A device and method for pretreatment and oil recovery of semi-coke wastewater

Abstract

This invention discloses an oil recovery device and method for pretreatment of semi-coke wastewater. The device includes a raw water settling tank, a light oil collection port, a first isolation manual valve, an electric two-position valve, an oil collection pipeline, a first oil collection main pipe, a pipe sight glass, a second isolation manual valve, a remote interface gauge, a third isolation manual valve, a light oil collection tank, a discharge pipeline, a nitrogen purging valve, a discharge drain valve, an inner tank light oil removal pipeline, a semi-coke wastewater inlet pipeline, a semi-coke wastewater outlet, a sewage tank, a sewage discharge pipe, a remote level gauge, a nitrogen purging pipeline, an oil removal main pipe, a second oil collection main pipe, and a DCS (Distributed Control System). The outer tank is equipped with several light oil collection ports. Different heights of light oil collection ports are selected based on the liquid level in the outer tank for oil collection, ensuring that the oil content of the semi-coke wastewater from the phenol and ammonia recovery unit meets the requirements. This method achieves effective recovery of light oil from the outer tank in the semi-coke wastewater tank-in-tank oil removal technology, with high oil recovery efficiency, ensuring controllable water quality and oil content in the outer tank effluent, and is safe and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of coal chemical wastewater, specifically a pretreatment oil recovery device and method for semi-coke wastewater. Background Technology

[0002] Semi-coke wastewater is generated during the low-temperature carbonization (500~650℃) of coal, mainly originating from the circulating water used for cooling and washing coal gas and the separation water from the chemical production process. Semi-coke is a product of low-temperature carbonization of coal, and its production process produces a large amount of tar and low-molecular-weight organic matter. Therefore, the wastewater contains a large amount of pollutants that have not been oxidized at high temperatures, with a concentration about 10 times higher than that of conventional coking wastewater. In particular, the content of oil pollutants (i.e., coal tar) is higher, and the oil / phenol ratio in the pollutants is significantly higher than that in conventional coking wastewater.

[0003] Currently, industrial semi-coke wastewater treatment systems mainly consist of two parts: pretreatment (oil removal section + phenol and ammonia recovery section) and biochemical treatment. Existing semi-coke wastewater, after oil removal and dust removal in the oil removal section, has an oil content of less than 1000 mg / L before entering the phenol and ammonia recovery section for further pretreatment. From actual operation, the combination of raw water tank sedimentation separation, type III hydrocyclone separation technology (i.e., tank-in-tank oil removal technology), and coalescing oil separator technology is the most effective oil removal method. However, in actual operation, the tank-in-tank oil removal technology only considers the removal of light and heavy oil in the inner tank, while the outer tank oil removal has certain drawbacks. The light oil separated on the water surface cannot be discharged, causing the oil to return to the wastewater, enter the phenol and ammonia recovery unit, and clog the trays and packing, affecting the extraction effect, resulting in substandard effluent, reduced unit operating cycle and production efficiency, and hindering long-term stable operation of the unit.

[0004] The literature with application number 202210582477.X discloses a method for adding heavy oil collection and transportation in phenol and ammonia recovery. It only talks about the heavy oil collection method and does not mention the method for removing light oil from the liquid surface of the outer tank. When the liquid level in the outer tank is high or low, the light oil on the water surface cannot be removed in time. Over time, the oil layer accumulates and thickens in the tank. When the liquid level in the outer tank is low or the water temperature is high (>50℃), the light oil enters the subsequent phenol and ammonia recovery unit with the raw water. After being stripped at high temperature in the deacidification and deammoniation tower, it enters the extraction unit and contaminates the extractant, affecting the extraction effect. Moreover, the oil quality changes after high temperature (similar to asphalt), clogging the trays and packing, reducing the separation efficiency of the unit, resulting in unqualified effluent indicators, and affecting the long-term stable operation of the unit. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is to provide an oil recovery device and method for the pretreatment of semi-coke wastewater.

[0006] The technical solution of the present invention to solve the technical problem of the aforementioned device is to provide a pretreatment oil recovery device for semi-coke wastewater, characterized in that the device includes a raw water settling tank, a light oil receiving port, a first isolation manual valve, an electric two-position valve, an oil receiving pipeline, a first oil receiving main pipe, a pipeline sight glass, a second isolation manual valve, a remote interface gauge, a third isolation manual valve, a light oil collection tank, a discharge pipeline, a nitrogen purging valve, a discharge drain valve, an inner tank light oil removal pipeline, a semi-coke wastewater inlet pipeline, a semi-coke wastewater outlet, a sewage tank, a sewage discharge pipe, a remote level gauge, a nitrogen purging pipeline, an oil removal main pipe, a second oil receiving main pipe, and a DCS;

[0007] The raw water settling tank consists of an outer tank and an inner tank. The inner tank is equipped with an oil removal device. The end of the semi-coke wastewater inlet pipeline is located in the oil removal device. The DCS is located in the central control room and is connected to an electric two-position valve, a remote interface gauge, and a remote level gauge. The outer tank is equipped with a remote level gauge, which is used by remote operators to observe the liquid level in the outer tank on the DCS. The semi-coke wastewater outlet is located at the bottom of the outer tank.

