A novel process for zero discharge of sewage from natural gas field development, including the following steps:
 Step 1: Clean up and divert various sewage in the gas field
 There are many types of sewage produced by the development of natural gas fields, and the pollutant composition of various sewage is different, and the pollution degree is also different. If the upstream sewage is not cleaned and separated, various types of sewage are mixed together, the water quality composition is more complicated, and the proportion of incoming water is unstable, resulting in large fluctuations in water quality, adding greater difficulties to the subsequent treatment process, and it is difficult to ensure the treatment effect.
 Therefore, the zero-discharge combination process of natural gas field development requires first cleaning and diversion. According to the characteristics of various types of sewage water quality (such as pollutant composition, pollutant concentration) and the purpose of sewage treatment, separate collection and storage are carried out, and then different treatment methods are adopted.
 The sewage in the gas field is divided into: normal production sewage, domestic sewage, maintenance sewage, accident waste liquid, rainwater, production waste water and gas field water, and collected separately; then normal production sewage, domestic sewage, maintenance sewage, accident waste liquid and Initial rainwater is introduced into the biochemical treatment unit, production wastewater is introduced into the electrodialysis treatment unit, and gas field water is introduced into the gas field water pretreatment unit. Among them:
 1. Biochemical processing unit
 The objects processed by the biochemical treatment unit are normal production sewage, domestic sewage, initial rainwater, maintenance sewage and accident waste liquid. The treated water can be used as greening water and site washing water in the plant, and the remaining part enters the evaporation crystallization unit for advanced treatment.
 The sewage is pretreated (pre-aeration-air flotation-hydrolysis acidification), then biochemical treatment of sewage (anoxia-aerobic-precipitation), and finally reclaimed water treatment (filtration-deodorization-sterilization), the effluent quality reaches After "Urban Sewage Reclamation and Utilization of Urban Miscellaneous Water Quality" (GB/T18920), it will be used as water for plant greening and site washing. The sludge treatment adopts the "gravity concentration-mechanical dewatering" process, and the dewatered sludge is finally landfilled or incinerated.
 The production sewage, domestic sewage, and initial rainwater pollutants that enter the production sewage adjustment tank through the clean sewage diversion have a low pollutant load and can directly enter the treatment process. The concentration of organic matter, H 2 S content and pollutant load are very high, so it needs to be mixed into low-concentration sewage into the treatment process daily to avoid the impact of ultra-high load on the treatment process. The accident waste liquid is abnormal sewage discharge, which is only generated in the accident state. It is collected through the accident pipe network and stored in the accident sewage tank. The pollutant load of this type of sewage is very high, so it needs to be mixed into low-concentration sewage daily Enter the processing flow. By comprehensively balancing the COD concentration of the main pollutants in various sewage, the normal value of the COD concentration of sewage entering the sewage treatment system should be controlled at 540~600mg/L, and the impact concentration is ≤800mg/L.
 1. Sewage pretreatment
 The purpose of sewage pretreatment is to adjust and balance sewage water quality, remove sulfide, avoid its harm to biochemical treatment, and reduce excessive organic concentration.
 1) Aeration adjustment
 Aeration adjustment refers to the effective adjustment of sewage water quality, water volume and water temperature in the aeration adjustment tank. The pH of sewage fluctuates greatly, the concentration of organic matter fluctuates, and the water volume is unstable. Through the adjustment and homogenization of the pool, the water quality and volume can become relatively stable. The aeration regulating tank is equipped with a blower, and the compressed air generated is distributed through the microporous aerator, and the air utilization rate is high, which can strengthen the regulation of water quality and quantity. Sewage contains highly toxic sulfide. Through the effect of air aeration, the highly reducing sulfide is easily oxidized by air to elemental sulfur, thiosulfate and sulfate, which can avoid toxicity to subsequent biological treatment. effect. When the water temperature is low in winter, saturated low-pressure steam is introduced, and the temperature of the steam-water mixing heater is controllable and adjustable to increase the temperature of the sewage to facilitate the removal of organic matter and total nitrogen in the sewage.
 2) Condensed air flotation
 The coagulation process is to add coagulant and coagulant aid to the sewage to destroy the stable state of colloidal particles in the water. Through collision and aggregation between colloidal particles, flocculent substances are separated from the water. The working principle of air flotation is to pass in or generate a large number of fine bubbles in the water to form a three-phase heterogeneous system of water, gas and the removed substance. Under the action of the interface capacity, the buoyancy of the bubbles and the hydrostatic pressure difference, the combined body of the bubbles and the removed substance is floated to the surface of the water to achieve separation from the water.
