Method and device for comprehensively utilizing process wastewater of polyvinyl alcohol manufacturing and recycling process

Abstract

The invention provides a comprehensive utilization method of process wastewater in a polyvinyl alcohol manufacturing and recycling process and a device for implementing the method, and the method comprises the following steps: arranging a pressurized rectifying tower and a second rectifying tower, feeding wastewater generated in a polyvinyl alcohol production process as a raw material into the pressurized rectifying tower after heat exchange with a feeding preheater, and feeding the wastewater into a second reboiler after heat exchange with the second reboiler; a kettle-out material serves as a heat source to be fed into a feeding preheater and then is fed into a flash tank to be subjected to flash evaporation after heat exchange is completed, the flash tank is subjected to grading treatment according to different components, a gas phase at the top of the pressurized rectifying tower serves as a heat source to be fed into a second reboiler, formed condensate is fed back to a pressurized reflux tank to be subjected to reflux and distillation, and a gas phase at the top of a second rectifying tower is divided into two paths to be fed out; one path is used for air blowing, and the other path is provided with a regulating valve, is sent into the condenser for condensation and then returns to the second reflux tank. The thermal coupling technology is introduced, heat in the wastewater is recycled, maximum utilization of energy is achieved, and meanwhile methanol and PVAC resin contained in the wastewater can be removed.

Description

Technical Field

[0001] The invention relates to the field of petrochemical industry, and more specifically to a method and device for comprehensively utilizing process wastewater from a polyvinyl alcohol manufacturing and recycling process. Background Art

[0002] Polyvinyl alcohol (PVA), as a polymer material with unique water activity, is widely used in the textile, construction, chemical, pharmaceutical and paper industries due to its excellent adhesion, gas barrier and wear resistance. However, a large amount of wastewater generated during its production process contains low concentrations of PVA and other organic pollutants. If it is discharged directly without treatment, it will cause serious pollution to the environment. Therefore, it is particularly important to develop efficient and economical polyvinyl alcohol wastewater treatment technology.

[0003] In the traditional polyvinyl alcohol (PVA) production process, wastewater treatment mainly relies on a combination of a series of physical, chemical and biological treatment methods in order to meet emission standards. These methods include but are not limited to precipitation, filtration, flocculation, biochemical treatment, etc. However, these traditional methods often have problems such as low treatment efficiency, high energy consumption, and secondary pollution, and it is difficult to meet increasingly stringent environmental protection requirements. Traditional wastewater treatment methods usually ignore the heat energy contained in the wastewater, resulting in a large amount of energy waste, and the removal effect of difficult-to-degrade substances such as polyvinyl acetate (PVAC) resin is limited, resulting in a high COD index after wastewater treatment. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a method for comprehensive utilization of process wastewater from the polyvinyl alcohol manufacturing and recycling process, and a device for comprehensive utilization of process wastewater from the polyvinyl alcohol manufacturing and recycling process for implementing the method. Thermal coupling technology is introduced to recycle the heat in the wastewater generated in the polyvinyl alcohol production process, thereby maximizing the utilization of energy and reducing energy consumption. At the same time, methanol and PVAC resin contained in the wastewater can be removed to reduce the COD index.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A method for comprehensive utilization of process wastewater from a polyvinyl alcohol manufacturing and recycling process, which is characterized by:

[0007] A pressurized distillation tower and a second distillation tower are provided, and a pressurized reboiler, a pressurized reflux tank, a feed preheater and a flash tank are configured for the pressurized distillation tower, and a second reboiler, a second reflux tank, a condenser and a regulating valve are configured for the second distillation tower;

[0008] The wastewater generated in the production process of polyvinyl alcohol is used as raw material. The raw material is sent to a pressurized distillation tower after heat exchange in a feed preheater. After heat exchange with a second reboiler, the material discharged from the kettle is sent to the feed preheater as a heat source for heating the raw material. After heat exchange, the material is sent to a flash tank for flash evaporation. The flash tank is graded according to different components. The gas phase at the top of the pressurized distillation tower is sent to the second reboiler as a heat source for heating the material at the bottom of the second distillation tower. The formed condensate is sent back to the pressurized reflux tank for reflux and distillation. The gas phase at the top of the second distillation tower is sent out in two ways, one way is sent out for air blowing, and the other way is provided with a regulating valve and sent to a condenser for condensation and then returned to the second reflux tank for reflux and distillation. The pressure at the top of the second distillation tower is adjusted by the regulating valve.

[0009] The flash tank sends out the top gas phase as flash steam, the middle liquid phase water is sent out through a pump, and the kettle discharges the heavy components to the incinerator.

[0010] The working principle of the present invention is that the raw materials are sent to a pressurized distillation tower after heat exchange in a feed preheater, and are separated and purified in the pressurized distillation tower, wherein the top gas phase is directly sent to the second reboiler of the second distillation tower as a heat source, and the condensate is sent to a pressurized reflux tank, a part of which returns to the pressurized distillation tower, and a part of which is sent to the tank area. After the pressurized distillation tower kettle exchanges heat with the feed, it enters a flash tank for flash evaporation, and the gas at the top of the flash tank is used as flash gas to be sent out for use, and the liquid phase water in the middle is sent out by a pump, and heat exchange or direct treatment is performed according to demand. The kettle discharges the heavy component PVAC resin and sends it to an incinerator for incineration; the gas phase at the top of the second distillation tower is divided into two streams, one of which is sent to other devices for gas blowing, and the other is condensed by a condenser and returned to the second reflux tank for reflux and distillation.

