U.S. patent application number 11/256113 was filed with the patent office on 2006-05-11 for method and apparatus for operating a burner of a heat engine, in particular of a gas turbine installation.
This patent application is currently assigned to ALSTOM TECHNOLOGY LTD. Invention is credited to Timothy Griffin, Dieter Winkler.
Application Number | 20060096297 11/256113 |
Document ID | / |
Family ID | 33304921 |
Filed Date | 2006-05-11 |
United States Patent
Application |
20060096297 |
Kind Code |
A1 |
Griffin; Timothy ; et
al. |
May 11, 2006 |
Method and apparatus for operating a burner of a heat engine, in
particular of a gas turbine installation
Abstract
The invention describes a method and an apparatus for operating
a burner of a heat engine, in particular of a gas turbine
installation, having a burner inlet, to which a mixture of a fuel
and an oxygen-enriched carrier gas is fed for combustion within a
combustion chamber which adjoins the burner inlet in the direction
of flow. The invention is distinguished by the following method
steps: providing a first oxygen-enriched carrier gas stream, known
as the first oxidizer mixture, with which the fuel is admixed to
form a first fuel/oxidizer mixture, and providing a second
oxygen-enriched carrier gas stream, known as the second oxidizer
mixture, catalyzing the first fuel/oxidizer mixture to form a
catalyzed first fuel/oxidizer mixture, in which the fuel is at
least partially oxidized, mixing the catalyzed first fuel/oxidizer
mixture with the second oxidizer mixture to form a second
fuel/oxidizer mixture, and igniting and burning the second
fuel/oxidizer mixture.
Inventors: |
Griffin; Timothy;
(Ennetbaden, CH) ; Winkler; Dieter; (Lauchringen,
DE) |
Correspondence
Address: |
BUCHANAN INGERSOLL PC;(INCLUDING BURNS, DOANE, SWECKER & MATHIS)
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
ALSTOM TECHNOLOGY LTD
Baden
CH
|
Family ID: |
33304921 |
Appl. No.: |
11/256113 |
Filed: |
October 24, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/CH03/00478 |
Jul 16, 2003 |
|
|
|
11256113 |
Oct 24, 2005 |
|
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Current U.S.
Class: |
60/777 ;
60/723 |
Current CPC
Class: |
Y02E 20/34 20130101;
Y02E 20/322 20130101; F23L 2900/07001 20130101; F23L 7/007
20130101; Y02E 20/344 20130101; Y02E 20/32 20130101; F23C
2900/13002 20130101; F23R 3/40 20130101; F23C 13/00 20130101 |
Class at
Publication: |
060/777 ;
060/723 |
International
Class: |
F23R 3/40 20060101
F23R003/40 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2003 |
DE |
103 18 669.7 |
Claims
1. A method for operating a burner of a heat engine, in particular
of a gas turbine installation, having a burner inlet, to which a
mixture of a fuel and an oxygen-enriched carrier gas is fed for
combustion within a combustion chamber which adjoins the burner
inlet in the direction of flow, comprising the following method
steps: providing a first oxygen-enriched carrier gas stream, known
as the first oxidizer mixture, with which the fuel is admixed to
form a first fuel/oxidizer mixture, and providing a second
oxygen-enriched carrier gas stream, known as the second oxidizer
mixture, catalyzing the first fuel/oxidizer mixture to form a
catalyzed first fuel/oxidizer mixture, in which the fuel is at
least partially oxidized, mixing the catalyzed first fuel/oxidizer
mixture with the second oxidizer mixture to form a second
fuel/oxidizer mixture, and igniting and burning the second
fuel/oxidizer mixture.
2. The method as claimed in claim 1, wherein the first and second
oxidizer mixtures are obtained in the following way: recirculating
at least some of the exhaust gas which emerges from the combustion
chamber, introducing the recirculated exhaust gas as carrier gas
for taking up oxygen into an oxygen separation device for producing
the oxygen-enriched carrier gas, known as the oxidizer mixture.
3. The method as claimed in claim 2, wherein the oxidizer mixture
is divided into the first oxidizer mixture and the second oxidizer
mixture, and wherein the first oxidizer mixture is mixed with the
fuel and brought into contact with catalyst material.
4. The method as claimed in claim 1, wherein the oxidizer mixture
provided is a gas mixture which substantially comprises the
following constituents: O.sub.2, CO.sub.2 and H.sub.2O, and wherein
the fuel provided is gaseous fuel, preferably methane
(CH.sub.4).
5. The method as claimed in claim 1, wherein the first
fuel/oxidizer mixture has an oxygen ratio .lamda..sub.1 and the
second fuel/oxidizer mixture has an oxygen ratio .lamda..sub.2, and
wherein the following relationship applies:
.lamda..sub.1<.lamda..sub.2, wherein the oxygen ratio is defined
as the ratio of the actual oxygen supply to the minimum oxygen
demand for complete combustion.
