阅读说明：本技术 一种串联的硫酸铵结晶方法及其装置 (Tandem ammonium sulfate crystallization method and device thereof ) 是由 杨春和 吴燕平 于 2020-04-14 设计创作，主要内容包括：本发明公开了一种串联的硫酸铵结晶方法及其装置,属于化工领域。该装置使用两个串联的结晶器,采用两效真空结晶工艺,第一效为中和蒸发,第二效为蒸发结晶。第一效中和蒸发产生浓度约为40％的硫酸铵溶液,送第二效为蒸发结晶系统,得到大颗粒硫酸铵比例较大的硫酸铵。该装置充分利用气氨溶解热和硫酸和氨中和反应的中和热,并利用中和蒸发器的二次蒸汽作为热源,减少循环水消耗,提高大颗粒硫酸铵的比例,同时减少己内酰胺的包裹损失。(The invention discloses a method and a device for crystallizing ammonium sulfate in series, belonging to the field of chemical industry. The device uses two crystallizers connected in series, and adopts a double-effect vacuum crystallization process, wherein the first effect is neutralization evaporation, and the second effect is evaporation crystallization. The first effect neutralizes and evaporates to produce ammonium sulfate solution with concentration of about 40%, and the second effect is the evaporating and crystallizing system to obtain ammonium sulfate with large ammonium sulfate particle ratio. The device makes full use of the heat of gas ammonia solution and the heat of neutralization of sulfuric acid and ammonia neutralization reaction, and utilizes the secondary steam of the neutralization evaporator as a heat source, thereby reducing the consumption of circulating water, improving the proportion of large-particle ammonium sulfate and reducing the wrapping loss of caprolactam.)

1. A ammonium sulfate crystallization device who establishes ties which characterized in that: the device comprises a primary-effect DTB type neutralization evaporator (1) and a secondary-effect OLSO type crystallizer (5), wherein the two devices are connected in series; the output end of the top of the first-effect DTB type neutralization evaporator (1) is connected with a shell pass inlet of a double-effect crystallizer circulating heater (4), a shell pass outlet of the double-effect crystallizer circulating heater (4) is connected with a vapor-liquid separation tank (8), and the lower part of the vapor-liquid separation tank (8) is connected with the bottom of the first-effect DTB type neutralization evaporator (1) through a condensate circulating pump (23); the output end of the top of the sedimentation separation area of the double-effect OLSO type crystallizer (5) is connected with a double-effect sedimentation separator (6), one output end of the bottom of the double-effect sedimentation separator (6) is connected with the lower part of the double-effect OLSO type crystallizer (5), and the other output end of the bottom of the double-effect sedimentation separator (6) is connected with a circulating heater (4) of the double-effect crystallizer through a double-effect circulating pump (7); the output end of the top end of the double-effect crystallizer circulating heater (4) is connected with the input end of an evaporation flash chamber at the upper part of the double-effect OLSO type crystallizer (5);

the output end of the bottom of the first-effect DTB type neutralization evaporator (1) is respectively connected with an upper evaporation chamber of the two-effect OLSO type crystallizer (5), and/or the inlet of the lower two-effect circulating pump (7) is connected, and/or the bottom of the two-effect OLSO type crystallizer (5) is connected, and/or the centrifugal mother liquor tank (12) is connected.

2. The ammonium sulfate crystallization apparatus in series as set forth in claim 1, wherein: the lower part of the single-effect DTB type neutralization evaporator (1) is also sequentially provided with an input end of water (17), an input end of rearrangement liquid (18) and an input end of ammonia gas (19).

3. The ammonium sulfate crystallization apparatus in series as set forth in claim 1, wherein: a stirrer (2) is arranged in an inner guide barrel of the single-effect DTB type neutralization evaporator (1).

4. The ammonium sulfate crystallization apparatus in series as set forth in claim 1, wherein: one output end at the top of the sedimentation separation area of the one-effect DTB type neutralization evaporator (1) is connected with one-effect sedimentation separator (3), caprolactam at the upper part of the one-effect sedimentation separator (3) is recovered through a pipeline (16), and the output ends at the middle part and the lower part of the one-effect sedimentation separator (3) are connected with the bottom of the neutralization crystallizer (1).

