CN115990388A - Gas recovery device and recovery method - Google Patents
Gas recovery device and recovery method Download PDFInfo
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Abstract
The present invention relates to a gas recovery apparatus and a recovery method. The gas recovery device comprises an absorption tower, a solvent recovery tower and a desorption tower; the top gas phase outlet of the absorption tower is connected with the bottom material inlet of the solvent recovery tower through a pipeline, the kettle liquid outlet of the absorption tower is connected with the material inlet of the desorption tower through a pipeline, and the kettle liquid outlet of the desorption tower is connected with the top material inlet of the absorption tower through a pipeline; a cooling unit is arranged on a connecting pipeline between a kettle liquid outlet of the desorption tower 3 and a top material inlet of the absorption tower; the top of the desorption tower is provided with a tower top condenser, and the tower bottom of the desorption tower is provided with a tower bottom reboiler. By the tail gas recovery device and the recovery method, chloromethane can be effectively recovered, the VOC value in the discharged tail gas is reduced, and the VOC emission standard is reached.
Description
Technical Field
The invention belongs to the technical field of chemical separation, relates to a gas recovery device and a recovery method, and particularly relates to a chloromethane tail gas recovery device and a recovery method in a glyphosate production process.
Background
Glyphosate is a systemic conduction type, efficient, low-toxicity, broad-spectrum and biocidal herbicide, occupies 30% of the herbicide market share, and is the most commonly used herbicide in the market. At present, the domestic preparation of glyphosate mainly adopts a glycine route and an iminodiacetic acid route, and chloromethane is inevitably produced in the process of producing glycine by the two routes.
Conventional chloromethane recovery is typically performed by cryogenic means to liquefy it. However, with the continuous improvement of environmental protection requirements, the concentration of VOC in the tail gas is still difficult to meet the environmental protection requirements even though the temperature after deep cooling is already low to-50 ℃, and biochemical or combustion treatment is still required. Moreover, because chloromethane is a difficult biochemical substance, the cost for performing biochemical treatment on chloromethane is very high; when the waste gas is burnt, the generated HCl can cause serious corrosion to corresponding equipment, and the safety production of the device is affected.
Disclosure of Invention
In order to improve the above problems, the present invention provides a gas recovery apparatus comprising an absorption column 1, a solvent recovery column 2, and a desorption column 3;
the top gas phase outlet of the absorption tower 1 is connected with the bottom material inlet of the solvent recovery tower 2 through a pipeline, the kettle liquid outlet of the absorption tower 1 is connected with the material inlet of the desorption tower 3 through a pipeline, and the kettle liquid outlet of the desorption tower 3 is connected with the top material inlet of the absorption tower 1 through a pipeline;
a cooling unit is arranged on a connecting pipeline between a kettle liquid outlet of the desorption tower 3 and a top material inlet of the absorption tower 1;
a feeding heat exchanger 9 of the desorption tower is arranged between the kettle liquid outlet of the desorption tower 3 and the top material inlet of the absorption tower 1, and the feeding heat exchanger 9 is positioned between the kettle liquid outlet of the desorption tower 3 and the cooling unit;
the top of the desorption tower 3 is provided with a tower top condenser, and the tower bottom of the desorption tower 3 is provided with a tower bottom reboiler.
According to an embodiment of the invention, the gas recovery device is selected from the group of tail gas recovery devices, preferably tail gas recovery devices produced in the synthesis of glyphosate.
According to an embodiment of the invention, the material inlet of the desorption column 3 is arranged at the top or in the middle of the desorption column 3.
According to an embodiment of the present invention, the absorption column 1, the solvent recovery column 2 and the desorption column 3 are selected from an atmospheric column or a pressurized column independently of each other. Illustratively, at least one of the absorber 1, the solvent recovery column 2, or the desorber 3 is a pressurized column.
According to an embodiment of the present invention, the absorption column 1, the solvent recovery column 2 and the desorption column 3 are selected from a tray column or a packed column independently of each other.
According to an embodiment of the invention, the column bottoms reboiler is selected from any one of a thermosiphon reboiler, a forced circulation reboiler, a kettle reboiler, or a falling film reboiler.
According to an embodiment of the invention, the overhead condenser is selected from any one of a shell and tube heat exchanger, a plate heat exchanger or an air cooler.
According to an embodiment of the invention, the cooling unit may be selected from an absorbent cooling unit comprising at least one of an absorbent cooler 6, an absorbent cryocooler 7 or an absorbent chiller 8.
According to a preferred embodiment of the invention, the absorbent cooling unit comprises an absorbent cooler 6, an absorbent cryocooler 7 and an absorbent chiller 8.
