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

  • Author / Creator
    Shahrukh, S M Hassan
  • 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.

  • Subjects / Keywords
  • Graduation date
    Fall 2015
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.