Ash deposition characteristics during oxy-fuel combustion of biomass in a drop tube furnace

The combination of biomass and oxy-fuel combustion technology integrates the advantages of biomass combustion and carbon capture and storage (CCS) technology. Because of its ability to achieve negative carbon emissions, it is widely considered one of the key technologies for eliminating atmospheric emissions and helping to achieve long-term decarbonization. However, problems such as ash deposition, slagging, and corrosion in combustion caused by a large amount of alkali metals in the biomass have limited the development of the technology. In this paper, an air-cooled steel probe in a drop tube furnace (DTF) was used as the simulation of heat transfer surface of biomass boilers to collect the deposits during biomass oxy-fuel combustion for analysis. Microscopic morphology and elements content of inner and outer layer of deposits were analyzed separately. K content and composition of the deposits were also analyzed. The effects of fuel particle size, combustion temperature, combustion atmosphere, and probe surface temperature on ash deposition were investigated. The results showed that the use of coarse-grained fuels produced a more complete inner layer of KCl, while fine-grained fuels significantly increased the mass of deposits. Combustion temperatures below 800 & DEG;C could reduce K content and ash deposition rate. Oxy-fuel combustion promoted sulphuration reactions compared to air combustion. Higher oxygen fraction increased the weight of deposits but reduced the K content. Probe surface temperature had a signification effect on the distribution of ash on the probe surface.

Automated summary

The combination of biomass and oxy-fuel combustion technology is regarded as a key technology for eliminating atmospheric emissions and achieving long-term decarbonization. However, problems such as ash deposition and corrosion caused by alkali metals in biomass have hindered its development. This study analyzed the deposits during biomass oxy-fuel combustion to understand the effects of different factors on ash deposition. It was found that coarse-grained fuels produced more complete inner layer of deposits, while fine-grained fuels increased the mass of deposits. Combustion temperatures below 800°C and higher oxygen fraction showed positive effects on reducing ash deposition.