The growing need for efficient electric power generation led to the use of pulverized coal as a basic fuel for large steam generating units in the United States around 1920. The combustion of coal that has been pulverized to tiny particles results in the creation of even smaller ash particles, known as flyash particles. About 80 percent of these flyash particles are swept up by by the moving stream of combustion gas and carried out of the boiler. Such particles would be discharged from the chimney and create a major air pollution problem in the atmosphere, unless they are removed from the flue gas.
Thus, an electrostatic precipitator was used to remove particulate matter (flyash) from the boiler flue gas prior to emission from the chimney. Electrostatic precipitators immediately achieved wide acceptance for the efficiency removal of flyash. For hot-side precipitator designs, ductwork designs included temperatures exceeding 700 F, which had to allow for “thermal breathing”. When these movements are restrained, large forces are created, which can cause tearing, cracking and buckling of the steel. Sliding supports, expansion joints, and appropriate elevated temperature structural design practices are therefore used to avoid restraining thermal movements.
O’Donnell Consulting was asked to perform structural and design life analyses of a electrostatic fly-ash precipitator system, determining errors in the original design of the ductwork system.