Intermediate pyrolysis of wheat straw and softwood pellets

  • Author / Creator
    Dhakal, Bijay
  • Rapid population growth and booming urbanization play an active role in world fuel demand. Today, primary fuel resources like coal and petroleum fulfill most of the energy supply and are the leading contributors to greenhouse gas (GHG) emissions. Biomass-based fuel technology can play a crucial role in reducing GHG emissions, because, as a renewable source, biomass can be converted into solid and liquid biofuels and these are nearly carbon neutral over its life cycle. Thermo-catalytic reforming (TCR©) is a thermo-chemical conversion process by which biomass can be converted into valorized products like bio-oil, biochar, and syngas and is based on intermediate pyrolysis. Conventionally, biomass is converted into bio-oil via various other thermochemical processes such as fast pyrolysis, gasification, hydrothermal processing and combustion; integrating intermediate pyrolysis and the post-reforming reaction are novel features of the TCR© process. A 2 kg/h lab scale unit (TCR-2) was used for the thermo-catalytic reforming for different feedstocks to convert organic material into valorized products like bio-oil, biochar, and syngas.
    In the first part of this study, the thermo-catalytic reforming performance of wheat straw pellets was explored. The experiments were carried out in a reactor temperature range of 400 to 550 ℃ and a reformer temperature range of 500 to 700 ℃. Bio-oil yield decreased with an increase in reactor or reformer temperature. The highest yield of bio-oil (8.43 wt.%) was obtained at 400 and 500 ℃ reactor and reformer temperatures. The lowest yield was obtained at 450 and 700 ℃ reactor and reformer temperatures, respectively. The bio-oil produced has a very low TAN (7.3 mg KOH/g) and low viscosity (3.9 mPas) at 550 and 700 ℃ reactor-reformer temperatures. At a high temperature, polyaromatic hydrocarbons (PAHs) and monoaromatic hydrocarbons (MAHs) increase, showing the better quality of the bio-oil at a higher temperature. The maximum higher heating value (HHV) of bio-oil is obtained at 35 MJ/Kg, and oxygen content in the bio-oil is below 9%. The syngas produced has very high hydrogen content (36.32 vol.%) at reactor-reformer temperatures of 450 and 600 ℃, and the biochar produced has a very low O/C and relatively high H/C ratio.
    In the second part of the study, Canadian softwood pellets were subjected to TCR© experiments, and products were tested for qualitative and quantitative performance. Softwood feedstock was tested at a fixed reformer temperature of 700 ℃ and a fixed reactor temperature of 400 ℃. The maximum bio-oil (7.994 wt.%) was found at a reactor temperature of 400 ℃ and reformer temperature of 500 ℃. The bio-oil produced is of superior quality with very low TAN and viscosity (3.14 mg KOH/g and 11.9 mPas, respectively). The char showed excellent stability with a very low O/C ratio and relatively high H/C ratio. The highest hydrogen content was observed at a reactor temperature of 500 ℃ and reformer temperature of 700 ℃. Finally, the HHV of the bio-oil produced was recorded in the range of 37.5 MJ/Kg. Low TAN and viscosity, and very low oxygenated compounds in the bio-oil as compared to fast pyrolysis oil showed better stability and minimum downstream post-processing required for utilization. High hydrogen content in the syngas and high HHV of biochar showed potential applications in the power generation.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • 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.