A system and method for removing mercaptans from liquid hydrocarbons

Abstract

The present disclosure relates to a system and method for removing mercaptans from liquid hydrocarbons, which comprises an extraction separation unit, an alkali liquor regeneration unit, a regenerated gas treatment unit and a second control unit; the alkali liquor regeneration unit comprises an oxygen inlet and an oxygen-containing gas phase inlet, an online analyzer is arranged on the pipeline of the oxygen-containing gas phase inlet; the regenerated gas treatment unit comprises a gas buffer tank, a pressure gauge is arranged on the gas buffer tank; the second control unit is electrically connected with the pressure gauge and the online analyzer, used for receiving the pressure signal of the pressure gauge and the oxygen content signal of the online analyzer, and controlling the oxygen flow and / or oxygen concentration entering the alkali liquor regeneration unit. The technical scheme of the present disclosure can improve the efficiency of removing mercaptans from liquid hydrocarbons, eliminate the safety hazards caused by excess gas emission, and realize the effects of no waste gas emission, no fuel gas consumption and long-period operation.

Description

Technical Field

[0001] This disclosure relates to the petrochemical field, and more specifically, to a system and method for removing liquid hydrocarbon mercaptan. Background Technology

[0002] Liquid hydrocarbons produced as a byproduct of oil processing in petrochemical enterprises, especially those from catalytic cracking and delayed coking processes, contain large amounts of thiols and other sulfides. Liquid hydrocarbon dethiolization, a system for removing these thiol-containing liquid hydrocarbons, utilizes the weak acidity of thiols. A 15-20% by mass NaOH solution (alkaline solution) is used as the extraction solvent. The thiols react with NaOH to form sodium thiolate, which dissolves in the alkaline solution and is thus removed from the liquid hydrocarbons. Specifically, the thiols in the liquid hydrocarbons first react with NaOH to form sodium thiolate, which enters the alkaline solution. Air is then introduced into the alkaline solution, and the oxygen in the air reacts with the sodium thiolate to form disulfides. Disulfides are soluble in oil but insoluble in the alkaline solution, allowing for direct sedimentation separation of the disulfides from the alkaline solution. Alternatively, the extracted oil can be used to enhance the sedimentation separation of the disulfides from the alkaline solution. The alkaline solution after the disulfides are separated is recycled, thereby achieving the removal of thiols from the liquid hydrocarbons.

[0003] In conventional liquid hydrocarbon desulfurization processes, liquid hydrocarbons and lean alkali solutions typically enter a desulfurization extraction tower or a combination of a reactor and a settling tank, respectively. The purified liquid hydrocarbons after desulfurization exit from the top of the extraction tower or settling tank, while the rich alkali solution goes to the alkali regeneration tower from the bottom. The alkali regeneration process directly uses factory air to enter the alkali regeneration tower or mixes it with the rich alkali solution outside the tower before entering the tower together for the oxidation of sodium thiolate. The reaction between the oxygen in the air and the sodium thiolate in the alkali solution is carried out. Since the oxidation reaction of sodium thiolate requires excess oxygen to be complete, with an excess oxygen amount of about 1-2 times the amount of oxygen used in the reaction, the excess gas from the reaction process needs to be discharged at the top of the alkali regeneration tower. The excess gas contains oxygen, hydrocarbons, and sulfides, and is a combustible mixture, belonging to the category of VOCs waste gas from refineries. Its disposal is one of the challenges faced by refineries. Currently, refineries typically add fuel gas to the excess gas at the top of the alkali regeneration tower to increase its hydrocarbon content before sending it to an incinerator or heating furnace for combustion. The flue gas from the furnace is then discharged into the atmosphere, alleviating the difficulty of treating the excess gas to some extent. However, with increasingly stringent national environmental regulations on flue gas emissions and other indicators, this treatment method has been limited. Furthermore, to ensure the safety of the excess gas transportation process, existing technologies require the use of stainless steel pipelines for transportation while simultaneously adding a large amount of fuel gas to the excess gas.

[0004] Typically, the feed to a liquid hydrocarbon desulfurization system is liquid hydrocarbons processed by the amine method for hydrogen sulfide removal. These liquid hydrocarbons not only retain residual hydrogen sulfide but also a large amount of amine impurities. The impact of amine impurities on the entire desulfurization system is often overlooked. With the expansion of oil processing scale, petrochemical enterprises are increasing their liquid hydrocarbon production and sulfur content, leading to an expansion of the processing capacity of liquid hydrocarbon desulfurization systems. Through extensive comparative analysis and research, we have found that as the processing capacity of liquid hydrocarbon desulfurization systems increases, the impact of amine impurities on the operation of the desulfurization system and the quality of liquid hydrocarbon products becomes more significant. Amine impurities are easily oxidized and degraded and accumulate within the system, which is one of the reasons for increased regeneration oxygen consumption, increased system pressure drop, and decreased desulfurization efficiency and effectiveness. During operation, this not only causes unstable oxygen consumption, difficulty in pressure control, and operational fluctuations but also results in poor desulfurization performance and substandard product quality. To overcome these problems, appropriate pretreatment measures should be adopted. Currently, to improve the desulfurization effect, the amount of plant air injected into the liquid hydrocarbon desulfurization system is often increased. This leads to an increase in the amount of fuel gas used with excess gas, resulting in increased energy consumption and increased flue gas emissions from combustion. In some refineries, problems such as excessive sulfur content in incinerator flue gas or corrosion of furnace tubes in heating furnaces have also occurred, seriously affecting the safe operation of refineries and the environmental conditions. In recent years, many petrochemical companies have used refined liquid hydrocarbons as raw materials for chemical production, raising the requirements for their mercaptan removal rate and residual sulfur (mercaptan sulfur + disulfide) indicators. Some companies have further increased the excess oxygen content from 1-2 times to improve the mercaptan removal rate of refined liquid hydrocarbons. The excess gas is a flammable mixture, and its residual oxygen content is uncontrollable, posing a great safety hazard. Summary of the Invention

[0005] The purpose of this disclosure is to provide a system and method for removing mercaptans from liquid hydrocarbons, in order to solve the problems of low mercaptan removal efficiency, safety hazards caused by residual oxygen in excess gas, difficulty in handling excess gas, fuel gas consumption and flue gas emissions in the prior art.

[0006] To achieve the above objectives, the first aspect of this disclosure provides a system for removing thiols from liquid hydrocarbons. This system includes an extraction and separation unit, an alkali regeneration unit, a regeneration gas treatment unit, and a second control unit. The extraction and separation unit includes a pre-treated liquid hydrocarbon inlet, a lean alkali inlet, a refined liquid hydrocarbon outlet, and a rich alkali outlet. The alkali regeneration unit includes an oxygen inlet, an oxygen-containing phase inlet, a rich alkali inlet, a regeneration gas phase outlet, a lean alkali outlet, and a disulfide oil outlet. The regeneration gas treatment unit includes a regeneration gas phase inlet, a first top gas phase outlet, and a second top gas phase outlet. The rich alkali outlet of the extraction and separation unit is connected to the rich alkali inlet of the alkali regeneration unit. The lean alkali outlet of the alkali regeneration unit is connected to the... The alkali regeneration unit has a lean alkali inlet connected to the regeneration gas phase outlet, which is connected to the regeneration gas phase inlet of the regeneration gas treatment unit. The first top gas phase outlet of the regeneration gas treatment unit is connected to a flare device, and the second top gas phase outlet of the regeneration gas treatment unit is connected to the oxygen-containing phase inlet of the alkali regeneration unit. The regeneration gas treatment unit includes a gas buffer tank, on which a pressure gauge is installed. An online analyzer is installed on the pipeline of the oxygen-containing phase inlet of the alkali regeneration unit. The second control unit is electrically connected to the pressure gauge and the online analyzer, and is used to receive the pressure signal from the pressure gauge and the oxygen content signal from the online analyzer, and to control the oxygen flow rate and / or oxygen concentration entering the alkali regeneration unit.

