A biomass boiler slag burning apparatus, comprising: a slag trough (1) provided at a lower end of a grate (2), and a slag discharging machine (3) provided below the slag trough (1); wherein a horizontally movable slag burning bed (4) is provided between the slag trough (1) and the slag discharging machine (3), the slag burning bed (4) is a cavity and is connected to a combustion-supporting gas, and a top surface of the slag burning bed (4) is provided with several air outlets (51); a slag scrapping component is provided on the slag trough (1) at a position near an outlet side of the slag burning bed (4); the slag burning bed (4) moves between a slag burning position and a slag discharging position, when the slag burning bed (4) is in the slag burning position, a top end of the slag burning bed (4) is engaged with a bottom end of the slag trough (1) and the top surface of the slag burning bed (4) receives slag burnt on the grate (2); and when the slag burning bed (4) is in the slag discharging position, the slag burning bed (4) is separated from the slag trough (1), the slag trough (1) communicates with the slag discharging machine (3) and completely burnt slag falls onto the slag discharging machine (3). The slag burning apparatus solves the technical problems of incomplete combustion of fuels and slag accumulation in existing biomass boilers.
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