Flexible Power & Biomass-to-Methanol plants: Design optimization and economic viability of the electrolysis integration

This paper assesses the optimal design criteria of a flexible power and biomass to methanol (PBtM) plant, conceived to operate both without green hydrogen addition (baseline mode) and with hydrogen addition (enhanced mode), following an intermittent use of the electrolysis system, which is turned on when the electricity price allows an economically viable hydrogen production. The assessed plant includes a gasification section, syngas cleaning and compression, methanol synthesis and purification and heat recovery steam cycle, to be flexibly operated. A sorption-enhanced gasification technology allows to produce a tailored syngas for the downstream synthesis in both the baseline and enhanced operating conditions, by controlling the in-situ CO2 separation rate. Two designs are assessed for the methanol synthesis unit, with two different reactor sizes: (i) a larger reactor, designed on the enhanced operation mode (enhanced reactor design – ERD) and (ii) a smaller reactor, designed on the baseline operation mode (baseline reactor design – BRD). The ERD design resulted to be preferable from the techno economic perspectives, resulting in 20% lower cost of the e-MeOH (30.80 vs. 37.76 €/GJLHV) with the baseline assumptions (i.e. 80% of electrolyzer capacity factor and 2019 Denmark day-ahead market electricity price). Other important outcomes are: (i) high electrolysis capacity factor is needed to obtain competitive cost of e-MeOH and (ii) advantages of flexibly operated PBtM plants with respect to inflexible PBtM plants are significant in scenarios with high penetration of intermittent renewables, leading to low average prices of electricity but also longer periods of high peak prices.