(681f) Increasing the Operating Range of an IGCC Plant with Carbon Capture through the Integration of a CaO-Based Thermal Storage System

Using pre-combustion CO₂-capture, IGCC plants show significant potential for efficient power generation with carbon capture. The gasification and gas processing steps however have multiple temperature and flow constraints which severely limit the flexibility of IGCC plants to meet the dynamic demands of the current grid [1]. To address this issue, the authors recently proposed a CaO-based energy storage system increasing the load range of a base IGCC plant by about ±20-25% with respect to its nominal output without the need to cycle the gasifier island and while maintaining its 90% CO₂-capture rate [2-3].

The storage system relies on the reversible decomposition of CaCO₃ into CaO and CO₂ (calcination) to store excess energy during  low electricity demand periods. This excess energy originates from the combustion of excess syngas produced in the gasifier and is stored chemically and thermally as hot CaO. During high demand periods, the stored energy can be recovered by recombining the CaO with CO₂ (carbonation) extracted from the IGCC plant. This recombination results in high grade reaction heat (at 650 °C) suited for steam and electricity production and hence results in a temporary increase of the IGCC power output. In this process, CO₂ is temporarily stored as CaCO_3, which allows to turndown the primary carbon capture system leading to a  reduction of the parasitic load of the primary carbon capture system and hence a further increase in the net output of the IGCC plant.

This presentation will give an overview of the proposed energy storage system and explore its integration into an IGCC plant equipped with CCS. Two different storage configurations are considered herein, using either an indirectly fired air-blown calciner or a directly fired oxygen-blown calciner. The system’s round-trip efficiency was found to vary between 60 and 70%, depending on the storage operating conditions and configuration [4]. The loss associated with the purge and replacement of the solid inventory required to maintain a sufficiently high CaO/CaCO₃-particle reactivity was found to be the dominant factor limiting the round-trip efficiency. The combustion of the syngas in the calciner instead of the combined cycle of the IGCC plant further results in increased heat losses as the efficiency of the Rankine steam cycle employed to convert the thermal energy in the calciner and carbonator into electric power is lower than the efficiency of the combined cycle. A high degree of internal heat recuperation minimizing the calciner syngas demand was therefore found to be essential to achieve a  high round-trip efficiency. Based on efficiency and storage size, the energy storage system was found to be competitive with other storage solutions proposed in the literature.

[1] IEAGHG, Operating Flexibility of Power Plants with CCS; June 2012

[2] Vandersickel, A., et al., Integration of a CaO-based energy and CO2 storage system in an IGCC plant with carbon capture, in ECOS 2013. 2013: Guilin, China

[3] Vandersickel, A., et al., A CaO-based energy and CO2 storage system for the flexibilization of an IGCC plant with carbon capture. sumitted to Industrial & Engineering Chemistry Research, 2014

[4] Vandersickel, A., et al., Integration of a CaO-based thermal storage szstem in an IGCC plant with carbon capture, submitted to IMECE 2014, Paper Nr. IMECE2014-38113