James H. Dooley

Woody biomass size reduction with selective material orientation

Background: Roundwood logs from forests and energy plantations must be chipped, ground, or otherwise comminuted into small particles prior to conversion to solid or liquid biofuels. Results & discussion: Rotary veneer followed by cross-grain shearing is demonstrated to be a novel and low energy consuming method for primary breakdown of logs into a raw material having high transport and storage density. Processing of high-moisture raw logs into 2.5–4.2-mm particles prior to drying or conversion consumes less than 20% of the energy required for achieving similar particle size with hammer mills, while producing a more uniform particle shape and size. Conclusion: Energy savings from the proposed method may reduce the comminution cost of woody feedstocks by more than half.

Engineering Factors for Biomass Baler Design

Woody biomass is a core element of our nations strategy to replace imported oil and natural gas with renewable resources. The challenge facing potential biomass users, however, is how to economically recover and transport the material from residential neighborhoods, urban centers and suburban landscapes to distant users. Our preferred solution is to bale the bulky biomass at the roadside to reduce the cost of at-site processing, increase payloads during hauling, and preserve physical properties for more appropriate feedstock processing by woody biomass users. A preliminary step towards this goal is determining the appropriate bale and baler size.

Large Rectangular Bales for Woody Biomass

Woody biomass from wildfire prevention and forest health improvement projects is a significant source of feedstock for bio refineries, combustion energy facilities and other value-added uses. Baling into large rectangular bales offers increased bulk density and easier handling for local and long-distance transportation. By preserving large piece sizes, value potential is maximized. We conducted a problem analysis across the Western US that included surveys, interviews and site visits. Subsequent technology analyses and ideation resulted in a conclusion that prefers large rectangular bales as the handling unit.

Low-energy Comminution of Woody Biomass to Create Precision Feedstock Particles

Under funding from DOE Office of Biomass Programs, engineers at Forest Concepts are working to apply low-energy comminution methods to produce improved biomass particle geometry and sizes optimal for biochemical and thermochemical conversion to liquid transportation fuels. Designs are constrained to concurrently achieve the DOE Uniform Feedstock Format criteria for bulk handling and flowability. The innovative comminution process independently controls shearing of biomass feedstocks parallel to the fiber orientation and cross-grain. Short-length cross grain shearing opens particles to high mass transport and eliminates fiber balls and other materials handling problems typically associated with hammer milling. The process is currently operating routinely at laboratory scale (200 kg/shift) on woody materials at a roundwood to 2mm cubic particle at a specific energy cost of approximately 150 MJ/odMg.

Shear Processing of Wood Chips into Feedstock Particles

We have an objective to convert cellulosic biomass raw materials into small particles that are optimized for biochemical and/or thermochemical conversion to liquid transportation fuels. As a side effort, we are interested in producing feedstocks for composite bioproducts, solid biofuels, and other uses. Wood chips that have a typical length of 50mm are a common raw material. This experiment seeks to evaluate the change in particle sieve analysis, geometric mean dimension, and particle shape as wood chips are processed through one or more rotary shear configurations as well as to determine the incremental specific energy consumption. Wood chips processed by two passes through a 4.8mm cutter set changed the geometric mean dimension from 26.4mm to 5.6mm at a total cost of less 30MJ/odt. Additional combinations are discussed.

Torque-arm Method to Measure Specific Energy in Laboratory Scale Biomass Preprocessing Equipment

Specific energy for comminution and mechanical processing of lignocellulosic feedstocks provides an economically important basis to compare equipment and to provide data for lifecycle analysis of complete systems. Measurement of specific energy during equipment design and development activities enables optimization of design parameters. Forest Concepts developed a torque-arm apparatus and LabView data acquisition method that has proven to be easily adapted for preprocessing equipment such as orbital sieves, flail debarkers, and comminution machinery. We provide a comparison of torque-based energy measurement versus electrical motor current based measurement to demonstrate the limitations of motor current methods.

Beneficiation of Chipped and Shredded Woody Biomass

Forest Concepts, with funding from USDA NIFA SBIR program, developed methods and equipment to reprocess low-value dirty forest chips, tree service chips, and hog fuel into high value clean wood fiber and other valuable fractions. Traditional clean sources of mill residuals (sawdust, shavings, and chips) are declining rapidly due to improved sawmilling efficiencies and a general decline in the number of sawmills in operation. Thus, competition for low-cost clean fiber is intense. A USDA NIFA SBIR supported beneficiation project sought to increase the clean fiber supply by tapping low grade, often inexpensive or negative cost raw materials. To validate the SBIR funded engineering science work, our engineers designed and built a set of demonstration-scale (one ton per hour) machines that can be mixed and matched to clean low grade woody biomass to meet nearly any ash or bark content specification. Results of validation tests demonstrate the performance of innovative methods for cleaning high-ash land clearing debris.

Field Experience with Street Legal Square Baler for Woody Biomass

We conducted a problem analysis in 2005 to recommend an optimal method for collection, transport, and handling of woody biomass in urban centers, suburban landscapes, and forested areas. The analysis concluded that street-legal biomass balers should replace tow-behind chippers to enable woody biomass to be packaged and handled just like other recyclables. Design and development of an engineering prototype street-legal baler for woody biomass was completed in early 2008. Two years of testing and demonstrations in urban, suburban, and forest settings have produced a wealth of technical and market information that will inform commercialization of woody biomass baling technologies. This paper reports on the results of baling and logistics trials across a range of operating environments and biomass materials.

Protocol for Assessing Particle Shape of Comminuted Biomass

Particle shape is increasingly important as a quality parameter for comminuted biomass. Shape affects flowability, pretreatment, rate of conversion, and performance of materials handling systems. This protocol applies to materials that have been subjected to commutation processes including but not limited to chunking, chipping, grinding or milling. Our objective is to enable a uniform terminology and method for characterizing particle shape of chipped, ground, or otherwise comminuted woody biomass. The protocol was specifically developed for chipped and ground woody biomass and may be applicable to other lignocellulosic raw materials and feedstocks. Results are presented for analysis of chipped and shredded forest derived woody biomass.

Modeling Energy Consumption for Crushing of Roundwood as a First Stage of Feedstock Preparation

Our objective is to apply an understanding of the modes of failure and structural biology to substantially reduce the comminution energy required to produce bioenergy feedstocks. This paper explores the modes of failure for wood materials subject to crushing forces and how they could be used to develop a mathematical model of crushing forces for a round roller acting on a round log. Our hypothesis is that crushing or roller-splitting is a low-energy and effective method to reduce the thickness of round logs and change the resulting shape for subsequent processing. Modes of failure during crushing suggest that a mathematical model could be developed to estimate required crushing forces and energy for round logs. Such a model has been called for since early work by the USDA Forest Products Laboratory and Tennessee Valley Authority more than 30 years ago. A model was developed by the authors and experimentally validated for the case of a round roller compressing a round log.