Combined alkali production tail gas treatment process and device

Abstract

The invention provides a combined alkali production tail gas treatment process and device, and belongs to the technical field of alkali production. The combined alkali production tail gas treatment process comprises an alkali production process and a tail gas treatment process, and the alkali production process comprises an alkali production tower and a cleaning tower; the tail gas treatment process comprises absorption operation and compression operation, the absorption operation is multi-stage absorption, and the multi-stage absorption comprises mother liquor absorption and washing water absorption; primary tail gas obtained by the alkali production tower and the cleaning tower is subjected to mother liquor absorption to obtain secondary tail gas, the secondary tail gas is subjected to washing water absorption to obtain tertiary tail gas, and the tertiary tail gas is compressed and then returns to the cleaning tower as cleaning gas. Aiming at the working condition that no by-product cleaning gas exists in the process of preparing synthetic ammonia from natural gas, the combined alkali-making tail gas treatment process disclosed by the invention does not need to be additionally matched with a nitrogen-making device used for producing nitrogen as the cleaning gas of a cleaning tower, so that the production cost is reduced, and meanwhile, the tail gas emission is also reduced.

Description

Technical Field

[0001] The invention relates to the technical field of alkali production, and in particular to a combined alkali production tail gas treatment process and device. Background Art

[0002] Soda ash (sodium carbonate, Na2CO3) is an important organic chemical raw material, mainly used in the production of glass products and ceramic glazes, and is also widely used in papermaking, textiles, daily chemicals and food processing industries. With the continuous development of domestic and international markets, the demand for soda ash products is growing, and the market prospects are broad.

[0003] Combined alkali production, also known as Hou's alkali production, is a process for producing soda ash and ammonium chloride at the same time. The main raw materials for combined alkali production are salt, ammonia and carbon dioxide. The specific process is as follows: first, ammonia and mother liquor are reacted to prepare ammonia mother liquor, and then carbon dioxide is introduced to produce sodium bicarbonate and ammonium chloride through carbonation reaction. Ammonium chloride can be used as a common nitrogen fertilizer in agricultural production. Sodium bicarbonate is filtered and washed to obtain pure sodium bicarbonate crystals, and finally soda ash is produced through calcination reaction. This process combines the synthetic ammonia industry with the alkali industry, and uses carbon dioxide, a by-product of the synthetic ammonia plant, as one of the raw materials, thereby improving the utilization rate of raw materials, reducing environmental pollution, and reducing production costs.

[0004] In the combined alkali production process, the carbonation reaction of ammonia mother liquor and carbon dioxide to produce sodium bicarbonate and ammonium chloride is mainly carried out in the carbonization tower. Since sodium bicarbonate accumulates and forms scars in the carbonization tower, if it is not cleaned for a long time, the channel of the carbonization tower will be blocked, thereby reducing the carbonization effect. For this reason, it is necessary to perform periodic cleaning operations on the carbonization tower. The conventional cleaning method for the carbonization tower mainly uses ammonia mother liquor and cleaning gas to clean the scars in the carbonization tower in the tower. During the cleaning process, the cleaning gas consumed generally comes from the synthetic ammonia unit. In the coal-to-synthetic ammonia process, cleaning gas is a by-product. However, in areas where coal resources are scarce and natural gas is abundant, natural gas is often used to produce synthetic ammonia. This process is different from coal-to-synthetic ammonia. It does not produce cleaning gas by-products. The cleaning gas needs to be produced by a separate nitrogen production device or directly use air as the cleaning gas. If a separate nitrogen production device is used to produce nitrogen as cleaning gas, the production cost will increase. If air is used as cleaning gas, because the air contains a high level of oxygen, it will aggravate the corrosion of the inner wall and the internal parts of the carbonization tower, affecting the normal operation of the equipment. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention discloses a combined alkali production tail gas treatment process and device.

