Failure mode analysis for lime/limestone FGD systems. Volume 1. Description of study and analysis of results. [Flue gas desulfurization]

Objective was to improve the reliability of lime/limestone FGD (flue gas desulfurization) systems by identifying the root cause of failure in full-scale installations so that recommendations for remedial measures could be made to system users. A systematic approach for determining FGD system failure causes and potential solutions were developed based upon past experience in field reliability studies. Visits were made to 37 utility sites which included 61 separate FGD systems to collect data for the reliability analysis. The FGD subsystems causing the most amount of downtime at the system and plant levels (rather than the module level) are ductwork, stacks, thickeners, and pipes and valves. The most troublesome failure modes for these key subsystems are acid attack of stack linings and corrosion of outlet ducts. The sulfur and chloride content of the coal affect FGD system reliability; reliability decreases as the sulfur or chloride content increases. For reliability purposes, FGD system designs should exclude subsystems that are nonessential for operation. Spare modules are recommended because they reduce the effects of failures on overall system operation. Subsystems with high failure rates (e.g., pumps) or major failure effects (e.g., outlet ducts and flues) should be considered as candidates for redundancy. Future studiesmore » should concentrate on the subsystems with the key failure modes: stack linings and outlet ducts.« less