Flame curtain kilns produce biochar from dry biomass with minimal methane emissions

Gerard Cornelissen; Erlend Sørmo; Ruy Korscha Anaya de la Rosa; Brenton Ladd

doi:10.1016/j.scitotenv.2023.166547

Flame curtain kilns produce biochar from dry biomass with minimal methane emissions

Sci Total Environ. 2023 Dec 10:903:166547. doi: 10.1016/j.scitotenv.2023.166547. Epub 2023 Aug 26.

Authors

Gerard Cornelissen¹, Erlend Sørmo², Ruy Korscha Anaya de la Rosa³, Brenton Ladd⁴

Affiliations

¹ Norwegian Geotechnical Institute (NGI), Oslo, Norway; Faculty of Environmental Sciences and Natural Resources (MINA), University of Life Sciences (NMBU), Ås, Norway. Electronic address: gco@ngi.no.
² Norwegian Geotechnical Institute (NGI), Oslo, Norway; Faculty of Environmental Sciences and Natural Resources (MINA), University of Life Sciences (NMBU), Ås, Norway.
³ Biocare, Sydney, NSW 2000, Australia.
⁴ Universidad Cientifica del Sur (UCSUR), Lima, Peru. Electronic address: bladd@cientifica.edu.pe.

PMID: 37640066
DOI: 10.1016/j.scitotenv.2023.166547

Abstract

Flame curtain kilns have emerged as the preferred biochar technology for smallholders but reported methane emissions (30 g kg^-1 biochar) have impeded carbon certification. Here, for flame curtain kilns we show almost no methane (0-3.6 g kg^-1 biochar) emissions for dry (<15 % moisture) feedstock consisting of twigs and leaves. Wet feedstock (>40 % moisture) however generated significant methane (>500 g kg^-1 biochar), underscoring that feedstock preparation is decisive for the carbon balance. Even for dry feedstock, both aerosol and CO emissions were significant (21-82 and 40-118 g kg^-1 biochar, respectively). The data demonstrate that certification of low-tech biochar made from dry twigs and leaves should not be objected to on the grounds of methane. Careful selection of feedstock and potential after-combustion of the syn-gases are probably needed to avoid CO and aerosol emissions. More data are needed on methane emissions of other dry feedstocks.