Abstract: A hot combustion gas recycle apparatus for a starved-air combustor for mixing hot combustion gas with significant amounts of air to heat the air. The heated air is injected as underfire air into the first combustion zone of the combustion chamber to heat and to dry the fuel in the fuel bed as an aid to combustion efficiency. The recycle device includes a temperature control system for controlling the ratio of gas to air and a control valve to completely shut off the flow of combustion gas to the recycle device if the gas and air mixture exceeds a preset maximum.

Abstract: A furnace and associated heat storage assembly includes a firebox arranged within a rock storage area that incorporates a recirculating flue arrangement for returning unburned gases to below a fuel grate for mixing with fresh inlet air. The rock in the heat storage area is heated by conduction of heat from the firebox, circulating flue gases and a smoke exhaust flue. Inlet air is preheated. An open grate arrangement provides for efficient burning of solid as-producing fuel. A system for circulating air and/or liquid through the rock can be provided, as can a water storage tank.

Abstract: A method for drying sludge which may contain combustible vapors in a manner to positively prevent fires and explosions within the sludge dryer and the associated sludge-drying piping. The method provides for a substantial reduction of the oxygen content of the sludge-drying vapors by deviating a part of the sludge-drying vapor stream from the principal vapor circuit and passing it as secondary combustion air into the combustion chamber which generates hot gases for drying the sludge. Furthermore, a portion of the hot effluents from the combustion chamber is deviated from the sludge-drying circuit and is used to heat the sludge-drying vapors whereafter it is vented to the atmosphere. In a variant of the invention, an acid scrubber is provided to remove hydrochloric acid. A number of embodiments is presented.

Abstract: A combustion system for particulate wood waste, coal, peat and other combustible materials is disclosed. The system comprises means for feeding combustion material into the combustion chamber of a furnace and means for recirculating a portion of the exhaust gases from the furnace back into the combustion chamber for increasing the temperature of the combustion chamber and so improve the thermal efficiency of the furnace.

Abstract: This invention relates to a burning furnace of hot gas recirculation type for minimizing fuel cost. The furnace includes a cyclone which receives dust-containing exhaust gases. One or more secondary air-introducing nozzles are provided for the cyclone at top of or in close proximity to the upper end of the cyclone leading concentrically to a flue gas passage such as funnel. Upon introducing secondary air under pressure into the cyclone, a downwardly directing swirling air flow is formed therein for the separation of heavier dust together with part of the fed exhaust gases. The thus separated air-hot gas mixture including heavier dust particles is returned to initial stage of the furnace for the recirculation through the furnace.

Abstract: A boiler having a hot gas generator for burning liquid or gaseous fuels. The hot gas generator comprises a combustion chamber unit, into the combustion chamber of which the fuel and air for combustion are introduced and in which the combustion of the fuel takes place. The combustion gases are conveyed out of the combustion chamber into a water cooled boiler firebox. A compressor supplies the air for combustion into the combustion chamber unit. A flue gas conduit, which leads to the flue gas vent of the boiler, at its inlet end, which is connected with the boiler firebox, is connected with the air intake of the compressor of the hot gas generator for recirculating a regulatable amount of flue gases into the combustion chamber unit of the hot gas generator. The flue gas conduit offers a resistance to the flow of flue gas therein, which resistance is greater than the chimney draft force present in the flue gas vent of the boiler.