Consensus on Operating Practices for Control of Water and Steam Chemistry in Combined Cycle and Cogeneration
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Lay-up and start-up of a combined cycle power plant are particularly important as the plants are often cycled regularly to meet peak demands. Start-up is not gradual, as in a conventional fossil-fired boiler, but very sudden because the combustion turbine exhaust gases produce very rapid heating of the tubes.
Combustion turbine purge cycles that occur just prior to ignition exacerbate the situation by pushing cold air through the HRSG followed by the engine ignition and sudden temperature rise. These factors can produce condensate in superheaters that can result in thermal low-cycle fatigue. This result can be minimized with proper design...