阅读说明：本技术 一种双效结晶法磷酸氢二钠大颗粒的制备方法 (Preparation method of disodium hydrogen phosphate large particles by double-effect crystallization method ) 是由 赵祥海 于 2020-04-02 设计创作，主要内容包括：本发明公开了一种双效结晶法磷酸氢二钠大颗粒的制备方法,以双效结晶的方式对磷酸钠盐产品进行结晶,结合二次加酸加碱的重结晶工艺,生产出二水磷酸氢二钠大颗粒产品；一方面由于可以连续进料浓缩,从而保证结晶颗粒稳定,提高产品合格率,保证系统蒸汽平衡稳定,并且降低蒸汽消耗；另一方面,双效浓缩结晶工艺结合二次加酸加碱的重结晶工艺,使得细小的结晶颗粒继续成长为中粗颗粒,可生产出二水磷酸氢二钠大颗粒产品。(The invention discloses a preparation method of disodium hydrogen phosphate large particles by a double-effect crystallization method, which comprises the steps of crystallizing a sodium phosphate product in a double-effect crystallization mode, and producing a disodium hydrogen phosphate large particle product by combining a secondary acid and alkali adding recrystallization process; on one hand, as the continuous feeding and concentration can be realized, the stability of crystal particles is ensured, the product percent of pass is improved, the steam balance and stability of the system are ensured, and the steam consumption is reduced; on the other hand, the double-effect concentration crystallization process is combined with a secondary acid and alkali adding recrystallization process, so that fine crystal particles continue to grow into medium coarse particles, and large-particle products of the disodium hydrogen phosphate dihydrate can be produced.)

1. A preparation method of disodium hydrogen phosphate large particles by a double-effect crystallization method is characterized by comprising the following steps:

s1, conveying the disodium hydrogen phosphate dilute solution to a two-effect separator through a feeding pump, then conveying the solution into a tube pass of a two-effect heater after kinetic energy is obtained by a two-effect circulating pump, heating the solution to a boiling point, conveying the solution into the two-effect separator to finish solvent vaporization and vapor-liquid separation, conveying a liquid phase of the two-effect separator into the two-effect circulating pump, and conveying the two-effect finished solution pressurized by the two-effect circulating pump into the next circulation;

s2, pressurizing the double-effect finished liquid by a double-effect discharge pump, then feeding the liquid into a single-effect evaporation crystallizer, then feeding the liquid into a single-effect circulating pump, feeding the liquid into a single-effect heater tube pass after the single-effect circulating pump obtains kinetic energy, heating the liquid to a boiling point, and feeding the liquid into the single-effect evaporation crystallizer to finish solvent vaporization and vapor-liquid separation again;

and S3, adding phosphoric acid and caustic soda into the primary-effect evaporation crystallizer again for neutralization, and performing secondary recrystallization to ensure that fine crystal particles in the primary-effect evaporation crystallizer continue to grow into medium coarse particles, thereby producing the large-particle disodium hydrogen phosphate dihydrate product.

2. The method for preparing disodium hydrogen phosphate granules by double effect crystallization as claimed in claim 1, wherein the condensed water from the double effect heater, the single effect heater and the condenser is collected into a condensed water tank, and finally discharged out of the system after being pressurized by a condensed water pump.

3. The method of claim 1, wherein the double effect heater and the single effect heater are forced circulation heaters.

4. The method for preparing disodium hydrogen phosphate large particles by double effect crystallization of claim 1, wherein the thickener is integrated at the lower part of the single effect evaporative crystallizer, the mother liquor phase of the single effect evaporative crystallizer enters the thickener through an underflow pipe and then settles to the bottom of the thickener to become thickened magma, the thickened magma is detected on line by a densimeter arranged on a magma circulating pipe, and the thickened magma is discharged out of the system when the detected density reaches a set value.

5. The method for preparing large disodium hydrogen phosphate particles by double-effect crystallization of claim 4, wherein the mother liquor of the less dense single-effect evaporative crystallizer is accumulated at the upper part of the thickener, and then enters the single-effect circulating pump, and after being pressurized by the single-effect circulating pump, the mother liquor enters the tube side of the single-effect heater to be continuously concentrated and crystallized.

6. The method of claim 1, wherein a portion of the primary steam generated from the primary evaporative crystallizer enters the TVR heat pump, and the TVR heat pump uses the raw steam as power to perform thermal compression on the primary steam; compressed steam of the TVR heat pump enters a shell pass of the single-effect heater to provide effective heat transfer temperature difference for system evaporation;

the other part of the primary steam enters the shell pass of the double-effect heater to become a heat source of the double-effect evaporation; and the secondary steam generated by the secondary evaporation enters the shell pass of the condenser and exchanges heat with the cooling water of the tube pass of the condenser, so that the secondary steam is condensed on the shell pass of the condenser.

7. The method for preparing the large disodium hydrogen phosphate particles by the double-effect crystallization method as claimed in claim 1, wherein the non-condensable gas of the system is discharged from the shell sides of the primary heater and the secondary heater and enters the shell side of the condenser together with the secondary steam for condensation; the residual non-condensable gas is pumped by a vacuum pump and exhausted to the atmosphere.

Technical Field

The invention relates to a preparation method of disodium hydrogen phosphate large particles, in particular to a method for producing sodium phosphate by adopting a double-effect crystallization method, crystallizing a sodium phosphate product in a double-effect crystallization mode, and combining a secondary acid and alkali adding recrystallization process to produce a disodium hydrogen phosphate dihydrate large particle product.

