Coal chemical phenolic wastewater extraction and solvent recovery system

Abstract

The utility model discloses a coal chemical phenolic wastewater extraction and solvent recovery system. The system comprises an extraction tower, a water tower, an oil-water separator, an extract separation tower, a water washing tower, an extract tank, a solvent circulating tank, a light oil tank and a crude phenol tank. By adding the water washing tower for washing, the content of phenol and homologues in crude phenol can be increased, and the content of neutral oil can be reduced, so that the crude phenol product meets the standard requirement; meanwhile, the quality of the recovered extraction solvent can be improved after water washing by the water washing tower, and impurities such as light oil in the extraction solvent can be removed in time, so that the extraction treatment effect of the wastewater can be improved, and the treatment load of a biochemical device can be reduced.

Description

Technical Field

[0001] The utility model belongs to the technical field of wastewater treatment, and particularly relates to an extraction and solvent recovery system for phenol-containing wastewater in coal chemical industry. Through this system, while further improving the effluent quality and solving the problem of wastewater pollution, the phenolic substances in the wastewater are recovered and purified into qualified crude phenol meeting the standard requirements. Background Art

[0002] When low-rank coal is gasified and dry-distilled (pyrolyzed), a large amount of high-concentration phenol-containing wastewater will be generated, with a phenol content as high as 5,000 - 25,000 mg / L. On the one hand, phenols have strong biological toxicity and pose a huge environmental risk. On the other hand, phenols are important chemical products and raw materials with relatively high economic value. Therefore, it is a common practice in the current coal chemical industry to use a phenol recovery device and adopt liquid-liquid extraction technology to extract the phenols in the wastewater as a by-product of crude phenol, while reducing the biological toxicity of the wastewater and improving its biodegradability. The crude phenol obtained by extraction is required to meet the requirements of Standard YB / T 5079 - 2012, that is, the content of phenols and homologues in the crude phenol is not less than 83%, and the content of neutral oil is not higher than 0.8%. The extraction agents currently used mainly include methyl isobutyl ketone, diisopropyl ether, methyl pentenone, etc.

[0003] Due to the very complex composition of coal chemical wastewater, during the extraction process, in addition to various phenols, a variety of organic substances such as aliphatic hydrocarbons, benzene series, and naphthalene are also extracted simultaneously and enter the extract. In the current setting of the phenol recovery device, binary distillation is used to separate the extract to recover the solvent, that is, the extract is distilled into a solvent and crude phenol. With such a configuration, for the conversion process with a higher temperature in the dry-distillation section, or when using coal with a higher degree of coalification as raw material, the COD of the treated wastewater can generally be reduced to below 3,000 mg / L, and the quality of the crude phenol can also meet the requirements of Standard YB / T 5079 - 2012. However, when using lignite with a lower degree of coalification as raw material and adopting medium and low-temperature dry-distillation to produce semi-coke, when using the above solvent recovery process, there are often phenomena such as higher oil content and COD in the effluent, the content of homologues in the crude phenol is far lower than 83%, and the content of neutral oil in the crude phenol also often far exceeds the standard value. We analyzed the composition of the extract and found that the extract in the semi-coke production process is more complex in composition than the gasification wastewater, especially the component content in the distillation range of 130 - 160 °C and higher than 210 °C is much higher than that of the gasification wastewater. When binary distillation is used for solvent recovery, the content of neutral oil represented by naphthalene in the crude phenol often reaches more than 1.5%, and the oil component content in the solvent can also reach 1% - 2%, resulting in a reduction in the extraction effect. Summary of the Utility Model

[0004] In view of the shortcomings of the prior art, the utility model provides a coal chemical industry phenol-containing wastewater extraction and solvent recovery system. The system can increase the content of phenol and homologues in crude phenol, and can also increase the purity of the recovered extraction solvent, thereby improving the wastewater treatment effect.

