CN111302309A - Process device and method for continuous crystal form passivation and modification of hydrotalcite product - Google Patents
Process device and method for continuous crystal form passivation and modification of hydrotalcite product Download PDFInfo
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Abstract
The invention provides a process unit and a method for continuous crystal form passivation and modification of hydrotalcite products, wherein the process unit comprises a preheater, a continuous passivation tower and a modification kettle, the top end of the preheater is connected with a slurry tank through a pipeline, and the bottom end of the preheater is connected with a feed inlet on the side wall of the continuous passivation tower through a pipeline; the continuous passivation tower is connected with a pressure reduction flash tank, and the pressure reduction flash tank is connected with the modification kettle; the preheater, the pressure reduction flash evaporator and the modification kettle are connected with a waste heat collecting system through waste heat recovery pipes; the preheater, the continuous passivation tower and the modification kettle are connected with a steam main pipe. The invention adopts a continuous production process, and has the advantages of high product yield, good quality, simple process and safety; the obtained product has narrow particle size distribution, more regular crystal form and more stable quality; the direct heat exchange of the steam is combined with the heating of the sieve plate, so that the heat efficiency is high; and the secondary steam is recycled, so that the energy is saved.
Description
Technical Field
The invention belongs to the technical field of hydrotalcite production, and relates to a process device and a method for continuous crystal form passivation and modification of hydrotalcite products.
Background
Hydrotalcite is widely applied to many aspects such as plastic heat stabilizer, greenhouse film heat preservation agent, flame retardant, catalyst, medicine, environment-friendly material and the like as a new functional material, but many problems to be solved in the large-scale production of hydrotalcite are urgently needed, and indexes such as hydrotalcite particle distribution, crystal morphology and the like have great influence on product quality. The hydrotalcite after reaction has fine crystals, high viscosity, easy adsorption of particles, uneven particle size, imperfect crystal morphology, poor fluidity and low purity, affects washing and modification, and cannot achieve ideal effects when being directly used, so that production enterprises mostly adopt a crystal form passivation process, and the hydrotalcite is kept for a certain time at a certain temperature and under a certain pressure, so that the crystals are recrystallized, the particles adhered together are easy to break, the fine particles are dissolved, the crystal form of the large particles is more regular, the whole particle size distribution is narrower, the crystal form is more standard, the fluidity is improved, and the product quality is improved. The traditional production process of the hydrotalcite adopts an intermittent crystal form passivation method, and has the advantages of long time consumption, high energy consumption, low yield, nonuniform crystallization, intermittent operation, easy change of the condition of each kettle and large product quality fluctuation.
The hydrotalcite is an inorganic compound and is often used as an additive of an organic matter in application, and the hydrotalcite and the organic matter are difficult to be directly fused into a whole, so modification is needed, and some modifiers are usually needed to be added so as to enable the hydrotalcite and the organic matter to be better fused. Due to different temperature requirements of crystal form passivation and modification, the modification temperature of hydrotalcite is generally lower than the crystal form passivation temperature, the temperature needs to be raised first for crystal form passivation, cold water needs to be used for cooling after the crystal form passivation is completed, energy and time are wasted, and crystallization agglomeration is easily caused due to long cooling time in the cooling process, so that the concentration and the content of slurry are not uniform, the proportion of the added modifier is not uniform, the modification is unbalanced, and the product quality is influenced.
Generally, the temperature and the pressure of the crystal form passivation are high, the intermittent crystal form passivation kettle generally needs to be sealed by magnetic force, and high-temperature and high-pressure faults are more, so that the leakage danger is easily caused, and the environment and the safety are influenced. Because the intermittent crystal form passivation operation is in a high-temperature high-pressure sealing state, slurry is put in under the lower-temperature pressure and needs to be discharged under the lower-temperature pressure under the general condition of safe operation, the whole operation time is about 7-12 h, and the time is long and the yield is low.