[0008] The outer tank has several light oil collection ports along its vertical height. Each light oil collection port is equipped with a remote interface gauge, allowing remote operators to observe the thickness of the light oil layer on the water surface in the outer tank via the DCS. Each light oil collection port is connected to the beginning of an oil collection pipeline. The ends of all oil collection pipelines converge into a first oil collection main pipe. The first oil collection main pipe is located next to the outer tank from top to bottom. Each horizontal oil collection pipeline is equipped with a first isolation manual valve and an electric two-position valve.

[0009] The first oil recovery manifold is connected to the end of the nitrogen purging line, which is equipped with a nitrogen purging valve. The end of the first oil recovery manifold is connected to the beginning of the second oil recovery manifold. According to the direction of liquid flow, the second oil recovery manifold is equipped with a pipe sight glass and a second isolation valve. On-site operators can monitor the purity of the light oil in the second oil recovery manifold more intuitively through the pipe sight glass and take timely measures to manually open and close the second isolation valve or remotely control the electric two-position valve through DCS to control the oil recovery quality.

[0010] A discharge drain valve is installed on the discharge pipeline, with its starting end connected to the lower middle part of the second oil collection main pipe. The connection point is located between the pipeline sight glass and the second isolation hand valve, and its end is connected to the sewage tank through the sewage discharge pipe. The inner tank is connected to the starting end of the deoiling main pipe through the inner tank light oil removal pipeline, and a third isolation hand valve is installed on the inner tank light oil removal pipeline. The end of the second oil collection main pipe is connected to the starting end of the deoiling main pipe. The end of the deoiling main pipe is connected to the light oil collection tank.

[0011] The technical solution of this invention to solve the aforementioned problem is to provide a method for pretreatment and oil recovery of semi-coke wastewater, characterized in that the method includes the following steps:

[0012] Step 1: The first isolation valve, the electric two-position valve, the second isolation valve, the third isolation valve, the nitrogen purging valve, and the discharge drain valve are all closed. The semi-coke wastewater enters the inner tank through the semi-coke wastewater inlet pipeline, where most of the oil and dust are removed using the tank-in-tank oil removal technology. The third isolation valve is opened, and the light oil in the inner tank enters the light oil collection tank through the inner tank light oil removal pipeline for normal collection. The semi-coke wastewater after oil and dust removal enters the outer tank, where the light oil floats on the surface after static sedimentation and separation, and the accumulation causes the light oil layer to continuously thicken.

[0013] Step 2: Select a suitable light oil inlet according to the liquid level height indicated by the remote level gauge, and then determine the thickness of the light oil layer on the water surface according to the interface indicated by the remote interface gauge at the selected light oil inlet.

[0014] Step 3: Before the outer tank collects oil, the inner tank should stop collecting oil, close the third isolation valve, and reduce the liquid level in the light oil collection tank to the minimum.

[0015] Step 4: When collecting oil from the outer tank, first open the first isolation hand valve, then open the electric two-position valve remotely via DCS, and finally open the second isolation hand valve and control the rate at which the liquid level in the light oil collection tank rises.

[0016] During the oil recovery process, the light oil fills the entire pipe sight glass. On-site operators visually observe the purity of the discharged light oil through the pipe sight glass. Based on the different purity of the discharged light oil during the oil recovery process, two working conditions are used for oil recovery:

[0017] Operating Condition 1: When the mass of water in the discharged light oil is less than 1 / 2 the diameter of the pipe sight glass, continue oil collection; when the liquid level in the light oil collection tank reaches the high level, the DCS remotely controls the closing of the electric two-position valve to stop oil collection; oil-water separation is carried out in the light oil collection tank, and after drainage, the qualified light oil is sent out of the boundary area, completing one light oil collection operation.

[0018] Operating Condition 2: When the mass of water in the discharged light oil is visually observed through the pipe sight glass to be at or above 1 / 2 the diameter of the pipe sight glass, the DCS remotely controls the closure of the electric two-position valve to stop oil collection; then the indication of the remote interface gauge is lowered to increase the thickness of the light oil layer. When the mass of water in the discharged light oil is visually observed through the pipe sight glass to be below 1 / 2 the diameter of the pipe sight glass, the DCS remotely controls the opening of the electric two-position valve to resume normal oil collection; when the liquid level in the light oil collection tank reaches the high level, the DCS remotely controls the closure of the electric two-position valve to stop oil collection; oil-water separation is performed in the light oil collection tank, and after drainage, the qualified light oil is sent out of the boundary area, completing one light oil collection operation;

[0019] Step 5: Repeat step 4. When it is visually observed through the pipe sight glass that all the discharged light oil is water, immediately close the second isolation valve manually and the DCS remote control to close the electric two-position valve to stop oil collection. Then open the discharge drain valve to discharge the water in the first and second oil collection mains to the sewage tank through the discharge pipeline and the sewage drain pipe. After all the water in the first and second oil collection mains has been drained, close the discharge drain valve.

[0020] Step 6: Open the second isolation valve and the nitrogen purging valve to purge all the residual oil in the first and second oil collection pipes into the light oil collection tank until the liquid level in the light oil collection tank stabilizes; then close the nitrogen purging valve to stop purging; then close the second isolation valve to end purging.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The outer tank of the present invention is provided with several light oil collection ports. The light oil collection ports of different heights are selected according to the liquid level of the outer tank for oil collection. The light oil on the water surface is discharged through the oil collection pipeline, the first oil collection main pipe and the second oil collection main pipe according to the liquid level height of the outer tank and the oil layer thickness, so as to ensure that the oil content of the semi-coke wastewater of the phenol and ammonia recovery device is qualified (oil content is less than 1000mg / L).

