Techno-economic assessment of algae conversion to biofuels.

Abstract

One of the most promising biomasses for the production of biofuels is microalgae. This is because microalgae have a high growth rate and a highiCO2icapture ability when compared to other biomasses. Furthermore, biofuels produced from microalgae are deemed eco-friendly due to their low sulphur content, superior lubricating efficiency, and non-toxicity nature. As opposed to carbon-based fuels, biofuels are viable alternatives with the potential to meet the increasing demand for energy (Jafari & Zilouei, 2016). Because of its potential of being inexhaustible and a low-cost renewable energy carrier, biofuels research has increased (Akobi et al., 2016). This research investigated the thermochemical and biochemical conversions for producing algal biofuels on a technical, economic, and environmental basis. The primary feed considered was wet algal biomass with a 20 wt%. Each investigated process was simulated on Aspen Plus ® v12. The processing units considered for the thermochemical conversion on Aspen Plus were hydrothermal liquefaction (HTL) for depolymerization, hydrotreating for removing contaminants by using H2, and hydrocracking for removing contaminants by using a high-activity catalyst and H2. The primary processing units considered for the biochemical conversion simulation included pre-treatment where dilute sulphuric acid is fed, conditioning with the assistance of dilute ammonia, fermentation with the aid of S. cerevisiae, purification, and finally, anaerobicidigestion of the production of biogas. The process properties for the investigated conversion methods wereiobtainedithroughimass and energy balance calculations. The thermochemical conversion had a mass ratio of 0,39 and an energy efficiency of 47,45%. The biochemical conversion had a mass ratio of 0,98 and an energy efficiency of 73,11%. The processes were both optimized using the Aspen Energy Analyzer (AEA). The thermochemical simulation had a 23,56% energy savings and a 17,3% carbon emissions reduction. The base case simulation for the biochemical conversion had no design alternatives to improve the heat exchanger network (HEN). The fixed capital investment (FCI) for the thermochemical conversion was 18,3% lower than for the biochemical conversion. The internalirateiofireturn (IRR) for the thermochemical method was 27,36% and 29,61% for the biochemical conversion. The economic evaluation was completed using the discounted cash flow analysis. Both the thermochemical and biochemical processes were profitable. The thermochemical method had a discounted payback period of 7,2 years (break-even point at seven years five months) and seven years (break-even point at six years ten months) for the biochemical method. The environmental impacts of both processes were evaluated using OpenLCA. Typically, OpenLCA employs the cradle-to-gate approach. The assessment used the Agribalyse v3.0.1 database, and the LCIA method used was the ReCiPe 2016 midpoint (H) method and the CML-IA baseline method. The thermochemical method was the more sustainable method. The global warming impact was 42,25% less, the human toxicity was 41,46% less, and the freshwater aquatic ecotoxicity was 38,3% lower than the biochemical method. The investigation is summarized in the Table 0-1 below: Table 0-1 : Summary of the processes studied.