Industrial Bioprocess Developments for Biogas and Ethanol Production

Sammanfattning: Current biofuels face a noteworthy misfortune on commercialization because of its economiccomparison with low-cost fuel from the oil reserves. To compete with gasoline as a fuel, thebiofuels need to be economically feasible and demonstrated on a large-scale. Biogas and ethanolhave a great potential as commercial biofuels, even though it has difficulties, for example, highcapitalinvestment, absence of demonstrated innovations, and availability of raw materials and soforth. This thesis focuses on different application-driven bioprocess developments for improvingthe techno-economic feasibility of the biogas and ethanol industries.The biogas industry was studied from three different perspectives:1) Modeling approach in which a Process Simulation Model (PSM) model was developed forpredicting the biogas productions, as exploiting new substrates is vital for a biogas industrygrowth. The PSM model was created using Aspen Plus® which includes 46 reactions of differentphases in the Anaerobic Digestion (AD) processes. It also contains certain important processparameters, thermodynamics, rate-kinetics, and inhibitions involved in the AD processes. PSMwas a library model for the AD processes, which was validated against the laboratory andindustrial data. The validation showed that the PSM predicted the biogas production about 5% inexcess, which could ease the biogas industry to predict biogas from new substrates.2) Simulation approach to study the imperative components affecting the profitability of theplant. For this purpose, a local municipality plant was studied under distinct situations. The choiceof upgrading method, capacity, cost of waste and its processing, number of digesters used, etc.were exploited. The results showed that the collection and transportation fee, landfilling fee, andthe reduced operation of a plant were the main considerations in influencing its profitability.Moreover, it was identified that for bigger cities the decentralization strategy could beat theexpense of collection and transportation of waste, and the plant could obtain a 17.8% return oninvestment.3) Rethinking digester technology in which the cost of the digester was significantly lessenedusing a cutting-edge textile, which was principally intended for developing countries. The digestercost played an important role in consuming biogas for different applications. The textile digesterwas tested on a laboratory scale, followed by field tests in different countries including India,Indonesia, and Brazil. Textile digesters cost one-tenth of the conventional digesters, and thepayback was more or less between 1–3 years, when replacing the Liquefied Petroleum Gas (LPG)and kerosene as a cooking fuel for households.When it comes to ethanol, the first generation ethanol production using grains was financiallypossible with a payback of about 13 years. Nonetheless, with the fluctuation of the oil prices, theethanol industries need to look for alternative sources of revenues. Different retrofits wereconsidered, including the effect of thin-stillage/whole-stillage to ethanol and biomass, in additionto the integration of the first and second generation ethanol production. The results revealed that4% additional ethanol could be obtained when the thin-stillage was converted into ethanol andfungal biomass, while the payback was reduced to 11.5 years. The integration of the first andsecond generation ethanol production revealed that it has a positive influence on the overalleconomics of the process with a payback of 10.5 years. This could help the ethanol industries toconsider a revamp for a better environmental, economic, and energy efficient process.