Air/Gas System Dynamics of Fossil-Fuel Power Plants. Volume 5. System Excitation Sources

摘要

The combustion air, flue gas, and recirculation gas systems of a number of fossil-fuel power plants have been subjected to large-amplitude, low-frequency pressure pulsations that have caused severe or catastrophic damage to plant equipment. Induced-draft and flue gas recirculating fan failures; boiler-casing leaks; excessive fan vibrations; and fatigue failure of mechanical structures, such as ducts, brackets, and bearings, are some of the effects caused by uncontrolled aerodynamic disturbances. This study addresses combustion air/flue gas system dynamic problems in fossil fuel power plants involving significant pressure and flow dynamic variations. A computer-based mathematical model developed for the study of air/gas system dynamic problems has been useful for studies of system stability, surging and transient response to changes in damper settings and disturbances generated by fans and other equipment. The analytical effort has been complemented by experimental transient measurements at oil-fired, balanced-draft plants. Low frequency periodic oscillations resulting from air preheater rotation and higher frequency disturbances resulting from forced-draft, induced-draft and recirculation fans were identified. Recirculation fans were found to produce the highest levels of disturbances. A fan-duct laboratory facility has been constructed and instrumented to obtain static and dynamic measurements of pressure disturbances as a function of fan operating conditions. Significant disturbances were found at frequencies corresponding to fan rotation speed and its harmonics, including blade passage frequency. As the fan was operated at flows corresponding to and less than the peak efficiency point, a disturbance associated with rotating stall at a frequency of approximately two thirds of rotation frequency was produced. This disturbance and its harmonics are significant and correspond to those observed in plant tests which led to significant vibrations. (ERA citation 07:003949)