Waste alkali liquor treatment system and treatment process

Abstract

The invention discloses a waste alkali liquor treatment system which comprises a gas stripping tank, a plurality of settling tanks, an oil phase collecting tank and a liquid discharge pipe, the settling tanks are sequentially and adjacently arranged, and a liquid inlet is formed in the bottom of the gas stripping tank; every two adjacent settling tanks are communicated through a first overflow hole, and the first settling tank is adjacent to the gas stripping tank and is communicated with the gas stripping tank through a flow guide hole; the oil phase collecting tank is arranged on one side of the settling tank, and the top of the oil phase collecting tank is communicated with the top of the settling tank through a flow guide pipe; the bottoms of the gas stripping tank and the settling tank are connected with liquid discharge pipes, a flash tank is further arranged on one side of the gas stripping tank, and a liquid outlet of the flash tank is communicated with a liquid inlet of the gas stripping tank; when the waste alkali liquor treatment system disclosed by the invention is used for treating waste alkali liquor, the equipment investment cost at the early stage is about 300,000, and the construction cost during treatment at the later stage is less than 200,000, so that the total cost is less than 500,000; and the cost is far lower than that of an incineration method for treating the same amount of waste alkali liquor, so that the cost can be effectively reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of coal-to-olefins, and in particular relates to a treatment system for coal-to-olefins waste alkali liquor. The invention also relates to a waste alkali liquor treatment process. Background Art

[0002] A large amount of gas produced by coal-to-olefins needs to be refined after alkali washing. This process will produce and discharge high-concentration alkaline waste liquid, which is a special organic waste liquid with high salt content, toxicity and difficulty in degradation. The waste alkali liquid has the characteristics of strong alkalinity, high COD (chemical oxygen demand) and high oil content. It mainly contains a small amount of inorganic salts such as sodium carbonate and sodium hydroxide produced in the alkali washing process and a large amount of organic matter such as aldehydes and ketones. At the same time, there is also oil-in-water emulsion butter in the waste alkali liquid, with a pH value greater than 12, which must be treated before it can be discharged. The treatment of waste alkali liquid in the coal-to-olefin industry has always been a problem that has plagued enterprises. Waste alkali liquid cannot be directly discharged into sewage stations for biochemical treatment.

[0003] At present, the most common industrial treatment method is incineration. During the incineration method, the waste alkali liquid is first pretreated, and then the pretreated waste alkali liquid is transported to the incinerator. In order to maintain high-temperature combustion during incineration, the incinerator usually requires fuel supply, such as natural gas, fuel oil or other combustibles. The exhaust gas after incineration still needs to be equipped with environmental protection facilities such as desulfurization and denitrification to ensure that the exhaust gas meets the emission standards. This treatment method requires a large amount of fuel when incinerating the waste alkali liquid, so this waste alkali liquid treatment method has a large investment and high cost. Summary of the invention

[0004] The purpose of the present invention is to provide a waste alkali solution treatment system and treatment process, which solves the problem of high cost of waste alkali solution treatment by incineration method.

[0005] The technical solution adopted by the present invention is a waste alkali solution treatment system, comprising:

[0006] An air stripping tank, wherein a liquid inlet is arranged at the bottom of the air stripping tank;

[0007] A plurality of sedimentation tanks are arranged adjacent to each other in sequence, wherein two adjacent sedimentation tanks are connected via a first overflow hole, wherein the first sedimentation tank is adjacent to the gas stripping tank and the two are connected via a guide hole;

[0008] The oil phase collecting tank is arranged on one side of the sedimentation tank, and the oil phase collecting tank and the top of the sedimentation tank are connected through a guide pipe;

[0009] A drainage pipe is connected to the bottom of the air lift tank and the sedimentation tank.

[0010] Two oil phase collecting tanks are provided, the two oil phase collecting tanks are arranged adjacent to each other and are connected through a second overflow hole, the top of one of the oil phase collecting tanks is connected to multiple sedimentation tanks through a guide pipe, and a centrifugal pump is provided at the bottom of the other oil phase collecting tank, and the liquid outlet of the centrifugal pump is connected to the distillation recycling device.

