DOI: 10.14457/tu.the.2018.921
title: Life cycle assessment of bioethanol production and solid sorbent for airborne pollution control processes

description: Increasing energy demand and associated airborne emissions create requirements of new approaches with pre-production/modified processes to improve the environmental sustainability of energy production and reduce airborne emissions from fossil fuels. Life Cycle Assessment (LCA) evaluates energy/resources utilization, environmental emissions/impacts, and extents of environmental sustainability improvements for pre-production/modified processes. In this dissertation, two approaches that contain pre-production/modified processes are studied for environmental sustainability improvements. The considered two approaches are (a) Bioethanol production from agricultural feedstocks (cassava, cane molasses, and rice straw) and (b) Airborne SO2/CO2 emissions reduction using solid sorbents (coal fly ash and bottom ash). Conventional methods for inventory data collection of pre-production/modified processes are time consuming and could be unfeasible due to the unavailability of relevant actual production plants or pilot plants. Comprehensive LCA evaluations require inventory data, collected from an identical method for comparisons among such pre-production/modified processes. The novelty of this Ph.D. research study is the integration of the process simulation technique, experiments, reliable literature-based data, and real plant data for comprehensive LCA evaluations, including the analyses of resources utilization, energy consumption, and environmental impacts of the selected process modifications. For bioethanol production, the study evaluates a comprehensive LCA comparison among cleaner production scenarios from cassava, cane molasses, and rice straw as feedstocks, based on process data from simulations and minimum variations in other settings, i.e., process fuel type, waste recovery options, etc. The results are comparable with actual bioethanol plant data that validates the reliability of the simulation technique. The results show that simulation-based cleaner process designs improve the energy efficiency, renewability, and environmentally benign aspects of the bioethanol feedstocks. Bioethanol from cassava shows the best values of net energy ratio (1.34), renewability (5.16), and reduced greenhouse gas emissions (410 kg CO2 eq/1,000 L). For SO2 reduction from a coal-fired power plant, the study evaluates the feasibility of using waste materials, i.e., coal fly ash and bottom ash as solid sorbents. The experimental results exhibit the capability of free lime contained fly ash/bottom ash to react with SO2 under the least efficient conditions. The scenario-based LCA results show that fly ash/bottom ash utilization can lower the SO2 load of untreated flue gas by 3.7–4.7%, before an existing Wet-limestone Flue Gas Desulfurization (WFGD) system. The combined desulfurization process with SO2 reduction can save the annual energy consumption by 4.0–5.0% and the environmental impacts by 3.0–5.0%, compared to the existing WFGD process. The study also proposes potential applications of the SO2 captured fly ash. In addition, the study evaluates an industrial scale CO2 capture process using fly ash/bottom ash as solid sorbents, including scenarios with free lime addition into fly ash and post-capture application modes. The results are compared with conventional CO2 capture processes. LCA findings show that fly ash and bottom ash with no external free lime addition are more suitable for sustainable CO2 capture. The useful LCA findings of the studied approaches in this dissertation contribute decision making for the environmental sustainability of future bioethanol industry and coal-fired electricity generation with partial reduction of SO2/CO2 emissions using in-plant fly ash/bottom ash.