The conversion of a 650-MW power station unit from oil to coal included conversion from forced to balanced draft boiler operation and the addition of two induced draft fans rated at over one million CFM each. The fans required 25 dB tonal noise reduction to meet nondegradation noise criteria. Two tuned reactive/absorptive discharge duct silencers were purchased. Detailed performance tests were required in the purchase specification and were conducted on a prototype silencer to assure the manufacturer's guarantee would be met. Several performance indices were measured: insertion loss, noise reduction, attenuation, and pressure drop. Narrow-band frequency analysis was utilized. Community noise measurements were made following silencer installation. They indicated the silenced fans were inaudible.
This paper is in two parts, and concerns the lateral dynamics of a large turbocharger rotor with overhung wheels. Initial rotor dynamic analysis indicated no excessive motion in the operating speed range. However, testing showed excessive motion, which was initially traced to the radial-inflow turbine wheel becoming loose on the shaft, due to transient differential thermal expansion in the wheel on startup. The attachment of the wheel was modified to eliminate this problem. The discussion up to this point is in Part I of the paper, and the remainder is in Part II. The wheel attachment modification extended the range of satisfactory operation upward considerably, but excessive lateral motion was again encountered near the upper end of the operating speed range. This behavior was traced to thermal bowing of the shaft at the turbine end, known as the Morton Effect. The turbine end bearing was modified to eliminate this problem, and satisfactory operation was then achieved throughout the operating speed range.
The sound from two 5600 HP induced draft fans at a 500-MW coal-fired power plant was a source of community annoyance. Each fan was retrofitted with a V-notch cutoff designed to reduce the noise generated at the blade passage frequency and its harmonics. The cutoff is the part of the fan casing at the discharge which is closest to the impeller blade tips. A conventional cutoff has a straight edge parallel to the blade tips, while the edges of a V-notch are askew to the blade tips. The V-notch design was based on aerodynamic tests of a 116 scale model fan with inlet and discharge ducts. In order to evaluate the performance of the V-notch cutoff, detailed sound measurements were taken in the community, near the fan cases and inside the stack (in 330°F hot flue gas) both before and after the fan modifications. In addition, the in-stack measurements were coincident with fan performance measurements and were taken for several operating conditions. A 5- to 7-dB reduction of the tones was achieved which significantly reduced complaints.
The evaluation of industrial sites, such as for nuclear or fossil power stations, often requires detailed analysis of the existing sound levels and acoustic impact of the proposed facility at each site. Such a study was performed for five potential power station sites according to the guidelines set forth by a state licensing agency with extensive site study requirements. As required by the state, ambient sound level contours, plant construction, operation and maintenance contours, and sound level impact contours were prepared for each site for the 12 required sampling periods. A variety of land uses ranging from rural to industrial-urban were included in the study. This paper summarized the techniques involved in developing and analyzing the contouring process to the various acoustic environments.
Prior to startup, many fossil fueled power stations clean the boiler piping to the turbine generator with high pressure steam. The steam is vented to the atmosphere in a series of several minute “blows” over a several week period. Steam conditions of up to 900 psi and 5000000 lb/hr are not unusual and sound levels from this activity can easily exceed 100 dBA at property lines. The traditional approach to the community noise associated with the blow has been to warn the neighbors, but the community reaction to the noise is still often significant. This paper describes the methodology and equipment used for quieting the blows. Sound level measurements of a number of steam blows, both silenced and unsilenced are presented and the resultant benefits are discussed.
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