[0005] The utility model provides a coal chemical industry phenol-containing wastewater extraction and solvent recovery system, which specifically comprises: a solvent circulation tank, which is used to store the extraction solvent and transport the extraction solvent to the extraction tower through the solvent circulation tank; the extraction tower, which is used to mix and extract most of the phenol-containing wastewater and the extraction solvent to obtain raffinate wastewater and extract; an extraction tank, which is used to store the extract obtained in the extraction tower; a water tower, which is used to strip the raffinate wastewater obtained in the extraction tower and recover the extraction solvent dissolved and entrained in the wastewater; an oil-water separator, which is used to separate the oil-water recovered in the water tower from the raffinate wastewater; and a water tower, which is used to separate the oil-water recovered in the water tower from the raffinate wastewater. The extraction solvent is separated into oil and water, the upper layer of the extraction solvent flows into the solvent circulation tank for recycling, and the lower layer of the aqueous phase is pumped to the water tower for stripping again; the extract separation tower is used to separate the extract stored in the extract tank to obtain light oil, heavy aromatics, and crude phenol, and to recover the extraction solvent; the light oil tank is used to store the light oil obtained by the extract separation tower; the water washing tower is used to wash the light oil stored in the light oil tank with a small part of phenol-containing wastewater, and pump a small part of the phenol-containing wastewater to the extraction tower; the crude phenol tank is used to store the crude phenol obtained by the extract separation tower.

[0006] A wastewater inlet is arranged at the top of the extraction tower, the extract outlet at the top of the extraction tower is connected to the inlet of the extraction tank, and the residual wastewater outlet at the bottom of the extraction tower is connected to the inlet at the top of the water tower; a wastewater outlet is arranged at the bottom of the water tower, the top outlet of the water tower is connected to the inlet of the oil-water separator, the lower outlet of the oil-water separator is connected to the upper inlet of the water tower, and the upper outlet of the oil-water separator is connected to the solvent inlet at the top of the solvent circulation tank; one outlet at the bottom of the solvent circulation tank is connected to the lower part of the extraction tower, and the other outlet is connected to the solvent inlet at the top of the extraction separation tower; the top outlet of the extraction separation tower is connected to the solvent The upper inlet of the agent circulation tank is connected, the upper extract inlet of the extract separation tower is connected to the extract tank outlet; the first side line production outlet of the extract separation tower is connected to the light oil tank inlet, and the second side line production outlet of the extract separation tower is connected to the crude phenol tank inlet; one outlet of the light oil tank bottom is connected to the first side line inlet of the extract separation tower, and the other outlet is connected to the bottom of the water washing tower, and the upper part of the water washing tower is provided with a wastewater inlet and a light oil outlet; two outlets are provided at the bottom of the crude phenol tank, one outlet is connected to the second side line inlet of the extract separation tower, and the other outlet is used to transport the crude phenol product.

[0007] Furthermore, it is preferred that the extract separation tower has 20 to 30 theoretical plates, and the feed inlet is located at the 8th to 17th theoretical plates.

[0008] Furthermore, it is preferred that the first side line outlet of the extract separation tower is located at the 3rd to 6th theoretical plates downward from the feed inlet.

[0009] Further, it is preferred that the second side draw outlet of the extract separation column is located at the 6th to 14th theoretical plate downward from the feed inlet.

[0010] Further, it is preferred that the theoretical stage number of the water washing column is 1 to 4 stages.

[0011] The beneficial effects of the present utility model are as follows:

[0012] After the phenol-containing wastewater of the present utility model is extracted and separated by an extraction column, the extract is separated into light oil, heavy aromatic hydrocarbons and crude phenol through an extract separation column. A part of the light oil is refluxed to the extract separation column, and the other part is sent to the light oil product tank after being washed by a water washing column; a part of the crude phenol is refluxed to the extract separation column, and the other part is sent to the crude phenol product tank; the raffinate wastewater is taken out through a water tower and separated by an oil-water separator to recover the extraction solvent, and the treated wastewater is sent to a biochemical process for further treatment or directly recycled. After being washed by the water washing column, the content of phenol and homologues in the crude phenol can be increased, and the content of neutral oil can be reduced, so that the crude phenol product meets the standard requirements; at the same time, after being washed by the water washing column, the quality of the recovered extraction solvent can also be improved, and impurities such as light oil in the extraction solvent can be removed in time, thereby improving the extraction treatment effect of the wastewater and reducing the treatment load of the biochemical device. Description of the Drawings

[0013] Figure 1 It is a structural diagram of the coal chemical industry phenol-containing wastewater extraction and solvent recovery system of the present utility model. Detailed Embodiments

[0014] The present utility model will be further described in detail below with reference to the drawings and embodiments, but the protection scope of the present utility model is not limited to the following embodiments.

