A system and method for pretreating high-chlorine-containing medium- and low-temperature coal tar

Abstract

The invention discloses a pretreatment system and method for high-chlorine-containing medium- and low-temperature coal tar, comprising a tar raw material tank, a raw material preheater, a desalting tank, a low-chlorine tar tank, and a desalted water cooler, an oil-water separation tank, an alkali liquid tank, an ammonia still, and a multiple-effect evaporator connected by pipelines. The high-chlorine-containing medium- and low-temperature coal tar is mixed with water and then enters the preheater for preheating and is transported to the desalting tank. After multi-stage desalination, the tar finally enters the low-chlorine tar tank, and the wastewater is cooled by the desalted water cooler and enters the oil-water separation tank; the tar in the oil-water separation tank is transported back to the tar raw material tank, and the wastewater and the alkali liquid from the alkali liquid tank are mixed and sequentially passed through the ammonia still and the multiple-effect evaporator; the ammonia water at the top of the ammonia still and the concentrated liquid at the bottom of the multiple-effect evaporator are recycled, and the fresh water at the top of the multiple-effect evaporator is returned to the desalting tank for recycling. The present invention can effectively reduce the chloride ion content in medium- and low-temperature coal tar, recycle and reuse desalted wastewater, and greatly reduce the cost of water treatment.

Description

Technical Field

[0001] The invention belongs to the field of coal chemical industry, and more specifically, relates to a high-chlorine-containing medium- and low-temperature coal tar pretreatment system and method. Background Art

[0002] Coal tar is a liquid product produced during coal gasification, coke production, semi-coke production, and low-rank coal processing and upgrading. Coal tar raw materials generally contain a lot of impurities such as water, coal powder, chlorides, sulfides, oxides, polyenes, and alkali metals. According to different production methods, the following four types of tar can be obtained: high-temperature coal tar, referred to as high-temperature tar (900℃-1000℃); medium-temperature vertical furnace coal tar, referred to as medium-temperature coal tar (700℃-900℃); low-temperature and medium-temperature generator coal tar, referred to as medium-low temperature coal tar (600℃-800℃); low-temperature pyrolysis coal tar, referred to as low-temperature tar (450℃-650℃).

[0003] Compared with high-temperature coal tar, medium-low temperature coal tar contains more aromatic compounds and less asphalt, making it more suitable for hydrogenation to produce fuel oil. However, medium-low temperature coal tar also contains a large amount of impurities such as moisture, ash, chlorides, etc. These impurities will have a very adverse effect on the subsequent deep processing of medium-low temperature coal tar, especially in the process of hydrogenation to prepare light fuel oil. Chlorides will not only cause catalyst poisoning and deactivation, but also seriously corrode the reaction equipment, and ammonium salt crystallization will cause equipment blockage. Therefore, before deep processing of medium-low temperature coal tar, it must be dechlorinated. At present, the commonly used dechlorination process for medium-low temperature coal tar is mainly the water washing method. According to the solubility of chloride in water is greater than that in coal tar, coal tar is mixed with water to dissolve the chloride in coal tar in water, and then the water and oil are separated to achieve the removal of chloride from coal tar. However, due to the different production processes of medium and low temperature coal tar and the different properties of raw coal by different manufacturers, the properties of medium and low temperature coal tar products vary greatly. The chloride ion content even ranges from tens of PPM to thousands of PPM. The excessively high chloride ion content makes coal tar very difficult to handle, and often requires extremely high water consumption, which also puts great pressure on corporate wastewater treatment.

[0004] The chlorine content in my country's coal tar is generally low. For this reason, most domestic coal tar processing companies use water washing and electrical desalination methods, which only require a small amount of water to remove the chloride ions in the coal tar for the next step of processing and utilization.

[0005] For example, the invention patent CN117535078A provides a multi-grade quality fractionation processing and utilization process for medium and low temperature coal tar, which greatly enhances and improves product performance, fully utilizes raw materials, avoids environmental pollution, and can realize industrial application.

