream 132 may be increased by increasing the water input to the FAWD.
The input rate, temperature, pressure, and output of FAWD module 116, and the regeneration process, such as process 300, 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 the 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 124 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. In an exemplary embodiment, reactant processing module 120 includes a hybrid autothermal steam reformer of the type described in Applicants' co-pending patent application entitled “Hybrid Autothermal Steam Reformer for Fuel Cell Systems,” U.S. Provisional Application Ser. No. 61/784,894, filed on Mar. 14, 2013, which is incorporated by reference for its disclosure of the same.
Reformate stream 136 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 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 400 shown in FIG. 5.
In PEM fuel cell 400, a membrane 404, such as, but not limited to, a phosphoric acid-doped cross-linked porous polybenzimidazole membrane, permits only protons 416 to pass between an anode 408 and a cathode 412. At anode 408, reformate stream 136 from reactant processing module 120 is reacted to produce protons 416 that pass through membrane 404. The electrons 420 produced by this reaction travel through circuitry 424 that is external to PEM fuel cell 400 to form an electrical current. At cathode 412, oxygen is reduced and reacts with protons 416 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 404 (each one being associated with a particular fuel cell) may be dispersed throughout the fuel cell stack between anodes 408 and cathodes 412 of different fuel cells. Electrically conductive gas diffusion layers (GDLs) 432 may be located on each side of each membrane 404 to act as a gas diffusion medium and in some cases to provide a support for fuel cell catalysts 428. In this manner, reactant gases from each side of the membrane 404 may pass along the flow channels and diffuse through the GDLs 432 to reach the membrane 404.
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 is shown in FIG. 7. In this embodiment, CCHP 500 includes the primary components of CCHP 100 (not labeled for clarity) in a single structure or enclosure 504, 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 508, auxiliary power equipment 512, and auxiliary cooling equipment 516, 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 500 is not “over-designed”. For example, CCHP 500 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 508 to provide the additional heat on those days. In this way, CCHP 500 is not overdesigned by being sized to handle all possible heating loads. Similarly, CCHP 500 need not be designed to meet all possible cooling or power loads, as auxiliary cooling equipment 516 and auxiliary power equipment 512 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 600 that can be used to implement a set of instructions for causing one or more components of CCHP system 100, for example, FAWD 116, control system 112, etc., to perform any one or more of the aspects and/or methodologies of the present disclosure. Device 600 includes a processor 605 and a memory 610 that communicate with each other, and with other components, such as control system 112, fuel cell system 104, or waste heat recovery system 108, via a bus 615. Bus 615 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 610 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 620 (BIOS), including basic routines that help to transfer information between elements within device 600, such as during start-up, may be stored in memory 610. Memory 610 may also include (e.g., stored on one or more machine-readable media) instructions (e.g., software) 625 embodying any one or more of the aspects and/or methodologies of the present disclosure. In another example, memory 610 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 600 may also include a storage device 630. Examples of a storage device (e.g., storage device 630) 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 630 may be connected to bus 615 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 630 may be removably interfaced with device 600 (e.g., via an external port connector (not shown)). Particularly, storage device 630 and an associated machine-readable medium 635 may provide nonvolatile and/or volatile storage of machine-readable instructions, data structures, program modules, and/or other data for device 600. In one example, instructions 625 may reside, completely or partially, within machine-readable medium 635. In another example, instructions 625 may reside, completely or partially, within processor 605.
Device 600 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 615 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 615, and any combinations thereof. Alternatively, in one example, a user of device 600 may enter commands and/or other information into device 600 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), touchscreen, and any combinations thereof.
A user may also input commands and/or other information to device 600 via storage device 630 (e.g., a removable disk drive, a flash drive, etc.) and/or a network interface device 645. A network interface device, such as network interface device 645, may be utilized for connecting device 600 to one or more of a variety of networks, such as network 650, and one or more remote devices 655 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 650, may employ a wired and/or a wireless mode of communication. In general, any network topology may be used. Information (e.g., data, instructions 625, etc.) may be communicated to and/or from device 600 via network interface device 655.
Device 600 may further include a video display adapter 660 for communicating a displayable image to a display device 665. Examples of a display device 665 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 665, device 600 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 615 via a peripheral interface 670. 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 665. Accordingly, a digitizer may be integrated with display device 665, or may exist as a separate device overlaying or otherwise appended to display device 665.
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 desulfurization appliance for producing a substantially desulfurized fuel comprising:

a hydrocarbon desulfurization bed having a fuel inlet, a refined fuel outlet, and an air/sulfur outlet and wherein said hydrocarbon desulfurization bed has a bed characterization limit;

a heat stream in thermal communication with said hydrocarbon desulfurization bed; and

a purge valve in fluid communication with said hydrocarbon desulfurization bed and said air/sulfur outlet, said purge valve configured to open when said bed characterization is exceeded.

