Device and process for recovering magnesium salt tablets from industrial magnesium salt-containing wastewater

Abstract

The invention relates to a device and a process for recovering magnesium salt tablets from industrial magnesium salt-containing wastewater, magnesium salt in industrial waste acid is recovered by adopting an evaporation mode, after the magnesium salt-containing wastewater is filtered and precipitated, a supernatant solution enters an evaporation system, evaporation and concentration are performed, a concentrated solution is recovered, cooling and flaking are performed, and flaked magnesium salt is collected. The evaporation system comprises an evaporator and a condenser. The evaporation system increases the evaporation speed by enhancing evaporation; through the characteristic of normal-pressure evaporation, the problems that the boiling point is increased due to the fact that the solubility of the solution is increased, and energy consumption is increased due to the fact that the requirement for the quality of a heat source is improved in a traditional boiling evaporation process link and the evaporation system works unstably are solved. Compared with the prior art, the use efficiency of energy is improved, the energy consumption is reduced, the operation stability of the system is improved, and the risk that the evaporator is scaled and blocked is avoided.

Description

Technical Field

[0001] The invention relates to a magnesium salt recovery technology, in particular to a device and a process for recovering magnesium salt tablets from industrial wastewater containing magnesium salt. Background Art

[0002] Industrial wastewater containing magnesium salts is a mixed wastewater containing a very small amount of organic matter and a single magnesium salt in the production process of chemical drugs. The conventional recovery processes generally include precipitation separation, magnesium oxide precipitation, and freezing crystallization. The existing technology currently has the following disadvantages:

[0003] (1) The precipitation separation method generally requires the addition of NH4F, and HF will be produced during the production process. It has the disadvantages of large investment, large losses, and the generation of Class 8 hazardous substances HF during the process.

[0004] (2) The magnesium oxide precipitation method uses magnesium oxide water reagent for neutralization precipitation, controls the pH value of the mother liquor to be neutral, and after precipitation, the precipitate is magnesium salt. The investment is still high, and sodium salt impurities may be generated during the pH adjustment process, so it is not very applicable.

[0005] (3) The freeze crystallization method has certain requirements on the concentration of magnesium salt. Magnesium salt with insufficient solubility cannot form good crystals at low temperatures, and the value of the recovered product is low. Summary of the invention

[0006] The purpose of the present invention is to overcome certain defects of the above-mentioned prior art and to provide a device and process for recovering magnesium salt tablets from industrial wastewater containing magnesium salts.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] One of the technical solutions of the present application provides a device for recovering magnesium salt tablets from industrial wastewater containing magnesium salts, the device comprising the following structures: a filter tank, a heat exchanger, an evaporator, a condenser, a heat preservation buffer tank, and a flake machine;

[0009] The heat exchanger has a first heat exchange channel and a second heat exchange channel, the evaporator has an inlet, an evaporation gas outlet and an evaporation concentrate outlet, and the filter tank, condenser, heat preservation buffer tank and flaker all include outlets and inlets;

[0010] The outlet of the filter tank is connected to the inlet of the evaporator through the first heat exchange channel of the heat exchanger; the evaporated gas outlet of the evaporator is connected to the inlet of the condenser, and the evaporated concentrated liquid outlet of the evaporator is connected to the insulation buffer tank; the outlet of the condenser is connected to the second heat exchange channel of the heat exchanger, or directly drained; the outlet of the insulation buffer tank is connected to the flaking machine; the structures are connected by pipelines.

[0011] Furthermore, the filter tank is connected to the water inlet, and the magnesium salt-containing wastewater will first be filtered and separated after entering the filter tank to remove some large particle impurities.

[0012] Furthermore, the heat exchanger is a steam heating heat exchanger, selected from any one of a plate heat exchanger, a shell and tube heat exchanger, an immersion heat exchanger, and a double shell heat exchanger.

[0013] Furthermore, the material of the steam heating heat exchanger is polyphenylene sulfide (PPS).

[0014] Furthermore, the evaporator is a columnar tower-shaped spray evaporator.

[0015] Furthermore, the evaporator is provided with an air blowing device for spraying the incoming liquid onto the inner wall of the evaporator to accelerate the evaporation speed.

[0016] Furthermore, the evaporator has a diameter of 0.8-4m, a height of 8-12m, and the filler is a spherical round filler or a corrugated filler.

