Novel intermittent solid slug feeder for fast pyrolysis reactors: Fundamentals and modeling

To prevent plugging and help the raw biomass particles effectively penetrate and spread into the pyrolysis fluidized beds, one could inject the particles using intermittent slugs created by propelling loosely packed particles with gas pulses and transporting them along horizontal or inclined feeding pipes into the fluidized bed section of the reactor; this would combine the advantages of the low gas consumption of the screw feeders and the short residence time in high temperature zones of dilute phase feeders. Dried distillers' grain (DOG) and meat and bone meal residues (MBM) were selected as model feedstocks for experimental testing and modeling of a novel intermittent solid slug feeder technology. These feedstocks were chosen as much work has been done to attempt to process them into value-added products via fast pyrolysis, but they also possess very challenging flow characteristics and properties that are very different from each other (particle size, cohesivity, temperature sensitivity, density). As a result, creating a predictive model that can successfully model these challenging feedstocks is the basis to model any biomass of interest. The biomass flow in the feeding tube begins as an induced dense-phase flow and develops into a high velocity 'aerated bed flow'. Gas leakage, solid friction and force-momentum balances were considered in the model. The model was developed from experimental data collected with simplified plugs (modified nylon ball), as well as real biomass slug flow. Several important variables were identified. They included the material flow properties, the gas capacitance pulse pressure and volume, and the length and material of feeding tube. The goals of this study were to (a) characterize the fundamental dynamic behavior of the biomass slugs in the feeder, (b) maximize the solid-to-gas feeding ratio, and thus minimize energy consumption, (c) minimize the accumulation of "straggler" biomass material in the feeding tube between pulses, and thus preventing biomass pre-cooking in the feeding tube and plugging (d) develop and validate a predictive model for the slug velocity at any point in the feeding tube (and thus the maximum feeding tube length), that can be applied for feeder and reactor design for any biomass feedstock, and (e) identify future areas of work for the ICFAR intermittent solid feeder. (C) 2013 Elsevier B.V. All rights reserved.