Optimization And Simulation Of Circulating Fluidized Bed Coal Gasification Process

Coal gasification technology,as the key technology of clean coal conversion,plays an important part in the efficient utilization of coal.As one of the coal gasification technology,the fluidized bed gasification technology has gotten widely concerned because of the moderate gasification temperature,good quality of gasification gas and excellent flexibility to coals.As one of the fluidized bed coal gasification technology,the circulating fluidized bed coal gasification technology which is independently designed by the Institute of Engineering Thermophysics,Chinese Academy of Sciences,has been widely used in industry.And there is a lot of running data in industry.However,because of the limitation of industrial operating conditions,we can only do the experiment within several operating conditions.So we can't obtain the rules of different operating conditions and coal types.At the same time,the high carbon content of fine ash from coal gasification causes the low carbon conversion rate.So the process of gasification still need to be optimized.Because of the variety of coal types and operating conditions,the experiment research is time-consuming and cost-consuming to study and optimize the process.So we can only do the experiment in several operating conditions.Therefore,the determination and optimization of operating parameters in industry is based on the experimental experience.All of these limit the optimization of circulating fluidized bed coal gasification.At present,the gasification results under different conditions can be obtained by process simulation software.And the conditions which can't be obtained from the experiment research can be obtained from the software.So,we can get the rules of different operating conditions.In this thesis,an industrial circulating fluidized bed coal gasification model was created by Aspen Plus.After verifying the accuracy of the model by industrial data,different factors in gasification process were investigated,including oxygen-coal ratio,stream-coal ratio,gasification pressure,air/stream preheating temperature and heat loss.The results show that the gas heating value decreases obviously with the increase of oxygen-coal ratio,the cold gas efficiency increases first and then decreases with oxygen-coal ratio increasing.The gas heating value and cold gas efficiency decrease slightly with the increase of stream-coal ratio.With the gasification pressure increasing,the gas heating value increases slightly and the cold gasification efficiency decreases.With the air/stream preheating temperature increasing,the gas heating value decreases and the cold gas efficiency increases.The gas heating value and cold gas efficiency decrease with the increase of heat loss.The effect of air/stream preheating temperature in different oxygen-coal ratio was studied.The results show that at a fixed air/stream preheating temperature,the gas heating value decreases with the increase of oxygen-coal ratio,the cold gas efficiency increases with the increase of oxygen-coal ratio.At a fixed oxygen-coal ratio,the cold gas efficiency increases with the increase of air/stream preheating temperature.The effect of oxygen-coal ratio,steam-coal ratio,gasification pressure and air/steam preheating temperature on gasification results was analyzed by orthogonal experiment.The results show that the effect of oxygen-coal ratio on gasification product(CO+H2),gas heating value,cold gas efficiency,gas yield and coal consumption rate is the most important.The steam-coal ratio is the second important factor on the gas heating value,and the influence on other indexes is the last.The gasification pressure has a great influence on the gas yield and oxygen consumption rate,it is the second important factor.The influence of air/steam preheating temperature on oxygen consumption rate is the most important.And the air/steam preheating temperature is the second important factor on gasification product(CO+H2),cold gas efficiency,gas yield and oxygen consumption rate.Therefore,the oxygen-coal ratio and the air/steam preheating temperature have a great influence on the main gasification indexes.The combustion process of fine ash from coal gasification was added to the original circulating fluidized bed coal gasification model.The high temperature flue gas in the combustion process was entered into the circulating fluidized bed gasifier.Different coal types in the gasification process were investigated,including Ruojin coal,Shuozhou coal and Shanlu Shenmu coal.The influence of excessive air coefficient,oxygen concentration and return ratio of high temperature flue gas on gasification results was studied.The results show that the carbon content of fine ash from coal gasification of Ruojin coal and Shanlu Shenmu coal is high,so the above two kinds of coal can reach the ash fusion temperature in air atmosphere.All the temperature should be higher than the ash fusion temperature,so the excessive air coefficient of Ruojin coal and Shanlu Shenmu coal should be above 0.7.The gas heating value and cold gas efficiency of the two kinds of coal decrease with the increase of the excessive air coefficient,and the temperature increases with the increase of excessive air coefficient.When the excessive air coefficient is 0.7,the oxygen concentration should be above 30 percent.The gasification product content and cold gas efficiency increase with the increase of return ratio of high temperature flue gas.Because the carbon content of Shuozhou coal is low,the oxygen concentration should be increased to ensure the ash fusion temperature.The cold gas efficiency and gas heating value decrease with the increase of excessive oxygen coefficient.The temperature should be higher than the ash fusion temperature,so the excessive air coefficient should be above 0.7.When the excessive air coefficient is 1.1,the oxygen concentration should be above 30 percent.