Abstract: A bellows arrangement for forming a gas leakage resistant pressure seal between ceramic heat exchange tubes has an elongated metallic bellows defining a central passageway with first and second ends. A metallic tube passes through the bellows and freely moves with respect to the second end of the bellows while defining a gas chamber between the tube and bellows. Axial expansion of the bellows under the influence of the internal pressure when such pressure is higher than the external pressure which may be the atmosphere acts to apply a force at the interface between the bellows assembly and the ceramic heat exchange tube which is proportional to the internal pressure of the heat exchange tube, thereby accommodating movement of the heat exchange tube and providing a pressure seal that is leak resistant.

Abstract: An insulated material comprises a first wall having a surface with a layer of insulation thereover. The insulation is anchored to the wall by a plurality of rods which are each attached to the wall and extends through the insulation. The rods are interlocked at expansion point means which allows expansion and contraction of the rods without permitting movement of the insulation from its position.

Abstract: Fuel and less than the amount of air for stoichiometric combustion are injected into a combustion chamber so that the fuel rich mixture burns as a core in the combustion chamber. The balance of the air for substantially stoichiometric combustion is injected coaxially and rotationally as a sheath or vortex which surrounds the core. Where the core is hot and rich, there is little mixing of the sheath air and core gases and the available oxygen combines preferentially with fuel components other than nitrogen so that little nitrogen oxides are produced. After some heat is extracted from the gases in the core, more complete mixing of the sheath air and core gases occurs. Under these lean and cool combustion conditions, production of nitrogen oxides is also unsubstantial. Means for mixing the gas streams may be disposed adjacent the exit end of the combustion chamber when necessary to promote turbulence and further mixing of the air and hot gases for bringing about complete combustion of any residual combustibles.

Abstract: Fuel is burned in a primary combustion chamber with less than the air required for stoichiometric combustion so that the combustion gases have a high carbon monoxide (CO) and hydrocarbon content and the temperature of the gases is held below that at which significant nitrogen oxides (NO.sub.x) would be produced. The combustion gases are then passed through a secondary combustion zone in which more air is injected into the gas stream to oxidize the CO and hydrocarbons to carbon dioxide (CO.sub.2). The secondary burner comprises a plurality of foraminous tubes through which secondary air is emitted. Combustion in the secondary zone is maintained at a temperature below that at which nitorgen oxides (NO.sub.x) will be produced in significant quantities.