According to an embodiment of the present invention, the cooling medium of the absorbent cooler 6 is selected from water (e.g., circulating water or normal temperature water) or air (e.g., normal temperature air), and the temperature of the cooling medium thereof is, for example, 32 to 38 ℃.
According to an embodiment of the invention, the cooling medium of the absorbent cryocooler 7 is selected from a cryogenic medium, such as water, for example, the cryogenic medium having a temperature of 7-12 ℃.
According to an embodiment of the invention, the cooling medium of the absorbent chiller 8 is a freezing medium, for example an aqueous ethylene glycol solution of the cryogenic medium, the temperature of which is illustratively-15 to-10 ℃.
According to an embodiment of the invention, the absorbent cooling unit may also be connected to a first absorbent replenishment device for replenishing the first absorbent.
According to an embodiment of the present invention, the absorber column 1 contains a first absorbent.
According to an embodiment of the present invention, the solvent recovery column 2 contains a second absorbent therein.
According to an embodiment of the invention, the gas recovery device further comprises a recovery system for the second absorbent. Preferably, the recovery system of the second absorbent is connected to the solvent recovery column 2 by a pipeline.
According to an embodiment of the invention, the first absorbent is different from the second absorbent. Preferably, the first absorbent is an organic substance; the second absorbent is an inorganic substance.
According to an embodiment of the present invention, the first absorbent is selected from one or a mixture of two or more of chloroform, diethyl ether, methanol, methylal, and acetone.
According to an embodiment of the present invention, the second absorbent is selected from one or a mixture of two or more of water, alkali metal hydroxide, ammonia. For example, the second absorbent is selected from one or a mixture of two or more of an aqueous solution of an alkali metal hydroxide and an aqueous solution of ammonia.
Preferably, when the second absorbent is selected from an aqueous solution of alkali metal hydroxide or ammonia, the mass concentration thereof is 1% to 30%, preferably 1%, 2%, 3%, 4%, 5%, 1%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30% or a range between any two of the above values.
The invention also provides application of the gas recovery device in gas recovery, such as tail gas recovery.
According to an embodiment of the invention, the gas or off-gas contains substances which are difficult to biochemically treat, such as methyl chloride.
The invention also provides a gas recovery method, which comprises the step of using the gas recovery device to treat the gas containing chloromethane.
According to an exemplary embodiment of the present invention, the recovery method includes the steps of:
(1) Countercurrent contact is carried out between the gas to be treated containing chloromethane and the first absorbent in the absorption tower 1, and the gas containing chloromethane and the first absorbent is extracted from the top of the absorption tower 1; the first absorbent rich in chloromethane is extracted from the bottom of the absorption tower 1;
(2) The first absorbent rich in chloromethane obtained in the step (1) enters a desorption tower 3, chloromethane is obtained at the top of the desorption tower 3, and the chloromethane is condensed by a tower top condenser of the desorption tower 3 to obtain chloromethane liquid or gas; the tower bottom of the desorption tower 3 is cooled to obtain a first absorbent which is used as the first absorbent of the absorption tower 1 for recycling;
(3) The gas containing chloromethane and the first absorbent obtained in the step (1) enters from the bottom of the solvent recovery tower 2, and is in countercurrent contact with the second absorbent in the solvent recovery tower 2, the second absorbent is discharged from the bottom of the solvent recovery tower 2, and the tail gas meeting the emission standard is discharged from the top of the solvent recovery tower 2.
According to an exemplary embodiment of the present invention, the recovery method includes the steps of:
(1) The gas to be treated containing the chloromethane enters from the bottom of the absorption tower 1, and the first absorbent enters from the top of the absorption tower 1, so that the gas to be treated containing the chloromethane contacts with each other in countercurrent in the absorption tower 1, and the absorption of the chloromethane by the first absorbent is realized; the tail gas containing the chloromethane and the first absorbent is extracted from the top of the absorption tower 1, and the first absorbent rich in chloromethane is extracted from the bottom of the absorption tower 1;
(2) The first absorbent rich in chloromethane obtained in the step (1) exchanges heat with the first absorbent obtained in the tower kettle of the desorption tower 3 in a feeding heat exchanger 9 of the desorption tower, and then enters the desorption tower 3, chloromethane is obtained at the tower top of the desorption tower 3, and the chloromethane is condensed by a tower top condenser of the desorption tower 3 to obtain chloromethane; the tower bottom of the desorption tower 3 is cooled to obtain a first absorbent which is used as the first absorbent of the absorption tower 1 for recycling;
(3) The tail gas containing the chloromethane and the first absorbent obtained in the step (1) enters from the bottom of the solvent recovery tower 2, and is in countercurrent contact with the second absorbent in the solvent recovery tower 2, and then the chloromethane and the first absorbent in the tail gas are further absorbed by the second absorbent; and the second absorbent is discharged from the bottom of the solvent recovery tower 2, and the tail gas meeting the emission standard is discharged from the top of the solvent recovery tower 2.
