To date, all of my articles have been technical in nature. This article is more of an editorial on the state of our powder handing industry. I presented this topic at the Powder Show in Houston in October of 2013, and would like to repeat some of the relevant topics here. My hope is that it will spark a discussion of trends and areas that need attention that will improve our industry in the future.
Any discussion of the state of an industry should begin with a brief history. Although there are many contributors to the success of our industry, these four stand out:
• Coulomb (1773) and Rankine (1857) did significant work on friction properties based on soil mechanics properties.
• Janssen (1895) developed a theory of pressure distribution in grain silos that is still used today.
• Jenike (1960s) developed a solids flow theory and testing device to measure solids flow properties. Jenike’s approach is the standard in Europe through European Federation of Chemical Engineers and in the U.S. through ASTM D 6927. Along with Jerry Johanson, he wrote what is considered the bible of our industry, Storage and Flow of Solids Bulletin 123 of The Utah Engineering Experiment Station.
The science of powder and bulk solids handling is dependent on knowledge of material flow properties and proper design technique to ensure practical solutions to problems. Before an attempt is made to design a handling system or solve a flow problem, it is critical to measure your powder’s flow properties.
The following are some of the challenges that face our industry today:
• The economy plays a major role in any industry. Within the powder handling industry, plants are being shut down as funds for upgrades to powder handling equipment are difficult to come by, and staff is being reduced, especially engineering staff.
• Research also plays a major role in our future. New technology is seemingly non-existent as companies are spending little on research and development in order to make ends meet.
• Education is critical to the future of our industry. Consider that the topic of bulk solids handling is not presented to university students. Most engineers graduate with no knowledge of the science of bulk solids handling and are challenged when asked to address solids handling problems. As well, most are not familiar with the fact that Bulletin 123 even exists.
• Luckily there are industry shows where someone new to bulk solids handling can be educated. The biannual Powder Show, produced by UBM Cannon and Powder & Bulk Solids, is available as a solution to the lack of education. This show has been around for years and continues to get better and better. Conferences are available, along with exhibitors displaying their equipment and eager to answer your questions.
Where is the industry heading in the next five years?
• The economy seems to be recovering, although slowly and volatile. However, aging equipment will have to be upgraded. This provides opportunities for reliable vendors to help customers solve their flow problems.
• Retrofitting existing equipment or purchasing new equipment is always a tough decision to make. As our economy continues to be erratic, companies are resorting to retrofitting existing equipment. This is not an entirely bad decision, because retrofitted equipment can perform quite reliably if done properly. I have spent years as a consultant modifying existing bins and feeders to improve flow and solve difficult flow problems. I would estimate that about 65% of my work involves retrofits. However, sometimes it is more practical to just build a new bin and feeder. An application I worked with recently required just that. The product was being handled in a square bin that was in an awkward location and was experiencing segregation problems. It was more advantageous to remove the troublesome equipment than to fix it. Providing a new bin in a different location was less expensive than modifying the existing bin.
• The need to eliminate the stagnation due to lack of education, as most engineers graduate with no knowledge of the science of bulk solids handling and are challenged when asked to address solids handling problems. The only university that I am aware of is that is offering at least a semester on solids handling is Purdue University. Penn State and Virginia Tech are doing some work in solids.
• Discrete Element Modeling (DEM) is an interesting tool for modeling solids flow (especially in chutes). Advances are being made to evaluate fine particle flow in a reasonable amount of time without use of a super computer.
• Biomass is becoming an increasingly popular approach to renewable energy. Plants and derived products are used either directly such as creating heat (wood chips, pellets), or indirectly to product Biofuels. It is estimated that 146 billion tons per year of biomass is used. Materials such as sugarcane, corn starch, switch grass, bamboo, palm leaves, etc., are used. Agricultural and municipal wastes are also being used.
What is important for the future of the industry?
• A correlation between a bulk solid’s flow properties (cohesive strength and wall friction properties) that can be applied to pneumatic conveyor design is necessary. It is important in pneumatic conveying to determine convey line pressure drops and pickup velocity. Is there a way aid in this analysis using the material’s flow properties?
Properties such as particle density, particle size distribution, and particle shape play a role in a properly operating pneumatic conveying system.
• Many silos experience quaking (vibrations) due to the flow of certain materials, especially when highly incompressible materials such as roofing granules, PET pellets, frac sand, etc., flow in mass flow. This causes significant vibrations (quaking) on the silo walls. Flow rate changes do not affect this phenomenon, and just changes the amplitude of vibration.
• Particle segregation is common in most solids handling applications. Addressing these problems can sometimes be very difficult, as you need to evaluate the entire process to determine where the product is segregating, how badly it is segregating, and how to solve the problem. Many industries are affected by segregation problems, especially the pharmaceutical industry.
• When Jenike developed his theories of solids flow, he found funnel flow problems to be particularly unpredictable. Mass flow is straightforward and predictable; not so funnel flow. The major problem with funnel flow is ratholing, and the approach used today is ultra conservative. A less conservative approach would be welcome.
• Testing elastic materials, such as flaky products, is particularly difficult as the direct shear devices that are typically used to evaluate material flow properties cannot handle the large particle materials that compose biomass, etc.
• As stated previously, education is critical to the future of our industry. Why is powder handling not taught at the university level? Industry needs to push for this information at local schools. Venues like the Powder Show in Chicago continue to provide relevant and timely information for those who experience powder and bulk solids handling problems and will play a much greater role in the future.
Obviously, the above editorial is my opinion as to the state of our industry. I would welcome your opinions as they relate to this topic. Please email me at [email protected] with your response and I will update the article periodically to reflect these opinions. Also, please track me down at the Powder Show in May in Rosemont, as I am conducting two seminars and will be around the show for its entire three days.
Joseph Marinelli is a consulting engineer and president of Solids Handling Technologies. He has been providing testing and consulting services since 1972. As a former consultant with Jenike & Johanson Inc., he has years of experience testing powders and designing bins and feeders for reliable flow. He lectures frequently on the topic of powder handling and has published several papers including and article in a chemical encyclopedia and two in a food powder book.
Solids Handling Technologies
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Fort Mill, SC 29708