Title of invention: Off-gas treatment device and fertilizer production plant equipped with this off-gas treatment device
Technical field
[0001]
　The present disclosure relates to an off-gas treatment apparatus and a fertilizer production plant equipped with the off-gas treatment apparatus.
Background technology
[0002]
　A fertilizer production plant that produces fertilizer using methane-containing gas such as natural gas includes an ammonia production unit that produces ammonia from methane-containing gas and a urea production unit that produces an aqueous urea solution by reacting ammonia with carbon dioxide. , Equipped with a urea granulation unit that produces granular solid urea from an aqueous urea solution. In the urea granulation unit, off-gas containing urea dust, which is a powder of solid urea, and ammonia is generated. The off-gas is released into the atmosphere by removing urea dust and ammonia by gas-liquid contact with water or an aqueous urea solution in the off-gas treatment apparatus.
[0003]
　Patent Document 1 describes a technique for gas-liquid contact between an acidic absorption liquid, particularly a sulfuric acid aqueous solution, and off-gas in order to increase the removal rate of ammonia in an off-gas treatment apparatus. Ammonium sulfate is produced by the reaction of ammonia and sulfuric acid. Although this is a raw material for fertilizer, it is often made into solid ammonium sulfate because it has poor handleability in liquid form. Patent Document 2 describes a process for reducing ammonia in off-gas as ammonium sulfate.
Prior art literature
Patent documents
[0004]
Patent Document 1: US Pat. No. 9,745,256,
Patent Document 2: US Pat. No. 9,464,09.
Outline of the invention
Problems to be solved by the invention
[0005]
　However, the process of reducing ammonia in off-gas as ammonium sulfate has the problem that the granulation equipment for ammonium sulfate is expensive, and the problems such as contamination by ammonium sulfate and measures for drainage equipment containing ammonium sulfate. A simple off-gas treatment device that does not generate ammonium sulfate is desired.
[0006]
　In view of the above circumstances, at least one embodiment of the present disclosure provides an off-gas treatment apparatus capable of treating off-gas containing ammonia without producing ammonium sulfate, and a fertilizer production plant including the off-gas treatment apparatus. The purpose.
Means to solve problems
[0007]
　The off-gas scrubber according to at least one embodiment of the present disclosure is an off-gas scrubber that treats off-gas containing ammonia, from an ammonia scrubber that brings an absorption liquid containing carbon dioxide water and off-gas into gas-liquid contact, and an ammonia scrubber. It is provided with a stripper for removing ammonia and carbon dioxide dissolved in the absorption liquid from the extracted absorption liquid. According to this configuration, by removing ammonia from the off-gas using an absorbent solution containing carbonated water, it is not necessary to use sulfuric acid, so that the off-gas containing ammonia can be treated without producing ammonium sulfate. ..
[0008]
　At least one embodiment of the present disclosure further comprises a carbonated water producing apparatus for producing carbonated water from carbon dioxide and water, and a decompressor for decompressing the carbonated water produced in the carbonated water producing apparatus to atmospheric pressure. The carbonated water that flows out of the vessel may be supplied to the ammonia scrubber. When the carbonated water produced by the carbonated water production apparatus is supplied to the ammonia scrubber as it is, a part of carbon dioxide is released from the carbonated water in the ammonia scrubber. Carbon dioxide emitted in the ammonia scrubber is usually difficult to recover. On the other hand, by dissipating a part of carbon dioxide from the carbonated water in the decompressor before flowing into the ammonia scrubber, the emission of carbon dioxide in the ammonia scrubber can be suppressed, and the carbon dioxide emitted in the decompressor can be suppressed. Since it can be recovered, the amount of carbon dioxide used can be reduced.
[0009]
　In at least one embodiment of the present disclosure, at least a portion of the absorption liquid from which ammonia and carbon dioxide have been removed in the stripper may be supplied to the ammonia scrubber. According to this configuration, by supplying the absorption liquid from which ammonia and carbon dioxide have been removed by the stripper to the ammonia scrubber, the ammonia concentration in the absorption liquid in the ammonia scrubber is reduced. As the concentration of ammonia in the absorption liquid is lower, the amount of ammonia absorbed by the absorption liquid in the ammonia scrubber increases, so that the efficiency of removing ammonia can be improved.
[0010]
　In at least one embodiment of the present disclosure, a dust scrubber that removes solid components from off-gas by gas-liquid contact with a cleaning solution before flowing into the ammonia scrubber is further provided, and the absorption liquid from which ammonia and carbon dioxide have been removed in a stripper. At least a portion may be supplied as at least a portion of the dust scrubber cleaning solution. According to this configuration, the amount of the cleaning liquid used can be reduced by using the absorbing liquid from which ammonia and carbon dioxide have been removed in the stripper as the cleaning liquid for the dust scrubber.
[0011]
　In at least one embodiment of the present disclosure, the ammonia scrubber comprises an absorbent circulation line for extracting the absorbent liquid stored therein and returning it to the gas phase in the ammonia scrubber, and the carbonated water becomes the absorbent liquid circulation line. It may be supplied. According to this configuration, by supplying carbonated water to the absorption liquid circulation line, the carbonated water is diluted by the absorption liquid flowing through the absorption liquid circulation line, so that compared with the case where the carbonated water is directly supplied to the inside of the ammonia scrubber. Therefore, the carbon dioxide concentration in the absorption liquid at the time of inflow to the ammonia scrubber becomes low. Then, the amount of carbon dioxide emitted from the absorption liquid having a low carbon dioxide concentration is suppressed as compared with the amount of carbon dioxide emitted from the carbonated water having a high carbon dioxide concentration, so that it is effectively used for removing ammonia in the ammonia scrubber. The amount of carbon dioxide produced can be increased, and the removal rate of ammonia can be improved.
[0012]
　In at least one embodiment of the present disclosure, a cooling device for cooling the carbonated water supplied to the ammonia scrubber may be further provided. In general, the solubility of a gas in a liquid increases as the temperature of the liquid decreases. Therefore, by providing a cooling device for cooling the carbonated water supplied to the ammonia scrubber, the temperature of the carbonated water supplied to the ammonia scrubber can be lowered, so that the amount of ammonia absorbed by the carbonated water increases, and the amount of ammonia is increased. The removal rate can be improved.
