What are industrial type gas turbines?
Industrial Type Gas Turbines are medium-range gas turbines and usually rated between 5-15 MW. These units are similar in design to the large heavy-duty gas turbines; their casing is thicker than the aero-derivative casing but thinner than the industrial gas turbines.
They usually are split-shaft designs that are efficient in part load operations. Efficiency is achieved by letting the gasifier section (the section which produces the hot gas) operate at maximum efficiency while the power turbine operates over a great range of speeds.
The compressor is usually a 10-16 stage subsonic axial compressor, which produces a pressure ratio from about 5:1-15:1. Most American designs use can-annular (about 5-10 combustor cans mounted in a circular ring) or annular-type combustors.
Most European designs use side combustors and have lower turbine inlet temperatures compared to their American counterparts. Figure below shows an Industrial Type Gas Turbine.
The gasifier turbine is usually a 2-3 stage axial turbine with an air-cooled first-stage nozzle and blade. The power turbine is usually a single- or two-stage axial-flow turbine. The medium-range turbines are used on offshore platforms and are finding increasing use in petrochemical plants.
The straight simple-cycle turbine is low in efficiency, but by using regenerators to consume exhaust gases, these efficiencies can be greatly improved. In process plants this exhaust gas is used to produce steam. The combined cycle (air-steam) cogeneration plant has very high efficiencies and is the trend of the future.
These gas turbines have in many cases regenerators or recuperators to enhance the efficiency of these turbines. Figure below shows such a new recuperated gas turbine design, which has an efficiency of 38%.
The term "regenerative heat exchanger" is used for this system in which the heat transfer between two streams is affected by the exposure of a third medium alternately to the two flows. (The heat flows successively into and out of the third medium, which undergoes a cyclic temperature.)
In a recuperative heat exchanger each element of heat-transferring surface has a constant temperature and, by arranging the gas paths in contraflow, the temperature distribution in the matrix in the direction of flow is that giving optimum performance for the given heat-transfer conditions.
This optimum temperature distribution can be achieved ideally in a contraflow regenerator and approached very closely in a cross-flow regenerator.
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