Biomass Could be a Potentially Clean Fuel Source for The Steel Industry

Halving CO₂ emissions by the steel industry by developing innovative processes is the objective set for the European ULCOS (Ultra Low CO₂ Steelmaking) project involving CIRAD. To this end, over the past two and a half years, the project has been pooling the research and development capacities of 47 partners in 15 European countries: steelmakers, builders, raw material suppliers, research laboratories and universities. The main European steelmakers are leading the project. The exploratory phase of the project, which ran for 18 months, was completed in March 2005, and the second phase is now under way.

Replacing fossil fuels with biomass, notably from forest plantations in the tropics, is the project's central theme. Two main points are being addressed: biomass availability from such plantations and the development of more efficient, less polluting processes for converting that biomass into charcoal, which is vital for steelmaking. CIRAD is contributing to this vast project through research on the production, supply and sustainable use of this woody biomass as a cleaner fuel source.

Brazil and central Africa are good candidates for biomass production

To supply such biomass in a sustainable way, it is necessary to assess the areas available for industrial-scale eucalyptus plantations. This fast-growing species could rapidly provide large quantities of biomass. As part of this assessment, researchers conducted a prospective study for the period up to 2050 of the socioeconomic and environmental constraints in various tropical countries. The following "candidates" were chosen to host such plantations: Brazil, with 46 million hectares available in 2050, and several central African countries, with 46 million hectares. More precisely, the zones concerned are the Brazilian states of Tocantins, Maranhão and Piaui, where the conditions are most suitable for forest plantations. In Africa, the zones concerned are Congo (South), the Democratic Republic of Congo (West), Angola (North and East), Zambia (West), Tanzania (West and South), Mozambique (North) and the Central African Republic (West and Centre). These zones have more than 1000 mm of rainfall a year over more than a third of their area, and a population density of fewer than 80 inhabitants/km2. The pressure on this land is thus low.

To establish indicators of high, sustained biomass production, CIRAD produced carbon, water and nutrient balances for eucalyptus plantations in Congo. The results showed that after a seven-year rotation, 36.7 t C/ha can be exported, ie the equivalent of 134.5 t of CO₂ per ha. The change in land use from grasslands to eucalyptus plantations would enable permanent storage of 28.8 t C/ha (105.5 t CO₂/ha) with 24.4 t C/ha in the biomass and 4.4 t C/ha in the litter, but 0 t C/ha in the soil. This change would affect the nitrogen balance, making it necessary to give the eucalyptus plantations appropriate fertilizers.

As for carbon flux within Brazilian plantations, it is twice as high as in Congolese plantations (20 t as opposed to 10 t of dry matter/year). Brazilian plantations thus have a much higher carbon sequestration potential than those in Congo.

Innovative thermochemical processes enabling lower CO₂ emissions

As regards converting biomass into charcoal, researchers have been concentrating on innovative thermochemical processes such as high-pressure pyrolysis. The results showed that high pressure and slow heating improved fixed carbon yields after carbonization from 26 to 33%. These conditions favour conversion of the lignocellulose compounds in the biomass (cellulose, hemicellulose, lignin) into solid carbon for charcoal production. They also help reduce gas emissions in relation to conventional processes under atmospheric pressure. High-pressure pyrolysis generates 1.5 million tonnes (Mt) of CO₂ for 1 Mt of charcoal, while pyrolysis under atmospheric pressure generates 2.5 Mt of CO₂ for an identical amount of charcoal produced. Moreover, the yield gains achieved in terms of charcoal production help to reduce the areas required for planting.

CIRAD and its partners are continuing their research in Congo and Brazil in order to confirm some of the results obtained during the exploratory phase, notably carbon, water and nutrient balances. Once this has been done, conclusions can be drawn concerning sustainable biomass supplies. The second phase of the project will also look at how to optimize the charcoal produced in line with the steel industry's requirements. The initial results have shown that the type of wood used affects charcoal quality, and subsequent research should make it possible to draw up long-term strategies for improving eucalyptus clones with a view to efficient biomass use for steelmaking. Studies are also planned of selected zones, to confirm the technical, social and economic viability of forest plantations for high-quality charcoal production. Particular attention will be paid to transport infrastructures between the conversion sites and ports, a stage which remains one of the main constraints on the biomass supply chain.