Research On The Technology And Design Of Process For Denitrification Wastewater Of Coke Wax Oil

A large amount of wastewater with high salinity was produced in the denitrification process of coker gas oil.The wastewater contained compounds such as Na₂SO₄ and Na₂HPO₄,both of which were widely used inorganic chemicals.The direct discharge of the wastewater was not only a waste of resources but severe pollution to the environment.Therefore,it was necessary to dispose of it.In this paper,the composition of the wastewater and the cause of odor were analyzed at first.The adsorption of the removal of organic impurities by activated carbon was studied,as well as the method of analyzing the phosphate ions in the laboratory.Then the separation efficiency of calcination,organic solvent treatment and chemical conversion method was compared,and the combination of chemical conversion method and organic solvent treatment was chosen for effective separation of the wastewater.The phosphate was converted into phosphoric acid and sodium sulfate by adding concentrated sulfuric acid into the waste liquid.And then the sodium sulfate and phosphoric acid were separated under the help of organic solvent.Secondly,the separation conditions were investigated and the best methods were shown as follows.8v%concentrated sulfuric acid was added in the sample during the preliminary crystallization process,followed by 30 h of static crystallization at 30?and filtering treatment.The secondary crystallization process was the addition of ethanol to the initial crystallization filtrate,with the ethanol/water volume ratio of 1:1.The crude sodium sulfate crystal from twice crystallization was then purified by recrystallization,and the water added per gram sodium sulfate was 3mL at 0?.The final sodium sulfate product was white and the purity could reach 99.5%,which met the requirement of industrial grade.Besides,the ethanol in secondary crystallization filtrate was recycled.The concentration of ethanol in tower top was 85v%and it was recycled to solvent out crystallization process.At the bottom of tower,the phosphoric acid solution was concentrated to 85wt%and the content of sodium sulfate was reduced to 1wt%.In this way,the effective separation of sodium sulfate and phosphoric acid could be achieved to make the product met the requirements of the industry.Finally,a set of 10 thousand tons per year denitrification wastewater treatment process was designed based on the experimental results.This process included five parts:pretreatment unit,crystallization unit,recrystallization unit,ethanol recovery unit and phosphoric acid concentration unit.According to technical requirements,the equipment type selections were carried out for one adsorption device,three filters and one rectifying tower involved in the process.Moreover,the design conditions and requirements of the non-standard crystalization equipment were proposed.