SAUNA · Sustainable pulping innovation achieving zero pollution through efficient wood residue feedstock utilisation

The kraft process accounts for 82% of global virgin pulp production, 180 Mt in 2020. The kraft process converts half of the wood feedstock into fibrous pulp, the rest is dissolved and mainly burnt in the energy and chemical recovery. Kraft process generates significant exhaust flows, containing air emissions and pollutants such as CO2, SO2, NOx, total reduced sulphur (TRS) and particulates, as well as waste waters, solid wastes and noise emissions. The SAUNA project addresses enhanced environmental performance of pulp production in comparison to the kraft process by developing a novel pulping concept, where feedstock, chemistry, unit operations and energy sources are reconsidered by 11 partners: 5 companies, 4 RTO’s and 2 universities. Higher product yield (90%) is achieved by targeted fractionation of wood applying hot water extraction followed by alkaline oxidation producing hemicellulose and water-soluble lignin in addition to fibrous pulp. Biogenic CO2 emissions will be reduced by 80% in comparison to kraft process. The products will be assessed for applications such as packaging, adhesives and polyurethane. Selected sulphur-free chemistry enables significantly simpler chemical recovery applying wet air oxidation, thus avoiding incineration in kraft recovery boiler and lime kiln, where fossil fuels are used for process control. This eliminates CO2, SO2, NOx, and TRS emissions, influencing climate change, acid rains, biodiversity in forests, soils and water systems, health risks for humans and odours. Biorefinery will be designed to utilise external energy from emerging renewable energy sources or power from small nuclear reactors. If in the future, all pulp biorefineries used the SAUNA technology rather than kraft pulping, and produced the current kraft pulp volume in Europe, there would be 300 SAUNA biorefineries, EU would save annually 49 Mt of CO2 (mainly biogenic CO2), 13.5 ktons of gaseous sulphur compounds (as S), and 36.5 ktons of NOx emissions (as NO2).