Impurity balance during 80 kWth pilot plant operation with bark and necessary gas cleaning steps

Chemical looping combustion (CLC) of biogenic fuels offers significant potential for achieving negative CO2 emissions by capturing CO2 during energy production. However, ensuring high purity of captured CO2 for compression, transport, and storage applications poses challenges, particularly due to potential impurities in biomass such as ash, phosphorus (P), sulfur (S), nitrogen (N), and chlorine (Cl). The distribution of these impurities among transport to the air reactor, binding to cyclone ash, or conversion to the gas phase, as well as their impact on reaction pathways, remains largely uncertain, varying greatly depending on the reactor system, fuel used, and oxygen carrier employed. This study focused on establishing impurity balances during pilot plant operation (80 kWth) using a synthetic manganese-iron-copper oxygen carrier with bark as fuel. Through detailed analysis of gas components in the fuel reactor (FR) exhaust gas, as well as examination of bed material after the FR and the FR cyclone, nitrogen and sulfur mass balances were determined. Approximately 90 wt% of the fuel's nitrogen was converted to gaseous N2, with the remainder mainly transported with the bed material to the air reactor (AR). Concentrations of unwanted nitrogen compounds such as NH3, NO, and N2O were each below 1 wt% of the fuel's nitrogen. The SO2 concentration of the gas was low due to separation during gas analysis via water condensation and washing with rapeseeds methyl ester. A discussion of possible gas cleaning routes to meet storage requirements is based on the measured impurity levels.