Mechanical-barrier screen filtration handles river-water organics
Small footprint, 2,700 gpm installation does job more often tackled with other filter media
Self-cleaning screen-filtration systems are, experienced plant managers say, a known quantity. After all, hundreds of them are installed worldwide every year. They are most appropriately used in “high-flow, low-load” environments and therefore not usually thought of as being effective when filtering organics.
However, some say the need to conserve water, space considerations and other factors are moving industrial companies to look anew at this common, but vital technology.
Dieppe, New Brunswick-based Irving Tissue had been using an older filtration technology to process raw intake water coming from a nearby river into its plant, but recently decided to replace the 18-year-old filtration system that had operated faithfully, even as plant equipment around it evolved.
The new installation has several advantages over the previous, including a patented, bi-directional, self-cleaning capability that involves no external motors or pistons. Moreover, "it demonstrates this technology's ability and efficacy to provide excellent filtration in these types of "organic / inorganic" environments," says Steve Springer, VP of sales and marketing at Arvada, Colorado-based VAF Filtration Systems.
“The automated, self-cleaning filter concept has been around more than 40 years,” Springer says. “No back flushing is necessary. This is not the case when a media tank is used. But, in addition, what Irving Tissue wanted and needed was a self-cleaning filter that included no external parts and had a body design that was all 316 stainless steel .”
In other words, to clean the filter media the interior of the filter screen is periodically hydraulically swept to clean away the collected solids (see figure 1). This can be accomplished several ways:
“With the old piston-type operation, the cleaning nozzles can only make one pass across the screen due to hydraulic forces encountered within the filter body. With the bi-directional hydrodynamic drive system, the body is 100 % sealed. The body has equalized pressure while flushing, which means that not only is the flow rate maintained during flushing, but the cleaning nozzles traverse back and forth multiple times across the screen,” says Springer.
“We chose VAF for our site for several reasons — it was the most effective system solution with the least amount of moving parts,” Trevor Downey, Irving Tissue project manager, says.
Compared to media tanks, the amount of water expended in flushing is minimal. For example, two 48-inch media tanks each with a 300 gpm capacity typically would take about one minute to back flush, expending about 600 gallons of either clean or plant water.
With a filtration tank, the cleaning cycle takes less than 15 seconds, with no interruption of flow or the filtration process. “In a comparable situation, the V-Series filters use only about 60 gallons of water for flushing, a 90% reduction in waste water,” Springer says.
The installed carbon-steel filter system, parts for which were already obsolescent, was replaced by a VAF V-1500, 316L stainless steel filters with custom 316 stainless steel manifold.
“It’s a first-rate system and looks great,” says Downey. Delivered and installed in 10 weeks, the V-Series filter system has a flushing volume of less than 1% of the total flow over the course of a year, thus the system substantially reduces flushing volume.
Downey concludes: “The follow-up from VAF has been great. They really back up their product.”
“Optimizing water usage, increasing productivity and identifying and analyzing the cost-benefits of an integrated system is what we do,” says Springer. “Without exterior shafts or seals, potential leak points are eliminated. Screen cleaning without electric motors, gear boxes, limit switches or controls is just inherently simpler than would otherwise be the case.“
In conclusion, given the above, it is Springer’s belief that filters and filtration systems more than a decade old may not meet filtration levels that deliver return on investment, especially given the availability of systems with continuous filtration and near zero water waste. A replacement can require less maintenance, less electricity and fewer parts.
VAF Filtration Systems makes individual, manifold and skid-mounted self-cleaning filtration systems in the United States. VAF V-Series filters remove suspended solids from 1500 to 10 micron. Applications include, but are not limited to pre-filtration of reverse osmosis, ultra-violet, cartridge, membrane and other micro-filtration technologies. VAF provides both individual filters and pre-assembled systems to meet any flow demand.