Chemical-looping combustion (CLC) is an indirect combustion process that utilises a regenerable solid sorbent (oxygen carrier, OC), typically a metal oxide, to transfer oxygen from the combustion air to the fuel such that direct contact between air and fuel is avoided. CLC is a variant on an oxy-fuel carbon capture system that offers the potential for a much lower energy penalty as CO2 separation is achieved intrinsically such that additional energy-intensive gas separation steps are avoided. Our research focuses on the development and optimisation of low-cost, iron and copper -based OCs for use with natural gas or gasified solid fuels. A strong emphasis is placed on developing simple, scalable fabrication techniques (many based on wet granulation). The OC particles are subjected to rigorous testing using a range of analytical methods to assess their physical and chemical properties and suitability for use in large-scale systems. Here, we present findings from our investigations into the performance of some successful OCs with syngas and natural gas. Three different reactor systems have been employed to assess the different OC's potential for scale up including a thermogravimetric analyser (TGA) and two state-of-the-art lab-scale reactors designed and constructed at Imperial College: a 3 kWe pressurised fluidised bed reactor  and a 6 kWe, pressurised two-stage, fixed-bed reactor capable of simulating CLC with ex-situ gasification of solid fuels. The TGA was employed for rapid screening of different OC formulations, the fluidised bed reactor to evaluate mechanical stability of the particles, and the fixed bed reactor for investigating the impact of solid fuel derived contaminants (e.g. tars) on the process. The reduction kinetics for the different OCs (the rate limiting step in the CLC of gaseous fuels) have also been assessed over repeated cycling at high temperatures and pressures up to 1 MPa.

Investigating the performance of Fe- and Cu-based oxygen carriers for pressurised chemical-looping combustion of gaseous fuels

248th National Meeting (2014)

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