Process for cleaning treatment for purifying ammonia-containing air

Abstract

A method for subjecting ammonia-containing air from a room to a cleaning process using a filtering unit, wherein the air to be purified is passed through a filter matrix through which a fluid can flow in a first direction and through which air can flow in a direction orthogonal to the first direction; an aqueous liquid is introduced onto the filter matrix at a relatively high position and flows over the matrix in the first direction; the ammonia-containing air flows through the filter matrix in the orthogonal direction (i.e., in a cross-flow); the aqueous liquid mixed with ammonia is collected at a relatively low position, so that the filtering unit is in liquid exchange contact with the filter matrix downstream of the filter matrix with respect to the air flow and includes at least one cloth.

Description

Technical Field

[0001] The present invention relates to a method of subjecting ammonia-containing air to be cleaned from a certain space to a cleaning process using a filter unit including a filter matrix through which a liquid can flow in a first direction and a gas can be passed in a second direction transverse to the first direction, - an aqueous liquid is introduced at a relatively high position on the filter matrix of the filter unit, - the ammonia-containing air to be cleaned is passed through the filter matrix (225) in the second direction, - an aqueous liquid mixed with ammonia is collected.

Background Art

[0002] Such a method is well known in the professional art, for example, from US Patent Publication US2006 / 0118058.

[0003] One problem is that the air needs to be purified over a wide range in order to suppress damage to the environment.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The object of the present application is to provide a method of the kind mentioned in the preamble that enables effective removal of ammonia from the air in a space.

Means for Solving the Problems

[0005] For this purpose, the method according to the preamble is characterized in that the filter unit includes at least one cloth, and the ammonia-containing air to be cleaned is passed through at least one cloth on the downstream side of the filter matrix, where at least one cloth is in liquid-exchanging contact with the filter matrix.

[0006] It has been found that using a wetted cloth can effectively reduce the ammonia concentration with a relatively low flow resistance (and consequently relatively low energy consumption). In this way, ammonia can be removed from the air in spaces such as livestock houses, manure digesters, and water treatment plants where ammonia is discharged and accumulates in the air of the space.

[0007] The aqueous liquid is usually an acidic liquid with a pH < 6.

[0008] The cloth is a common woven fabric.

[0009] The number of canvas is preferably at most 8, and preferably 2.

[0010] It is preferred that the filter unit includes at least two cloths, and the ammonia-containing air to be cleaned is passed through at least two cloths on the downstream side of the filter matrix, and the cloths are in liquid exchange contact with the filter matrix.

[0011] Without being bound by theory, the absorption of ammonia is promoted by the transition (rotation) from one cloth to the downstream cloth, which is considered to be more beneficial than shortening the diffusion distance by selecting a small mesh size for a single cloth, which can cause a relatively large pressure drop. The pressure drop is preferably between 0.5 and 1000 Pascals, and even more preferably between 0.5 and 300 Pascals, for better performance.

[0012] An advantageous embodiment has the special feature that at least one cloth has an average mesh size of less than 4 square millimeters, preferably less than 2 square millimeters, and even more preferably between 0.5 and 1.5 square millimeters.

[0013] In this way, the stream containing contaminated air has ammonia removed even more efficiently. A better quality cloth with a regular mesh size relatively close to an average mesh size of about 1 square millimeter has the advantage that the mesh size is such that the air flow can pass through well, but when the fabric fibers of the cloth expand by absorbing the aqueous liquid, the mesh size does not become too small to overly impede the flow of the ammonia-containing air to be cleaned.

[0014] A convenient embodiment has the particularity that at least one of the cloths contains natural plant fibers, preferably jute.

[0015] As a result, the energy consumption remains in a relatively stable state regardless of humidity and temperature. Linen and cotton produce better results than wool, and jute produces the best results. Preferably, all the cloths are therefore made of a material containing at least 8% lignin with respect to the weight of the fibers and optionally at least 10%, preferably at least 20%, of hemicellulose and / or pectin.

[0016] A convenient embodiment has the particularity that the ammonia-containing air to be cleaned is passed through a filter matrix made of coconut fibers.

[0017] Thus, better humidification of the cloth with the aqueous liquid is achieved, which improves the absorption of ammonia.

[0018] A convenient embodiment has the particularity that the ammonia-containing air cleaned from the space is passed through a dust filter upstream of the filter matrix. In this way, the increase in flow resistance over time is suppressed.