5. The ammonium sulfate crystallization apparatus in series as set forth in claim 1, wherein: the output end of the bottom end of the double-effect OLSO type crystallizer (5) is respectively connected with a centrifugal machine (9), a dryer (10) and a sieving machine (11).

6. The ammonium sulfate crystallization apparatus in series as set forth in claim 5, wherein: the centrifuge (9) is connected with a mother liquor tank (12), the bottom of the mother liquor tank (12) is connected with a mother liquor circulating pump (13), and the outlet of the mother liquor circulating pump (13) is respectively connected with the bottom of the two-effect OLSO type crystallizer (5), the inlet of the two-effect circulating pump (7) and the bottom of the one-effect DTB type neutralization evaporator (1).

7. A method for realizing ammonium sulfate crystallization in series by using the device is characterized in that: the method comprises the following steps: 1) the rearrangement liquid from a rearrangement system of a caprolactam device enters a guide cylinder of a primary-effect DTB neutralization evaporator through a nozzle on a distributor of the primary-effect DTB type neutralization evaporator, ammonia gas outside a boundary area is sent to the lower part of the guide cylinder of the primary-effect DTB neutralization evaporator, neutralization reaction is carried out on the rearrangement liquid and sulfuric acid in the primary-effect DTB neutralization evaporator under the conditions that the pressure is 15 kPa-95 kPa and the temperature is 60-95 ℃, the ammonium sulfate solution in the guide cylinder absorbs the heat released by the neutralization reaction and the ammonia dissolution, part of materials are vaporized and the density is reduced, so that the density difference between the inside and the outside of the guide cylinder is formed, and the solution in the guide cylinder is pushed to rise;

2) after the liquid of the first-effect DTB neutralization evaporator is discharged from the guide shell, settling separation is carried out, the caprolactam solution is positioned at the upper layer in a settling area, the middle layer is dilute ammonium sulfate, and the lower layer is concentrated ammonium sulfate; ammonium sulfate-containing crystal material coming out of the bottom of the first-effect DTB neutralization evaporator automatically flows to an evaporation chamber of a two-effect OLSO type crystallizer or is sent to an inlet of a two-effect circulating pump, is pumped by the pump to be heated and then is sent to the evaporation chamber of the two-effect OLSO type crystallizer or is sent to the bottom of the two-effect OLSO type crystallizer or is simultaneously sent to the evaporation chamber of the two-effect, the inlet of the two-effect circulating pump, the bottom of the two-effect crystallizer and a centrifugal mother liquor tank; the operating pressure of the double-effect OLSO type crystallizer is 10KPa to 50KPa, and the temperature is 50 ℃ to 65 ℃;

3) the inside of the two-effect OLSO type crystallizer is divided into an evaporation chamber and a crystallization settling zone, circulating liquid is sent to the evaporation chamber for gas-liquid separation, gas is sent to a vacuum system, liquid is concentrated ammonium sulfate solution and enters the bottom of the crystallization settling zone from a guide cylinder, the density of the circulating liquid is smaller than that of thick slurry at the bottom of the settling zone, the thick slurry zone at the bottom of the two-effect OLSO type crystallizer is in a fluidized state, the fluidized state can accelerate the collision and growth of crystals, the material in the thick slurry zone is sent to a centrifuge for separation, mother liquid is sent to a mother liquid tank and is sent to the bottom of the two-effect OLSO type crystallizer, an inlet of a two-effect circulating pump and the bottom of a one-effect DTB type neutralization evaporator by a pump, wet solid ammonium sulfate separated by;

4) the upper part of the crystallization settling zone of the double-effect OLSO type crystallizer contains water and small ammonium sulfate particles, and part of wrapped organic matters released by dissolution and recrystallization of the small crystals, and the organic matters are pumped out of a circulating heater of the double-effect crystallizer by a double-effect circulating pump, heated and then sent to an evaporation zone for evaporation and concentration.

8. The method of claim 7, wherein: and (3) the solution from the upper part of the first-effect DTB neutralization evaporation settling zone in the step 2) enters a first-effect settling separator, the upper layer of the first-effect settling separator is a caprolactam-containing crude product and is sent to caprolactam for refining, the middle layer is dilute ammonium sulfate and the lower layer is concentrated ammonium sulfate and returns to the bottom of the first-effect DTB neutralization crystallizer.