6. The method as claimed in claim 5, characterized in that wherein
the oxygen ratios .lamda..sub.1 and .lamda..sub.2 are set in such a
manner that the following relationship applies:
0.2.ltoreq..lamda.1.ltoreq.0.5, preferably
.lamda..sub.1.apprxeq.0.25, and .lamda..sub.2.gtoreq.1.
7. The method as claimed in claim 5, wherein the fuel CH.sub.4
contained within the first fuel/oxidizer mixture, during the
catalysis, is at least partially converted into the reaction
products H.sub.2 and CO, which are contained in the catalyzed first
fuel/oxidizer mixture and are mixed with the second oxidizer
mixture without ignition phenomena occurring.
8. The method as claimed in claim 1, wherein the second
fuel/oxidizer mixture is reacted in a further catalytic
converter.
9. The method as claimed in claim 1, wherein the second
fuel/oxidizer mixture is ignited and burnt within a premix
burner.
10. An apparatus for operating a burner of a heat engine, in
particular of a gas turbine installation, having a burner inlet, to
which a mixture of a fuel and an oxygen-enriched carrier gas, known
as an oxidizer mixture, can be fed for combustion within a
combustion chamber which adjoins the burner inlet in the direction
of flow, characterized in that wherein at least one means for
feeding in the oxidizer mixture and a fuel feed unit are provided
in the region of the burner inlet, wherein a catalytic converter
unit is provided in the region of the burner inlet, downstream of
the means for feeding in the oxidizer mixture and of the fuel feed
unit, and wherein at least one bypass line, which bypasses or
passes through the catalytic converter unit and connects the region
of the burner inlet upstream of the catalytic converter unit to the
region of the burner inlet downstream of the catalytic converter
unit, is provided.
11. The apparatus as claimed in claim 10, wherein the catalytic
converter unit is integrated in a support structure, which is
provided downstream of the means for feeding in the oxidizer
mixture and of the fuel feed unit, in the region of the burner
inlet, and has a multiplicity of through-passages which are
oriented in the direction of flow and a first group of which are
provided with a catalyst material on the inner wall and constitute
the catalytic converter unit, whereas a second group of
through-passages consist of substantially chemically inert material
which form at least one bypass line.
12. The apparatus as claimed in claim 11, wherein the first and
second groups of through-passages are arranged in a
three-dimensionally periodic ordered pattern.
13. The apparatus as claimed in claim 11, wherein the
through-passages are arranged in matrix form within the support
structure.
14. The apparatus as claimed in claim 12, wherein the first and
second groups are arranged in alternating rows, columns or in
checkerboard pattern.
15. The apparatus as claimed in claim 10, wherein the support
structure is formed in the style of a honeycomb structure.
16. The apparatus as claimed in claim 10, wherein at least one
flow-guiding means, which spatially separates a first flow region
from a second flow region, is provided upstream of the catalytic
converter unit, wherein a mixture of fuel and oxidizer mixture can
be introduced into the first flow region, and exclusively oxidizer
mixture can be introduced into the second flow region, and wherein
the first flow region is connected to the catalytic converter unit
and the second flow region is connected to the bypass line.
17. The apparatus as claimed in claim 16, wherein the flow-guiding
means has a multiplicity of first and second flow regions, which
are arranged in such a manner that the first flow regions are in
communication with the catalytic converter unit and the second flow
regions are in communication with the at least one bypass line.
18. The apparatus as claimed in claim 16, wherein a perforated
plate is arranged between the flow-guiding means and the catalytic
converter unit.
19. The apparatus as claimed in claim 10, wherein a further
catalytic converter unit is provided downstream of the catalytic
converter unit and upstream of the combustion chamber, to form a
catalytic burner arrangement.
20. The apparatus as claimed in claim 10, wherein a premix burner
is arranged downstream of the first catalytic converter unit.
21. The apparatus as claimed in claim 10, wherein the oxidizer
mixture can be provided by the following components: a
recirculation line is used to pass some of the exhaust gases which
emerge from the combustion chamber as carrier gas into an oxygen
separation device, from which the oxygen-enriched carrier gas
emerges and can be provided directly or indirectly via the means
for feeding in oxidizer mixture and can be introduced into the at
least one bypass line.
22. The apparatus as claimed in claim 21, wherein the oxygen
separation device has at least one MCM membrane.
Description
TECHNICAL FIELD
[0001] The invention relates to a method and an apparatus for
operating a burner of a heat engine, in particular of a gas turbine
installation, having a burner inlet, to which a mixture of a fuel
and an oxygen-enriched carrier gas is fed for combustion within a
combustion chamber which adjoins the burner inlet in the direction
of flow.
