CN215974993U

CN215974993U - Magnesium hydroxide production device for positive pressure magnesium precipitation and dry method negative pressure ammonia distillation

Info

Publication number: CN215974993U
Application number: CN202122404746.7U
Authority: CN
Inventors: 王德喜; 王猛; 周士海
Original assignee: Liaoning Boshi Venture Service Center Management Co ltd
Current assignee: Liaoning Boshi Venture Service Center Management Co ltd
Priority date: 2021-09-30
Filing date: 2021-09-30
Publication date: 2022-03-08
Anticipated expiration: 2031-09-30

Abstract

The utility model relates to a magnesium hydroxide production device for positive pressure magnesium precipitation and dry negative pressure ammonia distillation, which belongs to the technical field of chemical industry, and comprises a dissolving tank, a centrifuge feeding tank, a horizontal double-drum centrifuge, an aerial fog magnesium precipitation tower, a jet magnesium precipitation reactor, a magnesium precipitation liquid flash tank, an expanding drum type filter, a belt type vacuum filter, a paddle dryer, a jet mill, a pre-ammonia distillation tank, a negative pressure ammonia distillation tower, a cavitation ammonia distillation reactor and an ammonia distillation liquid flash tank; the cavitation ammonia evaporation reactor and the jet magnesium deposition reactor enhance heat transfer and mass transfer; secondary water vapor is recovered from the reaction liquid of ammonia distillation and magnesium precipitation through flash evaporation to provide an auxiliary heat source for ammonia distillation reaction, the water vapor separated by drying provides an auxiliary heat source for a paddle dryer, and the reaction heat of all calcium oxide is recovered through dry-method negative-pressure ammonia distillation; the energy-saving effect is obvious, and the device can save energy by 25% comprehensively; the quality of the prepared magnesium hydroxide is higher than the national standard of industrial products. The utility model has the advantages of mature process, continuous operation, high automation degree, cyclic utilization of resources and environmental protection.

Description

Magnesium hydroxide production device for positive pressure magnesium precipitation and dry method negative pressure ammonia distillation

Technical Field

The utility model belongs to the technical field of chemical industry, and particularly relates to a magnesium hydroxide production device for positive pressure magnesium precipitation and dry negative pressure ammonia distillation.

Background

The industrial production method of magnesium hydroxide generally adopts ammonia method and caustic soda method, etc., and mainly adopts ammonia method to prepare magnesium hydroxide. The main raw materials are light calcined powder, brine and the like, and if the raw materials are not properly treated, the crystal form of magnesium hydroxide is affected, and the quality of the magnesium hydroxide is further affected. The preparation process of the magnesium hydroxide generally adopts a kettle type reactor and mechanical stirring, and the preparation equipment has the defects of low heat transfer and mass transfer efficiency; the reaction period is long, the energy consumption is high, the cost is increased due to the increase of the energy consumption, and the industrial production is not facilitated.

The art is eagerly looking for a low energy consumption and environment-friendly process for preparing magnesium hydroxide, which can overcome the above technical problems. The novel equipment is adopted to prepare the magnesium hydroxide from bischofite and industrial calcium oxide powder which are byproducts in potassium fertilizer preparation through ammonia evaporation reaction and magnesium precipitation reaction, so that the high-quality magnesium hydroxide is produced, the process is simple, the quality is stable, and the typical green chemical process belongs to an environment-friendly process.

SUMMERY OF THE UTILITY MODEL

Aiming at the engineering problems and the market demand and overcoming the problems in the prior art, the utility model provides the magnesium hydroxide production device for positive pressure magnesium precipitation and dry negative pressure ammonia distillation, and the device has the advantages of simple process flow, continuous operation, high automation degree, resource recycling and environmental friendliness.

In order to achieve the purpose, the utility model adopts the following technical scheme: the magnesium hydroxide production device comprises a dissolving tank, a centrifuge feeding tank, a horizontal double-drum centrifuge, an aerial fog magnesium precipitation tower, a jet magnesium precipitation reactor, a magnesium precipitation liquid flash tank, an expansion drum type filter, a belt type vacuum filter, a paddle dryer and an air flow crusher which are sequentially connected; the dissolving tank is used for dissolving bischofite; the centrifuge feeding tank is used for intermediate storage of bischofite solution; the horizontal double-drum centrifuge is used for carrying out liquid-solid separation on the bischofite solution and solid impurities; the aerial fog magnesium precipitation tower is used for atomizing the separated refined magnesium liquid and performing magnesium precipitation reaction with ammonia gas; the jet magnesium precipitation reactor is used for precipitating magnesium liquid and ammonia gas to continue magnesium precipitation reaction; the magnesium precipitation liquid flash tank is used for carrying out flash evaporation on the magnesium precipitation liquid; the expansion drum type filter is used for concentrating the magnesium precipitation flash evaporation liquid; the belt type vacuum filter is used for carrying out liquid-solid separation on the concentrated solution of the expansion drum type filter; the paddle dryer is used for drying the filtered magnesium hydroxide filter cake of the vacuum filter; the jet mill is used for grinding and grading the magnesium hydroxide powder dried by the paddle dryer;

the device also comprises a mother liquor tank, a pre-ammonia distillation tank, a cavitation ammonia distillation reactor and an ammonia distillation flash tank which are connected in sequence; the mother liquor tank is connected with the expansion drum type filter and the belt type vacuum filter and is used for collecting the ammonium chloride mother liquor separated by the expansion drum type filter and the belt type vacuum filter; the pre-steamed ammonia tank is used for digesting calcium oxide powder and ammonium chloride mother liquor and pre-steaming ammonia; the cavitation ammonia distillation reactor is used for ammonia distillation reaction of calcium hydroxide and ammonium chloride mother liquor; the ammonia evaporation liquid flash tank is used for carrying out flash evaporation on the ammonia evaporation liquid; and a negative-pressure ammonia still is arranged above the cavitation ammonia still reactor and is used for separating ammonia and water vapor.

Furthermore, the outer wall of the cavitation ammonia evaporation reactor is provided with an airflow cavitation nozzle for introducing steam into the reactor, the inner wall of the cavitation ammonia evaporation reactor is provided with a tooth-shaped baffle, a hollow stirring heat transfer rotor is arranged in the reactor, and the outer wall of the stirring heat transfer rotor is provided with a plurality of layers of blades.

Furthermore, the multiple layers of blades are 45-degree 12-blade turbine blades uniformly distributed on the stirring heat transfer rotor, and the blades of each layer are staggered with the teeth of the toothed baffle in the horizontal direction; the tooth-shaped baffles are four and are symmetrically arranged on the inner wall of the reactor at intervals of 90 degrees.

Further, a gas-liquid two-phase atomizing nozzle is arranged at the lower part in the gas-fog magnesium precipitation tower, a demister and a spray header are arranged at the upper part from top to bottom, a liquid seal pipe is arranged at the bottom of the tower, and the liquid seal pipe extends to a position below the liquid level in the jet magnesium precipitation reactor; and a demister, a built-in cooler and white steel structured packing are arranged in the negative pressure ammonia distillation tower from top to bottom.

Further, the jet magnesium deposition reactor adopts jet stirring and adopts jacket heat exchange; the cavitation ammonia-steaming reactor directly exchanges heat through steam introduced into the stirring heat transfer rotor and water vapor introduced into the airflow cavitation nozzle.

Further, the apparatus further comprises: a gas-liquid separation tank, an ammonia buffer tank and an ammonia compressor; the inlet of the gas-liquid separation tank is connected with an unreacted ammonia gas outlet of the jet magnesium deposition reactor and an ammonia gas outlet at the top of the negative pressure ammonia distillation tower, and is used for carrying out gas-liquid separation on the collected ammonia gas; the input end of the ammonia gas compressor is connected with a gas phase outlet of the gas-liquid separation tank, the output end of the ammonia gas compressor is connected with an inlet of the ammonia gas buffer tank, and an outlet of the ammonia gas buffer tank is connected with an ammonia gas inlet of the aerial fog magnesium precipitation tower.

Further, the apparatus further comprises an ammonia gas, water vapor compressor (MVR); the input end of the ammonia gas and water vapor compressor is connected with the ammonia evaporation liquid flash tank and the magnesium precipitation liquid flash tank, and the output end of the ammonia gas and water vapor compressor is connected with the airflow cavitation nozzle of the cavitation ammonia evaporation reactor.

