A method for removing water from a fischer-tropsch synthesis

Abstract

The application provides a method for removing oil from Fischer-Tropsch synthesis water, which comprises the following steps: feeding emulsified Fischer-Tropsch synthesis water into a raw material water tank for standing, separating to obtain an oil phase product and a water phase product, and mixing the water phase product with oily substances at a high temperature to separate oil and water, so as to achieve the purpose of removing oil from the Fischer-Tropsch synthesis water. The method can be advantageously used for removing oil from the emulsified Fischer-Tropsch synthesis water, and effectively separates the emulsified oil contained in the Fischer-Tropsch synthesis water, so that the oil content in the obtained Fischer-Tropsch synthesis water is greatly reduced, the COD in the waste water is greatly reduced, the oil product yield is effectively improved, and the economic benefit is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of purification treatment of chemical wastewater, and particularly relates to a method for removing oil from Fischer-Tropsch synthesis water. BACKGROUND

[0002] Fischer-Tropsch synthesis reaction is a process in which carbon-containing resources such as coal, natural gas, biomass, organic garbage and sludge are first converted into synthesis gas (CO and H2), and then converted into hydrocarbon organic matter (mainly including n-alkanes, a small amount of isomeric alkanes, alkenes, etc.) through a specific catalyst, while a large amount of water and part of low-carbon number oxygen-containing organic matter (mainly including alcohol, aldehyde, ketone, acid and ester, etc.) are also generated, and a large amount of heat is released. In the process of iron-based Fischer-Tropsch synthesis reaction, the yield of water is generally more than one time of the yield of synthetic oil.

[0003] After the Fischer-Tropsch synthesis reaction, the generated Fischer-Tropsch synthesis water and Fischer-Tropsch synthesis hydrocarbons need to be separated. This preliminary separation process can be described as follows: the gas phase product of the Fischer-Tropsch reactor is flash evaporated by cooling, a part of which is cooled into a liquid phase fluid, and the liquid phase fluid is separated into a water phase fluid containing a small amount of dissolved organic matter (hydrocarbons and oxygen-containing organic matter) and a small amount of suspended matter through an oil-water separator, i.e. the Fischer-Tropsch synthesis water to be treated in the present application.

[0004] In the process of Fischer-Tropsch synthesis, due to the differences in Fischer-Tropsch synthesis process technology, Fischer-Tropsch synthesis catalyst and synthesis reaction operation parameters, the composition of the Fischer-Tropsch synthesis water phase by-product is also different. Generally, the Fischer-Tropsch synthesis water phase contains 70wt%-97wt% of water and 3wt%-30wt% of organic oxygen-containing compounds. According to the data of Fischer-Tropsch synthesis water provided by the current commercialization project, the composition of the Fischer-Tropsch synthesis water obtained by the applicant using the high-temperature slurry bed iron-based Fischer-Tropsch synthesis technology of the China Synfuel Technology Co., Ltd. is as follows: in addition to water, the content of C5-C20 hydrocarbons is generally less than 1000 ppm, the carbon number of oxygen-containing organic matter is generally less than 8, and the content is generally not higher than 5wt% (among them, the content of alcohol (C1-C8 alcohol) is generally not higher than 2wt%, the content of acid (C1-C6 acid) is generally not higher than 1wt%, and there are aldehyde (acetaldehyde and propyl aldehyde), ketone (acetone and butanone), ester (ethyl formate, ethyl acetate), the content of the three is not higher than 0.5wt%); COD = 15000-60000 mg / L; pH = 2-4; total oil is not higher than 2000 mg / L, and petroleum is not higher than 1000 mg / L.

[0005] Due to the presence of hydrocarbons and oxygen-containing organic matter, the Fischer-Tropsch synthesis water does not meet the standards for discharge or recycling, and especially the acid organic matter in the Fischer-Tropsch synthesis water can also cause corrosion to the equipment. Therefore, it is necessary to treat the Fischer-Tropsch synthesis water before discharge or utilization. This is very necessary for reducing environmental pollution, recovering high-value-added organic matter and improving the economic benefits of the Fischer-Tropsch process.

[0006] There are many patents on the recovery and utilization of Fischer-Tropsch synthesis water, such as ZL03814122.1, ZL03814125.6 and ZL03814127.2 each discloses a purification method of Fischer-Tropsch reaction water. The main process operation units involved in the patents include: ordinary rectification, evaporation, extraction, biological treatment, solid-liquid separation and reverse osmosis, etc. In the process involved, the water-containing substance at the bottom of the rectification tower is first subjected to biological treatment, and then subjected to reverse osmosis to obtain high-purity water. In addition, ZL201010512405.5, ZL201310368576.9, ZL201310424500.3 and ZL201510940955.X each discloses a separation and recovery method of Fischer-Tropsch synthesis water-phase organic oxygen-containing compounds, and the main operation units involved in the patents include: acid-base neutralization, rectification, reverse osmosis, biological treatment, advanced oxidation, etc. By adding inorganic base to the Fischer-Tropsch synthesis water to neutralize the carboxylic acid in the Fischer-Tropsch synthesis water to form carboxylic acid salt, the pH value is adjusted to neutral, and then the neutralized Fischer-Tropsch synthesis water is sent to the rectification tower for rectification, thereby reducing the corrosion of the equipment.

