Low Load Operation Concept for Alstom's GT26 Gas Turbine

摘要

Operation of gas turbine power plants is possible 24 hours a day 7 days a week. However, there is often not enough demand overnight to warrant keeping the plant at full capacity continuously, or it is simply not economically viable. Currently there are two scenarios that are possible:rna) Shut down the unit at night and start-up again in the morning, resulting in additional thermal stress to the entire combined cycle plant,rnorrnb) Continue to run the plant with low electricity prices compared to high gas prices at minimum combined cycle load at which emission regulations are still fulfilled (usually about 60% plant load).rnNow there is a third option developed by Alstom for its large advanced class GT26 sequential combustion gas turbine. This is the so-called "Low Load Operation Concept (LLOC)". This option allows the plant to be operated in combined cycle (CC) mode at very low load (< 25%), at low emission levels, keeping the water-steam cycle up-and-running with an acceptable overall CC efficiency. The result is a concept that avoids the need for a plant shut-down in the evening and start-up in the morning.rnUntil now, it has not been possible to operate in such low load regions due to exceeding the emission limits or too low plant efficiency (GT only in operation) resulting in negative revenue for the operation hours. These problems have been overcome by exploiting the intrinsic advantage of sequential combustion that is offering the GT26 gas turbine more freedom to tune the operating concept of the two combustion chambers in a specific combination. This paper will describe for the first time Alstom's Low Load Operation Concept in more detail, which is developed to enable operators to run the plant at very low power output levels, whilst maintaining low exhaust emission requirements, keeping the water-steam cycle running and achieving a reasonable plant efficiency.