Alkali Emission from Birchwood Particles during Rapid Pyrolysis

Abstract

The emission of potassium- and sodium-containing compounds during rapid birchwood pyrolysis was studied. Birchwood particles (2−130 mg) were inserted into a preheated furnace at constant temperature (350−850 °C) and the alkali emission was measured. Particle mass, furnace temperature, and moisture were varied. At temperatures ≤ 500 °C, the alkali emission from birchwood particles took place solely during the pyrolysis phase. At temperatures ≥ 600 °C, alkali evaporation from the ash increased. The total alkali release increased with temperature in the range studied and the release during the pyrolysis was larger or equal to the release from the ash phase. Small particles (2−10 mg) emitted more alkali per unit mass than large ones (60−130 mg) and this tendency increased with temperature. At 800 °C the emission per unit mass from small particles was 10 times the one for large particles. Wet particles went through a drying phase, which delays the heating, and thereby the alkali emission. The present findings are of importance for actions aimed at minimizing alkali related problems during large-scale biomass conversion.

Mild pyrolysis of fast-growing wood species (Caribbean pine and Rose gum): Dimensional changes predicted by the global mass loss

“…Among other alterations, it is well known that this process induces dimensional changes (shrinkage), but the majority of studies just measured sample dimensions before and after the heat process. Indeed, works that monitored dimensional changes during the process were focused on charcoal production, thus applying temperature levels higher than 300 C. For example, Davidsson and Pettersson [19] monitored through a video camera the size changes of birch wood during rapid pyrolysis (350e900 C, time < 1400 s). Yet, due to the magnitude (up to several times the hygroscopic shrinkage) these dimensional changes have significant impacts, either during the process itself (stress field in large particles, change in thick bed height, change in bed porosity, change in characteristic diffusion time) or to the final product (density, checks, mechanical resistance).…”

Particulate emission from the gasification and pyrolysis of biomass: Concentration, size distributions, respiratory deposition-based control measure evaluation

“…Trace metals emission and size distribution of PM generated from biomass gasification were reported in several studies (Min et al, 2016;Nzihou and Stanmore, 2013;Pudasainee et al, 2014). The emission of potassium-and sodium-containing compounds during rapid birchwood pyrolysis was also studied (Davidsson et al, 2002). The results showed that the alkali emission per unit mass for small particles was higher than that for large ones and this tendency increased with temperature.…”

Toxic and nontoxic elemental enrichment in biochar at different production temperatures

“…Some studies have suggested that the reason for the lower enrichment of NTEs at HPT is as a result of cation exchange reactions, Chen et al (2014) suggested that at HPTs, the NTEs such as K, Ca and Mg, are released and the exchange sites are taken over by other cations. On the other hand, compared to HPT, NTEs exhibited the maximum mass loss at LPT 400 C for pyrolyzed wood biomass (Davidsson et al, 2002). The authors suggested that at this temperature, the greatest metal enrichment occurs.…”

“…Similarly, metal release in the ash fraction is accomplished at temperatures above 600 C (Davidsson et al, 2002). According to Davidsson et al (2002) between 400 and 500 C, the NTEs released from biochar corresponds to the mass loss characteristics thereby indicating that the metals are bonded to the C atoms in the biomass. However, at 600 C, the metal release becomes considerable following the termination of mass loss.…”