Washing treatment method for purifying ammonia-containing air

Abstract

A method of washing ammonia-containing air from a room using a filter unit in which the air to be purified passes through a filter substrate through which a fluid can flow in a first direction and through which air can flow in a direction orthogonal to the first direction; the aqueous liquid is introduced onto the filtration substrate at a relatively high location and flows through the substrate in a first direction; ammonia-containing air flows through the filter substrate in an orthogonal direction (i.e., transverse flow); ammonia-rich aqueous liquid is collected at a relatively low location, wherein the filtration unit comprises at least one cloth located downstream of and in liquid exchange contact with the filtration substrate with respect to the gas stream.

Description

Technical Field

[0001] The invention relates to a method for scrubbing ammonia-containing air to be purified from a space using a filter unit, the filter unit comprising a filter matrix capable of being penetrated by liquid in a first direction and permeable to gas in a second direction perpendicular to the first direction;

[0002] in

[0003] - introducing the aqueous liquid at a relatively high point on the filter matrix of the filter unit,

[0004] - the ammonia-containing air to be purified passes through the filter matrix (225) in a second direction, and - the ammonia-rich aqueous liquid is collected. Background Art

[0005] Such methods are well known in the art, for example from US patent publication US 2006 / 0118058.

[0006] One problem is the need for extensive air purification to limit damage to the environment. Summary of the invention

[0007] It is an object of the present application to provide a method of the type mentioned in the introduction which can effectively remove ammonia from the air of a space.

[0008] To this end, the method according to the introduction is characterized in that the filter unit comprises at least one cloth through which the ammonia-containing air to be cleaned passes downstream of the filter matrix, wherein the at least one cloth is in liquid-exchanging contact with the filter matrix.

[0009] It has been found that the use of humidifying cloths can effectively reduce the concentration of ammonia while having relatively low flow resistance (and associated relatively low energy consumption). In this way, ammonia can be removed from the air of spaces such as livestock houses, manure digesters and water treatment plants where ammonia is emitted into the air of the space and accumulates.

[0010] Aqueous liquids are usually acidic liquids with a pH < 6.

[0011] The cloth is common woven cloth.

[0012] The number of canvases is preferably at most 8, preferably 2.

[0013] The filter unit preferably comprises at least two cloths through which the ammonia-laden air to be cleaned passes downstream of the filter matrix, the cloths being in liquid-exchanging contact with the filter matrix.

[0014] Without being bound by any theory, it is believed that the absorption of ammonia is promoted by the transition (swirl) from one cloth to the downstream cloth, which is more beneficial than shortening the diffusion distance by choosing a smaller mesh size for the single cloth, which will result in a relatively large pressure drop, wherein the pressure drop is preferably between 0.5 and 1000 Pascals for better performance, and even more preferably between 0.5 and 300 Pascals.

[0015] An advantageous embodiment has the particular feature that the average mesh size of at least one of the cloths is less than 4 square millimeters, preferably less than 2 square millimeters, even more preferably between 0.5 and 1.5 square millimeters.

[0016] In this way, the ammonia in the air stream containing the polluted air is more effectively removed. The better quality cloth has a conventional mesh size, relatively close to an average mesh size of about 1 square millimeter, which has an advantageous effect because the mesh size allows the air stream to pass well, but is also large enough that if the cloth fibers made of the cloth swell by absorbing an aqueous liquid, the mesh size does not become too small and excessively hinder the flow of the ammonia-containing air to be cleaned.

[0017] An advantageous embodiment is characterized in that at least one cloth comprises natural plant fibers, preferably jute.

[0018] Thus, the energy consumption remains relatively constant, regardless of humidity or temperature. Linen and cotton provide better results than wool, jute providing the best results. Thus, preferably, all cloths consist of a material comprising at least 8% lignin and optionally at least 10%, preferably at least 20% hemicellulose and / or pectin (relative to the weight of the fiber).

[0019] An advantageous embodiment has the feature that the ammonia-containing air to be cleaned is passed through a filter matrix made of coconut fibers.