[0007] In the above-mentioned patent technologies, whether it is to recover the organic matter in the Fischer-Tropsch synthesis water or to purify the Fischer-Tropsch synthesis water, it is necessary to first remove the oil from the Fischer-Tropsch synthesis water, which is also the key to determine whether the above-mentioned patent technologies can be successfully implemented. However, during the entire commercialization project operation process, the gas-phase product of the Fischer-Tropsch reactor is cooled and flashed to obtain a fluid that enters an oil-water separator, but the oil and water cannot be completely separated, and at the same time, the gas-phase product at the top of the reactor also contains small-sized catalyst particles, which causes a large-area blockage of the coalescer when further removing oil with the coalescer, thereby causing the entire oil removal unit to not operate normally, the treatment load is greatly reduced, the water quality indicators at the outlet of the oil removal unit cannot meet the design requirements, and in severe cases, it will affect the stable operation of the downstream synthesis water treatment unit, ultimately leading to the stagnation of the synthesis water treatment process, and even shutdown, therefore, the stable operation of the oil removal process is also related to the stable operation of the entire production process, which is very important for the commercialization of Fischer-Tropsch synthesis.

[0008] In addition, during the oil-water separation process of the Fischer-Tropsch synthesis water, there is often an oil-water emulsification problem, so that the oil content in the water-phase product separated initially is still high, and if the emulsification state of the Fischer-Tropsch synthesis water cannot be fundamentally solved, it will still have an adverse effect on the purification and separation process of the Fischer-Tropsch synthesis water. SUMMARY

[0009] In view of the above problems, the present application provides a method for removing oil from Fischer-Tropsch synthesis water, which is simple in process and can be continuously operated in industry, by transferring the emulsified oil in the water-phase product separated from the Fischer-Tropsch synthesis water to the oil phase in an oil-water mixed manner at high temperature, and then separating the oil and water by an oil-water separator, thereby breaking the emulsion of the water-phase product and removing the emulsified oil in the water-phase product from the water-phase product.

[0010] In one aspect, the present application provides a method for removing oil from Fischer-Tropsch synthesis water, comprising:

[0011] (1) feeding the emulsified Fischer-Tropsch synthesis water into a raw water tank for standing, to separate an oil phase product and an aqueous phase product;

[0012] (2) heating the aqueous phase product to a temperature of not less than 80°C using a heat exchanger, and mixing the heated aqueous phase product with oily substances to obtain a mixture, wherein the oily substances are Fischer-Tropsch synthesis light oil, Fischer-Tropsch synthesis heavy oil and / or Fischer-Tropsch synthesis heavy wax, and the volume ratio of the aqueous phase product to the oily substances is 1:10 to 10:1;

[0013] (3) feeding the mixture into an oil-water separator for oil-water separation;

[0014] (4) mixing a part or all of the oil phase product from the oil-water separator with the oil phase product from the raw water tank, and outputting the mixture to a downstream unit;

[0015] (5) cooling the aqueous phase fluid separated from the oil-water separator using a heat exchanger, filtering the cooled aqueous phase fluid, and feeding the filtered aqueous phase fluid into a synthesis water treatment unit for oxygen-containing organic matter separation and synthesis water purification treatment.

[0016] The method of the present application for removing oil from emulsified Fischer-Tropsch synthesis water can exhibit the following technical advantages, but is not limited thereto:

[0017] 1. The method of the present application is a continuous operation, and the processing capacity can be adjusted according to the actual requirements of the plant site, is easy to realize industrialization, has low investment and operating cost, and is environmentally friendly;

[0018] 2. The oily substances used in the present application are Fischer-Tropsch synthesis products, which can be recycled and reused, effectively reducing process costs and not introducing impurities from outside the system;

[0019] 3. The method of the present application can be advantageously used for removing oil from emulsified Fischer-Tropsch synthesis water, and by effectively separating the emulsified oil contained in the Fischer-Tropsch synthesis water, the oil can be sent to a downstream unit for treatment, effectively improving the oil yield and economic benefits;

[0020] 4. After removing oil using the method of the present application, the oil content in the Fischer-Tropsch synthesis water is greatly reduced, and the COD in the wastewater is greatly reduced, which has good environmental benefits. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 Figure 1 is a flow diagram of an exemplary Fischer-Tropsch synthesis water oil removal method of the present application.

