Abstract: The tubular heater in the refinery unit provides heat to the process flow. The main combustion control objectives of heater include maintaining the process medium temperature at the heater outlet, ensuring no risk of combustible material accumulation in the heater and achieving safe operation and high energy efficiency. In many oversea projects, the combustion design of heaters with operation mode of balance draft and force draft adopts "fuel-air ratio control"scheme. Upon an increasing variation of heat demand, air flow increases before fuel does. On the other hand, upon a reduction of heat demand, fuel gas flow decreases before air does. This is to ensure excess air during the combustion change process in the heater and avoid insufficient oxygen supply and incomplete combustion, and reduce the safety risk due to combustible material accumulation.Compared with conventional combustion control design, the fired heaters with "fuel-air ratio control" have smaller excess air coefficient and less flue gas emissions; the thermal efficiency as well as safety have been improved;and the operating cost has been reduced. Under the goal of carbon neutrality, the "fuel-air ratio control" scheme for heaters is a feasible solution to improve fuel efficiency and reduce CO₂ emissions.

Key words: tubular heater, combustion control, fuel-air ratio control, excess air coefficient, fume emission