[0020] Thus, better wetting of the cloth with the aqueous liquid is achieved, thereby improving the absorption of ammonia.

[0021] An advantageous embodiment has the feature that the ammonia-containing air to be cleaned from the room passes through the dust removal filter upstream of the filter matrix. Thus, an increase in flow resistance over time is suppressed.

[0022] An advantageous embodiment has the feature that the aqueous liquid comprises an acid and has a pH value between 1.0 and 6.0, preferably, at least initially, between 1.0 and 3.0, more preferably, at least initially, between 1.0 and 2.0.

[0023] The acid is preferably a weak acid with a pKa>1, such as citric acid. Preferably, the concentration of citric acid is 10% or more, preferably higher than 25%, preferably about 50% by weight relative to the weight of the aqueous liquid.

[0024] An advantageous embodiment has the following features: the acid in the aqueous liquid is an acid whose ammonium salt is less soluble in the aqueous liquid than the acid, and the concentration of the acid is chosen so that in the absence of ammonia, the concentration is at least 50% higher, preferably at least 100% higher, more preferably at least 150% higher than the concentration of the maximum solubility of the ammonium salt of the acid.

[0025] Thus, the ability to absorb ammonia from the ammonia-containing air to be cleaned is improved. For example, a suitable concentration of citric acid is at least 40%.

[0026] An advantageous embodiment is characterized in that the water vapor concentration in the ammonia-containing air to be cleaned is increased.

[0027] Thus, evaporation of water in the filter is reduced and the risk of dehydration thereof is reduced. Advantageously, the air downstream of the dust filter is humidified. Additionally or alternatively, the air is preferably humidified with water obtained by condensation. This water does not contain salt. This water can advantageously be obtained by dehumidifying the air in the space using a dehumidifier.

[0028] An advantageous embodiment has the feature that, for cleaning the air, the ammonia-containing air to be cleaned is passed through the filter unit at a first flow rate and the aqueous liquid is periodically introduced into the filter unit at a second air flow rate which is lower than the first air flow rate.

[0029] Therefore, the foaming of the filter matrix downstream is reduced. The second air flow rate is advantageously zero. After a period of time of passing the ammonia-containing air with the first flow rate, the aqueous liquid in the filter unit is replaced again. Advantageously, between these two steps, the ammonium salt of the crystallization is washed away with a washing liquid (e.g. water, preferably water obtained by condensation).

[0030] An advantageous embodiment has the feature that the ammonia-containing air to be cleaned is passed through at least one further filter unit upstream of the filter matrix and, if applicable, downstream of the dust filter and / or the fan, wherein the at least one further filter unit comprises a further plurality of cloths and a further filter matrix.

[0031] Therefore, by using several filter units, each filter unit having a stack of cloth and a layer of filter matrix, the ammonia concentration in the ammonia-containing air to be cleaned can be reduced more efficiently than with a purification device having only one filter unit (which includes a stack of cloth and an equal amount of filter matrix).

[0032] An advantageous embodiment has the feature that a relatively clean aqueous liquid is applied to a filter unit and a relatively ammonia-contaminated aqueous liquid is applied to at least one further filter unit.

[0033] Thus, a higher efficiency of absorbing ammonia from the ammonia-containing air to be cleaned can be achieved using the same amount of aqueous liquid.

[0034] An advantageous embodiment has the following feature: the air depleted of ammonia is passed downstream of the filter unit through a grid having at least one slat, wherein the at least one slat consists of a plane with a downstream edge and has an upstream edge, the upstream edge of which is located lower than the downstream edge.

[0035] In this way, any foam downstream of the filter matrix is ​​collected on the cloth and slats, and the ammonia-rich aqueous liquid is returned to the cloth to flow to a relatively low point and be collected there.

[0036] An advantageous embodiment has the feature that the air depleted of ammonia flows through a layer of coarse mesh material downstream of the filter matrix and the cloth and upstream of the grid, optionally with slats.

