AU2012200908A1

AU2012200908A1 - Method and device for treating a carbon dioxide-containing gas stream

Info

Publication number: AU2012200908A1
Application number: AU2012200908A
Authority: AU
Inventors: Roland Ritter; Dirk Spenner
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2011-03-22
Filing date: 2012-02-16
Publication date: 2012-10-11
Also published as: CA2771558A1; US20120240616A1; ZA201202071B; DE102011014678A1; EP2503271A2

Abstract

Abstract Method and device for treating a carbon dioxide-containing gas stream 5 The invention relates to a method and a device for treating a carbon dioxide-containing gas stream, in particular from a large-scale furnace plant, e.g. from a power plant. The precompressed gas stream (1) is partially liquefied in a cryogenic carbon dioxide purification stage (2, 3, 4). The liquid is subsequently separated off. From the liquid that is separated off, a gas stream having an elevated carbon dioxide content (carbon 10 dioxide gas stream) (7) is obtained by reevaporation. From the non-liquefied raw gas, a gas stream having a reduced carbon dioxide content (vent gas stream) is obtained. The vent gas stream is expanded in at least one expansion turbine (5, 6) and the refrigeration generated in this process is recovered for cooling the raw gas stream. The carbon dioxide gas stream is compressed (8) to a final pressure and fed to further 15 utilization and/or storage. In particular, by injecting the carbon dioxide below ground, the emission of gases that are harmful to the climate can be reduced. For improving the energy efficiency, it is proposed 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 20 phase (9) to further utilization and/or storage (10). (Fig. 3) .Fig. 3

Description

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL Name of Applicant: Linde-KCA-Dresden GmbH Actual Inventors: Roland Ritter and Dirk Spenner Address for Service is: SHELSTON IP 60 Margaret Street Telephone No: (02) 9777 1111 SYDNEY NSW 2000 Facsimile No. (02) 9241 4666 CCN: 3710000352 Attorney Code: SW Invention Title: Method and device for treating a carbon dioxide-containing gas stream The following statement is a full description of this invention, including the best method of performing it known to me/us: File: 73812AUP00 2 Description Method and device for treating a carbon dioxide-containing gas stream The invention relates to a method for treating a carbon dioxide-containing gas stream 5 (raw gas stream), in particular of a large-scale furnace plant, wherein the precompressed raw gas stream is partially liquefied in a cryogenic carbon dioxide purification stage, the liquid is separated off and a gas stream having an elevated carbon dioxide content (carbon dioxide gas stream) is obtained therefrom by reevaporation, whereas a gas stream having a reduced carbon dioxide content (vent 10 gas stream) is obtained from the non-liquefied raw gas, the 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 and the carbon dioxide gas stream is compressed to a final pressure and fed to further utilization and/or storage, and also relates to a device for carrying out the method. 15 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 20 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. 25 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 30 gas, which is also termed flue gas, contains principally carbon dioxide (CO2) 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 3 dioxide into the atmosphere. The harmful climatic effect of greenhouse gases such as carbon dioxide is to be reduced thereby. Such power plants are termed in the specialist field "oxyfuel" power plants. 5 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 10 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 15 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

2 ) and argon (Ar) and oxygen (02). 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. 20 Usually, the raw gas stream is precompressed to 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. 25 In EP 1952874 Al and EP 1953486 Al (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. Utilization of the energy liberated in the turbine expansion, in particular of the refrigeration capacity produced in the expansion process, it is not envisaged in this case, however. 30 In DE 102009039898 Al (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 35 compressor (booster) which compresses the raw gas stream and/or the carbon dioxide 4 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. 5 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. 10 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 15 pure product can be brought to the necessary final pressure by way of a pump. The use of a refrigeration plant (external refrigeration) increases the necessary energy consumption, however. Any discussion of the prior art throughout the specification should in no way be 20 considered as an admission that such prior art is widely known or forms part of common general knowledge in the field. It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative. 25 The object of the present invention in its preferred form is to design a method of the type mentioned at the outset and also a device for carrying out the method in such a manner that the energy efficiency can be further improved. 30 This preferred object is 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.