Further, the device also comprises a steam ejector (TVR) and a condensed water flash tank; the steam jet device is connected with the paddle dryer, the paddle dryer adopts steam heating jacket heat exchange and steam heating stirring paddle heat exchange to dry the magnesium hydroxide filter cake, and the generated secondary water steam is used as an auxiliary heat source and enters the paddle dryer steam heating jacket and the steam heating stirring paddle again through the steam jet device to dry materials; the stirring heat transfer rotor of the cavitation ammonia-steaming reactor takes steam as a heat source, the condensed water flash tank is used for collecting steam condensed water generated by the heat transfer rotor of the cavitation ammonia-steaming reactor and the blade dryer, and the collected steam condensed water is used for filtering cakes of the horizontal double-drum centrifuge and filtering cake washing water of the belt type vacuum filter after secondary steam is flashed.

A magnesium hydroxide production method based on the device specifically comprises the following steps:

(1) feeding the bischofite and water into a dissolving tank, and dissolving the bischofite under the stirring of a mechanical stirrer;

(2) continuously feeding the bischofite solution in the dissolving tank into a centrifuge feeding tank by gravity, and feeding the bischofite solution into a horizontal double-drum centrifuge by a bischofite solution pump;

(3) feeding the bischofite solution into a horizontal double-drum centrifuge for liquid-solid separation; the separated waste residue enters a waste residue treatment system; the separated refined magnesium liquid enters a refined magnesium liquid tank and continuously enters an aerosol magnesium precipitation tower through a refined magnesium liquid pump;

(4) the refined magnesium liquid in the refined magnesium liquid tank continuously enters a spray header at the upper part and a gas-liquid two-phase atomizing nozzle at the lower part in the aerosol magnesium precipitation tower through a refined magnesium liquid pump, and the atomized refined magnesium liquid and ammonia gas are subjected to magnesium precipitation reaction; unreacted ammonia gas is discharged out of the tower through a demister and enters a coupler of the spray magnesium precipitation reactor, and magnesium precipitation liquid enters the liquid level in the spray magnesium precipitation reactor through a liquid seal pipe;

(5) the power fluid pump of the jet magnesium deposition reactor feeds the magnesium deposition liquid into the coupler, and the magnesium deposition reaction is continued through the ejector and ammonia gas; the precipitated magnesium liquid enters a precipitated magnesium liquid flash tank through a precipitated magnesium liquid pump;

(6) the precipitated magnesium liquid enters a precipitated magnesium liquid flash tank, ammonia gas and water vapor are subjected to adiabatic flash evaporation, enter an ammonia gas and water vapor compressor, are heated and pressurized and then are used as secondary water vapor (containing a small amount of ammonia gas); the flash liquid in the magnesium precipitation flash tank enters an expansion drum type filter through gravity;

(7) the flash liquid in the magnesium precipitation flash tank enters an expansion drum type filter for concentration through gravity; the separated clear liquid enters an air fog magnesium precipitation tower through a clear liquid pump part to be used as demister spray liquid, and the clear liquid enters a mother liquid tank; concentrated solution in the expansion drum type filter enters a belt type vacuum filter through a concentrated solution pump;

(8) concentrated solution in the expansion drum type filter enters a belt type vacuum filter through a concentrated solution pump to carry out liquid-solid separation; the separated mother liquor enters a mother liquor tank and is pumped to a pre-evaporation ammonia tank; the separated magnesium hydroxide filter cake enters a paddle dryer through a spiral conveyer;

(9) the magnesium hydroxide filter cake enters a paddle dryer for drying through a spiral material conveyor, and the paddle dryer adopts steam heating jacket heat exchange and steam heating stirring paddle heat exchange to dry the magnesium hydroxide filter cake; the magnesium hydroxide powder dried by the paddle dryer enters a jet mill through a spiral feeder;

(10) after entering a jet mill for grinding and grading, the magnesium hydroxide powder dried by the paddle dryer is subjected to gas-solid separation by a cyclone separator and a bag filter, and then enters a magnesium hydroxide powder bin;

(11) the mother liquor and calcium oxide powder from the mother liquor tank enter a pre-ammonia distillation tank, under the action of mechanical stirring, calcium oxide is digested and dissolved, the generated settled sand enters a sand discharge system through a sand discharge device, calcium oxide digestion liquid overflows to a cavitation ammonia distillation reactor, and the generated ammonia gas and water vapor are discharged from the top of the pre-ammonia distillation tank and enter the bottom of a negative pressure ammonia distillation tower;

(12) ammonia gas and water vapor from the top of the pre-ammonia distillation tank enter the bottom of the negative pressure ammonia distillation tower, ammonia gas and water vapor generated in the cavitation ammonia distillation reactor enter the bottom of the negative pressure ammonia distillation tower, and ammonia gas and water vapor are separated in the negative pressure ammonia distillation tower;

(13) in the cavitation ammonia-steaming reactor, calcium oxide digestive liquid is subjected to ammonia-steaming reaction in the cavitation ammonia-steaming reactor; the gas phase in the cavitation ammonia evaporation reactor enters a negative pressure ammonia evaporation tower, and the liquid phase in the cavitation ammonia evaporation reactor enters an ammonia evaporation liquid flash tank through an ammonia evaporation liquid pump;

(14) the liquid phase in the cavitation ammonia distillation reactor enters an ammonia distillation liquid flash tank, ammonia gas and water vapor are subjected to adiabatic flash evaporation, and enter an ammonia gas and water vapor compressor together with the ammonia gas and water vapor from a magnesium precipitation liquid flash tank, and the ammonia gas and water vapor are used as secondary water vapor after being heated and pressurized, and meanwhile, the material in the cavitation ammonia distillation reactor is heated; a flash evaporation liquid calcium chloride removal recovery system in an ammonia evaporation liquid flash evaporation tank.

Further, the raw materials comprising bischofite (mass content is more than 96%), waste residue washing water and process water are added into the dissolving tank in the step (1), and are stirred by a mechanical stirrer to be dissolved; bischofite mass concentration expressed as MgCl₂The content is 30-33%, the temperature in the dissolving tank is 50-55 ℃, the pressure is normal pressure, and the retention time of the materials is 2-2.5 h.

Further, in the step (2), the temperature in the feeding tank of the centrifuge is 45-50 ℃, the pressure is normal pressure, and the retention time of the materials is 1-1.5 h;

further, the outer rotary drum of the horizontal double-drum centrifuge in the step (3) is 2350rpm, the inner rotary drum is 2400rpm, the temperature of an impurity filter cake is 40-45 ℃, and the moisture content is 15-20%;

further, carrying out magnesium precipitation reaction on the atomized refined magnesium liquid in the step (4) and ammonia gas from an ammonia gas buffer tank; the temperature of the top of the aerial fog magnesium precipitation tower is 80-85 ℃, the pressure is 0.15-0.17 MPa, the temperature of the bottom of the aerial fog magnesium precipitation tower is 110-115 ℃, the pressure is 0.2-0.22 MPa, the molar ratio of magnesium chloride to ammonia gas is 1: (6-7).

Further, the ammonia gas and the water vapor in the magnesium injection and precipitation reactor in the step (5) are condensed by a condenser and then enter a gas-liquid separation tank, and the separated ammonia gas enters an ammonia gas buffer tank through an ammonia gas compressor; the precipitated magnesium liquid enters a precipitated magnesium liquid flash tank through a precipitated magnesium liquid pump; the temperature in the jet magnesium deposition reactor is 120-125 ℃, the pressure is 0.25-0.30 MPa, and the retention time of the materials is 2-2.5 h;

further, the adiabatic flash temperature of the magnesium deposition liquid flash tank in the step (6) is 60-65 ℃, and the retention time of the material is 1-1.5 h.

Further, in the step (7), the temperature in the drum type filter is 50-55 ℃, the pressure is normal pressure, the retention time of the materials is 0.5-1 h, and the mass content of the concentrated magnesium hydroxide is 30-35%.

Further, the pressure of the belt type vacuum filter in the step (8) is 0.030MPa to 0.035MPa, the moisture content of the magnesium hydroxide filter cake is 15 percent to 20 percent (wet basis), and the temperature is 40 ℃ to 45 ℃.

Further, in the step (9), the temperature in the blade dryer is 130-135 ℃, the pressure is 0.27-0.315 MPa, the moisture content of the dried magnesium hydroxide powder is 0.1-0.2% (wet basis), and the retention time of the material is 0.75-1 h; the adiabatic flash temperature of the condensed water flash tank is 60-65 ℃, and the retention time of the material is 1-1.5 h.

Further, the particle size of the magnesium hydroxide ground and classified by the airflow pulverizer in the step (10) is less than 5 μm.

