Life cycle greenhouse gas emission analysis of co-processing of algal bio-oil and vacuum gas oil in an existing refinery

The co-processing of algal bio-oil and vacuum gas oil (VGO) within existing refineries to generate gasoline and diesel represents a financially advantageous strategy for the integration of third-generation biofuels. Microalgae cultivation can be facilitated through the utilization of algal turf scrubbers (ATS) and open raceway ponds (ORP), with algal bio-oil extraction achievable via hydrothermal liquefaction (HTL) and fast pyrolysis (FP). Four distinct algal bio-oil production processes, namely ORP&HTL, ORP&FP, ATS&FP, and ATS&HTL, have been identified for the integration of algae cultivation and algal bio-oil production. To assess the global warming potential (GWP) of the five co-processing scenarios, the four algal bio-oils co-processed with VGO, along with pure VGO cracking, underwent evaluation utilizing the CML 2001 method. The investigation revealed that the ORP&HTL scenario exhibited the lowest GWP among the five scenarios. In the ORP scenarios, KNO3 and Ca(H2PO4)2·CaHPO4 were utilized as nitrogen (N) and phosphorus (P) sources during the algae production stage, resulting in a GWP 3.86 and 2.01 times higher than that observed in the ATS scenarios during this phase. Subsequent sensitivity analysis demonstrated that optimizing the reduction of GWP entails diminishing electricity and nutrient consumption within the algal production processes, alongside augmenting the proportion of algal bio-oil in the feed. This strategic approach effectively mitigates the GWP associated with the co-processing endeavor.