A system and method for comprehensive utilization of semi-carbon wastewater based on membrane separation

Abstract

The present invention relates to a comprehensive utilization system of blue carbon wastewater based on membrane separation, comprising: an ammonia evaporation system, an ultrafiltration membrane filtration system, an evaporator A, an evaporator B, a primary RO system and a secondary RO system. The beneficial effects of the present invention are as follows: by adopting a method combining ammonia evaporation, ultrafiltration, two-stage reverse osmosis and evaporation concentration, there is no need to perform long-term sedimentation to remove tar, fly ash and other pretreatment operations on blue carbon wastewater, thereby simplifying the pretreatment technology of blue carbon wastewater, eliminating the biochemical treatment process, and recovering ammonia water, phenol oil concentrate and membrane separation water from the wastewater; compared with the disclosed deamination-extraction-biochemical technology, the present invention does not need to add sulfuric acid to adjust the pH, nor does it need an extraction solvent, thereby greatly reducing investment and operating costs, and will not produce the secondary pollution problem of sulfate; compared with the disclosed deamination-evaporation-membrane separation technology, the present invention greatly reduces the amount of wastewater treated by evaporation, greatly reduces steam consumption, and reduces operating costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and in particular relates to a system and method for comprehensive utilization of semi-coke wastewater based on membrane separation, which is used to treat wastewater generated in the production process of coal chemical enterprises. Background Art

[0002] Lignite, also known as semi-coke, is a low-volatile solid carbonaceous product obtained by dry distillation and pyrolysis of low-grade coal (e.g., long flame coal, non-caking coal, and slightly caking coal) at medium-low temperatures (600-800°C). Lignite wastewater refers to industrial wastewater generated during the medium-low temperature dry distillation process, as well as during gas purification and steam quenching of lignite. This wastewater has a complex composition and contains numerous persistent and highly toxic pollutants (see Table 1 below). These include high concentrations of ammonia nitrogen, benzene derivatives, significant amounts of phenols, polycyclic aromatic hydrocarbons, oils, and nitrogen-oxygen heterocyclic compounds, as well as inorganic pollutants such as heavy metals. This represents a typical example of highly polluting and toxic industrial wastewater. Driven by enormous market demand, the lignite industry has experienced rapid growth, but environmentalists have not kept pace with the research on lignite wastewater. Consequently, wastewater pollution issues faced by most established lignite production enterprises have severely hampered their sustainable development.

[0003] Table 1 Water quality analysis of semi-coke wastewater

[0004] project COD mg / L Ammonia nitrogen mg / L Phenol mg / L Oil mg / L Suspended matter mg / L content ＞30000 ＞4000 ＞5000 ＞2000 ＞3000

[0005] Currently, incineration or biochemical treatment is the most common method for treating semi-coke wastewater. Due to the high energy consumption of incineration, companies cannot afford the high investment and operating costs. Furthermore, during incineration, harmful substances in the wastewater are released into the atmosphere as vapor, causing secondary pollution. Biochemical treatment, by contrast, offers the advantages of lower investment and operating costs. Conventional biochemical treatment processes for semi-coke wastewater first remove oil and ammonia, then perform extensive dilution or extraction to remove phenols, or use advanced oxidation methods to reduce the wastewater's toxicity to microorganisms. The process then undergoes traditional anaerobic or aerobic biochemical treatment. To address the biodegradability of semi-coke wastewater, large amounts of domestic sewage, sugars, and urea must be added to regulate the wastewater, significantly increasing operating costs. Because the wastewater contains numerous toxic substances that inhibit microbial growth, biochemical treatment is difficult to meet standards. Furthermore, the process is lengthy, requires significant land use, and requires high investment (>2 million yuan per ton of wastewater). Furthermore, the high operating costs (>100 yuan per ton of wastewater) make it unaffordable for companies. Practice has proven that these wastewater treatment results are unsatisfactory.

[0006] Studies have shown that the treatment of semi-coke wastewater can draw on the same treatment processes for coking wastewater with similar water quality. The process flow used includes oil removal, phenol-ammonia recovery, biochemical treatment, advanced treatment, desalination, and evaporation crystallization. However, the water quality of semi-coke wastewater is 10 times worse than that of coking wastewater, and its biodegradability is even worse. Furthermore, various treatment processes currently face serious challenges in their promotion and application, such as high initial investment costs, high operating expenses, harsh reaction conditions, extractant poisoning, fouling, or scaling, blockage in ammonia vaporization pipelines, and unstable operation. These challenges make it difficult to address the issues facing semi-coke wastewater treatment.

