Optimization Study On Multi-Effect Evaporation Zero Liquid Discharge Treatment System For Oilfield Wastewater

In order to achieve the goal of zero liquid discharge for multi-effect evaporation system,this paper carries out a series of experimental work on multi-effect evaporation system and proposes a system optimization scheme and system design ideas aiming at zero liquid discharge technology requirements.This paper provides ideas for oilfield enterprises to save resources,to improve efficiency and to reduce pollution,and offers the possibility of zero liquid discharge treatment of oilfield wastewater.The following are the main work and conclusions of this paper.(1)Through system experiments,the operational problems of the existing six-effect evaporation experimental platform were investigated,and operational adjustments and replacement of supporting equipment were carried out.After the adjustment,the temperature of each effect of the system was increased by more than 5?,and the maximum increase could be more than 10?;the temperature of raw material liquid after preheating was increased by more than 10?;meanwhile,the temperature difference of each effect of the system was also more stable,and the temperature fluctuation was significantly smaller.Regarding the system performance,the adjusted system has improved the concentration ratio by about 25%compared with the original system.(2)The dynamic performance and steady-state performance of the system were studied using the adjusted operation flow.It was found that the system takes about 40 min from start-up to the formation of stable temperature difference,and the optimal performance of the system is 300 kg/h feed flow rate and 110 kg/h raw steam flow rate,at which time the fresh water output of the system can be over 250 kg/h and the concentration ratio can be more than 6.In the analysis of the steady-state performance,a series of unreasonable points of the system were found.(3)The working principles of the multi-effect evaporator and crystallizer were introduced,and mathematical modeling and validation work was carried out for both parts.The models developed based on material and heat balances differed from the actual situation within 5%.(4)Based on the problems in the steady state of the system,a set of design ideas was proposed with the dryness at the outlet of the evaporator hot end as the adjustment port and the raw material liquid temperature after preheating as the convergence criterion.The design idea was applied to the six-effect evaporation experimental platform,and an optimization scheme mainly based on the adjustment of evaporator and preheater design was formed to further improve the performance of the system.(5)Based on the obtained design idea,a DTB-type crystallizer was coupled into the system to design two systems,and the feasibility of zero liquid discharge was judged by calculation.In addition,the two systems were compared,and their respective characteristics and operating stability were analyzed.