Furnace Technology
Turn down ratio of a burner

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

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Furnace Technology
Which is not accomplished in an underfired furnace?

Elimination of cold spot at the bottom of the charge
Portection of the periphery of the charge from excessive radiation
Reduction in the temperature of furnace gases
Increase in heating capacity/m² of floor space

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Furnace Technology
In practical operation of any furnace, zero oxygen percentage or theoretical CO₂ percentage in flue gas is rarely achieved, because of

Use of pulverised solid fuels
Use of non-preheated combustion air
Use of excessive positive draft in the furnace
Imperfect mixing of fuel & air and infiltration of air

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