Retrofitting Duct Burners for CO Control

Duct burners are often installed in gas turbine cogeneration or combined cycle systems to add supplementary heat to the turbine exhaust gas (TEG) stream upstream of the heat recovery steam generator (HRSG). The turbine exhaust gas usually contains enough oxygen to sustain combustion and the duct burner is designed to use the TEG as combustion air. Although duct burners produce relatively low NOx levels due to the low oxygen content of the TEG, the levels of CO and VOC's can be greatly influenced by the composition, temperature, velocity and turbulence of the TEG stream. In some applications, steam is added to the TEG to reduce NOx emissions produced by the turbine or to augment the power produced by the turbine. This steam further depresses the oxygen content of the TEG and can lead to increases in combustible emissions from the duct burners. An improved, low emission duct burner design has been developed to significantly minimize the effect of steam addition, turbulence and TEG velocity on combustible emissions. Data are shown for a gas turbine application that has been retrofitted with the improved design.