Possibility of renewable energy production and CO2 mitigation by thermochemical liquefaction of microalgae

The energy balance and CO2 mitigating effect of a liquid fuel production pr ocess from microalgae using thermochemical liquefaction were studied. Therm ochemical liquefaction has the advantage of treating wet materials compared with direct combustion, gasification and pyrolysis, because it does not re quire a drying process. The yield of liquid fuel produced from Botryococcus braunii and its lower heating value were high compared with those of Dunal iella tertiolecta; therefore, the energy inputs for cultivation and separat ion of B. braunii were calculated to be smaller than those of D. tertiolect a. The energy input for fertilizers of B. braunii was also smaller than tha t of D. tertiolecta. Based on these differences, the liquefaction process u sing B. braunii was suggested to produce net renewable energy, but not that with D. tertiolecta. if a 100 MW thermal plant using coal would be replace d by liquid fuel produced from B. braunii, the quantity of CO2 mitigation c ould be 1.5 x 10(5) t year(-1) and 8.4 x 10(3) ha of microalgal cultivation area could be necessary. (C) 1999 Elsevier Science Ltd. All rights reserve d.