[0017] Furthermore, the material of the evaporator is modified polypropylene (ppH), wherein the material of the filler is polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF).

[0018] Furthermore, the condenser is a columnar tower condenser, selected from any one of a water-cooled condenser, an air-cooled condenser, an evaporative condenser, and a spray condenser.

[0019] Furthermore, the condenser has a diameter of 0.8-4m, a height of 8-12m, and the filler is a spherical round filler or a corrugated filler.

[0020] More preferably, the condenser is made of glass fiber reinforced polypropylene (FRPP), wherein the filler is made of polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF).

[0021] Furthermore, the inlet of the second heat exchange channel of the heat exchanger is not only connected to the outlet of the condenser, but also connected to a steam heating tank. In application, the heat of the water produced and reused in the condenser is often insufficient to support the heating of the incoming water, so steam heating is required to make the raw water (the upper solution after the filter tank treatment) reach the required temperature.

[0022] Furthermore, a centrifugal pump is provided on the connecting pipeline between the structures for conveying liquid.

[0023] The second technical solution of the present invention provides a process for recovering magnesium salt tablets from industrial wastewater containing magnesium salt, comprising the following steps:

[0024] S1. The industrial magnesium salt wastewater to be treated is pumped into the filter tank, the magnesium salt wastewater is filtered and precipitated, and the upper solution is taken;

[0025] S2. The upper layer solution obtained in step S1 is preheated in a heat exchanger and then passed into an evaporator for heating and evaporation to obtain an evaporation concentrate and an evaporated gas;

[0026] S3. The evaporated gas obtained in step S2 is passed into a condenser for collection, and the evaporated concentrate obtained in step S2 is passed into an insulation buffer tank for collection;

[0027] S4. The evaporated concentrated liquid collected in step S3 is stored in a heat-insulated manner, and then transported to a flake forming machine in sections in a heat-insulated manner, and cooled and flaked into magnesium salt tablets.

[0028] Furthermore, in step S1, the flow rate of the industrial magnesium salt-containing wastewater to be treated is 50 to 4500 L / h, the magnesium salt contained is magnesium chloride, and the concentration of the magnesium chloride is 8 to 12%.

[0029] Furthermore, in step S2, the preheating is performed in a steam heating heat exchanger, and the preheating heat source is selected from raw steam, secondary steam or water at a temperature of 95°C. The raw steam is generated by a steam supplementary heat tank, the secondary steam comes from steam used by the factory production line, the temperature is not enough for the production line, and it can be used as the evaporator heat source. The water at a temperature of 95°C comes from the recycled water produced by the condenser.

[0030] Furthermore, in step S2, the temperature of the upper solution after preheating is 85-95°C.

[0031] Furthermore, in step S2, the heating evaporation process is blast evaporation, which is used to separate salt and water; the blast evaporation temperature is 90°C, and the blast volume is 1.5 to 2.8 times the flow rate of the magnesium salt-containing wastewater, in units of m 3 / h.

[0032] The concentrated crystallization is in a positive pressure blast evaporation state, which avoids the problem that in the traditional boiling evaporation process, as the temperature rises, the solubility of magnesium chloride increases, thereby causing the boiling point of the magnesium chloride solution to increase. The traditional boiling evaporation needs to provide a higher temperature heat source to meet the boiling state, which leads to the increase in the quality requirements of the heat source, the increase in heat consumption and the resulting problem of unstable system operation.

[0033] Furthermore, in step S3, the final condensation temperature is 35-45°C. After cooling by the condensation tower and waste heat recovery, the temperature reaches the acceptable water inlet temperature for the wastewater biochemical treatment process of general production enterprises. The condenser serves as a heat source recovery structure, and the water produced after condensation can be reused to heat the inlet water in step S2, thereby reducing energy consumption. In the entire process, the temperature of the water in the condenser does not drop at the beginning, and the temperature is relatively high, which has the utilization value of waste heat recovery. During the recovery process, the temperature of this part of the water will gradually decrease. When it drops to a level that has no recovery value, the produced water is no longer provided for heat exchange and is discharged as wastewater.

