| Summary: | 博士 === 國立臺灣大學 === 環境工程學研究所 === 89 === Oil sludge, if unused, is one of the major industrial wastes requiring treatment from petroleum refinery plants or the petrochemical industry. It contains a large amount of combustibles with high heating values. The oil sludge waste investigated in this study is obtained from the oil storage tank of a typical petroleum refinery plant located in the northern Taiwan. By using the methods of sole pyrolysis, oxidative thermal decomposition, thermal degradation in the presence of carbon dioxide, adding inexpensive additives in pyrolysis and mutilstage thermal operation in the thermal treatment of oil sludge, one can not only solve the disposal problems but also have the appeal of resource utilization. Therefore, one can finally propose a practical thermal treatment process of oil sludge.
In the kinetics of sole pyrolysis, oxidative thermal decomposition and thermal degradation with the presence of carbon dioxide of oil sludge, a temperature-programmed dynamic thermogravimetric analysis ( TGA ) is used for studying the phenomena of reactions with different carrier gases. In the sole pyrolysis and thermal degradation of oil sludge with the presence of carbon dioxide, three - parallel - reaction models are proposed to describe the results and give the best fit. Including the sole pyrolysis reactions, the overall oxidative thermal decomposition of oil sludge can be adequately described by a five — parallel — reaction model.
In the major products obtained from the sole pyrolysis, the major gaseous products ( noncondensable gases at 298 K ) excluding N2 are CO2 ( 50.88 wt. % ), HCs ( hydrocarbons, 25.23 wt. % ), H2O ( 17.78 wt. % ) and CO ( 6.11 wt. % ). The HCs mainly consist of low molecular paraffins and olefins ( C1 ~ C2, 51.61 wt. % of HCs ). The distillation characteristics of liquid product ( condensate of gas at 298 K ) from the pyrolysis of oil sludge is close to diesel oil. However, it contains a significant amount of vacuum residue of about 9.57 wt. %. In the major products obtained from the oxidative thermal decomposition of oil sludge, the higher O2 concentration would enhance the oxidative thermal decomposition reactions and reduce the residual mass. The major emitted gases ( noncondensable gases at 298 K ) excluding N2 are CO, CO2, hydrocarbons ( HCs ), H2O and H2. The HCs mainly consist of low molecular paraffins, especially C1. The distillation characteristics of the oil portion of liquid products ( condensates of gas at 298 K ) from the oxidative thermal treatment of oil sludge at T of 378 ~ 873 K, low oxygen conditions ( ie. 1.09 vol. % O2 ) not only accelerate the thermal reaction of oil sludge, but also at the same time avoid or reduce the production of water.
In the use of inexpensive and non-harmful additives on the possible improvement of the sole pyrolysis of oil sludge, the dynamic thermogravimetric analysis ( TGA ) is used again. It appears that the above additives enhance the conversions ( X ) when the temperatures ( T ) are in 650 ~ 740 K. At 720 K, the largest differences of conversion ( ΔX ) are adding K2CO3, fly ash and KOH. The additives achieve the largest improvement of the quality ( q ) of pyrolysis oil ( as sum of light and heavy naphtha and light gas oil ) are adding CaO, KOH and fly ash. The largest ratios of instantaneous reaction rates ( r = dX/dt ) in the presence and absence of additives with the deductions of additives in the pyrolysis of oil sludge are about 1.47 for adding NaOH and 1.4 for adding fly ash at 680 K.
In the multistage thermal operation of treating oil sludge, one can propose a 3 - stage thermal operation process by combing the best and effective additives, sole pyrolysis and oxidative thermal decomposition of oil sludge. The distillation characteristics of the 1 - stage oil ( condensates of gas at 298 K ) from the pyrolysis of oil sludge at T of 378 K and retaining 4 hours give the best results and the 1 - stage oil is very close to diesel oil. In the 2 - stage, the 2 - stage oil with adding 10 wt. % CaO and 100 vol. % N2 at 378 to 653 K and retaining 10 minutes gives the best distillation results. Therefore, among the 3-stage oils, the oil without additives and of 20.95 vol. % O2 at 653 to 743 K and retaining 30 minutes ( with 2 - stage of 100 vol. % N2 and without additives ) gives the best distillation results and that is better than gasoline. However, it needs to be separated from water before use. Meanwhile, with 20.95 vol. % O2 and without additives, the amounts of residue of thermal treatment of oil sludge will achieve minimum. Among the waterless 3 - stage oils, the oil with adding 10 wt. % CaO and 1.09 vol. % O2 gives the best distillation results.
Finally, according the results, one can propose a practical thermal treatment process of oil sludge and provide for the commercial designs and runs of thermal treatment of oil sludge.
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