Issues with the secondary combustion air in exhaust gas incinerators

The primary purpose of providing secondary combustion air in the exhaust gas incinerator is to increase combustion efficiency and improve combustion conditions. An exhaust gas incinerator is a device used to treat waste gases or exhaust fumes generated in industrial production; by burning these gases, environmental pollution can be reduced. The function of the secondary combustion air is to introduce additional air into the furnace chamber, where it mixes thoroughly with the exhaust gases, thereby improving combustion efficiency and reducing the emission of harmful substances. The introduction of secondary combustion air can enhance combustion by providing sufficient oxygen for the burning process, allowing the fuel to burn more completely and reducing the generation of harmful gases and particulates during combustion. Furthermore, the secondary combustion air can also adjust the temperature distribution within the furnace, improve temperature control during combustion, and enhance the thermal efficiency inside the furnace chamber. Although in theory, air can be introduced at once into the burner in front of the furnace to burn together with the fuel gas, doing so may lead to incomplete combustion; the fuel cannot burn completely, resulting in the generation of large amounts of harmful substances. Additionally, the temperature distribution within the furnace becomes uneven, which affects the combustion efficiency and the efficiency of heat generation. Therefore, to ensure efficient and environmentally friendly combustion, secondary combustion air is usually required to assist the combustion process. .

Current exhaust gas incinerators are basically low-NOX burners, and secondary air is provided to reduce the generation of NOX. The earliest concept was proposed by Duke Combustion Engineering Company. In China, the secondary air in exhaust gas incinerators refers mainly to the air required for complete combustion of the exhaust gases along with a 3-5% excess of oxygen, while the primary air is the air needed for the complete combustion of the gas used in the incinerator. Of course, once the air enters the burner of the incinerator, it is redistributed; for example, an incomplete combustion zone is formed at the front (receiving 60% of the combustion air equivalent to the fuel), a reduction zone (receiving 30% of the combustion air equivalent to the fuel), and a complete combustion zone (receiving 15–20% of the combustion air equivalent to the fuel). Therefore, the primary air in the exhaust gas incinerator is used primarily to ensure complete combustion of the fuel gas, while the secondary air is used mainly to ensure that the exhaust gases are completely burned.

Thank you for your reply. I introduced all the combustion air at once to the burner; the calculated flue gas temperature was 1200°C, with an oxygen concentration of 16% in the flue gas. Then I introduced the Claus off-gases into the middle of the furnace, where the hydrogen sulfide concentration in those off-gases was 1.9%. The theoretical oxygen concentration in the final process gas was 2.5%. I wonder if the combustion efficiency of exhaust gases will be good with this design?

The secondary combustion air can also adjust the temperature distribution within the furnace, improve temperature control during combustion, and enhance the thermal efficiency inside the furnace chamber.

The secondary air design facilitates staged combustion in the burner, while the oxygen-deficient incomplete combustion of the primary air reduces the flame temperature, which helps to lower the formation of thermally generated NOX during incineration; the secondary air ensures complete combustion of the flue gases.