[0022] In the figures, the reference signs represent the following: T1 feed water tank; P1 feed pump; M1 static mixer; T2 oil-water separator; E1 heat exchanger;

[0023] 101 Fischer-Tropsch synthesis water, 102 oil phase product from the feed water tank, 103 water phase product from the feed water tank, 104, 105 mixed liquid, 106 oil phase product from the oil-water separator, 107 part of the oil phase product 106, 108 another part of the oil phase product 106; 109 water phase fluid. DETAILED DESCRIPTION

[0024] The following describes exemplary embodiments of the present application, but those skilled in the art will understand that the scope of protection of the present application is not limited thereto.

[0025] In this document, unless otherwise specified, the term "a part" or "part" means that the amount of the object being modified is greater than 0% to less than 100% relative to the total amount of the same kind of object.

[0026] In this document, unless otherwise specified, the term "room temperature" refers to a temperature of 10°C to 40°C.

[0027] In one embodiment, the present application relates to a method for removing oil from Fischer-Tropsch synthesis water, comprising:

[0028] (1) supplying emulsified Fischer-Tropsch synthesis water to a feed water tank for standing, and separating to obtain an oil phase product and a water phase product;

[0029] (2) mixing the water phase product with an oily substance after heating the water phase product to not less than 80°C by a heat exchanger to obtain a mixed liquid, the oily substance being Fischer-Tropsch synthesis light oil, Fischer-Tropsch synthesis heavy oil and / or Fischer-Tropsch synthesis heavy wax, the volume ratio of the water phase product to the oily substance being 1:10 to 10:1;

[0030] (3) supplying the mixed liquid to an oil-water separator for oil-water separation;

[0031] (4) mixing part or all of the oil phase product from the oil-water separator with the oil phase product from the feed water tank and outputting to a downstream unit;

[0032] (5) cooling the water phase fluid separated in the oil-water separator by heat exchange, and then filtering and sending to a synthesis water treatment unit for oxygen-containing organic matter separation and synthesis water purification treatment.

[0033] In the present application, the Fischer-Tropsch synthesis water is obtained by cooling and flash evaporation of the gas phase product from the Fischer-Tropsch synthesis reactor, and then separating the liquid phase product to obtain a water phase product containing a small amount of dissolved organic matter (hydrocarbons and oxygen-containing organic compounds) and a small amount of suspended matter.

[0034] In some embodiments, in step (1), the total content of oxygen-containing organic compounds in the Fischer-Tropsch synthesis water is 2wt% to 5wt%, COD = 15000 to 60000 mg / L (e.g. 15000 to 55000 mg / L), pH = 2 to 4 (e.g. 2.5 to 3.5), total oil is not more than 10000 mg / L (e.g. 500 mg / L to 2000 mg / L), and petroleum is not more than 2000 mg / L (e.g. 100 mg / L to 1000 mg / L). The oxygen-containing compounds include alcohols, aldehydes, acids, esters and ketones, etc., wherein the content of alcohols (mainly C1-C8 alcohols) is generally not more than 3wt%, the content of acids (mainly C1-C6 acids) is generally not more than 2wt%, and the total content of aldehydes (mainly acetaldehyde and propyl aldehyde), ketones (mainly acetone and butanone) and esters (mainly ethyl formate and ethyl acetate) is not more than 1wt%.

[0035] In some embodiments, in step (2), the water phase product is heated to 80°C to 300°C, e.g. 150°C to 240°C, by a heat exchanger. After the temperature of the water phase product is raised, in order to prevent the water therein from being vaporized, a very high pressure needs to be applied to the oil removal system (i.e. the system for implementing step (2)) when the temperature is too high (therefore, the water phase product is preferably heated to below 300°C, more preferably below 240°C by the heat exchanger, to ensure the stable and long-term operation of the reaction system and to reduce the adverse effects of the high pressure required for maintaining the high temperature on the system), e.g. a back pressure can be applied to the oil removal system by pressurization, which can be implemented by introducing N2 or water vapor into the system or by self-pressurization by water vaporization in the system. The back pressure should be not less than the saturated vapor pressure of water vapor at the temperature of the water phase product after heating in the oil removal system. In the present application, the back pressure of the oil removal system (i.e. the pressure in step (2)) is 1 atm or more, e.g. when the water phase product is heated to 150°C, the back pressure of the oil removal system should be not less than 0.5 MPa, and when the water phase product is heated to 250°C, the back pressure of the oil removal system should be not less than 4.0 MPa, so that the mixing is carried out at this back pressure.

[0036] In some embodiments, in step (2), the volume ratio of the water phase product to the oily substance can be 1:5 to 5:1, more preferably 1:2 to 2:1, e.g. 1:1 to 2:1.

[0037] In some embodiments, in step (2), the water phase product is mixed with the oily material using a static mixer. Through the mixing, the emulsified oil product and oxygen-containing organic matter entrained in the water phase product can be extracted into the oil phase, thus the water phase product can be demulsified and the emulsified oil can be separated out.

