Piloting of bio-CLC for BECCS

A new 10-50 kWth scale dual fluidized bed (DFB) chemical looping combustion (CLC) process development unit (PDU) applicable for biomass was constructed during 2015-16, located in VTT's new piloting center Bioruukki in Finland. The DFB-CLC test rig consists of a circulating fluidized bed (CFB) air reactor interconnected with a bubbling fluidized bed (BFB) fuel reactor. A set of tests were carried out with ilmenite as oxygen carrier, using white and black wood pellets as fuels. The main targets were to study main operational and process parameters for CLC using biomass-based fuels with a high volatile content. Another interest was to assess the risk for high-temperature corrosion in the flue gas path of the air reactor to evaluate the possibility for improving power generation efficiency by using enhanced steam values. The DFB-PDU was operated with biofuel in total for 16 h for 9 tests. The main challenge encountered was an insufficient bed temperature of the fuel reactor (900-950ºC targeted, 840-860ºC achieved) causing a relatively high oxygen demand (29-41%). The main reason for this was that the DFB-PDU was originally designed for gasification. A clear dependency of the fluidization velocity on the CO2 capture efficiency and oxygen demand was found and explained. As the fuel is fed and gasified in the fuel reactor, fuel leakage to the air reactor was low and alkaline components were not accumulated to the surface of oxygen carrier particles, it can be concluded that concentrations of vaporized alkali chlorides components in air reactor flue gas are much lower than in conventional biomass combustion applications. The results indicate that the risk of high-temperature corrosion of superheater tubes is lower in bio-CLC than conventional biomass combustion, making it possible to to use higher steam values (temperature, pressure) in bio-CLC improving the power generation efficiency from biomass.