A fairly rapid chemical reaction, i.e., hydrogenation of ethylene by palladium catalyst, was carried out at a room temperature in a two dimensional fluidised bed with a perforated plate distributor.The results were considerably affected by the behaviour of the bed near its bottom.The measured hydrogen conversion was compared with that predicted by the so-called "coalescence model". Consistency of the experimental and calculated results was fairly good. The significance of various parameters included in the model was also investigated. The parameters examined were the gas interchange coefficients, the volume fraction of particles in the bubble, and the gas flow rate as bubbles.In conclusion, it was pointed out that the deviation of gas flow rate as bubbles from that predicted by the two phase theory at the bottom of bed aflFected significantly the conversion of a rapid chemical reaction.