EXHAUST AIR SCREEN WITH INTERNAL AIR EXHAUST

Description

[0001] The present invention relates to exhaust air scrubbers, in particular for ammonium nitrate, calcium ammonium nitrate or LDAN (low density ammonium nitrate) plants with improved design.

[0002] In the production of fertilizers and other nitrogen-based products, particularly in the granulation and prilling processes, large quantities of air are used to dry and cool the solids. The dust and product debris generated during the mechanical processes are carried away by this process air and must be removed in downstream process steps to prevent human and environmental pollution and product loss. Furthermore, ammonia is often released during the drying of fertilizers. This gas must also be removed from the exhaust air before it leaves the plant.It has been proven that (for products containing ammonium nitrate) acidic wet scrubbing is the most effective method for exhaust air purification: the dust is wetted by the scrubbing liquid; the water-soluble components (ammonium nitrate) dissolve, while the insoluble components (e.g., additives such as fillers and additives) are suspended. The ammonia gas is also dissolved in the scrubbing liquid and then neutralized by the free acid to form an ammonia salt. The air scrubbed in this way contains only small amounts of dust and ammonia. If nitric acid is used as the acidifying agent, the scrubbed ammonia is converted to ammonium nitrate, which can be recycled into the production process as a valuable material.To increase the contact area between the process air to be cleaned and the scrubbing solution, packing is used (usually a loose packing, as it is easy to install and less susceptible to blockage by solids). The scrubbing solution is fed through liquid distribution systems above the packing. Circulation pumps return the scrubbing liquid from the scrubber sump to the liquid distribution system above the packing. To prevent scrubbing liquid droplets from being entrained into the exhaust air duct, a mist eliminator is typically used.

[0003] Plants for the production of AN / CAN / LDAN plants (plants for the production of ammonium nitrate, calcium ammonium nitrate, or low-density ammonium nitrate) are known. These plants typically use wet scrubbers with packings to clean dust-laden and ammonia-containing exhaust gases. These scrubbers are generally circular, with diameters of up to over 6 m and a height of approximately 20 m. The air supply is located below the packing, and the cleaned air is extracted at the top of the scrubber. In such plants, the downstream fan is generally installed on the floor for various reasons, so the air duct must be led back to the floor outside the scrubber. Since these ducts have a diameter of up to over 2000 mm, they must be protected by steel construction, and thermal expansion must be compensated for. This is complex and expensive.

[0004] Corresponding systems in which the exhaust air is discharged from the top of the housing are known, for example, from JP 2012 / 187515 or US 4,487,748. GB 794 060 A or DE 10 2008 046 820 A1 can also be cited as prior art. Furthermore, reference is made to the following patent literature: CN 203725013 U, CN 204 107 330 U, and CN 105 236 609 B.

[0005] However, the operation and design of such systems faces several challenges: Since large volumes of warm, dry air are scrubbed and therefore become enriched with water, water must be continuously added to the scrubber. The concentration of the scrubbing solution must be monitored and limited to prevent the solution from becoming oversaturated with ammonium nitrate. Otherwise, the packing would become clogged, the airflow would be impeded, pressure loss and flow velocity would increase, and the scrubber's cleaning performance would decrease. Because the separated dust also contains components that are insoluble in the scrubbing liquid, sludge accumulates at the bottom of the scrubber during operation. This sludge causes problems for the circulation pumps and blowdown valves.The pH value of the scrubbing liquid must be continuously measured and readjusted by adding acid to ensure both optimal ammonia removal and material-friendly operation. The air extraction at the top of the scrubbing column requires considerable piping and pipe support due to the large pipe diameters. The often quite large diameters of the scrubbers require complex support structures for the packing support grids, the packing retainers, and the liquid distributors.

[0006] The object of the present invention was accordingly, among other things, to find ways to improve existing systems, exhaust air scrubbers and processes in such a way that the equipment and financial expenditure can be significantly reduced and the further operational disadvantages and difficulties can be reduced.