According to the embodiment of the invention, the second absorbent discharged from the bottom of the solvent recovery tower 2 enters a recovery system of the second absorbent and is recycled after being treated.
According to an embodiment of the invention, the gas to be treated is selected from the group consisting of gases comprising methyl chloride, for example tail gases comprising methyl chloride, preferably tail gases comprising methyl chloride produced in the synthesis of glyphosate.
According to an embodiment of the present invention, the gas comprising methyl chloride may be selected from gases produced in the synthesis of compounds, such as gases comprising methyl chloride produced in the synthesis of glyphosate.
According to an embodiment of the invention, in step (1), the feed mass ratio of the first absorbent to the gas to be treated is 0.2-50:1, for example 0.2:1, 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 15:1, 20:1, 25:1:1, 30:1, 35:1, 40:1, 45:1, 50:1 or a range between any two of the above values is selected. Preferably, the feeding mass ratio of the first absorbent to the gas to be treated is 0.2-10:1; more preferably, the feed mass ratio of the first absorbent to the gas to be treated is 0.2-5:1.
According to an embodiment of the invention, in step (1), the feeding temperature of the gas to be treated is-25 to 50 ℃, preferably-10 ℃, 0 ℃, 5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃ or a range between any two of the above values is selected.
According to an embodiment of the invention, in step (1), the feeding temperature of the first absorbent is-25 to 50 ℃, preferably-10 ℃, 0 ℃, 5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃ or a range between any two of the above values is selected.
According to an embodiment of the present invention, in step (1), the top operation pressure of the absorption column 1 is 0.01 to 2MPa, preferably 0.01MPa, 0.05MPa, 0.1MPa, 0.11MPa, 0.2MPa, 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, 1.0MPa, 1.5MPa, 2MPa, or a range between any two of the above values is selected. Preferably, the operation pressure of the top of the absorption tower 1 is 0.01-1.0 MPa.
According to an embodiment of the invention, the operating temperature of the top of the absorber column 1 is-25 to 50 ℃, preferably-10 to 30 ℃, such as-25 ℃, -20 ℃, -15 ℃, -10 ℃, -5 ℃, 0 ℃, 5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃ or a range between any two of the above values is selected.
Preferably, the operating temperature of the top of the absorption column 1 is 0 to 50 ℃.
According to an exemplary embodiment of the present invention, the operation temperature of the top of the absorption tower 1 is 10 ℃, the feeding temperature of the first absorbent is 10 ℃, and the feeding temperature of the chloromethane tail gas is 20 ℃.
According to an embodiment of the present invention, in step (2), the top operating pressure of the desorption column 3 is 0.01 to 2MPa, preferably 0.01MPa, 0.05MPa, 0.1MPa, 0.11MPa, 0.2MPa, 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, 1.0MPa, 1.5MPa, 2MPa, or a range between any two of the above values is selected.
According to an embodiment of the present invention, in step (2), the operation temperature of the top of the desorption column 3 is-25 to 50 ℃, preferably-10 ℃, 0 ℃, 5 ℃, 10 ℃, 20 ℃, 30 ℃, 40 ℃, 50 ℃, or a range between any two of the above values is selected.
According to an embodiment of the present invention, in step (2), at least part of the resulting chloromethane liquid may be refluxed to the desorber 3. Preferably, the reflux ratio is 0.5 to 20. The reflux ratio refers to the ratio of the reflux amount and the extraction amount of chloromethane liquid at the top of the tower.
According to the embodiment of the invention, in the step (2), the additional first absorbent can be used as the first absorbent of the absorption tower 1 after being supplemented; for example, before or after the cooling of the first absorbent, an additional first absorbent is mixed therewith and used as the first absorbent of the absorption tower 1.
The cooling mode of the absorbent cooling unit according to the embodiment of the present invention is not particularly limited as long as the above-described feeding temperature requirement of the first absorbent can be satisfied.
According to an embodiment of the invention, in step (3), the feed mass ratio of the second absorbent to the gas to be treated is 0.2-50:1, for example 0.2:1, 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1 or a range between any two of the above values is selected. Preferably, the feeding mass ratio of the second absorbent to the gas to be treated is 0.2-10:1; more preferably, the feed mass ratio of the second absorbent to the gas to be treated is 0.2-5:1.
