Nickel-catalysed steam gasification was examined for two Japanese and three German coals which had been pretreated with liquid ammonia. Reaction temperatures range from 923 to 1123 K. The greatest enhancement in reactivity by ammonia treatment and 1 wt % nickel loading was observed for Leopold coal. With this treatment, the temperature could be lowered by about 55 K to achieve the same conversion level as the original coal. The apparent activation energy decreased from 220 to 140 J/mot. The crucible swelling number decreased from 1% to 0. The surface of the char after gasification was examined by a scanning electron microscope. The role of the catalyst and the interaction of nickel with sulphur are discussed.
In previous pape~s'-~, we have studied the catalytis gasification of coals pretreated with liquid ammonia. In these studies, the reaction temperature was raised at a constant rate such as 5 K/min until it reached 1273 K. The greatest enhancement in reactivity was observed above 1073 K. This treatment was more effective in hydrogasitication than in steam gasification. The coals most suitable for this treatment were high-volatile bituminous coals.
In the present study we intended to check the effectiveness of this treatment for gasification under more practical conditions.
First, the temperature was raised as quickly as possible to the reaction temperature.
Secondly, an aqueous somtion of hexammine nickel carbonate was used as a starting material for impregnation, because our colleagues had found that the most promising method for nickel recovery from ash might be an ammonia leaching method'. Nickel can be recovered in a yield of more than 99%. From this recovery system, we would obtain the ammoniacal aqueous solution of nickel salt mentioned above. Thirdly, we used only 1% of nickel as compared to 5% of nickel nitrate in the preceding studies. Thus, the loss of nickel can be estimated at less than 100 g per ton of coal.
Carbonization and gasification were carried out in a kind of therrnobalance.
The rate of gasification was obtained directly from the weight change. Gas analyses were made by gas chromatography.
The resulting char was examined by a scanning electron microscope, and electronprobe microanalysis.