[0006] Invention patent CN107603656A provides a method for dechlorinating medium and low temperature coal tar, which selects polyether surfactant as dechlorinating agent, combines static dechlorination, and electric desalination process to achieve a chlorine removal rate of 95%, and greatly reduces costs, simplifies procedures and reduces the size of equipment.

[0007] Invention patent CN108822882A mixes light oil with low-temperature coal tar to obtain mixed oil, and then mixes the mixed oil with desalted water and demulsifier for electric desalination and / or membrane desalination to achieve a better pretreatment effect. However, up to now, there has been no report on the method for removing chloride ions from high-chlorine coal tar. Summary of the invention

[0008] The purpose of the present invention is to overcome the deficiencies in the prior art and to propose a high-chlorine-containing medium- and low-temperature coal tar pretreatment system and method which has a simple production process, controllable product quality, and is more energy-saving and environmentally friendly.

[0009] The purpose of the present invention can be achieved through the following technical solutions.

[0010] The high-chlorine-content medium- and low-temperature coal tar pretreatment system of the present invention comprises a tar raw material tank, wherein the discharge port of the tar raw material tank is connected to the tar inlet of a desalting tank through a pipeline via a raw material preheater, the tar outlet of the desalting tank is connected to the low-chlorine tar tank through a pipeline, the desalting water outlet of the desalting tank is connected to the feed port of an oil-water separator through a pipeline via a desalting water cooler, the tar outlet of the oil-water separator is connected to the feed port of the tar raw material tank through a pipeline, the water outlet of the oil-water separator is connected to the feed port of an ammonia still through a pipeline, and the pipeline is also connected to the discharge port of an alkali liquid tank, the bottom outlet of the ammonia still is connected to the feed port of a multiple-effect evaporator through a pipeline, and the top outlet of the multiple-effect evaporator is connected to the tar inlet of the desalting tank through a pipeline.

[0011] Furthermore, the desalting tanks are arranged in 2 to 5 numbers, which are connected in series in sequence through the tar inlet and the tar outlet. The coal tar from the tar outlet of the upper desalting tank is transported to the tar inlet of the adjacent lower desalting tank through a pipeline. The desalted water from the desalting water outlet of the lower desalting tank is transported to the tar inlet of the adjacent upper desalting tank through a pipeline. The coal tar from the tar outlet of the last desalting tank is transported to the low-chlorine tar tank through a pipeline. The desalted water from the desalting water outlet of the first desalting tank is transported to the feed inlet of the desalting water cooler through a pipeline. The desalted water from the desalting water outlet of the second desalting tank is transported to the raw material preheater through a pipeline, and is mixed with the high-chlorine and medium-temperature coal tar in the tar raw material tank for preheating before entering the first desalting tank. The fresh water from the multi-effect evaporator is transported to the last desalting tank through a pipeline for recycling.

[0012] Furthermore, the raw material preheater and the desalted water cooler both adopt a shell and tube structure.

[0013] Furthermore, the tar raw material tank, desalting tank, oil-water separator, ammonia distillation tower and multiple-effect evaporator are all provided with vents.

[0014] The purpose of the present invention can also be achieved through the following technical solutions.

[0015] The high chlorine-containing medium-low temperature coal tar pretreatment method of the present invention based on the high chlorine-containing medium-low temperature coal tar pretreatment system comprises the following steps:

[0016] Step S1, high chlorine-containing medium-low temperature coal tar is mixed with water and then enters a raw material preheater for preheating, and then enters a desalting tank for water washing to achieve oil-water separation;

[0017] Step S2, transporting the high-chlorine-containing wastewater from the outlet of the desalting tank to a desalting water cooler for cooling, and the tar finally coming out of the desalting tank enters a low-chlorine tar tank;

[0018] Step S3, the high-chlorine wastewater cooled by the desalted water cooler is passed through an oil-water separation tank for oil-water separation;

[0019] Step S4, the high-chlorine-containing wastewater from the oil-water separation tank is mixed with the alkali solution in the alkali solution tank, and the wastewater mixed with the alkali solution is evaporated through an ammonia distillation tower, the ammonia water obtained at the top of the tower is recovered, and the water after deammoniation at the bottom of the tower enters a multiple-effect evaporator;

[0020] Step S5, the concentrated liquid at the bottom of the multiple-effect evaporator is recovered and processed, and the water obtained at the top of the tower is returned to the desalination tank for recycling.

