U.S. patent application number 13/425567 was filed with the patent office on 2012-09-27 for method and device for treating a carbon dioxide-containing gas stream.
This patent application is currently assigned to LINDE AKTIENGESELLSCHAFT. Invention is credited to Roland RITTER, Dirk Spenner.
Application Number | 20120240616 13/425567 |
Document ID | / |
Family ID | 45877940 |
Filed Date | 2012-09-27 |
United States Patent
Application |
20120240616 |
Kind Code |
A1 |
RITTER; Roland ; et
al. |
September 27, 2012 |
METHOD AND DEVICE FOR TREATING A CARBON DIOXIDE-CONTAINING GAS
STREAM
Abstract
The invention relates to a method and an apparatus for treating
a carbon dioxide-containing gas stream. Precompressed raw gas
stream (1) is partially liquefied in a cryogenic carbon dioxide
purification stage (2, 3, 4). Part of the resultant liquid is used
to obtain a gas stream having an elevated carbon dioxide content
(7). From the non-liquefied raw gas, a gas stream having a reduced
carbon dioxide content is obtained. This vent gas stream is
expanded and the refrigeration generated is recovered for cooling
the raw gas stream. The carbon dioxide gas stream is compressed (8)
to a final pressure and fed to further utilization and/or storage.
Another part of the liquid from the cryogenic carbon dioxide
purification stage is fed in a liquid phase (9) to further
utilization and/or storage (10).
Inventors: |
RITTER; Roland; (Dresden,
DE) ; Spenner; Dirk; (Kesselsdorf, DE) |
Assignee: |
LINDE AKTIENGESELLSCHAFT
Munchen
DE
|
Family ID: |
45877940 |
Appl. No.: |
13/425567 |
Filed: |
March 21, 2012 |
Current U.S.
Class: |
62/606 ;
62/617 |
Current CPC
Class: |
F25J 2270/02 20130101;
F25J 2290/62 20130101; F25J 2235/80 20130101; Y02C 20/40 20200801;
F15B 15/10 20130101; F25J 3/067 20130101; F25J 2215/04 20130101;
F25J 2230/32 20130101; F25J 2210/70 20130101; F25J 2220/82
20130101; Y02C 10/12 20130101; F25J 2230/80 20130101; F25J 2230/30
20130101; F25J 2270/06 20130101 |
Class at
Publication: |
62/606 ;
62/617 |
International
Class: |
F25J 1/00 20060101
F25J001/00; F25J 3/08 20060101 F25J003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2011 |
DE |
102011014 678.4 |
Claims
1. A method for treating a carbon dioxide-containing gas stream
comprising: partially liquefying precompressed raw carbon
dioxide-containing gas stream in a cryogenic carbon dioxide
purification stage, removing from said cryogenic carbon dioxide
purification stage a liquid stream having an elevated carbon
dioxide content and a gas stream having a reduced carbon dioxide
content, reevaporating a first portion of the liquid stream having
an elevated carbon dioxide content to obtain a gas stream having an
elevated carbon dioxide content, expanding the gas stream having a
reduced carbon dioxide content in at least one expansion turbine
and recovering the resultant refrigeration generated in this
expansion for cooling the precompressed raw carbon
dioxide-containing gas stream, compressing the gas stream having an
elevated carbon dioxide content to a final pressure, and feeding
the resultant compressed gas stream having an elevated carbon
dioxide content to further utilization and/or storage, wherein a
second portion of the liquid stream having an elevated carbon
dioxide content removed from said cryogenic carbon dioxide
purification stage is fed in a liquid phase to further utilization
and/or storage.
2. The method according to claim 1, wherein said precompressed raw
carbon dioxide-containing gas stream is a raw gas stream form a
large-scale furnace plant.
3. The method according to claim 1, wherein the second portion of
the liquid stream having an elevated carbon dioxide content is 5 to
25% of the total liquid removed from the cryogenic carbon dioxide
purification stage.
