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Energy Return on Investment and Techno-economics of Pellet Production from Steam Pretreated Biomass Open Access


Other title
Energy Return on Investment
Process Modeling
Type of item
Degree grantor
University of Alberta
Author or creator
Shahrukh, S M Hassan
Supervisor and department
Kumar, Amit (Mechanical Engineering)
Examining committee member and department
Arvind Rajendran (Chemical and Materials Engineering)
Yongsheng Ma (Mechanical Engineering)
Department of Mechanical Engineering
Engineering Management
Date accepted
Graduation date
Master of Science
Degree level
Utilization of raw ligno-cellulosic biomass for energy use is limited because of its low heating value and low yield per unit area of biomass. Pellets are densified and compressed form of biomass which has less moisture and higher energy density compared to raw biomass. Pellets are typically produced by the forest industry from residues generated at the mills. This thesis aims are technical and economic assessment of the production of pre-treated biomass based pellets. Steam-pretreated biomass-based pellets have improved mechanical strength, hydro-phobicity, and energy density compared to wood pellets. A process model was developed for the production of pellets from stream-pretreated biomass. The process models were developed for three feedstocks, forest residues, agricultural residues, and switchgrass. These process models were developed to determine the net energy ratio (NER) for both regular and steam pretreated pellet processes and were validated through experimental work. NER is a ratio of the net energy output to the total net energy input from non-renewable energy source into the system. The results show that steam pretreated wood-based pellets has the lowest process NER at 1.29 followed by pellets from stream-pretreated switchgrass at 1.37. The highest NER is for the pellets from steam-pretreated straw at 1.76. The main reason for high NER of straw is that less energy is required for steam pretreatment and drying for straw than for the other two feedstocks. A techno-economic model was also developed for the three feedstocks to evaluate production cost of steam-pretreated biomass-based pellets. Minimum production cost and optimum plant size were determined for pellet plants for the same three biomass feedstocks. The life cycle cost, from harvesting to the delivery of the steam-pretreated biomass-based pellets to the co-firing facility, was evaluated and compared to the conventional pellets. The values vary from 116-122 $ tonne-1 for regular pellets and 180-190 $ tonne-1 for steam pretreated pellets. The difference in the cost of producing regular and steam pretreated pellets per unit energy is in the range of 2-3 $ GJ-1. The economic optimum plant size (i.e., the size of the production plant at which the cost of production is minimum) is found to be 190,000 tonnes for regular pellet production and 250,000 tonnes for steam pretreated pellets. Model sensitivities and uncertainty analyses were carried out to identify sensitivity parameters and effects of error in the model error.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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