Combustion of Gas

Pulverised fuel-fired furnaces with gas burners are arranged, if boilers are heated by gas. Gas and air are supplied through burners into the furnaces.

According to specific features of combustion burners are divided into external mixing, internal mixing and partially internal mixing. In the burners of external mixing air and gas are supplied into the furnace by separate channels and mix due to diffusion having flown out of a burner. Combustion is delayed because some time is required to form a mixture and rather a long torch is formed. Such combustion is called diffusive and burners are called torcheous.

If gas and air mix in the burner then already prepared mixture flows out of it, burning right here. Then a torch is very short and the duration of combustion depends on the chemical reaction rate. Mixture burns in case of high temperature for rather short time. Such combustion is called kinetic and burners are called unflamed.

In the burner of partial internal mixing gas mixes with a part of air necessary for combustion and with the other one already flown out of the burner. Two fronts of combustion: kinetic and diffusive are formed near the nozzle of the burner.

Heating a boiler by gas of large combustion heat (natural) a small amount of gas to mix with a large volume of air is necessary, e.g. burning of 1 m3 of gas requires about 10 m3 of air. Gas is supplied into turbulent vortex flow by thin streams for better mixing with air. Gas supplied by its central pipe mixes with air. Gas flows by streams into it through small gaps, making 30┬░angle with axis of the burner. Air gains speed turning round not only by guiding blades, but also due to its tangential flow into the burner. Since gas and air mix easily, little surplus air is enough.

Injection burners are often used in small boilers. It is not necessary to supply air by force into them. Gas flowing out of the nozzle with great velocity sucks into air and mixes with it in the cylindrical part of the burner and diffuser. Besides, in this diffuser velocity of mixture decreases and its pressure increases, so mixture is blown (injected) into the furnace. Mixture from the injection burner gets into the furnace through stabilizer fixed in the nozzle of a diffuser. Mixture flames up easier due to existing stabilizer – steel lattice. Flame does not jump over into a diffuser, if loading of the burner decreases. Constant ratio of air and gas amounts is kept, changing output of the burner because sucked amount of air is approximately proportional to the gas quantity.