Shutdown and startup scenarios of a pilot plant

“1.Gas turbine shutdown

The shutdown sequence represents a realistic scenario based on the shutdown sequence of a modern NGCC plant. The gas turbine ramp rates in this and the gas turbine startup scenario are characteristic of a SIEMENS STG5-4000F (Eisfeld and Feldmüller, 2013), and are detailed in Sections 5.1 Gas turbine shutdown5.2 Gas turbine startup respectively. The method by which the plant is shut down directly impacts its performance upon restart. Ceccarelli et al. (2014) model two generation/capture plant shutdown cases, one of which is implemented in this work. Liquid and gas flow rates are ramped down simultaneously, maintaining a constant L/G flow ratio over the course of the shutdown operation until both reach 30% of baseload. Gas flow continues to ramp down to zero, while liquid flow is maintained at 30% to make use of the plant’s cooling duty, resulting in a cooler solvent and promoting CO2 absorption upon startup. There is, however, some trade-off in implementing this strategy, as the continued circulation causes lean and rich solvent loadings to converge due to mixing effects. This may affect CO2 absorption performance when the plant is restarted.


Gas turbine startup

Plant startup is simulated to follow a shutdown event in which the flow of solvent has been maintained at 30% of baseload, causing solvent temperature to be reduced to <35 °C, and lean and rich loading to begin to converge due to mixing. Before the startup sequence is initiated, liquid flow rate is stabilised at 30% of baseload flow rate. Ramp rates for the startup operation are based on an NGCC plant using a state-of-the-art SIEMENS STG5-4000F gas turbine (Eisfeld and Feldmüller, 2013), as with the gas-turbine shutdown scenario, and are provided in Section 5.2. Liquid flow rate is ramped proportionally to that of the gas, maintaining a constant L/G flow ratio.

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