EXHAUST GAS SCRUBBER WITH ENERGY INTEGRATION

Abstract

A gas scrubber may include an absorption apparatus configured for receiving a gas and absorbing the gas in an absorption medium, as well as an evaporation apparatus configured for evaporating at least a part of the liquid that is introduced. The absorption apparatus may have an introduction apparatus for the gas, an apparatus for circulating the absorption solution that has reacted with the gas, a discharge apparatus for at least a part of the absorption solution that has reacted with the gas, and a cooling system for the circulating absorption solution. The absorption apparatus and the evaporation apparatus can be connected via a heat exchanger such that heat content of the absorption solution that has reacted with the gas is used at least in part for the evaporation.

Claims

1.-15. (canceled)

16. A gas scrubber comprising: an absorption apparatus configured to receive a gas and to absorb the gas in an absorption medium, wherein the absorption apparatus comprises: an introduction apparatus for the gas, an apparatus for circulating an absorption solution that has reacted with the gas, a discharge apparatus for at least a part of the absorption solution that has reacted with the gas; a cooler for the absorption solution that circulates; and an evaporation apparatus configured to evaporate at least a part of a liquid that is introduced, wherein the cooler and the evaporation apparatus are connected via a heat exchanger or are configured as a heat exchanger such that heat content of the absorption solution that has reacted with the gas is used at least in part for the evaporation.

17. The gas scrubber of claim 16 configured for treatment of an ammonia-containing offgas and for absorption with an aqueous solution containing nitric acid or sulfuric acid.

18. The gas scrubber of claim 16 wherein the heat exchanger is a recuperator.

19. The gas scrubber of claim 16 wherein the absorption apparatus is a column comprising internals or a venturi scrubber.

20. The gas scrubber of claim 16 wherein the heat exchanger is configured such that a circulated portion of a salt solution is guided as a heating medium through the heat exchanger and such that a branched-off portion of the salt solution is guided in counter-current into the heat exchanger as a medium to be evaporated.

21. The gas scrubber of claim 20 configured to set a temperature of the circulated portion of the salt solution entering the heat exchanger to be higher than a temperature of the branched-off portion of the salt solution entering the heat exchanger.

22. The gas scrubber of claim 16 comprising an apparatus for reducing a pressure on an evaporator side of the heat exchanger.

23. The gas scrubber of claim 16 comprising an apparatus for feeding in fresh absorption medium.

24. The gas scrubber of claim 16 comprising at least one of: a second heat exchanger arranged in a circuit of the circulating absorption solution and configured to regulate a temperature of the circulating absorption solution, wherein the second heat exchanger is configured to use steam or process heat as a heat transfer medium; a second evaporation stage arranged downstream of the evaporation apparatus; a second heat exchanger arranged in a circuit of the circulating absorption solution and configured to regulate a temperature of the circulating absorption solution, wherein the second heat exchanger is configured to use steam or process heat as a heat transfer medium, and a second evaporation stage arranged downstream of the evaporation apparatus; a second heat exchanger or a heating apparatus configured for additional heating of a salt solution discharged from an acid scrubber prior to entering the evaporation apparatus; a second evaporation stage configured for further evaporation of a concentrated salt solution after leaving the evaporation apparatus; or a second heat exchanger or a heating apparatus configured for additional heating of a salt solution discharged from an acid scrubber prior to entering the evaporation apparatus, and a second evaporation stage configured for further evaporation of a concentrated salt solution after leaving the evaporation apparatus.

25. A process for scrubbing gas comprising: introducing a gas into an absorption apparatus; circulating an absorption solution; discharging a part of the circulating absorption solution; and concentrating a discharged solution, which is the part of the circulating solution that is discharged, by evaporating at least a part of an absorption medium, wherein heat content of the circulating absorption solution is used at least in part for the evaporation.

26. The process of claim 25 wherein either: the gas is an ammonia-containing offgas; the absorption medium is an aqueous solution containing nitric acid or sulfuric acid; or the gas is an ammonia-containing offgas and the absorption medium is an aqueous solution containing nitric acid or sulfuric acid.

27. The process of claim 25 comprising conducting the circulating absorption solution and the discharged solution separately through a heat exchanger, wherein the circulating absorption solution is fed to the heat exchanger as heating medium and the discharged solution is fed to the heat exchanger in counter-current as medium to be evaporated.

28. The process of claim 27 wherein a temperature of the circulating absorption solution entering the heat exchanger is higher than a temperature of a solution exiting an evaporator used for the evaporation.

