EP2473254A1

EP2473254A1 - Method and device for treating a carbon dioxide-containing gas flow, wherein the energy of the vent gas (work and cold due to expansion) is used

Info

Publication number: EP2473254A1
Application number: EP10749788A
Authority: EP
Inventors: Roland Ritter; Annett Kutzschbach
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2009-09-03
Filing date: 2010-08-26
Publication date: 2012-07-11
Also published as: WO2011026587A1; DE102009039898A1; CA2772146A1; AU2010291532A1; ZA201201477B; US20120240619A1; AU2010291532B2

Abstract

The invention relates to a method and a device for treating a carbon dioxide-containing gas flow, in particular from a large combustion plant, for example a power plant. The pre-compressed gas flow is separated in a carbon dioxide scrubbing stage into a partial gas flow having an increased carbon dioxide content (carbon dioxide product flow) and a partial gas flow having a reduced carbon dioxide content (vent gas flow). The carbon dioxide product flow is fed to further processing and/or storage. In particular, by compressing the carbon dioxide underground, the emission of climate-damaging gases can be reduced. In order to improve the energy efficiency, the vent gas flow is expanded in at least one expansion turbine, and the developing kinetic energy as well as the cooling energy created in the process are used for energy recovery. In order to use the kinetic energy, the expansion turbine can be coupled to a compressor (booster) that compresses the raw gas flow and/or the carbon dioxide product flow. In order to use the cooling energy created during expansion, the at least partially expanded vent gas flow can be brought into heat exchange with process flows to be cooled, for example the raw gas flow and/or the carbon dioxide product flow.

Description

description

METHOD AND DEVICE FOR TREATING A CARBON DIOXIDE-CONTAINING GAS STREAM WHERE THE ENERGY OF THE VENT GAS (WORK AND COLD THROUGH

EXPANSION) IS USED

The invention relates to a process for the treatment of a carbon dioxide-containing gas stream, in particular from a large combustion plant, wherein the precompressed crude gas stream is separated in a carbon dioxide purification stage in a partial gas stream with increased carbon dioxide content (carbon dioxide product stream) and a partial gas stream with reduced carbon dioxide content (Ventgasstrom) and the

Carbon dioxide product stream is supplied to a further utilization and / or storage, and an apparatus for performing the method.

Carbon dioxide-containing gas streams are produced by all large-scale combustion plants that run on fossil fuels such as coal, oil or natural gas. These include in particular power plants, but also industrial furnaces, steam boilers and similar large-scale thermal plants for power and / or heat generation. In addition, carbon dioxide-containing gas streams also occur in process plants of the chemical or petrochemical industry, such as e.g. in cracking furnaces of olefin plants or in steam reformers of synthesis gas plants. Due to the climate-damaging effect of carbon dioxide gas, solutions are sought to reduce the emissions of carbon dioxide-containing exhaust gases to the atmosphere.

Recently, new power plant concepts have been proposed in which the fossil fuel, e.g. Coal is burned with an oxygen-rich combustion gas, in particular with technically pure oxygen or with oxygen-enriched air (oxygen combustion gas process). The oxygen content of this combustion gas is e.g. 95 to 99.9% by volume. The resulting exhaust gas, which is also referred to as flue gas, contains mainly carbon dioxide (C02) with a share of about 70 to 85 vol .-%. The aim of these new concepts is to compress the carbon dioxide produced during combustion of the fossil fuels and concentrated in the flue gas in suitable deposits, in particular in certain rock layers or salt water bearing layers, and thus to limit carbon dioxide emissions to the atmosphere. This soll.die climate damaging effect of

Greenhouse gases such as carbon dioxide are reduced. Such power plants are referred to in the art as so-called "oxyfuel" power plants. In the previously known concepts, dedusting, denitrification and desulfurization of the flue gas take place in successive steps. Following this flue gas cleaning, the thus treated, carbon dioxide-rich exhaust gas is compressed and fed to a carbon dioxide purification stage. There will be

Typically, by a cryogenic separation process produces a partial gas stream with reduced carbon dioxide content and another partial gas stream with increased carbon dioxide content. The partial gas stream with increased carbon dioxide content represents the desired carbon dioxide product stream, which has a carbon dioxide content of e.g. more than 95 vol .-% is obtained and for further use, especially for transport to

Lageruhgsstätten, is provided. The partial gas flow with reduced

Carbon dioxide content falls as a side stream (so-called Ventgas) at 15 to 30 bar, preferably 18- 25 bar, and contains predominantly the not intended for compression components, in particular inert gases such as nitrogen (N2) and argon (Ar) and oxygen (02). In this partial gas stream but are still shares in

Carbon dioxide in a concentration of about 25- 35 vol .-% present. This vent gas is currently being vented to the atmosphere.