According to an embodiment of the present invention, in step (3), the overhead operating pressure of the solvent recovery column 2 is 0.1 to 2MPa, preferably 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, 1.0MPa, 1.5MPa, 2MPa, or a range between any two of the above values is selected.
According to an embodiment of the present invention, in step (3), the overhead operating temperature of the solvent recovery column 2 is-25 to 50 ℃, preferably-10 ℃, -5 ℃, 0 ℃, 5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃ or a range between any two of the above values is selected.
According to an embodiment of the present invention, the content of chloromethane in the tail gas discharged from the top of the step (3) is less than 20mg/Nm 3 . Preferably, the content of chloromethane and the first absorbent is less than 20mg/Nm 3 . More preferably, the total content of methyl chloride and the first absorbent is less than 10mg/Nm 3 。
According to an exemplary embodiment of the present invention, the top operating pressure of the absorption column 1 is greater than the operating pressure of the solvent recovery column 2. For example, the top operating pressure of the absorber 1 is greater than 0.5Mpa, preferably greater than 0.6Mpa; the operating pressure of the solvent recovery column 2 is slightly less than the operating pressure of the absorber column 1 to ensure that the gas phase at the top of the absorber column 1 can enter the solvent recovery column 2. Illustratively, the operating pressure at the top of the absorption column 1 is 0.7MPa, the operating pressure at the top of the solvent recovery column 2 is 0.6MPa, and the operating pressure at the top of the desorption column 3 is 1MPa.
Advantageous effects
Since the solubility of difficult biochemical substances such as methyl chloride is generally very low in inorganic absorbents, absorption with organic absorbents is required. Based on the phase balance principle, the tail gas discharged from the top of the absorption tower necessarily contains a certain proportion of organic absorbent, so that the VOC requirement can not be met, and the standard emission can be realized; after the absorption tower 1, the solvent recovery tower 2 and the desorption tower 3 are adopted to recover and treat substances difficult to be biochemically contained in the tail gas (such as chloromethane), the VOC index in the discharged tail gas can be reduced to reach the discharge standard by simplifying the process operation condition of the absorption tower 1 (such as increasing the feeding temperature) and simultaneously using the second absorbent to secondarily absorb the first absorbent in the tail gas of the absorption tower 1 on the premise of ensuring the recovery rate of chloromethane.
Furthermore, the organic solvent and the inorganic solvent are sequentially adopted as the absorbent, so that residual refractory substances (such as chloromethane) and the first absorbent in the tail gas can be recovered more efficiently, and the VOC content in the tail gas is obviously improved. Meanwhile, the absorption tower 1 does not need to adopt harsh process conditions, and can realize the recovery of chloromethane under the conditions of improving the feeding temperature of the first absorbent and the tail gas and reducing the dosage of the first absorbent (such as the feeding mass ratio of the first absorbent to the tail gas), thereby effectively reducing the energy consumption generated by maintaining the low-temperature absorption of the absorption tower 1 and the recovery of the solvent of the desorption tower 3 in the recovery process. By the tail gas recovery device and the tail gas recovery method, the VOC value in the tail gas can be reduced without increasing the material consumption and the running cost of the system, and the VOC emission standard is reached.
Moreover, by the device and the process, not only the recovery of the chloromethane which is difficult to biochemically substance in the tail gas is realized, but also the chloromethane with high purity can be produced with high recovery rate. In addition, after the chloromethane in the tail gas is recovered, the content of refractory substances in the tail gas discharged by the tail gas recovery device and the tail gas recovery method can be reduced to be lower than 20mg/Nm 3 Recovery of chloromethane>99%. In addition, the device and the process of the invention also avoid the generation of HCl when the waste gas is burnt, thereby causing serious corrosion of equipment and having higher production safety.
Drawings
FIG. 1 shows a recovery apparatus for chloromethane tail gas according to the present invention;
FIG. 2 is a recovery apparatus for chloromethane tail gas of comparative example 1;
FIG. 3 is a recovery apparatus for chloromethane tail gas of comparative example 2;
in fig. 1: 1-absorption tower, 2-solvent recovery tower, 3-desorption tower, 4-tower kettle reboiler, 5-tower top condenser, 6-absorbent cooler, 7-absorbent cryocooler, 8-absorbent cryocooler, 9-desorption tower feeding heat exchanger.
