U.S. patent application number 11/756365 was filed with the patent office on 2007-12-06 for process and device for feeding oxidizing agent into a combustion system.
This patent application is currently assigned to Linde Aktiengesellschaft. Invention is credited to Gerhard Beysel, Klaus Ohlig.
Application Number | 20070281255 11/756365 |
Document ID | / |
Family ID | 38512389 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070281255 |
Kind Code |
A1 |
Beysel; Gerhard ; et
al. |
December 6, 2007 |
PROCESS AND DEVICE FOR FEEDING OXIDIZING AGENT INTO A COMBUSTION
SYSTEM
Abstract
A process and device for feeding oxygen-containing gas into the
firebox of a combustion system is disclosed. A sub-quantity of the
flue gas stream exiting from the combustion system (recycle gas) is
subjected to pressure elevation and subsequently recycled to the
firebox. An oxygen-containing gas which is present at a
sufficiently high pressure is added to the recycle gas downstream
of the pressure elevation.
Inventors: |
Beysel; Gerhard;
(Wolfratshausen, DE) ; Ohlig; Klaus; (Gauting,
DE) |
Correspondence
Address: |
CROWELL & MORING LLP;INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
Linde Aktiengesellschaft
Wiesbaden
DE
|
Family ID: |
38512389 |
Appl. No.: |
11/756365 |
Filed: |
May 31, 2007 |
Current U.S.
Class: |
431/9 ;
423/115 |
Current CPC
Class: |
Y02E 20/34 20130101;
Y02E 20/344 20130101; F23C 9/00 20130101 |
Class at
Publication: |
431/009 ;
423/115 |
International
Class: |
F23M 3/00 20060101
F23M003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 1, 2006 |
DE |
10 2006 025 681.6 |
Claims
1. A process for feeding oxygen-containing gas into a firebox of a
combustion system, a sub-quantity of a flue gas stream exiting from
the combustion system as a recycle gas is subjected to a pressure
elevation and subsequently recycled to the firebox, wherein an
oxygen-containing gas which is present at a sufficiently high
pressure is added to the recycle gas downstream of the pressure
elevation.
2. The process according to claim 1, wherein the oxygen-containing
gas is air and/or oxygen and/or nitrogen-enriched oxygen.
3. The process according to claim 2, wherein the oxygen or
nitrogen-enriched oxygen is obtained from an air fractionation
system.
4. The process according to claim 1, wherein the recycle gas is
cleaned flue gas.
5. The process according to claim 1, wherein the oxygen-containing
gas is fed into the firebox of a steam generator of a thermal power
station.
6. A device for feeding oxygen-containing gas into a firebox of a
combustion system, wherein a sub-quantity of a flue gas stream
exiting from the combustion system as a recycle gas is subjected to
a pressure elevation and subsequently recycled to the firebox,
wherein an oxygen-containing gas which is present at a sufficiently
high pressure is fed via a mixing system to the recycle gas
downstream of the pressure elevation.
7. The device according to claim 6, wherein in an immediate
vicinity of the combustion system, an air fractionation system is
provided from which the oxygen-containing gas which is oxygen or
nitrogen-enriched oxygen is obtained at the sufficiently high
pressure.
8. The device according to claim 7, wherein the air fractionation
system is a cryogenic air fractionator or a pressure-swing
adsorption system (PSA).
9. The device according to claim 6, wherein the combustion system
is a steam generator of a thermal power station.
10. A method for feeding an oxygen-containing gas into a firebox of
a combustion system, comprising the steps of: removing a quantity
of a flue gas exiting from the combustion system; adding air to the
quantity of the flue gas to form an air/flue gas stream;
compressing the air/flue gas stream; adding a gas containing oxygen
to the air/flue gas stream to form the oxygen-containing gas; and
supplying the oxygen-containing gas to the firebox.
11. The method according to claim 10, wherein the air/flue gas
stream is compressed from a pressure which is lower than an
atmospheric pressure to a pressure that is higher than the
atmospheric pressure.
12. The method according to claim 10, further comprising the step
of removing ash and water from the flue gas exiting from the
combustion system prior to the step of removing the quantity of the
flue gas.
13. An apparatus for feeding an oxygen-containing gas into a
firebox of a combustion system, comprising: a recycle line, wherein
a quantity of a flue gas exiting from the combustion system is
removed; an air supply line coupled to the recycle line, wherein
air is added to the quantity of the flue gas by the air supply line
to form an air/flue gas stream; a compressor, wherein the
compressor compresses the air/flue gas stream; an oxygen containing
gas supply line, wherein the oxygen containing gas supply line adds
a gas containing oxygen to the compressed air/flue gas stream to
form the oxygen-containing gas; and an oxygen-containing gas supply
line, wherein the oxygen-containing gas supply line supplies the
oxygen-containing gas to the firebox.
14. The apparatus according to claim 13, wherein the
oxygen-containing gas supply line is coupled to an air
fractionator.