PRIOR ART
[0002] As part of the desire to reduce the emission of greenhouse
gases into the atmosphere, considerable efforts are being
undertaken in particular in the field of power generation to reduce
in particular the emission of CO.sub.2 as a result of the
combustion of fossil fuels. In this context, development work is
being carried out on a gas turbine concept for generating
electrical power which is known by the acronym "AZEP" (advanced
zero emissions power) to achieve combustion of fossil fuels
virtually without any nitrogen oxides and, moreover, offers the
possibility of completely avoiding the free discharge of CO.sub.2
into the atmosphere.
[0003] The abovementioned gas turbine concept is based on the
combustion of fossil fuels, in particular gaseous fuels, such as
for example methane, in the presence of a mixture of recirculated
exhaust gas, in which CO.sub.2, H.sub.2O and oxygen are used as
oxidizing agents and not, as in conventional combustion processes,
to form a fuel/air mixture which contains considerable quantities
of nitrogen.
[0004] With the proposed combustion concept based on the AZEP
principle, it is possible, for example during combustion of methane
(CH.sub.4) as the gaseous fossil fuel used in the presence of
oxygen as oxidizing agent, to obtain substantially only CO.sub.2
and H.sub.2O as combustion products. The water content contained in
the exhaust-gas stream can if necessary be completely separated
from the exhaust-gas stream with the aid of condensers which are
simple and inexpensive to implement, so that ultimately it is
possible to obtain an exhaust-gas stream which is made up of
virtually pure CO.sub.2, assuming that the combustion is complete
and any CO is oxidized to CO.sub.2 in the presence of oxygen. The
CO.sub.2 exhaust-gas stream is in part fed back to the gas turbine
process as part of part-stream recirculation as CO.sub.2 mass flow
for the combustion, while the remaining residual exhaust-gas stream
is taken for suitable utilization or is converted into compressed
form for final land filling in suitable geological strata, which
means that it is completely withdrawn from acting as a harmful
greenhouse gas in the open atmosphere.
[0005] Successful and inexpensive implementation of the AZEP gas
turbine concept requires a reliable and inexpensive method of
producing oxygen. What are known as oxygen separation devices,
which are equipped with a membrane which conducts oxygen ions and
electrons, known as an MCM (mixed conducting membrane), are
suitable for this purpose. A preferred apparatus for producing and
preparing an oxygen-enriched carrier gas stream which, having been
mixed with fuel, is ignited and burnt within a combustion chamber,
is described in EP 1 197 257 A1, in which a partial exhaust-gas
stream which emerges from the combustion chamber is introduced into
an oxygen separation device and emerges in the form of an
oxygen-enriched carrier gas stream. Since the oxygen-enriched
carrier gas stream consists exclusively of CO.sub.2, H.sub.2O and
pure oxygen as oxidizer, this mass flow is also referred to below
as the oxidizer mixture.
[0006] The oxidizer mixture obtained with the aid of the oxygen
separation device is then mixed with gaseous fuel, preferably
CH.sub.4, and, as a fuel/oxidizer mixture, ignited for combustion
within the combustion chamber.
[0007] To increase the efficiency of the oxygen separation device,
it is important to produce the maximum possible driving gradient
between the permeate side and retentate side of the MCM membrane.
Therefore, the recirculated exhaust-gas stream which is to be
enriched with oxygen, on the permeate side, is passed through the
oxygen separation device at a high flow rate along the MCM
membrane, with the result that the oxygen concentration on the
permeate side is reduced and the driving gradient between the
retentate side, through which a preheated, oxygen-containing gas is
flowing, and the permeate side is increased. Despite the oxygen
enrichment, the oxygen content within the oxygen-enriched carrier
gas stream which emerges from the oxygen separation device is too
low to achieve stable and effective combustion of the fuel/oxidizer
mixture which forms with the aid of conventional combustion
techniques.
[0008] Even using diffusion burners, which are known for a high
combustion stability even at an oxygen ratio of .lamda.=1 (.lamda.
indicates the ratio of actual oxygen supply to the minimum oxygen
demand for complete combustion), the highly dilute oxygen content
within the oxidizer mixture means that the combustion results which
can be achieved are unsatisfactory. In particular, it has been
found that the ignitability of a fuel/oxidizer mixture of this
type, even at mixture temperatures of between 400.degree. C. and
750.degree. C., using premix burner techniques which are known per
se, is much lower than in cases using conventional fuel/air
mixtures. Moreover, it has been found that the ignition delay times
of a fuel/oxidizer mixture using the AZEP technique are at least an
order of magnitude greater than those which are measured when using
conventional combustion techniques. Furthermore, the time-delayed
ignition behavior also has a detrimental effect on the residence
times required for complete combustion of the ignited fuel/oxidizer
mixture within the combustion chamber, and moreover the CO and
unburnt hydrocarbon contents which are formed during the combustion
are well above the levels obtained with conventional combustion
technology. Finally, the reduced ignitability or reactivity of the
fuel/oxidizer mixture also has a reducing action on the flame
velocity, with the result that what are known as the lean
extinction limits are reduced.