[0034] Furthermore, in step S3, the magnesium salt-containing wastewater to be treated is concentrated by 1.5-5.8 times after heating and evaporation, that is, the volume of the concentrated wastewater is reduced by 1.5-5.8 times compared with the volume of the original water. The evaporated concentrated liquid obtained in step S3 is kept warm in step S4, and then transported to a flake machine for freezing and flake cutting to finally obtain magnesium salt tablets; the magnesium salt tablets are magnesium chloride hexahydrate crystals.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention adopts a normal pressure evaporation method, which does not need to meet the restriction condition that the solution must reach the boiling point for rapid evaporation in conventional boiling evaporation, thereby avoiding the difficulty that the boiling point of the solution increases as the solubility increases with the increase of temperature.

[0037] (2) The equipment used in the present invention is made of high temperature resistant and corrosion resistant plastic material, which effectively solves the problem of rapid corrosion and short service life of metal materials.

[0038] (3) During the heating and evaporation process of the present invention, a circulating pump is used to continuously spray the filtrate and ventilate it, thereby increasing the contact area between the two, ensuring sufficient heat exchange and reducing heat loss.

[0039] (4) The present invention recovers the heat of the primary condensed water, thereby effectively reducing the heat consumption by 20%-50%, thereby saving the cost of magnesium salt recovery.

[0040] (5) The tablets finally obtained by the present invention are magnesium chloride hexahydrate tablets without the generation of other by-products. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Process flow chart for recovering magnesium salt tablets from industrial wastewater containing magnesium salts;

[0042] The symbols in the figure indicate:

[0043] 1 is a filter tank, 2 is a heat exchanger, 3 is an evaporator, 4 is a condenser, 5 is a heat preservation buffer tank, and 6 is a flake machine. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below in conjunction with specific embodiments. It should be noted that the following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, several variations and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0045] All raw materials of the present invention have no particular restrictions on their sources, and can be purchased on the market or prepared according to conventional methods known to those skilled in the art. In the following embodiments or examples, if there is no special description of the equipment, it indicates that they are all conventional equipment used in the art to achieve the corresponding functions.

[0046] Example 1

[0047] The equipment has a processing capacity of 50L / h and a temperature of 30°C, and contains wastewater with a concentration of 12% magnesium chloride and a small amount of low-boiling-point organic matter.

[0048] The process of treating wastewater includes the following steps:

[0049] S1. filtering and precipitating the above industrial wastewater containing magnesium salt to obtain an upper solution;

[0050] S2. Control the evaporation air volume to 75-100m 3 / h, the filtrate is heated to 95°C through an evaporative heating heat exchanger, the heat sources are steam, hot water at 95°C and heat source recycled from the condenser; the heated filtrate enters the evaporator, and the temperature in the evaporator is controlled to be 90°C. The filtrate is concentrated by about 2.9 times ((47%-12%) / 12%) in volume in the evaporator to reach a solid solution with a content of about 47%, namely the evaporative concentrated solution.

[0051] S3. Condensing the evaporated gas, the final temperature of the circulation system after condensation is about 35°C (the initial condensation temperature in the condenser is 60-70 degrees, and after heat recovery, the temperature in the circulation system reaches about 35 degrees). About 3% to 5% of the tail gas pipeline overflows, and the collected condensed water enters the biochemical pool for treatment and then directly discharged; the concentrated liquid enters the insulation buffer tank for stirring, and then is continuously transported to the freezing flake machine through the insulation pipeline to finally obtain magnesium chloride tablets.

[0052] The total steam consumption in the process is 0.4-0.45 tons of steam / ton of wastewater, and 255 kg of magnesium salt is finally recovered / ton of wastewater.

[0053] Example 2

[0054] The equipment has a processing capacity of 1400L / h, a temperature of 30°C, and the solution contains 8% magnesium chloride and very little organic matter.

[0055] The process of treating wastewater includes the following steps:

[0056] (1) filtering the above industrial magnesium salt-containing wastewater in sequence to obtain a filtrate;

[0057] (2) Control the evaporation air volume to 2600-3900m 3 / h, the filtrate is heated to 95℃ by the evaporative heating heat exchanger, the heat source is steam at 135℃ and the heat source recycled from the condenser; the heated filtrate enters the evaporator, the temperature in the evaporator is controlled at 90℃, the filtrate is concentrated by about 5.87 times in the evaporator, evaporated until crystals are precipitated, the solution density is about 1.85g / cm 3 .

