The invention relates to a melting unit and method in which: a melting chamber is heated by means of combustion, the combustion fumes are used to heat the air used as a heat-transfer gas, the heated air is used to pre-heat the combustion oxygen and/or the gaseous fuel, the tempered air resulting from the pre-heating is compressed, the compressed tempered air is heated by means of heat exchange with the combustion fumes, and the mechanical and/or electrical energy is generated by expansion of the heated compressed air.

An improved fired heater with air preheating provided by one or more heat pipes. The fired heater may include at least one burner for combusting a fuel stream and an air stream and producing heated exhaust gases; a hot gas flow path and at least one conduit containing a process fluid to be heated by heat transfer from the heated exhaust gases; and an air preheater comprising at least one heat pipe having a first section exposed to the heated exhaust gases and a second section exposed to the air stream, wherein the heat pipe is positioned and arranged to transfer heat from the heated exhaust gases to the air stream, wherein the at least one heat pipe contains a working fluid sealed within the heat pipe, wherein said working fluid transfers heat from the heated exhaust gas to the air stream to be preheated.

Described herein is an apparatus and method for avoiding frost buildup on the air intake and or ice buildup on the ice condensing surfaces of the exhaust vent of a condensing appliance. The apparatus comprises a heat-conducting path that extends between the exhaust gas in the exhaust vent of the appliance, and the frost condensing surfaces at or near the air intake opening of the combustion air vent. The heat-conducting path has a first section in thermal contact with the exhaust gas and a second section in thermal contact with the frost condensing surfaces at or near the air intake. In one configuration, the heat-conducting path is a heat pipe. In one configuration the heat-conducting path is a heat exchanger assembly. The passive transfer of heat energy via the heat-conducting path, from the exhaust gas to the frost condensing surfaces at or near the air intake, avoids frost buildup.

A carbon fiber production method includes a carbon fiber production step including an oxidation step and a carbonization step; and an exhaust gas processing step including a heat exchange step; an external air mixing step; and a mixed external air supplying step in which the mixed external air is supplied to at least one step that uses heated gas in the steps in the carbon fiber production step; and among the exhaust gases, a high heating value exhaust gas having a heating value of 250 kcal/Nm.sup.3 or higher is supplied to an inlet side of an exhaust gas combustion apparatus and a low heating value exhaust gas having a heating value lower than 150 kcal/Nm.sup.3 is supplied to an outlet side of the exhaust gas combustion apparatus, respectively.

A heat exchanger includes a hollow heat exchanger main body that is enclosed in a radiant tube, and a heat conductor that is disposed on outer periphery of the heat exchanger main body. The heat exchanger performs heat exchange between a first gas flowing in between the radiant tube and the heat exchanger main body and a second gas flowing in hollow interior of the heat exchanger main body, and the heat exchanger comprises a turbulence flow generation promoting unit configured to promote generation of a turbulence flow from the first gas flowing in between the radiant tube and the heat exchanger main body, the turbulence flow generation promoting unit being disposed on the outer periphery of the heat exchanger main body without welding.

Furnace operation includes consecutive cycles of a heating step, a stopping step and a restarting step. The fuel and/or the oxidizing agent is preheated upstream of the furnace by indirect exchange with the discharged fumes through a medium passing through a chamber. A first wall separates the fumes from the medium in the chamber. The fuel and/or oxidizing agent is separated from the medium in the chamber by a second wall. During restarting, the medium's flow rate Dm is regulated to limit the heating rate of the first wall until it reaches the operational temperature at an end thereof.

The present disclosure provides for improving flame propagation in a combustor, particularly in a combustor for use in a power production system and method. At least one stream being passed into the combustor (e.g., a fuel, an oxidant, a diluent, a coolant, a working fluid, water, or steam) can be independently heated to a temperature that is about the autoignition temperature of the fuel or greater. Further, flame stabilization, including promoting ignition, can be improved as described herein through controlled addition of one or more NOx species into the combustor or combustion chamber.

A radiative recuperator preheats oxidant and/or fuel for combustion at one or more burners of a furnace. The recuperator includes a duct, at least portions of which comprise a material having a thermal conductivity of greater than 1 W/(m.Math.K), preferably greater than 3 W/(m.Math.K), that receives hot flue gas produced by the burner(s). The duct radiatively transfers heat to oxidant or fuel (for preheating) flowing through one or more metallic pipes disposed in between the duct and an insulating wall.

A carbon fiber production method includes a carbon fiber production step including an oxidation step and a carbonization step; and an exhaust gas processing step including a heat exchange step; an external air mixing step; and a mixed external air supplying step in which the mixed external air is supplied to at least one step that uses heated gas in the steps in the carbon fiber production step; and among the exhaust gases, a high heating value exhaust gas having a heating value of 250 kcal/Nm.sup.3 or higher is supplied to an inlet side of an exhaust gas combustion apparatus and a low heating value exhaust gas having a heating value lower than 150 kcal/Nm.sup.3 is supplied to an outlet side of the exhaust gas combustion apparatus, respectively.

Method for indirectly preheating a fluid upstream of a furnace, wherein the fluid is preheated by indirect heat exchange with fumes discharged from the furnace through a medium in a chamber, and wherein the flow rate of the medium in the chamber is adjusted on the basis of at least one of the following temperatures: the temperature of the discharged fumes, the temperature of the medium in the chamber, the temperature of the preheated fluid, and the temperature of the wall separating the discharged fumes from the medium in the chamber.