9. The method of claim 7, wherein: secondary steam generated from the top of the primary-effect DTB neutralization evaporator enters a circulating heater of a secondary-effect OLSO type crystallizer to heat a secondary-effect material, the secondary steam is condensed and then enters a gas-liquid separator, non-condensable gas enters a vacuum system, and liquid condensate is circularly pumped to the primary-effect neutralization evaporator by using a condensate liquid to keep the water amount balance; or the condensate is sent to intermittently clean the demister of the crystallizer by a condensate circulating pump; or the condensate circulating pump is used for sending the condensate to flush the centrifuge; or a condensate circulating pump is used for sending the condensate to flush the instrument pipeline; or with a condensate circulation pump to flush the pump seals.

The technical field is as follows:

the invention relates to the field of chemical devices, in particular to a method and a device for crystallizing ammonium sulfate in series, which are applied to a caprolactam device.

Background

Caprolactam is an important organic chemical raw material and is mainly used for producing nylon 6 engineering plastics and nylon 6 fibers. The nylon 6 engineering plastic is mainly used as components and assemblies of automobiles, ships, electronic appliances, industrial machinery and daily consumer goods, the nylon 6 fiber can be made into textiles, industrial yarns, yarns for carpets and the like, besides, the caprolactam can also be used for producing antiplatelet drugs, producing laurocapram and the like, and the application is very wide. The main production methods of caprolactam include:

1. cyclohexanone-hydroxylamine process

The method is a main method for producing caprolactam by using cyclohexanone as a raw material. The production process routes of hydroxylamine are three, namely an HSO method, an HPO method and an NO method, which are respectively and briefly described as follows:

1) and HSO method (UBE method produced by Japan).

Part of the liquid ammonia is made into ammonia water, and part of the liquid ammonia is oxidized into nitrogen oxide. Absorbing sulfur dioxide (at normal temperature), nitrogen oxide and nitrogen dioxide (both at low temperature) with ammonia water in sequence to obtain hydroxylamine disulfonate, and heating and hydrolyzing to obtain hydroxylamine sulfate.

The obtained hydroxylamine sulfate reacts with cyclohexanone to generate cyclohexanone oxime. The cyclohexanone oxime is subjected to Beckmann molecular rearrangement in fuming sulfuric acid to obtain a caprolactam crude product, and then the caprolactam crude product is subjected to refining means such as extraction, ion exchange, thin film distillation and the like to obtain a finished product.

2) The HPO process (see DSM, the Netherlands for example).

Nitric oxide and nitrogen dioxide produced by ammoxidation are absorbed by the mixed solution of phosphoric acid, and the absorbed mixed solution reacts with hydrogen in the presence of a catalyst to form hydroxylamine phosphate.

Reacting hydroxylamine phosphate with cyclohexanone to generate cyclohexanone oxime, carrying out Beckmann molecular rearrangement in the fuming sulfuric acid removal of the cyclohexanone oxime, neutralizing the rearrangement reaction liquid with ammonia to remove the sulfuric acid to form crude caprolactam, and then purifying to obtain a product caprolactam

3) NO method (example of Germany BASF method)

Nitrogen and oxygen are oxidized into nitrogen monoxide under the dilution of steam, and the nitrogen and the oxygen are introduced into sulfuric acid solution containing Pt catalyst taking active carbon as a carrier together with hydrogen, so that NO is reduced into NH₂OH and sulfuric acid are combined into hydroxylamine sulfate, caprolactam is obtained through oximation and transposition, and the crude caprolactam is extracted and distilled to obtain a finished product.

2. Toluene method (example of SNIA in Italy)

Oxidizing toluene under 1MPa at 150-178 ℃ to obtain benzoic acid, purifying and hydrogenating to obtain hexahydrobenzoic acid.

Oxidizing ammonia into nitrogen oxide, and absorbing with fuming sulfuric acid to obtain nitroso sulfuric acid. In another tower, the hexahydrobenzoic acid is absorbed by nitroso sulfuric acid, and then the crude caprolactam is obtained under the action of oleum.

After the crude caprolactam product is subjected to second-stage extraction and oxidation treatment, the crude caprolactam product is sent to a film evaporator to be evaporated to obtain a finished product.