[0009] The generally critical effects on the combustion behavior
when using a fuel/oxidizer mixture which have been listed above are
even more serious if account is taken of the fact that the maximum
temperature of the exhaust-gas products formed as a result of the
combustion should be relatively low, for example at most
1250.degree. C., in order to avoid damage to the components
provided along the exhaust-gas recirculation path, such as for
example MCM membrane within the oxygen separation device and the
high-temperature heat exchanger for preheating the
oxygen-containing gas to be fed to the oxygen separation device on
the retentate side.
[0010] It is also important to keep the thermal stresses, caused by
the combustion process, on the individual components which come
into contact with the exhaust gases at a substantially constant,
relatively low temperature level (less than 1250.degree. C.), in
order to be able to substantially preclude thermally induced
material degradation within the individual components. For this
reason, conventional premix combustion methods, which are based
exclusively on aerodynamic stabilizing effects and require the use
of very hot flame temperatures, are unsuitable.
[0011] Although the use of catalytic combustion techniques is able
to help with maintaining the required temperature conditions, the
steam which is formed within the exhaust gases, under lean fuel
mixture conditions, contributes to increasing the ignition
temperature for the catalytic oxidation of the fuel. In order
nevertheless to achieve increased ignition temperatures within the
fuel/oxidizer mixture, it is necessary to ensure that the
temperature of the oxidizer mixture which is mixed with the fuel
upstream of the burner inlet is increased, with the result that the
temperature level of the recirculating exhaust-gas stream
automatically has to be increased. In this context, it ultimately
remains a problem that the catalyst material which is required for
catalytic oxidation of the fuel, typically platinum or palladium,
is applied to support materials, such as for example aluminum
oxide, silicon oxide or zirconium oxide, which are or start to
become unstable at such high temperatures with a steam content of
greater than 50%.
SUMMARY OF THE INVENTION
[0012] The invention is based on the object of developing a method
and an apparatus for operating a burner of a heat engine, in
particular of a gas turbine installation, having a burner inlet, to
which a mixture of a fuel and an oxygen-enriched carrier gas is fed
for combustion within a combustion chamber which adjoins the burner
inlet in the direction of flow, in such a manner that the drawbacks
and technical difficulties which have been mentioned above in
connection with the prior art can be avoided. In particular, it is
to be possible, using conventional combustion techniques, to
provide a working gas for operation of a burner based on the AZEP
principle which allows stable and complete combustion within the
combustion chamber while complying with all the temperature limits
imposed by the components required to provide the working gas.
[0013] The solution to the object on which the invention is based
is described in claim 1 and claim 10. Features which refine the
concept of the invention in an advantageous way form the subject
matter of the subclaims and are also to be found in the description
with reference to the exemplary embodiments.
[0014] As was mentioned in the introduction, the reduced
ignitability or reactivity of the fuel/oxidizer mixture on account
of the highly dilute oxygen content within the oxidizer mixture
contributes to unsatisfactory results being achieved during the
combustion operation with the aid of burner techniques which are
known per se. To avoid all the negative effects on the combustion
process of the fuel/oxidizer mixture provided which have been
described above, the method in accordance with the preamble of
patent claim 1 according to the invention provides the following
method steps:
[0015] a first oxidizer mixture, i.e. an oxygen-enriched carrier
gas stream, which is obtained in a manner known per se, as
mentioned above, is provided upstream of the burner inlet. Fuel,
preferably gaseous fossil fuel, such as for example methane, is
admixed with this first oxidizer mixture to form a first
fuel/oxidizer mixture. A second oxidizer mixture, the composition
of which is identical to that of the first oxidizer mixture, is
likewise provided.
[0016] In a second method step, the first fuel/oxidizer mixture is
fed to a catalytic converter unit, within which the fuel content
contained in the first fuel/oxidizer mixture is at least partially
catalytically oxidized. If the gaseous fossil fuel used is methane
(CH.sub.4), the catalyst products formed are hydrogen H.sub.2 and
substantially steam and carbon dioxide (CO.sub.2). In particular
the formation of hydrogen subsequently contributes to drastically
increasing the reactivity of the fuel/oxidizer mixture, which has
an advantageous effect in terms of shortening the ignition time of
the fuel/oxidizer mixture. However, before the catalyzed, first
fuel/oxidizer mixture is ignited and burnt, it is mixed with the
second oxidizer mixture which was initially provided, to form a
second fuel/oxidizer mixture. Only after the second fuel/oxidizer
mixture has formed is the latter ignited and burnt within the
combustion chamber.
