A closed heat pump energy-saving rectification system for wastewater desolventization

Abstract

The application discloses a wastewater desolventizing closed heat pump energy-saving rectification system and relates to the technical field of wastewater treatment. In view of the high energy consumption of the existing wastewater desolventizing treatment process, the heat pump system is adopted to exchange the low-grade heat of a large amount of solvent-free wastewater at the bottom of the tower to the solvent-containing wastewater to be treated twice, so that the temperature of the high-temperature solvent-free wastewater at the bottom is reduced to about 40 DEG C close to normal temperature, the heat of the high-temperature solvent-free wastewater at the bottom is effectively recovered, and the energy consumption in the wastewater desolventizing process is reduced by about 27%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, in particular to a closed heat pump energy-saving distillation system for wastewater desolventization. BACKGROUND

[0002] In pharmaceutical production (such as antibiotics, organic synthesis), some solvents are often used as extractants, and a certain amount of organic solvent is dissolved in the aqueous phase after organic solvent extraction. For example, in the process of extracting antibiotics, butyl acetate is used to extract the target drug components from the fermentation broth. The aqueous phase after extraction will contain trace amounts of butyl acetate (usually 0.1%~1%), forming high-COD, non-biodegradable wastewater. If directly discharged, it will have toxic effects on aquatic ecosystems, so wastewater desolventization treatment is required.

[0003] The wastewater desolventization treatment can be directly treated by distillation or stripping process, that is, the wastewater containing low concentration of solvent is continuously introduced into the middle part of the distillation column, the low-pressure steam is indirectly heated by the reboiler or directly introduced into the bottom of the distillation column for direct heating, the solvent in the raw material is vaporized by heating, and by controlling the "reflux ratio at the top of the column", the mixed solvent can be continuously collected at the top of the column, and the wastewater without solvent can be continuously collected at the bottom of the column. After cooling, the part of wastewater is transferred to the sewage treatment system.

[0004] The existing distillation process or stripping process can completely meet the requirements of wastewater treatment from the index of wastewater treatment, but the energy consumption is high and the energy-saving effect is poor. SUMMARY

[0005] The technical problem to be solved by the present application is how to reduce the energy consumption in the process of wastewater desolventization treatment.

[0006] The specific technical solution of the present application to solve the above technical problem is:

[0007] A closed heat pump energy-saving distillation system for wastewater desolventization, comprising a distillation column, a top condenser and a heat pump system, the heat pump system comprising a heat pump compressor, a heat pump condenser, a heat pump evaporator and an expansion device;

[0008] High-temperature solvent-containing wastewater is introduced into the top of the distillation column, where it is heated and the solvent is vaporized. The vaporized solvent is then collected and condensed in the top condenser. High-temperature solvent-free wastewater is collected from the bottom of the column and undergoes preliminary heat exchange with the room-temperature solvent-containing wastewater in the bottom heat exchanger. After the first heat exchange, the bottom wastewater enters the tube side of the heat pump evaporator, where it releases heat to heat the liquid refrigerant into a gaseous state, reducing the temperature of the bottom wastewater to about 40°C before discharge. After the first heat exchange and temperature increase, the solvent-containing wastewater enters the tube side of the heat pump condenser, where it absorbs heat from the high-temperature, high-pressure refrigerant pressurized by the heat pump compressor, liquefying the high-temperature, high-pressure refrigerant. Simultaneously, it undergoes a second temperature increase to become high-temperature solvent-containing wastewater, which is then introduced into the top of the distillation column, and the cycle repeats.

[0009] Furthermore, the heat pump system also includes a subcooler, through which the liquid refrigerant obtained by cooling and condensing in the heat pump condenser is further cooled before entering the expansion device.

[0010] Furthermore, it also includes a condensate separator, in which the oil-water mixed solvent undergoes static stratification, with the upper oil phase serving as the solvent and being recovered, while the lower aqueous phase is refluxed to the distillation column.

[0011] Furthermore, the refrigerant is R245fa.

[0012] Furthermore, it also includes a liquid storage tank, which is connected after the expansion valve, for storing low-temperature, low-pressure, gas-liquid mixed refrigerant.

[0013] Furthermore, the subcooler is provided with cooling capacity via circulating cooling water.

[0014] Furthermore, the distillation column is heated by low-pressure steam.

