1. A treatment method suitable for removing sodium sulfate from viscose acid bath is characterized by comprising the following steps:

taking out the acid bath to be treated from the acid bath circulating system of the viscose fiber, heating the acid bath taken out to 40-100 ℃, and carrying out evaporation concentration under the saturated steam pressure corresponding to each temperature to separate out sodium sulfate crystals to obtain crystal mush containing the sodium sulfate crystals;

solid-liquid separation is carried out to obtain sodium sulfate crystals in the crystal mush;

adding alkali to neutralize the sodium sulfate crystals, and adjusting the pH value to 5-7;

and carrying out secondary solid-liquid separation to obtain a neutralized sodium sulfate crystal.

2. The process for removing sodium sulfate from viscose fiber acid bath according to claim 1, wherein the acid bath in the withdrawn part is gradually evaporated and concentrated by a multi-effect evaporator to separate out sodium sulfate crystals.

3. The method as claimed in claim 2, wherein the secondary steam generated by evaporation in each evaporator except the last evaporator in the multiple evaporators is used as the steam heat source of the next evaporator to heat the acid bath.

4. The process for removing sodium sulfate from viscose acid bath according to claim 3, wherein the secondary steam generated by the evaporation of the evaporator in the last effect in the multi-effect evaporator enters the condenser for condensation.

5. The process for removing sodium sulfate from viscose fiber acid bath according to claim 1, wherein in the step of evaporation concentration, the evaporator for separating out sodium sulfate crystals and obtaining the crystal slurry is provided with a clear liquid separator, and the separated clear liquid is sent back to the acid bath circulation system and added into the acid bath circulation system.

6. The process for the acid bath removal of sodium sulfate for viscose fiber according to claim 1, wherein the acid bath taken out of the section is concentrated by evaporation using an MVR evaporator to separate out sodium sulfate crystals.

7. The process for acid bath sodium sulfate removal for viscose fibers according to claim 1, further comprising: and (3) mother liquor obtained in the solid-liquid separation step and the secondary solid-liquid separation step is returned to the acid bath circulation system and added into the acid bath circulation.

8. The process for the acid bath removal of sodium sulfate for viscose fiber according to claim 1, further comprising the steps of, after obtaining the sodium sulfate crystals after the second solid-liquid separation: and drying and packaging the sodium sulfate crystals to produce anhydrous sodium sulphate.

9. The process for removing sodium sulfate from viscose fiber acid bath according to claim 1, wherein the acid bath taken out is concentrated by evaporation using a combination of MVR evaporator and multi-effect evaporator to separate out sodium sulfate crystals.

10. A processing apparatus suitable for removing sodium sulfate from viscose acid bath, comprising:

an evaporative crystallizer for removing excess sodium sulfate crystals and moisture from the viscose acid bath;

the primary solid-liquid separator is connected with a discharge port of the magma thickener of the evaporative crystallizer;

the neutralization tank is connected with a solid outlet of the primary solid-liquid separator;

and the secondary solid-liquid separator is connected to the outlet of the neutralization tank.

11. The apparatus for removing sodium sulfate from viscose fiber acid bath according to claim 10, wherein the evaporation crystallizer is a multi-effect evaporator or an MVR evaporator connected in a cascade manner.

12. The apparatus for removing sodium sulfate from viscose fiber acid bath according to claim 10, wherein the primary solid-liquid separator is a centrifuge or a cyclone.

13. The apparatus for removing sodium sulfate from viscose fiber acid bath according to claim 10, wherein the evaporation crystallizer is a multi-effect evaporator or an MVR evaporator or a combination of the MVR evaporator and the multi-effect evaporator connected in series.

14. The apparatus for acid bath sodium sulfate removal from viscose fiber according to claim 10, wherein the magma thickener is a salt leg or a settler.

Background

In the production process of viscose, acid bath consisting of sulfuric acid, zinc sulfate and the like in a certain proportion is needed to solidify viscose fiber tows sprayed out of a spinning machine. During the process of coagulating the tow, a large amount of water and sodium sulfate are generated due to acid-base neutralization, and the water and the sodium sulfate must be separated out, so that the acid bath can be recycled.