[0011] A flash tank is also arranged on one side of the air stripping tank, and the liquid outlet of the flash tank is communicated with the liquid inlet of the air stripping tank.

[0012] A branch-shaped air lift distributor is arranged at the top of the air lift tank slot. The air lift distributor includes a main pipeline horizontally arranged at the top of the air lift tank slot. The main pipeline is arranged along the length direction of the air lift tank. A plurality of branch pipelines are arranged downwardly inclined on the main pipeline, and each branch pipeline is provided with a plurality of air outlets.

[0013] The angle between the center line of the branch pipe and the main pipe is 40°-45°.

[0014] There are four sedimentation tanks, and a ball ring is arranged in the second sedimentation tank.

[0015] A filter screen is arranged on the diversion hole.

[0016] Another technical solution adopted by the present invention is a waste alkali solution treatment process, based on a waste alkali solution treatment system disclosed above, specifically comprising the following steps:

[0017] The waste alkali solution is transferred to the gas stripping tank through the flash tank, and carbon dioxide is introduced into the gas stripping tank through the gas stripping distributor for neutralization reaction, so that the pH value of the neutralized solution is reduced to neutral or weakly acidic;

[0018] The oil phase in the upper layer of the sedimentation tank is transferred to the oil phase collection tank through the draft tube;

[0019] The oil phase in the oil phase collection tank is distilled and recycled by the centrifugal pump;

[0020] The liquid in the drainage pipe is discharged for unified biochemical treatment.

[0021] After the liquid is introduced into the air stripping tank, polyaluminium chloride is added into the air stripping tank at the same time.

[0022] The pH value of the solution after neutralization is 7-8.

[0023] The beneficial effects of the present invention are:

[0024] The invention discloses a waste alkali liquid treatment system and treatment process. When treating the waste alkali liquid, a large amount of cost-free carbon dioxide is first introduced into a gas stripping tank for neutralization and gas stripping. The waste alkali liquid after gas stripping overflows into a sedimentation tank, and after multi-stage static sedimentation, the oil phase after demulsification automatically floats to the upper layer, and finally the oil phase enters an oil phase collection tank and is finally distilled and recycled. During the recycling, mixed pentene and related heavy components (C5+ components) can be extracted. The lower waste alkali liquid layer after separation is bright yellow, and meets the biochemical treatment conditions through analysis, and can be directly transported to a sewage treatment station for biochemical treatment. When using the waste alkali liquid treatment system disclosed by the invention to treat the waste alkali liquid, the initial equipment investment cost is about 300,000 yuan, and the construction cost is less than 300,000 yuan when the treatment is carried out in the later stage, so the total cost is less than 500,000 yuan. When treating the same amount of waste alkali liquid by incineration method, not only fuel is consumed, but also supporting VOCs (volatile organic compounds) related facilities are required, and the cost is more than 10 million yuan. In summary, the waste alkali liquid treatment system of the invention can effectively reduce the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of a waste alkali solution treatment system of the present invention;

[0026] Figure 2 The present invention is a schematic structural diagram of an upper air lift distributor in a waste alkali solution treatment system.

[0027] In the figure, 1. air lift tank, 2. sedimentation tank, 3. first overflow hole, 4. guide hole, 5. guide pipe, 6. oil phase collection tank, 7. drain pipe, 8. second overflow hole, 9. air lift distributor, 10. main pipeline, 11. branch pipeline, 12. flash tank. DETAILED DESCRIPTION

[0028] The present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection solution of the present invention.

[0029] A large amount of gas produced by coal-to-olefins needs to be refined after alkali washing. This process will produce and discharge high-concentration alkaline waste liquid, which is a special organic waste liquid with high salt content, toxicity and difficulty in degradation. The waste alkali liquid has the characteristics of strong alkalinity, high COD (chemical oxygen demand) and high oil content. It mainly contains a small amount of inorganic salts such as sodium carbonate and sodium hydroxide produced in the alkali washing process and a large amount of organic matter such as aldehydes and ketones. At the same time, there is also oil-in-water emulsion butter in the waste alkali liquid, with a pH value greater than 12, which must be treated before it can be discharged. The treatment of waste alkali liquid in the coal-to-olefin industry has always been a problem that has plagued enterprises. Waste alkali liquid cannot be directly discharged into sewage stations for biochemical treatment.

