To provide a decompression tower capable of efficiently removing adhered ash inside a decompression tower.SOLUTION: The drum 2 having the top plate 10, the inlet duct 3, the outlet duct first part 11 extending upward and the outlet duct second part 13 connected downstream of the outlet duct first part 11 And a plurality of ash falling mechanisms 6 for dropping attached ash adhering to the drum 2, wherein the inlet duct 3 and the outlet duct 4 are arranged such that the axis A 2 of the inlet duct 3 and the outlet duct And the axis A3 of the two portions 13 is disposed so as to be at least 45 and not more than 135 in plan view, and the ash falling mechanism 6 has a plurality of circumferentially equally spaced apart The first ash falling mechanism 6a and the second range near the boundary line connecting the top plate 10 and the side plate 8 and in two ranges obtained by dividing the top plate 10 by the axis A3 of the outlet duct second part 13 In the inlet duct 3, a range on the downstream side in the flow direction of the exhaust gas E And a plurality of second ash drop mechanisms 6b disposed on the top plate or the side plate of the ash.(FIG.
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