Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Chemical and Biochemical Engineering

Supervisor

Prof. Berruti Franco & Prof. Briens Cedric

Abstract

Abstract

Biochar is a valuable co-product with increasing agronomic and environmental values produced during pyrolysis, which is a thermochemical conversion process of biomass in the absence of oxygen. Accumulation of biochar in the bed may result in poor fluidization performance and product quality. The efficient removal of the separated biochar from the fluidized bed is therefore crucial for economical reasons.

This thesis is structured in three sections. Section 1, provides an introduction and literature review on biomass pyrolysis covering the main types of processes and reactors focusing on fluidized bed technologies. It section addresses the mechanisms associated with mixing and separation processes in fluidized beds are briefly discussed. The significance of biochar recovery is also emphasized and the various current recovery methods are reviewed and discussed. Section 2 describes the methodology, the operating conditions and the variables investigated and measured in this work to generate the experimental data and ensure process reproducibility and accuracy experimental findings. Following this section, the section 3, addresses the experimental results and analysis leading to the conclusions and recommendations for future research directions.

The primary objective of this research is to describe, through experimental investigations, the effects of geometrical and operating parameters on the separation efficiency and the yield of the recovered biochar in a cold simulator laboratory scale bubbling fluidized bed. A section of the bed simulates the pyrolysis reactor bed, is fluidized at high gas velocity to provide intense mixing, and a second section operates at a lower gas velocity to promote particle separation. Biochar is continuously fed to the well mixed zone to simulate the production in the reactor bed. An automated pulsating feeding inlet regulated by sleeve valves allowed continuous feeding of biochar while overflow ports in the separation section allowed for the continuous discharge of the biochar.

The lab scale bubbling fluidized bed unit, made it feasible for continuous segregation and removal of biochar at an optimized separation efficiency range of 96.40 % to 98 % while operating at vigorous bubbling conditions, optimizing the separation efficiency of the biochar solids was necessary at a desirable superficial gas velocity along with the best fit submergence of the vertical baffle plate height (Ph) above the bed in preventing back mixing and bubbles from the segregation zone preventing biochar accumulation into the well mixed zone which might if not addressed result into defluidization quality in pyrolysis units.

These research experimental analyses produced better results with improved separation efficiency of 92 % unlike 80 % separation efficiency achieved in previous conducted experiment. In addition, the elutriation encountered in earlier experiments accounted for > 20 % fraction of the biochar fed, while the presently conducted and investigated findings successfully documented elutriation of < 3 % fraction of the biochar fed into the lab scale bubbling fluidized bed unit.

Following modifications of the bubbling fluidized bed pyrolyzer, the unit proved efficient in handling range of feed rates and also capable of processing different particle sizes attaining very high separation efficiency and stability (yield) states. Further optimization and adaptation for large industrial applications can be achieved through further research investigations and recommendations as suggested below.

Keywords: Fluidization, Biochar, Pyrolysis, Bubbling Fluidized Bed, Biomass, Segregation, Yield, Layer Inversion, Binary mixture, Elutriation, Gas velocity, Separation Efficiency


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