[0021] Furthermore, the preheating temperature in the raw material preheater in step S1 is 90-140°C.

[0022] Furthermore, the desalination tanks in step S1 are set to 2 to 5, which are connected in series, the temperature in each desalination tank is 90 to 140° C., the pressure in each desalination tank is 0.3 to 0.5 MPa, and the residence time in each desalination tank is 1 to 8 hours.

[0023] Furthermore, the cooling temperature of the desalted water cooler in step S2 is 50-70°C.

[0024] Furthermore, in step S4, the high-chlorine-containing wastewater from the oil-water separation tank is mixed with the alkali solution in the alkali solution tank, so that the phenolic compounds in the water react to form sodium phenolate, and the ammonium chloride in the water reacts to form sodium chloride.

[0025] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0026] The present invention can effectively reduce the chloride ion content in the medium and low temperature coal tar by desalting the medium and low temperature coal tar with high chlorine content for multiple times. The desalted wastewater is reused after oil-water separation, ammonia distillation, evaporation and other treatments, which greatly reduces the water treatment cost. The production process is simple, and the product quality can be controlled and adjusted by controlling the temperature and pressure of the distillation, and the energy utilization is intensive. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the high-chlorine-content medium-low temperature coal tar pretreatment system (secondary desalination) of the present invention.

[0028] Figure 2 It is a schematic diagram of the high-chlorine-content medium-low temperature coal tar pretreatment system (three-stage desalination) of the present invention.

[0029] Figure 3 It is a schematic diagram of the high-chlorine-content medium-low temperature coal tar pretreatment system (five-stage desalination) of the present invention.

[0030] Figure numerals: 1-tar raw material tank, 2-raw material preheater, 3-desalting tank, 4-low-chlorine tar tank, 5-desalting water cooler, 6-oil-water separator, 7-ammonia distillation tower, 8-multiple-effect evaporator, 9-alkali liquid tank. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with the accompanying drawings and implementation cases. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0032] like Figures 1 to 3 As shown, the high-chlorine-containing medium-low temperature coal tar pretreatment system of the present invention mainly includes a tar raw material tank 1, a raw material preheater 2, a desalting tank 3, a low-chlorine tar tank 4, a desalted water cooler 5, an oil-water separator 6, an ammonia distillation tower 7, a multi-effect evaporator 8, and an alkali liquid tank 9 connected by pipelines. Preferably, the multi-effect evaporator 8 can be a triple-effect evaporator.

[0033] The discharge port of the tar raw material tank 1 is connected to the tar inlet of the desalting tank 3 through the raw material preheater 2 through a pipeline, the tar outlet of the desalting tank 3 is connected to the low-chlorine tar tank 4 through a pipeline, the desalted water outlet of the desalting tank 3 is connected to the feed port of the oil-water separator 6 through a pipeline through the desalted water cooler 5, the tar outlet of the oil-water separator 6 is connected to the feed port of the tar raw material tank 1 through a pipeline, the water outlet of the oil-water separator 6 is connected to the feed port of the ammonia evaporation tower 7 through a pipeline, and the pipeline is also connected to the discharge port of the alkali liquid tank 9, the bottom outlet of the ammonia evaporation tower 7 is connected to the feed port of the multi-effect evaporator 8 through a pipeline, and the top outlet of the multi-effect evaporator 8 is connected to the tar inlet of the desalting tank 3 through a pipeline. The oil-water separator 6 is used to recycle wastewater.

[0034] In the above system, preferably, the desalting tanks 3 are set to 2 to 5, which are connected in series through the tar inlet and the tar outlet. The tar outlet of the upper desalting tank is connected to the tar inlet of the adjacent lower desalting tank through a pipeline, and the desalted water outlet of the lower desalting tank is connected to the tar inlet of the adjacent upper desalting tank through a pipeline. The tar outlet of the last desalting tank is connected to the low-chlorine tar tank 4 through a pipeline, the desalted water outlet of the first desalting tank is connected to the feed port of the desalted water cooler 5 through a pipeline, the desalted water outlet of the second desalting tank is connected to the feed port of the raw material preheater 2 through a pipeline, and the top outlet of the multi-effect evaporator 8 is connected to the tar inlet of the last desalting tank through a pipeline. Except for the first desalting tank, the tar inlets of all other desalting tanks can be provided with static mixers for fully mixing coal tar and desalted water.