15. The apparatus according to claim 13, further comprising a flue
gas cleaning system coupled to the firebox in a downstream flow
direction of the flue gas.
16. The apparatus according to claim 15, wherein the flue gas
cleaning system removes ash and water from the flue gas.
17. The apparatus according to claim 16, wherein the recycle line
is disposed in the downstream flow direction from the flue gas
cleaning system.
18. The apparatus according to claim 13, wherein the compressor
compresses the air/flue gas stream from a pressure which is lower
than an atmospheric pressure to a pressure that is higher than the
atmospheric pressure.
Description
[0001] This application claims the priority of German Patent
Document No. 10 2006 025 681.6, filed Jun. 1, 2006, the disclosure
of which is expressly incorporated by reference herein.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] The invention relates to a process for feeding
oxygen-containing gas into the firebox of a combustion system, a
sub-quantity of the flue gas stream exiting from the combustion
system (recycle gas) being subjected to pressure elevation and
subsequently recycled to the firebox, and also to a device for
carrying out the process.
[0003] The flue gases formed in the combustion of carbonaceous
energy sources such as coal or petroleum contain, in addition to
water and carbon dioxide, a number of substances harming the
environment, such as nitrogen oxides (NO.sub.x) and sulphur dioxide
(SO.sub.2), for example. In industrial energy generation plants,
therefore, inter alia flue gas cleaning installations are connected
downstream of the combustion systems, in order to decrease the
pollutant fraction in the flue gas. Flue gas cleaning, such as
desulphurization, dedusting and denitrification, for example, is
included among the secondary measures which make the entire energy
conversion process more environmentally friendly. However, measures
can also be taken to act in a primary manner, in order to
substantially minimize the formation of the corresponding
pollutants as early as in the combustion process.
[0004] To comply with the progressively lower emitting pollutant
values and to lower the expense for secondary measures, primary
measures for avoiding pollutant formation are becoming increasingly
important. In the avoidance of dust formation, these principally
consist in the combustion conditions, and in the reduction of
sulphur-containing pollutants, in the selection of the fuels.
[0005] Great efforts for reducing NO.sub.x emissions are also being
taken. Seven different nitrogen oxides are known of which nitrogen
monoxide (NO) and nitrogen dioxide (NO.sub.2) are the most stable,
and therefore essentially make up the NO.sub.x load of flue gases.
Nitrogen monoxide is principally formed solely from the nitrogen of
the fed combustion air at temperatures above 1000.degree. C. and at
sufficiently high oxygen concentration. Since the combustion air
consists of 78% nitrogen, the nitrogen oxides formed from
atmospheric nitrogen make up a majority of the pollutant load.
Depending on the fuel and type of firing, the NO.sub.x content in
the flue gas is between 500 and 2000 mg/m.sub.N3.
[0006] In the laid-open application DE 10356701, a process is
described for combustion of fossil fuels in a steam generator. The
combustion air here is replaced by an oxidizing agent which is
essentially composed of carbon dioxide (CO.sub.2) which is
separated off from the flue gas formed in the combustion, and
oxygen, and the combustion is carried out with the exclusion of
air. Because of the substantial lack of nitrogen in the oxidizing
agent, the flue gases only contain the amounts of NO.sub.x which
are formed from the nitrogen bound in the fuel, and consist
virtually exclusively of water and CO.sub.2.
[0007] The decisive reason for replacing the combustion air by an
oxidizing agent which is essentially composed of carbon dioxide
(CO.sub.2) and oxygen is, however, the possibility of being able to
separate off readily, after combustion with fossil fuels, the
CO.sub.2 by condensation of water and to sequester it. This aspect
is increasingly gaining importance, since in the context of
worldwide climate change, the CO.sub.2 emissions which are formed
by processing non-renewable energy sources must be reduced. The
Kyoto protocol controls the permissible CO.sub.2 emissions of the
individual member countries and specifies the emission reductions
to be achieved in forthcoming years.
[0008] The object of the present invention is to specify a process
and also a device of the type described at the outset which make it
possible to feed oxygen-containing gas with low energy and control
expenditure into the firebox of a combustion plant.
[0009] This object is achieved according to the invention in terms
of the process by the fact that an oxygen-containing gas which is
present at a sufficiently high pressure is added to the recycle gas
downstream of the pressure elevation.
[0010] The pressure of an oxygen-containing gas is considered to be
"sufficiently high" in this case when it is at least sufficiently
above the pressure which the recycle gas has downstream of the
pressure elevation such that solely owing to the difference between
the two gas pressures the maximum amount of oxygen-containing gas
required for the combustion process flows into the recycle gas and
is homogeneously mixed with this, and with gas streams possibly fed
to the recycle gas at other points.
[0011] In order to be able to feed the correct amount of an
oxygen-containing gas which is present at a sufficiently high
pressure to the combustion system in any operating state, one
embodiment of the process according to the invention provides that
the oxygen-containing gas is conducted via a throttling element
which can be set in a logical manner, a pressure drop being
generated via the throttling element which is of a size such that
the oxygen-containing gas flows in the correct amount into the
recycle gas and is homogeneously mixed with this, and with gas
streams possibly fed to the recycle gas stream at other points.
