Assessment on bulk solids best practice techniques for flow characterization and storage/handling equipment design for biomass materials of different classes

Abstract

This paper shows the results of a collaborative project in which four different laboratories have carried out complementary characterization tests on samples of the same set of lignocellulosic biomass materials with the objectives of better understanding their properties and identifying any critical features of the different characterization procedures. Three different types of material were used as model biomasses: 1) Scots pine wood chips, as an example of a coarse and flaky particulate biomass with some elastic properties; 2) chopped straw of reed canary grass as a nesting biomass having long and flaky fibers; 3) Scots pine wood powder as a fine particulate with elastic and cohesive properties. Particle size and shape analyses were carried out with; calipers, 2D image analysis, 3D image analysis (ScanChip) and through mechanical sieving. Applications and validity limits of each of these techniques are evaluated and discussed. The flow function and internal friction 2 were determined with a Schulze ring shear tester, a Brookfield powder flow tester and a large ring shear tester. No significant differences in the results generated by these shear testing techniques were found. Wall friction measurements were carried out with a Schulze ring shear tester; a Brookfield powder flow tester; a large Jenike shear tester and a Casagrande shear box. Results, in this case, showed significant differences with a higher wall friction coefficient obtained with the larger shear cell. Additionally, tensile strengths of biomass materials were measured by the use of a novel measurement technique. Arching tests were carried out in a pilot scale plane silo with variable hopper geometry and results were compared with those predicted by applying the Jenike procedure and a modified procedure which assumed tensile strength was the controlling material property (rather than unconfined yield strength). Finally, safety of handling and storage was assessed by carrying out explosion tests on dusts from Scots pine and reed canary grass.KEYWORDS: lignocellulosic biomass, particle size, particle shape, flowability, arching, explosion RESEARCH HIGHLIGHTS: Suitable test methods were classified for three biomass classes  Different particle sizing methods give a wide range of results  Shear tests do not discriminate flowability differences between the biomass classes  Arching behavior depends more on tensile strength than on compressive strength  Scots pine and reed canary grass dusts are flammable

On the challenges facing the handling of solid biomass feedstocks

“…To facilitate a basis for the design of efficient and adaptive handling, storage, and transportation systems, characterisation of the biomass feedstock properties is necessary. A number of researchers have undertaken this task by evaluating relationships to traditional flow parameters and using well established, consolidation based equipment or defining new equipment most appropriate for the tested feedstock. Undoubtedly, these methods are derived from mined resources (e.g.…”

“…A number of studies into the characterisation of biomass are available. Such programmes have identified areas requiring further research to better define biomass behaviour during pre‐processing, storage, flow and handling and include quantifying particle size and morphology, flowability, strength, elasticity and compressibility, durability, deconstruction, self‐ignition/oxidation and explosibility.…”

Computational and Experimental Studies of Flexible Fiber Flows in a Normal‐Stress‐Fixed Shear Cell

“…Most importantly, the parameters that quantify flowability are necessary inputs for the proper design of bulk solids handling equipment such as hoppers, silos, feeders, and blenders. The Schulze ring shear tester (SRST) is one of the most popular bulk solids flow testers (ASTM Standards, Designation D 6773), and it has been utilized to measure the flow properties of a wide range of granular materials, such as pharmaceuticals, food stuffs, construction materials, and biomass . In tests using the SRST, the shear stresses ( σ xy ) under various normal stresses ( σ yy ) are directly measured.…”

Mass flow and variability in screw feeding of biomass powders — Relations to particle and bulk properties

“…Barletta et al [8] tried to differentiate three different biomass fuels with regards to their arching behavior. Flow functions based on standard shear tests could not predict differences in flow behavior and resulting silo designs were heavily over-dimensioned compared to the results of actual arching tests.…”