DE102017108846A1 - Device and method for waste gas scrubbing and urea plant with a waste gas scrubbing - Google Patents

Abstract

The present invention relates to a device (1) for removing a gaseous chemical compound from an exhaust gas, wherein the gaseous chemical compound can be converted into an aqueous liquid phase by reaction with a washing solution (22), with a channel (5) having a washing area (5). 12) having n washing stages arranged such that an exhaust gas is feasible along a transport direction (T) from a first washing stage to an nth washing stage, where n is at least two, each one of the n washing stages
a surface enlargement structure (3), in particular a bed or a packing, and
a spraying device (2) for spraying the surface enlarging structure (3) with a solvent (22),
a drain (35) for collecting a sump liquor discharged from said surface enlarging structure (3) containing said washing solution (22), and
- a return line (4) connected to the drain (35) for returning a first partial flow of the sump solution to the spray device (2), and with the exception of the outlet (35) of the first washing step, the drain (35) of each washing step a washing stage connecting line (7) for the passage of a second partial flow of the sump solution with the return line (4) opposite to the transport direction (T) immediately adjacent washing stage is connected and wherein the n-th washing stage an inlet (51) for supplying the return line (4 ) of the nth wash step with fresh wash solution (22).

Description

Technical field of the invention

The invention relates to a device for removing a gaseous chemical compound from an exhaust gas, wherein the gaseous chemical compound is convertible by reaction with a washing solution in an aqueous liquid phase, with a channel having a washing area with n washing stages, which are arranged such that an exhaust gas along a transport direction from a first washing stage to an n-th washing stages is feasible, where n is at least two. Furthermore, the invention relates to a method for removing a gaseous chemical compound from an exhaust gas, wherein the gaseous chemical compound is converted into an aqueous liquid phase by reaction with a washing solution, wherein the exhaust gas through a washing region of a channel along a transport direction from a first washing step up to an n-th washing stage is performed, where n is at least two.

State of the art

Such a device with several washing stages is from the US 5,403,568 A known. The washing stages of this apparatus each have a surface-enlarging structure formed as a package, which is sprayed with a washing solution by a spraying device. The bottoms streams flowing from the surface augmentation structures of the individual washing stages are combined, mixed with fresh wash solution, and then returned to the sprayers of the individual washing stages. In this device, it has been found to be disadvantageous that the concentration of sprayed washing solution in all washing stages is identical, so that the detergent mass flow, for example, an acid mass flow, can be set in each washing step exclusively on the spray rate with which sprays the detergent to the surface enlargement structure becomes. This limits the efficiency of the device.

Against this background, it is an object of the present invention to provide an apparatus and a method for removing a gaseous chemical compound from an exhaust gas, with which the efficiency for the removal of the chemical compound, from the exhaust gas over those of the prior art is improved.

Disclosure of the invention

• - eine Oberflächenvergrößerungsstruktur, insbesondere eine Schüttung oder eine Packung, und
• - eine Sprühvorrichtung zum Besprühen der Oberflächenvergrößerungsstruktur mit einem Lösungsmittel,
• - einen Abfluss zum Sammeln einer von der Oberflächenvergrößerungsstruktur abgelaufenen Sumpflösung, welche die Waschlösung enthält, und
• - eine mit dem Abfluss verbundene Rückführleitung zur Rückführung eines ersten Teilstroms der Sumpflösung zu der Sprühvorrichtung umfasst,

und wobei mit Ausnahme des Abflusses der ersten Waschstufe, der Abfluss jeder einzelnen Waschstufe über eine Waschstufen-Verbindungsleitung zur Durchleitung eines zweiten Teilstroms der Sumpflösung mit der Rückführleitung der entgegen der Transportrichtung unmittelbar benachbarten Waschstufe verbunden ist und wobei die n-te Waschstufe einen Zulauf zur Versorgung der Rückführleitung der n-ten Waschstufe mit frischer Waschlösung umfasst.The object is achieved by a device for removing a gaseous chemical compound from an exhaust gas, wherein the gaseous chemical compound can be converted by reaction with a washing solution in an aqueous liquid phase, with a channel having a washing area with n washing stages, which are arranged in that an exhaust gas along a transport direction from a first washing stage to an n-th washing stages is feasible, where n is at least two, wherein each one of the n washing stages

