WO2015062393A1

WO2015062393A1 - Solid-liquid separation process with multi-effect evaporation in combination with stirring evaporation

Info

Publication number: WO2015062393A1
Application number: PCT/CN2014/088163
Authority: WO
Inventors: 许松伟; 彭为骏; 张�杰; 陆庆权; 沈贵文; 于星; 法伦丹尼斯; 崔磊
Original assignee: 南通醋酸纤维有限公司
Priority date: 2013-10-28
Filing date: 2014-10-09
Publication date: 2015-05-07
Also published as: CN104548634A; CN104548634B

Abstract

A solid-liquid separation process, comprising the following steps: A. concentrating an aqueous solution or a mixed solution in water-organic solvents containing soluble solids at a low concentration to give a medium-concentrated mixed solution; B. discharging the medium-concentrated mixed solution into a stirring evaporation kettle (9), and further concentrating same by evaporation to give a high-concentrated mixed solution; and C. controlling the solid content of the high-concentrated mixed solution to ensure that same is discharged out of the stirring evaporation kettle (9) in the liquid form; returning the vapour generated in step B to the multi-effect evaporation system and heating the liquid while the vapour phase is condensing, such that the heat is recovered and the recovery of the solution is ensured. The high-concentrated mixed solution discharged in the liquid form in step C is cooled and solidified.

Description

Solid-liquid separation process of multi-effect evaporation combined with stirring evaporation

Technical field

The invention relates to a process method for solid-liquid separation by multi-effect evaporation combined with stirring evaporation, belonging to the technical field of chemical engineering and process solid-liquid separation, in particular to a solid solution of a water-organic solvent mixture containing a low concentration of dissolved solids. Liquid separation process.

Background technique

Separation of dissolved materials from solution is a common chemical problem. According to the solubility of the soluble substance in the solvent, the parameters such as temperature, pH, and solution concentration are generally adjusted to achieve the purpose of precipitation of the soluble matter. Direct evaporation of a solution is a simple and straightforward method to achieve solid-liquid separation by changing the concentration of solute in the solution, but the problem of direct evaporation is high energy consumption, and the solid content increases with the precipitation of solute in the solution during evaporation. It is easy to cause equipment fouling and blockage. Multi-effect evaporation is a commonly used solid-liquid separation and separation method. Although the multi-effect evaporation energy consumption is lower than that of direct evaporation, there is also a problem that when the last effect is excessive evaporation, the equipment is easy to scale. In order to prevent equipment fouling and clogging, Chinese patent CN102641602A is provided with at least one mechanical separation device downstream of the primary effect evaporator component and upstream of the final effect evaporator component for reducing the flow into the final effect evaporator component. The concentration of the material to prevent fouling and clogging in the final effect evaporator components. Although the purpose of controlling the material concentration can be achieved by the external mechanical separation device, the cost of the input device is increased. The invention can achieve solid content concentration control without adding separation equipment inside the multi-effect evaporation section.

In addition, as the solid content concentration increases, the equilibrium partial pressure of the liquid decreases, which also leads to a decrease in the efficiency of the multi-effect evaporation treatment.

In addition, for the solid-liquid separation operation, Chinese patent CN101152969 adds the additive to the acid precipitation by adding an additive to obtain a solid-liquid mixture, and then the solid-liquid separation of the mixture, the treatment process is complicated; the Chinese patent CN101306260 after multi-effect evaporation Centrifugal separators are used, but for materials with too small crystalline particles, centrifugation may not be suitable. The present invention performs a solid-liquid separation operation by stirring and evaporation without using an additional additive.

Summary of the invention

The present invention is directed to providing a solid-liquid separation process for overcoming the deficiencies of the prior art, which achieves solid-liquid separation by multi-effect evaporation combined with agitation evaporation.

