According to Riebau, only a small amount of the sediment could get captured in a 200-micron sidestream bag filter — requiring a manual cleaning process.
The total suspended solids (TSS) in the process water was repeatedly in the low- to mid-30 parts per million.
So Riebau embarked on research into filters.
Online searches for a whole process, inline, flow-through filter yielded some options. Forsta Filters Inc. stood out because of its comprehensive website and quick replies to Riebau's initial inquiries, he said.
Engineers from Forsta Filters, which is based in Burbank, Calif., sized a system to handle GI Plastek's maximum water flow capacity of 300 to 380 gallons per minute. The location that was selected for the filter had an operating pressure from about 35-50 psi, so it was suitable for Forsta's hydraulically driven 180 Series filters.
Forsta sized the filter for the maximum flow rate at 100-micron filtration, to have less than 1 psi of pressure loss across a clean screen. The B4-180 model filter — which GI Plastek installed in November of 2015 — would provide 5.25 square feet of screen area, integrating easily with the straight four-inch pipeline.
After the installation, Riebau contacted Forsta Filters to give a good report: “The filter has been operational for approximately two-and-one-half weeks. The results were immediately obvious with our process water clearing up quickly after weekly plant startups. The installation was done almost entirely in-house and went smoothly.”
The system is self-cleaning, using guidelines from Forsta Filter about inlet pressure and flush outlet pressure during backwash. GI Plastek set the duration rate of the backwash, based on its plant conditions.
How did the Forsta unit compare to the former sidestream bag filter? No contest. “The sidestream filter captured only a sample of the process water from the tower water holding tank and the bag filter cleaning process was more involved,” he said. And the bag filter was 200-micron, while the Forsta unit is half that, so the company can capture tinier particles, as well.
Like many plastics factories, GI Plastek runs 24 hours a day for five, six or even seven days a week. The filters get a workout.
“Now, every ounce of our process water goes through the Forsta B4-180 filter,” Riebau said. “It is during startup that the return water, which empties back into the tower water holding tank, carries sediment from the process plumbing back to the tank. Obviously, before we were cleaning only a small amount of that from our process water, now we clean virtually all of it.”
The backwash frequency varies on the B4-180. The highest frequency happens during startup after a normal weekend shutdown, when the filler will discharge up to 10 times in the first half-hour. According to Riebau, the rate drops off significantly as the day, and then the week, moves forward.
“It is normal for our B4-180 to backwash 30 to 80 times in the first 36 to 48 hours after startup,” he said. “By the end of the week the frequency is usually reduced to two to four times per 24-hour period.”
The custom molder reduced downtime of its ancillary equipment caused by clogged valves.
“We spend less time cleaning those pieces of equipment, and since molds are less clogged, the time cleaning them is reduced,” he said. “Those together mean more problem-free production.”
And that's what it's all about in the competitive world of plastics molding. In plastics processing, any advantage you can get pays off — including cleaner process water.