Furnace Technology
In a furnace, the heat taken by the charge/stock and the heat lost to the furnace structure & flue gases depends on the

Rate of firing and emissivity of flame
All of these
Thermal conductivity of the charge & structural materials of furnace
Nature of process ; whether batch, continuous or intermittant

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Furnace Technology
Recuperator is

Not used for fuel gas preheating
A continuous waste heat recovery equipment
Heavier than regenerator meant for the same duty
An intermittant waste heat recovery equipment

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