 3) Hydrolysis and acidification
 Hydrolysis and acidification means that in the hydrolysis and acidification tank, the hydrolysis and acidification microorganisms convert insoluble organic suspended matter into soluble organic matter, and the soluble and refractory organic matter is transformed into relatively easily degradable organic matter, thereby improving the biodegradability. Although the hydrolysis acidification tank has no obvious effect on the degradation of COD and BOD, it can promote the subsequent biochemical treatment. The combined filler is set in the hydrolysis acidification tank, so that the microorganisms in the tank are fixed on the filler in a three-dimensional distribution, which can not only improve the efficiency, but also prevent the loss of microorganisms and save the lost sludge return equipment.
 2. Wastewater biochemical treatment
 1) Hypoxia pool
 Denitrifying microorganisms in the anoxic tank can remove NO 2 - And NO 3 - Reduce it to N under the condition of supplying organic electrons 2 Spill into the atmosphere, reducing eutrophic substances into the sewage body. The organic electron donor comes from the abundant organic matter in the effluent of the hydrolysis acidification tank, NO 2 - And NO 3 - It comes from the larger mud-water reflux ratio in the subsequent sedimentation tank. A microporous aerator is installed in the anoxic tank to supply a small amount of air to keep the sludge in a good suspension state and ensure the smooth completion of denitrification.
 2) Aerobic pool
 There are two baffle walls in the aerobic tank, and the aerobic tank is divided into 3 grids. Each aerobic tank is fully mixed aeration, and the three grids are connected in series to make the aerobic tank a plug flow aeration. Carbon-containing organic matter and nitrogen-containing organic matter are first carbonized and ammoniated, and finally nitrified.
 3) Sedimentation tank
 The sedimentation tank performs solid-liquid separation of the mixed liquid discharged from the aerobic tank. The separated clarified water flows into the safety tank, and the sludge at the bottom is returned to the anoxic tank for denitrification and denitrification. The sludge return ratio is set to 100%, and the sedimentation The pool adopts vertical flow sedimentation tank.
 4) Insurance pool
 The clarified water overflowing from the top of the sedimentation tank flows into the insurance tank, part of the water is upgraded to the reclaimed water treatment equipment for further treatment and then reused as greening water and site washing water, and the remaining part enters the evaporation crystallization unit for advanced treatment.
 2. Electrodialysis processing unit
 Circulating cooling water system sewage, boiler sewage and other production wastewater enter the electrodialysis treatment unit for desalination treatment, the treated fresh water is used as supplement water for the circulating cooling water system, and the concentrated water enters the evaporation crystallization unit.
 The main problems of circulating cooling water system sewage and boiler house sewage are total hardness, total alkalinity, turbidity, chloride ions, conductivity and other water quality exceeding the standard, so a combination of pretreatment and desalination treatment is required. Among them:
 (1) Pretreatment:
 The pretreatment is divided into three parts: electric flocculation reaction tank, sedimentation tank and filter tank, of which:
 (1) Electric flocculation reaction tank:
 An electrochemical device is placed in the electro-flocculation reaction cell, and the electrode plate is energized. Under the action of an electric field, the metal plate produces highly active adsorption groups to absorb colloidal particles, suspended matter, insoluble organic matter (COD), and heavy metals in the water. Ion, SiO 2 And other impurities, forming a larger floc structure to precipitate out of the water; at the same time, add liquid caustic soda in the reaction tank to adjust the pH value, so that the calcium and magnesium ions in the water are precipitated in an insoluble combined state, and then adsorbed by the adsorption group produced by electrolysis. Form flocs and precipitate out of the water. In the whole treatment process, there are always electric field effect, flocculation effect, adsorption bridging effect and net trapping and sweeping effect.
 (2) Sedimentation tank:
 The water treated by the electric flocculation reaction tank enters the inclined plate sedimentation tank of the integrated device. The sedimentation tank is designed using the principle of shallow filtration and adopts the form of an inclined plate sedimentation tank. The flocs formed by the reaction are precipitated in the sedimentation tank. After precipitation, the remaining small amount of fine flocs enter the filter tank.
 (3) Filter pool:
 The filter tank is filtered with dual-media filter media (quartz sand, anthracite) to remove the remaining fine flocs, suspended matter, silt, rust, large particles and other mechanical impurities in the water to ensure the turbidity of the effluent. The filter tank needs to be backwashed after running for a period of time. The backwash water is filtered water from the filtered pool, and the backwash discharge water is directly discharged into the sewage pipeline in the plant.
 Pretreatment can not only remove turbidity and suspended matter in water, but also remove most of colloids, heavy metal ions, oil and part of COD, etc., so as to provide better water inlet conditions for subsequent electrodialysis desalination equipment.