[0013]
　In at least one embodiment of the present disclosure, a cooling device for cooling the absorbent liquid flowing through the absorbent liquid circulation line may be further provided. Even if the temperature of the carbonated water or absorption liquid that comes into gas-liquid contact with the off-gas is lowered to improve the removal rate of ammonia from the off-gas, if the temperature of the absorption liquid stored in the ammonia scrubber is high, it will be stored in the ammonia scrubber. Ammonia may be released from the absorbing liquid. However, by providing a cooling device that cools the absorption liquid flowing through the absorption liquid circulation line, the temperature of the absorption liquid stored in the ammonia scrubber can be lowered, so that the amount of ammonia absorbed by the absorption liquid increases and ammonia is removed. The rate can be improved.
[0014]
　In at least one embodiment of the present disclosure, the ammonia scrubber is provided with a plurality of shelves therein, and the carbonated water may be supplied separately from two or more different positions in the height direction of the ammonia scrubber. Good. According to this configuration, the amount of ammonia absorbed by the carbonated water is increased as compared with the case where the carbonated water is supplied to the ammonia scrubber without being divided, so that the removal rate of ammonia can be improved.
[0015]
　In at least one embodiment of the present disclosure, the inside of the ammonia scrubber is provided with a downcomer configured so that the absorbent liquid on the shelf can flow downward, and at least one of the two or more positions. The carbonated water supplied from the down feathers may be supplied into the downcomer. The absorbent liquid that flows down the ammonia scrubber spreads in the radial direction on the shelf, but when it flows down from a certain shelf to the lower shelf, it becomes a downcomer with a relatively narrow flow path. Gather and flow down. By supplying the carbonated water into the downcomer, the carbonated water can be dispersed better in the absorption liquid as compared with the case where the carbonated water is supplied to the absorption liquid spreading in the radial direction on the shelf step portion. it can. As a result, the amount of ammonia absorbed by the absorbing liquid is increased, and the removal rate of ammonia can be improved.
[0016]
　In at least one embodiment of the present disclosure, the water supplied to the ammonia scrubber (hereinafter referred to as make-up water) is higher in the height direction of the ammonia scrubber than the position where the carbonated water and the absorbent liquid are supplied to the ammonia scrubber. It may be supplied from the position. According to this configuration, the carbonated water and the absorbing liquid are supplied below the make-up water supplied to the ammonia scrubber. Then, since the emission of carbon dioxide from the upper surface of the carbonated water is reduced by the make-up water, it is possible to suppress a decrease in the amount of ammonia absorbed in the absorption liquid and suppress a decrease in the ammonia removal rate.
[0017]
　The fertilizer production plant according to at least one embodiment of the present disclosure is a fertilizer production plant for producing fertilizer from a raw material gas containing methane, and is an ammonia production unit for producing ammonia from the raw material gas, and ammonia and carbon dioxide. It is provided with a urea production unit for producing an aqueous urea solution by reacting with, a urea granulation unit for producing granular solid urea from an aqueous urea solution, and an off-gas treatment device for treating off-gas generated from the urea granulation unit. .. According to this configuration, by removing ammonia from the off-gas generated from the urea granulation unit of the fertilizer production plant using an absorbent solution containing carbonated water, it is not necessary to use sulfuric acid, so that the off-gas containing ammonia Can be treated without producing ammonium sulfate.
[0018]
　In at least one embodiment of the present disclosure, the stripper may be configured to supply ammonia and carbon dioxide removed from the absorbent to the urea production unit. According to this configuration, ammonia and carbon dioxide removed from the absorption liquid in the stripper can be used for fertilizer production, so that the fertilizer production cost in the fertilizer production plant can be reduced.
Effect of the invention
[0019]
　According to at least one embodiment of the present disclosure, by removing ammonia from off-gas using an absorbent solution containing carbonated water, sulfuric acid does not need to be used, so that off-gas containing ammonia does not generate ammonium sulfate. Can be processed into.
A brief description of the drawing
[0020]
FIG. 1 is a block diagram showing a configuration of a fertilizer production plant according to the first embodiment of the present disclosure.
FIG. 2 is a configuration diagram of an off-gas treatment apparatus of a fertilizer production plant according to the first embodiment of the present disclosure.
FIG. 3 is a configuration diagram of a modified example of an off-gas treatment apparatus of a fertilizer production plant according to a first embodiment of the present disclosure.
FIG. 4 is a configuration diagram of an off-gas treatment apparatus of a fertilizer production plant according to a second embodiment of the present disclosure.
FIG. 5 is a configuration diagram of an experimental device for confirming the operation and effect of the off-gas treatment device of the fertilizer production plant according to the second embodiment of the present disclosure.
FIG. 6 is a configuration diagram of a modified example of an off-gas treatment apparatus of a fertilizer production plant according to a second embodiment of the present disclosure.
FIG. 7 is a configuration diagram of an off-gas treatment apparatus of a fertilizer production plant according to a third embodiment of the present disclosure.
FIG. 8 is a configuration diagram of an experimental device for confirming the action and effect of the off-gas treatment device of the fertilizer production plant according to the third embodiment of the present disclosure.
Mode for carrying out the invention
[0021]
　Hereinafter, some embodiments of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited to the following embodiments. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the following embodiments are not intended to limit the scope of the present invention only to them, but are merely explanatory examples.
[0022]
(Embodiment 1) As
　shown in FIG. 1, the fertilizer production plant 100 according to the first embodiment of the present disclosure includes an ammonia production unit 10 that produces ammonia by using a raw material gas such as a natural gas containing methane. The urea production unit 20 that produces an aqueous urea solution by reacting ammonia with carbon dioxide, the urea granulation unit 60 that produces a granular solid urea from the aqueous urea solution and urea, and the off gas generated from the urea granulation unit 60. It is provided with an off-gas processing device 80 for processing the urea. The fertilizer production plant 100 includes a reformer 1 that reforms the raw material gas, a modifier 2 that modifies carbon dioxide and water vapor in the gas supplied from the reformer 1, and a gas flowing out from the modifier 2. A carbon dioxide recovery device 3 for recovering carbon dioxide and a methanizer 4 for converting carbon dioxide and carbon monoxide in the gas flowing out from the carbon dioxide recovery device 3 into methane, respectively, may be further provided. In this case, the methanizer 4 and the ammonia production unit 10 are connected.
