Safety and Prevention at the Heart of Powder and Bulk Materials Transfer

Explosion prevention and suppression in powder and bulk transfer is a top-of-mind concern for regulators and inspectors. Fortunately, suppliers with broad material-handling expertise help deal with it.

By Kevin T. Higgins, Managing Editor

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Doan Pendleton

Doan Pendleton demonstrates the hydraulic jack that lifts Vac-U-Max’s “swing-way” filter top. The innovation is designed to speed the cleaning process.

Mergers and acquisitions are more than fodder for the business pages. They also can signal broader vendor competence in helping food manufacturers address process challenges and opportunities.

Proof of that was evident at the May International Powder & Bulk Solids Conference & Exhibition in Rosemont, Ill. Many manufacturers want to pare down the number of vendors they work with and have a go-to supplier for critical systems, and exhibitors were eager to demonstrate how their evolving competence profile can deliver single source, integrated solutions.

A recent example involves Schenck AccuRate, a Whitewater, Wis., fabricator of feeders and weighing equipment for dry materials in process industries, and Kansas City-based Mac Process, a supplier of pneumatic conveying and air filtration systems. The two firms completed their merger in January, and the new entity, Schenck Process LLC, demonstrated the synergy by showcasing a continuous dense-phase conveying system that leverages Schenck’s weigh-belt expertise.

Because it runs continuously, no surge capacity is needed. Blowers operate at lower velocity, boosting energy efficiency, according to Mark Nagely, industry manager-food. The system handles both fine particles and coarse materials, gently moving them at a rate of about 800 ft. per min.

Three months before Schenck Process was established, pneumatic conveying and gravimetric feeder specialist K-Tron became Coperion K-Tron. The newly minted organization was in Rosemont to showcase its expanded capabilities. For food processors, the most meaningful capability is tighter integration of extruders and loss-in-weight feeders, with sanitary design and quick-release connections incorporated into all components.

The merger of Taylor Products and Smoot to create Magnum Systems occurred a dozen years ago, but R&D is ratcheting up to meet emerging process needs. The Kansas City-based organization displayed a pneumatic conveying system that combines elements of dilute, dense and semi-dense phase systems that is particularly suited to fine powders. Called the Ecophase, the system throttles back on the blower but runs it continuously. The result is a horsepower reduction that cuts energy consumption as much as 30 percent.

Coperion K Tron Stuart Wilson

Coperion K-Tron’s Stuart Wilson exposes the interior of the firm’s new sanitary filter receiver. The side-entry access door supports the filter media without horizontal supports and other potential harborage points, speeding the cleaning process between recipe changes.

One of the biggest suppliers of powder and bulk handling equipment is Flexicon Corp. The Bethlehem, Pa., firm isn’t active in the merger area, but it is expanding its process options.

​Dilute phase positive pressure and vacuum conveyors long have been part of Flexicon’s product portfolio, and the firm recently added tubular cable conveyors for fragile and brittle products susceptible to damage in dense phase conveying. Flexible screw conveyors have been a part of Flexicon’s product line since the founding of the company in 1974, notes David Boger vice president of global business development and marketing. He added that they are economical to operate, easy to clean and are well-suited to a wide range of materials.​

Pressure release

Ten days before the show kicked off, a dust explosion in a bag room at Georgia-Pacific’s Corrigan, Texas, plywood mill created a fire that critically injured three workers. It was a painful reminder of the 2008 dust explosions at Imperial Sugar’s Port Wentworth, Ga., mill that killed 14 and injured scores. The 2008 disaster triggered an overhaul of explosion control regulations, and a number of specialists in fire suppression and explosion protection for pneumatic conveying systems were on hand at the Powder & Bulk Solids show to promote their solutions.

In case anyone was unaware of the potential dangers when handling small particles under pressure, Johannes Lotterman, head-project control at Rembe Inc., Charlotte, N.C., demonstrated the danger twice a day with controlled explosions. Lotterman placed a few tablespoons of combustible dust in a 3-liter container, pressurized it to 2 bar (about 29 psi), then delivered an ignition spark to create an explosion and flameball through a pressure-relief vent. He then repeated the demonstration with a flame-arresting device for “flameless venting” inside a facility.

NFPA 654, the National Fire Protection Assn.’s standard for the prevention of fire and dust explosions while handling combustible particulate solids, was created after the sugar mill disaster and underwent its second revision last year. The frequent changes have contributed to manufacturer confusion about proper venting and explosion protection in their facilities.

The vast majority of food powders meet the standard’s combustion threshold, according to Flexicon’s Boger, but combustibility levels vary, and the standard is somewhat vague about necessary safeguards. “Depending on the equipment we’re trying to protect, it could double the cost of a project,” he says.

The added cost is particularly challenging for small food companies, many of which operate without any suppression or control systems, suggests Helen Sztarkman, Rembe’s sales manager. The introduction of new venting and suppression technologies also has left regulators playing catch-up. Four OSHA inspectors visited her booth, she said, to learn about remediation options as they prepare to enforce higher standards.

