U.S. patent application number 15/123807 was filed with the patent office on 2017-01-19 for device and method for using carbon dioxide originating from a combustion process.
This patent application is currently assigned to Siemens Aktiengesellschaft. The applicant listed for this patent is Siemens Aktiengesellschaft. Invention is credited to Mike Rost, Rudiger Schneider, Henning Schramm, Nicolas Vortmeyer, Gerhard Zimmermann.
Application Number | 20170016355 15/123807 |
Document ID | / |
Family ID | 52727079 |
Filed Date | 2017-01-19 |
United States Patent
Application |
20170016355 |
Kind Code |
A1 |
Rost; Mike ; et al. |
January 19, 2017 |
DEVICE AND METHOD FOR USING CARBON DIOXIDE ORIGINATING FROM A
COMBUSTION PROCESS
Abstract
A device for using carbon dioxide originating from the
combustion of a byproduct has a preparing unit which is connected
to a delivery station for fossil fuels, which has a burner for
combusting a byproduct that is released when the fuel is delivered,
and an exhaust gas line that is connected to the burner. A
depositing device is fluidically connected to the preparing unit
via the exhaust gas line, for carbon dioxide. The depositing device
is fluidically connected to the delivery station to redeliver fuel
via a supply line for carbon dioxide. Such a device allows the
production and the subsequent controlled use of carbon dioxide from
previously unused byproducts in the production of crude oil. A
corresponding method by which carbon dioxide originating from the
combustion of a byproduct is used in a controlled manner, in
particular as part of a fossil fuel extraction process.
Inventors: |
Rost; Mike; (Burgthann,
DE) ; Schneider; Rudiger; (Eppstein, DE) ;
Schramm; Henning; (Hofheim am Taunus, DE) ;
Vortmeyer; Nicolas; (Erlangen, DE) ; Zimmermann;
Gerhard; (Hochstadt/Aisch, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Siemens Aktiengesellschaft |
Munich |
|
DE |
|
|
Assignee: |
Siemens Aktiengesellschaft
Munich
DE
|
Family ID: |
52727079 |
Appl. No.: |
15/123807 |
Filed: |
March 2, 2015 |
PCT Filed: |
March 2, 2015 |
PCT NO: |
PCT/EP2015/054249 |
371 Date: |
September 6, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F23J 15/04 20130101;
F01K 17/04 20130101; Y02E 20/12 20130101; Y02C 20/40 20200801; F23J
2219/40 20130101; F23G 7/06 20130101; Y02C 10/06 20130101; E21B
43/164 20130101; F23J 15/00 20130101; F01K 13/006 20130101 |
International
Class: |
F01K 17/04 20060101
F01K017/04; F23J 15/04 20060101 F23J015/04; F01K 13/00 20060101
F01K013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2014 |
DE |
102014204646.7 |
Claims
1. A device for using carbon dioxide formed in the combustion of a
gaseous by-product, comprising a treatment unit which is
connectable to a recovery site for fossil fuel and having a burner
for combustion of a by-product that is released in the fuel
recovery and having an exhaust gas line that is connected to the
burner, and a carbon dioxide separation device that is
flow-connected via the exhaust gas line to the treatment unit,
wherein the separation device is flow-connectable to the recovery
site for renewed fuel recovery via a feed line for carbon
dioxide.
2. The device as claimed in claim 1, further comprising a fuel feed
line for feeding the by-product which is connected to the burner of
the treatment unit.
3. The device as claimed in claim 1, further comprising an air feed
line for supplying combustion air which is connected to the burner
of the treatment unit.
4. The device as claimed in claim 1, wherein the separation device
comprises an absorber for separating off the carbon dioxide from
the exhaust gas by means of a scrubbing medium, and also a desorber
that is flow-connected to the absorber for releasing the carbon
dioxide from the scrubbing medium.
5. The device as claimed in claim 4, wherein the desorber of the
separation device is flow-connected to the recovery site via the
feed line for carbon dioxide.