4. The method according to claim 3, wherein the second portion of
the liquid stream having an elevated carbon dioxide content is 10
to 15% of the total liquid removed from the cryogenic carbon
dioxide purification stage.
5. The method according to claim 1, wherein the second portion of
the liquid stream having an elevated carbon dioxide content is
introduced into the gas stream having an elevated carbon dioxide
content after compression of the second portion of the liquid
stream having an elevated carbon dioxide content to the final
pressure.
6. The method according to claim 5, wherein the second portion of
the liquid stream is compressed to the final pressure by way of a
liquid pump before it is introduced into the gas stream having an
elevated carbon dioxide content.
7. The method according to claim 1, wherein said second portion of
the liquid stream having an elevated carbon dioxide content is
temporarily stored in a liquid gas tank for further use.
8. The method according to claim 3, said second portion of the
liquid stream having an elevated carbon dioxide content is used as
transport medium for the pneumatic transport of feedstocks.
9. An apparatus for treating a carbon dioxide-containing gas
stream, said apparatus comprising: a carbon dioxide purification
appliance comprising an inlet for introducing a precompressed raw
carbon dioxide-containing gas stream, an outlet line for removal of
a gas stream having an elevated carbon dioxide content and another
outlet line for removal of a gas stream having a reduced carbon
dioxide content, said outlet line for removal of a gas stream
having an elevated carbon dioxide content being connected via a
final compressor to a utilization appliance and/or repository, said
another outlet line for removal of a gas stream having a reduced
carbon dioxide content being connected to at least one expansion
turbine comprising an outlet line for removal of at least partially
expanded gas stream having a reduced carbon dioxide content which
is connected to an inlet of a heat-exchange appliance, and said
heat exchange appliance further having inlets for introduction of
said precompressed raw gas stream and said gas stream having an
elevated carbon dioxide content, wherein said carbon dioxide
purification appliance additionally comprises an outlet line for a
liquid stream having an elevated carbon dioxide content, which
bypasses said heat-exchange appliance and said final compressor,
and is connected directly to a utilization appliance and/or storage
appliance for liquid having an elevated carbon dioxide content.
10. The apparatus according to claim 9, wherein said outlet line
for a liquid stream having an elevated carbon dioxide content
comprises a liquid pump and, downstream of said final compressor,
outlet line for a liquid stream having an elevated carbon dioxide
content communicates with said the outlet line for removal of a gas
stream having an elevated carbon dioxide content being.
Description
SUMMARY OF THE INVENTION
[0001] The invention relates to a method for treating a carbon
dioxide-containing gas stream (raw gas stream), in particular a
carbon dioxide-containing gas from a large-scale furnace plant. The
precompressed raw gas stream is partially liquefied in a cryogenic
carbon dioxide purification stage, and the liquid is separated off
from which a gas stream having an elevated carbon dioxide content
(carbon dioxide gas stream) is obtained by reevaporation. In
addition, a gas stream having a reduced carbon dioxide content
(vent gas stream) is obtained from the non-liquefied raw gas. This
vent gas stream is expanded in at least one expansion turbine and
the refrigeration generated in this process is recovered for
cooling the raw gas stream. The carbon dioxide gas stream is
compressed to a final pressure and fed to further utilization
and/or storage. The invention also relates to an apparatus for
carrying out the above-described method.
[0002] Carbon dioxide-containing gas streams are produced in all
large-scale furnace plants which are operated with fossil fuels
such as coal, oil or natural gas. These include, in particular,
power plants, but also industrial furnaces, steam kettles and
similar large-scale thermal plants for power and/or heat
generation. In addition, carbon dioxide-containing gas streams are
also formed in process plants of the chemical or petrochemical
industry, such as cracking furnaces of olefin plants or steam
reformers of synthesis gas plants. Owing to the harmful climatic
effect of carbon dioxide gas, solutions are being sought in order
to decrease the emissions of carbon dioxide-containing exhaust
gases into the atmosphere.