In fig. 2: 1-absorption tower, 3-desorption tower, 4-tower kettle reboiler, 5-tower top condenser, 6-absorbent cooler, 7-absorbent cryocooler, 9-absorption tower top refrigerator, 10-absorption tower top storage tank, 11-absorption tower gas phase feeding refrigerator and 12-absorbent storage tank.
In fig. 3: 1-absorber, 3-desorber, 4-tower reboiler, 5-tower top condenser, 6-absorber cooler, 7-absorber cryocooler, 8-absorber cryocooler, 11-absorber gas phase feed cryocooler.
Detailed Description
The technical scheme of the invention will be further described in detail below with reference to specific embodiments. It is to be understood that the following examples are illustrative only and are not to be construed as limiting the scope of the invention. All techniques implemented based on the above description of the invention are intended to be included within the scope of the invention.
Unless otherwise indicated, the starting materials and reagents used in the following examples were either commercially available or may be prepared by known methods.
As shown in fig. 1, the invention provides a recovery device of chloromethane tail gas, which comprises an absorption tower 1, a solvent recovery tower 2 and a desorption tower 3;
the top gas phase outlet of the absorption tower 1 is connected with the bottom material inlet of the solvent recovery tower 2 through a pipeline, and the kettle liquid outlet of the absorption tower 1 is connected with the material inlet of the desorption tower 3 through a pipeline; the kettle liquid outlet of the desorption tower 3 is connected with the top material inlet of the absorption tower 1 through a pipeline, and a first absorbent cooling unit for cooling a first absorbent is arranged on the connecting pipeline; the top condenser 5 and the tower kettle reboiler 4 are respectively arranged at the top and the tower kettle of the desorption tower 3; the material inlet of the desorption tower 3 is arranged at the top or the middle part of the desorption tower 3.
And a feeding heat exchanger 9 of the desorption tower is arranged between the kettle liquid outlet of the desorption tower 3 and the top material inlet of the absorption tower 1, and the feeding heat exchanger 9 is positioned between the kettle liquid outlet of the desorption tower 3 and the cooling unit.
The absorption tower 1 is a pressurized tower or an atmospheric tower, preferably a pressurized tower; the solvent recovery tower 2 is a pressurized tower or an atmospheric tower, preferably a pressurized tower; the desorption column 3 is a pressure column or an atmospheric column, preferably a pressure column.
The absorption tower 1, the solvent recovery tower 2 and the desorption tower 3 are selected from plate towers or packed towers.
The tower kettle reboiler 4 is selected from any one of a thermosiphon reboiler, a forced circulation reboiler, a kettle reboiler or a falling film reboiler. The top condenser 5 is selected from any one of a shell-and-tube heat exchanger, a plate heat exchanger or an air cooler.
The first absorbent cooling unit comprises an absorbent cooler 6, an absorbent cryocooler 7, an absorbent chiller 8 and an absorbent heat exchanger 9. The cooling medium of the absorbent cooler 6 is selected from circulating water or air, and the temperature of the cooling medium is 32-38 ℃. The cooling medium of the absorbent cryocooler 7 is a cryogenic medium, for example, water, and the temperature of the cryogenic medium is 7-12 ℃. The cooling medium of the absorbent cryocooler 8 is a freezing medium, for example, a cryogenic medium glycol aqueous solution, and the temperature of the freezing medium is-15 to-10 ℃. The heat exchange medium of the absorbent heat exchanger 9 is the discharge of the tower bottom of the absorption tower 1 and the discharge of the tower bottom of the desorption tower.
The first absorbent cooling unit is also connected with a first absorbent supplementing device for supplementing the first absorbent.
Example 1
The recovery of chloromethane tail gas was performed in the recovery apparatus shown in fig. 1.