[0019] A convenient embodiment has the particularity that the aqueous liquid contains an acid and has a pH between 1.0 and 6.0, preferably between 1.0 and 3.0, more preferably between 1.0 and 2.0, at least initially.

[0020] The acid is preferably a weak acid with a pKa > 1, for example, citric acid. Preferably, the concentration of citric acid is 10% or more, preferably 25% or more, preferably about 50% with respect to the weight of the aqueous liquid.

[0021] An advantageous embodiment has the particularity that the acid in the aqueous liquid is an acid whose ammonium salt in the aqueous liquid has a worse solubility than the acid itself, and the concentration of the acid is selected to be at least 50% higher, preferably at least 100% higher, and more preferably at least 150% higher than the concentration of the maximum solubility of the ammonium salt of the acid in the absence of ammonia.

[0022] As a result, 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%.

[0023] An advantageous embodiment has the particularity that the water vapor concentration in the ammonia-containing air to be cleaned increases.

[0024] As a result, the evaporation of water in the filter decreases and the risk of its dehydration decreases. Advantageously, the air is humidified downstream of the dust filter. Additionally or alternatively, the air is preferably humidified with water obtained by condensation. This does not contain salts. This water can be advantageously obtained by dehumidifying the air in the space with a dehumidifier.

[0025] An advantageous embodiment has the particularity that for the cleaning of the air, the ammonia-containing air to be cleaned is passed through the filter unit at a first air 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.

[0026] As a result, foaming on the downstream side of the filter matrix is reduced. The second air flow rate is advantageously zero. After the ammonia-containing air has been passed at the first flow rate for a certain period of time, the aqueous liquid in the filter unit is replaced again. Advantageously, between these two steps, the crystallized ammonium salt is flushed out with a washing liquid such as water, preferably water obtained by condensation.

[0027] An advantageous embodiment has the particularity that the ammonia-containing air to be cleaned is passed through at least one further filter unit on the upstream side of the filter matrix and, where applicable, downstream of the dust filter and / or the fan, and the at least one further filter unit comprises a plurality of further fabrics and a further filter matrix.

[0028] Thus, by using several filter units, each filter unit comprising a stack of fabrics and a layer of filter matrix, the ammonia concentration in the ammonia-containing air to be cleaned can be reduced more efficiently compared to a purification device with only one filter unit comprising a stack of one fabric and an equal amount of filter matrix.

[0029] An advantageous embodiment has the particularity that a relatively clean aqueous liquid is applied to the filter unit and a relatively ammonia-contaminated aqueous liquid is applied to at least one further filter unit.

[0030] As a result, a higher efficiency of ammonia absorption from the ammonia-containing air to be cleaned is obtained with the same amount of aqueous liquid.

[0031] An advantageous embodiment has the particularity that the air from which ammonia has been removed is passed through a grid with at least one slat on the downstream side of the filter unit, and the at least one slat consists of a plane with a downstream edge and has an upstream edge which is positioned lower than the downstream edge.

[0032] In this way, the foaming on the downstream side of the cloth and the filter matrix on the slats are collected, and the aqueous liquid mixed with ammonia flows towards a relatively low point and is returned to the cloth so as to be collected there.

[0033] An advantageous embodiment has the particularity that the air from which ammonia has been removed flows through a layer of a coarse-mesh material on the downstream side of the filter matrix and the cloth, and optionally on the upstream side of a grid with slats.

[0034] In this way, the foaming on the downstream side of the cloth and the filter matrix is reduced using a layer of a foam-reducing material, and the liquid mixed with ammonia is guided through the layer of the foam-reducing material to a relatively low point and collected there. Preferably, the material is hydrophobic or has a rough surface for a stronger foam-breaking effect. The material is relatively coarse-mesh compared to the upstream plastic layer, the filter matrix and / or the cloth.

[0035] An advantageous embodiment has the particularity that the ammonia-containing air to be cleaned is supplied through the cloth by a fan arranged on the upstream side of at least one of the filter matrix and the dust filter, and preferably the fan is adjustable.

[0036] As a result, an overpressure in the internal space between 0.5 and 300 Pascals can be achieved with respect to the environment of the device.

[0037] The present invention will now be described with reference to the drawings.

