CN114247172A - Method and device for removing water solution volatile impurities and preparing crystallized product by air circulation gas stripping concentration - Google Patents
Method and device for removing water solution volatile impurities and preparing crystallized product by air circulation gas stripping concentration Download PDFInfo
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- CN114247172A CN114247172A CN202011006416.6A CN202011006416A CN114247172A CN 114247172 A CN114247172 A CN 114247172A CN 202011006416 A CN202011006416 A CN 202011006416A CN 114247172 A CN114247172 A CN 114247172A
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
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- B01D9/0018—Evaporation of components of the mixture to be separated
- B01D9/0027—Evaporation of components of the mixture to be separated by means of conveying fluid, e.g. spray-crystallisation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/34—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping with one or more auxiliary substances
- B01D3/38—Steam distillation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D9/005—Selection of auxiliary, e.g. for control of crystallisation nuclei, of crystal growth, of adherence to walls; Arrangements for introduction thereof
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- B—PERFORMING OPERATIONS; TRANSPORTING
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Abstract
A method and apparatus for removing the volatile impurities from aqueous solution and preparing crystallized product by air circulation stripping concentration features that a group of vertical corrugated plate arrays and their gas-liquid distribution structures connected to upper and lower parts are used to form gas-liquid countercurrent heat and mass transfer on the dual-side falling-film surfaces of corrugated plates, so concentrating the aqueous solution containing water (not less than 40%) and volatile impurities (not more than 3.0%) to water content (less than 35%) and volatile impurities (less than 0.1%), preparing crystal slurry from the aqueous solution containing water (not less than 15%) whose ratio of crystal particles to solute (greater than 40%), and passing through pressure-stabilizing tower and constant-pressure water-sealed tank to form a constant-mass-flow air closed circulation system. The invention has the advantages of energy saving, closed cycle and no discharge, for example, the energy consumption for preparing 400kg of silver nitrate crystal from 82.34% silver nitrate aqueous solution is not more than 5 kW.h, and the energy consumption for air cycle for defluorinating 1000kg of wet-process phosphoric acid solution containing 2.0% fluorine is not more than 100 kW.h.
Description
Technical Field
The invention relates to inorganic chemical industry, resource and energy recycling, energy conservation and emission reduction, in particular to the technical field of removing volatile impurities in aqueous solution and crystallizing and refining by adopting air closed circulation to strengthen heat and mass transfer.
Background
Impurity separation is an essential step in the preparation of high purity soluble products from aqueous solutions. The product may be separated from non-volatile impurities by removing the gas phase components of the aqueous solution (stripping) to separate volatile impurities, or by extracting crystals from the aqueous solution. For example, the phosphoric acid (wet-process phosphoric acid) aqueous solution obtained by wet processing of phosphate ore contains various impurities contained in ore, and fluorine and silicon in the impurities easily escape from the phosphoric acid liquid phase with higher concentration to the gas phase, so that the gas stripping is a method for purifying the wet-process phosphoric acid by defluorination and desilication. Hydrometallurgy often employs crystallization from an ore breakdown solution to extract the product, so supersaturated solution crystallization is one method of separating the product from non-volatile impurities in the solution. Both methods rely on heat and mass transfer in aqueous solution and between gas-liquid and solid-liquid phase interfaces, and no other chemical additives are needed. However, the high-concentration and high-viscosity solution not only has larger transfer resistance in a liquid phase, but also has large reduction range of the vapor pressure of the solution and weak mass transfer driving force of a gas-liquid interface, thereby limiting the industrial application of the gas stripping and crystallization technology of the high-concentration and high-viscosity solution. For example, the viscosity of the solution increases with the concentration to increase the magnitude of the concentration, which hinders the escape of fluorine, so that the gas stripping and the fluorine removal can be completed for several hours (futures, etc., research on air stripping and fluorine removal of concentrated wet-process phosphoric acid, phosphate fertilizer and compound fertilizer, 2013, 28 (4): 24-25). The concentration and crystallization of the high-viscosity solution are similar, for example, multiple