6. The device as claimed in claim 1, wherein the exhaust gas line
is heat-connected to a steam generator.
7. The device as claimed in claim 6, wherein the steam generator is
flow-connected to a steam turbine.
8. The device as claimed in claim 7, further comprising a generator
which is connected to the steam turbine.
9. The device as claimed in claim 7, further comprising a steam
circuit of the steam turbine which is heat-connected to the
separation device.
10. The device as claimed in claim 7, wherein the steam turbine is
constructed as a counterpressure turbine.
11. The device as claimed in claim 4, wherein the exhaust gas line
is flow-connected to a feed line of the absorber of the separation
device via a withdrawal line.
12. The device as claimed in claim 1, wherein the exhaust gas line
is flow-connected to the burner of the treatment unit via a return
line.
13. The device as claimed in claim 3, further comprising a heat
exchanger for preheating the combustion air which is connected into
the air feed line.
14. The device as claimed in claim 4, wherein the scrubbing medium
used for separating off the carbon dioxide from the exhaust gas is
an amino acid salt solution.
15. A method for using carbon dioxide formed in the combustion of a
gaseous by-product, the method comprising: wherein feeding a
by-product released from a recovery site in a fuel recovery to a
treatment unit, burning the by-product with feed of air in the
treatment unit, feeding the carbon dioxide-containing exhaust gas
formed in the combustion to a carbon dioxide separation device, and
feeding the carbon dioxide that is separated off from the exhaust
gas in the separation device to the recovery site for renewed fuel
recovery.
16. The method as claimed in claim 15, wherein the carbon dioxide
present in the exhaust gas is separated off from the exhaust gas by
means of a scrubbing medium in an absorber of the separation
device, and wherein the carbon dioxide is released from the
scrubbing medium in a desorber of the separation device that is
flow-connected to the absorber.
17. The method as claimed in claim 15, wherein the carbon dioxide
that is separated off from the exhaust gas in the separation device
is fed to the recovery site proceeding from the desorber.
18. The method as claimed in claim 15, wherein the heat that is
formed in the combustion is removed via a steam generator that is
connected downstream of the combustion, and wherein steam is formed
in the steam generator by the heat formed in the combustion.
19. The method as claimed in claim 18, wherein the steam formed in
the steam generator is expanded in a steam turbine.
20. The method as claimed in claim 19, wherein a generator is
operated by means of the steam turbine.
21. The method as claimed in claim 19, wherein the steam expanded
in the steam turbine is used for separating off the carbon dioxide
from the exhaust gas in the separation device.
22. The method as claimed in claim 19, wherein a counterpressure
turbine is used as steam turbine.
23. The method as claimed in claim 16, wherein a first substream of
the exhaust gas of the combustion is fed via a withdrawal line to
the absorber of the separation device.
24. The method as claimed in claim 15, wherein a second substream
of the exhaust gas of the combustion is fed via a return line to
the combustion of the by-product.
25. The method as claimed in claim 23, wherein the first substream
of the exhaust gas preheats the combustion air before entry into
the absorber.
26. The method as claimed in claim 15, wherein the scrubbing medium
used for separating off the carbon dioxide from the exhaust gas is
an amino acid salt solution.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2015/054249 filed Mar. 2, 2015, and claims
the benefit thereof. The International Application claims the
benefit of German Application No. DE 102014204646.7 filed Mar. 13,
2014. All of the applications are incorporated by reference herein
in their entirety.
FIELD OF INVENTION
[0002] The invention relates to a device for using carbon dioxide
that is formed in the combustion of particularly a gaseous
by-product, in particular in the context of producing a fossil
fuel. In addition, the invention relates to a method for using
carbon dioxide formed in the combustion of particularly a gaseous
by-product.
BACKGROUND OF INVENTION
[0003] The deposits of fossil fuels stored in the ground such as,
for example, natural gas, or in particular oil, which are
obtainable economically with current technology serve as energy
reserves in order to cover the constantly increasing energy
consumption of current times. Oil in this case is used as one of
the most important raw materials for generating electricity, as a
power fuel for vehicles and means of transport, and also as a
starting material for numerous products of the chemical
industry.
