Device and method for separating carbon dioxide from a gas stream, in particular from a flue gas stream, comprising a cooling water system

Abstract

A device for separating carbon dioxide from a gas stream, in particular from a flue gas stream, includes an absorber for separating the carbon dioxide from the gas stream by means of a washing medium, a desorber which is fludically connected to the absorber to release the absorbed carbon dioxide from the washing medium, a gas cooler which is fludically connected upstream of the absorber to cool the gas stream, and a processing unit which is connected downstream of the gas cooler and which is equipped and designed to clean water from the gas cooler. A method separates carbon dioxide from a gas stream.

Claims

1. A removal apparatus for carbon dioxide from a gas stream, comprising: an absorber configured to separate carbon dioxide from the gas stream by means of a scrubbing medium, a desorber which is connected hydrodynamically to the absorber and configured to liberate absorbed carbon dioxide from the scrubbing medium, wherein a discharge line from the desorber is connected hydrodynamically to a feed line of the absorber, a gas cooler which is located hydrodynamically upstream of the absorber, which is configured to cool the gas stream, and which is configured to produce a stream of water, a spray cooling unit configured to use a spray cooling medium to spray cool a first portion of the stream of water discharged from the gas cooler; a treatment unit which is located downstream of the gas cooler and is configured for purifying a second portion of the stream of water discharged from the gas cooler, a connection configured to deliver purified water from the treatment unit to the spray cooling unit where the purified water is used as the spray cooling medium, and an absorber spray cooling unit configured to use a respective spray cooling medium to spray cool the scrubbing medium fed to the absorber, wherein the absorber spray cooling unit is connected hydrodynamically to the treatment unit, which absorber spray cooling unit is installed in the feed line of the absorber, and wherein the purified water from the treatment unit is used as the respective spray cooling medium in the absorber spray cooling unit.

2. The removal apparatus as claimed in claim 1, wherein the treatment unit comprises a reverse osmosis plant.

3. The removal apparatus as claimed in claim 1, wherein the treatment unit comprises a stock tank.

4. The removal apparatus as claimed in claim 1, wherein the treatment unit is configured for feeding purified water to the gas cooler.

5. The removal apparatus as claimed in claim 1, wherein a direct contact cooler is used as the gas cooler.

6. The removal apparatus as claimed in claim 1, wherein the absorber is connected hydrodynamically via a discharge line to a feed line of the desorber.

7. The removal apparatus as claimed in claim 1, wherein the desorber comprises a discharge line for a gas outlet stream in which a desorber spray cooling unit connected hydrodynamically to the treatment unit is installed, wherein the desorber spray cooling unit is configured to use a respective spray cooling medium to spray cool the gas outlet stream, and wherein the purified water from the treatment unit is used as the respective spray cooling medium in the desorber spray cooling unit.

8. The removal apparatus as claimed in claim 1, wherein the treatment unit is connected hydrodynamically via a feed line to the gas cooler.

9. The removal apparatus as claimed in claim 8, wherein the gas cooler is installed in a coolant circuit which is connected hydrodynamically via the feed line to the treatment unit.

10. The removal apparatus as claimed in claim 9, wherein the treatment unit is configured for feeding purified water to the coolant circuit of the gas cooler.

11. A process for removing carbon dioxide from a gas stream, the process comprising: feeding a gas stream to a gas cooler, cooling the gas stream within the gas cooler and condensing water out of the gas stream, taking water from the gas cooler, wherein at least a substream of the water from the gas cooler is fed to a treatment unit in which the water is purified for a further use in the process, spray cooling a second substream of the water from the gas cooler in a spray cooling unit configured to use water purified in the treatment unit as a spray cooling medium, returning water than has been spray cooled to the gas cooler, and feeding the cooled gas stream to an absorber of a removal apparatus in which carbon dioxide present in the gas stream is separated from the gas stream by means of a scrubbing medium, wherein the scrubbing medium loaded with carbon dioxide from the absorber is fed to a desorber of the removal apparatus in which the absorbed carbon dioxide is liberated from the scrubbing medium, and wherein the scrubbing medium loaded with carbon dioxide is fed into the desorber from the absorber without being preheated.

12. The process as claimed in claim 11, wherein the substream is taken from a coolant circuit of the gas cooler.

13. The process as claimed in claim 12, wherein the water which has been purified in the treatment unit is fed to the coolant circuit.

14. The process as claimed in claim 11, wherein the purification of the water in the treatment unit is effected by means of reverse osmosis.

15. The process as claimed in claim 11, wherein the water which has been purified in the treatment unit is fed to the gas cooler.