[0006] On the one hand, the present invention proposes a combined alkali production tail gas treatment process, including an alkali production process and a tail gas treatment process, the alkali production process includes an alkali production tower and a cleaning tower; the tail gas treatment process includes an absorption operation and a compression operation, the absorption operation is a multi-stage absorption, and the multi-stage absorption includes mother liquor absorption and washing water absorption; the first-stage tail gas obtained by the alkali production tower and the cleaning tower is subjected to mother liquor absorption to obtain a second-stage tail gas, the second-stage tail gas is subjected to washing water absorption to obtain a third-stage tail gas, and the third-stage tail gas is compressed and returned to the cleaning tower as a cleaning gas.

[0007] The absorption operation of the combined alkali production tail gas treatment process of the present invention includes mother liquor absorption and washing water absorption, and the primary tail gas generated in the alkali production process can be treated in stages. The absorption liquid of the mother liquor absorption is mother liquor (the main components are 2-8% NH3, 15-30% NH4Cl, 5-15% NaCl, 2-8% CO2, and the rest is water), which can absorb ammonia in the primary tail gas. At the same time, the use of mother liquor can improve the utilization of raw materials and reduce production costs; the absorption liquid of the washing water absorption is washing water, which is used to further wash and absorb ammonia in the secondary tail gas and the mother liquor that may be entrained, so that the ammonia content in the tertiary tail gas is less than 1000ppm, meeting the tail gas emission requirements and improving the purification efficiency. The present invention absorbs ammonia in the tail gas in steps through different absorption media, which can make the absorption process more thorough and improve the overall treatment efficiency.

[0008] The tail gas after washing water absorption in the present invention is tertiary tail gas, the main component of which is nitrogen, contains a small amount of oxygen and water vapor, and basically does not contain ammonia and carbon dioxide.

[0009] The combined alkali production tail gas treatment process of the present invention treats the tail gas generated in the alkali production process through absorption operation and compression operation, and the absorption operation and the compression operation are both indispensable. If the tail gas generated by the alkali-making process is mixed and sent to absorption, under ideal conditions, ammonia will be absorbed after absorption treatment, and the remaining gas is mainly nitrogen and a small amount of oxygen, which are directly discharged into the atmosphere. However, in actual production, ammonia still exists in the tail gas after absorption treatment. If it is directly discharged into the atmosphere, it will cause air pollution; if the tail gas generated by the alkali-making process is directly compressed and recycled without absorption, the tail gas from the alkali-making process will carry mother liquor, which contains chloride ions, etc., which will corrode related equipment such as compressors; if the absorption process is replaced by a gas-liquid separation process, because the gas-liquid separation can only perform simple gas-liquid separation, the separation capacity in the soda ash industry is limited, and a small amount of mother liquor will still exist in the compression process with the tail gas, which will cause corrosion of the compression equipment. Therefore, the tail gas generated by the alkali-making process of the present invention is compressed after absorption and washing, which can reduce the corrosion of the compression equipment by the tail gas. At the same time, the tertiary tail gas is compressed and returned to the cleaning tower in the alkali-making process to serve as the cleaning gas of the cleaning section, thereby reducing production costs and reducing the emission of tail gas.

[0010] The cleaning tower in the combined alkali tail gas treatment process of the present invention comprises ammonia mother liquor entering the cleaning tower from the upper part, and cleaning gas entering the cleaning tower from the lower part. The ammonia mother liquor and the cleaning gas flow in the tower in reverse direction to wash the cleaning tower. The cleaning tower inner wall and the tower internal parts are cleaned. The principle is to use NH3·H2O in the ammonia mother liquor and HCO3 in the crystallization component to － The reaction produces NH4 + and CO3 2- , thereby converting the low-solubility hydrocarbon salts into high-solubility carbonates, achieving the purpose of removing the scars, and the exhaust gas generated by the cleaning tower is discharged from the top of the tower.

