Supercritical Water Oxidation Of Coking Wastewater

The coke plant effluents contained high concentrations of ammonia, phenols, cyanide and other aromatic organics, such as quinoline, indole, naphthalene etc. Most of the substances were bio-toxical and so the traditional activated sludge degradation process was failed for the elimination of chemical oxygen demand (COD), ammonia and color causing compounds. So, it is very essential to find an effective treatment process to decompose these toxically refractory compounds to meet the demand of environment protection.Supercritical water oxidation (SCWO) was recognized as a promising technology for the wastewater treatment, and had attracted great interest recently. SCWO of actual coking wastewater was studied in present work for the evaluation of the technical feasibility, which will provide some profitable referencesfor the theoretical investigation and practical application. Oxidation of NH3, NH3/Phenol mixture and real coking wastewater were investigated in supercritical water in a tubular continuous flow reactor. Some primary experimental results were obtained as follows:1. Ammonia can be destructed effectively in supercritical water at moderate reaction conditions. The primary product was nitrogen gas. The conversion of ammonia was increased with the increase of temperature and the prolong of residence time. There were no significant influences when oxidant amounts reach to some extent. From the range of subcritical to supercritical conditions, the pressure had a slightly promotion for the conversion of ammonia. The kinetics regression of ammonia oxidation showed that the reaction order with respect to ammonia was 0.89, the activation energy was 156.8kJ-mor', and the Arrhenius pre-exponential factor was 10 .2. For the SCWO of aqueous mixture system of NH₃/Phenol, At the absence of oxidant conditions, phenol converted into hydrogen, methane and carbon dioxide by the routing ofhydrothermal decomposition. With the increase of oxidant amounts, - the intermediate gases were oxidized to water and carbon dioxide ultimately. The presence of ammonia in the mixture have no perceptible effect for the conversion of phenol. However, the inhibit of ammonia destruction was observed by the present of hydrogen and methane as intermediate products of phenol destruction.3. For the SCWO of actual coking wastewater, the industrial water quality index such as volatile phenolic compounds, COD and SCN' can be decomposed easily compared with the ammonia. The destruction of ammonia was influenced by the reaction temperature and oxidant quantity evidently. The nitrogen-containing compounds from the coking wastes such as quinoline and indole were oxidized in supercritical water, which may produce ammonia as intermediate product. In the optimal operation'conditions, the concentration of ammonia below 5mg/L in the effluent, and other pollutions destructed completely almost. The effluent steams were cleaning and transparent after disposing.4. By utilizing the solubility character of salts in supercriticalwater, a majority of the salts can be depositted and aparted by simple separating operation before entering the reactor. The SCWO technology combined the wastewater treating and salts separation into one step.5. There was a low uniform corrosion rate using lCrl8Ni9Ti stainless steel reactor during the process of SCWO for coking wastewater, which may be for the reason that most of the salts had been separated during the salts separator. So the concentration of caustic ions in the reactor system were low enough.