Costs of biomass pyrolysis as a negative emission technology: A case study

Biomass pyrolysis is a promising method for the creation of biochar, a potentially long-lived carbon sink, and renewable fuels. While a number of studies of the costs of pyrolysis exist, many fail to value the carbon storage benefit associated with biochar. Here, we evaluate the costs of three types of small-scale pyrolysis systems (slow and fast, compared with gasification) in Costa Rica. We find that under many combinations of model parameters, fast and slow pyrolysis models are cost-effective. Net present values are positive for slow pyrolysis at carbon prices above $7 t(-1), indicating that a low carbon price is required to make slow pyrolysis cost-effective. Likewise, fast pyrolysis is cost-effective at any positive carbon price. Gasification is generally more costly than fast or slow pyrolysis, and the net present value of the gasification system is only positive at electricity prices over $0.15 kWh(-1) or carbon prices over $150 t(-1). Thus, both fast and slow pyrolysis models are promising methods for atmospheric CO2 reduction.