Christopher T. Wright

Uniform-Format Solid Feedstock Supply System: A Commodity-Scale Design to Produce an Infrastructure-Compatible Bulk Solid from Lignocellulosic Biomass -- Executive Summary

This report, Uniform-Format Solid Feedstock Supply System: A Commodity-Scale Design to Produce an Infrastructure-Compatible Bulk Solid from Lignocellulosic Biomass, prepared by Idaho National Laboratory (INL), acknowledges the need and provides supportive designs for an evolutionary progression from present day conventional bale-based supply systems to a uniform-format, bulk solid supply system that transitions incrementally as the industry launches and matures. These designs couple to and build from current state of technology and address science and engineering constraints that have been identified by rigorous sensitivity analyses as having the greatest impact on feedstock supply system efficiencies and costs.

A REVIEW ON BIOMASS DENSIFICATION TECHNOLOGIE FOR ENERGY APPLICATION

The world is currently facing challenges to reduce the dependence on fossil fuels and to achieve a sustainable renewable supply. Renewable energies represent a diversity of energy sources that can help to maintain the equilibrium of different ecosystems. Among the various sources of renewable energy, biomass is finding more uses as it is considered carbon neutral since the carbondioxide released during its use is already part of the carbon cycle (Arias et al., 2008). Increasing the utilization of biomass for energy can help to reduce the negative CO2 impact on the environment and help to meet the targets established in the Kyoto Protocol (UN, 1998). Energy from biomass can be produced from different processes like thermochemical (combustion, gasification, and pyrolysis), biological (anaerobic digestion, fermentation) or chemical (esterification) where direct combustion can provide a direct near-term energy solution (Arias et al., 2008). Some of the inherent problems with raw biomass materials, like low bulk density, high moisture content, hydrophilic nature and low calorific value, limit the ease of use of biomass for energy purposes (Arias et al., 2008). In fact, due to its low energy density compared to fossil fuels, high volumes of biomass will be needed; adding to problems associated with storage, transportation and feed handling at a cogeneration plant. Furthermore, grinding biomass pulverizes, can be very costly and in some cases impractical. All of these drawbacks have given rise to the development of new technologies in order to increase the quality of biomass fuels. The purpose of the work is mainly in four areas 1) Overview of the torrefaction process and to do a literature review on i) Physical properties of torrefied raw material and torrefaction gas composition. 2) Basic principles in design of packed bed i) Equations governing the flow of material in packed bed ii) Equations governing the flow of the gases in packed bed iii) Effect of physical properties of the raw materials on the packed bed design 3) Design of packed bed torrefier of different capacities. 4) Development of an excel sheet for calculation of length and diameter of the packed bed column based on the design considerations.

A Technical Review on Biomass Processing: Densification, Preprocessing, Modeling and Optimization

Biomass from plants can serve as an alternative renewable and carbon-neutral raw material for the production of bioenergy. Low densities of 40–60 kg/m3 for lignocellulosic and 200–400 kg/m3 for woody biomass limits their application for energy purposes. Prior to use in energy applications these materials need to be densified. The densified biomass can have bulk densities over 10 times the raw material helping to significantly reduce technical limitations associated with storage, handling and transportation. Pelleting, briquetting, and other extrusion processes are commonly used methods for densification. The aim of the present research is to develop a comprehensive review of biomass processes including densification, preprocessing, modeling and optimization. Specific objectives include performing a technical review on (a) mechanisms of particle bonding during densification; (b) methods of densification including extrusion, briquetting, pelleting, and agglomeration; (c) effects of process and feedstock variables on biomass chemical composition and densification (d) effects of preprocessing (e.g., grinding, preheating, steam explosion, and torrefaction) on biomass quality and binding characteristics; (e) models for understanding compression characteristics; and (f) procedures for response surface modeling and optimization.

A Review on Biomass Classification and Composition, Co-firing Issues and Pretreatment Methods

Presently, around the globe, there is a significant interest in using biomass for power generation as power generation from coal continues to raise environmental concerns. Using just biomass for power generation can bring a lot of environmental benefits. However the constraints of using biomass alone can include high investments costs for biomass feed systems and also uncertainty in the security of the feedstock supply due to seasonal variations, and in most countries, limited infrastructure for biomass supply. Alternatively, co-firing biomass along with coal offers advantages like a) reducing the issues related to biomass quality and buffers the system when there is insufficient feedstock quantity and b) costs of adapting the existing coal power plants will be lower than building new systems dedicated only to biomass. However, with the above said advantages there exists some technical constrains including low heating and energy density values, low bulk density, lower grindability index, higher moisture and ash content. In order to successfully cofire biomass with coal, biomass feedstock specifications need to be established to direct pretreatment options that may include increasing the energy density, bulk density, stability during storage and grindability. Impacts on particle transport systems, flame stability, pollutant formation and boiler tube fouling/corrosion must also be minimized by setting feedstock specifications including composition and blend ratios if necessary. Some of these limitations can be overcome by using preprocessing methods. This paper discusses the impact of feedstock preprocessing methods like sizing, baling, pelletizing, briquetting, washing/leaching, torrefaction, torrefaction and pelletization and steam explosion in attainment of optimum feedstock characteristics to successfully cofire biomass with coal.

