Monday, April 23, 2018

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2.9. INLET AND EXHAUST SECTIONS

General
It is necessary to treat incoming atmospheric air before it enters the turbine in order to adapt to the environment and realize the desired machine performance. Specially designed equipment is installed to modify the quality of the incoming air to make it suitable for use in the unit. It is necessary also to attenuate the high frequency noise in the air inlet, caused by the rotating compressor blading.

At the exhaust end of the gas turbine, gases produced as the result of combustion in the turbine require specific equipment according to their exhaust to atmosphere or towards heat recovery boilers.

2.9.1. AIR INLET SYSTEM
The air inlet system, down-stream of the air filtering installation, is not described in details in this paragraph as it is not a part of the gas turbine assembly itself. It consists of an air duct, followed by sections of parallel baffles silencers, then a screen system located in an inlet elbow, and an expansion joint after which air will reach the gas turbine air inlet plenum. The gas turbine inlet plenum contains the compressor inlet casing.

The silencers are of baffle-type construction to attenuate the high frequency noise in the air inlet, caused by the rotating compressor blading. More details are given in the "Auxiliary plants and systems" volume, especially about the filtering installation.

2.9.2. EXHAUST SYSTEM
In the exhaust section, the gases which have been used to power the turbine wheels are redirected to be either released to atmosphere, or towards a heat recovery boiler when it is the case.

After leaving the exhaust frame, the hot gases reach the diffuser, located in the exhaust plenum.

On the exhaust plenum wall facing the exhaust diffuser, a circular arrangement of thermocouples permits exhaust gas temperature measurement. The thermocouples send their signals to the gas turbine temperature control and protection system. The exhaust plenum configuration is that of a box open at the top and welded to an extension of the turbine base. Insulation in the plenum fabrication provides thermal and acoustical protection. A flow path from the exhaust plenum open side to a duct is provided by an extension plenum and an expansion joint.

Two silencers are installed in series in the duct (the first one for the low frequency noises, the second one for the high frequency noises), after which there is another expansion joint, before exhaust either to atmosphere, upwards, or to a recovery boiler.

The exhaust system, down-stream of the exhaust plenum, is not described in detail here as it is not a part of the gas turbine assembly itself. More details are given in the "Auxiliary plants and systems".


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