1 Introduction

The main objective of this Section F is to assess the operating flexibility of NGCC power plants, with post-combustion capture of the CO2 from the HRSG flue gases.

The considerations shown in this section are based on the assumption that these plant types will be requested to operate in the mid and peak merit market in order to meet recent power market requirements and generally following a weekly demand curve as shown in Figure 1-1.

Figure 1-1: NGCC plant load operation

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From the above graph, it can be drawn that the NGCC plants will be maintained at base load for 80 hours per week, while being shutdown during the remaining 88 hours.

The capability of these plant types for a flexible operation is mainly affected by the constraints related to CO2 capture and compression units, as well as the transportation pipeline. To investigate these main features, the following cases are presented in this section:

Case 1a: This case assesses the constraints given by the CO2 capture unit in a conventional NGCC plant, mainly in relation to their frequent start-ups/shut-downs and rapid load change requirements.
Case 1b: This case considers the rich solvent storage, in order to minimize the plant power consumption and increase the overall power production during peak load demand period.
Case 1c: This case makes an assessment of capturing the CO2 from the flue gases of an aero-derivative gas turbine, coupled with a once through steam generator, generally used to cover peak grid demand.
Case 1d: This case assesses the introduction in the power plant of a CO2 storage system, which allows to maintain a constant CO2 flowrate in the pipeline, despite the cycling operation of the plant, thus avoiding a two-phase flow or a significant change of the physical properties.
Case 1e: This case evaluates the possibility of tuning ON/OFF the CO2 capture in the plant, depending on the possible CO2 allowance cost fluctuations.

In addition, the following case has been investigated using an alternative weekly demand curve, based on the assumption that the plant will need to provide two hours of peak operation per each working day, while it is shutdown during night and weekend (off-peak):

Case 1f: This case considers the rich solvent storage during peak demand mode, in order to minimize the plant power consumption and increase the overall power production. In fact, regeneration is shut down for the two hours of peak demand during the day and the stored rich solvent is regenerated during the rest of the daytime, thus leading to an oversize of the regenerator.