• a surface enlargement structure, in particular a bed or a packing, and
• a spraying device for spraying the surface enlarging structure with a solvent,
• a drain for collecting a sump liquor discharged from the surface enlargement structure containing the wash solution, and
• a return line connected to the drain for returning a first partial flow of the sump solution to the spray device,

and wherein, with the exception of the outflow of the first washing stage, the outflow of each individual washing stage is connected via a washing stage connecting line for passing a second partial stream of the sump solution to the return line of the directly adjacent to the transport direction adjacent washing stage and wherein the n-th washing stage an inlet for supply the return line of the n-th washing stage with fresh wash solution.

The object is further achieved by a method for removing a gaseous chemical compound from an exhaust gas, wherein the gaseous chemical compound is converted by reaction with a washing solution into an aqueous liquid phase, wherein the exhaust gas through a washing area of a channel along a transport direction of a first washing stage is conducted to an n-th washing stage, where n is at least two, wherein in each of the n washing stages each a surface enlargement structure, in particular a bed or a pack, is sprayed by means of a spray device with the washing solution, a running from the surface enlargement structure sump solution collected and a first partial flow of the sump solution is returned via a return line to the spray device, wherein, with the exception of the first washing step, a second partial flow of the sump solution of each washing step via a connecting line in the Return line of the counter to the transport direction immediately adjacent washing stage is passed, and wherein the return line of the n-th washing stage is supplied via an inlet fresh washing solution.

In the apparatus according to the invention and the method according to the invention, the sump solution is fed to a washing stage via a connecting line of the respective washing stage immediately opposite to the transport direction. In this respect, a flow of the washing solution against the transport direction of the exhaust gas can be made possible. Further, the nth washing step includes an inlet for supplying the return line of the nth washing step with fresh washing solution, so that the concentration of the washing solution sprayed in the nth washing step is increased. In the apparatus, therefore, a concentration gradient of the spray solution sprayed in the individual washing stages can be adjusted, such that the concentration of the washing solution in the transport direction of the exhaust gas increases. In the nth washing stage, a maximum of the concentration of the washing solution results, whereby the residual content of undesired chemical compounds in the exhaust gas can be reduced to a minimum. An apparatus and method is provided with improved efficiency over the prior art.

The first to (n-1) th washing stage preferably does not comprise an inlet for supplying the return line of the respective washing stage with fresh washing solution.

By the concentration of the washing solution in a certain stage is meant the mole fraction in mol% of a detergent component in the washing solution in this stage, i. with respect to the washing solution which is sprayed at this stage. In the operation of the device, the mole fraction in mol% of said detergent component per mole of detergent in the n-th stage is preferably one and a half times or twice or three times or four times or five times as large as in the first stage. During operation of the plant, the molar fraction in mol% of said detergent component per mol of detergent decreases in the direction of transport and starting at the nth stage and ending in the first stage depending on the degree of conversion of the component to be washed out of the gas stream, preferably per Washing step by 4 mol% or 8 mol% or 12 mol% or 16 mol% or 20 mol% or 24 mol% or 28 mol% or 32 mol% or 36 mol% or 40 mol% or 44 mol% or 48 mol% or 52 mol% or 56 mol% or 60 mol%.

The device according to the invention is intended to deposit gaseous chemical compounds which are present in the exhaust gas and can be integrated into an aqueous liquid phase by an acid-base reaction, in order to prevent that officially prescribed threshold values in the exhaust gas emitted by the device are exceeded ,

Preferably, the wash solution is an acidic wash solution. Particularly preferably, the acidic wash solution comprises sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, or mixtures of sulfuric acid, nitric acid, hydrochloric acid and / or phosphoric acid, or mixtures of sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid and / or urea solution.

Alternatively, it is preferred if the wash solution is a base. Preferably, the wash solution comprises a strong and / or a weak base. Preferably, the washing solution comprises a strong inorganic and / or a weak inorganic and / or a strong organic and / or a weak organic base. Preferably, the washing solution comprises sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia solutions and / or calcium hydroxide (Ca (OH) ₂ ).

