Study On The Application Of Internal Circulating Fluidized Bed-ozone Catalytic Oxidation In Industrial Wastewater Treatment

Catalytic ozone oxidation technology has been widely used in the field of industrial wastewater treatment,and the common reaction form is fixed bed.In recent years,a large number of engineering applications have exposed some problems in the practical application of fixed bed ozone catalytic oxidation process.The main problems are that the catalyst dosage is large,the catalyst is easy to deactivate after long-term use,and regular backwashing is required during operation to ensure the process effect.In this paper,a Cu-Mn/γ-Al₂O₃ ozone catalyst for fluidized bed process was prepared for the above problems.By combining the internal circulating fluidized bed process with the ozone catalytic oxidation technology,the problems existing in the fixed-bed ozone catalytic oxidation process were solved in the fluidized bed operation form.Meanwhile,systematic tests on the treatment,comparison and optimization of industrial wastewater were carried out compared with the fixed-bed ozone catalytic oxidation.The main conclusions are as follows:（1）Fluidized bed catalyst has outstanding adsorption properties.The average particle size of the fluidized bed catalyst is about 0.5 mm,which is significantly smaller than that of the conventional fixed bed catalyst（3～5 mm）,which is conducive to the fluidization state.Its specific surface area（151.44 m²/g）is smaller than that of the fixed bed catalyst（236.73 m²/g）,and the average pore size（11.18 nm）is larger than that of the fixed bed catalyst（7.20 nm）.The adsorption capacity of the fluidized bed catalyst is obviously stronger than that of the fixed bed catalyst,and the 3g fluidized bed catalyst can adsorb 28.31%TOC in the petrochemical secondary effluent within 60min.The fixed bed catalyst of the same mass can only adsorb 11.48%under the same conditions.（2）Fluidized bed catalyst has good abrasion resistance and catalytic stability.It was found that the wear of fluidized bed catalyst mainly occurred in the surface layer,and the catalyst loss rate was 2.75%after 100 h wear test,and only 1%after 240 h continuous use in the subsequent test,and the treatment effect was stable.（3）The process conditions of internal circulating fluidized bed-ozone catalytic oxidation process for the treatment of petrochemical secondary effluent were optimized.The TOC removal rate of petrochemical secondary effluent can reach 46.47%under the conditions of inlet gas 600 m L/min,ozone dosage 75 mg/L,catalyst dosage 40 g/L and reaction time 60 min.（4）The flow pattern in the reactor was simulated by computational fluid dynamics（CFD）.The results show that the mixing and reaction of catalyst with ozone and water mainly occur in the internal area of the draft tube.There is obvious turbulence at the inlet of the bottom of the draft tube,which may aggravate the wear of the catalyst.There is a small amount of solid dead zone at the bottom of the reactor,resulting in the waste of some catalysts.（5）A comparative study of fluidized bed and fixed bed processes was carried out with petrochemical secondary effluent as the treatment object.The results show that under the same conditions,the TOC removal effect of the fluidized bed process is significantly stronger than that of the fixed bed process.When the removal effect is similar（46.47%）,the amount of catalyst used in the fluidized bed process is only 1/10of that in the fixed bed process.The fluidized bed process can greatly reduce the dosage of catalyst in engineering applications and save material costs.（6）The anti-pollutant deposition ability of different processes was studied by using petrochemical secondary effluent.The results showed that the fixed-bed catalyst was obviously deactivated during long-term use.The effluent TOC value increased from 9.20 mg/L to 13.45 mg/L after 240 h of operation,which was due to the adsorption of a large number of extracellular polymers,inorganic salts,inorganic crystals or other refractory substances on the catalyst surface.The TOC removal efficiency of the fluidized bed process is relatively stable during operation.The TOC value of the effluent has been fluctuating around 12 mg/L during the 240 h running time.This is due to the catalyst in the fluidized state.The dynamic update of the catalyst surface can be achieved through the shear force of water flow and air and the friction force of collision between particles,thus ensuring the stability of the fluidized bed process and avoiding backwashing.（7）The anti-hardening ability of different processes was studied by using the biochemical effluent of brewing.The results show that under the same reaction conditions,the unit calcium ion adsorption capacity of the fluidized bed catalyst is 29.6%lower than that of the fixed bed catalyst,and the unit magnesium ion adsorption capacity is 33.3%lower than that of the fixed bed catalyst,which can effectively avoid the occurrence of catalyst hardening in long-term use.This is also due to the dynamic renewal of the surface of the fluidized bed catalyst.