[0023]
　The urea production unit 20 includes a compressor 21 and a urea production apparatus 22. The compressor 21 and the urea production apparatus 22 are connected via a pipe 121. The carbon dioxide recovery device 3 and the compressor 21 are connected via a pipe 122. The ammonia supply line 123 is provided so that the ammonia produced by the ammonia production unit 10 is supplied to the pipe 121, and the ammonia supply line 123 is provided with a compressor 76 for boosting the ammonia. The carbon dioxide supply line 118 branches from the upstream side of the position where the ammonia supply line 123 joins in the pipe 121, and the carbon dioxide supply line 118 is connected to the carbonated water production apparatus 116 (see FIG. 2) described later.
[0024]
　The off-gas treatment apparatus 80 includes a dust scrubber 80A that removes solid components such as urea dust from the off-gas generated from the urea granulation unit 60, and an ammonia scrubber 80B that removes ammonia from the off-gas from which the solid components have been removed in the dust scrubber 80A. I have. The urea granulation unit 60 and the dust scrubber 80A are connected via an off-gas distribution line 111. The dust scrubber 80A and the ammonia scrubber 80B are connected to each other via a pipe 112. The ammonia scrubber 80B is provided with an exhaust line 113 for discharging the off-gas processed in the ammonia scrubber 80B into the atmosphere.
[0025]
　As shown in FIG. 2, the dust scrubber 80A has a housing 81 having an internal space 81a through which off-gas flows, and neutral water (pH 7) such as wash water (for example, fresh water, reclaimed water, industrial water, etc.) in the internal space 81a. Degree)) is provided with a nozzle 83 for sprinkling water and a washing water supply line 87 for supplying washing water to the nozzle 83. Since the inside of the dust scrubber 80A is usually at a high temperature, liquid water (washing water) evaporates. Further, as will be described later, a part of the washing water staying in the internal space 81a is drained. The nozzle 83 is for sprinkling water in order to replenish the washing water reduced by such evaporation and drainage.
[0026]
　The dust scrubber 80A further includes a wash water circulation line 86, a pump 82, and a nozzle 84. The wash water circulation line 86 is for extracting the wash water (including dissolved solid components; the same applies to the retained wash water below) retained in the internal space 81a to the outside of the housing 81. The pump 82 is for flowing a part of the washing water staying in the internal space 81a to the washing water circulation line 86. The nozzle 84 is for sprinkling the water flowing through the washing water circulation line 86 into the gas phase of the internal space 81a. Further, the nozzle 84 may be configured to inject water toward a tray 85 (for example, composed of a perforated plate) installed in the housing 81. The number of trays 85 may be one, or may be any number of two or more.
[0027]
　In order to drain a part of the washing water from the internal space 81a for the purpose of suppressing the concentration of solid components in the washing water staying in the internal space 81a, the drainage line 88 branches from the washing water circulation line 86 on the downstream side of the pump 82. ing. The drainage line 88 may be connected to a wastewater treatment device (not shown) or the like.
[0028]
　The ammonia scrubber 80B is connected to the dust scrubber 80A via a pipe 112. One end of the pipe 112 is connected to the top of the dust scrubber 80A, and the other end of the pipe 112 is connected between the top and bottom of the ammonia scrubber 80B. One end of the exhaust line 113 is connected to the top of the ammonia scrubber 80B.
[0029]
　The ammonia scrubber 80B includes a housing 91 having an internal space 91a through which off-gas from which solid components have been removed flows in the dust scrubber 80A, a nozzle 93 for sprinkling make-up water in the internal space 91a, and make-up water in the nozzle 93. It is equipped with a make-up water supply pipe 97 for supplying water. Since the inside of the scrubber 80B is usually hot, liquid water evaporates. Further, as will be described later, a part of the absorbing liquid staying in the internal space 91a is drained. The nozzle 93 is for sprinkling make-up water in order to replenish the absorbing liquid reduced by such evaporation and drainage.
[0030]
　The ammonia scrubber 80B includes an absorbent liquid circulation line 96, a pump 92, and a nozzle 94. The absorption liquid circulation line 96 is for extracting a part of the absorption liquid supplied to and staying in the internal space 91a to the outside of the housing 91 by the operation described later. The pump 92 is for flowing the absorbing liquid staying in the internal space 91a to the absorbing liquid circulation line 96. The nozzle 94 is for sprinkling the absorbing liquid flowing through the absorbing liquid circulation line 96 into the gas phase of the internal space 91a. Further, the nozzle 94 may be configured to inject water toward a tray 98 (for example, composed of a perforated plate) installed in the housing 91. The number of trays 98 may be one, or may be any number of two or more.
[0031]
　The off-gas treatment device 80 further includes a carbonated water production device 116 that produces carbonated water contained in the absorption liquid supplied to the ammonia scrubber 80B. In the first embodiment, the carbonated water production device 116 will be described as a microbubble generator, but any device may be used as long as it can produce carbonated water from carbon dioxide and water. A water supply line 115 for supplying water and a carbon dioxide supply line 118 for supplying carbon dioxide are connected to the carbonated water production apparatus 116.
[0032]
　A decompressor 130 may be provided on the downstream side of the carbonated water production apparatus 116, although it is not an essential configuration. The decompressor 130 has a container capable of receiving carbonated water produced by the carbonated water production apparatus 116, and the inside of the container is substantially atmospheric pressure. The other end of the purge line 131, one end of which is connected to the pipe 122 (see FIG. 1), is connected to the top of the container of the decompressor 130. One end of the carbonated water supply line 132 is connected to the bottom of the container of the decompressor 130, and the other end of the carbonated water supply line 132 is connected to the absorption liquid circulation line 96 on the downstream side of the pump 92. The carbonated water supply line 132 is provided with a carbonated water pump 133.
[0033]
　The off-gas processing device 80 further includes a stripper 140. As will be described later, the absorption liquid staying in the internal space 91a of the ammonia scrubber 80B contains carbonated water and the ammonia removed from the off-gas is absorbed, and the stripper 140 uses this absorption liquid. This is for removing ammonia and carbon dioxide dissolved in the absorption liquid.
