Study And Optimization Of Some Key Issues Of A Combined FB Retorting System Of Oil Shale

The uncertainty in current petroleum prices, its growing worldwideconsumption and limited availability have motivated many countries rich inoil shale resource to explore more efficient retorting technologies to widelyproduce and use shale oil as an alternative. On the basis of the retortingtechnology progress and the characteristics of oil shale, this paperrecommends a new retort system of oil shale with a fluidized bed (FB)reactor, realizing the effective and clean use of oil shale.Firstly, the technical procedure of the new oil shale FB retort system wasdiscussed in this paper. The fluidized bed (FB) retort and circulating fluidizedbed (CFB) boiler are arranged side-by-side, and hot circulating ash andsemicoke will be conveyed from one side to the other. Both CFB circulatingash and fuel gases as fluidizing gases of the FB retort are proposed to be heatcarriers together, transferring the combustion heat of semicoke and fuel gasesto oil shale retort. Then, the effects of retorting temperature, heat carriers andother key issues on the yield of pyrolytic products, compositions of shale oiland combustion characteristic of semicoke were further discussed. Theretorting temperature of460oC-490oC is recommended for the new retortsystem. Under the condition of self-energy balance of the whole system,more fuel gases should be used to provide more heat for oil shale retorting,thus decreasing the chemisorption and catalysis effects of oil-shale ash on shale oil.The oil-shale ash, as one of the heat carriers, has strong chemisorptionand catalysis properties, which may affect the yield and components pyrolyticproducts. Retorting experiments of oil shale and fine oil-shale ash mixtureswere conducted by low heating rate and quick heating rate respectively toinvestigate the effects of fine oil-shale ash on pyrolytic products andcharacteristics of shale oil and fuel gases. FTIR and MRU gas analyzer,CHNOS elemental analyzer, high temperature simualated distillation(HTSD)analyzer and GC-MS analyzer were used to investigate the components andcharacteristics of shale oil and fuel gases. It was found that, with the increaseof ash/shale mass ratio, the compositions of shale oil showed the tendencyfrom heavy oil to light oil. When the ash/shale mass ratio is lower than1:2,enhancing the mixing ratio of oil-shale ash could increase shale oil yield.However, excessive oil-shale ash would result yield reduction of shale oil andobvious yield increase of fuel gases.Coordination and optimization of process parameters of the newretorting system of oil shale are very significant for achieving the maximumeconomic and environmental benefit under stable operation. In this paper, athermal balance calculation of the system was performed by coupling AspenPlus process simulator with a self-developed thermal balance calculationprogram of the CFB boiler. The mass and energy distribution of the systemwere presented, and the effects of some key parameters were also discussedto optimize the new retorting system of oil shale.