AMMONIA DECOMPOSITION DEVICE

An ammonia decomposition system includes: a reactor filled with a catalyst for a decomposition reaction where ammonia which is a raw material is decomposed into hydrogen and nitrogen; a diluent gas supply line for supplying a diluent gas having a lower ammonia concentration than the raw material, such that the diluent gas is mixed with the raw material before the raw material flows into the catalyst; and an ammonia combustor for burning part of the ammonia. The reactor includes a catalyst containing part for containing the catalyst. The reactor is internally divided into a first chamber supplied with the raw material, and a second chamber located downstream of the first chamber in a direction in which the raw material flows. The catalyst containing part is disposed so as to communicate with each of the first chamber and the second chamber and to extend in the second chamber. An outflow gas line through which a crude cracked gas produced from the raw material by the decomposition reaction flows after flowing out from the reactor as an outflow gas communicates with the second chamber upstream of a communication portion where the catalyst containing part communicates with the second chamber, and a combustion gas from the ammonia combustor is supplied to the second chamber.