[0004] For oil extraction, it is recovered from subterranean
reservoirs. In this case, in principle three recovery phases are
distinguished. Primary recovery denotes the recovery phase in which
the fuel is recovered by the naturally occurring overpressure of
the oil, termed the reservoir pressure.
[0005] If, in the course of the primary oil recovery, the reservoir
pressure falls, in the framework of the second recovery phase,
secondary recovery, water or inert gas can be injected using
injection probes installed by wells, and the reservoir pressure
thus increased again in this manner, up to 40% of the oil present
in total can be recovered.
[0006] The residual increasingly viscous and dense bituminous oil,
however, makes this further recovery difficult. In this case, use
is made of tertiary oil recovery (Enhanced Oil Recovery (EOR)). For
the tertiary oil recovery, large amounts of carbon dioxide
(CO.sub.2) are required which are forced at high pressure into the
oil reservoirs. The injected carbon dioxide dissolves in the oil,
swells it and thus lowers its viscosity, in such a manner that the
oil can more readily flow in the direction of the recovery site or
the recovery well, finally be conveyed with the aid of pumps.
[0007] Possible sources for the carbon dioxide required for the
recovery are, for example, natural reservoirs, exhaust gases of
industrial processes or power plant exhaust gases. Since the carbon
dioxide that is utilizable from these sources, however, is
customarily not present in the concentration required for oil
recovery, a corresponding concentration is necessary. For this
purpose, known methods are available, such as physical or chemical
absorption, adsorption or separation by means of selective
membranes, which, however, are associated with high operational
costs.
[0008] In addition, it is possible to recover carbon dioxide from
fossil fuels by means of the oxyfuel method. In this case, a fuel
is burnt with pure oxygen, wherein an exhaust gas is formed, the
main constituents of which are substantially carbon dioxide and
steam. The carbon dioxide can then be concentrated by condensing
the steam. For use in tertiary oil recovery, the oxyfuel method,
however, is possibly not usable economically.
[0009] In addition, it is necessary to consider that even with a
sufficiently high concentration and the required purity of the
carbon dioxide, the sites where CO.sub.2-rich exhaust gases or
other CO.sub.2 sources are accessible are customarily spatially far
removed from the recovery sites for oil production.
[0010] The supply of carbon dioxide to the corresponding recovery
sites is therefore associated with corresponding additional
complexity and high costs.
SUMMARY OF INVENTION
[0011] A first object of the invention is to specify a device that,
with the lowest possible operating and capital costs, permits the
production of economically usable carbon dioxide.
[0012] A second object of the invention is to specify a method
which uses the advantages of the device and thus permits
corresponding provision of the required carbon dioxide.
[0013] The first object of the invention is achieved according to
the invention by a device for using carbon dioxide formed in the
combustion of particularly a gaseous by-product, comprising a
treatment unit which is connectable to a recovery site and having a
burner for combustion of the by-product that is released in the
fuel recovery and having an exhaust gas line that is connected to
the burner, and also comprising a carbon dioxide separation device
that is flow-connected via the exhaust gas line to the treatment
unit. The separation device is in this case flow-connectable to the
recovery site for renewed fuel recovery via a feed line for carbon
dioxide.
[0014] In a first step, the invention proceeds from the fact that,
in the context of oil recovery, together with the recovered oil,
by-products, in particular gaseous fuel gases, always exit from a
recovery well. Since, however, the costs of transporting these, in
particular gaseous, by-products and/or treatment thereof usually
exceed the expected sales proceeds, the use of the by-products, in
particular the fuel gases, or treatment thereof is usually
dispensed with solely for economic reasons. Instead, the
by-products produced in oil recovery, in the absence of policy
requirements, are usually flared off unused and the resultant
pollutant emissions, such as, in particular carbon dioxide
emissions, into the atmosphere are accepted.
