Oxy-co-firing in fluidized beds: control of sulfur emissions and assessment of corrosion issues

Abstract

The main objective of this work is to experimentally analyse the effect of firing blends of coal and biomass in oxy-firing atmospheres on SO2 emissions and deposition/corrosion issues. The research has been conducted in a lab-scale fluidized bed unit, and chemical reactivity of deposited species has been simulated at bench scale. Two very different Spanish coals were selected for the oxy-combustion experiments: anthracite, with a very low volatile matter, and lignite with high sulphur content. As concerns the biomass, a short campaign was conducted with forest residues, but most effort was done firing corn stover (with three different chlorine levels). The experimental matrix was designed to analyse the effects of the following parameters: atmosphere (air vs. O2/CO2), coal-to-biomass ratio in the blend (90/10% vs. 80/20%) and bed temperature (850-900ºC). Control of SO2 emissions was largely dependent on the governing desulfurization mechanism, while chlorine in the biomass plays a role in the condensed alkali sulfates. No significant deposition rates were detected even for the higher biomass shares in the blend (20%). Only when corn stover with the highest chlorine content (2%) was fired, a thick deposition scale was found. For the original corn stover, oxy-firing barely affects the deposition rate and slightly reduces the corrosion risk in comparison to conventional air-firing.