A lime-ammonia carbonate carbonation process for alkali production

Abstract

This invention belongs to the field of lime-ammonia carbonate process for alkali production technology, specifically relating to a carbonation process for alkali production using the lime-ammonia carbonate process. A pre-carbonation liquid is introduced into a carbonation tower, where it undergoes a carbonation reaction with intermediate and lower stage gases to produce alkali solution. Unreacted carbon dioxide gas enters a tail gas tower, where it undergoes a pre-carbonation reaction with a cleaning liquid to produce a pre-carbonation liquid. Unreacted carbonation tail gas enters a calcium removal tower, where it undergoes a calcium removal reaction with primary brine to produce calcium-removed brine. The calcium-removed brine undergoes clarification and sedimentation to obtain a supernatant. This supernatant is then sent to a tubular membrane filter to obtain low-turbidity purified brine. This process uses a tubular membrane to reduce the turbidity of the purified brine and decrease the amount of carbon dioxide required from the carbonation tail gas for calcium removal, thus improving the carbonation process.

Description

Technical Field

[0001] This invention belongs to the field of lime-ammonia carbonate alkali production technology, specifically relating to a lime-ammonia carbonate alkali carbonation process. Background Technology

[0002] The existing lime-ammonia carbonate process for producing alkali uses carbonation tail gas containing carbon dioxide and ammonia to remove calcium ions from brine to obtain refined brine. The specific steps are as follows:

[0003] The pre-carbonation liquid, intermediate gas, and lower gas are fed into the carbonation tower to produce an alkaline solution through a carbonation reaction. Unreacted carbon dioxide gas is discharged from the top of the carbonation tower and then fed into the tail gas tower, where it comes into countercurrent contact with the cleaning liquid to undergo a pre-carbonation reaction, producing a pre-carbonation liquid. The unreacted carbon dioxide gas, i.e., the carbonation tail gas, is discharged from the top of the tail gas tower and fed into the calcium removal tower to undergo a calcium removal reaction with the primary brine, producing calcium-removed brine. After clarification and sedimentation, a clear supernatant with a turbidity of 10-50 NTU is obtained, which is the refined brine. The turbidity of the refined brine is one of the important indicators for ensuring brine quality, mainly reflecting the degree of calcium ion removal. The turbidity control index for refined brine is below 10 NTU. When the turbidity of the refined brine exceeds the control index, the amount of residual calcium ion impurities in the refined brine increases. These calcium ions enter subsequent processes, which not only accelerates internal scaling in the equipment, affecting production stability, but also impacts the quality of the soda ash product.

[0004] In the lime-ammonia carbonate process for alkali production, the carbon dioxide in the intermediate and lower stage gases needs to be allocated and used in the carbonation and brine refining processes. First, it is supplied to the carbonation process for the alkali production reaction, and then to the brine refining process for calcium removal. In actual production, the following problems exist:

[0005] First, the turbidity of refined brine is affected by fluctuations in carbonization tail gas. When production fluctuates, such as during carbonization tower modification, shutdown of the decalcification tower, start-up or shutdown of the production system, production reduction and troubleshooting, or production load adjustment, the carbon dioxide content or volume of the carbonization tail gas fluctuates, causing changes in the operating conditions within the decalcification tower, which in turn leads to excessive turbidity in the refined brine. Therefore, during production fluctuations, it is necessary to appropriately increase the concentration of carbon dioxide in the carbonization tail gas to ensure the effective decalcification of the brine.

[0006] Secondly, under high-load production conditions, the demand for carbon dioxide in the brine refining process increases. In order to ensure the calcium removal effect of the brine and stabilize product quality, it is necessary to prioritize the carbon dioxide demand for calcium removal in the brine. Under these circumstances, it is necessary to sacrifice carbonization conditions to increase the carbon dioxide concentration in the carbonization tail gas, which in turn leads to insufficient gas volume in the carbonization process, affecting carbonization indicators and soda ash production.

