Method for treating sulfur-containing sewage of oil and gas field by utilizing kitchen waste hydrothermal carbon

Abstract

The invention discloses an oil and gas field sulfur-containing sewage adsorption treatment method. According to the method, the sulfur-containing sewage of the oil and gas field is treated by using a dynamic adsorption technology in which kitchen waste hydrothermal carbon which is impregnated by alkali or metal oxide or modified by nitrogen doping is used as an adsorbent. After the treatment is finished, the resource recovery of the adsorbed sulfur-containing compound and the regeneration of the hydrothermal carbon are realized by water washing and high-temperature activation. The kitchen waste hydrothermal carbon is used as an adsorbent, has the advantages of being wide in source, environmentally friendly and low in price, and is suitable for industrial scale application. Alkali or ZnFe2O4 is adopted for dipping, or nitrogen-doped functional modified hydrothermal carbon with melamine as a precursor is adopted, the adsorption capacity and the catalytic oxidation capacity of the hydrothermal carbon can be enhanced at the same time, and the treatment effect is greatly improved. And finally, recovery of adsorbed sulfur-containing substances and regeneration of hydrothermal carbon are realized by using water washing and high-temperature activation, so that secondary pollution can be effectively reduced, sustainable utilization of resources is realized, and the operation cost is reduced. The method for treating the sulfur-containing sewage of the oil and gas field is efficient, simple to operate, green, environment-friendly and relatively low in cost.

Description

Technical Field

[0001] The invention belongs to the field of sewage treatment, and in particular relates to a method for treating sulfur-containing sewage in oil and gas fields. Background Art

[0002] The production process of oil and gas fields usually produces 2- 、SO 4 2- , HS - And a small amount of S 2 O 3 2- Sulfur-containing wastewater is a kind of wastewater containing sulfur in the form of organic sulfur. It mainly comes from the decomposition of sulfur compounds in drilling fluid, the dissolution of sulfur-containing crude oil / natural gas in the formation, and the reduction of sulfate-reducing bacteria. Sulfur-containing wastewater is highly toxic and corrosive. On the one hand, it brings great harm to human health and environmental ecology; on the other hand, it seriously hinders the normal operation of oil and gas production, such as corroding metal equipment, causing crude oil emulsification problems, and causing wellbore blockage. Therefore, long-term and stable treatment of sulfur-containing wastewater is particularly necessary. At present, the treatment technologies of sulfur-containing wastewater can be roughly divided into two categories: physical and chemical technology and biotechnology. They can be further divided into microbial method, (common physical solvents, alkanolamines, ionic liquids) absorption method, adsorption method, oxidation method, electrochemical method, membrane separation, gas stripping / vacuum extraction method, chemical precipitation method, etc. Although the microbial method does not require the addition of chemicals, is simple to operate, and has mild conditions, its high investment cost limits its wide application. Various solvent absorption methods have problems such as high solvent regeneration cost and complex operation. The elemental sulfur produced by the electrochemical method is deposited on the electrode, which seriously affects its treatment effect. The oxidation method and gas stripping / vacuum extraction method have high requirements on equipment materials, reaction conditions, investment and operating costs. The membrane separation system is compact and lightweight, more suitable for small-scale applications, and its operating and investment costs are also high. The chemical precipitation method requires the addition of a large amount of reagents, so the operating cost is high, and the sludge containing a large amount of reduced sulfur is easy to cause secondary pollution. The adsorption method is less affected by water quality fluctuations, has low cost, high flexibility and energy efficiency, and is easy to operate. It shows great advantages in the treatment of high-sulfur wastewater in oil and gas fields.

[0003] Adsorption is a surface-based process that transfers substances from the liquid phase to the adsorbent (solid phase) surface. Depending on the strength of the adsorbent-adsorbate interaction, adsorption can be divided into physical adsorption, which is mainly based on van der Waals forces and / or electrostatic (weak) interactions, and chemical adsorption, which is mainly based on covalent bonds and / or hydrogen bonds (strong) interactions. In general, an ideal adsorbent material should have high treatment capacity and selectivity for target pollutants, chemical and thermal stability, and structural regeneration ability. Carbon-based materials have attracted attention due to their large specific surface area and pore volume, good thermal stability, and controllable surface chemical properties (which can determine the degree of physical and chemical adsorption). They are widely used as low-temperature desulfurization adsorbents. In addition, waste biomass resources (such as kitchen waste) can be used to prepare carbon-based adsorbents, thereby reducing adsorption costs and improving resource efficiency.