The washing solution preferably comprises mono-, bi- and / or trifunctional amines, more preferably MDEA (methyldiethanolamine).

• - regellose Strukturelemente ausgewählt aus der Gruppe bestehend aus Raschig-Ringen, Pall-Ringen, Sattel-Körpern, Feder-typischen Körpern und Kombinationen davon; und/oder
• - strukturierte Strukturelemente ausgewählt aus der Gruppe bestehend aus Blechen, gewellten Blechen, geformten Blechen und Kombinationen davon; und/oder
• - Materialien ausgewählt aus der Gruppe bestehend aus Metall, Glas, Kunststoff, Carbonfasern und Kombinationen davon.

Preferably, the surface enlarging structure is designed as an installation in the washing area of the channel, which leads to a corresponding enlargement of the surface, but opposes little resistance to the exhaust gas flowing in the transport direction due to the generated pressure loss. The surface enlarging structure preferably comprises random packings and / or structured packings. Preferably, the surface enlargement structure comprises random beds selected from the group consisting of Raschig rings, saddles, spirals, and combinations thereof. The surface enlargement structure preferably comprises structured packings selected from the group consisting of fabric packs, sheet metal packings, expanded metal packs, plastic packs, grid packings and combinations thereof. Preferably, the surface augmentation structure comprises random beds selected from the group consisting of Raschig rings, calipers, spirals, and combinations thereof, and structured packings selected from the group consisting of fabric packs, sheet metal packings, expanded metal packs, plastic packs, grid packings, and combinations thereof. Preferably, the surface enlargement structure comprises

• random structure elements selected from the group consisting of Raschig rings, Pall rings, saddle bodies, spring-type bodies and combinations thereof; and or
• - structured structural elements selected from the group consisting of sheets, corrugated Sheets, shaped sheets and combinations thereof; and or
• Materials selected from the group consisting of metal, glass, plastic, carbon fibers and combinations thereof.

Preferably, n is equal to two - i. the device has exactly two washing stages - so that a device with a minimum investment cost is obtained. Alternatively, n may be three or four or five or six or seven or eight or nine or ten.

An advantageous embodiment of the invention provides that each one of the n washing stages comprises a conveying device, in particular a pump, for conveying the first partial flow of the sump solution through the return line. By means of the conveyors, the spray rate in each washing stage can be adjusted independently of the spray rates of the other washing stages. For this purpose, a quantity control, a frequency control, a voltage control, a current control or the return of a partial flow from a pressure side to a suction side of the conveyor (partial feedback) can be used.

Preferably, the outflow of the first washing stage via a discharge line for passing a second partial flow of the sump solution with a measuring device for determining the pH of the second partial flow of the sump solution and / or with a measuring device for determining the concentration of the washing solution in the second partial flow of the sump solution connected. Based on the pH and / or the concentration of the washing solution, the amount of fresh washing solution to be supplied to the nth washing stage can be determined.

In this context, it has been found to be advantageous if the measuring device for determining the pH of the second partial flow of the sump solution and / or the measuring device for determining the concentration of the washing solution in the second partial flow of the sump solution with a regulating device for regulating the above Feed supplied amount of fresh wash solution is connected. As a result, it is possible to implement a control circuit with which the desired replenishment of the washing solution sprayed in the nth washing stage can be provided.

Preferably, all the washing stage connecting pipes have a regulating device for adjusting the amount of passed through sump solution. Preferably, the regulation devices are valves. By means of the regulating device, in each case the concentration of the washing solution in the two washing stages connected via the washing stage connecting line can be advantageously influenced in each case.

Each of the n washing stages preferably comprises a measuring device for determining the filling level of the sump solution in a sump of the respective washing stage. The measuring device for determining the level of the sump solution may be connected to a regulating device of the respective washing stage connecting line, which is connected to the outlet of the washing stage. In such an embodiment, the discharge of the sump solution from a washing stage can be adjusted in an advantageous manner as a function of the filling level in the bottom of the washing stage.