The current technology is to separate the water and sodium sulfate in the acid bath as follows: evaporating and concentrating the acid bath by using a flash evaporation device, separating water in the acid bath, then cooling the concentrated acid bath at low temperature, and crystallizing to obtain mirabilite, namely sodium sulfate decahydrate. Sodium sulfate is only 42% in mirabilite, which cannot be sold as a product, so the mirabilite must be melted, evaporated, separated, dried and the like to obtain a glauber salt product. The production device is a production device which is not changed at home and abroad for decades. The details are discussed in "rayon factory equipment", published by Qingdao ocean university Press, 6 months 1993, and so far there has been only a change in scale and no improvement in the art.

Chemical knowledge teaches that sodium sulfate crystallizes at less than 32.4 degrees as sodium sulfate decahydrate and at greater than 32.4 degrees as anhydrous sodium sulfate. The existing flash evaporation device is only suitable for concentration and is not suitable for crystallization, because if crystallization occurs, equipment is blocked and a pipe is blocked. While the general evaporator can cause scaling and pipe blockage, and moreover, the graphite pipe is not easy to realize because the graphite pipe is used for evaporating the acid bath and cannot resist the abrasion of anhydrous sodium sulphate particles and the corrosion during alkali liquor cleaning.

Disclosure of Invention

Aiming at the technical problems existing in the prior art, the invention provides a treatment method and a treatment device suitable for removing sodium sulfate in viscose acid bath, which have the advantages of short process route, simple equipment, low process temperature and reduced equipment corrosion.

The first aspect of the invention provides a treatment method suitable for removing sodium sulfate from viscose acid bath, which comprises the following steps:

taking out the acid bath to be treated from the acid bath circulating system of the viscose fiber, heating the acid bath taken out to 40-100 ℃, and carrying out evaporation concentration under the saturated steam pressure corresponding to each temperature to separate out sodium sulfate crystals to obtain crystal mush containing the sodium sulfate crystals;

solid-liquid separation is carried out to obtain sodium sulfate crystals in the crystal mush;

adding alkali to neutralize the sodium sulfate crystals, and adjusting the pH value to 5-7;

and carrying out secondary solid-liquid separation to obtain a neutralized sodium sulfate crystal.

The treatment method is further improved in that the acid bath taken out of the part is gradually evaporated and concentrated by a multi-effect evaporator to separate out the sodium sulfate crystals.

The treatment method is further improved in that secondary steam generated by evaporation of each effect evaporator except for the last effect evaporator in the multiple effect evaporators is used as a steam heat source of the next effect evaporator to heat the acid bath.

The treatment method is further improved in that the secondary steam generated by evaporation of the evaporator in the last effect in the multi-effect evaporator enters the condenser for condensation.

In the step of evaporation and concentration, an evaporator for separating out the sodium sulfate crystals and obtaining the crystal mush is provided with a clear liquid separator, and the separated clear liquid is sent back to the acid bath circulating system and added into the acid bath circulating system.

The treatment method is further improved in that the acid bath taken out of the part is circularly evaporated and concentrated for multiple times by adopting an MVR evaporator to separate out the sodium sulfate crystals.

The processing method of the invention is further improved in that the method also comprises the following steps: and (3) mother liquor obtained in the solid-liquid separation step and the secondary solid-liquid separation step is returned to the acid bath circulation system and added into the acid bath circulation.

The treatment method of the invention is further improved in that after the sodium sulfate crystals after the secondary solid-liquid separation are obtained, the method also comprises the following steps: and drying and packaging the sodium sulfate crystals to produce anhydrous sodium sulphate.

The treatment method is further improved in that the acid bath taken out of the part is evaporated and concentrated by adopting a combination of an MVR evaporator and a multi-effect evaporator to separate out the sodium sulfate crystals.

A second aspect of the invention provides a treatment apparatus suitable for removing sodium sulfate from a viscose acid bath, comprising:

an evaporative crystallizer for removing excess sodium sulfate crystals and moisture from the viscose acid bath;

the primary solid-liquid separator is connected with a discharge port of the magma thickener of the evaporative crystallizer;

the neutralization tank is connected with a solid outlet of the primary solid-liquid separator;

and the secondary solid-liquid separator is connected to the outlet of the neutralization tank.