[0023] (2) The switching signal and electrical signal of the electric two-position valve of the present invention are introduced into DCS to realize remote control. The electric two-position valve is opened remotely to discharge the light oil on the water surface to the underground light oil collection tank with mature design, so as to further separate the oil and water and recover valuable substances, namely light oil, to generate benefits. At the same time, the automation level of the oil collection device is improved and the labor intensity of the operator is reduced.

[0024] (3) The present invention is equipped with an oil collection system heating device to ensure that the discharged light oil can smoothly enter the light oil collection tank and prevent the oil from solidifying and sticking to the wall and clogging the pipeline and valve when the oil is at low temperature.

[0025] (4) A pipe sight glass is provided on the second oil collection main pipe of the present invention to facilitate on-site operators to monitor the purity of the extracted light oil online and prevent the semi-coke wastewater in the outer tank from entering the light oil collection tank and reducing the oil collection quality.

[0026] (5) The outer tank of the present invention is equipped with several remote interface meters. The interface indication signal is introduced into the DCS to realize remote monitoring of the thickness of the light oil layer on the liquid surface of the outer tank. The interface is raised and lowered in time according to the thickness of the light oil layer to improve the removal efficiency of light oil. It prevents the light oil layer from being too thick and entering the subsequent phenol and ammonia recovery device with the semi-coke wastewater, contaminating the extractant, clogging the equipment and packing, affecting the long-term stable operation of the device, or the light oil layer being too thin and the collected light oil is water-laden, resulting in a decrease in the quality of oil collection. At the same time, it reduces the workload of operators to frequently climb the tank to open the valve to discharge and confirm the purity of the light oil.

[0027] (6) The present invention uses a nitrogen purging valve and a nitrogen purging pipeline to purge and unclog the first and second oil collection main pipes, preventing long-term oil accumulation and adhesion to the wall, which would reduce the pipe diameter and affect the oil collection effect; at the same time, it provides a convenient nitrogen purging and replacement gas source for process isolation during equipment maintenance, so that no additional nitrogen replacement gas source is required.

[0028] (7) The outer tank of the present invention is equipped with a remote liquid level gauge, and the liquid level indication signal is introduced into the DCS to realize remote monitoring of the liquid level height in the outer tank. The nearest light oil de-oiling port is selected for de-oiling according to the liquid level indication height of the outer tank.

[0029] (8) This invention realizes the effective recovery of light oil in the outer tank of the semi-coke wastewater tank-in-tank oil removal technology. It has high oil recovery efficiency, saves manpower and material resources, and ensures that the water quality and oil content of the outer tank are controllable. It is both safe and environmentally friendly. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of the device of the present invention.

[0031] In the diagram, the components are: outer tank 1, inner tank 2, light oil receiving port 3, first isolation hand valve 4, electric two-position valve 5, oil receiving pipeline 6, first oil receiving main pipe 7, pipeline sight glass 8, second isolation hand valve 9, remote interface gauge 10, third isolation hand valve 11, light oil collection tank 12, discharge pipeline 13, nitrogen purging valve 14, discharge drain valve 15, inner tank light oil removal pipeline 16, semi-coke wastewater inlet pipeline 17, semi-coke wastewater outlet 18, sewage tank 19, sewage discharge pipe 20, remote level gauge 21, nitrogen purging pipeline 22, oil removal main pipe 23, and second oil receiving main pipe 24. Detailed Implementation

[0032] Specific embodiments of the present invention are given below. These specific embodiments are only used to further illustrate the present invention in detail and do not limit the scope of protection of the present invention.

[0033] This invention provides a pretreatment oil recovery device for semi-coke wastewater (hereinafter referred to as the device), characterized in that the device includes a raw water settling tank with tank-in-tank oil removal technology, a light oil receiving port 3, a first isolation manual valve 4, an electric two-position valve 5, an oil receiving pipeline 6, a first oil receiving main pipe 7, a pipeline sight glass 8, a second isolation manual valve 9, a remote interface gauge 10, a third isolation manual valve 11, a light oil collection tank 12, a discharge pipeline 13, a nitrogen purging valve 14, a discharge drain valve 15, an inner tank light oil removal pipeline 16, a semi-coke wastewater inlet pipeline 17, a semi-coke wastewater outlet 18, a sewage tank 19, a sewage discharge pipe 20, a remote level gauge 21, a nitrogen purging pipeline 22, an oil removal main pipe 23, a second oil receiving main pipe 24, and a DCS (Distributed Control System);

[0034] The raw water settling tank consists of an outer tank 1 and an inner tank 2. The inner tank 2 is equipped with an oil removal device. The end of the semi-coke wastewater inlet pipeline 17 is located in the oil removal device. The DCS is located in the central control room and is connected to the electric two-position valve 5, the remote interface gauge 10, and the remote level gauge 21. The outer tank 1 is equipped with a remote level gauge 21, which is used by remote operators to observe the liquid level height (i.e., the total liquid level height of water and light oil) of the outer tank 1 on the DCS screen. The lower part of the outer tank 1 is equipped with a semi-coke wastewater outlet 18.