[0038] In some embodiments, in step (2), the Fischer-Tropsch synthesis light oil can be hydrocarbons and oxygen-containing organic matter with a distillation temperature of 0-500°C, IBP = 0-50°C, FBP = 300-500°C, 50% distillation temperature = 150-250°C, and carbon number distribution approximately C4-C37; the Fischer-Tropsch synthesis heavy oil can be hydrocarbons and oxygen-containing organic matter with a distillation temperature of 100-700°C, IBP = 100-200°C, FBP = 500-700°C, 50% distillation temperature = 300-400°C, and carbon number distribution approximately C6-C54; and the Fischer-Tropsch synthesis heavy wax can be hydrocarbons and oxygen-containing organic matter with a distillation temperature of 200-750°C, IBP = 200-300°C, FBP = 650-750°C, 50% distillation temperature = 500-600°C, and carbon number distribution C8-C90 and above.

[0039] In some embodiments, in step (3), the operating temperature of the oil-water separator can be the same as or substantially the same as the temperature of the water phase product after being heated by the heat exchanger, for example, can be 80-300°C, preferably 80-240°C; the pressure can be 0-5 MPa in gauge pressure, preferably 0.1-3.5 MPa, for example, 0.1-2.5 MPa.

[0040] In some embodiments, in step (4), a part of the oil phase product coming out of the oil-water separator can be returned to step (2) to be mixed with the water phase product again (for example, by being returned to the inlet of the static mixer to be mixed with the water phase product again), so that the oil phase product from the oil-water separator can be recycled; at this time, another part of the oil phase product coming out of the oil-water separator can be mixed with the oil phase product coming out of the raw material water tank and then output to the downstream unit for further processing.

[0041] In some embodiments, the volume ratio between the oil phase product coming out of the oil-water separator and returned to step (2) and the oil phase product coming out of the oil-water separator and output to the downstream unit is 10:1 to 1:10, for example, 10:1 to 1:1 (for example, 5:1, 2:1).

[0042] In some further preferred embodiments, in step (5), the heat exchange cooling can include cooling to room temperature, or can also be cooled to the temperature required by the downstream processing unit (e.g. the synthetic water processing unit). As an example, in step (5), the aqueous phase fluid can be heat-exchanged and cooled to 20-60°C, for example 30-50°C.

[0043] In some further preferred embodiments, in step (5), the filtration removes the suspended particles in the aqueous phase fluid, preferably, the filtration can be performed using a filter core with a pore size of no more than 10 μm, preferably no more than 5 μm, more preferably no more than 1 μm. After filtration, the filtered aqueous phase fluid is sent to the synthetic water processing unit for oxygen-containing organic matter separation and synthetic water purification treatment to further improve the quality of the water product.

[0044] In some preferred embodiments, the present application also provides a method for removing oil from Fischer-Tropsch synthesis water, comprising the following steps:

[0045] (i) feeding the emulsified Fischer-Tropsch synthesis water 101 into a raw water tank T1 for standing to separate an oil phase product 102 and an aqueous phase product 103;

[0046] (ii) feeding the aqueous phase product 103 into a heat exchanger E1 to heat to no less than 80°C, and then mixing with an oily substance 104 in a static mixer M1 to obtain a mixture 105, the oily substance being Fischer-Tropsch synthesis light oil, Fischer-Tropsch synthesis heavy oil and / or Fischer-Tropsch synthesis heavy wax, the volume ratio of the aqueous phase product to the oily substance being 1:10 to 10:1;

[0047] (iii) feeding the mixture 105 into an oil-water separator T2 for oil-water separation;

[0048] (iv) mixing a part 107 of the oil phase product 106 from the oil-water separator T2 with the oil phase product 102 from the raw water tank, and then outputting to a downstream unit, and returning another part 108 of the oil phase product 106 to the static mixer M1 inlet to re-mix with the aqueous phase product 103;

[0049] (v) heat-exchange cooling the aqueous phase fluid 109 separated from the oil-water separator T2, and then directly sending to a synthetic water processing unit for oxygen-containing organic matter separation and synthetic water purification treatment after filtration.

[0050] In some embodiments, the raw water tank T1, the static mixer M1 and the oil-water separator T2 can be atmospheric and / or high-pressure equipment according to the mixing conditions, and the temperature and pressure resistance conditions can be determined according to the material properties and mixing and separation conditions.

[0051] In some embodiments, the heat exchanger can be a double-pipe heat exchanger, a plate heat exchanger, etc., and the heat exchange mode of the heat exchanger can be steam or electric heating. When steam heat exchange is used, the steam for heat exchange can be saturated steam at 0.5 MPa, 1.5 MPa, 2.0 MPa, 2.5 MPa, 3.0 MPa, 4.0 MPa, 5.0 MPa, or 6.0 MPa,

[0052] In some embodiments, the volume ratio of the oil-water mixture can be 1:5 to 5:1, and more preferably 1:2 to 2:1, for example, 1:1 to 2:1.

