DE102017108845A1 - Device and method for waste gas scrubbing and urea plant with a waste gas scrubbing - Google Patents

Abstract

The present invention relates to a process for the removal of gaseous chemical compounds from an exhaust gas, wherein at least one gaseous chemical compound is converted by reaction with a washing solution (22) into an aqueous liquid phase, wherein an exhaust gas is passed through a horizontal channel (5) , which has a washing area (12), wherein in the washing area (12) a surface enlarging structure (3) is arranged, which extends in the vertical direction and which is sprayed with the washing solution (22)
- Only an upper portion of the surface enlargement structure (3) is sprayed
or
- An upper portion of the surface enlargement structure (3) is sprayed with a first spray rate and a lower portion of the surface enlargement structure (3) is sprayed with a second spray rate, wherein the first spray rate is greater than the second spray rate.

Description

Technical field of the invention

The invention relates to a method for the removal of gaseous chemical compounds from an exhaust gas, wherein at least one gaseous chemical compound is converted by reaction with a washing solution in an aqueous liquid phase, wherein an exhaust gas is passed through a horizontal channel having a washing area, wherein in the washing area, there is disposed a surface enlarging structure which extends in the vertical direction and which is sprayed with the washing solution. Furthermore, the invention relates to a device for removing gaseous chemical compounds from an exhaust gas, wherein at least one gaseous chemical compound can be converted into an aqueous liquid phase by a reaction with a washing solution, wherein an exhaust gas can be guided through a horizontal channel which has a washing region, wherein in the washing area a surface enlargement structure is arranged, which extends in the vertical direction and which can be sprayed by means of a spray device with the washing solution.

State of the art

Such methods and devices are known from the prior art and may for example be integrated in a urea plant. In this case, the device is intended to remove gaseous ammonia by integration into the aqueous liquid phase in a washing area by using an acidic washing solution which forms ammonium by reaction and then leads to the removal of ammonia accordingly.

In the spray device according to the prior art are nozzle sticks, in each case a plurality of nozzles are arranged horizontally in a plane. The nozzle sticks are preferably distributed vertically over the height. With the same spray rate of each nozzle, it can be observed that in the height profile the wash solution film in a surface enlargement structure, at which the transition to the liquid phase takes place, in particular a bed or a pack, is thinner in an upper section, increases in height from top to bottom and in a lower section is the highest. As a result, the gas velocity is highest in the upper portion of the surface enlargement structure and lowest in the lower portion of the package, steadily descending from top to bottom. In addition, due to the limited mass flow of wash solution in each height element under consideration, there is not enough washing solution available, especially in the upper part, for e.g. Ammonia in sufficient amount from the exhaust gas to bind as ammonium. Because of this bypass, e.g. the ammonia leaching incomplete and can lead to failure to achieve the required ammonia deposition.

This incomplete ammonia leaching may cause the purified effluent leaving the apparatus to exceed the maximum permissible limits for ammonia (typically less than 30 mg / Nm ³ in the US, but less than 50 mg / Nm ³ otherwise).

Disclosure of the invention

It is therefore an object of the present invention to provide an apparatus and a method for waste gas scrubbing, with which the efficiency for the removal of said chemical compounds, in particular of ammonia, from the exhaust gas over those of the prior art is improved.

• - ausschließlich ein oberer Abschnitt der Oberflächenvergrößerungsstruktur besprüht wird oder
• - ein oberer Abschnitt der Oberflächenvergrößerungsstruktur mit einer ersten Sprührate besprüht wird und ein unterer Abschnitt der Oberflächenvergrößerungsstruktur mit einer zweiten Sprührate besprüht wird, wobei die erste Sprührate größer als die zweite Sprührate ist.

The object is achieved by a method for removing gaseous chemical compounds from an exhaust gas, wherein at least one gaseous chemical compound is converted by reaction with a washing solution in an aqueous liquid phase, wherein an exhaust gas is passed through a horizontal channel having a washing area wherein in the washing area a surface enlarging structure is arranged, which extends in the vertical direction and which is sprayed with the washing solution, wherein

• - Only an upper portion of the surface enlargement structure is sprayed or
• - Spraying an upper portion of the surface enlargement structure with a first spray rate and spraying a lower portion of the surface enlargement structure with a second spray rate, wherein the first spray rate is greater than the second spray rate.

