Research On Comprehensive Treatment Technology Of Produced Water In Sulfur-bearing Gas Fields

The produced water quality of sulfur-bearing gas fields is complex and contains hydrogen sulfide,inorganic salts and refractory organic matter.At present,the three main treatment modes of produced water in sulphur-bearing gas fields are reinjection,discharge and comprehensive utilization.The reinjection cost is high and there is a risk of polluting groundwater.The discharge is prohibited in most areas due to the implementation of the national ecological civilization strategy.Therefore,the comprehensive utilization of produced water will be the main processing mode in sulphur-bearing gas fields in the future.Based on the above problems,this study proposes to use the stage evaporation process to dispose of produced water,and studies the technological parameters of pretreatment,evaporation treatment and advanced treatment.The results show that the technology scheme can realize the separation of water,salt and pollutants,water reuse and salt take-out,thus realizing the comprehensive utilization of produced water in sulfur-bearing gas fields.In this study,glass electrode method,potassium dichromate method,iodometry and other detection methods were used to detect pH,COD,sulfide and other indicators in water quality,and the organic matter in the extracted water was qualitatively analyzed by ultraviolet spectroscopy and GC-MS.The results show that the sulfide content in produced water of sulfur-bearing gas field is 5.10*102 mg/L,chloride ion content is 2.14*104 mg/L,COD content is 1.20*103 mg/L,and contains many organic compounds with benzene ring structure,such as styrene,benzaldehyde,etc.It is a typical gas field wastewater with high sulfur content,high salt content and difficult biodegradability.The combined technology of air stripping and alkali precipitation pretreats the produced water,realizes the removal of hydrogen sulfide,calcium and magnesium,suspended matter in the produced water.The results show that the removal rate of hydrogen sulfide is 91.8%when the pH is 7.5,the temperature is 27℃ and the gas-water ratio is 700:1.Sodium hydroxide 1.2g/L and sodium carbonate 1.0g/L can effectively remove calcium and magnesium and suspended solids,of which the removal rate of calcium and magnesium is 95.8%and the removal rate of suspended solids is 96.5%.The pretreated water is treated by the technology of stage evaporation and concentration.Conditions such as evaporation temperature,pH and first-stage evaporation volume are carried out.Salt crystallization and electrolytic oxidation experiments of mother liquor were carried out.The results showed that when the pH was 11,the evaporation temperature was 90℃and the first-stage evaporation volume was 20%,most of ammonia nitrogen and a little of COD were enriched in the first-stage condensation water,and then treated by stripping and fractional breakpoint chlorination,the water quality reached the reuse standard.The remaining produced water enters the second-stage evaporation,and its evaporation volume is 70%.The indexes of pH,chloride ion,COD and ammonia nitrogen in the second-stage condensation water reach the reuse standard.20%of the produced water enters the first-stage condensation water and 70%of the extracted water enters the second-stage condensation water,thus greatly reduced the treatment scale of the produced water and improved the treatment efficiency.After two stages of evaporation,10%mother liquor remained.The mother liquor enriched most of the COD in the produced water.BDD electrode was used to electrolytically oxidize the extracted water for 7 hours at current 4.8A and voltage 30V.The COD removal rate of mother liquor was 96.6%.The sodium hypochlorite solution with an effective chlorine content of more than 1%could be obtained,which could be used for the removal of COD in the pretreatment process.Through the research on integrated technology of the produced water in sulphur-bearing gas field,the comprehensive treatment technology of produced water in sulphur-bearing gas field has been formed.The treated water meets the standard of "Design Code for Petrochemical Circulating Water Field"(GB/T 50746-2012),and the separated salt meets the standard of "Industrial Salt"(GB 5462-2003).