[0007] Optionally, the system further includes a pressure swing adsorption (PSA) oxygen generation unit, which includes a third control unit, an industrial air feed main line, an oxygen discharge main line, and at least two adsorption branches; each adsorption branch line is equipped with an exhaust branch line; each adsorption branch line is sequentially equipped with an inlet regulating valve, an exhaust outlet, an adsorption tower, and an outlet regulating valve along the gas flow direction; the exhaust branch line is equipped with an exhaust regulating valve; an oxygen analyzer is installed at the outlet of the oxygen discharge main line; the inlet of the industrial air feed main line is connected to an industrial air source, and the outlet of the industrial air feed main line is connected to the inlet of the adsorption branch line; The outlet of the adsorption branch is connected to the inlet of the main oxygen discharge line, and the outlet of the main oxygen discharge line is connected to the oxygen inlet of the alkali regeneration unit; the inlet of the exhaust branch is connected to the exhaust gas outlet of the adsorption branch, and the outlet of the exhaust branch is used to communicate with the atmosphere; the third control unit is electrically connected to the inlet regulating valve, the outlet regulating valve, the exhaust regulating valve and the second control unit; the third control unit is used to receive the regulation signal of the second control unit and control the opening or closing time of the inlet regulating valve, the outlet regulating valve and the exhaust regulating valve.

[0008] Optionally, the oxygen inlet pipeline of the alkali regeneration unit is equipped with an oxygen flow regulating valve and an oxygen flow meter; the second control unit is electrically connected to the oxygen flow regulating valve and the oxygen flow meter to receive the flow signal from the oxygen flow meter and control the opening degree of the oxygen flow regulating valve; the alkali regeneration unit also includes a nitrogen inlet, the nitrogen inlet pipeline being used to connect to a nitrogen source; the nitrogen inlet pipeline is equipped with a nitrogen flow regulating valve and a nitrogen flow meter; the system also includes a fourth control unit; the fourth control unit is electrically connected to the oxygen flow meter, the nitrogen flow regulating valve, and the nitrogen flow meter; the fourth control unit is used to receive the flow signals from the oxygen flow meter and the nitrogen flow meter and control the opening degree of the nitrogen flow regulating valve.

[0009] Optionally, a gas shut-off valve and a fuel gas inlet are sequentially provided along the material flow direction on the pipeline of the first top gas phase outlet; the fuel gas inlet of the first top gas phase outlet pipeline is used to connect with the outlet of the fuel gas pipeline; the inlet of the fuel gas pipeline is used to connect with the fuel gas source; a fuel gas shut-off valve is provided on the fuel gas pipeline; the system also includes a first control unit, which is electrically connected to the pressure gauge of the gas buffer tank, the gas shut-off valve and the fuel gas shut-off valve; the first control unit is used to receive the pressure signal from the pressure gauge of the gas buffer tank and control the opening degree of the gas shut-off valve and the fuel gas shut-off valve.

[0010] The second aspect of this disclosure employs the method for removing thiols from liquid hydrocarbons as described in the first aspect of this disclosure. The method includes: introducing pretreated liquid hydrocarbons into an extraction unit for extraction by contacting an extraction solvent to obtain refined liquid hydrocarbons and a rich alkali solution; the extraction solvent being an alkali solution; introducing the rich alkali solution into an alkali regeneration unit for regeneration by contacting oxygen to obtain a lean alkali solution, disulfide oil, and a regenerated gas phase; returning the lean alkali solution to the extraction unit as an extraction solvent for continued use; introducing the regenerated gas phase into a gas buffer tank for gas-liquid separation, compressing at least a portion of the gas stream obtained at the top of the tank and returning it to the alkali regeneration unit; detecting the pressure signal at the top of the gas buffer tank and the oxygen content signal of the gas stream returning to the alkali regeneration unit, and controlling the oxygen flow rate and / or oxygen concentration entering the alkali regeneration unit based on the pressure signal and the oxygen content signal.

[0011] Optionally, the oxygen entering the alkali regeneration unit comes from the pressure swing adsorption (PSA) oxygen generator unit. The method further includes: when the pressure signal at the top of the gas buffer tank is above a first threshold and the oxygen content signal of the online analyzer is above a second threshold, the second control unit sends a signal to the third control unit to reduce the oxygen production of the PSA oxygen generator unit while maintaining the original oxygen concentration output by the PSA oxygen generator unit; when the pressure signal at the top of the gas buffer tank is above the first threshold and the oxygen content signal of the online analyzer is below the second threshold, the second control unit sends a signal to the third control unit to increase the oxygen concentration entering the alkali regeneration unit from the PSA oxygen generator unit; the first threshold is selected from any value between 0.45 and 0.55 MPa, and the second threshold is selected from any value between 5.5 and 6.5% by volume.

[0012] Optionally, the oxygen entering the alkali regeneration unit comes from the oxygen inlet pipe. The method further includes introducing nitrogen into the alkali regeneration unit through the nitrogen inlet pipe; using a fourth control unit to acquire the oxygen flow rate signal of the oxygen inlet pipe and the nitrogen flow rate signal of the nitrogen inlet pipe, and calculating the oxygen-nitrogen volumetric flow rate ratio; optionally, the method further includes: using a second control unit to acquire the tank top pressure signal and the oxygen content signal of the online analyzer, and adjusting the oxygen flow rate entering the alkali regeneration unit and / or the oxygen-nitrogen volumetric flow rate ratio of the fourth control unit according to the tank top pressure signal and the oxygen content signal; when the second control unit detects that the tank top pressure signal of the gas buffer tank is above a first threshold and the oxygen content signal of the online analyzer is above a second threshold, reducing the oxygen flow rate on the oxygen inlet pipe. The opening of the gas flow regulating valve is kept constant while maintaining the oxygen-nitrogen volumetric flow rate ratio to reduce the oxygen flow rate entering the alkali regeneration unit. When the second control unit detects that the pressure signal at the top of the gas buffer tank is above a first threshold and the oxygen content signal of the online analyzer is below a second threshold, the second control unit keeps the opening of the regulating valve on the oxygen inlet pipe constant and sends a signal to the fourth control unit to increase the oxygen-nitrogen volumetric flow rate ratio, causing the fourth control unit to reduce the opening of the nitrogen flow regulating valve on the nitrogen inlet pipe to reduce the nitrogen flow rate entering the alkali regeneration unit. The first threshold is selected from any value between 0.45 and 0.55 MPa, the second threshold is selected from any value between 5.5 and 6.5% by volume, and the oxygen-nitrogen volumetric flow rate ratio is (1 to 20):1.

[0013] Optionally, the method further includes controlling another portion of the gaseous stream and fuel gas to enter the flare for combustion and venting based on the tank top pressure signal; optionally, when the first control unit detects that the tank top pressure signal of the gas buffer tank is above a third threshold, the fuel gas cut-off valve and the gas cut-off valve are opened sequentially, so that the fuel gas and another portion of the gaseous stream enter the flare line sequentially to mix and obtain flare feed gas, and the flare feed gas enters the flare device for combustion and venting; when the first control unit detects that the tank top pressure signal of the gas buffer tank is less than a fourth threshold, the gas cut-off valve and the fuel gas cut-off valve are closed sequentially, so that all the gaseous stream is compressed and returned to the alkali regeneration unit; the third threshold is selected from any value from 0.55 to 0.6 MPa, and the fourth threshold is selected from any value from 0.45 to 0.55 MPa.

[0014] Optionally, the oxygen content of the gaseous stream entering the alkali regeneration unit is 5-8% by volume; the oxygen concentration of the oxygen entering the alkali regeneration unit is 50-95% by volume; the method further includes mixing the rich alkali solution with the catalyst and the extraction oil before entering the alkali regeneration unit; the volume flow ratio of the extraction oil to the rich alkali solution is 0.05-0.4; and the operating pressure of the gas buffer tank is 0.2-0.55 MPa.

[0015] Optionally, the method further includes, before performing the extraction process, pre-treating the sulfur-containing liquid hydrocarbon and demineralized water into a pre-treatment unit to obtain the pre-treated liquid hydrocarbon and amine-containing water; returning a portion of the amine-containing water to the pre-treatment unit and using the other portion as a discharged amine-containing water system; wherein the weight ratio of the amine-containing water returned to the pre-treatment unit to the discharged amine-containing water is (2-20):1; and the weight ratio of the total weight of the demineralized water and the amine-containing water returned to the pre-treatment unit to the weight of the sulfur-containing liquid hydrocarbon is (0.05-0.5):1.

