Sustainability study of an innovative technology for biodiesel production

The use of biomass as energy source is a well-known technology, and is rapidly growing. In this work the combination between an anaerobic digester and a gasification process was considered. As a case study was used the region Gnas. Gnas is one of the 26 municipalities in the district of Sudostsyteiermark (South- East Styria, Austria). The feedstock taken in account were manure for the anaerobic digester and wheat straw for the gasification. The supply chain of the feedstock was proposed by considering that only the 1% of the final energy produced in the process can be spent for the transportation, in order to maintain the process competitive. It has been found that the limiting feedstock was the manure due to the low energy density. Therefore were evaluated two scenarios one considering the manure as limiting feedstock (Case B) and the other without considering the manure as a limiting feedstock but considering the first transportation limit (Case A). The calculations for the production and cleaning of syngas were made by the use of the process simulation software. The Fischer-Tropsch synthesis was then evaluated by using the literature data with an efficiency of 50% depending also from the scale of the plant. The final diesel production was of 21.4 m3/h for the regional scale plant (Case A) and 0.08 m3/h for the farm scale plant (Case B). A preliminary economic evaluation was carried out identifing main cost factors in the process. An environmental evaluation was carried out by using the Sustainable Process Index (SPI). This index gave an amount of area needed to satisfy the ecological footprint of the plant. The safety evaluation was done by using a consequence based approach to the quantitative assessment of inherent safety.