Trace metals emission in syngas from biomass gasification

• Trace metals in feedstocks and emission concentration in syngas were measured.
• Increased volatility of trace metals in syngas was observed.
• Mercury in syngas was speciated mainly into elemental form.
• Fly ash influenced the distribution behavior, mainly of As, Be and Pb.

In this paper, trace metals (As, Be, Cd, Cr, Hg Ni, Pb, Se and V) emission from the atmospheric entrained flow gasifier REGA at Karlsruhe Institute of Technology, Germany is presented. Elemental composition and metals concentration in glycol (model fuel) and straw char samples were determined. In order to achieve well defined and reproducible operating conditions, gasification experiments were carried out with glycol and slurry (straw char mixed with glycol) as fuel. Trace metals emission and distribution into particle and gas phase in syngas from gasification were measured according to US EPA method 29. During glycol gasification, metals concentration in syngas ranged from 0.1 μg/Nm3 (V) to 4.6 μg/Nm3 (Cr). In slurry gasification, metals concentration in syngas ranged from 2.4 μg/Nm3 (Hg) to 53.2 μg/Nm3 (Ni). Trace metals tend to volatilize more in reducing gasification environment. Tendency of metals to speciate into particle phase increased in slurry gasification than glycol gasification due to increased in particle concentration and unburned carbon content in syngas. The increase of particle and carbon content in syngas possessed strong influence in distribution behavior of As, Be and Pb, however, such influence was less for other metals studied. Mercury in syngas was speciated predominantly into elemental form followed by oxidized form whereas share of particle bond mercury was the least.