Reducing agent injection device and exhaust gas treatment method

A reducing agent injection device, comprising:

• a honeycomb structure that has a pillar-shaped honeycomb structure body having partition walls defining and forming a plurality of cells which is through channels of a fluid and extends from a first end face being an end face on an inflow side of the fluid to a second end face being an end face on an outflow side of the fluid, and that has at least a pair of electrode members arranged on a side surface of the honeycomb structure body, for causing the honeycomb structure body to generate heat such that the temperature in the first end face becomes 900° C. or less;
• a tubular outer cylinder that houses the honeycomb structure and forms an ammonia injection port downstream of the outflow side of the honeycomb structure;
• and
• a urea spraying device that sprays a urea water solution in mist form,
• wherein each of the pair of electrode members extends in a cell extending direction of the honeycomb structure body, and one electrode member of the pair of electrode members is arranged on an opposite side of the other electrode member of the pair of electrode members with respect to a center of the honeycomb structure body sandwiched by the pair of electrode members, in a cross section perpendicular to the cell extending direction,
• a carrier gas inlet connected to the tubular outer cylinder to introduce carrier gas directly into a urea spraying space inside the tubular outer cylinder between the urea spraying device and the honeycomb structure, for promoting the flow of gas in the honeycomb structure,
• the urea water solution sprayed from the urea spraying device is supplied into the cells from the first end face of the honeycomb structure body, and urea in the urea water solution supplied into the cells is heated and hydrolyzed in the honeycomb structure body in which the temperature in the first end face is electrically heated to 900° C. or less to generate ammonia, and the ammonia is discharged outside the honeycomb structure body from the second end face and is injected outside through the ammonia injection port.