热脱附尾气中DDTs在模拟水泥窑中的去除效果

On the DDTs-removing effect in the thermal desorption-off gas via the simulated cement kiln

为了降低滴滴涕(DDTs)污染土壤热脱附修复的成本,分析了水泥窑技术去除污染土壤热脱附尾气中DDTs的可行性。主要考察了处理温度、停留时间、氧气体积分数对DDTs去除的影响。结果表明:随处理温度升高和停留时间延长,DDTs的去除率逐渐升高,当处理温度为900℃、停留时间为2 s时,其去除率为99.46%;模拟水泥窑处理后尾气中p,p'-DDT的比例降低,p,p'-DDE成为尾气中DDTs的主要成分;DDTs的降解产物有1,1-双(对氯苯)-2-氯乙烯、2,4'-二氯苯甲酮、二苯甲烷、苯甲酮和二苯甲醇,其最大质量浓度分别为0.08μg/m^3、0.24μg/m^3、1.07μg/m^3、2.56μg/m^3和0.52μg/m^3;处理过程中伴有少量的二噁英产生,但二噁英的质量浓度满足GB30485—2013《水泥窑协同处置固体废物污染物控制标准》的要求。研究表明,水泥窑工艺可以有效去除污染土壤热脱附尾气中的DDTs。

In this paper,we would like to make an investigationand assessment of the feasibility and the performance features of the destruction function of DDTs in the thermal desorption off-gas by using the cement kiln. In the testing experiment,we have worked out the destruction efficiency of DDTs and done the measurements of the degradation products under the different operation conditions,including the temperature,the initial oxygen volume fraction,as well as the gas residence time through the laboratory experiments. As a matter of fact,the thermal desorption is known as a soil remediation processing technique with high removal efficiency and quick time turning,though,for the time being,the application of the conventional technical level for off-gas treatment remains insufficient enough to meet the economic and technical expectations simultaneously. In spite of this,the destruction efficiency of DDTs can be expected to rise with the increase of temperature and extension of the residence time. For example,the destruction efficiency of DDTs can be expected to increase by a percentage of 99. 46% when the offgas can be treated at temperature of 900 ℃ for the residence time of 2 s. What is more,the concentrations of DDTs in the exhaust stay at 1. 13 μg/m^3,1. 36μg/m^3 and 1. 85 μg/m^3 on the condition,when the initial DDTs concentration of 0. 25 mg/m^3 is treated at the temperature of 900℃ for 2 s with the initial volume fraction of 2%,5% and 8%,respectively,which implies that the destruction efficiency of DDTs tends to slightly decrease with the increase of the oxygen volume fraction. Considering the thermal destruction of DDTs in engineering applications,the temperature in the main burner and the precalciner are in favor of the destruction of DDTs,the gas residence time and the initial oxygen volume fraction are all to meet the demands of the destruction of DDTs. Through treating,the ratio of p,p＇-DDT tends to decrease whereas the p,p＇-DDE tends to increase and then turns to be the main component of DDTs in the exhaust,suggesting that p,p＇-DDE should be one of the main degradation products of p,p＇-DDT. At the same time,the 1-chloro-2,2-bis（ p-chlorophenyl） ethylene,2,4＇-dichlorobenzophenone, diphenylmethane, benzophenone, and the benzhydrol,should all turn to be the dechlorinated products of DDTs with their highest concentrations being 0. 08 μg/m^3,0. 24μg/m^3,1. 07 μg/m^3,2. 56 μg/m^3 and 0. 52 μg/m^3,respectively. However,the PCDD/Fs concentrations in the exhaust may turn to be lower than the standard for pollution control on the coprocessing of the solid wastes in the cement kiln. Thus,it can be seen that the results we have gained can be expected to provide a more advanced economic remediation method for treating the thermal desorption offgas for the future engineering applications.