[0034]
　The absorption liquid extraction line 141 branches from the absorption liquid circulation line 96 on the downstream side of the pump 92, and the absorption liquid extraction line 141 is connected to the stripper 140. One end of the absorbent liquid supply line 142 is connected to the bottom of the stripper 140, and the other end of the absorbent liquid supply line 142 is connected to, for example, a washing water supply line 87. As will be described later, the absorption liquid from which ammonia and carbon dioxide have been removed is retained inside the stripper 140, but the absorption liquid retained inside the stripper 140 is supplied to the absorption liquid supply line 142. An absorbent pump 143 is provided to allow the line 142 to circulate. One end of a removal gas flow line 144 through which carbon dioxide and ammonia removed from the absorption liquid flow is connected to the top of the stripper 140. The other end of the removal gas flow line 144 may be connected to, for example, the vacuum condenser of the urea production apparatus 22.
[0035]
　Next, the operation of the fertilizer production plant 100 according to the first embodiment of the present disclosure will be described. As shown in FIG. 1, the raw material gas is reformed by air and steam in the reformer 1 to become a gas containing at least hydrogen and carbon dioxide. Since the reformer 1 also takes in air, the gas discharged from the reformer 1 and supplied to the reformer 2 in the subsequent stage also includes components derived from air. Specifically, the gas discharged from the reformer 1 also includes nitrogen and the like. In addition, this gas also contains carbon monoxide, and carbon monoxide is converted into carbon dioxide and hydrogen by a chemical reaction with water in the modifier 2 in the subsequent stage.
[0036]
　By recovering carbon dioxide in the gas, the carbon dioxide recovery device 3 downstream of the denaturant 2 can suppress the introduction of carbon dioxide into the ammonia production unit 10 and suppress the influence on the ammonia production catalyst. .. The carbon dioxide recovery in the carbon dioxide recovery device 3 can be performed, for example, by bringing an alkaline aqueous solution into contact with gas. The recovered carbon dioxide is separated from the alkaline aqueous solution by heating the alkaline aqueous solution or the like, and then supplied to the carbonated water production apparatus 116 of the urea production unit 20 and the off-gas treatment apparatus 80, as will be described later.
[0037]
　In the methanizer 4 downstream of the carbon dioxide recovery device 3, the carbon dioxide that could not be recovered by the carbon dioxide recovery device 3 and the carbon dioxide that was not converted into carbon dioxide by the modifier 2 and not recovered by the carbon dioxide recovery device 3 Carbon dioxide and carbon dioxide are each converted to methane. By removing carbon monoxide, carbon dioxide and other carbon oxides in the methanizer 4, the introduction of carbon oxides into the ammonia production unit 10 is suppressed. As a result, the influence of carbon oxide on the ammonia production catalyst can be suppressed.
[0038]
　The gas flowing out of the methane conversion apparatus 4 and flowing into the ammonia production unit 10 contains hydrogen and nitrogen, and contains methane as an impurity. In the ammonia production unit 10, by using an arbitrary ammonia production catalyst, a chemical reaction represented by the following chemical formula (1) occurs to produce ammonia.
　　N 2 + 3H 2 → 2NH 3　... Equation (1)
[0039]
　The generated ammonia sequentially flows through the ammonia supply line 123 and the pipe 121 by the compressor 76 and flows into the urea production apparatus 22 of the urea production unit 20. Further, the carbon dioxide recovered by the carbon dioxide recovery device 3 flows out from the carbon dioxide recovery device 3 and flows through the pipe 122, is boosted by the compressor 21, and flows into the urea production apparatus 22 through the pipe 121. ..
In the urea production apparatus 22, urea (urea aqueous solution) is produced from carbon dioxide and ammonia by a chemical reaction represented by the following chemical formula (2).
　　2NH 3 + CO 2 → (NH 2 ) 2 CO + H 2 O ・ ・ ・ Equation (2)
[0040]
　The urea aqueous solution produced by the urea production unit 20 flows into the urea granulation unit 60. In the urea granulation unit 60, the urea supplied from the urea production unit 20 is granulated. Granular urea obtained by granulating urea is shipped and used as fertilizer.
[0041]
　In the urea granulation unit 60, off-gas containing urea dust (hereinafter referred to as a solid component) such as a powder of solid urea and ammonia is generated during the granulation of urea. The off-gas flows through the off-gas distribution line 111 and flows into the off-gas processing apparatus 80. In the off-gas processing apparatus 80, the solid component is removed from the off-gas by gas-liquid contact between the washing water and the off-gas in the dust scrubber 80A. The off-gas from which the solid component has been removed flows into the ammonia scrubber 80B through the pipe 112. In the ammonia scrubber 80B, ammonia is removed from the off-gas by gas-liquid contact between the absorbing liquid containing carbonated water and the off-gas. The off-gas from which ammonia has been removed is released into the atmosphere through the exhaust line 113.
[0042]
　Next, the operation of processing the off-gas in the off-gas processing device 80 will be described in detail with reference to FIG. The off-gas that has flowed into the dust scrubber 80A via the off-gas distribution line 111 flows upward in the internal space 81a of the housing 81. At this time, the off-gas comes into gas-liquid contact with the washing water sprinkled by the nozzles 83 and 84, so that the solid component is removed from the off-gas, and the solid component removed from the off-gas flows down the internal space 81a together with the washing water. Further, the off-gas comes into contact with the tray 85 as it flows upward in the internal space 81a. As a result, the solid component contained in the off-gas is deposited on the tray 85. Here, if the nozzle 84 is configured so that the washing water is ejected toward the tray 85, the solid component deposited on the tray 85 is washed away by the washing water jetted from the nozzle 84. As a result, the precipitation of excess solid components is suppressed in the tray 85, and the increase in pressure loss of off-gas is suppressed.
[0043]
　On the other hand, the off-gas from which the solid component has been removed flows out from the top of the dust scrubber 80A and flows through the pipe 112. The off-gas flowing through the pipe 112 flows into the ammonia scrubber 80B. In the ammonia scrubber 80B, the off-gas flowing upward in the internal space 91a of the housing 91 and the absorbing liquid (including carbonated water) injected from the nozzle 94 through the washing water circulation line 96 by the pump 92 are both concerned. By liquid contact, the ammonia contained in the off-gas is absorbed by the absorbing liquid, and the ammonia is removed from the off-gas. In the absorption liquid retained in the internal space 91a, ammonia is present in the liquid in the form of at least one of ammonia molecules and ammonium ions.
