Quantification of trace element emissions from low-carbon emission energy sources: (I) Ca-looping cycle for post-combustion CO2 capture and (II) fixed bed, air blown down-draft gasifier

Abstract

The integrated technologies of gasification and the calcium looping cycle represent the opportunity to produce H2 as an energy carrier while ensuring inherent CO2 capture, thus producing a near-zero or negative emission fuel. Gasification of waste-derived fuel including demolition wood and low density plastic is gaining in interest due to the potential to minimise waste to landfill, whilst also representing a carbon-neutral energy source. However, potential trace element emissions from the gasification of such fuels require investigation to ensure compliance with targets under the EU Ambient Air Quality Directive 2008 and the UK Air Quality Standards Regulations 2010. Likewise, contaminants present in limestone have the potential to be released to the environment under the operating regimes required for carbonation and calcination in the calcium looping cycle for CO2 capture. Solid samples (offline), liquids (offline) and gaseous (offline/online and in-situ mobile ICP-OES) products from a pilot scale fixed bed, air-blown down-draft gasifier and from a pilot scale CO2 capture reactor comprising of the calcium looping cycle, have been collected and analysed in order to gain further understanding of the likely trace element partitioning in both processes. Results showed that a number of trace element contaminants present in the original CO2 sorbent and gasifier fuel samples were also present in the flue gas from both the CO2 capture and gasification processes, implying that integration of the technologies may result in enhanced contamination in the final gaseous product. The main outputs of this study assist in analysing plant requirements, for example gas cleaning, and identifying the environmental emissions and residual disposal.