Fluegas

Flue gas is the exhaust produced by burning fuels in devices such as boilers, furnaces, and engines, and is carried away by a flue, stack, or chimney. It is a gaseous mixture that may carry heat and, in some installations, energy can be recovered from it. The term distinguishes the emitted gas from the fuel and the ash.

Main products of complete combustion are water vapor and carbon dioxide, produced from hydrogen and carbon in the fuel. The gas also contains nitrogen from the surrounding air. Depending on the fuel and operating conditions, flue gas may include oxygen (unreacted), carbon monoxide, sulfur oxides from sulfur in the fuel, nitrogen oxides formed at high temperatures, and varying amounts of particulates from solid fuels.

Environmental concerns focus on NOx, SOx, and particulates, which can contribute to smog, acid rain, respiratory problems, and climate impacts through CO2. Regulations typically set limits on emissions and energy authorities encourage or require emission-control measures.

Control technologies include flue gas desulfurization to remove SO2, selective catalytic or non-catalytic reduction to reduce NOx, and particulate control devices such as electrostatic precipitators or fabric filters. In some cases, carbon capture or heat recovery systems are used to improve efficiency.

Monitoring of flue gas composition is standard in industry, with analysers reporting O2, CO2, CO, SO2, NOx, and particulates to guide operation and compliance.