3. Light nitrosation method (taking PNC method of Dongli corporation of Japan as an example)

Cyclohexane and nitrosyl chloride react at 20-30 ℃ under the irradiation of light, oily substances formed at the bottom of the reactor are separated out and dissolved in water, sodium carbonate is used for neutralizing until the pH value is 6 to obtain cyclohexanone oxime, and the cyclohexanone oxime is transposed to obtain caprolactam.

4、H₂O₂Aminooximation process

The process comprises the steps of placing cyclohexanone, ammonia and 60% hydrogen peroxide in the same reactor, synthesizing cyclohexanone oxime in n-butyl alcohol (TBA) solvent through reaction under the action of a Ti-Si catalyst taking Si as a carrier, rectifying and recovering a mixture produced through the reaction through TBA, extracting cyclohexanone oxime toluene, rectifying and other processes to obtain cyclohexanone oxime, carrying out Beckmann rearrangement reaction on the cyclohexanone oxime under the action of oleum to generate crude caprolactam, extracting and distilling the crude caprolactam to obtain a finished product of caprolactam

The most of the above process technologies adopt the liquid phase rearrangement method of cyclohexanone oxime to prepare caprolactam, that is, cyclohexanone oxime undergoes molecular rearrangement in oleum to obtain crude caprolactam, and then the crude caprolactam is neutralized to remove sulfuric acid. Ammonia is generally adopted in a caprolactam device to neutralize cyclohexanone oxime to carry out molecular rearrangement in oleum to obtain sulfuric acid in crude caprolactam to generate ammonium sulfate.

At present, the rearrangement reaction of the main production process of caprolactam in China adopts a two-stage or three-stage process, and the process has no great difference. The neutralization of the rearrangement reaction liquid includes a process of neutralizing with ammonia to produce ammonium sulfate and then evaporating and crystallizing to obtain solid ammonium sulfate, and a process of neutralizing with gaseous ammonia in a vacuum crystallizer to evaporate water by using reaction heat to obtain solid ammonium sulfate. The second ammonium sulfate neutralization crystallization device utilizes the solution heat of the ammonia gas and the neutralization heat of the reaction of the ammonia and the sulfuric acid, saves the steam consumption, reduces the circulating water consumption consumed by the solution heat of the cooling gas ammonia and the neutralization heat of the reaction of the ammonia and the sulfuric acid, has certain economical efficiency, and is widely adopted in a newly-built caprolactam device.

At present, the ammonium sulfate neutralization crystallization method widely adopted in a domestic caprolactam device is to introduce rearrangement reaction liquid into a DTB type evaporator to finish the neutralization evaporation process, but in the prior art, a single DTB type ammonium sulfate neutralization crystallizer is adopted, and the inventor finds that the ammonium sulfate neutralization crystallization process has the following problems:

a) the single DTB type ammonium sulfate neutralization crystallizer widely adopted at present has the advantages that the majority of solid ammonium sulfate particles are 0.6-1.2 mm, the proportion of ammonium sulfate crystals with the solid ammonium sulfate particle size of more than 2mm is less than 10%, generally about 5%, the proportion of the ammonium sulfate crystals with the particle size of more than 2mm is less, the solid particle size is small, the price of large ammonium sulfate crystals is higher than that of small ammonium sulfate crystals by about 30-45 dollars/t ammonium sulfate, namely about 200-300 RMB/t ammonium sulfate, the ammonium sulfate yield of a caprolactam device is large, about 1.5t ammonium sulfate/t caprolactam is obtained, and the economical efficiency of the ammonium sulfate crystallization device is poor due to the small ammonium sulfate particle proportion process technology.

b) The caprolactam content in the existing ammonium sulfate crystal is usually about 0.1 percent by weight, which causes caprolactam loss, and a space for reducing caprolactam loss exists in the technology;

c) the single DTB type ammonium sulfate neutralizes the secondary steam generated at the top of the crystallization tower, and generally adopts circulating cooling water for cooling, so that the energy is not reasonably utilized, and the consumption of the cooling water is relatively large.

