Drying and absorption towers are formed as the same as packed tower to be. The tower shell is made of steel. The acid proof coating and acid proof bricks are lined in the internal wall. The under part of tower is support structure with ball arches or beams, the middle part is filled in with packing while the upper part is equipped with acid distributing tank or tube acid distributor. The wire mesh demister or fiber demister is set up in the top of the tower to reduce entrainment in the furnace gas out from the tower.