Study On Reactor Design And Technology Of Microwave Enhanced Fenton Process For Treatment Of Coal Chemical Industry Wastewater

Coal chemical industry wastewater （CCIW） is a typical wastewater containing more than 240 refractory organics. The discharged CCIW treated by conventional biochemical method still involves a huge amount of refractory organics and needs further treatment. The study of wastewater treatment system and technology for the advanced treatment of CCIW has important practical significance and academic value. In this paper, a microwave （MW）-assited wastewater treatment （MWT） reactor was designed using COMSOL Multiphysics, and based on this reactor, microwave-enhanced Fenton （MW-Fenton） process was studied for the treatment of refractory organic matter. A shell-tube heat exchanger was designed for the recovery of waste heat in the treated water and the amount of heat transferred by the heat exchanger was calculated. By combining the MWT reactor and the heat exchanger together, the microwave-assisted heat exchange wastewater treatment （MHW） system was established and the microwave-enhanced Cu²⁺-Fenton （MW-Cu+-Fenton） process was developed based on the MHW system for the advanced treatment of CCIW. The related fundamental research with application value was developed thoroughly.COMSOL Multiphysics was applied to develop a MWT reactor. The installation of magnetron and the diameter of coil tube were optimized and the removal rate of pollutant in the optimized reactor reached 89.1%. A corresponding MW-assisted wastewater treatment reactor with 22 kg h-1 of treatment quantity was customized and used to verify the numerical simulated results by means of the physical experiments. The results show that the coincidence degree of the distribution curve of hydraulic retention time is good, the root mean square error of outlet temperature is 2.80-3.54℃ and the electric intensity on different cross sections in MW oven have a good coincidence. This could provide a reliable reference for the following amplification design.Taking p-nitrophenol （PNP） as the target contaminant and the MWT reactor customized as the experimental platform, the MW-Fenton process was established and studied for the advanced treatment of CCIW. The results show that the mixing methods of reagents, wastewater pH, H₂O₂ dosage and Fe2+ dosage have significant effects on the treatment efficiency. Mixing H₂O₂ and wastewater together firstly and then adding catalyst could have better wastewater treatment efficiency. The optimum experimental condition of MW-Fenton process is determined as:pH is equal to 4,340.0 mg L-1 of H₂O₂,7.0 mg L-1 of Fe2+, and hydraulic retention time （HRT） is 30 min. In this situation, the treatment efficiency of PNP was more than 92%.A shell-tube heat exchanger that can satisfy the requirement of heat recovery in the wastewater treatment was simulated and optimized by COMSOL Multiphysics. The results reveal that the baffle gap height （H） and distance （B） have significant effect on the performance of heat exchanger. When Y=H/D, X=B/D （D is the shell inner diameter）, the relationship between X and Y is Y=-0.446X2+0.13X+0.419 which can be used for the optimization of H and B. According to the simulation results, the simulated outlet temperature of cold fluid in the optimized shell-tube heat exchanger （H=0.35D; B=0.45D） is 14.7℃. A shell-tube heat exchanger was customized and utilized to verify the simulation results by means of experimental results. The results illustrate that the relative mean error of outlet temperature of cold fluid is 0.13% and that of total pressure is 13.99%. Under the optimum experimental conditions and pH is equal to 3, the heat energy of 43.7 kJ kg-1 can be saved by the heat exchanger and the energy consumption can be reduced 45.5%. The MHW system consists of the MWT reactor and the heat exchanger has many advantages such as energy saving, cost reducing, reactions accelerating and effectively wastewater treated.Based on above research, taking a refractory organic matter （3-nitrophenol,3-NA） in CCIW as the target contaminant, the MW-Cu²⁺-Fenton process was established and studied for the treatment of wastewater. The results indicate that the pH, H₂O₂ dosage, Fe2+ dosage and Cu²⁺ dosage have remarkable effects on the treatment of wastewater. The optimum experimental condition is determined as:pH is equal to 5,443.0 mg L-1 of H₂O₂,9.0 mg L-1 of Fe2+,0.3 mg L-1 of Cu²⁺. In this case, the removal rate of 3-NA can reach more than 90% when HRT was 15 min. In comparison with MW-Fenton process, the MW-Cu+-Fenton process can treat organic wastewater within shorter time and in a wider pH range. The experimental results of advanced treatment of biologically treated CCIW show that the removal rate of COD is 69.2%, and the residual COD is 44.9 mg L"1 which meet the first-class standard of Integrated Wastewater Discharge Standard.The mechanism of treating organc wastewater by means of MW-Fenton/Cu²⁺-Fenton was proposed. The result reveals that the thermal and non-thermal effect of MW irradiation can accelerate the generation rate of-OH, increase its generation amount and then enhance wastewater treatment process. A synergistic effect exists among Cu²⁺, Fe2+ and H₂O₂. The coupling of Cu²⁺ and Fe2+ has a better catalytic performance than that when Cu²⁺/Fe2+works alone. In the MW-Cu²⁺-Fenton system the relationship of the apparent kinetic rate constant （kap） of degrading 3-NA with the concentrations of reactants is:kapThe MHW system designed and the MW-Cu²⁺-Fenton process studied in this paper has many advantages such as high wastewater treatment efficiency, short HRT, small area needed, easy operation, energy saved and environment friendly. It is easy for MHW system to achieve automatic control and industrial application. The study provides an effective solution method for the advanced treatment of CCIW and has a promising application prospect in the treatment of other refractory organic wastewater.