[0011] The combined alkali production tail gas treatment process of the present invention comprises a alkali production tower, wherein the ammonia mother liquor enters the tower from the upper part of the alkali production tower, the carbon dioxide enters the tower from the lower part of the alkali production tower, the mother liquor and the carbon dioxide flow in the tower in reverse, the sodium bicarbonate generated by the reaction is taken out from the bottom of the tower, and the tail gas generated by the alkali production tower is discharged from the top of the tower. The tail gas generated by the cleaning tower and the alkali production tower is mixed to obtain the primary tail gas described in the present invention, and the main component of the primary tail gas is nitrogen, which contains a small amount of ammonia, carbon dioxide, oxygen and water vapor.

[0012] Furthermore, the volume fraction of the inert gas in the cleaning gas is not less than 80%. Nitrogen is usually used as an inert gas in the cleaning tower. It can effectively prevent oxidation reactions caused by other active gases (such as oxygen), thereby protecting the cleaned equipment or materials from damage; inert gases include nitrogen, argon and other inert gases, among which nitrogen occupies a dominant position in the cleaning process and can effectively play its protective role. Optionally, nitrogen can be supplemented according to the nitrogen content in the tertiary tail gas to ensure that the volume fraction of the inert gas is above 90%.

[0013] Furthermore, a portion of the tertiary tail gas is discharged. According to the operation of the alkali tower and the cleaning tower, the amount of tail gas entering the compression can be adjusted, and the excess tail gas can be discharged. Optionally, when the amount of tertiary tail gas from the absorption operation is greater than the amount of cleaning gas required by the cleaning tower, the discharge amount can be adjusted according to the cleaning effect of the cleaning tower. Each ton of alkali requires 100 to 170 Nm of cleaning gas. 3 When it exceeds this range, the venting volume can be adjusted for venting.

[0014] Furthermore, the secondary tail gas is subjected to water washing absorption after gas-liquid separation. The secondary tail gas will carry mother liquor, so through gas-liquid separation, the gas after gas-liquid separation is further subjected to water washing absorption, and the liquid after gas-liquid separation is returned to the mother liquor absorption as mother liquor for reuse. This process can reduce the loss of mother liquor in mother liquor absorption; secondly, it can prevent too much mother liquor from entering the water washing absorption and affecting the water washing absorption.

[0015] Furthermore, the washing water outputted by the washing water absorption is cooled and then circulated. The washing water after the washing water absorption is cooled by using a cooling device such as a heat exchanger to reduce the temperature of the washing water, and the washing water after the absorption can be reused.

[0016] Furthermore, the mother liquid absorption temperature is 25-45°C and the pressure is 0-0.1MPaG;

[0017] And / or, the washing water absorption temperature is 25-45°C and the pressure is 0-0.1 MPaG.

[0018] Preferably, the temperature of the mother liquor absorption is 30-40°C and the pressure is 0.02-0.05MPaG; and / or, the temperature of the wash water absorption is 25-35°C and the pressure is 0.01-0.03MPaG. The temperature of the mother liquor absorption is controlled at 30-40°C. Within this temperature range, the absorption liquid mother liquor can effectively react with the ammonia in the primary tail gas, thereby achieving a higher absorption efficiency; the pressure of the mother liquor absorption is set to 0.02-0.05MPaG. The appropriate pressure helps to increase the contact area and contact time between the primary tail gas and the absorption liquid mother liquor, thereby improving the absorption efficiency. The temperature and pressure of the wash water absorption are lower than those of the mother liquor absorption. The temperature is controlled at 25-35°C and the pressure is 0.01-0.03MPaG.

[0019] Optionally, the multi-stage absorption also includes acid absorption, and the temperature of the acid absorption is 25-45°C and the pressure is 0-0.1MPaG. The first-stage tail gas is successively absorbed by mother liquor, acid, and washing water to obtain a third-stage tail gas. The acid that can be selected in the acid absorption is an inorganic acid such as hydrochloric acid and sulfuric acid. After the mother liquor absorption, acid absorption is further adopted to further absorb the ammonia in the tail gas. Combined with the specific working conditions, if it is necessary to control the ammonia content in the third-stage tail gas below 100ppm, a multi-stage absorption method of successively mother liquor absorption, acid absorption, and washing water absorption can be adopted. If it is necessary to control the ammonia content in the third-stage tail gas below 1000ppm, a multi-stage absorption method of successively mother liquor absorption and washing water absorption can be adopted.