Usually, the crude gas stream is precompressed in upstream plant parts to pressure and, for example, dried in adsorbent stations. This means that the vent gas is initially still in the compressed state. Currently, this pressure level is reduced by expansion valves.

It has already been proposed in EP 1952874 A1 and EP 1953486 A1, after heating the vent gas and further heating by means of waste heat from the compression, to carry out turbine venting of the vent gas flow. However, use of the energy released during the turbine decompression, in particular the cooling capacity occurring during the decompression process, is not provided here.

The present invention is based on the object, a method of the type mentioned and an apparatus for performing the method so

to design that energy efficiency in obtaining the

Carbon dioxide product flow can be improved. This object is achieved by the method in that the Ventgasstrom is relaxed in at least one expansion turbine, which is recovered by using both the resulting kinetic energy and the cold generated thereby energy.

The invention is based on the consideration that in the relaxation of the

Use Ventgasstrom's released energy to improve the energy efficiency of the overall process. The work-performing expansion of the vent gas in an expansion turbine offers the possibility of cheap energy recovery.

To use the kinetic energy, the expansion turbine is expediently coupled to at least one compressor (booster) so 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. To use at the

When the cold is released, the at least partially relaxed vent gas stream is preferably heat exchanged with process streams to be cooled, e.g. the

Crude gas stream / and or the carbon dioxide product stream brought. By the

Relaxation of the Ventgases can be provided in-process cooling capacity and thus save foreign cold.

According to a particularly preferred embodiment of the invention, the

Vent gas stream gradually expanded in at least two expansion turbines. By gradually relaxing the Ventgasstromes the formation of solid carbon dioxide in Ventgas can be reliably prevented. In the relaxation of the vent gas from the compressed state to ambient pressure namely the

Sublimation properties of carbon dioxide are noted. If the sublimation temperature falls below a defined partial pressure of the carbon dioxide (depending on the composition and the expansion pressure of the vent gas), solid carbon dioxide is formed. Thus, the expansion pressure of the vent gas after the expansion turbine is limited by the achievement of the solid phase of the carbon dioxide and the existing pressure level of Ventgases can not be fully utilized. The use of a single expansion turbine requires either a strong heating in the complete relaxation or only a partial relaxation in order not to get into the carbon dioxide solid phase. By the step relaxation one can use the whole pressure level. Advantageously, in stepwise relaxation of Ventgasstroms in

at least two expansion turbines each after a stage of relaxation of Ventgasstrom in heat exchange with cooled process streams, in particular the crude gas stream and / or the carbon dioxide product stream brought. At a

Two-stage relaxation so the Ventgasstrom is expediently warmed in a heat transfer unit after relaxation in the first expansion turbine and then in the second expansion turbine to close

Atmospheric pressure relaxed and warmed up again in the heat transfer unit. Thus, the existing pressure level of Ventgases can be fully utilized.

The kinetic energy accumulating during the expansion of the vent gas in the expansion turbine can also be used to drive at least one generator instead of driving at least one compressor. The in the

Relaxation turbine generated power can thus be used to generate electricity.

In addition to the gradual relaxation in at least two expansion turbines can be worked only with an expansion turbine. But then you do not use the possible pressure level and the rest relaxation is by means of

Relaxation valve performed. But even here you use the won

Cooling potential in the heat transfer unit off. Is the requirement of very high product purities, such as a

Reduction of the oxygen content in the carbon dioxide product stream, especially when injected into depleted natural gas or oil fields, but also when transferred to industrial use, is a simple purification of the raw gas stream by

Deposition of carbon dioxide no longer applicable. In this case, a

Rectification column integrated into the process. Again, the vent gas can be braked with a booster-braked expansion turbine or generator-braked

Expansion turbine can be relaxed and thus reduced energy consumption.

