The Experimental Study On Combustion Characteristic Of Low Calorific Value Oil Shale Semi-coke In Fluidized Bed

The demand of each country for primary energy is ever-increasing with the rapidly development of economy in the world.However,it has taken great pressure to the development of human society and people’s daily life that we haven’t enough primary energy anymore.Particularly,the energy structure which is more coal less oil impels a great deal of import of oil for consumption in China.Under this rigorous situation,development and utilization of new-type energy comes up to be the hottest project today.Oil shale is one kind of sedimentary rock which contains organic material,it has high oil content and rich in natural resources of China.We can get high calorie oil and gas from it by distillation technology,but the oil shale semi-coke is unemployed because of its low calorie specialty,its huge range not only pollute the environment,but also waste the resources.So,if we can use the semi-coke which has low calorific value by burning,apart from solving the pollution of environment,we can use the heat substitute for a part of fossil energy.Bubbling fluidized bed combustion is the first choice for combusting low calorific value of waste,it has great advantage in aspects of operating cost,fuel flexibility,pollutant emission and so on.In this paper,we use the oil shale semi-coke from a factory of Fushun in Liaoning province,the kind of semi-coke has extremely low calorific value,there isn’t any experimental study on it.we get some detailed understanding of its combustion characteristic and stability by experiment of TGA(Thermogravimetric Analysis) and BFB(Bubbling Fluidized Bed) combustion,this study wides the range of adaptable calorific value in BFB,and offers basises of theory and experiment for semi-coke’s industrial utilization.This paper crushes and screens the oil shale semi-coke firstly,then conduct the experiment of TGA,study the influences of heating rate and sieved size on the combusting of semi-coke.And then we burn it in a small scale fluidized bed combustor to study the phase of firing up and stability characteristics of the fuel,analyze the influences of the dense-phase zone temperature,fluidization wind temperature and bed layer height on combustion of semi-coke and its pollutant emission.we get the typical working condition under which the oil shale semi-coke can combusting steadily and has low pollutant emission.Results of the study shows:①In TGA,with the improvement of heating rate,the ignition temperature gets higher,the maximum weight loss rate speeds up;the burnout temperature become higher because of thermal hysteresis.With the shrink of grain diameter,maximum weight loss rate speeds up too,but the burnout temperature’s changing has no clear regularity;we can only see one weightlessness peak in DTG because the burning times of carbon and high temperature type volatile are very close.②From characteristic parameters,we can see that under the working condition of smaller grain and higher heating rate,the oil shale semi-coke can be combusting easier and more stability.③With the cold fluidized test,we get that the critical fluidization velocity of bed material is about 0.4m/s under cold condition.④By calculation of heat balance for the oil shale semi-coke in the fluidized bed,we prove that the semi-coke can combust in BFB steadily.⑤In the process of burning,improve the temperature of dense-phase zone can increase the burnout rate of semi-coke,lower the oxygen content in flue gas.The mean detention time of the fuel shortened because of accretion of discharge quantity;carbon content of fly ash goes down with the temperature of dense-phase zone goes up,the carbon content in the bottom ash maintains the low level,which is below 1%.⑥Influenced by the relative height of feeding inlet and bed positon,the combustion is the best when the bed height ratio is 0.16,the flue gas oxygen content and average residence time have higher value at this condition.⑦The decreasing range of temperature in furnace slows down when temperature of fluidization wind goes up,carbon content of fly ash goes down too, and its decreasing range is about 2%,the carbon content in bottom ash maintains about 0.9%.⑧The concentration of fly ash is the lowest under the working condition in which the dense-phase zone is 900℃.The concentrations of SO2 and NOx in flue gas become higher with the increasing temperature of dense-phase zone.⑨By comparative analysis of different working conditions on the combustion characteristics and pollutant emission, we determine one working condition:dense-phase zone temperature-900℃,temperature of fluidization wind-400℃,bed height ratio-0.16.This working condition can be the reference data of the design of industrial boiler.