[0007] The object is achieved within the scope of the present invention by the subject matter of the appended claims, wherein the subclaims represent preferred embodiments.

[0008] Further embodiments according to the invention and in particular preferred embodiments emerge from the following description.

[0009] In one embodiment, the present invention relates to an exhaust air scrubber for removing dust, product abrasion and water-soluble components from process exhaust air, comprising in a housing at least one cleaning stage, at least one packing, optionally at least one scrubbing tray, at least one inlet device for process exhaust air, at least one extraction device for scrubbing solution, at least one extraction line for the cleaned exhaust air, at least one feed line for scrubbing solution in the upper part of the housing.

[0010] The exhaust air scrubbers according to the invention are characterized in that the exhaust duct for the cleaned exhaust air i) begins inside the housing above at least one cleaning stage, ii) is directed downwards inside the housing and iii) is directed out of the housing in the lower area of ​​the housing, below the cleaning stage(s).

[0011] In a further embodiment, the present invention relates to a method for exhaust air purification during the production of or in plants for the production of prilled or granulated products containing ammonium nitrate or urea, preferably ammonium nitrate fertilizer (HDAN), porous ammonium nitrate (LDAN), calcium ammonium nitrate (CAN / KAS), ammonium nitrate sulfate fertilizer (ASN) or urea fertilizer, characterized in that an exhaust air scrubber according to the invention is used.

[0012] In yet another embodiment, the present invention relates to a plant for producing ammonium nitrate- or urea-containing prilled or granulated product, preferably ammonium nitrate fertilizer (HDAN), porous ammonium nitrate (LDAN), calcium ammonium nitrate (CAN / KAS), ammonium nitrate sulfate fertilizer (ASN) or urea fertilizer, which comprises at least one exhaust air scrubber according to the invention.

[0013] In another embodiment, the present invention relates to the use of exhaust air scrubbers according to the invention for exhaust gas purification in the production of ammonium nitrate- or urea-containing prilled or granulated product, preferably ammonium nitrate fertilizer (HDAN), porous ammonium nitrate (LDAN), calcium ammonium nitrate (CAN / KAS), ammonium nitrate sulfate fertilizer (ASN) or urea fertilizer.

[0014] In embodiments of the present invention, an aqueous solution is used as the scrubbing liquid. In some embodiments, this solution can be withdrawn from the bottom of the scrubber and reapplied above the scrubbing stage(s).

[0015] In some embodiments, this solution may contain dissolved or suspended substances that have been washed out of the air stream or formed from washed-out substances in a chemical reaction. These substances may be, for example, ammonium nitrate, limestone, urea, ammonia, nitric acid, or sulfuric acid. To establish a material equilibrium, a portion of the scrubbing solution is preferably continuously withdrawn from the circulation, and the water removed thereby and by water evaporation is added by adding a suitable aqueous feed, preferably purified water, steam, or process condensate.

[0016] In the exhaust air scrubbers of the present invention, the cleaned air flow is already directed downwards within the scrubber and exits the housing below the packings, preferably approximately at the level of the fan inlet, via which the cleaned exhaust air is discharged from the housing.

[0017] The required scrubber diameter remains virtually unchanged thanks to the inventive design. Furthermore, the ring geometry simplifies the distribution of the scrubbing water among the packings. Furthermore, the effort and time required for assembly and pre-assembly of the system are reduced.

[0018] Packings that are particularly suitable are random packings, but in principle any other packings familiar to the person skilled in the art are also suitable. Examples of packings that can be used within the scope of the present invention are conventional random packings or structured packings, preferably complex-shaped plastic packings such as those sold under the brand names Snowflakes®, Tellerette®, or Q-Pac®.

[0019] In further embodiments of the present invention, scrubbing trays can be inserted between the packing and the droplet separator in the exhaust air scrubber according to the invention to further increase the separation efficiency. In the context of the present invention, scrubbing trays used can be conventional scrubbing trays familiar to those skilled in the art, e.g., bubble-cap, valve-cap, or tunnel trays.