[0007] Therefore, reducing the amount of carbon dioxide required for calcium removal in brine while ensuring its effectiveness in calcium removal, in order to improve the carbonization process, has become an urgent technical problem to be solved. Summary of the Invention

[0008] The purpose of this invention is to provide a lime-ammonia carbonate carbonation process for alkali production. This process uses a tubular membrane to reduce the turbidity of the refined brine and reduce the amount of carbon dioxide required in the carbonation tail gas for calcium removal from the brine, thereby improving the carbonation process.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for refining low-turbidity brine includes the following steps:

[0011] (1) After cooling the pre-carbonized liquid, it is introduced into the upper part of the carbonization tower. The middle section gas is introduced from the middle of the carbonization tower, and the lower section gas is introduced from the lower part of the carbonization tower. The pre-carbonized liquid, the middle section gas, and the lower section gas are in countercurrent contact to produce carbonization reaction, thus producing alkaline solution.

[0012] (2) Carbon dioxide gas that has not participated in the carbonization reaction is introduced from the top of the carbonization tower to the bottom of the tail gas tower and comes into countercurrent contact with the cleaning liquid introduced from the top of the tail gas tower to obtain pre-carbonized liquid. The pre-carbonized liquid is then returned to step (1).

[0013] (3) Carbonized tail gas is introduced from the top of the tail gas tower into the bottom of the calcium removal tower, and comes into countercurrent contact with the primary brine introduced from the top of the calcium removal tower to produce calcium removal brine.

[0014] (4) The calcium-free brine is clarified and settled to obtain the supernatant. The supernatant is pressurized and sent into a tubular membrane for filtration to obtain low-turbidity refined brine.

[0015] In step (1), the temperature of the pre-carbonized liquid after cooling is 33-35℃, the concentration of the middle section gas is 38-42%, the temperature of the middle section gas is 34-37℃, and the inlet pressure of the middle section gas is 0.257-0.26MPa; the concentration of the lower section gas is 90-93%, the temperature of the lower section gas is 28-32℃, and the inlet pressure of the lower section gas is 0.342-0.345MPa; the pressure at the bottom of the carbonization tower is 0.327-0.33MPa; and the ratio of the inlet volume of the middle section gas, the inlet volume of the lower section gas, and the inlet volume of the pre-carbonized liquid is 58-60:43-45:1.

[0016] Preferably, in step (2), the carbonization degree of the pre-carbonized liquid is 60-62tt.

[0017] Preferably, in step (3), the excess carbon dioxide content in the calcium-free saline solution is 30-35 ml / 20 ml.

[0018] Preferably, in step (4), the pressure of the supernatant after pressurization is 0.65-0.68 MPa, and the turbidity of the supernatant is 10-50 NTU; the turbidity of the refined brine is less than 8 NTU; more preferably, the turbidity of the refined brine is less than 1 NTU.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) The present invention provides a solution by clarifying and settling calcium-free brine to obtain a supernatant with a turbidity of 10-50 NTU. The supernatant is then sent to a tubular membrane filter to obtain a low-turbidity refined brine with a turbidity of 0.3-1 NTU. Compared with the prior art, the refined brine has a lower turbidity and is more stable, which reduces the formation of scale in subsequent processes and improves product quality.