2. A desulfurization appliance according to claim 1, wherein said heat stream is provided by a heat source, and wherein said heat source is a thermal management module that is a component of a combined cooling, heating, and power system.

3. A desulfurization appliance according to claim 2, wherein the desulfurization appliance is configured to provide the substantially desulfurized fuel as an input to a fuel cell system, and wherein said heat source is one or more of the components of said fuel cell system.

4. A desulfurization appliance according to claim 1, further including an air stream in fluid communication with said hydrocarbon desulfurization bed when said bed characterization is exceeded.

5. A desulfurization appliance according to claim 1, further including a control system including a sensor configured to monitor a sulfur content proximate said refined fuel outlet and wherein said hydrocarbon desulfurization bed has a bed characterization limit and said control system determines whether said bed characterization limit has been exceeded based upon said sulfur content.

6. A desulfurization appliance according to claim 5, wherein said control system includes a sulfur compound sensor configured to detect a purge sulfur content proximate said air/sulfur outlet and to transmit a signal to said control system indicative of said purge sulfur content.

7. A desulfurization appliance according to claim 1, wherein said control system is further configured to determine an air/purge sulfur content proximate said air/sulfur outlet, and wherein said heat stream is further configured to cease providing thermal energy to said hydrocarbon desulfurization bed when said air/purge sulfur content is below a predetermined amount, and wherein said purge valve is further configured to close when said air/purge sulfur content is below said predetermined amount.

8. A desulfurization appliance for a fuel cell system, the desulfurization appliance being capable of self-regeneration of a hydrocarbon desulfurization bed contained therein, the desulfurization appliance comprising:

a fuel inlet valve in fluid communication with the hydrocarbon desulfurization bed;

a refined fuel outlet valve in fluid communication with the hydrocarbon desulfurization bed and the fuel cell system;

a heat stream in thermal communication with the hydrocarbon desulfurization bed;

a purge valve in fluid communication with the hydrocarbon desulfurization bed and an air/sulfur outlet;

an air stream in fluid communication with the hydrocarbon desulfurization bed; and

a control system configured to:

determine a sulfur content proximate said refined fuel outlet;

compare said sulfur content to a first predetermined sulfur amount and/or a bed characterization limit;

direct said fuel inlet valve to close, said refined fuel outlet valve to close, said purge valve to open, said heat stream to provide thermal energy, and said air stream to provide air, when said sulfur content exceeds said first predetermined sulfur amount and/or said bed characterization limit is reached.

9. A desulfurization appliance according to claim 8, wherein said control system is further configured to determine an air/purge sulfur content proximate said air/sulfur outlet, and wherein said heat source is further configured to cease providing thermal energy to said hydrocarbon desulfurization bed when said air/purge sulfur content is below a second predetermined amount, and wherein said purge valve is further configured to close when said air/purge sulfur content is below said second predetermined amount.

10. A desulfurization appliance according to claim 8, wherein said control system is further configured to direct said fuel inlet valve to open, said refined fuel outlet valve to open, said purge valve to close, said heat source to cease providing thermal energy, and said air source to cease providing air, after a predetermined amount of time.

11. A desulfurization appliance according to claim 8, wherein said heat source is a component of the fuel cell system.

12. A desulfurization appliance according to claim 11, further including a sulfur capture device in fluid communication with said air/purge outlet.

13. A desulfurization appliance according to claim 12, wherein said sulfur capture device bubbles an exhaust gas received from said air/purge outlet through a fluid, wherein said exhaust gas includes sulfur and said fluid removes sulfur from said exhaust gas.

14. A desulfurization appliance according to claim 8, wherein said heat source and said air source are portable external components configured to be connectable to the desulfurization appliance.

15. A desulfurization appliance according to claim 8, wherein said control system includes a sulfur compound sensor configured to detect sulfur proximate said refined fuel outlet valve and to transmit a signal indicative of said sulfur content to said control system.

16. A method of operating a fuel cell system comprising:

providing a desulfurization appliance having a hydrocarbon desulfurization bed;

determining a sulfur content in a refined fuel exiting the hydrocarbon desulfurization bed;

comparing the sulfur content to a predetermined sulfur limit;

self-regenerating the hydrocarbon desulfurization bed when the sulfur content exceeds the predetermined sulfur limit.

17. A method according to claim 16, wherein said self-regenerating includes:

elevating the temperature of the hydrocarbon desulfurization bed;

directing air over the hydrocarbon desulfurization bed; and

collecting sulfur compounds in a sulfur capture system.

18. A method according to claim 17, wherein said self-regenerating further includes monitoring said collecting.

19. A method according to claim 17, further including providing a heat source, wherein said heat sources is a component of the fuel cell system and wherein said elevating the temperature is accomplished by the heat source.

20. A method according to claim 16, further including:

determining a second sulfur content during said self-regenerating;

comparing the second sulfur content with a second predetermined sulfur limit; and

restarting the desulfurization appliance when the second sulfur content drops below the second predetermined sulfur limit.