U.S. patent application number 09/934695 was filed with the patent office on 2002-03-07 for method and device for generating a hydrogen-rich gas.
Invention is credited to Boneberg, Stefan, Schafer, Martin, Schussler, Martin, Theis, Erik.
Application Number | 20020026748 09/934695 |
Document ID | / |
Family ID | 7653514 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020026748 |
Kind Code |
A1 |
Boneberg, Stefan ; et
al. |
March 7, 2002 |
Method and device for generating a hydrogen-rich gas
Abstract
A method for operating a gas-generation device, which comprises
a partial oxidation reactor with a downstream steam reformer,
includes in order to start the gas-generation device, a quantity of
air in all the operating phases is set in such a way that oxygen
levels in the partial oxidation product gas caused by unburnt air
constituents are minimized. Furthermore, an adiabatic, catalytic
after-treatment stage, in which oxygen constituents of the partial
oxidation product gas are converted, is connected between the
partial oxidation reactor and the steam reformer.
Inventors: |
Boneberg, Stefan; (Beuren,
DE) ; Schafer, Martin; (Kirchheim/Teck, DE) ;
Schussler, Martin; (Ulm, DE) ; Theis, Erik;
(Kirchheim/Teck-Nabern, DE) |
Correspondence
Address: |
CROWELL & MORING, L. L. P.
P.O. Box 14300
Washington
DC
20044-4300
US
|
Family ID: |
7653514 |
Appl. No.: |
09/934695 |
Filed: |
August 23, 2001 |
Current U.S.
Class: |
48/197R ; 48/116;
48/199FM; 48/199R; 48/61 |
Current CPC
Class: |
C01B 2203/82 20130101;
C01B 3/36 20130101; C01B 3/382 20130101; C01B 2203/143
20130101 |
Class at
Publication: |
48/197.00R ;
48/199.00R; 48/199.0FM; 48/61; 48/116 |
International
Class: |
C10J 001/00; C10K
003/06; C10J 001/20 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2000 |
DE |
100 41 384.6 |
Claims
What is claimed is:
1. A method for operating a gas-generation device for generating a
hydrogen-rich gas from at least one of partial oxidation of an
oxygen/fuel mixture or catalytic steam reforming of a water/fuel
mixture, said method comprising: metering a fuel into a partial
oxidation reactor; starting combustion of the fuel by metering in
oxygen-containing gas into the partial oxidation reactor, wherein a
quantity of oxygen-containing gas corresponds at most to the
stoichiometric ratio for complete fuel conversion; heating at least
the partial oxidation reactor of the gas-generation device by heat
from said combusting; reducing the quantity of the
oxygen-containing gas and metering in water when an operating
temperature for the partial oxidation reactor is reached, wherein
at least one of a quantitative flow of the oxygen-containing gas or
of the water is set such that an oxygen/fuel/water mixture is
converted into hydrogen as completely as possible; and further
reducing the quantity of the oxygen-containing gas when the
operating temperature of a downstream steam reformer is reached, so
that only partial conversion of the fuel takes place in the partial
oxidation reactor, and a remaining part of the fuel is converted in
the downstream steam reformer.
2. A method according to claim 1, wherein, when the operating
temperature of the steam reformer is reached, the supply of the
oxygen-containing gas is interrupted.
3. A method according to claim 1, further comprising heating the
steam reformer.
4. A method according to claim 1, further comprising: passing
product gas that is generated in the partial oxidation reactor (1)
through an adiabatic, catalytic after-treatment stage; and
converting unburnt parts of the fuel/oxygen mixture or of the
fuel/oxygen/water mixture of the product, thereby minimizing an
oxygen content in the product gas before it is fed to the steam
reformer.
5. A gas-generation device for generating a hydrogen-rich gas from
at least one of partial oxidation of an oxygen/fuel mixture or
catalytic steam reforming of a water/fuel mixture, comprising: a
partial oxidation reactor; a steam reformer downstream of the
partial oxidation reactor; an adiabatic, catalytic after-treatment
stage arranged between the partial oxidation reactor and the steam
reformer.
6. A device according to claim 5, wherein the catalytic
after-treatment stage comprises a precious metal-containing
catalyst.
7. A device according to claim 5, wherein the catalytic
after-treatment stage comprises a catalyst support having a low
heat capacity.
8. A device according to claim 5, further comprising heating means
for heating at least one of the steam reformer or the adiabatic,
catalytic after-treatment stage.
