| Oil shale,as an unconventional oil sources,is used to producing shale oil through pyrolysis process in China.The most widely used pyrolysis technology is Fushun process with advantage of available for low quality of oil shale.However,there are some disadvantages for Fushun process such as low utilization coefficient of oil shale and low oil yield(65%of Fischer Assay).Furthermore,the produced char with extremely low heat value in the Fushun process has adverse effect on the environment because it contains polycyclic aromatic hydrocarbons and phenolic compounds.As increasing focus on environment protection,those have become factors that hinder the use of oil shale resource.Therefore,a comprehensive utilization process of oil shale resource(SCSR process)is developed based on oil shale pyrolysis with solid heat carrier.This process results in oil,steam product.In this work,the emphasis is put on the combustion characteristic of char,which provide heat for the whole pyrolysis process.Meanwhile,a few experiments on oil shale pyrolysis is conducted in a laboratory scale fixed-bed furnace and pilot-scale oil shale pyrolysis/char combustion plant with capacity of 10t/d to achieve valuable information about pyrolysis and combustion of char.Furthermore,a simulation for oil shale pyrolysis/combustion of char is conducted with Aspen Plus and economic performance of SCSR process is analyzed based on experimental and simulated results.The main achievements are listed in the following:Oil shale and its char prepared under different pyrolysis temperature as well as four coal samples(YangQuan anthracite,SMbitumite coal and GYbitumite coal,Huolinhe lignite coal)are analyzed by the thermogravimetric analyzer.The results show that ignition temperature of samples is related to the volatile content and its type.The ignition temperature of samples are sorted in descending order:YangQuan anthracite>SMbitumite>600? char>GYbitumite>550? char>500? char>450? char>lignite>oil shale.The combustion apparent active energy are analyzed by thermogravimetric analyzer through FAW method.The results show that combustion apparent active energy for coals decreaseas as the conversion increases,while increase for oil shale and its char.This distinguish phenomenon is attributed to the high mineral content of oil shale and its char.The higher combustion temperature results in higher emission of NO and SO2 and lower N2O emission,especially,zero emission of N2O at 10000C for combustion of oil shale and its char in drop tube furnace.Drop-tube conversion proceeds almost synchronously with the particle burnout,while the hydrogen conversion is faster and that of nitrogen and sulphur conversions lower than the particle burnout.The kinetic behavior of char combustion is analyzed by drop tube furnace experiments at combustion temperature of 800? to 1000?,and the kinetic expression is ks=26.3exp(-65800/(R·Tp))(ks,g/(cm2· s·atm)).The effective ash layer diffusional coefficient is measured for char through specially prepared cubic char particle.The results indicate that effective diffusional coefficient perpendicular to the bedding plane is 1.246×10-5m2/s and is 2.938×10-5m2/s with direction parallel to the bedding plane.The weighted means of diffusional coefficient for 2-3mm and 9-10mm particles is 1.83×10-5m2/s,1.96×10-5m2/s.The single particles combustion model is built based on mass and energy balance combined the combustion kinetics of char as well as the weighed means of ash layer diffusional coefficient.By comparison,the model could moderately predict the burnout time of char particles.It also is shown that combustion temperature has a limitted effect on burnout time for char paticles of 2.5mm that is average particle size for char particles less 10mm,while the combustion reaction is mainly controlled by ash diffusion resistance.The pilot scale experiments results show that oil and gas yield is up to 11%,oil yield is higher than 5.7%and 6.0%for pyrolysis temperature of 573? and 541? with 99.6%of Fischer assay yield.The heat value of pyrolysis gas is higher than 22.80 and 22.25MJ/Nm3 with pyrolysis temperature of 573? and 541?C;The carbon content of bottom ash is less than 0.7%with burnout of 95%and its content of fly ash is 1.52%with burnout of 92%;When pyrolysis temperature is 57? and 541?,the emission concentration of NO is 80 mg/Nm3,73 mg/Nm3 and emission of SO2 is 54mg/Nm3 and 66mg/Nm3,respectively with 9%O2 in the flue gas.A flow sheet of oil shale pyrolysis with in downer coupled char combustion in circulated fluidized bed combustor with capacity of 300t/h oil shale is built through Aspen Plus.The oil yield is 51.7t/h and 61.7t/h with pyrolysis temperature of 450?and 500?,respectively.The steam(3.82MPa,450?)yield is 296.9t/h and 168.9t/h and energy conversion efficiency is 81%and 82%with all pyrolysis gas combusted in the combustor,respectively.The emission NO and N2O is reduced due to the addition of pyrolysis gas to the combustor based on the simulation results.A circulating fluidized bed combustor containing cyclone,loop seal and air distributor is designed.The economic analysis for the comprehensive utilization of oil shale based on oil shale pyrolysis with solid heat carrier is made and compared with that of Fushun process(FSSR process).The results show that total capital investment for FSSR and SCSR is 1141 million CNY and 2403 million CNY.The breakeven price of oil shale for FSSR and SCSR process is 2940CNY/t and 2150CNY/t,respectively.When price of oil is 4000 and 4500CNY/t,inner rate of return is 0.05 and 0.10 for FSSR process,while inner rate of return is 0.22 and 0.28 higher for SCSR process.The payback period for FSSR and SCSR process is 10.6/5.5 year and 6.6/4.4 year when price of oil is 4000 and 4500CNY/t,respectively.The steam yield is higher and oil yield is lower when oil shale is pyrolyzed at 450? compared with that at 500 °C.The economic analysis results show that production income is higher with oil price lower than 3200CNY/t when oil shale is pyrolyzed at 450? compared with that at 500?. |
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