[0015] Example 1

[0016] As Figure 1As shown in the figure, the phenol-containing wastewater extraction and solvent recovery system of this embodiment includes: an extract tank 1, an extraction tower 2, a water tower 3, an oil-water separator 4, an extract separation tower 5, a light oil tank 6, a water washing tower 7, a crude phenol tank 8, and a solvent circulation tank 9. Among them, the solvent circulation tank 9 is used to store the extraction solvent and transport the extraction solvent to the extraction tower 2 through the solvent circulation tank 9; the extraction tower 2 is used for mixing and extracting most of the phenol-containing wastewater and the extraction solvent to obtain raffinate wastewater and an extract; the extract tank 1 is used to store the extract obtained in the extraction tower 2; the water tower 3 is used for stripping the raffinate wastewater obtained in the extraction tower 2 to recover the extraction solvent dissolved and entrained in the wastewater; the oil-water separator 4 is used to separate the oil and water of the extraction solvent recovered in the water tower 3, the upper extraction solvent flows into the solvent circulation tank 9 for recycling, and the lower water phase is pumped to the water tower 3 for re-stripping; the extract separation tower 5 is used to separate the extract stored in the extract tank 1 to obtain light oil, heavy aromatic hydrocarbons, and crude phenol, and recover the extraction solvent; the light oil tank 6 is used to store the light oil obtained in the extract separation tower 5; the water washing tower 7 is used to wash the light oil stored in the light oil tank 6 with a small part of the phenol-containing wastewater and pump the small part of the phenol-containing wastewater to the extraction tower 2; the crude phenol tank 8 is used to store the crude phenol obtained in the extract separation tower 5.

[0017] A wastewater inlet is provided at the upper part of the extraction tower 2. The upper extract outlet of the extraction tower 2 is connected to the inlet of the extract tank 1 through a pipeline. The bottom raffinate wastewater outlet of the extraction tower 2 is connected to the top inlet of the water tower 3 through a pipeline; a wastewater outlet is provided at the bottom of the water tower 3. The top outlet of the water tower 3 is connected to the inlet of the oil-water separator 4 through a pipeline. The lower outlet of the oil-water separator 4 is connected to the upper inlet of the water tower 3 through a pipeline. The upper outlet of the oil-water separator 4 is connected to the upper solvent inlet of the solvent circulation tank 9 through a pipeline; one outlet at the bottom of the solvent circulation tank 9 is connected to the lower part of the extraction tower 2 through a pipeline, and the other outlet is connected to the upper solvent inlet of the extract separation tower 5 through a pipeline; the top outlet of the extract separation tower 5 is connected to the upper inlet of the solvent circulation tank 9 through a pipeline. The upper extract inlet of the extract separation tower 5 is connected to the outlet of the extract tank 1 through a pipeline; the first side line extraction outlet of the extract separation tower 5 is connected to the inlet of the light oil tank 6 through a pipeline. The second side line extraction outlet of the extract separation tower 5 is connected to the inlet of the crude phenol tank 8 through a pipeline; one outlet at the bottom of the light oil tank 6 is connected to the first side line inlet of the extract separation tower 5 through a pipeline, and the other outlet is connected to the bottom of the water washing tower 7 through a pipeline. A wastewater inlet and a light oil outlet are provided at the upper part of the water washing tower 7; there are 2 outlets at the bottom of the crude phenol tank 8. One outlet is connected to the second side line inlet of the extract separation tower 5 through a pipeline, and the other outlet is used to transport the crude phenol product.

[0018] The number of theoretical plates of the above-mentioned extract separation column 5 is 20 - 30, and the feed inlet is located at the 8th - 17th theoretical plate; the first side draw outlet of the extract separation column 5 is located at the 3rd - 6th theoretical plate downward from the feed inlet; the second side draw outlet of the extract separation column 5 is located at the 6th - 14th theoretical plate downward from the feed inlet; the number of theoretical stages of the water washing column 7 is 1 - 4. In this embodiment, the number of theoretical plates of the extract separation column 5 is 20, the feed inlet is located at the 8th theoretical plate, the first side draw outlet is located at the 3rd theoretical plate downward from the feed inlet, and the second side draw outlet is located at the 7th theoretical plate downward from the feed inlet. The number of theoretical stages of the water washing column 7 is 1 stage.

