DEVELOPMENT OF A TORREFACTION PROCESS APPLIED TO WET WASTES FOR BIOFUEL REVALORIZATION

Enerkem, a Quebec-based technology company, is tackling the challenge of ultimate wastes revalorization, otherwise buried or burned, into transportation biofuels. Its first commercial plant, in Edmonton, produces bioethanol from RDF type residues, a world premiere. Its thermochemical process starts with a fluidized bed gasification step, particularly well suited to the physico-chemical heterogeneity of the wastes. However, most of the wastes (municipal, ICI and CRD [Appendix B]) can’t be efficiently gasified due to their high level of moisture. A predrying is therefore necessary, through the emission of 5.5 kgCO2eq per dry ton and per percentage of extracted moisture.
To better use wet ultimate wastes, Enerkem aims for the development of a new pretreatment process by torrefaction, which will position itself advantageously compared to current drying techniques. The advantage is in the recycling of the energy contained in the torrefaction gases and the downstream increased gasification efficiency. Homogeneity, hydrophobicity (ease of storage), ease of grinding and sorting, more stable transfer into pressurized hold and high energy density (close to coal) are other important gains of the torrefaction product.
Once integrated to the Enerkem process and considering raw material containing 40% moisture, torrefaction-produced GHG reductions are superior to drying by a difference of 141 kgCO2eq per dry ton of raw material. For a standard Enerkem plant processing 100,000 t/y dry basis, the GHG reduction improvement resulting directly from this project reaches 14,083 tCO2eq/yr, for a total reduction of 168,000 tCO2eq/yr for a plant. Moreover, through the techno-economic advantages expected from the project, Enerkem contemplates the possibility of one more plant in Quebec by 2025, i.e. 336 000 tCO2eq/yr.
The torrefaction’s numerous benefits are drawing the attention of the scientific community. Still, its specific applicability to ultimate wastes is a largely unexplored novelty. A R&D effort is therefore necessary to fill the technological gap in order to achieve commercialization. This collaborative project aims to close the gap with a basic research project on torrefaction applied to Quebec ultimate wastes. The project specific goals are of a fundamental nature and included complementary experimental and numerical components. On one side, on laboratory tests benches, the waste torrefaction study will provide the understanding and the quantification of the physico-chemical transformations and the granular flow with heat and mass transfer. On the other side, predictive numerical models will be developed and validated to provide the biofuel production process scaling and integration.