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The inlet and exhaust systems in gas turbines are described. The inlet andexhaust systems consist of an inletfilter， silencers， ducting， and expansion joints. The design of these systems can be critical to the overall design of agas turbine. Proper filtration is a must， otherwise problems of blade con-tamination and erosion ensue. The standards are minimal for specifications， calling for a coarse metal screen to prevent debris from entering， a rain orsnow shield for protection from the elements， and a differential pressure alarm. Most manufacturers are now suggesting so-called high-efficiencyfilters that have two stages offiltration， an inertia stage to remove particles above five microns followed by one or more filterscreens， self cleaningfilters， pad type pre-filters， or a combination ofthem， to remove particles below five microns. Differential pressure alarms are provided by manufac-turers， but the trend among users has been to ignore them. It is suggested thatmore attention be paid to differential pressure， than in the past， to assure high-efficiency operation.
Silencers are also minimally specified.认ork in this area has progressed dramatically in the past few years with the NASA quiet engine program.There are some good silencers now available on the market， and inlets can be acoustically treated.
Starting equipment willvary， depending on the location of the unit.Starting drives include electric motors， steamturbines， diesel engines， expan-sion turbines， and hydraulic motors. The sizing of a starting unit will depend on whether the unit is a single-shaft turbine or a multiple-shaft turbine with a free-power turbine. The vendor is required to produce speed-torque curves of the turbine and driven equipment with the starting unit torque super-imposed. In a free-power turbinedesign， the starting unit has to overcomeonly the torque to start the gas generator system. In a single-shaft turbine， the starting unit has to overcome the total torque. Turning gears are recom-mended in the specifications， especially on large units to avoid shaft bowing. They should always be turned on after the unit has been ..brought down.. and should be kept operational until the rotor is cooled.
The gears should meet API Standard 613. Gear units should be double-helical gears provided with thrust bearings. Load gears should be provided with a shaft extension to permit torsional vibration measurements. On high-speedgears， proper use of the lubricant as a coolant should be provided. Spraying oil as a coolant on the teeth and face of the units is recommended to prevent distortion. chapter 14 details the design and operation characteristics of gears.
couplings should be designed to take the necessary casing and shaft expan-sion. Expansion is one reason for the wide acceptance of the dry flexible coupling. A flexible diaphragm coupling is more forgiving in angular align-ment; however， a gear-type coupling is better for axial movement access for hot alignment checks must be provided. The couplings should be dynamically balanced independently of the rotor system. chapter 18 deals with the various types of couplings and the alignment techniques for gas turbines.
controls， instrumentation， and electrical systems in a gas turbine are defined. The outline in the standard is the minimum a user needs for safe operation of a unit. More details of the instrumentation and controls are given in chapter 19.
The starting system can be manual， semiautomatic， or automatic， but in all cases should provide controlled acceleration to minimum governor speedandthen， although not called for in the standards， to full speed. Units that do not have controlled acceleration to full speed have burned out first-and second-stage nozzles when combustion occurred in those areas instead of in the combustor. Purging the system of the fuel after a failed start is manda-tory， even in the manual operation mode. Sufficient time for the purging of the system should be provided so that the volume of the entire exhaust system has been displaced at least five times.
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燃气涡轮工程手册 Gas Turbine Engineering Handbook 1(61)