[0044]
　The carbonated water contained in the absorption liquid is produced by the carbonated water production apparatus 116. Water is supplied to the carbonated water production apparatus 116 via the water supply line 115, and a part of carbon dioxide flowing through the pipe 121 (see FIG. 1) is supplied via the carbon dioxide supply line 118 to supply water. Carbon dioxide is dissolved in the water to produce carbonated water. Although not limited, when a microbubble generator is used as the carbonated water production apparatus 116, bubbles having a size of, for example, about 100 nanometers to several hundreds of micrometers are generated in water. Specifically, for example, as the size of the bubbles immediately after the generation by the micro-bubble generator, for example, bubbles having a size of about 100 nm or more and 500 μm or less are generated. As a result, the presence time of carbonic acid in water can be lengthened. The specific configuration of the micro-bubble generator is not particularly limited, and any method such as an ejector method, a cavitation method, a swirling flow method, and a pressure melting method can be adopted.
[0045]
　The carbonated water produced by the carbonated water production apparatus 116 may be supplied to the ammonia scrubber 80B as it is, but it is preferable that the carbonated water is flowed into the decompressor 130 to reduce the pressure to atmospheric pressure before that. When the carbonated water produced by the carbonated water production apparatus 116 is supplied to the ammonia scrubber 80B as it is, a part of carbon dioxide is released from the carbonated water in the ammonia scrubber 80B. The carbon dioxide emitted in the ammonia scrubber 80B flows out of the ammonia scrubber 80B together with the off-gas from which ammonia has been removed and is released into the atmosphere, so that it is usually difficult to recover. On the other hand, by dissipating a part of carbon dioxide from the carbonated water in the decompressor 130 before flowing into the ammonia scrubber 80B, the emission of carbon dioxide in the ammonia scrubber 80B can be suppressed and the carbon dioxide is dissipated in the decompressor 130. Since the carbon dioxide can be recovered to the urea production unit 20 via the purge line 131 and the pipe 122, the amount of carbon dioxide used can be reduced.
[0046]
　The carbonated water decompressed to atmospheric pressure in the decompressor 130 is extracted from the decompressor 130 by the carbonated water pump 133 and flows through the carbonated water supply line 132. The carbonated water flowing through the carbonated water supply line 132 flows into the absorption liquid circulation line 96, is mixed with the absorption liquid flowing through the absorption liquid circulation line 96, and is injected from the nozzle 94 into the internal space 91a of the ammonia scrubber 80B. ..
[0047]
　In the first embodiment, the carbonated water is configured to flow into the absorption liquid circulation line 96, but the carbonated water can be injected as it is into the internal space 91a. However, by supplying the carbonated water to the absorption liquid circulation line 96, the carbonated water is diluted by the absorption liquid flowing through the absorption liquid circulation line 96, so that ammonia is compared with the case where the carbonated water is directly supplied to the internal space 91a. The concentration of carbon dioxide in the absorption liquid at the time of inflow into the scrubber 80B becomes low. Then, the amount of carbon dioxide emitted from the absorption liquid having a low carbon dioxide concentration is suppressed as compared with the amount of carbon dioxide emitted from the carbonated water having a high carbon dioxide concentration, so that the ammonia scrubber 80B is effective in removing ammonia. The amount of carbon dioxide used can be increased and the removal rate of ammonia can be improved.
[0048]
　As the removal of ammonia from the off-gas in the ammonia scrubber 80B continues, the concentration of ammonia in the absorption liquid staying in the internal space 91a increases, so the ammonia removal rate decreases, and eventually the removal of ammonia. Can no longer be done. Therefore, a part of the absorption liquid flowing through the absorption liquid circulation line 96 is supplied to the stripper 140 via the absorption liquid extraction line 141. In the stripper 140, ammonia and carbon dioxide dissolved in the absorption liquid are removed from the absorption liquid by heating with steam or the like. Ammonia and carbon dioxide removed from the absorption liquid flow out from the top of the stripper 140, flow through the removal gas distribution line 144, and are used as a raw material for urea by supplying, for example, to the vacuum condenser of the urea production apparatus 22. can do.
[0049]
　On the other hand, the liquid obtained by removing ammonia and carbon dioxide from the absorption liquid in the stripper 140 is extracted from the bottom of the stripper 140, circulates in the absorption liquid supply line 142 by the absorption liquid pump 143, and flows into the washing water supply line 87. Then, it can be reused as a part of the washing water of the dust scrubber 80A. As a result, the amount of washing water used in the dust scrubber 80A can be reduced.
[0050]
　The liquid obtained by removing ammonia and carbon dioxide from the absorption liquid may be used as a part of the washing water of the dust scrubber 80A, or may be supplied to the ammonia scrubber 80B instead, and may be supplied to the absorption liquid circulation line 96. Alternatively, it may be supplied to the make-up water supply pipe 97, or may be supplied directly to the internal space 91a. Since the solution obtained by removing ammonia and carbon dioxide from this absorption solution has a lower ammonia concentration than the absorption solution retained in the internal space 91a, the ammonia concentration of the absorption solution retained in the internal space 91a is increased by supplying the ammonia scrubber 80B. descend. The lower the ammonia concentration in the absorption liquid, the more ammonia absorbed by the absorption liquid in the ammonia scrubber 80B, so that the efficiency of removing ammonia in the ammonia scrubber 80B can be improved.
[0051]
　For example, it is assumed that the absorption liquid of 18 ton / hr is withdrawn from the absorption liquid circulation line 96 to the absorption liquid extraction line 141, and the ammonia concentration in the absorption liquid is 1200 ppm. Assuming that ammonia and carbon dioxide are removed from the absorption liquid in total by 3 tons / hr in the stripper 140, the absorption liquid supplied from the stripper 140 to at least one of the dust scrubber 80A and the ammonia scrubber 80B is 15 tons / hr, and this absorption liquid The ammonia concentration in it is 30 ppm.
[0052]
　By removing ammonia from the off-gas using an absorbing solution containing carbonated water in this way, it is not necessary to use sulfuric acid, so that the off-gas containing ammonia can be treated without producing ammonium sulfate.
[0053]
　In the first embodiment, the off-gas treatment apparatus 80 includes a carbonated water production apparatus 116 for producing carbonated water by dissolving carbon dioxide in water, but the present invention is not limited to this embodiment. You may use carbonated water prepared in advance or carbonated water generated in another plant.
[0054]
　In the first embodiment, the off-gas treatment device 80 is a two-tower type in which the dust scrubber 80A and the ammonia scrubber 80B are separate, but is a one-tower type in which the ammonia scrubber is arranged at the upper part and the dust scrubber is arranged at the lower part. May be good. FIG. 3 shows the configuration of a one-tower integrated scrubber 80C in which the ammonia scrubber 80B is arranged at the upper part and the dust scrubber 80A is arranged at the lower part.
