On the use of electrolytic hydrogen from variable renewable energies for the enhanced conversion of biomass to fuels

Abstract

Biomass is a promising CO 2-neutral carbon source for fuel products, but it is deficient in hydrogen for that purpose. On the other hand, hydrogen is the fuel that is most readily made from renewable power (wind, wave, solar, etc.) by the electrolysis of water, but it is also a challenge to store, transport or distribute. By augmenting biofuel synthesis gas with hydrogen from electrolysis, we can design processes that will enhance both the ability to derive liquid fuels from renewable electricity, and also the ability to convert biomass to fuels efficiently. In this paper, we discuss the example of methanol synthesis from woodchips to illustrate the potential of this approach; and we present mass and energy balances in the cases of gasification by oxygen. In the combined gasification plus electrolysis (GPE) process, the avoidance of a shift step and of CO 2 elimination can contribute to more effective utilisation of the biomass, increasing conversion to methanol by up to 130%. Since land availability and the competition with food (or animal feed) crops are factors that could severely limit the contribution of biofuels to a low-carbon economy, this type of process is of particular interest. We take into account the need to operate the process over a large turn-down ratio, due to the variable power input from renewable sources. This is of particular importance when selecting the type of methanol synthesis reactor as well as the gasifier. Finally we present an economic study for the process, complemented by a sensitivity analysis.