Effect Of Particle Size Of Powdered Coal On Shell Coal Gasification Process

The particle size of coal is an important parameter affecting the stable and high efficiency operation of Shell gasifier.The fluctuation of particle size not only influences the flowability of powder during pneumatic conveying,but also results in the change of gasification efficiency during gasification.Six different rank coal samples with median diameter from 20?m to 60?m were selected according to the coal particle size distribution of Shell gasifier.The influence of particle size on the flow characteristics for different rank coal samples was investigated by using a powder comprehensive measuring instrument.The effect of particle size on CO₂ gasification reaction characteristics of different rank coal samples was studied by using thermogravimetric analyzer.Through the data of Distributed control system,the influence of particle size fluctuation of coal sample on Shell gasification process was analyzed.The main conclusions are as follows:?1?The particle size has the same effect on the powder flow characteristics of different rank coal samples.With the decrease of particle size,the porosity and compressibility of powders increased gradually,the particle distribution coefficient increased,the fractal dimension decreased and the mobility index of coal samples showed a decreasing trend.When the particle size of coal samples drops from D50=40?m to D50=20?m,the mobility index is basically unchanged.However,when the particle size of coal samples drops from D50=60?m to D50=40?m,the mobility index changes greatly.Through the particle size gradation of YA coal samples,it is found that the wider the particle size distribution,the higher the content of large particles is beneficial to improve the flow characteristics of coal samples in the same median diameter.With more than 90?m above the particles accounted for proportion increased,liquidity index increased significantly.With less than 40?m accounted for the proportion of particles increased,the power flow characteristics reduced significantly.The best proportion for less than 40?m particles is less than 40%.?2?With the decrease of particle size,the CO₂ gasification reactivity of coal samples increased,the weight loss rate and activation energy of coal samples decreased.When the particle size was reduced from D50=40?m to D50=20?m,the weight loss rate and activation energy decreased not obviously.The weight loss rate and the activation energy of the sample are greatly changed when the particle size of the coal sample decreases from D50=60?m to D50=40?m.With the increase of metamorphic degree of coal samples,the activity of CO₂ gasification reaction of coal sample decreased in the same median diameter.Through the particle size gradation of YA coal samples,it is found that the activity of gasification decreased obviously with more than 90?m above the particles increased.With less than 40p?m accounted for the proportion of particles increased,the activity of gasification increased significantly.?3?Through the operation data of Shell gasifier in a plant,it is found that the particle size fluctuation affects the nozzle flow rate of the gasifier,thus affecting the change of oxygen coal ratio in the furnace.The change of oxygen coal ratio leads to the fluctuation of furnace temperature,which results in the increase of the content of methane gas in the rarnace and the decrease of the yield of synthetic gas.When the medium diameter of coal feed into the furnace is 46?m,the yield of synthetic gas is 144%of the medium diameter in 30?m and 104%of the medium diameter in 52?m.The average diameter of the coal sample in the furnace is controlled from 40?m to 50?m for the best.The particles less than 40?m are between 30?40%,larger than 90?m are between 20-30%and the maximum particle size is not more than 200?m.