[0011] The present invention is also characterized in that:

[0012] The pressure of the pressurized distillation tower is 200-400 KPaG, and the top temperature is 90-110°C.

[0013] The tower pressure of the second distillation tower is 0-80KPaG, and the kettle temperature is 80-105°C.

[0014] The kettle liquid level of the second distillation tower is 50%-80%. The present invention can control the tower pressure and top temperature of the pressurized distillation tower by controlling the tower kettle liquid level height of the second distillation tower. If the kettle liquid level of the second distillation tower is too low, the kettle temperature of the second distillation tower and the top temperature and tower pressure of the pressurized distillation tower will gradually increase. At the same time, a gas-liquid phase equilibrium is formed between the second reboiler and the pressurized reflux tank of the pressurized distillation tower, which can greatly reduce steam consumption.

[0015] The top pressure of the second distillation tower is adjusted between ±10KPa by a regulating valve. The top pressure of the second distillation tower is controlled by a regulating valve from the top gas phase to the condenser, which is conducive to stabilizing the flow rate of the gas blowing streams of other devices, and the top pressure fluctuation range is small, which reduces the impact of the second distillation tower on other devices.

[0016] The condenser is an air cooler.

[0017] The heavy components discharged from the flash tank include PVAC resin.

[0018] The present invention also proposes a device for comprehensive utilization of process wastewater from the polyvinyl alcohol manufacturing and recycling process, which is used to implement the above-mentioned method for comprehensive utilization of process wastewater from the polyvinyl alcohol manufacturing and recycling process. The device includes a pressurized distillation tower and a second distillation tower;

[0019] The feed end of the pressurized distillation tower is connected to the feed preheater, and the lower part is connected to the pressurized reboiler. The bottom discharge end of the kettle is connected to the heating medium inlet of the feed preheater through a pipeline, and the heating medium outlet of the feed preheater is connected to the inlet of the flash tank through a pipeline. The top discharge end is connected to the heating medium inlet of the second reboiler through a pipeline, and the inlet of the pressurized reflux tank is connected to the heating medium outlet of the second reboiler through a pipeline. Among the two outlets, one is refluxed to the pressurized distillation tower through a pipeline, and the other outlet is used for distillation;

[0020] The second distillation tower is respectively connected with a second reboiler, a second reflux tank, a condenser and a regulating valve. The material is received through the feed end and the lower part is connected with the second reboiler. The top discharge end of the tower divides the top gas phase into two routes for delivery. One route is output through a pipeline for gas blowing, and the other route is connected to the inlet of the condenser through a pipeline with a regulating valve. The outlet of the condenser is connected to the inlet of the second reflux tank through a pipeline. Of the two outlets of the second reflux tank, one route is refluxed to the second distillation tower through a pipeline, and the other outlet is used for distillation.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] The refined methanol extracted from the top of the pressurized distillation tower can be used in other processes. The water in the bottom of the tower is sent to the flash tank for flash evaporation after heat exchange with the feed. The flash tank is used to perform graded treatment according to different components, which can reduce the COD value of the wastewater while efficiently utilizing the energy in it, greatly reducing the consumption of public works such as steam and circulating water, and achieving significant energy-saving effects;

[0023] Energy saving is achieved between the pressurized distillation tower and the second distillation tower through thermal coupling technology. The gas phase at the top of the pressurized distillation tower is all used to heat the second distillation tower. While saving energy, it can also purify the methanol contained in the wastewater and make full use of the wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1It is a process flow chart of the present invention.

[0025] In the figure, 1, raw material; 2, feed preheater; 3, pressurized distillation tower; 4, pressurized reflux tank; 5, pressurized reboiler; 6, second reboiler; 7, flash tank; 8, flash gas; 9, waste water; 10, heavy component; 11, product; 12, steam; 13, second distillation tower; 14, condenser; 15, second reflux tank; 16, other devices; 17, top distillation of second distillation tower; 18, feed of second distillation tower; 19, bottom outlet of second distillation tower. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Example 1