[0021] (2) The inventors discovered that in the existing lime-ammonia carbonate process for alkali production, under high-load production conditions or during production fluctuations, in order to stabilize the turbidity of the refined brine, the operation of the carbonation tower must take into account the carbon dioxide requirements of both carbonation for alkali production and calcium removal from the brine. In order to ensure the carbon dioxide requirements of calcium removal from the brine, the carbon dioxide content in the carbonation tail gas must be controlled above 8%. In order to increase the carbon dioxide content in the carbonation tail gas, the carbonation tower adopts the "high tower temperature, low liquid level" operation method, controlling the temperature of the 20 cycles of the carbonation tower at 55-60℃ and the bottom pressure at 0.32-0.325 MPa (the bottom pressure of the carbonation tower is commonly used in the soda ash industry to represent the liquid level in the carbonation tower), so as to increase the pre-carbonation liquid. The release of carbon dioxide provides sufficient carbon dioxide for calcium removal from brine. The technical solution of this invention utilizes a tubular membrane to control the turbidity of the purified brine, which reduces the dependence of calcium removal from brine on carbonation tail gas and lowers the carbon dioxide content in the carbonation tail gas. Compared with the existing lime-ammonia carbonate process for alkali production, to reduce the carbon dioxide content in the carbonation tail gas, firstly, the temperature of the pre-carbonation liquid is reduced from 36-38℃ to 33-35℃; the temperature of the intermediate gas is reduced from 38-42℃ to 34-37℃, thereby lowering the temperature of the carbonation tower for 20 cycles to 50-53℃. This increases the solubility of carbon dioxide in the pre-carbonation liquid, reduces carbon dioxide release, improves carbon dioxide utilization, and ultimately increases the carbonation conversion rate.

[0022] (3) The inventors discovered that during the carbonization reaction, there is a problem of liquid carryover in the carbonization tower. That is, unreacted carbon dioxide gas in the carbonization tower will carry some pre-carbonized 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 tower is related to the liquid level in the carbonization tower and the amount of gas flow in the middle section. The greater the gas flow in the middle section or the higher the liquid level in the carbonization tower, the more frequent the liquid carryover in the carbonization tail gas. Therefore, in order to prevent liquid carryover in the carbonization tower, the liquid level in the carbonization tower cannot be controlled too high. The industry usually uses the bottom pressure index to characterize the liquid level in the tower. In the existing alkali production process, the bottom pressure of the carbonization tower should be controlled at 0.32-0.325 MPa. Compared with the existing alkali production process, the technical solution of this invention improves the carbonization conversion rate by increasing the solubility of carbon dioxide in the pre-carbonized liquid, thereby generating more gas in the lower section during the calcination process. In order to control the gas-liquid balance in the carbonization tower, the amount of gas in the middle section can be appropriately reduced. The ratio of gas flow rate, lower section gas flow rate, and liquid inlet flow rate is adjusted from 62-64:40-42:1 to 58-60:43-45:1. Due to the reduction in the gas flow rate in the middle section, the problem of liquid carryover in the carbonization tower is reduced. Therefore, the liquid level in the carbonization tower can be appropriately increased. This invention controls the bottom pressure of the carbonization tower at 0.327-0.330 MPa. The problem of liquid carryover in the carbonization tail gas will not occur when the bottom pressure is controlled within this range. By increasing the bottom pressure of the carbonization tower, the carbonization reaction space can be increased, further improving the conversion rate.

[0023] (4) The inventors discovered that the upper section of the carbonization tower is the region where sodium bicarbonate crystal nuclei are generated. The number of sodium bicarbonate crystal nuclei is mainly affected by the amount of gas entering the middle section. The larger the amount of gas entering the middle section, the higher the carbonization degree of the reaction liquid in the upper section of the carbonization tower, and the more crystal nuclei are generated. The lower section of the carbonization tower is the region where crystal nuclei grow. The size of sodium bicarbonate particles in the alkali solution is mainly affected by the gas in the lower section. Compared with the existing alkali production process, the gas entering the middle section of the present invention is small, and the number of sodium bicarbonate crystal nuclei generated is reduced accordingly. The gas entering the lower section is large, and the particle size of sodium bicarbonate particles in the alkali solution is increased accordingly. This optimizes the particle size distribution of sodium bicarbonate and reduces the settling time of sodium bicarbonate. In the subsequent filtration and light ash calcination processes, it can improve the filtration and washing effect, reduce the amount of washing water, reduce washing loss, reduce the water content of sodium bicarbonate material, and thus reduce the amount of steam used in light ash calcination.