The treatment capacity of the chloromethane tail gas is 1000kg/h, wherein the mass content of the chloromethane is 80%, the balance is air, and the feeding temperature of the chloromethane is 20 ℃. The first absorbent is methanol, the feeding temperature is 10 ℃, the second absorbent is water, the feeding temperature is 35 ℃, the feeding mass ratio of the first absorbent to the tail gas is 5, and the feeding mass ratio of the second absorbent to the tail gas is 4; the pressure of the absorption tower 1 is 0.7MPa, and the operating pressure of the solvent recovery tower 2 is 0.6MPa; the operating pressure of the desorption column 3 is 1MPa; the temperature at the top of the absorption tower 1 is 10 ℃, the temperature at the top of the solvent recovery tower 2 is 35 ℃, and the temperature at the top of the desorption tower 3 is 45 ℃. The recovery method comprises the following steps:
(1) The chloromethane tail gas and the methanol of the first absorbent enter the absorption tower 1 through the lower part and the top of the absorption tower 1 respectively, and are in countercurrent contact in the tower to realize the absorption of the chloromethane by the first absorbent; tail gas containing trace chloromethane and a first absorbent is extracted from the top of the absorption tower 1; the first absorbent rich in chloromethane is extracted from the bottom of the absorption tower 1;
(2) The first absorbent rich in chloromethane at the bottom of the absorption tower 1 and the obtained first absorbent at the bottom of the desorption tower are subjected to heat exchange in a feeding heat exchanger 9 of the desorption tower and then enter a desorption tower 3, and chloromethane is obtained at the top of the desorption tower 3; the tower bottom of the desorption tower 3 is cooled by a cooling unit to obtain a first absorbent, and the first absorbent returns to the absorption tower 1 for recycling;
(3) The tail gas containing chloromethane and a first absorbent at the top of the absorption tower 1 enters from the bottom of the solvent recovery tower 2, and after countercurrent contact with a second absorbent in the solvent recovery tower 2, the first absorbent and chloromethane in the tail gas are further absorbed, and the second absorbent is discharged from the bottom of the solvent recovery tower 2 and enters a second absorbent treatment system for recycling after treatment; the tail gas obtained from the top of the solvent recovery tower 2 is directly discharged.
The process parameters and material take-off for each column are shown in Table 1.
TABLE 1 extraction of column materials from example 1
Wherein, in the discharged tail gas obtained from the top of the solvent recovery tower 2, the content of chloromethane in the discharged tail gas is 2.58mg/Nm 3 The methanol content of the first absorbent was 0.02mg/Nm 3 Total 2.6mg/Nm 3 ' all less than the limit of the emission standard of 20mg/Nm 3 . The recovery rate of chloromethane is more than 99 percent, and the discharged tail gas meets higher VOC discharge standard.
In the embodiment, the circulating absorbent extracted from the tower kettle exchanges heat with the tower kettle material of the absorption tower 1 firstly, so that on one hand, the energy consumption of a reboiler of the desorption tower can be saved, and on the other hand, the amount of circulating water required by cooling the absorbent can be saved.
Comparative example 1
The raw material composition and the absorbent of the chloromethane tail gas are the same as in example 1, the absorbent is dichloroethane, the mass ratio of the consumption to the chloromethane tail gas treatment amount is 8, and the recovery operation is carried out by adopting a single absorption tower recovery process, and the detailed description is shown in a recovery device of fig. 2. The operation pressure of the absorption tower 1 is 0.3MPa, the operation pressure of the desorption tower 3 is 0.6MPa, the cooling temperature of the absorbent is 20 ℃, the feeding temperature of the chloromethane-containing tail gas is 0 ℃, the temperature of the top of the desorption tower 3 is 28 ℃, the tail gas from the top of the absorption tower 1 is cooled to 0 ℃, the tail gas enters the tower top storage tank 10, the gas phase after flash evaporation is the discharged tail gas, the liquid phase is cooled to 20 ℃ after being mixed with the absorbent extracted from the tower bottom of the desorption tower 3, the mixture enters the absorption tower 1 again, the qualified chloromethane is extracted from the liquid phase of the partial condenser at the top of the desorption tower, and the gas phase is the waste gas containing chloromethane. The process parameters and material take-off for each column are shown in Table 2.
Table 2 comparative example 1 conditions of extraction of materials from each column
The recovery rate of chloromethane in this comparative example was more than 97%, but the content of chloromethane in the exhaust gas obtained from the top of the absorption column 1 was 0.39mg/Nm 3 But the ethylene dichloride content of the absorbent is as high as 41925mg/Nm 3 The first absorbent in the exhaust is far greater than the limit value of the emission standard of 20mg/Nm 3 . Simultaneously, 25kg/h of off-grade gas containing 90% of chloromethane is also arranged at the top of the desorption tower and is far higher than the emission standard.
Comparative example 2
The raw material composition of the chloromethane tail gas and the first absorbent were the same as in example 1, and the recovery operation was performed by using the recovery apparatus of fig. 3, wherein the absorption tower 1 was operated at normal pressure, the feeding temperature of the first absorbent was 10 ℃, the mass ratio of the first absorbent to the chloromethane treatment amount was 8, the operating pressure of the desorption tower 3 was 1MPa, the reflux ratio was 2, and the extraction conditions of the materials of each tower were as shown in table 3.
