The migration, transformation and control of trace metals during the gasification of rice straw.

This research investigates the trace metals speciation, partitioning and removal in rice straw gasification equipped with an integrated hot gas cleaning (HGC) system. The experiments were conducted by fluidized bed gasifier and controlled at 800 °C with equivalence ratio (ER) varied between 0.2 and 0.4. The experimental results indicated that the concerned trace metals Zn, Cr, Cd, and Pb partitioning in the gas phase were increased significantly with an increase in ER. This is because the exothermic reaction could enhance the trace metals reacted with chlorine and/or sulfur as well as correspondingly formed highly volatile metals compounds. However, other tested metals Cu, Na, K, Ca, Mg partitioning was obviously decreased in the gas phase with ER increasing. These tested metals tend to form oxides speciation leading the variation in their partitioning characteristics. The XRD identification and thermodynamic equilibrium simulation results were also confirmed the tested metals speciation and partitioning characteristics. The dominant gaseous species produced from rice straw gasification, such as KCl (g) , NaCl (g) , KO (g) , K 2 O (g) , ZnCl 2(g) , CrO 2 Cl 2(g) , CuCl 2(g) , PbCl 2(g) , PbO (g) , and Cd (g) , were predicted by thermodynamic equilibrium model. The tested metals removal by adsorbents of hot gas cleaning system was found to be adsorbed in decreasing order as: K > Cr > Ca > Pb > Mg > Cd > Na > Zn > Cu. Activated carbon was used in hot gas cleaning system and showed a good performance for adsorbing tested metals, especially for Pb, Cd, Cr, Ca, K, and Mg. In summary, HGC system is proposed as an effective way for improving the syngas quality and reducing trace contaminants emission in rice straw gasification. • Concerned trace metal speciation and partitioning characteristic in rice straw gasification has been successfully developed. • The trace metals Zn, Cr, Cd, and Pb partitioning in the gas phase were increased with equivalence ratio increased. • The metals removal by the hot gas cleaning system was found in decreasing order as: K > Cr > Ca > Pb > Mg > Cd > Na > Zn > Cu. • Activated carbon showed a good performance for adsorbing Pb, Cd, Cr, Ca, K, and Mg. • The hot gas cleaning system could play a key role in removing concerned trace metals. [ABSTRACT FROM AUTHOR]