[0053] In some embodiments, the Fischer-Tropsch synthesis light oil can be hydrocarbons and oxygen-containing organic compounds with a distillation temperature of 0°C to 500°C, IBP = 0°C to 40°C, FBP = 300°C to 500°C, 50% distillation temperature = 150°C to 250°C, and a carbon number distribution of approximately C4-C37; the Fischer-Tropsch synthesis heavy oil can be hydrocarbons and oxygen-containing organic compounds with a distillation temperature of 100°C to 700°C, IBP = 100°C to 200°C, FBP = 500°C to 700°C, 50% distillation temperature = 300°C to 400°C, and a carbon number distribution of approximately C6-C54; and the Fischer-Tropsch synthesis heavy wax can be hydrocarbons and oxygen-containing organic compounds with a distillation temperature of 200°C to 750°C, IBP = 200°C to 300°C, FBP = 650°C to 750°C, 50% distillation temperature = 500°C to 600°C, and a carbon number distribution of C8-C90 and above. The oil-water separator T4 separates oil and water based on the density difference between the Fischer-Tropsch synthesis products and water. To improve separation efficiency, baffle plates, coalescing plates, and other separation internals can be added to the oil-water separator, for example, the turbulent flow after oil-water mixing can be converted to laminar flow by the baffle plates, and the coalescing plates can further improve the oil-water separation efficiency.

[0054] For example, the Fischer-Tropsch synthesis heavy wax, the operating temperature of the oil-water separator T2 can be 150°C to 240°C, and preferably 180°C to 230°C; and the pressure can be 0 to 5 MPa in gauge pressure, and preferably 0.1 to 3.5 MPa, for example, 0.1 to 2.5 MPa.

[0055] In some embodiments, a portion 107 of the oil phase product 106 is output to a downstream unit, and another portion 108 (or mixed with externally introduced material as stream 104) is returned to the static mixer M1 inlet for secondary mixing with the water phase product 103, wherein the volume ratio between the returned 108 and the output 107 to the downstream unit is 10:1 to 1:10, and preferably 10:1 to 1:1.

[0056] In some embodiments, the filtration to remove suspended particles in the aqueous phase fluid can be performed using a filter having a pore size of no more than 10 μm, preferably no more than 5 μm, more preferably no more than 1 μm, and the filtered aqueous phase fluid is then fed to a synthetic water treatment unit for oxygen-containing organic matter separation and synthetic water purification treatment.

[0057] In the following, the solutions of the present application are further illustrated by means of the numbered paragraphs below:

[0058] 1. A method for removing oil from Fischer-Tropsch synthesis water, comprising:

[0059] (1) feeding emulsified Fischer-Tropsch synthesis water to a raw water tank for standing, to separate an oil phase product and an aqueous phase product;

[0060] (2) heating the aqueous phase product to a temperature of no less than 80°C using a heat exchanger and mixing the heated aqueous phase product with oily substances to obtain a mixture, the oily substances being Fischer-Tropsch synthesis light oil, Fischer-Tropsch synthesis heavy oil and / or Fischer-Tropsch synthesis heavy wax, the volume ratio of the aqueous phase product to the oily substances being 1:10 to 10:1;

[0061] (3) feeding the mixture to an oil-water separator for oil-water separation;

[0062] (4) mixing a part or all of the oil phase product from the oil-water separator with the oil phase product from the raw water tank and outputting the mixture to a downstream unit;

[0063] (5) cooling the aqueous phase fluid separated from the oil-water separator using a heat exchanger, filtering the cooled aqueous phase fluid, and feeding the filtered aqueous phase fluid to a synthetic water treatment unit for oxygen-containing organic matter separation and synthetic water purification treatment.

[0064] 2. The method of paragraph 1, wherein in step (1), the total content of oxygen-containing organic matter in the Fischer-Tropsch synthesis water is 2 wt% to 5 wt%, the COD is 15000 to 60000 mg / L, the pH is 2 to 4, and the total oil is no more than 10000 mg / L, and the petroleum is no more than 2000 mg / L.

[0065] 3. The method of paragraph 1 or 2, wherein in step (2), the aqueous phase product is heated to a temperature of 80°C to 300°C using a heat exchanger.

[0066] 4. The method of any one of paragraphs 1 to 3, wherein in step (2), the mixing is performed at a pressure of 1 atmosphere or higher.

[0067] 5. The method of any one of paragraphs 1 to 4, wherein in step (2), the volume ratio of the aqueous phase product to the oily substances is 1:5 to 5:1.

[0068] 6. The method of any one of paragraphs 1-5, wherein in step (2), the aqueous phase product is mixed with the oily substance using a static mixer.

[0069] 7. The method of any one of paragraphs 1-6, wherein in step (3), the operating temperature of the oil-water separator is 80-300 °C; and the pressure is 0-5 MPa in gauge pressure.