[0058] (3) The evaporated gas is condensed, and the final temperature of the circulation system after condensation is about 35°C (the initial condensation temperature in the condenser is 60-70 degrees, and after heat recovery, the temperature in the circulation system reaches about 35 degrees), and the condensed water enters the Fenton processor for treatment; the concentrated liquid is stored in an insulation buffer tank, and is continuously transported to a freezing flake machine through a heat-tracing insulation pipeline to finally obtain magnesium chloride hexahydrate tablets.

[0059] The total steam consumption in the process is 0.35-0.45 tons of steam / ton of water, and the final concentration can reach 5.87 times, and 170 kg of magnesium salt is finally recovered per ton of wastewater.

[0060] Example 3

[0061] The equipment has a processing capacity of 4500L / h and a temperature of 30°C, containing a 10% magnesium chloride solution and a very small amount of low-boiling organic matter.

[0062] The process of treating wastewater includes the following steps:

[0063] (1) performing flotation precipitation on the industrial magnesium salt-containing wastewater to obtain a relatively clear upper liquid;

[0064] (2) Control the evaporation air volume to 9000-12000m 3 / h, the filtrate is heated to 95°C through an evaporative heating heat exchanger, the heat source is 180°C steam and the heat source recycled from the condenser; the heated filtrate enters the evaporator, and the temperature in the evaporator is controlled to be 95°C. The filtrate can be concentrated by about 4.5 times in the evaporator to reach a 45% magnesium chloride solid solution, which is the evaporative concentrate.

[0065] (3) The evaporated gas is condensed, and the final temperature of the circulation system after condensation is about 35°C (the initial condensation temperature in the condenser is 60-70 degrees, and after heat recovery, the temperature in the circulation system reaches about 35 degrees). The condensed water is collected and used as a pickling cleaning agent for the surface of the equipment in the factory; the concentrated liquid is stored in an insulation buffer tank and continuously transported to a freezing flake machine through a pipeline to obtain magnesium chloride hexahydrate tablets. The final magnesium salt recovery efficiency is about 220kg / ton of wastewater.

[0066] The total steam consumption of the process is 0.5-0.6 tons of steam per ton of water, and the final concentration can reach 4.5 times. The final magnesium salt recovery efficiency is about 220kg per ton of wastewater.

[0067] In summary, the present invention provides a process for recovering magnesium salt tablets from industrial magnesium salt-containing wastewater, and its working principle is: after filtering the wastewater containing magnesium salt to be treated, the filtrate is pumped into an evaporation system. The evaporation system includes an evaporator and a condenser. While spraying the filtrate through the evaporator, the evaporator uses the blast air to convect with it, thereby increasing the specific surface area and accelerating the evaporation rate. The heat of the condensed water of the condenser is recovered by a recovery heat exchanger and used for heating the filtrate, thereby effectively reducing energy consumption by 20%-50%. Through the use of an anti-corrosion evaporator, magnesium salts can be separated from solvents and recovered separately. The entire evaporation process is evaporation at normal pressure, which solves the problem that the solubility of magnesium salts increases with the increase of temperature, thereby increasing the boiling point, increasing the requirement for heat sources, and increasing energy consumption, and the resulting instability of the entire evaporation system in the traditional boiling evaporation process.

[0068] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A device for recovering magnesium salt tablets from industrial wastewater containing magnesium salts, characterized in that: The device comprises the following structures: a filter tank (1), a heat exchanger (2), an evaporator (3), a condenser (4), a heat-insulating buffer tank (5), and a flaker (6); The heat exchanger (2) has a first heat exchange channel and a second heat exchange channel, the evaporator (3) has an inlet, an evaporation gas outlet and an evaporation concentrate outlet, and the filter tank (1), the condenser (4), the heat preservation buffer tank (5) and the flaker (6) all include an outlet and an inlet; The filter pool (1) is connected to the water inlet; the outlet of the filter pool (1) is connected to the inlet of the evaporator (3) through the first heat exchange channel of the heat exchanger (2); the evaporation gas outlet of the evaporator (3) is connected to the inlet of the condenser (4), and the evaporation concentrated liquid outlet of the evaporator (3) is connected to the insulation buffer tank (5); the outlet of the condenser (4) is connected to the second heat exchange channel of the heat exchanger (2), or directly drained; the outlet of the insulation buffer tank (5) is connected to the flaking machine (6); the structures are connected by pipelines; in addition to being connected to the outlet of the condenser (4), the inlet of the second heat exchange channel of the heat exchanger is also connected to a steam heat supplement tank.