Disclosure of Invention
The invention provides a process device and a method for continuous crystal form passivation and modification of hydrotalcite products, and solves the problems of more faults, easy leakage, danger, long production time, low yield and unbalanced modification of an intermittent crystal form passivation method in the prior art. By adopting the continuous production method, the invention reduces the time for heating, pressure increasing, temperature reducing and pressure reducing of the slurry, improves the efficiency and increases the yield. Due to the adoption of the continuous production method, the slurry concentration is more uniform, the process parameters are more stable, the operation is easier to control, the product quality is more stable, the particle size distribution of hydrotalcite crystals is narrower, the crystal morphology is more regular, and the product quality is more excellent.
In order to achieve the purpose, the invention adopts the following technical scheme:
a process unit for continuous crystal form passivation and modification of hydrotalcite products comprises a preheater, a continuous passivation tower and a modification kettle, wherein the top end of the preheater is connected with a slurry tank through a pipeline, and the bottom end of the preheater is connected with a feed inlet on the side wall of the continuous passivation tower through a pipeline; the continuous passivation tower is connected with a pressure reduction flash tank, and the pressure reduction flash tank is connected with the modification kettle; the preheater, the pressure reduction flash evaporator and the modification kettle are connected with a waste heat collecting system through waste heat recovery pipes; the preheater, the continuous passivation tower and the modification kettle are connected with a steam main pipe.
Preferably, a plurality of sieve plates are arranged in the continuous passivation tower from top to bottom, and the sieve plates are baffle plates with sieve pores uniformly distributed; the side wall of the continuous passivation tower is provided with a middle section steam inlet and a lower section steam inlet, and a slurry inlet of the continuous passivation tower is positioned at the upper part of the continuous passivation tower; a steam outlet is formed in the top end of the continuous passivation tower, and a slurry outlet is formed in the bottom end of the continuous passivation tower; the steam outlet is connected with the steam main pipe.
Preferably, the sieve plates are provided with a plurality of layers, and the plurality of layers of sieve plates are uniformly arranged from top to bottom. The spacing between each screen deck is 500 mm.
Further preferably, the baffle plate is of an arch structure, the area of a cut is 5-20%, the aperture of each sieve pore is phi 10-20%, and the aperture ratio is 20-30%.
Preferably, the side surface of the continuous passivation tower is also provided with an overflow pipe, and the overflow pipe is arranged between the sieve plate layers to prevent the tower from flooding.
Preferably, the bottom end of the modifying kettle is connected with a centrifuge. And separating out water by a centrifugal machine to obtain the hydrotalcite wet material. Preferably, the modification kettle is connected with a modification material tank, and the bottom end of the modification material tank is connected with a centrifuge.
Preferably, pumps are arranged on a pipeline between the slurry tank and the preheater, a pipeline between the preheater and the continuous passivation tower, and a pipeline between the modification kettle and the centrifuge.
A process method for passivating and modifying a continuous crystal form of a hydrotalcite product comprises the following steps:
1) after being washed and filtered, the slurry after the hydrotalcite reaction is pumped into a preheater by a pump and is preheated to a certain temperature;
2) the preheated slurry is pressurized by a pump and then enters the continuous passivation tower from a slurry inlet of the continuous passivation tower; the slurry flows from top to bottom and enters a heating section; the continuous crystal form passivation tower adopts a tower type sieve plate structure; the slurry entering from the upper part is subjected to direct convection heat exchange by the rising steam, flows through the baffle plate and downwards flows through the sieve holes, and enters the constant temperature section; heating and pressurizing the slurry, and discharging the slurry from a slurry outlet at the bottom of the tower after the slurry is reserved for a certain time to complete the crystal form passivation;
3) enabling the slurry subjected to crystal form passivation to flow into a pressure reduction flash tank under self pressure, removing secondary steam generated after pressure reduction flash tank to a waste heat recovery system, and feeding the slurry subjected to flash tank flash cooling to 85-105 ℃ into a modification kettle for modification; adding a modifier into the hydrotalcite slurry through a modifier feed inlet of the modification kettle, stirring the modifier and the hydrotalcite slurry together, uniformly mixing the modifier and the hydrotalcite slurry, distributing the mixture in the kettle, and keeping the temperature and the time for modifying the slurry;
4) and separating the modified slurry by a centrifuge, drying the wet slurry in a drying system, and recycling water.