recrystallization and impurity removal are needed for preparing high-purity silver nitrate, and the crystallization process is controlled by mass transfer and needs to last for about 10 hours under the freezing condition of-5 ℃ (Roobao et al. silver nitrate crystal preparation process, electrical material, 2014 03: 16-18). The scientific principle breaking through the technical bottleneck of impurity removal and refining of high-concentration and high-viscosity solutions is to strengthen the mass transfer kinetic conditions of the solutions, and the technical route is as follows: 1) the heat and mass transfer specific surface area of the solution is improved; 2) the heat and mass transfer distance is shortened; 3) the driving force of heat transfer and mass transfer is improved; 4) the resistance in the heat and mass transfer process is reduced. The invention discloses a method and a device for removing volatile impurities in aqueous solution and preparing a crystallized product by air circulation stripping, which take closed circulation air as a carrier and distribute water on the surfaces of corrugated plates which regularly change in the vertical directionThe solution falling film directly contacts with the countercurrent heat and mass transfer to promote the volatile impurities to be wrapped by the vapor generated by the evaporation of the solution to enter a gas phase, thereby realizing the concentration of the solution and simultaneously removing the volatile impurities by gas stripping. The concentration and gas stripping processes are carried out at a gas-liquid interface, the mass transfer distance in a liquid phase is less than 1mm, the surface of a liquid film is continuously updated and strengthened, the mass transfer distance in a gas phase is less than 3mm, the gas-liquid interface is turbulently mixed, and the mass transfer area of the gas-liquid interface, expanded on the surface of a corrugated plate, of a unit volume solution is more than 1000 m2/m3High heat and mass transfer efficiency, and high unit volume production intensity (55% of H) in 1 ton3PO4) For example, the wet-process phosphoric acid air circulation air stripping defluorination requires that the air circulation energy consumption is not more than 3 kW.h, and the concentration of the phosphoric acid solution after concentration defluorination is improved to 70 percent (H)3PO4) The fluorine content is not more than 0.05 percent (F). The method and apparatus are also suitable for crystallization at a concentration of 82.3% (AgNO) of 800kg3) For example, the silver nitrate solution is subjected to gas stripping, concentration, cooling and crystallization on the surface of a corrugated plate, and 400kg of silver nitrate (AgNO) is extracted3) The air circulation energy consumption required by crystallization is not more than 5 kW.h. The process of air circulation gas stripping concentration for removing water solution volatile impurities and preparing crystals is completed in a closed system, and the method is environment-friendly and has no emission.
Disclosure of Invention
The invention discloses a method and a device for removing water solution volatile impurities and preparing a crystallized product by air circulation gas stripping concentration. The method is suitable for air circulation concentration and air stripping of the aqueous solution with the water content not lower than 40 percent (mass concentration, the same below) and the volatile impurity content not higher than 3.0 percent, the volatile impurity is removed to ensure that the concentration of the volatile impurity is lower than 0.1 percent, and simultaneously the water content of the concentrated solution is not higher than 35 percent; it is also suitable for preparing crystallized products by gas stripping and concentration of aqueous solution with the water content of not less than 15 percent. The viscosity of the water solution is more than 5 times larger than that of water at the same temperature, and the vapor pressure of the solution is more than 30 percent lower than the saturated vapor pressure of water at the same temperature. Aiming at the characteristics of the aqueous solution, the method has the common characteristic that the aqueous solution is sprayed from the upper part of a corrugated plate array which is vertically arranged and has a rectangular cross section, so that the wave-fold change of the aqueous solution in the vertical direction is realizedThe corrugated plates form wavy falling film flow on the surfaces of the two sides, the thickness of the film is not more than 1mm, the distance between the corrugated plates is 4-8 mm, and the ratio of the height of the vertical plate to the width of the horizontal plate is not less than 1.2; circulating air subjected to compression-expansion dehydration is uniformly distributed below the corrugated plate array, flows through a flow channel between the corrugated plates from bottom to top, has the flow rate of not less than 2m/s, is in direct contact with an aqueous solution flowing in a falling film on the surface of the corrugated plates for countercurrent heat and mass transfer, and enters a gas phase together