The processing device is further improved in that the evaporation crystallizer adopts a multi-effect evaporator or an MVR evaporator which are connected step by step.

The processing device of the invention is further improved in that the primary solid-liquid separator adopts a centrifuge or a cyclone.

The processing device of the invention is further improved in that the evaporation crystallizer adopts a multi-effect evaporator or an MVR evaporator or a combination of the MVR evaporator and the multi-effect evaporator which are connected step by step.

A further improvement of the treatment plant according to the invention is that the magma thickener is a salt leg or settler.

Due to the adoption of the technical scheme, the invention has the following technical effects:

compared with the traditional multistage flash evaporation process, the invention adopts multiple-effect evaporative crystallization and MVR evaporative crystallization processes and twice solid-liquid separation, simplifies the process route, reduces the number of effective bodies, has low process temperature and reduces the corrosion of equipment under the condition of meeting the concentration and crystallization of sodium sulfate; the crystallization effect body is provided with a clear liquid separator for separating crystallization and clear liquid, a belt filter required by the traditional process is not needed, the process links are reduced, and the sewage production is greatly reduced.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a flow chart of a treatment process for removing sodium sulfate from a viscose acid bath in accordance with an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1, an embodiment of the present invention provides a processing method and a processing apparatus suitable for removing sodium sulfate in a viscose acid bath, wherein the processing method for removing sodium sulfate in the viscose acid bath includes the following steps:

the method comprises the following steps: taking out the acid bath to be treated from the acid bath circulating system of the viscose fiber, heating the acid bath taken out to 40-100 ℃, and carrying out evaporation concentration under the saturated steam pressure corresponding to each temperature to separate out sodium sulfate crystals to obtain crystal mush containing the sodium sulfate crystals;

step two: solid-liquid separation is carried out to obtain sodium sulfate crystals in the crystal mush;

step three: adding alkali to neutralize the sodium sulfate crystals, and adjusting the pH value to 5-7;

step four: and carrying out secondary solid-liquid separation to obtain a neutralized sodium sulfate crystal.

Specifically, in the first step, the acid bath circulation system for viscose fibers is a conventional system, and mainly includes a coagulation bath 11, a bottom tank 12, and a head tank 13, and the acid bath circulates among the coagulation bath 11, the bottom tank 12, and the head tank 13, and during the spinning process, the spinning process is performed in the coagulation bath 11, the acid bath in the head tank 13 is directly supplied to the coagulation bath 11, the acid bath diluted after being used in the coagulation bath 11 flows into the bottom tank 12, the acid bath in the bottom tank 12 further flows into the head tank 13, and the acid bath in the head tank 13 is recycled, and the concentration and temperature of the acid bath are adjusted in the head tank 13 so as to be suitable for the acid bath process.

In the above viscose acid bath circulation system, viscose has a large amount of water and sodium hydroxide solution before being sprayed from a nozzle into the coagulation bath 11, the main components in the coagulation bath 11 are water, sulfuric acid, sodium sulfate and zinc sulfate, and after the viscose enters the coagulation bath 11, the sodium hydroxide and the sulfuric acid react to generate sodium sulfate and water. The sodium sulfate produced and the water carried in by the viscose need to be removed from the acid bath by evaporative crystallization.

Therefore, in the first step, a part of the acid bath is taken out from the head tank 13 of the acid bath circulation system, and the part of the acid bath is introduced into the evaporation crystallizer 14, and the acid bath is heated to 40 to 100 ℃ by using steam as a heat source, and is maintained at a saturated steam pressure corresponding to each temperature, so that the heated acid bath is saturated, and water is evaporated to generate secondary steam, and the part of the acid bath is concentrated. Wherein, the feed inlet of the evaporative crystallizer 14 is connected with one branch of the outlet of the elevated tank 13, the other branch of the outlet of the elevated tank 13 is connected with the inlet of the coagulating bath 11, the outlet of the coagulating bath 11 is connected with one branch of the inlet of the bottom tank 12, and the outlet of the bottom tank 12 is connected with the inlet of the elevated tank 13.