To achieve the above object, the present invention adopts the following technical solutions:

A solid-liquid separation process comprising the following steps:

A. multiple effect evaporation, the aqueous solution containing a low concentration of dissolved solids or a water-organic solvent mixed solution is concentrated to produce a medium concentration mixed solution;

B. discharging the medium concentration mixed solution into a stirred evaporation kettle, further evaporating and concentrating to produce a high concentration mixed solution;

C. Controlling the solid content of the high-concentration mixed solution, ensuring that the stirred evaporating kettle is discharged as a fluid, and the discharged high-concentration mixed solution is at least partially solidified upon cooling to normal temperature.

In the present invention, unless otherwise defined, the concentrations referred to refer to mass concentrations, for example, the mass percentage of solutes in solution. All "in-range" include end values, for example 25% to 50% including 25% and 50%.

The low-concentration mixed solution has a soluble solid mass ranging from 0.1% to 5%, preferably from 0.3% to 2%.

In the multi-effect evaporation process of step A, the concentration of the dissolved solid in the medium concentration mixed solution is controlled to ensure that the total treatment capacity of the multi-effect evaporation is reduced by less than 20% due to the increase of the solid concentration, and the multi-effect evaporation apparatus is not fouled and clogged, and the stirring in step B is performed. The energy consumed for evaporation is less than 5% of the total evaporated energy.

In the present invention, the total processing capacity refers to the amount of feed per unit time of the multi-effect evaporation system, for example, kg/hr.

In the present invention, the total evaporation energy is the sum of the energy consumed by the multi-effect evaporation of step A and the energy consumed by the stirring of step B.

Controlling the concentration of dissolved solids in the medium concentration mixed solution can achieve the following objectives: (1) ensuring that the total treatment capacity is reduced by less than 20%, (2) preventing fouling of the multi-effect evaporation equipment, and (3) ensuring that the energy consumed by the agitation evaporation is less than 5% of total evaporation energy.

In step A, the multi-effect evaporation is three to five-effect evaporation. The first-effect evaporator adopts positive pressure or micro-negative pressure, and is heated by an external heat source. The second effect uses one-effect evaporated steam as a heat source, and the third-effect uses two-effect evaporated steam as a heat source to heat. If it is greater than three-effect, Such a push; one-effect separator, two-effect evaporator and separator, three-effect evaporator and separator, and evaporator and separator larger than three-effect, condenser use negative pressure; one-effect vacuum is greater than two-effect vacuum The second-effect vacuum is greater than the three-effect vacuum. If it is greater than the three-effect, then the final effect is greater than the condenser vacuum.

In the step A, the dissolved solid is an organic substance, a mixture of more than one organic substance, a mixture of an organic substance and one or more inorganic substances, or one or more organic substances and one or more inorganic substances. a mixture of things. In the multi-effect evaporation operating temperature condition, when the mass percentage of the soluble solid in the medium concentration mixed solution is in the range of 20% to 50%, preferably in the range of 25% to 40%, the medium concentration mixed solution is mainly present in a liquid state, At least 90% is liquid (liquid mass / medium concentration mixed solution mass), preferably at least 95% is liquid. Controlling the solids in the medium concentration mixed solution at a lower level can effectively prevent fouling of the multi-effect evaporation equipment.

The organic compound has a melting point in the range of 75 to 250 ° C and is a mixture of one or more of an organic phosphoric acid and a salt thereof, acetamide or ammonium acetate. The organic phosphoric acid is methyl phosphoric acid and/or dimethyl phosphoric acid.

The inorganic substance is one or a mixture of one or more kinds of phosphoric acid and salts thereof, sulfates, and the like. Multi-effect evaporation operation Under temperature conditions, the solubility of phosphate and sulfate inorganic substances in the medium concentration mixed solution is greater than the concentration in the medium concentration mixed solution, and basically no precipitation is formed, ensuring that the multi-effect evaporation device does not foul and block.

The organic solvent is an organic substance having a boiling point of less than 150 ° C or a mixture of more than one organic substance, which is miscible with water in a treatment concentration range, preferably one or a kind of methanol, ethanol, formic acid, acetic acid or acetone. The above mixture.

The external heat source of the multi-effect evaporation process is hot water, steam or heat transfer oil; the heat exchange mode adopts forward flow, reverse flow or cross flow.

In step C, the cooling method is natural cooling, water cooling or air cooling.