Further, the mother liquor from the mother liquor tank in the step (11) is preheated by a cooler arranged in the negative pressure ammonia still and then enters the pre-ammonia still together with 75 μm calcium oxide (mass content is more than 97%) powder; the temperature in the pre-ammonia distillation tank is 80-85 ℃, the pressure is 0.095-0.097 MPa, the molar ratio of ammonium chloride to calcium oxide is 1: 0.60-1: 0.65, and the retention time of the materials is 2-2.5 h.

Further, in the step (12), ammonia and water vapor are separated in a negative pressure ammonia still, the ammonia enters a condenser for condensation after being demisted, and condensed water and ammonia are separated out through a gas-liquid separation tank; the condensed water enters the top of the negative pressure ammonia distillation tower through a condensed water pump to be used as demister spray water, and the condensed water enters the pre-ammonia distillation tank to be used as ingredient water of calcium oxide powder; compressing ammonia gas by an ammonia gas compressor and then feeding the compressed ammonia gas into an ammonia gas buffer tank; the temperature at the top of the negative pressure ammonia still is 75-80 ℃, and the pressure at the top of the negative pressure ammonia still is 0.090 MPa-0.092 MPa.

Further, the temperature in the hollow ammonia distillation reactor in the step (13) is 85-90 ℃, the pressure is 0.096-0.098 MPa, and the retention time of the materials is 2-2.5 h.

Further, in the step (14), the adiabatic flash temperature of the ammonia evaporation flash tank is 60-65 ℃, and the retention time of the material is 1-1.5 h.

The magnesium hydroxide production device for positive pressure magnesium precipitation and dry negative pressure ammonia distillation simultaneously adopts advanced cavitation ammonia distillation reactors, negative pressure ammonia distillation towers, jet magnesium precipitation reactors, aerial fog magnesium precipitation towers, MVR, TVR and other equipment; the cavitation ammonia evaporation reactor and the jet magnesium deposition reactor are adopted to directly replace a mechanical stirring kettle type reactor, the safety and the energy conservation are realized, the TVR is adopted to recover the water vapor generated in the drying process and the secondary vapor flashed out from the water vapor condensate, the MVR is adopted to recover the heat of the magnesium deposition liquid and the ammonia evaporation liquid, the energy consumption is greatly reduced, and the reasonable utilization of the resources in the magnesium hydroxide preparation process is realized.

Compared with the prior art, the utility model has the beneficial effects that:

1. the ammonia gas is hermetically recycled, so that the environment is friendly; low-pressure water vapor is flashed to MVR from the material flow after the ammonia evaporation and magnesium deposition reaction, and secondary water vapor can provide an auxiliary heat source and cavitation airflow for a cavitation ammonia evaporation reactor for ammonia evaporation reaction; the secondary water vapor generated by flashing steam and water vapor condensate water separated by the paddle dryer provides an auxiliary heat source for the paddle dryer; the water vapor condensed water after flash evaporation is used as filter cake washing water; the resources are effectively utilized, the energy is saved, and the environment is protected.

2. The jet magnesium deposition reactor, the cavitation ammonia distillation reactor, the aerosol magnesium deposition tower with white steel structured packing and the negative pressure ammonia distillation tower with white steel structured packing are adopted, so that the heat transfer and mass transfer are enhanced, the production efficiency is improved, and the reaction time is shortened; the aerial fog magnesium deposition creates a prerequisite for the completeness of the crystal form of the magnesium hydroxide, and the high-temperature magnesium deposition of the jet magnesium deposition reactor provides a hydrothermal condition for the completeness of the crystal form of the magnesium hydroxide;

3. the yield of the magnesium hydroxide is more than 90 percent, and the quality of the magnesium hydroxide is superior to the national standard of industrial products; the dry method negative pressure ammonia distillation recovers all reaction heat of calcium oxide; the utility model has the advantages of mature process, continuous operation, high automation degree, resource recycling, environment friendliness and 25 percent of comprehensive energy conservation of the device.

Drawings

FIG. 1 is a schematic diagram of a magnesium hydroxide production apparatus for positive pressure magnesium precipitation and dry negative pressure ammonia distillation according to the present invention;

FIG. 2 is a schematic diagram of a cavitation ammonia distillation reactor according to the present invention;

reference numerals: 1. a dissolving tank 1-1, a mechanical stirrer; 2. a centrifuge feeding tank, 2-1, a mechanical stirrer and 2-2 of a bischofite solution pump; 3. 3-1 parts of a horizontal double-drum centrifuge, 3-2 parts of a refined magnesium liquid tank and a refined magnesium liquid pump; 4. 4-1 parts of an aerial fog magnesium precipitation tower, 4-2 parts of a demister, 4-3 parts of a spray header, 4-4 parts of a gas-liquid two-phase atomizing nozzle and a liquid seal pipe; 5. 5-1 parts of a jet magnesium precipitation reactor, 5-2 parts of a coupler, 5-3 parts of an injector, 5-4 parts of a power fluid pump, 5-5 parts of a condenser and a magnesium precipitation pump; 6. a magnesium precipitation liquid flash tank, 6-1, and a mechanical stirrer; 7. 7-1 parts of an expansion drum type filter, 7-2 parts of a filter bag, 7-3 parts of a concentrated liquid pump and a clear liquid pump; 8. a belt type vacuum filter 8-1, a vacuum chamber 8-2, a buffer tank 8-3, a vacuum pump 8-4, a water washing pump 8-5, a mother liquor tank 8-6 and a mother liquor pump; 9. 9-1 parts of a paddle dryer, 9-2 parts of a spiral conveyor, 9-3 parts of a condensed water flash tank, 9-4 parts of a condensed water pump, 9-5 parts of a steam ejector (TVR), 9-6 parts of a steam heating jacket and 9-6 parts of steam heating stirring blades; 10. 10-1 of an airflow crusher, 10-1 of a cyclone separator, 10-2 of a bag filter, 10-3 of a magnesium hydroxide powder bin; 11. a pre-ammonia-steaming tank 11-1, a calcium oxide powder feeder 11-2, a mechanical stirrer 11-3 and a sand discharger; 12. 12-1 parts of a negative pressure ammonia distillation tower, 12-2 parts of a demister, 12-3 parts of a built-in cooler, 12-4 parts of a white steel structured packing, 12-5 parts of a condenser, 12-6 parts of a gas-liquid separation tank, 12-7 parts of a condensate pump, 12-8 parts of an ammonia gas compressor and an ammonia gas buffer tank; 13. 13-1 parts of a cavitation ammonia distillation reactor, 13-2 parts of a stirring heat transfer rotor, 13-3 parts of a mechanical seal, 13-4 parts of a tooth-shaped baffle (four uniformly distributed), 13-5 parts of an airflow cavitation nozzle, 13-6 parts of 45-degree 12-blade turbine blades (four layers), and 13-6 parts of an ammonia distillation pump; 14. ammonia evaporation liquid flash tank, 14-1, mechanical stirrer, 14-2 ammonia gas and water vapor compressor.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the utility model and are not intended to limit the utility model.

Example 1

As shown in fig. 1 and 2, the magnesium hydroxide production device for positive pressure magnesium precipitation and dry negative pressure ammonia distillation comprises a dissolving tank 1, a centrifuge feeding tank 2, a horizontal double-drum centrifuge 3, an aerial fog magnesium precipitation tower 4, a jet magnesium precipitation reactor 5, a magnesium precipitation liquid flash tank 6, an expansion drum type filter 7, a belt type vacuum filter 8, a paddle dryer 9 and an air flow crusher 10 which are connected in sequence; the dissolving tank is used for dissolving bischofite; the centrifuge feeding tank is used for intermediate storage of bischofite solution; the horizontal double-drum centrifuge is used for carrying out liquid-solid separation on the bischofite solution and solid impurities; the aerial fog magnesium precipitation tower is used for atomizing the separated refined magnesium liquid and performing magnesium precipitation reaction with ammonia gas; the jet magnesium precipitation reactor is used for precipitating magnesium liquid and ammonia gas to continue magnesium precipitation reaction; the magnesium precipitation liquid flash tank is used for carrying out flash evaporation on the magnesium precipitation liquid; the expansion drum type filter is used for concentrating the magnesium precipitation flash evaporation liquid; the belt type vacuum filter is used for carrying out liquid-solid separation on the concentrated solution of the expansion drum type filter; the paddle dryer is used for drying the filtered magnesium hydroxide filter cake of the vacuum filter; the jet mill is used for grinding and grading the magnesium hydroxide powder dried by the paddle dryer;

the device also comprises a mother liquor tank 8-5, a pre-ammonia distillation tank 11, a cavitation ammonia distillation reactor 13 and an ammonia distillation flash tank 14 which are connected in sequence; the mother liquor tank is connected with the expansion drum type filter and the belt type vacuum filter, and is used for collecting ammonium chloride mother liquor separated by the expansion drum type filter and the belt type vacuum filter to be used as a batching solution for dissolving calcium oxide; the pre-steamed ammonia tank is used for digesting calcium oxide powder and ammonium chloride mother liquor and pre-steaming ammonia; the cavitation ammonia distillation reactor is used for ammonia distillation reaction of calcium hydroxide and ammonium chloride mother liquor; the ammonia evaporation liquid flash tank is used for carrying out flash evaporation on the ammonia evaporation liquid; a negative pressure ammonia still 12 is arranged above the cavitation ammonia still reactor and is used for separating ammonia and water vapor;

the jet magnesium deposition reactor adopts jet stirring and adopts jacket heat exchange; the cavitation ammonia-steaming reactor directly exchanges heat through steam introduced into the stirring heat transfer rotor and water vapor introduced into the airflow cavitation nozzle.