[0016] Through the above technical solution, this disclosure obtains refined liquid hydrocarbons and alkali solution to be regenerated after processing liquid hydrocarbons through a pretreatment unit and an extraction and separation unit. This can improve the desulfurization efficiency of the liquid hydrocarbon desulfurization process and reduce the oxygen consumption of subsequent regeneration. At the same time, the alkali solution to be regenerated is introduced into the alkali regeneration unit with a certain concentration of oxygen and a certain oxygen content of oxygen-containing phase controlled by the second control unit. This can solve the problems of circulation and process safety of oxygen-containing combustible gas mixture, so as to achieve the safety of excess gas circulation, achieve zero waste gas emission and long-term safe and stable operation, thereby reducing the environmental impact of liquid hydrocarbon desulfurization excess gas treatment, reducing the related costs of transmission pipelines, and eliminating fuel gas consumption.

[0017] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0019] Figure 1 This is a schematic diagram of a system for removing thiols from liquid hydrocarbons, as used in Embodiment 1 of this disclosure.

[0020] Figure 2 This is a schematic diagram of a pressure swing adsorption oxygen generation unit in a system for removing thiols from liquid hydrocarbons disclosed herein.

[0021] Figure 3 This is a schematic diagram of a system for removing thiols from liquid hydrocarbons, as used in Embodiment 2 of this disclosure.

[0022] Figure 4 A schematic diagram of a system for removing thiols from liquid hydrocarbons, used in Comparative Example 1 of this disclosure.

[0023] Explanation of reference numerals in the attached figures

[0024] 1. Pretreatment tank; 2. Amine-containing water circulating pump; 3. Extraction reactor; 4. Extraction settling tank; 5. Alkali regeneration tower; 6. Alkali settling tank; 7. Alkali circulating pump; 8. Gas buffer tank; 9. Circulating gas compressor; 10. Online analyzer; 11. Flare vent line; 12. Gas shut-off valve; 13. Fuel gas shut-off valve; 14. First control unit; 15. Second control unit; 16. Heat exchanger; 17. Pressure swing adsorption oxygen generation unit; 18. First adsorption tower; 19. Second adsorption tower; 20. First inlet regulating valve; 21. First exhaust regulating valve; 22. First outlet regulating valve; 23. Second inlet regulating valve; 24. Second exhaust regulating valve; 25. Second outlet regulating valve; 26. Pressure equalization regulating valve; 27. Third control unit; 28. Oxygen analyzer; 29. ​​Oxygen flow regulating valve; 30. Oxygen flow meter; 31. Nitrogen flow regulating valve; 32. Nitrogen flow meter; 33. Fourth control unit; 34. Incinerator;

[0025] a. Sulfur-containing liquid hydrocarbons; b. Demineralized water; c. Amine-containing water discharge; d. Refined liquid hydrocarbons; e. Oxygen; f. Disulfide oil; g. Fuel gas; h. Factory air; i. Extracted oil; j. Nitrogen; k. Catalyst; l. Fresh alkali solution; m. Waste alkali solution; n. Combustion flue gas; o. Air. Detailed Implementation

[0026] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0027] In this disclosure, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its normal operating state, for example, as shown in the reference. Figure 1 In the drawing orientation, "inner" and "outer" refer to their relative to the outline of the device. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," "third," or "fourth" may explicitly or implicitly include one or more of that feature. In the description of this disclosure, "a plurality of" means two or more, unless otherwise explicitly specified.

[0028] This disclosure provides a system for removing thiols from liquid hydrocarbons. The system includes an extraction and separation unit, an alkali regeneration unit, a regeneration gas treatment unit, and a second control unit 15. The extraction and separation unit includes a pre-treated liquid hydrocarbon inlet, a lean alkali inlet, a refined liquid hydrocarbon outlet, and a rich alkali outlet. The alkali regeneration unit includes an oxygen inlet, an oxygen-containing phase inlet, a rich alkali inlet, a regeneration gas phase outlet, a lean alkali outlet, and a disulfide oil outlet. The regeneration gas treatment unit includes a regeneration gas phase inlet, a first top gas phase outlet, and a second top gas phase outlet. The rich alkali outlet of the extraction and separation unit is connected to the rich alkali inlet of the alkali regeneration unit, allowing the rich alkali to enter the alkali regeneration unit from the extraction unit for regeneration. The lean alkali outlet of the alkali regeneration unit is connected to the lean alkali inlet of the extraction and separation unit, allowing the lean alkali to enter the extraction unit as an extraction solvent. The regenerated gas phase outlet of the alkali regeneration unit is connected to the regenerated gas phase inlet of the regenerated gas treatment unit so that the regenerated gas can be further processed; the first top gas phase outlet of the regenerated gas treatment unit is connected to a flare device so that a portion of the gas phase can be combusted; the second top gas phase outlet of the regenerated gas treatment unit is connected to the oxygen-containing gas phase inlet of the alkali regeneration unit so that another portion of the gas phase can be returned to the alkali regeneration unit for recycling; the regenerated gas treatment unit includes a gas buffer tank 8, and a pressure gauge is installed on the gas buffer tank 8; an online analyzer 10 is installed on the pipeline of the oxygen-containing gas phase inlet of the alkali regeneration unit; the second control unit 15 is electrically connected to the pressure gauge and the online analyzer 10, and is used to receive the pressure signal from the pressure gauge and the oxygen content signal from the online analyzer 10, and to control the oxygen flow rate and / or oxygen concentration entering the alkali regeneration unit.

[0029] Through the above technical solution, this disclosure obtains refined liquid hydrocarbon d and alkali solution to be regenerated after processing liquid hydrocarbons through a pretreatment unit and an extraction and separation unit. This can improve the desulfurization efficiency of the liquid hydrocarbon desulfurization process and reduce the oxygen consumption of subsequent regeneration. At the same time, the alkali solution to be regenerated is introduced into the alkali regeneration unit for regeneration with a certain concentration of oxygen and a certain oxygen content of oxygen-containing phase controlled by the second control unit 15. This can solve the problems of circulation and process safety of oxygen-containing combustible mixed gas, so as to achieve the safety of excess gas circulation, achieve zero waste gas emission and long-term safe and stable operation, thereby reducing the environmental impact of liquid hydrocarbon desulfurization excess gas treatment, reducing the related costs of transmission pipelines, and eliminating fuel gas consumption.

[0030] In one embodiment, the system further includes a pretreatment unit, which includes a sulfur-containing liquid hydrocarbon inlet, a demineralized water inlet, an amine-containing water outlet, and a pretreated liquid hydrocarbon outlet. The sulfur-containing liquid hydrocarbon inlet of the pretreatment unit is connected to a sulfur-containing liquid hydrocarbon source, and the demineralized water inlet is connected to a demineralized water source, so that the liquid hydrocarbons and demineralized water can enter the pretreatment unit for pretreatment. The pretreated liquid hydrocarbon outlet of the pretreatment unit is connected to the pretreated liquid hydrocarbon inlet of the extraction and separation unit, so that the pretreated liquid hydrocarbons can enter the extraction unit for extraction to remove mercaptans.

[0031] like Figure 1 Figure 3 As shown, the apparatus used in the pretreatment unit of this disclosure is a conventional choice in the art. For example, in one specific embodiment of this disclosure, the pretreatment unit is a horizontal pretreatment tank 1. Liquid hydrocarbons and demineralized water b are mixed in the tank to remove water-soluble impurities (such as alkanolamines) from the liquid hydrocarbons. The inlet of the demineralized water b can be located at the top of the pretreatment tank 1 so that the demineralized water b can come into countercurrent contact with the liquid hydrocarbons, thereby increasing the pretreatment effect. In addition, an amine-containing water circulation pump 2 is also provided on the amine-containing water outlet pipeline of the pretreatment tank 1 so that a portion of the amine-containing water is circulated back to the pretreatment tank 1 through the amine-containing water circulation pump 2, saving the consumption of demineralized water b and reducing the environmental impact of amine-containing water discharge.