In the step C, the high-concentration mixed liquid in the form of a fluid refers to a small amount of water or water and an organic solvent remaining under the operating temperature of the stirring evaporating tank, and/or due to one or a kind of dissolved solids. The above organic matter is in a molten state, resulting in a solid solution in which a part of the high-concentration mixed solution has a higher melting point than the operating temperature of the stirred evaporating kettle, so that the high-concentration mixed liquid has better fluidity. The mass of the soluble solid in the high concentration mixed solution is in the range of 70% to 95%, preferably in the range of 85% to 95%, more preferably 90% to 95%. The discharged high concentration mixture is at least partially cured upon cooling to ambient temperature, preferably at least 50% cure, more preferably at least 60% cure, more preferably at least 70% cure, more preferably at least 80% cure, more preferably at least 90% cure, Most preferably at least 100% cure. Depending on the season and location, the ambient temperature may be in the range of -40 to 50 °C. Under the same conditions of the same soluble solid content, the degree of curing will be different depending on the ambient temperature.

A three-effect evaporation solid-liquid separation process comprising the following steps:

An aqueous solution containing a low concentration of dissolved solids or a mixed solution of water-organic solvent enters a one-effect separator in a three-way evaporation system, and the material is circulated between each effect separator and the evaporator, and the first effect separator and the second effect separator Between the two-effect separator and the three-effect separator, between the three-effect separator and the stirring evaporation kettle, the materials are respectively transported by the circulation pump, and further, the three-effect evaporation system is adjusted by the vacuum pump and the pressure in the evaporation evaporator is stirred;

The low-concentration mixed solution is heated by an external heat source in an effect evaporator. During the heating process, part of the solution is evaporated into a vapor phase, and the vapor-liquid mixture enters a one-effect separator to realize vapor-liquid separation, and the separated vapor phase is passed into a two-effect evaporator. The heat source of the second-effect evaporation, the condensate is stored in the storage tank after the heat exchange; the separated liquid phase is partially collected and transported into the second-effect separator, and partially recycled into the first-effect evaporator to continue to evaporate.

In the two-effect evaporator, the liquid phase from the one-effect separator is heated and evaporated by the vapor phase from the one-effect separator, and the vapor-liquid mixture enters the two-way vapor-liquid separator to realize vapor-liquid separation, and the separated vapor phase is introduced into the three-effect. The evaporator is used as a heat source for three-effect evaporation. After the heat exchange, the condensate is stored in the storage tank; the separated liquid phase is partially collected and transported into the three-effect separator, and partially recycled into the two-effect evaporator to continue to evaporate.

In the three-effect evaporator, the liquid phase from the second-effect separator 3 is heated and evaporated by the vapor phase from the two-effect separator, and the vapor-liquid mixture enters the three-way separator to realize vapor-liquid separation, and the separated vapor phase is passed to the condenser. The condensate obtained by condensation is the mesh The product is stored in a storage tank; the separated liquid phase is partially circulated into the three-effect evaporator, and partially recovered and sent to the stirring evaporation vessel for further separation operation.

The medium-concentration mixture from the three-way separator is again evaporated in the stirring evaporation vessel, and the steam is returned to the three-effect evaporation system. After the temperature in the kettle is no longer raised, the formed high-concentration mixed solution is discharged and naturally cooled to be solidified.

The low-concentration mixture is the original feed, and the medium-concentration mixture is formed in the last-effect separator of multi-effect evaporation after multi-effect evaporation (in this case, three-effect evaporation, so it is generated in three effects). The separator 5), the medium concentration mixed solution is evaporated again after entering the stirring evaporator 9 to become a high concentration mixed solution.

The invention solves the problem that the total treatment capacity of the multi-effect evaporation is reduced due to the increase of the solid concentration and the partial pressure change, and the excessive evaporation device is easy to foul and block by controlling the concentration of the solution in the last effect of the multi-effect evaporation. In the invention, the moderately concentrated solution is separately stirred and evaporated, which does not affect the treatment efficiency of multi-effect evaporation, and the energy consumed for controlling the stirring evaporation is less than 5% of the total evaporation energy, and a balance is obtained between energy saving and efficiency. Moreover, it is also possible to return the steam generated by the agitation evaporation to the evaporation system, which not only solves the entrainment problem in the evaporation process, but also realizes energy integration and comprehensive utilization.