5 According to a first aspect, the present invention provides a method for treating a carbon dioxide-containing gas stream (raw gas stream), wherein the precompressed raw gas stream is partially liquefied in a cryogenic carbon dioxide purification stage, the liquid is separated off and a gas stream having an elevated carbon dioxide content 5 (carbon dioxide gas stream) is obtained therefrom by reevaporation, whereas a gas stream having a reduced carbon dioxide content (vent gas stream) is obtained from the non-liquefied raw gas, the 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 and the carbon dioxide gas stream is compressed to a final pressure and 10 fed to further utilization and/or storage, wherein 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. 15 According to a second aspect, the present invention provides a device for treating a carbon dioxide-containing gas stream (raw gas stream), having a carbon dioxide purification appliance that is charged with the precompressed raw gas stream, which 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 20 gas stream having a reduced carbon dioxide content (vent gas stream), wherein 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, which outlet line is connected to a heat 25 exchange appliance which is chargeable with the precompressed raw gas stream, the carbon dioxide gas stream and the vent gas stream, wherein the carbon dioxide purification appliance additionally comprises an outlet line for a liquid stream having an elevated carbon dioxide content (carbon dioxide liquid stream) which, bypassing the heat-exchange appliance and the final compressor, is connected directly to a utilization 30 appliance and/or storage appliance for liquid having an elevated carbon dioxide content. According to a third aspect, the present invention provides a liquid stream having an elevated carbon dioxide content when produced by the method according to the first 35 aspect.

6 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 5 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 10 provided without further energy consumption. 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 is obtained from 5 to 25%, preferably 10 to 15%, of the liquid that is separated off in the 15 cryogenic carbon dioxide purification stage. 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 20 compressed to the final pressure by way of a liquid pump before it is fed to the carbon dioxide gas stream. 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. 25 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. A further possibility of use is in the use of the carbon dioxide liquid stream, after 30 evaporation, as transport medium for the pneumatic transport or as a lock gas of feedstocks, in particular coal dust, in large-scale furnace plants. 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 35 compresses the raw gas stream and/or the carbon dioxide product stream during the at 7 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 5 gas, process-internal refrigeration output can be provided and external refrigeration can be spared thereby. The invention further relates to a device for treating a carbon dioxide-containing gas stream (raw gas stream), in particular from a large-scale furnace plant, having a carbon 10 dioxide purification appliance that is charged with the precompressed raw gas stream, which 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), wherein the outlet line for the carbon dioxide gas stream is connected via a final 15 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, which outlet line 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. 20 The object in question is achieved in terms of the device 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) which, bypassing the heat-exchange appliance and the final compressor, is connected directly to a utilization 25 appliance and/or storage appliance for liquid having an elevated carbon dioxide content. Preferably, the outlet line for the carbon dioxide liquid stream comprises a liquid pump and, downstream of the final compressor, opens out into the outlet line for the carbon 30 dioxide gas stream. 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 35 for power and/or heat generation. The invention can be used particularly 8 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 2 coal power plants which are operated 5 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 ("C02 capture technology"). The invention is associated with a large number of advantages: 10 The final compressor for the carbon dioxide gas stream is relieved, which leads to energy savings and also to a reduction of 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 15 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. 20 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). 25 On multistage compression 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 30 requirement of the subsequent compressor stages/pumps for achieving the required final pressure falls. 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 35 comparison with the previous prior art.

9 In the figures: Figure 1 shows a block diagram of a carbon dioxide treatment plant with 5 expansion of the vent gas via an expansion turbine as per the prior art according to EP 1952874 Al Figure 2 shows a block diagram of a carbon dioxide treatment plant with expansion of the vent gas via expansion turbines with energy recovery 10 as per the prior art according to DE 102009039898 Al Figure 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 15 transport Figure 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 extemal use 20 In the figures, in each case the same plant components are provided with the same reference numbers. Figure 1 shows a conventional treatment of a carbon dioxide-containing raw gas 25 stream from a coal power plant as per the prior art according to EP 1952874 Al (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 fed via the heat-exchange unit 2 to a secondary separator 4. The carbon dioxide product stream is withdrawn respectively 30 from the bottom of the carbon dioxide separator 3 and 4 and fed via the central heat exchange unit 2 (and in the case of the vent gas from the primary separator 3 additionally via a C02 product compressor 7) 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 35 separator 4, likewise passed via the central heat-exchange unit 2 and finally, 10 downstream of a further warming in the heat exchanger 5, expanded via a turbine 6 in order to be delivered to the atmosphere. In contrast to the method shown in Figure 1 for carbon dioxide treatment, the method 5 according to DE 102009039898 Al (Linde) that is shown in Figure 2 offers the advantage of energy recovery in the expansion of the vent gas. In this method, as in the method shown in Figure 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 Figure 1, however, simple expansion of the vent gas via a single turbine does not proceed, but a 10 stepwise expansion via two expansion turbines 5 and 6. 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 15 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. 20 Figure 3 shows a carbon dioxide treatment according to the invention. The process procedure differs from that shown in Figure 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 2 pipeline 10. In this 25 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. Because of the bypassing of the final compressor 8, this can be relieved, whereby the energy efficiency is increased and the capital costs can be reduced. The energy balance at the heat-exchange unit 12 can be used optimally. The intake temperature at the final 30 compressor 10 can be adjusted in such a manner that simpler materials (e.g. no high alloy steels) can be used. In the variant of the invention shown in Figure 4, the liquid carbon dioxide that is separated off in the primary separator 3 is first temporarily stored in a liquid carbon 35 dioxide tank 11. The liquid carbon dioxide can be fed, as required, via the liquid pump 9 11 to the CO 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 2 evaporator 13 and provided for internal utilization (e.g. as start-up or feed gas).