In the method of the present invention, only an upper portion of the surface enlarging structure is sprayed or an upper portion of the surface enlarging structure becomes larger in spraying rate than a lower portion of the surface enlarging structure. The spray rate is understood to mean the sprayed amount of wash solution per unit time and area sprayed. The washing solution sprayed onto the surface enlarging structure can be downwardly moved by the influence of gravity from the upper portion and increase the layer thickness of the washing solution film in the lower portion of the surface enlarging structure. This results in a substantially uniform layer thickness profile, in particular in the vertical direction the wash solution film on the entire surface enlargement structure. As such, the distribution of the amount of washing solution in the surface enlarging structure, especially in the vertical direction, is substantially uniform. By the, in particular in the vertical direction, substantially uniform wash solution film is obtained, in particular in the vertical direction, substantially uniform exhaust gas velocity through the surface enlargement structure, so that, in particular in the vertical direction, substantially uniform removal of the at least one gaseous chemical compound is realized , In addition, it is achieved that in each vertical section of the surface enlargement structure sufficient washing solution is available, which allows a complete absorption of the component to be washed out of the gas. A method is provided with improved efficiency over the prior art.

Preferably, the second spray rate is at least 5% of the first spray rate, or at least 10% or at least 15% or at least 20% or at least 25% or at least 30% or at least 35% or at least 40% or at least 45% or at least 50% or at least 55% or at least 60% or at least 65% or at least 70% or at least 75% or at least 80% or at least 85% or at least 90% or at least 95%.

Preferably, the second spray rate is at most 5% of the first spray rate, or at most 10% or at most 15% or at most 20% or at most 25% or at most 30% or at most 35% or at most 40% or at most 45% or at most 50% or maximum 55% or maximum 60% or maximum 65% or maximum 70% or maximum 75% or maximum 80% or maximum 85% or maximum 90% or maximum 95%.

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 enlargement structure comprises random beds selected from the group consisting of Raschig rings, calipers, spirals, and combinations thereof, and structured packages selected from the group consisting of fabric packages, sheet metal packages, expanded metal packages, plastic packages, grid packages, 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.

According to a preferred embodiment, it is provided that the surface enlarging structure, in particular exclusively, is sprayed by means of a spraying device arranged above the surface enlarging structure. As a result, the design effort for the sprayer can be reduced.

It is advantageous if the surface enlarging structure, in particular exclusively, is sprayed by means of a spraying device arranged laterally of the surface enlarging structure. The spraying device may be arranged in front of the surface enlarging structure in the transport direction of the exhaust gas, so that the sprayed washing solution is entrained by the exhaust gas in the direction of the surface enlarging structure. It is possible for the surface enlarging structure to be sprayed both by means of a spraying device arranged above the surface enlarging structure and by means of a spraying device arranged laterally of the surface enlarging structure.

A preferred embodiment provides that a middle section arranged between the upper section and the lower section of the surface enlargement structure is sprayed with a third spray rate, wherein the third spray rate is less than the first spray rate and greater than the second spray rate. That is, the spray rate decreases from the upper portion over the middle portion to the lower portion.

Preferred is an embodiment in which the spraying device has one or more upper spray nozzles for spraying the upper portion of the surface enlarging structure and one or more lower spraying nozzles for spraying the lower portion of the surface enlarging structure. Particularly preferably, the upper spray nozzles are connected to each other via a common upper manifold and are identical in their construction and dimensioning, so that the spray rates of the upper spray nozzles are identical. The lower spray nozzles can be connected to each other via a common lower manifold, wherein preferably the spray rates of these spray nozzles can be adjusted independently of the spray rates of the nozzles in the upper nozzle.

In this connection, it is preferable that the spraying device has one or more central spray nozzles for spraying a middle portion of the surface enlarging structure disposed between the upper portion and the lower portion of the surface enlarging structure. Particularly preferably, the central spray nozzles are connected to one another via a common middle distributor tube, so that the spray rate of the central spray nozzles is identical. Preferably, the spraying device comprises more than three distributor tubes, which are arranged spaced apart in the vertical direction, wherein each distributor tube is in each case connected to a plurality of spray nozzles.

