Vortex® Multi-Port Wye Line Diverter™ - Antimony Oxide Powder

Directing pneumatic conveying traffic

At a single keystroke, computer-controlled diverter valves route powder through a pneumatic conveying system to multiple destinations.

By working with a valve manufacturer, a Texas chemical company automated their pneumatic conveying system so the operator can direct powder to several destinations – simply by sitting at a computer.

Laurel Industries, a division of Occidental Chemical Corp., produces antimony oxide at their plant in La Porte, Tex. The fine powder is primarily used as a fire retardant in plastics and as a catalyst in the polyester industry.

Ingots of pure antimony metal and powdered crude antimony oxide are shipped to the plant for antimony oxide production. The ingots arrive in boxes or on pallets. The crude antimony oxide arrives in 2,000-pound bulk bags.

A belt conveyor carries the antimony ingots to a furnace. A pneumatic conveyor transports the crude antimony oxide from an unloading station to a feed tank, where it's gravity fed into a separate furnace. Michael Sergi, project engineer at Laurel Industries, said no other raw materials are added to either furnace to product antimony oxide.

“In the ingot furnace, a metal-oxygen reaction takes place,” Sergi said. “In the case of the powder (crude antimony oxide), it’s a refining step. Basically an oxidation reaction happens in both furnaces to form the final product.” The antimony oxide's physical properties can be changed by controlling furnace conditions as the powder reacts.

After the reacted antimony oxide leaves each furnace, it's immediately cooled to powder form. The powder is dispersed in an airstream to one of five baghouses.

“We actually have a big draft fan that pulls (the antimony oxide) from the furnace through basically just duct-work,” Sergi said. “It's essentially pneumatic conveying, but we're using 30-inch ducts.”

The antimony oxide is transported to each baghouse and is separated from the airstream. From each baghouse, the powder is routed via pneumatic conveying lines to one of 19 possible destinations. The powder can travel to any of four product hoppers, each of which has four subcompartments. The other three destinations are set aside for off-spec materials.

By using product hoppers with four subcompartments, Sergi said antimony oxide with different characteristics can be blended according to their customer's needs. Some product hoppers are also connected to additional processing equipment. Depending on a customer's further processing needs, antimony oxide is directed to the designated product hopper.

“[Which product hopper receives the powder] depends on whether we're making the antimony oxide for a fire retardant or a catalyst,” Sergi said. “Or it just may be that a different company may want further treatment done to their powder. But the main reason [to direct powder flow] is that whichever hopper or storage area is open, that's what we'll fill up.”

In the past, antimony oxide was routed from a baghouse to the appropriate product hopper by manually changing the pneumatic conveying line's configuration.

“Somebody would take a flexible hose and make the connection between the line and the intended product hopper.” Sergi said. “So basically it was just a manual [line switching] process.”

Manual switching is time-consuming and prone to error

As operators continually disconnected pneumatic conveying lines and used hoses to connect the lines to product hoppers, the process began to show its flaws. The manual line switching was inefficient.

“It was time-consuming and prone to error,” he said. “It was also a source of leakage. Either the flexible hosing would leak itself or the couplings would blow apart.”

While making the connections between conveying lines and hoppers took time, cleaning up dust from hose leaks took even longer. “It wasn't really dangerous,” Sergi said. “It would just require cleanup. Someone would have to go in there, vacuum off the equipment, and sweep up.”

In addition to downtime, errors in the manual switching process caused cross-contamination or sent powder to the wrong processing line.

Directing powder flow

In late 1996, Laurel Industries learned of a particular manufacturer of a four-way diverter valve for pneumatic conveying systems. Sergi said the valve could divert powder from one pneumatic conveying line to four other lines. Laurel Industries’ plans included automating plant operations, so the company decided to install a four-way diverter valve on a pneumatic conveying line supplying antimony oxide from one of the five baghouses.

Controlled by a computer, the diverter valve was able to divert powder to any of one product hopper's four subcompartments. Sergi said the valve installation success led Laurel Industries to search for ways to automate the entire operation. Their search led them back to the original diverter valve manufacturer.

“We did some literature searches,” Sergi said. “but nobody else was making anything close to what [the manufacturer] was making, in our opinion. The valve fit nicely into our automation plans.”

Laurel Industries was pleased with the installed diverter valve's performance, Servi said, especially because the valve operated without problems and was computer controlled. The company chose Salina Vortex to automate the plant's entire pneumatic conveying system with Wye Line Multi-Port Diverter valve assemblies.

Laurel Industries had a definite plan for a multiple-port diverting operation. Antimony oxide would be diverted from any of the five baghouses to any of the product hoppers and subcompartments. With this idea in mind, the company approached the valve manufacturer.

“We had the idea for the diverting operation,” Sergi said. “Basically, we sat down with the manufacturer and said this is what we want to do. We gave them an idea of how we wanted it put together. They took that idea and refined it into a custom unit for us.”

Multiple diverters automate pneumatic conveying system

In November 1997, the valve manufacturer installed four multiple-port diverter valve assemblies at Laurel Industries. Each assembly is made up of a combination of nine four-way and four two-way Wye Line Diverters with serially interfaced air controls and position indicating switches. While customizing their equipment for Laurel Industries’ needs, the manufacturer also incorporated a networked control package, which integrates the DeviceNet¹ communication protocol system in the valve assembly design. Sergi said the control package monitors the entire pneumatic conveying system.

“We knew there was a heavy input and output load in the system,” Sergi said. “We happened to see [the control package] at a trade show. We went to the valve manufacturer and said, ‘You know, we'd really like to have this in the system.’ So they worked with the control package manufacturer to incorporate it into each valve assembly.”

Without the unique computer control package, Sergi said automating the pneumatic conveying lines would have been a large undertaking.

“There are all kinds of position sensors on the valves to help us check where they are,” Sergi said. “And then there's all the equipment that actually moves the valve's position. So there's a huge amount of instrumentation that goes along with that.

“What it requires is a lot of wiring. Each instrument would have been wired separately [without the control package]. I think we estimated that 3 or 4 miles of wiring would have been required at the plant.”

The control package connects the pneumatic conveying system components through two wires, Sergi said.

The communication protocol allows modules to “talk” over the system to monitor what is going on as well as send commands, such as an operator's instructions to open and shut selected valves.

“It's a networked system. This essentially allows us to control the whole pneumatic conveying system using two wires,” Sergi said. “All we had to do was provide air, a single source of power, and the two wire connections to our computer hardware. The manufacturer did all of the wiring.”

Diverting powder flow with a keystroke

Sergi said the new diverter valve assemblies and the computer automation have made diverting antimony oxide flow simply a matter of pushing a key or clicking a mouse. “Actually, the best part of the entire system is the computer nature of it,” he said.

Plant operators can now view a flow diagram of the entire pneumatic conveying system on a computer screen that shows which conveying lines are open and where antimony oxide is flowing. A simple keystroke can divert the powder flow, with four lines operating simultaneously. Sergi said the greatest improvements with such an operation are the labor and downtime reductions.

“No one has to take the time to manually divert the lines,” he said. “Now diverting flow requires no labor; it takes a matter of seconds.”

The time and mess associated with powder leaking from connecting hoses have also been eliminated. “Powder no longer releases into the plant,” he said. “All of the flexible hoses are gone. All of the connections are permanent now.

“We're satisfied. So far, the multiple-port diverters have been working very well for us.”

Reference
¹DeviceNet, Open DeviceNet Vendor Association (ODVA), 954/340-5412, fax 954/340-5413.

Courtesy of Powder and Bulk Engineering, October 1998