Upgrading the value of anaerobic digestion via chemical production from grid injected biomethane

Abstract

Anaerobic digestion can already at small scale effectively convert (waste) biomass to biogas. This biogas is typically combusted to generate electricity and heat, which is incentivized by regulatory support schemes. Because biogas can also be upgraded to biomethane and subsequently injected into the gas grid, the anaerobic digester can be considered as a means to connect decentralized biomass production to a centralized gas grid. We currently estimate the level of required government support to realize a profitable investment in Europe at 20–50 € MWh_e⁻¹ for the valorization of an average biogas in a combined heat and power unit, and at 15–25 € MWh⁻¹ for the production of pipeline-quality biomethane, typically used as fuel. Here we explore, both technically and economically, an alternative scenario where biogas is upgraded to biomethane, injected into the existing gas grid, and used elsewhere to produce CO, syngas or H₂. The super-dry reforming of CH₄, a chemical looping approach using up to three CO₂ molecules per CH₄, allows an intensified production of CO as a feedstock for synthesis of platform chemicals and fuels through CO₂ utilization. Even without subsidies, at present values and costs, this creates an economically positive case which can promote anaerobic digestion as an important driver for a new bio-industry. This approach avoids biomass transportation, in contrast with present biorefineries, while effectively valorizing decentralized biomass feedstocks such as agricultural waste or energy crops.