The invention further relates to a device for treating a

carbon dioxide-containing gas stream (crude gas stream), in particular from a A large combustion plant comprising a carbon dioxide purifier charged with the precompressed crude gas stream having a derivative for a partial gas stream with increased carbon dioxide (carbon dioxide product stream) and a derivative for a reduced carbon dioxide (vent gas) fractional gas stream, the carbon dioxide product stream effluent having a recovery facility and / or storage site communicates.

On the device side, the stated object is achieved in that the discharge for Ventgasstrom with at least one expansion turbine is in communication, which is coupled to at least one means for using the accumulating in the expansion turbine kinetic energy and having a derivative for at least partially relaxed Ventgasstrom, the is connected to a heat transfer device, which can be charged with cooled process streams. Preferably, the device for utilizing the kinetic energy accumulating in the expansion turbine is designed as a compressor (booster), which can be acted upon by the raw gas stream and / or the carbon dioxide product stream.

Another advantageous variant provides that the device for utilizing the kinetic energy accumulating in the expansion turbine is designed as a generator for generating electricity.

The invention is suitable for all conceivable large combustion systems in which carbon dioxide-containing gas flows incurred. These include e.g. Fossil-fueled power plants, industrial furnaces, steam boilers and similar thermal power plants

Large plants for power and / or heat generation. With particular advantage, the invention can be used in large combustion plants, which are supplied with technically pure oxygen or oxygen-enriched air as fuel gas and which consequently incurred exhaust gas streams with high carbon dioxide concentrations. In particular, the invention is suitable for so-called C02-poor coal power plants, which are operated with oxygen as fuel gas ("oxyfuel" power plants) and in which the carbon dioxide contained in the exhaust gas in high concentration is separated and pressed in the underground ("C02 Capture Technology "). There are a number of advantages associated with the invention: By using the released energy of the expansion turbine to drive the booster, an immediate energy return takes place in the process. Of the

Carbon dioxide raw gas stream is recompressed in the booster. This can do this

Compression energy can be saved in the upstream crude gas compressor (assuming that the same intermediate pressure is to be achieved).

Likewise, the use of the released energy of the expansion turbine to drive a booster to increase the pressure of the carbon dioxide product stream can be used. The existing pressure level of the vent gas can be fully utilized.

By the gradual relaxation of the Ventgases can in the central

Heat transfer unit Cooling capacity from in-process resources

to be provided. Thus, the use of external refrigeration can be saved or reduced.

In addition, the cooling of the carbon dioxide-containing vent gas occurring during the stepwise expansion of the vent gas can take place in such a way that the risk of the sublimation temperature dropping below is avoided. This prevents carbon dioxide solids (dry ice) from forming, causing them to fail and interfering with the process.

The invention and further embodiments of the invention are explained in more detail below with reference to embodiments schematically illustrated in the figures compared to the prior art.

1 is a block diagram of a carbon dioxide treatment plant with relaxation of the vent gas via relaxation valves according to the prior art for high purities of the carbon dioxide product stream, a block diagram of a carbon dioxide treatment plant with relaxation of the vent gas via a turbine according to the prior art

Figure 3 is a block diagram of a carbon dioxide treatment plant with gradual Relaxation of the vent gas via booster-braked expansion turbines with energy recovery according to the invention

Figure 4 is a block diagram of a carbon dioxide treatment plant with gradual

Relaxation of the vent gas via generator-braked

Expansion turbines with energy recovery according to the invention

Figure 5 is a block diagram of a carbon dioxide treatment plant with

Rectification column to obtain high carbon dioxide product purities and relaxation of the vent gas via a Boosterberkemst expansion turbine with energy recovery according to the invention

In Figure 1 is a conventional treatment of a carbon dioxide-containing

Crude gas flow from a prior art coal power plant to recover high carbon dioxide product purities shown. The crude gas stream is not shown in the figure pre-compression and drying via line (1) a