[0020] An essential aspect of the present invention is the internal air outlet duct in the exhaust air scrubber.

[0021] Advantages of the present invention include compact design, smaller footprint for installation, savings on external air duct and possibly steel construction, savings on air duct installation, etc.

[0022] These advantages mean that financial savings can be realized with the present invention. Furthermore, the exhaust air scrubbers according to the invention require significantly less equipment and are therefore more advantageous than previous systems.

[0023] If the exhaust air from the scrubber of the present invention is to be extracted by more than one fan, the air outlet duct can be divided within the scrubber and routed to the fans through multiple casing openings. This saves both costs compared to a conventional external airflow division.

[0024] The fact that the cleaned exhaust air stream is not drawn off axially at the top of the scrubbing column and led through an external pipe to the scrubber blower, but is directed back down inside the scrubber and discharged laterally, results in several advantages: The mass of installed piping material and associated supports (balance space between scrubber and scrubber blower) is significantly reduced, the assembly effort during installation is significantly reduced, and the internal pipe can also serve as an attachment point for the (many) internal supports for fixing the packing and the liquid distribution systems.

[0025] In preferred embodiments of the present invention, the exhaust air scrubber according to the invention is designed so that its lower part is conical, with the tip pointing downward. This creates a conical scrubber sump with the outlet to the circulation pumps located in the center. This enables a very uniform sludge removal.

[0026] By tangentially injecting a partial flow of the circulated scrubbing solution into the conical sump, it is possible to further reduce the deposition of solids. This flow is also ideal for assessing the properties of the scrubbing solution, such as temperature, density, concentration, and pH, since the low volume flow requires only measuring devices with a small pipe cross-section. For this reason, a corresponding tangential injection or an exhaust air scrubber with a device for tangential injection are preferred designs.

[0027] Within the scope of the present invention, it is furthermore possible in further embodiments to design the exhaust air scrubber according to the invention in such a way that it can contain one or more cleaning stages which can be operated with the same or different inserts and the same or different process conditions.

[0028] The present invention also makes it possible to further increase the water evaporation capacity of the scrubber in order to remove suitable excess process wastewater from a plant complex in a comparatively inexpensive manner. This is preferably done by heating the circulating scrubbing solution in an external heat exchanger, which can be heated, for example, by low-calorie process media and which can otherwise even be cooled with cooling water. An exemplary application is the condensation of process vapors from an upstream ammonium nitrate evaporation process by using the circulating scrubbing solution as a cooling medium. The energy input is transferred from the scrubbing solution to the scrubber air and causes a temperature increase in the cleaned air, which therefore carries a higher water load.

[0029] In further embodiments of the present invention, nozzles can be installed upstream of the droplet separator in the direction of flow, allowing water or other substances, such as acid, to be sprayed onto the separator. Any accumulation of ammonium nitrate-containing solid deposits can be easily removed, as ammonium nitrate and urea are highly soluble in water. Non-water-soluble deposits can be dissolved by adding acid (e.g., nitric acid).

[0030] In further embodiments of the present invention, a heat exchanger package can be inserted into the internal air exhaust duct. For this purpose, the duct can be modified in size and shape to accommodate the heat exchanger package, e.g., made of tubes, heat exchanger plates, or spiral tubes, in a flow-optimized manner. Air heated in this way after absorbing water in the scrubber has a reduced relative humidity and therefore leads to a weather-dependent, low visibility of the water vapor plume from the exhaust air stack. Air cooled further here contains an absolutely lower water load and can be used for subsequent applications without another external air cooler.

[0031] In further embodiments of the present invention, the exhaust air scrubber according to the invention can be designed in several stages, wherein each of the individual scrubbing stages can be operated with its own scrubbing liquids, additives and conditions such as pH, concentration or temperature.