29. The process of claim 27 comprising adjusting or regulating a pressure on a side of the heat exchanger at which the evaporation takes place such that the pressure is lower than a pressure on a side of the heat exchanger through which the circulating absorption solution is conducted.

30. The process of claim 27 comprising adjusting or regulating a pressure on a side of the heat exchanger at which the evaporation takes place such that the pressure is lower than a pressure on a side of the heat exchanger through which the circulating absorption solution is conducted and such that an exit temperature of the absorption medium to be evaporated is below an entry temperature of the circulating absorption solution.

31. The process of claim 27 comprising adjusting or regulating a pressure on a side of the heat exchanger at which the evaporation takes place such that the pressure is lower than a pressure on a side of the heat exchanger through which the circulating absorption solution is conducted and such that a boiling temperature of the absorption medium to be evaporated is below a temperature of the circulating absorption solution.

32. The process of claim 27 wherein at least one of: a salt solution exiting an acid scrubber is heated prior to entering the heat exchanger; or a concentrated salt solution is evaporated after leaving an evaporator used for the evaporation.

33. The process of claim 25 performed using a gas scrubber that comprises: an absorption apparatus configured to receive a gas and to absorb the gas in an absorption medium, wherein the absorption apparatus comprises: an introduction apparatus for the gas, an apparatus for circulating an absorption solution that has reacted with the gas, a discharge apparatus for at least a part of the absorption solution that has reacted with the gas; a cooler for the absorption solution that circulates; and an evaporation apparatus configured to evaporate at least a part of a liquid that is introduced, wherein the cooler and the evaporation apparatus are connected via a heat exchanger or are configured as a heat exchanger such that heat content of the absorption solution that has reacted with the gas is used at least in part for the evaporation.

Description

[0038] Embodiment I. A gas scrubber comprising [0039] a) an absorption apparatus configured for receiving a gas and absorbing the gas in an absorption medium, wherein the absorption apparatus [0040] i) has an introduction apparatus for the gas, [0041] ii) has an apparatus for circulating the absorption solution that has reacted with the gas, [0042] iii) has a discharge apparatus for at least a part of the absorption solution that has reacted with the gas, this portion preferably being determined depending on the desired concentration of the bleed and the amount and loading of the absorbed gas, [0043] b) a cooler for the circulating absorption solution, [0044] c) an evaporation apparatus configured for evaporating at least a part of the liquid introduced, characterized in that the cooler and the evaporation apparatus are connected via a heat exchanger in such a way or are designed as a heat exchanger in such a way that the heat content of the absorption solution that has reacted with gas is used at least in part for the evaporation.

[0045] Embodiment II. The gas scrubber according to embodiment I, characterized in that the gas scrubber is configured for the treatment of an offgas, in particular an ammonia-containing offgas, and for absorption with an acid-containing scrubbing medium, in particular an aqueous solution containing nitric acid or sulfuric acid.

[0046] Embodiment III. The gas scrubber according to either of embodiments I and II, characterized in that the heat exchanger is a recuperator, preferably a falling-film evaporator, particularly preferably a shell and tube heat exchanger.

[0047] Embodiment IV. The gas scrubber according to any of the preceding embodiments, characterized in that the absorption apparatus is a column comprising internals (random packing, structured packing, separating trays) or a venturi scrubber.

[0048] Embodiment V. The gas scrubber according to any of the preceding embodiments, characterized in that the heat exchanger is configured such that the circulated absorption solution that has reacted with the gas is guided as heating medium into the heat exchanger, and the portion diverted from the absorption solution that has reacted with the gas is guided in counter-current into the heat exchanger as a medium to be evaporated, wherein the gas scrubber is preferably configured to set the temperature of the circulated absorption solution that has reacted with the gas and is entering the heat exchanger to be higher than the temperature of the portion diverted from the absorption solution that has reacted with the gas and entering the heat exchanger.

[0049] Embodiment VI. The gas scrubber according to any of the preceding embodiments, additionally comprising an apparatus for reducing the pressure on the cooler side of the heat exchanger. As a matter of principle, this leads to flash evaporation, since the pressure on the cooler side is necessarily reduced to boiling condition in order to achieve the required lower temperature level.

[0050] Embodiment VII. The gas scrubber according to any of the preceding embodiments, additionally comprising an apparatus for the feeding in of fresh absorption medium.