Preferably, the slurry in the preheater is heated by secondary steam from the top of the continuous passivation tower, and is regulated by primary steam when the heat of the secondary steam is insufficient; stirring at a low speed in the preheater, wherein the stirring speed is 60-90 revolutions per minute.
Preferably, the preheating temperature in the step 1) is 60-90 ℃.
Preferably, the steam in the step 2) enters the tower from the middle part and the lower part of the tower in two ways and is used for heating the slurry and adjusting the temperature of the tower; the temperature in the tower is 135-180 ℃; the pressure is 0.3-1.0 MPa, and the slurry is kept for 4-6 hours.
Preferably, the heating steam entering the continuous passivation tower in the step 2) is subjected to heat exchange, then is subjected to liquid separation in the vapor-liquid separation section at the top of the tower, and then enters a steam outlet to be used as secondary steam for preheating the hydrotalcite cold slurry.
Preferably, the temperature in the kettle in the step 3) is kept at 90-110 ℃ for 1-3 hours.
One or more embodiments provided by the embodiments of the present invention have at least the following technical effects:
(1) continuous production process, high yield, high quality, simple process and high safety.
(2) The product has narrow particle size distribution, more regular crystal form and more stable quality;
(3) the direct heat exchange of the steam is combined with the heating of the sieve plate, so that the heat exchange efficiency is high;
(4) the secondary steam is reused, and energy is saved.
The continuous crystal form passivation tower adopts a heat preservation and pressure maintaining design, and the inner layer main body is sequentially provided with a plurality of layers of sieve plates from top to bottom; the sieve plates are distributed in the tower in a mode of interval uniform arrangement, and are baffle plates with uniformly distributed sieve pores; the upper end in the tower body is provided with a gas-liquid separation layer, and the lower part of the tower body is provided with a liquid retention layer; the outer layer of the tower body is distributed with a slurry inlet, a slurry outlet, a middle and lower section steam inlet and a tower top steam outlet.
The invention utilizes the device and adopts a method of continuous feeding and continuous discharging, slurry is fed from the upper part of the continuous crystal form passivation tower and then is uniformly distributed on the sieve plate, and the slurry continuously flows from the upper part of the tower to the lower part of the tower between the sieve plate and the sieve plate, and is uniformly crystallized; by adopting the continuous production method, the time for heating, pressure increasing, temperature decreasing and pressure reducing of the slurry is reduced, the efficiency is improved, and the yield is increased. Due to the adoption of the continuous production method, the slurry concentration is more uniform, the process parameters are more stable, the operation is easier to control, the product quality is more stable, the particle size distribution of hydrotalcite crystals is narrower, the crystal morphology is more regular, and the product quality is more excellent. The process device adopts the slurry after the crystal form passivation to directly enter the pressure reduction flash tank for instantaneous evaporation cooling, has short time and high speed, has looser particles due to the quick volatilization of steam, reduces the process of temperature reduction and pressure reduction of the high-temperature and high-pressure slurry after the crystal form passivation because cold water is not adopted for temperature reduction, not only saves energy, but also ensures that the slurry is not accumulated due to the long-time temperature reduction of the cold water, and better improves the crystallization dispersity. By adopting a cold slurry preheating and hot slurry flashing process, the process that an intermittent crystal form passivation method adopts a process of firstly heating, increasing pressure, then cooling and reducing pressure is reduced, so that the crystal form passivation time which is the longest in time consumption in the hydrotalcite production process is greatly reduced, and the heating, increasing pressure, cooling and reducing pressure and the crystal form passivation of the slurry are simultaneously carried out, so that the heating, increasing pressure, cooling and reducing pressure time (about 3-4 h) is saved, and the cold slurry is preheated, enters a crystal form passivation tower and is directly heated by hot steam, so that the heat exchange efficiency is high, and the temperature increasing speed is high; the slurry flows on a sieve plate in the crystal passivation kettle through a baffle plate, so that the retention time of the slurry is prolonged, the slurry flows from top to bottom through the opening of the sieve plate, hot steam heats the sieve plate from bottom to top, and the hot steam flows upwards through the sieve holes in a convection contact manner with the hot slurry; the slurry flows and is stirred by steam, the particle dispersion degree is higher, the agglomeration is reduced, and the particle size distribution is narrower; the slurry has high temperature and pressure, the heat efficiency in the heat exchange process is high, the crystal form passivation speed is high, the time is short, the yield is high, and the time is reduced from the intermittent passivation time of 7-12 hours to 4-6 hours; the yield is improved by 1-2 times compared with the intermittent passivation. Continuous production is adopted, so that the process parameters are more stable, and the product quality is more stable.