[0032] Furthermore, it is possible to install several exhaust air scrubbers according to the invention in one system; for example, several exhaust air scrubbers according to the invention can be connected or arranged in series or in parallel.

[0033] It is preferred within the scope of the present invention if the exhaust air scrubber has a circular surface and the air extraction device, i.e. the extraction line for the cleaned exhaust air beginning above the at least one cleaning stage, is arranged centrally, in particular concentrically.

[0034] In further preferred embodiments of the present invention, the air extraction device is a pipe or a pipe bundle.

[0035] In particular embodiments, the first scrubbing stage in the direction of air flow can be operated at a neutral or alkaline pH to scrub dust from the exhaust air without chemically altering the dust (e.g., through acid attack, which can lead to the formation of undesirable / harmful byproducts). In the second stage, for example, the previously dedusted air can then be subjected to an acid scrub to scrub out gases. In variants of the present invention, the elutriation from the second stage can be used as the feed liquid for the first stage.

[0036] In the context of the present invention, the contaminated process exhaust air is accordingly first passed through a packing, then optionally through a scrubbing tray, and then past a droplet separator before entering the discharge line for the cleaned exhaust air.

[0037] The present invention also relates, inter alia, to the following embodiments designated with Roman numerals: Embodiment I Exhaust air scrubber for removing dust, product abrasion and water-soluble components from process exhaust air comprising in a housing I) at least one cleaning stage comprising a) a droplet separator, preferably designed as a wire mesh or lamella separator b) below this at least one packing, preferably designed as a random packing, c) optionally between droplet separator and packing at least one scrubbing tray, II) at least one inlet device for process exhaust air, arranged in the lower part of the housing, preferably below the at least one cleaning stage, III) at least one extraction device for scrubbing solution, which may also contain solids, preferably at the lower end of the housing, IV) at least one extraction line for the cleaned exhaust air V) at least one feed line for scrubbing solution in the upper part of the housing, above the at least one cleaning stage.characterized in that the exhaust line for the cleaned exhaust air i) begins inside the housing above the at least one cleaning stage, ii) is led downwards inside the housing and iii) is led out of the housing in the lower region of the housing, below the cleaning stage(s). Embodiment II Exhaust air scrubber according to embodiment I, characterized in that the housing is designed to taper downwards at the lower end, preferably conically, and the at least one extraction device for scrubbing solution is arranged at the lower end of the housing. Embodiment IIIa Exhaust air scrubber according to embodiment II, characterized in that the lower tapered end is used as a sump at least partially filled with scrubbing liquid, or that the scrubbing liquid is alternatively collected and stored in a separate container below the scrubber.Embodiment IIIb: An exhaust air scrubber according to embodiment II, characterized in that the at least one extraction device for scrubbing solution is arranged at the lowest point in the center of the housing taper and is optionally connected to at least one circulation pump for scrubbing solution extraction. Embodiment IV: An exhaust air scrubber according to one of the preceding embodiments, characterized in that the extraction line is arranged in the center of the housing, preferably concentrically to circular side walls of the housing.Embodiment V Exhaust air scrubber according to one of the preceding embodiments, characterized in that the exhaust duct for the cleaned exhaust air is led out of the housing laterally in the lower part of the housing, below the cleaning stage(s). Embodiment VI Exhaust air scrubber according to one of the preceding embodiments, characterized in that the exhaust duct located inside the housing is also designed as an attachment point for internal attachments, preferably including an attachment point for the elements of the cleaning stage(s). Embodiment VII Exhaust air scrubber according to one of the preceding embodiments, characterized in that the exhaust duct located inside the housing is connected, optionally via additional ducts, to at least one suction device and / or at least one exhaust air fan.Embodiment VIII: Exhaust air scrubber according to one of the preceding embodiments, characterized in that a portion of the scrubbing solution drawn off at the bottom or another suitable process medium, such as the feed water or process condensate accumulating elsewhere, is injected, preferably tangentially, into the conically shaped lower part of the housing. Embodiment IX: Exhaust air scrubber according to one of the preceding embodiments, characterized in that a device for heating the