[0007] Chinese patent application CN104445815A discloses a process and apparatus for resource utilization of semi-coke production wastewater, comprising three steps: deep oil-water separation, efficient complex extraction dephenolization, and ammonia evaporation. This technology suffers from the multi-stage filtration process, resulting in a lengthy process and numerous unit operations. Complex extraction requires the introduction of hazardous chemicals for stripping. Furthermore, extraction dephenolization requires the addition of sulfuric acid to adjust the wastewater pH to approximately 3.0, while ammonia evaporation requires the addition of alkali to adjust the wastewater pH to above 10.5. The artificially added sulfuric acid and caustic soda neutralize the wastewater, forming an inorganic salt concentration of approximately 2% Na2SO4, which remains in the wastewater. Treatment of the semi-coke wastewater results in highly saline wastewater, making it difficult to recycle the reclaimed water. Further membrane separation equipment, such as nanofiltration and reverse osmosis, is employed to reuse the membrane separation water and recover the sodium sulfate solid waste through evaporation and crystallization. While this solution achieves approximately 70% reclaimed water reuse, it also increases investment and operating costs.

[0008] Chinese patent application CN101665309 discloses a process for treating coal gasification wastewater containing phenol and ammonia, including technologies such as steam stripping deamination and extractive dephenolization, using methyl isobutyl ketone (MIBK) as a dephenolization extractant. However, this process is not ideal for treating semi-coke wastewater with a high oil / phenol ratio, and the extractant loses a lot, resulting in high extraction and back-extraction costs. In particular, the extractant is easily contaminated by coal tar, and must be completely regenerated after a period of extraction operation. Secondly, like Chinese patent application CN104445815A, there are problems such as high acid and alkali consumption and high salt concentration in the effluent.

[0009] The document "Effect of Different Dephenolization Extractants on the Biodegradability of Wastewater after Stripping" (Huang Huihua et al., Guangzhou Chemical Industry, February 2014, 103-104) discloses the extraction effect of phenol-containing wastewater using one or a mixture of two of methyl isobutyl ketone, butyl acetate, and diisopropyl ether. It is believed that the use of a 1:1 mixed extractant of methyl isobutyl ketone and butyl acetate has a better extraction effect and a higher biodegradability of the wastewater after extraction. However, due to the relatively high oil and phenol content in semi-coke wastewater, the extraction effect is not ideal when using the mixed extractant in the above ratio.

[0010] In summary, the existing treatment process for semi-coke wastewater mainly adopts a combination of pretreatment oil removal, dephenolization, deamination and biochemical treatment. The existing treatment process for semi-coke wastewater has the following problems:

[0011] (1) There are many unit operation procedures and the process is long, which leads to large investment, large land occupation and high operating costs;

[0012] (2) The consumption of raw materials such as sulfuric acid and caustic soda is high, the operating cost is high, and the concentration of Na2SO4 inorganic salts in the wastewater is high. Because dephenolization usually requires operation at a pH value of around 3.0, sulfuric acid needs to be added to the wastewater, and deamination requires operation at a pH value above 10.5, so caustic soda needs to be added to the wastewater. The artificially added sulfuric acid and caustic soda eventually form Na2SO4 inorganic salts that remain in the wastewater;

[0013] (3) The efficiency of biochemical treatment is low, and the effluent after treatment is difficult to reuse or meet discharge standards. Extraction dephenolization is difficult to reduce the phenol content in the wastewater to below 500 mg / L. The residual phenol after entering the biochemical treatment system inhibits the activity of the residual sludge, making it difficult for the biochemical system to effectively degrade COD, and the biochemical effluent is difficult to reuse or meet discharge standards;

[0014] (4) After biochemical treatment, a large amount of residual sludge is produced, causing secondary pollution, and the cost of harmless disposal of the sludge is also very high. Summary of the Invention

[0015] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a system and method for comprehensive utilization of semi-coke wastewater based on membrane separation.

[0016] This membrane separation-based semi-coal wastewater comprehensive utilization system includes: an ammonia distillation system, an ultrafiltration membrane filtration system, an evaporator A, an evaporator B, a primary RO system, and a secondary RO system;

[0017] A steam inlet is provided at the bottom of the ammonia distillation system, and a semi-coke wastewater inlet is provided at the top of the ammonia distillation system. The steam pipe is connected to the steam inlet of the ammonia distillation system, and the semi-coke wastewater pipe is connected to the semi-coke wastewater inlet. The ammonia distillation system is also provided with a water outlet and an ammonia water outlet. The ammonia water outlet of the ammonia distillation system is connected to the water inlet of the boiler flue gas denitrification device through a pipe.