with water vapor generated by evaporation of the solution and entrained volatile impurities, so that solution concentration is realized and the volatile impurities are removed; the water solution flowing in the falling film on the surface of the corrugated plate is directly contacted with circulating air for adiabatic gasification, the temperature of the solution is reduced while the concentration of the solution is increased, and crystal nuclei can be formed in the falling film when the solution reaches the crystallization state point; circulating air rises, flows, transfers heat and mass, takes away water vapor evaporated by solution and volatile impurities contained in the water vapor, the temperature and the moisture content of the gas continuously rise, the flow rate of the gas entering a gas-liquid separation space above the corrugated plate array is not more than 2m/s, the gas is compressed to the pressure of not more than 200kPa (absolute pressure) after the required subsequent purification steps of absorption, water washing, demisting and the like, the temperature is reduced to not more than 40 ℃ by water washing again, and the demisting is carried out, then the gas is adiabatically expanded to the temperature of not less than 1 ℃ by an expander, and the pressure is not less than the local atmospheric pressurep oAnd after the condensed liquid separated by expansion is separated and demisted, the condensed liquid is guided to the lower part of the corrugated plate array, thereby forming air circulation. The non-condensable gas accumulated in the air circulation loop in the air stripping process is automatically discharged through the air pressure-stabilizing washing tower and the constant-pressure liquid seal tank, and the overflow port of the constant-pressure liquid seal tank is arranged at a position higher than the lower edge of the opening of the air pressure-stabilizing washing tower immersed in the tankHWhere the air pressure-stabilizing washing tower design pressurep i(absolute pressure), once the difference between the actual pressure in the column and the local atmospheric pressure exceeds the design value Δp= (p i−p o) = ρgH(in the formulaρIs the density of the water and is,gis gravity acceleration), the overpressure air passes over the lower edge of the opening of the air pressure stabilizing washing tower immersed in the constant-pressure liquid-sealed tank and bubbles through the openingHThe high water seal is released through a liquid level which is communicated with the atmosphere. After air is circularly stripped by the corrugated plate array, the temperature of wet gas is 40-100 ℃, and water vapor is contained in the wet gasThe partial pressure should not be greater than the vapor pressure of the aqueous solution at the corresponding temperature, thereby determining the amount of air circulation and the ability of the gas stripping to concentrate and remove volatile impurities. The volatile impurities are absorbed by pure water to form a recoverable impurity solution having a temperature of no more than 65 ℃ and a mole fraction of impurities in a vapor phase in equilibrium with the solution of no more than 0.03%.
As shown in figure 1, the air circulation method and device for stripping and concentrating crystallized products from high-concentration and high-viscosity aqueous solution, wherein a stripping and concentrating crystallizer 1 is composed of a group of vertical corrugated plate arrays with equilateral rectangular cross sections, a circular cross section crystal growing tank with the lower part connected by a square-to-circle shape, and a circular cross section gas-liquid separation cylinder with the upper part connected by a square-to-circle shape; spraying an aqueous solution with the temperature of 60-100 ℃ and the water content of not less than 15% by using spray heads arranged in a gas-liquid separation cylinder, uniformly distributing the aqueous solution on the cross section of the corrugated plate array, forming falling film flows with the film thickness of not more than 1mm on the surfaces of two sides of each corrugated plate, and enabling the solution flow to be 100-260 kg/h.m calculated according to the width of the corrugated plate in the horizontal direction; after the circulating air output from the expander of the air compression-expansion unit 2 is subjected to gas-liquid separation, demisting and dehumidification, the pressure is 1.0-2.0 kPa higher than the atmospheric pressure, the temperature is not lower than 1 ℃, the partial pressure of contained water vapor is lower than the vapor pressure of a solution in a crystal growing tank of the gas stripping concentration crystallizer 1, the circulating air is uniformly distributed in air channels between every two adjacent corrugated plates of the corrugated plate array from bottom to top through an air distribution pipe arranged in the crystal growing tank, and the flow rate is 2-15 m/s; the method comprises the following steps of (1) carrying out gas-liquid countercurrent heat and mass transfer in a corrugated plate array, carrying out adiabatic evaporation, cooling and thickening on a falling film solution, enabling