[0051] Embodiment VIII. The gas scrubber according to any of the preceding embodiments, additionally comprising [0052] a heat exchanger additionally arranged in the circuit of the circulating solution and configured for regulating the temperature of the circulating solution, in particular for increasing the temperature of the circulating solution, where steam or process heat can be used as the heat transfer medium, or [0053] a second evaporation stage arranged downstream of the first evaporation stage, or [0054] a heat exchanger arranged in the circuit of the circulating solution and configured for regulating the temperature of the circulating solution, in particular for increasing the temperature of the circulating solution, where steam or process heat can be used as the heat transfer medium, and a second evaporation stage arranged downstream of the first evaporation stage, or [0055] a further heat exchanger or a heating apparatus configured for additional heating of the salt solution discharged from the acid scrubber prior to entering the, or [0056] at least one further evaporator stage configured for further evaporation of the concentrated salt solution after leaving the evaporator, especially comprising [0057] a further heat exchanger or a heating apparatus configured for additional heating of the salt solution discharged from the acid scrubber prior to entering the, or [0058] at least one further evaporator stage configured for further evaporation of the concentrated salt solution after leaving the evaporator, or very particularly preferably comprising [0059] a further heat exchanger or a heating apparatus configured for additional heating of the salt solution discharged from the acid scrubber prior to entering the, and at least one further evaporator stage configured for further evaporation of the concentrated salt solution after leaving the evaporator.

[0060] Embodiment IX. A process for scrubbing gas, comprising the following process steps: [0061] I) introducing a gas into an absorption apparatus, [0062] II) circulating the absorption solution, [0063] III) discharging a part of the circulating solution produced by step II), [0064] IV) concentrating the discharged solution by evaporating at least a part of the absorption medium, characterized in that the heat content of the circulating solution is used at least in part for the evaporation in step IV).

[0065] Embodiment X. The process according to embodiment IX, characterized in that the circulating solution and the discharged solution are both conducted separately through a common heat exchanger, the circulating solution being fed to the heat exchanger as heating medium and the discharged solution being fed to the heat exchanger in counter-current as medium to be evaporated.

[0066] Embodiment X. The process according to either of embodiments IX and X, characterized in that the gas is an offgas, in particular an ammonia-containing offgas.

[0067] Embodiment XII. The process according to any of embodiments IX to XI, characterized in that the absorption medium is an acid-containing scrubbing medium, in particular an aqueous solution containing nitric acid or sulfuric acid.

[0068] Embodiment XII. The process according to any of embodiments IX to XII, characterized in that the temperature of the circulating solution entering the heat exchanger is higher than the solution present in the evaporator.

[0069] Embodiment XIV. The process according to any of embodiments IX to XIII, characterized in that the pressure on the side of the heat exchanger at which the evaporation takes place is adjusted or regulated such that it is lower than the pressure on the side of the heat exchanger through which the circulating solution is conducted, preferably such that the temperature of the solution to be evaporated is below the temperature of the circulating solution, especially such that the boiling temperature of the solution to be evaporated is below the temperature of the circulating solution.

[0070] Embodiment XV. The process according to any of embodiments IX to XIV, characterized in that in addition either the salt solution discharged from the acid scrubber is additionally heated prior to entering the heat exchanger, preferably by means of a further heat exchanger or a heating apparatus, or the concentrated salt solution after leaving the evaporator is further evaporated, preferably by at least one further evaporator stage, or both the salt solution discharged from the acid scrubber is additionally heated prior to entering the heat exchanger, preferably by means of a further heat exchanger or a heating apparatus, and the concentrated salt solution after leaving the evaporator is further evaporated, preferably by at least one further evaporator stage.

[0071] Embodiment XVI. The process according to any of embodiments IX to XV, characterized in that it is carried out using a gas scrubber according to any of embodiments I to VII.

[0072] The present invention is elucidated in more detail hereinbelow with reference to the drawings. The drawings are not to be interpreted as limiting and are not to scale. The drawings moreover do not contain all of the features comprised by customary plants but rather are reduced to the features essential to the present invention and for the understanding thereof. Identical reference signs in the various figures each have the same meaning, as given in the list of reference signs.

[0073] FIG. 1 illustrates a conventional process according to the prior art to date.

