Method for recycling baking soda carbonization tail gas

Abstract

The invention discloses a method for recycling baking soda carbonization tail gas, and belongs to the technical field related to industrial tail gas treatment, the baking soda carbonization tail gas is recycled, is subjected to heat exchange and gas-liquid separation and then is fed into a first-stage carbonization tower for a first-stage carbonization reaction, an obtained first-stage outlet alkali liquid enters a second-stage carbonization tower for a second-stage carbonization reaction, and a second-stage outlet alkali liquid enters a third-stage carbonization tower for a second-stage carbonization reaction; and carrying out centrifugal separation and drying on the secondary outlet alkali liquor to obtain the baking soda. The baking soda carbonization tail gas is recycled and then used for preparing the baking soda product, the utilization rate of carbon dioxide is increased, and carbon emission is reduced; the purposes of optimizing the particle size distribution of the baking soda product, reducing the product hardening, prolonging the equipment operation cycle and improving the carbonization reaction conversion rate are achieved by adjusting the liquid inlet temperature of the second-stage carbonization tower, reducing the gas-liquid ratio, improving the gas inlet pressure, improving the liquid level in the carbonization tower and the like.

Description

Technical Field

[0001] This invention belongs to the field of industrial exhaust gas treatment technology, specifically relating to a method for recovering and utilizing sodium bicarbonate carbonization exhaust gas. Background Technology

[0002] Currently, the main domestic production processes for sodium bicarbonate include the traditional synthesis method, the metathesis method, and the natural alkali method. Among them, the traditional synthesis method is the mainstream production process, and the specific operation steps are as follows: Carbon dioxide gas with a concentration of 38-40% is pressurized to 0.175-0.190 MPa and sent to a sieve plate carbonation tower, where it comes into countercurrent contact with sodium carbonate solution to undergo a carbonation reaction, producing sodium bicarbonate slurry. The sodium bicarbonate slurry is then thickened, centrifuged, and dried to obtain the sodium bicarbonate product. In this process, the carbonate concentration in the sodium carbonate alkali solution is 60 mmol / L, the temperature is 85-88℃, the temperature of the carbon dioxide gas is 35-40℃, the pressure at the bottom of the carbonation tower is 0.165-0.175 MPa, and the ratio of carbon dioxide gas inlet flow rate to sodium carbonate solution inlet flow rate is 45-55:1.

[0003] The advantages of this method are that the process flow is short, easy to operate and simple to react. The main drawbacks are: (1) The exhaust gas discharged from the carbonization tower contains 15%-20% carbon dioxide, and the effective utilization rate of carbon dioxide gas is only 50-62.5%; (2) Baking soda products are prone to caking during storage and transportation; (3) The carbonization tower sieve plate is prone to scaling and clogging of the sieve holes, resulting in a short carbonization tower operation cycle. It is necessary to boil the tower with high temperature steam regularly to eliminate the scaling inside the tower, which causes a waste of manpower and material resources. Summary of the Invention

[0004] The purpose of this invention is to provide a method for recovering and utilizing the carbonization tail gas of baking soda. This method recovers the carbonization tail gas of baking soda and uses it to prepare baking soda products, thereby improving the utilization rate of carbon dioxide gas, extending the operating cycle of the carbonization tower, and eliminating the problem of caking of baking soda products.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for recovering and utilizing the exhaust gas from sodium bicarbonate carbonization includes the following steps: (1) The carbonization tail gas of baking soda is heat exchanged and separated into gas and liquid to obtain carbon dioxide gas with a concentration of 15-20%; (2) Pressurize the carbon dioxide gas obtained in step (1) to 0.08-0.09 MPa and send it to the bottom of the first-stage carbonization tower. It will come into countercurrent contact with the sodium carbonate solution introduced at the top of the first-stage carbonization tower to carry out the carbonization reaction and obtain the first-stage alkaline solution. The carbon dioxide tail gas that did not participate in the reaction will be discharged into the air. (3) The primary alkaline solution is heated to 78-80℃ and sent to the top of the secondary carbonization tower. It is then contacted countercurrently with carbon dioxide gas of 38-40% introduced from the bottom of the secondary carbonization tower to carry out the carbonization reaction and obtain the secondary alkaline solution. The carbon dioxide gas that did not participate in the reaction is recovered as sodium bicarbonate carbonization tail gas to step (1). (4) The secondary alkaline solution is centrifuged and dried to obtain sodium bicarbonate.

[0006] Preferably, in step (1), the temperature of the carbon dioxide gas after heat exchange is 35-40°C, and the heat is sent to the sodium carbonate dissolving device for preheating to increase the temperature of the sodium carbonate solution.

