Behavior of Heavy Metals in Steam Fluidized Bed Gasification of Contaminated Biomass

Heavy metal phytoextraction by growing energy crops such as flax could be a promising approach for remediation of brownfields with energy benefits. The present paper deals with flax (40 wt %) and hardwood (60 wt %) cogasification with particular focus on the distribution of heavy metals to both solid and gaseous gasification products. The blended fuel was gasified by steam in a fluidized bed gasifier at about 850 °C and steam to biomass ratio of 1.01 kg kg^–1. Concentrations of selected heavy metals (Cd, Cu, Ni, Pb, and Zn) were determined in bed ash, cyclone ash, and in downstream producer gas. From the analysis, it follows that under the given experimental conditions the subsequent order of heavy metals volatility can be found: Cd (mostly in producer gas) > Pb > Zn > Cu > Ni. Heavy metals concentrations in the producer gas (nitrogen free, dry gas) were determined in the range of 0.37–4.2 mg m^–3

Fluidized Bed Incineration of Sewage Sludge in O₂/N₂ and O₂/CO₂ Atmospheres

Sewage sludge incineration in a fluidized bed is considered to be one of the most suitable ways of sewage sludge disposal. This process reduces the volume of the waste and causes the destruction of organic contaminants such as POPs, pharmaceuticals, and other compounds with endocrine-disrupting potential. Oxygen-enriched air combustion and oxy–fuel combustion can increase the combustion efficiency, reduce the amount of flue gas, and make possible CO₂ capture more effective. However, the influence of incineration medium composition has not yet been thoroughly investigated in the case of sewage sludge incineration. In this paper, the incineration of sewage sludge in a bubbling fluidized bed reactor was studied at oxygen-enriched air conditions, oxy–fuel conditions, and oxy–fuel conditions with zero and nonzero concentrations of steam, CO, NO, N₂O, and SO₂ in the inlet combustion medium. Consequently, the effects of various operating parameters on pollutants formation were comprehensively described with emphasis on aforementioned sewage sludge incineration processes. An increase in combustion temperature resulted in an increase in NO_<i>x</i> and SO₂ emissions and in a decrease in N₂O emissions. Increase in inlet oxygen concentration led to a decrease in NO_<i>x</i> and N₂O emissions. N₂O and SO₂ emissions were higher in CO₂-rich atmosphere (oxy–fuel combustion conditions). The presence of water vapor in the inlet combustion medium resulted mainly in the reduction of NO_<i>x</i> emissions. The presence of CO, NO, N₂O, and SO₂ in the dry inlet combustion medium reduced mainly overall nitrogen-to-NO_<i>x</i> conversion, while the effect on SO₂ removal efficiency was only marginal