[0037] Thus, any foam downstream of the cloth and filter matrix is ​​reduced by means of the foam degrading material layer, and the ammonia-rich liquid is guided to relatively low-lying points by the foam degrading material layer and collected there. Preferably, the material is hydrophobic or has a rough surface to obtain a stronger foam-destroying effect. The material has a relatively coarse mesh compared to the upstream plastic layer, filter matrix and / or cloth.

[0038] An advantageous embodiment has the feature that the ammonia-containing air to be cleaned is conveyed through the cloth by a fan located upstream of at least one of the filter matrix and the dust collector, the fan preferably being adjustable.

[0039] Thus, an overpressure of between 0.5 and 300 Pascals in the interior relative to the environment of the device can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will now be explained based on the accompanying drawings, in which

[0041] Figure 1 An isometric perspective view of an apparatus for scrubbing ammonia-containing air to be purified is shown;

[0042] Figure 2 shows a schematic cross section of an apparatus for cross-flow scrubbing of ammonia-containing air to be purified; and

[0043] Figure 3 Shown according to Figure 1 A different, more extensive embodiment of a purification device. DETAILED DESCRIPTION

[0044] Figure 1 An isometric cross-sectional view of a purification device for ammonia-containing air is shown. The purification device 100 consists of a housing 101 enclosing an internal space 102 by 6 walls, a side wall 103 with an opening 110, three side walls 104, an upper wall 107 and a lower wall 108. The housing 101 rests on a chassis 109. The side wall 103 includes an opening 110, which serves as an air inlet for the ammonia-containing air to be purified to enter the internal space 102. A fan 111 is installed in the opening 110 to allow the ammonia-containing air to be purified to enter. For the fan 111, a dust filter 112 is also provided to remove dust particles in the ammonia-containing air. Three side walls 104 include openings used as air outlets, wherein two side walls 104 are adjacent to the side wall 103 with the opening 110, and one side wall 104 is opposite to the side wall 103. The opening is covered by a grid 113. The grid 113 includes slats 114. The slat 114 has a guide slat surface 115, a proximal edge 116 attached to the wall, and a distal edge 117, wherein the slat is inclined so that the distal edge 117 is located relatively high relative to the proximal edge 116 and the guide slat surface 115 of the slat 114 faces the opening.

[0045] In the opening of the side wall 104, the 3D matrix 120 is contained in a frame 125, which is arranged in a sealed manner on the outer wall 104. The connection between the frame and the side wall 104 is such that during operation, the ammonia-containing air to be cleaned in the inner space 102 can only flow in through the 3D matrix surface of the 3D matrix 120 facing the inner space 102 and then leave the inner space 102 through the 3D matrix 120. The composition of the 3D matrix 120 is as follows Figure 2 shown.

[0046] The 3D matrix 120 comprises filter units, each filter unit comprising a filter matrix sandwiched between 2 laminates, each laminate having 2 layers of jute cloth (not shown, see Figure 2). Above all 3D matrices 120, an irrigation device 130 is arranged, which can apply aqueous liquid to the filtering matrix and jute cloth through the liquid outlet in the irrigation device 130. The irrigation device 130' and the irrigation device 130" are arranged on the top of the 3D matrices 120' and 120", respectively. The irrigation device 130' is connected to a supply pipe for supplying aqueous liquid, and the irrigation devices 130" and 130" (not visible) are connected in series with the intermediate connecting pipe to the 130' irrigation device so that these irrigation devices can also be supplied with aqueous liquid. The irrigation device 130'" also includes an overflow port so that the pressure of the aqueous fluid in the connectedly coupled irrigation devices does not increase under the pressure from the pump (not shown) supplying the aqueous liquid. In operation, the aqueous liquid can flow downward through the filtering matrix contained in the 3D matrix 120 under the influence of gravity.

[0047] Below the 3D matrix 120, a collection container 140 is installed, which can collect and gather the aqueous liquid that has flowed through the 3D matrix 120. The collection container 140 is formed by the lower parts of the side walls 103, 104 of the housing 101 and the lower wall 108.

