Reverbatory furnace

A reverberatory furnace is a metallurgical or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases. The term reverberation is used here in a generic sense of rebounding or reflecting, not in the acoustic sense of echoing.

Chemistry determines the optimum relationship between the fuel and the material, among other variables. The reverberatory furnace can be contrasted on the one hand with the blast furnace, in which fuel and material are mixed in a single chamber, and, on the other hand, with crucible, muffling, or retort furnaces, in which the subject material is isolated from the fuel and all of the products of combustion including gases and flying ash. There are, however, a great many furnace designs, and the terminology of metallurgy has not been very consistently defined, so it is difficult to categorically contradict the other view.

The applications of these devices fall into two general categories, metallurgical melting furnaces, and lower temperature processing furnaces typically used for metallic ores and other minerals.

A reverberatory furnace is at a disadvantage from the standpoint of efficiency compared to a blast furnace due to the spatial separation of the burning fuel and the subject material, and it is necessary to effectively utilize both reflected radiant heat and direct contact with the exhaust gases (convection) to maximize heat transfer. Historically these furnaces have used solid fuel, and bituminous coal has proven to be the best choice. The brightly visible flames (due to the substantial volatile component) give more radiant heat transfer than anthracite coal or charcoal. Contact with the products of combustion, which may add undesirable elements to the subject material, is used to advantage in some processes. Control of the fuel/air balance can alter the exhaust gas chemistry toward either an oxidizing or a reducing mixture, and thus alter the chemistry of the material being processed. For example, cast iron can be puddled in an oxidizing atmosphere to convert it to the lower-carbon mild steel or bar iron. The Siemens-Martin oven in open hearth steelmaking is also a reverbetratory furnace.

...
Wikipedia