[0024] (5) Compared with the existing alkali production process, the carbonization tower has a higher bottom pressure. In order to introduce the middle section gas and the lower section gas into the carbonization tower, the inlet pressure must be increased accordingly. The inlet pressure of the middle section gas in the carbonization tower of this invention should be controlled at 0.257-0.26 MPa, and the inlet pressure of the lower section gas should be controlled at 0.342-0.345 MPa. Increasing the inlet pressure 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 screen plate of the carbonization tower, reduces the scaling of the screen plate, and further extends the operating cycle of the carbonization tower.

[0025] (6) Compared with the existing alkali production process, the present invention has the advantage that the turbidity of the refined brine decreases as the tubular membrane filtration runs longer. Therefore, there is no need to manually sample and test the turbidity of the refined brine, which reduces labor intensity.

[0026] (7) The technical solution of the present invention can reduce the turbidity of refined brine to 0.3-1 NTU through tubular membrane filtration, which is far below the control index of 10 NTU for refined brine turbidity. According to the changes in production conditions, the operating rate of the tubular membrane can be adjusted to optimize the equipment operating scale and reduce production consumption while ensuring that the turbidity of refined brine is qualified. In addition, it reduces the demand for carbon dioxide for calcium removal of brine and ensures the demand for carbon dioxide in the carbonization process. It provides room for optimization and improvement of the carbonization process. By adjusting the operating parameters such as the temperature of pre-carbonization liquid, the temperature of middle section gas, the gas-liquid ratio, the liquid level of carbonization tower, the pressure of middle section gas, and the pressure of lower section gas, the technical effects of improving carbonization conversion rate, optimizing sodium bicarbonate crystal particle size distribution, reducing sodium bicarbonate moisture, improving washing effect, extending the carbonization tower operating cycle, and reducing calcination gas consumption can be achieved. Attached Figure Description

[0027] Figure 1 The present invention provides a process flow diagram of a specific embodiment of the lime-ammonia carbonate carbonation process for alkali production. Detailed Implementation

[0028] Terminology Explanation

[0029] Intermediate gas: Kiln gas containing 38-42% carbon dioxide, produced by calcining limestone in a lime kiln. The kiln gas is washed and electrostatic precipitator is used to remove impurities. Then, it is pressurized by a compressor to become intermediate gas and sent to the carbonization tower for carbonization reaction.

[0030] Lower stage gas: High-concentration carbon dioxide gas produced by calcining sodium bicarbonate in the calcining furnace, with a carbon dioxide content of about 90%. After being washed and pressurized by a compressor, it becomes the lower stage gas and is sent to the carbonization tower for carbonization reaction.

[0031] Cleaning solution: Refined brine is sent to the absorption tower to absorb ammonia to obtain ammonia brine. The ammonia brine is then sent to the cleaning and carbonization tower to clean the scale and become the cleaning solution. It is then sent to the tail gas tower to absorb carbon dioxide from the tail gas to obtain the pre-carbonization solution.

[0032] Primary brine: refers to the crude brine produced after initial dissolution, precipitation, and filtration of raw salt (such as NaCl). The crude brine still contains a small amount of calcium. 2+ Mg 2+ To remove impurities, lime milk and polyacrylamide flocculant are added to the crude brine to clarify and settle out magnesium ion impurities. The resulting supernatant is the primary brine. The primary brine is then sent to a calcium removal tower to react with carbonized tail gas to produce calcium-removed brine.

[0033] Tubular membranes are a type of pressure-driven, high-efficiency separation membrane technology. Their structure is tubular (typically made of polymers, ceramics, or metals), with pore sizes ranging from 0.01 to 0.1 micrometers. When a liquid flows across the membrane surface under pressure, water, small molecules, and dissolved ions permeate through the pores (becoming the permeate), while larger molecules (such as proteins, colloids, bacteria, and suspended particles) are retained because their size exceeds the pore size (becoming the concentrate).