[0032] The extraction and separation unit disclosed herein includes an extraction reactor 3 and an extraction settling tank 4 integrated below the extraction reactor 3. The top of the extraction reactor 3 has a pre-treated liquid hydrocarbon inlet and a lean alkali inlet. The top of the extraction settling tank 4, away from the extraction reactor 3, has a refined liquid hydrocarbon outlet, and the bottom has a rich alkali outlet. Furthermore, along the fluid flow direction, the rich alkali outlet pipeline of the extraction settling tank 4 is sequentially equipped with a heat exchanger 16, a catalyst feed pipeline inlet, and an extraction oil feed pipeline inlet. The catalyst feed pipeline inlet is connected to a catalyst source, and its outlet is connected to the catalyst feed pipeline inlet. The extraction oil feed pipeline inlet is connected to the extraction oil source of other devices, and its outlet is connected to the extraction oil feed pipeline inlet.

[0033] The alkali regeneration unit used in this disclosure is a conventional choice in the art, specifically including an alkali regeneration tower 5 and an alkali settling tank 6. The alkali regeneration tower 5 has a feed inlet at the bottom, an oxygen inlet at the bottom, an oxygen-containing phase inlet, and a first-part regeneration gas phase outlet at the top. The oxygen used in the alkali regeneration tower 5 comes from the pressure swing adsorption oxygen generation unit 17. The alkali settling tank 6 has a disulfide oil outlet and a second-part regeneration gas phase outlet at the top, and a lean alkali outlet at the bottom. This configuration allows the regenerated alkali to enter the alkali settling tank 6 for separation, and then the first-part regeneration gas phase obtained from the alkali regeneration tower 5 mixes with the second-part gas phase generated at the top of the alkali settling tank 6 to form a regeneration gas phase that enters subsequent units. Furthermore, an alkali circulation pump 7 is installed on the lean alkali outlet pipeline of the alkali settling tank 6 to allow the generated lean alkali to be recycled back to the extraction reactor 3 for reuse. In a further embodiment, a fresh alkali inlet pipeline can also be installed on the lean alkali outlet pipeline of the alkali settling tank 6, and the inlet of the fresh alkali inlet pipeline is used to connect with a fresh alkali source.

[0034] The regenerated gas treatment unit used in this disclosure includes a gas buffer tank 8, which can be used to send the regenerated gas phase into the gas buffer tank 8 for gas-liquid separation to obtain a gas phase stream with fewer impurities, and then process the gas phase stream.

[0035] like Figure 1 As shown, a gas shut-off valve 12 and a fuel gas inlet are sequentially arranged along the material flow direction on the pipeline of the first top gas phase outlet; the fuel gas inlet of the pipeline of the first top gas phase outlet is used to connect with the outlet of the fuel gas pipeline, and the inlet of the fuel gas pipeline is used to connect with the fuel gas source so that the fuel gas can be mixed with the first top gas phase; a fuel gas shut-off valve 13 is provided on the fuel gas pipeline; the system also includes a first control unit 14, which is electrically connected to the pressure gauge of the gas buffer tank 8, the gas shut-off valve 12 and the fuel gas shut-off valve 13; the first control unit 14 is used to receive the pressure signal from the pressure gauge of the gas buffer tank 8 and control the opening degree of the gas shut-off valve 12 and the fuel gas shut-off valve 13.

[0036] In one embodiment, the oxygen used in the alkali regeneration tower 5 can be generated by the pressure swing adsorption oxygen generation unit 17, such as... Figure 2As shown, the pressure swing adsorption (PSA) oxygen generation unit 17 used in this disclosure includes an industrial air feed main line, an oxygen discharge main line, and at least two adsorption branches; each adsorption branch line is provided with an exhaust branch line; each adsorption branch line is sequentially provided with an inlet regulating valve, an exhaust outlet, an adsorption tower, and the exhaust regulating valve along the gas flow direction; the exhaust branch line is provided with an exhaust regulating valve; an oxygen analyzer 28 is provided at the outlet of the oxygen discharge main line; the inlet of the industrial air feed main line is connected to an industrial air source, and the outlet of the industrial air feed main line is connected to the inlet of the adsorption branch line, so that the industrial air can enter the adsorption tank for adsorption treatment; the outlet of the adsorption branch line is connected to the inlet of the oxygen discharge main line, and the outlet of the oxygen discharge main line is connected to the outlet of the adsorption branch line. The outlet is connected to the oxygen inlet of the alkali regeneration unit so that the produced oxygen can enter the alkali regeneration unit; the inlet of the exhaust branch is connected to the exhaust outlet of the adsorption branch, and the outlet of the exhaust branch is used to connect with the atmosphere so that excess industrial air can be discharged into the air through the exhaust branch; the pressure swing adsorption oxygen generation unit 17 also includes a third control unit 27; the third control unit 27 is electrically connected to the inlet regulating valve, the outlet regulating valve, the exhaust regulating valve and the second control unit 15; the third control unit 27 is used to receive the regulation signal of the second control unit 15 and control the opening or closing time of the inlet regulating valve, the outlet regulating valve and the exhaust regulating valve.

[0037] In one specific embodiment, the pressure swing adsorption oxygen generation unit 17 is provided with two adsorption branches. The first adsorption branch is provided with a first inlet regulating valve 20, a first adsorption tower 18 and a first outlet regulating valve 22 in sequence along the airflow direction. The second adsorption branch is provided with a second inlet regulating valve 23, a second adsorption tower 19 and a second outlet regulating valve 25 in sequence along the airflow direction. An exhaust pipeline is connected between the first inlet regulating valve 20 and the first adsorption tower 18, and a first exhaust regulating valve 21 is provided on the pipeline. An exhaust pipeline is connected between the second inlet regulating valve 23 and the second adsorption tower 19, and a second exhaust regulating valve 24 is provided on the pipeline. Furthermore, the pipelines between the first adsorption tower 18 and the first outlet regulating valve 22, as well as between the second adsorption tower 19 and the second outlet regulating valve 25, are interconnected by equalization pipelines, and equalization regulating valves 26 are provided on the pipelines. The third control unit 27 is electrically connected to the first intake regulating valve 20, the first exhaust regulating valve 21, the first outlet regulating valve 22, the second intake regulating valve 23, the second exhaust regulating valve 24, the second outlet regulating valve 25, the pressure equalization regulating valve 26, and the second control unit 15. It receives the regulation signal from the second control unit 15 and controls the opening or closing time of the first intake regulating valve 20, the second intake regulating valve 23, the first outlet regulating valve 22, the second outlet regulating valve 25, the first exhaust regulating valve 21, and the second exhaust regulating valve 24 to regulate the oxygen content of the discharged material.

[0038] In the above embodiment, the outlet pipelines of the first exhaust regulating valve 21 and the second exhaust regulating valve 24 are connected to the atmosphere, allowing for high-level venting. The pressure equalization pipeline enables pressure equalization between the two tanks.

[0039] In another embodiment, the oxygen used in the alkali regeneration tower 5 can be obtained from an oxygen source. To ensure the amount of inert gas in the regeneration gas, oxygen and nitrogen can be mixed, such as... Figure 3 As shown, the oxygen inlet pipeline of the alkali regeneration unit is equipped with an oxygen flow regulating valve 29 and an oxygen flow meter 30; the second control unit 15 is electrically connected to the oxygen flow regulating valve 29 and the oxygen flow meter 30 to receive the flow signal from the oxygen flow meter 30 and control the opening degree of the oxygen flow regulating valve 29; the alkali regeneration unit also includes a nitrogen inlet, the nitrogen inlet pipeline being used to connect to a nitrogen source; the nitrogen inlet pipeline is equipped with a nitrogen flow regulating valve 31 and a nitrogen flow meter 32; the system also includes a fourth control unit 33; the fourth control unit 33 is electrically connected to the oxygen flow meter 30, the nitrogen flow regulating valve 31 and the nitrogen flow meter 32; the fourth control unit 33 is used to receive the flow signals from the oxygen flow meter 30 and the nitrogen flow meter 32 and control the opening degree of the nitrogen flow regulating valve 31.