Application-specific solutions are proliferating, agrees Wylie Musel, regional sales manager with BS&B Safety Systems Ltd. in Minneapolis. “It used to be either vent or suppress; now there are multiple options,” he says. Insurance companies are ratcheting up the pressure on manufacturers to either address the issue or face sharply higher premiums, lending immediacy to the selection of appropriate safety solutions.

NFPA 654 only applies to vessels and enclosures that are 8 cubic ft. or larger, points out Nick Hayes, president of Volkmann Inc., a Bristol, Pa., supplier that focuses primarily on dense-phase vacuum conveying. With U.S. standards still evolving, the gold standard for equipment operating in environments with explosive atmospheres is the EU’s ATEX directive, according to some safety experts. Sugar and flour dust have low ignition points, Hayes points out, and his equipment often is used in those applications. Volkmann’s equipment is certified under ATEX by TUV, the German safety-validation equivalent of UL.

Volkmann supplies some positive-pressure systems, but most of its pneumatic installations are vacuum conveyors. Dust-free material transfer is easier with vacuum, since a leak in the line will draw in air rather than expel dust, and specialized filters within the receiver ensure dust-tight operation.

Scientific understanding

Conveying food powders and bulk solids is an exercise in applied physics, with particle size, density, water content and other variables affecting performance. “No two powders are ever the same,” notes Hayes. “My advice: test, test, test.

“As an engineer, I hate to say it, but powder conveying is more art and experience than science.”

“Bulk-solids handling traditionally has been based on heuristics and trial and error,” suggests Mark Jackson, head of Kansas State University’s engineering technology department, which hopes to advance material-science research and develop general equipment requirements and resolve common problems at a new technology center.

Until then, the specific needs of food processors are driving vendor innovations. One example is reducing the time required to clean filters and prevent cross-contamination between production runs.

Cleaning the filter required to serve an 8 cubic ft. vacuum receiver can take a couple of hours, according to Doan Pendleton, vice president of Vac-U-Max, Belleville, N.J. His firm’s solution is the “swing way” cover for large vessels. A hydraulic jack lifts the filter’s top, which then pivots to the side to expose the bank of filters, which can then be accessed and changed in about 20 minutes. The company still offers filters with side-door access, but “this is the direction we want to move in,” Pendleton explains.

Faster filter cleaning also was goal for a sanitary filter receiver (SFR) introduced by Coperion K-Tron. Fabricated in 304 stainless with polished surfaces and available in 36- and 48-in. diameters, SFR employs spunbond-polyester tube filters supported on a single hinge for quick removal and replacement, eliminating the horizontal ledges needed to support pleated filters in a typical design. If allergen cross-contamination isn’t an issue, sequential pulses of compressed air from a mounted accumulator automates the cleaning process.

Pneumatic conveyors typically are stationary, though mobility is a desirable attribute in some applications. That’s the domain of flexible screw conveyors. Simplicity of design is one of their strengths, and suppliers like Hapman Inc. are reluctant to introduce changes unless they address end-user needs, such as faster cleaning.

For example, a quick-release discharge box recently was added to Hapman’s Helix flexible screw conveyor, says product manager Mike Zeluff. Tri-clover clamps on the Kalamazoo, Mich., firm’s “dairy style” units were added a few years ago, he adds.

Customized changes are often made by end users. Zeluff cites the case of Guixens Food Group Inc., a Miami-based processor that opened a second plant in Tampa two years ago. Inspired by the trolley lines used in meatpacking plants, Guixens installed a ceiling trolley that suspends the motor end of the conveyor. Operators roll a floor-level hopper between filling machines, dragging the motor at the other end of the tube to the next location.

“It’s a little unusual: most of the time you see a dedicated conveyor going to a dedicated line,” says Zeluff, but Guixens’ solution reduced capital costs and takes full advantage of flexible screw conveying’s mobility.

A close cousin of the flexible screw conveyor is the tubular drag conveyor with a cable or chain to drive flights. Powders and sticky products are inappropriate for these enclosed systems, allows Bert Bertolo, regional sales manager with Spiroflow Systems Inc., Monroe, N.C. On the other hand, large particles and products requiring gentle handling are a good fit for Spiroflow’s tubular drag conveyor, which features a stainless steel cable and plastic flights impregnated with metal-detectable material. Bertolo says a constant-tension system reduces the likelihood of cable stretch.

An abundance of bulk bag filling and discharge systems were on display in Rosemont. According to Bertolo, the point of distinction of Spiroflow’s CTE bulk-bag filler is the vibrating cone table that breaks up material being fed in and helps pack more of it into the bag at a high fill rate. For high-volume applications of 5,000 totes a month, he estimates the system delivers an ROI in about a year by packing 10 percent more material into each tote.

Incremental improvement is the general rule in process industries. As suppliers expand their capabilities and the understanding of bulk material and powder flow advances, the pace of change in dry material handling is likely to accelerate.

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