[0003] Very recently, novel power plant concepts are proposed in
which the fossil fuel, e.g. coal, is burnt with an oxygen-rich
combustion gas, in particular with technically pure oxygen, or with
oxygen-enriched air (oxygen combustion gas method). The oxygen
fraction of this combustion gas is, e.g., 95 to 99.9% by volume.
The resultant exhaust gas, which is also termed flue gas, contains
principally carbon dioxide (CO.sub.2) at a fraction of
approximately 70 to 85% by volume. The purpose of these novel
concepts is to inject the carbon dioxide formed in the combustion
of the fossil fuels and present in concentrated form in the flue
gas into suitable repositories, in particular into certain rock
strata or salt water-bearing strata, and thereby to limit the
emission of carbon dioxide into the atmosphere. The harmful
climatic effect of greenhouse gases such as carbon dioxide is
thereby reduced. Such power plants are termed in the specialist
field "oxyfuel" power plants.
[0004] In the concepts known to date, a dedusting, denitrification
and desulphurization of the flue gas proceed in sequential steps.
Subsequently to this flue gas purification, the carbon dioxide-rich
exhaust gas thus treated is compressed and fed to a carbon dioxide
purification stage. There, typically, a gas substream having a
reduced carbon dioxide content and another gas substream having an
elevated carbon dioxide content are generated by way of a cryogenic
separation method. The gas substream having an elevated carbon
dioxide content is the desired carbon dioxide product stream, which
is produced having a carbon dioxide content of, e.g., greater than
95% by volume and is provided for further use, in particular for
transport to repositories. The gas substream having a reduced
carbon dioxide content is produced as a subsidiary stream (what is
termed vent gas) at 15 to 30 bar, preferably 18 to 25 bar, and
contains predominantly the components not intended for the
injection, in particular inert gases such as nitrogen (N.sub.2) and
argon (Ar) and oxygen (O.sub.2). However, in this gas substream,
fractions of carbon dioxide are also still present at a
concentration of approximately 25 to 35% by volume. This vent gas
is currently blown off into the atmosphere.
[0005] Usually, the raw gas stream is precompressed to a desired
pressure in upstream plant parts and dried, e.g., in adsorber
stations. This means that the vent gas also is first still present
in the compressed state. At present this pressure level is reduced
by expansion valves.
[0006] In EP 1952874 A1 and EP 1953486 A1 (Air Products) it has
already been proposed, after warming the vent gas and further
heating by means of waste heat from the compression, to carry out a
turbine expansion of the vent gas stream. However, utilization of
the energy liberated in the turbine expansion, in particular of the
refrigeration capacity produced in the expansion process, is not
envisaged in this case.
[0007] In DE 102009039898 A1 (Linde), for improving the energy
efficiency, it is proposed that the vent gas stream is expanded in
at least one expansion turbine and both the resultant kinetic
energy and also the refrigeration generated are utilized for energy
recovery. For utilizing the kinetic energy, the expansion turbine
can be coupled to a compressor (booster) which compresses the raw
gas stream and/or the carbon dioxide gas stream. For utilizing the
refrigeration generated in the expansion, the at least partially
expanded vent gas stream can be brought into heat exchange with
process streams that are to be cooled, e.g. the raw gas stream
and/or the carbon dioxide gas stream.
[0008] The carbon dioxide gas stream is usually compressed by way
of a final compressor to the required final pressure of above 80
bar (preferably 120 to 150 bar) for transport and subsequent
sequestration.
[0009] Alternatively, for the carbon dioxide gas stream
compression, liquefaction of the separated-off carbon dioxide-rich
gas with subsequent pressure elevation by way of pumps is also
possible. Here, however, the use of refrigerant is necessary. When
external refrigeration from a refrigeration plant is used, a liquid
carbon dioxide pure product is already present after the cryogenic
separation, which liquid carbon dioxide pure product can be brought
to the necessary final pressure by way of a pump. However, the use
of a refrigeration plant (external refrigeration) increases the
necessary energy consumption.
[0010] An object of the present invention is to design a method of
the type mentioned at the outset and also an apparatus for carrying
out the method in such a manner that the energy efficiency can be
further improved.