the falling film solution to have a concentration higher than the solubility at a temperature of more than 2% and crystal nuclei separated out when the falling film solution flows into a crystal growing tank below, staying for 30-60 minutes in the crystal growing tank at a stirring rotating speed of 20-60 revolutions per minute to finish a crystallization process, wherein the ratio of the amount of crystal particles in crystal slurry output from the bottom of the tank to the total amount of solute is more than 40%; when air rises to pass through the corrugated plate array and the solution for countercurrent heat and mass transfer, temperature rise and humidification, and flows into the gas-liquid separation barrel above, the air temperature is 40-80 ℃, the moisture content is 25-150 g/kg-a, the pressure is higher than the local atmospheric pressure by more than 0.5kPa, the air enters the upright air pressure-stabilizing washing tower 3 through pipeline connection, and after the air is cooled and dehumidified by countercurrent heat and mass flow of washing water which is sprayed from the top of the tower and has the temperature lower than 45 ℃, the air is subjected to countercurrent heat and mass transfer, and the mass flow is constantThe fixed circulating air is sent out from the top of the tower, the gas phase non-condensable gas is accumulated in the gas stripping process to increase the air pressure of the closed cycle, and once the pressure in the air pressure-stabilizing washing tower exceeds the design valuep iAnd the difference between the measured pressure and the local atmospheric pressure exceeds the design value deltap= (p i−p o) = ρ gHThe overpressure air can pass through the opening of the lower edge of the tower immersed in the constant-pressure water-sealed tank 4 and bubble outwardsHThe high water seal layer and the escaped liquid level are released through a pipeline communicated with the atmosphere, so that the pressure stabilizing washing tower is restored to the design pressure; circulating air with constant mass flow is defoamed by a foam catcher 5, then is sucked into a compressor inlet of an air compression-expansion unit 2, is pressurized to be not more than 200kPa, is subjected to pressurized water washing by an air secondary washer 6 to be cooled, dehumidified and demisted again, has the gas temperature of not higher than 40 ℃, enters an expander of the compression-expansion unit 2, is subjected to adiabatic expansion, temperature reduction, dehumidification and demisting, and is circularly conveyed to a gas distribution pipe in a crystal growing tank of a gas stripping concentration crystallizer 1 for recycling after being dehumidified; the mechanical work generated by the air adiabatic expansion, temperature reduction and dehumidification is directly used for driving the air compressor, and the input power consumption is reduced.
As shown in figure 2, the air circulation air stripping concentration water solution and volatile impurity removal method and device, the air stripping concentration purifier 8 by a group of upright, equilateral rectangular cross section corrugated plate array and its lower part by the square to round the circular cross section connected by the fluid reservoir and the upper part by the square to round the circular cross section gas-liquid separation cylinder to form, the temperature of 80~120 ℃, the water content is not less than 25% circulating concentrate from the top to the bottom of the spray head arranged in the gas-liquid separation cylinder evenly spray on the corrugated plate array cross section, in each corrugated plate two side surface formed film thickness is not more than 1mm of the falling film flow, according to the horizontal corrugated plate width calculation solution flow is 800~2000 kg/h.m; the air pressure output from the expander of the air compression-expansion unit 2 and subjected to gas-liquid separation and demisting is 1.0-3.0 kPa higher than the local atmospheric pressure, the temperature is not lower than 1 ℃, the partial pressure of contained water vapor is lower than the vapor pressure of the concentrated and purified solution in the liquid receiving tank, the air distribution pipe arranged in the liquid receiving tank is uniformly distributed in the air channel between every two adjacent corrugated plates of the corrugated plate array from bottom to top, and the flow velocity is10-20 m/s; the method comprises the steps of performing gas-liquid countercurrent heat and mass transfer in a corrugated plate array, enabling a falling film solution to flow into a liquid receiving tank below the corrugated plate array after adiabatic evaporation, gas stripping and impurity removal, reducing the water content by more than 10%, enabling the content of volatile impurities to be not more than 0.1% and the temperature to be not more than 60 ℃, enabling the solution passing through the liquid receiving tank (the liquid level in the tank is not less than 2 m) to be used as concentrated and purified liquid to be conveyed to a post process from a tank bottom connecting pipe, enabling the rest solution to be pressurized through a solution circulating pump 