[0017] The method according to the invention therefore provides a
combination of catalysis of a fuel-rich or rich fuel/oxidizer
mixture to form reactive hydrogen and subsequent combustion of a
lean fuel/oxidizer mixture, for example within a conventional
premix burner. The lean depletion of the catalyzed, first
fuel/oxidizer mixture is effected by admixing the second oxidizer
mixture which has been provided, with the result that the fuel
content by volume is reduced.
[0018] The measures of the invention lead to a number of
advantages: the ignition temperature of the catalytically oxidized
fuel, which is fed to a catalytic converter unit in the form of a
rich fuel/oxidizer mixture, is significantly reduced. The reduction
in the ignition temperature, as well as the stabilization of the
flame front which is formed within a combustion chamber downstream
of a premix burner, is attributable to the formation of hydrogen
which is formed during the catalytic oxidation of the fuel
CH.sub.4.
[0019] Furthermore, an apparatus for operating a burner of a heat
engine, in particular of a gas turbine installation, having the
features of the preamble of claim 10, is used to carry out the
method according to the invention, which apparatus according to the
invention is distinguished by the fact that at least one means for
feeding in the oxidizer mixture and a fuel feed unit are provided
in the region of the burner inlet. The means for feeding in the
oxidizer mixture and the fuel feed unit are arranged in the region
of the burner inlet, in such a manner that substantially complete
mixing between the gaseous fuel and the oxidizer mixture supplied
is ensured. Furthermore, a catalytic converter unit, through which
the fuel/oxidizer mixture which forms flows, is provided in the
region of the burner inlet downstream of the means for feeding in
oxidizer mixture and of the fuel feed unit. Finally, there is at
least one bypass line which bypasses or passes through the
catalytic converter unit, connecting the region of the burner inlet
upstream of the catalytic converter unit to the region of the
burner inlet downstream of the catalytic converter unit.
Exclusively pure oxidizer mixture is passed through the at least
one bypass line, and this pure oxidizer mixture, downstream of the
catalytic converter unit, is admixed to the catalyzed fuel/oxidizer
mixture for the purpose of targeted lean depletion of the fuel
content.
[0020] It is advantageous for the oxidizer mixture to be produced
using means which are known per se by some of the exhaust gases
which emerge from the combustion chamber being introduced as
carrier gas into an oxygen separation device by means of a
recurculation line, with the oxygen-enriched carrier gas emerging
from the oxygen separation device and being made available in the
usual way via a heat exchanger in order to be introduced into the
burner inlet, as described in EP 1 197 257 A1.
[0021] The oxidizer mixture is provided uniformly both for feeding
into the bypass line in order to bypass the catalytic converter
unit and for introduction into the means for feeding in oxidizer
mixture, by which some of the oxidizer mixture is mixed with fuel
and fed to the catalytic converter unit as fuel/oxidizer
mixture.
[0022] Further details, relating to both the method principle
according to the invention and the apparatus designed according to
the invention for carrying out the method, for operating a burner
of a heat engine, in particular of a gas turbine arrangement, are
to be found below with reference to the exemplary embodiments.
BRIEF DESCRIPTION OF THE INVENTION
[0023] The invention is described by way of example below, without
restricting the general concept of the invention, on the basis of
exemplary embodiments and with reference to the drawing in
which:
[0024] FIG. 1 shows a diagrammatic illustration for preparing an
ignitable fuel/oxidizer mixture using the method according to the
invention;
[0025] FIG. 2 illustrates a catalytic converter unit with a
flow-guiding means arranged upstream;
[0026] FIG. 3 shows an alternative form of a catalytic converter
unit, and
[0027] FIG. 4a-d show alternative embodiments of the catalytic
converter unit in the form of cross-sectional illustrations.
WAYS OF CARRYING OUT THE INVENTION, INDUSTRIAL APPLICABILITY
[0028] As has already been mentioned above, an oxygen separation
device with an MCM membrane, into which some of the exhaust gas
which emerges from the combustion chamber is recirculated and, as
oxygen-enriched carrier stream, fed back to the burner inlet as
oxidizer mixture via a preheating unit, is used to produce the
oxygen-enriched carrier gas, i.e. the oxidizer mixture. An
apparatus of this type is described, for example, in EP 1 197 257
A1.
[0029] Based on this initial statement, reference will be made
below to a burner inlet 1, which is diagrammatically depicted in
FIG. 1, of a gas turbine installation, which is not otherwise
illustrated; medium flows through the burner inlet from the
left-hand side to the right-hand side to form an ignitable
fuel/oxidizer mixture, and in the region of the right-hand side the
burner inlet opens out into the combustion chamber 9. It will be
assumed that an oxidizer mixture is fed into the left-hand inlet
opening of the burner inlet 1 as a gaseous stream consisting of
CO.sub.2, H.sub.2O and O.sub.2 at a temperature T of between 450
and 600.degree. C.