9. A device according to claim 5, wherein the adiabatic catalytic
after-treatment is integrated into the partial oxidation reactor or
the steam reformer.
Description
[0001] This application claims the priority of German application
No. 100 41 384.6, filed Aug. 23, 2000, the disclosure of which is
expressly incorporated by reference herein.
BACKGROUND AND SUMMARY OF INVENTION
[0002] The present invention relates to a method and a device for
generating a hydrogen-rich gas. The present invention relates in
particular to a method for starting a gas-generation device.
[0003] Hydrogen can be generated from suitable fuels by exothermic
partial oxidation, referred to below as POX, in accordance with the
following equation
--(CH.sub.2)--+1/20.sub.2(air)=>H.sub.2+CO.sub.2.
[0004] and/or endothermic steam reforming in accordance with the
following equation:
--(CH.sub.2)--+2H.sub.2O (air)=>3H.sub.2+CO.sub.2.
[0005] It is also possible to use a combination of the two
processes, which may lead to an autothermal operating method.
Suitable fuels are, in particular, methanol and other hydrocarbon
derivatives, such as higher alcohols, petroleum, diesel, LPG
(liquid petroleum gas) or NG (natural gas).
[0006] U.S. Pat. No. 3,982,910 discloses a hydrogen generator and a
method for generating a soot-free, hydrogen-rich gas by partial
oxidation. To start the generator up, air is mixed with a spray
mist of liquid hydrocarbon fuel and ignited in the generator. The
heat of combustion is used to preheat air which is to be supplied
to a predetermined temperature. When this temperature, which is
higher than the boiling temperature of the liquid fuel, is reached,
operation switches over to normal operation. In normal operation,
the fuel is evaporated, mixed with the preheated air and then the
hydrogen-rich gas is generated from the fuel mixture of partial
oxidation in a fuel chamber of the generator. When the generator is
being started, the air/fuel ratio is set in such a way that it is
higher than that of normal operation with evaporated fuel.
[0007] EP 0 646 093 (U.S. Pat. No. 5,143,647) discloses a method
for starting up a steam reforming/partial oxidation process for
converting a methane-containing starting gas into a hydrogen-rich
gas using a fluidized-bed or slugging fluidized-bed catalyst, in
which the tendency of the catalyst material to lump together is
reduced. In this method, in a first step a fluidized bed comprising
inert particles, preferably of aluminium, is heated to the reaction
temperature in an oxidizing atmosphere in the presence of oxygen
and in the absence of a reforming catalyst. Then, a reducing
atmosphere is generated, before the reforming catalyst, preferably
a nickel-containing catalyst, is introduced into the fluidized bed.
The starting gas is then converted into a hydrogen-rich gas at the
catalyst in the presence of oxygen.
[0008] EP 0 887 306 (U.S. Pat. No. 6,241,792) discloses a method
for starting a gas-generation device with downstream gas-cleaning
stage, in which a hydrogen-rich gas is generated from a fuel of
partial oxidation and/or steam reforming. To clean the gas, a
selective CO oxidation stage, which generally comprises a
platinum-containing catalyst, is used. During the starting phase,
the gas-cleaning stage is temporarily used as a catalytic burner,
as a result of oxygen being admixed with the fuel and the direction
of flow being reversed in such a way that medium flows first
through the gas-cleaning stage and then through the gas-generation
device. During starting, the device is rapidly heated to operating
temperature by the gas-cleaning stage, which is operated as a
burner.
[0009] EP 0 924 163 (U.S. Pat. No. 6,268,075) discloses a method
for starting steam reforming by a reforming reactor, an evaporator,
a catalytic burner and a membrane module in order to separate out
hydrogen. During a cold start, a heating operation is carried out,
during which, in a first operating phase, the reforming reactor and
the evaporator are heated by the burner. In a second operating
phase, the reforming reactor is operated with a water/hydrocarbon
ratio which is higher than that used in normal operation, and the
reformate gas is fed to the catalytic burner via the membrane
module. In a third operating phase of the heating, the supply of
hydrogen or hydrocarbon to the catalytic burner is reduced. As the
operating temperature of the membrane module rises, the proportion
of hydrocarbon in the hydrocarbon/steam mixture in the evaporator
is increased up to the mixing ratio used during normal
operation.