Review on Biomass Torrefaction Process and Product properties and Design of Moving Bed Torrefaction System Model Development

Biomass Torrefaction is gaining attention as an important preprocessing step to improve the quality of biomass in terms of physical properties and chemical composition. Torrefaction is a slow heating of biomass in an inert or reduced environment to a maximum temperature of approximately 300°C. Torrefaction can also be defined as a group of products resulting from the partially controlled and isothermal pyrolysis of biomass occurring in a temperature range of 200–280oC. Thus, the process can be called a mild pyrolysis as it occurs at the lower temperature range of the pyrolysis process. At the end of the torrefaction process, a solid uniform product with lower moisture content and higher energy content than raw biomass is produced. Most of the smoke-producing compounds and other volatiles are removed during torrefaction, which produces a final product that will have a lower mass but a higher heating value.

GC Analysis of Volatiles and Other Products from Biomass Torrefaction Process

Gas chromatography (GC) is a common method used to analyze gases produced during various chemical processes. Torrefaction, for example, is a method for pretreating biomass to make it more suitable for bioenergy applications that uses GC to characterize products formed during the process. During torrefaction, biomass is heated in an inert environment to temperatures ranging between 200–300°C. Torrefaction causes biomass to lose low-energy condensables (liquids) and non-condensable volatiles, initially in gas form, thereby making biomass more energy dense.

Optimizing hammer mill performance through screen selection and hammer design

Background: Mechanical preprocessing, which includes particle-size reduction and mechanical separation, is one of the primary operations in the feedstock supply system for a lignocellulosic biorefinery. It is the means by which raw biomass from the field or forest is mechanically transformed into an on-spec feedstock with characteristics better suited for the fuel conversion process. Results: This work provides a general overview of the objectives and methodologies of mechanical preprocessing and then presents experimental results illustrating improved size reduction via optimization of hammer mill configuration, improved size reduction via pneumatic-assisted hammer milling and improved control of particle size and particle-size distribution through proper selection of grinder process parameters. Conclusion: Optimal grinder configuration for maximal process throughput and efficiency is strongly dependent on feedstock type and properties, such as moisture content. Tests conducted using a HG200 hammer grinder indicate that tip speed, screen size and optimizing hammer geometry can increase grinder throughput as much as 400%.

Biomechanics of wheat/barley straw and corn stover

A cost effective and sustainable supply of biomass feedstocks is a critical component of a viable biorefinery industry that is capable of making a credible impact on petroleum displacement. Feedstock costs can amount to a very significant fraction of the cost of the final biorefinery product. Thus, the reduction of the costs of feedstock production, harvest, collection, transportation, storage, and preprocessing can have a direct and positive effect on the overall viability of a given biorefinery. In addition, the feedstock and technology choices that are made for maintaining a sustainable biomass supply will have important implications not only for the biorefinery industry, but also for society as a whole. This session focused on feedstock supply, logistics, processing and composition, all of which are important elements of the feedstock supply chain.

Structural Analysis of Wheat Stems

Design and development of improved harvesting, preprocessing, and bulk handling systems for biomass requires knowledge of the biomechanical properties and structural characteristics of crop residue. Structural analysis of wheat stem cross-sections was performed using the theory of composites and finite element analysis techniques. Representative geometries of the stems structural components including the hypoderm, ground tissue, and vascular bundles were established using microscopy techniques. Material property data for the analysis was obtained from measured results. Results from the isotropic structural analysis model were compared with experimental data. Future work includes structural analysis and comparison with experimental results for additional wheat stem models and loading configurations.

Proximate and Ultimate Compositional Changes in Corn Stover during Torrrefaction using Thermogravimetric Analyzer and Microwaves

Energy from biomass is considered carbon-neutral because the carbon dioxide released during its use is already part of the carbon cycle. Increasing the use of biomass for energy can help to reduce the negative CO2 impact on the environment. There are many challenges in using biomass for energy applications, such as low bulk density, high moisture content, irregular size and shape, hydrophilic nature, and low calorific value. In commercial scale operations where large quantities of biomass are needed, these limitations will create problems associated with storage and transportation. Furthermore, grinding raw biomass with high moisture content is very challenging as there is no specific equipment, which can increase costs, and in some cases becomes highly impossible. All of these drawbacks led to the development of some pretreatment techniques to make biomass more suitable for fuel applications. One of these is torrefaction. Torrefaction is the heating of biomass in an inert or reduced oxygen environment. During torrefaction, biomass losses moisture, becomes more brittle, and increases energy density values. Several technologies exist for the torrefaction of biomass—fixed bed, bubbling sand bed, screw extruder, and moving bed are the most commonly used. The use of microwaves for the torrefaction of biomass has not been explored at present. In the present study, we looked into the torrefaction of biomass using the established methods as well as by using microwaves and their effect on proximate and ultimate composition. Studies indicated that microwave torrefaction is a good way to pretreat the biomass in short periods of time. A maximum calorific value of 21 MJ/kg is achievable at 6 min residence time as compared to 15 min using the dry torrefaction technique. Increasing the residence time also increased the carbon content where a maximum carbon content of 52.20% was achievable at a lower residence time. The loss of volatiles is comparatively lower as compared to the dry torrefaction technique. Moisture content of microwave torrefied samples was in between 2–2.5% (w.b).