[0004] Hydrothermal carbonization is a green, environmentally friendly, and simple carbon material synthesis technology. Biomass hydrothermal carbonization usually refers to the treatment of biomass in a closed reactor with water or aqueous solution as the medium, at high temperature (generally 160~350℃) and high pressure (milder than other thermochemical technologies), to produce solids (i.e., hydrothermal carbonization), oily liquids, and gases similar to biochar, resulting in hydrolysis, dehydration, and decarboxylation reactions. Therefore, it is very promising to use kitchen waste with a high water content as a raw material. Compared with traditional activated carbon adsorbents, the oxygen-containing functional groups on the surface of hydrothermal carbon give it better chemical adsorption properties. Moreover, physical or chemical activation can be used to functionalize hydrothermal carbon to meet different adsorption requirements. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a highly efficient, easy-to-operate, environmentally friendly and low-cost oil and gas field sulfur-containing wastewater treatment technology.

[0006] The present invention is achieved through the following technical solutions: The technology with kitchen waste hydrothermal carbon adsorbent as the core is used to treat sulfur-containing wastewater in oil and gas fields. The specific technical scheme is: the hydrothermal carbon obtained by hydrothermal carbonization of kitchen waste is functionally modified by alkali or metal oxide impregnation and nitrogen doping to improve its adsorption capacity for sulfides in wastewater. The sulfur-containing wastewater in oil and gas fields is treated by dynamic adsorption. After the treatment, water washing and high-temperature activation are used to realize the resource utilization of the adsorbed sulfur-containing substances and the regeneration of kitchen waste hydrothermal carbon. The technical conditions of each stage are as follows: 1. In the hydrothermal carbon modification method of the present invention, the alkali impregnation uses KOH, NaOH or Ca(OH) 2 The mixture was reacted in distilled water at a temperature of 15-35 °C for 12-36 h with an alkali-carbon ratio of 5:1-1:1 and dried at 60-90 °C for 6-24 h. 2The mixture was heated to 600-900 °C at a rate of 2-20 °C / min under a carbon atmosphere and maintained for 0.5-5 h. The specific surface area and pore volume of the obtained kitchen waste hydrothermal carbon adsorbent can reach 500 m 2 / g and 0.5 cm 3 / g or above.

[0007] 2. Metal oxide impregnation using zinc salt (ZnCl 2 、ZnSO 4 or Zn(NO 3 ) 2 ) and iron salts (FeCl 3 , Fe 2 (SO 4 ) 3 or Fe 2 (NO 3 ) 3 ) was dissolved in distilled water at a molar ratio of Zn:Fe of 1 to 2, and then a certain amount of hydrothermal carbon was added (to make the ZnFe 2 O 4 The reaction mixture was heated at 15-35 °C for 0.5-2 h and dried at 30-50 °C for 6-24 h. 2 The mixture was heated to 300-600 °C at a rate of 2-20 °C / min under a carbon atmosphere and maintained for 1-4 h. The specific surface area and pore volume of the obtained kitchen waste hydrothermal carbon adsorbent can reach 1200 m 2 / g and 0.3 cm 3 / g or above.

[0008] 3. Nitrogen doping: Melamine is heated to 450-650°C at a rate of 5-15°C / min. The obtained yellow solid (i.e., carbon-nitrogen compound) is mixed with hydrothermal carbon in a mass ratio of 0.4-4, reacted in a potassium carbonate aqueous solution (the mass ratio of potassium carbonate to hydrothermal carbon is 1-3) at a temperature of 15-35°C for 1-5 h, and dried at 90-120°C for 12-36 h. Then, the obtained mixture is heated to 400°C for 12 hours. 2 The mixture was heated to 600-1200 °C at a rate of 2-10 °C / min under a carbon atmosphere and maintained for 1-4 h. The specific surface area and pore volume of the obtained kitchen waste hydrothermal carbon adsorbent can reach 1000 m 2 / g and 0.6 cm 3 / g or above.

