Low-pressure calcination to enhance the calcium looping process for thermochemical energy storage

Abstract

The Calcium-Looping (CaL) process based on the multicyclic calcination-carbonation of CaCO3/CaO is at the root of a promising Thermochemical Energy Storage (TCES) technology to be integrated in high temperature solar thermal plants. As a novelty, this work proposes a CaL integration that considers low-pressure calcination under pure CO2 at a reduced temperature. Low-pressure calcination (0.01 bar) provides a suitable solution to mitigate CaO sintering and its consequent loss of reactivity in the carbonation stage. Since the temperature for quick calcination in a pure CO2 atmosphere is decreased (from around 950ºC at 1 bar to 765ºC at 0.01 bar), the energy losses at the receiver are minimized. In addition, a reduced calcination temperature allows using metallic receivers already tested at the MW scale, which notably increases the CSP-CaL integration reliability. Moreover, the multicycle CaO reactivity in short residence times is promoted, which allows using a simpler reactor design. The proposed plant proposes a smooth integration of the CaL process in CSP plants, with a moderate storage level and supported by a natural gas back-up system (solar share higher than 50%). Results show that the solar thermal-to electric efficiency is above 30%.