Self-cleaning filters

Manufacturers are using self-cleaning filters to minimize waste and maximize profits


Until recently, liquid process filtration has tended to be an afterthought in many manufacturing facilities. But this view is rapidly changing due to increased environmental pressures, regulatory requirements, and yield targets - not to mention shrinking profits, and staffing and capital budgets.

As result, many manufacturers are re-evaluating their filtration strategy and turning to self-cleaning filters, which not only minimize waste at the source but also maximize productivity and increase profits.

In accordance with the recommendations of the EPA's Priority Hierarchy of Waste Management, manufacturers have shifted their focus from end-of-pipe pollution controls to minimizing waste at the source. The reasons for this shift are well documented. Minimizing waste at the source provides a cleaner, safer environment; saves resources and money - in some cases millions of dollars - and reduces long-term risk and liability.

Also, by filtering early in the manufacturing process, the cost of filtration decreases significantly because capturing and eliminating undesirable solids is often much more difficult later in the process. Simply put, generating less waste makes good business sense.

Costs of disposable media filters

Traditionally, engineers have opted for disposable media filters such as bags or cartridges due to their lower initial cost. While initial cost may be lower for small batch operations, this is seldom true for continuous operations which require a costly, redundant filtration system - including piping, valves, support, and service connections - to maintain production.

Moreover, there are significant hidden costs associated with disposable media filters. To begin with, there's the ongoing disposable filter purchase price, which typically runs at least $3 per bag or cartridge per day, plus the ongoing cost of waste disposal. For non-hazardous waste, disposal is already $400-$800 USD per drum, while that of hazardous waste is approaching $1,000 per drum. It's not unusual for the typical manufacturer to produce about 20 drums per year of filter media for disposal, not including the cost of treating or eliminating any run-off process fluids.

Significant labor costs are also involved with transporting, handling, and storing disposable filter media, as well as with replacing it. For example, for just a small 30-gpm cartridge filter with six 10-inch cartridges, the operator must remove 16 separate parts including the cover, compression seals, cartridges, and seal plates. The operator must reassemble all 16 parts with proper alignment to ensure good seals. Then someone must haul away the spent filter media.

There's also a housekeeping cost for cleaning any spillage from disposable media, along with increased emissions, safety risk, and liability. Then there's the potential cost of disposable media rupturing or overflowing (as bags sometimes do), contaminating product or machinery downstream and slowing production.

Finally, add the cost of buying, maintaining, and cleaning workers' protective clothing for replacing disposable media, as well as the extra time and labor required to fill out MSDS forms and other paperwork required for items hauled to landfills or incinerators.

Bottom-line boosting alternative

With the hidden, ongoing costs of disposable filter media, the trend in manufacturing is now toward self-cleaning filtration with minimal need for labor. Variations of this, such as disc clean filters (DCF), are helping manufacturers improve profit, worker safety, and waste minimization goals, as operations become more efficient.

Though an upfront capital expense, companies and their plant engineers are now realizing the extent that self-cleaning filters add to the bottom line. Since a self-cleaning filter system automatically cleans itself while in use, this allows a simple single piping arrangement, minimal valving, and fewer connections, instead of complex, redundant systems. This translates into lower total system cost and reduced waste. A number of other benefits accrue as well, including:

Automated cleaning minimizes disposal waste and labor costs

With cleanable filter media, there are no bags or cartridges to landfill or incinerate. Self-cleaning filter systems clean themselves within seconds. They can be automated to clean themselves according to schedule, or only when necessary.

Self-cleaning filters dramatically reduce emissions and future liability. With disposable media, the filter is opened every time the media is replaced and this can potentially expose workers and the environment to VOC's (volatile organic compounds) or other toxic emissions.

Disposable filters also routinely spill some liquid when removed and placed in disposal drums. Quite often, workers simply hose this process liquid to a drain, which adds to potential exposure and waste treatment cost.