[0040] The second aspect of this disclosure employs the method for removing thiols from liquid hydrocarbons as described in the first aspect of this disclosure. The method includes: introducing pretreated liquid hydrocarbons into an extraction unit for extraction by contacting an extraction solvent to obtain refined liquid hydrocarbons and a rich alkali solution; the extraction solvent being an alkali solution; introducing the rich alkali solution into an alkali regeneration unit for regeneration by contacting oxygen to obtain a lean alkali solution, disulfide oil, and a regenerated gas phase; returning the lean alkali solution to the extraction unit as an extraction solvent for continued use; introducing the regenerated gas phase into a gas buffer tank 8 for gas-liquid separation, compressing at least a portion of the gas stream obtained at the top of the tank and returning it to the alkali regeneration unit; detecting the pressure signal at the top of the gas buffer tank 8 and the oxygen content signal of the gas stream returning to the alkali regeneration unit, and controlling the oxygen flow rate and / or oxygen concentration entering the alkali regeneration unit based on the pressure signal and the oxygen content signal.

[0041] Through the above technical solution, this disclosure first pre-treats the liquid hydrocarbons, and then uses the alkaline solution as the extraction solvent for extraction treatment, which enables more thiols in the liquid hydrocarbons to enter the alkaline solution, thereby enhancing the removal rate of thiols in the liquid hydrocarbons; then, the rich alkaline solution is regenerated with oxygen of a certain concentration, so that the alkaline solution can be regenerated, and the excess gas generated in the regeneration process is further regenerated, controlling the top pressure of the gas buffer tank 8 and the oxygen content of the oxygen-containing phase returned to the alkaline solution regeneration unit, eliminating the safety hazards caused by excess gas emissions, and also significantly reducing fuel gas consumption.

[0042] In one embodiment, the method further includes, before performing the extraction process, pre-treating the sulfur-containing liquid hydrocarbon a and demineralized water b into a pre-treatment unit to obtain the pre-treated liquid hydrocarbon and amine-containing water; returning a portion of the amine-containing water to the pre-treatment unit; wherein the weight ratio of the amine-containing water returned to the pre-treatment unit to the discharged amine-containing water c is (2-20):1; and the weight ratio of the total weight of the demineralized water b and the amine-containing water returned to the pre-treatment unit to the weight of the liquid hydrocarbon is (0.05-0.5):1.

[0043] In one embodiment, the oxygen entering the alkali regeneration unit comes from the pressure swing adsorption (PSA) oxygen generator unit 17. The method further includes: when the pressure signal at the top of the gas buffer tank 8 is above a first threshold and the oxygen content signal of the online analyzer 10 is above a second threshold, causing the second control unit 15 to send a signal to the third control unit 27 to reduce the oxygen production of the PSA oxygen generator unit 17 while maintaining the original oxygen concentration output by the PSA oxygen generator unit 17; when the pressure signal at the top of the gas buffer tank 8 is above the first threshold and the oxygen content signal of the online analyzer 10 is below the second threshold, causing the second control unit 15 to send a signal to the third control unit 27 to increase the oxygen concentration entering the alkali regeneration unit from the PSA oxygen generator unit 17; the first threshold is selected from any value between 0.45 and 0.55 MPa, and the second threshold is selected from any value between 5.5 and 6.5% by volume.

[0044] In this embodiment, when the oxygen content of the oxygen-containing phase stream returning to the alkali regeneration tower 5 changes, detected by the online analyzer 10, the second control unit 15 calculates the required oxygen flow rate and concentration for the pressure swing adsorption (PSA) oxygen generation unit 17, compares it with the existing oxygen flow rate and concentration, and finally sends a signal to the third control unit 27 to increase or decrease the oxygen flow rate and / or increase or decrease the oxygen concentration. The third control unit 27 controls the opening or closing time of the inlet regulating valve, outlet regulating valve, and exhaust regulating valve in the PSA oxygen generation unit 17 to ensure that the output of the PSA oxygen generation unit 17 reaches the oxygen flow rate and oxygen concentration calculated by the second control unit 15. The oxygen content of the gaseous stream entering the alkali regeneration unit is 5-8% by volume; the oxygen concentration of the oxygen entering the alkali regeneration unit is 50-95% by volume.

[0045] In another embodiment, the oxygen entering the alkali regeneration unit comes from the oxygen inlet pipe. The method further includes introducing nitrogen into the alkali regeneration tower 5 through the nitrogen inlet pipe; using a fourth control unit 33 to acquire the oxygen flow rate signal of the oxygen inlet pipe and the nitrogen flow rate signal of the nitrogen inlet pipe, and calculating the oxygen-nitrogen volumetric flow rate ratio; optionally, the method further includes: using a second control unit 15 to acquire the tank top pressure signal and the oxygen content signal of the online analyzer 10, and adjusting the oxygen flow rate entering the alkali regeneration unit and / or the oxygen-nitrogen volumetric flow rate ratio of the fourth control unit 33 according to the tank top pressure signal and the oxygen content signal. Specifically, the second control unit 15 adjusts the opening of the oxygen flow regulating valve 29 on the oxygen inlet pipe according to the tank top pressure signal and the oxygen content signal to regulate the oxygen flow rate entering the alkali regeneration unit; after receiving the signal from the second control unit 15, the fourth control unit 33 controls the oxygen-nitrogen volumetric flow rate ratio by controlling the opening of the nitrogen flow regulating valve 31.

[0046] In one specific embodiment, when the second control unit 15 detects that the pressure signal at the top of the gas buffer tank 8 is above a first threshold and the oxygen content signal of the online analyzer 10 is above a second threshold, it reduces the opening of the oxygen flow regulating valve 29 on the oxygen inlet pipe and keeps the oxygen-nitrogen volumetric flow rate ratio of the fourth control unit 33 unchanged, thereby reducing the oxygen flow rate entering the alkali regeneration unit; when the second control unit 15 detects that the pressure signal at the top of the gas buffer tank 8 is above a first threshold and the oxygen content signal of the online analyzer 10 is below a second threshold, the second control unit 15 keeps the opening of the oxygen flow regulating valve 29 on the oxygen inlet pipe unchanged and sends a signal to the fourth control unit 33 to increase the oxygen-nitrogen volumetric flow rate ratio, causing the fourth control unit 33 to reduce the opening of the regulating valve on the nitrogen inlet pipe, thereby reducing the nitrogen flow rate entering the alkali regeneration unit; the first threshold is selected from any value from 0.45 to 0.55 MPa, the second threshold is selected from any value from 5.5 to 6.5 volume%, and the oxygen-nitrogen volumetric flow rate ratio is (1 to 20):1.

[0047] In one embodiment, the gaseous stream needs to be pressurized by the circulating gas compressor 9 before at least a portion of it is returned to the alkali regeneration tower 5.

[0048] In one embodiment, the method further includes controlling another portion of the gaseous stream and fuel gas to enter the flare for combustion and venting based on the tank top pressure signal; optionally, when the first control unit 14 detects that the tank top pressure signal of the gas buffer tank 8 is above a third threshold, the fuel gas cut-off valve 13 and the gas cut-off valve 12 are opened sequentially, so that the fuel gas and another portion of the gaseous stream enter the flare vent line 11 sequentially to mix and obtain flare feed gas, and the flare feed gas enters the flare device for combustion and venting; when the first control unit 14 detects that the tank top pressure signal of the gas buffer tank 8 is less than the fourth threshold, the gas cut-off valve 12 and the fuel gas cut-off valve 13 are closed sequentially, so that all the gaseous stream is compressed and returned to the alkali regeneration unit; the third threshold is selected from any value from 0.55 to 0.6 MPa, and the fourth threshold is selected from any value from 0.45 to 0.55 MPa.

[0049] In one embodiment, before entering the alkali regeneration unit, the rich alkali solution is mixed with the catalyst and the extraction oil; the volumetric flow rate ratio of the extraction oil to the rich alkali solution is 0.05–0.4. The operating pressure of the gas buffer tank 8 is 0.2–0.55 MPa.