 A sludge tank is set directly below the pretreatment equipment, and a sludge hopper is set under the reaction tank and the sedimentation tank. The sewage in the sludge hopper is regularly discharged to the sludge tank, and the supernatant is discharged into the electrodialysis treatment unit adjustment tank after the sludge settles. , The sludge is lifted to the sludge thickening tank of the biochemical treatment unit by a pump, and the sludge of the biochemical treatment unit is subjected to gravity thickening and mechanical dehydration together. Finally, the moisture content of the sludge can be reduced to less than 75%, and it is transported to landfill or Incineration disposal.
 After pretreatment, the removal rate of turbidity, suspended matter and colloid is ≥90%, the removal rate of total hardness and total alkalinity is ≥60%, the removal rate of oil is ≥90%, the removal rate of total phosphorus is ≥90%, SiO 2 The removal rate is ≥60%, the removal rate of Fe, Mn and other heavy metal ions is ≥90%, and the COD removal rate can reach 20%-40%.
 (2) EDR electrodialysis desalination:
 Since the fresh water produced by the desalination treatment will be reused as the replenishment water of the circulating cooling water system, the salt content of the water quality is not demanding, and a moderate desalination process can be selected for desalination treatment. Therefore, the desalination process considers the use of a two-stage EDR electrodialysis process, instead of using a deep desalination reverse osmosis process. At the same time, the EDR electrodialysis desalination process has the characteristics of wide range of inlet water quality, strong membrane resistance to pollution, low operating cost, high water recovery rate (75%) of the designed system, stable desalination effect, and no need for scale inhibitors and reducing agents. It is more suitable Applied to wastewater reuse treatment, the operating cost is also lower than the reverse osmosis process.
 After pretreatment, the effluent enters the filtered pool, and after sterilization, it is pressurized and filtered into a precision filter to further ensure the turbidity and suspended matter requirements of the subsequent EDR electrodialysis desalination equipment. The effluent from the precision filter enters the EDR electrodialysis desalination equipment for desalination. The desalination equipment is designed as a two-stage. After being separated by the first-level desalination equipment, the fresh water from the fresh water end enters the finished product pool, and the concentrated water from the concentrated water end enters the second Class-level desalination equipment: After being separated by the second-level desalination equipment, the fresh water from the fresh water end enters the finished product pool, and the concentrated water from the concentrated water end enters the evaporation crystallization treatment unit for advanced treatment. The product pool water is pressurized and reused for supplemental water in the circulating water system of the plant.
 The water quality treated by the electrodialysis treatment unit can reach the water quality standard of circulating cooling water in the "Design Specification for Industrial Circulating Cooling Water Treatment" (GB50050).
 3. Gas field water pretreatment unit
 The gas field water needs to be pre-treated first. After pre-treatment, the water quality reaches the water quality standard of the "Gas Field Water Reinjection Method" (SY/T6596), and at the same time meets the water intake index of the evaporation crystallization unit, and then enters the evaporation crystallization treatment unit.
 The gas field water is collected by the gas field water collection system to the gas field water storage tank of the sewage treatment device, and then pressurized into the CPI inclined plate deoiler, coagulation sedimentation tank, DGF air flotation device, and then pressurized to the multi-media filter. The above treatment process can remove oil, organic matter, colloid, suspended matter, etc. in the water, and finally enter the evaporation crystallization treatment unit. A small amount of sludge produced in the gas field water pretreatment process is stored in a slop tank and enters the condensate oil stabilization device in the plant or is transported for treatment; the small amount of sludge produced is lifted to the sludge thickening tank of the biochemical treatment unit by a pump , Gravity thickening and mechanical dehydration are carried out together with the sludge of the biochemical treatment unit, and finally the moisture content of the sludge can be reduced to less than 75%, and it can be transported to landfill or incineration.
 Step 2. The unused up-to-standard sewage after treatment by the biochemical treatment unit, the concentrated water produced by the electrodialysis treatment unit and the gas field water treated by the gas field water pretreatment unit all enter the evaporation crystallization unit for advanced treatment. Reuse is supplementary water for circulating cooling water or other production water in the gas field. Pollutants are precipitated from sewage in the form of crystalline salt, and the crystalline salt is landfilled or recycled as industrial salt.
 The treatment process of the evaporative crystallization unit adopts the treatment process of "four-effect mixed condensate water preheating vacuum desalination", and the product water can meet the cooling water quality requirements of "Urban Wastewater Reclamation-Industrial Water Quality" (GB/T19923). The circulating cooling water system is supplemented with water, and the pollutants are precipitated as crystal salts, and finally zero discharge of sewage is realized.