[0035] The outer tank 1 has several (preferably at least three, more preferably three) light oil collection ports 3 along the vertical height direction; each light oil collection port 3 is equipped with a remote interface meter 10, which is used for remote operators to observe the thickness of the light oil layer on the water surface in the outer tank 1 on the DCS screen; each light oil collection port 3 is connected to the beginning of an oil collection pipeline 6; the ends of all oil collection pipelines 6 converge to the first oil collection main pipe 7; the first oil collection main pipe 7 is arranged from top to bottom next to the outer tank 1; each horizontal pipeline of the oil collection pipeline 6 is equipped with a first isolation hand valve 4 and an electric two-position valve 5;

[0036] The beginning of the first oil recovery main pipe 7 is connected to the end of the nitrogen purging line 22, and a nitrogen purging valve 14 is installed on the nitrogen purging line 22; the end of the first oil recovery main pipe 7 is connected to the beginning of the second oil recovery main pipe 24; according to the liquid flow direction, a pipe sight glass 8 and a second isolation valve 9 are installed on the second oil recovery main pipe 24 in sequence. The on-site operator can more intuitively monitor the purity of the light oil in the second oil recovery main pipe 24 through the pipe sight glass 8, and take timely measures to manually open and close the second isolation valve 9 or remotely control the electric two-position valve 5 through DCS to control the oil recovery quality;

[0037] A discharge drain valve 15 is installed on the discharge pipeline 13. The beginning end is connected to the lower middle part of the second oil collection main pipe 24. The connection point is located between the pipeline sight glass 8 and the second isolation hand valve 9, and close to the second isolation hand valve 9. The end end is connected to the sewage tank 19 through the sewage discharge pipe 20, which facilitates the isolation and drainage of the residual medium in the first oil collection main pipe 7 and the second oil collection main pipe 24. The sealed setting allows for centralized collection and treatment, preventing the oil odor from spreading and polluting the environment during the isolation discharge process of the unit maintenance. The inner tank 2 is connected to the beginning end of the deoiling main pipe 23 through the inner tank light oil removal pipeline 16. A third isolation hand valve 11 is installed on the inner tank light oil removal pipeline 16. The end of the second oil collection main pipe 24 is connected to the beginning end of the deoiling main pipe 23. The end of the deoiling main pipe 23 is connected to the light oil collection tank 12.

[0038] Preferably, several light oil receiving ports 3 at different heights are evenly distributed on the tank body of the outer tank 1 along the vertical height direction; the positions of the uppermost and lowermost light oil receiving ports 3 are fixed, and multiple light oil receiving ports 3 in the middle part are set as needed; in this embodiment, the uppermost light oil receiving port 3 is level with the position of the high liquid level control (i.e., the highest limit of the liquid level operation parameter 80%) of the outer tank 1, and the lowermost light oil receiving port 3 is set at an elevation of 5 meters of the outer tank 1 and is located above the semi-coke wastewater outlet 18.

[0039] Preferably, the negative pressure side interface of each remote interface meter 10 is located at the same elevation as the corresponding light oil receiving port 3.

[0040] Preferably, the first oil collection main pipe 7 is vertically arranged next to the outer tank 1, and the second oil collection main pipe 24 is inclined. The angle between the first oil collection main pipe 7 and the second oil collection main pipe 24 in the same vertical plane is ≥90° and <180°, which is conducive to the light oil discharged from the outer tank 1 flowing smoothly into the light oil collection tank 12 by gravity in the pipeline, reducing the difficulty of oil collection.

[0041] Preferably, in accordance with the direction of liquid flow, each horizontal pipeline of the oil receiving line 6 is sequentially equipped with a first isolation hand valve 4 and an electric two-position valve 5, with the first isolation hand valve 4 as close as possible to the light oil receiving port 3.

[0042] Preferably, the end of the nitrogen purging line 22 is higher than the uppermost light oil receiving port 3; the nitrogen purging valve 14 is located near the first oil receiving main pipe 7.

[0043] Preferably, the connection between the discharge line 13 and the second oil return main 24 is located at the lowest point before the second isolation hand valve 9 on the second oil return main 24.

[0044] Preferably, the third isolation hand valve 11 is located as close as possible to the connection between the second oil receiving manifold 24 and the oil removing manifold 23.

[0045] Preferably, the switching and electrical signals of the electric two-position valve 5 are introduced into the DCS to realize remote control; the liquid level indication signal of the remote level gauge 21 is introduced into the DCS to realize remote monitoring of the liquid level height of the outer tank 1; and the interface indication signal of the remote interface gauge 10 is introduced into the DCS to realize remote monitoring of the thickness of the light oil layer on the water surface of the outer tank 1.

[0046] Preferably, the diameter of the light oil receiving port 3 is DN50, the diameter of the oil receiving pipeline 6 is DN50, the diameter of the first oil receiving main pipe 7 is DN80, the diameter of the discharge pipeline 13 is DN25, the diameter of the nitrogen purging pipeline 22 is DN25, and the diameter of the second oil receiving main pipe 24 is DN80.

[0047] Preferably, the first isolation hand valve 4, the electric two-position valve 5, the oil collection pipeline 6, the first oil collection main pipe 7, the pipeline sight glass 8, the second isolation hand valve 9, the remote interface gauge 10, the third isolation hand valve 11, the light oil collection tank 12, the discharge pipeline 13, the discharge drain valve 15, the inner tank light oil removal pipeline 16, the sewage discharge pipe 20, the remote level gauge 21, the oil removal main pipe 23, and the second oil collection main pipe 24 are all equipped with oil collection system heating devices to prevent oil from solidifying and sticking to the walls and clogging the pipelines and valves at low temperatures, and to ensure normal operation according to the outdoor temperature.

