Low sulfur fuel oil from blends of microalgae pyrolysis oil and used lubricating oil: Properties and economic evaluation

Abstract

Microalgae pyrolysis oil (MPO) is one of the most promising alternative renewable fuels to replace fossil fuel oil due to its high heating value, low sulfur content and environmentally sustainable production. Used lubricating oil (ULO) is another attractive alternative fuel with a relatively low cost. It is classified as a hazardous waste that is encouraged to be recycled. The International Maritime Organization (IMO) has mandated the use of low sulfur fuel oil (LSFO) (sulfur < 0.5% m/m) for marine transportation in the year 2020. Blends of MPO and ULO have an opportunity to satisfy the growing LSFO demand while the world is still facing challenges of LSFO production from fossil sources, due to cost and processing. MPO was derived from the Spirulina platensis specie due to its ease of harvesting and high yield of pyrolysis oil. The dried algae were fed into a continuous pyrolysis reactor to produce pyrolysis oil, from which MPO was extracted. ULO from vehicle engine was obtained from a vehicle service center and treated by flocculating and filtering. The blends were prepared to 100:0, 80:20, 50:50, 20:80 and 0:100 of MPO and ULO ratios, and tested for properties in accordance to ISO 8217, residual marine fuels. The results of the testing demonstrate that the blend of 20% MPO and 80% ULO, termed Microalgae Lubricant Blend (MLB20), can be a promising low sulfur marine fuel. The property tested and their results for MLB20, are as follows: 910.9 kg/m3density at 15 °C, 87.26 mm2/s kinematic viscosity at 50 °C, 0.461 %wt sulfur content, 0.515 %wt ash, 4.1 %vol. water content, and a total acid number of 5.4 mg KOH/g. MLB20 meets the majority of ISO 8217 specifications except for relatively high ash, acidity and water content. The pyrolysis process produced a yield of 41.37% liquid phase with MPO yield of 18.65%. The total cost of MPO production was 953.23 THB/liter, of which 73% is attributed to the algae nutrient cost. From the blending calculation, it was determined that the MLB20 cost is 198.65 THB/liter which is approximately 171 THB/liter higher than the LSFO market price. The barriers to MLB20 viability as LSFO are mainly the ISO 8217 standard’s strict ash, acidity and moisture requirements and MPO cost; specifically the nutrient cost.