As a preferred embodiment, the present invention provides two kinds of evaporative crystallizers: one is a multiple effect evaporator and the other is an MVR (mechanical Vapor recompression) evaporator.

When the multi-effect evaporator is adopted, the evaporator comprises four (or more) effect bodies, and the effect bodies with four (or more) rising film (or falling film or forced or mixed) circulation (natural circulation or forced circulation) form the four (or more) effect evaporator. The first, second, third (or more) effect bodies are used for evaporation concentration of viscose fiber acid bath with lower concentration, the last effect body is an evaporation concentration crystallizer used for evaporation concentration of viscose fiber acid bath with higher concentration and crystallization of inorganic salt (namely sodium sulfate), and concentrated acid liquor and crystal mush of inorganic salt crystallization are discharged from the effect; the first, second, fourth and third (or more) effect bodies can also be used for the evaporation concentration of the viscose fiber acid bath with lower concentration, the third (or last) effect body is an evaporation concentration crystallizer and is used for the evaporation concentration of the viscose fiber acid bath with higher concentration and the crystallization of inorganic salt, and concentrated acid liquid and crystal mush of the inorganic salt crystallization are discharged from the effect.

When the multi-effect evaporator is adopted, secondary steam generated in one effect is used as a heat source of the next effect, the concentrated acid bath also enters the next effect, the concentrated acid bath is heated to a saturated state by the secondary steam, water is evaporated, secondary steam is generated, and the acid bath is further concentrated; the concentrated acid bath also enters the next effect, the secondary steam heats the concentrated acid bath to a saturated state, water is evaporated to generate secondary steam, the acid bath is further concentrated, and sodium sulfate is saturated in the process and crystals are separated out after multiple times of evaporation and concentration; and the secondary steam evaporated in the last effect enters a condenser, is condensed by circulating water and then is sent out of the system. Preferably, the multi-effect evaporator main body can adopt metal materials to replace graphite materials, so that the equipment has longer service life and improved thermal efficiency, and the investment and operation cost of the equipment is lower.

When an MVR evaporator is adopted, the generated secondary steam is compressed by the MVR to be heated and then is used as a heat source again, and after evaporation and concentration, sodium sulfate is saturated to separate out crystals. Among these, MVR evaporators and their related evaporation techniques are prior art and are not cumbersome here.

It should be noted that, in the step of evaporation concentration, the temperature needs to be controlled between 40 ℃ and 100 ℃, and the pressure is ensured to be maintained at the saturated vapor pressure corresponding to each temperature, so that the temperature is too high, which may aggravate the corrosion of the equipment, and the temperature is too low, which may not be advantageous in terms of energy consumption.

In addition, the steam heat source can adopt raw steam (or secondary steam after mechanical compression, or the raw steam is used for pushing the TVR heat pump), preferably, the raw steam is used for pushing the TVR heat pump, specifically, the secondary steam generated by evaporation of the first effect evaporator or the second effect evaporator is partially sent to the next effect evaporator to be used as a heat source for evaporation and concentration of the next effect, and the other part is mixed with the raw steam by using a TVR steam booster pump, is pressurized and warmed and then returns to the first effect to be used as heating steam, so that more efficient utilization of heat energy can be realized.

The last effect or the next last effect (or other effects) of the multi-effect evaporator can be used as a crystallization effect body, a clear liquid separator is arranged on the crystallization effect body, a clear liquid outlet of the clear liquid separator is connected with one branch of an inlet of the bottom tank 12 of the acid bath circulation system through a pump, and when the multi-effect evaporator is used, clear liquid separated from the crystallization effect body is directly discharged into the bottom tank 12 of the acid bath circulation system to continuously participate in acid bath circulation. Similarly, a clear liquid separator may be provided in the crystallization effect body of the MVR evaporator, and a clear liquid outlet of the clear liquid separator is connected to one branch of the inlet of the bottom tank 12 of the acid bath circulation system via a pump, and the separated clear liquid is discharged into the bottom tank 12 of the acid bath circulation system. By arranging the clear liquid separator, crystallization and clear liquid are separated, a belt filter is not needed like the traditional process, the process links are reduced, and the sewage yield is greatly reduced.