[0010] EP 0 924 161 discloses a method for operating an
installation having a reactor which is suitable for both steam
reforming and partial oxidation, an evaporator and a membrane
module. A catalytic burner is provided, in order to bring the
reactor, the evaporator and the membrane module up to operating
temperature. When the installation is started, the reactor, in a
first operating phase, is operated as a partial oxidation reactor
with an operating pressure which is lower than that used in normal
operation. In a second operating phase, the reactor is switched
over to reforming operation, and the pressure is increased from the
heat-up operating pressure to normal operating pressure.
[0011] WO 99/31012 discloses a method for operating an installation
for steam reforming of a hydrocarbon, in which part of a reforming
reactor is designed as a multifunctional reactor unit. During the
cold start, the multifunctional reactor unit, in a first operating
phase, is operated with fuel and oxygen-containing gas supplied
simultaneously, as a catalytic burner, and in a second operating
phase is operated as a partial oxidation reactor (POX reactor).
During the transition from the first operating phase to the second
operating phase, water is metered to the fuel/oxygen mixture and/or
the quantitative flow of fuel is increased as the temperature of
the multifunctional reactor unit rises and/or the quantitative flow
of the oxygen-containing gas is set to a substoichiometric ratio
even during the first operating phase. The substoichiometric ratio
is intended to promote the generation of cleaved products, such as
hydrogen, by thermal decomposition of the fuel. To establish
suitable conditions for the partial oxidation of the fuel in the
second operating phase, the ratio of oxygen-containing gas and fuel
is reduced compared to that used in the first operating phase. The
remaining part of the reactor, i.e. the area which is not provided
as a multifunctional reactor unit, is used as a further reforming
unit and CO shift converter stage during the second operating
stage. In normal operation, the multifunctional reactor unit is at
least from time to time used as a reforming unit for hydrogen
generation.
[0012] By contrast, an object of the present invention is
generating a hydrogen-rich gas by partial oxidation and steam
reforming, thereby preventing aging of the catalyst of the steam
reformer.
[0013] The method according to the present invention ensures that
the oxygen content in the product gas of the POX reactor is
minimized in every operating phase. Unburnt oxygen fractions would
oxidize the catalyst of the steam reformer and therefore lead to
increased aging of the catalyst.
[0014] In an advantageous refinement of the method, the steam
reformer is heated by heating means. Therefore, the heat of
combustion of the fuel can substantially be used to heat the POX
reactor. As a result, the POX reactor is rapidly brought to the
operating temperature for the partial oxidation, so that even after
a short time hydrogen-rich gas is available via the partial
oxidation.
[0015] According to a further advantageous configuration of the
present invention, product gas which is generated in the POX
reactor is passed through an adiabatic, catalytic after-treatment
stage, in order for unburnt parts of the fuel/oxygen mixture or of
the fuel/oxygen/water mixture of the product gas to be converted in
the after-treatment stage, so that the oxygen content in the
product gas before it is fed to the steam reformer is minimized.
During the burning of fuel in the POX reactor and in particular at
low temperatures, unburnt fractions of the fuel/oxygen mixture may
still occur in the product stream of the POX reactor. Converting
these residual fractions in the after-treatment stage prevents them
from being able to cause aging of the catalyst of the reformer.
[0016] A gas-generation device according to the present invention
comprises at least one POX reactor with downstream steam reformer,
an adiabatic, catalytic after-treatment stage being arranged
between the POX reactor and the steam reformer. During starting,
hydrogen-rich gas can be generated using the POX reactor after only
a short time. If the POX reactor is designed suitably, the starting
materials for the steam reforming can also be heated or evaporated
in the POX reactor. Unburnt oxygen fractions of the POX product
stream are converted in the catalytic after-treatment stage, so
that a minimized oxygen content is ensured even at the beginning of
the starting phase and at low temperature, and aging of the
catalyst of the reformer is counteracted.
[0017] In an advantageous refinement, the adiabatic, catalytic
after-treatment stage comprises a precious-metal-containing
catalyst. Precious metals, such as platinum, are catalytically
active even at low temperatures and are therefore particularly
suitable.
[0018] In a further advantageous refinement, the adiabatic,
catalytic after-treatment stage comprises a catalyst support with a
low heat capacity. As a result, the after-treatment stage can be
heated to operating temperature quickly and with little consumption
of thermal energy.
[0019] In an advantageous refinement, heating means are provided
for heating the steam reformer and/or the adiabatic, catalytic
after-treatment stage. Consequently, heating is possible
independently of the heat of combustion of the POX reactor. In
particular, the after-treatment stage can be brought to operating
temperature at the very beginning of the starting phase, so that
the oxygen content of the product gas of the POX reactor is
minimized even at the start of combustion.
