Process design and economic analysis of a citrus waste biorefinery with biofuels and limonene as products

Process design and economic analysis of a biorefinery for the treatment of citrus wastes (CW) at different capacities was carried out. The CW is hydrolyzed using dilute sulfuric acid and then further processed to produce limonene, ethanol and biogas. The total cost of ethanol for base case process with 100,000 tons/year CW capacity was calculated as 0.91 USD/L, assuming 10 USD/ton handling and transportation cost of CW to the plant. However, this price is sensitive to the plant capacity. With constant price of methane and limonene, changing the plant capacity from 25,000 to 400,000 tons CW per year results in reducing ethanol costs from 2.55 to 0.46 USD/L in an economically feasible process. In addition, the ethanol production cost is sensitive to the transportation cost of CW. Increasing this cost from 10 to 30 USD/ton for the base case results in increasing the ethanol costs from 0.91 to 1.42 USD/L.