[0020] On the other hand, the present invention also provides a combined alkali production tail gas treatment device, comprising a cleaning tower, an alkali production tower, an absorption tower and a compression device, wherein the absorption tower comprises an absorption tower upper section and an absorption tower lower section;

[0021] The side line liquid inlet of the cleaning tower is connected to the ammonia mother liquor supply pipeline, an air inlet for inputting cleaning gas is arranged at the bottom of the cleaning tower, and the bottom liquid outlet of the cleaning tower is connected to the liquid inlet of the alkali making tower; the bottom air inlet of the alkali making tower is connected to the raw gas pipeline, and a liquid outlet is arranged at the bottom of the alkali making tower, and the top exhaust port of the cleaning tower and the top exhaust port of the alkali making tower are connected to the air inlet of the lower section of the absorption tower through the tail gas pipeline;

[0022] The liquid inlet of the lower section of the absorption tower is connected to the mother liquid supply pipeline, the liquid outlet of the lower section of the absorption tower is connected to the mother liquid outlet pipeline, the gas outlet of the lower section of the absorption tower is connected to the gas inlet of the upper section of the absorption tower, the liquid inlet of the upper section of the absorption tower is connected to the wash water supply pipeline, the liquid outlet of the upper section of the absorption tower is connected to the wash water outlet pipeline, and the gas outlet of the upper section of the absorption tower is connected to the bottom gas inlet of the cleaning tower through a compression device.

[0023] In the combined alkali production tail gas treatment device of the present invention, the tail gas generated by the cleaning of the cleaning tower and the tail gas generated by the alkali production tower both enter the absorption tower for separation. After the tail gas is absorbed by the absorption tower, it is compressed and pressurized by the compression equipment and used as the cleaning gas of the cleaning tower, and the scars are cleaned in the cleaning tower together with the ammonia mother liquor.

[0024] The present invention achieves the purpose of fully absorbing ammonia and carbon dioxide in the tail gas by bringing the tail gas into reverse contact with the absorption liquid. In the lower section of the absorption tower, the liquid inlet of the lower section of the absorption tower is located at the upper part of the lower section of the absorption tower, the absorption liquid mother liquor is input from the liquid inlet of the lower section of the absorption tower, and the primary tail gas is input from the air inlet of the lower section of the absorption tower. After reverse absorption in the lower section of the absorption tower, the absorbed mother liquor is discharged from the liquid outlet located at the lower part of the lower section of the absorption tower, and the gas discharged from the exhaust port located at the upper part of the lower section of the absorption tower is the secondary tail gas after absorbing ammonia.

[0025] In the upper section of the absorption tower, the liquid inlet of the upper section of the absorption tower is located at the upper part of the upper section of the absorption tower, the absorption liquid washing water is input from the liquid inlet of the upper section of the absorption tower, and the secondary tail gas is input from the air inlet of the upper section of the absorption tower. After reverse absorption in the upper section of the absorption tower, the mother liquor entrained in the tail gas is washed, and the absorbed washing water is discharged from the liquid outlet located at the lower part of the upper section of the absorption tower. The tail gas that has absorbed ammonia and carbon dioxide is connected to the bottom air inlet of the cleaning tower from the air outlet of the upper section of the absorption tower through the cleaning gas pipeline of the internal compression equipment.

[0026] Optionally, the compression equipment includes any one of a screw compressor and a centrifugal compressor.

[0027] Furthermore, a venting branch is provided on the pipeline connecting the absorption tower and the compression device; and an inert gas supplementing branch is provided on the pipeline connecting the compression device and the cleaning tower. The circulating cleaning gas passing through the absorption tower is used as the main cleaning gas source by the compression device, and the excess tail gas is normally vented. In the normal production process, only a small amount of low-pressure nitrogen needs to be supplemented, which reduces the cost of low-pressure nitrogen consumption, and NH3 in the circulating cleaning gas is absorbed and utilized in the circulation process, thereby reducing the ammonia content in the tail gas.

