Solutions to Prevent Wear Resulting from Burning Powder River Basin Coal (PBRC) on Primary Air and Induced Draft Fans

摘要

Many companies today are burning Powder River Basin coal (PRBC) to benefit from its relatively low sulfur content and economic price. The use of PRBC allows a power plant to meet stringent requirements on SO{sub}2 emissions without the major investment of pollution control equipment such as a scrubber. However, PRBC also has an elevated calcium content that creates equipment erosion problems. In addition, PBRC has as a lower heating value than eastern bituminous coals and requires that more coal be burned to achieve maximum boiler loads. The increased calcium content in the coal can cause accelerated wear in primary air and induced draft fans. It is not uncommon to have the induced draft fan situated upstream of the baghouse or electrostatic precipitator, allowing for these components to be under positive pressure. In situations like this, because the fan handles all the dust loading, serious operational problems can result. Also, most rotary regenerative air heaters in power plants today experience 20% to 50% leakage, so the more highly abrasive ash that leaks by the air heater causes unexpected wear on primary air fans. Most primary air fans were not designed with wear protection since Midwestern and Eastern bituminous coal ashes do not have a high level of abrasive constituents. This paper discusses methods to prevent and/or slow the erosion and allow for longer periods of time between repairs. It also discusses how to monitor the fan equipment for reliable and safe operation. Prevention includes cleaning the fuel as well as the use of upstream multiple tube mechanical dust collectors, and positioning of the fan in the system. Other techniques to deal with wear include changing materials of construction, adding wear resisting materials such as quenched and tempered steels, chromium carbides, or tungsten carbides. For intense wear situations, a continuous vibration monitoring system should be used to record and track the rate of increase in vibration so predictions can be made and outages scheduled and planned. A program of recording impeller component thicknesses can determine the rate of wear and provide trending that allows for repairs and replacements at scheduled outages.