Design and development of a novel centrifuge ablative pyrolysis approach for biomass conversion to bio-oil and bio-char

Abstract

Pyrolysis has evolved as a 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 requirement of large volumes of carrier gases necessitates cumbersome downstream 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 forces on biomass particles during pyrolysis. In a recent alternative approach, 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. Unlike other centrifuge pyrolysis reactors, the novel rotor mechanism incorporated in this reactor system facilitates constant centrifugal force as well continuous propagation of biomass feeds. The 10 kg/hr thermo-mechanical pyrolysis system has been successfully commissioned using hardwood sawdust. Properties of bio-oil and bio-char produced in this new reactor have been compared to products from fluid bed pyrolysis system. 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 adjustable product distribution.