Research On Process And Optimization Of Coal Gas Wastewater Treatment And Reuse Technology

In this paper,the actual project of 12 million Nm3 organic wastewater in Nissan,which is a natural gas project in Inner Mongolia,is taken as the object of study.The wastewater content in the actual project is: plant sewage,coal gas wastewater and methanol wastewater.The Coal gas comprehensive effluent quality test is : CODcr >2350mg/L,BOD>950mg /L,ammonia nitrogen>115 mg/L,total nitrogen>930mg/L,petroleum> 120mg/L,SS>450mg/L,which is a high concentration,toxic and organic wastewater Difficult to biodegradable,it will have a great harm to the surrounding environment.In order to achieve zero pollution to the surrounding environment,minimize the project cost,we do a research on the process of wastewater treatment and optimization of process and reuse technology.The integrated sewage of Coal Gas first advanced balance tank,add alkaline reagents for PH adjustment,enable it is in the best treatment state.And then physical and chemical treatment,biochemical treatment and deep processing of three stages.In this project,the dephenolization,deacidification,Ammonnia Distillation and degreasing methods are used to pretreat the waste water produced in the process of coal gas production.The coal gas waste water contains a large amount of ammonia and phenols,and the recovery of ammonia and phenolic in the wastewater will be helpful for reusing of resources,reducing project costs as well as reducing recovery difficulties of the wastewater after the physical and chemical treatment.The process of the dephenolization of this project takes the solvent extraction.The extractant was diisopropane.The removal efficiency of nonvolatile phenol and volatile phenol in the wastewater was 60% and 45%.The concentration of CO2 and H2 S which is Acidic chemicals in the wastewater is relatively large,the too high content of CO2 will cause the blockage of the ammonium bicarbonate crystal pipe and equipment in the process later,which will affect the normal use of the system;Gas H2 S will affect the extraction efficiency of the recovery of phenol,and corrosion the equipment of extraction and even cause scaling And obstruction.Enable that the Wastewater generated by the Coal Gas flow through the deacidification tower,in the process the acid gases such as H2 S and CO2 are separated from the wastewater and then do extractation to the wastewater.The use of the ammonia removal technology of this Coal gas waste water project is the steam stripping of ammonia.The ammonia in the coal gas effluent exists in the form of free ammonia and solid ammonia,adding alkaline liquid to the wastewater to enhance the pH value of the wastewater so that the conversion of the solid ammonia to the free ammonia can promote,therefore the ammonia removal efficiency can improve.The ammonia steam generated by Stripping can achieve the recovery of ammonia after the separation,distillation and other steps.In the process of ammonia distillation,when takeing the Lurgi gasification process technology,the ammonia nitrogen content in the waste water before distilled is 4300 ~ 7100 mg / L,but the concentration of ammonia nitrogen in the effluent waste water can be controlled below 510 mg / L.The oil contentcan not exceed 100mg/L after the biological treatment of the waste water,otherwise it will reduce the microbial activity in the biochemical process,even produced unnecessary foam in the later subsequent aerobic process,which may affect the good running of the entire project.This project makes use of grease traps in the degreasing process,and use the difference in density between oil and water,the oil compounds of the smaller density will gradually float to the surface in the slow flow of waste water,then use oil scraper to bring the oil on the surface into the storage tank.A small amount of heavy oil and impurities will precipitate to the bottom of the grease trap,and regularly discharged by the discharge pipe.Slanting or filler can also be added to the Grease traps,it is useful for enhancing the oil removal effect.The measures adoped in the biochemical treatment of the project are SBR method,which is an improved activated sludge process and running in the intermittent aeration mode,the process includes Precipitation,homogenization,phosphorus and nitrogen removal,biodegradation etc except sludge reflow process.The measures adopted in the deep treatment of this project include mixed solvent precipitation,adsorption,membrane separation,advanced oxidation and other treatment process.The chemical reagents used in the coagulation sedimentation method are poly aluminum chloride,and the removal efficiencies of COD and suspended solids are 31.1%and 50.1% respectively.The compound of porous,pore size are taken in the adsorption method,which adsorbe debirs in polluted wastewater trought the form of adsorption to make the polluted waste water clean.The micropore size of the membrane is used to remove and contaminate the pollution in the waste water selectively to achieve the purpose of reducing the concentration of effluent contaminants in the membrane treatment process.The immersion ultrafiltration and reverse osmosis process are adopped in Wastewater reuse of this project.The designed influent quantity of the ultrafiltration device of reuse is 825m3/h(including the backwash water of the ultrafiltration device),the water of this section is the effluent after the biochemical treatment of the sewage.The pollutants in the water after the biochemical treatment are presumed to be unbiodegradable macromolecules,cyclic structures,organic compounds with functional groups that inhibit the microbes,and add flocculants in their pre-treatment processes.In this paper,the A/O process in the integrated wastewater treatment of coal gas is improved.The change of nitrogen and ammonia and COD removal rate in different pH environment is studied to determine the optimal PH value of the treatment wastewater.The coagulant is improved,the catalysis of removal efficiency of COD,color,SS under different coagulants was studied to determine the optimal coagulant.Adding the sludge recovery process,so that sludge can be recycled and become a new packaging materials.In this paper,the improvement of the reuse technology of coal gas synthesis wastewater treatment was studied,and the comparative test of fiber membrane in the polypropylene at different pH value,operating period and operating pressure was studied,to obtaine the optimum value of each parameter.The improvement of reverse osmosis technology in the reuse of the comprehensive wastewater treatment is studied,the study focus on the comparative test of the silicon carbide ceramic membrane at different pHvalue,operating period and operating pressure to obtaine the optimal value of each parameter in running state.