[0055]
　In the dust scrubber 80A, an off-gas discharge port 181 is formed on the upper surface of the internal space 81a. Further, a member 191 that narrows upward is provided above the off-gas discharge port 181. The lower end of the member 191 is open, and an off-gas discharge port 181 is formed at the lower end of the member 191. The upper end of the member 191 is also open, and the tubular member 193 is connected to the upper end of the member 191. An umbrella member 192 is arranged above the tubular member 193 so that the invasion of the absorbing liquid into the tubular member 193 is suppressed.
[0056]
　The umbrella member 192 is fixed to the tubular member 193 by a support member 194 arranged with gaps at equal intervals in the circumferential direction of the tubular member 193. An off-gas supply port 195 for supplying off-gas to the internal space 91a of the ammonia scrubber 80B is formed between the adjacent support members 194.
[0057]
　The off-gas supplied through the off-gas supply port (not shown) formed below the dust scrubber 80A flows upward through the internal space 81a of the dust scrubber 80A. At this time, the solid component in the off-gas is removed by the gas-liquid contact between the off-gas and the washing water.
[0058]
　The off-gas flowing upward in the internal space 81a flows into the inside of the member 191 through the off-gas discharge port 181. The off-gas flowing into the inside of the member 191 flows through the inside of the tubular member 193 and the off-gas supply port 195 as shown by a thick arrow. As a result, off-gas is supplied to the internal space 91a of the ammonia scrubber 80B. In the ammonia scrubber 80B, the ammonia in the off-gas is absorbed by the absorbing liquid. The off-gas after removing the ammonia flows out from the top of the ammonia scrubber 80B and is discharged through the exhaust line 113. The operation of producing carbonated water, the operation of removing ammonia and carbon dioxide from the absorption liquid extracted from the ammonia scrubber 80B, and the like are the same as those in the first embodiment.
[0059]
　By using the integrated scrubber 80C for the off-gas treatment device 80, the ammonia scrubber 80B can be integrally configured with the dust scrubber 80A above the dust scrubber 80A, so that the installation area of ​​the off-gas treatment device 80 can be reduced. ..
[0060]
(Embodiment 2)
　Next, the fertilizer production plant according to the second embodiment will be described. The fertilizer production plant according to the second embodiment is obtained by adding a cooling device for cooling the absorption liquid to the first embodiment. In the second embodiment, the same components as those of the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. Unless otherwise specified, the first embodiment includes not only the embodiments shown in FIGS. 1 and 2, but also the embodiments shown in FIG. 3 and some modifications described in the first embodiment.
[0061]
　As shown in FIG. 4, in the off-gas treatment apparatus 80 according to the second embodiment of the present disclosure, the absorption liquid circulation line 96 cools the absorption liquid flowing through the absorption liquid circulation line 96 on the downstream side of the pump 92. A cooling device 150 is provided. Other configurations are the same as those in the first embodiment. As the cooling device 150, for example, a heat exchanger that exchanges heat with a fluid having a temperature lower than that of the absorbing liquid flowing through the absorbing liquid circulation line 96 can be used, although it is not limited. Any fluid can be used as the fluid, but liquid ammonia produced by the ammonia production unit 10 of the fertilizer production plant 100 can also be used.
[0062]
　The operation of the off-gas treatment device 80 according to the second embodiment of the present disclosure is that the absorption liquid flowing through the absorption liquid circulation line 96 is discharged from the pump 92, cooled by the cooling device 150, and injected from the nozzle 94 into the internal space 91a. It is the same as the operation of the first embodiment except that.
[0063]
　Next, the effect of lowering the temperature of the absorbing liquid injected into the internal space 91a will be described. FIG. 5 shows the configuration of a small experimental ammonia scrubber 200. The ammonia scrubber 200 includes a housing 201 having an internal space 201a, a supply line 202 for supplying gas containing ammonia to the internal space 201a, and an exhaust line 203 for gas flowing out from the top of the housing 201. It is provided with an absorption liquid circulation line 204 for extracting the absorption liquid staying in the internal space 201a and supplying the absorption liquid to the gas phase of the internal space 201a, and a pump 205 provided in the absorption liquid circulation line 204. .. The absorption liquid circulation line 204 is connected to a sampling line 206 for collecting a part of the absorption liquid flowing through the absorption liquid circulation line 204 and a carbonated water supply line 207 for supplying carbonated water to the absorption liquid circulation line 204. Has been done. The outer diameter of the housing 201 is 25 mm, and the internal space 201a is filled with a 1/4 inch metal Raschig ring as a filler at a filling height of 470 mm.
[0064]
　In the ammonia scrubber 200, when the temperature of the absorbing liquid staying in the internal space 201a is set to 36.9 ° C. and 20 ° C., the absorbing liquid in the internal space 201a flows through the absorbing liquid circulation line 204 and is in the internal space. Air containing ammonia (inlet gas) was supplied to the internal space 201a via the supply line 202 while being supplied into the gas phase of 201a. In the internal space 201a, the air containing ammonia was gas-liquid contacted with the absorbing liquid and then exhausted from the internal space 201a via the exhaust line 203. The air flowing out from the exhaust line 203 (exhaust gas) was sampled and the ammonia concentration was measured by gas chromatography. In addition, the ammonia concentration and carbon dioxide concentration in the absorption liquid collected through the collection line 206 were measured by liquid chromatography. The results are summarized in Table 1.
[0065]
[table 1]

[0066]
　In general, the solubility of a gas in a liquid increases as the temperature of the liquid decreases, but as shown in Table 1, the lower the temperature of the absorbing solution, the greater the amount of carbon dioxide and ammonia dissolved. As a result, the lower the temperature of the absorbing liquid, the higher the ammonia removal rate. Therefore, as shown in FIG. 4, the temperature of the carbonated water supplied to the ammonia scrubber 80B can be lowered by providing the cooling device 150 for cooling the carbonated water supplied to the ammonia scrubber 80B. The amount of ammonia absorbed can be increased, and the removal rate of ammonia can be improved.
