Furnace Technology
Circulation of gases in furnace is caused by the

All of these
Furnace pressure in conjunction with draft in flues
Difference in density between hot and cold gases
Change in volume during a change of temperature

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Furnace Technology
Recuperator is

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

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