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Ever had a problem getting powders or other bulk solids to flow out of a bin or silo?  Sure, it's a common enough problem.  Material flow problems can create major headaches and cost your company in lost production, increased labor and maintenance as well as opportunity losses associated with diminished throughput.  In addition, you can have lost product due to caking and even vessel failures as a result of flow problems.  This all means lost money, profit, etc.  That's why it's important.

The Cause
When powders are placed in a bin or storage silo it enters the vessel in a 2-phase form as a mixture of particulate and air.  Often powders are conveyed pneumatically, introducing additional air.  Flow problems will occur as the air entrained in the 2-phase mixture is expelled and the particulate packs together.  The degree of flow problem can be dependent on many factors including the material agglomeration factors and coefficients of friction.

Once entrained air escapes and the powder packs, a number of conditions can be created.  These include ratholing, bridging and flooding problems.  The illustrations here show what a rathole or bridge may look like.  Flooding is uncontrollable material flow, usually resulting from a collapsing rathole.

Solutions
Like many other things, there is "more than one way to skin the cat" (where did that expression come from?..... click here to find out ).  First, and most obvious to me is to eliminate the cause with something you can control, and do it before you have a problem.  What I am getting at is the bin or silo design.  Jennike & Johansen are experts in this field so I'll let them do the talk and just provide a link to a PDF document for more information on mass flow bin/silo design.  But don't wait until you have a problem to solve.  Consider this before you decide on what silo to buy and use.

However, most problems are existing which means the bin/silo is already in place and you can't get the powder out properly.  You need a solution quickly.  The next alternative, and not necessarily the best, is to use an external source of vibration to shake everything up so the material flows.  Does this work?  Yes, but....... it can create problems too.  Vibrators (Cougar, NAVCO, VIBCO and others) can actually pack the material by shaking it and removing remaining air.  Vibrators are typically only used when the flow of material is required.  The selection and application of an appropriate vibrator should be carefully considered and reputable companies should be consulted.

Another solution is the use of aeration devices to fluidize the powder (adding air) creating a flowable state, thereby initiating material flow.  There is a wide variety of aerating devices that come in all shapes and sizes.  The proper selection, quantity and location must be done based on experience in order to produce the desired results.  Aerating devices add entrained air back into the material creating the natural 2-phase mixture allowing it to flow.  This is successfully used on many types of powders and the aerating device itself is relatively inexpensive ($15 and up per each).  Multiple aerators will be required.  The aerators are typically in operation full time, unlike vibrators.  One example is a cement silo where 8-12 aerators are used in the cone section to promote material flow.  Each of these aerators cost about $20.  In addition, dry plant air is required along with all of the piping.  For more information on using bin aeration devices to solve flow problems, click on the image to the left.


Joe Lewis
Vice President - Marketing & Sales
Monitor Technologies LLC
jlewis@monitortech.com
www.monitortech.com
www.flexar.info

Several years ago, Pennsylvania Crusher added a new model, the Mountaineer^® Sizer, which has enjoyed a surprisingly rapid rate of adoption as a replacement for older crusher designs and as new crushing systems are installed – especially in the coal business where increased demand has occurred. This is not your typical scenario in capital equipment purchases, where industrial end users tend to approach change slowly. Existing equipment, however old, is normally expected to reach the very end of its useful service life before replacement is considered. Also, few industry users really care to be the very first to install a new piece of machinery that can range in cost from $175,000 up to $650,000, depending on the variables.

The newer Sizer designs differ substantially from more familiar size reduction machinery, such as roll crushers, that were traditionally used at some installations. Like crushers, sizers still reduce by mechanical forces but rely predominately on shear force as opposed to impact and compression forces. The Mountaineer uses tooth shapes that are nothing new, but the sizer design concept involves two revolving rolls bearing rows of teeth that rotate inward or outward at slow rotational speeds to reduce the material, which is a fairly new development.

Changing to a sizer means you spend less total money for the machine and the structure required to support that machine. Sizers are very compact and considerably less expensive to install than other crushers, which are typically much taller and bulkier. With these advantages, the Mountaineer Sizer is proving to be very desirable -- and saleable. A number of coal mines in the U.S. have already installed our sizer, as did a coal mine in Indonesia, just last year. 

And now, in a rapid succession of firsts, the Mountaineer Sizer has had:

• The first sale in the U.S. to a non-coal application, purchased by National Gypsum in Garden City, Georgia, where the sizer will crush--what else--gypsum
• The first sale in Russia, to a coal preparation plant
• The first sale in China, also to a coal preparation plant

Of course, every machine installed tends to increase the chances of more machines going into that industry or region. Plant managers know each other, people change jobs but stay within the industry, and everyone likes to keep up on news about equipment in other plants.  This informal grapevine is where users learn how well a machine’s working (or not working). Judging from industry acceptance so far, on several continents, it appears that the Mountaineer Sizer will have a long and productive career at Pennsylvania Crusher.

For more information on the Mountaineer Sizer, contact Scott Eck at seck@penncrusher.com, or visit www.penncrusher.com.

Scott Eck
Product Manager for Mountaineer® Sizers
Pennsylvania Crusher