Effect of coal ash and coal char on gasification syngas water gas shift reaction

The water gas shift reaction (WGSR) of gasification syngas in short residence time (1-2 s) and high temperature was carried out in a tubular reactor. The effect of coal ash and coal char on WGSR was studied. The results indicate that when the temperature was below 900 ℃ ,the water gas shift reaction of syngas was difficult to occur,and the CO conversion rate was close to 0. However,the reverse shift reaction occurred at 1 300 ℃ ,but it was not easy to reach chemical equilibrium state. Coal ash could promote the water gas shift reaction,which only accelerated the reaction rate without affecting the reaction direction. Although the coal ash had sintering phenomenon at high temperature,the promotion effect of coal ash on the reaction was more obvious at higher temperature. The CO conversion of syngas increased by 0. 9% ,0. 8% and 2. 3% at 700 ℃ ,900 ℃ and 1 100 ℃ respectively after adding coal ash. For dry syngas,no reaction was detected at 700 ℃ ,and CO2 conversion increased by 0. 9% and 2. 4% at 900 ℃ and 1100 ℃ ,respectively. The surface area provided by coal ash and the catalysis of iron and other metal elements in coal ash might be the reasons for promoting the reaction. However,poor gas-solid contact and small surface area limited the promotion effect. Coal char had a similar promoting effect on WGSR to coal ash. The effect of particle size of coal char on WGSR was significant. The influence of coal char particle size on shift reaction had a better value. The coal char particle size increased while the surface area decreased,and the promoting effect decreased. Minor particle size could also contribute to low promoting effect due to uneven gas distribution. Under the experimental conditions,the coal char with particle size of 0. 8 -1. 5 mm had the most significant promotion effect,and the CO conversion of syngas at 700 ℃ increased by 1. 7% compared with the blank experiment.