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Design Considerations for Air Dilution
Cooling of Gas Turbine Exhaust
Presented at the Symposium of the Industrial Applications of Gas Turbines Committee
Banff, Alberta CA - October 19-21, 2009
Author:
Christian Kaufmann P.Eng., Innovative Steam Technologies
Industrial gas turbine exhaust temperatures regularly exceed 538°C (1000°F) during part and base load operation. In combined cycle applications with heat recovery steam generators or simple cycle applications with NOx reduction equipment, the maximum gas temperature must be controlled to maintain equipment integrity and/or maximize emission reduction efficiency.
Various methods can be used to control the gas turbine exhaust temperature. One method of cooling gas turbine exhaust is air injection. This involves the controlled introduction of ambient air into the exhaust duct to uniformly reduce temperatures at the heat recovery steam generator (HRSG) boiler tubes or selective catalytic reduction (SCR) catalyst blocks. However, certain gas turbine (GT) exhaust phenomena, such as turbine swirl and back pressure limitations, must be considered in order to optimize temperature control and steady-state GT performance.
A case study involving a GE Frame 6FA turbine will be used as an example to describe in the steps required to ensure a uniform temperature profile after air injection. This will encompass computational fluid dynamics (CFD) modelling, ducting design and equipment selection.
ASC is a proud contributor of this project with all CFD modelling for Innovative Steam Technologies.
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