[0011] Upon further study of the specification and appended claims,
other objects and advantages of the invention will become
apparent.
[0012] These objects are achieved in terms of the method in that,
from some of the liquid that is separated off in the cryogenic
carbon dioxide purification stage, a liquid stream having an
elevated carbon dioxide content (carbon dioxide liquid stream) is
obtained which is fed in a liquid phase to further utilization
and/or storage.
[0013] Using the invention, an energy-sparing operation of the
carbon dioxide purification stage is made possible without using
external refrigeration from an external refrigeration plant. The
refrigeration necessary for cooling and partial condensation of the
raw gas stream can be provided via heat exchange with the
evaporating liquid forming the carbon dioxide gas stream and also
by heat exchange with the vent gas stream that is cooled by
expansion in the expansion turbine. By branching off a carbon
dioxide liquid stream, the final compression of the carbon dioxide
gas stream can be relieved, whereby, in total, an improvement of
the energy efficiency is achieved. Furthermore, in this manner an
additional liquid carbon dioxide product can be provided without
further energy consumption.
[0014] It has proved in this case that operation of the carbon
dioxide purification stage without an external refrigeration plant
is expedient when the carbon dioxide liquid stream amounts to 5 to
25%, preferably 10 to 15%, of the total liquid that is separated
off in the cryogenic carbon dioxide purification stage.
[0015] According to a particularly advantageous embodiment of the
invention, the carbon dioxide liquid stream is fed to the carbon
dioxide gas stream after compression thereof to the final pressure.
In this case the carbon dioxide liquid stream is expediently
compressed to the final pressure by way of a liquid pump before it
is fed to the carbon dioxide gas stream.
[0016] Another variant of the invention provides that the carbon
dioxide liquid stream is temporarily stored in a liquid gas tank
for further use, in particular in the food industry. Customers'
wants can thereby be met by an additional liquid carbon dioxide
product without additional energy expenditure and without the use
of an external refrigeration plant.
[0017] A further possibility of use is in the use of the carbon
dioxide liquid stream, after evaporation, as transport medium for
the pneumatic transport (i.e., entrainment of solid particles, such
as coal dust, by a gas stream) or as a lock gas of feedstocks, in
particular coal dust, in large-scale furnace plants. For example,
during preparation of combustible material (coal/lignite) for coal
fired power plants, contact with oxygen has to be minimized. Carbon
dioxide is possible gas to use for displacing air, thereby acting
as a lock gas.
[0018] For utilization of the kinetic energy, the expansion turbine
can also be coupled to at least one compressor (booster), in such a
manner that the expansion turbine compresses the raw gas stream
and/or the carbon dioxide product stream during the at least
partial expansion of the vent gas stream. For utilization of the
refrigeration generated in the expansion, the at least partially
expanded vent gas stream is preferably brought into heat exchange
with process streams that are to be cooled, e.g. the raw gas stream
and/or the carbon dioxide product stream. By expansion of the vent
gas, process-internal refrigeration output can be provided and
external refrigeration can thereby be spared.
[0019] The invention further relates to an apparatus for treating a
carbon dioxide-containing gas stream (raw gas stream), in
particular from a large-scale furnace plant, having a carbon
dioxide purification appliance that is charged with the
precompressed raw gas stream. The carbon dioxide purification
appliance comprises an outlet line for a gas stream having an
elevated carbon dioxide content (carbon dioxide gas stream) and an
outlet line for a gas stream having a reduced carbon dioxide
content (vent gas stream). The outlet line for the carbon dioxide
gas stream is connected via a final compressor to a utilization
appliance and/or repository, whereas the outlet line for the vent
gas stream is connected to at least one expansion turbine which
comprises an outlet line for the at least partially expanded vent
gas stream. The outlet line for the at least partially expanded
vent gas stream is connected to a heat-exchange appliance which is
chargeable with the precompressed raw gas stream, the carbon
dioxide gas stream and the vent gas stream.
