Low Emission Combustion Technology for Stationary Gas Turbine Engines

The need to control exhaust emissions from stationary power sources is dictated by environmental regulations that limit the amount of smoke (particulates), sulfur dioxide, carbon monoxide, hydrocarbons, and oxides of nitrogen or NOx that can be exhausted into the atmosphere. In areas where atmospheric pollution is a serious concern, as in the Los Angeles basin, very low emission levels are demanded. A brief review of the emission regulations in force in the United States and Europe is given. The mechanisms that give rise to the formation of the regulated pollutants in a gas turbine combustion system burning hydrocarbon fuels are described and the conflicting requirements for producing low emission levels of nitrogen oxides while at the same time controlling carbon monoxide and hydrocarbon levels are explained. The operation of a conventional diffusion flame combustion system is discussed and the concept of using water injection in such a system to control nitrogen oxide emissions is explained. The emission levels achievable with this type of system are given. A lean premixed low emission combustion system is described and the problems that must be overcome if the operation of the gas turbine is not to be compromised are referred to. The features of an ultra lean premixed combustion system are described that allow this system to produce single digit emission levels. The operation and attributes of a catalytic combustion system are described.