[0009] 4. Use fixed bed, moving bed or fluidized bed reactors to adsorb and treat sulfur-containing wastewater in oil and gas fields. The aspect ratios of the three reactors are 2~5. Among them, the bed height of fixed bed adsorption is 0.5~2 m, the sewage flow rate is 0.1~1 m / h, the hydraulic retention time is 5~30 min, and it operates at room temperature and pressure; the adsorbent loading height of moving bed adsorption is 1~3 m, the adsorbent and sewage flow rate is 0.1~1 m / h, the adsorption time is 15~60 min, and it operates at room temperature and pressure; the sewage flow rate of fluidized bed adsorption is 0.3~1 m / s, the hydraulic retention time is 10~60 min, and it operates at room temperature and pressure. Under the optimal operating conditions, the kitchen waste water hot carbon impregnated with alkali or metal oxides and modified by nitrogen doping has a strong effect on the sulfide (in terms of H 2 The adsorption capacity of S can reach 50~200 mg / g or more.

[0010] 5. In addition to significantly enhancing the adsorption capacity, the catalytic oxidation performance of the modified kitchen waste hydrothermal carbon is also significantly improved. 2- It is mainly oxidized to elemental sulfur (accounting for more than 50%), sulfite and sulfate. Using pure water gradient washing at a temperature of 4~80 ℃ can effectively recover sulfur-containing compounds.

[0011] 6. The hydrothermal carbon after washing is regenerated by high-temperature activation method. The temperature of drying, carbonization and activation stages are controlled at 100~150℃, 150~200℃, 750~850℃ respectively, and the regeneration time is 0.5~3h. The tail gas generated during the regeneration process can be further collected in the absorber and converted into high value-added products. The activated carbon loss rate is 5~25%, and the regeneration rate is greater than 75%.

[0012] The oil and gas field sulfur-containing wastewater adsorption treatment method described in the present invention has the following advantages compared with the prior art: Kitchen waste hydrocharcoal is a typical product of biomass resource recycling, which is environmentally friendly and in line with the concept of green economy and circular economy. Its raw materials are widely available, the preparation cost is low, and it has obvious economic advantages and is suitable for large-scale sewage treatment. 2 O 4 The impregnation and nitrogen doping functionalization modification method using melamine as a precursor is not only technically stable and reliable, but also achieves the simultaneous enhancement of hydrothermal carbon adsorption and catalytic oxidation capabilities, and its performance is far superior to traditional activated carbon adsorbents. The recovery of sulfur-containing compounds and high-temperature regeneration of hydrothermal carbon can effectively reduce secondary pollution, achieve sustainable resource utilization, and significantly reduce operating costs. DETAILED DESCRIPTION

[0013] The following is a more specific description of the method for adsorption treatment of sulfur-containing wastewater in oil and gas fields of the present invention in conjunction with embodiments. Example

[0014] Hydrochar uses a cross-type fixed bed carrier to reduce sulfur pollutants in oil and gas field wastewater in the form of multi-media filtration and oxidation, supplemented by pre- and post-treatment processes such as filtration and precipitation. Sulfur-containing wastewater passes through a 2 m high fixed bed at a flow rate of 0.8 m / h, and the hydraulic retention time is controlled at 25 min. At a water temperature of 5~38°C, the sulfur concentration of wastewater with a concentration of 100 mg / L can be reduced to less than 3 mg / L. The average adsorption capacity (in terms of H 2 S) reaches 180 mg / g, mainly existing in the adsorption material in the form of sulfur. After the saturated adsorption, the hydrothermal carbon is washed with pure water at 60°C to recover the sulfide. After drying, carbonization and activation, the activated carbon loss rate is 5-10% and the regeneration rate is 90-95%. Example

[0015] Hydrothermal charcoal exists in a suspended state inside the fluidized bed device, with an expansion rate of about 200%. Sulfur-containing wastewater is passed into the device from bottom to top, and 75 mg / L sulfide in the wastewater is captured, oxidized and retained by the flowing biochar. The organic matter components in the wastewater are carried into the fluidized bed by the higher rising velocity of 0.8~1 m / s and enter the subsequent coagulation and sedimentation unit. The sulfide concentration of the effluent is less than 4 mg / L. Within 10~15 days, 20~25% of the biochar inside the device is recovered, and the corresponding proportion of regenerated biochar is added. After drying, carbonization and activation, the recovered biochar has an activated carbon loss rate of 20~25% and a regeneration rate of 75~80%.