[0019] Using the system of this embodiment to treat the wastewater from a coal pyrolysis plant, the wastewater production is 120 tons per hour, and the phenol content is 15,000 mg / L. The specific treatment steps are as follows:

[0020] Step 1: Extraction

[0021] The phenol-containing wastewater is divided into two parts with a split ratio of 1:10. Most of the phenol-containing wastewater enters the extraction column 2, and a small part of the phenol-containing wastewater enters the water washing column 7. The phenol-containing wastewater entering the extraction column 2 contacts with the extraction solvent methyl isobutyl ketone from the solvent circulation tank 9 to complete the extraction process, and the extraction temperature is 30 - 40°C; the extract obtained after extraction overflows into the extract tank 1 and then is pumped to the extract separation column 5 for separation of the extract; the raffinate wastewater after extraction is pumped from the bottom of the extraction column 2 to the water tower 3 to strip and recover the extraction solvent dissolved and entrained in the wastewater.

[0022] Step 2: Extract Separation

[0023] The extract obtained in Step 1 enters the column from the middle upper part of the extract separation column 5 for distillation separation. The operating pressure of the extract separation column 5 is -0.09 MPa, the number of theoretical plates is 20, and the feed inlet is located at the 8th theoretical plate. The extraction solvent is drawn from the top of the extract separation column 5, and the top temperature is 46 - 48°C. The first side draw outlet of the extract separation column 5 is located at the 3rd theoretical plate downward from the feed inlet, and the temperature at the first side draw outlet is 65°C. After the light oil is drawn and cooled to 30°C, it enters the light oil tank 6. A part of the light oil in the light oil tank 6 is refluxed to the extract separation column 5 with a reflux ratio of 0.2 - 0.3, and the other part is sent to the water washing column 7 for water washing. The second side draw outlet of the extract separation column 5 is located at the 7th theoretical plate downward from the feed inlet, and the temperature at the second side draw outlet is 120 - 124°C. After the crude phenol is drawn and cooled to 60 - 80°C, it enters the crude phenol tank 8. A part of the crude phenol in the crude phenol tank 8 is refluxed to the extract separation column 5 with a reflux ratio of 0.2 - 0.3, and the other part is sent to the crude phenol product tank. The bottom temperature of the extract separation column 5 is 160 - 162°C, and the bottom heavy aromatics are cooled and sent to the heavy aromatics product tank.

[0024] Step 3: Solvent Stripping

[0025] The raffinate wastewater obtained in Step 1 enters from the top of the water tower 3. After the overhead product of the water tower 3 is condensed, it enters the oil-water separator 4 for oil-water separation. The upper-layer extraction solvent overflows into the solvent circulation tank 9 for recycling; the lower-layer aqueous phase returns to the water tower 3 for re-stripping; the wastewater discharged from the bottom of the water tower 3 is the treated wastewater, which is sent to the biochemical treatment for further treatment or directly reused.

[0026] Step 4: Light Oil Water Washing

[0027] The light oil entering the water washing tower 7 in Step 2 is in countercurrent contact with a small part of the phenol-containing wastewater entering the water washing tower 7 in Step 1 to complete the water washing. The water washing tower 7 is configured as a liquid-liquid extraction tower with a theoretical stage number of 1. The washed light oil is sent to the light oil product tank; the extraction solvent entrained in the light oil is eluted into the phenol-containing wastewater, and the phenol-containing wastewater is pumped from the bottom of the water washing tower 7 to the extraction tower 2 for extraction and phenol removal treatment.

[0028] In this embodiment, compared with the prior art, the content of phenol and homologues in the crude phenol in the crude phenol product tank has increased from about 55% to 85%, and the content of neutral oil has decreased from more than 2.0% to less than 0.5%; the oil content in the recovered solvent has decreased from about 1.5% to less than 0.05%, the oil content of the treated wastewater discharged from the bottom of the water tower 3 has decreased from 180 mg / L to less than 60 mg / L, and the COD has decreased from more than 3,800 mg / L to less than 2,800 mg / L. The obtained light oil and heavy aromatics also meet the corresponding product quality standards.

