Powder & Solids

Pneumatic Conveying Gets Fresh Air

Tougher processing requirements and technology developments drive growth

By Seán Ottewell, Editor at Large

The market for pneumatic conveying systems in the United States will rise from $4.5 billion this year to $6 billion in 2022, predicts “Pneumatic Conveying System Market Analysis…,” a report issued in September 2015 by Grand View Research, San Francisco. A combination of factors, including demand for improved process hygiene, reduced end-product contamination, worker health and safety issues, and advances in technology that integrate compact pressure-vessel technology with intelligent control, are driving the growth, note the report’s authors. The ability to further increase productivity, improve product quality and boost cost savings also may further fuel demand significantly, they add.

The experiences of vendors such as Nol-Tec Systems, Hapman and Gericke — together with their customers — illustrate how these various demands are playing out in the plant.

One of the game changers now is automation, says Mike Weyandt, corporate sales manager, Nol-Tec Systems, Lino Lakes, Minn. He cites a plant that invested in servo motors, pressure transducers and more, all of which could be accessed from the control room. “This customer had experienced upsets in his automation process caused by improper adjustment of the valves on a manually adjusted system. This resulted in quality control issues, excessive use of conveying air, system plugging and downtime. By spending the money to make the system ‘smart,’ he reduced long-term costs by eliminating these problems. He was thinking big picture, long term.”

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In addition, the growing affordability of technologies such as variable frequency drives, inverter motors and pressure transducers will increase their use in pneumatic conveying technologies demanded by chemical companies, he believes.

Basic Steps

Identifying the best technology for the particular application is key to achieving benefits, stresses Weyandt. “When we are contacted by a customer, our first question is always about the material in question and its physical characteristics. Then we move on to the environment within the plant, i.e., whereabouts the conveying equipment is to be located.”

From here, the first decision is determining if dilute-phase or dense-phase conveying is best for the material. Then, the company considers the choice among vacuum, positive pressure differential or negative pressure differential operation. Vacuum often is preferred if a material is toxic or explosive.

Complexity of installation is another consideration. “If it is just a pipe going straight up and a little bit of horizontal, a bucket elevator or belt conveyor might be more appropriate. However, if there are lots of turns involved, the system rapidly becomes more difficult to service. Here, pneumatic would be better because the system is mostly comprised of pipe which can usually be supported from the structural members which are holding up the roof or walls of the building,” he says.

Ease and cost of maintenance are important issues, too, Weyandt notes. Users of mechanical systems usually are very aware of the maintenance costs involved with all their assorted shafts and bearings, he believes. “Our experience has shown that the maintenance costs of a pneumatic conveying system are substantially less than a comparable mechanical system.”

Pneumatic systems also are easier to keep clean than mechanical ones, he notes. So, they are gaining growing use where this is a crucial need, for example, in pharmaceutical and fine chemical manufacturing.

In general, whenever a customer has a dry chemical powder and is concerned with degradation, dense phase is the best option, says Weyandt. He cites the experience of a manufacturer needing to pelletize virgin carbon-black powder, both for hygiene reasons and mixing effectiveness. It switched to dense-phase conveying because the lower transfer velocity minimized product degradation. Avoiding product degradation also was the driver for a terephthalic acid manufacturer to replace a dilute-phase system with a dense-phase one, he notes.

However, if separation and breakage aren’t issues with a material, then 99 times out of a 100, dilute phase is chosen, Weyandt says. “Dilute phase is much more commonly used and is much better researched because its principles of operation are very simple.”

Common Challenges

For its part, Hapman, Kalamazoo, Mich., has identified what it calls the six main materials-handling challenges in the chemical industry.

“At Hapman, the focus is on offering technologies that can overcome the chemical industry’s major materials-handling challenges, notably dusting, segregation, degradation, batching inefficiencies, precision and flow issues, and cleaning and sanitation problems,” notes director of marketing Chris Gibbs.

As a consequence, vacuum conveying systems are at the forefront of its recent project installations. One is for Werner G. Smith (WGS), Cleveland, which manufactures fatty oils and synthetic esters and also processes vegetable and fish oils, blown oils and non-ionic emulsifiers.

WGS’s interest in vacuum conveyor systems started when it won a long-term contract from a new customer. This required blending a granular powder with an aqueous chemical solution.

The building where the product initially was made had no loading dock, which meant 55-lb bags of raw material had to be hauled and processed manually. Each production batch took 16 hours to make and required more than 200 55-lb bags. The company needed to run four batches per week.

The system Hapman recommended consists of a loss-in-weight bulk-bag unloader with a vacuum conveyor. The system, which was designed with safety, ease of maintenance, and automation in mind, includes fine filters, reverse-air-pulse cleaning mechanisms and an integral control panel.

For WGS, the savings began immediately. Batch time has fallen by several hours, the five employees who originally had to handle the heavy bags have returned to process-related duties, and improved housekeeping has reduced the amount of waste generated by 80%.

Another project involves a customer that required batch processing of major and minor ingredients to create a blended mixture for further processing downstream (Figure 1). “The vacuum system is sized to handle the maximum required flow rate of the blended product. An actuated diverting valve allows for controlled filling of the holding tanks. The integral regenerative blower on each conveyor generates the vacuum that effectively pulls material through the piping and into the tanks. No expensive plant air is required to operate the conveyors,” notes Gibbs. The batch controls allow operators to adjust the mixture and ratios on demand, and so provide the ability to create thousands of recipe variations within the framework of a single system.

More Customization

Gericke, Regensdorf, Switzerland, increasingly is tailoring its offerings to specific customer demands, especially when they combine dense-phase conveying systems and pressure vessels, notes Tobias Weber, product manager pneumatic conveying.

“We are delivering many such systems. Typically, the batch is either directly weighed in the pressure vessel or weighed upfront in a weighing hopper. The conveying distance varies from a few meters up to more than 100 meters to either one or several reactors.”

The system (Figure 2) eschews rotary valves and is completely gas- and dust-tight, he notes; so, it eliminates the leakage air associated with using a rotary valve and avoids conveying gas and product losses.

“Because this method allows a high conveying pressure, it is ideal for densely packed solid gas flow to convey materials over long distances while minimizing material attrition and conveying line wear,” adds Weber.

Other benefits include minimizing the de-mixing effect during transport and the lower maintenance requirements of the butterfly and gate valves used compared to rotary valves.

A Solvay plant that makes special rubbers, polyvinyl-chloride stabilizers and associated products illustrates many of these advantages, he says. The conveying system must transport products — some very poor flowing — with diverse bulk densities over 200 meters to a reaction vessel. Material from a bag emptying station goes into a conveying vessel mounted on load cells. Each batch is weighed, and then moved using Gericke’s dense-phase PHF conveying system to an agitated reaction vessel. The over-pressure in the reactor varies between 0.1 and 2 bar; an intelligent control unit ensures the correct conveying pressure in the PHF system. Using this direct introduction technology, Solvay has improved both the mixing and dissolving process. In addition, avoiding the need for additional equipment such as hoppers and rotary valves has provided cost savings.

“The coming years in pneumatic conveying technology will be dominated by further increases in productivity brought about by reductions in costs and energy consumption — together with a strong focus on H&S [health and safety] issues,” Weber believes.

Seán Ottewell is Chemical Processing's Editor at Large. You can email him at sottewell@putman.net.