U.S. patent application number 10/873078 was filed with the patent office on 2005-12-22 for maintaining oxygen/carbon ratio with temperature controlled valve.
Invention is credited to Isom, Joshua D., Kabir, Zakiul, Yokose, Masaki M..
Application Number | 20050282096 10/873078 |
Document ID | / |
Family ID | 35480989 |
Filed Date | 2005-12-22 |
United States Patent
Application |
20050282096 |
Kind Code |
A1 |
Kabir, Zakiul ; et
al. |
December 22, 2005 |
Maintaining oxygen/carbon ratio with temperature controlled
valve
Abstract
Fuel from a source (6) passes through a hydrogen desulfurizer
(8) and a proportioning mixing valve (10) to a CPO (31), the
temperature of the output of the CPO being monitored (50) to
provide a signal (51) which a controller (52) utilizes to adjust
the valve (10). The output of the CPO may be passed through a water
gas shift reactor (35) and a preferential CO oxidizer (40) to
provide fuel to a fuel cell system (26). The air provided to the
valve (10) may be humidified, such as by an enthalpy recovery
device (21) receiving the oxidant outflow (24) from the fuel cell
system.
Inventors: |
Kabir, Zakiul; (Glastonbury,
CT) ; Isom, Joshua D.; (South Windsor, CT) ;
Yokose, Masaki M.; (Tolland, CT) |
Correspondence
Address: |
M. P. Williams
210 Main Street
Manchester
CT
06040
US
|
Family ID: |
35480989 |
Appl. No.: |
10/873078 |
Filed: |
June 21, 2004 |
Current U.S.
Class: |
431/2 |
Current CPC
Class: |
F23C 2900/03002
20130101; F23C 13/00 20130101; F23N 1/022 20130101; F23N 2225/26
20200101; F23K 2900/05001 20130101 |
Class at
Publication: |
431/002 |
International
Class: |
F23C 011/04 |
Claims
We claim:
1. A catalytic partial oxidizer system comprising: a catalytic
partial oxidizer having an inlet and an outlet; a fuel supply; a
source of air; a proportioning mixing valve having two inlets and
an outlet and controllable so as to determine the proportion of
gases at the respective inlets which will be provided to the
outlet, one inlet being connected to said fuel supply and the other
inlet being connected to said source of air, the outlet of said
valve being connected to the inlet of said CPO; a temperature
sensor for providing a signal indicative of the temperature of flow
at the outlet of said CPO; and a controller responsive to said
signal to control said valve and thereby control the proportions of
gas at the respective inlets which are provided through said valve
to said CPO.
2. A system according to claim 1 wherein: said controller processes
said signal with proportional and integral gain.
3. A system according to claim 1 wherein: the outflow of said CPO
is provided to a fuel cell system having a cathode exhaust passing
through an enthalpy recovery device which comprises said source of
air.
4. A system according to claim 1 wherein: said source of air is a
source of humidified air.
5. A system according to claim 1 wherein: said fuel supply provides
fuel selected from natural gas and liquified petroleum gas.
6. A system according to claim 1 wherein: said fuel supply includes
a hydrodesulfurizer.
Description
TECHNICAL FIELD
[0001] This invention relates to using a fuel/air ratio valve at
the inlet of a catalytic partial oxidizer (CPO) to control CPO exit
temperature in the presence of disturbances, such as changes in air
or fuel composition or temperature.
BACKGROUND ART
[0002] The conversion of hydrocarbon fuel such as natural gas or
propane to a hydrogen-rich gas is particularly useful to provide
fuel for a fuel cell power plant. Catalytic partial oxidation (CPO)
reactors require that the oxygen to carbon (fuel) molar ratios be
maintained within a narrow range in order to maintain proper
reactor operating temperatures. If the temperature of the catalyst
is not maintained between about 750.degree. C. and 850.degree. C.,
the production of hydrogen falls off. Furthermore, if the
temperature of the catalyst rises above about 900.degree. C., the
catalyst is damaged and production is permanently impaired.
[0003] To maintain nominal catalyst temperature, it is necessary to
carefully control the air and fuel flow rates to maintain proper
molar ratios. However, the composition of the fuel stream at the
CPO inlet can change due to changes in the composition of an
external fuel supply, or due to internal changes resulting from a
hydrodesulfurization process. If humidified air is used at the
inlet of the CPO, the manner of its humidification, such as from an
enthalpy recovery device, can cause variations in the humidity of
the air from time to time, causing lowering of oxygen partial
pressure.
