| Upcoming Training Courses:
Atlanta, Georgia December 10-12, 2008
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| Greetings!
Greetings!
Welcome to the premier issue of Jenike & Johanson's chemicals e-newsletter, which focuses on bulk material handling challenges and approaches that are relevant to the chemical industry. |
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Do You Need A Cost-Effective Method For Removing Residual Moisture or Volatiles?
Evaporation of moisture or VOCs (volatile organic compounds) from solids usually takes place in two stages, one in which the drying rate is constant, and the second in which the rate decreases over time.
 Devolatilization during the first stage is rapid and can be readily accomplished in flash, spray, or fluidized bed dryers. In the second stage, however, the VOC or moisture removal rate is diffusion limited, and several hours of residence time are often necessary. To meet low moisture or low VOC targets, two unit operations are usually needed.
An economical way to provide the long residence time required for slow, diffusion-limited drying is to use a modified bin or silo to allow injection of a sweeping gas and, in some cases, provide heating. Relative to other methods, such as heated screws, paddles, or disks, fluidized bed processors, and tray dryers, modified bins or silos offer several advantages:
- The capital cost of a modified vessel can dwarf that of a fluid bed processing unit or heated screws.
- Modified bins and silos have no mechanical agitators or other moving parts, which eliminates the maintenance costs associated with such devices.
- Adapted vessels provide a longer residence time than most other technologies.
To ensure homogeneous heating of the bulk solids  stream, the solids and gas streams must move through the vessel at a uniform rate. To achieve a nearly constant solids velocity profile, the walls in the converging section of the silo must be steep enough and have low enough friction to ensure flow along the walls, i.e., allow mass flow. Our patented J-PURGE™ technology provides a uniform distribution of the sweeping gas.
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Why Vibration Isn't Always Effective In Improving Flow
When arching occurs in a bin or silo, you may be tempted to install a vibrating device to impart additional stress to dislodge the obstructed material. In some cases, vibrating devices may be effective. In other cases, a vibrator may make matters worse and cause arching to happen more frequently. Why is this so?
A cohesive arch results when the strength that a bulk solid under construction in a bin or silo is high enough to support its own weight. The purpose of a vibrator is to promote flow by imparting enough stress to the obstruction to cause it to fail. However, vibration may also result in further consolidation of the bulk solid, thereby increasing its cohesive strength. Hence, vibration may not be effective and can actually make arching problems more severe. In addition, because vibrators are attached directly to the vessel wall, the stresses that can be imparted to the material are limited. Also, a structural check may be necessary, as cyclical loading from a vibrator can cause structural damage or failure to occur.
A better approach to solving an arching problem is to modify the hopper. First, the flow properties of the bulk solid, i.e., its cohesive strength, compressibility, and wall friction are measured. Then, using the flow properties, an engineering analysis is carried out to determine the outlet size and hopper geometry that ensures that stable arches cannot form.
Contact Jenike & Johanson to find solutions to your material handling problems.
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Course Offering - Flow of Solids in Bins, Hoppers, Chutes & Feeders
December 10-11, 2008 in Atlanta
This course will include topics such as:
- Equipment types and the solutions to flow problems commonly associated with each of
 them.
- How friction, cohesion, compressibility, and other properties affect the flow of solids through various types of feeders, chutes, reactors, bins and hoppers.
- How to specify and select hardware best suited to avoid various bulk solid flow problems and objectives, including how to retrofit existing equipment to correct flow problems.
- Solving problems associated with solids handling, such as lost production, downtime, extra labor, poor quality control, degraded material, and unreliable equipment.
An additional one-day course on pneumatic conveying will be held on December 12. Although pneumatic conveying systems have been designed and operated for many years, their successful operation is still more often based on experience rather than science. This course will cover pneumatic conveying fundamentals, system layout and selection, and troubleshooting.
Visit ASME's web site to learn more & register. |
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Greg Mehos, Ph.D., P.E. appointed to AIChE Particle Technology Forum Executive Committee
 The Particle Technology Forum (PTF) is an international and interdisciplinary forum that promotes information exchange, scholarship, research, and education in the field of particle technology. Its executive committee consists of four members from academia and four members from industry. Greg Mehos, project engineer, Jenike & Johanson, was appointed to serve on the committee during 2009-2012.
"Compared to liquids and gases, my university education in handling bulk solids was somewhat lacking," says Greg, a chemical engineer. "Without a good understanding of bulk solids technology, specifying processes for handling solids can be a daunting task. I am excited to be a part of PTF's effort to improve chemical engineers' understanding of bulk solids." |
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Recent Chemical Publications
For more information on the following publications, please contact Greg Mehos via email or telephone at 978-649-3300.
- "Successfully Scale-up Solids Handling", J. Carson, T. Troxel, and K.E. Bengston, Chemical Engineering Progress, April 2008
- "Hopper/Bin Design" , J. Carson, D. McGlinchey, ed., Bulk Solids Handling, Equipment Selection and Operation, Hoboken, NJ, 2008
- "Modifying Your Storage Vessel for Trouble-free Continuous Purging or Conditioning - Part 1", G. Mehos, Powder and Bulk Engineering, November 2008
- "Preventing Caking and Unwanted Agglomeration" , G. Mehos and S. Clement, Chemical Engineering, August 2008
- "Using Silos to Heat or Cool Solids", G. Mehos and B. Pittenger, Chemical Engineering, August 2007
- "Uniform Purging of Resins in Contact Bed Purge Vessels", B. Pittenger, J. Carson, J. Prescott, and H. Purutyan, Polymer Engineering and Science, September 1999
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Background of Jenike & Johanson
Jenike & Johanson is a consulting engineering firm specializing in the science and technology of bulk solids handling. In our four laboratories in the United States, Canada, and Chile, we have tested more than 8,000 bulk solids and used the results to design accurate, cost-effective solutions to flow-related problems for more than 3,000 companies around the world in such industries as cement, chemicals, pharmaceuticals, food, energy, mining, consumer goods, solid waste, and more.
Learn more about Jenike & Johanson's role in the chemical industry. | |
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We look forward to providing you with practical, cost-effective solutions to your bulk solids handling problems.
Sincerely, |
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Greg Mehos, Ph.D., P.E.
Jenike & Johanson, Inc.
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