[0035] The high-chlorine-content medium-low-temperature tar comes out of the tar raw material tank 1 and is mixed with water through a pipeline and transported to the first-stage desalting tank 3, and oil-water separation is performed through the series of desalting tanks. During the oil-water separation process, the desalted water output by the next-stage desalting tank will be transported to the previous-stage desalting tank; the desalted water output from the desalting water outlet of the second-stage desalting tank is transported to the raw material preheater 2 through a pipeline, mixed with the high-chlorine-content medium-low-temperature coal tar in the tar raw material tank 1 and preheated before entering the first-stage desalting tank; the coal tar output from the tar outlet of the last-stage desalting tank 3 is transported to the low-chlorine tar storage tank 4 through a pipeline; the desalted water discharged from the first-stage desalting tank 3 enters the desalted water cooler 5 for cooling and then transported to the feed port of the oil-water separator 6. The tar from the oil-water separator 6 is returned to the tar raw material tank 1 through a pipeline; the waste water from the oil-water separator 6 is mixed with the alkali solution in the alkali solution tank 9 through a pipeline and then transported to the ammonia still 7; the ammonia water from the top of the ammonia still 7 is recovered and processed, and the water from the bottom of the tower is transported to the multiple-effect evaporator 8 through a pipeline; the concentrated liquid from the bottom of the multiple-effect evaporator 8 is recovered and processed, and the fresh water from the top of the tower is transported to the last-stage desalination tank 3 through a pipeline for recycling.

[0036] Example 1: Figure 1 As shown, two desalting tanks are provided, the tar from the tar outlet of the first-stage desalting tank and the water from the top outlet of the multi-effect evaporator 8 are transported to the tar inlet of the second-stage desalting tank, the desalted water discharged from the desalted water outlet of the first-stage desalting tank is transported to the desalted water cooler 5 for cooling, the tar from the tar outlet of the second-stage desalting tank is transported to the low-chlorine tar tank 4 through a pipeline, the desalted water from the desalted water outlet of the second-stage desalting tank is transported to the raw material preheater 2 through a pipeline, and is mixed with the high-chlorine and medium-temperature coal tar from the tar raw material tank 1 for preheating before entering the first-stage desalting tank.

[0037] Example 2: Figure 2As shown, three desalting tanks are provided, the desalting water discharged from the desalting water outlet of the first-stage desalting tank is transported to the desalting water cooler 5 for cooling, the tar from the tar outlet of the first-stage desalting tank and the desalting water from the third-stage desalting tank are transported to the tar inlet of the second-stage desalting tank, the desalting water from the desalting water outlet of the second-stage desalting tank is transported to the raw material preheater 2 through a pipeline, mixed with the high-chlorine-containing medium- and low-temperature coal tar from the tar raw material tank 1 for preheating, and then enters the first-stage desalting tank, the tar from the tar outlet of the second-stage desalting tank and the water from the top outlet of the multi-effect evaporator 8 are transported to the tar inlet of the third-stage desalting tank, and the tar from the tar outlet of the third-stage desalting tank is transported to the low-chlorine tar tank 4 through a pipeline.

[0038] Example 3: Figure 3 As shown, five desalting tanks are provided, the desalting water discharged from the desalting water outlet of the first-stage desalting tank is transported to the desalting water cooler 5 for cooling, the tar from the tar outlet of the first-stage desalting tank and the desalting water from the third-stage desalting tank are transported to the tar inlet of the second-stage desalting tank, the desalting water from the desalting water outlet of the second-stage desalting tank is transported to the raw material preheater 2 through a pipeline, mixed with the high-chlorine-containing medium- and low-temperature coal tar from the tar raw material tank 1 for preheating, and then enters the first-stage desalting tank, the tar from the tar outlet of the second-stage desalting tank and the desalting water from the fourth-stage desalting tank are transported to the tar inlet of the third-stage desalting tank, the tar from the tar outlet of the third-stage desalting tank and the desalting water from the fifth-stage desalting tank are transported to the tar outlet of the fourth-stage desalting tank, the tar from the tar outlet of the fourth-stage desalting tank and the water from the top outlet of the multi-effect evaporator 8 are transported to the tar inlet of the fifth-stage desalting tank, and the tar from the tar outlet of the fifth-stage desalting tank is transported to the low-chlorine tar tank 4 through a pipeline.

