Design, Development and Characterization of a Micro-Reactor for Fast Pyrolysis of Biomass Feedstocks

This paper presents the latest results in the design, development and performance characterization of a novel prototype micro-reactor system that is uniquely capable of capturing the transient product evolution history of the fast pyrolysis of biomass products. With strong demand driving the technological development of sustainable energy solutions, the consideration of optimal conversion methodologies for biomass energy feedstocks has received a great deal of attention recent years. [1, 2] The pyrolysis of soft woods, in particular spruce and pine, has emerged as a credible alternative to bio-digestive strategies that are reliant on fermentation processes, typically of corn feedstocks. The design objectives for the micro-reactor system are reviewed, highlighting the multi-physics and multi-disciplinary complexity in designing for transient characterization of the pyrolized products by the micro-reactor system. One of the dominant challenges in the design of the micro-reactor for fast pyrolysis reactions is the requirement of very high heating rates for the feedstock, on the order of 100°C/s. A 1D transient thermal model of the reactor is developed that considers the average particle size and morphology, the initial surface temperature of the reaction surface within the micro-reactor, the heat loss to the ambient atmosphere in the reactor, the heat loss through the contact resistance between the sample and the reaction surface and the thermal capacitance of the reaction surface. A parametric evaluation of the design space was performed using the 1D model in order to identify a preferred range of particle size, reactor surface area and thermal input power. Based on the results for the domain reduction study, multi-physics thermo-mechanical 3D FEA was used to undertake a brute-force optimization process of the final design. The key metric considered in the FEA study was the maximum thermal gradient in the reaction surface and was driven to a minimum value. The thermal response of the prototype micro-reactor has been evaluated using infra-red thermography measurement techniques. Thermographical analysis of the results has demonstrated negligible thermal gradients in the reaction plane up to the maximum reaction setpoint of 450°C. Based on the results of the thermal testing of the micro-reactor, the achieved peak heating rates of the sample have been estimated to be on the order of 400°C/s, meeting and exceeding the design requirement.