HEALTH MANAGEMENT OF UTILITY COAL PULVERIZERS

摘要

Coal-fired power plants utilize coal pulverizers in a direct-fire system to grind the fuel to an appropriate fineness just before it enters the boiler. Pulverizer health management is therefore vital in efficient power plant operation. The 2007-2011 North American Electric Reliability Council Generating Availability Data System (NERC/GADS) report [2] indicates that pulverizer-related problems are one of the most frequent causes of partial forced outages in coal-fired power plants. On average, there have been more than ten occurrences per year of forced unit derations caused by pulverizer problems during the five years included in the report. This is by far the largest cause of forced derations in the power plant. Although these outages typically do not result in removal of the unit from service, these problems, including drive shaft failures, excessive component wear, and bearing failures, do increase maintenance expenditures throughout the year. Also well documented is the influence pulverizers have on combustion, NOx formation, unburned carbon and slag. There are several issues that can reduce mill efficiency including, but not limited to: broken springs; worn rolls; roll eccentricity; journal bearing failures; plugged feeder; excessive mill inventory and recirculation. These cases can lead to fatigue failures of larger mill components. Unscheduled mill downtime can lead to output losses and increased maintenance costs. A key concern is main vertical shaft failure due to an unbalanced load from the journals. For large mills, taking into consideration parts, labor and down time, costs related to a main shaft failure can easily exceed $500,000. Instrumenting these mills can prove challenging with the harsh coal environment in which they are located. This paper discusses methods to instrument and monitor pulverizers utilizing Advanced Pattern Recognition (APR) to mitigate common failure modes. Continuous monitoring of the mills aids in condition based maintenance programs and provides early detection of deteriorating conditions.