Drawings
FIG. 1 is a flow diagram of a continuous crystal form passivation modification process apparatus of the present invention;
FIG. 2 is a schematic structural diagram of a continuous crystal form passivation tower of the present invention;
FIG. 3 is an SEM image of batch type crystal form passivation for producing magnesium aluminum hydrotalcite;
FIG. 4 is an SEM image of continuous crystal form passivation for producing magnesium aluminum hydrotalcite;
FIG. 5 is a particle size distribution diagram of magnesium aluminum hydrotalcite produced by intermittent crystal form passivation;
fig. 6 is a particle size distribution diagram of magnesium aluminum hydrotalcite produced by continuous crystal form passivation.
Reference numerals:
1-slurry tank; 2-a preheater; 3-a continuous passivation tower; 4-a reduced pressure flash tank; 5-a modification kettle; 6-modified material tank; 7-a centrifuge; 31-a steam outlet; 32-slurry inlet; 33-an overflow pipe; 34-a middle section steam inlet; 35-lower section steam inlet; 36-a slurry outlet; 37-sieve plate; s1-steam header; s2-waste heat recovery tube.
Detailed Description
The invention is described in further detail below with reference to the following figures and specific embodiments:
as shown in fig. 1 and fig. 2, which are flow charts of the continuous crystal form passivation improved process device of the present invention, a feed inlet of a slurry tank 1 is connected with a hydrotalcite slurry feed pipeline, and an outlet of the slurry tank 1 is connected with an inlet of a hydrotalcite slurry delivery pump through a pipeline; the outlet of the hydrotalcite slurry conveying pump is connected with the cold slurry inlet of the hydrotalcite slurry preheater 2 through a pipeline, the hot slurry outlet of the hydrotalcite slurry preheater 2 is connected with the inlet of the hot slurry conveying pump 6 through a pipeline, and the outlet of the hot slurry conveying pump 6 is connected with the preheated slurry inlet 32 of the continuous passivation kettle 3 through a pipeline; the steam inlet of the preheater 2 is connected with the upper steam outlet 31 of the continuous passivation tower 3 and a steam header pipe S1 through pipelines; a steam outlet of the preheater 2 is communicated with a waste heat recovery system through a waste heat recovery pipe S2; the slurry outlet 36 of the continuous passivation tower 3 is connected with the inlet of the decompression flash evaporator 4 through a pipeline with a control valve; the middle section steam inlet 34 and the lower section steam inlet 35 of the continuous passivation tower 3 are connected with a steam main pipe S1 through pipeline valves; the outlet steam of the pressure reduction flash evaporator 4 goes to a waste heat recovery system. A modifier feeding port is arranged on the modifying kettle 5; the outlet of the modified slurry pump is connected with the inlet of the modified slurry tank 6 through a pipeline; a steam pipeline inlet of the modification kettle 5 is connected with a steam main pipe through a valve, and a steam outlet is connected with a waste heat recovery system through a waste heat recovery pipe S2; the outlet of the modified material tank 6 is connected with the feed inlet of the centrifuge 7 through a pipeline, the liquid phase outlet of the centrifuge 7 is connected with a washing pipe, and the solid phase outlet of the centrifuge 7 is connected with a solid phase hydrotalcite wet material conveying device.