Preferably, at least one spray nozzle is a hollow cone nozzle. Preferably, at least one spray nozzle is a full cone nozzle. Preferably, at least one spray nozzle is a flat jet nozzle. Preferably, at least one spray nozzle is a full jet nozzle. Preferably, at least one spray nozzle is a spiral nozzle. Preferably, at least one spray nozzle is a spray nozzle. Preferably, the spray nozzles are of the same type. Alternatively, the spray nozzles may be of different types.

According to an advantageous embodiment, the exhaust gas is an exhaust gas of a urea plant and the at least one chemical compound is gaseous ammonia. In this case, the exhaust gas of the urea plant is guided in a horizontal direction through the washing area.

According to an alternative advantageous embodiment, the at least one chemical compound is selected from the group consisting of gaseous NO, gaseous NO ₂ , gaseous SO ₂ , gaseous CO ₂ , a gaseous inorganic fluorine compound and combinations thereof.

• - ausschließlich ein oberer Abschnitt der Oberflächenvergrößerungsstruktur (3) besprühbar ist oder
• - ein oberer Abschnitt der Oberflächenvergrößerungsstruktur (3) mit einer ersten Sprührate besprühbar ist und ein unterer Abschnitt der Oberflächenvergrößerungsstruktur (3) mit einer zweiten Sprührate besprühbar ist, wobei die erste Sprührate größer als die zweite Sprührate ist.

The object mentioned at the outset is furthermore achieved by a device for removing gaseous chemical compounds from an exhaust gas, wherein at least one gaseous chemical compound can be converted into an aqueous liquid phase by a reaction with a washing solution (22), an exhaust gas being conveyed through a horizontal channel ( 5), which has a washing area (12), wherein in the washing area (12) a surface enlarging structure (3) is arranged which extends in the vertical direction and which can be sprayed by means of a spraying device (2) with the washing solution (22) wherein the spraying device (2) is designed such that

• - Only an upper portion of the surface enlargement structure (3) is sprayable or
• - An upper portion of the surface enlargement structure (3) is sprayable with a first spray rate and a lower portion of the surface enlargement structure (3) is sprayable with a second spray rate, wherein the first spray rate is greater than the second spray rate.

To solve the problem mentioned above, a urea plant is further proposed, comprising a device described above for the removal of gaseous chemical compounds from an exhaust gas of the urea plant.

In the device according to the invention and the urea plant, the same advantages as in the method according to the invention can be achieved.

In the case of the urea plant, the device is intended to remove gaseous ammonia in the washing area by integration into the aqueous liquid phase, by using an acidic washing solution which forms ammonium by reaction with ammonia and then leads to the removal of ammonia.

All embodiments described in connection with the method according to the invention apply analogously to the device according to the invention and the urea system 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 preferred 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 FIG. 2 is a schematic top view of an exhaust scrubber according to a first exemplary embodiment of the present invention. FIG.
• In 2 is a schematic side view of the washing area of the device for waste gas according to 1 shown.
• In 3 is a schematic side view of a washing area of a device for exhaust gas scrubbing according to a second exemplary embodiment of the present invention shown.
• In 4 is a schematic side view of a washing area of a device for exhaust gas scrubbing according to a third exemplary embodiment of the present invention is shown.
• In 5 is shown in a schematic side view of a washing area of a device for waste gas scrubbing according to the prior art.

Embodiments of the invention

The 1 shows a schematic plan view of a device 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 takes place in the washing area 12 , The cleaned exhaust gas leaves the device 1 over the exit opening 20 ,

In the transport direction T of 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.

For removal of ammonia is in the wash area 12 arranged surface enlargement structure 3 with the help of a spraying device 2 with a washing solution 22 sprayed.

The device comprises a spraying device 2 with several distribution pipes 30 at which spaced apart individual spray nozzles 31 are arranged. In the 1 is just an upper manifold 30 to see. However, the spraying device has at least one further distribution tube, which is below the upper distributor tube 30 is arranged. About the spray nozzles 31 of the upper manifold becomes an upper portion of the surface enlargement structure 3 sprayed.