[0039] In the above system, preferably, the raw material preheater 2 and the desalted water cooler 5 can both adopt a shell and tube structure.

[0040] In the above system, preferably, the tar raw material tank 1, the desalting tank 3, the oil-water separator 6, the ammonia distillation tower 7, and the multiple-effect evaporator 8 are all provided with vents for easy maintenance.

[0041] Based on the above-mentioned high-chlorine-content medium-low temperature coal tar pretreatment system, the present invention also proposes a high-chlorine-content medium-low temperature coal tar pretreatment method, comprising the following steps:

[0042] Step S1, high chlorine-containing medium and low temperature coal tar is mixed with desalted water and then enters the raw material preheater 2 for preheating, and then enters the desalting tank 3 for water washing to achieve oil-water separation. The preheating temperature can be determined according to the viscosity of the tar and the requirements for water washing; preferably, the preheating temperature is 90-140°C.

[0043] Preferably, the desalting tank 3 is set to 2 to 5, which are connected in series. The last stage desalting tank removes the chloride ions in the medium and low temperature coal tar, and the water consumption should be 25% to 35%. The temperature in each desalting tank 3 is 90 to 140 ° C, the pressure in each desalting tank 3 is 0.3 to 0.5 MPa, and the residence time in each desalting tank 3 is 1 to 8 hours. The operating temperature, pressure and residence time of each desalting tank 3 can be the same or different, and can be adjusted according to the requirements of different medium and low temperature coal tar. The desalted water output by the next stage desalting tank will be transported to the previous stage desalting tank, and the desalted water from the desalting water outlet of the second stage desalting tank is transported to the raw material preheater 2 through a pipeline, and mixed with the high chlorine-containing medium and low temperature coal tar in the tar raw material tank 1 for preheating before entering the first stage desalting tank. The chloride ion content in the low-chlorine coal tar from the last stage desalting tank should be below 20ppm. If the secondary desalting does not meet the requirements, the water consumption should be increased or more desalting tanks should be set.

[0044] Step S2, the high chlorine-containing wastewater from the outlet of the desalted water of the first stage desalting tank 3 is transported to the desalted water cooler 5 for cooling to 50-70°C, and the tar finally coming out of the last stage desalting tank 3 enters the low chlorine tar tank 4 for storage.

[0045] Step S3, the high-chlorine-containing wastewater cooled by the desalted water cooler 5 passes through the oil-water separation tank 6 for oil-water separation.

[0046] In step S4, the tar from the oil-water separation tank 6 is returned to the tar raw material tank 1 through a pipeline, and the high-chlorine-containing wastewater from the oil-water separation tank 6 is mixed with the alkali solution in the alkali solution tank 9, so that the phenolic compounds in the water react to form sodium phenolate salts, and the ammonium chloride in the water reacts to form sodium chloride. The wastewater mixed with the alkali solution is evaporated through an ammonia distillation tower 7, and the ammonia water obtained at the top of the tower is recovered and processed, and the water after deammoniation at the bottom of the tower enters a multiple-effect evaporator 8.

[0047] Step S5, the concentrated solution containing sodium chloride and sodium phenolate at the bottom of the multiple-effect evaporator 8 is recovered and processed, and the water obtained at the top of the tower has a low chlorine content and can be returned to the last stage desalination tank 3 for recycling. Among them, the chloride ion of the fresh water coming out of the multiple-effect evaporator 8 should be below 20ppm, meeting the reuse standard.