[0030] Downstream of the inlet region of the burner inlet 1, there
is a support structure 3 which, as seen in the direction of flow,
has a multiplicity of through-passages 4, 5, of which one group of
flow passages 4 is lined in thin-walled form with a catalyst
material, for example Pt or Pd, while the other group of
through-passages 5 consists of the material of the support
structure itself, preferably an inert material, for example
AlO.sub.3, SiO.sub.2 or ZrO. Immediately upstream of the catalytic
converter unit 3, in each case in the flow region ahead of the
through-passages 4 lined with catalyst material, there is a fuel
feed unit 6, through which gaseous fossil fuel, preferably methane
(CH.sub.4), is fed into the burner inlet to form a first
fuel/oxidizer mixture 7. In this case, a first part-stream passes
from the oxidizer mixture 2 provided by the oxygen separation
device into the inflow region of the gaseous fuel provided by the
fuel feed unit, to form the first fuel/oxidizer mixture 7. The
remaining part of the oxidizer mixture 2 which is provided flows
through the through-passages 5 designed as bypass lines.
[0031] The first fuel/oxidizer mixture 7 which is formed includes a
gas mixture consisting of oxygen, carbon dioxide, water and methane
as fuel, the so-called oxygen ratio .lamda..sub.1 of which, i.e.
the ratio of the actual oxygen supply to the minimum oxygen demand
for complete combustion, is less than 1, preferably 0.25. Within
the catalytic converter unit, comprising the through-passages 4
lined with catalyst material, this relatively fuel-rich or rich gas
mixture comes into surface contact with the catalyst material, for
example rhodium (Rh), platinum (Pt), palladium (Pd) or nickel (Ni),
with the result that the fossil fuel gas is at least partially
catalytically oxidized and chemically converted. Hydrogen and
carbon monoxide or carbon dioxide are formed as chemical
by-products of the exothermic chemical reactions, with the result
that the process temperature within the catalytic converter unit
rises to temperatures between 550 and 1000.degree. C., and the
entire stream of substance passing through the catalytic converter
unit and therefore also the support structure 3, consisting of the
first fuel/oxidizer mixture and the second oxidizer mixture, which
passes through the through-passages 5, is correspondingly heated.
The heat quantity which is released by the exothermic reaction, and
the resulting process temperature, depend on the oxygen content
within the fuel/oxidizer mixture and can be influenced by
controlling the oxygen content.
[0032] As will become clear below, in particular with reference to
FIGS. 2 and 3, the support structure 3 is preferably designed in
the form of a honeycomb structure with a multiplicity of parallel
through-passages passing through it, a first group 4 of which, as
has been stated, are lined with catalytically active material on
the inner wall. Of course, it is also possible for the support
structure to be designed in other ways, for example in a simple
case by forming a bundle of tubes.
[0033] Upper operating temperature limits, which are in the range
between 700 and 900.degree. C., preferably 750.degree. C., are
imposed by the choice of materials with regard to support structure
and catalyst material. If these temperature limits are exceeded for
process reasons, material degradation or detachment of the catalyst
material from the corresponding support structure is likely, which
limits the operating life of the catalytic converter unit. However,
to maintain an optimum operating temperature, the ratios of the
individual constituents of the fuel/oxidizer mixture which reacts
chemically within the catalytic converter unit, i.e. fuel, oxygen,
CO.sub.2 and water, have to be set in a targeted way to achieve a
desired cooling action.
[0034] Passive cooling by selecting the proportion of the volume
formed by the bypass lines passing through the support structure,
within which no exothermic chemical reactions take place, is also
possible, with the result that the oxidizer mixture which flows
through the bypass lines or the through-passages 5 can be
considered as a cooling flow.
[0035] Immediately after the support structure 3 within the burner
inlet 1, as seen in the direction of flow, the catalyzed first
fuel/oxidizer mixture is mixed with the pure oxidizer mixture which
has been supplied through the through-passages 5, with the result
that the volumetric content of the fuel within the second
fuel/oxidizer mixture which forms in the region 8 of the burner
inlet 1 decreases, so that the second fuel/oxidizer mixture is much
leaner than the first fuel/oxidizer mixture fed to the catalytic
converter unit. The mixing of the two streams is so efficient and
fast that no ignition phenomena occur before complete mixing has
taken place.
[0036] The requirement that the mixing of the catalyzed
fuel/oxidizer mixture which emerges from the catalytic converter
unit and the pure oxidizer mixture supplied via the bypass lines or
through-passages 5 be as effective and fast as possible is derived
from the very high reactivity of the hydrogen contents formed by
the catalytic oxidation which have to be mixed with the oxidizer
mixture supplied.