[0067]
　In the second embodiment, the cooling device 150 is provided on the absorbing liquid circulation line 96, but the cooling device 150 is not limited to this embodiment. The cooling device 150 may be arranged anywhere as long as the absorption liquid can be cooled. For example, as shown in FIG. 6, the cooling device 150 may be provided on the downstream side of the carbonated water pump 133 in the carbonated water supply line 132. However, in this configuration, the temperature of the absorbing liquid in gas-liquid contact with the off-gas in the internal space 91a is lowered and the removal rate of ammonia from the off-gas is improved, but the temperature of the entire absorbing liquid stored in the internal space 91a cannot be cooled. , Ammonia may be released from the absorption liquid stored in the internal space 91a. However, since the temperature of the absorbing liquid stored in the internal space 91a can be lowered by providing the cooling device 150 in the absorbing liquid circulation line 96, the configuration of FIG. 4 is more suitable for the absorbing liquid than the configuration of FIG. The amount of ammonia absorbed can be increased, and the removal rate of ammonia can be improved.
[0068]
　As described above, the second embodiment has been described as a modification of the first embodiment. Therefore, in the second embodiment, as shown in FIGS. 4 and 6, the absorption liquid circulation line 96 is provided via the absorption liquid extraction line 141. Although a part of the absorbing liquid to be distributed is supplied to the stripper 140, this absorbing liquid may be supplied to the urea production apparatus 22.
[0069]
(Embodiment 3)
　Next, the fertilizer production plant according to the third embodiment will be described. The fertilizer production plant according to the third embodiment supplies the carbonated water to the first or second embodiment by dividing the carbonated water from two or more different positions in the height direction of the ammonia scrubber 80B. In the following, the third embodiment will be described in which the carbonated water is divided and supplied with respect to the configuration of the first embodiment, but the carbonated water is divided and supplied with respect to the configuration of the second embodiment. The third embodiment may be configured in this way. In the third embodiment, the same components as those of the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. Unless otherwise specified, the first embodiment includes not only the embodiments shown in FIGS. 1 and 2, but also the embodiments shown in FIG. 3 and some modifications described in the first embodiment.
[0070]
　As shown in FIG. 7, three trays 98 (shelf steps) made of a perforated plate are provided in the housing 91 of the ammonia scrubber 80B at different positions in the height direction of the ammonia scrubber 80B. There is. Inside the housing 91, a downcomer 99 is provided so that the absorbing liquid on each tray 98 can flow downward. A carbonated water supply branch line 134 branches from the carbonated water supply line 132, and the carbonated water supply branch line 134 is one of the downcomers 99 (in FIG. 7, the top of the three downcomers 99). It is connected to the housing 91 at the position of. Other configurations are the same as those in the first embodiment.
[0071]
　In the operation of the off-gas treatment device 80 according to the third embodiment of the present disclosure, not only the carbonated water flowing through the carbonated water supply line 132 is supplied to the absorption liquid circulation line 96, but also a part of the carbonated water supply branch line 134 is supplied. It is the same as the first embodiment except that it is directly supplied into the internal space 91a via the above. Since the carbonated water supply branch line 134 is connected to the housing 91 at the position of the downcomer 99, the carbonated water flowing through the carbonated water supply branch line 134 is mixed with the absorbing liquid flowing down the downcomer 99.
[0072]
　In the internal space 91a, the absorbing liquid is ejected from the nozzle 94 toward the tray 98. Although a plurality of holes are formed in the tray 98, since the off-gas rising in the internal space 91a mainly passes through these holes, most of the absorbing liquid cannot flow downward through these holes. Absent. Most of the absorbent liquid on the tray 98 is collected toward the downcomer 99 having a cross-sectional area significantly smaller than the cross-sectional area of ​​the internal space 91a, flows down the downcomer 99, and flows down the tray 98 one step below. Fall up. In the internal space 91a, the absorbing liquid repeats this operation, flows down between the trays, and stays at the bottom of the internal space 91a.
[0073]
　The absorbent liquid flowing down the internal space 91a spreads in the radial direction on the tray 98, but when flowing down from a certain tray 98 toward the tray 98 below it, it gathers in the downcomer 99 having a relatively narrow flow path. And flow down. By supplying the carbonated water into the downcomer 99, the carbonated water can be dispersed better in the absorption liquid as compared with the case where the carbonated water is supplied to the absorption liquid spreading in the radial direction on the tray 98. it can. As a result, the amount of ammonia absorbed by the absorbing liquid is increased, and the removal rate of ammonia can be improved.
[0074]
　Next, the action and effect of supplying carbonated water in a divided manner will be described. FIG. 8 shows the configuration of a small experimental ammonia scrubber 300. The ammonia scrubber 300 includes a housing 301 having an internal space 301a, a supply line 302 for supplying a gas containing ammonia (inlet gas) to the internal space 301a, and an exhaust for gas flowing out from the top of the housing 301. The line 303, the absorption liquid circulation line 304 for extracting the absorption liquid (carbonated water) staying in the internal space 301a, and supplying the absorption liquid into the gas phase of the internal space 301a, and the absorption liquid circulation line 304 are provided. It is equipped with a pump 305. The absorption liquid circulation line 304 is connected to a sampling line 306 for collecting a part of the absorption liquid flowing through the absorption liquid circulation line 304 and a carbonated water supply line 307 for supplying carbonated water to the absorption liquid circulation line 304. Has been done.
[0075]
　Inside the housing 301, three trays 308 made of perforated plates are provided at different positions in the height direction of the housing 301. A downcomer 309 is formed in the housing 301 so that the absorbing liquid on each tray 308 can flow downward. A carbonated water supply branch line 310 branches from the carbonated water supply line 307, and the carbonated water supply branch line 310 is one of the downcomers 309 (in FIG. 8, the top of the three downcomers 309). It is connected to the housing 301 at the position of. The carbonated water supply branch line 310 is provided with an on-off valve 311.
[0076]
　In the ammonia scrubber 300, when the on-off valve 311 is closed and when it is opened, in other words, when the carbonated water is supplied without being divided and when the carbonated water is divided into two and supplied, respectively. The absorbed liquid in the internal space 301a was supplied to the gas phase of the internal space 301a through the absorbing liquid circulation line 304, and the inlet gas was supplied to the internal space 301a via the supply line 302. In the internal space 301a, the inlet gas was gas-liquid contacted with the absorbing liquid and then exhausted from the internal space 301a via the exhaust line 303. The gas (outlet gas) flowing out from the exhaust line 303 was collected and the ammonia concentration was measured by gas chromatography. In addition, the ammonia concentration and carbon dioxide concentration in the absorption liquid collected through the collection line 306 were measured by liquid chromatography. The results are summarized in Table 2.