[0048] Example 1

[0049] In this embodiment, the number of desalting tanks 3 is 2. In this embodiment, the method for pretreating high-chlorine-containing medium- and low-temperature coal tar specifically includes the following steps:

[0050] Step S1, the high chlorine-containing medium-low temperature coal tar in the tar raw material tank 1 is fully mixed with the desalted water discharged from the secondary desalter, and then transported to the raw oil preheater 2 to be preheated to 90°C and then sent to the primary desalter for water washing. The coal tar from the primary desalter is mixed with 25% (accounting for the tar content) of fresh water from the top of the multi-effect evaporator 8 through a static mixer and then enters the secondary desalter for water washing. Among them, the temperature in the primary desalter and the secondary desalter is 90°C, the pressure is 0.4MPa, and the residence time is 8h.

[0051] Step S2, the tar discharged from the secondary desalting tank enters the low-chlorine tar tank 4, and the water discharged from the desalting water outlet of the primary desalting tank enters the desalting water cooler 5 and is cooled to 50°C.

[0052] Step S3, the waste water cooled by the desalted water cooler 5 enters the oil-water separation tank 6 for oil-water separation.

[0053] In step S4, the tar coming out of the oil-water separation tank 6 is returned to the tar raw material tank 1 through a pipeline, the high-chlorine-containing wastewater coming out of the oil-water separation tank 6 is mixed with the alkali solution in the alkali solution tank 9 and then enters the ammonia evaporation tower 7 for evaporation treatment, the ammonia water obtained at the top of the ammonia evaporation tower 7 is recovered and treated, and the water discharged from the bottom of the tower enters the multi-effect evaporator 8.

[0054] Step S5, the concentrated liquid containing sodium chloride and sodium phenolate is extracted from the bottom of the multi-effect evaporator 8 for recycling, and the fresh water from the top of the tower is mixed with the coal tar from the primary desalination tank and then enters the secondary desalination tank for recycling.

[0055] The raw material tar used in this embodiment has a chloride ion content of 1500ppm. After two desalination processes, the chloride ion content is 70ppm. After the desalted water passes through the final multi-effect evaporator 8, the chloride ion content of the fresh water coming out of the top is 15ppm, which meets the reuse requirements.

[0056] Example 2

[0057] In this embodiment, the number of desalting tanks 3 is 3. In this embodiment, the method for pretreating high-chlorine-containing medium- and low-temperature coal tar specifically includes the following steps:

[0058] Step S1, the high-chlorine-containing medium-low temperature coal tar in the tar raw material tank 1 is fully mixed with the desalted water discharged from the secondary desalter, and then transported to the raw oil preheater 2 to be preheated to 120°C and then sent to the primary desalter for water washing; the coal tar discharged from the primary desalter is mixed with the desalted water discharged from the tertiary desalter and then enters the secondary desalter for water washing; the coal tar discharged from the secondary desalter is mixed with 30% (accounting for the tar content) of fresh water discharged from the multi-effect evaporator 8 and then enters the tertiary desalter for water washing. Among them, the temperature in the primary desalter, the secondary desalter, and the tertiary desalter is 120°C, the pressure is 0.3MPa, and the residence time is 5h.

[0059] Step S2, the tar discharged from the tertiary desalting tank enters the low-chlorine tar tank 4 for storage, and the water discharged from the outlet of the desalting water of the primary desalting tank enters the desalting water cooler 5 for cooling to 60°C.

[0060] Step S3, the waste water cooled by the desalted water cooler 5 enters the oil-water separation tank 6 for oil-water separation.

[0061] In step S4, the tar coming out of the oil-water separation tank 6 is returned to the tar raw material tank 1 through a pipeline, the high-chlorine-containing wastewater coming out of the oil-water separation tank 6 is mixed with the alkali solution in the alkali solution tank 9 and then enters the ammonia evaporation tower 7 for evaporation treatment, the ammonia water obtained at the top of the ammonia evaporation tower 7 is recovered and treated, and the water discharged from the bottom of the tower enters the multi-effect evaporator 8.

[0062] Step 5, the concentrated liquid containing sodium chloride and sodium phenolate is extracted from the bottom of the multi-effect evaporator 8 for recycling, and the fresh water from the top of the tower is mixed with the coal tar from the secondary desalination tank and then enters the tertiary desalination tank for recycling.