9, mixing with a supplemented and added raw material solution (the water content is not less than 40%, the content of volatile impurities is not more than 3.0% and the temperature is not less than 20 ℃), enabling the rest solution to enter a shell-and tube heater 10 from the bottom for convection heat transfer, condensing and heating to 80-120 ℃ by steam outside the tube, and enabling the solution to enter gas stripping and concentrating solution for circulation. Circulating air rises through a corrugated plate array, flows into an upper gas-liquid separation cylinder after countercurrent heat and mass transfer, temperature rise and humidification with a falling film solution, enters a volatile impurity absorption tower 11 through a connecting pipeline after the temperature is 60-100 ℃, the moisture content is 145-650 g/kg-a and the pressure is higher than the local atmospheric pressure by more than 1.0kPa, flows downwards with absorption liquid with the temperature lower than 60 ℃ sprayed from the top of the tower, flows in heat and mass transfer, cools and dehumidifies, enters an upright air pressure stabilizing washing tower 12 with the designed pressure higher than the local atmospheric pressure by more than 0.5kPa through the connecting pipeline, and is sent out from the top of the tower after countercurrent heat and mass transfer with washing water with the temperature lower than 40 ℃ sprayed from the top of the tower, cools to the temperature lower than 45 ℃, and the circulating air with constant mass flow rate is sent out from the top of the tower, and the air accumulated and increased in the air stripping process bubbles outwards through the opening along the lower edge of the washing tower immersed in a constant pressure water seal tank 13HThe high water seal layer escapes from the liquid level and is guided by the pipeline to be released to the atmosphere, so that the pressure stabilizing washing tower is restored to the design pressure; demisting the circulating air output from the top of the 12 washing tower by a mist eliminator 5, sucking the demisted circulating air into a compressor inlet of an air compression-expansion unit 2, pressurizing to no more than 200kPa, then washing with water again by a secondary air scrubber 6 for cooling, dehumidifying and demisting, introducing the gas with the temperature not higher than 35 ℃ into an expander of the compression-expansion unit 2, carrying out adiabatic expansion, cooling, condensation and dehumidification, separating condensate, demisting, and conveying the demisted circulating air to an air distribution pipe of a gas stripping concentration purifier 8 for recycling; mechanical work generated by air adiabatic expansion, temperature reduction and dehumidification is directly used for driving an air compressor, and input power consumption is reduced; enter the absorption of volatile impuritiesThe absorption liquid in the tower 11 is lifted to a position 6-8 m higher than the liquid level of the absorption liquid in the tower through a section of vertical ascending pipe from a tower bottom connecting pipeline, then enters a flash evaporator 14, is subjected to flash evaporation under the pressure of 10-15 kPa (absolute pressure), flows out from the bottom of a vertical descending central pipe immersed 1.0-2.0 m below the liquid level of a liquid seal tank 17, wherein no more than one tenth of the absorption liquid is output as an impurity solution recovery product, and the rest absorption liquid is conveyed into an impurity absorption tower 11 through an impurity absorption liquid circulating pump 16 for circulation; the ratio of the mass of the low-pressure steam generated by the flash evaporator 14 to the mass of the stripping steam of the stripping concentration purifier 8 is 0.25-0.55, and the flash-evaporated low-pressure steam passes through the water injector 15 and is sprayed and condensed by circulating water with the temperature lower than 40 ℃ and is carried to a cooling water system.
Drawings
FIGS. 1 and 2 are schematic diagrams of a method and a device for removing aqueous solution volatile impurities and preparing a crystallized product by air circulation stripping concentration.
In the attached figure 1: 1-gas stripping concentration crystallizer; 2-air compression-expansion dehumidifying unit; 3-an air pressure-stabilizing washing tower; 4-constant pressure water seal tank; 5-a foam washing and catching device; 6-air two-wash device; 7-demisting and dehumidifying device;
in the attached fig. 2: 8-gas stripping concentration purifier; 9-solution circulating pump; 10-shell and tube heater; 11-a volatile impurity absorber; 12-an air pressure stabilization washing tower; 13-constant pressure water seal tank; 14-a flash evaporator; 15-a water jet; 16-absorption liquid circulating pump; 17-liquid seal groove.
Detailed Description
The following examples, which are not intended to be limiting, illustrate specific embodiments of the present invention
Example 1: silver nitrate (AgNO) with the temperature of 100 ℃ and the mass concentration of 82.34 percent3) The aqueous solution is stripped and concentrated to prepare 400kg/h of silver nitrate crystals.