[0048] Preferably, the remote interface gauge 10 is a dual-flange remote interface gauge, and the remote level gauge 21 is a dual-flange remote level gauge.

[0049] Preferably, the first isolation hand valve 4, the second isolation hand valve 9, the third isolation hand valve 11, the nitrogen purging valve 14, and the discharge drain valve 15 are all gate valves, and the electric two-position valve 5 is an electric ball valve.

[0050] This invention also provides a method for oil recovery from pretreated semi-coke wastewater based on a semi-coke wastewater pretreatment and oil recovery device (hereinafter referred to as the method), characterized in that the method includes the following steps:

[0051] Step 1: The first isolation valve 4, the electric two-position valve 5, the second isolation valve 9, the third isolation valve 11, the nitrogen purging valve 14, and the discharge drain valve 15 are all closed. The semi-coke wastewater with a temperature of 37~45℃ enters the inner tank 2 through the semi-coke wastewater inlet pipeline 17. Most of the oil and dust are removed in the inner tank 2 through the tank-in-tank oil removal technology. The light oil in the inner tank 2 is removed through a well-designed process route, that is, the third isolation valve 11 is opened, and the light oil in the inner tank 2 enters the light oil collection tank 12 through the inner tank light oil removal pipeline 16 for normal collection. The semi-coke wastewater after oil and dust removal enters the outer tank 1. The semi-coke wastewater entering the outer tank 1 still contains a large amount of dissolved and entrained oil. After static sedimentation and separation, the light oil floats on the water surface. The accumulation over a long period of time causes the light oil layer to continuously thicken.

[0052] Preferably, in step 1, the temperature of the semi-coke wastewater entering the outer tank 1 is controlled at 37~45℃ to reduce the solubility of oil in the wastewater and improve the oil-water separation effect and oil recovery rate.

[0053] Step 2: Select a suitable light oil inlet 3 according to the liquid level height indicated by the remote level gauge 21, and then determine the thickness of the light oil layer on the water surface according to the interface indicated by the remote interface gauge 10 at the selected light oil inlet 3.

[0054] Preferably, in step 2, under normal circumstances, when the remote level gauge 21 maintains a high level (i.e., 75-80% of the total height of the outer tank 1) during operation, the uppermost light oil receiving port 3 is used to collect oil. When the level of the outer tank 1 is lower than the high level control or when the raw water settling tank is under maintenance and drained, the middle part and the lowermost light oil receiving port 3 are selected to collect oil.

[0055] Step 3: Before the outer tank 1 collects oil, the inner tank 2 stops collecting oil, closes the third isolation valve 11, and lowers the liquid level of the light oil collection tank 12 to the minimum.

[0056] Step 4: When receiving oil from outer tank 1, first open the first isolation hand valve 4, then open the electric two-position valve 5 remotely via DCS, and finally slowly open the second isolation hand valve 9 and control the rate of increase of the liquid level in light oil collection tank 12.

[0057] During the oil recovery process, the light oil fills the entire pipe sight glass 8. On-site operators visually observe the purity of the discharged light oil through the pipe sight glass 8. Based on the different purity of the discharged light oil during the oil recovery process, two working conditions are used for oil recovery:

[0058] Operating Condition 1: When it is visually observed through the pipe sight glass 8 that the mass of water in the discharged light oil is less than 1 / 2 of the diameter of the pipe sight glass 8 (Note: water is at the bottom and light oil is at the top inside the pipe sight glass 8), continue to slowly collect the oil; when the liquid level in the light oil collection tank 12 reaches the high level (i.e., 75~80% of the total height of the light oil collection tank 12), the DCS remotely controls the closing of the electric two-position valve 5 to stop collecting the oil; oil and water are separated in the light oil collection tank 12, and after drainage, the qualified light oil is sent out of the boundary area for recycling and sale to generate benefits, thus completing one light oil collection operation;

[0059] Operating Condition 2: When the mass of water in the discharged light oil is visually observed through the pipe sight glass 8 to be at or above 1 / 2 the diameter of the pipe sight glass 8, the DCS remotely controls the closure of the electric two-position valve 5 to stop oil collection; then the indication of the remote interface gauge 10 is lowered to increase the thickness of the light oil layer. When the mass of water in the discharged light oil is visually observed through the pipe sight glass 8 to be below 1 / 2 the diameter of the pipe sight glass 8, the DCS remotely controls the opening of the electric two-position valve 5 to resume normal oil collection; when the liquid level in the light oil collection tank 12 reaches the high level, the DCS remotely controls the closure of the electric two-position valve 5 to stop oil collection; oil-water separation is performed in the light oil collection tank 12, and after drainage, the qualified light oil (the water content of the collected light oil is controlled below 4wt% to be qualified) is sent out of the boundary area for recycling and sale to generate benefits, completing one light oil collection operation;

[0060] Preferably, in step 4, if a malfunction occurs during the oil recovery process and equipment maintenance is required, the system is drained and purged in sequence, then the equipment is maintained, and the oil recovery process continues after the maintenance is completed.

[0061] The specific process of draining is as follows: manually close the second isolation valve 9 on site and remotely close the electric two-position valve 5 via DCS control, open the drain valve 15, and discharge the oil in the first oil collection main pipe 7 and the second oil collection main pipe 24 to the sewage tank 19 through the discharge pipeline 13 and the sewage discharge pipe 20.

