Dual fluidized bed gasification configurations for carbon recovery from biomass

Abstract

Techniques that produce chemicals and fuels from sustainable carbon sources will have to maximize the carbon recovery to support circularity. In dual fluidized bed (DFB) gasification, to facilitate carbon recovery, the CO2 from the flue gas can be concentrated using pure oxygen as an oxidant. The heat required by the process can also be provided electrically or by oxidizing an oxygen-carrying bed material, rather than combusting part of the char, thereby concentrating all of the carbon in the syngas. In this work, the three configurations of oxyfuel, electrical, and chemical-looping gasification (CLG) are compared to each other, as well as to the standard or “air” configuration, which corresponds to the combustion of char with air and the separation of CO2 from both the flue gas and syngas. The configurations are compared based on their carbon distributions and energy demands for CO2 separation. We show that the air and oxyfuel configurations lead to similar carbon distributions, whereas the CLG configuration gives the lowest carbon recovery in the form of an end product. The oxyfuel and CLG configurations show the lowest energy demands for CO2 separation, while the air configuration exhibits the highest. The electrical configuration has the lowest potential to benefit from heat integration to cover this energy demand. An investigation into the optimal gasification temperature for the air and oxyfuel configurations shows that there is no driver for operation at high temperatures.