[0028] Furthermore, the combined alkali production tail gas treatment device also includes a gas-liquid separation device, the gas outlet of the lower section of the absorption tower is connected to the gas-liquid separation device, the gas outlet of the gas-liquid separation device is connected to the gas inlet of the upper section of the absorption tower, and the liquid outlet of the gas-liquid separation device is connected to the lower section of the absorption tower. The tail gas absorbed by the lower part of the absorption tower will carry part of the mother liquid, and after separation by the gas-liquid separation device, the mother liquid returns to the lower section of the absorption tower. First, it can reduce the loss of mother liquid in the lower section of the absorption tower; second, it can prevent too much mother liquid from entering the upper section of the absorption tower and affecting the upper section of the absorption tower.

[0029] Optionally, the gas-liquid separation equipment includes any one of a gravity separator, a filter separator, and a high-efficiency blade separator.

[0030] Furthermore, the combined alkali production tail gas treatment device also includes a heat exchanger, the liquid outlet of the upper section of the absorption tower is connected to the inlet of the heat exchanger, and the outlet of the heat exchanger is connected to the liquid inlet of the upper section of the absorption tower.

[0031] Optionally, the heat exchanger includes any one of a shell and tube heat exchanger, a plate heat exchanger, and a double-tube heat exchanger.

[0032] Optionally, the absorption tower also includes a middle section of the absorption tower, the gas outlet of the lower section of the absorption tower is connected to the gas inlet of the middle section of the absorption tower, the liquid inlet of the middle section of the absorption tower is connected to the acid liquid supply pipeline, the liquid outlet of the middle section of the absorption tower is connected to the acid liquid outlet pipeline, and the gas outlet of the middle section of the absorption tower is connected to the gas inlet of the upper section of the absorption tower.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) In view of the operating condition in which there is no by-product cleaning gas in the natural gas to synthetic ammonia process, the combined alkali production tail gas treatment process of the present invention does not require an additional nitrogen production device for producing nitrogen as cleaning gas for the cleaning tower, thereby reducing production costs and also reducing tail gas emissions.

[0035] (2) The combined alkali production tail gas treatment device of the present invention reuses the tail gas generated by the cleaning tower and the alkali production tower through the absorption tower and the compression equipment, thereby increasing the utilization rate of raw materials and reducing the amount of waste gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0037] Figure 1 A schematic diagram showing a combined alkali production tail gas treatment device of the present invention;

[0038] The above drawings include the following reference numerals:

[0039] 1. Cleaning tower, 2. Alkali tower, 3. Absorption tower, 31. Lower section of absorption tower, 32. Upper section of absorption tower, 4. Compression equipment, 5. Gas-liquid separation equipment, 6. Heat exchanger, 7. Ammonia mother liquor supply pipeline, 8. Raw gas pipeline, 9. Tail gas pipeline, 10. Mother liquor supply pipeline, 11. Mother liquor outlet pipeline, 12. Wash water supply pipeline, 13. Wash water outlet pipeline, 14. Vent branch, 15. Inert gas supplement branch. DETAILED DESCRIPTION

[0040] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below, and preferred embodiments of the present invention are given. However, it should be understood that these embodiments are only used for more detailed description, and should not be understood as limiting the present invention in any form, that is, not limiting the scope of protection of the present invention. Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs.

[0041] Example 1

[0042] A combined alkali tail gas treatment device, such as Figure 1 As shown, it includes a cleaning tower 1, an alkali tower 2, an absorption tower 3 and a compression device 4, and the absorption tower includes an absorption tower upper section 32 and an absorption tower lower section 31;

[0043] The side line liquid inlet of the cleaning tower 1 is connected to the ammonia mother liquor supply pipeline 7, the bottom of the cleaning tower 1 is provided with an air inlet for inputting cleaning gas, and the bottom liquid outlet of the cleaning tower 1 is connected to the liquid inlet of the alkali making tower 2; the bottom air inlet of the alkali making tower 2 is connected to the raw gas pipeline 8, and the bottom of the alkali making tower 2 is provided with a liquid outlet, and the top exhaust port of the cleaning tower 1 and the top exhaust port of the alkali making tower 2 are connected to the air inlet of the lower section 31 of the absorption tower through the tail gas pipeline 9;

