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In This Issue:

• Ask an Expert: Non-free-flowing coal in railroad bins
• Feature: Choosing the right pneumatic conveying system
• Feature: New elbows prevent material leaks
• Industry News

Q: We need some way to handle a coal with 12% moisture. We’re currently unloading our railroad bins by gravity, but with this amount of moisture it’s practically impossible to get the coal to discharge completely. What do you suggest? -- G. Mendoza, Anahuac, Mexico

John Carson, Jenike & Johanson, says:
Getting a cohesive (i.e., non-free-flowing) bulk solid such as 12%-moisture coal to discharge reliably from bins and silos is a common problem, so you're not alone.

The first step in solving this problem is to determine the coal's flow properties. The friction that develops between the coal particles and the hopper surface determines the required hopper angles and outlet size. Run standard test procedures, such as ASTM D6128 or ASTM D6773 (www.astm.org), on a representative sample of your coal, simulating continuous flow and storage time at rest. The results can help you analyze the bin to determine why the coal isn't flowing properly and how to modify the equipment to solve this problem.

The flow pattern in the bin determines how well your material discharges. There are two flow patterns that typically develop in a bin: funnel flow and mass flow. With cohesive bulk solids it usually is essential to develop a mass flow pattern in the bin.

In a funnel flow pattern, when you discharge material from the bin, the material directly over the discharge opening may move out of the bin, while material nearer the bin’s walls remains stagnant. This often happens when a bin’s hopper wall surfaces are rough or the wall angle is shallow.
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John Carson is a consulting engineer and president of Jenike & Johanson in Tyngsboro, Mass., and a member of PBE’s Editorial Advisory Board.

Editor’s note: To send your comments or questions about this or other issues related to handling and processing dry bulk solids, send an e-mail to holly@cscpub.com.

A pneumatic conveying system is efficient and inherently dust-tight, making it the most practical equipment for moving large quantities of many dry powders, granules, and pellets. The system uses an airstream to push or pull material through a fully enclosed horizontal or vertical conveying line (pipe or tubing). There are several types of pneumatic conveying system, so how do you decide which will work best for your application?

Pneumatic conveying systems can use pressure or vacuum, and both can be used for either dense-phase (high-pressure, low-velocity) or dilute-phase (low-pressure, high-velocity) conveying. Many factors, including your conveying distance and velocities and your air-to-material ratio, will affect your choice.

You’ll want to consult with a pneumatic conveying specialist (a consultant, engineering firm, or equipment supplier) before making your system choice. You can find many consultants and engineers in Powder and Bulk Engineering’s annual “Reference and Buyers’ Resource Issue", which is published each August. Prepare for your discussion by answering the following questions:
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A southern US company manufactures small ceramic beads (called proppants) that are used by the oil and natural gas industries in drilling applications. The company produces about 750,000 pounds of proppants a day in several different sizes, the largest of which is about the size of a grain of sand. The proppants are classified by size, and the company uses several dense-phase conveying lines to move each size of proppants into one of 10 large outdoor silos.

Each conveying line’s 6-inch-diameter schedule 80 piping runs horizontally from the plant to a silo, where a 90-degree elbow transitions the piping vertically upward. At the silo’s top, another 90- degree elbow transitions the piping horizontally, directing it to the silo’s inlet. A 90-degree elbow at the inlet transitions the piping vertically downward into the silo.

The conveying system operates 24 hours a day, 7 days a week, cycling about 25 to 30 times an hour. However, the abrasive proppants were causing big problems for the company. The tiny beads wore holes in the conveying system’s elbows in only a few months. Constantly having to patch and replace elbows and clean up spillage impaired the company’s operations. When the maintenance supervisor and crew had to tend to an elbow, the conveying line had to be shut down.

After replacing several T-elbows, the company decided to install two hard-surfaced long-radius sweep elbows to see if they would perform better than the T-elbows. But within days, the sweep elbows had holes in them, and patches didn’t last any longer than the original elbows.

To find out how the company solved its elbow wear problem, you can read “Case history: New elbows help company’s conveying system turn corner toward improvement” from the October 2006 issue of Powder and Bulk Engineering. To read it today, click here.

ANSI sponsors conference to discuss chemical controls.
The American National Standards Institute will host a conference on August 9-10 at the Hyatt Regency in Baltimore on the impact of domestic and foreign chemical controls, including REACH, RoHS, WEEE, SAICM, and GHS.

The conference, “Action and Reaction: Developing a sustainable approach to emerging chemical issues” will bring together stakeholders from the public and private sectors to address the mounting pressure on global manufacturers arising from these controls. Participants will discuss solutions to meet these controls in an efficient and sustainable way.

To read more about the conference, click here.

Feeding: Troubleshooting and Maintenance, September 11, 12:00 Eastern Daylight Time. Web seminar sponsored by Powder and Bulk Engineering. Presenter John Carson will discuss bin flow patterns and design, as well as design techniques for various types of feeders. To register, click here.

2007 IBA Conference, October 21-24 at the Hilton Savannah DeSoto in Savannah, Georgia. Sponsored by the Institute for Briquetting and Agglomeration (IBA). Contact Tom Feldkamp at 715-543-2750, fax 715-543-2751 (tnfeldkamp@centurytel.net; www.agglomeration.org).

Solids Handling: Bins, Feeders, and Pneumatic Conveying Systems, September 5-7, Madison Concourse Hotel in Madison, Wisc. Sponsored by the University of Wisconsin-Madison Department of Engineering Professional Development. Course will cover practical information for avoiding or solving solids handling problems, including flow problems and their effects, feeders, bin dimensions, and other handling principles. Contact Elaine Bower at 800-462-0876 or 608-262-2061 (bower@engr.wisc.edu or custserv@engr.wisc.edu; http://epdweb.engr.wisc.edu).