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

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

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Furnace Technology
Turn down ratio of a burner

Should be 1:1 for a batch type furnace.
Is normally much more for a continuous furnace as compared to a batch furnace
Should be as low as possible i.e., 1 : 2
Is the ratio of maximum to minimum permissible heat input rates

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