[0048] In operation, the fan 111 draws ammonia-contaminated air from the vicinity of the device 100. The ammonia-contaminated air is first cleaned of dust particles by passing through the dust filter 112. The ammonia-contaminated air cleaned of dust particles through the opening 110 then flows into the interior space 102, and the overpressure generated in the interior space 102 is about 0.75 Pa higher than the air pressure in the vicinity of the device 100. The ammonia-contaminated air cleaned of dust particles flows out of the interior space 102 through the 3D matrix 120 due to the overpressure. At the same time, the irrigation device 130 irrigates the 3D matrix 120 from above with an aqueous liquid containing a buffer. Therefore, the fluid flow of the aqueous liquid can receive ammonia from the lateral airflow of the ammonia-contaminated air flowing through the 3D matrix 120. The aqueous liquid flows from the lower side of the 3D matrix 120 at the lower wall 108 of the device 100 and is collected there. From the collection container, the aqueous liquid can be reused by the irrigation device 130 until the purification capacity is below the required threshold. The disadvantage of the transverse airflow is that the aqueous liquid can be carried along in the form of droplets, aerosols or foams, which can be captured by the guide slat surfaces and then flow back to the 3D matrix 120 under the action of gravity. In this way, the outflowing airflow is partially cleaned of dust, ammonia and the aqueous liquid used for purification.

[0049] In the alternative circulation method in this embodiment and other embodiments of the present invention, when the aqueous liquid containing the buffer is applied to the 3D matrix 120 by the irrigation device 130, the fan 111 is turned off or in a relatively low power state. Preferably, the amount of liquid applied is sufficient to saturate the material, and the excess aqueous liquid is discharged into the collection container 140. After stopping the application of the washing liquid that absorbs ammonia, the ammonia-contaminated air is drawn from the vicinity of the device 100 and blown into the internal space 102 of the device 100 to establish an airflow of ammonia-contaminated air through the 3D matrix 120 at an overpressure of 0.75 Pa relative to the vicinity of the device. By this mode of operation, the risk of foaming downstream of the filter matrix and the loss of water in the aqueous liquid can be reduced. The humidity can be determined using a hygrometer (not shown), and the duration between consecutive cycles can be determined according to the above-mentioned circulation method. At the same time, if the ability of the aqueous liquid to absorb ammonia from the ammonia-contaminated air is still sufficient, additional water can be applied to the 3D matrix 130 in one or more washing steps to compensate for the water loss caused by the evaporation of the aqueous liquid, and it is best to turn off the fan 111 or operate at a relatively low power to prevent foaming. The washing step reduces the use of the aqueous liquid and its components, including citric acid. The concentration of citric acid is 50% of the weight of the aqueous liquid applied to the filter unit. The allowable water loss in the aqueous solution and the duration of operation of the fan 111 can be determined before the citric acid and / or ammonia dissolved in the 3D matrix 120 crystallize or precipitate, depending on the temperature and humidity of the ammonia-contaminated air. Additionally or alternatively, the ammonia-containing air to be cleaned can be humidified so that fewer or no washing steps are required before replacing the aqueous liquid.

[0050] Figure 2 Shows Figure 1Schematic cross section of a 3D matrix in an embodiment. The 3D matrix 120 is a multilayer component, whose side 221 faces the interior space 102 and whose side 222 faces the grid 113 with slats 114. The air flow flows through the 3D matrix from the side 221 to the side 222. The 3D matrix 120 is constructed from one side 221 to the side 222, and from the side 222 facing the interior space 102 is constructed as follows: a first plastic layer 223, through which air can flow; a first jute cloth stack 224, which has a first jute cloth 224' and a second jute cloth 224", both of which have a mesh size corresponding to the mesh surface transverse to the air flow, which is about 1 mm. The stacking of the first jute cloth 224' and the second jute cloth 224" is such that the mesh of the first jute cloth 224' does not completely coincide with the mesh of the second jute cloth 224" in most cases. Next, a filter matrix 225 consisting of a coconut fiber layer follows, which is also One side is also connected to a second jute stack, wherein the second jute stack 226' consists of a third jute 226' and a fourth jute 226", wherein the properties of the third jute 226' and the fourth jute 226" are the same as the properties of the first jute 224' and the second jute 224", and the stacking method is the same as the stacking method of the first jute 224' and the second jute 224" in the first stack 224. The filter matrix and the cloth together form a filter unit. The side of the jute 226 of the second stack is connected to a second plastic layer 227, through which air can flow. On the side 222 facing the grid 113 with slats 114, a foam crushing layer 228 made of coarse plastic fibers is applied.

