Improving carbon efficiency and profitability of the biomass to liquid process with hydrogen from renewable power

TLDR

The study compares a power‑and‑biomass‑to‑liquid (PBtL) process that integrates renewable hydrogen production with a conventional biomass‑to‑liquid (BtL) concept. PBtL uses solid‑oxide electrolysis cells (SOEC) powered by electrical energy to split water/steam at ~850 °C, producing hydrogen that replaces part of the heat requirement and reduces the electrical energy needed to 9.5 kWh per liter of syncrude, as evaluated in a techno‑economic analysis. Adding renewable hydrogen raises the carbon efficiency of BtL from 38 % to over 90 %, increases fuel output 2.4‑fold, cuts the levelized cost to 1.7 $/l (≈30 % lower), and demonstrates that excess renewable power can be stored as high‑energy‑density biofuel.

Abstract

A process where power and biomass are converted to Fischer-Tropsch liquid fuels (PBtL) is compared to a conventional Biomass-to-Liquid (BtL) process concept. Based on detailed process models, it is demonstrated that the carbon efficiency of a conventional Biomass to Liquid process can be increased from 38 to more than 90% by adding hydrogen from renewable energy sources. This means that the amount of fuel can be increased by a factor of 2.4 with the same amount of biomass. Electrical power is applied to split water/steam at high temperature over solid oxide electrolysis cells (SOEC). This technology is selected because part of the required energy can be replaced by available heat. The required electrical power for the extra production is estimated to be 11.6 kWh per liter syncrude (C5+). By operating the SOEC iso-thermally close to 850 °C the electric energy may be reduced to 9.5 kWh per liter, which is close to the energy density of jet fuel. A techno-economic analysis is performed where the total investments and operating costs are compared for the BtL and PBtL. With an electrical power price of 0.05 $/kWh and with SOEC investment cost of the 1000 $/kW(el), the levelized cost of producing advanced biofuel with the PBtL concept is 1.7 $/liter, which is approximately 30% lower than for the conventional BtL. Converting excess renewable electric power to advanced biofuel in a PBtL plant is a sensible way of storing energy as a fuel with a relatively high energy density.