In order to experimentally study the corresponding temperatures of ammonium salt recrystallization in the injection pipeline of solid state selective catalytic reduction system （SSCR）

a SSCR injection system test device was established. The recrystallization temperatures of ammonium salt were determined by adjusting the pipeline temperature to crystallize the gas in a fixed position and passing laser through the crystallizing part to reach the photoresistor module

and then measuring the change of output voltage of the photoresistor module. Results show that the recrystallization temperature of ammonium carbamate is higher than that of ammonium carbonate

and the recrystallization temperatures of ammonium carbamate and ammonium carbonate are obtained under different injection pressures.