Generation Characteristics Of Tar And Combustible Gas During Co-gasification Of Zhundong Coal And Pine Sawdust In A Fluidized Be

Zhundong coal field is the largest integrated coal field in China.Zhundong coal has high volatile content and is suitable as raw material for gasification.Pine trees account for about half of the forest stock in China,and produce a large amount of wood chips in the production every year.If abandoned pine sawdust and Zhundong coal are coalized,environmental pollution and CO₂ emission caused by Zhundong coal can be reduced.However,the tar produced in the gasification process will not only affect the calorific value of gas production,but also cause pollution to the downstream gas pipeline and gas equipment.The catalytic gasification process can effectively reduce the tar concentration in the gasification gas.The characteristics of fluidized bed gasifier are high heat and mass transfer rate and high thermal inertia.And the fluidized bed gasifier has wide adaptability to raw materials and is suitable for catalytic co-gasification of many kinds of raw materials.Taking calcined dolomite with catalytic removal as the bed material,the formation characteristics of tar and combustible gas in the catalytic co-gasification of coal and pine chips were studied.According to this,the adjustment of gasification parameters can reduce tar production and improve the quality of high-yield gas.Firstly,the synergistic effect in the cogasification process of Zhundong coal and pine sawdust was studied.The synergistic effects of the two raw materials were analyzed in the co-pyrolysis.The kinetic parameters were calculated too.At the same time,XRF technology was used to test the main components of Zhundong coal and pine sawdust ash,and then the possible catalytic effects of alkali metal elements were analyzed.The highest H₂ concentration in the product gas was produced when calcined dolomite was used as the bed material compared to quartz sand and dolomite,while the tar concentration was significantly lower.Calcined dolomite is suitable for use as the bed material.Compared to gasifying pine sawdust alone,adding Zhundong coal to the feedstock could be beneficial in reducing the tar concentration and did not significantly impact product gas quality.When the blending ratio of Zhundong coal was increased in the range of 0⁴0%,the tar concentration in the product gas showed a significant decreasing trend,while the concentrations of CO and H₂ changed slightly.After the experiment,the calcined dolomite was taken out and weighed.The weight of the calcined dolomite was increased.When the blending ratio of Zhundong coal was increased in the range of 0⁴0%,the tar concentration in the product gas showed a significant decreasing trend,while the concentrations of CO and H₂ changed slightly.Co-gasification has obvious positive synergistic effect on reducing tar content and improving combustible gas quality.Secondly,the subsequent experimental conditions were chosen as calcined dolomite bed material and a 40% blending ratio of Zhundong coal.The effects of parameters such as gasification temperature,air equivalent ratio,superficial gas velocity,and feedstock particle size,upon the generation amount of tar in the product gas under air and air-gasification were studied.Compared with air gasification,using air-steam as gasification agent can reduce the tar production.When the gasification temperature increased from 650℃ to 850℃,the tar concentration in product gas decreased from 10.35 g·Nm^-3 to 3.15 g·Nm^-3.When the air equivalent ratio increased from 0.24 to 0.36,the tar concentration in product gas decreased from 7.35 g·Nm^-3 to3.36 g·Nm^-3.But their adjustment was limited by the process requirements of the gasifier.To increase the superficial gas velocity or the particle size of feedstock,the tar concentration in the product gas showed a decrease followed by an increase.This is mainly related to fluidization state,reaction rate,heat and mass transfer effect and particle residence time.Finally,the signal of pressure fluctuation was studied to determine the change of gas-solid flow state in the furnace when bed temperature,air equivalent ratio,superficial gas velocity,and feedstock particle size were changed.The generation characteristics of combustible gas are analyzed.Compared with air gasification,air-steam gasification promoted the water-gas conversion reaction,resulting in a significant increase of H₂ and CO₂ concentrations,a decrease of CO concentration,and little change of CH₄ concentration.The increase of gasification temperature enhanced the heat and mass transfer effect in the furnace,and also promoted the cracking and reforming of macromolecular hydrocarbons and the endothermic reaction.For example,H₂ concentration in product gas during air-steam gasification increased from 6.01% at 650℃ to 16.34% at 850℃,and the calorific value of gas production and H₂/CO ratio also increased.The increase of superficial gas velocity promoted the contact mixing ability between gas-solid two phases,improved the heat and mass transfer effect and the gasification reaction rate,but also made the gasification raw materials tend to be distributed on the surface of the bed,and the gas production residence time was shortened.Therefore,the concentration of H₂ and CO in the gasification gas showed showed an increase followed by a decrease.