[0044] The liquid inlet of the lower section 31 of the absorption tower is connected to the mother liquid supply pipeline 10, the liquid outlet of the lower section 31 of the absorption tower is connected to the mother liquid outlet pipeline 11, the gas outlet of the lower section 31 of the absorption tower is connected to the gas inlet of the upper section 32 of the absorption tower, the liquid inlet of the upper section 32 of the absorption tower is connected to the wash water supply pipeline 12, the liquid outlet of the upper section 32 of the absorption tower is connected to the wash water outlet pipeline 13, and the gas outlet of the upper section 32 of the absorption tower is connected to the bottom gas inlet of the cleaning tower 1 through the compression equipment 4.

[0045] The compression device 4 may be any known device having a gas compression function, and may be a screw compressor or a centrifugal compressor.

[0046] Example 2

[0047] Based on a combined alkali production tail gas treatment device shown in Example 1, this embodiment is a preferred embodiment, and a venting branch 14 is provided on the pipeline connecting the absorption tower 3 and the compression device 4; an inert gas supplementary branch 15 is provided on the connecting pipeline between the compression device 4 and the cleaning tower. When the amount of tail gas produced by the absorption tower 3 is greater than the amount of cleaning gas required by the cleaning tower 1, the excess tail gas can be normally vented through the venting branch 14; the inert gas can be supplemented through the inert gas supplementary branch 15 according to the nitrogen content in the tertiary tail gas to ensure that the volume fraction of the inert gas in the cleaning gas is not less than 80%.

[0048] Example 3

[0049] Based on a combined alkali production tail gas treatment device shown in Example 1, this embodiment is a preferred embodiment, and the combined alkali production tail gas treatment device of the present invention further includes a gas-liquid separation device 5, the gas outlet of the lower section 31 of the absorption tower is connected to the gas-liquid separation device 5, the gas outlet of the gas-liquid separation device 5 is connected to the gas inlet of the upper section 32 of the absorption tower, and the liquid outlet of the gas-liquid separation device 5 is connected to the lower section 32 of the absorption tower. The tail gas absorbed by the lower part 31 of the absorption tower will carry part of the mother liquid, and after separation by the gas-liquid separation device 5, the mother liquid returns to the lower section 31 of the absorption tower. The gas-liquid separation device can adopt any known device with gas-liquid separation function, and optionally, the gas-liquid separation device includes a gravity separator, a filter separator, and a high-efficiency blade separator.

[0050] Optionally, the combined alkali production tail gas treatment device of the present invention further includes a heat exchanger 6, the liquid outlet of the upper section 32 of the absorption tower is connected to the inlet of the heat exchanger 6, and the outlet of the heat exchanger 6 is connected to the upper section 32 of the absorption tower. The heat exchanger can be any known device with a heat exchange function, and optionally, the heat exchanger includes a shell and tube heat exchanger, a plate heat exchanger, and a double-tube heat exchanger.

[0051] Example 4

[0052] Based on a combined alkali production tail gas treatment device shown in Example 1, this embodiment is a preferred embodiment. The absorption tower in the combined alkali production tail gas treatment device of the present invention also includes a middle section of the absorption tower, the gas outlet of the lower section of the absorption tower is connected to the gas inlet of the middle section of the absorption tower, the liquid inlet of the middle section of the absorption tower is connected to the acid liquid supply pipeline, the liquid outlet of the middle section of the absorption tower is connected to the acid liquid outlet pipeline, and the gas outlet of the middle section of the absorption tower is connected to the gas inlet of the upper section of the absorption tower.

[0053] Example 5

[0054] This embodiment shows the process flow of combined alkali tail gas treatment under specific working conditions. It should be noted that this process flow is only a demonstration of a better process and does not limit the protection scope of the present invention.

