A Study On Zero Liquid Discharge Technology From Coal Chemical Industry And Development Of Treatment Process Of High Concentrated Phenolic Ammonia Wastewater

Geographical maldistribution of coal and water resource and national energy security has promoted the development of coal chemical industry,also led to huge water consumption that posed great challenges to coal chemical wastewater treatment.Achieving wastewater‘Zero Liquid Discharge'has become one of the most imperative problems around nationwide coal chemical projects.From the aspect of industrial wastewater treatment system design,the frame of‘Pretreatment-Biochemical treatment-Advanced treatment-Brine treatment-Vaporization and Crystallization'has been basically established.However,several inadequacies of this process exposed when treating partical coal chemical wastewater,inclusive of low removal efficiency of pretreatment units,inferior reuse water quality,high treatment cost,low reuse ratio and lack of top-level design of treatment system.This restricts the coal clean and efficient utilization and sustainable development of coal chemical industry.Therefore,this research investigates and analyzes the life cycle costs of nine different types of coal chemical wastewater.The cost advantage comparison of wastewater treatment when achieving first category integrated wastewater discharge and zero liquid discharge standards has been accomplished by the introduction of surface water treatment cost and environment damages value.Besides,the consumed water of planning advanced coal chemical projects of2018 is calculated based on the present water consumption index.According to the results,the total cost of first category integrated wastewater discharge is 7.17 CNY/t water higher than that of zero liquid discharge.and the planned projects took up 2.8%of total industrial water supply.It is suggested that‘Zero Liquid Discharge'policies and water resources appraisal should be introduced to improve and strengthen the development of coal chemical industry.Crushed coal pressurized gasification technology has a high cold gasi efficiency but difficult to realize wastewater‘Zero Liquid Discharge'.By contrast,coal-water slurry gasification is easy to reuse treated water while it has low carbon utilization efficiency when producing clean fuels and chemical products.For achieving complementary advantages,this study proposed a novel process to integrate two gasification technologies.Results show that the new process improves carbon conversion efficiencies of coal-to-olefin and coal-to-ethylene glycol by 24.95%and 13.55,abates unit cost by 19.72%and 9.27%,reduces CO₂ emission by83.10%and 83.50%in the context of achieving‘Zero Liquid Discharge'standard.This presents good application prospect in the future.On the contrary,coal-to-SNG process still need further exploration.Currently,semi-coking wastewater pretreatment process has low performance of oil,dust and phenols removal and consumes a large amount of high-grade steam.This results in not only the fouling even breakdown of whole treatment system,but also far exceeding the semi-coke plants'utilities supply capacity.This research identified several bottlenecks of current process,proposed according novel hybrid process based on the benchmark treatment capacity of 240m³/d,and verified the reliability and feasibility through a lab-trial study of industrial wastewater.According to the results,acidification affects?potential and extraction efficiency,the separation of deacidification and deamination units,as well as the negative operation of solvent recovery tower,lowered the steam demand of reboilers.The effluent concentrations of oil,sour gas,total phenols,ammonia and COD decreases to 20 mg/L,10 mg/L,270 mg/L,50 mg/L and3050 mg/L,respectively.The estimated investment cost reduces by 57.9%and the net cost decreases from 53.40 CNY/t to 50.69 CNY/t water.Coal chemical wastewater with high concentrated phenol and ammonia need to remove acid gas,ammonia and phenols to recover aqua ammonia and crude phenol.Phenol and ammonia recovery process,developed by South China University of Technology,has obtained widely recognition of industrial circle.This process adopts a single tower to strippe out sour gas and ammonia simultaneoursly,and then extracts phenols by solvent MIBK to recover crude phenol.However,this process consumes a large amount of hot utilities.The paper fixates on the further improvement of energy efficiency by integrating thermo-vapor compressors.Two scenarios have been proposed and analyzed following pinch analysis and grand composite curve.The technical and economic results show that the integrated process requires 53.7%less hot utilities and 57.5%less cooling water consumption at the expense of 662 k W more electricity use,as suggested in simulation results.The estimated treatment cost saving is 8.19CNY/t water,about 6.552 million CNY/y,and the emission reduction is 5237 t CO₂ e/y.