[0028] According to the test, the main components of the wastewater produced in the existing polyvinyl alcohol production process are 70% methanol, 30% water and some polyvinyl acetate (PVAC) resin brought by the previous device. 3 / h processing capacity as an example, the wastewater is heated to 112℃ by the feed preheater, and the pressure of the pressurized distillation tower is raised to 270KPaG. The heat released by the 100℃ gas phase at the top of the pressurized distillation tower is used to heat the bottom liquid phase of the second distillation tower through the second reboiler, thereby realizing the thermal coupling of the two towers. The top of the pressurized distillation tower can fully recover the methanol in the wastewater, and the purity can reach 99.9%. The bottom water of the pressurized distillation tower exchanges heat with the feed in the feed preheater, and after the temperature drops from 141℃ to 110℃, it is sent to the flash tank, and the polyvinyl acetate ( PVAC) resin, the top gas phase of the flash tank flashes out 850kg / h of steam, which is sent to the flash tank as supplementary gas. The wastewater on the side is sent to other distillation towers for heat exchange due to its high temperature. The COD of this wastewater can reach 50mg / L and is directly discharged. The feed of the second distillation tower comes from the crude methanol solution of other distillation towers. After heat exchange in the pressurized distillation tower, 99.5% methanol is obtained at the top. To ensure that the top methanol gas phase can be sent to other distillation towers, the top pressure is controlled to 65KPaG by a regulating valve, and the second distillation tower kettle temperature is controlled at 85℃. After implementing this solution, the total heat load is about 15000KW, which saves 25% of energy consumption compared with the traditional process.

[0029] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for comprehensive utilization of process wastewater from a polyvinyl alcohol manufacturing and recovery process, characterized in that: A pressurized distillation tower and a second distillation tower are provided, and a pressurized reboiler, a pressurized reflux tank, a feed preheater and a flash tank are configured for the pressurized distillation tower, and a second reboiler, a second reflux tank, a condenser and a regulating valve are configured for the second distillation tower; The wastewater generated in the production process of polyvinyl alcohol is used as raw material. The raw material is sent to a pressurized distillation tower after heat exchange in a feed preheater. After heat exchange with a second reboiler, the material discharged from the kettle is sent to the feed preheater as a heat source for heating the raw material. After heat exchange, the material is sent to a flash tank for flash evaporation. The flash tank is graded according to different components. The gas phase at the top of the pressurized distillation tower is sent to the second reboiler as a heat source for heating the material at the bottom of the second distillation tower. The formed condensate is sent back to the pressurized reflux tank for reflux and distillation. The gas phase at the top of the second distillation tower is sent out in two ways, one way is sent out for air blowing, and the other way is provided with a regulating valve and sent to a condenser for condensation and then returned to the second reflux tank for reflux and distillation. The pressure at the top of the second distillation tower is adjusted by the regulating valve. The flash tank sends out the top gas phase as flash steam, the middle liquid phase water is sent out through a pump, and the kettle discharges the heavy components to the incinerator.

2. The method for comprehensive utilization of process wastewater from the polyvinyl alcohol manufacturing and recovery process according to claim 1, characterized in that: The pressure of the pressurized distillation tower is 200-400 KPaG, and the top temperature is 90-110°C.

3. The method for comprehensive utilization of process wastewater from the polyvinyl alcohol manufacturing and recovery process according to claim 1, characterized in that: The tower pressure of the second distillation tower is 0-80KPaG, and the kettle temperature is 80-105°C.

4. The method for comprehensive utilization of process wastewater from the polyvinyl alcohol manufacturing and recovery process according to claim 1 or 3, characterized in that: The kettle liquid level of the second distillation tower is 50%-80%.

5. The method for comprehensive utilization of process wastewater from the polyvinyl alcohol manufacturing and recovery process according to claim 1 is characterized by: The top pressure of the second distillation tower is adjusted between ±10 KPa by a regulating valve.

6. The method for comprehensive utilization of process wastewater from the polyvinyl alcohol manufacturing and recovery process according to claim 1, characterized in that: The condenser is an air cooler.

7. The method for comprehensive utilization of process wastewater from the polyvinyl alcohol manufacturing and recovery process according to claim 1 is characterized by: The heavy components discharged from the flash tank include PVAC resin.

8. A device for comprehensive utilization of process wastewater from the recovery process of polyvinyl alcohol manufacturing, characterized by: Used to implement the method for comprehensive utilization of process wastewater from the polyvinyl alcohol manufacturing and recycling process according to any one of claims 1 to 7, the device comprises a pressurized distillation tower and a second distillation tower; The feed end of the pressurized distillation tower is connected to the feed preheater, and the lower part is connected to the pressurized reboiler. The bottom discharge end of the kettle is connected to the heating medium inlet of the feed preheater through a pipeline, and the heating medium outlet of the feed preheater is connected to the inlet of the flash tank through a pipeline. The top discharge end is connected to the heating medium inlet of the second reboiler through a pipeline, and the inlet of the pressurized reflux tank is connected to the heating medium outlet of the second reboiler through a pipeline. Among the two outlets, one is refluxed to the pressurized distillation tower through a pipeline, and the other outlet is used for distillation; The second distillation tower is respectively connected with a second reboiler, a second reflux tank, a condenser and a regulating valve. The material is received through the feed end and the lower part is connected with the second reboiler. The top discharge end of the tower divides the top gas phase into two routes for delivery. One route is output through a pipeline for gas blowing, and the other route is connected to the inlet of the condenser through a pipeline with a regulating valve. The outlet of the condenser is connected to the inlet of the second reflux tank through a pipeline. Of the two outlets of the second reflux tank, one route is refluxed to the second distillation tower through a pipeline, and the other outlet is used for distillation.

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