[0037] Should ignition phenomena nevertheless occur before complete
mixing of the two streams has taken place, they would lead to what
are known as hot spots, which produce a heterogeneous temperature
profile within the region 8 of the burner inlet 1 and would
ultimately lead to local overheating of material at those
components which come into contact with the exhaust-gas streams
formed.
[0038] The aim of rapid mixing downstream of the support structure
2 is to produce a complete, uniformly mixed, lean-depleted,
catalyzed fuel/oxidizer mixture with an oxygen ratio
.lamda..sub.2>1, which is ultimately burnt within a combustion
chamber 9 that adjoins the burner inlet 2.
[0039] The combustion of the lean catalyzed fuel/oxidizer mixture
is typically carried out within an inherently standard premix
burner or as part of catalytic combustion. To explain the latter
combustion variant, a further catalytic converter unit 10, which
initiates the catalytic combustion, is provided upstream of the
entry to the combustion chamber 9.
[0040] During catalytic oxidation of gaseous fossil fuel using a
rich fuel/oxidizer mixture, the method according to the invention
provides for controlled generation of highly reactive hydrogen,
which considerably increases the reactivity of the catalyzed
fuel/oxidizer mixture which forms. The actual combustion of the
catalyzed fuel/oxidizer mixture which has been lean-depleted by the
additional admixing of an oxidizer mixture is effected by the
presence of hydrogen with very short ignition delay times and at
temperatures of less than 1250.degree. C.
[0041] Therefore, the ignition temperature and the lean extinction
temperature within the combustion chamber can be significantly
reduced by the targeted conversion of fossil fuel, preferably
CH.sub.4, into hydrogen and carbon monoxide or carbon
dioxide/steam. With the aid of the method according to the
invention for operating a burner, it is possible to keep the
exhaust-gas temperatures below those which would lead to
destruction of all the components within the oxygen-enriching
device.
[0042] FIG. 2 illustrates an exemplary embodiment for a support
structure 3, which has a multiplicity of through-passages which are
arranged in rows and columns and are rectangular in cross section.
Through-passages 4 which are lined with a catalyst material on the
inner wall and through-passages 5 which consist of chemically
substantially inert material and are designed as bypass lines are
provided in an arrangement of alternating rows. Of course, it is
possible for the cross-sectional shape and arrangement of the
respective through-passages 4 and 5 to be arranged and designed in
an equivalent, alternative three-dimensional ordered pattern, for
example in a honeycomb structure, a checkerboard arrangement or
similar embodiments.
[0043] A flow-guiding means 11, which is connected upstream of the
support structure 3 as seen in the direction of flow and is
illustrated separately from the support structure 3 purely to
provide a better view, is used to spatially separately supply the
respective streams into the through-passages 4 and 5, which have
been divided into groups. Normally, the flow-guiding means 11 is
fixedly joined in a gastight manner directly to the left-hand front
of the support structure 3 facing it as seen in the direction of
flow. The flow means 11 has an arrangement of compartments which is
matched to the arrangement of the through-passages 4 and 5 in rows
within the support structure 3, with this arrangement of
compartments providing inlet side flanks 12, 13 which are open on
alternate sides relative to the direction of flow through the
through-passages 4 and 5 in the support structure 3. For example,
in the exemplary embodiment shown in FIG. 2, it is assumed that the
first fuel/oxidizer mixture 7 is introduced along the inlet side
flanks 12 of the flow-guiding means 11 and is diverted by the
otherwise trapezoidal design of the flow-guiding means 11 toward
the through-passages 4 lined with catalyst material. Alternatively,
it is also possible for fuel and oxidizer mixture to be supplied
separately through the inlet side flanks 12 of the flow-guiding
means 11. In this case, the mixing of fuel and oxidizer mixture
takes place within the flow-guiding means 11, which in the interior
provides suitable means for initiating flow turbulence to achieve
intimate mixing.
[0044] The flow diversion in each case takes place in rows within
the flow-guiding means 11, corresponding to the arrangement of the
through-passages 4 in rows. This ensures that only the
fuel/oxidizer mixture 7 flows through the through-passages 4 lined
with catalyst material. The pure oxidizer mixture is supplied in
the same way via the inlet side flanks 13 of the flow-guiding means
11. The flow of the respective streams which enter via the inlet
side flanks 12, 13 is in each case diverted by a closed side wall,
which lies opposite the open inlet side flanks in each row plane in
the direction of incoming flow and diverts the respective streams
into the direction of passage through the through-passages 4,
5.