[0050] In one implementation, such as Figure 1 As shown, methods for removing thiols from liquid hydrocarbons include:

[0051] Demineralized water b and sulfur-containing liquid hydrocarbon a are introduced into pretreatment tank 1 for pretreatment. The pretreated liquid hydrocarbon is discharged from the top of pretreatment tank 1, and amine-containing water is discharged from the bottom. A portion of the amine-containing water is returned to pretreatment tank 1 via amine-containing water circulation pump 2, and the other portion is discharged as amine-containing water c from the system. The weight ratio of the total weight of the demineralized water b and the amine-containing water returned to the pretreatment unit to the weight of the liquid hydrocarbon is (0.05~0.5):1; the weight ratio of the amine-containing water returned to the pretreatment unit to the discharged amine-containing water c is (2~20):1.

[0052] The pretreated liquid hydrocarbons are introduced into the extraction reactor 3 of the extraction unit to contact the extraction medium for extraction treatment. The resulting pretreated liquid hydrocarbons are then introduced into the extraction settling tank 4 of the extraction unit for separation. The upper part of the extraction settling tank 4 yields refined liquid hydrocarbons d, and the bottom yields an alkaline-rich solution. The extraction conditions include: a temperature of 35-45℃, a pressure of 1.0-1.8MPa, and a weight flow ratio of pretreated liquid hydrocarbons to extraction medium of (2-10):1.

[0053] The rich alkali solution is heated to 40-55°C by heat exchanger 16, and then enters the alkali regeneration tower 5 in the alkali regeneration unit along with catalyst k, extraction oil i, and oxygen e for regeneration treatment. A mixture is obtained from the top of the tower, and a first portion of regenerated gas phase is obtained from the top of the tower. The regeneration conditions include a temperature of 40-55°C and a pressure of 0.2-0.4 MPa. The obtained mixture enters the alkali settling tank 6 for gas-liquid separation. A second portion of regenerated gas phase and disulfide oil f are obtained from the top of the tank, and lean alkali solution is obtained from the bottom of the tower. The first and second portions of regenerated gas phase are mixed and sent to the subsequent treatment unit as regenerated gas phase. A portion of the lean alkali solution is mixed with fresh alkali solution l and returned to the extraction reactor 3 via alkali circulation pump 7. Another portion of the lean alkali solution is discharged as waste alkali solution m.

[0054] The regenerated gas phase is introduced into the gas buffer tank 8 for gas-liquid separation, so that the obtained top gas phase is divided into a first top gas phase and a second top gas phase.

[0055] When the first control unit 14 detects that the pressure signal of the gas buffer tank 8 is above the third threshold, it sequentially opens the fuel gas cut-off valve 13 and the gas cut-off valve 12 so that the first top gas phase can be mixed with the fuel gas g, and the resulting flare feed gas enters the flare device for processing; when the first control unit 14 detects that the pressure signal of the gas buffer tank 8 is below the fourth threshold, it sequentially closes the gas cut-off valve 12 and the fuel gas cut-off valve 13 so that the first top gas phase does not enter the flare device; the volume flow ratio of fuel gas to the first top gas phase is (2~5):1, the third threshold is selected from any value in the range of 0.55~0.6MPa, and the fourth threshold is selected from any value in the range of 0.45~0.55MPa;

[0056] When the second control unit 15 detects that the pressure signal of the gas buffer tank 8 is above the first threshold and the oxygen content signal of the online analyzer 10 is above the second threshold, the second control unit 15 sends a signal to the third control unit 27 to reduce the oxygen production, causing the third control unit 27 to reduce the oxygen production of the pressure swing adsorption oxygen generation unit 17; when the oxygen content signal of the online analyzer 10 is below the second threshold, the second control unit 15 sends a signal to the third control unit 27 to increase the oxygen concentration, causing the third control unit 27 to increase the oxygen concentration of the pressure swing adsorption oxygen generation unit 17; the first threshold is selected from any value from 0.45 to 0.55 MPa, and the second threshold is selected from any value from 5.5 to 6.5 vol%.

[0057] Example 1

[0058] like Figure 1 and Figure 2 As shown, the method for removing liquid hydrocarbon thiols includes:

[0059] Demineralized water (b) and sulfur-containing liquid hydrocarbons (a) are introduced into pretreatment tank 1 for pretreatment. The pretreated liquid hydrocarbons are discharged from the top of pretreatment tank 1, and amine-containing water is discharged from the bottom. A portion of the amine-containing water is returned to pretreatment tank 1 via amine-containing water circulation pump 2, while the other portion is discharged as amine-containing water (c) out of the system. The pretreatment conditions include: a temperature of 40°C, a pressure of 1.6 MPa, a weight ratio of the total weight of the demineralized water (b) and the amine-containing water returned to the pretreatment unit to the weight of the liquid hydrocarbons of 0.2:1, and a weight ratio of the amine-containing water returned to the pretreatment unit to the discharged amine-containing water (c) of 19:1.

[0060] The pretreated liquid hydrocarbons are introduced into the extraction reactor 3 of the extraction and separation unit to contact the extraction medium for extraction treatment. The resulting pretreated liquid hydrocarbons are then introduced into the extraction settling tank 4 of the extraction and separation unit for separation. The upper part of the extraction settling tank 4 yields refined liquid hydrocarbons d, and the bottom yields an alkaline-rich solution. The extraction conditions include: a temperature of 40°C, a pressure of 1.55 MPa, and a weight flow ratio of pretreated liquid hydrocarbons to extraction medium of 4.55:1.

[0061] The rich alkali solution is heated to 50°C by heat exchanger 16, and then enters the alkali regeneration tower 5 in the alkali regeneration unit along with catalyst k, extraction oil i, and oxygen e for regeneration treatment. The mixture obtained from the top of the tower and the first part of the regeneration gas phase are obtained from the top of the tower. The oxygen e comes from the pressure swing adsorption oxygen generation unit 17, with an oxygen generation rate of 6 kg / h. The regeneration conditions include: temperature of 50°C, reaction pressure of 0.4 MPa, and weight flow ratio of oxygen to rich alkali solution of 0.0006:1. The resulting mixture is fed into an alkali settling tank 6 for gas-liquid separation. A second portion of regenerated gas phase and disulfide oil f are obtained from the top of the tank, while lean alkali solution is obtained from the bottom. The first and second portions of regenerated gas phase are mixed and sent to the subsequent processing unit as regenerated gas phase. A portion of the lean alkali solution is mixed with fresh alkali solution l and returned to the extraction reactor 3 via an alkali circulation pump 7. Another portion of the lean alkali solution is discharged as waste alkali solution m. The weight ratio of waste alkali solution m to lean alkali solution is 0.0005 to 0.005:1.

[0062] The regenerated gas phase is introduced into the gas buffer tank 8 for gas-liquid separation, so that the obtained top gas phase is divided into a first top gas phase and a second top gas phase.

[0063] When the first control unit 14 detects that the pressure signal of the gas buffer tank 8 is above the third threshold, it sequentially opens the fuel gas cut-off valve 13 and the gas cut-off valve 12 to allow the first top gas phase to mix with the fuel gas g, and the resulting flare feed gas enters the flare device for processing; when the first control unit 14 detects that the pressure signal of the gas buffer tank 8 is below the fourth threshold, it sequentially closes the gas cut-off valve 12 and the fuel gas cut-off valve 13 to prevent the first top gas phase from entering the flare device; the cross-sectional area ratio of the fuel gas pipeline to the first top gas phase pipeline is 2.5:1, the third threshold is 0.55 MPa, and the fourth threshold is 0.45 MPa;

[0064] When the second control unit 15 detects that the pressure signal of the gas buffer tank 8 is above the first threshold and the oxygen content signal of the online analyzer 10 is above the second threshold, the second control unit 15 sends a signal to the third control unit 27 to reduce the oxygen production, causing the third control unit 27 to reduce the oxygen production of the pressure swing adsorption oxygen generation unit 17; when the oxygen content signal of the online analyzer 10 is below the second threshold, the second control unit 15 sends a signal to the third control unit 27 to increase the oxygen concentration, causing the third control unit 27 to increase the oxygen concentration of the pressure swing adsorption oxygen generation unit 17; the first threshold is 0.5 MPa, and the second threshold is 6% by volume. The results are shown in Table 1.

