CN-118771528-B - System and method for treating mercury-containing sewage of oil and gas field by combining photocatalytic oxidation and mercury removal agent

CN118771528BCN 118771528 BCN118771528 BCN 118771528BCN-118771528-B

Abstract

The invention discloses a system and a method for treating mercury-containing sewage of an oil-gas field by combining photocatalytic oxidation and a mercury removal agent, and belongs to the technical field of oil extraction gas engineering. The adopted tubular ultraviolet light oxidation reactor comprises a TiO 2 catalyst supported on the inner surface of a reaction tube, mercury-containing sewage enters the tubular reactor from a water inlet and pumped air, oxygen in the air oxidizes organic mercury and low-valence inorganic mercury in the sewage into Hg (II) under the action of the TiO 2 catalyst on the inner wall of the reactor, and then the oxidized mercury-containing sewage enters a mixing reactor and is added with a mercury removal agent for reaction, so that the mercury pollution in the sewage is removed up to the standard, and the method has the advantages of simplicity in operation, good removal effect, environment friendliness and the like.

Inventors

GAO NING
CAO LIHU
ZHANG JUANTAO
WU HONGJUN
FAN LEI
SHANG XUFENG

Assignees

中国石油天然气集团有限公司
中国石油集团工程材料研究院有限公司
西安三环石油管材科技有限公司

Dates

Publication Date: 20260512
Application Date: 20230410

Claims (9)

1. The application method of the oil and gas field mercury-containing sewage treatment system combining photocatalytic oxidation and mercury removal agent is characterized by comprising the following steps: The method comprises the steps of S1, firstly setting the flow rate of wastewater, the power of an ultraviolet lamp (5), the residence time of the wastewater in a pipe and the flow ratio of air to the wastewater, opening a power connector (7), opening the ultraviolet lamp (5), enabling air to enter a reaction pipe (8) through an air inlet (2), enabling mercury-containing wastewater to flow into the reaction pipe (8) from a wastewater inlet (1) for reaction, and after the reaction is finished, enabling the obtained oxidized mercury-containing wastewater to flow out from a wastewater outlet (6) and then flow into a mixing reactor when the obtained oxidized mercury-containing wastewater does not contain organic mercury and low-valence inorganic mercury after detection; s2, adding a mercury removal agent into the mixing reactor for reaction, and obtaining treated water after the reaction is finished; The mercury removal agent comprises polyaluminum chloride, sodium sulfide and para-position substituent-containing benzyl mercaptan, wherein the para-position substituent-containing benzyl mercaptan is benzo-18-crown-6 connected by ether bonds; The oil-gas field mercury-containing sewage treatment system combining photocatalytic oxidation and mercury removal agent comprises a tubular ultraviolet oxidation reactor and a mixing reactor which are connected in sequence; The tubular ultraviolet oxidation reactor comprises a reaction tube (8), wherein a TiO 2 coating (4) is coated on the inner surface of the reaction tube (8), a wastewater inlet (1) and an air inlet (2) are formed in one end of the reaction tube (8), a wastewater outlet (6) and a power connector (7) are formed in the other end of the reaction tube (8), a glass tube (3) is arranged in the reaction tube (8), and an ultraviolet lamp (5) connected with the power connector (7) is arranged in the glass tube (3).
2. The method for using the oil-gas field mercury-containing sewage treatment system combining photocatalytic oxidation and mercury removal agent according to claim 1, wherein when the oxidized mercury-containing wastewater obtained at the wastewater outlet (6) still contains organic mercury and low-valence inorganic mercury, the tubular ultraviolet light oxidation reactor is replaced by a tubular ultraviolet light oxidation reactor group, and the tubular ultraviolet light oxidation reactor group is connected with the mixing reactor; The tubular ultraviolet light oxidation reactor group comprises a plurality of tubular ultraviolet light oxidation reactors, and the tubular ultraviolet light oxidation reactors are connected in parallel or in series.
3. The method for using the oil and gas field mercury-containing sewage treatment system combining photocatalytic oxidation and mercury removal agent according to claim 2, wherein the detection is carried out by adopting an inductively coupled plasma mass spectrometer and a cold atom absorption method.
4. The method for using the oil and gas field mercury-containing sewage treatment system with combination of photocatalytic oxidation and mercury removal agent according to claim 1, wherein the glass tube (3) is made of quartz glass.
5. The method for using the oil and gas field mercury-containing sewage treatment system combining photocatalytic oxidation and mercury removal agent according to claim 1, wherein the mixing reactor is further connected with an air floatation tank, a reinjection water storage tank and a reinjection system in sequence.
6. The method for using the oil-gas field mercury-containing sewage treatment system combining photocatalytic oxidation and mercury removal agent according to claim 1, wherein an inductively coupled plasma mass spectrometer and a cold atomic absorption method are adopted to detect mercury-containing wastewater after oxidation treatment, and if organic mercury and low-valence inorganic mercury are also contained in the mercury-containing wastewater after oxidation treatment, a tubular ultraviolet light oxidation reactor is replaced by a tubular ultraviolet light oxidation reactor group, and the tubular ultraviolet light oxidation reactor group is sequentially connected with a mixing reactor; The tubular ultraviolet light oxidation reactor group comprises a plurality of tubular ultraviolet light oxidation reactors, and the tubular ultraviolet light oxidation reactors are connected in parallel or in series.
7. The method for using the oil-gas field mercury-containing sewage treatment system combining photocatalytic oxidation and mercury removal agent according to claim 1, wherein an inductively coupled plasma mass spectrometer is used for detecting the oxidized mercury-containing sewage, and if the oxidized mercury-containing sewage also contains organic mercury and low-valence inorganic mercury, the method for reducing the flow rate of effluent water in the later stage of the treatment process of the mercury-containing oil-gas production sewage from the sewage inlet (1) into the reaction tube (8) and improving the power of an ultraviolet lamp or the flow ratio of air to the mercury-containing sewage is adopted until the oxidized mercury-containing sewage does not contain the organic mercury and the low-valence inorganic mercury.
8. The method for using the oil-gas field mercury-containing sewage treatment system combining photocatalytic oxidation and mercury removal agent according to claim 1, wherein the mixing reactor is further connected with an air floatation tank, a reinjection water storage tank and a reinjection system in sequence, and the treated water obtained in the step S2 flows into the air floatation tank, the reinjection water storage tank and the reinjection system in sequence.
9. The method for using the oil-gas field mercury-containing sewage treatment system combining photocatalytic oxidation and mercury removal agent according to claim 1, wherein the usage amount of polyaluminium chloride is 40-200 g per cubic meter of mercury-containing wastewater after oxidation treatment, the usage amount of sodium sulfide is 1.2-1.5 times of the total mercury mole measured in the mercury-containing wastewater after oxidation treatment, and the usage amount of para-substituent-containing benzyl mercaptan is 0.5-1.0 times of the total mercury mole measured in the mercury-containing wastewater after oxidation treatment.