[0018] The water outlet of the ammonia distillation system is connected to the wastewater inlet of the ultrafiltration membrane filtration system through a pipeline. The ultrafiltration membrane filtration system is also provided with a permeate outlet and a concentrate outlet. The permeate outlet of the ultrafiltration membrane filtration system is connected to the water inlet of the primary RO system through a pipeline, and the concentrate outlet of the ultrafiltration membrane filtration system is connected to the water inlet of the evaporator A through a pipeline.

[0019] The concentrated liquid outlet of the primary RO system is connected to the concentrated liquid inlet of evaporator B through a pipeline; the permeate outlet of the primary RO system is connected to the permeate inlet of the secondary RO system through a pipeline; the concentrated liquid outlet of the secondary RO system is connected to the water inlet of the primary RO system through a pipeline; the produced water outlet of the secondary RO system is connected to the water inlet of the semi-coke quenching device through a pipeline;

[0020] The condensate outlet of evaporator B is connected to the water inlet of the primary RO system, and the concentrate outlet of evaporator B is connected to the water inlet of evaporator A through a pipeline; the condensate outlet of evaporator A is connected to the wastewater inlet on the ultrafiltration membrane filtration system through a pipeline; the phenol and oil concentrate outlet of evaporator A is connected to the fuel collection device.

[0021] Preferably, the ammonia distillation system is a plate distillation tower.

[0022] Preferably, a reboiler is further provided at the bottom of the plate distillation tower, and the reboiler is used to assist the steam partition in heating the wastewater at the bottom of the distillation tower.

[0023] Preferably, the evaporator A is a single-effect falling film scraper evaporator or a multi-effect forced external circulation evaporator.

[0024] Preferably, the evaporator A is a single-effect falling film scraper evaporator.

[0025] Preferably, the evaporator B is a single-effect falling film scraper evaporator, an MVR or a multi-effect forced external circulation evaporator.

[0026] Preferably, the evaporator B is a multi-effect forced external circulation evaporator.

[0027] The working method of this membrane separation-based blue carbon wastewater comprehensive utilization system includes the following steps:

[0028] The ammonia distillation system performs stripping distillation: semi-coal wastewater is added from the semi-coal wastewater inlet at the top of the ammonia distillation system. Under the action of gravity, the semi-coal wastewater flows from top to bottom inside the ammonia distillation system, and steam enters the bottom of the ammonia distillation system from the steam inlet and flows from bottom to top. The semi-coal wastewater and steam are in countercurrent contact inside the ammonia distillation system to transfer mass and heat, removing volatile nitrogen ammonia and low-boiling point components in the semi-coal wastewater. Ammonia nitrogen is condensed to obtain ammonia water;

[0029] The semi-coke wastewater after deammoniation in the ammonia distillation system enters the ultrafiltration membrane filtration system, which uses the ultrafiltration membrane to perform cross-flow filtration on the influent to obtain concentrated liquid A and permeate A.

[0030] The concentrated liquid A from the ultrafiltration membrane filtration system enters the evaporator A, which evaporates and concentrates its influent to obtain condensate A, phenol concentrate, and oil concentrate; the obtained condensate A is input into the ultrafiltration membrane filtration system, and is combined with the semi-coke wastewater after deammoniation in the ammonia distillation system, and together they serve as the influent of the ultrafiltration membrane filtration system;

[0031] The permeate A output from the ultrafiltration membrane filtration system enters the primary RO system, and the primary RO membrane of the primary RO system performs cross-flow filtration on its influent to obtain concentrate B and permeate B;

[0032] Concentrated liquid B from the primary RO system enters evaporator B, which evaporates and concentrates its influent to produce condensate B and concentrated liquid D. Condensate B is fed into the primary RO system and combined with permeate A output from the ultrafiltration membrane filtration system to serve as the influent to the primary RO system. Concentrated liquid D is fed into evaporator A and combined with concentrated liquid A from the ultrafiltration membrane filtration system to serve as the influent to evaporator A.

[0033] The permeate B from the primary RO system enters the secondary RO system, and the secondary RO membrane in the secondary RO system performs cross-flow filtration on its influent to obtain concentrated liquid C and produced water; the concentrated liquid C is input into the primary RO system and combined with the permeate A output from the ultrafiltration membrane filtration system and the condensate B output from the evaporator B, and together they serve as the influent of the primary RO system.