[0034] Figure 1 The process flow of a specific embodiment of the lime-ammonia carbonate carbonation process for alkali production according to the present invention is shown. The pre-carbonation liquid is introduced into the upper part of the carbonation tower at 33-35°C, where it comes into countercurrent contact with the middle section gas introduced into the tower at a pressure of 0.257-0.26 MPa, a carbon dioxide concentration of 38-42%, and a temperature of 34-37°C. A carbonation reaction occurs, generating a crystalline liquid with fine sodium bicarbonate crystal nuclei. The crystalline liquid continues to flow downwards, coming into countercurrent contact with the lower section gas introduced into the tower at a pressure of 0.342-0.345 MPa, a carbon dioxide concentration of 90-93%, and a temperature of 28-32°C. Simultaneously, cooling water is turned on to lower the temperature, and the carbonation reaction continues, with the sodium bicarbonate crystal nuclei continuously growing to form sodium bicarbonate particles. The product is obtained at a temperature of 28-32°C. The alkali solution at ℃, the unreacted carbon dioxide is discharged from the top of the carbonization tower and introduced into the bottom of the tail gas tower, where it comes into countercurrent contact with the cleaning liquid introduced from the top of the tail gas tower to carry out a pre-carbonization reaction, producing a pre-carbonized liquid with a carbonization degree of 60-62tt. The pre-carbonized liquid is sent to the carbonization tower, and the carbon dioxide gas that did not participate in the pre-carbonization reaction, i.e., the carbonization tail gas, is discharged from the top of the tail gas tower and introduced into the bottom of the calcium removal tower, where it comes into countercurrent contact with the primary brine introduced from the top of the calcium removal tower to carry out a calcium removal reaction, producing a calcium-removed brine with an excess carbon dioxide content of 30-35ml / 20ml. The calcium-removed brine is sent to a clarification tank for clarification and sedimentation, resulting in a supernatant with a turbidity of 10-50NTU. The supernatant is pressurized and sent to a tubular membrane for filtration to obtain a low-turbidity purified brine in the range of 0.3-1NTU.

[0035] When the unit is started up, ammonia brine and intermediate gas are introduced into the carbonization tower and produced by countercurrent contact. The alkaline solution is then filtered, washed, centrifuged, and calcined to obtain sodium carbonate product and high-concentration carbon dioxide gas, i.e., lower gas. The unreacted carbon dioxide gas is introduced into the tail gas tower from the top of the carbonization tower and produced by countercurrent contact with ammonia brine to prepare pre-carbonized liquid. After the operating conditions stabilize, the inlet liquid of the carbonization tower is switched from ammonia brine to pre-carbonized liquid, and the lower gas is recovered into the carbonization tower. Start-up is then completed, and normal operation begins.

[0036]

[0037]

[0038] 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

[0039] (1) The pre-carbonized liquid is introduced into the upper part of the carbonization tower, the middle section gas is introduced into the middle part of the carbonization tower, and the lower section gas is introduced into the lower part of the carbonization tower. The pre-carbonized liquid comes into countercurrent contact with the middle section gas and the lower section gas to produce carbonization reaction and produce alkaline solution.

[0040] Specific operating parameters: pre-carbonization liquid temperature 33℃, mid-section gas concentration 38%, mid-section gas temperature 34℃, mid-section gas inlet pressure 0.257MPa; lower-section gas concentration 90%, lower-section gas temperature 28℃, lower-section gas inlet pressure 0.342MPa; carbonization tower bottom pressure 0.327MPa; carbonization tower 20-cycle temperature 50℃; carbonization tower mid-section temperature 60℃; ratio of mid-section gas inlet flow rate, lower-section gas inlet flow rate to pre-carbonization liquid inlet flow rate 58:43:1; alkali outlet temperature 28℃.

[0041] (2) The carbon dioxide gas that did not participate in the carbonization reaction was discharged from the top of the carbonization tower and introduced into the bottom of the tail gas tower. It came into countercurrent contact with the cleaning liquid introduced into the upper part of the tail gas tower and a pre-carbonization reaction was carried out to obtain a pre-carbonized liquid with a concentration of 60tt. The pre-carbonized liquid was sent to the carbonization tower.