scrubbing solution to be introduced into the housing is arranged outside the housing, preferably in the form of a heat exchanger arranged on the supply line for the scrubbing solution.Embodiment X: Exhaust air scrubber according to one of the preceding embodiments, characterized in that a device for measuring physical parameters of material accumulating in the lower part of the housing is included, preferably comprising devices for measuring the pH value and concentration of the scrubbing solution and the fill level in the exhaust air scrubber. Embodiment XI: Exhaust air scrubber according to one of the preceding embodiments, characterized in that a control device is included with which the supply quantity of process exhaust air is regulated, preferably via a level- and concentration-controlled make-up feed. Embodiment XII: Exhaust air scrubber according to one of the preceding embodiments, characterized in that nozzles are attached upstream of the droplet separator in the flow direction, which nozzles are configured to spray water onto the droplet separator.Embodiment XIII: Exhaust air scrubber according to one of the preceding embodiments, characterized in that at least one heat exchanger or heat exchanger package is installed downstream of the uppermost purification stage in the flow direction. Embodiment XIV: Exhaust air scrubber according to one of the preceding embodiments, characterized in that a manually or automatically controlled gas or air supply device, preferably controlled based on temperature, weather, or visual parameters, is arranged downstream of the uppermost purification stage in the flow direction, preferably configured to introduce gas or air into the internal exhaust air duct or the internal part of the exhaust air duct.Embodiment XV Exhaust air scrubber according to one of the preceding embodiments, characterized in that in the case of several cleaning stages for the individual cleaning stages A) each cleaning stage has its own independent supply and control devices for the washing liquids, additives and / or operating parameters to be used in the cleaning stage, or B) some, but not all, cleaning stages have common supply and control devices for the washing liquids, additives and / or operating parameters to be used in the cleaning stage, or C) all cleaning stages have common supply and control devices for the washing liquids, additives and / or operating parameters to be used in the cleaning stages.Embodiment XVI Exhaust air scrubber according to one of the preceding embodiments, characterized in that two cleaning stages are arranged one after the other, wherein 1) the first cleaning stage in the direction of air flow is configured for alkaline and neutral, preferably unregulated pH operation and 2) the second cleaning stage is configured for acidic pH operation. Embodiment XVII Exhaust air scrubber according to one of the preceding embodiments, characterized in that the scrubbing solution drawn off at the bottom is guided in whole or in part to the feed point in the upper part of the housing, preferably by means of a pump. Embodiment XVIII Exhaust air scrubber according to one of the preceding embodiments, characterized in that at least a partial flow of the previously pre-cleaned air flows through a further cleaning stage.Embodiment XIX: Exhaust air scrubber according to one of the preceding embodiments, characterized in that at least one purification stage can be adjusted in its pH value by adding a mineral acid, preferably nitric or sulfuric acid. Embodiment XX: Exhaust air scrubber according to one of the preceding embodiments, characterized in that it is configured as part of a plant for producing ammonium nitrate- or urea-containing prilled or granulated product, preferably ammonium nitrate fertilizer (HDAN), porous ammonium nitrate (LDAN), calcium ammonium nitrate (CAN / KAS), ammonium nitrate sulfate fertilizer (ASN), or urea fertilizer.Embodiment XXI A process for exhaust air purification during the production of, or in plants for the production of, prilled or granulated products containing ammonium nitrate or urea, preferably ammonium nitrate fertilizer (HDAN), porous ammonium nitrate (LDAN), calcium ammonium nitrate (CAN / KAS), ammonium nitrate sulfate fertilizer (ASN), or urea fertilizer, characterized in that an exhaust air scrubber according to one of embodiments I to XX is used. Embodiment XXII Plant for the production of prilled or granulated products containing ammonium nitrate or urea, preferably ammonium nitrate fertilizer (HDAN), porous ammonium nitrate (LDAN), calcium ammonium nitrate (CAN / KAS), ammonium nitrate sulfate fertilizer (ASN), or urea fertilizer, characterized in that the plant comprises an exhaust air scrubber according to one of embodiments I to XX.Embodiment XXIII Use of an exhaust air scrubber according to one of embodiments I to XX for exhaust gas purification in the production of ammonium nitrate- or urea-containing prilled or granulated products, preferably ammonium nitrate fertilizer (HDAN), porous ammonium nitrate (LDAN), calcium ammonium nitrate (CAN / KAS), ammonium nitrate sulfate fertilizer (ASN) or urea fertilizer.