[0030] At present, the most common industrial treatment method is incineration. During the incineration method, the waste alkali liquid is first pretreated, and then the pretreated waste alkali liquid is transported to the incinerator. In order to maintain high-temperature combustion during incineration, the incinerator usually requires fuel supply, such as natural gas, fuel oil or other combustibles. The exhaust gas after incineration still needs to be equipped with environmental protection facilities such as desulfurization and denitrification to ensure that the exhaust gas meets the emission standards. This treatment method requires a large amount of fuel when incinerating the waste alkali liquid, so this waste alkali liquid treatment method has a large investment and high cost.

[0031] A waste alkali solution treatment system, such as Figure 1 As shown, it includes: an air stripping tank 1, a plurality of sedimentation tanks 2 arranged adjacent to each other in sequence, an oil phase collecting tank 6 and a drainage pipe 7, wherein a liquid inlet is arranged at the bottom of the air stripping tank 1; two adjacent sedimentation tanks 2 are connected through a first overflow hole 3, wherein the first sedimentation tank 2 is adjacent to the air stripping tank 1 and the two are connected through a guide hole 4, and a small-aperture filter is arranged on the guide hole 4, and the turbulence degree of the waste alkali liquid entering the first sedimentation tank is reduced by the filter; the oil phase collecting tank 6 is arranged on one side of the sedimentation tank 2, and the oil phase collecting tank 6 and the top of the sedimentation tank 2 are connected through a guide pipe 5; the bottoms of the air stripping tank 1 and the sedimentation tank 2 are both connected with a drainage pipe 7, and a flash tank 12 is also arranged on one side of the air stripping tank 1, and the liquid outlet of the flash tank 12 is connected to the liquid inlet of the air stripping tank 1.

[0032] The waste alkali liquid treatment system disclosed in the present invention first introduces a large amount of free carbon dioxide into the gas stripping tank 1 for neutralization and gas stripping when treating the waste alkali liquid. During the gas stripping process, an appropriate amount of polyaluminium chloride PAC can be added to the gas stripping tank 1. The polyaluminium chloride is a yellow or light yellow solid powder. During the hydrolysis process, physical and chemical processes such as coagulation, adsorption and precipitation occur. In the turbulent state of the gas stripping tank 1, the hydrolysis of PAC is more favorable, and the demulsified oil phase is polymerized to form macromolecules floating on the upper layer; the waste alkali liquid after gas stripping overflows to the sedimentation tank, undergoes multi-stage static sedimentation, and through the addition of agents, fillers and other processes, the demulsified oil phase will automatically float to the upper layer, and finally the oil phase enters the oil phase collection tank. The waste alkali liquid is treated in the distillation tower for recycling, during which the mixed pentene and related heavy components (C5+ components) can be extracted; the lower waste alkali liquid layer after separation is bright yellow, and the biochemical treatment conditions are met through analysis, and it can be directly transported to the sewage treatment station for biochemical treatment; when using the waste alkali liquid treatment system disclosed in the present invention to treat the waste alkali liquid, the initial equipment investment cost is about 300,000 yuan, and the construction cost is less than 200,000 yuan in the later treatment, so the total cost is less than 500,000 yuan; the incineration method not only consumes fuel when treating the same amount of waste alkali liquid, but also requires supporting VOCs related facilities, and the cost is more than 10 million yuan. In summary, the waste alkali liquid treatment system of the present invention can effectively reduce costs.