[0063] The chloride ion content of the raw material tar used in this embodiment is 1500ppm. After three desalination processes, the chloride ion content is 25ppm. After the desalted water passes through the final multi-effect evaporator 8, the chloride ion content of the fresh water coming out of the top is 13ppm, which meets the reuse requirements.

[0064] Example 3

[0065] In this embodiment, the number of desalting tanks 3 is set to 5. In this embodiment, the method for pretreating high-chlorine-containing medium- and low-temperature coal tar specifically includes the following steps:

[0066] Step S1, the high-chlorine-containing medium-low temperature coal tar in the tar raw material tank 1 is fully mixed with the desalted water discharged from the secondary desalter, and then transported to the raw oil preheater 2 for preheating to 140°C and then sent to the primary desalter for water washing; the coal tar discharged from the primary desalter is mixed with the desalted water discharged from the tertiary desalter and then enters the secondary desalter for water washing; the coal tar discharged from the secondary desalter is mixed with the desalted water discharged from the quaternary desalter and then enters the tertiary desalter for water washing; the coal tar discharged from the tertiary desalter is mixed with the desalted water discharged from the fifth desalter and then enters the fourth desalter for water washing; the coal tar discharged from the fourth desalter is mixed with 35% (accounting for the tar content) of fresh water discharged from the multi-effect evaporator 8 and then enters the fifth desalter for water washing. Among them, the temperature in the primary desalter, the secondary desalter, and the tertiary desalter is 140°C, the pressure is 0.5MPa, and the residence time is 1h.

[0067] Step S2, the tar discharged from the fifth-stage desalting tank enters the low-chlorine tar tank 4, and the water discharged from the outlet of the desalting water of the first-stage desalting tank enters the desalting water cooler 5 and is cooled to 70°C.

[0068] Step S3, the waste water cooled by the desalted water cooler 5 enters the oil-water separation tank 6 for oil-water separation.

[0069] In step S4, the tar coming out of the oil-water separation tank 6 is returned to the tar raw material tank 1 through a pipeline, the high-chlorine-containing wastewater coming out of the oil-water separation tank 6 is mixed with the alkali solution in the alkali solution tank 9 and then enters the ammonia evaporation tower 7 for evaporation treatment, the ammonia water obtained at the top of the ammonia evaporation tower 7 is recovered and treated, and the water discharged from the bottom of the tower enters the multi-effect evaporator 8.

[0070] Step 5, the concentrated liquid containing sodium chloride and sodium phenolate is extracted from the bottom of the multi-effect evaporator 8 for recycling, and the fresh water from the top of the tower is mixed with the coal tar from the fourth-stage desalination tank and then enters the fifth-stage desalination tank for recycling.

[0071] The raw material tar used in this embodiment has a chloride ion content of 1500ppm. After five desalinations, the chloride ion content is 15ppm. After the desalted water passes through the final multi-effect evaporator 8, the chloride ion content of the fresh water coming out of the top is 10ppm, which meets the reuse requirements.

[0072] Although the functions and working processes of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific functions and working processes. The above-mentioned specific implementation methods are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which are all within the protection of the present invention.

Claims

1. A high-chlorine-containing medium-low temperature coal tar pretreatment system, comprising a tar raw material tank (1), characterized in that: The discharge port of the tar raw material tank (1) is connected to the tar inlet of the desalting tank (3) through a pipeline via a raw material preheater (2); the tar outlet of the desalting tank (3) is connected to the low-chlorine tar tank (4) through a pipeline; the desalted water outlet of the desalting tank (3) is connected to the feed port of the oil-water separator (6) through a pipeline via a desalted water cooler (5); the tar outlet of the oil-water separator (6) is connected to the feed port of the tar raw material tank (1) through a pipeline; the water outlet of the oil-water separator (6) is connected to the feed port of the ammonia evaporation tower (7) through a pipeline, and the pipeline is also connected to the discharge port of the alkali liquid tank (9); the bottom outlet of the ammonia evaporation tower (7) is connected to the feed port of the multi-effect evaporator (8) through a pipeline; and the top outlet of the multi-effect evaporator (8) is connected to the tar inlet of the desalting tank (3) through a pipeline.

