Research On Combustion Treatment Technology Of Oil Sludge Char In Fluidized Bed

Oil sludge char is one type of solid wastes produced after pyrolysis of the hazardous waste sludge for recovery of oil.So far,due to the lack of technology for the disposal of bulk oil sludge char,mainly based on stacking has the risk of potential environmental pollution.Therefore,the harmless treatment of oil sludge char is a problem that must be solved in the ultimate disposal of sludge.As a kind of inferior fuel with high ash content and low heating value,it’s naturally an important technical method to recover its heat through clean combustion.However,there are many technical difficulties such as achieving efficient combustion efficiency,control of flue gas pollution,and solidification of harmful substances.In order to develop efficient and clean combustion technology of oil sludge char,this study carried out combustion experiments of oil sludge char in milligram,gram,and kilogram levels,that systematically studied the combustion characteristics of oil sludge char and pollutant emission rules at the laboratory scale,and obtained the following results:(1)The combustion characteristics of oil sludge char,brown coal,and it’s mixtures at different heating rates were studied by thermogravimetric analysis.The kinetic parameter was calculated using Kissinger-Akahira-Sunose(KAS),Flynn-Wall-Ozawa(FWO),and Friedman(FR)methods.The results indicated that the combustion of the oil sludge char was mainly a fixed carbon combustion process,while that of the brown coal was characterized by a process of continuous combustion with a large amount of volatile and little fixed carbon.Compared with the combustion of the oil sludge char,the brown coal had a better combustion performance and its average activation energy was much lower.There was a significant positively synergistic interaction in the co-combustion process of the oil sludge char and the brown coal.When the proportion of brown coal in the blends reached up to 75%,the positively synergistic interaction effect was the strongest.The FR method better reflected the trend of the process,but its generated results were less accurate compared to that from KAS and FWO models.By comparing the theoretical and experimental values of the co-combustion kinetic parameters of the sludge char and the brown coal,it was found that application of thermogravimetric analysis to predict the combustion properties of the mixed fuel exhibited a high reliability,which can thus play an importantly guiding role in the application of the co-combustion technology of the oil sludge char and the brown coal.(2)The study of oil sludge char combustion and NO_x emission characteristic was carried out with a small-scale fluidized bed.Mainly studies NO_x emission characteristics of oil sludge char combustion at different temperatures and particle sizes.The combustion experiments of oil sludge char indicated that its generated NO_x was mainly from coke-N and less from volatile-N.Reduction in the combustion temperature and the particle size to a proper extent can not only ensure full combustion of oil sludge char,but also inhibit NO_x emission.When conducting air-staging combustion,by optimizing the excess air ratio,proportion of secondary air and position of secondary air inlet,the NO_x emission was considerably reduced,and meanwhile the generation of fly ash was restrained,helpful for the ultimate treatment of the flue gas.When ER=1.1and the ratio of upper secondary air is 40%,the denitration efficiency is improved by52.1%compared with traditional combustion,and the fly ash volume and CO emissions are controlled within a reasonable range.(3)Based on the conclusions of small-scale experiments,with the aid of a kg/h scale fluidized bed,simulated the influence of the combustion stability and NO_x emission characteristics of oil sludge char in a boiler with changes in furnace temperature and excess air coefficient,and the effect of SNCR technology on NO_x emissions were investigated.The results indicated that a reasonable feed position can effectively improve the combustion efficiency,change the axial temperature distribution of the fluidized bed,and reduce the amount of fly ash.Although the addition of brown coal can significantly improves the combustion characteristics of the fuel,the large amount of heat released by brown coal combustion easily causes slagging in the furnace,and the combustion temperature in the main combustion zone should be appropriately reduced.In order to ensure the denitration efficiency of the SNCR technology,a two-stage combustion method(deeper zone 880℃,upper zone 920℃)can be used,which not only ensures the denitration efficiency,but also prevents the main combustion zone temperature from being too high to form slagging.