[0074] To this end, acid 1 and water 2 are introduced into an acid scrubber 4 and additionally ammonia-containing offgas 3; cleaned offgas 3a then exits the acid scrubber. A salt solution (ammonium nitrate solution) is formed from the acid and the gas in the acid scrubber and exits downwards as salt solution 5. A part of this salt solution 5 is circulated and fed back to the acid scrubber 4 as a scrubbing solution. As part of this circulation of the salt solution 5, the latter is cooled by a circulation cooler 6. The temperature T.sub.SS,1 is the temperature at which the salt solution 5 enters the circulation cooler 6 and the temperature T.sub.SS,2 is the temperature at which the salt solution 5 exits the circulation cooler 6 again. The acid scrubber 4 is operated here with a pressure p.sub.SCR. The portion of the salt solution 5 that is not circulated is then conducted to an evaporator 7. This salt solution 5 has an entry temperature into the evaporator 7 T.sub.E,1. The salt solution 5 is concentrated in the evaporator 7 in that a part of the liquid is evaporated and leaves the evaporator 7 as steam 9. The concentrated salt solution 5a leaves the evaporator 7 at a lower temperature T.sub.E,2. The evaporator 7 is operated with a pressure p.sub.Evap. The heat of reaction Q.sub.R is used in the acid scrubber 4. In the circulation cooler 6, the temperature of the salt solution 5 is lowered and heat is removed as cooling power Q.sub.C. In the evaporator 7 heat energy is input via the heating power Q.sub.H.

[0075] According to this conventional prior art process, two different apparatuses are needed in order firstly to cool the salt solution (the circulation cooler) and in order secondly to concentrate the salt solution by evaporation, namely the evaporator.

[0076] FIG. 2 describes a process according to the invention which is based on the same premises as the conventional process shown in FIG. 1.

[0077] Here, too, acid and water or makeup water 2 are reacted with offgas 3 in an acid scrubber 4 and cleaned offgas 3a is obtained. Salt solution 5 is discharged from the acid scrubber 4 and sent to further processing. In contrast to the conventional prior art process, however, an integrated cooler-evaporator 8 is used in the process according to the invention, in which the cooling of the salt solution 5 and the evaporation of the salt solution 5 take place together. Here too, the salt solution 5 has an entry temperature T.sub.SS,1 which is higher than the exit temperature T.sub.SS,2, before a part of the salt solution 5 is then recycled back into the acid scrubber 4. In contrast to the processes and/or apparatuses of the prior art, however, in the integrated cooler-evaporator 8 according to the present invention, the absorption apparatus 4 and the evaporation apparatus 7 are connected via a heat exchanger in such a way that the heat content of the salt solution that has reacted with gas is not extracted via a circulation cooler and then lost, but is instead also used directly for evaporation of the salt solution 5 to give a concentrated salt solution 5a with the release of steam 9. For this, FIG. 2 illustrates that, prior to entering the integrated cooler-evaporator 8, the salt solution 5 is divided and only the part circulating via the scrubber is led through the cooler-evaporator 8 for cooling and another part is branched off, routed around the cooling unit and is introduced on the other side of the integrated cooler-evaporator unit 8 with the temperature T.sub.E,1 and finally leaves the integrated cooler-evaporator unit 8 as concentrated salt solution 5a with the temperature T.sub.E,2. In this integrated process, the pressure p.sub.SCR in the acid scrubber 4 is greater than the pressure p.sub.Evap in the integrated cooler-evaporator 8.

[0078] In FIG. 2, the letters A and B furthermore show two different options which can be present independently of one another, but do not have to be. Option 1, shown with the letter A, comprises additional preheating of the salt solution (absorption solution). The second option, shown with the letter B, comprises the one additional evaporation unit. Both option A and option B require the supply of amounts of heat Q and are, as already stated, optional.

[0079] It is pointed out that, in the legend to the figures and the description thereof, the Q, illustrated scientifically correctly, would have to be a Q with a dot on top, but for typesetting and printing reasons in the context of the present description is illustrated as a simple Q; in the figures it is correctly represented as Q with dot.

LIST OF REFERENCE SIGNS

[0080] 1 acid [0081] 2 water (makeup) [0082] 3 offgas [0083] 3a cleaned offgas [0084] 4 acid scrubber [0085] 5 salt solution [0086] 5a concentrated salt solution [0087] 6 circulation cooler [0088] 7 evaporator [0089] 8 integrated cooler-evaporator (according to the invention) [0090] 9 steam [0091] T.sub.E,1 entry temperature of the solution to be evaporated at the evaporator [0092] T.sub.E,2 exit temperature of the solution to be evaporated at the evaporator [0093] T.sub.SS,1 entry temperature of the circulating stream to be cooled at the cooler [0094] T.sub.SS,2 exit temperature of the circulating stream to be cooled at the cooler [0095] Q heat/amount of heat [0096] Q.sub.R heat of reaction [0097] Q.sub.C cooling power [0098] Q.sub.H heating power [0099] p.sub.SCR scrubber pressure [0100] p.sub.Evap evaporator pressure [0101] A option 1 [0102] B option 2