Ambitious renewable energy targets in European countries drive an increasing biomass demand to a point where domestic resources are insufficient, leading to emergence of international bioenergy supply chains. This work aims to examine the feasibility of biomass torrefaction downstream in long-distance international bioenergy supply chains for co-firing and to investigate the effect of various biomass co-firing ratios on the whole supply and energy conversion system performance from a technical, environmental and economic aspect. A techno-economic analysis together with a CO2 emissions assessment is performed, adopting a whole systems approach. In particular, Palm Kernel Shell biomass from Malaysia is considered for co-firing in UK. Findings indicate that downstream torrefaction is profitable under the current conditions for 100% biomass and marginally unprofitable for 50% biomass co-firing. The financial yield exhibits high sensitivity on the price of coal, biomass, Renewable Obligation Certificates, the torrefaction facility investment and biomass sea transportation costs. From an environmental perspective, higher co-firing ratios lead to higher emissions per unit of renewable energy generated. The findings can support policy makers and investors in adopting lower biomass co-firing, ratios with torrefaction instead of 100% biomass conversion, leading to improved environmental benefits from a whole system's perspective. (C) 2016 Elsevier Ltd. All rights reserved.