[0070] 8. The method of any one of paragraphs 1-7, wherein in step (4), a portion of the oil phase product from the oil-water separator is returned to step (2) to be mixed with the aqueous phase product again, and another portion of the oil phase product from the oil-water separator is mixed with the oil phase product from the feed water tank and then output to a downstream unit for further processing.

[0071] 9. The method of paragraph 8, wherein the volume ratio between the oil phase product from the oil-water separator that is returned to step (2) and the oil phase product from the oil-water separator that is output to the downstream unit is 10: 1 to 1: 10.

[0072] 10. The method of any one of paragraphs 1-9, wherein in step (5), the heat exchange cooling comprises cooling to room temperature, or to a downstream unit processing temperature according to the requirement of the downstream processing unit.

[0073] 11. The method of any one of paragraphs 1-10, wherein in step (5), the aqueous phase fluid is heat exchanged and cooled to 20-60 °C.

[0074] 12. The method of any one of paragraphs 1-11, wherein in step (5), the filtration is performed using a filter element with a pore size of no more than 10 pm.

[0075] 13. The method of any one of paragraphs 1-12, comprising the following steps:

[0076] (i) feeding the emulsified Fischer-Tropsch synthesis water into a feed water tank for standing, to separate an oil phase product and an aqueous phase product;

[0077] (ii) feeding the aqueous phase product into a heat exchanger to be heated to no less than 80 °C, and then mixing the aqueous phase product with an oily substance in a static mixer to obtain a mixed liquid, the oily substance being Fischer-Tropsch synthesis light oil, Fischer-Tropsch synthesis heavy oil, and / or Fischer-Tropsch synthesis heavy wax, and the volume ratio between the aqueous phase product and the oily substance being 1: 10 to 10: 1;

[0078] (iii) feeding the mixed liquid into an oil-water separator for oil-water separation;

[0079] (iv) a portion of the oil phase product from the oil-water separator is mixed with the oil phase product from the feed water tank and output to a downstream unit, and another portion of the oil phase product from the oil-water separator is returned to the static mixer inlet and re-mixed with the water phase product;

[0080] (v) the water phase fluid separated in the oil-water separator is heat-exchanged to reduce the temperature, and then filtered and directly sent to a synthetic water treatment unit for oxygen-containing organic matter separation and synthetic water purification treatment.

[0081] 14. The method of paragraph 13, wherein the heat exchanger is a double-pipe heat exchanger or a plate heat exchanger.

[0082] 15. The method of paragraph 14, wherein the heat exchanger is steam or electrically heated.

[0083] Embodiments

[0084] The present application will be further described with reference to the following examples, which are intended to be illustrative only and not limiting of the scope of the application, which includes but is not limited to the following examples.

[0085] Unless otherwise indicated, the materials, devices and test methods referred to in the following examples are conventional materials, devices and test methods known in the art.

[0086] Example 1

[0087] (1) Feed Fischer-Tropsch synthesis water 101 at a flow rate of 1 m 3 / h into a feed water tank T1 for standing, to separate an oil phase product 102 and a water phase product 103.

[0088] (2) The water phase product 103 is fed into a heat exchanger E1 (a plate heat exchanger) to heat to 150°C, and a N2 back pressure system is used for the oil removal system, with a pressure of 2.4 MPa. The water phase product 103 is mixed with Fischer-Tropsch synthesis heavy wax (distillation temperature of about 300°C to about 700°C, IBP = about 300°C, FBP = about 700°C, 50% distillation temperature = about 550°C, carbon number distribution of C9-C77) in a volume ratio of 1:1 in a static mixer M1 to obtain a mixed liquid 105.

[0089] (3) The mixed liquid 105 is fed into an oil-water separator T2 to separate the oil and water at a temperature of 150°C and a pressure of 2.4 MPa.

[0090] (4) A portion 107 of the oil phase product 106 from the oil-water separator T2 is mixed with the oil phase product 102 from the raw water tank and then output to a downstream unit, and another portion 108 of the oil phase product 106 is returned to the static mixer Ml inlet for secondary mixing with the water phase product 103, wherein the volume ratio of 107 to 108 is 1:5.

[0091] (5) The water phase fluid 109 (0.99 m 3 / h) separated in the oil-water separator is heat-exchanged and cooled to 40°C, filtered through a filter screen with a pore size of 5 μm, and then directly sent to a synthetic water treatment unit for oxygen-containing organic matter separation and synthetic water purification treatment.

[0092] Table 1 Water quality index analysis of streams 101 and 109

[0093]

[0094] Example 2

[0095] (1) The Fischer-Tropsch synthetic water 101 with a flow rate of 1 m 3 / h is supplied to the raw water tank Tl for standing, and the separated oil phase product 102 and water phase product 103 are obtained.

