Optimization of Energy Consumption and Cost in Solvent Recovery Section for Large-Scale Biofuel Production from Microalgae

Abstract

Biofuel from microalgae is an alternative to petroleum because growth rate of microalgae is high and also microalgae contain lots of lipids. In this study an attempt is made to optimize both heat and power consumption of the hexane recovery section after lipid extraction by introducing mechanical vapor recompression (MVR) or self-heat recuperation (SHR) technology. We evaluated primary energy consumption in the base case, MVR and SHR models of the distillation process with heat recovery by using a commercial process simulator Aspen Plus^® ver. 8.6. We also evaluated its capital and operating costs of the process with Aspen Process Economic Analyzer^® ver. 8.4 and literature data. Results show primary energy consumption of the base case was 46.24 kW when 99.75% of hexane was separated from the feed that consists of hexane 330.15 kg/h and lipid (tripalmitin, C₅₁H₉₈O₆) 11.30 kg/h. In MVR and SHR models, the primary energy consumption can be reduced to 20.91 and 19.70 kW by enhancing heat recovery of the heat of the separated hexane vapor at the optimum split ratio of the feed stream and compressor discharge pressure. It was found the capital cost of compressor was much higher than that of other units. The utility cost slightly decreased in MVR and SHR models compared with the base case model. Total oil-production cost was in base case was 1.50×10³ JPY/kg-oil and that in MVR and SHR models increased to 1.99×10³ and 2.51×10³ JPY/kg-oil, respectively. By 10 times scale up of this process, the total oil-production cost can be reduced to 178, 217 and 270 JPY/kg-oil in base case, MVR and SHR models, respectively because of insignificant increase in capital cost, General and Administrative (G and A) expense, and maintenance expense by the scale up.