Temperature and pressure measuring devices are arranged at the top, the bottom and the middle part of the passivation tower 3 and are used for measuring the temperature and the pressure of each section in the tower; the upper part of the modifying kettle 5 and the upper part of the preheater 2 are both provided with temperature measuring devices for measuring the internal temperatures of the modifying kettle 5 and the preheater 2. A flow meter is arranged on a preheating pipeline of the preheater 2 and used for controlling the flow of the material.
Specifically, a plurality of sieve plates 37 are arranged in the continuous passivation tower 3 from top to bottom, and the sieve plates 37 are baffle plates with uniformly distributed sieve holes; the side wall of the continuous passivation tower 3 is provided with a middle-section steam inlet 34 and a lower-section steam inlet 35, and the slurry inlet 32 of the continuous passivation tower 3 is positioned at the upper part of the continuous passivation tower 3; the top end of the continuous passivation tower 3 is provided with a steam outlet 31, and the bottom end is provided with a slurry outlet 36; the steam outlet 31 is connected to a steam header S1. The sieve plates 37 are provided with a plurality of layers, and the plurality of layers of sieve plates 37 are uniformly arranged from top to bottom. And the side surface of the continuous passivation tower is also provided with an overflow pipe 33, the overflow pipe 33 is arranged between the sieve plate layers, and the overflow pipe 33 is arranged to prevent the tower from flooding.
Example 1 passivation and modification of magnesium-aluminum binary hydrotalcite:
after being washed and filtered, slurry obtained after the reaction of the magnesium-aluminum hydrotalcite is pumped into a hydrotalcite slurry tank 1, the slurry is pumped into a preheater 2 by a pump 3, the slurry in the preheater 2 is heated by secondary steam from a continuous crystal form passivation tower 3, the slurry is stirred at a low speed (60-90 rpm), the slurry is preheated to the temperature of 60-90 ℃, and when the heat of the secondary steam is insufficient, the slurry is regulated by primary steam; and pressurizing the hydrotalcite solution with the preheating temperature of 60-90 ℃ to 0.3-0.5 MPa by a pump, sending the hydrotalcite solution into an upper slurry inlet 32 of the continuous crystal form passivation tower 3, and allowing the hydrotalcite solution to flow from top to bottom to enter a heating section. The continuous crystal form passivation tower 3 adopts a tower-type sieve plate structure, and the sieve plate 37 is a baffle plate with evenly distributed sieve pores and is evenly arranged from top to bottom. The slurry entering from the upper part is subjected to direct convection heat exchange by ascending steam, flows downwards through the sieve holes and enters the heating section; overflow pipes 33 are arranged among the layers of the sieve plates to prevent the tower from flooding; the steam enters the tower from the middle part and the lower part of the tower in two ways and is used for heating the slurry and adjusting the temperature of the tower; keeping the temperature in the tower at 135-180 ℃; the pressure is 0.3-1.0 MPa; heating and pressurizing the slurry, keeping for 4-6 h, discharging the slurry after passing through a constant temperature section at the bottom of the tower, and keeping the slurry in a pressure reduction flash tank 4; the heating steam entering the continuous crystal form passivation tower 3 is subjected to heat exchange, then is subjected to liquid separation in a tower top vapor-liquid separation section, and then enters a tower top vapor outlet 31 to serve as secondary steam for preheating the hydrotalcite cold slurry.
The slurry after the crystal form passivation is subjected to secondary steam after the pressure reduction flash vaporization through a pressure reduction flash vaporizer 4, and then is sent to a waste heat recovery system, and the slurry after the pressure reduction flash vaporizer 4 is subjected to flash vaporization and is cooled to (80-105 ℃) is sent to a modification kettle 5 for modification; adding a modifier into the passivated hydrotalcite slurry through a modifier feed inlet on the modification kettle 5, stirring the modifier with the slurry, uniformly mixing the modifier with the hydrotalcite slurry, distributing the mixture in the kettle, and keeping the temperature of 90-110 ℃ for 1-3 h through jacket steam; and the outlet steam of the modification kettle 5 is sent to a waste heat recovery system. The modified slurry is fed into a modified slurry tank 6, and after being separated by a centrifuge 7, the wet slurry is sent to a drying system, and the moisture is recycled. The comparison results of the products of the magnesium-aluminum hydrotalcite obtained by the continuous passivation process and the batch process are shown in table 1.
