HOT|COOL NO.2/2021 - "Economics, Finance & Money"

Energy from local woody greenwaste in Metropole Rouen, France

By: Ann Bouisset, Sales Director - Dall Energy

The French government and the energy agency ADEME have a clear strategy of using local biomass, which would otherwise just rotten and compost - emitting large amounts of methane gas and CO2.

The history of updraft gasification The principle of updraft gasification has been known for centuries and was used in Europe from the 1850s for city gas production based on hard coal. In the 1980s, several updraft gasifiers entered commercial operation in Scandinavia, but this required heavy maintenance because of the external combustion of the gases. The new Biomass Gasification Furnace System The Dall Energy furnace combines updraft gasification with gas combustion in the same chamber, which results in full performance and environmental benefits without the historical problems related to external combustion. In the new BGFS, biomass is dried and pyrolyzed at the top of the fuel layer. Further down, the biomass is converted into a burnable gas and fine ash. The heat for the drying and pyrolysis process combines convective heat from the gasification gases below and radiation heat from the gas combustion part above. Primary air injection is about half of what is used in traditional grate incineration, and, with a large furnace bottom-area, the gas velocity in the bottom part is low. Consequently, particles remain here, and dust emission from the furnace is very low too. Gas from the bottom part is combusted in the top section. The gas combustion (flow, temperatures, emissions, etc.) is stable and is controlled via flue gas recirculation. The control allows operation with lower excess air ratios resulting in higher overall efficiency.

The large energy company Dalkia is operating the district energy plant in Metropole Rouen, France. They wanted to support the national strategy and examined the opportunities for optimizing the sourcing of biomass fuel within a radius of 100 km from the heating plant. They found the solution in a new biomass gasifier furnace system (BGFS) from Dall Energy that enables utilizing a wide range of fuels, even cut-off green park and garden biomass with moisture levels up to 60%. Their decision points were fuel flexibility, low air emissions, and fast response to fluctuating heat demands as the district heating (DH) network in Metropole Rouen has no buffer tanks.

The French legislation requires the biomass used in heating plants to come from sources within a close distance of the plant - an eco-friendly rule preventing emissions from transporting biomass over long ranges

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