As an improvement of the technical scheme, an airflow cavitation nozzle 13-4 for introducing steam into the reactor is arranged on the outer wall, a tooth-shaped baffle 13-3 is arranged on the inner wall, a hollow stirring heat transfer rotor 13-1 is arranged in the reactor, a plurality of layers of blades are arranged on the outer wall of the stirring heat transfer rotor, the plurality of layers of blades are 45-degree 12-blade turbine blades uniformly distributed on the stirring heat transfer rotor, and each layer of blades and each tooth of the tooth-shaped baffle are staggered in the horizontal direction; the tooth-shaped baffles are four and are symmetrically arranged on the inner wall of the reactor at intervals of 90 degrees. The cavitation ammonia-steaming reactor adopts steam to cavitate through the airflow cavitation nozzle and heat materials at the same time, and cavitation can also be generated between the 45-degree 12-blade turbine blades (four layers) and the tooth-shaped baffles (four uniform distribution); cavitation can generate strong shock waves and micro-jet in a very small range and cause the generation of hot spots, the temperature can reach 10000K, the pressure is about 100MPa, and correspondingly cavitation effects such as hot spot effect, mechanical effect, chemical effect and the like occur, thereby being beneficial to the digestion reaction of calcium oxide particles.

As an improvement of the technical solution, the apparatus further comprises: 12-5 parts of a gas-liquid separation tank, 12-8 parts of an ammonia buffer tank and 12-7 parts of an ammonia compressor; the inlet of the gas-liquid separation tank is connected with an unreacted ammonia gas outlet of the jet magnesium deposition reactor and an ammonia gas outlet at the top of the negative pressure ammonia distillation tower, and is used for carrying out gas-liquid separation on the collected ammonia gas; the input end of the ammonia gas compressor is connected with a gas phase outlet of the gas-liquid separation tank, the output end of the ammonia gas compressor is connected with an inlet of the ammonia gas buffer tank, and an outlet of the ammonia gas buffer tank is connected with an ammonia gas inlet of the aerial fog magnesium precipitation tower. Unreacted ammonia in the jet magnesium precipitation reactor and separated ammonia in the negative pressure ammonia still are condensed by a condenser, gas-liquid separation is carried out, the ammonia compressed by an ammonia compressor enters an ammonia buffer tank, and the ammonia collected by the ammonia buffer tank enters an aerosol magnesium precipitation tower.

As a technical scheme improvement, the device also comprises ammonia gas and a water vapor compressor (MVR) 14-2; the input end of the ammonia gas and water vapor compressor is connected with the ammonia evaporation liquid flash tank and the magnesium precipitation liquid flash tank, and the output end of the ammonia gas and water vapor compressor is connected with the airflow cavitation nozzle of the cavitation ammonia evaporation reactor. And ammonia gas and water vapor which are adiabatically flashed in the ammonia evaporation liquid flash tank and the magnesium precipitation liquid flash tank enter an ammonia gas and water vapor compressor to be heated and pressurized to form secondary water vapor, and the secondary water vapor enters an airflow cavitation nozzle on the side wall of the cavitation ammonia evaporation reactor to be used as cavitation airflow of the airflow cavitation nozzle of the cavitation ammonia evaporation reactor and also to be used as an auxiliary heat source of the cavitation ammonia evaporation reactor.

As the improvement of the technical proposal, the device also comprises a steam ejector (TVR)9-4 and a condensed water flash tank 9-2; the steam jet device is connected with the paddle dryer, the paddle dryer adopts steam heating jacket heat exchange and steam heating stirring paddle heat exchange to dry the magnesium hydroxide filter cake, and the generated secondary water steam is used as an auxiliary heat source and enters the paddle dryer steam heating jacket and the steam heating stirring paddle again through the steam jet device to dry materials; the stirring heat transfer rotor of the cavitation ammonia distillation reactor takes water vapor as a heat source, the condensed water flash tank is used for collecting water vapor condensed water generated by the heat transfer rotor of the cavitation ammonia distillation reactor and the blade dryer, after secondary water vapor is flashed from the collected water vapor condensed water, the flash condensed water is conveyed to the horizontal double-drum centrifuge and the belt vacuum filter through the condensed water pump 9-3 and is used for filter cakes of the horizontal double-drum centrifuge and filter cake washing water of the belt vacuum filter.

The cavitation ammonia-steaming reactor heat transfer rotor takes water vapor as a heat source, and the paddle dryer takes the water vapor, secondary water vapor generated by the paddle dryer and secondary water vapor generated by flash evaporation of water vapor condensate water as the heat source.

Wherein:

the magnesium tower is composed of a demister 4-1, a spray header 4-2, a gas-liquid two-phase atomizing nozzle 4-3 and a liquid seal pipe 4-4; the lower part in the aerial fog magnesium precipitation tower is provided with a gas-liquid two-phase atomizing nozzle, the upper part is provided with a demister and a spray header from top to bottom, and the bottom of the tower is provided with a liquid seal pipe which extends to a position below the liquid level in the jet magnesium precipitation reactor.

The jet magnesium settling reactor consists of a coupler 5-1 and an injector 5-2, and related components further comprise a power fluid pump 5-3, a condenser 5-4 and a magnesium settling fluid pump 5-5; the coupler consists of a mixed liquid inlet pipe, a mixed liquid distribution cavity, a gas suction pipe, a gas distribution cavity and the like; the ejector adopts the venturi jet principle and consists of a power fluid inlet, a flow guide ring, a power fluid nozzle, a gas suction inlet, a mixing cavity, a diffusion cavity and a mixed liquid outlet; the mixed liquid in the suction device of the power fluid pump is operated and pumped into the coupler, the power fluid passes through the nozzle to form high-speed fluid, the kinetic energy of the fluid is maximum, the potential energy is minimum, negative pressure is generated at the gas suction inlet, then the gas is sucked, the sucked gas is rapidly expanded in a negative pressure area and is beaten into tiny bubbles by the power fluid, the gas and the liquid are fully mixed in the coupler and are accelerated to be discharged due to energy exchange, the potential energy of the mixed liquid is increased to the maximum value through the pressure expansion cavity, and the mixing and stirring effects are enhanced by the dragging effect of the mixed fluid; the ammonia gas is sucked by the coupler, so that high-speed jet flow close to the speed of sound can be generated, and heat and mass transfer among mixed liquor is facilitated to carry out magnesium precipitation reaction;

the belt type vacuum filter consists of a vacuum chamber 8-1, a buffer tank 8-2, a vacuum pump 8-3 and a washing water pump 8-4; the concentrated solution passes through a vacuum chamber 8-1, under the action of a vacuum pump 8-3, the mother solution firstly enters a buffer tank 8-2 and then enters a mother solution tank 8-5, and a washing pump 8-4 is used for washing primary filter cakes by primary washing water;

the negative pressure ammonia distillation tower consists of a demister 12-1 from top to bottom, a built-in cooler 12-2 and a white steel structured packing 12-3, and related components further comprise a condenser 12-4, a gas-liquid separation tank 12-5, a condensate pump 12-6, an ammonia gas compressor 12-7 and an ammonia gas buffer tank 12-8; the cavitation ammonia distillation reactor plays a role of a negative pressure ammonia distillation tower reboiler, ammonia and water vapor are separated in the negative pressure ammonia distillation tower through white steel structured packing, an internal cooler can generate internal reflux, cooled ammonia enters an ammonia compressor after being demisted by a demister, and compressed ammonia enters an aerosol magnesium precipitation tower through an ammonia buffer tank;

the cavitation ammonia distillation reactor consists of a hollow stirring heat transfer rotor 13-1, a mechanical seal 13-2, a tooth-shaped baffle (four uniformly distributed) 13-3, an airflow cavitation nozzle 13-4 and a 45-degree 12-blade turbine blade (four layers) 13-5, and related components also comprise an ammonia distillation liquid pump 13-6; the calcium oxide digestion slurry is subjected to ammonia evaporation reaction in a cavitation ammonia evaporation reactor, and generates cavitation effect under the combined action of an airflow cavitation nozzle, four layers of 12-blade turbine blades with 45 degrees on a high-speed stirring heat transfer rotor and a tooth-shaped baffle plate, so that a hydration layer is effectively stripped; the instant local high temperature and high pressure, micro jet and shock wave caused by cavitation provide good physicochemical environment for the chemical reaction, improve the chemical reaction rate and provide chemical reaction power; the macro-mixing and micro-mixing in the flow field are improved, and the gas phase, the liquid phase and the solid phase have extremely high mass transfer rate.