Claims

1. A coal chemical industry phenolic wastewater extraction and solvent recovery system, characterized in that: include: A solvent circulation tank (9) is used to store the extraction solvent and to transport the extraction solvent to the extraction tower (2) through the solvent circulation tank (9); An extraction tower (2) is used for mixed extraction of most of the phenol-containing wastewater and the extraction solvent to obtain raffinate wastewater and an extract; An extract tank (1) for storing the extract obtained in the extraction tower (2); A water tower (3) is used to strip the raffinate wastewater obtained in the extraction tower (2) and recover the extraction solvent dissolved and entrained in the wastewater; The oil-water separator (4) is used to separate the oil and water of the extraction solvent recovered from the water tower (3), the upper layer of the extraction solvent flows into the solvent circulation tank (9) for recycling, and the lower layer of the water phase is pumped to the water tower (3) for stripping again; An extract separation tower (5) is used to separate the extract stored in the extract tank (1) to obtain light oil, heavy aromatic hydrocarbons, and crude phenol, and to recover the extraction solvent; A light oil tank (6) for storing the light oil obtained by the extract separation tower (5); A water washing tower (7) is used to wash the light oil stored in the light oil tank (6) with a small portion of phenol-containing wastewater, and pump the small portion of phenol-containing wastewater to the extraction tower (2); The crude phenol tank (8) is used to store the crude phenol obtained from the extract separation tower (5).

2. The coal chemical industry phenolic wastewater extraction and solvent recovery system according to claim 1, characterized in that: The upper part of the extraction tower (2) is provided with a wastewater inlet, the upper extract outlet of the extraction tower (2) is connected to the inlet of the extraction tank (1), and the raffinate wastewater outlet at the bottom of the extraction tower (2) is connected to the top inlet of the water tower (3); the bottom of the water tower (3) is provided with a wastewater outlet, the top outlet of the water tower (3) is connected to the inlet of the oil-water separator (4), the lower outlet of the oil-water separator (4) is connected to the upper inlet of the water tower (3), and the upper outlet of the oil-water separator (4) is connected to the upper solvent inlet of the solvent circulation tank (9); one outlet at the bottom of the solvent circulation tank (9) is connected to the lower part of the extraction tower (2), and the other outlet is connected to the upper solvent inlet of the extract separation tower (5); the top of the extract separation tower (5) is connected to the solvent inlet of the extract separation tower (5). The outlet is connected to the upper inlet of the solvent circulation tank (9), and the upper extract inlet of the extract separation tower (5) is connected to the outlet of the extract tank (1); the first side line production outlet of the extract separation tower (5) is connected to the inlet of the light oil tank (6), and the second side line production outlet of the extract separation tower (5) is connected to the inlet of the crude phenol tank (8); one outlet at the bottom of the light oil tank (6) is connected to the first side line inlet of the extract separation tower (5), and the other outlet is connected to the bottom of the water washing tower (7), and the upper part of the water washing tower (7) is provided with a wastewater inlet and a light oil outlet; the bottom of the crude phenol tank (8) is provided with two outlets, one outlet is connected to the second side line inlet of the extract separation tower (5), and the other outlet is used to transport the crude phenol product.

3. The coal chemical industry phenolic wastewater extraction and solvent recovery system according to claim 2, characterized in that: The number of theoretical plates of the extract separation tower (5) is 20 to 30, and the feed inlet is located at the 8th to 17th theoretical plates.

4. The coal chemical industry phenolic wastewater extraction and solvent recovery system according to claim 2, characterized in that: The first side line extraction port of the extract separation tower (5) is located at the 3rd to 6th theoretical plates downward from the feed inlet.

5. The coal chemical industry phenolic wastewater extraction and solvent recovery system according to claim 2, characterized in that: The second side line outlet of the extract separation tower (5) is located at the 6th to 14th theoretical plates downward from the feed inlet.

6. The coal chemical industry phenol-containing wastewater extraction and solvent recovery system according to claim 2, characterized in that: The theoretical number of stages of the water washing tower (7) is 1 to 4.

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