As shown in attached figure 1, 800kg/h of silver nitrate aqueous solution with the temperature of 100 ℃ and the mass concentration of 82.34 percent is taken as a raw material, 1000kg/h of air circulation is used for air stripping and concentration to prepare 400kg/h of silver nitrate crystals. The side length of the rectangular cross section of the corrugated plate array of the air stripping concentration crystallizer 1 is 0.2m, and the array is formed by 30 vertical triangular corrugated plates with the width of 0.2m and the height of 0.5mThe orientations are uniformly arranged, the plate spacing is 6.9mm, the corrugation pitch is 30mm, and the corrugation inclination angle is 30 degrees. Silver nitrate aqueous solution raw materials are uniformly distributed on the cross section of the corrugated plate array through spraying, and falling film flow with the film thickness not more than 1mm is formed on the surfaces of two sides of each corrugated plate; after being dehumidified and demisted, the circulating air output from the expansion machine of the air compression-expansion unit 2 has the pressure higher than the atmospheric pressure by 1.6kPa, the temperature of 2 ℃ and the water vapor partial pressure of 0.71kPa, the circulating air uniformly distributed between every two adjacent corrugated plates of the corrugated plate array flows upwards through an air distribution pipe, gas-liquid countercurrent heat and mass transfer is carried out on the surfaces of the corrugated plates, falling film solution is subjected to adiabatic evaporation, temperature reduction, thickening and crystal nucleus precipitation, the falling film solution flows into a crystal growing tank below the array and stays for 40 minutes at the stirring speed of 20 ℃ and 30 revolutions per minute to complete the crystallization process, and crystal pulp 774kg/h is output from a connecting pipeline at the bottom of the tank, wherein the content of crystal particles is not less than 400 kg/h. The temperature of the gas flowing into the gas-liquid separation cylinder from the upper part of the array is 80 ℃, the humidity content is 30g/kg-a, the pressure is higher than the local atmospheric pressure by 0.6kPa, the gas enters the air pressure stabilizing washing tower 3, and after the gas and the washing water with the temperature of 30 ℃ sprayed from the top of the tower are subjected to counter-current heat transfer, mass transfer, temperature reduction and dehumidification, the circulating air with the constant mass flow of 1000kg/h is sent out from the top of the tower, once the gas phase accumulated in the gas stripping process leads the pressure in the air pressure stabilizing washing tower to exceed the design value and the difference with the local atmospheric pressure to exceed the design value deltap= (p i−p o) And when the pressure is not higher than 0.6kPa, the air with overpressure can bubble outwards from the lower edge opening of the tower, which is immersed below the liquid level of the overflow port of the constant-pressure liquid seal tank 4 by 0.06m, across the lower part of the tower, passes through the liquid seal layer, and then escapes and is released. And circulating air sent out from the tower top is sucked into a compressor of the air compression-expansion unit 2 after defoaming and is pressurized to 180kPa, after pressurization, the air is washed again to reduce the temperature, reduce the humidity and remove the foam, the air is returned to an expander of the compression-expansion unit 2 at the temperature of not higher than 40 ℃ and is subjected to adiabatic expansion, temperature reduction and dehumidification, after gas-liquid separation and defoaming, the air with the temperature of 2 ℃, the pressure of 1.6kPa higher than the atmospheric pressure and the water vapor partial pressure of 0.71kPa is conveyed to a gas distribution pipe of the gas stripping concentration crystallizer 1 to be recycled, and the air circulating power consumption is not more than 5 kW.h.
Example 2: for a concentration of 50000kg/H of 55% (H)3PO4) The wet-process phosphoric acid solution is subjected to gas stripping concentration defluorination to ensure that the concentration of the phosphoric acid solution isIncreased to 70% (H)3PO4) The fluorine content is not more than 0.05 percent (F).