[0033] The waste alkali liquid after gas lift overflows to multiple sedimentation tanks for sedimentation in turn. The sedimentation is mainly achieved by the static stratification of the oil phase and the water phase, so a longer static stratification time is required. In order to extend the stratification time, each sedimentation tank directly adopts a diversion design at different positions, that is, two adjacent first overflow holes 3 are respectively arranged on the upper side or the lower side of the sedimentation tank, so that the oil phase and the water phase have enough time to stratify. The sedimentation time is determined by the feed amount of the gas lift liquid separation tank and the design size of the tank. The smaller the feed amount and the larger the sedimentation tank, the longer the sedimentation time; there are four sedimentation tanks 2 in this embodiment, and the volume of the second sedimentation tank 2 is the largest. A certain amount of filler (ball ring) is added to the second sedimentation tank 2. The addition of filler can increase the standing time of water and oil and enhance the separation effect; the waste alkali liquid after gas lift is subjected to multi-stage static sedimentation through different diversion paths, so that the demulsified oil phase floats to the upper layer.

[0034] Furthermore, the oil phase collecting tanks 6 disclosed in the present embodiment are provided with two, the two oil phase collecting tanks 6 are arranged adjacent to each other and are connected through the second overflow hole 8, the top of one of the oil phase collecting tanks 6 is connected to the multiple sedimentation tanks 2 through the guide pipe 5, and the bottom of the other oil phase collecting tank 6 is provided with a centrifugal pump, and the liquid outlet of the centrifugal pump is connected to the distillation recycling device. The two oil phase collecting tanks 6 are provided because the oil phase entering the first oil phase collecting tank 6 through the guide pipe 5 will inevitably carry a part of water, and after the oil phase and water entering the first oil phase collecting tank 6 are allowed to stand and separate in the first oil phase collecting tank 6, the oil phase enters the second oil phase collecting tank 6 from the second overflow hole 8 at the top, and the water phase remains in the first oil phase collecting tank 6, and the bottom of the first oil phase collecting tank 6 is also connected with a drain pipe 7, so that the purity of the oil phase in the second oil phase collecting tank 6 can be ensured to be high.

[0035] like Figure 2 As shown, in order to allow the carbon dioxide gas to fully contact with the waste alkali liquid, a tree-shaped gas stripping distributor 9 is provided at the top of the notch of the gas stripping tank 1 disclosed in this embodiment. The gas stripping distributor 9 includes a main pipeline 10 horizontally arranged at the top of the notch of the gas stripping tank 1. The main pipeline 10 is arranged along the length direction of the gas stripping tank 1. A plurality of branch pipelines 11 are arranged downwardly inclined on the main pipeline 10, and each branch pipeline is provided with a plurality of air outlets. The angle between the center line of the branch pipeline 11 and the main pipeline 10 is 40°-45°. The specific main pipe is DN40, the branch pipe is DN25, and each branch pipe has about 8 openings with an aperture of about 6mm. After the carbon dioxide gas enters the gas stripping distributor, it is discharged from the aperture of each branch pipe, presenting a uniformly distributed, downward airflow, so that the carbon dioxide can fully contact with the waste alkali liquid.

[0036] The waste alkali liquid treatment system of the present invention adopts the acid-base neutralization method to treat the waste alkali liquid in combination with the company's own characteristics. A large amount of cost-free carbon dioxide is introduced into the waste alkali liquid for neutralization and gas stripping, so that the pH value is maintained at neutral or weak alkaline. In this environment, aldehydes, ketones and other organic substances are not prone to hydroxyaldehyde condensation; a large amount of emulsified oil phase is demulsified under the action of gas stripping and floats on the upper layer. At the same time, saturated hydrocarbons in the waste alkali liquid can also be gas stripped out, so that it is close to or reaches the VOCs emission standard.

[0037] The waste alkali liquid after gas stripping overflows into the sedimentation tank, and after multi-stage static sedimentation and through the addition of reagents, fillers and other processes, the oil phase after demulsification will automatically float to the upper layer and be sent to the distillation tower for re-refining to extract the C5+ components; the lower layer of waste alkali liquid after separation is bright yellow, and through analysis, it meets the biochemical treatment conditions and is transported to the sewage treatment station for biochemical treatment.

