油污染场地土壤热解终温试验研究

On the final pyrolysis temperature of the soil contaminated by oil splits

目前,含油污染场地土壤处理中对终温影响的研究不够。采用固定反应床对该类污染土壤进行热解处理终温模拟试验。在升温速率、终温时间及真空度(20℃/min、30 min和70 k Pa)不变的条件下,考察了不同热解终温下热解残渣的含油率,并利用GC-MS对不同热解温度下含油土壤热解油进行了分析。结果表明:随热解终温不断提高,各试验土壤样品热解残渣的含油率均逐渐降低,0~260℃范围内热解残渣的含油率下降最快,其中260℃下热解速率分别为2.93mg/min、1.99 mg/min、1.57 mg/min、1.39 mg/min、1.15 mg/min,之后下降速率减缓,到300℃后基本保持不变;含油土壤最宜热解终温为260℃,此时含油土壤中石油烃质量比低于3 000 mg/kg(初始质量比为17 438~42 656 mg/kg);热解油中高分子碳氢化合物含量随热解终温不断提高而逐渐升高。

This paper intends to make a simulated study of the final temperature pyrolysis in the condition of the oil contaminated soil in hoping to use widely the vacuum pyrolysis technology to the soil remediation with a fixed-bed reactor. For the said purpose,we have made an investigation of the oil content rates in the pyrolysis residue at different final pyrolysis temperatures under the conditions of the constant heating rate,the final temperature and vacuum degrees,e. g. 20 ℃/min,30 min and 70 k Pa. At thesame time,the pyrolysis oil and pyrolysis residue in the oil-contaminated soil have been analyzed with the GC-MS and X-ray fluorescence spectra respectively at different pyrolysis temperatures.The experimental results we have gained can be illustrated as follows： First of all,the oil content rate in the pyrolysis residue has been found gradually decreased with the increase of the final pyrolysis temperature and the oil content rate of the pyrolysis residue quickly dropping to a range between 0-260 ℃. As a result,the pyrolysis rates have turned to be 2. 93 mg/min,1. 99 mg/min,1. 57 mg/min,1. 39 mg/min,and 1. 15 mg/min at 260 ℃,respectively. Later,then,the dropping rate would become bit by bit slower. However,the oil content of the pyrolysis residue and the removing rate of the oil components would remain basically unchanged after the temperature went up to 300 ℃. Besides,the optimum final pyrolysis temperature of the oil-contaminated soil should be 260 ℃,and the oil content of the petroleum hydrocarbons in the said soil is less than 3 000 mg/kg（ the initial concentration was 17 438-42 656 mg/kg）,which can be taken to meet the commercial land standards of 2-nd grade in the Environmental Quality Standard for Soils（ GB 15618—2008）. Moreover,the initial oil content has little effect on the removal rate of high-temperature pyrolysis that may have a great effect on the low-temperature pyrolysis. Thus,it can be said that,the higher the initial oil content,the greater the removal rate would be. Thus,in final analysis,the content of the macro-molecular hydrocarbons in the pyrolysis oil tends to increase gradually with the increase of the final pyrolysis temperature,whereas at low-temperatures,it is possible to separate a large amount of light oil. Apart from it,the sampling cases of the soil samples here involved are rich in silicon aluminum oxide,with the pyrolysis residue enjoying a certain recycling value for the simulation practice in hoping to popularize the vacuum pyrolysis technology for soil remediation.