As shown in figure 2, the raw wet-process phosphoric acid solution is 50000kg/H, and the concentration is 55 percent (H)3PO4) 2 percent of fluorine (F) and 40 ℃; the concentration of the fluorine is increased to 70 percent (H) by using 22000kg/H air circulation to carry out air stripping concentration and defluorination3PO4) And the fluorine content is reduced to 0.05 percent (F). The corrugated plate array of the gas stripping concentration purifier 8 has the cross section of an equilateral rectangle with the side length of 1.1m, the array is formed by uniformly arranging 220 vertical triangular corrugated plates with the width of 1.1m and the height of 2.8m in the same direction, the plate spacing is 5mm, the corrugated pitch is 30mm, and the corrugated inclination angle is 30 degrees. 443000kg/h of circulating concentrated solution with the temperature of 115 ℃ and the water content of 31-32% is uniformly sprayed on the cross section of the corrugated plate array from top to bottom through spray heads arranged in the gas-liquid separation cylinder, and falling film flow with the film thickness not more than 1mm is formed on the two side surfaces of each corrugated plate in the array; the air pressure output from the expander of the air compression-expansion unit 2 and subjected to gas-liquid separation and demisting is higher than the local atmospheric pressure by 2.2kPa, the temperature is 5 ℃, the water vapor partial pressure is 0.872kPa, the air is uniformly distributed in air channels among corrugated plate arrays and the falling film solution on the corrugated plate surfaces to carry out gas-liquid countercurrent heat and mass transfer, so that the solution flows into a liquid receiving tank below the corrugated plate arrays after adiabatic evaporation and air stripping defluorination, and the concentration reaches 70 percent (H)3PO4) The fluorine content is reduced to be below 0.05 percent (F), the temperature is not higher than 60 ℃, wherein 39200kg/h is taken as a concentrated defluorinated purified phosphoric acid product and is output from a connecting pipe at the bottom of a liquid receiving tank, the rest is pressurized by a solution circulating pump 9 and is mixed with a supplemented raw material wet-process phosphoric acid solution, the mixture enters a shell-and-tube heater 10 pipe from the bottom to be heated to 115 ℃, and the mixture is sent to a stripping concentrated solution for circulation. Circulating air ascends through a corrugated plate array to transfer heat and mass, heat and humidify, the air temperature is 95 ℃, the moisture content is 456g/kg-a, the fluorine content is not lower than 44g/kg-a, the pressure is higher than the local atmospheric pressure by more than 1.2kPa when the circulating air flows into an upper gas-liquid separation cylinder, entrained mist is separated, the circulating air enters a fluorine absorption tower 11 through a connecting pipeline, and enters air with the designed pressure of 0.8kPa when the circulating air and the 50 ℃ absorption liquid sprayed from the top of the tower downwards flow to transfer heat and mass, cool, condense and dehumidifyThe gas pressure stabilizing washing tower 12 is cooled by the countercurrent of washing water at 35 ℃ sprayed from the top of the tower to be lower than 40 ℃, the circulating air with constant mass flow of 22000kg/h is sent out from the top of the tower, once the pressure in the air pressure stabilizing washing tower exceeds the design value and the difference between the pressure and the local atmospheric pressure exceeds the design value deltap= (p i−p o) And when the pressure is not higher than 0.8kPa, the air with overpressure can bubble outwards from the lower edge opening of the tower, which is immersed below the liquid level of the overflow port of the constant-pressure liquid seal tank 13 by 0.08m, in the tower, passes through the liquid seal layer and escapes. The circulating air output from the washing tower 12 enters a compressor of the air compression-expansion unit 2 after being demisted by the mist eliminator 5, is pressurized to 180kPa, is washed by water again by the air secondary washing device 6 for cooling, dehumidifying and demisting, the temperature of the gas is not higher than 35 ℃, the gas enters an expander of the compression-expansion unit 2 for adiabatic expansion, cooling, condensation and dehumidification, the condensate is separated and demisted and then is conveyed to a gas distribution pipe of the gas stripping concentration purifier 8 for recycling, and the air circulating power consumption is not more than 100 kW.h. The mechanical work generated by the air adiabatic expansion, temperature reduction and dehumidification is directly used for driving the air compressor, and the input power consumption is reduced. The absorption liquid entering the fluorine absorption tower 11 is lifted to a position 6-8 m higher than the liquid level of the absorption liquid in the tower through a section of vertical ascending pipe from a tower bottom connecting pipeline, then enters a flash evaporator 14, is subjected to flash evaporation under the pressure of 12kPa (absolute pressure), and the absorption liquid with the temperature not higher than 50 ℃ after flash evaporation flows out through the bottom of a vertical descending central pipe immersed 1.5m below the liquid level of a liquid seal tank 17, wherein the concentration of 8300kg/H is 15 percent (H)2SiF6) The fluosilicic acid aqueous solution is taken as a recovered product and is output to the outside, and the rest 80000kg/h is sent to the impurity absorption tower 11 through an impurity absorption liquid circulating pump 16 for circulation. The mass flow rate of low-pressure steam generated by the flash evaporator 14 is 2500kg/h, and the low-pressure steam is sprayed and condensed by circulating water with the temperature lower than 40 ℃ through a water sprayer 15 and is carried to a cooling water system.