Claims

1. Method for treating a carbon dioxide-containing gas stream (raw gas stream), wherein the precompressed raw gas stream is partially liquefied in a cryogenic 5 carbon dioxide purification stage, the liquid is separated off and a gas stream having an elevated carbon dioxide content (carbon dioxide gas stream) is obtained therefrom by reevaporation, whereas a gas stream having a reduced carbon dioxide content (vent gas stream) is obtained from the non-liquefied raw gas, the vent gas stream is expanded in at least one expansion turbine and the 10 refrigeration generated in this process is recovered for cooling the raw gas stream and the carbon dioxide gas stream is compressed to a final pressure and fed to further utilization and/or storage, wherein 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 15 obtained which is fed in a liquid phase to further utilization and/or storage.

2. Method according to Claim 1, wherein the carbon dioxide liquid stream is obtained from 5 to 25% of the liquid that is separated off in the cryogenic carbon dioxide purification stage. 20

3. Method according to claim 2 wherein the carbon dioxide liquid stream is obtained from 10 to 15% of the liquid that is separated off in the cryogenic carbon dioxide purification stage. 25

4. Method according to any one of claims 1 to 3, wherein the carbon dioxide liquid stream is fed to the carbon dioxide gas stream after compression thereof to the final pressure.

5. Method according to Claim 4, wherein the carbon dioxide liquid stream is 30 compressed to the final pressure by way of a liquid pump before it is fed to the carbon dioxide gas stream.

6. Method according to any one of Claims 1 to 5, wherein the carbon dioxide liquid stream is temporarily stored in a liquid gas tank for further use. 35

7. Method according to claim 6 wherein the use is in the food industry. 13

8. Method according to any one of Claims 2 to 7, wherein the carbon dioxide liquid stream is used as transport medium for the pneumatic transport of feedstocks in large-scale furnace plants. 5

9. Method according to claim 8 wherein the feedstock is coal dust.

10. A method according to any one of the preceding claims wherein the carbon dioxide-containing gas stream is generated from a large-scale furnace plant. 10

11. Device for treating a carbon dioxide-containing gas stream (raw gas stream), having a carbon dioxide purification appliance that is charged with the precompressed raw gas stream, which carbon dioxide purification appliance comprises an outlet line for a gas stream having an elevated carbon dioxide 15 content (carbon dioxide gas stream) and an outlet line for a gas stream having a reduced carbon dioxide content (vent gas stream), wherein 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 20 at least partially expanded vent gas stream, which outlet line 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, wherein the carbon dioxide purification appliance additionally comprises an outlet line for a liquid stream having an elevated carbon dioxide content (carbon dioxide liquid 25 stream) which, bypassing the heat-exchange appliance and the final compressor, is connected directly to a utilization appliance and/or storage appliance for liquid having an elevated carbon dioxide content.

12. Device according to Claim 11, wherein the outlet line for the carbon dioxide liquid 30 stream comprises a liquid pump and, downstream of the final compressor, opens out into the outlet line for the carbon dioxide gas stream.

13. Device according to claim 12 or claim 13 wherein the carbon dioxide-containing gas stream is generated from a large-scale furnace plant. 35

14. A liquid stream having an elevated carbon dioxide content when produced by the method according to any one of claims 1 to 10. 14

15. Method for treating a carbon dioxide-containing gas stream, device for treating a carbon dioxide-containing gas stream, or a liquid stream having an elevated carbon dioxide content when produced by the method substantially as herein 5 described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.