[0096] (2) The water phase product 103 is supplied to the heat exchanger E1 (a double-pipe heat exchanger) through a feed pump P1 and heated to 220°C, and a N2 back pressure system is used for the oil removal system with a pressure of 2.4 MPa. The water phase product 103 is mixed with Fischer-Tropsch heavy wax (distillation temperature of about 280°C to about 650°C, IBP = about 280°C, FBP = about 650°C, 50% distillation temperature = about 520°C, carbon number distribution of C9-C77) in a volume ratio of 2:1 in the static mixer Ml to obtain a mixed liquid 105.

[0097] (3) The mixed liquid 105 is supplied to the oil-water separator T2 for oil-water separation under the conditions of a temperature of 220°C and a pressure of 2.4 MPa.

[0098] (4) A portion 107 of the oil phase product 106 from the oil-water separator T2 is mixed with the oil phase product 102 from the raw water tank and then output to a downstream unit, and another portion 108 of the oil phase product 106 is returned to the static mixer Ml inlet for secondary mixing with the water phase product 103, wherein the volume ratio of 107 to 108 is 1:10.

[0099] (5) The water phase fluid 109 (0.99 m 3 / h) separated in the oil-water separator is heat-exchanged and cooled to 40°C, filtered through a filter screen with a pore size of 1 μm, and then directly sent to a synthetic water treatment unit for oxygen-containing organic matter separation and synthetic water purification treatment.

[0100] Table 2 Water quality index analysis of streams 101 and 109

[0101]

[0102] Example 3

[0103] (1) The Fischer-Tropsch synthesis water 101 with a flow rate of 1 m 3 / h was supplied to the raw water tank Tl for standing, and the separated oil phase product 102 and the water phase product 103 were obtained.

[0104] (2) The water phase product 103 was supplied to the heat exchanger El (a double pipe heat exchanger) via the feed pump Pl and heated to 180°C, and the oil removal system used N2 back pressure with a pressure of 2.4 MPa. The water phase product 103 and the Fischer-Tropsch synthesis heavy wax (distillation temperature of about 280°C to about 650°C, IBP = about 280°C, FBP = about 650°C, 50% distillation temperature = about 520°C, carbon number distribution = C9-C77) were mixed in the static mixer Ml at a volume ratio of 2: 1 to obtain the mixed liquid 105.

[0105] (3) The mixed liquid 105 was supplied to the oil-water separator T2, and oil-water separation was performed at a temperature of 180°C and a pressure of 2.0 MPa.

[0106] (4) A part 107 of the oil phase product 106 from the oil-water separator T2 was mixed with the oil phase product 102 from the raw water tank and then output to the downstream unit, and the other part 108 of the oil phase product 106 was returned to the static mixer Ml inlet and mixed with the water phase product 103 again, wherein the volume ratio of 107 and 108 was 1: 1.

[0107] (5) The water phase fluid 109 (0.99 m 3 / h) separated in the oil-water separator was heat-exchanged and cooled to 40°C, filtered through a filter screen with a pore size of 0.5 μm, and then directly sent to the synthesis water treatment unit for oxygen-containing organic matter separation and synthesis water purification treatment.

[0108] Table 3 Water quality index analysis of streams 101 and 109

[0109]

[0110] Example 4

[0111] (1) The Fischer-Tropsch synthesis water 101 with a flow rate of 1 m 3 / h was supplied to the raw water tank Tl for standing, and the separated oil phase product 102 and the water phase product 103 were obtained.

[0112] (2) The water phase product 103 is fed into the heat exchanger El (plate heat exchanger) by feed pump Pl to be heated to 80°C, and the oil removal system uses N2 back pressure with a pressure of 2.4 MPa. The water phase product 103 is mixed with the Fischer-Tropsch heavy oil (distillation temperature of about 100°C to about 600°C, IBP = about 100°C, FBP = about 600°C, 50% distillation temperature of about 350°C, carbon number distribution of C6-C54) in a volume ratio of 2:1 in the static mixer Ml to obtain the mixed liquid 105.

[0113] (3) The mixed liquid 105 is fed into the oil-water separator T2 to separate the oil and water under the conditions of a temperature of 80°C and a slight positive pressure.

[0114] (4) A part 107 of the oil phase product 106 from the oil-water separator T2 is mixed with the oil phase product 102 from the raw water tank and then output to the downstream unit, and another part 108 of the oil phase product 106 is returned to the inlet of the static mixer Ml to be mixed with the water phase product 103 again, wherein the volume ratio of 107 and 108 is 1:1.

[0115] (5) The water phase fluid 109 (1 m 3 / h) separated from the oil-water separator is cooled to 40°C by heat exchange and then filtered through a filter screen with a pore size of 0.1 μm and directly sent to the synthetic water treatment unit for oxygen-containing organic matter separation and synthetic water purification treatment.

[0116] Table 4 Water quality index analysis of streams 101 and 109

[0117]

[0118]

[0119] Comparative Example 5

[0120] (1) The Fischer-Tropsch synthesis water 101 with a flow rate of 1 m 3 / h is fed into the raw water tank Tl to be static, and the separated oil phase product 102 and water phase product 103 are obtained.

