U.S. patent application number 14/210213 was filed with the patent office on 2014-09-18 for hybrid autothermal steam reformer for fuel cell systems.
This patent application is currently assigned to Combined Energies LLC. The applicant listed for this patent is Combined Energies LLC. Invention is credited to Donald Frank Rohr, John Anthony Vogel.
Application Number | 20140272636 14/210213 |
Document ID | / |
Family ID | 51521477 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140272636 |
Kind Code |
A1 |
Rohr; Donald Frank ; et
al. |
September 18, 2014 |
Hybrid Autothermal Steam Reformer for Fuel Cell Systems
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.
Inventors: |
Rohr; Donald Frank;
(Rexford, NY) ; Vogel; John Anthony; (Charlton,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Combined Energies LLC |
Latham |
NY |
US |
|
|
Assignee: |
Combined Energies LLC
Latham
NY
|
Family ID: |
51521477 |
Appl. No.: |
14/210213 |
Filed: |
March 13, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61788532 |
Mar 15, 2013 |
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61788300 |
Mar 15, 2013 |
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61781965 |
Mar 14, 2013 |
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61784894 |
Mar 14, 2013 |
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Current U.S.
Class: |
429/415 ;
429/423 |
Current CPC
Class: |
B01D 2259/40098
20130101; B01D 2253/108 20130101; B01D 2257/308 20130101; H01M
8/04007 20130101; B01D 2257/304 20130101; B01D 2259/40056 20130101;
G05D 23/1917 20130101; B01D 53/02 20130101; H01M 2008/1095
20130101; H01M 8/04097 20130101; B01D 2257/306 20130101; H01M
8/0618 20130101; B01D 53/0462 20130101; B01D 53/0454 20130101; G06Q
10/06315 20130101; H01M 8/0675 20130101; Y02E 60/50 20130101; B01D
2257/302 20130101 |
Class at
Publication: |
429/415 ;
429/423 |
International
Class: |
H01M 8/06 20060101
H01M008/06; H01M 8/04 20060101 H01M008/04 |
Claims
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.
Description
RELATED APPLICATION DATA
[0001] 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
[0002] 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
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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
[0007] 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.
[0008] 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.
[0009] 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
[0010] 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:
[0011] FIG. 1 is a block diagram of a combined cooling, heating,
and power system according to an embodiment of the present
invention;
[0012] FIG. 2 is a block diagram of a fuel cell system according to
an embodiment of the present invention;
[0013] 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;
[0014] FIG. 4 is a block diagram of a process of operating a steam
reformer according to an embodiment of the present invention;
[0015] FIG. 5 is a schematic of a high temperature polymer
electrolyte membrane fuel cell according to an embodiment of the
present invention;
[0016] FIG. 6 is a block diagram of a waste heat recovery system
according to an embodiment of the present invention;
[0017] FIG. 7 is a block diagram of a combined cooling, heating,
and power system according to another embodiment of the present
invention; and
[0018] 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
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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 H.sub.2, CO,
CO.sub.2, CH.sub.4, N.sub.2 and H.sub.2O. 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).
1/2O.sub.2+CH.sub.4.fwdarw.2H.sub.2+CO Equation (1):
H.sub.2O+CH.sub.4.fwdarw.3H.sub.2+CO Equation (2):
[0028] 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.degree. 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.
[0029] 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.
[0030] 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.degree. 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+H.sub.2O.fwdarw.H.sub.2+CO.sub.2 Equation (3):
CO+1/2O.sub.2.fwdarw.CO.sub.2 Equation (4):
[0031] 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.degree. 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.degree. 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.
[0032] 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.degree. 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.degree. C. and about 190.degree.
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).
[0039] 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.
[0040] 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%.
[0041] 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.
[0042] 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.
[0043] 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:
H.sub.2.fwdarw.2H.sup.++2e.sup.- Equation (1):
O.sub.2+4H.sup.++4e.sup.-.fwdarw.2H.sub.2O Equation (2):
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] Among the advantages of one or more of the exemplary CCHP
systems as described herein are:
[0057] 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%.
[0058] 2. Substantial energy recovery is achieved by storing
thermal energy produced by the fuel cell system.
[0059] 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.
[0060] 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.
[0061] 5. The CCHP system uses close-coupled heating and cooling
systems, which share plumbing and heat transfer media, thereby
creating a simple, integrated appliance.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
* * * * *