[0015] This invention introduces closed-loop heat pump technology based on existing processes. It extracts heat from high-temperature wastewater using refrigerant, and then recompresses and heats the extracted refrigerant before reusing it to heat the feed (containing solvent wastewater) of the distillation column. This increases the feed temperature and reduces the energy consumption of the distillation and solvent removal process. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the wastewater desolvation closed-loop heat pump energy-saving distillation system of the present invention;

[0017] The following is a list of component names represented by the reference numerals in the attached diagram:

[0018] 1. Distillation column; 2. Top condenser; 3. Condensate separator; 4. Bottom heat exchanger; 5. Heat pump evaporator; 6. Heat pump compressor; 7. Heat pump condenser; 8. Subcooler; 9. Expansion valve; 10. Storage tank. Detailed Implementation

[0019] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0020] like Figure 1 As shown, a closed-loop heat pump energy-saving distillation system for wastewater desolvation includes a distillation column 1, a column top condenser 2, a condensate stratification tank 3, a column bottom heat exchanger 4, a heat pump evaporator 5, a heat pump compressor 6, a heat pump condenser 7, a subcooler 8, an expansion valve 9, and a storage tank 10.

[0021] The wastewater containing butyl acetate solvent to be treated (hereinafter referred to as "solvent-containing wastewater") and the high-temperature solvent-free wastewater collected from the bottom of distillation column 1 (hereinafter referred to as "bottom wastewater") exchange heat in the bottom heat exchanger 4 to obtain the solvent-containing wastewater after one stage of heating and the bottom wastewater after one stage of heat exchange. The solvent-containing wastewater after one stage of heating enters the tube side of the heat pump condenser 7 for further heat exchange and temperature increase to obtain the solvent-containing wastewater after two stages of heating, namely the high-temperature solvent-containing wastewater. The high-temperature solvent-containing wastewater is introduced into distillation column 1 from the top of the column and falls from the top of the column under the action of gravity. Low-pressure steam is directly introduced into the bottom of distillation column 1 and moves upward to further heat the high-temperature solvent-containing wastewater. During the heating process, the butyl acetate solvent in the water is vaporized by heat and moves to the top of the column. After being condensed into liquid in the top condenser 2, it is allowed to stand and separate into layers in the condensate separation tank 3. The lower aqueous phase after separation is returned to distillation column 1 as reflux liquid to continue participating in distillation. The upper oil phase is mainly butyl acetate and can be collected and recovered.

[0022] The refrigerant selected is R245fa, a gas-liquid mixture at 0.57 MPa. R245fa exchanges heat with the bottom wastewater after the first heat exchange in the heat pump evaporator 5, further recovering the heat from the bottom wastewater. The low-pressure gas-liquid mixture of R245fa is heated and becomes gaseous R245fa, which then enters the heat pump compressor 6. The heat pump compressor 6 compresses the gaseous R245fa to obtain high-temperature, high-pressure gaseous R245fa, which exchanges heat with the solvent-containing wastewater after the first stage of heating in the heat pump condenser 7, resulting in solvent-containing wastewater after two stages of heating. The wastewater temperature rises to near the bubble point and enters the distillation column 1 for treatment. At the same time, the originally high-temperature and high-pressure gaseous R245fa is transformed into high-pressure and low-temperature liquid R245fa due to heat release. The high-pressure and low-temperature liquid R245fa is then further cooled by the subcooler 8 to obtain subcooled liquid R245fa. The subcooled liquid R245fa is depressurized by the expansion valve 9 and its volume expands rapidly, becoming a low-temperature and low-pressure gas-liquid mixture, which is then used as a cold source to enter the heat pump evaporator 5 for heat exchange. If there is a large amount of refrigerant, it is buffered in the storage tank 10, and this cycle continues.

[0023] In the above case, the solvent-containing wastewater at room temperature, after passing through the heat exchanger 4 at the bottom of the tower, can have its temperature raised from room temperature to 60℃~65℃. After passing through the heat pump condenser 7, the temperature further rises to 85℃, close to the bubble point temperature. The temperature of the wastewater at the bottom of the tower is 60℃~65℃ after one heat exchange, and after passing through the heat pump evaporator 5 again, the temperature can be reduced to about 40℃. Thus, most of the heat contained in the wastewater at the bottom of the tower is recovered and utilized. Due to the compression work of the heat pump compressor 6, the pressure of the refrigerant R245fa is increased from 0.57MPa to 2.1MPa, and its saturation temperature also increases from 38℃ to 90℃. When the refrigerant operates at 38°C, it acts as a cold source to extract heat from the wastewater at the bottom of the column and recover heat. After being compressed by the heat pump compressor 6, it can also act as a heat source to heat the solvent-containing wastewater, raising the temperature before entering the column and reducing the amount of steam consumed in the distillation column 1. Thus, it is equivalent to using refrigerant R245fa to transfer the heat from the wastewater at the bottom of the column to the solvent-containing wastewater, which greatly improves the heat utilization rate and reduces the desolventizing energy consumption.