[0121] (2) The water phase product 103 is fed into the heat exchanger El (plate heat exchanger) by feed pump Pl to be heated to

[0122] 40°C, and the oil removal system is under normal pressure. The water phase product 103 is mixed with the Fischer-Tropsch light oil (distillation temperature of about 40°C to about 300°C, IBP = ~ 40°C, FBP = about 300°C, 50% distillation temperature of about 200°C, carbon

[0123] number distribution of C6-C20) in a volume ratio of 2:1 in the static mixer Ml to obtain the mixed liquid 105.

[0124] The mixture of the water phase product 103 and the oil phase product 102 is mixed in a static mixer Ml at a volume ratio of 1:1 to obtain a mixed solution 105.

[0125] The mixed solution 105.

[0126] (3) The mixed solution 105 is supplied to an oil-water separator T2, and oil-water separation is performed at normal pressure and 40°C.

[0127] Water separation.

[0128] (4) A part 107 of the oil phase product 106 from the oil-water separator T2 is mixed with the oil phase product 102 from the raw material tank, and then output to a downstream unit.

[0129] Another part 108 of the oil phase product 106 is returned to the static mixer Ml inlet for secondary mixing with the water phase product 103, wherein the volume ratio of 107 and 108 is 1:1.

[0130]

[0131] The volume ratio of 107 and 108 is 1:1.

[0132] (5) The water phase fluid 109 (1 m 3 / h) obtained from the oil-water separation is sampled and analyzed.

[0133] Table 3 Water quality index analysis of streams 101 and 109

[0134]

[0135] From the above analysis results, when the oil-water mixing is performed at a lower temperature, the petroleum content in the water phase fluid obtained after the oil removal treatment increases, indicating that in the treatment process involving oil-water mixing at a lower temperature, the oil-water is further emulsified due to the failure to achieve effective oil removal, resulting in an increase in the petroleum content in the water.​

Claims

1. A method for removing oil from Fischer-Tropsch synthesis water, comprising: (1) The emulsified Fischer-Tropsch synthesis water is fed into the raw material water tank for settling, and the oil phase product and the aqueous phase product are separated. (2) The aqueous product is heated to 80°C to 300°C by a heat exchanger and then mixed with an oily substance to obtain a mixture. The oily substance is Fischer-Tropsch light oil, Fischer-Tropsch heavy oil and / or Fischer-Tropsch heavy wax. The volume ratio of the aqueous product to the oily substance is 1:10 to 10:

1. (3) The mixture is fed into an oil-water separator for oil-water separation; (4) A portion of the oil phase product from the oil-water separator is mixed with the oil phase product from the raw material water tank and then output to the downstream unit. Another portion of the oil phase product from the oil-water separator is returned to the inlet of the static mixer to be mixed with the aqueous phase product again. (5) The aqueous phase fluid separated in the oil-water separator is cooled by heat exchange, and then filtered before being sent to the synthetic water treatment unit for separation of oxygen-containing organic matter and purification of synthetic water.

2. The method as described in claim 1, wherein, In step (1), the total content of oxygenated organic matter in the Fischer-Tropsch synthesis water is 2wt%~5wt%; COD=15000~60000 mg / L; pH=2~4; total oil not higher than 10000 mg / L, and petroleum not higher than 2000 mg / L.

3. The method as described in claim 1 or 2, wherein, In step (2), the mixing is carried out at a pressure of 1 standard atmosphere or higher.

4. The method as described in claim 1 or 2, wherein, In step (2), the volume ratio of the aqueous product to the oily substance is 1:5 to 5:

1.

5. The method as described in claim 1 or 2, wherein, In step (2), the aqueous product is mixed with the oily substance using a static mixer.

6. The method as described in claim 1 or 2, wherein, In step (3), the operating temperature of the oil-water separator is 80℃~300℃; the pressure is 0~5MPa as measured by a gauge.

7. The method as described in claim 1 or 2, wherein, The volume ratio between the oil phase product exiting the oil-water separator in step (2) and the oil phase product exiting the oil-water separator and output to the downstream unit is 10:1 to 1:

10.

8. The method as claimed in claim 1 or 2, wherein, In step (5), the heat exchange cooling includes cooling to room temperature or cooling to the downstream unit processing temperature according to the requirements of the downstream processing unit.

9. The method as claimed in claim 1 or 2, wherein, In step (5), the aqueous fluid is cooled to 20°C to 60°C through heat exchange.

10. The method as claimed in claim 1 or 2, wherein, In step (5), a filter element with a pore size of no more than 10 μm is used for filtration.

11. The method as claimed in claim 1 or 2, wherein, The heat exchanger is a shell-and-tube heat exchanger or a plate heat exchanger.

12. The method of claim 11, wherein, The heat exchanger uses steam or electric heating for heat exchange.

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