[0062] The purging process is as follows: After all the oil in the first oil collection manifold 7 and the second oil collection manifold 24 has been drained, the nitrogen purging valve 14 is opened to purge the remaining oil in the first oil collection manifold 7 and the second oil collection manifold 24 into the sewage tank 19 through the discharge pipeline 13 and the sewage discharge pipe 20 until the liquid level in the sewage tank 19 is stable; then the nitrogen purging valve 14 is closed to stop the purging; then the discharge drain valve 15 is closed to end the purging process.

[0063] Step 5: Repeat step 4. When it is visually observed through the pipe sight glass 8 that the discharged light oil is entirely water within the entire range of the pipe sight glass 8 (i.e., all the light oil in the outer tank 1 has been collected), immediately close the second isolation hand valve 9 manually and the DCS remote control closed electric two-position valve 5 to stop oil collection and prevent discharge into the light oil collection tank 12 to ensure the purity of the light oil in the light oil collection tank 12; then open the discharge drain valve 15 to discharge the water in the first oil collection main pipe 7 and the second oil collection main pipe 24 to the sewage tank 19 through the discharge pipeline 13 and the sewage discharge pipe 20; after all the water in the first oil collection main pipe 7 and the second oil collection main pipe 24 has been drained, close the discharge drain valve 15; this condition indicates that there is little light oil on the surface of the semi-coke wastewater in the outer tank 1 and the light oil layer is thin, and the water quality at the semi-coke wastewater outlet 18 is qualified, meeting the subsequent phenol and ammonia unit operation requirements;

[0064] Step 6: Open the second isolation valve 9 and the nitrogen purging valve 14 to purge all the residual oil in the first oil collection manifold 7 and the second oil collection manifold 24 into the light oil collection tank 12. During the purging process, control the pressure of the light oil collection tank 12 within the design range until the liquid level in the light oil collection tank 12 stabilizes and then stop. Then close the nitrogen purging valve 14 to stop purging. Finally, close the second isolation valve 9 to end the purging process.

[0065] Preferably, in step 6, if the liquid level in the light oil collection tank 12 is lower than the high liquid level after the purging is completed, the third isolation hand valve 11 is opened to restore the light oil removal function of the inner tank 2.

[0066] Preferably, in step 6, the first isolation hand valve 4 remains open, and the electric two-position valve 5 can be opened remotely by DCS the next time oil is removed. This reduces the workload of on-site operators who frequently climb tanks and operate the valve, reduces the number of times the first isolation hand valve 4 is opened and closed, and improves work efficiency and the degree of automation of the oil collection device.

[0067] After the above steps, the oil content in the semi-coke wastewater is less than 1000 mg / L, ensuring the long-term stable operation of the phenol and ammonia recovery unit.

[0068] Preferably, when the device undergoes planned maintenance, isolation, drainage, and purging are performed sequentially, with the specific steps as follows:

[0069] S1. Isolation of the oil collection device: Stop the collection of light oil on the surface of the semi-coke wastewater in the outer tank 1, and then manually close the first isolation valve 4 and the second isolation valve 9 on site.

[0070] S2. Drainage of the oil collection device: The DCS remotely controls the opening of the electric two-position valve 5, and the on-site manual opening of the discharge drain valve 15, so that the oil in the oil collection pipeline 6, the first oil collection main pipe 7 and the second oil collection main pipe 24 are discharged into the sewage tank 19 through the discharge pipeline 13 and the sewage discharge pipe 20.

[0071] S3. Purging of the oil collection device: Open the nitrogen purging valve 14 to purge all the residual oil in the oil collection line 6, the first oil collection main pipe 7 and the second oil collection main pipe 24 into the sewage tank 19 until the liquid level in the sewage tank 19 is stable and the purging is qualified; then close the nitrogen purging valve 14 to stop purging; then close the discharge drain valve 15 to end the purging.

[0072] Preferably, in step S3, when purging the oil recovery pipeline 6, the flange detachment port of the first isolation hand valve 4 is purged as a discharge port. After passing the test, the nitrogen purging valve 14 is closed, and the flange detachment port of the first isolation hand valve 4 is closed and reset.

