Value chains for integrated production of liquefied bio-SNG at sawmill sites - Techno-economic and carbon footprint evaluation

Industry's increasing demand for liquefied natural gas could be met in the future by liquefied methane produced from biomass feedstock (LBG - liquefied biogas). This study presents results from an investigation of value chains for integrated production of LBG at a generic sawmill site, based on gasification of sawmill waste streams and forest residues. The objective was to investigate the cost for, as well as the carbon footprint reduction associated with, production and use of LBG as a fuel. Five different LBG plant sizes were investigated in combination with three different sawmill sizes. The resulting cases differ regarding biomass feedstock composition, biomass transportation distances, LBG plant sizes, how efficiently the excess heat from the LBG plant is used, and LBG distribution distances. Pinch technology was used to quantify the heat integration opportunities and to design the process steam network. The results show that efficient use of energy within the integrated process has the largest impact on the performance of the value chain in terms of carbon footprint. The fuel production cost are mainly determined by the investment cost of the plant, as well as feedstock transportation costs, which mainly affects larger plants. Production costs are shown to range from 68 to 156 EUR/MW h(fuel) and the carbon footprint ranges from 175 to 250 kg GHG-(eg)/MW h(net) (biomass) assuming that the product is used to substitute fossil LNG fuel. The results indicate that process integration of an indirect biomass gasifier for LBG production is an effective way for a sawmill to utilize its by-products. Integration of this type of biorefinery can be done in such a way that the plant can still cover its heating needs whilst expanding its product portfolio in a competitive way, both from a carbon footprint and cost perspective. The results also indicate that the gains associated with efficient heat integration are important to achieve an efficient value chain.