Acoustics – Sound-modifying means – Sound absorbing panels
Reexamination Certificate
1997-01-15
2001-07-24
Dang, Khanh (Department: 2837)
Acoustics
Sound-modifying means
Sound absorbing panels
C181S224000
Reexamination Certificate
active
06263998
ABSTRACT:
AREA OF THE INVENTION
The present invention relates to panels within an exhaust stream that are intended to reduce the noise of the exhaust stream. Particularly, the invention is directed to panels for use in power generation equipment, these panels being placed in the exhaust stream of a gas turbine so as to reduce the noise level of that exhaust stream.
BACKGROUND OF THE INVENTION
The gas turbines used to produce electrical power emit an exhaust stream. That exhaust stream is of a relatively high noise level such that it is desirable to quiet the noise level to more acceptable levels. Traditionally, the quieting has been done by what is known as a “silencer” or a “silencing system” which serves to attenuate the sound. The silencing system generally consists of a silencer chamber attached to the exhaust plenum downstream from the gas turbine. Within the silencing chamber a series of silencer panels are arrayed. The silencer panels are generally of a rectangular shape and spaced apart. The size and thickness of the silencer panels as well as their spacing serve to determine how much sound attenuation is accomplished and at what frequencies.
Generally, the silencer panel is designed to be extremely rigid to take the stresses encountered in the gas turbine exhaust stream. These include a very turbulent gas stream and an extreme of temperatures ranging from sub zero, such as prior to start up in a cold climate, to 1,250° F., when the system reaches operating temperature. Likewise, the system can cycle through these temperature extremes such as when the gas turbine is shut down for maintenance. Because of the extremes of temperature, the silencer panel expands and contracts. The silencer panel is full of acoustical insulation which also acts as a thermal insulator to the internal structure of the panel. Therefore, the interior of the panel expands and contracts at a different rate than the exterior. This can cause high localized stresses and consequently, a short life expectancy for the silencer panel.
The silencer panels have typically been made out of stainless steel such as a ASTM type 409. Newer technology for gas turbines has resulted in higher firing temperatures. These higher firing temperatures have required different material to take the higher temperatures. For example, austenitic stainless steel is often used in place of type 409 stainless steel. The austenitic stainless steel has a higher thermal coefficient of expansion and hence, accentuates the localized thermal stresses during cycling of the system, and with current designs would be expected to lead to an even shorter life span for the silencer panels.
BRIEF DESCRIPTION OF THE INVENTION
The present invention describes a new silencer panel design that reduces the problems of localized stresses throughout the silencer panel. This is accomplished by utilizing a lightweight framework to make up the silencer panel. The silencer panel is generally constructed from a stainless steel frame that generally defines the outer periphery of the silencer panel. That framework is tied together by internal (within the periphery) webbing welded to the inside of the frame. Sections of acoustical insulation are placed within the framework. Septums in the form of e.g. wire mesh can be placed adjacent to the webbing to prevent the insulation from shifting through the perforations of the webbing during use. Preferably the septum is free floating, i.e., not tied to the frame. Cladding in the form of perforated stainless steel sheets is then placed over the assembly and attached to the framework to retain the insulation within the framework. The silencer panel is then mounted within the silencer chamber by a variety of means, such as suspension. Therefore, the silencer accomplishes the objectives of being able to take the localized stresses due to thermal expansion and contraction without internal breakdown of the silencer panel for longer periods of time, translating into longer service life, fewer shutdowns and reduced costs.
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Daniels David W.
Farabee Leland Matt
Mills Thomas Richard
Schockemoehl Gene F.
Braden Manufacturing, L.L.C.
Dang Khanh
Harness & Dickey & Pierce P.L.C.
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