[0020] The objects are achieved in terms of the apparatus in that
the carbon dioxide purification appliance additionally comprises an
outlet line for a liquid stream having an elevated carbon dioxide
content (carbon dioxide liquid stream). This outlet line bypasses
the heat-exchange appliance and the final compressor and is
connected directly to a utilization appliance and/or storage
appliance for liquid having an elevated carbon dioxide content.
[0021] Preferably, the outlet line for the carbon dioxide liquid
stream comprises a liquid pump and, downstream of the final
compressor, the carbon dioxide liquid stream is introduced into the
outlet line for the carbon dioxide gas stream.
[0022] The invention is suitable for all conceivable large-scale
furnace plants in which carbon dioxide-containing gas streams are
produced. These include, e.g., fossil-fuel-fired power plants,
industrial furnaces, steam kettles and similar large-scale thermal
plants for power and/or heat generation. The invention can be used
particularly advantageously in large-scale furnace plants which are
supplied with technically pure oxygen or oxygen-enriched air as
combustion gas and in which, accordingly, exhaust gas streams
having high carbon dioxide concentrations are produced. In
particular, the invention is suitable for what are termed
low-CO.sub.2 coal power plants which are operated with oxygen as
combustion gas ("oxyfuel" power plants) and in which the carbon
dioxide that is present in the exhaust gas in high concentration is
separated off and injected below ground ("CO.sub.2 capture
technology").
[0023] The invention is associated with a large number of
advantages.
[0024] The final compressor for the carbon dioxide gas stream is
relieved, which leads to energy savings and also to a reduction of
capital costs. The demands on the operation of the final compressor
are reduced so, for example, a smaller compressor can be used
thereby reducing capital costs. In addition, the energy balance at
the heat-exchange appliance is optimally utilized. In some
circumstances, the intake temperature at the final compressor can
be adjusted in such a manner that simpler materials (no high-alloy
steels) can be used. Furthermore, a prepurified liquid carbon
dioxide product can be provided from the system which can be
utilized, for example, for treatment to give a food-specific carbon
dioxide product (external utilization) or else also as liquid store
in a tank system.
[0025] The carbon dioxide liquid stream can also be used for other
applications (e.g. treatment to give purified seal gas for the
oxyfuel process, use as transport medium for the pneumatic
transport of coal dust in the oxyfuel process, storage of liquid
carbon dioxide for use as start-up gas or charge gas after
evaporation).
[0026] When multistage compression is used to bring the pressure of
the carbon dioxide gas stream to the required final pressure, the
carbon dioxide liquid stream, after a supercritical compression of
the carbon dioxide gas stream (>72 bar), can be fed (in the
supercritical state) upstream of the suction side of the
next-following compressor stage (or pump). The temperature falls
and the density increases thereby. Owing to the higher density, the
energy requirement of the subsequent compressor stages/pumps for
achieving the required final pressure falls.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The invention and further embodiments of the invention are
described in more detail hereinafter with reference to working
examples shown schematically in the figures, in comparison with the
previous prior art. Various other features and attendant advantages
of the present invention will be more fully appreciated as the same
becomes better understood when considered in conjunction with the
accompanying drawings, in which like reference characters designate
the same or similar parts throughout the several views, and
wherein:
[0028] FIG. 1 shows a block diagram of a carbon dioxide treatment
plant with expansion of the vent gas via an expansion turbine as
per the prior art according to EP 1952874 A1;
[0029] FIG. 2 shows a block diagram of a carbon dioxide treatment
plant with expansion of the vent gas via expansion turbines with
energy recovery as per the prior art according to DE 102009039898
A1;
[0030] FIG. 3 shows a block diagram of a carbon dioxide treatment
plant with removal of a separate carbon dioxide liquid stream with
subsequent compression by way of a liquid pump to the required
final pressure for pipeline transport; and
[0031] FIG. 4 shows a block diagram of a carbon dioxide treatment
plant with removal of a separate carbon dioxide liquid stream with
subsequent temporary storage for external use.
