Overall Mathematical Model On A Differential Density Fluidized Bed For The Incineration Of Oily Sludge

Oily sludge is one kind of hazardous sludge, which is usually, generated during the crude oil exploitation and processing activities. Oily sludge has contamination on soil, air, and underground water. According to the combustion characteristics of oily sludge, incineration of oily sludge in the differential density circulating fluidized bed is generally adopted. As mentioned herein, the term"different density circulating fluidized bed"refers to a circulating fluidized bed with an interior horizontal cyclone separator, variable section, and quartzite particles as its bed materials. In order to optimize this kind technology, an overall mathematical model on differential density fluidized beds for the incineration of oily sludge was developed. Some parameters were obtained from a compute program. And the computed value from the overall model was close to the experimental value.Firstly, the proximate analysis, ultimate analysis, low heating value, contents and group composition of chloroform extract and the inorganic materials of the oily sludge were given. In order to further investigate and obtain the combustion characteristics of oily sludge, the pyrolysis and combustion of oily sludge were studied through some thermal analyses, which included the thermogravimetric (TG) analysis and the differential thermal analytical (DTA) analysis. It was found that the combustion of oily sludge might be the combustion of the products of its pyrolysis. Secondly, an experiment for measurements of main components of the volatile from oily sludge pyrolysis was carried out. Some mathematic correlations about the compositions of volatile from oily sludge devolatilization were achieved on the experimental results. Finally, the combustion experiment of oily sludge was carried out in a lab-scale circulating fluidized bed. It was found that the release and combustion of volatiles from oily sludge took place not only in the dense region but also in the dilute region.Secondly, some sub-models of the differential density circulating fluidized bed including the heat transfer model and the hydrodynamics model were developed. Morevoer, the model on attrition and fragmentation of quartzite particles as medium material, the model on solids entrainment flux on the surface of the dense region, and the model on separation efficiency on cyclone separator, and so on, were especially studed. On the other hand, a kind of so-called unequal height cell model combining the above-discussed sub-models was developed so as to achieve the temperature distribution, the heat exchange coefficient distribution, and concentration profiles of the main combustible components of the oily sludge combusted in the bed.Finally, some experiments were carried out in one 20t/h differential density circulating fluidized bed. To the beginning, the startup, debug, and operation of the 20t/h differential density circulating fluidized bed were introduced. And then, we compared the experimental results of three behaviour of co-firing of oily sludge with coal–water slurry with their predicted results. It was found that the experimental results were close to the simulation results from the developed overall mathematical model, which showed that the overall mathematical model was appropriate and reliable for simulation of the incineration of oily sludge in a differential density fluidized bed. Based on this developed overall mathematical model, some main parameters were introduced to simulate incineration of oily sludge in a differential density fluidized bed. Those parameters included the feed of oily sludge, the volatile content of oily sludge, the ash content of oily sludge, the water content of oily sludge, the excess air factor, the height of the bed, and the aera of the heat exchange. The results of simulations showed that the bed temperature increases with the increase of the feed of oily sludge, the increase of the volatile content of oily sludge, the decrease of the ash content of oily sludge, the decrease of the water content of oily sludge, the decrease of the height of the bed, and the decrease of the area of the heat exchange. However, in the lower part of bed, the bed temperature decreases with the increase of the excess air factor, but in the upper part of bed, it was found that the bed temperature would decrease while the excess air factor deviates from some value of the excess air factor. In addition, the simulations of the changes of those parameters to the heat transfer coefficient and the main flue components were done simultaneously.