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The concept

The H2020 project FlexSNG is an EU-Canada jointly funded action that aims at developing a flexible and cost-effective gasification-based process for the production of pipeline-quality biomethane (bio-based synthetic natural gas, bio-SNG), high-value biochar and renewable heat from a wide variety of low-quality biomass residues and biogenic waste feedstocks.

 

The FlexSNG gasification concept is based on the “one plant, two modes” approach where the plant can switch between:

1) co-production of biomethane, biochar and heat;

2) maximised production of biomethane and heat.

1) Co-production mode

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2) Maximised production of biomethane

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The key idea is that the plant can adapt to changes in market conditions or feedstock availability and price by switching operation mode. At the core of the FlexSNG plant is a flexible gasifier that either co-produces biochar and syngas or maximises syngas production:

1) In co-production mode, the aim in gasification is to restrict the feedstock carbon conversion into gas to a level of 70-80% and thus enable the production of solid biochar alongside synthesis-quality gas. This is accomplished by lowering the gasification temperature to around 700-800 °C.

2) When maximising the production of biomethane and heat, feedstock conversion into syngas is maximized in the gasifier by increasing the gasification temperature to ca. 850-900 °C and lowering the biomass throughput of the plant so that also the biomass charcoal is gasified (>99% carbon conversion achieved). One key innovative feature in this operation mode is the possibility to switch to using lower-grade waste feedstocks. This is accomplished by co-feeding biochar: mixing biochar with waste allows to “upgrade” these more challenging feedstocks into suitable feeds for gasification.

Main challenges of state-of-the-art gasification concepts VS FlexSNG solutions:

The gasification process often requires a high amount of pure oxygen and thus investing in a costly oxygen production unit. The novel oxygen production method based on oxygen transport membranes (OTMs) reduces energy consumption by 50% compared to state-of-the-art cryogenic air separation and enables cost-effective oxygen production already on a smaller scale. Further cost savings comes from reduced oxygen consumption in low temperature gasification.
The gas clean-up process is often far too complex and may involve multiple scrubbing steps. The FlexSNG gas clean-up process is simplified and does not involve capital-intensive wet scrubbing steps, which leads to 10% reduction in conversion costs.
The gasification process requires high operation temperature to maximise biomass conversion into gas, which in turn limits the feedstock base. The low gasification temperature and co-feeding of biochar in FlexSNG enable the use of a significantly wider range of feedstocks and also lower grade feeds, which also reduces feedstocks costs.
Gasification processes that aim for advanced biofuel production are traditionally designed for extremely large scale, which ultimately results in excessively high investment costs and hinders the market up-take of such technologies. The FlexSNG process is economically viable already in medium-scale (50-150 MW) owing to the coupling of gasification with the compact VESTA methanation process. Smaller scale also enables the use of local biomass residues and wastes, which reduces feedstock transportation distance and related costs.