[0065] Example 2

[0066] like Figure 3 As shown, the system for removing liquid hydrocarbon mercaptan is the same as in Example 1, except that an oxygen flow regulating valve 29 and an oxygen flow meter 30 are installed on the oxygen inlet pipeline of the alkaline regeneration tower 5; the second control unit 15 is electrically connected to the oxygen flow regulating valve 29 and the oxygen flow meter 30 to receive the flow signal from the oxygen flow meter 30 and control the opening degree of the oxygen flow regulating valve 29.

[0067] The alkali regeneration tower 5 is also equipped with a nitrogen inlet, and a nitrogen flow regulating valve 31 and a nitrogen flow meter 32 are installed on the nitrogen inlet pipeline; the pressure swing adsorption oxygen generation unit 17 in Example 1 is replaced with a fourth control unit 33, which is electrically connected to the oxygen flow meter 30, the nitrogen flow regulating valve 31 and the nitrogen flow meter 32; the fourth control unit 33 is used to receive the flow signals from the oxygen flow meter 30 and the nitrogen flow meter 32 and control the opening degree of the nitrogen flow regulating valve 31;

[0068] The method for removing liquid hydrocarbon mercaptan is the same as in Example 1, except that oxygen is sent into the alkaline regeneration tower 5 through the oxygen inlet pipe and nitrogen is sent into the alkaline regeneration tower 5 through the nitrogen inlet pipe; the fourth control unit 33 is used to obtain the oxygen inlet flow signal of the oxygen inlet pipe and calculate the oxygen-nitrogen volume flow ratio.

[0069] The second control unit 15 acquires the tank top pressure signal and the oxygen content signal, and adjusts the oxygen flow rate entering the alkali regeneration unit and / or the oxygen-nitrogen volume flow rate ratio of the fourth control unit 33 according to the tank top pressure signal and the oxygen content signal.

[0070] When the second control unit 15 detects that the pressure signal at the top of the gas buffer tank 8 is above 0.5 MPa and the oxygen content signal of the online analyzer 10 is greater than 6% by volume, the second control unit 15 reduces the opening of the oxygen flow regulating valve 29 on the oxygen inlet pipe to reduce the oxygen flow into the alkali regeneration unit, while maintaining the oxygen-nitrogen volumetric flow rate ratio calculated by the fourth control unit 33 at 10:1. When the second control unit 15 detects that the pressure signal at the top of the gas buffer tank 8 is above 0.5 MPa and the oxygen content signal of the online analyzer 10 is below 6% by volume, the second control unit 15 keeps the opening of the regulating valve on the oxygen inlet pipe unchanged and sends a signal to the fourth control unit 33 to increase the oxygen-nitrogen volumetric flow rate ratio. The fourth control unit 33 then reduces the opening of the nitrogen flow regulating valve 31 on the nitrogen inlet pipe to reduce the nitrogen flow into the alkali regeneration unit until the oxygen-nitrogen volumetric flow rate ratio calculated by the fourth control unit 33 is 10:1. The results are shown in Table 1.

[0071] Comparative Example 1

[0072] like Figure 4 As shown, sulfur-containing liquid hydrocarbon a is introduced into the extraction reactor 3 of the extraction unit and comes into contact with the extraction medium for extraction and separation. The resulting stream is then introduced into the extraction settling tank 4 of the extraction unit for further separation. Refined liquid hydrocarbon d is obtained from the upper part of the extraction settling tank 4, and an alkaline-rich solution is obtained from the bottom. The extraction conditions include: a temperature of 40°C, a pressure of 1.6 MPa, and a weight flow ratio of pretreated liquid hydrocarbon to extraction medium of 4.55:1.

[0073] The rich alkali solution is heated to 50°C by heat exchanger 16, and then enters the alkali regeneration tower 5 in the alkali regeneration unit along with catalyst k, extraction oil i, and plant air h for regeneration. The mixture obtained from the top of the tower and the first excess gas obtained from the top of the tower are obtained. The regeneration conditions include a temperature of 50°C and a reaction pressure of 0.4 MPa. The obtained mixture enters the alkali settling tank 6 for gas-liquid separation. The second excess gas and disulfide oil f are obtained from the top of the tank, and the lean alkali solution is obtained from the bottom of the tank. The first excess gas and the second excess gas are mixed and sent to the subsequent processing unit as excess gas. A portion of the lean alkali solution is mixed with fresh alkali solution l and then returned to the extraction reactor 3 via alkali circulation pump 7.

[0074] Excess gas is fed into a gas buffer tank 8 for gas-liquid separation. The resulting excess gas from the top of the tank, fuel gas g, and air o are then fed into the incinerator 34 for combustion, and the resulting flue gas n is discharged from the system. The results are shown in Table 1.

[0075] Table 1 Results of Examples and Comparative Examples

[0076]

[0077] As can be seen from the data in Table 1, by comparing the data in Examples 1-2 and Comparative Example 1, the technical solution of this application can improve the efficiency of liquid hydrocarbon desulfurization, eliminate the safety hazards caused by excess gas emissions, achieve zero waste gas emissions, zero fuel gas consumption, stable system operating pressure, and long-term operation.

[0078] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0079] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0080] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A system for removing thiols from liquid hydrocarbons, characterized in that, The system includes an extraction and separation unit, an alkali regeneration unit, a regeneration gas treatment unit, and a second control unit (15). The extraction and separation unit includes a pre-treatment liquid hydrocarbon inlet, a lean alkali inlet, a refined liquid hydrocarbon outlet, and a rich alkali outlet; the alkali regeneration unit includes an oxygen inlet, an oxygen-containing phase inlet, a rich alkali inlet, a regenerated gas phase outlet, a lean alkali outlet, and a disulfide oil outlet; the regeneration gas treatment unit includes a regeneration gas phase inlet, a first top gas phase outlet, and a second top gas phase outlet. The rich alkali solution outlet of the extraction and separation unit is connected to the rich alkali solution inlet of the alkali solution regeneration unit; the lean alkali solution outlet of the alkali solution regeneration unit is connected to the lean alkali solution inlet of the extraction and separation unit; the regeneration gas phase outlet of the alkali solution regeneration unit is connected to the regeneration gas phase inlet of the regeneration gas treatment unit; the first top gas phase outlet of the regeneration gas treatment unit is connected to the flare device; and the second top gas phase outlet of the regeneration gas treatment unit is connected to the oxygen-containing phase inlet of the alkali solution regeneration unit. The regenerated gas treatment unit includes a gas buffer tank (8), on which a pressure gauge is provided; an online analyzer (10) is provided on the pipeline of the oxygen-containing phase inlet of the alkali regeneration unit; the second control unit (15) is electrically connected to the pressure gauge and the online analyzer (10), and is used to receive the pressure signal of the pressure gauge and the oxygen content signal of the online analyzer (10), and control the oxygen flow rate and / or oxygen concentration entering the alkali regeneration unit; The oxygen inlet pipeline of the alkali regeneration unit is equipped with an oxygen flow regulating valve (29) and an oxygen flow meter (30); the second control unit (15) is electrically connected to the oxygen flow regulating valve (29) and the oxygen flow meter (30) to receive the flow signal of the oxygen flow meter (30) and control the opening degree of the oxygen flow regulating valve (29); The alkaline regeneration unit also includes a nitrogen inlet, the nitrogen inlet pipeline being used to connect to a nitrogen source; the nitrogen inlet pipeline is equipped with a nitrogen flow regulating valve (31) and a nitrogen flow meter (32). The system also includes a fourth control unit (33); the fourth control unit (33) is electrically connected to the oxygen flow meter (30), the nitrogen flow regulating valve (31) and the nitrogen flow meter (32); the fourth control unit (33) is used to receive the flow signals of the oxygen flow meter (30) and the nitrogen flow meter (32) and control the opening degree of the nitrogen flow regulating valve (31).

