Calculate thermal efficiency to optimize fired heater operation.

The article presents a case study on the fired heater operation in a polybutylene terephthalate (PBT) unit. The thermal efficiency of the fired heater was calculated through determining the net calorific value (NCV), heat loss from stack and radiation, and heat supplied by air and fuel. Several tables which show the NCV calculation, oxygen flow rates, and stack flue gas flow components are also presented.