2. The device for recovering magnesium salt tablets from industrial wastewater containing magnesium salt according to claim 1, characterized in that: The heat exchanger (2) is a steam heating heat exchanger, selected from any one of a plate heat exchanger, a shell and tube heat exchanger, an immersion heat exchanger, and a double shell heat exchanger; the material of the steam heating heat exchanger is polyphenylene sulfide.

3. The device for recovering magnesium salt tablets from industrial magnesium salt-containing wastewater according to claim 1, characterized in that: The evaporator (3) is a columnar tower-shaped spray evaporator; an air blowing device is arranged inside the evaporator (3) for spraying the incoming liquid onto the inner wall of the evaporator; the diameter of the evaporator (3) is 0.8-4m, the height is 8-12m, and the filler is a spherical round filler or a corrugated filler; the material of the evaporator (3) is modified polypropylene, and the material of the filler in the evaporator (3) is polytetrafluoroethylene or polyvinylidene fluoride.

4. The device for recovering magnesium salt tablets from industrial magnesium salt-containing wastewater according to claim 1, characterized in that: The condenser (4) is a columnar tower condenser, selected from any one of a water-cooled condenser, an air-cooled condenser, an evaporative condenser, and a spray condenser; the diameter of the condenser (4) is 0.8-4m, the height is 8-12m, and the filler is a spherical round filler or a corrugated filler; the material of the condenser (4) is glass fiber reinforced polypropylene, and the material of the filler in the condenser (4) is polytetrafluoroethylene or polyvinylidene fluoride.

5. A process for recovering magnesium salt tablets from industrial wastewater containing magnesium salts, characterized in that: The device according to any one of claims 1 to 4 comprises the following steps: S1. The industrial magnesium salt-containing wastewater to be treated is pumped into the filter tank (1), the magnesium salt-containing wastewater is filtered and precipitated, and the upper solution is taken; S2. The upper layer solution obtained in step S1 is preheated in a heat exchanger (2), and then introduced into an evaporator (3) for heating and evaporation to obtain an evaporation concentrate and an evaporated gas; S3. The evaporated gas obtained in step S2 is passed into a condenser (4) for collection, and the evaporated concentrated liquid obtained in step S2 is passed into an insulation buffer tank (5) for collection; S4. The evaporated concentrated liquid collected in step S3 is stored in a heat-insulated manner, and then transported to a flake forming machine (6) in sections in a heat-insulated manner, and cooled and flaked into magnesium salt tablets.

6. The process for recovering magnesium salt tablets from industrial wastewater containing magnesium salt according to claim 5, characterized in that: In step S1, the flow rate of the industrial magnesium salt-containing wastewater to be treated is 50-4500 L / h, the magnesium salt contained is magnesium chloride, and the concentration of the magnesium chloride is 8-12%.

7. The process for recovering magnesium salt tablets from industrial wastewater containing magnesium salt according to claim 5, characterized in that: The preheating is carried out in a steam-heated heat exchanger (2). The preheating heat source is selected from raw steam, secondary steam or water at a temperature of 95°C; The raw steam is generated by a steam heating tank, the secondary steam is steam above 120 degrees, and the water at a temperature of 95 degrees C comes from the recycled water produced by the condenser (4); The temperature of the upper layer solution after the preheating is 85-95°C.

8. The process for recovering magnesium salt tablets from industrial magnesium salt-containing wastewater according to claim 5, characterized in that: The heating evaporation process is blast evaporation; the blast evaporation temperature is 90°C, and the blast volume is 1.5 to 2.8 times the flow rate of the magnesium salt-containing wastewater, and the unit is m 3 / h.

9. The process for recovering magnesium salt tablets from industrial magnesium salt-containing wastewater according to claim 5, characterized in that: In step S3, the final condensation temperature is 35-45°C.

10. The process for recovering magnesium salt tablets from industrial wastewater containing magnesium salt according to claim 5, characterized in that: In step S3, the volume of the concentrated wastewater after heating and evaporation is reduced by 1.5-5.8 times compared with the volume of the magnesium salt-containing wastewater to be treated; and in step S4, the magnesium salt tablets finally obtained are magnesium chloride hexahydrate crystals.

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