Syngas production via Biomass Chemical Looping Gasification (BCLG) in a 50 kWth unit using ilmenite as oxygen carrier

Biomass Chemical Looping Gasification (BCLG) is an innovative process that uses lattice oxygen from a solid oxygen carrier to produce high-quality synthesis gas without CO2 emissions. It is well known that one of the main targets for the reduction of greenhouse gas emissions (GHG) is to replace the use of fossil fuels in the transport sector with renewable sources. In this work, the BCLG technology is used to obtain clean synthesis gas from biomass for the production of liquid biofuels through Fischer Tropsch (FT) synthesis. The BCLG process is based on the circulation of a solid oxygen carrier between two interconnected fluidized bed reactors, the fuel and air reactors, providing the oxygen needed for the partial oxidation of the biomass to generate a non-nitrogen diluted syngas with low tar content. Also, the oxygen carrier is responsible for transporting the heat required for the endothermic reactions occurring in the fuel reactor from the heat generated in the exothermic reactions occurring in the air reactor, thus reaching autothermal conditions. In addition, negative emissions could be achieved by combining this technology with CO2 storage since biomass is a carbon-neutral fuel. The experimental campaign of this work was carried out in a BCLG unit at 18 kWth power during 60 hours of continuous operation with ilmenite as oxygen carrier and wheat straw pellets as fuel. The main factors affecting the syngas production was the oxygen-to-biomass ratio and char conversion. Increasing temperature showed a considerable effect on the char conversion in the fuel reactor since caused an increase in the gasification rate; also, the char conversion was affected by the mean residence time in the fuel reactor. The existing carbon stripper in the CLG unit did not show the ability to separate the unconverted char entrained from the fuel reactor since char still retained its initial pellet form. However, carbon stripper behaves as a secondary gasifier when using steam as fluidi