[0045] To achieve intimate mixing of the catalyzed fuel/oxidizer
mixture with the pure oxidizer mixture which is as efficient as
possible and commences immediately after the respective streams
have emerged through the support structure 3, before any of the
ignition phenomena can precede complete mixing, the
through-passages 4, 5 are to be arranged as closely adjacent to one
another as possible and are to be provided with the minimum
possible dimensions in cross section. Therefore, during mixing, it
is appropriate to select the mixing length to be as short as
possible, i.e. complete mixing of the streams which emerge from the
through-passages 4, 5 should take place as close as possible to the
emergence of the flow from the support structure 3.
[0046] FIG. 3 provides a variant embodiment of the support
structure 3, which produces particularly effective mixing of the
streams which emerge from the through-passages 4, 5. According to
this variant, the through-passages 4 which are lined with the
catalyst material on the inner wall and the uncoated
through-passages 5 are arranged in a checkerboard pattern. Although
in the exemplary embodiment shown the through-passages only provide
rectangular cross sections, these cross sections may also adopt
different shapes, such as for example hexagonal shapes. To separate
the flow supply between the respective through-passages 4, 5, a
perforated plate 14, which has passage openings 15 corresponding to
the respective through-passages 4, 5, is provided between the
flow-guiding means 11, which is designed identically to that shown
in FIG. 2, and the support structure 3. The perforated plate 14
ensures targeted supply of the fuel/oxidizer mixture exclusively
through the through-passages 4 lined with catalyst material, and
the same correspondingly also applies to the supply of the pure
oxidizer mixture to be fed through the through-passages 5. Once
again, the components illustrated in FIG. 3, comprising
flow-guiding means 11, perforated plate 14 and support structure 3,
are illustrated separately from one another purely to improve the
clarity of the illustration. In a practical embodiment, the three
components are joined to one another in a gastight manner, which
ensures the desired supply of substance flow through the respective
through-passages 4, 5.
[0047] FIGS. 4a-d illustrate details from cross sections through
the support structure 3 which show regions of through-passages 4
lined with catalyst material on the inner wall and through-passages
5 whose passage walls consist solely of the material of the support
structure 3 itself, and in this respect have no catalytic effect on
the stream passing through the through-passages 5. The level of the
catalyzing reactions and the associated release of exothermic
energy within the support structure 3 can be influenced by suitable
selection of the ratio between the catalyzing surface area and the
inert surface areas along the through-passages.
[0048] For example, the exemplary embodiment shown in FIG. 4a shows
a relatively large proportion of the area being formed by
through-passages 4 with catalyst material, particularly since the
through-passages 4 have four micro-passages on the inner wall. An
arrangement of this type produces high catalytic reaction levels,
which lead to increased exothermic reactions and ultimately to
increased production of hydrogen. By contrast, the cross-sectional
arrangement shown in FIG. 4b provides a greater proportion of
through-passages 5 along which the oxidizer mixture is supplied. A
cross-sectional arrangement of this type is suitable for improving
the cooling.
[0049] Finally, if the arrangement of through-passages shown in the
exemplary embodiments illustrated in FIGS. 4c and 4d are compared,
it can be seen that the cross-sectional proportions between the
through-passages lined with catalyst material and the chemically
inert through-passages 5 is the same, but the arrangement shown in
FIG. 4d allows the streams which emerge from the support structure
to be mixed more efficiently than in the case shown in FIG. 4c.
[0050] To summarize, the following statements can be made in
connection with the method according to the invention and the
apparatus required to implement it:
1. The method according to the invention allows stable combustion
of a gaseous fossil fuel using the AZEP principle, forming
exclusively CO.sub.2 and water.
[0051] 2. The targeted production of hydrogen within the catalyzed
fuel/oxidizer mixture considerably reduces the ignition temperature
of the mixture, with the result that further combustion of the
fuel/oxidizer mixture under lean conditions is completely possible
even using conventional premix burners with or without catalyzed
combustion.
[0052] 3. With the aid of the support structure provided within the
burner inlet and the flow-guiding means provided upstream of the
support structure, as seen in the direction of flow, it is possible
to completely and effectively mix the catalyzed fuel/oxidizer
mixture with the pure oxidizer mixture before ignition phenomena
occur.
LIST OF DESIGNATIONS
[0053] 1 Burner inlet [0054] 2 Oxidizer mixture [0055] 3 Support
structure [0056] 4 Through-passages lined with catalyst [0057] 5
Through-passages, bypass line [0058] 6 Fuel feed unit [0059] 7
First fuel/oxidizer mixture [0060] 8 Region within the burner inlet
[0061] 9 Combustion chamber [0062] 10 Catalytic converter unit
[0063] 11 Flow-guiding means [0064] 12, 13 Inlet side flanks [0065]
14 Perforated plate. [0066] 15 Holes
* * * * *