Poc Gas Temperature History Through a Furnace

To reduce fuel cost and improve productivity, an engineer must be able to adjust furnace gas temperatures to change the furnace temperature profile. In a longitudinally fired furnace, shortening the flame will raise the temperature near the burner wall. This can be accomplished by spinning the combustion air and/or fuel, which in turn spins the poc. The resultant increase in heat transfer near the burner wall will reduce the flue gas exit temperature, raising the % available heat. 

In furnaces with top and bottom heat and preheat zones, there is greater resistance to poc gas flow below the loads and their conveyor. That resistance causes the bulk of the bottom gases to flow into the top zones, reducing the effective heat transfer exposure areas significantly. This movement of combustion gases into the top zones reduces productivity and lowers available heat, increasing fuel use per ton of product. 

Lowering the firing rate will lower flue gas exit temperature because of lower poc temperature, thus raising %available heat. However, if the firing rate is so low that 

Residence time was mentioned as a factor in cumulative heat transfer as gases flow through a furnace, but its function is often misunderstood. 

Fossil fuel combustion transforms chemical energy into sensible heat, raising the temperature of the combustion gases. The resultant hot poc immediately transfer heat by convection and gas radiation to cooler solids and gasses, at rates proportional to their temperature differences. 

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