[0015] In a second step, the invention takes into account the fact
that the processes underlying pollutant minimization, in particular
carbon dioxide separation, are already part of intensive research
in other fields. For instance, in particular in the case of
fossil-fuelled power plants for generating electrical energy, more
and more frequently separation devices are being used that permit a
targeted separation of pollutants and carbon dioxide present in
exhaust gases, and thus markedly decrease the atmospheric pollution
(Post-Combustion Capture Process).
[0016] In a third step, the invention recognizes that such a
separation device already tested in power plants is also suitable
for use in oil recovery. Owing to the combination with a suitable
treatment unit, by-products that are produced during oil recovery,
and have to date been unused, can be used in a targeted manner. In
other words, the device permits, in particular, an on-site
production and use of carbon dioxide at the recovery site of the
oil.
[0017] The treatment unit that can be associated with the recovery
site, serves in this case first generating a carbon
dioxide-containing exhaust gas by combustion of the by-products. In
the separation device that is flow-connected to the treatment unit
via an exhaust gas line, the carbon dioxide can be separated off
from the exhaust gas and fed to the recovery site for subsequent
oil recovery. The feed in this case proceeds via a feed line that
represents the flow connection between the separation device and
the recovery site.
[0018] Overall, the use of such a device can markedly improve the
economic efficiency of the oil recovery process. Since the carbon
dioxide separated off from the combustion exhaust gas, in the ideal
case, is produced directly at the site of use and used for oil
recovery, the costs of providing and transporting carbon dioxide
are absent. In addition, by the targeted treatment of the exhaust
gas from the combustion of the by-products produced in the oil
recovery, which exhaust gas is not technically utilizable to date,
unwanted emissions of carbon dioxide into the atmosphere may be
prevented or at least markedly decreased. The recovery site in this
case, depending on the recovery operation, can have one or more
recovery wells and corresponding injection wells.
[0019] Advantageously, a fuel feed line for feeding the by-products
is connected to the burner of the treatment unit. Thus, a fuel gas
exiting from the recovery site, or from a corresponding recovery
well of the recovery site, can be fed to the burner and there burnt
with formation of a carbon dioxide-containing exhaust gas.
[0020] The combustion proceeds in this case in particular
atmospherically, with supply of air, for which purpose an air feed
line for supplying combustion air is connected to the burner of the
treatment unit. In particular, a gas mixer can further be connected
into the air feed line, which gas mixer serves for setting the
concentration of the carbon dioxide in the combustion exhaust
gas.
[0021] In principle, for separating off the carbon dioxide from the
exhaust gas, all methods are usable that have sufficiently high
selectivity and a low energy requirement. Thus, in principle,
absorption and adsorption processes, or else the use of membranes,
would be conceivable.
[0022] Particularly, the carbon dioxide is separated off
wet-chemically. For this purpose, the separation device comprises
an absorber for separating off the carbon dioxide from the exhaust
gas by means of a scrubbing medium, and also a desorber that is
flow-connected to the absorber for releasing the carbon dioxide
from the scrubbing medium. In the absorber, the carbon dioxide is
removed from the exhaust gas by absorption in the scrubbing medium.
In order to remove the absorbed carbon dioxide from the scrubbing
medium and thus produce carbon dioxide, the loaded scrubbing medium
is fed to the desorber. For this purpose the absorber is
expediently flow-connected via a withdrawal line to a feed line of
the desorber. In the desorber, the absorbed carbon dioxide is
released from the scrubbing medium by thermal desorption and the
regenerated scrubbing medium is fed back to the absorber for
repeated absorption of carbon dioxide. For this purpose, the
desorber is advantageously flow-connected via a withdrawal line to
a feed line of the absorber.
[0023] The desorbed carbon dioxide, after it is separated off, can
be used for oil recovery. For this purpose, the desorber of the
separation device is particularly advantageously flow-connected to
the recovery site via the feed line for carbon dioxide. Thus, the
carbon dioxide that is released can be used on site for oil
recovery. Expediently, the feed line for the carbon dioxide is
connected to the top of the desorber.