TABLE 3 comparative example 2 production of column materials
The recovery rate of chloromethane of the comparative example is more than 99%. However, it was found from the calculation that the mixed exhaust gas obtained from the top of the absorption column 1 and the top of the desorption column had a chloromethane content of as high as 11197mg/Nm 3 The first absorbent has a content of up to 88210mg/Nm 3 A limit value of 20mg/Nm far greater than the emission standard 3 。
As is apparent from the comparison of the above-mentioned experimental results, the content of chloromethane in the gas discharged by the recovery apparatus and method of the present invention was 2.58mg/Nm 3 The first absorbent content was 0.02mg/Nm 3 The' exhaust emission can meet the requirement of higher VOC emission standard; in the exhaust gas of comparative examples 1 and 2, the content of chloromethane was respectively0.06mg/Nm 3 And 11197mg/Nm 3 The first absorbent contents were 41925mg/Nm, respectively 3 And 88210mg/Nm 3 It is difficult for the contents of methyl chloride and the first absorbent in the exhaust gas discharged from comparative examples 1 and 2 to satisfy the high VOC emission standard.
In addition, compared with comparative examples 1 to 2, the apparatus and the operation conditions of the present invention are simple, and the feeding conditions of the absorption column 1 are mild and the energy consumption is low. The energy consumption results of example 1 and comparative examples 1 to 2 are shown in Table 4.
TABLE 4 comparison of energy consumption for example 1 and comparative examples 1-2
Comparing the data in table 4, it can be seen that the total energy consumption of the device of the present invention is lower than that of comparative examples 1 and 2. For example, the reboiler duty for example 1 was 77% and 40.7% for comparative example 1 and comparative example 2, respectively, with the same chloromethane tail gas throughput. The top temperature of the desorber 3 of example 1 was 45 ℃, so both the desorber condenser and the absorbent cooler could use circulating water cooling; whereas the temperature of the top of the desorber 3 in comparative example 1 was 20 ℃, the top condenser could not be cooled with circulating water; the overhead condenser in comparative example 2 may use circulating water cooling. As can be seen from Table 4, the total loads of the low-temperature water and the deep-cold water coolers employed in the present invention were 33% and 62% of those of comparative examples 1 and 2, respectively, and the total loads of the circulating water were 99% and 34.2% of those of comparative examples 1 and 2, respectively. From a comparison of the data in Table 4, it can be seen that the energy consumption of the present invention is lower because the apparatus and operating conditions of the present invention are simple and the feeding conditions of the absorption column 1 are mild.
The above description of exemplary embodiments of the invention has been provided. However, the scope of protection of the present application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, or the like, which are within the spirit and principles of the present invention, should be made by those skilled in the art, and are intended to be included within the scope of the present application.
Claims (10)
1. A gas recovery device comprises an absorption tower (1), a solvent recovery tower (2) and a desorption tower (3);
the top gas phase outlet of the absorption tower (1) is connected with the bottom material inlet of the solvent recovery tower (2) through a pipeline, the kettle liquid outlet of the absorption tower (1) is connected with the material inlet of the desorption tower (3) through a pipeline, and the kettle liquid outlet of the desorption tower (3) is connected with the top material inlet of the absorption tower (1) through a pipeline;
a cooling unit is arranged on a connecting pipeline between a kettle liquid outlet of the desorption tower (3) and a top material inlet of the absorption tower (1);
the tower top of the desorption tower (3) is provided with a tower top condenser, and the tower bottom of the desorption tower (3) is provided with a tower bottom reboiler;
a feeding heat exchanger (9) of the desorption tower is arranged between a kettle liquid outlet of the desorption tower (3) and a top material inlet of the absorption tower (1), and the feeding heat exchanger (9) is positioned between the kettle liquid outlet of the desorption tower (3) and a cooling unit;
preferably, the gas recovery device is selected from a tail gas recovery device, preferably a chloromethane tail gas recovery device produced in the synthesis of glyphosate.
2. The gas recovery device according to claim 1, wherein the desorber (3) material inlet is provided at the top or in the middle of the desorber (3);
the absorption tower (1), the solvent recovery tower (2) and the desorption tower (3) are independently selected from an atmospheric tower or a pressurized tower;
preferably, at least one of the absorption column (1), the solvent recovery column (2), and the desorption column (3) is a pressurized column.
3. The gas recovery device according to claim 1 or 2, wherein the absorption column (1), solvent recovery column (2), desorption column (3) is selected from a tray column or a packed column;
preferably, the column bottoms reboiler is selected from any one of a thermosiphon reboiler, a forced circulation reboiler, a kettle reboiler, or a falling film reboiler;
preferably, the overhead condenser is selected from any one of shell-and-tube heat exchanger, plate heat exchanger or air cooler.
