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A novel solution has been proposed for low load parking and fast restart of combined cycle plants. The solution was proposed at Power Gen International 2019 by S Can Gülen, Ilya Yarinovsky and Mark Boulden of Bechtel Infrastructure & Power, Inc.
The solution assumes a 2 X 1 configuration: two gas turbines, each with their own HRSG, but one bottoming cycle steam turbine.
The authors say fast start technology has problems. For instance, terminal attemperation may be theoretically sound but historically problematic and maintenance intensive. Water induction risk to the turbine must always be considered. Steam turbine stress controllers are necessary to have, but consideration must be given to the design basis assumptions. Change in operating tempo can result in unexpected stress accumulation, they add.
The solution they suggest has the following sequence.
There is no cold start when gas turbines restart. One gas turbine at MECL provides substantial ability for low load parking of the power block, but bleed can be used across the entire load range. Cross bleed maintains the offline HRSG(s) sufficiently hot to allow unlimited ramp-up to full load and keeps the SCR at operating temperature, reducing start-up emissions. The plant is faster to start, faster to full load, lower startup emissions and reduced use of steam attemperators.