超临界水氧化法处理焦化废水

Degradation of coke plant wastewater by supercritical water oxidation

对超临界水氧化技术处理焦化废水进行了试验研究,以H_2O_2作为氧化剂,研究了氧化剂用量、反应温度、停留时间和压力等影响因素。试验结果表明H_2O_2用量的增加有利于污染物降解,但是当用量为理论用量1.6倍时,其影响已不明显。废水的COD_(Cr)去除率随着反应温度、压力和停留时间的增大而提高。另外,在所有影响因素中反应温度是影响焦化废水降解的主要因素。试验确定了最适宜工艺条件为:H_2O_2用量为理论用量1.6倍,反应温度540℃,反应压力28MPa,反应时间大于120 s。在此工艺条件下,废水的COD_(Cr)去除率达99.4%。

The paper is to present our investigation and analysis of the degradation rate change of the wastewater left-over by processing coke through supercritical water oxidation. As is known, the wastewater left-over by processing coke is a kind of intractable wastewater, whose composition is complicated and therefore uneasy to be treated. However, supercritical water oxidation can be expected to achieve great effect on the organic decomposition, whose treating can be done in a continuous flow reactor. For this purpose, we have performed homogeneous and non-catalytic SCWO over the coke wastewater and examined the oxidation efficiency and the influential factors, such as H2O2 excessive multiple, the reaction temperature, pressure and resi-dence time of the coke wastewater in the supercritical water. The experimental results we have gained show that the degradation rate of the wastewater increases with the increase of the reaction temperature, pressure, residence time and multiples of excessive H2O2, among which the reaction temperature remains the chief influential factors on the degradation rate of the organic pollutants. Moreover, it has been found that mineral precipitation problem has been solved by using mineral liquid separator in the experimental instruments during the experiments. In addition, supereritical water has been found acting as a non-polar solvent of high diffusivity and fine transport properties. The oxidation reaction can be made to proceed rapidly without any inter-phase mass transferring limitations. In addition, the organic compounds in the wastewater were found to have been totally oxidized in a period from a few seconds to a few minutes. Our experiments have also confirmed the suitable conditions of the degradation of the wastewater. That is to say, under the conditions of the multiples of oxygen in excess of 1.6, at the temperature of 540 ℃, at a pressure of 28 MPa with the residence time over 120 s, the removing rate of CODcr can be expected to reach 99.4 %. When the coke wastewater was treated by using the supereritical water oxidation process in accordance with the above conditions, it would be possible to lower the chemical oxygen demand （CODcr）of the treated wastewater to 43.8 mg/L, with its effluent quality getting to GB 8978, that is, coming to the 1996 state discharge standard with SCWO for treating elements.