The half-inch hole created by the mere passage of lime powder through a bend in a line, called a sweep elbow in the industry, had blown the fine powder all over the building, creating not only a gigantic, slippery mess, but hazards to breathing, above-acceptable air quality levels, and danger to sensitive electronic controls — not to mention the cost of downtime on the line.
And this was but one of dozens of sweep elbows at the plant, all of which failed in a similar manner every six months or so, said Forgione, operations and maintenance director for the Upper Occoquan Sewage Authority.
The plant’s chemical treatment system relies on a non-stop supply of pebble lime to raise the pH to levels where bacteria and phosphorous can be efficiently removed. After off-loading, the lime is pneumatically conveyed up to one of six silos. Transporting this huge volume of abrasive material with three to four percent grit at high velocities proved far too demanding for every type of elbow Forgione and his mechanics and engineers could find. Schedule 80 steel sweep elbows had worn through in a few months. So did short-radius welded steel elbows, along with similar, long-radius steel elbows. Ductile iron piping and elbows lasted nearly a year. Then longer 10-foot radius steel sweep elbows were installed. They lasted for a year and a half.
Nothing seemed capable of providing a long lifespan while conveying the abrasive material, and Forgione needed a solution. In a plant that handles 30 million gallons of wastewater daily for more than 300,000 customers in Fairfax and Prince William counties — one of the most densely populated areas of Northern Virginia — in a plant that wasn’t designed for unscheduled downtime — he needed it fast.
Every time there was a failure, the line had to be shut down and its silo taken offline. Inspecting elbows became a daily ritual while maintenance personnel became experts at welding temporary patches to keep the 17 elbows intact. Eventually, these would also wear beyond repair, and each time an elbow had to be replaced, it consumed hours and dollars.
“It’s very difficult for us to replace an elbow,” Forgione said. “Not technically, but the elbows at ground level are not easily accessed and the ones on top of the silos are four stories up. It’s a safety concern as well as a cost concern.”
On top of that, operations personnel were being diverted from their more formal responsibilities to help with the cleanups. “We needed to make the elbows last longer and we needed it done fast,” said Forgione. “As far as the type of elbow or material, we’d hit a brick wall.”
Then Forgione heard about the Smart Elbow deflection elbow from HammerTek Corp. in Bethlehem, Pennsylvania. The Smart Elbow deflection elbow is based on the natural flow patterns of fluids. It combines a rounded chamber on a tight radius elbow in a single, rugged unit. The conveyed particles gather and swirl inside the chamber in a slowly-rotating, self-renewing ball, absorbing new material while gradually releasing it in a first-in, first-out progression. Incoming particles deflect off of this rotating ball of air and material and continue to the silo. Rather than inviting the material to collide with the elbow wall, this elbow virtually eliminates such wearing impact, instead causing gentle deflections that promote directional change without affecting system pressure.
Forgione installed Smart Elbow units on one line and noted that it ran for an entire year without any signs of wear. So he replaced more elbows where the trucks offload the lime and at the top of his storage silos. And four years later, he has his solution and the proof of time. There hasn’t been a single blowout of lime dust and the hazardous conditions it creates.
“As an engineer, it doesn’t matter what I think,” he said. “What matters is results. The fact is, the Smart Elbow deflection elbow is working, we’re happy with it, and I would recommend it to anyone involved in handling lime.”
To read the full case study, please visit the HammerTek website.