Wastewater Treatment Of Fluid Catalytic Cracking Unit Based On Bipolar Membrane Electrodialysis And Extraction Method

Fluid catalytic cracking?FCC?is the main petroleum conversion technology in the oil refinery,which produces most gasoline for vehicles and a significant fraction of propylene for the polymer industry.While FCC brings great economic benefits to enterprises,it also generates two types of wastewater.The first is high salt wastewater,mainly produced by the sodium hydroxide solution in treating the flue gas of reaction regeneration system.This wastewater is difficult to treat because of its high salt content.The other is phenol-containing wastewater,which comes from almost each section of FCC.Its main characteristics are high organic content and high oil content.It is of great significance to effectively treat wastewater and improve atomic utilization in China whose water resource per capita is less than 2000 m³.This paper first simulates the wastewater generation process.Aspen Hysys software is employed to perform the simulation for the flue gas wet desulfurization.This process produces high salt wastewater at the bottom of the NaOH absorption column.The mass concentration of SO₄^2-in this wastewater is 86.62 g/L.Aspen Plus software is used to simulate the fractionation process of FCC.A phenol-containing wastewater is generated at the bottom of the oil-gas separator,in which the mass concentration of phenol is 3.55 g/L and the mass fraction of oil is 7.33 g/L.The above wastewater is then treated.A treatment method based on bipolar membrane electrodialysis?BMED?is proposed for above high salt wastewater.The effects of current density and operating time on processing efficiency and energy consumption are studied experimentally.Based on the experimental data,the USER2module is used to customize the BMED device in the Aspen Plus software,and then the treatment effect is studied by combining experiment and simulation.The BMED method is also compared with the multi-effect evaporation method.For the phenol-containing wastewater,the extraction method is used in designing the wastewater treatment process to achieve oil-water separation,phenol removal from wastewater and phenol removal from oil.The Gaussian 09 software is used to analyze the extraction mechanism from the micro-level,realizing the multi-dimensional study of wastewater treatment effect.Aiming at the use of clean energy and energy conservation,the above treatment methods are further optimized.For the treatment of high salt wastewater by BMED method,the solar organic rankine cycle?SORC?is used to optimize its power supply.The simulation results show that the mass fraction of sodium sulfate in the treated wastewater decreases from 8%to 0.37%,the mass fraction of sulfuric acid production is 7.66%,and that of sodium hydroxide is 6.43%.SORC generates 2.88 kW of power to support the BMED process at the same time.Compared with the multi-effect evaporation method,bipolar membrane electrodialysis coupled solar organic rankine cycle?BMED-SORC?not only achieves the expected treatment effect,but also generates additional valuable substances like H₂SO₄ and NaOH.For the phenol-containing wastewater,the heat exchange between streams is realized through the optimization of heat exchange network,which can save both the utility and the treatment cost.The simulation results show that the extraction rate of phenol in the oil reaches 97.75%,the recovery rate of the extractant is 91.91%.The extraction rate of phenol in wastewater is 98.66%,and the mass fraction of water in the treated wastewater is 99.99%.Dynamic simulation is finally carried out,in which level,flow,temperature and proportional controller are added,to analyze the stability of this optimized phenol-containing wastewater treatment process when facing feed disturbance.