2. The high chlorine-containing medium and low temperature coal tar pretreatment system according to claim 1 is characterized in that: The desalting tanks (3) are arranged in 2 to 5 numbers, which are connected in series in sequence through tar inlets and tar outlets. The coal tar from the tar outlet of the previous desalting tank is transported to the tar inlet of the adjacent next desalting tank through a pipeline. The desalted water from the desalted water outlet of the next desalting tank is transported to the tar inlet of the adjacent previous desalting tank through a pipeline. The coal tar from the tar outlet of the last desalting tank is transported to the low-chlorine tar tank (4) through a pipeline. The desalted water from the desalted water outlet of the first desalting tank is transported to the feed inlet of the desalted water cooler (5) through a pipeline. The desalted water from the desalted water outlet of the second desalting tank is transported to the raw material preheater (2) through a pipeline, and is mixed with the high-chlorine and medium-temperature coal tar in the tar raw material tank (1) for preheating before entering the first desalting tank. The fresh water from the multi-effect evaporator (8) is transported to the last desalting tank (3) through a pipeline for recycling.

3. The high chlorine-containing medium and low temperature coal tar pretreatment system according to claim 1 is characterized in that: The raw material preheater (2) and the desalted water cooler (5) both adopt a shell and tube structure.

4. The high chlorine-containing medium- and low-temperature coal tar pretreatment system according to claim 1, characterized in that: The tar raw material tank (1), the desalting tank (3), the oil-water separator (6), the ammonia distillation tower (7), and the multiple-effect evaporator (8) are all provided with vents.

5. A method for pretreating high-chlorine-containing medium-low-temperature coal tar based on the high-chlorine-containing medium-low-temperature coal tar pretreatment system according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step S1, high chlorine-containing medium-low temperature coal tar is mixed with water and then enters the raw material preheater (2) for preheating, and then enters the desalting tank (3) for water washing to achieve oil-water separation; Step S2, transporting the high-chlorine-containing wastewater from the desalting water outlet of the desalting tank (3) to the desalting water cooler (5) for cooling, and the tar finally discharged from the desalting tank (3) enters the low-chlorine tar tank (4); Step S3, the high-chlorine-containing wastewater cooled by the desalted water cooler (5) passes through an oil-water separation tank (6) for oil-water separation; Step S4, the high-chlorine-containing wastewater from the oil-water separation tank (6) is mixed with the alkali solution in the alkali solution tank (9), and the wastewater mixed with the alkali solution is evaporated through an ammonia evaporation tower (7), the ammonia water obtained at the top of the tower is recovered, and the water after deammoniation at the bottom of the tower enters a multiple-effect evaporator (8); Step S5, the concentrated liquid at the bottom of the multiple-effect evaporator (8) is recovered and processed, and the water obtained at the top of the tower is returned to the desalination tank (3) for recycling.

6. The method for pretreating high chlorine-containing medium- and low-temperature coal tar according to claim 5, characterized in that: The preheating temperature in the raw material preheater (2) in step S1 is 90-140°C.

7. The method for pretreating high chlorine-containing medium- and low-temperature coal tar according to claim 5, characterized in that: In step S1, the number of the desalination tanks (3) is 2 to 5, which are connected in series. The temperature in each desalination tank (3) is 90 to 140° C., the pressure in each desalination tank (3) is 0.3 to 0.5 MPa, and the residence time in each desalination tank (3) is 1 to 8 hours.

8. The method for pretreating high chlorine-containing medium- and low-temperature coal tar according to claim 5, characterized in that: The cooling temperature of the desalted water cooler (5) in step S2 is 50-70°C.

9. The method for pretreating high chlorine-containing medium- and low-temperature coal tar according to claim 5, characterized in that: In step S4, the high-chlorine-containing wastewater from the oil-water separation tank (6) is mixed with the alkali solution in the alkali solution tank (9), so that the phenolic compounds in the water react to form sodium phenolate, and the ammonium chloride in the water reacts to form sodium chloride.

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