Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Chemical and Biochemical Engineering

Supervisor

Franco Berruti

2nd Supervisor

Cedric Briens

Joint Supervisor

Abstract

The slow pyrolysis of different biomasses (maple wood, birch bark, switch grass, coffee pulp and corn stalk) was studied with the aim to produce a solid pyrolysis product (bio-coal) with promising properties and potential for use in traditional fossil-coal applications. Batch pyrolysis experiments were conducted in a Mechanically Fluidized Reactor (MFR) at temperatures ranging from 143 to 665 oC, which includes the torrefaction temperature range (200-300 oC). The effects of temperature and holding time on bio-coal mass yields were determined. The bio-coals were characterized in detail and a highly-controlled study on bio-coal hygroscopicity is presented. Optimal conditions for bio-coal production ranged from a top temperature of 238 °C for maple wood to 286 °C for birch bark. Converting these two feedstocks to bio-coal reduces hygroscopy by about 60 % and increases the heating value by 20 to 36 %, respectively. In both cases, 84 to 89 % of the energy of the original biomass is recovered in the bio-coal.

Surface area enhancement of the different biomasses was studied through pyrolysis (MFR) and CO2 activation in a fixed bed reactor. Only birch bark and maple wood provided activated carbon with a high surface area of about 400 m2/g. Interestingly, carbon dioxide activation greatly increases the surface areas of birch bark char but does not have a significant effect on maple wood char.

For birch bark, activation was performed either consecutively on the MFR, or as a second stage on a fixed bed reactor. Technologies provided activated carbons with similar surface areas and were compared according to their mass yield. The MFR provides a higher activated carbon yield, a more homogenous product and a more controllable process than the fixed bed reactor.

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