[0012] An oxygen-containing gas which is present at a pressure
which is equal to or lower than the "sufficiently high pressure" is
according to the invention added to the recycle gas upstream of the
pressure elevation. If appropriate, the pressure of the
oxygen-containing gas is increased or reduced in order to achieve
the oxygen-containing gas flowing into the recycle gas in the
amount required for the combustion process, and being mixed with
it.
[0013] As oxygen-containing gases, according to the invention air
and/or oxygen and/or nitrogen-enriched oxygen are introduced into
the recycle gas, preferably homogeneously mixed with it, which is
subsequently introduced into the firebox.
[0014] In a further development of the process of the invention, it
is proposed that oxygen or nitrogen-enriched oxygen is fed from an
air fractionation system which is expediently operated in the
immediate vicinity of the combustion system.
[0015] Preferably, the process of the invention is used for
operating a combustion system in which the flue gas is cleaned of
ash and water before a part of the flue gas is recycled as recycle
gas.
[0016] Particularly preferably, the combustion system is the steam
generator of a thermal power station.
[0017] The object in question is achieved according to the
invention in terms of the device by the fact that an
oxygen-containing gas which is present at a sufficiently high
pressure can be fed via a mixing system to the recycle gas
downstream of the pressure elevation.
[0018] Preferably, the mixing system has at least connections for
the oxygen-containing gas and recycle gas, and at least one outlet
from which can be taken off a substantially homogeneous gas mixture
consisting of the oxygen-containing gas, recycle gas and any gas
streams fed to the recycle gas stream at other points.
[0019] Particularly preferably, the connections to the mixing
system are positioned with respect to one another in such a manner
that an at least approximately homogeneous mixing of the media
respectively introduced there among one another is ensured. Via
suitable positioning of the connections, the flow behavior of the
incoming gases can be influenced, as a result of which the mixing
can be controlled. Mixing chambers have proved particularly
advantageous, for example, which have connections which effect
tangential inflow of gases.
[0020] An expedient embodiment of the device according to the
invention provides that, in the immediate vicinity of the
combustion system, an air fractionation system is arranged from
which an oxygen-containing gas which is oxygen or nitrogen-enriched
oxygen can be obtained at a sufficiently high pressure. Preferably,
the air fractionation system is a cryogenic air fractionator or a
pressure-swing adsorption system (PSA).
[0021] In order to be able to add oxygen-containing gas to the
recycle gas at any time in the amount required for the combustion
process, in the flow path of the oxygen-containing gas, a suitable
throttling system is provided which expediently can be set in such
a manner that the oxygen-containing gas, on its flow through the
throttling system, at all times experiences a suitably high
pressure drop.
[0022] A preferred embodiment of the device according to the
invention provides that the combustion system is the steam
generator of a thermal power station.
BRIEF DESCRIPTION OF THE DRAWING
[0023] The invention will be described in more detail hereinafter
with reference to an example shown diagrammatically in the FIGURE,
in which a recycle gas is mixed with air and oxygen to give an
oxidizing agent and recirculated to the combustion process.
DETAILED DESCRIPTION OF THE DRAWING
[0024] In the firebox F of a combustion system V, by combustion of
a fuel fed via line 1, a flue gas is generated, the sensible heat
of which is for the most part utilized in a following process which
is not shown. The cooled flue gas is taken off from the combustion
system via line 2 and introduced into the flue gas cleaning system
R from which, cleaned of ash and water, it is removed via line 3. A
part of the ash- and water-free flue gas subsequently flows via
line 4 to a flue gas treatment and CO.sub.2 sequestration (not
shown), while the remaining residue is recycled via line 5 as
recycle gas upstream of the combustion system. Owing to the
pressure drops in the combustion system, the flue gas cleaning
system and the piping, the recycle gas, upstream of the compressor
G, is at a pressure which is lower than atmospheric pressure. Via
line 6, an air stream, the magnitude of which is controlled via the
adjustable control element a, is introduced into the recycle gas
stream 5 upstream of the compressor G. The gas stream thus
generated which consists of air and recycle gas is introduced into
the compressor G via line 7, where it experiences pressure
elevation to a value which is markedly higher than atmospheric
pressure and is passed on via line 8.
[0025] In the air fractionator L, oxygen is generated at a pressure
which is higher than the pressure of the gas stream consisting of
air and recycle gas in line 8. Via line 9 an oxygen stream, the
magnitude of which is controlled via the adjustable control element
b, is passed from the air fractionator L and introduced into the
gas stream consisting of air and recycle gas downstream of the
compressor G. The gas stream thus generated is fed via line 10 to
the combustion system V, a substantially homogeneous gas mixture
being generated which is introduced as oxidizing agent into the
firebox F.
[0026] 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.
* * * * *