[0051] The different layers of the 3D matrix are composed in such a way that a pressure difference of at least 0.75 Pa can be established by the fan. If the power of the ventilator allows, one or more additional stacks of at least two jute cloths can be installed upstream of the first plastic layer 223 and / or between the second plastic layer 227 and the foam crushing layer, so that the capacity can be increased.

[0052] In operation, foaming in the 3D matrix on the side of the grid 113 can be reduced by passing the airflow that may contain foam through the foam breaking layer 228. If the airflow still contains foam after leaving the foam breaking layer 228, the foam will be collected on the guide slat surface 115 of the slat 114, where the foam can be further decomposed, and the resulting aqueous liquid containing any contaminants can flow back to the proximal edge 116 of the slat 114 to flow through the foam breaking layer 228 to the collection container (not shown) below the 3D matrix and be collected in the collection container. In this way, the consumption of aqueous liquid required to purify the air is reduced.

[0053] Figure 3 Shows Figure 1 Another, more extensive embodiment of the purification device shown. This embodiment is provided according to Figure 1 All aspects of the purification device shown, but in addition to the usual 3D matrix 120 arranged near the grid 113, additional 3D matrices 321 and 3D matrices 322 are provided. 3D matrix 321 is adjacent to 3D matrix 320 on the side of matrix 320 facing the interior space 102. 3D matrix 322 is adjacent to 3D matrix 321 on the side of matrix 321 facing the interior space 102. Above each 3D matrix 120, 321, 322, an irrigation device 130, 331, 332 is provided, which can supply aqueous liquid to the filter layer and the jute cloth.

[0054] Irrigation devices 130', 130", and 130'" are respectively disposed on the top of 3D matrix 120. Irrigation device 130' is provided with a supply pipe 340 for supplying aqueous liquid, and supply pipe 340 is connected in series with irrigation device 130" and irrigation device 130'" through connection pipe 341 and connection pipe 342, respectively. Excess aqueous liquid can flow back to the first reservoir through overflow device 343, and supply pipe 340 is connected to the first reservoir to supply aqueous liquid.

[0055] Irrigation devices 331', 331", and 331"' are disposed above each of the 3D matrices 321. Irrigation device 331' is provided with a supply pipe 350 for supplying an aqueous liquid, and supply pipe 350 is connected in series with irrigation device 331" and irrigation device 331'" through connection pipe 351 and connection pipe 352, respectively. Excess aqueous liquid can flow back to the second reservoir through overflow device 353, and supply pipe 350 is connected to the second reservoir to supply the aqueous liquid.

[0056] Irrigation devices 332', 332", and 332'" are disposed above each of the 3D matrices 322. Irrigation device 332' is provided with a supply pipe 360 ​​for supplying an aqueous liquid, and supply pipe 360 ​​is connected in series to irrigation device 332" and irrigation device 332'" through connection pipe 361 and connection pipe 362, respectively. Excess aqueous liquid may flow back to the third reservoir through overflow device 363, to which supply pipe 360 ​​is connected to supply the aqueous liquid.

[0057] The aqueous liquid that flows through the 3D matrix 120 and contains absorbed ammonia can be collected in the second reservoir. The aqueous liquid that flows through the 3D matrix 321 and contains more absorbed ammonia can be collected in the third reservoir. The aqueous liquid that flows through the 3D matrix 322 and contains more absorbed ammonia can also be collected in the third reservoir. For example, during operation, the first reservoir is filled with a relatively pure aqueous liquid, the second reservoir is filled with a relatively impure aqueous liquid, and the third reservoir is filled with the least pure aqueous liquid. This matrix, perfusion device and piping arrangement in the treatment plant can more effectively extract ammonia from the ammonia-containing air to be purified.

