Ash deposition impacts in the power industry

There have been great strides in understanding the fundamental underpinnings of the slagging and fouling phenomena. Unfortunately as fuel quality changes due to coal pricing, mine closures, government regulations, market forces, etc., boilers and boiler operators continue to be plagued by poorer operating performance than desired. While improvements have been made, the need to address fundamental coal quality issues and how they affect deposition, emissions, handling, and combustion continues to be relevant.This paper presents the results of a study to assess how prevalent coal quality issues are to the power generation industry. A survey of selected EPRI members was made to determine the major areas where coal quality effects power generation and a reliability and availability assessment of the NERC GADS database for the years 1995 to 2004 was completed. This database was used to determine the lost generation through either forced outages, forced derates or planned outages and derates due to coal quality or slagging and fouling issues.The results clearly demonstrated that slagging, fouling, corrosion and fuel blending continue to be the leading coal quality concerns of utility personnel. Ash chemistry resulting from fuel blending and new coals being utilized continue to be the main area for needed utility support. A minimum estimated annual economic impact of over $1.2 billion was calculated for all coal- and lignite-fired boilers in the US based on coal quality and deposition occurrences. While this annual economic loss is huge, these outages and derates account for only about 1.6% of the total number of outages and derate occurrences and 2.5% of the total lost MW-hour generation. An annual evaluation of the coal quality and deposition-based outages and derates did not show a clear trend. In fact, the coal quality-based outages and derates generally increased over the ten-year period.