16. The process as claimed in claim 11, wherein a direct contact cooler is used as the gas cooler.

17. The process as claimed in claim 11, spray cooling scrubbing medium fed to the absorber in an absorber spray cooling unit configured to use water purified in the treatment unit as a respective spray cooling medium.

18. The process as claimed in claim 11, spray cooling carbon dioxide liberated in the desorber in a desorber spray cooling unit configured to use water purified in the treatment unit as a respective spray cooling medium.

19. A removal apparatus for carbon dioxide from a gas stream, comprising: an absorber configured to separate carbon dioxide from the gas stream by means of a scrubbing medium, a desorber which is connected hydrodynamically to the absorber and configured to liberate absorbed carbon dioxide from the scrubbing medium, a gas cooler which is located hydrodynamically upstream of the absorber , which is configured to cool the gas stream, and which is configured to produce a stream of water, a spray cooling unit configured to use a spray cooling medium to spray cool a first portion of the stream of water discharged from the gas cooler; a treatment unit which is located downstream of the gas cooler and is configured for purifying a second portion of the stream of water discharged from the gas cooler, and a connection configured to deliver purified water from the treatment unit to the spray cooling unit where the purified water is used as the spray cooling medium, wherein the scrubbing medium is fed into the desorber from the absorber without being preheated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A working example of the invention is described in more detail below with the aid of a drawing.

DETAILED DESCRIPTION OF INVENTION

(2) The sole FIGURE shows a removal apparatus 1 for carbon dioxide from a flue gas stream. The removal apparatus 1 comprises an absorber 3 and a desorber 5 which is hydrodynamically connected to the absorber 3. A gas cooler 7 configured as flue gas cooler, to which a treatment unit 9 for water is assigned, is located hydrodynamically upstream of the absorber 3.

(3) In order to purify flue gas, which is obtained, for example, as combustion offgas in the combustion of fossil fuels in power stations, and in particular to separate the carbon dioxide present in the flue gas from the flue gas, a flue gas stream is firstly fed via a flue gas line 11 to the removal apparatus 1. The flue gas flows via the flue gas line 11 into the flue gas cooler 7 which is configured as a direct contact cooler and is operated using water as coolant. The flue gas is cooled in the flue gas cooler 7 before it is fed to the absorber 3 of the removal apparatus 1.

(4) The flue gas cooler 7 itself is installed in a coolant circuit 13 which comprises a warm water line 15, a cold water line 17 and a cooling unit 19 which is configured as air cooler and is installed between the two lines 15, 17. The water which has been heated during cooling of the flue gas is discharged from the flue gas cooler 7 via the warm water line 15, cooled in the cooling unit 19 and fed via the cold water line 17 back to the flue gas cooler 7 for renewed cooling of the flue gas stream.

(5) Since not only carbon dioxide but also water is present as combustion product in the flue gas, this water condenses out during cooling of the flue gas in the flue gas cooler 7 and mixes with the cooling water stream. In order to keep the amount of water required for cooling of the flue gas constant within the coolant circuit 13, excess water is therefore in the present case continuously taken off in the flue gas cooler 7 from the water stream 21 leaving the gas cooler 7 via the warm water line 15, for which purpose a substream 23 is taken off.

(6) Instead of discarding the excess part of the water as has hitherto been usual, the substream 23 of the water from the flue gas cooler 7 is fed via a feed line 25 to the treatment unit 9. In the treatment unit 9, the water which has been taken off is purified by means of reverse osmosis in a corresponding reverse osmosis plant 27. The purified water is then stored in a stock tank 29, which is part of the treatment unit 9.

(7) The water stored in the stock tank 29 can then be used as required for cooling apparatus components and/or fluid streams used in the removal apparatus 1. In the present case, the water from the stock tank 29 is used, in particular, for cooling the air cooler 19 in the coolant circuit 13 in the form of spray cooling, which is indicated by the broken line 31. In other words, the stock tank 29 and the treatment unit 9 are connected to the air cooler 19 in order to introduce water for the purpose of cooling. As an alternative, the water can also be transported in another way from the stock tank 29 to the air cooler 19. The treatment unit 9 can also be configured for discharging the purified water to the coolant circuit 13 and/or to the gas cooler 7. This is depicted in FIG. 1 by a corresponding discharge line 30.