During operation of the device, the surface enlargement pattern becomes 3 continuously with the washing solution 22 sprayed so that a liquid film along one side, in particular along one of the spray device 2 facing side, the surface enlargement structure 3 formed.

To improve the removal of the ammonia from the exhaust gas is provided that the surface enlargement structure 3 such with washing solution 22 is sprayed that the washing solution 22 on the surface enlargement structure 3 evenly distributed while having a wash solution film having at least one side of the surface enlargement structure 3 forms substantially uniform layer thickness. This is the upper portion of the surface enlargement structure 3 sprayed with a first spraying rate and a lower portion of the surface augmenting structure 3 is sprayed with a second spray rate, wherein the first spray rate is greater than the second spray rate.

By this type of spraying is one, especially caused by gravity, irregular or adverse Layer thickness distribution counteracted, in which a section through the wash solution 22 on the surface magnification structure 3 formed wash solution film is thinner than in another section and consequently sets a higher gas velocity in this section with the thinner wash solution film. This phenomenon is at the in 5 to observe the device shown in the prior art. The layer thickness 41 of the wash solution film is above the height of the surface enlargement structure 3 applied. Further, the gas velocity 42 above the height of the surface enlargement structure 3 applied. Because of the limited mass flow of wash solution 22 In the individual sections, this unequal distribution leads to the layer thickness 41 or the gas velocity 42 ultimately, in the higher gas velocity sections, which is equivalent to higher gas flow rates, insufficient wash solution can be provided to sufficiently sequester the ammonia from the exhaust gas as ammonium. This results in incomplete ammonia leaching.

In 2 is schematically the washing area of the device according to the exhaust gas scrubbing 1 in a side view, which is configured according to an exemplary embodiment of the present invention.

Here, the exhaust gas scrubbing serves the surface enlargement structure 3 which with a washing solution 22 is sprayed. The sprayers 2 sprayed side of the surface enlargement structure 3 is essentially vertical.

The upper section 3.1 of the surface enlargement structure 3 gets over the top spray nozzles 31.1 sprayed with a first spraying rate and the lower section 3.2 of the surface enlargement structure 3 gets over the lower spray nozzles 31.2 sprayed with a second spray rate, wherein the first spray rate is greater than the second spray rate. In that the surface enlargement structure 3 from the upper spray nozzles 31.1 the spray device 2 is sprayed with a larger spray rate than from the lower spray nozzles 31.2 , During spraying, a substantially uniform layer thickness in the vertical direction 41 realized the wash solution film. The gas speed 42 is distributed substantially uniformly in the vertical direction. The distribution of the gas velocity in the vertical direction is further indicated by the arrows 32 visualized.

According to 2 are between the upper spray nozzles 31.1 and the lower spray nozzles 31.2 further, in particular two further groups of spray nozzles arranged. The spray rate of these other groups of spray nozzles is chosen such that the spray rate starting from the upper spray nozzles 31.1 decreases towards the bottom.

In 3 schematically a washing area of a device for exhaust gas scrubbing according to a second exemplary embodiment of the present invention is shown.

In this apparatus, the spraying apparatus is arranged such that only an upper portion of the surface enlarging structure 3 is sprayed. In other words, the spray device 2 is arranged such that the washing solution 22 substantially in a direction predetermined by gravity following the surface magnification structure 3 is sprayed. In particular, the washing solution 22 on the front side of the surface enlargement structure 3 and then flows under the influence of gravity along the surface enlargement structure 3 down to form a wash solution film of substantially uniform layer thickness.

With the devices described above, a method of removing gaseous chemical compounds from an exhaust gas may be performed, wherein at least one gaseous chemical compound is formed by a reaction with a washing solution 22 is transferred to an aqueous liquid phase, wherein an exhaust gas through a horizontal channel 5 which is a washing area 12 wherein, in the washing area 12 a surface enlargement structure 3 is arranged, which extends in the vertical direction and which with the washing solution 22 is sprayed, wherein only an upper portion of the surface enlargement structure 3 is sprayed or an upper portion of the surface enlargement structure 3 is sprayed with a first spray rate and a lower portion of the surface enhancement structure 3 is sprayed with a second spray rate, wherein the first spray rate is greater than the second spray rate.

