| Oil sludge is currently an urgent problem to be solved due to the characteristics of large sludge reserves,strong environmental hazards,and high resource utilization values.However,current treatment technologies,including incineration,pyrolysis,and gasification,have the disadvantages of high energy consumption and poor economics when treating sludge with high water content and low calorific value,and these technologies cannot meet the requirements of harmlessness and resource utilization.requirements,Therefore,it is urgent to explore new oil sludge treatment technologies.Smoldering is a slow,low-temperature,flameless combustion.Previous studies have shown that smoldering has natural advantages in the treatment of nonaqueous liquid waste,which makes it a good choice for the treatment of oil sludge.This paper systematically investigates the oil sludge smoldering technology through experiment and simulation.The influence of water content of oil sludge,filling ratio,filling medium size,and air velocity on the smoldering characteristics of oil sludge is explored.The results show that the moisture content of oil sludge has a significant impact on the smoldering characteristics.The oil sludge with high moisture content fails to ignite successfully due to the downward migration of free water in the upper part of the smoldering reactor.The increase in the moisture content of the oil sludge reduces the peak temperature and velocity of smoldering,which is not conducive to the smoldering process.Oil sludge smoldering with a filling ratio in the range of 1:3-2:1 can be achieved successfully.However,the excessive proportion of quartz sand results in a reduced burnout rate.The influence of the size of the filling medium on the smoldering characteristics is mainly reflected in the air permeability of the sample.Too large or too small will reduce the air permeability of the sample,resulting in the oil sludge reduced burnout rate.The sample with medium-sized quartz sand exhibited the most favorable state for smoldering.Under the oxygen-limited condition,air velocity determines the propagation velocity of smoldering.In this paper,the characteristics of smoldering products of oil sludge were investigated to evaluate the harmless and resource level of oil sludge treatment.The detection result of gas chromatography shows that the removal efficiency of petroleum hydrocarbons(C10-C40)in the sludge can reach 99.99%,and there is no volatile organic matter in solid products.The black residue coming from low burnout rate conditions is mainly composed of amorphous carbon and graphite,which is harmless to the environment.Moreover,most of the metal elements in the oil sludge were concentrated into solid products after smoldering,which contains some harmful heavy metal elements.The smoldering treatment of oil sludge has great advantages in resource recovery,and half of the petroleum hydrocarbons in oil sludge can be recovered by off-gas condensation.The numerical model of one-dimensional oil sludge smoldering was established in this paper.The calculation results of the model show that the one-dimensional smoldering propagation model neglecting the oxidation reaction of the material is suitable for the oxygenlimited smoldering process.The simulation results show that the heat released by the oxidation reaction in the smoldering can balance the energy loss such as water evaporation and pyrolysis of oil sludge,demonstrating that the oil sludge smoldering is stable. |
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