Design and Development of a Novel Centrifuge Ablative Pyrolysis Approach for Biomass Conversion to Bio-oil and Bio-char

Pyrolysis has evolved as key pre-treatment step to produce renewable fuels and chemicals from agricultural and forestry residues. In the past few years, there have been different directions in the development of pyrolysis... [ view full abstract ]

Pyrolysis has evolved as key pre-treatment step to produce renewable fuels and chemicals from agricultural and forestry residues. In the past few years, there have been different directions in the development of pyrolysis reactors. For example, in vortex and cyclone approaches, biomass particles are suspended in a flow of high supersonic velocities to ensure enough centrifugal forces for pressing the particles against the heated reactor surface. Although simple in design, the main problem with these reactors is their requirement of large volumes of carrier gases relative to biomass feed, which necessitates cumbersome gas separation, resulting in thermodynamic penalties and higher capital equipment costs.  In ablative systems, with little or no carrier gases, the key challenge relates to using an appropriate mechanism to continuously apply force on biomass particles during pyrolysis. As an alternative approach recently, thermo-mechanical rotors at very high rpm have been used to create the required centrifugal forces  for pressing the biomass particles against the heated walls of a concentric shell.   In the current approach, a modular centrifuge pyrolysis system has been designed using Biot and Thiele numbers as key constraints for characterizing ablative regimes. Reactor design is based on heat transfer coefficients as high as 300 W.m^-2.K^-1. Unlike other centrifuge pyrolysis reactors, the novel rotor mechanism incorporated in this reactor system facilitates constant centrifugal force as well continuous axial propagation of biomass feeds. The 10 kg/hr thermo-mechanical pyrolysis system has been successfully commissioned generating 0.8 kG force using hardwood sawdust. Properties of bio-oil and bio-char produced in this new reactor are comparable to products from other fast pyrolysis processes. In addition to its compact and modular design suitable for mobile pyrolysis units, it can be operated in variable regimes of pyrolysis e.g. slow to fast modes, allowing  product distribution to be adjusted.