Oxy-combustion characteristics of torrefied biomass and blends under O-2/N-2, O-2/CO2 and O-2/CO2/H2O atmospheres

The combined use of bio-fuels along with CO2 capture techniques is the basis for the so-called negative emissions energy systems. In this paper, oxy-fuel combustion of two torrefied biomasses is experimentally investigated in a lab-scale entrained flow reactor. The torrefied biomasses are fired alone, and co-fired with coal (50%). Two oxygen concentrations (21% and 35%) and four steam concentrations are tested: 0% (dry recycle oxy-combustion), 10% (wet recycle oxy-combustion), 25% and 40% (towards the concept of oxy-steam combustion). The tests are designed to get the same mean residence time for all the fuels and conditions. Burnout degrees are significantly increased (up to 9 and 16 percentage points) when the share of torrefied biomass is raised, with a slightly better behavior of the torrefied pine in comparison to the torrefied agro-biomass. C-fuel conversion to CO2 follows a similar trend to the observed for the burnout degrees. NO formation rates are reduced when oxy-firing torrefied biomass alone in comparison to the blends, with maximum diminutions of 16.9% (torrefied pine) and 8.5% (torrefied agro-biomass). As regards the effect of steam, the best results are found for the 25% H2O atmospheres in most of the cases, yielding maximum conversions along with minimum NO levels.

Automated summary

The oxy-fuel combustion of two torrefied biomasses is experimentally investigated in this study. It is found that increasing the share of torrefied biomass leads to significantly higher burnout degrees and CO2 conversion rates. When torrefied biomass is used alone, the formation rates of NO are reduced. The best results are obtained with 25% H2O atmospheres in most cases.