[0020] Other objects, advantages and novel features of the present
invention will become apparent from the following detailed
description of the present invention when considered in conjunction
with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
[0021] The sole FIGURE shows a diagrammatic block diagram of a
gas-generation device according to the present invention.
DETAILED DESCRIPTION OF THE DRAWING
[0022] The gas-generation device according to the present
invention, which is illustrated in the figure, comprises a partial
oxidation reactor 1 (POX reactor), a steam reformer 2, an
adiabatic, catalytic after-treatment stage 3, which is connected
between POX reactor 1 and steam reformer 2, and heating means 7 for
heating the steam reformer 2 and/or the after-treatment stage
3.
[0023] Conventional reactors and/or reformers which are known to
the person skilled in the art can in particular be used as the POX
reactor and the steam reformer. The catalysts used may, by way of
example, be copper-containing and/or platinum-containing catalysts.
The adiabatic, catalytical after-treatment stage 3 comprises a
catalyst support with a low heat capacity and a
precious-metal-containing catalyst, for example based on platinum.
The after-treatment stage 3 may preferably be integrated in the
collector manifold (not specifically shown) of the POX reactor 1 or
in the distributor manifold of the reformer 2.
[0024] Starting materials for the generation of the hydrogen-rich
gas are fuel, oxygen-containing gas, and/or water. A preferred fuel
is methanol. However, it is also possible to use other hydrocarbon
derivatives, such as higher alcohols, petroleum, diesel, LPG
(liquid petroleum gas) or NG (natural gas). The oxygen-containing
gas used is preferably air. All the starting materials can be fed
to the gas-generation device via an inlet side 4 of the POX reactor
1. In this case, a feed 5 for the liquid starting materials, such
as fuel and water, and a feed 6 for metering in air are
provided.
[0025] To start the gas-generation device, first of all fuel is
metered into the POX reactor 1. Then, air is admixed for
homogeneous and/or catalytic combustion of the fuel. This order
ensures that, when the device is starting, no unburnt air passes
out of the POX reactor 1 into the reformer 2. The quantity of air
is set in such a way that it at most corresponds to the
stoichiometric ratio of complete combustion with the corresponding
quantity of fuel which is supplied. This promotes complete
conversion of the air in the POX reactor 1 (i.e. oxygen levels in
the POX product gas are minimized). The heat of combustion which is
generated is used to bring the POX reactor 1 to operating
temperature. The heat of combustion can also be used to heat
further parts of the installation, such as the catalytic
after-treatment stage 3 or the reformer 2 to operating temperature,
at least as an auxiliary measure. In order for the gas-generation
device to be started rapidly, however, separate heating means, such
as burners or electrical heaters, are preferred.
[0026] In the next operating phase, when the operating temperature
for partial oxidation in the POX reactor 1 is reached, the quantity
of air supplied is reduced, since the partial oxidation of the fuel
requires considerably less oxygen than the combustion. At the same
time, water is metered in, in order to prevent overheating during
the catalytic combustion and to prepare for transition to the steam
reforming of the fuel. In this phase, the quantity of air and/or
water is regulated in such a way that complete conversion of the
fuel/oxygen/water mixture into hydrogen takes place. Consequently,
in this operating phase too, oxygen levels in the POX gas caused by
unburnt air constituents are minimized.
[0027] When the operating temperature of the steam reforming in the
steam reformer 2 is reached, the quantity of air supplied is
reduced further or the supply of air is interrupted. Consequently,
only part of the fuel which is supplied is converted in the POX
reactor 1. Most of the fuel is converted into hydrogen, with
corresponding metering of water, in the downstream steam reformer
2, which has a better system efficiency than the POX reactor 1. It
is advantageous to maintain the POX operation, since, by metering
liquid fuel into the POX reactor 1, it is possible to react more
quickly to load changes than by changing the quantity of the
fuel/steam mixture in the reformer 2. The use of the adiabatic,
catalytic after-treatment stage 3 ensures that oxygen fractions
which are still present in the product gas of the POX reactor, as
may occur in particular at low temperatures on account of unburnt
air constituents, are catalytically converted, and this counteracts
aging of the reformer catalyst 2.
[0028] The foregoing disclosure has been set forth merely to
illustrate the invention and is not intended to be limiting. Since
modifications of the disclosed embodiments incorporating the spirit
and substance of the invention may occur to persons skilled in the
art, the invention should be construed to include everything within
the scope of the appended claims and equivalents thereof.
* * * * *