[0042] (3) The carbon dioxide gas that did not participate in the pre-carbonization reaction, i.e. the carbonization tail gas, was discharged from the top of the tail gas tower and passed into the bottom of the calcium removal tower. It came into countercurrent contact with the primary brine passed into the top of the calcium removal tower and a calcium removal reaction was carried out to produce calcium removal brine with an excess carbon dioxide concentration of 30 ml / 20 ml.

[0043] (4) The calcium-free brine is sent to a clarification device for clarification and sedimentation to obtain a supernatant. The supernatant is pressurized to 0.65 MPa and then sent to a tubular membrane for filtration to obtain a low-turbidity purified brine of 0.3 NTU. Example 2

[0044] (1) The pre-carbonized liquid is introduced into the upper part of the carbonization tower, the middle section gas is introduced into the middle part of the carbonization tower, and the lower section gas is introduced into the lower part of the carbonization tower. The pre-carbonized liquid comes into countercurrent contact with the middle section gas and the lower section gas to produce carbonization reaction and produce alkaline solution.

[0045] Specific operating parameters: pre-carbonization liquid temperature 34℃, mid-section gas concentration 40%, mid-section gas temperature 35℃, mid-section gas inlet pressure 0.258MPa; lower-section gas concentration 91.5%, lower-section gas temperature 30℃, lower-section gas inlet pressure 0.343MPa; carbonization tower bottom pressure 0.328MPa; carbonization tower 20-cycle temperature 52℃; carbonization tower mid-section temperature 62℃; ratio of mid-section gas inlet flow rate, lower-section gas inlet flow rate to pre-carbonization liquid inlet flow rate 59:44:1; alkali outlet temperature 30℃.

[0046] (2) The carbon dioxide gas that did not participate in the carbonization reaction was discharged from the top of the carbonization tower and introduced into the bottom of the tail gas tower. It came into countercurrent contact with the cleaning liquid introduced into the upper part of the tail gas tower and a pre-carbonization reaction was carried out to obtain a pre-carbonized liquid with a concentration of 61tt. The pre-carbonized liquid was sent to the carbonization tower.

[0047] (3) The carbon dioxide gas that did not participate in the pre-carbonization reaction, i.e. the carbonization tail gas, was discharged from the top of the tail gas tower and passed into the bottom of the calcium removal tower. It came into countercurrent contact with the primary brine passed into the top of the calcium removal tower and a calcium removal reaction was carried out to produce calcium removal brine with an excess carbon dioxide concentration of 33 ml / 20 ml.

[0048] (4) The calcium-free brine is sent to a clarification device for clarification and sedimentation to obtain a supernatant. The supernatant is pressurized to 0.68 MPa and then sent to a tubular membrane for filtration to obtain a low-turbidity purified brine of 0.8 NTU. Example 3

[0049] (1) The pre-carbonized liquid is introduced into the upper part of the carbonization tower, the middle section gas is introduced into the middle part of the carbonization tower, and the lower section gas is introduced into the lower part of the carbonization tower. The pre-carbonized liquid comes into countercurrent contact with the middle section gas and the lower section gas to produce carbonization reaction and produce alkaline solution.

[0050] Specific operating parameters: pre-carbonization liquid temperature 35℃, mid-section gas concentration 42%, mid-section gas temperature 37℃, mid-section gas inlet pressure 0.26MPa; lower-section gas concentration 93%, lower-section gas temperature 32℃, lower-section gas inlet pressure 0.345MPa; carbonization tower bottom pressure 0.33MPa; carbonization tower 20-cycle temperature 53℃; carbonization tower mid-section temperature 63℃; ratio of mid-section gas inlet flow rate, lower-section gas inlet flow rate to pre-carbonization liquid inlet flow rate 60:45:1; alkali outlet temperature 32℃.

[0051] (2) The carbon dioxide gas that did not participate in the carbonization reaction was discharged from the top of the carbonization tower and introduced into the bottom of the tail gas tower. It came into countercurrent contact with the cleaning liquid introduced into the upper part of the tail gas tower and a pre-carbonization reaction was carried out to obtain a pre-carbonized liquid with a concentration of 62tt. The pre-carbonized liquid was sent to the carbonization tower.

