Gasification reactor engineering approach to understanding the formation of biochar properties

Abstract

The correlation between thermochemical provenance and biochar functionality is poorly understood. To this end, operational reactor temperatures (spanning the reduction zone), pressure and product gas composition measurements were obtained from a downdraft gasifier and compared against elemental composition, surface morphology and polyaromatic hydrocarbon content (PAH) of the char produced. Pine feedstock moisture with values of 7% and 17% was the experimental variable. Moderately high steady-state temperatures were observed inside the reactor, with a ca 50°C difference in how the gasifier operated between the two feedstock types. Both chars exhibited surface properties comparable to activated carbon, but the relatively small differences in temperature caused significant variations in biochar surface area and morphology: micropore area 584 against 360 m2 g−1, and micropore volume 0.287 against 0.172 cm3 g−1. Differences in char extractable PAH content were also observed, with higher concentrations (187 µg g−1 ± 18 compared with 89 ± 19 µg g−1 Σ16EPA PAH) when the gasifier was operated with higher moisture content feedstock. It is recommended that greater detail on operational conditions during biochar production should be incorporated to future biochar characterization research as a consequence of these results.

Integration of Hydrothermal Carbonisation with Anaerobic Digestion; Opportunities for Valorisation of Digestate

“…Pilot scale investigations of low temperature gasification of anaerobically digested materials also produce solids with high nutrient content [29,30] which have better energy recoveries. However the char is also enriched with high levels of ash [31] and potentially contain enriched levels of contaminants, including polycyclic aromatic hydrocarbons (PAH), making its application challenging, especially with feedstocks with high moisture content [32].…”

A critical review on sustainable biochar system through gasification: Energy and environmental applications

“…The physical properties may 102 affect the chemical properties of gasification biochar. For example, larger surface area and 103 micropore volume have been found to be correlated with higher total polycyclic aromatic 104 hydrocarbons (PAHs) on biochar surface (Rollinson, 2016). Alkali and alkaline earth metallic 105 (AAEM) species (e.g., K, Na, Ca, Fe, and Mg) are commonly observed in biomass.…”

Towards practical application of gasification: a critical review from syngas and biochar perspectives

“…Naphthalene accounted for approximately 40 -60 wt. % of the PAHs on gasification biochar and it was the dominant PAH component among the 16 priority PAHs (Rollinson, 2016).…”

“…larger specific surface area, 67% larger micropore volume, and 62% larger micropore area than that from the feedstock with the moisture of 17 wt. % (Rollinson, 2016). Furthermore, the biochar from the lower moisture pine wood contained a higher concentration (187 µg g -1 ) of 16 priority polycyclic aromatic hydrocarbons (PAHs) than that (89 µg g -1 ) from the higher moisture pine wood.…”

“…Wang et al (2016) found that the reaction rate of CO2 gasification of biomass chars increased from 0.0186 -0.036 min -1 to 0.1104 -0.3486 min -1 as the temperature increased from 850 to 1000 o C at atmospheric pressure. Rollinson (2016) found that a higher moisture content in pine wood decreased the CO content but increased the CO2 content in the product gas, because the higher moisture content lowered the temperature of the reduction zone via the evaporation of H2O that favored the exothermic water gas shift (WGS) reaction (Eq. (6)) and suppressed the endothermic reactions (Eq.…”