Background

The traditional production process flow of sodium phosphate is as follows: and (3) pumping the disodium hydrogen phosphate neutralization solution prepared in the neutralization process into a concentration kettle through a feeding pump, simultaneously starting the concentration kettle for stirring, paying attention to the liquid level of the concentration kettle, starting an atmospheric condenser water supply pump of the concentration kettle while feeding, and closing an emptying valve of the concentration kettle. And after the feeding is finished, backflushing the feeding pipeline by using steam, stopping the feeding pump and the feeding valve of the concentration kettle, and starting the steam valve of the tube-array heater of the concentration kettle to start concentration. When the concentration is ready for a large amount of particles, the circulating water pump is turned off and emptied. And opening a discharge valve of the concentration kettle, putting the material into the crystallization kettle, naturally cooling to 65-80 ℃, and taking out for dehydration.

This discontinuous feed concentration process suffers from the following drawbacks: 1. the crystal particles are easy to fluctuate greatly, and the product percent of pass is influenced; 2. the steam is also used discontinuously, which is not beneficial to the steam balance of the production system; 3. the steam consumption is large, and the steam consumption is increased.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defects of large fluctuation of crystallized particles and large steam consumption in the discontinuous feeding concentration process adopted in the production of sodium phosphate in the prior art, and provides a method for preparing large disodium hydrogen phosphate particles by a continuous feeding concentration double-effect crystallization method.

In order to solve the technical problems, the invention provides the following technical scheme:

firstly, material flow:

a preparation method of disodium hydrogen phosphate large particles by a double-effect crystallization method comprises the following specific steps:

s1, conveying the disodium hydrogen phosphate dilute solution to a two-effect separator through a feeding pump, then conveying the solution into a tube pass of a two-effect heater after kinetic energy is obtained by a two-effect circulating pump, heating the solution to a boiling point, conveying the solution into the two-effect separator to finish solvent vaporization and vapor-liquid separation, conveying a liquid phase of the two-effect separator into the two-effect circulating pump, and conveying the two-effect finished solution pressurized by the two-effect circulating pump into the next circulation;

s2, pressurizing the double-effect finished liquid by a double-effect discharge pump, then feeding the liquid into a single-effect evaporation crystallizer, then feeding the liquid into a single-effect circulating pump, feeding the liquid into a single-effect heater tube pass after the single-effect circulating pump obtains kinetic energy, heating the liquid to a boiling point, and feeding the liquid into the single-effect evaporation crystallizer to finish solvent vaporization and vapor-liquid separation again;

and S3, adding phosphoric acid and caustic soda into the primary-effect evaporation crystallizer again for neutralization, and performing secondary recrystallization to ensure that fine crystal particles in the primary-effect evaporation crystallizer continue to grow into medium coarse particles, thereby producing the large-particle disodium hydrogen phosphate dihydrate product.

Second, steam and noncondensable gas flow path

One part of primary-effect secondary steam generated by the primary-effect evaporation crystallizer enters the TVR heat pump, and the TVR heat pump carries out thermal compression on the primary-effect secondary steam by taking the generated steam as power; compressed steam of the TVR heat pump enters a shell pass of the single-effect heater to provide effective heat transfer temperature difference for system evaporation;

the other part of the primary steam enters the shell pass of the double-effect heater to become a heat source of the double-effect evaporation; and the secondary steam generated by the secondary evaporation enters the shell pass of the condenser and exchanges heat with the cooling water of the tube pass of the condenser, so that the secondary steam is condensed on the shell pass of the condenser.

The non-condensable gas of the system is discharged from the shell passes of the primary-effect heater and the secondary-effect heater, and enters the shell pass of the condenser together with the secondary steam for condensation; the residual non-condensable gas is pumped by a vacuum pump and exhausted to the atmosphere.

Third, condensed water flow

Condensed water of the two-effect heater, the one-effect heater and the condenser is concentrated into a condensed water tank, and is finally discharged out of the system after being pressurized by a condensed water pump.

Furthermore, the two-effect heater and the one-effect heater are forced circulation heaters.

Further, a thickener is integrated at the lower part of the first-effect evaporative crystallizer, a mother liquor phase of the first-effect evaporative crystallizer enters the thickener through a bottom flow pipeline and then is settled to the bottom of the thickener to form thickened crystal slurry, the thickened crystal slurry is detected on line through a densimeter arranged on a crystal slurry circulating pipeline, and the thickened crystal slurry is discharged out of the system when the detected density reaches a set value; the mother liquor of the less dense one-effect evaporative crystallizer is gathered at the upper part of the thickener, then enters the one-effect circulating pump, is pressurized by the one-effect circulating pump, and then enters the tube side of the one-effect heater to be continuously concentrated and crystallized.

Has the advantages that:

the invention adopts a double-effect crystallization method to prepare the large disodium hydrogen phosphate particles, on one hand, the crystallization particles are ensured to be stable and the product percent of pass is improved because the continuous feeding and concentration can be carried out, the product percent of pass is improved to 80 percent of the patent from about 50 percent of the traditional process, the steam balance and stability of the system are ensured, the steam consumption is reduced, and the steam consumption is reduced to 2t/h from 2.5t/h of the traditional process; on the other hand, the double-effect concentration crystallization process is combined with a secondary acid and alkali adding recrystallization process, so that fine crystal particles continue to grow into medium coarse particles, and large-particle products of the disodium hydrogen phosphate dihydrate can be produced.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is a schematic diagram of a system for preparing large disodium hydrogen phosphate particles by a double-effect crystallization method according to the present invention;

1, a one-effect evaporative crystallizer; 2, a two-effect separator; 3, a one-effect heater; 4, a double-effect heater; 5, a condenser; 6, a condensed water tank; 7, a clear liquid groove; 8, a feed pump; 9, a two-effect circulating pump; 10, a double-effect discharge pump; 11, a one-effect circulating pump; 12, a crystal slurry circulating pump; 13, a condensate pump; 14, a vacuum pump; 15, TVR heat pump.

Detailed Description

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.