[0052] (3) The carbon dioxide gas that did not participate in the pre-carbonization reaction, i.e. the carbonization tail gas, was discharged from the top of the tail gas tower and passed into the bottom of the calcium removal tower. It came into countercurrent contact with the primary brine passed into the top of the calcium removal tower and a calcium removal reaction was carried out to produce calcium removal brine with an excess carbon dioxide concentration of 35 ml / 20 ml.

[0053] (4) The calcium-free brine is sent to a clarification device for clarification and sedimentation to obtain a supernatant. The supernatant is pressurized to 0.66 MPa and then sent to a tubular membrane for filtration to obtain 1 NTU of low-turbidity purified brine.

[0054]

[0055] As can be seen from the data in the table above, the technical solution of this invention, compared with the prior art, greatly reduces the turbidity of refined brine by adding a tubular membrane. On this basis, by adjusting the operating parameters such as the temperature of the pre-carbonation liquid, the temperature of the middle section gas, the gas-liquid ratio, the liquid level of the carbonation tower, the pressure of the middle section gas, and the pressure of the lower section gas, several beneficial effects are achieved, such as increased carbonation conversion rate, increased sodium bicarbonate crystal particle size, reduced moisture content of heavy alkali, reduced filtration loss, and reduced light ash steam consumption.

Claims

1. A lime-ammonia carbonate carbonation process for alkali production, characterized in that, Includes the following steps: (1) After cooling the pre-carbonized liquid, it is introduced into the upper part of the carbonization tower. The middle section gas is introduced from the middle of the carbonization tower, and the lower section gas is introduced from the lower part of the carbonization tower. The pre-carbonized liquid, the middle section gas, and the lower section gas are in countercurrent contact to produce carbonization reaction, thus producing alkaline solution. (2) Carbon dioxide gas that has not participated in the carbonization reaction is introduced from the top of the carbonization tower to the bottom of the tail gas tower and comes into countercurrent contact with the cleaning liquid introduced from the top of the tail gas tower to obtain pre-carbonized liquid. The pre-carbonized liquid is then returned to step (1). (3) Carbonized tail gas is introduced from the top of the tail gas tower into the bottom of the calcium removal tower, and comes into countercurrent contact with the primary brine introduced from the top of the calcium removal tower to produce calcium removal brine. (4) The calcium-free brine is clarified and settled to obtain the supernatant. The supernatant is pressurized and sent into a tubular membrane for filtration to obtain a low-turbidity refined brine. The turbidity of the refined brine is less than 1 NTU. In step (1), the temperature of the pre-carbonized liquid after cooling is 33-35℃, the concentration of the middle section gas is 38-42%, the temperature of the middle section gas is 34-37℃, and the inlet pressure of the middle section gas is 0.257-0.26MPa; the concentration of the lower section gas is 90-93%, the temperature of the lower section gas is 28-32℃, and the inlet pressure of the lower section gas is 0.342-0.345MPa; the pressure at the bottom of the carbonization tower is 0.327-0.33MPa; and the ratio of the inlet volume of the middle section gas, the inlet volume of the lower section gas, and the inlet volume of the pre-carbonized liquid is 58-60:43-45:

1.

2. The lime-ammonia carbonate carbonation process for alkali production according to claim 1, characterized in that, In step (2), the carbonization degree of the pre-carbonized liquid is 60-62tt.

3. The lime-ammonia carbonate carbonation process for alkali production according to claim 1, characterized in that, In step (3), the excess carbon dioxide content of the calcium salt solution is 30-35 ml / 20 ml.

4. The lime-ammonia carbonate carbonation process for alkali production according to claim 1, characterized in that, In step (4), the pressure of the supernatant after pressurization is 0.65-0.68 MPa, and the turbidity of the supernatant is 10-50 NTU; the turbidity of the refined brine is less than 8 NTU.

Images