Process efficiency and syngas quality from autothermal operation of a 1 MWth chemical looping gasifier with biogenic residues

Abstract

Chemical looping gasification is a novel dual fluidized bed technology for the conversion of solid feedstock to a nitrogen-free syngas without the need of pure oxygen. While multiple electrically heated lab-scale experiments have been performed, data on gas quality including tars formed during operation have not been reported yet for autothermal process operation. In this study we present autothermal operation of a chemical looping gasifier with a thermal input in the 1 MW_th range, utilizing two circulating fluidized bed reactors with foresting residue and industrial wood pellets as feedstock and Norwegian ilmenite as bed material. A cold gas efficiency of around 50 % was achieved in the non optimized pilot plant, indicating that higher values can be reached in a commercial unit when minimizing heat losses. The carbon conversion was around 90 %, and this value is expected to increase to almost 100 % when raising the temperature, residence time, and cyclone efficiency in a commercial unit. The syngas has a very high quality with methane concentrations in the range of 7 vol.-% to 10 vol.-% and gravimetric tar content below 1 g/Nm³ measured via tar protocol.