[0038] The various embodiments, embodiments and variants of the present invention, for example, but not limited to, the various claims, can be combined with one another as desired, provided that such combinations do not contradict one another.

[0039] The present invention is explained in more detail below with reference to the drawings. The drawings are not to be interpreted in a limiting sense and are not to scale. Furthermore, the drawings do not contain all features found in conventional systems, but are reduced to those features essential to the present invention and its understanding. Character description:

[0040] Figure 1 shows an exhaust air scrubber according to the invention.

[0041] The process exhaust air 3 to be cleaned is fed via a supply line into the housing 0a of the exhaust air scrubber 0. At the same time, the cleaned exhaust air is extracted via the exhaust air blower 7 at another point in the exhaust air scrubber 0. Due to the pressure difference thus generated, the process exhaust air 3 introduced into the exhaust air scrubber 0 is conveyed through the packing 2 or packings, a scrubbing base 9 (if present), shown here in the drawing, and via a droplet eliminator 1 into the upper region of the exhaust air scrubber 0. The process exhaust air 3 is cleaned by a countercurrent of an aqueous scrubbing solution. The process exhaust air cleaned in this way then enters the centrally arranged exhaust line 13, which is preferably designed as a pipe, for the exhaust air 8 in the upper region of the exhaust air scrubber 0 and is conveyed out of the exhaust air scrubber 0 via the exhaust air blower 7 and discharged as cleaned exhaust air.Alternatively, the air can also be conveyed via a fan connected upstream of the exhaust air scrubber 0. The scrubbing solution 11, which can preferably be an aqueous solution of the scrubbed substances and which is introduced above the scrubbing stage 2 in the upper region of the exhaust air scrubber 0, flows obeying gravity in countercurrent to the process exhaust air 3 to be cleaned through the scrubbing base 9 and the packing 3 downwards into the lower region of the exhaust air scrubber 0. The scrubbing solution 11 is fed into the scrubber, for example, via conventional liquid distributors, such as pipe or trough distributors. The figure shows a preferred embodiment of the present invention, in which the lower region of the exhaust air scrubber 0 is shown conical, although this is not absolutely necessary for the present invention. The scrubbing stage 2 can also consist of several scrubbing stages, each with its own associated scrubbing water circulation.At the lower end of the exhaust air scrubber 0, in the drawing at the tip of the conical part, there is a discharge device 4 for the scrubbing solution. The scrubbing solution is withdrawn from the lower area of ​​the exhaust air scrubber 0 via the circulation pump 5 and returned to the upper part of the exhaust air scrubber 0. Deviating from . Figure 1 The washing solution can also flow from the bottom of the washer into a separate container and from there be fed to the circulation pump 5. In the Figure 1a reintroduction of the supplied, circulated washing solution 11 between the packing 2 and the washing base 9 is shown, however it is also possible to introduce the circulated washing solution within the packing area. Likewise, the figure shows in a simplified manner that the circulated washing solution 11 is returned to the exhaust air scrubber 0 at one point; however, it is also possible and encompassed by the present invention that the washing solution can be led into the housing 0a of the exhaust air scrubber 0 at several points. Furthermore, the drawing shows that the washing liquid withdrawn from the lower end of the exhaust air scrubber 0 can be cleaned of accumulating impurities via a blowdown 6. Within the scope of the present invention, this blowdown orCleaning of the scrubbing liquid depends on the degree of contamination of the scrubbing liquid, and thus also depends on the degree of contamination of the supplied process exhaust air 3. The drawing shows the addition of feed water 10, which is fed to the pumped scrubbing solution 11. This water addition can also take place at a different location, for example, directly into the scrubber or upstream of the circulation pump 5. The figure shows water additions 14a for rinsing the droplet separator 1 and 14b for an optionally used scrubbing tray. These water additions can have the same origin as the feed water 10, but can also originate from various other systems. In the drawing, stream 12 is shown as an example of a scrubbing solution stream introduced preferably tangentially into the tapered lower scrubber section. However, another medium, such as the feed water 10, can also be used for this stream 12.In the drawing, stream 15 represents the addition of a mineral acid to capture ammonia from the air 3 to be cleaned. This addition can, for example, also take place upstream of the circulation pump 5 or directly into the exhaust air scrubber 0. The measurement of the pH value required for control can take place in the direction of flow before or after the acid is added. In the drawing, the part 13 of the exhaust air exhaust duct 8 located inside the housing 0a is shown arranged centrally in the housing 0a of the exhaust air scrubber 0, and the outlet of the exhaust air exhaust duct 8 from the housing 0a is shown opposite the inlet of the process exhaust air 3 into the housing 0a of the exhaust air scrubber 0 at approximately the same height of the housing 0a. This represents a preferred embodiment of the present invention.It is not absolutely necessary that the part 13 of the exhaust air duct 8 located inside the housing 0a be arranged exactly in the center of the exhaust air scrubber 0, although this is advantageous. Likewise, within the scope of the present invention, it is possible for the exhaust air duct 8 to exit the housing 0a at a different location.