[0034] As a preference:

[0035] All the following concentrations are mass percentage concentrations and pressures are gauge pressures;

[0036] The steam pressure entering the ammonia distillation system is 0.05-0.4 MPa. The ammonia distillation method inside the ammonia distillation system is negative pressure distillation or atmospheric distillation. The internal pressure of the ammonia distillation system corresponding to negative pressure distillation is -0.05-0.09 MPa, and the internal pressure of the ammonia distillation system corresponding to atmospheric distillation is 0-0.02 MPa. The concentration of ammonia water flowing out of the ammonia water outlet of the ammonia distillation system is 10-20%, and the ammonia nitrogen content in the wastewater flowing out of the water outlet of the ammonia distillation system is less than 50 mg / L;

[0037] The molecular weight cutoff of the ultrafiltration membrane in the ultrafiltration membrane filtration system is 100,000 to 300,000 Daltons (Dal), and the filtration pressure of the ultrafiltration membrane is 0.2 to 0.5 MPa; the concentrated liquid A obtained by the ultrafiltration membrane filtration system accounts for 3 to 10% of the influent volume of the semi-coke wastewater after deammoniation by the ammonia distillation system; the permeate A obtained by the ultrafiltration membrane filtration system accounts for 90 to 97% of the influent volume of the semi-coke wastewater after deammoniation by the ammonia distillation system;

[0038] Evaporator A uses a single-effect falling film scraper evaporator or a multi-effect forced external circulation evaporator to perform evaporation and concentration at 40-90°C. The solid concentration of the obtained phenol concentrate and oil concentrate is 50-70%; the phenol concentrate and oil concentrate are high-boiling-point phenols and tar;

[0039] The cross-flow filtration pressure of the first-stage RO system is 0.3-0.5 MPa; the molecular weight cut-off of the first-stage RO membrane is 100,000-300,000 Daltons (Dal); the concentrate B output from the first-stage RO system accounts for 40-50% of the inlet water volume, and the permeate B accounts for 50-60% of the inlet water volume;

[0040] Evaporator B uses a single-effect falling film scraper evaporator or a multi-effect forced external circulation evaporator to perform evaporation at 40-100°C; the concentrated liquid D obtained by evaporation and concentration in evaporator B has a solid concentration of 20-45%;

[0041] The cross-flow filtration pressure of the secondary RO system is 2-5 MPa; the molecular weight cut-off of the secondary RO membrane is 50-100 Daltons (Dal); the concentrate C accounts for 10-20% of the inlet volume, and the produced water accounts for 80-90% of the inlet volume.

[0042] Preferably, the COD of the water produced by the secondary RO system is less than 60 mg / L, the volatile phenols in the water are less than 10 mg / L, and the petroleum is less than 1 mg / L, and it is used for the quenching process of lignite production.

[0043] The beneficial effects of the present invention are:

[0044] The present invention does not require long-term sedimentation of semi-coke wastewater to remove tar, fly ash and other pretreatment operations, simplifies the pretreatment technology of semi-coke wastewater, eliminates the biochemical treatment process, and recovers ammonia water, phenol oil concentrate and membrane separation water (high-purity water) from the wastewater. The water recovery rate is ≥95%, the COD of the water is ≤60 mg / L, the volatile phenol is ≤10 mg / L, and the petroleum is ≤1 mg / L. At the same time, pretreatment equipment is saved and the project cost is reduced. The recovered ammonia water can be used as a raw material for boiler flue gas denitrification, the phenol oil concentrate can be directly used as fuel, and the membrane separation water can be reused in the semi-coke quenching process, thereby realizing the comprehensive utilization of products, not only solving the wastewater pollution problem, but also having good economic benefits.

[0045] The present invention adopts a combined method of ammonia evaporation, ultrafiltration, two-stage reverse osmosis and evaporation concentration. Compared with the known deamination-extraction-biochemical technology, the present invention does not require the addition of sulfuric acid to adjust the pH, nor does it require an extraction solvent, thereby significantly reducing investment and operating costs, and does not cause secondary sulfate pollution problems. Compared with the known deamination-evaporation-membrane separation technology, the present invention significantly reduces the amount of wastewater treated by evaporation, thereby significantly reducing steam consumption and reducing operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a flow chart of the comprehensive utilization method of lignite wastewater based on membrane separation. DETAILED DESCRIPTION

[0047] The present invention will be further described below with reference to the following examples. The following examples are provided only to facilitate understanding of the present invention. It should be noted that, without departing from the principles of the present invention, it is possible for a person skilled in the art to make various modifications to the present invention, and such improvements and modifications fall within the scope of the claims of the present invention.