[0024] In a particularly advantageous embodiment, the exhaust gas
line is heat-connected to a steam generator. The steam generator is
expediently connected into a steam circuit. The steam circuit, also
termed water-steam circuit, serves for removing heat formed during
the combustion. The hot combustion exhaust gas in this case is
conducted past the steam generator and heats in this case water
circulating in the steam circuit with formation of steam. The
exhaust gas itself cools and can then be fed to the separation
device to separate off the carbon dioxide that is present in the
exhaust gas.
[0025] To use the resultant steam, it is, in particular,
advantageous when the steam generator is flow-connected to a steam
turbine. In other words, the steam turbine is integrated into the
steam circuit. Since, in the combustion of the exhaust gas, more
heat is produced than is originally necessary for the production of
steam, in particular for the production of heating steam for a
reboiler, the steam generator can advantageously be designed in
such a manner that it is suitable for generating a higher-grade
steam of high pressure which can then be expanded in the steam
turbine and used for generating electrical power.
[0026] To generate the electrical power, expediently, a generator
is connected to the steam turbine. The electrical power can then be
used to cover the electrical requirement of the separation device
itself. Alternatively, it can be used for compression of the carbon
dioxide produced or fed into the general electric consumer
grid.
[0027] It is particularly advantageous when the steam turbine in
the steam circuit is heat-connected to the separation device. The
steam that is expanded in the steam turbine to a predetermined
pressure and temperature level can thus be used to support the
desorption process. For this purpose, the steam turbine is
expediently constructed as a counterpressure turbine. Alternative
embodiments of the steam turbine include, for example, familiar
condensation turbines in combination with a corresponding heating
steam take-off at the steam turbine or at the steam generator.
[0028] In an embodiment of the heat connection of the steam turbine
to the separation device in the steam circuit, the steam expanded
in the steam turbine is fed via a steam line of the steam circuit
to a reboiler. The reboiler, which is expediently connected to the
desorber of the separation device functions in this case as a
condenser for the steam circuit. Within the reboiler, the steam is
conducted through a heat exchanger having scrubbing medium taken
off from the desorber and condensed. The condensed steam can then
be fed back to the steam generator via a condensate line of the
steam circuit that is flow-connected to the steam line, and there,
again used for heat removal from the combustion exhaust gas and at
the same time for operating the steam turbine.
[0029] Expediently, the exhaust gas line is flow-connected to a
feed line of the absorber of the separation device via a withdrawal
line. Thus, the carbon dioxide present in the combustion exhaust
gas, after it is cooled by the steam generator, can be removed from
the exhaust gas by an absorption-desorption process within the
separation device, and then fed to the oil recovery. Expediently,
in this case, a first substream of 50% to less than 100% of the
total combustion exhaust gas is fed to the absorber.
[0030] Particularly, the exhaust gas line is flow-connected to the
burner via a return line. Via the flow connection, a substream of
the exhaust gas, after it passes through the steam generator, is
fed back to the burner. The recirculation in this case proceeds
advantageously via a gas mixer connected into the air feed line and
permits a recirculation of the combustion exhaust gas around the
steam generator. Such a recirculation permits the targeted setting
of the concentration of the carbon dioxide which otherwise could
only be set via the air excess in the combustion, that is to say
via the ratio of the actual amount of air to the amount of air
required for stochiometric combustion. The desired high carbon
dioxide concentration would be ensured in this case only by a
slight air excess. However, with a slight air excess, to ensure a
stochiometric combustion, high combustion temperatures are
necessary. For corresponding combustion temperatures, at all
events, the required hot gas parts are only available at very high
costs and would require complex cooling. In addition, at high
combustion temperatures, the concentration of nitrogen oxides in
the exhaust gas increases.