[0024] Compared with traditional distillation technology, this invention makes full use of the sensible heat in the wastewater at the bottom of the column and uses a heat pump compressor 6 to convert electrical energy into heat energy, effectively reducing the amount of circulating water used and reducing steam consumption, thereby achieving the goal of reducing operating energy consumption.

[0025] Case Study: Assume a wastewater treatment capacity of 600m³ 3 The wastewater contains 1% butyl acetate per day. Using conventional distillation, the required steam consumption is 48 tons / day, and the required water consumption is 2400m³ / day. 3 It requires 360 kWh of electricity. Using the closed-loop heat pump distillation process of this invention, the required steam consumption is 18 tons / day and 1200 m³ of ambient temperature water. 3 It requires 7200 kWh of electricity. Based on steam costing 260 yuan / ton, industrial electricity costing 0.65 yuan / kWh, and room temperature water (electricity cost) converted to 0.12 yuan / m³, the total cost is approximately [amount missing]. 3 Calculations show that using conventional distillation technology, the annual wastewater treatment cost is approximately 4.3 million yuan, while using the closed-loop heat pump distillation technology of this invention, the annual wastewater treatment cost is approximately 3.15 million yuan, resulting in an energy saving rate of 27%.

[0026] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A closed-loop heat pump energy-saving distillation system for wastewater desolventizing, comprising a distillation column and a top condenser, characterized in that, It also includes a heat pump system, which comprises a heat pump compressor, a heat pump condenser, a heat pump evaporator, and an expansion device; High-temperature, solvent-containing wastewater is introduced into the top of the distillation column, where it is heated and the solvent is vaporized. The vaporized solvent is then collected and condensed in the top condenser. High-temperature, solvent-free wastewater is collected from the bottom of the column and undergoes a preliminary heat exchange with the room-temperature solvent-containing wastewater. This bottom wastewater, after the first heat exchange, enters the tube side of the heat pump evaporator, where it releases heat to heat the liquid refrigerant into a gaseous state, further reducing the temperature of the bottom wastewater before discharge. The refrigerant is R245fa. After the first heat exchange and temperature increase, the solvent-containing wastewater enters the tube side of the heat pump condenser, absorbing heat from the high-temperature, high-pressure refrigerant pressurized by the heat pump compressor, liquefying the refrigerant. Simultaneously, its temperature is raised a second time, resulting in high-temperature, solvent-containing wastewater, which is then introduced into the top of the distillation column, and the cycle repeats. The high-temperature, high-pressure gaseous R245fa is transformed into a high-pressure, low-temperature liquid R245fa due to heat release. The heat pump system also includes a subcooler. The liquid refrigerant obtained by cooling and condensing in the heat pump condenser is further cooled by the subcooler and then enters the expansion device. The high-pressure, low-temperature liquid R245fa is further cooled by the subcooler to obtain subcooled liquid phase R245fa. The subcooled liquid phase R245fa is depressurized by the expansion valve and its volume expands rapidly, becoming a low-temperature, low-pressure gas-liquid mixture, which is then used as a cold source to enter the heat pump evaporator for heat exchange.

2. The wastewater desolventizing closed-loop heat pump energy-saving distillation system according to claim 1, characterized in that, It also includes a condensate separator, in which the oil-water mixture undergoes static stratification. The upper oil phase, which is the solvent, is recovered, while the lower water phase is returned to the distillation column for further distillation.

3. The wastewater desolventizing closed-loop heat pump energy-saving distillation system according to claim 1 or 2, characterized in that, It also includes a liquid storage tank, which is connected to the expansion device and is used to store low-temperature, low-pressure, gas-liquid mixed refrigerant.

4. The wastewater desolvation closed-loop heat pump energy-saving distillation system according to claim 2 or 3, characterized in that, The subcooler is cooled by circulating cooling water.

5. The wastewater desolvation closed-loop heat pump energy-saving distillation system according to claim 2 or 3, characterized in that, The distillation column is heated by low-pressure steam.

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