COMBUSTION
CONTROLLING COMBUSTION IN FIRED PROCESS HEATERS
Fired process heaters are integral to hydrocarbon processing. Specifically designed for the reaction of fuel and air to produce extremely high gas temperatures, heaters transfer this energy to potentially highly flammable process fluids via heat exchangers.
They consume large quantities of fuel, produce large quantities of emissions, and are a potential safety hazard to personnel and plant. However, they are currently irreplaceable within many petrochemical processes – so they warrant the highest levels of understanding and care in their operation and control.
The cornerstone of a well-controlled combustion process is an optimized air-tofuel ratio for efficient fuel consumption. This produces considerable benefits, in the form of efficiency, reduced emissions, safety, and extended life of equipment.
Before analyzer technologies were developed to measure excess air in the products of combustion, fired heaters were run in conditions of high excess air. Although this meant inefficient and costly fuel consumption, it was the only way to avoid the creation of low-oxygen, fuel-rich conditions that could lead to a potentially dangerous explosion.
Too much oxygen leads to cooler burning, causing a significant reduction in combustion efficiency due to an increased loss of heat to the atmosphere, while the excess of oxygen available combines with nitrogen and sulfur to produce undesirable emissions.
The understanding that a fuel-rich( high carbon monoxide) situation is a potential source of explosions has caused the measurement of carbon monoxide to move from a supporting combustion measurement to a key safety measurement.
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