Gas Combustion 

Safe System Design and Gas Composition

A safe system design is determined by the composition of gas used in the system. Any combustion system is always designed for a specific type of gas, and variation in gas composition can lead to serious safety hazards. A system designed for Propane or Natural Gas cannot operate safely with Butane due to its lower self-ignition temperature (450°C). This may cause flashback and explosion, as the self-ignition temperature of Propane is 550°C and Natural Gas is 750°C.

Chemistry of Combustion

Generally, carbon dioxide (CO₂) and water vapor (H₂O) are formed as by-products of the complete combustion of hydrocarbons. For example:

CH₄ + 2O₂ → CO₂ + 2H₂O + Heat

Construction of MFB Burner

A thin perforated sheet supports the burner, as the burner cloth does not have sufficient structural strength on its own. There is equal distribution of premix gas because the burner is fully welded with internal diverters. The housing is made of SS304 and can be supplied with or without a collar. Gas can enter either from the back or from the side; however, the overall height increases in case of side gas entry. MFB Cloth 100 is used for blue flame applications due to its low density of 1.5 kg/m².

Radiant / Blue Flame Modes

With premix flow leading to heat intensity in the range of 100–500 kW/m², most of the combustion takes place within the surface of the burner itself. This causes the surface to heat up, glow, and transfer heat in radiant form (infrared mode). In this mode, the surface temperature can reach up to 1050°C.

If the premix quantity is increased, the burner surface cools down due to excess nitrogen flow. Combustion then takes place outside the burner surface, known as blue flame mode. In this case, heat transfer occurs primarily through convection. Intensities as high as 20 MW/m² are possible. In both modes, flue gases are released into the atmosphere.

For radiant operation, λ = 1.05 to 1.1.
For blue flame mode, λ = 1.1 to 1.2.

Efficiencies in Radiant Mode

At lower intensities, a higher proportion of combustion occurs within the burner surface. Around 125 kW/m², radiant efficiency is at its peak, approximately 55–60%. Below 100 kW/m², the flame cannot be sustained. Efficiency is higher in the face-down position and can be further improved in any position by adding a grid in front of the burner.