[0073] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A device for pretreatment and oil recovery of semi-coke wastewater, characterized in that, The device includes a raw water settling tank, a light oil receiving port (3), a first isolation hand valve (4), an electric two-position valve (5), an oil receiving pipeline (6), a first oil receiving main pipe (7), a pipeline sight glass (8), a second isolation hand valve (9), a remote interface gauge (10), a third isolation hand valve (11), a light oil collection tank (12), a discharge pipeline (13), a nitrogen purging valve (14), a discharge drain valve (15), an inner tank light oil removal pipeline (16), a semi-coke wastewater inlet pipeline (17), a semi-coke wastewater outlet (18), a sewage tank (19), a sewage discharge pipe (20), a remote level gauge (21), a nitrogen purging pipeline (22), an oil removal main pipe (23), a second oil receiving main pipe (24), and a DCS; The raw water settling tank consists of an outer tank (1) and an inner tank (2); the inner tank (2) is equipped with an oil removal device; the end of the semi-coke wastewater inlet pipeline (17) is located in the oil removal device; the DCS is located in the central control room and is connected to the electric two-position valve (5), the remote interface gauge (10) and the remote level gauge (21) respectively; the outer tank (1) is equipped with a remote level gauge (21) for remote operators to observe the liquid level of the outer tank (1) on the DCS; the lower part of the outer tank (1) is equipped with a semi-coke wastewater outlet (18). The outer tank (1) has several light oil collection ports (3) along the vertical height direction; each light oil collection port (3) is equipped with a remote interface gauge (10) for remote operators to observe the thickness of the light oil layer on the water surface in the outer tank (1) on the DCS; each light oil collection port (3) is connected to the beginning of an oil collection pipeline (6); the ends of all oil collection pipelines (6) converge to the first oil collection main pipe (7); the first oil collection main pipe (7) is set from top to bottom next to the outer tank (1); each oil collection pipeline (6) is equipped with a first isolation hand valve (4) and an electric two-position valve (5) on the horizontal pipeline; The beginning of the first oil collection manifold (7) is connected to the end of the nitrogen purging line (22), and a nitrogen purging valve (14) is installed on the nitrogen purging line (22); the end of the first oil collection manifold (7) is connected to the beginning of the second oil collection manifold (24); according to the direction of liquid flow, a pipe sight glass (8) and a second isolation hand valve (9) are installed on the second oil collection manifold (24) in sequence. On-site operators can more intuitively monitor the purity of light oil in the second oil collection manifold (24) through the pipe sight glass (8), and take timely measures to manually switch the second isolation hand valve (9) or remotely control the electric two-position valve (5) through DCS to control the oil collection quality. A discharge drain valve (15) is installed on the discharge pipeline (13). The beginning end is connected to the middle and lower part of the second oil collection main pipe (24). The connection point is located between the pipeline sight glass (8) and the second isolation hand valve (9). The end end is connected to the sewage tank (19) through the sewage discharge pipe (20). The inner tank (2) is connected to the beginning end of the deoiling main pipe (23) through the inner tank light oil removal pipeline (16). A third isolation hand valve (11) is installed on the inner tank light oil removal pipeline (16). The end end of the second oil collection main pipe (24) is connected to the beginning end of the deoiling main pipe (23). The end end of the deoiling main pipe (23) is connected to the light oil collection tank (12).

2. The oil recovery device for pretreatment of semi-coke wastewater according to claim 1, characterized in that, Several light oil collection ports (3) at different heights are evenly distributed on the tank body of the outer tank (1) along the vertical height direction; the positions of the uppermost light oil collection port (3) and the lowermost light oil collection port (3) are fixed, and multiple light oil collection ports (3) in the middle part are set as needed; the uppermost light oil collection port (3) is flush with the position of the high liquid level control of the outer tank (1).

3. The oil recovery device for pretreatment of semi-coke wastewater according to claim 1, characterized in that, The negative pressure side interface of each remote interface meter (10) is at the same elevation as the corresponding light oil receiving port (3).

4. The oil recovery device for pretreatment of semi-coke wastewater according to claim 1, characterized in that, The first oil collection pipe (7) is vertically installed next to the outer tank (1), and the second oil collection pipe (24) is inclined. The angle between the first oil collection pipe (7) and the second oil collection pipe (24) in the same vertical plane is ≥90° and <180°.

5. The oil recovery device for pretreatment of semi-coke wastewater according to claim 1, characterized in that, According to the direction of liquid flow, each oil receiving pipeline (6) is equipped with a first isolation hand valve (4) and an electric two-position valve (5) in sequence on the horizontal pipeline. The first isolation hand valve (4) is close to the light oil receiving port (3). The end of the nitrogen purging line (22) is higher than the uppermost light oil receiving port (3); the nitrogen purging valve (14) is located near the first oil receiving main pipe (7).

6. The oil recovery device for pretreatment of semi-coke wastewater according to claim 1, characterized in that, The connection between the discharge line (13) and the second oil return main (24) is located at the lowest point before the second isolation hand valve (9) on the second oil return main (24); The third isolation hand valve (11) is located near the connection between the second oil receiving manifold (24) and the oil removal manifold (23).

7. The oil recovery device for pretreatment of semi-coke wastewater according to claim 1, characterized in that, The diameter of the light oil receiving port (3) is DN50, the diameter of the oil receiving pipeline (6) is DN50, the diameter of the first oil receiving main pipe (7) is DN80, the diameter of the discharge pipeline (13) is DN25, the diameter of the nitrogen purging pipeline (22) is DN25, and the diameter of the second oil receiving main pipe (24) is DN80. The first isolation hand valve (4), the electric two-position valve (5), the oil collection line (6), the first oil collection main pipe (7), the pipeline sight glass (8), the second isolation hand valve (9), the remote interface gauge (10), the third isolation hand valve (11), the light oil collection tank (12), the discharge line (13), the discharge drain valve (15), the light oil removal line of the inner tank (16), the sewage discharge pipe (20), the remote level gauge (21), the oil removal main pipe (23), and the second oil collection main pipe (24) are all equipped with oil collection system heat tracing devices.

8. The oil recovery device for pretreatment of semi-coke wastewater according to claim 1, characterized in that, The remote interface gauge (10) adopts a dual-flange remote interface gauge, and the remote level gauge (21) adopts a dual-flange remote level gauge. The first isolation hand valve (4), the second isolation hand valve (9), the third isolation hand valve (11), the nitrogen purging valve (14) and the discharge drain valve (15) are all gate valves, and the electric two-position valve (5) is an electric ball valve.

