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Nitrogen and sulphur in algal biocrude: A review of the HTL process, upgrading, engine performance and emissions

Obeid, Farah, Chu Van, Thuy, Brown, Richard, Rainey, Thomas
Energy conversion and management 2019 v.181 pp. 105-119
activated carbon, algae, algae culture, biofuels, desulfurization, diesel engines, drying, emissions, harvesting, hydrothermal liquefaction, nitrogen, nitrogen content, nitrogen oxides, nutrients, potassium carbonate, sulfur
Nitrogen (N) and sulphur (S) play an important role in algae cultivation as they are important nutrients for its growth. They also affect the conversion route, the product distribution (i.e. yield), elemental and chemical composition of the end products. Hydrothermal liquefaction (HTL) is one of the most suitable processes to convert high-moisture algae to biocrude without drying. The high protein fraction in algae species causes high N (5–8 wt%) and S (0.5–1.5 wt%) in the biocrude. In this review, only two approaches for algae biocrude upgrading for N and S removal were identified from the literature, two-stage HTL and catalytic HTL (e.g. K2CO3 and activated carbon promoted denitrogenation and desulphurization). Most published research presumed that high N content in biocrude will result in high NOx when biocrude is used in a diesel engine. However, NOx emissions are heavily dependent on engine operating conditions as well as on fuel properties and to our knowledge, no study investigated emissions of N-S containing biofuel and the consequent effect on emissions has been done, requiring further study. This review will consider cultivation and harvesting techniques, the conversion routes (especially HTL), the quality of the biofuels and the engine performance and emissions focusing on the role N and S each play.