The power generation industry is currently in a very difficult period of business restructuring. All the while, the demands to reduce emissions of NOx, SOx and particulates in accordance with the Clean Air Act continue. The high capital and operating cost of post-combustion NOx controls like Selective Catalytic Reduction (SCR) is leading to greater interest in finding methods to reduce NOx formation during combustion. The most cost effective means of reducing any pollutant is to never form it in the first place. The science behind combustion NOx control uses techniques which limit the amount of air available in the high temperature combustion zones where thermal NOx forms. Minimum NOx formation occurs when fuel and air mixing are carefully controlled to maintain required stoichiometric ratios. Additionally, controlling coal and air flow minimizes excess air requirements, can reduce unburned carbon resulting in better electrostatic precipitator performance and improved overall boiler efficiency. Thus maintaining fuel and air flow at optimal levels becomes a major concern if one wishes to achieve minimum NOx formation during combustion and maintain optimum boiler performance throughout the units load range. Since pulverized coal is transported by primary air in a two phase flow it has been difficult, if not impossible, in the past to measure coal mass flow on a continuous basis. Typically, coal flow and fineness have been measured on an intermittent basis using extractive techniques. This paper serves to introduce a real-time “flow measuring system” for pulverized coal, based on the use of microwave technology. It will describe how microwaves are used to obtain very accurate coal flow measurements. Comparisons of data obtained using the microwave system will be made with measurements obtained using extractive isokinetic methods. Some relevant operational effects from both US and German installations will be discussed and projections of operational savings will be made especially when using the system on an SCR equipped installation.
Experimental Investigation of an Atmospheric Rectangular Rich Quench Lean Combustor Sector for Aeroengines