Disclosure of Invention

The invention aims to provide a method and a device for crystallizing ammonium sulfate in series connection, aiming at the technical problems, the device fully utilizes the solution heat of gas ammonia and the neutralization heat of the neutralization reaction of sulfuric acid and ammonia, and utilizes secondary steam of a neutralization crystallizer as a heat source, thereby reducing the consumption of circulating water, improving the proportion of large-particle ammonium sulfate and reducing the loss of caprolactam.

The purpose of the invention can be realized by the following technical scheme:

a tandem ammonium sulfate crystallization device comprises a primary-effect DTB type neutralization evaporator and a secondary-effect OLSO type crystallizer, wherein the two crystallizers (devices) are connected in series; the output end of the top of the first-effect DTB type neutralization evaporator is connected with a shell pass inlet of a circulating heater of the double-effect crystallizer, a shell pass outlet of the circulating heater of the double-effect crystallizer is connected with a vapor-liquid separation tank, and the lower part of the vapor-liquid separation tank is connected with the bottom of the first-effect DTB type neutralization evaporator through a condensate circulating pump; the output end of the top of the sedimentation separation area of the double-effect OLSO type crystallizer is connected with the lower part of the double-effect OLSO type crystallizer through a double-effect sedimentation separator, one output end of the bottom of the double-effect sedimentation separator is connected with the lower part of the double-effect OLSO type crystallizer, the other output end of the bottom of the double-effect sedimentation separator is connected with a circulating heater of the double-effect crystallizer through a double-effect circulating pump, and the organic phase at the top of the double-effect sedimentation separator is externally sent to caprolactam for refining; the output end of the top end of the circulating heater of the double-effect crystallizer is connected with the input end of an upper evaporation flash chamber of the double-effect OLSO type crystallizer;

the output end of the bottom of the first-effect DTB type neutralization evaporator is respectively connected with an upper evaporation chamber of the two-effect OLSO type crystallizer, and/or the inlet of the lower two-effect circulating pump is connected, and/or the bottom of the two-effect OLSO type crystallizer is connected, and/or the centrifugal mother liquor tank is connected. In some preferred embodiments: the output end of the bottom of the first-effect DTB type neutralization evaporator is connected with a centrifugal mother liquor tank.

The technical scheme of the invention is as follows: the lower part of the one-effect DTB type neutralization evaporator is also sequentially provided with a water input end, a rearrangement liquid input end and an ammonia gas input end.

The technical scheme of the invention is as follows: the inner guide barrel of the single-effect DTB type neutralization evaporator is internally provided with a stirrer. The technical scheme of the invention is as follows: an output end at the top of the settling separation area of the first-effect DTB type neutralization evaporator is connected with the first-effect settling separator, caprolactam at the upper part of the first-effect settling separator is recovered through a pipeline, and output ends at the middle part and the lower part of the first-effect settling separator are connected with the bottom of the neutralization crystallizer.

The technical scheme of the invention is as follows: and the output end of the bottom end of the double-effect OLSO type crystallizer is respectively connected with a centrifugal machine, a dryer and a screening machine.

The technical scheme of the invention is as follows: the centrifuge is connected with a mother liquor tank, the bottom of the mother liquor tank is connected with a mother liquor circulating pump, and an outlet of the mother liquor circulating pump is respectively connected with the bottom of the double-effect OLSO type crystallizer, an inlet of the double-effect circulating pump and the bottom of the first-effect DTB type neutralization evaporator.

A method for realizing ammonium sulfate crystallization by using the device comprises the following steps:

1) the rearrangement liquid from a rearrangement system of a caprolactam device enters a guide cylinder of a primary-effect DTB neutralization evaporator through a nozzle on a distributor of the primary-effect DTB type neutralization evaporator, ammonia gas outside a boundary area is sent to the lower part of the guide cylinder of the primary-effect DTB neutralization evaporator, neutralization reaction is carried out on the rearrangement liquid and sulfuric acid in the primary-effect DTB neutralization evaporator under the conditions that the pressure is about 15 kPa-95 kPa and the temperature is 60-95 ℃, the ammonium sulfate solution in the guide cylinder absorbs the heat released by the neutralization reaction and the ammonia dissolution, part of materials are vaporized and the density is reduced, so that the density difference between the inside and the outside of the guide cylinder is formed, and the solution in the guide cylinder is pushed to rise;

