Biomass Material Handling

Characterization, receiving, conveying and preprocessing feedstock
By Yuri Chocholko | April 27, 2012

To the laymen, the rapidly developing second-generation cellulosic ethanol industry may very well appear to be an alchemistical pursuit. But where the public may see similarities between the two, a good solution provider understands that there’s nothing magical about the processes involved in creating cellulosic ethanol.

As long as all parts of the process work together, turning something of little value into something of great (and it seems, constantly increasing) value can be done on a large scale—without the use of magic. Material handling and feedstock preparation, while only one part of a complex process, is equally important to the success of a cellulosic ethanol production facility as feedstock selection or any of the different chemical processes, or “black boxes,” generating final product. A summary of feedstock material handling can simplify it to show four main areas: characterization, receiving, conveying and preprocessing.

Characterization of feedstock requires understanding its properties. Moisture, bulk density, particle size and range, seasonal properties, abrasiveness and contaminants are just a few of the items that should be considered as they all effect the equipment selection and material flow during processing. A woody biomass system differs from a switchgrass or corn stover system in many ways, so knowing the material properties and characteristics is an essential part of the solution provider’s task to configure the correct equipment and processing methods. A hammermill used to reduce wood size may not perform the same task on straw; a dual-shaft shredder that can handle entire bales, the string that binds them and any loose rocks may better serve those needs.

Receiving and storage methods for feedstock are largely determined by the characterization results, as well as how the material is transported to site. If blending different feedstocks together, allowing separate systems to handle the incoming material may be necessary. Miscanthus bails cannot be processed or stored the same as a truckload of wood chips, so blending the materials together requires additional equipment and expenses. Reducing material decomposition and accelerated decay in storage can be done via a first-in/first-out (FIFO) material flow and protecting product from the elements. These factors effect material flow options and decisions made when the facility is laid out.

Conveying may seem like a simple operation of getting from point A to B, but it can be a continual problem area in biomass processing operations. The answers gained during characterization will govern many decisions here. Distance, angle and throughput are all obvious questions that must be asked. Conveyor type, style and maintenance needs are must also be considered. Will a belt conveyor suffice, or should a chain conveyor be considered over steep angles and long distances? What is the material’s angle of repose and what cleat configuration would work best? If selecting a drag-chain conveyor, should you use a single- or double-chain configuration? How far can we transport the material with a single drive? In the event of a blockage, is a screw conveyor reversible for maintenance and clean out? Do you need to provide explosion and fire protection at certain transfer points? Many operators look past moving material a short distance, a seemingly simple task, but poor conveyor selection and design can be, and often is, a bottleneck in an otherwise successful operation. Be very particular and detailed in this area of your design—understanding the way feedstocks react to differing conveying methods is critical to achieving any operation’s throughput requirements.

Preprocessing covers a wide range of operations, but two main categories require focus: size reduction and contaminant removal. Hammermills, pelletizers and briquetters have been used for years in the biomass industry, but slow-speed single- and dual-shaft shredders are becoming more prominent amongst leading cellulosic ethanol companies. Particle size consistency, ease of maintenance, power consumption and reduced risk of fire or explosion are driving factors behind this trend. Screening, tramp metal detection and fines-removal systems all play a large part in protecting the equipment and end product. “Black-box” methods of breaking down sugars, and finally producing ethanol, differ but they all have a common need; contaminant-free feedstock with consistent particle size enables their most effective, efficient results. The preprocessing equipment and methods will greatly determine an operator’s achievable levels of success.

Finding an integrated solutions provider with equipment, experience and expertise to meet your requirements is perhaps the most important consideration to ensure all the puzzle pieces fit together correctly and work to achieve the same throughput. Look for a company that can test your materials. Work with someone who provides a complete package (hardware and software) that is intuitive and flexible, and can adapt to the constantly evolving cellulosic ethanol industry.

Author: Yuri Chocholko
North American Sales Manager: Wood,
Biomass & Fuels, Vecoplan LLC
(336) 861-6070