Biomass Particle Models with Realistic Morphology and Resolved Microstructure for Simulations of Intraparticle Transport Phenomena

Abstract

Biomass exhibits a complex microstructure of directional pores that impact how heat and mass are transferred within biomass particles during conversion processes. However, models of biomass particles used in simulations of conversion processes typically employ oversimplified geometries such as spheres and cylinders and neglect intraparticle microstructure. Here we develop 3D models of biomass particles with size, morphology, and microstructure based on parameters obtained from quantitative image analysis. We obtain measurements of particle size and morphology by analyzing large ensembles of particles that result from typical size reduction methods, and we delineate several representative size classes. Microstructural parameters, including cell wall thickness and cell lumen dimensions, are measured directly from micrographs of sectioned biomass. A general constructive solid geometry algorithm is presented that produces models of biomass particles based on these measurements. Next, we employ the parameters obtained from image analysis to construct models of three different particle size classes from two different feedstocks representing a hardwood poplar species (Populus tremuloides, quaking aspen) and a softwood pine (Pinus taeda, loblolly pine). Finally, we demonstrate the utility of the models and the effects explicit microstructure by performing finiteelement simulations of intraparticle heat and mass transfer, and the results are compared to similar simulations using traditional simplified geometries. We show how the behavior of particle models with more realistic morphology and explicit microstructure departs from that of spherical models in simulations of transport phenomena and that species-dependent differences in microstructure impact simulation results in some cases.

What limits the yield of levoglucosan during fast pyrolysis of cellulose?

“…[123] Data for biomass and its main model compounds changing during pyrolysis are still being studied in the academic community. [124][125][126] To better understand the regime of pyrolysis utilized in experiments, time scale analysis is used. First, the Biot number (Bi) >0.1 indicates that the particle tends to form temperature gradients within it, this case should be avoided.…”

Progress in understanding the four dominant intra-particle phenomena of lignocellulose pyrolysis: chemical reactions, heat transfer, mass transfer, and phase change

“…4 provides one example of a large particle in which temperature was measured in situ. Though spherical particles are not representative of industrially-relevant biomass feed-stocks, 93 the thermal pathway is still characteristic of wood. Here it can be seen that endothermic phenomena occur around 400-500°C and exothermic phenomena dominate between 600 and 800°C.…”

“…The shape and hierarchical pore structure also impact the heat and mass transfer properties of wood. Ciesielski et al 93 have shown, for example, that spherical representations of realistic biomass feedstocks fail to accurately capture the thermal gradients in a particle, though some effort has also been made to employ develop low-order mathematical approximations in spherical models to make them more accurate. 213 Pecha et al have further illustrated that the pore structure between even pine and poplar wood makes for differences in the external heat transfer coefficients.…”

“…100,231 Similar results have been reported elsewhere. 11,24,37,68,69,84,131 The anisotropic pore structure 93 of most lignocellulose species (like wood) leads to differences in gas permeabilities in the axial and radial directions of up to 4 orders of magnitude. 232 Permeability scales with pore size to the second power, so this is to be expected.…”

“…Although many single particle models have been developed, only a few have looked at the explicit species-specific microporosity of cell walls. 93,214 See Table 5 for examples. The majority of models at the particle level developed until now do not consider the intermediate liquid phase evolution.…”