Abstract: A convection pass enclosure for a boiler comprising a front wall having a gas inlet for receiving gases from the boiler; right and left side walls connected to the front wall; a rear wall having a gas outlet, the rear wall being connected between the right and left side walls; and a roof, at least one of the front wall, right side wall, left side wall and rear side wall having a heat exchanger surface in the form of a horizontal spiral tube assembly.

Abstract: A spout for channeling smelt from a boiler through an opening in the walls of the boiler comprises a jacket having an inner wall and an outer wall. The outer wall is spaced a distance away from the inner wall and the jacket has one end insertable into the opening of the wall. The jacket defines a trough for carrying smelt from the boiler. An inlet communicates with the jacket for delivering a water flow to the jacket between the inner wall and the outer wall. An O-shaped tube communicates with the jacket at the inserted end of the jacket for receiving the water flow from between the inner wall and the outer wall of the jacket. An outlet communicates with the O-shaped tube near the inserted end for channeling the water flow from the O-shaped tube and out of the spout. A vacuum is used near the outlet for insuring a proper low pressure drop.

Abstract: A system for controlling sulfur dioxide (SO.sub.2) in a flue gas produced by a boiler comprises an air heater connected to the boiler for cooling the flue gas produced by the boiler. A dry scrubber is connected to the air heater and a slurry source for receiving the heated flue gas and a slurry in order to remove SO.sub.2 from the flue gas. A particulate collector is connected to the dry scrubber in order to collect particles from the flue gas. Heat is recovered from the flue gas by connecting a condensing heat exchanger to the particulate collector; and a condensate recycler is connected to the condensing heat exchanger and the slurry source for reducing the water requirements for the system.