Ultra-low NO_x emission retrofitting for small scale circulating fluidized bed(CFB) boilers has become the important project for further promoting the ultra-low emission retrofitting for industrial sources currently. In this study

the denitration system of a 75 t/h CFB boiler was diagnosed and upgraded. Moreover

the performance of the denitration system to achieve ultra-low emissions was tested. The results show that

during the whole test

the original mass concentration of NO_x generated in the boiler was 210～270 mg/m~3. After the retrofitting

the NO_x emission mass concentration decreased to 28.7 mg/m~3 while the injection amount of urea solution increased to 89 L/h(mass fraction 40%) without in-furnace desulfurization. The NO_x emission mass concentration decreased to 48.10 mg/m~3 while the injection amount of urea solution increased to 95.2 L/h with in-furnace desulfurization. The denitration efficiency of the original selective non-catalytic reduction(SNCR) denitration system was only 22.29%～64.46%

which was relatively low

and after the retrofitting

it reached about 90% without in-furnace desulfurization

and 77.5% with in-furnace desulfurization. The technical route for efficiency improvement of the SNCR denitration system was suitable for ultra-low NO_x emission of small CFB boilers

but the effect of in-furnace desulfurization should be minimized. This study will provide an important reference for ultra-low NO_x emission retrofitting of nationalwide small-scale CFB boilers.