[0077]
[Table 2]

[0078]
　According to Table 2, the ammonia removal rate is 1.38 times higher when the carbonated water is divided into two and supplied as compared with the case where the carbonated water is supplied without being divided. From this result, when the carbonated water is divided into two parts and supplied, the amount of ammonia absorbed by the carbonated water increases as compared with the case where the carbonated water is supplied to the ammonia scrubber without being divided. Can be improved.
[0079]
　In the third embodiment, the carbonated water is divided into two parts and supplied, but may be divided into three or more parts and supplied. Further, in this case, the portion that directly supplies the carbonated water into the housing 91a does not necessarily have to be the downcomer 99. Further, the shelf step portion does not have to be a perforated plate, and a plurality of trays on which a filling material is placed may be provided at intervals from each other.
[0080]
　In the third embodiment, three trays 98 are provided in the housing 91, but the number is not limited to three. One or two trays may be provided, or four or more trays may be provided.
[0081]
　As described above, the third embodiment has been described as a modification of the first embodiment. Therefore, in the third embodiment, as shown in FIG. 7, the absorption flowing through the absorption liquid circulation line 96 via the absorption liquid extraction line 141. Although a part of the liquid is supplied to the stripper 140, this absorbing liquid may be supplied to the urea production apparatus 22.
[0082]
　In each of the first to third embodiments, as shown in FIGS. 2 to 4, 6 and 7, the position where the make-up water is supplied to the ammonia scrubber 80B is the position where the carbonated water is supplied (the absorption liquid circulation line 96). It is preferable to supply the ammonia scrubber 80B from a higher position in the height direction than (including the case where it is mixed and supplied in the flowing absorption liquid). According to this configuration, carbonated water is supplied to the ammonia scrubber 80B below the make-up water supplied to the ammonia scrubber 80B. Then, since the emission of carbon dioxide from the upper surface of the carbonated water is reduced by the make-up water, it is possible to suppress a decrease in the amount of ammonia absorbed in the absorption liquid and suppress a decrease in the ammonia removal rate.
[0083]
　In each of the first to third embodiments, the off-gas treatment apparatus 80 is for treating the off-gas generated in the fertilizer production plant 100, but is not limited to this embodiment. The off-gas treatment apparatus 80 of the present disclosure can be used in any plant or the like as long as the purpose is to remove ammonia from the gas containing ammonia.
Description of the sign
[0084]
10 Ammonia production unit
20 Urea production unit
60 Urea granulation unit
80 Off-gas treatment equipment
80A Dust scrubber
80B Ammonia scrubber
96 Absorbent liquid circulation line
98 Tray (shelf)
99 Downcomer
100 Fertilizer production plant
116 Carbonated water production equipment
130 Decompressor
140 stripper
150 cooling device
The scope of the claims
[Claim 1]
　An off-gas
　scrubber that treats off-gas containing ammonia, from an ammonia scrubber that brings the absorption liquid containing carbonated water into gas-liquid contact with the off-gas
　, and the absorption liquid extracted from the ammonia scrubber into the absorption liquid. An
off-gas treatment device including a stripper for removing dissolved ammonia and carbon dioxide .
[Claim 2]
　A carbonated water producing apparatus for producing the carbonated water from carbon dioxide and water
　, and a decompressor for decompressing the carbonated water produced in the carbonated water producing apparatus to atmospheric pressure
are further provided, and the carbonated water
　flowing out from the decompressor is further provided. The off-gas treatment apparatus according to claim 1, wherein water is supplied to the ammonia scrubber.
[Claim 3]
　The off-gas treatment apparatus according to claim 1 or 2, wherein at least a part of the absorbing liquid from which ammonia and carbon dioxide have been removed in the stripper is supplied to the ammonia scrubber.
[Claim 4]
　A dust scrubber that removes solid components from the off-gas by gas-liquid contact with a cleaning liquid before flowing into the ammonia scrubber is further provided,
　and at least a part of the absorbing liquid from which ammonia and carbon dioxide are removed by the stripper is the dust. The off-gas treatment apparatus according to any one of claims 1 to 3, which is supplied as at least a part of the cleaning liquid of the scrubber.
[Claim 5]
　The ammonia scrubber includes an absorption liquid circulation line for extracting the absorption liquid stored inside and returning it to the gas phase in the ammonia scrubber, and the
　carbonated water is supplied to the absorption liquid circulation line. The off-gas treatment apparatus according to any one of Items 1 to 4.
[Claim 6]
　The off-gas treatment device according to any one of claims 1 to 5, further comprising a cooling device for cooling the carbonated water supplied to the ammonia scrubber.
[Claim 7]
　The off-gas treatment device according to claim 5, further comprising a cooling device for cooling the absorption liquid flowing through the absorption liquid circulation line.
[Claim 8]
　The ammonia scrubber includes a plurality of shelves inside, and the
　carbonated water is divided and supplied from two or more different positions in the height direction of the ammonia scrubber, according to any one of claims 1 to 7. The off-gas treatment apparatus according to item 1.
[Claim 9]
　Inside the ammonia scrubber, a downcomer is provided so that the absorbing liquid on the shelf can flow downward, and
　carbonated water supplied from at least one of the two or more positions. The off-gas treatment apparatus according to claim 8, wherein the water is supplied into the downcomer.
[Claim 10]
　The make-up water supplied to the ammonia scrubber is supplied from a position higher in the height direction of the ammonia scrubber than the position where the carbonated water and the absorption liquid are supplied to the ammonia scrubber, claims 1 to 9. The off-gas treatment apparatus according to any one of the above.
[Claim 11]
　A fertilizer production plant for producing fertilizer from a raw material gas containing methane, which
　is an ammonia production unit that produces ammonia from the raw material gas
　and a urea production unit that produces an aqueous urea solution by reacting the ammonia with carbon dioxide. The 　off-gas treatment according to any one of claims 1 to 10
　,
wherein the urea granulation unit for producing granular solid urea from the urea aqueous solution and the off-gas generated from the urea granulation unit are treated. A
fertilizer production plant equipped with equipment .
[Claim 12]
　The fertilizer production plant according to claim 11, wherein the ammonia and the carbon dioxide removed from the absorption liquid in the stripper are supplied to the urea production unit.