Boiler heating surface contamination preventing system of double-fluidized-bed combustion furnace

The invention relates to a boiler heating surface contamination preventing system of a double-fluidized-bed combustion furnace. The system comprises a fluidized-bed combustion furnace and a fluidized-bed pyrolyzing furnace, the temperature of coal ash generated by burning in the fluidized-bed combustion furnace is high, the high temperature coal ash is collected through a cyclone separator, enters into the fluidized-bed pyrolyzing furnace through a coal ash distributor and is uniformly mixed with fed raw coal pulverized coal, the pulverized coal is pyrolyzed in the fluidized-bed pyrolyzing furnace by the heat of the coal ash and smoke of the fluidized-bed combustion furnace, alkali metals in the pulverized coal are volatilized and enter into a pyrolysis gas at the high temperature, the pyrolysis gas enters into a purifying device through a pyrolysis separator at the top of the fluidized-bed pyrolyzing furnace, the alkali metals are removed by purification, and the pysrolysis gas is fed into a furnace to burn; cokes and coal ash mixtures at an outlet of the fluidized-bed pyrolyzing furnace pass through a return feeder to server as coal as fired to be fed into the fluidized-bed combustion furnace for burning; and the alkali metals in the cokes are greatly reduced, an initial layer of contamination caused by the fact that alkali metal compounds in the smoke are cooled to adhere to the convection heating surface pipe wall is prevented, and the initial condition of forming the contamination is damaged.