A graphite and carbon processing plant used a bulk bag filling specialist to reduce dust and other particles escaping in their Netherlands facility
Learning Objectives
- Understand how accuracy improved in filling fine particles into bulk bags at a graphite plant.
- Learn about the conveying and filling process and the equipment needed to ensure the bags are filling accurately.
Bulk handling insights
- Asbury Graphite & Carbons plant operators experienced problems with inaccurate fill weights of milled graphite, as well as issues with dust control.
- They changed their bulk bag discharging and filling systems, reducing dust in the plant and obtaining clean fills at the target weight.
Asbury Graphite & Carbons is one of the largest global processors of graphite and other carbon materials used in the plastics, automotive, lubrication, powder metallurgy, petroleum and coatings industries. Its European installation in the Netherlands opened in 2014 to take in raw graphite from around the world, reduce it into fine particles through a variety of milling and screening processes and fill 2,200 lb bulk bags and smaller bags, based on customer needs.
The plant operators had experienced problems with inaccurate fill weights of milled graphite, as well as issues with dust control.
“We hadn’t decided what equipment we should go with,” said Marc Stassen, former general manager of European operations. The existing equipment was rudimentary and produced off-weight bags. “We would only find out when the product reached the shipping department that we filled 2,024 lb instead of 2,200 lb, for example.”
The bulk bag filler frames operated with a poorly designed bag spout seal that wasn’t reliable. “Very often, the seal inflated incorrectly or wasn’t strong enough or exploded,” Stassen said.
As a result, dust and fine particles escaped, putting the plant’s compliance with Dutch health and safety guidelines at risk. Spills were also occurring with the original bulk bag dischargers. “We had to do something else,” Stassen said.
On the recommendation of Dutch distributor Matec Techniek, the company turned to Flexicon (Europe) Ltd., which specializes in bulk bag filling and discharging systems.
“We tried one bulk bag filling station, and that reduced our dust big time,” Stassen said. “So we chose to go forward with Flexicon for all 11 stations, followed over the years by nine bulk bag dischargers and numerous flexible screw conveyors. They reduced dust tremendously in the plant.”
Clean fills at the target weight
The bulk bag fillers are arranged in pairs beneath bins holding the finished graphite product. An operator inserts the bag loops into the fill head’s four retractable hooks and pulls the inlet spout of the bulk bag upward over a heavy-duty flexible collar, which inflates to create a dust-tight seal. A filtered air displacement vent at the fill head prevents escape of dust during filling.
The operator sets the target weight on the programmable logic controller (PLC) and initiates the filling cycle.
A slide gate opens above the filling chute and a rotary valve meters product from the bin above. Load cells beneath the deck are linked to the PLC, which closes the slide gate when the bag reaches the target weight. As the bag fills, a densification/deaeration deck vibrates to stabilize the bag for storage and shipment. The operator deflates the bag spout seal, ties off the bag and removes it with a forklift.
Each operator runs two fillers side by side, connecting a second bag while the first one is filling. When the first bag is full, the PLC automatically signals the system to begin filling the empty bag. “The operator is continuously busy hanging new bags and taking away full bags,” Stassen said.
Dust-free bulk bag discharging and conveying
The plant unloads incoming raw materials with nine bulk bag dischargers, designed to eliminate dust during discharging, collapse and removal of empty bulk bags, increasing plant safety.
Bulk bags of incoming material are loaded by forklift into the discharger frames. Operators create a dust-free bag/hopper interface by connecting the bag spout to the clamp ring which sits atop the telescoping tube. During discharge, the telescoping tube lowers the clamp ring as the bag empties, applying continual downward tension to keep the spout taut.
Promoting evacuation, extension arms on the dischargers’ upper frames automatically raise the bulk bag into a steep V shape. Bulk bag activator plates raise and lower the opposite bottom edges of the bag, directing material toward the bag outlet spout.
“In the past,” Stassen said, “we hung the bag from a frame and let the material gravity fall. The bag would look empty but still had 44 or 66 lb. inside and, when we removed the bag, the material ended up on the floor. Now no material remains.”
Different conveyors move different materials
From the 5-cu ft floor hopper below each bulk bag discharger, a fully-enclosed flexible screw conveyor ranging in length between 26 to 52 ft moves the material to several silos.
The conveyors specified are designed to propel difficult-to-move materials that tend to pack, cake, smear, plug or fluidize — or break and slip in the case of graphite — without crushing or grinding material against the tube wall.
Feeding the jet mill line, a tubular cable conveyor moves graphite and coke powder from a dedicated bulk bag discharger. The fine particles exiting the bag flow into a rotary valve that meters them into the conveyor, which consists of ultra-high molecular weight polyethylene conveying discs attached to a steel cable and enclosed inside a polymer tube.
The convey line is a continuous circuit, kept under tension by a wheel near the inlet end and driven by another wheel at the discharge end. The material rides gently in the spaces between the discs. The convey line makes a 90° turn past the inlet and moves vertically to 30 ft (9 m) in height before turning 90° again to the discharge point above the feed hopper and downspouting to the jet mill. The gentle movement reduces risk of abrasion and the enclosed circuit ensures dust-free operation.
After processing, another set of flexible screw conveyors, ranging from 13 to 26 ft, transfers the materials to the bins above the bulk bag filling stations.
