Fired heaters process side

The heat of combustion in a process heater may liberate 100 x 10 Btu/h. If the heater s efficiency is 78 percent, the heat absorbed by the tubes should be 78 x lO Btu/h. When observing a heater s operation, it is a good idea to check this heat balance by calculation. 

The heat of combustion is a product of the amount of fuel consumed and the net heating value of the fuel. The heater s efficiency is a function of the flue-gas stack temperature, the excess air or oxygen, and the ambient-heat losses from the firebox and the convective-section structures. 

The heat absorbed by the tubes is the sum of the heat of vaporization of the process liquid to vapor, plus the increase in the sensible-heat content of the flowing process fluid. 

If the heat picked up from the combustion of the fuel does not equal the heat absorbed by the process fluid, then something is amiss with the data. Often, determining the cause of such an inconsistency will reveal several fundamental operating or measurement problems with a fired heater. Quite commonly, we may find that the metered fuel-gas rate is wrong, or that the ambient-heat losses are much greater than anticipated in our calculations. 

When fuel is burned in a fired heater, there are three major products of combustion  

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