Claims

1. A method for scrubbing ammonia-containing air to be purified from a space using a filter unit, the filter unit comprising a filter matrix (225) which is permeable to liquid in a first direction and permeable to gas in a second direction perpendicular to the first direction; in - introducing an aqueous liquid at a relatively high point on the filter matrix (225) of the filter unit, - passing the ammonia-containing air to be cleaned through the filter matrix (225) along the second direction, and - Collecting the ammonia-rich aqueous liquid at a relatively low point, It is characterized in that The filter unit comprises at least one cloth (226', 226"), and the ammonia-containing air to be cleaned downstream of the filter matrix (225) passes through the at least one cloth (226', 226"), wherein the at least one cloth (226', 226") is in liquid-exchange contact with the filter matrix (225).

2. The method according to claim 1, wherein the filter unit comprises at least two pieces of cloth (226', 226"), and the ammonia-containing air to be cleaned passes downstream of the filter matrix (225) through the at least two pieces of cloth (226', 226"), and the cloth (226', 226") is in liquid exchange contact with the filter matrix (225).

3. The method according to claim 1 or 2, wherein at least one cloth (226', 226") has an average mesh size of less than 4 square millimeters, preferably less than 2 square millimeters and preferably between 0.5 and 1.5 square millimeters.

4. Method according to one of the preceding claims, wherein at least one of the cloths (226', 226") comprises natural plant fibers, preferably jute.

5. The method according to one of the preceding claims, wherein the ammonia-laden air to be cleaned is passed through the filter matrix (225) made of coconut fibers.

6. The method according to one of the preceding claims, wherein the ammonia-containing air to be cleaned from the space is passed through a dust removal filter (112) upstream of the filter matrix (225).

7. The method according to one of the preceding claims, wherein the aqueous liquid contains an acid and has a pH value between 1.0 and 6.0, preferably, at least initially, between 1.0 and 3.0, more preferably, at least initially, between 1.0 and 2.

0.

8. The method according to claim 1 , wherein the acid in the aqueous liquid is an acid whose ammonium salt is less soluble in the aqueous liquid than the acid, and the concentration of the acid is selected such that in the absence of ammonia, the concentration is at least 50% higher, preferably at least 100% higher, more preferably at least 150% higher than the concentration of the maximum solubility of the ammonium salt of the acid.

9. The method according to one of the preceding claims, wherein the water vapor concentration in the ammonia-containing air to be cleaned is increased.

10. The method according to one of the preceding claims, wherein: In order to clean the air, the ammonia-containing air to be cleaned is passed through the filter unit at a first flow rate, and the aqueous liquid is periodically introduced into the filter unit at a second air flow rate lower than the first air flow rate.

11. The method according to one of the preceding claims, wherein the ammonia-containing air to be cleaned is passed through at least one further filter unit upstream of the filter matrix (225) and, if applicable, downstream of a dust filter (112) and / or a fan (111), wherein the at least one further filter unit comprises a further plurality of cloths and a further filter matrix (225).

12. The method of claim 11, wherein a relatively clean aqueous liquid is applied to the filtration unit and a relatively ammonia-contaminated aqueous liquid is applied to at least one further filtration unit.

13. The method according to claim 1 , wherein the ammonia-depleted air is passed downstream of the filter unit through a grid (113) having at least one slat, wherein the at least one slat (114) consists of a plane (115) having a downstream edge (117) and having an upstream edge (116) which is positioned lower than the downstream edge (117).

14. The method according to one of the preceding claims, wherein the ammonia-depleted air downstream of the filter matrix (225) and the cloth (226', 226") and upstream of the grid (113) optionally with slats (114) flows through a layer of coarse mesh material (228).

15. The method according to one of the preceding claims, wherein the ammonia-containing air to be cleaned is conveyed through the cloth (226', 226") by a fan (111), the fan (111) being located upstream of at least one of the filter matrix (225) and the dust removal filter (112), preferably the fan (111) being adjustable.

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