[0038] When the waste alkali liquid enters the gas stripping tank 1 from the bottom of the flash tank 12, four purposes are achieved at the same time: (1) it reacts with the large amount of free carbon dioxide from the company's purification device to neutralize it. The carbon dioxide is fully in contact with the waste alkali liquid through the tree-shaped gas stripping distributor, which can reduce its pH to about 7-8; (2) in this environment, aldehydes, ketones and other organic substances are not easy to undergo hydroxyaldehyde condensation, that is, it is not easy to generate red oil; (3) and a large amount of emulsified oil phase is demulsified under the action of a large amount of gas stripping; (4) adding an appropriate amount of polyaluminium chloride to the turbulent state of the gas stripping tank 1 helps small molecules of oil phase to synthesize large molecules and float to the upper layer of the liquid separation tank; (4) at the same time, the saturated hydrocarbons mixed in the waste alkali liquid can also be gas stripped out to reduce the enrichment of hydrocarbons in the closed space.

[0039] The waste alkali liquid after gas lift enters the sedimentation tank 2 through the diversion hole for sedimentation. A small-aperture filter is added to the diversion hole to reduce the turbulence of the waste alkali liquid entering the sedimentation tank 2. When the first sedimentation tank is full of liquid, it overflows from the top to the second sedimentation tank. The second sedimentation tank is equipped with a ball ring to increase the standing time of water and oil and enhance the separation effect. Then, multi-stage static precipitation is carried out through different diversion paths to make the demulsified oil phase float to the upper layer. The upper oil phase floating in each sedimentation tank is finally transported to the oil phase collection tank for collection after a period of enrichment, and then transported to the debutanizer by the centrifugal pump at the bottom of the oil phase collection tank for rectification and refining to extract the C5+ component; the waste alkali liquid discharged from the bottom of each sedimentation tank is finally collected in a pipeline. It is bright yellow and meets the biochemical treatment conditions, and is uniformly transported to the sewage treatment station for biochemical treatment.

[0040] After a period of time, some of the condensed red oil will float on the top of the 7# tank. The upper layer of red oil will be collected into a ton barrel through the scraper plate and sent out for hazardous waste treatment.

[0041] A waste alkali solution treatment process, based on a waste alkali solution treatment system disclosed above, specifically comprises the following steps:

[0042] The waste alkali liquid is transferred to the stripping tank 1 through the flash tank 12, and excess carbon dioxide is introduced into the stripping tank 1 through the stripping distributor 9 for neutralization reaction, so that the pH value of the neutralized solution is reduced to 7-8. During the stripping process, an appropriate amount of waste alkali liquid neutralized by polyaluminium chloride PAC can be added to the stripping tank 1, and then the waste alkali liquid after stripping overflows to multiple sedimentation tanks, and after multi-stage static precipitation, and by adding agents, fillers and other processes, the oil phase after demulsification will automatically float to the upper layer;

[0043] The oil phase in the upper layer of the sedimentation tank 2 flows to the oil phase collection tank 6 through the guide pipe 5;

[0044] The heavy oil phase in the oil phase collection tank 6 is transported to the distillation refining device through a centrifugal pump to extract the C5+ component (mixed pentene and related heavy components). After a period of time, part of the condensed red oil will float on the upper part of the oil phase collection tank 6. The upper red oil is collected into a ton barrel through a scraper plate and sent out for hazardous waste treatment.

[0045] The liquid in the drain pipe 7 is led out for unified biochemical treatment.

[0046] The waste alkali liquid treated by this method meets the conditions for biochemical treatment and is sent to the company's existing sewage treatment system without causing other impacts on the sewage treatment system.

[0047] The invention discloses a waste alkali solution treatment process, which can effectively replace the incineration treatment method, and has the characteristics of single material consumption source, strong industrial feasibility, low cost, simple process flow and convenient operation;

[0048] The invention discloses a waste alkali solution treatment process, wherein the oil phase separated by gas stripping can be distilled and recycled to extract C5+, thereby increasing the added value of the product;

[0049] The invention discloses a waste alkali solution treatment process, CO 2 The large-scale consumption also reduces the company's total "carbon emissions", which is in line with the requirements of relevant national policies.