[0048] Example 1

[0049] Example 1 of the present application provides a Figure 1 The membrane separation-based semi-coal wastewater comprehensive utilization system shown includes: a plate distillation tower, an ultrafiltration membrane filtration system, a single-effect falling film scraper evaporator, a multi-effect forced external circulation evaporator, a primary RO system and a secondary RO system;

[0050] A steam inlet is provided at the bottom of the plate distillation tower, and a semi-coal wastewater inlet is provided at the top of the plate distillation tower. The steam pipe is connected to the steam inlet of the plate distillation tower, and the semi-coal wastewater pipe is connected to the semi-coal wastewater inlet. The plate distillation tower is also provided with a water outlet and an ammonia outlet. The ammonia outlet of the plate distillation tower is connected to the water inlet of the boiler flue gas denitrification device through a pipe. A reboiler is also provided at the bottom of the plate distillation tower, and the reboiler is used to assist the steam partition in heating the wastewater at the bottom of the distillation tower.

[0051] The water outlet of the plate distillation tower is connected to the wastewater inlet of the ultrafiltration membrane filtration system through a pipeline. The ultrafiltration membrane filtration system is also provided with a permeate outlet and a concentrate outlet. The permeate outlet of the ultrafiltration membrane filtration system is connected to the water inlet of the primary RO system through a pipeline. The concentrate outlet of the ultrafiltration membrane filtration system is connected to the water inlet of the single-effect falling film scraper evaporator through a pipeline.

[0052] The concentrated liquid outlet of the primary RO system is connected to the concentrated liquid inlet of the multi-effect forced external circulation evaporator through a pipeline; the permeate outlet of the primary RO system is connected to the permeate inlet of the secondary RO system through a pipeline; the concentrated liquid outlet of the secondary RO system is connected to the water inlet of the primary RO system through a pipeline; the produced water outlet of the secondary RO system is connected to the water inlet of the semi-coke quenching device through a pipeline;

[0053] The condensate outlet of the multi-effect forced external circulation evaporator is connected to the water inlet of the primary RO system, and the concentrated liquid outlet of the multi-effect forced external circulation evaporator is connected to the water inlet of the single-effect falling film scraper evaporator through a pipeline; the condensate outlet of the single-effect falling film scraper evaporator is connected to the wastewater inlet on the ultrafiltration membrane filtration system through a pipeline; the phenol and oil concentrate outlet of the single-effect falling film scraper evaporator is connected to the fuel collection device.

[0054] Example 2

[0055] Example 2 of the present application provides a working method of a blue carbon wastewater comprehensive utilization system based on membrane separation:

[0056] The semi-coke wastewater enters the ammonia distillation system, and the plate distillation tower is directly heated by saturated water vapor at a pressure of 0.05Mpa. The top pressure of the plate distillation tower is -0.09Mpa, which removes ammonia nitrogen from the wastewater. The ammonia nitrogen content in the ammonia distillation effluent is 28mg / L, and ammonia water with a concentration of 10% (w / w) is obtained at the same time.

[0057] The deammoniation-treated semi-coke wastewater and the evaporated condensate A from evaporator A are combined and enter the ultrafiltration membrane filtration system. The ultrafiltration membrane has a molecular weight cutoff of 100,000 Daltons and an ultrafiltration pressure of 0.5 MPa to obtain ultrafiltration concentrate A and permeate A. The concentrate A accounts for 10% of the inlet volume, and the rest is permeate A.

[0058] The permeate A obtained by ultrafiltration, the concentrated liquid C from the secondary RO and the evaporated condensate B from the evaporator B are combined and enter the primary RO system. The molecular weight cut-off of the primary RO membrane is 200,000 Daltons (Dal), and the filtration pressure is 0.3 MPa. The concentrated liquid B and the permeate B are obtained. The concentrated liquid B accounts for 40% of the volume of the primary RO inlet water.

[0059] The permeate B of the primary RO enters the secondary RO system. The molecular weight cutoff of the secondary RO membrane is 50 Daltons (Dal), and the filtration pressure is 5 MPa. The concentrate C and product water are obtained. The concentrate B accounts for 10% of the secondary RO inlet volume.

[0060] The concentrated liquid A from ultrafiltration and the concentrated liquid D from evaporator B are combined and fed into evaporator A. Evaporator A uses a single-effect falling film scraper evaporator with an evaporation temperature of 50-55°C. Evaporation and concentration are performed to obtain evaporation condensate A and phenol and oil concentrates. The solid concentration of the phenol and oil concentrates is 50%.

