J&J’s Tracy Holmes Offers Advice on Powder Flow Issues

May 10, 2019

6 Min Read
J&J’s Tracy Holmes Offers Advice on Powder Flow Issues
Tracy Holmes of Jenike & Johanson

In advance of her appearance at this year’s Powder Show Toronto running from June 4-6 at the Toronto Congress Center in Canada, Tracy Holmes, the president of Jenike & Johanson, Ltd., answered a few questions from Powder & Bulk Solidson common powder handling and flow issues and how operators can take steps to fix or prevent them. On June 4, Holmes will offer a presentation, "Help! My Powder or Bulk Solid Won't Flow from my Bin, Hopper or Silo!" at the event's Center Stage (Booth 170) from 10:30 a.m. to 11 a.m. and host "True or False: Bulk Solids Edition" from 1:29 p.m. to 2:15 p.m. at the Tech Theatre (Booth 127).

PBS: Why is the handling and processing of powders so challenging? Is there an easy fix for flow issues?

TH: One challenge comes from the variability and range of powders and their properties. Another challenge comes from the wide range of potential applications and their associated flow problems. 

The flow behavior of powders can change with even slight changes in intrinsic properties (e.g. particle size and distribution, moisture content) and environmental conditions (e.g. temperature and relative humidity, storage time at rest). In addition to intrinsic properties and environmental conditions, powder flow behavior is affected by the equipment geometry and interior (sliding) surface. Matching the flow properties with the design of the equipment, results in controlled flow. If these are not well matched, poor flow or no flow will result. In short, if the equipment is not engineered based on the appropriate material properties, flow issues are very likely. 

The easiest “fix” is prevention. Our best advice is to measure and consider flow properties from the outset while engineering a new system or changes to an existing system. J&J has developed a proven scientific approach to address the toughest bulk material handling issues. 

PBS: What are the top five most common flow-related problems that those handling or processing powders face? Why do those issues occur?

TH: The most common flow-related problems with powders are no flow (arching, ratholing), flooding (uncontrolled flow), limited discharge rate, segregation, and caking. As mentioned before, the key factors in handling powders are the material properties and equipment design. 

These problems typically occur when the designs selected are not appropriate for the powders handled. For example, there is a minimum hopper outlet size that is required to prevent arching of a given powder under certain handling conditions.  If the hopper outlet is selected to be smaller that this minimum size, flow stoppages are likely.  The minimum outlet to prevent arching (hence prevent flow stoppages) can be determined based on flow properties of the powder being handled.

PBS: How can material characterization improve the handling and processing of powders?

TH: Material characterization is extremely important. Just as the design of a pumping system requires knowledge of the fluid’s properties, friction factors, etc. powder handling system design requires powder flow characteristics.  Powder characterization allows a better understanding of the effects that variables, such as moisture content, particle size distribution, and storage time at rest have on flow properties. This knowledge allows the proper selection of equipment geometry and operating conditions to match the flow properties and provide reliable flow. This information can also be used to determine what design changes can be made to solve existing problems.

PBS: What are some ways to improve flow of powders beyond characterizing your material? What other actions should operators take?

TH: The solution(s) to any flow problem will typically require changes in one or more of the three following areas:

1. The powder (or bulk solid) (e.g. size distribution, moisture content, chemical flow aid)
2. The equipment (e.g. material of construction, interior surface, wall slope, outlet size, mechanical flow aid, additional process step)
3. The operating conditions (e.g. storage time at rest, humidity, temperature, pressure)

Usually there is more than one way to achieve improvements and a good understanding of the flow properties is fundamental to a proper assessment of the options. For example, let’s say we are experiencing arching after storage time at rest, and by characterizing the powder, we learn that the current outlet size will prevent arching under continuous flow conditions, but that the material gains strength with time and therefore, the outlet is too small to prevent an arch formation after time at rest. We could choose to change our operation to reduce storage time at rest, or we could choose to add a vibrator or an air cannon to be used occasionally when an arch forms after storage at rest, or a combination of the two. Flow properties are critical in assessing which option is likely to be effective.

PBS: Who would benefit the most from attending your panels at the Powder Show Toronto this June?

Anyone who is involved with or has experienced or wishes to avoid problems in handling and processing of powders will benefit from attending. This includes owners, operators, engineers, and equipment fabricators. The topics discussed will be beneficial to all industries, including food processing, chemicals, plastics, metallurgical, energy, environmental, and much more.

Get information or register for Powder Show Toronto, June 4-6, 2019

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