[0007] Preferably, in step (2), the temperature of the sodium carbonate solution is 80-82℃; the carbonate concentration in the sodium carbonate solution is 50-60 t; and the bottom pressure of the primary carbonation tower is 0.06-0.07 MPa.

[0008] Preferably, in step (2), the ratio of the carbon dioxide gas intake to the sodium carbonate solution intake is 45-55:1.

[0009] Preferably, in step (3), the temperature of the carbon dioxide gas is 35-40℃, and the pressure at the bottom of the secondary carbonization tower is 0.175-0.185MPa.

[0010] Preferably, in step (3), the ratio of the carbon dioxide gas intake to the primary alkaline solution intake is 40-50:1.

[0011] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The method for recovering and utilizing sodium bicarbonate carbonization tail gas disclosed in this invention adopts a two-stage carbonization process. First, the sodium bicarbonate carbonization tail gas is sent to the first-stage carbonization tower to undergo a preliminary carbonization reaction with sodium carbonate solution to obtain the first-stage alkaline solution. Then, the first-stage alkaline solution is sent to the second-stage carbonization tower to undergo a second-stage carbonization reaction with high-concentration carbon dioxide gas to obtain the second-stage alkaline solution. Through the two-stage carbonization process, the utilization rate of carbon dioxide is improved and carbon emissions are reduced. Compared with the traditional sodium bicarbonate production process, the carbon dioxide concentration in the sodium bicarbonate carbonization tail gas is reduced from 15-20% to 10-15%, and the effective utilization rate of carbon dioxide is increased from 50-62.5% to 62.5-75%.

[0012] (2) The inventors found that the main reason why baking soda products are prone to caking during storage and transportation is that the particle size distribution of baking soda products prepared by the traditional synthesis method is unreasonable. The proportion of baking soda products with a particle size of 150 mesh or above is between 47-50%. The particle size of baking soda particles is too small. During the drying process, small particles are prone to agglomerate into balls, resulting in incomplete evaporation of water and poor drying effect. As a result, baking soda products are prone to caking after being squeezed during storage and transportation. When preparing baking soda products by the traditional synthesis method, the carbonization degree of sodium carbonate solution must first be increased so that a certain number of sodium bicarbonate crystal nuclei are formed in the reaction liquid in the upper part of the sieve plate carbonization tower. As the reaction liquid moves down, the carbonization degree of the reaction liquid is further increased, and sodium bicarbonate is precipitated. The sodium bicarbonate crystals then attach to the crystal nuclei, causing them to gradually grow and eventually form sodium bicarbonate particles. This invention first utilizes the carbonization tail gas of sodium bicarbonate to conduct a preliminary carbonization reaction with a sodium carbonate solution in a primary carbonization tower, increasing the carbonization degree of the reaction liquid and forming sodium bicarbonate crystal nuclei to obtain a primary alkali solution. The primary alkali solution containing the crystal nuclei is then sent to a secondary carbonization tower for a secondary carbonization reaction with high-concentration carbon dioxide gas, further increasing the carbonization degree of the reaction liquid and promoting crystal nuclei growth. Compared with traditional synthesis methods, this invention advances the crystal nuclei formation stage to the primary carbonization tower. Consequently, the growth space for the crystal nuclei in the secondary carbonization tower is greatly increased, resulting in larger sodium bicarbonate particles with a more reasonable particle size distribution, thereby improving the drying effect and reducing the problem of sodium bicarbonate product caking. The inventors discovered that the carbonization reaction temperature affects the growth rate of crystal nuclei. The inlet temperature of the secondary carbonization tower, i.e. the temperature of the first-stage alkali solution after heat exchange, should be controlled at 78-80℃. This temperature range can better control the concentrated distribution of crystallization particle size in the 120-150 mesh range, reduce the proportion of small particles, and optimize the particle size distribution of sodium bicarbonate products.

[0013] (3) The inventors discovered that the operating cycle of the carbonization tower is related to the particle size of sodium bicarbonate crystals in the reaction solution. In the traditional synthesis method, the growth space of sodium bicarbonate crystals is small during the carbonization reaction, resulting in small particle size and easy aggregation at the sieve holes to form scale. This invention advances the crystal nucleation stage to the first-stage carbonization tower, where the sodium bicarbonate crystals have a larger growth space and larger particle size, making them less likely to aggregate on the sieve plate and form scale during the carbonization reaction, thus extending the operating cycle of the carbonization tower. The process of this invention extends the operating cycle of the carbonization tower from 24 hours to 36-48 hours, producing better results.