Rektifikationskolonne (2) fed, in which the carbon dioxide is largely separated from the crude gas. For this purpose, raw gas and circulated

enriched carbon dioxide gas via line (3) from the reboiler of

Rectification column (4) via a heat exchanger (5) and with a refrigerant via line (6) supplied to the condenser (7) to the top of the rectification column. (2) directed. The resulting, highly enriched with carbon dioxide

Carbon dioxide product stream is withdrawn via line (8) from the rectification column (2) and may be e.g. crushing in the ground or a C02

Liquid storage are supplied. The low-carbon vent gas is withdrawn via line (9) from the rectification column (2) and fed via the heat exchanger (5) to a carbon dioxide separator (10), in which the vent gas is largely freed from carbon dioxide still contained. The separated carbon dioxide is withdrawn from the bottom of the carbon dioxide and via line (11) and a

Return compressor (12) returned to the rectification column (2). The largely freed of carbon dioxide vent gas is withdrawn from the head of Kohlendioxidabscheiders (10), in a relaxation valve (13) pre-tensioned, then passed through the heat exchanger (5) and finally released in a second expansion valve (14) and released to the atmosphere. The variant of the prior art shown in Figure 2 differs from that shown in Figure 1 in that instead of a rectification column two carbon dioxide (1) and (2) for the separation of the line (3) supplied raw gas after cooling and partial condensation in the central

Heat transfer unit (4) in the carbon dioxide product stream and the

low-carbon vent gas are provided. The carbon dioxide product stream is respectively withdrawn from the bottom of the carbon dioxide separators (1, 2) and fed via a central heat transfer unit (4) to a product compaction (7), not shown, to be finally e.g. to be pressed in the underground. The vent gas is in each case withdrawn from the top of the carbon dioxide separator (1, 2), also via the central heat transfer unit (4) and finally after further heating in the heat exchanger (8) via a turbine (5) relaxed to the atmosphere (6) to be delivered. Such a procedure is e.g. in EP 1952874 A1.

In contrast to the method shown in Figures 1 and 2 for

Carbon dioxide treatment according to the prior art, the embodiments of the present invention shown in Figures 3 to 5, the advantage of energy recovery in the relaxation of the vent gas.

In the embodiment of the invention shown in FIG. 3, as in the variant of the prior art shown in FIG. 2, two carbon dioxide separators (1) and (2) and a central heat transfer unit (3) are provided. In contrast to the prior art, however, there is no mere relaxation of the vent gas via a single turbine, but a gradual relaxation over two

Expansion turbines (4) and (5) driving compressors (booster) (6) and (7) which compress the raw gas stream and the carbon dioxide product stream. In this case, the energy released during the expansion of the vent gas in the expansion turbines (4) and (5) can be recovered in an efficient manner. The operation of this arrangement can be described as follows:

With the released energy of the expansion turbine (4) booster (6) is driven. With the booster (6) of the carbon dioxide from the separator (2) coming

Carbon dioxide product stream having the lower pressure to the higher pressure of the carbon dioxide product stream coming from the other carbon dioxide separator (1) first precompressed and raised via another compressor (8) to the pressure level. With the released energy of the second expansion turbine (5) of the second booster (7) is driven. With this booster (7) can be compressed via line (9) coming from the drying and precompression, not shown raw gas to a higher pressure. The stepwise expansion of the vent gas stream can prevent the formation of solid carbon dioxide in the vent gas. After relaxation in the first expansion turbine (4) the

Vent gas stream in the central heat transfer unit (3) warmed and then in the second expansion turbine (5) further relaxed to near atmospheric pressure and in turn warmed in the central heat transfer unit (3). Thus, the existing pressure level of Ventgases can be fully utilized. The vent gas, which is cold after the expansion, is heated in the central heat transfer unit against the process streams to be cooled. Thus, the vent gas provides a part of the cooling capacity necessary in the process.

FIG. 4 shows a variant of the exemplary embodiment of FIG. 3, which differs in that the expansion turbines (4) and (5) instead of

Compressors (booster) Power generators (12) and (13) to generate electricity. Herewith, an energy recovery can be made possible.