In the second step, a crystal mush thickener is arranged at the discharge hole of the crystallization effect body, the crystal mush thickener can adopt a salt leg or a settler to form a salt leg or a settler discharge hole, the inlet of the primary solid-liquid separator 15 is connected with the discharge hole of the salt leg (or the settler), sodium sulfate crystals precipitated from the crystallization effect body are collected through the salt leg (or the settler), crystal mush containing sodium sulfate crystals enters the primary solid-liquid separator 15 to carry out primary solid-liquid separation (namely, primary solid-liquid separation), sodium sulfate crystals and mother liquor after the primary solid-liquid separation are obtained, the liquid outlet of the primary solid-liquid separator 15 is connected with one branch of the inlet of the bottom tank 12, the mother liquor is sent back to the bottom tank 12 of the acid bath circulation system, and continues to participate in the acid bath circulation; wherein, the primary solid-liquid separator 15 can adopt a centrifuge or a cyclone.

In the third step, water is added into the sodium sulfate crystal obtained after the first solid-liquid separation in the neutralization tank 16, sodium sulfate crystal slurry is obtained after mixing, and sodium hydroxide is added to adjust the pH value to 5-7, wherein the sodium hydroxide is used as alkali for neutralizing the sodium sulfate crystal slurry, and the generation of impurities can be reduced.

In the fourth step, the neutralized sodium sulfate crystal slurry is sent to the secondary solid-liquid separator 17 for secondary solid-liquid separation (i.e. secondary solid-liquid separation), so as to obtain sodium sulfate crystals and mother liquor after secondary solid-liquid separation, the liquid outlet of the secondary solid-liquid separator 17 is connected with one branch of the inlet of the bottom tank 12, and the mother liquor is also sent back to the bottom tank 12 of the acid bath circulation system to continue to participate in the acid bath circulation; wherein, the secondary solid-liquid separator 17 may be a centrifuge.

And finally, after the four steps are completed, obtaining relatively pure sodium sulfate crystals, sending the sodium sulfate crystals into a drying and packaging system 18, and drying and packaging to produce anhydrous sodium sulphate.

The embodiment of the invention also provides a treatment device suitable for removing sodium sulfate in the viscose acid bath, which can be used for realizing the treatment method suitable for removing sodium sulfate in the viscose acid bath. The processing device mainly comprises:

an evaporative crystallizer 14 for evaporative concentration of the viscose acid bath;

a primary solid-liquid separator 15 connected to the discharge port of the magma thickener of the evaporative crystallizer 14, wherein the magma thickener can adopt salt or a settler to form a salt leg or a settler discharge port;

a neutralization tank 16 connected to a solid outlet of the primary solid-liquid separator 15;

a secondary solid-liquid separator 17 connected to an outlet of the neutralization tank 16;

and a dry packaging system 18 connected to a solid outlet of the secondary solid-liquid separator 17.

The evaporator-crystallizer 14 may be a multi-effect evaporator or an MVR evaporator connected in a cascade manner, or a combination of the multi-effect evaporator and the MVR evaporator. The multi-effect evaporator and the MVR evaporator are suitable for the viscose fiber acid bath field and belong to the first time, but the multi-effect evaporation crystallization and MVR evaporation crystallization processes are mature in other fields, and have multiple improvement points in the field, wherein one of the improvement points is temperature control, over-high temperature aggravates equipment corrosion, and the energy consumption is not superior if the temperature is too low; and secondly, the crystallization and the clear liquid are separated, a belt filter is not needed like the traditional process, the process links are reduced, and the sewage production is greatly reduced.

