A Microalgae-based Biorefinery Plant for the Production of Valuable Biochemicals: Design and Economics

In the present work, a mathematical model for the conceptual design of a plant, with annual capacity of 200,000 t of microalgal biomass, for the production of sugars (as hydrolysis products of carbohydrates), proteins and lipids, from Stichococcus sp. was developed, using the Aspen Plus platform. The model was used to estimate the complete mass and energy balances, the equipment sizing and the utilities consumption. Subsequently, the cost of each process unit and stage was calculated resulting in the total capital investment (I), the annual production cost (CTW) and the annual production cost per produced biomass (CTW). It was found that the CTW is significantly larger when the plant is designed to produce a unique biochemical product (i.e., sugars or proteins or lipids) from the biorefinery case, where the plant is designed to produce the three biochemicals in cascade sub-processes. Namely, the CTW for sugars, as single product, is 1.47 (sic)/kg, for proteins 1.84 (sic)/kg and for lipids 2.45 (sic)/kg. On the other hand, the CTW for total bioproducts is 0.84 (sic)/kg. In the biorefinery case, I and CTW were calculated equal to 161.1 M(sic) and 167.3 M(sic)/y, respectively, while the total revenue from the bioproducts is 219 M(sic)/y. The annual profits before and after taxes are 51.7 M(sic)/y and 31 M(sic)/y, respectively. For the economic evaluation of the plant, the following criteria were calculated: pay out time 3.11 y, return on investment 0.19 and retained earnings 2.03 M(sic)/y. The present approach is able to advance the commercialization effort of microalgal bioproducts and to enable the economic viability of the plant.