TABLE E-1 Summary of Common Repair and Replacement Activities, Frequencies, and Cost for Coal-Fired Electricity-Generating Facilities

Category

Description

Repair or Replacement Needs

Boiler-tube assemblies

Rows or bundles of heat-exchanger tubes

Wear and periodic failure attributable to erosion, corrosion, and temperature/pressure-related stresses, leading to such outcomes as leaks, forced outages, loss of reliability, and potential for substantial boiler failure

Air heaters

Heat exchangers that transfer heat from flue gas to incoming combustion air

Exposure to ash, condensate, and acid gases in flue-gas path can lead to plugging, corrosion, and erosion, leading to loss of heat-transfer efficiency. Leakages or pluggage in the air preheater can reduce effective capacity at the plant

Fans

Forced-draft fans push combustion air into the furnace; induced-draft fans pull flue gas from the furnace. A balanced-draft system has both. Other typical fans include primary air fans for pneumatic transport of pulverized coal and flue-gas recirculation fans for NOx control

Erosion and cyclic fatigue; fans exposed to flue gases often subject to higher temperatures as well as erosive ash and corrosive acid gases. Reduced effectiveness of fan reduces plant output; failure leads to shutdown

Mills/feeders

System for feeding and pulverizing coal into a fine powder

Abrasion due to hard minerals in coal, and erosion where solids/powder strikes interior surfaces, including deterioration of rollers, tables, balls, classifiers, bearings, seals, motors, belts, flow-control devices, and piping

Turbines and generators

Steam turbines are composed of a shell, blades, nozzles, diaphragms, and rotors. Generators are composed of rotors and stators, including windings and insulation

Turbine blades experience wear due to impurities in steam, requiring replacement of blades (usually with better designed shapes and more recently available alloys). Generator insulation can deteriorate because of exposure to heat or contaminants

Condensers

Typically, a shell and tube heat exchanger in which river water flows on the tube side and low-temperature steam and low pressure (at a vacuum compared with ambient) are on the shell side

Flow on either side can lead to erosion. Impurities in steam or water can lead to corrosion. Biologic fouling on the water side is also possible. Partial or full pluggage of tubes reduces heat transfer, and tube failure leads to contamination of the steam cycle



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