Intensified phenols extraction and oil removal for industrial semi-coking wastewater: A novel economic pretreatment process design

Current semi-coking wastewater treatment process has low performance of pollutants removal and consumes a large amount of high-grade steams. It far exceeds the semi-coke plants’ utilities supply capacity and easily lead to the breakdown of whole treatment system. This paper identified the bottleneck of current process as followed: low removal efficiency of oil and dust; poor extraction conditions caused by the high pH value and the fouling and plugging of internals; high-grade steam requirement and investment cost. To improve the deficiencies of current process, a novel hybrid process is proposed based on the benchmark treatment capacity of 240 m3/d. The effects of acidification and extraction conditions on ζ potential and extraction efficiency have been analyzed following industrial semi-coking wastewater experiments. The results show that the concentrations of oil and dust are reduced less than 50 mg/L when pH value is lower than 4.8. The removal efficiencies of COD and total phenols after extracted are increasing as pH value decreases. The conceptual design is accomplished based on the experimental and simulative analysis. The concentrations of sour gas, total phenols, ammonia and COD decreases to 10 mg/L, 270 mg/L, 50 mg/L and 3050 mg/L, respectively. It also eliminates 2.5 MPag and 1.0 MPag steam demand at the expense of 24.1 kW more electricity uses and 70.84 kg/h reagents consumption, as suggested in simulation results. The estimated investment cost saving are 0.77 million US$, and the net cost reduction is 0.63 US$/t water. •The bottleneck of current process applied in semi-coke plants is analyzed.•A new pretreatment process is presented based on industrial wastewater experiments.•New design performs better in oil, phenols and COD removal.•Process simulation and hydraulic calculation are used for industrial base design.•New design decreases investment cost, treatment cost and steam requirement sharply.