The raw materials adopted in the embodiment are bischofite (mass content is more than 96%), 75 μm calcium oxide (mass content is more than 97%) powder; the used water vapor of the public engineering is back pressure water vapor of 0.45MPa and 245 ℃ of a self-contained power plant; the utility steam mainly provides a heat source for the blade dryer and also provides a heat source for the cavitation ammonia distillation reactor.

When the production device is started, the dissolving tank adopts process water for proportioning, and the cavitation ammonia-steaming reactor adopts public engineering water vapor to heat materials through the stirring heat transfer rotor; when the production device is started, ammonia gas is supplemented from an ammonia buffer tank, the material is heated by the aid of public engineering water vapor through a jacket in the magnesium deposition jet reactor until the whole production device operates normally, and the reaction is continued by switching to cooling water; the devices are connected through corresponding pipelines, and when the pipelines in the figure 1 are crossed on the figure and actually do not intersect, the pipelines are drawn according to the principle of vertical and continuous intersection.

The method for producing magnesium hydroxide by positive pressure magnesium precipitation and dry negative pressure ammonia distillation specifically comprises the following steps:

(1) raw materials of bischofite, washing water from a waste residue treatment system and process water enter a dissolving tank 1, and bischofite is dissolved under the stirring of a mechanical stirrer 1-1;

(2) the bischofite solution in the dissolving tank continuously enters a centrifuge feeding tank 2 through gravity, and enters a horizontal double-drum centrifuge 3 through a bischofite solution pump 2-2 under the stirring of a mechanical stirrer 2-1;

(3) the bischofite solution in the centrifuge feed tank enters a horizontal double-drum centrifuge through a bischofite solution pump for liquid-solid separation; the separated waste residue enters a waste residue treatment system; the separated refined magnesium liquid enters a refined magnesium liquid tank 3-1 and continuously enters an aerosol magnesium precipitation tower 4 through a refined magnesium liquid pump 3-2; washing waste residues (containing a small amount of bischofite) in a waste residue treatment system, and conveying washing water to a dissolving tank 1;

(4) refined magnesium liquid in the refined magnesium liquid tank continuously enters a spray header 4-2 at the upper part and a gas-liquid two-phase atomizing nozzle 4-3 at the lower part in the aerosol magnesium precipitation tower through a refined magnesium liquid pump, and the atomized refined magnesium liquid and ammonia gas from an ammonia gas buffer tank 12-8 are subjected to magnesium precipitation reaction; unreacted ammonia gas is discharged out of the tower through a demister 4-1 and enters a coupler 5-1 of the spray magnesium deposition reactor, and magnesium deposition liquid enters the liquid level in the spray magnesium deposition reactor 5 through a liquid seal pipe 4-4;

(5) magnesium deposition liquid in the aerial fog magnesium deposition tower enters the position below the liquid level in the jet magnesium deposition reactor through a liquid seal pipe, the power fluid pump 5-3 of the jet magnesium deposition reactor enters the magnesium deposition liquid into the coupler 5-1, and the magnesium deposition reaction is continuously carried out through the ejector 5-2 and ammonia gas; ammonia gas and water vapor in the jet magnesium deposition reactor are condensed by a condenser 5-4 and then enter a gas-liquid separation tank 12-5, and the separated ammonia gas enters an ammonia gas buffer tank 12-8 (the pressure is higher than the tower bottom pressure of the aerosol magnesium deposition tower) through an ammonia gas compressor 12-7; the precipitated magnesium liquid enters a precipitated magnesium liquid flash tank 6 through a precipitated magnesium liquid pump 5-5;

(6) the precipitated magnesium liquid enters a precipitated magnesium liquid flash tank, a mechanical stirrer 6-1 is used for stirring, ammonia gas and water vapor are subjected to adiabatic flash evaporation, and the ammonia gas and the water vapor enter an ammonia gas and water vapor compressor 14-2 for temperature rise and pressure rise and then are used as secondary water vapor (containing a small amount of ammonia gas); the flash liquid in the magnesium precipitation flash tank enters an expansion drum type filter 7 through gravity;

(7) the flash liquid in the magnesium precipitation flash tank enters an expansion drum type filter for concentration through gravity; the clear liquid separated by the filter bag 7-1 partially enters the gas fog magnesium precipitation tower 4 through a clear liquid pump 7-3 to be used as demister spray liquid, and partially enters a mother liquid tank 8-5; concentrated solution in the expansion drum type filter enters a belt type vacuum filter 8 through a concentrated solution pump 7-2;

(8) concentrated solution in the expansion drum type filter enters a belt type vacuum filter through a concentrated solution pump to carry out liquid-solid separation; the separated mother liquor enters a mother liquor tank and is sent to a pre-ammonia distillation tank through a mother liquor pump 8-6; the separated magnesium hydroxide filter cake enters a paddle dryer 9 through a spiral conveyer 9-1;

(9) the magnesium hydroxide filter cake enters a paddle dryer for drying through a spiral material conveyor, and the paddle dryer adopts a steam heating jacket 9-5 for heat exchange and a steam heating stirring paddle 9-6 for heat exchange to dry the magnesium hydroxide filter cake; steam discharged from the blade dryer, secondary steam flashed by steam heating jacket heat exchange and steam heating stirring blade heat exchange condensate water, and then enter the steam heating jacket and the steam heating stirring blade through a steam ejector (TVR)9-4 as an auxiliary heat source; the condensed water after flash evaporation is used as the washing water of the waste residue of the horizontal double-drum centrifuge and the washing water of the magnesium hydroxide filter cake of the belt vacuum filter; the magnesium hydroxide powder dried by the paddle dryer enters the jet mill 10 through the spiral feeder;

(10) after entering a jet mill for grinding and grading through a spiral material conveyer, feeding the magnesium hydroxide powder dried by a paddle dryer, carrying out gas-solid separation through a cyclone separator 10-1 and a bag filter 10-2, and feeding the magnesium hydroxide powder into a magnesium hydroxide powder bin 10-3;

(11) preheating mother liquor from a mother liquor tank through a negative pressure ammonia still built-in cooler 12-2, then feeding the mother liquor and calcium oxide powder into a pre-ammonia still 11, feeding the calcium oxide through a calcium oxide powder feeder 11-1, digesting and dissolving the calcium oxide under the action of a mechanical stirrer 11-2, feeding the generated settled sand into a sand discharge system through a sand discharge device 11-3, overflowing calcium oxide digestion liquid into a cavitation ammonia still 13, and discharging the generated ammonia gas and water vapor from the top of the pre-ammonia still to the bottom of the negative pressure ammonia still 12;

(12) ammonia gas and water vapor from the top of the pre-ammonia distillation tank enter the bottom of a negative pressure ammonia distillation tower, ammonia gas and water vapor generated in the cavitation ammonia distillation reactor enter the bottom of the negative pressure ammonia distillation tower, ammonia and water vapor are separated in the negative pressure ammonia distillation tower, the ammonia gas is demisted and then enters a condenser 12-4 for condensation, and condensed water and ammonia gas are separated out through a gas-liquid separation tank; part of condensed water enters the top of the negative pressure ammonia distillation tower through a condensate pump 12-6 to be used as spray water of a demister 12-1, and part of condensed water enters a pre-ammonia distillation tank to be used as ingredient water of calcium oxide powder; compressing ammonia gas by an ammonia gas compressor 12-7 and then entering an ammonia gas buffer tank 12-8;

(13) in the cavitation ammonia-steaming reactor, calcium oxide digestive liquid is subjected to ammonia-steaming reaction in the cavitation ammonia-steaming reactor; in the cavitation ammonia-steaming reactor, secondary water vapor (containing a small amount of ammonia gas) is adopted to cavitate through the airflow cavitation nozzle 13-4 and heat materials at the same time, and cavitation can also be generated between the 45-degree 12-blade turbine blade 13-5 (four layers) and the tooth-shaped baffle 13-3 (four uniform distribution); the material is heated by the water vapor through the stirring heat transfer rotor 13-1, the gas phase in the cavitation ammonia distillation reactor enters a negative pressure ammonia distillation tower, and the liquid phase in the cavitation ammonia distillation reactor enters an ammonia distillation flash tank 14 through an ammonia distillation liquid pump 13-6;

(14) liquid phase in the cavitation ammonia-steaming reactor enters an ammonia-steaming liquid flash tank through an ammonia-steaming liquid pump, a mechanical stirrer 14-1 is used for stirring, ammonia gas and water vapor are subjected to adiabatic flash evaporation, and enter an ammonia gas and water vapor compressor 14-2 together with ammonia gas and water vapor from a magnesium-precipitating liquid flash tank, secondary water vapor (containing a small amount of ammonia gas) after temperature and pressure rise is used as cavitation airflow of an airflow cavitation nozzle of the cavitation ammonia-steaming reactor, and materials in the cavitation ammonia-steaming reactor are heated at the same time; a flash evaporation liquid calcium chloride removal recovery system in an ammonia evaporation liquid flash evaporation tank.