[0050] The embodiments described above are only preferred specific implementation methods of the present invention, and the protection scope of the present invention is not limited thereto. Any simple changes or equivalent replacements of the technical solutions that can be obviously obtained by any technician familiar with the field within the technical scope disclosed in the present invention belong to the protection scope of the present invention.

Claims

1. A waste alkali solution treatment system, characterized in that: include: An air stripping tank (1), wherein a liquid inlet is provided at the bottom of the air stripping tank (1); A plurality of sedimentation tanks (2) are arranged adjacent to each other in sequence, wherein two adjacent sedimentation tanks (2) are connected via a first overflow hole (3), wherein the first sedimentation tank (2) is adjacent to the gas stripping tank (1) and the two are connected via a guide hole (4); An oil phase collecting tank (6) is arranged on one side of the sedimentation tank (2), and the oil phase collecting tank (6) and the top of the sedimentation tank (2) are connected via a flow guide pipe (5); A liquid discharge pipe (7), the bottoms of the gas stripping tank (1) and the sedimentation tank (2) are connected with a liquid discharge pipe (7).

2. A waste alkali solution treatment system according to claim 1, characterized in that: Two oil phase collecting tanks (6) are provided, the two oil phase collecting tanks (6) are arranged adjacent to each other and are connected via a second overflow hole (8), the top of one of the oil phase collecting tanks (6) is connected to the plurality of sedimentation tanks (2) via the guide pipe (5), and a centrifugal pump is provided at the bottom of the other oil phase collecting tank (6), and the liquid outlet of the centrifugal pump is connected to a distillation recycling device.

3. A waste alkali solution treatment system according to claim 2, characterized in that: A flash tank (12) is also provided on one side of the gas stripping tank (1), and a liquid outlet of the flash tank (12) is connected to a liquid inlet of the gas stripping tank (1).

4. A waste alkali solution treatment system according to claim 3, characterized in that: A tree-shaped air stripping distributor (9) is arranged at the top of the slot of the air stripping tank (1), and the air stripping distributor (9) comprises a main pipeline (10) horizontally arranged at the top of the slot of the air stripping tank (1), the main pipeline (10) is arranged along the length direction of the air stripping tank (1), and a plurality of branch pipelines (11) are arranged on the main pipeline (10) in a downwardly inclined manner, and each branch pipeline is provided with a plurality of air outlet holes.

5. A waste alkali solution treatment system according to claim 4, characterized in that: The angle between the center line of the branch pipeline (11) and the main pipeline (10) is 40°-45°.

6. A waste alkali solution treatment system according to claim 1, characterized in that: Four sedimentation tanks (2) are provided, and a ball ring is provided in the second sedimentation tank (2).

7. A waste alkali solution treatment system according to claim 1, characterized in that: A filter screen is arranged on the guide hole (4).

8. A waste alkali solution treatment process, based on a waste alkali solution treatment system disclosed in claim 1 above, characterized in that: The specific steps include: The waste alkali solution is transferred to the stripping tank (1), and carbon dioxide is introduced into the stripping tank (1) for neutralization reaction, so that the pH value of the neutralized solution is reduced to neutral or weakly acidic; The waste alkali liquid after gas stripping overflows to multiple sedimentation tanks, and after multi-stage static sedimentation, the oil phase after demulsification is separated to the upper layer; The oil phase in the upper layer of the sedimentation tank (2) is transferred to the oil phase collection tank (6) through the flow guide pipe (5); Refining the oil phase in the oil phase collection tank (6); The liquid in the drainage pipe (7) is discharged and uniformly subjected to biochemical treatment.

9. A waste alkali solution treatment process according to claim 8, characterized in that: After the liquid is introduced into the stripping tank (1), polyaluminium chloride is added into the stripping tank (1) at the same time.

10. A waste alkali solution treatment process according to claim 8, characterized in that: The pH value of the solution after neutralization is 7-8.

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