In 4 an embodiment is shown in which a part of the washing solution is added via the top side of the surface enlarging structure and another part of the washing solution via the front side. In this respect, the surface enlargement structure becomes 3 by means of one above the surface enlargement structure 3 arranged spraying device 2 and additionally by means of a laterally of the surface enlargement structure 3 arranged spraying device 2 sprayed. In this case, the upper section 3.1 of the surface enlargement structure 3 sprayed with a first spraying rate and the lower section 3.2 of the surface enlargement structure 3 sprayed with a second spray rate, wherein the first spray rate is greater than the second spray rate.

LIST OF REFERENCE NUMBERS

1

contraption

2

sprayer

3

Enlarged surface structure

5

channel

10

entrance opening

12

washing area

20

output port

22

wash solution

30

manifold

31

spray nozzles

31.1

upper spray nozzles

31.2

lower spray nozzles

32

Gas velocity distribution

41

Layer thickness of the wash solution film

42

gas velocity

T

transport direction

Claims (10)

Method for removing gaseous chemical compounds from an exhaust gas, wherein at least one gaseous chemical compound is converted into an aqueous liquid phase by a reaction with a washing solution (22), wherein an exhaust gas is passed through a horizontal channel (5) which forms a washing area ( 12), wherein in the washing area (12) a surface enlarging structure (3) is arranged, which extends in the vertical direction and which is sprayed with the washing solution (22), characterized in that - only an upper portion of the surface enlarging structure (3) is sprayed or - an upper portion of the surface enlargement structure (3) is sprayed with a first spray rate and a lower portion of the surface enlargement structure (3) is sprayed with a second spray rate, wherein the first spray rate is greater than the second spray rate. Method according to Claim 1 in that the surface enlarging structure (3) is sprayed, in particular exclusively, by means of a spraying device (2) arranged above the surface enlarging structure (3). Method according to one of the preceding claims, wherein the surface enlarging structure (3) is sprayed, in particular exclusively, by means of a spraying device (2) arranged laterally of the surface enlarging structure (3). A method according to any one of the preceding claims, wherein a central portion disposed between the upper portion and the lower portion of the surface enlarging structure (3) is sprayed with a third spray rate, the third spray rate being less than the first spray rate and greater than the second spray rate. Method according to Claim 3 or 4 wherein the spraying device (2) comprises one or more upper spray nozzles for spraying the upper portion of the surface enlarging structure (3) and one or more lower spraying nozzles for spraying the lower portion of the surface enlarging structure (3). Method according to Claim 5 wherein the spraying device (2) comprises one or more central spray nozzles for spraying a central portion of the surface enlarging structure (3) disposed between the upper portion and the lower portion of the surface enlarging structure (3). Method according to one of the preceding claims, wherein the exhaust gas is an exhaust gas of a urea plant and the at least one chemical compound is gaseous ammonia. Method according to one of Claims 1 to 6 wherein the at least one chemical compound is selected from the group consisting of gaseous NO, gaseous NO ₂ , gaseous SO ₂ , gaseous CO ₂ , gaseous inorganic fluorine compound, and combinations thereof. Device for removing gaseous chemical compounds from an exhaust gas, wherein at least one gaseous chemical compound can be converted into an aqueous liquid phase by a reaction with a washing solution (22), wherein an exhaust gas can be passed through a horizontal channel (5) which forms a washing area (5) 12), wherein in the washing area (12) a surface enlarging structure (3) is arranged which extends in the vertical direction and which can be sprayed by means of a spraying device (2) with the washing solution (22), characterized in that the spraying device (2 ) is formed such that - only an upper portion of the surface enlargement structure (3) is sprayable or - an upper portion of the surface enlargement structure (3) is sprayable with a first spray rate and a lower portion of the surface enlargement structure (3) with a second spray rate is sprayable, wherein the first spray rate is greater than the second spray rate. Urea plant with a device for the removal of gaseous chemical compounds from an exhaust gas of the urea plant according to Claim 9 ,

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