Example 2

The magnesium hydroxide production method based on the positive pressure magnesium deposition and the dry negative pressure ammonia distillation of the device in the embodiment 1 comprises the following steps:

(1) 200kg/h of bischofite (mass content is more than 96 percent), waste residue washing water and process water are added into a dissolving tank, and the materials are dissolved under the stirring of a mechanical stirrer; bischofite mass concentration expressed as MgCl₂The content is 30%, the temperature in the dissolving tank is 50 ℃, the pressure is normal pressure, and the retention time of the materials is 2 hours;

(2) continuously feeding the bischofite solution in the dissolving tank into a centrifuge feeding tank by gravity, and feeding the bischofite solution into a horizontal double-drum centrifuge by a bischofite solution pump; the temperature in the centrifuge feeding tank is 45 ℃, the pressure is normal pressure, and the retention time of the materials is 1 h;

(3) the bischofite solution in the centrifuge feed tank enters a horizontal double-drum centrifuge through a bischofite solution pump for liquid-solid separation; the separated waste residue enters a waste residue treatment system; the separated refined magnesium liquid enters a refined magnesium liquid tank and continuously enters an aerosol magnesium precipitation tower through a refined magnesium liquid pump; the outer rotary drum of the horizontal double-drum centrifuge is 2350rpm, the inner rotary drum is 2400rpm, the temperature of an impurity filter cake is 40 ℃, and the moisture content is 15 percent (wet basis);

(4) the refined magnesium liquid in the refined magnesium liquid tank continuously enters a spray header at the upper part and a gas-liquid two-phase atomizing nozzle at the lower part in the aerosol magnesium precipitation tower through a refined magnesium liquid pump, and the atomized refined magnesium liquid and ammonia gas from an ammonia gas buffer tank are subjected to magnesium precipitation reaction; unreacted ammonia gas is discharged out of the tower through a demister and enters a coupler of the spray magnesium precipitation reactor, and magnesium precipitation liquid enters the liquid level in the spray magnesium precipitation reactor through a liquid seal pipe; the temperature of the top of the aerial fog magnesium precipitation tower is 80 ℃, the pressure is 0.15MPa, the temperature of the bottom of the aerial fog magnesium precipitation tower is 110 ℃, the pressure is 0.2MPa, and the molar ratio of magnesium chloride to ammonia gas is 1: 6;

(5) magnesium deposition liquid in the aerial fog magnesium deposition tower enters the position below the liquid level in the jet magnesium deposition reactor through a liquid seal pipe, the power fluid pump of the jet magnesium deposition reactor enables the magnesium deposition liquid to enter the coupler, and the magnesium deposition reaction is continuously carried out through the ejector and ammonia gas; condensing ammonia gas and water vapor in the jet magnesium precipitation reactor through a condenser, then feeding the condensed ammonia gas and water vapor into a gas-liquid separation tank, and feeding the separated ammonia gas into an ammonia gas buffer tank through an ammonia gas compressor; the precipitated magnesium liquid enters a precipitated magnesium liquid flash tank through a precipitated magnesium liquid pump; the temperature in the jet magnesium deposition reactor is 120 ℃, the pressure is 0.25MPa, and the retention time of the materials is 2 h;

(6) the precipitated magnesium liquid enters a precipitated magnesium liquid flash tank, ammonia gas and water vapor are subjected to adiabatic flash evaporation, enter an ammonia gas and water vapor compressor, are heated and pressurized and then are used as secondary water vapor (containing a small amount of ammonia gas); the flash liquid in the magnesium precipitation flash tank enters an expansion drum type filter through gravity; the adiabatic flash temperature of the magnesium precipitation liquid flash tank is 60 ℃, and the retention time of the material is 1 h;

(7) the flash liquid in the magnesium precipitation flash tank enters an expansion drum type filter for concentration through gravity; the separated clear liquid enters an air fog magnesium precipitation tower through a clear liquid pump part to be used as demister spray liquid, and the clear liquid enters a mother liquid tank; concentrated solution in the expansion drum type filter enters a belt type vacuum filter through a concentrated solution pump; the temperature in the drum type filter is 50 ℃, the pressure is normal pressure, the retention time of the material is 0.5h, and the mass content of the concentrated magnesium hydroxide is 30%;

(8) concentrated solution in the expansion drum type filter enters a belt type vacuum filter through a concentrated solution pump to carry out liquid-solid separation; the separated mother liquor enters a mother liquor tank and is pumped to a pre-evaporation ammonia tank; the separated magnesium hydroxide filter cake enters a paddle dryer through a spiral conveyer; the pressure of the belt type vacuum filter is 0.030MPa, the moisture content of the magnesium hydroxide filter cake is 15% (wet basis), and the temperature is 40 ℃;

(9) the magnesium hydroxide filter cake enters a paddle dryer for drying through a spiral material conveyor, and the paddle dryer adopts steam heating jacket heat exchange and steam heating stirring paddle heat exchange to dry the magnesium hydroxide filter cake; steam discharged from the blade dryer, a steam heating jacket and secondary steam flashed by steam heating stirring blade condensed water enter the steam heating jacket and the steam heating stirring blade through a steam ejector (TVR) as an auxiliary heat source; the condensed water after flash evaporation is used as the washing water of the waste residue of the horizontal double-drum centrifuge and the washing water of the magnesium hydroxide filter cake of the belt vacuum filter; the magnesium hydroxide powder dried by the paddle dryer enters a jet mill through a spiral feeder; the temperature in the paddle dryer is 130 ℃, the pressure is 0.27MPa, the moisture content of the dried magnesium hydroxide powder is 0.2% (wet basis), and the retention time of the material is 0.75 h; the adiabatic flash temperature of the condensed water flash tank is 60 ℃, and the retention time of the material is 1 h;

(10) after entering a jet mill for grinding and grading through a spiral conveyor, feeding the magnesium hydroxide powder dried by the paddle dryer into a cyclone separator and a bag filter, carrying out gas-solid separation, and feeding 50kg/h of magnesium hydroxide powder into a magnesium hydroxide powder bin; the particle size of the magnesium hydroxide ground and classified by the jet mill is less than 5 mu m;

(11) preheating mother liquor from a mother liquor tank through a cooler arranged in a negative pressure ammonia still, then feeding the mother liquor and 75 mu m calcium oxide (mass content is more than 97%) powder 60kg/h into a pre-ammonia still, digesting and dissolving the calcium oxide under the action of mechanical stirring, feeding the generated settled sand into a sand discharge system through a sand discharge device, overflowing calcium oxide digestion liquid into a cavitation ammonia still reactor, discharging generated ammonia gas and water vapor from the top of the pre-ammonia still, and feeding the ammonia gas and the water vapor into the bottom of the negative pressure ammonia still; the temperature in the pre-ammonia distillation tank is 80 ℃, the pressure is 0.095MPa, the molar ratio of ammonium chloride to calcium oxide is 1:0.60, and the retention time of the materials is 2 h;

(12) ammonia gas and water vapor from the top of the pre-ammonia distillation tank enter the bottom of a negative pressure ammonia distillation tower, ammonia gas and water vapor generated in the cavitation ammonia distillation reactor enter the bottom of the negative pressure ammonia distillation tower, ammonia and water vapor are separated in the negative pressure ammonia distillation tower, the ammonia gas is demisted and then enters a condenser for condensation, and condensed water and ammonia gas are separated out through a gas-liquid separation tank; the condensed water enters the top of the negative pressure ammonia distillation tower through a condensed water pump to be used as demister spray water, and the condensed water enters the pre-ammonia distillation tank to be used as ingredient water of calcium oxide powder; compressing ammonia gas by an ammonia gas compressor and then feeding the compressed ammonia gas into an ammonia gas buffer tank; the tower top temperature of the negative pressure ammonia still is 75 ℃, and the tower top pressure is 0.090 MPa;