[0042] Please note that the drawing is not to scale and is a simplified representation. Common details or necessities that are not necessary for understanding the present invention and are familiar to those skilled in the art have been omitted (such as screws, valves, or the like). List of reference symbols:

[0043] 0 Exhaust air scrubber 0a Housing 1 Droplet eliminator 2 Packing 3 Process air to be cleaned 4 Extractor (for scrubbing solution) 5 Circulation pump 6 Blowdown 7 Exhaust fan 8 Extractor line (for cleaned exhaust air) 9 Wash tray 10 Water addition (e.g. water, process condensate, diluted process solution) 11 Circulating scrubbing solution 12 Injected scrubbing solution 13 Internal part of the air extraction line 14 a,b Water addition to droplet eliminator / wash tray 15 Mineral acid (e.g. nitric acid, sulfuric acid) A Flow direction of the scrubbing solution B Flow direction of the air

Claims

1. An exhaust air scrubber (0) for removing dust, abraded product and water-soluble constituents from process exhaust air comprising in one housing (0a) I) at least one cleaning stage comprising a) a droplet separator (1), preferably in the form of a knitted mesh or lamellar separator, b) arranged therebelow at least one packing (2), preferably in the form of a random packing, c) optionally between the droplet separator (1) and the packing (2) at least one scrubbing tray (9), II) at least one inlet apparatus for process exhaust air (3) arranged in the lower portion of the housing, preferably below the at least one cleaning stage, III) at least one withdrawal apparatus for scrubbing solution (4) which may also contain solids, preferably at the lower end of the housing (0a), IV) at least one withdrawal conduit (8, 13) for the cleaned exhaust air V) at least one feed conduit (11) for scrubbing solution in the upper portion of the housing, above the at least one cleaning stage, characterized in that - the withdrawal conduit (8,13) for the cleaned exhaust air i) begins inside the housing (0a) above the at least one cleaning stage, ii) is passed downward inside the housing (0a) and iii) is passed out of the housing to the outside in the lower region of the housing (0a) below the cleaning stage(s).