[0031] Thanks to the recirculation, simple components can be made
use of and owing to the lower combustion temperature, unwanted
increase in harmful emissions of nitrogen oxides and carbon
monoxide in the combustion can also be prevented. In other words,
owing to the exhaust gas recirculation, the exhaust gas temperature
can be held at a technically manageable level, with simultaneously
an effective increase in the carbon dioxide concentration in the
combustion exhaust gas.
[0032] The fraction of the substream which is reused via the return
line for combustion of the influent gaseous by-product, that is to
say the fuel gas, is in this case advantageously in a range from
more than 0% to 50% of the total combustion exhaust gas.
[0033] It is additionally advantageous when a heat exchanger for
preheating the combustion air is connected into the air feed line.
For this purpose, the first substream of the heated exhaust gas,
after passage through the steam generator, is passed via the heat
exchanger. The substream and the combustion air are conducted in
heat exchange here, wherein the combustion air takes up the waste
heat of the exhaust gas and is preheated. The first exhaust gas
substream fed to the separation device is in this case
advantageously precooled to the absorption temperature necessary in
the absorber.
[0034] Advantageously, the scrubbing medium used for separating off
the carbon dioxide from the exhaust gas is an amino acid salt
solution. An aqueous amino acid salt solution, and in particular a
potassium-containing aqueous amino acid salt solution is expedient
in this case. The use of in particular an aqueous amino acid salt
solution is suitable in this case, in particular, since an amino
acid salt has a negligibly low vapor pressure and does not vaporize
even at high temperatures. As a result, in particular unwanted
emissions into the atmosphere are avoided, and in addition, a
decrease in the concentration of the active component of the
scrubbing medium is prevented.
[0035] The second object of the invention is achieved according to
the invention by a method for using carbon dioxide formed in the
combustion of particularly a gaseous by-product, wherein a
by-product released from a recovery site in a fuel recovery is fed
to a treatment unit, wherein the by-product is burnt with feed of
air in the treatment unit, wherein the carbon dioxide-containing
exhaust gas formed in the combustion is fed to a carbon dioxide
separation device, and wherein the carbon dioxide that is separated
off from the exhaust gas in the separation device is fed to the
recovery site for renewed fuel recovery.
[0036] The carbon dioxide which is produced by means of such a
method can be used in a simple and inexpensive manner for oil
recovery. By the targeted utilization of the by-products that are
unused to date and arise during oil recovery, in addition, a
contribution to climate protection can be achieved by preventing
the carbon dioxide being emitted into the atmosphere.
[0037] Further advantageous embodiments result from the subclaims
directed to the method. Said advantages of the device and
advantageous developments thereof can be applied as appropriate to
the method and developments thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Hereinafter, an exemplary embodiment of the invention will
be described in more detail with reference to a drawing.
[0039] FIG. 1 shows a device for using carbon dioxide according to
an embodiment of the invention.
DETAILED DESCRIPTION OF INVENTION
[0040] FIG. 1 shows a device 1 for using carbon dioxide formed in
the combustion of in particular a gaseous by-product of oil
recovery. The device 1 comprises a treatment unit 3 having a burner
5 and a steam generator 7. In addition, the device 1 comprises a
carbon dioxide separation device 9 that is flow-connected to the
treatment unit 3. In the separation device 9, carbon dioxide that
is formed in the context of the combustion is separated off from
the exhaust gas by means of a scrubbing medium. For this purpose,
the separation device 9 comprises an absorber 11 and a desorber 13
that is flow-connected thereto.
[0041] The device 1 permits an on-site production and subsequent
utilization of carbon dioxide in tertiary oil recovery. In tertiary
oil recovery, the oil that is to be recovered is produced by
injecting carbon dioxide into corresponding wells of a recovery
site 15. In addition to the oil, in this case, fuel gases that are
no longer technically utilizable, that is to say gaseous
by-products, are released. Instead of flaring off these fuel gases
as is usual to date, the fuel gas stream is fed via a fuel feed
line 17 to the burner 5 of the treatment unit 3. In the burner 5,
the fuel gas is burnt atmospherically with feed of air. The air is
fed to the burner 5 via an air feed line 19.
