| Hot-state experiments of two-stage gasification process were mainly carried out in the self-built experimental apparatus. The reaction characteristics of Shenfu bituminous coal (SF) in the second gasification reaction zone were studied, as well as the effect of different catalysts loaded. The gas releasing characteristics of coal samples were also investigated when falling within the high-temperature environment and staying until the end of pyrolysis process. The research results in this paper have great theoretical significance in guiding the further work of optimizing the combined gasification process of entrained-flow bed and fixed-bed.The comparing research of SF bituminous coal and Inner Mongolia lignite set as the second-stage bed was carried out in order to make the reaction characteristics clear of these two coals. Research showed that the difference of gasification parameters of SF bituminous coal is little compared with the Inner Mongolia lignite. Under the existing experimental condition, different types of catalysts and it loading amounts were added into the second stage coal samples. The results showed that the adding of potassium salt, sodium salt and iron salts on the second stage coal samples played a certain role in promoting the gasification reaction. When the potassium salt was added in the coal, the gasification reaction of two-stage was enhanced, and the gasification indexes increased with the increasing of the loading dosageof potassium salt. When the dosage of potassium salt was 5% and 8%, the effective gas content at the gasifier export was increased by 2.5% and 3.8%, respectively, compared with raw coal. In order to describe catalyst amount and the ratio of coal sample the parameter of y as metal carbon mole ratio was introduced to determine the dosage of catalysts at different conditions. The results showed that the catalytic effect of sodium salt was worse than potassium sodium, when the the parameter y was same. If continuing adding more sodium salt when the dosage had reached 5%, the enhancing effect was a bit worse than when adding the same dosage of potassium salt. When the loading dosage of sodium salt increased from 5% to 8%, the effective gas content value was increased just from 3% to 4%. The catalytic effect of sodium salt was weaker than potassium sodium salt in the experimental conditions. According to the experiment results the catalytic effect was arranged by 8%K> 8%Na> 5%K≈5%Na> 5%Fe.The pyrolysis experiments of three types of coal sample were studied in the tubular reaction reactor to simulate the reactions in the second stage. The results showed that the increasing of temperature played a certain role in decomposing hydrogen/oxygen functional groups in these three coals. When the temperature rising from 873K to 1273K, the emission amount of H2 and CO were increased by 4-5 times. At high temperature of 1173K and 1273K, the coal rank had less effect on the effective composition of gaseous product from pyrolysis reaction.The gasification reaction of the second stage fluidized bed was simulated by Aspen Plus. The results showed that the best range of coal feed ratio in the second stage fluidized bed was 18%-20%. In the best range of coal feed ratio, the gasification efficiency and effective gas yield could be significantly improved. The most representative work condition, which was chosen from in the optimum operating range could greatly improve the efficiency of second stage gasification process. In the condition of oil feed rate 2.94kg/h, the oxygen flow 5kg/h (O2/oil ratio 1.7) in first stage and coal feed rate 0.55kg/h (coal feed ratio 18.7%), the effective gas yield could reach 2.07 Nm3/kg (coal) and 84.81% for the cold gas efficiency. This process simulation had a great theoretical significance in guiding the further research of optimizing two-stage gasification process. |
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