[0061] The concentrated liquid B from the first-stage RO enters the evaporator B, where it is evaporated and concentrated to obtain the evaporated condensate B and the concentrated liquid D. The evaporator B adopts an MVR evaporator with an evaporation temperature of 40-60°C. The solid concentration of the concentrated liquid D is 20%.

[0062] The COD of the secondary RO produced water obtained in this embodiment is 60 mg / L, the volatile phenol is 6.2 mg / L, and the petroleum is less than 0.3 mg / L, and can be reused in the quenching process of semi-coke production.

[0063] Example 3

[0064] Example 3 of the present application provides another working method of a comprehensive utilization system of semi-coal wastewater based on membrane separation:

[0065] The semi-coke wastewater from production enters the ammonia distillation system and is indirectly heated by a reboiler. The steam pressure is 0.2 MPa, the pressure of the ammonia distillation tower is -0.08 MPa, and the ammonia nitrogen content in the ammonia distillation effluent is 10 mg / L. At the same time, ammonia water with a concentration of 15% (w / w) is recovered.

[0066] The deammoniation-treated semi-coke wastewater and the evaporation condensate A from evaporator A are combined and fed into the ultrafiltration membrane filtration system. The ultrafiltration membrane has a molecular weight cutoff of 200,000 Daltons (Dal) and a filtration pressure of 0.4 MPa. Ultrafiltration concentrate A and permeate A are obtained. Concentrate A accounts for 3% of the influent volume.

[0067] The permeate A obtained by ultrafiltration, the concentrate C from the secondary RO, and the evaporated condensate B from the evaporator B are combined and fed into the primary RO system. The molecular weight cut-off of the primary RO membrane is 100,000 Daltons (Dal), and the filtration pressure is 0.4 MPa. The concentrate B and permeate B are obtained. The concentrate B accounts for 45% of the primary RO inlet volume.

[0068] The permeate B of the primary RO enters the secondary RO system. The molecular weight cutoff of the secondary RO membrane is 80 Daltons (Dal), and the filtration pressure is 4 MPa. The concentrate C and product water are obtained. The concentrate B accounts for 12% of the secondary RO inlet volume.

[0069] The concentrated liquid A from the ultrafiltration and the concentrated liquid D from the evaporator B are combined and enter the multi-effect forced external circulation evaporator of evaporator A. The evaporation temperature is 60-90°C. The evaporation condensate A and phenol and oil concentrates are obtained by evaporation and concentration. The solid concentration of the phenol and oil concentrates is 55%.

[0070] The concentrated liquid B from the first-stage RO enters the evaporator B, where it is evaporated and concentrated to obtain the evaporated condensate B and the concentrated liquid D. The evaporator B adopts a multi-effect forced external circulation evaporator with an evaporation temperature of 8 to 100°C. The solid concentration of the concentrated liquid D is 30%.

[0071] The secondary RO produced water obtained in Example 3 has a COD of 55 mg / L, volatile phenols of 10 mg / L, and petroleum less than 0.37 mg / L, and can be reused in the quenching process of semi-coke production.

[0072] Example 4

[0073] Example 4 of the present application provides another working method of a comprehensive utilization system of semi-coal wastewater based on membrane separation:

[0074] The semi-coke wastewater from production enters the ammonia distillation system and is directly heated by steam with a steam pressure of 0.4 MPa and an ammonia distillation tower pressure of 0.02 MPa. The ammonia nitrogen content in the ammonia distillation effluent is 50 mg / L, and ammonia water with a concentration of 20% (w / w) is recovered at the same time.

[0075] The deammoniation-treated semi-coke wastewater and the evaporated condensate A from evaporator A are combined and fed into the ultrafiltration membrane filtration system. The ultrafiltration membrane has a molecular weight cutoff of 300,000 Daltons (Dal) and a filtration pressure of 0.5 MPa. Ultrafiltration concentrate A and permeate A are obtained. Concentrate A accounts for 5% of the influent volume.

[0076] The permeate A obtained by ultrafiltration, the concentrate C from the secondary RO, and the evaporated condensate B from the evaporator B are combined and fed into the primary RO system. The molecular weight cut-off of the primary RO is 300,000 Daltons (Dal), and the filtration pressure is 0.5 MPa. The concentrate B and permeate B are obtained. The concentrate B accounts for 50% of the inlet water volume.