The invention has the following beneficial effects;

Compared with the direct evaporation process, the energy consumption of the evaporative crystallization solid-liquid separation is greatly reduced by the present process. Under the same evaporation condition, the heating steam consumed by the multi-effect evaporation only accounts for about 40% of the heating steam required for direct evaporation. By controlling the concentration of the solution in the last effect of multi-effect evaporation, the process solves the technical problems such as the decrease of the solid concentration, the partial pressure change, the reduction of the total treatment capacity of the multi-effect evaporation, and the excessive evaporation of the equipment. In the invention, the moderately concentrated solution is separately stirred and evaporated, which does not affect the treatment efficiency of multi-effect evaporation, and the energy consumed for controlling the stirring evaporation is less than 5% of the total evaporation energy, and a balance is obtained between energy saving and efficiency. Moreover, after stirring and evaporating, the high-concentration solution is discharged in a liquid form, and partially or completely solidified after cooling, thereby improving transportation convenience, and returning the steam generated by the agitation evaporation to the evaporation system, thereby not only solving the entrainment problem in the evaporation process, but also solving the entrainment problem in the evaporation process. Energy integration and comprehensive utilization can be achieved.

DRAWINGS

1 is a schematic diagram of a solid-liquid separation process of three-effect evaporation combined with stirring evaporation in an embodiment of the present invention.

The figures are:

1. One-effect separator, 2. One-effect evaporator,

3, two-effect separator 4, two-effect evaporator

5, three-effect separator 6, three-effect evaporator

7, condenser 8, storage tank

9, stirring

evaporation kettle

10, 11, 12 circulating pump

13 vacuum pump.

detailed description

The invention is further illustrated by the following examples, but the invention is not limited to the scope of the embodiments shown.

Example 1

The acetic acid-aqueous solution system contains potassium chloride, phosphoric acid and its metal and ammonium salts, organic phosphoric acid and its metal and ammonium salts, and acetamide, and has a total mass content of about 4.5%.

The pretreated acetic acid-water solution is sent to the three-effect evaporation device through the feed pump for evaporation treatment, and the steam is used as the external heat source in the first-effect evaporator, and the acetic acid-aqueous solution system is heated in a downstream manner as the three-effect separator. When the concentration of dissolved solids in the mixed solution reaches 35% (this can ensure that the total treatment capacity of multi-effect evaporation is reduced by less than 20% due to the increase of solid concentration, ensuring that the multi-effect evaporation equipment is not fouled and blocked, and the energy consumed by stirring evaporation is ensured. Less than 5% of the total evaporation energy, the mixed solution is discharged into a stirred evaporation kettle and further evaporated and concentrated to produce a high-concentration mixed solution. After the temperature in the stirred evaporating tank is no longer rising, the high-concentration mixture remaining in the stirred evaporating kettle is discharged. The solution, at this time, the concentration of the high-concentration mixed solution discharged is about 95%, and because of its high temperature, it remains in a fluid state, and partially or completely solidifies into a solid state after being discharged through water cooling.

Example 2

The formic acid-aqueous solution system contains sodium chloride, diammonium hydrogen phosphate, and ammonium acetate, and the total mass content thereof reaches 0.5%.

The pretreated formic acid-water solution is sent to a four-effect evaporation device for evaporation treatment by a feed pump, and the hot water is used as an external heat source in an effect evaporator, and the formic acid-water solution system is heated by a countercurrent method, and the four-effect separator is used as a four-effect separator. When the concentration of dissolved solids in the mixed solution reaches 25% (this can ensure that the total treatment capacity of multi-effect evaporation is reduced by less than 20% due to the increase of solid concentration, ensuring that the multi-effect evaporation equipment does not foul and block, and the energy consumed by stirring evaporation is ensured. Less than 5% of the total evaporation energy, the mixed solution is discharged into a stirred evaporation kettle and further evaporated and concentrated to produce a high-concentration mixed solution. After the temperature in the stirred evaporating tank is no longer rising, the high-concentration mixture remaining in the stirred evaporating kettle is discharged. The solution, at this time, the concentration of the high-concentration mixed solution discharged is about 85%, and because of its high temperature, it remains in a fluid state, and partially or completely solidifies into a solid state after being discharged through air-cooling.