(13) in the cavitation ammonia-steaming reactor, calcium oxide digestive liquid is subjected to ammonia-steaming reaction in the cavitation ammonia-steaming reactor; in the cavitation ammonia-steaming reactor, secondary water vapor (containing a small amount of ammonia gas) is adopted to perform cavitation through the airflow cavitation nozzle and heat materials at the same time, and cavitation can also be generated between the 45-degree 12-blade turbine blade (four layers) and the tooth-shaped baffle (four uniform distribution); the material is heated by the water vapor through the stirring heat transfer rotor, the gas phase in the cavitation ammonia-steaming reactor enters the negative pressure ammonia-steaming tower, and the liquid phase in the cavitation ammonia-steaming reactor enters the ammonia-steaming flash tank through the ammonia-steaming liquid pump; the temperature in the cavitation ammonia-steaming reactor is 85 ℃, the pressure is 0.096MPa, and the retention time of the materials is 2 h;

(14) the liquid phase in the cavitation ammonia distillation reactor enters an ammonia distillation flash tank through an ammonia distillation liquid pump, ammonia gas and water vapor are subjected to adiabatic flash evaporation and enter an ammonia gas and water vapor compressor together with the ammonia gas and the water vapor from a magnesium precipitation flash tank, the secondary water vapor (containing a small amount of ammonia gas) after temperature and pressure rise is used as cavitation gas flow of a cavitation ammonia distillation reactor airflow cavitation nozzle, and meanwhile, materials in the cavitation ammonia distillation reactor are heated; a flash evaporation liquid calcium chloride removal recovery system in the ammonia evaporation liquid flash evaporation tank; the adiabatic flash temperature of the ammonia evaporation liquid flash tank is 60 ℃, and the retention time of the material is 1 h.

Example 3

(1) 200kg/h of bischofite (mass content is more than 96 percent), waste residue washing water and process water are added into a dissolving tank, and the materials are dissolved under the stirring of a mechanical stirrer; bischofite mass concentration expressed as MgCl₂The content is 33 percent, the temperature in the dissolving tank is 55 ℃, the pressure is normal pressure, and the retention time of the materials is 2.5 hours;

(2) continuously feeding the bischofite solution in the dissolving tank into a centrifuge feeding tank by gravity, and feeding the bischofite solution into a horizontal double-drum centrifuge by a bischofite solution pump; the temperature in the centrifuge feeding tank is 50 ℃, the pressure is normal pressure, and the retention time of the materials is 1.5 h;

(3) the bischofite solution in the centrifuge feed tank enters a horizontal double-drum centrifuge through a bischofite solution pump for liquid-solid separation; the separated waste residue enters a waste residue treatment system; the separated refined magnesium liquid enters a refined magnesium liquid tank and continuously enters an aerosol magnesium precipitation tower through a refined magnesium liquid pump; the outer rotary drum of the horizontal double-drum centrifuge is 2350rpm, the inner rotary drum is 2400rpm, the temperature of an impurity filter cake is 45 ℃, and the moisture content is 20 percent (wet basis);

(4) the refined magnesium liquid in the refined magnesium liquid tank continuously enters a spray header at the upper part and a gas-liquid two-phase atomizing nozzle at the lower part in the aerosol magnesium precipitation tower through a refined magnesium liquid pump, and the atomized refined magnesium liquid and ammonia gas from an ammonia gas buffer tank are subjected to magnesium precipitation reaction; unreacted ammonia gas is discharged out of the tower through a demister and enters a coupler of the spray magnesium precipitation reactor, and magnesium precipitation liquid enters the liquid level in the spray magnesium precipitation reactor through a liquid seal pipe; the temperature of the top of the aerial fog magnesium precipitation tower is 85 ℃, the pressure is 0.17MPa, the temperature of the bottom of the aerial fog magnesium precipitation tower is 115 ℃, the pressure is 0.22MPa, and the molar ratio of magnesium chloride to ammonia gas is 1: 7;

(5) magnesium deposition liquid in the aerial fog magnesium deposition tower enters the position below the liquid level in the jet magnesium deposition reactor through a liquid seal pipe, the power fluid pump of the jet magnesium deposition reactor enables the magnesium deposition liquid to enter the coupler, and the magnesium deposition reaction is continuously carried out through the ejector and ammonia gas; condensing ammonia gas and water vapor in the jet magnesium precipitation reactor through a condenser, then feeding the condensed ammonia gas and water vapor into a gas-liquid separation tank, and feeding the separated ammonia gas into an ammonia gas buffer tank through an ammonia gas compressor; the precipitated magnesium liquid enters a precipitated magnesium liquid flash tank through a precipitated magnesium liquid pump; the temperature in the jet magnesium deposition reactor is 125 ℃, the pressure is 0.30MPa, and the retention time of the materials is 2.5 h;

(6) the precipitated magnesium liquid enters a precipitated magnesium liquid flash tank, ammonia gas and water vapor are subjected to adiabatic flash evaporation, enter an ammonia gas and water vapor compressor, are heated and pressurized and then are used as secondary water vapor (containing a small amount of ammonia gas); the flash liquid in the magnesium precipitation flash tank enters an expansion drum type filter through gravity; the adiabatic flash temperature of the magnesium precipitation liquid flash tank is 65 ℃, and the retention time of the material is 1.5 h;

(7) the flash liquid in the magnesium precipitation flash tank enters an expansion drum type filter for concentration through gravity; the separated clear liquid enters an air fog magnesium precipitation tower through a clear liquid pump part to be used as demister spray liquid, and the clear liquid enters a mother liquid tank; concentrated solution in the expansion drum type filter enters a belt type vacuum filter through a concentrated solution pump; the temperature in the drum type filter is 55 ℃, the pressure is normal pressure, the retention time of the material is 1h, and the mass content of the concentrated magnesium hydroxide is 35%;

(8) concentrated solution in the expansion drum type filter enters a belt type vacuum filter through a concentrated solution pump to carry out liquid-solid separation; the separated mother liquor enters a mother liquor tank and is pumped to a pre-evaporation ammonia tank; the separated magnesium hydroxide filter cake enters a paddle dryer through a spiral conveyer; the pressure of the belt type vacuum filter is 0.035MPa, the moisture content of the magnesium hydroxide filter cake is (wet basis) 20 percent, and the temperature is 45 ℃;

(9) the magnesium hydroxide filter cake enters a paddle dryer for drying through a spiral material conveyor, and the paddle dryer adopts steam heating jacket heat exchange and steam heating stirring paddle heat exchange to dry the magnesium hydroxide filter cake; steam discharged from the blade dryer, a steam heating jacket and secondary steam flashed by steam heating stirring blade condensed water enter the steam heating jacket and the steam heating stirring blade through a steam ejector (TVR) as an auxiliary heat source; the condensed water after flash evaporation is used as the washing water of the waste residue of the horizontal double-drum centrifuge and the washing water of the magnesium hydroxide filter cake of the belt vacuum filter; the magnesium hydroxide powder dried by the paddle dryer enters a jet mill through a spiral feeder; the temperature in the paddle dryer is 135 ℃, the pressure is 0.315MPa, the moisture content of the dried magnesium hydroxide powder is 0.1% (wet basis), and the retention time of the material is 1 h; the adiabatic flash temperature of the condensed water flash tank is 65 ℃, and the retention time of the material is 1.5 h;

(10) after entering a jet mill for grinding and grading through a spiral material conveyer, feeding the magnesium hydroxide powder dried by a paddle dryer, separating gas and solid through a cyclone separator and a bag filter, and feeding 51kg/h of magnesium hydroxide powder into a magnesium hydroxide powder bin; the particle size of the magnesium hydroxide ground and classified by the jet mill is less than 5 mu m;

(11) preheating mother liquor from a mother liquor tank through a cooler arranged in a negative pressure ammonia still, then feeding the mother liquor and 75 mu m calcium oxide (mass content is more than 97%) powder 60kg/h into a pre-ammonia still, digesting and dissolving the calcium oxide under the action of mechanical stirring, feeding the generated settled sand into a sand discharge system through a sand discharge device, overflowing calcium oxide digestion liquid into a cavitation ammonia still reactor, discharging generated ammonia gas and water vapor from the top of the pre-ammonia still, and feeding the ammonia gas and the water vapor into the bottom of the negative pressure ammonia still; the temperature in the pre-ammonia distillation tank is 85 ℃, the pressure is 0.097MPa, the molar ratio of ammonium chloride to calcium oxide is 1:0.65, and the retention time of the materials is 2.5 h;