2) after the liquid of the first-effect DTB neutralization evaporator is discharged from the guide shell, settling separation is carried out, the caprolactam solution is positioned at the upper layer in a settling area, the middle layer is dilute ammonium sulfate, and the lower layer is concentrated ammonium sulfate; ammonium sulfate-containing crystal material coming out of the bottom of the first-effect DTB neutralization evaporator automatically flows to an evaporation chamber of a two-effect OLSO type crystallizer or is sent to an inlet of a two-effect circulating pump, is pumped by the pump to be heated and then is sent to the evaporation chamber of the two-effect OLSO type crystallizer or is sent to the bottom of the two-effect OLSO type crystallizer or is simultaneously sent to the evaporation chamber of the two-effect, the inlet of the two-effect circulating pump, the bottom of the two-effect crystallizer and a centrifugal mother liquor tank; the operating pressure of the double-effect OLSO type crystallizer is 10KPa to 50kPa, and the temperature is 50 ℃ to 65 ℃;

3) the inside of the two-effect OLSO type crystallizer is divided into an evaporation chamber and a crystallization settling zone, circulating liquid is sent to the evaporation chamber for gas-liquid separation, gas is sent to a vacuum system, liquid is concentrated ammonium sulfate solution and enters the bottom of the crystallization settling zone from a guide cylinder, the density of the circulating liquid is smaller than that of thick slurry at the bottom of the settling zone, the thick slurry zone at the bottom of the two-effect OLSO type crystallizer is in a fluidized state, the fluidized state can accelerate the collision and growth of crystals, the material in the thick slurry zone is sent to a centrifuge for separation, mother liquid is sent to a mother liquid tank and is sent to the bottom of the two-effect OLSO type crystallizer, an inlet of a two-effect circulating pump and the bottom of a one-effect DTB type neutralization evaporator by a pump, wet solid ammonium sulfate separated by;

4) the upper part of the crystallization settling zone of the double-effect OLSO type crystallizer contains water and small ammonium sulfate particles, and part of wrapped organic matters released by dissolution and recrystallization of the small crystals, and the organic matters are pumped out of a circulating heater of the double-effect crystallizer by a double-effect circulating pump, heated and then sent to an evaporation zone for evaporation and concentration.

The method comprises the following steps: and (3) the solution from the upper part of the first-effect DTB neutralization evaporation settling zone in the step 2) enters a first-effect settling separator, the upper layer of the first-effect settling separator is a caprolactam-containing crude product and is sent to caprolactam for refining, the middle layer is dilute ammonium sulfate and the lower layer is concentrated ammonium sulfate and returns to the bottom of the first-effect DTB neutralization crystallizer.

The method comprises the following steps: secondary steam generated from the top of the primary-effect DTB neutralization evaporator enters a circulating heater of a secondary-effect OLSO type crystallizer to heat a secondary-effect material, the secondary steam is condensed and then enters a gas-liquid separator, non-condensable gas enters a vacuum system, and liquid condensate is circularly pumped to the primary-effect neutralization evaporator by using a condensate liquid to keep the water amount balance; or the condensate is sent to intermittently clean the demister of the crystallizer by a condensate circulating pump; or the condensate circulating pump is used for sending the condensate to flush the centrifuge; or a condensate circulating pump is used for sending the condensate to flush the instrument pipeline; or with a condensate circulation pump to flush the pump seals.

The double-effect sedimentation separation zone is externally provided with a double-effect circulating pump, materials are pumped out of the upper part of the sedimentation separator, pumped out of a circulating heater of the double-effect crystallizer by the double-effect circulating pump, heated and then sent to the evaporation zone for evaporation and concentration.

The device uses two vacuum evaporators connected in series, a first-effect DTB neutralization crystallizer completes neutralization reaction, solution is evaporated and concentrated to generate secondary steam, the first effect is neutralization evaporation, and the second effect is evaporative crystallization. The solution generated by the neutralization evaporation does not contain crystal particles in the first effect, and is sent to a second effect evaporation crystallization system to obtain the ammonium sulfate with large proportion of large-particle ammonium sulfate. Meanwhile, the encapsulation loss of caprolactam is reduced.