Brief Description of the Drawings

[0038]

Figure 1

Figure 2

Figure 3

Best Mode for Carrying Out the Invention

[0039] FIG. 1 shows an isometric cutaway view of a purification device for performing a cross-flow cleaning process on ammonia-containing air. The purification device 100 consists of a housing 101 that encloses an internal space 102 with six walls, a side wall 103 having an opening 110, three side walls 104, an upper wall 107, and a lower wall 108. The housing 101 is placed on a chassis 109. The side wall 103 includes an opening 110 that functions as an air inlet to the internal space 102 for the ammonia-containing air to be cleaned. A fan 111 is installed within the opening 110 to allow the ammonia-containing air to enter. A dust filter 112 is also arranged to remove dust particles from the ammonia-containing air with respect to the fan 111. Two of the three side walls 104 are adjacent to the side wall 103 having the opening 110, and one side wall 104 faces the side wall 103 and includes an opening that functions as an air outlet. The opening is covered with a grid 113. The grid 113 includes slats 114. The slats 114 have an induction slat surface 115, a proximal edge 116 attached to the wall, and a distal edge 117. The distal edge 117 is positioned at a relatively higher position with respect to the proximal edge 116, and the slats are inclined such that the induction slat surface 115 of the slats 114 faces the opening.

[0040] Within the opening of the side wall 104, a 3D matrix 120 is included within a frame 125, and the frame is arranged to seal on the outer wall 104. The connection of the frame to the side wall 104 is such that during operation, the ammonia-containing air to be cleaned can only flow into the internal space 102 through the 3D matrix surface of the 3D matrix 120 facing the internal space 102 within the internal space 102, and then exit from the internal space 102 through the 3D matrix 120. The configuration of the 3D matrix 120 is shown in FIG. 2.

[0041] The 3D matrix 120 includes a filter unit that includes a filter matrix, each sandwiched between two stacks (not shown, see Figure 2) of two layers of jute fabric. Above all the 3D matrices 120, an irrigation device 130 is arranged through which an aqueous liquid can be applied to the filter matrix and the jute fabric via a liquid outlet in the irrigation device 130. The irrigation devices 130' and 130'' are arranged on the 3D matrices 120' and 120'', respectively. The irrigation device 130' is connected to a supply pipe for the supply of an aqueous liquid, and the irrigation devices 130'' and 130'' (not visible) are continuously connected to the irrigation device 130' by an intermediate connecting pipe, so that these irrigation devices can also be supplied with an aqueous liquid. The irrigation device 130''' also includes an overflow, so that the pressure of the aqueous liquid in the irrigation device, which is communicatively connected, does not rise under the pressure from a pump (not shown) supplying the aqueous liquid. During operation, the aqueous liquid can flow downstream through the filter matrix contained in the 3D matrix 120 under the influence of gravity.

[0042] Below the 3D matrix 120, a collection container 140 is installed that can collect 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 and the bottom wall 108 of the housing 101.

[0043] During operation, the fan 111 sucks in air contaminated with ammonia from the vicinity of the apparatus 100. The air contaminated with ammonia first has dust particles removed by passing it through the dust filter 112. The ammonia-contaminated air from which the dust particles have been removed passes through the opening 110 and then flows into the internal space 102, where an overpressure of about 0.75 Pa higher than the air pressure in the neighboring area where the apparatus 100 is installed is established. The ammonia-contaminated air from which the dust particles have been removed flows out of the internal space 102 through the 3D matrix 120 due to the overpressure. At the same time, the perfusion device 130 perfuses the 3D matrix 120 from above with an aqueous liquid containing a buffering agent. As a result, the fluid flow of the aqueous liquid receives ammonia from the cross-flow of the ammonia-contaminated air flowing through the 3D matrix 120. The aqueous liquid flows from the lower side of the 3D matrix 120 to the collection container 140 at the lower wall 108 of the apparatus 100, where it is collected. From the collection container, the aqueous liquid can be reused by the perfusion device 130 until the purification capacity falls below the desired threshold. The cross-flow has the drawback that aqueous liquid in the form of droplets, aerosols or foam is carried along together, and this form of aqueous liquid can be captured by the guiding slat surface after it returns to the 3D matrix 120 under the influence of gravity. In this way, the outflow air stream has had dust, ammonia and the aqueous liquid useful for purification removed to some extent.