Each of the n washing stages preferably comprises a barrier for preventing the mixing of the sump solution of a washing stage with the sump solution of one of the remaining washing stages, in particular an immediately adjacent washing stage. A barrier ensures that the bottoms solution of one wash step does not mix with the bottoms solution of another wash step, especially an immediately adjacent wash step.

The device according to the invention comprises a channel. Preferably, the channel is single-walled. Preferably, the channel is multi-walled. In a direction along the transport direction of the exhaust gas, a change in cross section preferably takes place via a step-shaped or an oblique course in a channel wall or a plurality of channel walls of the channel. Preferably, the change in cross section is adapted to the respective space given situation of a urea plant. The term cross-section is understood to mean the surface provided by the channel for conveying the exhaust gas, perpendicular to the flow direction.

Preferably, the device is designed such that the channel in the installed state of the device, in particular in a urea plant, extends substantially horizontally.

Preferably, the spraying device comprises one or more spray nozzles for spraying the washing solution.

According to an advantageous embodiment, the device has a dust removal area in which dust present in the exhaust gas can be deposited. The dust removal area is preferably arranged in the transport direction of the exhaust gas upstream of the washing area with the n washing stages.

The object mentioned at the outset is also achieved by a urea plant with a device for removal as described above a gaseous chemical compound from an exhaust gas.

By means of the apparatus, ammonia can be removed from the exhaust gas of the urea plant to such an extent that its remaining proportion in the exhaust gas is below a critical or officially prescribed threshold value. This means that the device according to the invention in the urea plant removes gaseous ammonia by integration into the aqueous liquid phase, by using an acid which forms ammonium by reaction and then leads accordingly to the removal of ammonia.

Preferably, gaseous ammonia is integrated into the aqueous liquid phase and removed from the device. In the liquid phase, the ammonia reacts instantaneously with an acidic wash solution and forms ammonium ions. As a result of this formation of ammonium ions, the ammonia partial pressure above the liquid phase is approximately zero, so that it is possible to remove the ammonia from the gas phase.

Preference is given to gaseous ammonia and / or gaseous NO and / or gaseous NO ₂ and / or gaseous SO ₂ , in particular in flue gas desulphurisation, and / or gaseous CO ₂ , in particular in the CO ₂ removal from the flue gas of fossil-fired power plants, and / or or HF, in particular in the acidic treatment of fluoride-containing ores, for example phosphate ores, into the aqueous liquid phase and removed from the device.

Gaseous reactive components, preferably inorganic or organic reactive components, are preferably integrated into the aqueous liquid phase and removed from the apparatus.

When used in a urea plant, urea dust is preferably separated off from the exhaust gas in a suitable manner known to the person skilled in the art, before the thus pre-cleaned exhaust gas enters the washing region of the device, which has the n washing steps.

According to an advantageous embodiment of the method according to the invention this takes place in a urea plant.

The exhaust gas is preferably passed through the washing area (12) at a speed of less than 20 m / s, preferably less than 10 m / s and particularly preferably less than 5 m / s.

Another aspect of the invention relates to the use of a device according to the invention in a method according to the invention.

All embodiments described in connection with the device according to the invention apply analogously to their use according to the invention and are therefore not repeated at this point.

Further details, features and advantages of the invention will become apparent from the dependent claims, the drawings, as well as from the following description of exemplary embodiments with reference to the drawings. The drawings illustrate only exemplary embodiments of the invention, which do not limit the inventive concept.

list of figures

• In 1 schematically a device for exhaust gas scrubbing according to a first exemplary embodiment of the present invention is shown.
• In 2 is schematically the washing area of the device according to the exhaust gas scrubbing 1 shown.

Embodiments of the invention

The 1 schematically shows an apparatus for exhaust gas scrubbing according to a first exemplary embodiment of the present invention. In particular, it is a device 1 , which is installed in a urea plant and with the purpose of the exhaust gas to remove ammonia so far that its remaining proportion in the exhaust gas is below a critical or officially prescribed threshold. For this purpose, the exhaust gas via an inlet opening 10 into a canal 5 the device 1 introduced and in the transport direction T guided through the canal.