Example 3

The ethanol-water solution system contains potassium sulfate, ammonium dihydrogen phosphate, and ammonium acetate, and the total mass content thereof reaches 0.1%. The pretreated ethanol-water solution is sent to the five-effect evaporation device for evaporation treatment through the feed pump, and the heat-transfer oil is used as the external heat source in the first-effect evaporator, and the ethanol-water solution system is heated by the cross-flow method. When the concentration of dissolved solids in the mixed solution reaches 30% (this can ensure that the total treatment capacity of multi-effect evaporation is reduced by less than 20% due to the increase of solid concentration, ensuring that the multi-effect evaporation equipment does not foul and block, and ensuring stirring and evaporation The energy consumed is less than the total evaporation energy 5%), the mixed solution is discharged into a stirring evaporating kettle and further evaporated and concentrated to produce a high-concentration mixed solution. After the temperature in the evaporating kettle is no longer rising, the high-concentration mixed solution remaining in the stirring evaporating kettle is discharged, and discharged at this time. The concentration of the high-concentration mixed solution is about 70%, and because of its high temperature, it remains in a fluid state, and is partially or completely solidified into a solid state after being discharged through natural cooling.

Example 4

As shown in the figure, the water-organic solvent mixed solution containing a low concentration of dissolved solids enters the three-effect evaporation system, and the material is circulated between the various effect separators and the evaporator, and the first effect separator 1 and the second effect separator 3 The material is transported by the pump between the two-stage splitter 3 and the three-effect separator 5, and the three-effect evaporation system is adjusted by the vacuum pump and the pressure in the evaporator is stirred.

The low-concentration mixed solution is heated by the external heat source in the first-effect evaporator 2, and part of the solution is evaporated into a vapor phase during the heating process, and the vapor-liquid mixture enters the first-effect separator 1 to realize vapor-liquid separation, and the separated vapor phase is passed into the second-effect evaporator. 4. As a heat source for the second-effect evaporation, the condensate is stored in the storage tank 8 after the heat exchange; the separated liquid phase is partially sent and transported into the second-effect separator 3, and partially recycled into the first-effect evaporator 2 to continue to evaporate.

In the two-effect evaporator 4, the liquid phase from the one-effect separator 1 is heated and evaporated by the vapor phase from the one-effect separator 1, and the vapor-liquid mixture enters the two-way vapor-liquid separator 3 to realize vapor-liquid separation, and the separated steam is obtained. The three-effect evaporator 6 is connected to the three-effect evaporator as a heat source for three-effect evaporation, and the condensed liquid is stored in the storage tank 8 after heat exchange; the separated liquid phase is partially collected and transported into the three-effect separator 5, and partially recycled into the two-effect evaporator. Continue to evaporate within 4.

In the three-effect evaporator 6, the liquid phase from the two-effect separator 3 is heated and evaporated by the vapor phase from the two-way separator 3, and the vapor-liquid mixture enters the three-way separator 5 to realize vapor-liquid separation, and the separated vapor phase is introduced. Condenser 7, the condensed liquid obtained by condensation is the target product, and is stored in the storage tank 8; the separated liquid phase is partially circulated into the three-effect evaporator, and partially recovered and transported into the stirring evaporation kettle for further separation operation.

The medium-concentration mixed solution from the three-way separator 5 is re-evaporated in the stirring evaporating tank 9, and the steam is returned to the three-effect evaporation system. After the temperature in the autoclave is no longer raised, the high-concentration mixed solution is partially or completely solidified after being cooled. .

