Optimal and Sustainable Design of Integrated Biorefineries for Microalgae and Municipal Solid Waste Processing
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Date
2023-01-20
Authors
Kim, Kyuyeon
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
With drastic advances occurred in society over decades, there have been growing concerns towards global energy demand and sustainable feedstock supply. Particularly, biomass emerged as one of the potential energy sources due to its renewability and sustainability. Biomass is characterized to contain a variety of compositions, which could be used to produce numerous products that ranges from energy, chemicals, and other value-added materials. However, economic uncertainties exist due to possibilities in processing multiple biomass sources. With a concept of biorefinery, a systematic framework is developed for the superstructure-based optimization of combined microalgae and municipal solid waste (MSW) processing pathways.
Microalgae and municipal solid waste (MSW) have great potential as feedstocks to produce a wide range of valuable end-products. The proposed superstructure includes all the potential technological alternatives for producing valuable products from microalgae and MSW. A mixed integer linear programming (MILP) model is developed and solved in GAMS to determine the optimal biorefinery configurations. With multiple feedstocks for multiple products, more complex decisions have to be made to determine the best combinations of feedstocks, technologies and products out of available options.
For this report, a case study was selected to assess economic feasibility of an integrated biorefinery in Seoul metropolitan area, South Korea. Being a highly industrialized city, solid waste management and energy supply issues have led social and environmental concerns. Given the superstructure-based model and case study parameters, a MILP problem was solved in GAMS for optimization. As a result, the optimal solution included a selection of technological pathways to yield $253,857,000 USD in and $1433,859,000 USD in annual profit and revenue, respectively. Top products included 403,520 tonnes of biodiesel, 742,370 tonnes of bioethanol, and 3,490,500 MWh of electricity production annually. The optimal solution omitted landfill of waste, and increase the waste directed to electricity, which were ideal suggestion for the case study scenario. Moreover, recycling of water and methanol within the process cycle could potentially save $116,171,320 USD per year.
Sensitivity analysis was done with three adjustable parameters: biodiesel market price, MSW composition, and microalgae cultivation efficiency. Biodiesel price was linearly correlated to total profit as it is one of the main products anticipated in this biorefinery. MSW composition caused a noticeable, exponential increase in profit as the proportion of recyclable components increased. Lastly, microalgae cultivation efficiency was selected to observe effects of potential weather variation on microalgal growth rate, and final profit. Profit value was linearly dependent on negative variation region of cultivation rate. This suggested extreme climate which hinders microalgae growth, could significantly affect the economic feasibility of this biorefinery.
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Keywords
biorefinery, optimization, GAMS, microalgae, municipal solid waste, biomass