[0032] FIG. 1 shows a conventional treatment of a carbon
dioxide-containing raw gas stream from a coal power plant as per
the prior art according to EP 1952874 A1 (Air Products). The raw
gas stream, after compression in the raw gas compressor 1, is fed
via a heat-exchange unit 2 to a primary separator 3 for separating
off carbon dioxide. The vent gas from the primary separator 3 is
introduced into the heat-exchange unit 2 and then fed to a
secondary separator 4. The carbon dioxide product stream is
withdrawn, respectively, from the bottoms of primary carbon dioxide
separator 3 and secondary separator 4, introduced into the central
heat-exchange unit 2 (and in the case of the vent gas from the
primary separator 3 additionally via a CO.sub.2 product compressor
7), and then subjected to a final compression 8 in order finally to
be fed via a pipeline (carbon dioxide pipeline) 9, e.g. to an
injection below ground. The vent gas of the secondary separator 4
is withdrawn from the top of the secondary separator 4, likewise
introduced into the central heat-exchange unit 2 and finally,
downstream of a further warming in the heat exchanger 5, expanded
via a turbine 6 in order to be delivered to the atmosphere.
[0033] In contrast to the method shown in FIG. 1 for carbon dioxide
treatment, the method according to DE 102009039898 A1 (Linde),
shown in FIG. 2, offers the advantage of energy recovery in the
expansion of the vent gas. In this method, as in the method shown
in FIG. 1, two carbon dioxide separators 3 and 4 and also a central
heat-exchange unit 2 are provided. In contrast to the method as per
FIG. 1, however, simple expansion of the vent gas via a single
turbine does not occur, but instead a stepwise expansion via two
expansion turbines 5 and 6 is performed. By way of the stepwise
expansion of the vent gas stream, the formation of solid carbon
dioxide in the vent gas can be prevented. Downstream of the
expansion in the first expansion turbine 5, the vent gas stream is
warmed in the central heat-exchange unit 2 and then expanded
further to close to atmospheric pressure in the second expansion
turbine 6 and again warmed in the central heat-exchange unit 2. The
available pressure level of the vent gas can thereby be completely
exploited. The vent gas that is cold after the expansion is warmed
in the central heat-exchange unit 2 against the process streams
that are to be cooled. The vent gas thereby provides some of the
refrigeration capacity necessary in the process.
[0034] FIG. 3 shows a carbon dioxide treatment according to the
invention. The process procedure differs from that shown in FIG. 2
in that some of the liquid carbon dioxide separated off in the
primary separator 3 is branched off and fed via a carbon dioxide
liquid pump 9 downstream of the final compressor 8 to the CO.sub.2
pipeline 10. In this procedure the carbon dioxide liquid stream is
brought to the required final pressure for the pipeline transport
by way of the carbon dioxide liquid pump 9. Since this carbon
dioxide liquid stream by passes the final compressor 8, the
operational demands on the final compression 8 are reduced thereby
increasing energy efficiency and reducing capital costs. The energy
balance at the heat-exchange unit 12 can be used optimally. The
intake temperature at the final compressor 8 can be adjusted in
such a manner that simpler materials (e.g. no high-alloy steels)
can be used.
[0035] In the variant of the invention shown in FIG. 4, the liquid
carbon dioxide that is separated off from the primary separator 3
is first temporarily stored in a liquid carbon dioxide tank 11. The
liquid carbon dioxide can be fed, as required, from tank 11 via the
liquid pump 9 to the CO.sub.2 pipeline 10 and/or loaded into a
transport vehicle 12 for further external utilization (e.g. in the
food industry) and/or evaporated in a CO.sub.2 evaporator 13 and
provided for internal utilization (e.g. as start-up or feed
gas).
[0036] The entire disclosure[s] of all applications, patents and
publications, cited herein and of corresponding German Application
No. 10 2011 014 678.4, filed Mar. 22, 2011, are incorporated by
reference herein.
[0037] The preceding examples can be repeated with similar success
by substituting the generically or specifically described reactants
and/or operating conditions of this invention for those used in the
preceding examples.
* * * * *