The removal of ammonia occurs gradually in the wash area 12 , The cleaned exhaust gas leaves the device 1 via the exit opening 20.

In the transport direction T the exhaust gas before the washing area 12 Optionally, a dust collecting area may be arranged in which dust present in the exhaust gas is separated.

The in 2 illustrated wash area 12 includes a total of three washing stages 41 . 42 . 43 (ie n = 3). In the following, the last of the exhaust gas flowed through the scrubbing stage as the primary washing stage 41 be designated. Contrary to the transport direction T the exhaust gas adjacent to the primary washing stage 41 is a secondary washing step 42 arranged. Contrary to the transport direction T the exhaust gas adjacent to the secondary washing stage 42 is a tertiary washing stage 43 arranged. The in 2 washing area shown 12 corresponds to the washing area 12 out 1 ,

These are the primary washing step 41 , the secondary washing stage 42 and the tertiary wash step 43 against one by the transport direction T the exhaust gas predetermined direction arranged one behind the other, wherein the exhaust gas first, the tertiary washing stage 43 and then the secondary washing step 42 happens. The primary washing stage 41 forms along the transport direction T seen the completion of the wash area 12 ,

Furthermore, it is envisaged that the primary washing stage 41 , the secondary washing stage 42 and the tertiary wash step 43 one outflow each 35 over which one of a surface enlargement structure 3 Expired bottoms solution containing the wash solution 22 contains, from the channel 5 is led out.

For recycling, ie for reuse of the wash solution contained in the sump solution 22 spraying a surface enlargement structure 3 , is provided that the primary washing stage 41 , the secondary washing stage 42 and the tertiary wash step 43 one return line each 4 have, each return line 4 the single drain 35 with the spray device 2 the respective washing stage 41 . 42 . 43 combines.

To that of the surface enlargement structure 3 expired bottoms solution 22 it is preferable to reuse that an acid concentration of the sump solution before re-spraying the surface enlargement structure 3 is increased again. This advantageously takes into account that by removing the ammonia from the exhaust gas by means of the surface enlargement structure 3 and the solvent 22 the acid concentration decreases. To refresh the acid concentration is provided that the return line 4 the primary washing stage 41 with a reservoir of fresh wash solution via an inlet 51 connected is. In particular, the feed comprises ( 51 ) another regulation device 11 , with the help of which the amount of from the reservoir of the return line 4 in the primary washing stage 41 controlled supply of fresh acid.

Furthermore, it is envisaged that the outflow 35 the primary washing stage 41 and the return line 4 the secondary washing stage 42 via a washing stage connection line 7 connected to each other. It is provided in particular that the sump solution, that of the surface enlargement structure 3 in the primary washing stage 41 has expired, at least partially via the washing stage connection line 7 in the return line 4 the secondary washing stage 42 there to provide there for an increase in the acid concentration of the sump solution, which of the surface enlargement structure 3 the secondary washing stage 42 has expired.

It is further provided that the return line 4 the tertiary washing stage 43 and the drain 35 the secondary washing stage 42 via a washing stage connection line 7 connected to each other. It is provided in particular that the sump solution that of the surface enlargement structure 3 in the secondary washing stage 42 has expired, via the washing stage connecting line 7 in the return line 4 the tertiary washing stage 43 there to provide there for an increase in the acid concentration of the sump solution, which of the surface enlargement structure 3 in the tertiary washing stage 43 has expired.

Through this cascading reuse of the wash solution 22 can be an acid concentration gradient between the wash solution 22 in the primary washing stage 41 , in the secondary washing stage 42 and the tertiary wash step 43 adjust the acid concentration in the primary wash step 41 largest and in the tertiary washing stage 43 is lowest.

It is further provided that the washing stage connecting line 7 which is the primary washing stage 41 and the secondary washing stage 42 connects together and the wash step connection line 7 which is the secondary washing stage 42 and the tertiary wash step 43 each other, each having a regulating device 9 exhibit. By means of such a regulating device 9 can be in each case advantageously between the individual washing stages 41 . 42 . 43 set transferred amount of sump solution.