An acid bath circulation system for viscose fibers is a conventional technique, and mainly comprises a coagulation bath 11, a bottom tank 12, and a head tank 13, wherein an acid bath circulates among the coagulation bath 11, the bottom tank 12, and the head tank 13, a spinning process is performed in the coagulation bath 11 during a spinning process, the acid bath in the head tank 13 is directly supplied to the coagulation bath 11, the acid bath diluted after being used in the coagulation bath 11 flows into the bottom tank 12, the acid bath in the bottom tank 12 further flows into the head tank 13, the acid bath in the head tank 13 is recycled, and the concentration and temperature of the acid bath are adjusted before the head tank 13 so as to be suitable for the acid bath process.

When the multi-effect evaporator or the MVR evaporator is used, the feed inlet is connected to a branch of the outlet of the head tank 13, and is used for obtaining a part of acid bath from the head tank 13, and after the part of acid bath is subjected to multiple evaporation concentration in the multi-effect evaporator or the MVR evaporator, a magma of concentrated acid liquor and sodium sulfate crystals is obtained, it should be noted that in the evaporation concentration process, the heating temperature is controlled to be 40 ℃ to 100 ℃, and is maintained at the saturated vapor pressure corresponding to each temperature.

The last effect or the next last effect (or other effects) of the multi-effect evaporator can be used as the crystallization effect, a clear liquid separator is arranged in the crystallization effect, a clear liquid outlet of the clear liquid separator is connected with one branch of an inlet of the bottom tank 12 of the acid bath circulation system, and clear liquid separated from the crystallization effect is directly discharged into the bottom tank 12 of the acid bath circulation system to continuously participate in the acid bath circulation. Similarly, a clear liquid separator is provided in the crystallization effect body of the MVR evaporator, and a clear liquid outlet of the clear liquid separator is connected to one branch of an inlet of the bottom tank 12 of the acid bath circulation system, and the separated clear liquid is discharged into the bottom tank 12 of the acid bath circulation system. By arranging the clear liquid separator, crystallization and clear liquid are separated, a belt filter is not needed like the traditional process, the process links are reduced, and the sewage yield is greatly reduced.

The primary solid-liquid separator 15 performs primary solid-liquid separation on the crystal mush output by the multi-effect evaporator or the MVR evaporator, a liquid outlet is connected to a mother liquor tank for collecting mother liquor generated after sequential solid-liquid separation, and the mother liquor tank is connected to the bottom tank 12 of the acid bath circulation system through a pump and is used for enabling acid liquor without sodium sulfate to flow back to the bottom tank 12 and continue to participate in acid bath circulation. Wherein, the primary solid-liquid separator 15 can adopt a centrifuge or a cyclone.

And (3) allowing the sodium sulfate crystals subjected to the primary solid-liquid separation to enter a neutralization tank 16, adding water into the sodium sulfate crystals obtained after the primary solid-liquid separation in the neutralization tank 16, mixing to obtain sodium sulfate crystal slurry, adding sodium hydroxide, and adjusting the pH value to 5-7.

The neutralized sodium sulfate crystals and the neutralized sodium sulfate solution are sent to a secondary solid-liquid separator 17 for secondary solid-liquid separation, a liquid outlet can also be connected to a mother liquor tank (which can share one mother liquor tank with the primary solid-liquid separation equipment), the mother liquor discharged by the secondary centrifuge 17 after the sodium sulfate removal is collected, and the mother liquor tank is connected with the bottom tank 12 of the acid bath circulation system through a pump and is used for flowing the sodium sulfate removal solution back to the bottom tank 12 to continue to participate in the acid bath circulation. Wherein, the secondary solid-liquid separator 17 may be a centrifuge.

Finally, pure sodium sulfate crystals are obtained and sent into a drying and packaging system 18 for drying and packaging, namely, anhydrous sodium sulphate is produced.

Compared with the traditional multistage flash evaporation process, the invention adopts multiple-effect evaporative crystallization and MVR evaporative crystallization processes and twice solid-liquid separation, simplifies the process route, reduces the number of effective bodies, has low process temperature and reduces the corrosion of equipment under the condition of meeting the concentration and crystallization of sodium sulfate; the crystallization effect is provided with a clear liquid separator for separating the crystallization and clear liquid, a belt filter required by the traditional process is not needed, the process links are reduced, and the sewage production is greatly reduced.

The parts not involved in the present invention are the same as or can be implemented by the prior art. Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.