Gas Turbines

Inlet air filtration is important for all gas turbines since the most common cause of reduced output (and falling efficiency) is air compressor fouling. Also, pressure drop across the filter can have a significant impact: 100 mm H2 O pressure drop reduces output by 1%. Choice of filter type depends on location.

Virtually all gas turbines except extremely small units use axial air compressors to compress the air prior to introduction of fuel in the combusters. It is common to carry out compressor cleaning on a fixed routine but monitored experience has shown that fouling is not a linear progression but occurs in steps depending on ambient conditions-weather, dust storms, etc. It is therefore better to monitor the air compressor efficiency and clean on as an 'as needed' basis. For efficiency monitoring see Section 8.2.1.3.

Downstream of the filter it can be attractive to use 'fogging'. As the same implies, this is ultrafine mist which produces evaporative cooling within the compressor section. The result is up to 2.5% efficiency improvement and up to 20% increase in output. As well as reducing CO2 emissions (less fuel), the system also gives lower NOx emissions.

All gas turbines have high exhaust temperature typically 500 °C-750 °C plus 15% or more oxygen in the exhaust. They are therefore well suited to combine with a heat recovery steam generator (HRSG). If duct burners are included to increase steam production, then the incremental steam is produced at close to 100% efficiency.

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