The primary washing stage 41 , the secondary washing stage 42 and the tertiary wash step 43 are in the channel 5 each through a barrier 60 or a separating element separately. In particular, the barrier provides 60 for being in the channel 5 the sump solution of a washing step not with the sump solution of one of the other washing steps 41 . 42 . 43 mixed.

Furthermore, the primary washing step include 41 , the secondary washing stage 42 and the tertiary wash step 43 one measuring device each 55 with which a property of the sump solution, for example the level of the sump solution, can be determined in the respective washing stage. The measuring devices 55 regulate the solvent levels in the swamps of the individual washing stages 41 . 42 and 43 about one with the drain 35 connected regulation device 9 ,

By means of the measuring device 56.1 which with the drain 35 the tertiary washing step, a pH is determined and from this value, the amount of fresh washing solution, that of the spray device 2 that of the primary washing stage 41 via the return line 4 is supplied by means of another regulating device 11 in the inflow 51 set.

By means of the measuring device 56.2 which with the drain 35 the tertiary washing step, the concentration of the washing solution is determined and based on this value, the amount of fresh washing solution, that of the spray device 2 that of the primary washing stage 41 via the return line 4 is supplied by means of another regulating device 11 in the inflow 51 set.

By means of measuring equipment 56.1 and 56.2 which with the drain 35 are connected to the tertiary washing stage, a pH and a concentration of the washing solution is determined and from these values the amount of fresh washing solution, that of the spray device 2 that of the primary washing stage 41 via the return line 4 is supplied by means of another regulating device 11 in the inflow 51 set.

Furthermore, it is envisaged that the primary washing stage 41 , the secondary washing stage 42 and the tertiary wash step 43 each designed as a pump conveyor 8th exhibit. As a result, the spray rates in the respective washing stage can be set individually in an advantageous manner.

Furthermore, it is provided that the circulation 4 in the tertiary washing stage 43 a process 52 includes, over which the sump solution of the tertiary washing stage 43 the device for exhaust gas purification 1 leaves again.

A person skilled in the art recognizes that when starting the device 1 first the primary, ie (nth), washing stage 41 is supplied with washing solution, ie no washing solution in the other washing stages 42 . 43 located. After starting the device 1 The wax solution first circulates in the primary washing stage 41 and is parallel to it via the wash step connection line 7 the secondary, ie (n-1) -th, washing stage 42 fed. Once the wash solution 22 in the secondary washing stage 41 circulates, wash solution 22 parallel to it via its washing stage connection line 7 the tertiary, ie (n-2) -th or first, washing stage fed. This process is repeated until every wash step 41 . 42 . 43 wash solution 22 circulated. Once wash solution 22 circulated in all washing stages, exhaust gas is passed through the duct 5 directed. This state corresponds to a device according to the invention, which is "in operation". In other words, according to the invention, the washing solution 22 in countercurrent to the gaseous chemical compound, which can be integrated into an aqueous liquid phase by an acid-base reaction. By circulation in a washing step, spraying is the surface enlarging structure 3 over the spray device 2 with the washing solution 22 , The drainage of the acid solution or base compared to the sprayed spray solution reduced sump solution over the drain 35 , and the forwarding of the sump solution (and in the case of the primary, ie n-th, washing stage 41 additionally the fresh wash solution) via the return line 4 back to the sprayer 2 to understand.

LIST OF REFERENCE NUMBERS

1

contraption

2

sprayer

3

structural element

4

circulation

5

channel

7

Washing stage connecting line

8th

Conveyor

9

regulating device

10

entrance opening

11

regulating device

12

washing area

22

solvent

35

outflow

41

primary washing stage

42

secondary washing stage

43

tertiary washing stage

51

Intake

52

procedure

55

measuring device

56.1

Measuring device for determining the pH value

56.2

Measuring device for determining the concentration of the washing solution

60

barrier

T

transport direction

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 5403568 A [0002]

Claims (16)