[0077] The permeate B of the primary RO enters the secondary RO system. The molecular weight cutoff of the secondary RO membrane is 100 Daltons (Dal), and the filtration pressure is 2 MPa. The concentrate C and product water are obtained. The concentrate B accounts for 20% of the inlet water volume.

[0078] The concentrated liquid A from the ultrafiltration and the concentrated liquid D from the evaporator B are combined and fed into the evaporator A. The evaporator A uses a single-effect falling film scraper evaporator with an evaporation temperature of 40-60°C. The evaporation and concentration are performed to obtain the evaporation condensate A and phenol and oil concentrates. The solids concentration of the phenol and oil concentrates is 70%.

[0079] The concentrated liquid B from the first-stage RO enters the evaporator B, where it is evaporated and concentrated to obtain the evaporated condensate B and the concentrated liquid D. The evaporator B adopts MVR, the evaporation temperature is 50-80℃, and the solid concentration of the concentrated liquid D is 45%.

[0080] The secondary RO produced water obtained in this embodiment has a COD of 32 mg / L, a volatile phenol of 4.5 mg / L, and a petroleum content of 1 mg / L, and can be reused in the quenching process of semi-coke production.

Claims

1. A comprehensive utilization system of semi-carbon wastewater based on membrane separation, characterized in that: include: Ammonia distillation system, ultrafiltration membrane filtration system, evaporator A, evaporator B, primary RO system and secondary RO system; A steam inlet is provided at the bottom of the ammonia distillation system, a semi-coal wastewater inlet is provided at the top of the ammonia distillation system, a steam pipe is connected to the steam inlet of the ammonia distillation system, and a semi-coal wastewater pipe is connected to the semi-coal wastewater inlet; a water outlet and an ammonia water outlet are also provided on the ammonia distillation system; The water outlet of the ammonia distillation system is connected to the wastewater inlet of the ultrafiltration membrane filtration system through a pipeline. The ultrafiltration membrane filtration system is also provided with a permeate outlet and a concentrate outlet. The permeate outlet of the ultrafiltration membrane filtration system is connected to the water inlet of the primary RO system through a pipeline, and the concentrate outlet of the ultrafiltration membrane filtration system is connected to the water inlet of the evaporator A through a pipeline. The concentrated liquid outlet of the primary RO system is connected to the concentrated liquid inlet of evaporator B through a pipeline; the permeate outlet of the primary RO system is connected to the permeate inlet of the secondary RO system through a pipeline; The concentrate outlet of the secondary RO system is connected to the water inlet of the primary RO system through a pipe; The condensate outlet of evaporator B is connected to the water inlet of the primary RO system, and the concentrate outlet of evaporator B is connected to the water inlet of evaporator A through a pipeline; the condensate outlet of evaporator A is connected to the wastewater inlet of the ultrafiltration membrane filtration system through a pipeline.

2. The membrane separation-based semi-carbon wastewater comprehensive utilization system according to claim 1 is characterized in that: The ammonia distillation system is a plate distillation tower.

3. The membrane separation-based semi-carbon wastewater comprehensive utilization system according to claim 2 is characterized in that: There is also a reboiler at the bottom of the plate distillation tower.

4. The membrane separation-based semi-carbon wastewater comprehensive utilization system according to claim 1 is characterized in that: Evaporator A is a single-effect falling film scraper evaporator or a multi-effect forced external circulation evaporator.

5. The membrane separation-based semi-carbon wastewater comprehensive utilization system according to claim 4 is characterized in that: Evaporator A is a single-effect falling film scraper evaporator.

6. The membrane separation-based semi-carbon wastewater comprehensive utilization system according to claim 1 is characterized in that: Evaporator B is a single-effect falling film scraper evaporator, MVR or multi-effect forced external circulation evaporator.

7. The membrane separation-based semi-carbon wastewater comprehensive utilization system according to claim 6 is characterized by: Evaporator B is a multi-effect forced external circulation evaporator.