The invention is not limited to the above-described embodiments, the technical solutions of which have been described in the summary of the invention.
Claims (4)
1. A method for removing water solution volatile impurities and preparing a crystallized product by air circulation gas stripping concentration is characterized in that water solution is sprayed from the upper part of a corrugated plate array which is vertically arranged and has a rectangular cross section, the water solution is spread on the surfaces of the two sides of a corrugated plate which changes in a wave manner in the vertical direction to form a wave-shaped falling film flow with the thickness of not more than 1mm, the wave-shaped falling film flow is directly contacted with circulation air which flows between corrugated plates from bottom to top and has the flow speed of not less than 2m/s for countercurrent heat and mass transfer, water vapor generated by the evaporation of the solution wraps volatile impurities and enters a gas phase, the water solution with the water content of not less than 40% and the volatile impurities of not more than 3.0% is concentrated until the water content is less than 35%, and the content of the volatile impurities is reduced to be less than 0.1%;
the water solution with the water content not lower than 15% flows in the falling film of the corrugated plate array, is directly contacted with circulating air with the flow rate not lower than 2m/s for countercurrent heat and mass transfer, the temperature of the water solution is reduced while the concentration of the water solution is increased, after crystal nuclei are generated in the falling film when the water solution reaches the crystallization state point, the water solution flows into a crystal growing tank below the array to carry out crystal growing for 30-60 minutes at the stirring rotating speed of 20-60 revolutions per minute to complete the crystallization process, and the ratio of the crystal grain amount to the total solute amount in the output crystal slurry is larger than 40%.
2. A method for maintaining constant mass flow of air circulation system features that an upright pressure-stabilizing tower with open lower end is immersed in the air circulation system whose pressure is higher than local atmospheric pressure and under the overflow surface of constant-pressure water-sealed tankHHeight, once the air quality in the air circulation system is accumulated, the pressure in the tower is increased to the difference value between the pressure and the local atmospheric pressure which is larger than the density and the gravity acceleration of the waterHProduct value ofρgHThe overpressure air passes over the lower edge of the opening of the pressure stabilizing tower and bubbles throughHReleasing the high water seal layer to restore the pressure stabilizing tower to the designed pressure.
3. A device for concentrating crystallized products by gas stripping of high-concentration aqueous solution is characterized by comprising a group of vertical corrugated plate arrays with equilateral rectangular cross sections, a circular cross section crystal growing tank with the lower parts connected by a square-to-circle mode and a circular cross section gas-liquid separation cylinder with the upper parts connected by a square-to-circle mode, wherein each corrugated plate array is formed by uniformly arranging triangular corrugated plates in the same direction, the plate spacing is 6-8 mm, the ratio of the height to the width of each plate is more than 1.2, the pitch of the triangular corrugations is 30mm, and the corrugation inclination angle is 30 degrees; the flow rate of the falling film solution distributed to the horizontal width of the corrugated plate from the upper part of the corrugated plate array is 100-260 kg/h.m, falling film flowing on the plate surface is concentrated to separate out crystal nuclei, then the crystal nuclei flow into the crystal growing tank from the lower part of the array, and the crystallization process is completed in 30-60 minutes at the stirring rotating speed of 20-60 revolutions per minute.
4. A device for concentrating and removing volatile impurities by gas stripping of a high-concentration aqueous solution is characterized by comprising a group of vertical corrugated plate arrays with equilateral rectangular cross sections, a liquid receiving tank with a round cross section and a gas-liquid separation tank with a round cross section, wherein the lower parts of the corrugated plate arrays are connected by a square circle, the liquid receiving tank is connected by a square circle, the upper parts of the corrugated plate arrays are connected by a square circle, the corrugated plate arrays are formed by uniformly arranging triangular corrugated plates in the same direction, the plate spacing is 6-8 mm, the ratio of the height to the width of the plates is more than 1.2, the pitch of the triangular corrugations is 30mm, and the inclination angle of the corrugations is 30 degrees; the flow rate of the falling film solution distributed to the horizontal width of the corrugated plate from the upper part of the corrugated plate array is 800-2000 kg/h.m, and the falling film solution flows and is concentrated on the plate surface, and simultaneously volatile impurities are removed, and then the falling film solution flows into a liquid receiving tank from the lower part of the array.
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