[0014] (4) This invention includes a two-stage carbonization reaction. Compared with the sodium carbonate solution in the traditional synthesis method, the first-stage reaction liquid has a higher degree of carbonization, thus reducing the ratio of carbon dioxide gas inlet to first-stage alkaline liquid inlet in the second-stage carbonization tower (gas-liquid ratio). The gas-liquid ratio of the second-stage carbonization tower in this invention is controlled at 40-50:1, which is lower than the gas-liquid ratio index of the traditional synthesis method (45-55:1). Compared with the traditional synthesis method, the second-stage carbonization tower of this invention has a lower gas flow rate. The inventors found that during the carbonization reaction, there is a problem of liquid carryover in the carbonization tail gas, that is, unreacted carbon dioxide gas will carry some reaction liquid into the gas outlet pipe at the top of the carbonization tower, causing pipe scaling and material waste. The frequency of liquid carryover in the carbonization tail gas is related to the liquid level in the carbonization tower and the gas flow rate. The higher the gas flow rate or the higher the liquid level in the carbonization tower, the more frequent the liquid carryover in the carbonization tail gas. Therefore, to prevent liquid carryover in the carbonization tail gas, the liquid level inside the carbonization tower cannot be controlled too high. The bottom pressure is typically used to characterize the liquid level. In traditional synthesis methods, the bottom pressure of the carbonization tower should be controlled between 0.165-0.175 MPa. Since the gas flow rate of the secondary carbonization tower in this invention is lower than that of the traditional synthesis method, the liquid level in the secondary carbonization tower can be increased accordingly. The inventors found that the bottom pressure of the secondary carbonization tower should be controlled between 0.175-0.185 MPa, within which the problem of liquid carryover in the carbonization tail gas is rare. Increasing the liquid level in the secondary carbonization tower further increases the growth space for crystal nuclei within the tower and prolongs the carbonization reaction time. This not only optimizes the particle size distribution of the sodium bicarbonate product but also improves the conversion rate of the carbonization reaction, thereby increasing sodium bicarbonate production.

[0015] (5) Compared with the traditional synthesis method, the bottom pressure of the secondary carbonization tower is higher. In order to introduce carbon dioxide gas into the carbonization tower, the inlet pressure of carbon dioxide gas must be increased accordingly. The inlet pressure of the secondary carbonization tower of this invention should be controlled at 0.185-0.200MPa. Increasing the inlet pressure of the secondary carbonization tower has the following beneficial effects: First, it increases the driving force of the carbonization reaction, which is conducive to improving the conversion rate of the carbonization reaction; Second, the carbon dioxide gas is stirred more violently in the carbonization tower, which reduces the deposition of sodium bicarbonate particles on the sieve plate, reduces the scaling of the sieve plate, and further extends the operating cycle of the carbonization tower.

[0016] (6) The method for recovering and utilizing the carbonization tail gas of baking soda disclosed in this invention recovers the carbonization tail gas of baking soda and uses it to prepare baking soda products, which is beneficial to improve the utilization rate of carbon dioxide and reduce carbon emissions. By adjusting the liquid inlet temperature of the secondary carbonization tower, reducing the gas-liquid ratio, increasing the gas inlet pressure, and increasing the liquid level in the carbonization tower, the purpose of optimizing the particle size distribution of baking soda products, reducing product caking, extending the equipment operation cycle, and improving the conversion rate of carbonization reaction can be achieved.

[0017] (7) By recycling the carbonization tail gas of baking soda, this invention improves the carbon dioxide utilization rate, reduces the carbon dioxide content of the tail gas, extends the carbonization tower operation cycle, reduces the cost of tower shutdown and cleaning, improves product quality, increases output, and increases sales revenue. It not only has environmental benefits but also good economic benefits. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of an apparatus for a specific embodiment of the sodium bicarbonate tail gas recovery and utilization method of the present invention. Detailed Implementation

[0019] like Figure 1 As shown, the recovered baking soda carbonation tail gas undergoes heat recovery through a heat exchanger. The heat is then sent to a sodium carbonate dissolving device for preheating to increase the temperature of the sodium carbonate solution. To prevent the condensate in the cooled tail gas from corroding the subsequent blower, it needs to be separated by gas-liquid separation to remove moisture, resulting in carbon dioxide gas with a concentration of 15-20%. This carbon dioxide gas is then pressurized to 0.08-0.09 MPa by the blower and sent to the bottom of the primary carbonation tower, where it comes into countercurrent contact with the sodium carbonate solution introduced from the top of the primary carbonation tower to carry out a carbonation reaction, yielding the primary alkali solution. The unreacted carbon dioxide tail gas is discharged into the air. The primary alkali solution is then heated to 78-80°C and sent to the top of the secondary carbonation tower, where it comes into countercurrent contact with carbon dioxide gas with a concentration of 38-40% introduced from the bottom of the secondary carbonation tower to carry out a carbonation reaction, yielding the secondary alkali solution. The unreacted carbon dioxide gas is recovered and reused as baking soda carbonation tail gas. The secondary alkali solution is then centrifuged and dried to obtain the baking soda product.