TABLE 1 comparison of continuous and intermittent passivation of crystal form of Mg-Al hydrotalcite
Example 2 modification of magnesium aluminum cerium ternary hydrotalcite:
washing and filtering the slurry obtained after the reaction of the magnesium-aluminum-cerium hydrotalcite, pumping the slurry into a hydrotalcite slurry tank 1, pumping the slurry into a preheater 2 by using a pump, heating the slurry in the preheater 2 by secondary steam from a continuous crystal form passivation tower 3, stirring at a low speed (60-90 rpm), preheating to the temperature of 60-90 ℃, and regulating by using primary steam when the heat of the secondary steam is insufficient; and pressurizing the hydrotalcite solution with the preheating temperature of 60-90 ℃ to 0.3-0.6 MPa by a pump, sending the hydrotalcite solution into an upper slurry inlet 32 of the continuous crystal form passivation tower 3, and allowing the hydrotalcite solution to flow from top to bottom to enter a heating section. The continuous crystal form passivation tower 3 adopts a tower type sieve plate structure, the sieve plate 37 is a baffle plate with sieve holes uniformly distributed, and the sieve plate 37 is uniformly arranged from top to bottom. The slurry entering from the upper part is subjected to direct heat exchange by ascending steam convection, flows downwards through the sieve holes and enters the heating section; overflow pipes 33 are arranged among the layers of the sieve plates to prevent the tower from flooding; steam enters the tower from the middle part and the lower part of the tower (a middle-section steam inlet 34 and a lower-section steam inlet 35) in two ways and is used for heating slurry to adjust the temperature of the tower; keeping the temperature in the tower at 135-180 ℃; the pressure is 0.3-1.0 MPa; heating and pressurizing the slurry, reserving for 2-4 h, discharging the slurry through a constant temperature section at the bottom of the tower, and reserving the slurry to enter a pressure reduction flash tank 4; the heating steam entering the continuous crystal form passivation tower 3 is separated from liquid through the vapor-liquid separation section at the top of the tower and then enters the exhaust pipe at the top of the tower (the vapor outlet 31 at the top of the tower) to be used as secondary steam for preheating the hydrotalcite cold slurry.
The slurry after the crystal form passivation is subjected to pressure reduction flash vaporization through a pressure reduction flash vaporizer 4, then secondary steam is sent to a waste heat recovery system, and the slurry after the pressure reduction flash vaporizer 4 is subjected to flash vaporization and temperature reduction (85-105 ℃) is sent to a modification kettle 5 for modification; the modifier is added into the passivated hydrotalcite slurry through a modifier feed inlet on the modification kettle 5, is stirred together with the slurry, is uniformly mixed with the hydrotalcite slurry and is distributed in the kettle, the temperature is kept at 95-100 ℃ through jacket steam and is kept for 1-3 hours, the slurry is modified, and the outlet steam of the modification kettle 5 is sent to a waste heat recovery system. The modified slurry is fed into a modified slurry tank 6, and after being separated by a centrifuge 7, the wet slurry is sent to a drying system, and the moisture is recycled. The results of comparing the products of the magnesium-aluminum-cerium hydrotalcite obtained by the continuous passivation process and the batch process are shown in table 2.
TABLE 2 continuous and intermittent comparison of crystal form passivation process of Mg-Al hydrotalcite
The invention is not limited to the above-mentioned magnesium-aluminum binary hydrotalcite and aluminum-cerium ternary hydrotalcite, and all similar hydrotalcite slurries are protected within the scope of the invention by a method of continuous passivation or modification using slight modification of the process equipment and method of the invention.