(8) In order to ensure the desired separation of carbon dioxide from the flue gas, the flue gas which has been cooled in the flue gas cooler 7 flows via a feed line 33 into the absorber 3 of the removal apparatus 1. Here, it is brought into contact with a scrubbing medium, namely a potassium-containing amino acid salt, in which the carbon dioxide present in the flue gas is absorbed. The scrubbing medium loaded with carbon dioxide is conveyed from the absorber 3 to the desorber 5. For this purpose, the loaded scrubbing medium is taken off from the absorber 3 via the discharge line 35.

(9) A first substream 37 is fed via a branch line 39 connected to the discharge line 35 of the absorber 3 into a first desorber stage 41 of the desorber 5 located downstream of the absorber 3, for which purpose the branch line 39 is hydrodynamically connected to a feed line 43 of the desorber 5. The first substream 37 is fed into the first desorber stage 41 without preheating at the top 45 of the desorber 5.

(10) A second substream 47 is fed to a second desorber stage 49 of the desorber 5 via a hydrodynamic connection of the discharge line 35 to a further feed line 51 of the desorber 5. Here, the second substream 47 firstly passes through the heat exchanger 53 and is preheated by the regenerated scrubbing medium recirculated from the desorber 5.

(11) In the desorber 5, the carbon dioxide absorbed in the scrubbing medium is liberated and taken off via a discharge line 55 at the top 45 of the desorber 5. A further cooling unit 57 configured as an air cooler which serves to cool the gas outlet stream is installed in the discharge line 55. This air cooler 57 is likewise cooled by means of water which has been purified in the treatment unit 9. The amount of water required for this purpose is taken from the stock tank 29 and utilized for spray cooling the air cooler 55. Here too, this utilization is indicated by a broken line 59. The broken line 59 can, in particular, be a connecting conduit for water or a transport connection for water. The cooled gas outlet stream is finally conveyed, for example, to an appropriate utilization facility 60, for example for storage and/or possible further utilization of the carbon dioxide.

(12) The scrubbing medium which has been freed of carbon dioxide collects at the bottom 61 of the desorber 5 and is fed to a pressure vessel 63 configured as lean solvent flash process. For this purpose, the desorber 5 is connected via a discharge line 65 to the pressure vessel 63. In the pressure vessel 63, the scrubbing medium is depressurized to form a gas phase and a liquid phase. The gas is fed via a discharge line 67 of the pressure vessel 63 to the desorber 5. Heat required for desorption of the carbon dioxide from the scrubbing medium can be recovered by subsequent condensation of the vaporous scrubbing medium in the desorber 5.

(13) In addition, a reboiler 69 is connected to the desorber 5 and, as bottom vaporizer, likewise supplies part of the regeneration heat for liberation of the carbon dioxide absorbed in the scrubbing medium.

(14) The liquid phase of the scrubbing medium is recirculated from the pressure vessel 63 to the absorber 3, for which purpose a discharge line 71 of the pressure vessel 63 is connected to a feed line 73 of the absorber 3. During this recirculation, the regenerated scrubbing medium likewise passes through the heat exchanger 53 and is cooled here by transfer of heat to the loaded scrubbing medium from the absorber 3.

(15) To ensure that the scrubbing medium has the low temperatures required for the absorption of carbon dioxide from the flue gas before entering into the absorber 3, a further cooling unit 75, by means of which the scrubbing medium is cooled further before entry into the absorber 5, is installed in the feed line 73 to the absorber 3. This cooling unit 75, too, is configured as an air cooler and is cooled by spray cooling using water taken from the stock tank 29, which is indicated by the broken line 77.

(16) The broken line 77 can, in particular, be a connecting conduit for water or a transport connection.

(17) In addition, there is a reclaiming apparatus 79 which, for further treatment of the scrubbing medium, in particular by removal of nitrogen oxides (NO.sub.x) and sulfur oxides (SO.sub.x), takes off part of the scrubbing medium from the feed line 73 and treats it appropriately. The scrubbing medium is then fed, after purification and treatment, to the absorber 3 and can there again be used for absorption of carbon dioxide from a flue gas.

(18) The cooling of the cooling units 19, 57, 75 by means of water from the stock tank 29 is essentially optional. It is thus possible to cool one, more than one or, as described here, all cooling units 19, 57, 75 by means of the water stored in the stock tank 29. Furthermore, it is likewise possible to use water-cooled cooling units instead of the air coolers 19, 57, 75. In the case of water-cooled cooling units, it is possible to use, for example, heat exchangers which use the water which has been purified in the treatment unit 9 as coolant in an appropriate coolant circuit. The cooling units can be connected directly via a water line to the treatment unit 9. The treated water can, as an alternative, also be transported as freight to the cooling units.