The above description of the embodiments is intended to facilitate the understanding and use of the invention by those skilled in the art. It will be apparent to those skilled in the art that various modifications can be readily made to these embodiments and the general principles described herein can be applied to other embodiments without the inventive work. Therefore, the present invention is not limited to the embodiments described above, and those skilled in the art should be able to make modifications and changes within the scope of the invention without departing from the scope of the invention.

Claims

A solid-liquid separation process characterized by comprising the steps of:

A. multiple effect evaporation, the aqueous solution containing a low concentration of dissolved solids or a water-organic solvent mixed solution is concentrated to produce a medium concentration mixed solution;

B. discharging the medium concentration mixed solution into a stirred evaporation kettle, further evaporating and concentrating to produce a high concentration mixed solution;

C. Controlling the solid content of the high-concentration mixture, discharging the stirred evaporation vessel as a fluid, and discharging the high-concentration mixture at least partially cured upon cooling to ambient temperature.
The solid-liquid separation process according to claim 1, characterized in that the concentration of the dissolved solids in the concentration mixed solution in the multi-effect evaporation process control achieves the following effects: (1) the total treatment capacity of the multi-effect evaporation due to the increase in the solid concentration The reduction is less than 20%, (2) the multi-effect evaporation equipment is basically not fouled and blocked, and (3) the energy consumed by stirring and evaporation is less than 5% of the total evaporation energy.
The solid-liquid separation process according to claim 1 or 2, wherein the multi-effect evaporation is three to five-effect evaporation.
The solid-liquid separation process according to claim 1 or 2, wherein the dissolved solid is an organic substance, a mixture of one or more organic substances, a mixture of an organic substance and one or more inorganic substances. , or a mixture of more than one organic substance and one or more inorganic substances.
The solid-liquid separation process according to claim 4, wherein the organic compound has a melting point in the range of 75 to 250 ° C and comprises organic phosphoric acid and salts thereof, acetamide and ammonium acetate.
The solid-liquid separation process according to claim 5, wherein the organic phosphoric acid is methylphosphoric acid and/or dimethylphosphoric acid.
The solid-liquid separation process according to claim 4, wherein the inorganic substance comprises phosphoric acid, salts thereof, and sulfates.
The solid-liquid separation process according to claim 1 or 2, wherein the organic solvent is an organic substance having a boiling point of less than 150 ° C or a mixture of more than one organic substance which is miscible with water in a treatment concentration range. .
The solid-liquid separation process according to claim 8, wherein the organic solvent is one or a mixture of one or more of methanol, ethanol, formic acid, acetic acid or acetone.
The solid-liquid separation process according to claim 1 or 2, wherein the multi-effect evaporation process is three to five-effect evaporation, and the first-effect evaporator adopts positive pressure or micro-negative pressure, and is heated by an external heat source. The effect is to use the steam evaporated by the first effect as the heat source, and the three-effect steam is used as the heat source by the steam evaporated by the second effect. If it is greater than the three effects, the analogy is the same; the first effect separator, the second effect evaporator and the separator, and the third effect The evaporator and the separator and the evaporator and the separator and the condenser larger than the three effects adopt the negative pressure; the one-effect vacuum is greater than the two-effect vacuum, and the second-effect vacuum is greater than the three-effect vacuum, and if it is greater than the three-effect, Then, the final effect vacuum is greater than the condenser vacuum.
The solid-liquid separation process according to claim 1 or 10, wherein the external heat source of the multi-effect evaporation process is hot water, steam or heat transfer oil; and the heat exchange mode adopts a forward flow, a reverse flow or a cross flow.
The solid-liquid separation process according to claim 1 or 2, wherein the low-concentration mixed solution has a soluble solid mass ranging from 0.1% to 5%.
The solid-liquid separation process according to claim 1 or 2, wherein the medium-concentration mixed solution has a soluble solid mass ranging from 20% to 50%.
The solid-liquid separation process according to claim 1 or 2, wherein the high-concentration mixed solution has a soluble solid mass ranging from 70% to 95%.
The solid-liquid separation process according to claim 1 or 2, wherein the cooling method is natural cooling, water cooling or air cooling.