8. A method for operating the membrane separation-based semi-coal wastewater comprehensive utilization system as claimed in claim 1, characterized in that: The following steps are involved: The ammonia distillation system performs stripping distillation: semi-coal wastewater is added from the semi-coal wastewater inlet at the top of the ammonia distillation system. Under the action of gravity, the semi-coal wastewater flows from top to bottom inside the ammonia distillation system, and steam enters the bottom of the ammonia distillation system from the steam inlet and flows from bottom to top. The semi-coal wastewater and steam are in countercurrent contact inside the ammonia distillation system to transfer mass and heat, thereby removing nitrogen and ammonia from the semi-coal wastewater. Ammonia nitrogen is condensed to obtain ammonia water; The semi-coke wastewater after deammoniation in the ammonia distillation system enters the ultrafiltration membrane filtration system, which uses the ultrafiltration membrane to perform cross-flow filtration on the influent to obtain concentrated liquid A and permeate A. The concentrated liquid A from the ultrafiltration membrane filtration system enters the evaporator A, which evaporates and concentrates its influent to obtain condensate A, phenol concentrate, and oil concentrate; the obtained condensate A is input into the ultrafiltration membrane filtration system, and is combined with the semi-coke wastewater after deammoniation in the ammonia distillation system, and together they serve as the influent of the ultrafiltration membrane filtration system; The permeate A output from the ultrafiltration membrane filtration system enters the primary RO system, and the primary RO membrane of the primary RO system performs cross-flow filtration on its influent to obtain concentrate B and permeate B; Concentrated liquid B from the primary RO system enters evaporator B, which evaporates and concentrates its influent to produce condensate B and concentrated liquid D. Condensate B is fed into the primary RO system and combined with permeate A output from the ultrafiltration membrane filtration system to serve as the influent to the primary RO system. Concentrated liquid D is fed into evaporator A and combined with concentrated liquid A from the ultrafiltration membrane filtration system to serve as the influent to evaporator A. The permeate B from the primary RO system enters the secondary RO system, and the secondary RO membrane in the secondary RO system performs cross-flow filtration on its influent to obtain concentrated liquid C and produced water; the concentrated liquid C is input into the primary RO system and combined with the permeate A output from the ultrafiltration membrane filtration system and the condensate B output from the evaporator B, and together they serve as the influent of the primary RO system.

9. The working method of the membrane separation-based semi-coal wastewater comprehensive utilization system according to claim 8, characterized in that: All the following concentrations are mass percentage concentrations and pressures are gauge pressures; The steam pressure entering the ammonia distillation system is 0.05-0.4 MPa. The ammonia distillation method inside the ammonia distillation system is negative pressure distillation or atmospheric distillation. The internal pressure of the ammonia distillation system corresponding to negative pressure distillation is -0.05-0.09 MPa, and the internal pressure of the ammonia distillation system corresponding to atmospheric distillation is 0-0.02 MPa. The concentration of ammonia water flowing out of the ammonia water outlet of the ammonia distillation system is 10-20%, and the ammonia nitrogen content in the wastewater flowing out of the water outlet of the ammonia distillation system is less than 50 mg / L; The molecular weight cutoff of the ultrafiltration membrane in the ultrafiltration membrane filtration system is 100,000 to 300,000 Daltons, and the filtration pressure of the ultrafiltration membrane is 0.2 to 0.5 MPa; the concentrated liquid A obtained by the ultrafiltration membrane filtration system accounts for 3 to 10% of the influent volume of the semi-coke wastewater after deammoniation by the ammonia distillation system; the permeate A obtained by the ultrafiltration membrane filtration system accounts for 90 to 97% of the influent volume of the semi-coke wastewater after deammoniation by the ammonia distillation system; Evaporator A uses a single-effect falling film scraper evaporator or a multi-effect forced external circulation evaporator to evaporate and concentrate at 40-90°C. The solid concentration of the obtained phenol concentrate and oil concentrate is 50-70%. The cross-flow filtration pressure of the first-stage RO system is 0.3-0.5 MPa; the molecular weight cut-off of the first-stage RO membrane is 100,000-300,000 Daltons; the concentrate B output by the first-stage RO system accounts for 40-50% of the inlet water volume, and the permeate B accounts for 50-60% of the inlet water volume; Evaporator B uses a single-effect falling film scraper evaporator or a multi-effect forced external circulation evaporator to perform evaporation at 40-100°C; the concentrated liquid D obtained by evaporation and concentration in evaporator B has a solid concentration of 20-45%; The cross-flow filtration pressure of the secondary RO system is 2-5 MPa; the molecular weight cut-off of the secondary RO membrane is 50-100 Daltons; the concentrate C accounts for 10-20% of the inlet volume, and the produced water accounts for 80-90% of the inlet volume.

10. The operating method of the membrane separation-based semi-coal wastewater comprehensive utilization system according to claim 9, characterized in that: The COD of the water produced by the secondary RO system is less than 60 mg / L, the volatile phenol in the water is less than 10 mg / L, and the petroleum is less than 1 mg / L.

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