Experimental Study on Tar-free Gasification of Coal in a Fixed Bed

Throated twin-oxidation zone gasifier of coal was exploited based on the characteristic analysis on the updraft gasifier and downdraft gasifier, and tar-free gasification of coal was experimentally investigated in the throated twin-oxidation zone gasifier. The effects of operational parameters, such as the ratio of grate air supplied gasifier by bottom to primary air (n_g/n_p), the ratio of secondary air supplied gasifier by upper oxidation zone to primary air supplied gasifier by top (n_s/n_p), the mass fraction ratio of steam to carbon in coal (n_st/n_c) on gasification performance indices, such as temperature distribution inside gasifier, gas composition, gas heating value, tar concentration of gas, gasification efficiency and carbon conversion rate were studied. The results showed that the throated twin-oxidation zone gasifier can reduce the tar content in the gas and raise the heating value of gas. The tar content in the gas and the heating value of gas can get 10mg/m³ and 6466.9kJ/m³, respectively. It entirely satisfy the various burners and heat technics´ needs and make tar-free gasification of coal come true. n_g/n_p, n_s/n_p, and n_st/n_c on coal gasification performance indices are realized essentially by changing the gasification temperature. The increase of gasification temperature can enhance reaction rate of tar pyrolysis. Consequently, the concentration of CO and H₂ increase and the concentration of CO₂ and tar content in the gas decrease, so the heating value of gas increase.