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Solids Processing

4 Modern solids handling systems, from silos via conveyors to bags or containers, have to be carefully engineered, installed and maintained. Eugene McCarthy reports.

Bulk solids handling – from silos to containers


hunseri Petrochem & Tea Ltd. (DPTL) is a leading global manufacturer of bottle-grade polyethylene terephthalate (PET) resin. The company’s plant is located

in the port city of Haldia in West Bengal, India. The facility is a continuous chemical process plant that operates non-stop, year-round. It produces 600t/d of PET resin. PET manufacturers around the globe typically

employ pneumatic conveyors to transport purified terephthalic acid (PTA) from storage silos and hoppers to downstream processing vessels. The Haldia plant was no exception. The facility receives PTA in 15 tonne bulk truckloads. From the massive hopper at ground level, 25m3

of PTA powder is

conveyed each hour up to a staging silo 35 metres above.

“Our original process relied upon pneumatic

conveyors to move PTA powder,” noted Subrata Mazumdar, senior general manager of engineering for DPTL. “The pneumatic conveying system - mainly nitrogen compressors - consumed an enormous amount of energy and nitrogen.” With the cost of energy and nitrogen

contributing to higher cost of production, an alternative conveying method was sought. “After much research we realised tubular drag

conveying would be the most efficient and effective means for conveying PTA powder,” said Mazumdar. “We chose Hapman because they provided a better design and robust construction of drag conveyor.” The tubular drag conveyor consists of a

stationary outer casing through which a chain is pulled by a sprocket drive. Flights are attached to the chain at regular intervals. As this endless chain and flight assembly moves through the casing, bulk material is pulled from the in-feed points to the discharge ports. “While similar in some ways to cable- and

16 Fig. 1. Modern silos have to

be carefully maintained.

aero-mechanical-style conveyors, tubular drag technology is superior to these systems because it utilises a heavy-duty chain to move material at a low velocity,” says Naresh Gandhi, md of Hapman India. “The result is a conveying method that is rugged yet gentle for the widest array of materials with virtually no maintenance, is quiet and consumes little power.” Gandhi also noted the slow-moving, positive- displacement action of the chain assembly is ideal for handling friable and/or blended materials without separation or degradation. Because the fully enclosed system does not introduce air, a constant

supply of nitrogen is not required for explosion suppression. The system does employ a purging system, which requires a little nitrogen. The Hapman conveyor’s 200mm casing is

constructed of stainless steel and employs three inlets and one outlet, as well as a discharge vibrator to ensure 100 per cent discharge of the powder. A low-horsepower (25hp) motor moves a stainless steel chain with polyethylene flights throughout the conveyor’s 99 metre circuit to a final discharge height of 35 metres at a 79° incline. “We’ve achieved our goal of reducing energy

and nitrogen consumption when conveying PTA by replacing the 320 kWh pneumatic conveyor with a 25hp tubular drag conveyor,” noted Mazumdar. “We are satisfied with this system.” Hapman continues to expand the capability of

its innovative Solidquid solid/liquid delivery system with numerous options to improve process efficiency and operator safety when dealing with materials that agglomerate.

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