[0042] The burner 5 is heat-coupled to the steam generator 7 via an
exhaust gas line 21 connected to the burner. The exhaust gas formed
in the combustion is conducted via a heat exchanger 23 of the steam
generator 7, via which the waste heat formed in the combustion can
be taken off. The steam generator 7 is connected into a steam
circuit 25, or water-steam circuit, in which water and/or steam
circulate. The circulating water is heated in the steam generator 7
with formation of steam. In order to utilize the steam, the steam
generator 7 is flow-connected to a steam turbine 27. The steam
turbine 27 is operated by means of the steam generated in the steam
generator 7. The steam is expanded within the steam turbine 27 and
operates a generator 29 that provides electric power which is used
for covering the electrical requirement of the separation device 9
itself.
[0043] The steam turbine 27 used for expanding the steam is in the
present case constructed as a counterpressure turbine. The
counterpressure turbine 27 expands the steam to a pressure and
temperature level required for separating off the carbon dioxide in
the separation device 9. The steam turbine 27 is heat-connected to
a reboiler 31 in the steam circuit 25, which reboiler is arranged
as bottoms evaporator at the bottom 33 of the desorber 13. The
expanded steam flows from the steam turbine 27 via a steam line 35
of the steam circuit 25 to the reboiler 31. The reboiler 31 acts in
this case as a condenser for the steam circuit 25. The steam
exiting from the steam turbine 27 gives off its heat to the
scrubbing medium circulating in the reboiler 31 and is itself
condensed in this case. The condensed steam is fed back to the
steam generator 7 via a condensate line 37 that is flow-connected
to the steam line 35 and at the steam generator takes up--with
cooling of the combustion exhaust gas and formation of new
steam--the heat provided in the steam generator 7. The heat
withdrawn in the reboiler 31 is used for desorption of the carbon
dioxide from the scrubbing medium in the desorber 13.
[0044] In order to separate the carbon dioxide from the exhaust
gas, the treatment unit 3 is flow-coupled to the separation device
9 via the exhaust gas line 21. A first substream 39 of the exhaust
gas is in this case fed to the absorber 11 via the connection of a
withdrawal line 41 to a feed line 43 of said absorber 11. In this
case, the exhaust gas substream 39 passes through a heat exchanger
45 which further precools the exhaust gas substream 39 before the
entry into the absorber 11. At the same time, the combustion air in
the air feed line 19 is in this way preheated before the entry into
the burner 5.
[0045] Within the absorber 11, the first substream 39 of the
exhaust gas, in the present case 50% of the total exhaust gas
stream, is contacted with the scrubbing medium and the carbon
dioxide present in the exhaust gas is absorbed in the scrubbing
medium.
[0046] The scrubbing medium used is in the present case an aqueous
potassium-containing amino acid salt solution. The loaded scrubbing
medium, for release of the carbon dioxide, flows into the desorber
13, where the carbon dioxide is thermally desorbed. The carbon
dioxide is taken off at the top 47 of the desorber, optionally
compressed and finally fed via a feed line 49 to the recovery site
15 for renewed fuel recovery.
[0047] A second substream 51 of the exhaust gas, in the present
case 50% of the entire exhaust gas stream, after it passes through
the steam generator 7 and after corresponding precooling in the
context of an exhaust gas recirculation 53, is fed back via a
return line 55 into the burner 7. In the exhaust gas recirculation
53, the second substream 51, before the entry into the burner, is
further fed to a gas mixer 57, into which the combustion air also
flows via the feed line.
[0048] Such an exhaust gas recirculation 53 ensures a sufficiently
high carbon dioxide concentration in the exhaust gas, which through
sole combustion of the exhaust gas with air could only be set via
the ratio of the actual amount of air to the amount of air required
for stochiometric combustion. In addition, thanks to the exhaust
gas recirculation 53, the exhaust gas temperature may be kept at a
technically manageable level.
* * * * *