Device (1) for removing a gaseous chemical compound from an exhaust gas, wherein the gaseous chemical compound can be converted into an aqueous liquid phase by reaction with a washing solution (22), with a channel (5) having a washing area (12) with n washing stages arranged such that an exhaust gas along a transport direction (T) from a first washing stage to an n-th washing stages is feasible, where n is at least two, wherein each one of the n washing stages a surface enlargement structure (3), in particular a bed or a packing, and a spraying device (2) for spraying the surface enlarging structure (3) with a solvent (22), a drain (35) for collecting a sump liquor discharged from said surface enlarging structure (3) containing said washing solution (22), and - a return line (4) connected to the drain (35) for returning a first partial flow of the sump solution to the spray device (2), and with the exception of the outlet (35) of the first washing step, the drain (35) of each washing step a washing stage connecting line (7) for the passage of a second partial flow of the sump solution with the return line (4) opposite to the transport direction (T) immediately adjacent washing stage is connected and wherein the n-th washing stage an inlet (51) for supplying the return line (4 ) of the nth wash step with fresh wash solution (22). Device according to Claim 1 where n is two. Device according to one of the preceding claims, wherein each one of the n washing stages comprises a conveying device (8), in particular a pump, for conveying the first part-stream of the sump solution (22) through the return line. Device according to one of the preceding claims, wherein the outflow (35) of the first washing stage via a discharge line (52) for passing a second partial flow of the sump solution with a measuring device for determining the pH (56.1) of the second partial flow of the sump solution and / or a measuring device for determining the concentration of the washing solution (56.2) is connected in the second partial flow of the sump solution. Device after Claim 4 wherein the measuring device for determining the pH (56.1) of the second partial stream of the sump solution and / or the measuring device for determining the concentration of the washing solution (56.2) in the second partial stream of the sump solution with a regulating device (11) for regulating the above Feed (51) supplied amount of fresh wash solution is connected. An apparatus according to any one of the preceding claims, wherein all the washing stage connecting pipes (7) comprise regulating means (9) for adjusting the amount of sump solution passed through. Device according to one of the preceding claims, wherein each one of the n washing stages comprises a measuring device (55) for determining the level of the sump solution in a sump of the respective washing stage. Device according to one of the preceding claims, wherein each one of the n washing stages comprises a barrier (60) for preventing the mixing of the sump solution of a washing stage with the sump solution of one of the remaining washing stages, in particular an immediately adjacent washing stage. Device according to one of the preceding claims, wherein the device is designed such that the channel (5) in the installed state of the device (1), preferably integrated in a urea plant, extends substantially horizontally. Device according to one of the preceding claims, wherein the spraying device (2) comprises one or more spray nozzles for spraying the washing solution. Device according to one of the preceding claims, wherein the device (1) has a Staubabscheidungsbereich in which dust present in the exhaust gas can be deposited, wherein the dust removal region is preferably arranged in the transport direction (T) of the exhaust gas in front of the washing area (12). Urea plant, characterized by a device for removing a gaseous chemical compound from an exhaust gas according to one of the preceding claims. A method for removing a gaseous chemical compound from an exhaust gas, wherein the gaseous chemical compound is converted into an aqueous liquid phase by reaction with a washing solution (22), wherein the exhaust gas through a washing area (12) of a channel (5) along a transport direction (T ) is conducted from a first washing stage to an n-th washing stage, where n is at least two, wherein in each of the n washing stages in each case a surface enlarging structure (3), in particular a bed or a packing, by means of a spraying device (2) is sprayed with the washing solution (22), collected from the surface enlargement structure (3) sump solution and a first partial stream of the sump solution via a return line (4) to the spray device (2) is returned, with the exception of the first washing stage, a second partial stream the sump solution of each individual washing step is passed via a connecting line (7) into the return line (4) of the immediately adjacent washing step opposite to the transport direction (T), and wherein the return line (4) of the nth washing step via a feed (51) fresh washing solution is supplied. Method according to Claim 13 , which takes place in a urea plant. Method according to Claim 13 or 14 , wherein the exhaust gas at a rate of less than 20 m / s, preferably less than 10 m / s and more preferably less than 5 m / s is passed through the washing area (12). Use of a device (1) according to one of Claims 1 to 12 in a method according to any one of Claims 13 to 15 ,

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