[0055] A combined alkali production tail gas treatment process, specifically: an ammonia mother liquor prepared by an ammonia reaction of ammonia gas and a mother liquor in a combined alkali production process enters a cleaning tower from a side line liquid inlet of a cleaning tower through an ammonia mother liquor liquid supply pipeline, a cleaning gas transported through a cleaning gas pipeline enters the cleaning tower from the lower part of the cleaning tower, the ammonia mother liquor and the cleaning gas flow in reverse directions in the cleaning tower, the tail gas generated by the cleaning tower is discharged from the top of the tower, the ammonia mother liquor cleaned by the cleaning tower is discharged from the cleaning tower kettle and transported to the liquid inlet of an alkali production tower, carbon dioxide enters the tower from a bottom air inlet of the alkali production tower, the mother liquor and the carbon dioxide flow in reverse directions in the alkali production tower, the sodium bicarbonate generated by the reaction is taken out from the bottom of the tower, the tail gas generated by the alkali production tower is discharged from the top of the tower, and the primary tail gas generated by the alkali production tower and the cleaning tower is mixed (the primary tail gas composition and content: nitrogen 74%, ammonia 11%, carbon dioxide 5%, oxygen 4%, water vapor 6%) and transported to the lower section of an absorption tower.

[0056] The temperature of the lower section of the absorption tower is 30-40°C, and the pressure is 0.02-0.05MPaG. After the primary tail gas and the mother liquor are reversely absorbed, the absorbed mother liquor is output from the lower part of the lower section of the absorption tower, and the secondary tail gas (the composition and content of the secondary tail gas are: 85% nitrogen, 1% ammonia, 6% carbon dioxide, 4% oxygen, 4% water vapor) absorbed by the lower section of the absorption tower is transported to the upper section of the absorption tower from the upper part of the lower section of the absorption tower through a gas-liquid separator; the absorption liquid in the upper section of the absorption tower is wash water, and the temperature of the upper section of the absorption tower is 25-35°C, and the pressure is 0.01-0.03MPaG. After the secondary tail gas and washing water are reversely absorbed, the absorbed washing water is output from the lower part of the upper section of the absorption tower, and the tertiary tail gas (the composition and content of the tertiary tail gas is 90% nitrogen, 5% oxygen, and 5% water vapor) after absorption by the lower section of the absorption tower is output from the upper part of the upper section of the absorption tower and pressurized by a centrifugal compressor and returned to the lower part of the cleaning tower for recycling as cleaning gas. If the amount of tail gas coming out of the absorption tower is greater than the amount of cleaning gas required by the cleaning tower, the excess tail gas is discharged normally, and the discharged tail gas meets the requirements of the tail gas emission index, and a small amount of nitrogen is added regularly. A nitrogen analyzer is set on the tail gas pipeline entering the cleaning tower, and nitrogen is added according to the nitrogen content in the tail gas to ensure that the nitrogen gas volume fraction is above 90%.

[0057] Example 6

[0058] Based on a combined alkali tail gas treatment process shown in Example 5, this embodiment is a preferred embodiment, and the multi-stage absorption also includes acid absorption, and the temperature of the acid absorption is 25-45°C and the pressure is 0-0.1MPaG. The first-stage tail gas is successively absorbed by mother liquor, acid absorption, and washing water to obtain the third-stage tail gas. The optional acid in the acid absorption is an inorganic acid such as hydrochloric acid and sulfuric acid. After the mother liquor absorption, acid absorption is further adopted to further absorb the ammonia in the tail gas. Combined with the specific working conditions, if it is necessary to control the ammonia content in the third-stage tail gas below 100ppm, a multi-stage absorption method of mother liquor absorption, acid absorption, and washing water absorption can be adopted. If it is necessary to control the ammonia content in the third-stage tail gas below 1000ppm, a multi-stage absorption method of mother liquor absorption and washing water absorption can be adopted.