2. The system according to claim 1, characterized in that, The system also includes a pressure swing adsorption (PSA) oxygen generation unit (17), which includes a third control unit (27), an industrial air feed main line, an oxygen discharge main line, and at least two adsorption branches; each adsorption branch is provided with an exhaust branch; each adsorption branch is provided with an inlet regulating valve, an exhaust outlet, an adsorption tower, and an outlet regulating valve in sequence along the gas flow direction; the exhaust branch is provided with an exhaust regulating valve; and an oxygen analyzer (28) is provided at the outlet of the oxygen discharge main line. The inlet of the industrial air feed main line is connected to the industrial air source, and the outlet of the industrial air feed main line is connected to the inlet of the adsorption branch line; the outlet of the adsorption branch line is connected to the inlet of the oxygen discharge main line, and the outlet of the oxygen discharge main line is connected to the oxygen inlet of the alkali regeneration unit; the inlet of the exhaust branch line is connected to the exhaust gas outlet of the adsorption branch line, and the outlet of the exhaust branch line is used to connect with the atmosphere. The third control unit (27) is electrically connected to the intake regulating valve, the exhaust regulating valve, the exhaust regulating valve and the second control unit (15); the third control unit (27) is used to receive the regulation signal from the second control unit (15) and control the opening or closing time of the intake regulating valve, the exhaust regulating valve and the exhaust regulating valve.

3. The system according to claim 1, characterized in that, A gas shut-off valve (12) and a fuel gas inlet are sequentially provided along the material flow direction on the pipeline of the first top gas phase outlet; the fuel gas inlet of the first top gas phase outlet pipeline is used to connect with the outlet of the fuel gas pipeline, and the inlet of the fuel gas pipeline is used to connect with the fuel gas source; a fuel gas shut-off valve (13) is provided on the fuel gas pipeline. The system also includes a first control unit (14), which is electrically connected to the pressure gauge of the gas buffer tank (8), the gas shut-off valve (12) and the fuel gas shut-off valve (13); the first control unit (14) is used to receive the pressure signal of the pressure gauge of the gas buffer tank (8) and control the opening degree of the gas shut-off valve (12) and the fuel gas shut-off valve (13).

4. A method for removing thiols from liquid hydrocarbons using the system described in any one of claims 1 to 3, characterized in that, The method includes: The pretreated liquid hydrocarbons are introduced into the extraction unit and come into contact with the extraction solvent for extraction treatment to obtain purified liquid hydrocarbons and an alkaline-rich solution; the extraction solvent is an alkaline solution. The rich alkali solution is introduced into the alkali regeneration unit and regenerated by contacting oxygen to obtain a lean alkali solution, disulfide oil, and regenerated gas phase; the lean alkali solution is then returned to the extraction unit as the extraction solvent for continued use. The regenerated gas phase is fed into a gas buffer tank (8) for gas-liquid separation, and at least a portion of the gas phase stream obtained from the top of the tank is compressed and returned to the alkali regeneration unit. The pressure signal at the top of the gas buffer tank (8) and the oxygen content signal of the gaseous stream returning to the alkali regeneration unit are detected, and the oxygen flow rate and / or oxygen concentration entering the alkali regeneration unit are controlled according to the pressure signal at the top of the tank and the oxygen content signal. The oxygen entering the alkaline regeneration unit comes from the oxygen inlet pipe. The method also includes introducing nitrogen into the alkaline regeneration unit through the nitrogen inlet pipe; using the fourth control unit (33) to obtain the oxygen flow rate signal of the oxygen inlet pipe and the nitrogen flow rate signal of the nitrogen inlet pipe, and calculating the oxygen-nitrogen volume flow rate ratio. The method further includes: using a second control unit (15) to acquire the tank top pressure signal and the oxygen content signal of the online analyzer (10), and adjusting the oxygen flow rate entering the alkaline regeneration unit and / or the oxygen-nitrogen volume flow rate ratio of the fourth control unit (33) according to the tank top pressure signal and the oxygen content signal.

5. The method according to claim 4, characterized in that, The oxygen entering the alkaline regeneration unit comes from the pressure swing adsorption oxygen generation unit (17). The method further includes: when the pressure signal at the top of the gas buffer tank (8) is above a first threshold and the oxygen content signal of the online analyzer (10) is above a second threshold, the second control unit (15) sends a signal to the third control unit (27) to reduce the oxygen production of the pressure swing adsorption oxygen generator (17) and maintain the original oxygen concentration output by the pressure swing adsorption oxygen generator (17); when the pressure signal at the top of the gas buffer tank (8) is above a first threshold and the oxygen content signal of the online analyzer (10) is below a second threshold, the second control unit (15) sends a signal to the third control unit (27) to increase the oxygen concentration output by the pressure swing adsorption oxygen generator (17). The first threshold is selected from any value in the range of 0.45 to 0.55 MPa, and the second threshold is selected from any value in the range of 5.5 to 6.5% by volume.

6. The method according to claim 4, characterized in that, When the second control unit (15) detects that the pressure signal at the top of the gas buffer tank (8) is above the first threshold and the oxygen content signal of the online analyzer (10) is greater than the second threshold, it reduces the opening of the oxygen flow regulating valve (29) on the oxygen inlet pipe and keeps the oxygen-nitrogen volume flow ratio of the fourth control unit (33) unchanged, so as to reduce the oxygen flow into the alkali regeneration unit; when the second control unit (15) detects that the pressure signal at the top of the gas buffer tank (8) is above the first threshold and the oxygen content signal of the online analyzer (10) is below the second threshold, the second control unit (15) keeps the opening of the oxygen flow regulating valve (29) on the oxygen inlet pipe unchanged, and gives the fourth control unit (33) a signal to increase the oxygen-nitrogen volume flow ratio, so that the fourth control unit (33) reduces the opening of the nitrogen flow regulating valve (31) on the nitrogen inlet pipe, so as to reduce the nitrogen flow into the alkali regeneration unit; The first threshold is selected from any value in the range of 0.45 to 0.55 MPa, the second threshold is selected from any value in the range of 5.5 to 6.5 volume%, and the oxygen-nitrogen volume flow rate ratio is (1 to 20):

1.

7. The method according to claim 4, characterized in that, The method also includes controlling another portion of the gaseous stream and fuel gas to enter the flare for combustion and then venting, based on the pressure signal at the top of the tank. When the first control unit (14) detects that the pressure signal at the top of the gas buffer tank (8) is above the third threshold, it sequentially opens the fuel gas cut-off valve (13) and the gas cut-off valve (12), so that the fuel gas and another part of the gas phase flow enter the flare line (11) in sequence to mix and obtain the flare feed gas, and the flare feed gas enters the flare device for combustion and then vents; when the first control unit (14) detects that the pressure signal at the top of the gas buffer tank (8) is less than the fourth threshold, it sequentially closes the gas cut-off valve (12) and the fuel gas cut-off valve (13), so that all the gas phase flow is compressed and returned to the alkali regeneration unit; The third threshold is selected from any value between 0.55 and 0.6 MPa, and the fourth threshold is selected from any value between 0.45 and 0.55 MPa.

8. The method according to claim 4, characterized in that, The oxygen content of the gaseous stream entering the alkali regeneration unit is 5-8% by volume; the oxygen concentration of the oxygen entering the alkali regeneration unit is 50-95% by volume. The method further includes mixing the rich alkali solution with the catalyst and the extraction oil before it enters the alkali regeneration unit; the volume flow ratio of the extraction oil to the rich alkali solution is 0.05~0.

4. The operating pressure of the gas buffer tank (8) is 0.2~0.55MPa.

9. The method according to claim 4, characterized in that, The method further includes, before performing the extraction process, pre-treating the sulfur-containing liquid hydrocarbon and demineralized water into a pre-treatment unit to obtain the pre-treated liquid hydrocarbon and amine-containing water; returning a portion of the amine-containing water to the pre-treatment unit and using the other portion as a discharged amine-containing water system; wherein the weight ratio of the amine-containing water returned to the pre-treatment unit to the discharged amine-containing water is (2~20):1; The total weight ratio of the demineralized water and the amine-containing water returned to the pretreatment unit to the weight ratio of the sulfur-containing liquid hydrocarbon is (0.05~0.5):1.

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