Fuels, Combustion, and Environmental Controls
Fuels, Combustion, and Environmental Controls
This domain covers fuel properties, combustion calculations, excess air, stack losses, and emissions controls. Expect questions on heating value, viscosity, flash point, sulfur, NOx, CO, and opacity.
Core rules
- Heating value is energy released per unit fuel; higher heating value includes latent heat of water vapor.
- Fuel oil viscosity affects atomization and pumpability; flash point is a safety property, not an ignition-temperature rating.
- Excess oxygen in flue gas indicates excess air; too little oxygen risks CO and smoke.
- NOx forms from fuel nitrogen and high-temperature nitrogen fixation; staged combustion and SCR/SNCR reduce it.
- Sulfur in fuel forms SO2; scrubbers or low-sulfur fuel reduce emissions.
Worked example
Fuel oil contains 0.5% sulfur by mass. Burning 1,000 lb of oil gives 5 lb sulfur. Sulfur dioxide mass = 5 x (64/32) = 10 lb SO2, because one sulfur atom combines with two oxygen atoms and the molecular mass ratio is about 64/32. Reason: emission estimates use fuel mass, sulfur fraction, and stoichiometry.
Traps
Do not confuse flash point with fire point; do not reduce excess air below the point of stable combustion to save fuel; do not ignore CO when optimizing O2; and do not assume visible smoke is the only emissions problem.