Coal Quality and Its Impact on Power Stations Emissions Control

Although coal fired power generation plant was originally designed to operate on a particular coal, increasingly stringent emissions regulations have led to modifications to both the coal type and firing mode. Low sulphur (S) coals minimize the requirement for sulphur dioxide (SO₂) scrubbing plant combustion modifications are used as the primary measure to reduce the emission of nitrogen oxides (NOx) and these changes in the firing regime and/or the coal type can also impact on the in boiler ash deposition, particulate collection and the overall efficiency of the boiler operation. Emission regulations requiring maximum NOx levels of 0.15lbs./MM.Btu. are at, or just below, the limit of NOx reduction achievable by primary measures and at this limit significant increases in unburnt carbon (UBC) in ash levels can be expected, which affect boiler efficiency and also the operation of any SO₂ and particulate collection plant. Coals are usually purchased, in addition to price, on quality based on the well established proximate and ultimate analyses, whereas parameters derived from these basic analyses may be more effective in defining the behaviour of a coal, substituted for the original design coal, in order to meet current emissions regulations whilst still maintaining an acceptable operating efficiency.