[0020] When starting up the unit, sodium carbonate solution and high-concentration carbon dioxide gas are first introduced into the secondary carbonization tower to produce secondary alkali solution through carbonization reaction. After the operating conditions of the secondary carbonization tower are stable, the sodium bicarbonate tail gas discharged from the secondary carbonization tower is recovered, and after heat exchange, gas-liquid separation, and compression, it is sent to the primary carbonization tower to produce primary alkali solution through carbonization reaction with sodium carbonate solution. After the operating conditions of the primary carbonization tower are stable, the inlet liquid of the secondary carbonization tower is switched from sodium carbonate solution to primary alkali solution, the start-up is completed, and normal operation begins.

[0021]

[0022] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but this should not be construed as limiting the present invention. Example 1

[0023] (1) The carbonization tail gas of baking soda is heat recovered through heat exchange, and the heat is used for preheating of the sodium carbonate dissolution device. After gas-liquid separation, carbon dioxide gas with a concentration of 20% is obtained. (2) The carbon dioxide gas with a concentration of 20% obtained in step (1) is pressurized to 0.085 MPa and sent to the bottom of the first-stage carbonization tower to come into countercurrent contact with the sodium carbonate solution introduced at the top of the first-stage carbonization tower. The gas inlet temperature is 40℃, the liquid inlet temperature is 78℃, the pressure at the bottom of the tower is 0.07 MPa, and the gas-liquid ratio is 50:1. The reaction produces the first-stage alkaline solution, and the unreacted carbon dioxide tail gas is discharged from the top of the first-stage carbonization tower. (3) The primary alkaline solution obtained in step (2) is sent to the top of the secondary carbonization tower and comes into countercurrent contact with the carbon dioxide gas with a concentration of 40% introduced at the bottom of the secondary carbonization tower. The gas inlet temperature is 38°C, the liquid inlet temperature is 81°C, the pressure at the bottom of the tower is 0.19 MPa, and the gas-liquid ratio is 45:1. The reaction yields the secondary alkaline solution, and the unreacted carbon dioxide gas is recovered as sodium bicarbonate carbonization tail gas to step (1). (4) After centrifugation and drying of the secondary alkaline solution, the finished sodium bicarbonate is obtained. Example 2

[0024] (1) The carbonization tail gas of baking soda is heat recovered through heat exchange, and the heat is used for preheating of the sodium carbonate dissolution device. After gas-liquid separation, carbon dioxide gas with a concentration of 15% is obtained. (2) The carbon dioxide gas with a concentration of 15% obtained in step (1) is pressurized to 0.08 MPa and sent to the bottom of the first-stage carbonization tower to come into countercurrent contact with the sodium carbonate solution introduced at the top of the first-stage carbonization tower. The gas inlet temperature is 35℃, the liquid inlet temperature is 75℃, the pressure at the bottom of the tower is 0.06 MPa, and the gas-liquid ratio is 45:1. The reaction produces the first-stage alkaline solution, and the unreacted carbon dioxide tail gas is discharged from the top of the first-stage carbonization tower. (3) The primary alkaline solution obtained in step (2) is sent to the top of the secondary carbonization tower and comes into countercurrent contact with the carbon dioxide gas with a concentration of 40% introduced at the bottom of the secondary carbonization tower. The gas inlet temperature is 35°C, the liquid inlet temperature is 78°C, the pressure at the bottom of the tower is 0.18MPa, and the gas-liquid ratio is 40:1. The reaction yields the secondary alkaline solution, and the unreacted carbon dioxide gas is recovered as sodium bicarbonate carbonization tail gas to step (1). (4) After centrifugation and drying of the secondary alkaline solution, the finished sodium bicarbonate is obtained. Example 3