Claims (10)
1. The process device for passivating and modifying the continuous crystal form of the hydrotalcite product is characterized by comprising a preheater (2), a continuous passivation tower (3) and a modification kettle (5), wherein the top end of the preheater (2) is connected with a slurry tank (1) through a pipeline, and the bottom end of the preheater (2) is connected with a feeding hole in the side wall of the continuous passivation tower (3) through a pipeline; the continuous passivation tower (3) is connected with a reduced-pressure flash evaporator (4), and the reduced-pressure flash evaporator (4) is connected with the modification kettle (5); the preheater (2), the reduced-pressure flash evaporator (4) and the modification kettle (5) are connected with a waste heat collecting system through a waste heat recovery pipe (S2); the preheater, the continuous passivation tower and the modification kettle are connected with a steam main pipe (S1).
2. The process device according to claim 1, characterized in that a plurality of sieve plates (37) are arranged in the continuous passivation tower (3) from top to bottom, and the sieve plates (37) are baffle plates with uniformly distributed sieve holes; the side wall of the continuous passivation tower (3) is provided with a middle-section steam inlet (34) and a lower-section steam inlet (35), a slurry inlet (32) of the continuous passivation tower (3) is positioned at the upper part of the continuous passivation tower (3), the top end of the continuous passivation tower (3) is provided with a steam outlet (31), and the bottom end of the continuous passivation tower is provided with a slurry outlet (36); the steam outlet (31) is connected to a steam header (S1).
3. A process arrangement according to claim 2, characterized in that the screening deck (37) is provided with a plurality of decks (37) which are arranged evenly from top to bottom.
4. A process unit according to claim 3, characterized in that the side of the continuous passivation tower is further provided with an overflow pipe (33), and the overflow pipe (33) is arranged between sieve plate layers.
5. A process method for passivating and modifying a continuous crystal form of a hydrotalcite product is characterized by comprising the following steps:
1) after being washed and filtered, the slurry after the hydrotalcite reaction is pumped into a preheater (2) by a pump and preheated to a certain temperature;
2) the preheated slurry is pressurized by a pump and then enters the continuous passivation tower (3) from a slurry inlet (32) of the continuous passivation tower (3); the slurry flows from top to bottom and enters a heating section; the continuous crystal form passivation tower (3) adopts a tower sieve plate structure; the slurry entering from the upper part is subjected to direct convection heat exchange by the rising steam, flows through the baffle plate, then flows downwards through the sieve holes and enters the constant temperature section; heating and pressurizing the slurry, and discharging the slurry (36) from the bottom of the tower after the slurry is reserved for a certain time to complete the crystal form passivation;
3) the slurry after the crystal form passivation flows into a pressure reduction flash evaporator (4) under self pressure, secondary steam generated after the pressure reduction flash evaporator is subjected to a waste heat recovery system, and the slurry after the pressure reduction flash evaporator (4) is subjected to flash evaporation and cooling enters a modification kettle for modification; the modifier is added into the hydrotalcite slurry through a modifier feed inlet of the modification kettle (5), is stirred together with the slurry, is uniformly mixed with the hydrotalcite slurry and is distributed in the kettle, and the temperature and the time are kept for a certain time, so that the slurry is modified;
4) and (3) separating the modified slurry by a centrifuge (7), drying the wet slurry by a drying system, and recycling water.
6. A process according to claim 5, characterized in that the slurry in the preheater (2) in step 1) is heated by secondary steam from the top of the continuous passivation column (3) and conditioned by primary steam when the heat of the secondary steam is insufficient.
7. The process of claim 5, wherein the preheating temperature in step 1) is 60 to 90 ℃.
8. The process method as claimed in claim 5, wherein the temperature in the tower in the step 2) is 135-180 ℃; the pressure is 0.3-1.0 MPa, and the slurry is kept for 4-6 hours.
9. The process according to claim 5, characterized in that the heating steam entering the continuous passivation column (3) in step 2) is heat-exchanged and then enters the steam outlet (31) after the liquid is separated in the overhead vapor-liquid separation section, and is used as secondary steam for preheating the hydrotalcite cold slurry.
10. A process method as claimed in claim 5, wherein the temperature in the kettle in the step 3) is kept at 90-110 ℃ for 1-3 hours.
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