Claims

1. A method for treating sulfur-containing wastewater in oil and gas fields using kitchen waste water hot charcoal, characterized in that: The method uses a dynamic adsorption technology using kitchen waste hydrochar impregnated with alkali or metal oxides or modified by nitrogen doping as an adsorbent. After the treatment, water washing and high-temperature activation are used to achieve resource recovery of the adsorbed sulfur-containing substances and regeneration of the hydrochar.

2. The method according to claim 1, characterized in that: The alkaline impregnation uses one or a mixture of two or more of KOH, NaOH, and Ca(OH)2, with an alkali-to-carbon ratio of 5:1 to 1:1, and reacts in distilled water at a temperature of 15 to 35 °C for 12 to 36 hours, and is dried at 60 to 90 °C for 6 to 24 hours. Then, the resulting mixture is heated to 600 to 900 °C at a rate of 2 to 20 °C / min in a N2 atmosphere and maintained for 0.5 to 5 hours.

3. The method according to claim 1, characterized in that: The metal oxide impregnation uses zinc salt (one of ZnCl2, ZnSO4 or Zn(NO3)2 or a mixture of two or more) and iron salt (one of FeCl3, Fe2(SO4)3 or Fe2(NO3)3 or a mixture of two or more) dissolved in distilled water with a Zn:Fe molar ratio of 1-2, and then a certain amount of hydrothermal carbon is added (so that the ZnFe2O4 loading of the prepared adsorbent is 5-40 wt%), reacted at 15-35°C for 0.5-2 h, and dried at 30-50°C for 6-24 h. Then, the resulting mixture is heated to 300-600°C at a rate of 2-20°C / min under N2 atmosphere and maintained for 1-4 h.

4. The method according to claim 1, characterized in that The nitrogen doping uses melamine to heat to 450-650°C at a rate of 5-15°C / min. The obtained solid is mixed with hydrothermal carbon in a mass ratio of 0.4-4, reacted in a potassium carbonate aqueous solution (the mass ratio of potassium carbonate to hydrothermal carbon is 1-3) at a temperature of 15-35°C for 1-5 hours, and dried at 90-120°C for 12-36 hours. Then, the obtained mixture is heated to 600-1200°C at a rate of 2-10°C / min under N2 atmosphere and maintained for 1-4 hours.

5. The method according to claim 1, characterized in that The dynamic adsorption technology uses a fixed bed, a moving bed or a fluidized bed reactor to adsorb and treat sulfur-containing wastewater in oil and gas fields. The aspect ratios of the three reactors are 2 to 5. Among them, the bed height of the fixed bed adsorption is 0.5 to 2 m, the sewage flow rate is 0.1 to 1 m / h, the hydraulic retention time is 5 to 30 min, and it operates at normal temperature and pressure; the adsorbent filling height of the moving bed adsorption is 1 to 3 m, the adsorbent and sewage flow rate is 0.1 to 1 m / h, the adsorption time is 15 to 60 min, and it operates at normal temperature and pressure; the sewage flow rate of the fluidized bed adsorption is 0.3 to 1 m / s, the hydraulic retention time is 10 to 60 min, and it operates at normal temperature and pressure.

6. The method according to claim 1, characterized in that The water washing method uses pure water at a temperature of 4 to 80° C. to wash the hydrothermal carbon in a gradient manner.

7. The method according to claim 1, characterized in that In the high-temperature activation method, the temperatures of the drying, carbonization and activation stages are controlled at 100-150°C, 150-200°C and 750-850°C, respectively, and the regeneration time is 0.5-3 h.