Incineration Of Oily Sludge In A Fluidized Bed And Its Combustion Mechanism

Oil sludge is a kind of hazardous petroleum waste, and accumulates from all kinds of craft processes in petroleum production including exploitation, transporting and refining processes. In China, more than 1000 000 tones of oil sludge are generated annually. However, there is not a method or craft can efficiently treat this kind of oil sludge by now. Environment issues in industries production have attracted more and more attention; the treatment and disposal of petroleum oily sludge represent major challenges for petroleum industries.Incineration technology is thought as one of the most practicable technology in the field of sludge treatment in the world. Aiming at existing state of treatment technology in China and development trend of treatment technology of sludge, fluidized bed (FB) incineration technology of treating oily sludge are proposed with its obvious advantages such as fast disposal speed, decreasing components efficiently and recycle energy as well. Incineration of oil sludge in FB a now subject, not much has been reported on the combustion mechanism of oily sludge in a fluidized bed. This research considered the application of incineration principles to petroleum oily sludge using a new technique. The fundamental fuel properties and its combustion process and mechanism in a fluidized bed are concerned.Physicochemical characteristics are basis for the oil sludge combustion in a FB, the petroleum oily sludge taken from the bottom of crude oil storage tanks was investigated by a series of experiment to gain organic group compositions, the chemical components, the thermal properties including pyrolysis and combustion and evolution of volatile and hydrocarbon release. For these proposes, various approaches including solvent extraction, GC/MS, thermogravimetric analysis (TGA), electrically heated fixed bed quartz reactor coupled with Vario Plus emission monitoring system, and oil-gas evaluation workstation (OGE-II) equipped with a flame ionization detector (FID) were used. The CHs (hydrocarbons) data from the OGE-II were used for kinetic analysis by Vyazovkin model-free iso-conversion approach to obtain activation energy (Eα) dependency on conversion (α) in the pyrolysis of oil sludge. The mechanism of the dependency of the activation energy on the degree of conversion was also discussed.Fragmentation and attrition of bed materials are very important for stable operation of the oil sludge incinerator. In the chapter 3, the fragmentation and attrition of bed materials in a hot FB were investigated. In the fragmentation experiment, the influences of a variety of factors such as the bed temperature (650-950oC), the size of particles (2.5-6mm) on the fragmentation of quartzite particles are studied. The research results show that the extent of fragmentation increases with increasing bed temperature and particle size. For the small particles at low bed temperature, the research shows that, it is compressive stresses within the outer region of particles cause the particle to fracture, with the characteristics that many small fragments peeled from the surface of the particles and the average particle size after fragmentation change very little. However, for the large particle at high bed temperature, it is tense stresses within the center of particle causing the particle to fracture, the particle is divided into several equivalent size particles, as a consequence, and a more intense size reduction after fragmentation is gained. In the attrition experiment, the influence of operating parameters such as bed temperature, mean diameter of bed particles, fluidizing number and height of bed materials on attrition process is investigated. The influential extent of operating parameters on attrition is sequenced by mean of the range analysis. The result is shown as follow: fluidizing number>mean diameter of particles >bed temperature> height of bed materials. Based on the grey theory, a grey forecasting model GM (1, 5) is developed to predict the attrition of the quartzite particles in a hot FB. The result demonstrates that the forecasted values are in good agreement with the experimental data with the average residual error lower than 0.508%.In the chapter 4, the combustion experiment of the oil sludge was carried out in a laboratory scale thermal fluidized bed. Firstly the pyrolysis and combustion properties of oil sludge ball in the hot FB are investigated. In pyrolysis experiment, the influence of oil sludge ball diameter on volatiles release time and contents of volatiles are considered; in the combustion experiment, the influences of bed temperature, ball diameter, superficial fluidization velocity and moisture content on combustion are studied. Secondly, under the stable combustion state of oil sludge in the fluidized bed, the influences of bed temperature and superficial fluidization velocity on combustion process are studied; the gas compositions along the bed height are analyzed. Finally, ash formation and its properties in the combustion process in the hot FB are discussed. The elutriation experiment was conducted in order to determine the elutriation rate constant of oil sludge ash in the fluidized bed.Based on the patent of oil sludge incineration in a FB and combustion mechanism oily sludge in a FB, a craft process and technical characteristics of an incineration treatment system of oily sludge are described in chapter 5, the design parameters and structure of a 20t/h circulating fluidized bed (CFB) boiler are introduced.In the chapter 6, the field test of the combustion of the oil sludge was carried out in the 20t/h CFB boiler treating oil sludge. Co-firing of oil sludge with coal-water slurry (CWS) was investigated in the new incineration system to study combustion characteristics, gaseous pollutant emissions and ash characteristics. The combustion along the furnace height was also investigated in order to understand the influences of feeding rate of oil sludge on temperature distribution along the furnace height. The study results show CWS as an auxiliary fuel can flexibly control the dense bed temperatures by adjusting its feeding rate. A one-dimention comprehensive mathematical CFB model for describing the co-firing process of oil sludge with CWS in a CFB is tested against the experimental data from the 20t/h FB boiler. The model results for the axial temperatures and gas concentrations along the furnace height are compared to experimental measurement. The general agreement is reached between the calculated and measured parameters.