9. A method for recovering oil from pretreated semi-coke wastewater based on the semi-coke wastewater pretreatment oil recovery device according to any one of claims 1-8, characterized in that, The method includes the following steps: Step 1: The first isolation valve (4), the electric two-position valve (5), the second isolation valve (9), the third isolation valve (11), the nitrogen purging valve (14), and the discharge drain valve (15) are all closed; the semi-coke wastewater enters the inner tank (2) from the semi-coke wastewater inlet pipeline (17), and most of the oil and dust are removed in the inner tank (2) through the tank-in-tank oil removal technology; the third isolation valve (11) is opened, and the light oil in the inner tank (2) enters the light oil collection tank (12) for normal collection through the inner tank light oil removal pipeline (16); the semi-coke wastewater after oil and dust removal enters the outer tank (1), and after static sedimentation and separation, the light oil floats on the water surface and accumulates, causing the light oil layer to continuously thicken; Step 2: Select a suitable light oil inlet (3) according to the liquid level height indicated by the remote level gauge (21), and then determine the thickness of the light oil layer on the water surface according to the interface indicated by the remote interface gauge (10) at the selected light oil inlet (3). Step 3: Before the outer tank (1) collects oil, the inner tank (2) stops collecting oil, closes the third isolation hand valve (11), and lowers the liquid level of the light oil collection tank (12) to the minimum. Step 4: When the outer tank (1) collects oil, first open the first isolation hand valve (4), then open the electric two-position valve (5) remotely controlled by DCS, and finally open the second isolation hand valve (9) and control the liquid level rise rate of the light oil collection tank (12); During the oil recovery process, the light oil fills the entire pipeline sight glass (8). On-site operators visually observe the purity of the discharged light oil through the pipeline sight glass (8). Based on the different purity of the discharged light oil during the oil recovery process, two working conditions are used for oil recovery: Operating Condition 1: When the mass of water in the discharged light oil is less than 1 / 2 of the diameter of the pipe sight glass (8) as observed visually through the pipe sight glass (8), continue to collect oil; when the liquid level in the light oil collection tank (12) reaches the high liquid level, the DCS remotely controls the closing of the electric two-position valve (5) to stop collecting oil; oil and water separation is carried out in the light oil collection tank (12), and after drainage, the qualified light oil is sent out of the boundary area to complete one light oil collection operation; Operating Condition 2: When the mass of water in the discharged light oil is visually observed through the pipe sight glass (8) to be equal to or greater than 1 / 2 of the diameter of the pipe sight glass (8), the DCS remotely controls the closing of the electric two-position valve (5) to stop oil collection; then the indication of the remote interface gauge (10) is lowered to increase the thickness of the light oil layer. When the mass of water in the discharged light oil is visually observed through the pipe sight glass (8) to be less than 1 / 2 of the diameter of the pipe sight glass (8), the DCS remotely controls the opening of the electric two-position valve (5) to collect oil normally; when the liquid level in the light oil collection tank (12) reaches the high liquid level, the DCS remotely controls the closing of the electric two-position valve (5) to stop oil collection; oil and water separation is performed in the light oil collection tank (12), and after drainage, the qualified light oil is sent out of the boundary area to complete one light oil collection operation; Step 5: Repeat step 4. When it is visually observed through the pipe sight glass (8) that all the discharged light oil is water, immediately close the second isolation hand valve (9) and the DCS remote control to close the electric two-position valve (5) to stop oil collection. Then open the discharge drain valve (15) to discharge the water in the first oil collection main pipe (7) and the second oil collection main pipe (24) to the sewage tank (19) through the discharge pipeline (13) and the sewage discharge pipe (20). After all the water in the first oil collection main pipe (7) and the second oil collection main pipe (24) is drained, close the discharge drain valve (15). Step 6: Open the second isolation hand valve (9) and the nitrogen purging valve (14) to purge all the residual oil in the first oil collection manifold (7) and the second oil collection manifold (24) into the light oil collection tank (12) until the liquid level in the light oil collection tank (12) is stable; then close the nitrogen purging valve (14) to stop purging; then close the second isolation hand valve (9) to end purging.

10. The method for pretreatment and oil recovery of semi-coke wastewater according to claim 9, characterized in that, In step 2, under normal circumstances, when the remote level gauge (21) is running at a high level, the uppermost light oil receiving port (3) is used to collect oil. When the level of the outer tank (1) is lower than the high level control or when the raw water settling tank is under maintenance and drained, the middle part and the lowermost light oil receiving port (3) are selected to collect oil. In step 4, if a malfunction occurs during the oil recovery process and equipment maintenance is required, the system shall be drained and purged in sequence, and then the equipment maintenance shall be carried out. After the maintenance is completed, the oil recovery process shall continue. The specific process of draining is as follows: manually close the second isolation hand valve (9) on site and remotely close the electric two-position valve (5) via DCS control, open the discharge drain valve (15), and discharge the oil in the first oil collection main pipe (7) and the second oil collection main pipe (24) to the sewage tank (19) through the discharge pipeline (13) and the sewage discharge ground pipe (20). The purging process is as follows: After all the oil in the first oil collection manifold (7) and the second oil collection manifold (24) has been drained, the nitrogen purging valve (14) is opened to purge the remaining oil in the first oil collection manifold (7) and the second oil collection manifold (24) into the sewage tank (19) through the discharge pipeline (13) and the sewage discharge pipe (20) until the liquid level in the sewage tank (19) is stable; then the nitrogen purging valve (14) is closed to stop the purging; then the discharge drain valve (15) is closed to end the purging process. In step 6, after the purging is completed, if the liquid level in the light oil collection tank (12) is lower than the high liquid level, the third isolation hand valve (11) is opened to restore the light oil removal function of the inner tank (2).

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