[0044] In an alternative circulation method for this and other embodiments of the present invention, during the application of the aqueous liquid containing the buffer agent by the perfusion device 130 on the 3D matrix 120, the fan 111 is turned off or placed in a relatively low output state. Preferably, a large amount of liquid is applied until the material is impregnated and excess aqueous liquid flows out into the collection container 140. After stopping the application of the cleaning liquid that absorbs ammonia, in order to establish an air flow of ammonia-contaminated air through the 3D matrix 120 with an overpressure of 0.75 Pa in the vicinity of the device 100, the ammonia-contaminated air is drawn from the vicinity of the device 100 and blown into the internal space 120 of the device 100. The risk of foaming and moisture loss from the aqueous liquid on the downstream side of the filter matrix is reduced by this operating method. The humidity can be determined with a hygrometer (not shown), and the period between consecutive cycles can be determined according to the aforementioned circulation method. On the other hand, 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 cleaning steps to compensate for the moisture loss due to evaporation from the aqueous liquid. Preferably, the fan 111 is then switched off or operates at a relatively low output to prevent foaming. The cleaning step reduces the amount of aqueous liquid and its components including citric acid used. The concentration of citric acid is 50% with respect to the weight of the aqueous liquid for application to the filter unit. Depending on the temperature and humidity of the ammonia-contaminated air, the allowable moisture loss from the aqueous solution and thus the operating period of the fan 111 before the citric acid and / or ammonia dissolved in the 3D matrix 120 crystallize or precipitate can be determined. Additionally or alternatively, the ammonia-containing air to be cleaned can be humidified, so that fewer or no cleaning steps are required before replacing the aqueous liquid.

[0045] Figure 2 shows a schematic cross-sectional view of the 3D matrix from the embodiment of Figure 1.

[0046] The 3D matrix 120 is a multi-layer assembly having a side surface 221 facing the internal space 102 and a side surface 222 facing the grid 113 with the slats 114. The air flow flows through the 3D matrix from the side surface 221 to the side surface 222. The 3D matrix 120 is constructed as follows from the side surface 222 facing the internal space 102 towards the side surface 221: a first plastic layer 223 through which air can flow, a first jute fabric stack 224 having a first jute fabric 224' and a second jute fabric 224'' with a mesh size corresponding to a mesh surface across which both have an air flow of approximately 1 millimeter. The stacking of the first jute fabric 224' and the second jute fabric 224'' is such that the mesh of the first jute fabric 224' does not generally completely coincide with the mesh of the second jute fabric 224''. Next, a filter matrix 225 consisting of a layer of coconut fibers follows, which is also arranged on the other side by a second stack of jute fabric, and the second stack of jute fabric 226' consists of a third jute fabric 226' and a fourth jute fabric 226'', and the characteristics of the third jute fabric 226' and the fourth jute fabric 226'' are the same as those of the first jute fabric 224' and the second jute fabric 224'', and the stacking method is the same as the stacking of the first jute fabric 224' and the second jute fabric 224'' in the first stack 224. Together, the filter matrix and the fabric form a filter unit. The second stack of jute fabric 226 then has a second plastic layer 227 arranged on the side through which air can flow. On the side surface 222 facing the grid 113 with the slats 114, a foamed destruction layer 228 of coarse synthetic resin fibers is added.

[0047] The different layers of the 3D matrix are configured in such a way that a pressure difference of at least 0.75 Pa can be established by the fan. If the output of the ventilation device permits, one or more additional stacks of at least two ducted fabrics can be installed upstream of the first plastic layer 223 and / or between the second plastic layer 227 and the foam-breaking layer, and the capacity can be improved using them.

[0048] During operation, foaming within the 3D matrix on the side surface of the grid 113 is reduced by the airflow containing bubbles passing through the foam-breaking layer 228. If the airflow still contains bubbles after leaving the foam-breaking layer 228, these bubbles are collected on the guiding slot surface 115 of the slat 114, where the bubbles can be further broken down, and the resulting aqueous liquid with some contaminants flows back towards the proximal edge 116 of the slat 114 and through the foam-breaking layer 228 towards a collection container, not shown, below the 3D matrix and is collected in the collection container. In this way, the consumption of the aqueous liquid for air purification is reduced.

[0049] Figure 3 shows a different, larger-scale embodiment of the purification device according to Figure 1. This embodiment comprises all aspects of the purification device according to Figure 1, but in addition to the normal 3D matrix 120 arranged adjacent to the grid 113, additional 3D matrices 321 and 322 are provided. The 3D matrix 321 is adjacent to the 3D matrix 320 on the side surface of the matrix 320 facing the internal space 102. The 3D matrix 322 is adjacent to the 3D matrix 321 on the side surface of the matrix 321 facing the internal space 102. On each of the 3D matrices 120, 321, 322, perfusion devices 130, 331, 332 for supplying the filter layer and the ducted fabric with the aqueous liquid are arranged.