 The various types of sewage stored in the original pool of evaporative crystallization will flow into the Ⅰ, Ⅱ, Ⅲ, and Ⅳ effect evaporators through the feed pump. The salt slurry produced by the evaporation and crystal concentration of each effect evaporator is discharged from the original effect and then turned in turn (Ⅰ→ Ⅱ→Ⅲ→Ⅳ) Enter the lower effect. The salt slurry discharged from the Ⅳ effect evaporator enters the thickener through the salt slurry pump, and then enters the centrifuge for dehydration and separation. The solid salt is sent to the waste salt transfer barrel through the conveyor belt for transportation, and the mother liquor is centrifuged. It flows into the centrifugal mother liquor bucket and returns to the IV effect by the centrifugal mother liquor pump.
 The raw steam from the boiler system is first injected into deionized water (use the softened and demineralized water of the condensate system before driving, and use the condensate from the first effect evaporator after driving) to eliminate overheating, and then send it to the first effect evaporator to transfer its latent heat Condense the sewage in the evaporator. The Ⅰ-effect steam condensate is flashed twice through "the first-effect condensate balance bucket→the first-effect condensate flash bucket→the first-effect condensate second flash bucket" to recover part of the heat energy and return to the boiler room as boiler supplementary water.
 The secondary steam discharged from the first-effect evaporator is sent to the second-effect evaporator. After condensation, the condensed water is sent to the second-effect balance bucket, and then flashes to the third-effect balance bucket.
 The secondary steam discharged from the second-effect evaporator is sent to the third-effect evaporator, where the condensed water is sent to the third-effect balance bucket, and then flashes to the fourth-effect balance bucket.
 The secondary steam discharged from the III-effect evaporator is sent to the IV-effect evaporator, where the condensed water is sent to the IV-effect balance bucket.
 The secondary steam discharged from the IV-effect evaporator is sent to the surface condenser, where the condensed water is sent to the mixed condensate bucket, and then the brine is preheated by the plate preheater, and then sent to the circulating cooling water system for reuse Used as supplementary water for circulating cooling water system or reused as production water in the plant. Non-condensable gases are separated in the form of water vapor in the condenser. These gases can be extracted from the condenser by a liquid ring vacuum unit and discharged into the atmosphere, which is beneficial to improve the vacuum. After the steam is condensed, a vacuum state is formed to reduce the evaporation temperature of the material, and a temperature gradient is formed between the I-IV effects, and a certain heat transfer is generated in each effect to promote the temperature difference, so that the steam heat can be used many times.
 The fresh water used in the device is used to flush the packing seal or mechanical seal of the pump. The flushing water of the pump is added to the seal to ensure that the internal pressure is higher than the delivery pressure of the pump to avoid leakage and damage to the pump.
 A small amount of sewage leaked from washing equipment, ground equipment and pipelines is collected in the mixing tank, re-evaporated and crystallized, and reused as supplementary water for the circulating cooling water system after the crystallization is separated. Wash the evaporation crystallization tank with mixed condensed water when parking. When the concentration of the tank is low, the washing water returns to the tank for storage. The next time the tank is used for reuse, it reaches 220-250g/l. When the tank washing effect is not good, it will be discharged to the accident bucket. Salt recycling.
 The temperature of the first-effect heating steam is 143℃, the temperature of the evaporative crystallization material liquid is 133.5℃; the second-effect heating steam temperature is 117℃, the temperature of the evaporating crystallization material liquid is 106.5℃; the third effect heating steam temperature is 92℃, the temperature of the evaporating crystallization material liquid It is 81.5℃; the temperature of the IV heating steam is 68℃, and the temperature of the evaporating crystal material liquid is 57.5℃;
 This type of evaporative crystallizer has the following advantages: high evaporation crystallization strength; short-circuit temperature loss is greatly reduced, so that the effective heat transfer temperature difference of the system is greatly increased; the additional load of the material-liquid circulating body on the circulating pump is greatly reduced, thereby effectively The power consumption of the circulating pump is reduced.
 The heating tube is made of titanium, the first and second effect heating tubes are made of titanium alloy (TA10), and the third and fourth effect heating tubes are made of pure titanium (TA2), which can resist Cl well. - The material of the evaporation crystallization chamber is made of 316L stainless steel composite plate; the shell of the heating chamber is made of 316L stainless steel composite plate; all sewage, brine, and salt slurry pipelines use 316L stainless steel pipe; the valve is made of stainless steel valve; sewage, brine , Salt slurry pump uses stainless steel pump.