Sustainable natural gas (SNG) and aluminium production via biomass gasification and enhanced waste heat recovery in Novelis plant in Sierre City

The Net Zero Lab is composed of different experts in areas of energy integration, modelling and simulation, life cycle analysis, furnaces operation and revamping, energy audit, and financial analysis. This team counts with the participation of practitioners and researchers from EPFL, HES SO, OIKEN and NOVELIS Sierre.

This detailed study aims to assess the sustainable utilization of renewable energy resources, especially biomass, in order to decarbonize heavy industries, such as secondary aluminium production. To this end, this study explores the feasibility of integrating biomass gasification to produce and supply fuel to high temperature furnaces in Novelis Sierre plant, whereas cascading the low-grade waste heat for district heating purposes and other cogeneration applications. The analysis of the additional sustainable biomass potential indicates the availability of sufficient resources for a project of this kind in nearby cantons including Valais, Vaud, Fribourg, and Bern. Unlocking only 10% of the additional sustainable potential of biomass for energy use in these cantons is sufficient to supply the needs of Novelis aluminium plant and Sierre city during the winter season. Sourcing biomass from various regions in Switzerland remains economically viable; yet, procurement of biomass resources in farther locations may significantly increase wood energy prices. The energy consumption in biomass transportation slightly varies for different moisture content scenarios, with pelletized wood showing the most significant reduction. However, in this study wood chips supply is evaluated due to the local availability and fewer processing steps. Different biomass energy conversion technologies for combined fuel, power and heat are analyzed to determine the most promising applications to use the limited valuable biomass resource. The biomass gasification system, which allows producing the synthetic natural gas (SNG) fed to Novelis aluminium plant, is compared to the conventional biomass boilers and cogeneration units. This analysis also encompasses the use of two different district heating networks, based either on the traditional water-based systems or new generation anergy distribution systems. Groundwater heat pumps (HP) are used to balance the space heating demand of the city. Eight biomass energy conversion scenarios are evaluated, namely:

1. SNG + water CAD: Biomass-to-SNG route with waste heat released to a water district heating network (CAD) without electricity generation.
2. SNG + cogeneration + water CAD: Similar to case 1, but with combined electricity and heat production in a Rankine cycle.
3. SNG + CO2 CAD: Similar to case 1, but the CAD consists of a CO2 district heating network, instead of a water-based CAD, without electricity generation.
4. SNG + cogeneration + CO2 CAD: Similar to case 3, but with combined electricity and heat production in a Rankine cycle.
5. Syngas for CHP engine + water CAD: Biomass-derived syngas is used directly t