[0025] (1) The carbonization tail gas of baking soda is heat recovered through heat exchange, and the heat is used for preheating of the sodium carbonate dissolution device. After gas-liquid separation, carbon dioxide gas with a concentration of 20% is obtained. (2) The carbon dioxide gas with a concentration of 20% obtained in step (1) is pressurized to 0.09 MPa and fed into the bottom of the first-stage carbonization tower, where it comes into countercurrent contact with the sodium carbonate solution introduced from the top of the first-stage carbonization tower. The inlet gas temperature is 35℃, the inlet liquid temperature is 80℃, the bottom pressure is 0.08 MPa, and the inlet gas flow rate is 600 Nm³. 3 / h, gas-liquid ratio 55%, the reaction produces first-stage alkaline solution, and unreacted carbon dioxide tail gas is discharged from the top of the first-stage carbonization tower; (3) The primary alkali solution obtained in step (2) is sent to the top of the secondary carbonization tower and comes into countercurrent contact with the carbon dioxide gas with a concentration of 40% introduced at the bottom of the secondary carbonization tower. The gas inlet temperature is 40℃, the liquid inlet temperature is 83℃, the pressure at the bottom of the tower is 0.20MPa, and the gas-liquid ratio is 50:1. The reaction yields the secondary alkali solution. The unreacted carbon dioxide gas is recovered as sodium bicarbonate carbonization tail gas and sent to step (1). (4) After centrifugation and drying of the secondary alkaline solution, the finished sodium bicarbonate is obtained. Experimental Example 1

[0026] Table 3: Comparison of the proportion of particle size distribution range in products from Examples 1-3 to the traditional synthesis method.

[0027] As can be seen from the table, in Examples 1-3, the particle size of baking soda particles is concentrated at around 80-150 mesh, which reduces the proportion of small particles of 200 mesh and below, and improves the distribution concentration and uniformity of particle crystals. Experimental Example 2

[0028] The effects of Examples 1-3 were compared with those of the traditional synthesis method.

[0029]

[0030] Analysis of the above data shows that: In terms of carbon dioxide utilization, the carbon dioxide utilization rate in Examples 1, 2, and 3 increased from 50% to 62.3-62.5%, indicating that the new process can improve the utilization rate of carbon dioxide and reduce carbon emissions.

[0031] In terms of particle size distribution, the proportion of sodium bicarbonate products with a particle size of less than 150 mesh in Examples 1, 2, and 3 decreased from 55% to less than 29.9-32.5%. The reduction in the proportion of small particles reduced the problem of poor drying effect caused by the agglomeration of small particles and alleviated the caking problem of sodium bicarbonate prepared by traditional synthesis method during storage and transportation.

[0032] Based on the carbonization operation cycle and production increase data, in Examples 1, 2, and 3, the carbonization operation cycle was extended from 24 hours to 36-48 hours due to the improved crystallization effect. The extended carbonization operation cycle resulted in increased production, with an increase of about 7-10.2 tons per day, resulting in good economic benefits.

Claims

1. A method for recovering and utilizing the exhaust gas from sodium bicarbonate carbonization, characterized in that, Includes the following steps: (1) The carbonization tail gas of baking soda is heat exchanged and separated into gas and liquid to obtain carbon dioxide gas with a concentration of 15-20%; (2) Pressurize the carbon dioxide gas obtained in step (1) to 0.08-0.09 MPa and send it to the bottom of the first-stage carbonization tower to come into countercurrent contact with the sodium carbonate solution introduced at the top of the first-stage carbonization tower to carry out the carbonization reaction and obtain the first-stage alkali solution. (3) The primary alkaline solution is heated to 78-80℃ and sent to the top of the secondary carbonization tower. It is then contacted countercurrently with the carbon dioxide gas with a concentration of 38-40% introduced at the bottom of the secondary carbonization tower to carry out the carbonization reaction and obtain the secondary alkaline solution. The carbon dioxide gas that did not participate in the reaction is recovered and returned to step (1) as sodium bicarbonate carbonization tail gas. (4) The secondary alkaline solution is centrifuged and dried to obtain sodium bicarbonate.

2. The method for recovering and utilizing sodium bicarbonate carbonization tail gas according to claim 1, characterized in that, In step (1), the temperature of the carbon dioxide gas after heat exchange is 35-40℃.

3. The method for recovering and utilizing sodium bicarbonate carbonization tail gas according to claim 1, characterized in that, In step (2), the temperature of the sodium carbonate solution is 80-82℃; the carbonate concentration in the sodium carbonate solution is 50-60 t; the bottom pressure of the first-stage carbonation tower is 0.06-0.07 MPa; and the ratio of the carbon dioxide gas inlet flow rate to the sodium carbonate solution inlet flow rate is 45-55:

1.

4. The method for recovering and utilizing sodium bicarbonate carbonization tail gas according to claim 1, characterized in that, In step (3), the temperature of the carbon dioxide gas is 35-40℃, the pressure at the bottom of the secondary carbonization tower is 0.175-0.185MPa, and the ratio of the carbon dioxide gas inlet flow rate to the primary alkaline solution inlet flow rate is 40-50:1.

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