2. The exhaust air scrubber (0) as claimed in claim 1, characterized in that - at the lower end the housing (0a) narrows in the downward direction and is preferably conical and - the at least one withdrawal apparatus for scrubbing solution (4) is arranged at the lower end of the housing (0a).

3. The exhaust air scrubber (0) as claimed in claim 2, characterized in that the at least one withdrawal apparatus for scrubbing solution (4) is arranged at the lowest point in the center of the housing narrowing and is optionally connected to at least one recirculation pump for scrubbing solution withdrawal.

4. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that the withdrawal conduit (8) is arranged in the middle of the housing (0a), preferably concentrically to the circular side walls of the housing (0a).

5. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that the withdrawal conduit (8) for the cleaned exhaust air is passed laterally outwards out of the housing in the lower portion of the housing (0a) below the cleaning stage(s).

6. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that the withdrawal conduit (8) inside the housing is simultaneously configured as an anchoring point for internal attachments, preferably including an anchoring point for the elements of the cleaning stage(s).

7. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that the withdrawal conduit (8) inside the housing is connected to at least one suction apparatus and / or at least one exhaust air blower optionally via additional conduits.

8. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that a portion of the scrubbing solution withdrawn at the bottom or another suitable process medium, for example the feed water or process condensate generated elsewhere, is injected into the conical lower portion of the housing (0a), preferably tangentially.

9. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that it comprises an apparatus for measuring physical parameters of material accumulating in the lower portion of the housing (0a), preferably comprising apparatuses for measuring the pH and the concentration of the scrubbing solution and the fill level in the exhaust air scrubber.

10. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that nozzles configured for spraying water onto the droplet separator (1) are attached upstream of the droplet separator (1).

11. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that at least one heat exchanger or heat exchanger package is installed downstream of the uppermost cleaning stage, preferably in the internal portion (13) of the air withdrawal conduit (8).

12. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that a manually or automatically controlled gas or air supplying means, preferably controlled on the basis of temperature or weather or visual parameters, is arranged downstream of the uppermost cleaning stage, preferably configured for introducing gas or air into the internal portion (13) of the exhaust air conduit (8).

13. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that in the case of a plurality of cleaning stages for the individual cleaning stages A) each cleaning stage has its own independent feed and control apparatuses for the scrubbing liquids, additions and / or operating parameters to be used in the cleaning stage, or B) some but not all cleaning stages have common feed and control apparatuses for the scrubbing liquids, additions and / or operating parameters to be used in the cleaning stage, or C) all cleaning stages have common feed and control apparatuses for the scrubbing liquids, additions and / or operating parameters to be used in the cleaning stages.

14. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that two cleaning stages are arranged in series, wherein 1) the first cleaning stage in the flow direction of the air is configured for alkaline and neutral, preferably uncontrolled pH, operation and 2) the second cleaning stage is configured for acidic pH operation.

15. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that the scrubbing solution withdrawn at the bottom is in whole or in part passed to the feed point (11) in the upper portion of the housing, preferably using a pump.

16. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that at least a substream of the previously pre-cleaned air passes through a further cleaning stage.

17. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that at least one cleaning stage may be pH-adjusted by addition of a mineral acid, preferably nitric or sulfuric acid.

18. The exhaust air scrubber (0) as claimed in any of the preceding claims, characterized in that it is configured as part of a plant for producing ammonium nitrate- or urea-containing prilled or granulated product, preferably ammonium nitrate fertilizer, porous ammonium nitrate, calcium ammonium nitrate, ammonium sulfate nitrate fertilizer (ASN) or urea fertilizer.

19. The use of an exhaust air scrubber as claimed in any of claims 1 to 18 for offgas cleaning in the production of ammonium nitrate-, ammonium sulfate- or urea-containing prilled or granulated product, preferably ammonium nitrate fertilizer, porous ammonium nitrate, calcium ammonium nitrate, ammonium sulfate fertilizer, ammonium sulfate nitrate fertilizer or urea fertilizer.