Utilization of Waste Heat from Solar Thermochemical Fuel Production for Point-Source Carbon Capture

Abstract

Point-source carbon capture is one of the key solutions for decarbonizing hard-to-abate sectors such as cement production. Under REDIII, captured CO2 from such sources qualify as a suitable feedstock for renewable fuels of non-biological origin (RFNBOs), opening the possibility for synergies between carbon capture facilities and green fuel production plants. Among the possible pathways for RFNBO production, solar thermochemical redox cycles are a promising alternative. The specific pathway in this work uses concentrated solar heat to reduce metal oxides monoliths (R2Mx technology), which react with water or CO2 to produce hydrogen or carbon monoxide. These intermediates can then be transformed into liquid fuels such as methanol or sustainable aviation fuel (SAF). As in other synthetic fuel production routes, solar thermochemical redox cycles generate a significant amount of waste heat, which could potentially be integrated into other heat-demanding processes such as carbon capture. As of today, the most mature technology for capturing CO2 from medium- and large-scale industrial units is amine gas scrubbing. In this process, flue gases are treated in an absorber, where the lean amine solution captures the majority of the incoming CO2. The enriched amine solution is then fed into the regenerator, where CO2 is stripped out, and the now depleted solution can be recirculated back to the absorber. This desorption step is the main energy consumer, demanding approximately 2.9 GJ per ton of CO2 captured at 140 °C, usually supplied as medium pressure steam. Direct waste heat integration between carbon capture and a solar thermochemical redox cycle is challenging because most of the waste heat is available during sunlight hours, whereas state-of-the-art carbon capture requires continuous operation. This work identifies several technical solutions to bridge the temporal gap between heat production and heat demand and evaluates which one is most suitable from an operational and economic perspective. These strategies are then compared against a baseline in which nighttime heat demand of the carbon capture plant is covered by a concentrated solar thermal (CST) facility with heat storage.