4. A gas recovery device according to any one of claims 1-3, wherein the cooling unit may be selected from an absorbent cooling unit comprising at least one of an absorbent cooler (6), an absorbent cryocooler (7) or an absorbent chiller (8);
preferably, the absorbent cooling unit comprises an absorbent cooler (6), an absorbent cryocooler (7) and an absorbent chiller (8).
5. A gas recovery device according to any one of claim 1 to 4,
the absorber column (1) may contain a first absorbent therein;
the solvent recovery column (2) may contain a second absorbent therein.
6. The gas recovery device according to any one of claims 1-5, wherein the absorbent cooling unit is further connected to a first absorbent make-up device;
preferably, the gas recovery device further comprises a recovery system of a second absorbent, which can be connected with the solvent recovery tower (2) through a pipeline;
preferably, the first absorbent is selected from one or more of chloroform, diethyl ether, methanol, methylal and acetone;
the second absorbent is selected from one or more of water, alkali metal hydroxide and ammonia, for example, one or more of alkali metal hydroxide aqueous solution and ammonia aqueous solution.
7. Use of a gas recovery device according to any one of claims 1-6 for gas recovery, such as tail gas recovery;
preferably, the gas or tail gas comprises methyl chloride.
8. A gas recovery process, such as a tail gas recovery process, comprising treating a gas comprising chloromethane using a gas recovery apparatus according to any one of claims 1 to 6.
9. The gas recovery method according to claim 8, comprising the steps of:
(1) Countercurrent contact is carried out between the gas to be treated containing methyl chloride and the first absorbent in the absorption tower (1), and the gas containing methyl chloride and the first absorbent is extracted from the top of the absorption tower (1); the first absorbent rich in chloromethane is extracted from the bottom of the absorption tower (1);
(2) The first absorbent rich in chloromethane obtained in the step (1) exchanges heat with the first absorbent at the tower bottom of the desorption tower (3) and then enters the desorption tower (3), chloromethane is obtained at the tower top of the desorption tower (3), and the chloromethane is condensed by a tower top condenser of the desorption tower (3) to obtain chloromethane liquid or gas; the tower bottom of the desorption tower (3) is provided with a first absorbent, and the first absorbent is used as the first absorbent of the absorption tower (1) for recycling after being cooled;
(3) The gas containing chloromethane and the first absorbent obtained in the step (1) enters from the bottom of the solvent recovery tower (2) and contacts with the second absorbent in the solvent recovery tower (2) in a countercurrent way, the second absorbent is discharged from the bottom of the solvent recovery tower (2), and the tail gas meeting the emission standard is discharged from the top of the solvent recovery tower (2);
preferably, the second absorbent discharged from the bottom of the solvent recovery tower (2) enters a recovery system of the second absorbent and is recycled after being treated;
preferably, the gas to be treated is selected from a gas comprising methyl chloride, for example a tail gas comprising methyl chloride, preferably a tail gas comprising methyl chloride produced in the synthesis of glyphosate.
10. The method for recovering gas according to claim 9, wherein,
in the step (1), the operation pressure of the top of the absorption tower (1) is 0.01-2 MPa, the operation temperature of the top of the absorption tower (1) is-25-50 ℃, and the feeding mass ratio of the first absorbent to the gas to be treated is 0.2-50:1;
preferably, in the step (2), the operation pressure of the top of the desorption tower (3) is 0.01-2 MPa, and the operation temperature of the top of the desorption tower (3) is-5-50 ℃;
preferably, in the step (3), the feeding mass ratio of the second absorbent to the gas to be treated is 0.2-50:1, the operation pressure of the top of the solvent recovery tower (2) is 0.1-2 MPa, and the operation temperature of the top of the solvent recovery tower (2) is-25-50 ℃;
more preferably, the operation pressure of the top of the absorption tower (1) is more than 0.6Mpa, and the operation pressure of the solvent recovery tower (2) is slightly less than that of the absorption tower (1), so as to ensure that the gas phase at the top of the solvent recovery tower (2) can enter the solvent recovery tower (2); the operation pressure of the top of the desorption column (3) is normal pressure.
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| CN202111216060.3A CN115990388A (en) | 2021-10-19 | 2021-10-19 | Gas recovery device and recovery method |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116392931A (en) * | 2023-05-15 | 2023-07-07 | 盐城优和博新材料有限公司 | System and method for treating tail gas generated in production of ultra-high-strength polyethylene fibers |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116392931A (en) * | 2023-05-15 | 2023-07-07 | 盐城优和博新材料有限公司 | System and method for treating tail gas generated in production of ultra-high-strength polyethylene fibers |
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