(12) ammonia gas and water vapor from the top of the pre-ammonia distillation tank enter the bottom of a negative pressure ammonia distillation tower, ammonia gas and water vapor generated in the cavitation ammonia distillation reactor enter the bottom of the negative pressure ammonia distillation tower, ammonia and water vapor are separated in the negative pressure ammonia distillation tower, the ammonia gas is demisted and then enters a condenser for condensation, and condensed water and ammonia gas are separated out through a gas-liquid separation tank; the condensed water enters the top of the negative pressure ammonia distillation tower through a condensed water pump to be used as demister spray water, and the condensed water enters the pre-ammonia distillation tank to be used as ingredient water of calcium oxide powder; compressing ammonia gas by an ammonia gas compressor and then feeding the compressed ammonia gas into an ammonia gas buffer tank; the temperature at the top of the negative pressure ammonia still is 80 ℃, and the pressure at the top of the negative pressure ammonia still is 0.092 MPa;

(13) in the cavitation ammonia-steaming reactor, calcium oxide digestive liquid is subjected to ammonia-steaming reaction in the cavitation ammonia-steaming reactor; in the cavitation ammonia-steaming reactor, secondary water vapor (containing a small amount of ammonia gas) is adopted to perform cavitation through the airflow cavitation nozzle and heat materials at the same time, and cavitation can also be generated between the 45-degree 12-blade turbine blade (four layers) and the tooth-shaped baffle (four uniform distribution); the material is heated by the water vapor through the stirring heat transfer rotor, the gas phase in the cavitation ammonia-steaming reactor enters the negative pressure ammonia-steaming tower, and the liquid phase in the cavitation ammonia-steaming reactor enters the ammonia-steaming flash tank through the ammonia-steaming liquid pump; the temperature in the cavitation ammonia-steaming reactor is 90 ℃, the pressure is 0.098MPa, and the retention time of the materials is 2.5 h;

(14) the liquid phase in the cavitation ammonia distillation reactor enters an ammonia distillation flash tank through an ammonia distillation liquid pump, ammonia gas and water vapor are subjected to adiabatic flash evaporation and enter an ammonia gas and water vapor compressor together with the ammonia gas and the water vapor from a magnesium precipitation flash tank, the secondary water vapor (containing a small amount of ammonia gas) after temperature and pressure rise is used as cavitation gas flow of a cavitation ammonia distillation reactor airflow cavitation nozzle, and meanwhile, materials in the cavitation ammonia distillation reactor are heated; a flash evaporation liquid calcium chloride removal recovery system in the ammonia evaporation liquid flash evaporation tank; the adiabatic flash temperature of the ammonia evaporation liquid flash tank is 65 ℃, and the retention time of the materials is 1.5 h.

The magnesium hydroxide production method adopting the positive pressure magnesium precipitation and the dry method negative pressure ammonia distillation has the advantages that the device is comprehensive and energy-saving by 25%; the quality of the magnesium hydroxide is higher than the standard of HG T3607-2007 industrial magnesium hydroxide.

The technical idea of the present invention is described in the above technical solutions, and the protection scope of the present invention is not limited thereto, and any changes and modifications made to the above technical solutions according to the technical essence of the present invention belong to the protection scope of the technical solutions of the present invention.

Claims

1. The magnesium hydroxide production device for positive pressure magnesium precipitation and dry negative pressure ammonia distillation is characterized in that: comprises a dissolving tank, a centrifuge feeding tank, a horizontal double-drum centrifuge, an aerial fog magnesium precipitation tower, a jet magnesium precipitation reactor, a magnesium precipitation liquid flash tank, an expansion drum type filter, a belt type vacuum filter, a paddle dryer and an air flow crusher which are connected in sequence; the dissolving tank is used for dissolving bischofite; the centrifuge feeding tank is used for intermediate storage of bischofite solution; the horizontal double-drum centrifuge is used for carrying out liquid-solid separation on the bischofite solution and solid impurities; the aerial fog magnesium precipitation tower is used for atomizing the separated refined magnesium liquid and performing magnesium precipitation reaction with ammonia gas; the jet magnesium precipitation reactor is used for precipitating magnesium liquid and ammonia gas to continue magnesium precipitation reaction; the magnesium precipitation liquid flash tank is used for carrying out flash evaporation on the magnesium precipitation liquid; the expansion drum type filter is used for concentrating the magnesium precipitation flash evaporation liquid; the belt type vacuum filter is used for carrying out liquid-solid separation on the concentrated solution of the expansion drum type filter; the paddle dryer is used for drying the filtered magnesium hydroxide filter cake of the vacuum filter; the jet mill is used for grinding and grading the magnesium hydroxide powder dried by the paddle dryer;

2. The magnesium hydroxide production device for positive pressure magnesium precipitation and dry negative pressure ammonia distillation according to claim 1, which is characterized in that: the outer wall of the cavitation ammonia evaporation reactor is provided with an airflow cavitation nozzle for introducing steam into the reactor, the inner wall of the cavitation ammonia evaporation reactor is provided with a tooth-shaped baffle, a hollow stirring heat transfer rotor is arranged in the reactor, and the outer wall of the stirring heat transfer rotor is provided with a plurality of layers of blades.

3. The magnesium hydroxide production device for positive pressure magnesium precipitation and dry negative pressure ammonia distillation according to claim 2, which is characterized in that: the multi-layer blades are 45-degree 12-blade turbine blades which are uniformly distributed on the stirring heat transfer rotor, and the blades of each layer are staggered with the teeth of the toothed baffle in the horizontal direction; the tooth-shaped baffles are four and are symmetrically arranged on the inner wall of the reactor at intervals of 90 degrees.

4. The magnesium hydroxide production device for positive pressure magnesium precipitation and dry negative pressure ammonia distillation according to claim 1, which is characterized in that: the lower part in the aerial fog magnesium precipitation tower is provided with a gas-liquid two-phase atomizing nozzle, the upper part is provided with a demister and a spray header from top to bottom, the bottom of the tower is provided with a liquid seal pipe, and the liquid seal pipe extends to a position below the liquid level in the jet magnesium precipitation reactor; and a demister, a built-in cooler and white steel structured packing are arranged in the negative pressure ammonia distillation tower from top to bottom.

5. The magnesium hydroxide production device for positive pressure magnesium precipitation and dry negative pressure ammonia distillation according to claim 1, which is characterized in that: the device further comprises: a gas-liquid separation tank, an ammonia buffer tank and an ammonia compressor; the inlet of the gas-liquid separation tank is connected with an unreacted ammonia gas outlet of the jet magnesium deposition reactor and an ammonia gas outlet at the top of the negative pressure ammonia distillation tower, and is used for carrying out gas-liquid separation on the collected ammonia gas; the input end of the ammonia gas compressor is connected with a gas phase outlet of the gas-liquid separation tank, the output end of the ammonia gas compressor is connected with an inlet of the ammonia gas buffer tank, and an outlet of the ammonia gas buffer tank is connected with an ammonia gas inlet of the aerial fog magnesium precipitation tower.

6. The magnesium hydroxide production device for positive pressure magnesium precipitation and dry negative pressure ammonia distillation according to claim 2, which is characterized in that: the device also comprises an ammonia gas and water vapor compressor; the input end of the ammonia gas and water vapor compressor is connected with the ammonia evaporation liquid flash tank and the magnesium precipitation liquid flash tank, and the output end of the ammonia gas and water vapor compressor is connected with the airflow cavitation nozzle of the cavitation ammonia evaporation reactor.

7. The magnesium hydroxide production device for positive pressure magnesium precipitation and dry negative pressure ammonia distillation according to claim 6, which is characterized in that: the device also comprises a steam ejector and a condensed water flash tank; the steam jet device is connected with the paddle dryer, the paddle dryer adopts steam heating jacket heat exchange and steam heating stirring paddle heat exchange to dry the magnesium hydroxide filter cake, the generated secondary water steam is used as an auxiliary heat source and enters the paddle dryer again through the steam jet device, and the steam heating jacket and the steam heating stirring paddle dry the materials; the stirring heat transfer rotor of the cavitation ammonia-steaming reactor takes water vapor as a heat source, and the condensed water flash tank is used for collecting the water vapor condensed water generated by the heat transfer rotor of the cavitation ammonia-steaming reactor and the paddle dryer.