Fuel desulfurization and denitrification system and method

The invention discloses a fuel desulfurization and denitrification system and method. The system comprises a circulating fluidized bed boiler, a gas preheater, a gas concentration mixer, a first desulfurizing agent silo and a second desulfurizing agent silo, wherein the circulating fluidized bed boiler comprises a furnace and a cyclone separator connected to the furnace, the furnace is provided with a feed port and a first air inlet, the gas concentration mixer is provided with a primary air pipe and a secondary air pipe, the primary air pipe is connected to the first air inlet, the secondaryair pipe is divided into a secondary split air nozzle and a tertiary air nozzle, both of which are connected to the furnace, a first nozzle and a second nozzle are respectively provided at the ends inthe furnace, the second nozzle is inclined downwardly, and the height of the second nozzle is greater than the height of the first nozzle. The method comprises crushing and then mixing coal and biomass, and processing the mix