[0004] None of the prior art systems are sensitive to the varying
compositions of the fuel and air. Mass flow controllers are very
expensive and tend to have a high pressure drop. In having both a
fuel blower and an air blower with variable speed drives, variation
in the speed of either blower may disturb the rate of flow from the
other blower, which can result in interaction of controls or
instability.
DISCLOSURE OF INVENTION
[0005] Objects of the invention include: precise control of the
oxygen/carbon ratio at the inlet of a CPO; controlling the fuel/air
mixture at the inlet to a CPO in a manner which is insensitive to
changes in the compositions of the inlet gases; improved generation
of hydrogen-rich gas in a CPO; improved generation of fuel for a
fuel cell power plant; and an inexpensive and accurate methodology
for controlling the oxygen/carbon ratio at the inlet of a CPO.
[0006] According to the present invention, the temperature of the
reformate generated in a CPO is utilized to control a mixing valve
that determines the proportion of fuel and air at the inlet of the
CPO. In further accord with the invention, a proportional/integral
controller is used to convert temperature at the outlet of the CPO
into a control signal for the valve. If desired, signal
modification may be used to accommodate the time differential of
temperature sensing vs. the proportioning of the molar ratio of
carbon to oxygen at the input to the CPO.
[0007] Other objects, features and advantages of the present
invention will become more apparent in the light of the following
detailed description of exemplary embodiments thereof, as
illustrated in the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The sole figure herein is a simplified schematic diagram of
a system generating hydrogen-rich reformate for a fuel cell system
employing the present invention.
MODE(S) FOR CARRYING OUT THE INVENTION
[0009] Referring to the figure, a fuel supply includes a source 6
of natural gas or liquified petroleum gas which provides fuel over
a conduit 7 to a hydrodesulfurizer 8, the output of which on a
conduit 9 is provided to a proportioning mixing valve 10 which has
two inlets 11, 12 and one outlet 13. The inlet 11 receives fuel
from the hydrodesulfurizer 8. The inlet 12 is connected by a
conduit 20 through a pump 22 to an energy recovery device 21 that
receives unhumidified air drawn by the pump 22 and derives heat and
moisture from air in a conduit 24 at the oxidant outlet 25 of a
fuel cell system 26. Some of the heat and humidity in the air
exhausting from the fuel cell within the conduit 24 is transferred
to the air passing through the enthalpy recovery device 21, before
the exhaust air passes to ambient 28. Humidified air from the pump
22 is passed in a conduit 29 to the air inlet 45 of the fuel cell
system as well as in the conduit 20 to the valve inlet 12.
[0010] The valve 10 provides an air/fuel mixture in a conduit 30 to
a catalytic partial oxidizer 31 (CPO). Therein, the fuel air
mixture is converted to a mixture which is, on a dry basis,
essentially 37% hydrogen, 15% CO, 4% CO.sub.2 and traces of other
gases including unconverted hydrocarbons. This reformate is passed
over a conduit 34 through a water gas shift reactor 35 which also
receives water over a conduit 36. In the water gas shift reactor
35, the water and carbon monoxide are converted to CO.sub.2 and
hydrogen, thereby enriching the flow within a conduit 39. Then, a
preferential CO oxidizer 40 converts significant amounts of the
remaining CO into CO.sub.2, which is less innocuous to the catalyst
in a fuel cell. The hydrogen-rich gas in a conduit 41, sometimes
referred to as "syngas", is passed through the anode flow fields of
the fuel cell system 26, the exhaust 27 of which may be returned in
a fuel recycle loop 24, and occasionally purged, all as is
conventional, and the details of which are not critical to the
present invention.
[0011] According to the invention, a temperature sensor 50 provides
a temperature signal on a line 51 to a controller 52, which in turn
determines, via a signal on a line 53, the positioning of the
proportioning mixing valve 10 so as to provide a substantially
perfect ratio of air to fuel, as is determined by the temperature
in the conduit 34. In the controller 52, the signal on the line 51
may be processed through a proportional and integral gain.
[0012] In certain implementations of the present invention, the air
in the conduit 20 may be unhumidified air, within the purview of
the invention. Typically, the blower 22 will operate at
substantially constant speed.
[0013] The description with respect to the figure is exemplary
merely, and indicative of a known system in which the present
invention can be utilized to great advantage. The invention may be
utilized in completely different systems, it sufficing that the
temperature of the outflow of a CPO is utilized to control the
proportions of air and fuel entering the CPO as reactants.
[0014] Thus, although the invention has been shown and described
with respect to exemplary embodiments thereof, it should be
understood by those skilled in the art that the foregoing and
various other changes, omissions and additions may be made therein
and thereto, without departing from the spirit and scope of the
invention.
* * * * *