1 Introduction

The main objective of this Section H is to assess the operating flexibility of USC-PC power plants, with post-combustion capture of the CO2 from the boiler 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 merit market, thus participating to the first step of the variable electricity and generally following a weekly demand curve as shown in Figure 1-1.

Figure 1-1: USC-PC plant load operation

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From the above graph, it can be drawn that the USC-PC plants will be maintained at base load for 80 hours per week, while 50% of their overall net power production capacity shall be generated 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 3a: This case assesses the constraints given by the CO2 capture unit in relation to the start-ups/shut-downs and rapid load change requirements of conventional PC-based power plants.
Case 3b: 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 3c: 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 3d: 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 turned down to 50% output during night and weekend (off-peak):

Case 3e: 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. Therefore, regeneration is shut down for two hours of “peak” demand during the day and the stored rich solvent is regenerated overnight, during off-peak demand.