[0059] It should be noted that the above contents are further detailed descriptions of the present invention in combination with specific implementation methods, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions; the dimensional data of this embodiment does not necessarily limit the technical solution, but only shows one of the specific working conditions. For ordinary technicians in the technical field to which the present invention belongs, several simple improvements and modifications can be made without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A combined alkali production tail gas treatment process, characterized in that: The method comprises an alkali making process and an exhaust gas treatment process, wherein the alkali making process comprises an alkali making tower and a cleaning tower; the exhaust gas treatment process comprises an absorption operation and a compression operation, wherein the absorption operation is a multi-stage absorption, and the multi-stage absorption comprises mother liquor absorption and washing water absorption; the first-stage exhaust gas obtained by the alkali making tower and the cleaning tower is subjected to mother liquor absorption to obtain a second-stage exhaust gas, and the second-stage exhaust gas is subjected to washing water absorption to obtain a third-stage exhaust gas, and the third-stage exhaust gas is returned to the cleaning tower as a washing gas after being compressed.

2. The combined alkali production tail gas treatment process according to claim 1, characterized in that: The volume fraction of the inert gas in the cleaning gas is not less than 80%.

3. The combined alkali production tail gas treatment process according to claim 1, characterized in that: A portion of the tertiary tail gas is vented.

4. The combined alkali production tail gas treatment process according to claim 1, characterized in that: The secondary tail gas is subjected to gas-liquid separation and then absorbed by wash water.

5. The combined alkali production tail gas treatment process according to claim 1, characterized in that: The washing water outputted by the washing water absorption is cooled and then circulated for application.

6. The combined alkali production tail gas treatment process according to claim 1, characterized in that: The mother liquid absorption temperature is 25-45°C and the pressure is 0-0.1MPaG; And / or, the washing water absorption temperature is 25-45°C and the pressure is 0-0.1 MPaG.

7. A combined alkali production tail gas treatment device, characterized in that: It includes a cleaning tower, an alkali-making tower, an absorption tower and a compression device, wherein the absorption tower includes an upper absorption tower section and a lower absorption tower section; The side line liquid inlet of the cleaning tower is connected to the ammonia mother liquor supply pipeline, an air inlet for inputting cleaning gas is arranged at the bottom of the cleaning tower, and the bottom liquid outlet of the cleaning tower is connected to the liquid inlet of the alkali making tower; the bottom air inlet of the alkali making tower is connected to the raw gas pipeline, and a liquid outlet is arranged at the bottom of the alkali making tower, and the top exhaust port of the cleaning tower and the top exhaust port of the alkali making tower are connected to the air inlet of the lower section of the absorption tower through the tail gas pipeline; The liquid inlet of the lower section of the absorption tower is connected to the mother liquid supply pipeline, the liquid outlet of the lower section of the absorption tower is connected to the mother liquid outlet pipeline, the gas outlet of the lower section of the absorption tower is connected to the gas inlet of the upper section of the absorption tower, the liquid inlet of the upper section of the absorption tower is connected to the wash water supply pipeline, the liquid outlet of the upper section of the absorption tower is connected to the wash water outlet pipeline, and the gas outlet of the upper section of the absorption tower is connected to the bottom gas inlet of the cleaning tower through a compression device.

8. The combined alkali production tail gas treatment device according to claim 7, characterized in that: A venting branch is provided on the pipeline connecting the absorption tower and the compression equipment, and an inert gas supplementing branch is provided on the pipeline connecting the compression equipment and the cleaning tower.

9. The combined alkali production tail gas treatment device according to claim 7, characterized in that: The device also includes a gas-liquid separation device, the gas outlet of the lower section of the absorption tower is connected to the gas-liquid separation device, the gas outlet of the gas-liquid separation device is connected to the gas inlet of the upper section of the absorption tower, and the liquid outlet of the gas-liquid separation device is connected to the lower section of the absorption tower.

10. The combined alkali production tail gas treatment device according to claim 7, characterized in that: The device also includes a heat exchanger, the liquid outlet of the upper section of the absorption tower is connected to the inlet of the heat exchanger, and the outlet of the heat exchanger is connected to the liquid inlet of the upper section of the absorption tower.

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