A zero discharge, carbon-neutral bi-fuel production process for algal biodiesel and renewable hydrogen

This work proposes a novel zero discharge, carbon-neutral bioprocess for the simultaneous production of algal biodiesel and renewable hydrogen. This innovative bi-fuel production process (BiFPP) consists of five units connected in series for biodiesel production, biodiesel purification, glycerol separation, glycerol steam reforming and hydrogen purification. To assess the techno-economic feasibility, the genetic algorithm based multi-objective optimization strategy is developed to minimize the total annual cost and CO2 emission level, and maximize the fuel purity. The optimal BiFPP scheme yields 97.3 mol % biodiesel and 98.8 mol % hydrogen, and thereby meets the standard specifications, ASTM D6751 and EN 14214. A heat exchanger network is designed with thermal coupling to secure the energy savings of 79.5% (heating load) and 50% (cooling load), leading to 93% reduction in utility cost. To achieve carbon neutrality, a CO2 sink for algae cultivation is finally proposed to integrate with this industrial-scale BiFPP process that overall yields a novel zero discharge bi-fuel production technology.