Experimental investigation of heavy metal release in entrained-flow biomass gasification

Entrained-flow gasification (EFG) of heavy-metal contaminated biomass from phytoremediation sites into biofuels via Biomass-to-Liquid (BtL) processes combines the two targets of recovering contaminated land for agricultural use and producing clean and sustainable biofuels with little risk of indirect land use change (ILUC). However, research on the fate of heavy metals during industrially relevant EFG of biomass is limited. In this study, methods to measure and predict the release of heavy metals during gasification were investigated and validated with experimental gasification results. For this purpose, an electrothermal vaporization coupled with inductively coupled plasma optical emission spectrometry (ETV-ICP-OES) unit was applied to measure the phase transition behavior of heavy metals (Cd, Cr, Ni, Pb, Zn) during biomass gasification fast and reliably. Pyrolysis and EFG experiments were conducted to validate these measurements. These findings were complemented by thermodynamic modeling using FactSage, demonstrating good agreement with experimental data at elevated temperatures, while lower release temperatures were predicted for volatile elements. Experimental and simulation results revealed that Cd, Pb, and Zn show volatile behavior and are entirely volatilized during entrained-flow gasification. The other heavy metals are rather non-volatile and are only partly released during gasification. The study underscores the release behavior's dependency on gasification conditions and reactor design, emphasizing the need for further research to optimize process efficiency and environmental safety.