In the invention, DTB type crystallizer is adopted for the first effect neutralization and evaporation, an inner guide barrel is arranged in the crystallizer, and a stirrer is arranged in the inner guide barrel. The stirrer functions as follows: on one hand, the heat transfer and the mass transfer in the guide flow cylinder are accelerated, the local overheating is avoided, the reaction materials are uniformly mixed, on the other hand, the ammonium sulfate solution in the inner guide flow cylinder is pushed to move upwards, and the materials in the inner guide flow cylinder are stirred and subjected to the combined action of the heat released by the ammonia solution heat and the heat released by neutralization to complete the neutralization reaction.

In the technical scheme of the invention, the first-effect neutralization evaporator integrates two process processes of neutralization and evaporation into one crystallizer to complete, water in the ammonium sulfate solution is evaporated by utilizing the ammonia gas solution heat and the neutralization reaction heat, a heating heat source is provided for the two-effect crystallizer, cooling water required for cooling secondary steam on the top of the first-effect neutralization evaporator is reduced, and the energy-saving effect is achieved.

If no crystal is generated in the single-effect evaporator, no single-effect external circulation pump is designed or no single-effect external circulation pump is operated. The technological process is to produce about 40 wt% ammonium sulfate solution in one-effect evaporator without producing ammonium sulfate crystal and eliminate coated caprolactam of ammonium sulfate in one-effect evaporator.

In the technical scheme of the invention, the pH value of the solution in the first-effect neutralization evaporator is controlled to be about 5-6.

In the technical scheme of the invention, the crystallization, sedimentation and separation area of the two-effect OLSO type crystallizer is divided into two layers, wherein the upper layer is mainly an ammonium sulfate aqueous solution containing small ammonium sulfate crystals and containing a small amount of caprolactam and other organic matters and is a slurry area of ammonium sulfate, the lower layer is mainly an ammonium sulfate aqueous solution containing ammonium sulfate crystals, and the materials in a thick slurry area and a thin slurry area of the ammonium sulfate in a thick slurry area of the ammonium sulfate are in a fluidized state.

The upper layer is mainly ammonium sulfate water solution containing ammonium sulfate small crystals, the ammonium sulfate water solution is pumped out of a double-effect crystallizer circulating heater by a double-effect circulating pump to be heated, part of small ammonium sulfate crystals are dissolved, and the small ammonium sulfate crystals are sent to an evaporation area to be evaporated and concentrated. Optionally, a secondary effect sedimentation separator is arranged outside the sedimentation area of the secondary effect crystallizer, part of liquid at the top of the upper layer of the crystallization sedimentation separation area of the secondary effect OLSO type crystallizer is introduced into the secondary effect sedimentation separator to separate out caprolactam and other organic matters, the liquid at the lower part of the secondary effect sedimentation separator is sent to the inlet of the secondary effect circulating pump or the bottom of the secondary effect OLSO type crystallizer, and the upper organic matters are discharged after accumulating to a certain amount so as to reduce the loss of caprolactam.

In the invention, the second-effect crystallizer is internally provided with the inner guide barrel, the stirrer is not arranged in the inner guide barrel, the ammonium sulfate crystals in the guide barrel move from top to bottom, the crystals become larger and reach the bottom of the sedimentation separation area of the crystallizer, and because a large amount of materials with small density are introduced into the bottom of the sedimentation separation area, the materials in the sedimentation separation area are in a fluidized state, so that the collision of the crystals is enhanced, and large ammonium sulfate particles are formed.

The invention has the beneficial effects that:

a) the OSLO type evaporative crystallizer has the characteristic of producing large ammonium sulfate particles, the proportion of the large ammonium sulfate particles is increased, the proportion of the ammonium sulfate particles with the particle size of more than 2mm is more than 30 percent, usually 40 percent, the proportion of the large ammonium sulfate particles with the particle size of far more than 5 percent by adopting the crystallization process, and the economical efficiency is obviously improved;

b) the external circulation heater of the OSLO type evaporative crystallizer eliminates fine crystals, the recrystallization process and the caprolactam packing loss in the crystallization process are reduced.

c) Secondary steam generated by the top of the primary-effect DTB neutralization evaporator is used as a secondary-effect crystallizer circulating heater to heat secondary-effect materials, extra steam is not needed, consumption of a heat source is saved, and circulating water consumption is reduced.

d) The large-flow double-effect circulating pump is used, so that the ammonium sulfate at the bottom of the double-effect crystallizer is in a fluidized state, the fluidization is enhanced, the collision of ammonium sulfate crystals and the timely elimination of fine ammonium sulfate crystals are enhanced, the specific gravity of large ammonium sulfate crystals is effectively improved, and the average particle size of the crystals is improved.