Description

System and method for treating mercury-containing sewage of oil and gas field by combining photocatalytic oxidation and mercury removal agent Technical Field The invention belongs to the technical field of oil and gas extraction engineering, and particularly relates to a system and a method for treating mercury-containing sewage of an oil and gas field by combining photocatalytic oxidation with a mercury removal agent. Background Mercury belongs to heavy metals and is the only metal element in liquid state at room temperature. Elemental mercury is volatile and is very low in abundance but widely available in nature. The natural sources mainly comprise volcanic activity, soil emission, natural weathering, vegetation release and the like, and the artificial sources mainly comprise mercury emission caused by human activities, and mainly comprise waste water, waste gas and waste residues from chemical industry, petrochemical industry, agriculture, pharmaceutical industry and chlor-alkali industry, gaseous mercury released into the atmosphere in smelting, coal burning and other processes and dry-wet sedimentation of the gaseous mercury. Metallic mercury has special properties of strong toxicity, volatility, mobility, bioagglomeration and the like. The mercury in the environment is mainly in the form of elemental mercury (HgO), inorganic mercury (Hg + and Hg 2+), and organic mercury 3. Elemental mercury is less commonly found in nature and mercury vapor that can be ingested through the respiratory tract is highly toxic, monovalent mercury salts are most commonly mercurous chloride, poorly soluble in water, and divalent mercury is commonly both mercurous chloride and mercurous sulfide. Mercury chloride is easily dissolved in water and has relatively strong toxicity, and mercury sulfide has extremely weak water solubility and very low toxicity. The organic mercury mainly comprises methylmercury (monomethyl mercury and dimethyl mercury), ethylmercury, phenylmercury and the like, and the most common and most harmful to human bodies and the environment is methylmercury. Methyl mercury has lipophilicity, stable chemical property, is easily absorbed by organisms, is difficult to metabolize and eliminate, can be enriched and amplified along with food chains, and increases concentration in high-nutrition-level organisms. It has been reported that freshwater fish and phytoplankton have a 1000-fold enrichment for mercury, 10-fold for freshwater invertebrates and 20-fold for marine animals. The enrichment coefficient of the methylmercury in the aquatic organisms can reach 10 4-107. The water body is one of important carriers after mercury enters the environment, and the mercury-containing wastewater is discharged into the water body, so that the wastewater can be diffused along with water flow to cause the change of space position, and the existence form of the wastewater can be changed in the diffusion process. Various forms of mercury may be converted to Hg 2+ in the water body, primarily to dimethyl mercury under anaerobic conditions and primarily to monomethyl mercury under aerobic conditions. Mercury methylation can occur in both slimes and aquatic organisms. Methylation can occur under the action of acetaldehyde, ethanol, methanol and ultraviolet rays if external photochemical conditions are satisfied even if there is no organism. Almost all forms of mercury accumulate in organisms through methylmercury forms, which are harmful to the organisms. The "water-borne disease event" occurring in panda county in 1952 is the first worldwide event of dimethyl mercury poisoning caused by industrial wastewater. In view of biological and environmental hazard of mercury, the integrated wastewater discharge standard of GB 8978-1996 prescribes that alkyl mercury cannot be detected in discharged water of a mercury-containing gas field, the total mercury content cannot be higher than 0.05mg/L, and the total mercury content of the discharged water after treatment is required to be smaller than 0.05mg/L in the discharge standard of industrial pollutants of GB 30770-2014 tin, antimony and mercury. Because mercury in the stratum has similar hiding conditions and mobility with hydrocarbons, and organic matters can well enrich mercury, partial natural gas reservoirs are also mineral source layers of mercury, and mercury coexists with natural gas in a volatile form. The mercury content of many gas wells in the Tarim basin and Songlao basin of China is counted to exceed 500 mug/m 3. The cognition of the existence and harm of mercury in the oil gas production process starts from the fact that after the damage accident of an aluminum heat exchanger of a natural gas liquefaction plant of Skikda in Aland Australia, the post analysis is caused by amalgam embrittlement corrosion attached to the wall of a metal after gaseous mercury is condensed, so that the perforation and the damage of equipment are caused. The mercury pollution caused by the oil g