Multidisciplinary use of LCA and empirical data to improve the environmental sustainability and industrial viability of Kraft pulp mill

Abstract

About 4% of the world energy is used to produce paper and it takes 300 -2600 m3 of water to produce 1 tonne of A4 sheet (Van Oel and Hoekstra 2012). Hence, the key aim of this research is to use a multi-disciplinary approach involving life cycle assessment (LCA) and empirical methodology to improve the environmental sustainability and industrial viability of the conventional Kraft pulp mill. The life cycle assessment methodology (LCA) used to study the Kraft pulp mill identified energy as the elementary flow with most impact closely followed by water. The chemical recovery unit was identified as the process unit of highest concern followed by the washing and screening process unit. The LCA study suggested that using smaller wood particle size during cooking would reduce energy consumption and emission to the air. Furthermore, the use of a re-usable liquid as part of the washing process could reduce water consumption and enable the recovery of extractable chemicals in the form of a green crude. The empirical data showed that reducing the particle size from 8mm currently used in the conventional Kraft process to < 2mm could save up to 20% energy during pulp production. Replacing part of the water during washing with recoverable hexane could reduce water consumption during the pulp washing close to 37%. In addition, using hexane as a replacement for water enabled approximately 19% green crude recovery from particle size <2mm cooked in 30mins based on initial dry wood weight. The recovery of green crude could transform the Kraft pulp mill into a potential biorefinery. The LCA outcome indicated that the impact of energy generation on climatic change is equivalent to about 713 kgCO2eq for a conventional Kraft mill and this was reduced by 20% to about 570 kgCO2eq for the proposed Kraft biorefinery. In conclusion, the combination of LCA and empirical methodology showed how a Kraft pulp mill could be transferred into a more sustainable and industrially viable biorefinery resulting in lower environmental impact and producing green chemicals from wood.