Finally, FIG. 5 shows a variant of the invention in which, for example, because of the requirement of high product purities instead of

Kohldioxidabscheidern a rectification column (2) for the separation of the

Carbon dioxide is provided from the raw gas. Here, the raw gas supplied via line (9) via the central heat transfer unit (3) and condenser (7) in the rectification column (2) in a carbon dioxide rich

Carbon dioxide product stream, which is withdrawn from the bottom of the rectification column (2), and a low-carbon Ventgasstrom, which is withdrawn from the top of the rectification column (2) separated. The carbon dioxide product stream is passed via line (13) via the central heat transfer unit (3) and can be supplied after a product compression (10), for example, a pressing in the ground. The vent gas is also conducted via line (14) via the central heat transfer unit (3) and a separator (1) abandoned, where it is largely freed from remaining carbon dioxide. The separated carbon dioxide is withdrawn from the bottom of the separator (1) and via line (15) and adding a recycle compressor (12) to the raw gas feed. The largely carbon dioxide-free vent gas is withdrawn from the head of the separator (1) and fed via line (17) via the central heat transfer unit (3) of the expansion turbine (4). The expansion turbine (4) drives a booster (6), which compresses the raw gas. The thereby warmed raw gas is used via line (18) for heating in the reboiler (5) of the rectification column (2). The vent gas expanded in the expansion turbine (4) is finally discharged via the central heat transfer unit (3) to the atmosphere (11).

Claims

claims

1. A process for the treatment of a carbon dioxide-containing gas stream (crude gas stream), in particular a large combustion plant, wherein the precompressed crude gas stream in a carbon dioxide purification stage in a partial gas stream with increased

Carbon dioxide (carbon dioxide product stream) and a partial gas stream with reduced carbon dioxide content (Ventgasstrom) is separated and the

Carbon dioxide product stream is sent for further utilization and / or storage,

characterized in that the vent gas flow in at least one

Expansion turbine is relaxed, whereby energy is recovered by using both the resulting kinetic energy and the cold generated thereby.

2. The method according to claim 1, characterized in that the Ventgasstrom is gradually reduced in at least two expansion turbines.

3. The method according to claim 1 or 2, characterized in that the

Expansion turbine drives at least one compressor (booster), the

Crude gas stream and / or compressed the carbon dioxide product stream.

4. The method according to any one of claims 1 to 3, that the expansion turbine

drives at least one generator for power generation.

5. The method according to any one of claims 1 to 4, characterized in that the expanded in the expansion turbine Ventgasstrom in heat exchange with

cooled process streams, in particular the crude gas stream and / or the carbon dioxide product stream is brought.

6. The method according to any one of claims 2 to 5, characterized in that with gradual relaxation of the Ventgasstroms in at least two

Expansion turbines in each case after a stage of relaxation of Ventgasstrom in heat exchange with the process streams to be cooled, in particular the crude gas stream and / or the carbon dioxide product stream is brought.

7. The method according to any one of claims 1 to 6, characterized in that the carbon dioxide purification stage comprises a rectification column.

8. An apparatus for treating a carbon dioxide-containing gas stream (crude gas stream), in particular from a large combustion plant, with one with the pre-compressed

Crude gas stream fed carbon dioxide purifier having a derivative for a partial gas stream with increased carbon dioxide content (carbon dioxide product stream) and a derivative for a partial gas stream with reduced carbon dioxide content (Ventgasstrom), wherein the derivation for the carbon dioxide product stream is in connection with a utilization device and / or storage location, characterized in that the discharge for the vent gas flow is connected to at least one expansion turbine which is coupled to at least one device for utilizing the kinetic energy accumulating in the expansion turbine and a discharge for the at least partially relaxed one

Ventgasstrom having, which is connected to a heat transfer device, which is charged with cooled process streams.

9. Apparatus according to claim 8, characterized in that the means for using the accumulated in the expansion turbine kinetic energy as

Compressor (booster) is formed, which is connected to the raw gas stream and / or the

Carbon dioxide product flow can be acted upon.

10. Apparatus according to claim 8 or 9, characterized in that the device is designed to use the energy accumulating in the expansion turbine kinetic energy as a generator for generating electricity.