Drawings

FIG. 1 is a schematic structural diagram of an ammonium sulfate crystallization device according to the present invention.

Wherein: the system comprises a primary-effect DTB type neutralization evaporator, a stirrer, a primary-effect sedimentation separator, a secondary-effect crystallizer circulating heater, a secondary-effect OLSO type crystallizer, a secondary-effect sedimentation separator, a secondary-effect circulating pump, a gas-liquid separation tank, a centrifugal machine, a dryer, a screening machine, a mother liquid tank, a mother liquid circulating pump, a small-particle ammonium sulfate, a large-particle ammonium sulfate, a CPL crude product, water, heavy liquid discharge, ammonia gas, a condensate, a vacuum removal system, a CPL crude product and a condensate circulating pump, wherein the primary-effect DTB type neutralization evaporator is 1, the stirrer is 2, the primary-effect sedimentation separator is 3, the secondary-effect crystallizer circulating heater is 4, the secondary-effect OLSO type crystallizer is 5, the.

Note: CPL is an abbreviation for caprolactam.

The specific implementation mode is as follows:

the invention is further illustrated by the following examples, without limiting the scope of the invention:

referring to fig. 1, a tandem ammonium sulfate crystallization apparatus comprises a single-effect DTB type neutralization evaporator 1 and a double-effect OLSO type crystallizer 5, which are connected in series; the output end of the top of the first-effect DTB type neutralization evaporator 1 is connected with the shell pass inlet of the double-effect crystallizer circulating heater 4, the shell pass outlet of the double-effect crystallizer circulating heater 4 is connected with the vapor-liquid separation tank 8, and the lower part of the vapor-liquid separation tank 8 is connected with the bottom of the DTB type neutralization evaporator 1 through a condensate circulating pump 23;

the output end of the top of the sedimentation separation area of the double-effect OLSO type crystallizer 5 is connected with a double-effect sedimentation separator 6, one output end of the double-effect sedimentation separator 6 is connected with the lower part of the double-effect OLSO type crystallizer 5, and the other output end is connected with a circulating heater 4 of the double-effect crystallizer through a double-effect circulating pump 7; the output end of the top end of the double-effect crystallizer circulating heater 4 is connected with the input end of an upper evaporation flash chamber of the double-effect OLSO type crystallizer 5;

the output end of the bottom of the first-effect DTB type neutralization evaporator 1 is respectively connected with the upper evaporation chamber of the two-effect OLSO type crystallizer 5, and/or the inlet of the lower two-effect circulating pump 7 is connected, and/or the bottom of the two-effect OLSO type crystallizer 5 is connected, and/or the centrifugal mother liquor tank 12 is connected.

The lower part of the single-effect DTB type neutralization evaporator 1 is also sequentially provided with an input end of water 17, an input end of rearrangement liquid 18 and an input end of ammonia 19.

The upper part of the vapor-liquid separation tank 8 is connected with a vacuum system 21.

An output end at the top of a sedimentation separation area of the first-effect DTB type neutralization evaporator 1 is connected with the first-effect sedimentation separator 3, caprolactam at the upper part of the first-effect sedimentation separator 3 is recovered through a pipeline 16, and output ends at the middle part and the lower part of the first-effect sedimentation separator 3 are connected with the bottom of the neutralization crystallizer (1).

The output end of the bottom end of the double-effect OLSO type crystallizer 5 is respectively connected with a centrifugal machine 9, a dryer 10 and a sieving machine 11.

The centrifuge 9 is connected with a mother liquor tank 12, the bottom of the mother liquor tank 12 is connected with a mother liquor circulating pump 13, and an outlet of the mother liquor circulating pump 13 is connected with the bottom of the two-effect OLSO type crystallizer 5, an inlet of the two-effect circulating pump 7 and the bottom of the one-effect DTB type neutralization evaporator 1.