[0050] The perfusion devices 130′, 130″, 130′″ are disposed on each of the 3D matrices 120. The perfusion device 130′ is provided with a supply pipe 340 for the supply of an aqueous liquid and is continuously connected to the perfusion devices 130″ and 130′″ by a connecting pipe 341 and a connecting pipe 342, respectively. Excess aqueous liquid can return through an overflow 343 into a first reservoir to which the supply pipe 340 for the supply of the aqueous liquid is connected.

[0051] The perfusion devices 331′, 331″, 331′″ are disposed on each of the 3D matrices 321. The perfusion device 331′ is provided with a supply pipe 350 for the supply of an aqueous liquid and is continuously connected to the perfusion devices 331″ and 331′″ by a connecting pipe 351 and a connecting pipe 352, respectively. Excess aqueous liquid can return through an overflow 353 into a second reservoir to which the supply pipe 350 for the supply of the aqueous liquid is connected.

[0052] The perfusion devices 332′, 332″, 332′″ are disposed on each of the 3D matrices 322. The perfusion device 332′ is provided with a supply pipe 360 for the supply of an aqueous liquid and is continuously connected to the perfusion devices 332″ and 332′″ by a connecting pipe 361 and a connecting pipe 362, respectively. Excess aqueous liquid can return through an overflow 363 into a third reservoir to which the supply pipe 360 for the supply of the aqueous liquid is connected.

[0053] The aqueous liquid that flows through the 3D matrix 120 and contains the 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 even more absorbed ammonia can also be collected in the third reservoir. For example, during operation, the first reservoir contains a relatively pure aqueous liquid, the second reservoir contains a relatively mixed aqueous liquid, and the third reservoir contains the most impure aqueous liquid. This arrangement of the matrices, perfusion devices, and pipes in the treatment plant extracts ammonia more efficiently from the ammonia-containing air to be cleaned.

Claims

1. A method of cleaning ammonia-containing air from a space using a filter unit that includes a filter matrix (225) that allows liquid to perfuse in a first direction and allows gas to pass in a second direction intersecting the first direction, - The aqueous liquid is introduced at a relatively high position on the filter matrix (225) of the filter unit. - The ammonia-containing air to be washed is passed through the filter matrix (225) in the second direction. - The aqueous liquid mixed with ammonia is collected at a relatively low position. The filter unit comprises at least one cloth (226', 226''), wherein the ammonia-containing air to be washed passes through at least one cloth (226', 226'') downstream of the filter matrix (225), and the at least one cloth (226', 226'') is in liquid exchange contact with the filter matrix (225). method.

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

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

4. The method according to claim 1, wherein at least one of the fabrics (226', 226") comprises natural plant fibers, preferably jute.

5. The method according to claim 1, wherein the ammonia-containing air to be washed is passed through the filter matrix (225) made of coconut fiber.

6. The method according to claim 1, wherein the ammonia-containing air to be cleaned from the space upstream of the filter matrix (225) is passed through a dust filter (112).

7. The method according to claim 1, wherein the aqueous liquid contains an acid and has a pH between 1.0 and 6.0, preferably between 1.0 and 3.0 at least initially, and more preferably between 1.0 and 2.0 at least initially.

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

9. The method according to claim 1, wherein the concentration of water vapor in the ammonia-containing air being washed increases.

10. The method according to claim 1, wherein, for the purpose of 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 lower than the first air flow rate.

11. The ammonia-containing air to be cleaned is passed through at least one further filter unit upstream of the filter matrix (225) and, where applicable, downstream of the dust filter (112) and / or fan (111), wherein the at least one further filter unit comprises a further plurality of cloths and a further filter matrix (225), according to claim 1.

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

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

14. The method according to claim 1, wherein the ammonia-free air flows through a layer of coarse material (228) downstream of the filter matrix (225) and the cloth (226', 226''), and optionally upstream of a grid (113) having slats (114).

15. The ammonia-containing air to be washed is supplied through the cloth (226', 226'') by a fan (111) located upstream of at least one of the filter matrix (225) and dust filter (112), preferably the fan (111) is adjustable, according to claim 1.

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