Moreover, with disposable filters such as cartridges, contaminants can travel downstream to ruin a product. This can happen, for example, when the knife-edges used to seal cartridges get nicked and permit solids to bypass the media. Contamination can also occur if cartridges aren't stacked properly in the housing, which is a common problem. In some cases, even the media itself can shed and cause downstream contamination.

With a self-cleaning filter, however, the filter is opened only for inspection. This drastically reduces emissions and their potential risks.

Savings per year in filters, labor, disposal, and clean-up

Flint Ink, an international ink supplier, depends on proper filtration to manufacture its ink products for industrial and commercial use. Jonathan Bernblum, a process engineer at Flint Ink's Lebanon, Ohio plant, aimed to streamline cost and quality in producing flexiographic ink for use in food packaging. He found the plant's existing bag and cartridge filters costly, messy, and labor intensive. Workers changed six disposable filters at a time, at least three times a day. When producing particularly viscous inks, production slowed up to 20 percent, as filters sometimes had to be replaced multiple times in a single batch.

"The disposable filters cost hundreds of dollars per day, all year round," said Bernblum. "At first, they had to be disposed of as a hazardous material in drums, at a cost of about $20,000 per year. Later, with modifications, we were able to dispose of them in dumpsters. Yet 95 percent of our waste stream was the filters themselves, along with good ink trapped inside.

"No one wanted to change out the bag or cartridge filters," continues Bernblum. "When hot melted varnish occasionally held them in place due to high processing temperatures, they had to be chipped out. It was a nasty, messy process to get them out. Ink spills required cleaning and added to the cost of labor and supplies. Altogether the bag and cartridge filters cost the plant about $70,000 per year in filters, labor, disposal, and clean up."

Moreover, the disposable filters compromised Flint Ink's commitment to quality. Improper filter installment or any lapse in replacing them could allow small foreign particles into ink products, which could damage client printing presses. Even a small amount of particulate, if present, could cause ink cross contamination and off-spec color as well. This could negatively affect multiple batches. Any such problems had to be troubleshot by managers and line staff, and procedures altered to prevent further incidents.

Bernblum proactively sought out RPA Process, who replaced the bag and cartridge filters with DCF-800 self-cleaning filters. The DCF's filtering screen has a 150-micron or 230-micron retention size, depending on the quality dictated by the application. At set intervals, or pre-determined changes in pressure, the DCF cleans the filtering screen then purges the trapped solids, without interrupting production. The DCF filters allow filtration and cleaning to occur simultaneously, which maximizes production.

"Ninety five percent of our waste stream is now eliminated with the self-cleaning DCF filters, and production is significantly streamlined," says Bernblum. "We're no longer paying for costly disposable filters or high disposal fees. We're no longer throwing out good salable ink along with filters to be landfilled.

"Since the DCF filters have integrated cleaning loops, no one has to deal with changing out messy filters," continues Bernblum. "Not only is ink quality higher, but the root cause of most quality issues was solved with the switch to DCF filters. Altogether we save about $70,000 per year in filters, labor, disposal, and clean up. We achieved about 7-month ROI, including higher, more reliable and flexible production capacity."

Four-month ROI on self-cleaning filters

PPG Architectural Finishes, a latex paint and stain manufacturer in Louisville, KY, knew its filling operation was overly complicated, noisy, and required far too much operator attention. More importantly, PPG experienced an unacceptable percentage of product loss in the filtering process.

An air-operated diaphragm pump at the base of a blend tank pumped product onto a large, open, vibrating screen. Product exiting the vibrating screen fed into an accumulating vessel, where another pump transferred product through a polishing filter into a rotary drum-filling machine. With the two pumps, vibrating screen, and open-air vessel, the system was complex, noisy, and wasteful.

To stay competitive in the tough, low-margin paint industry, Doug Story, Plant Engineer at the Louisville site, aimed to streamline the company's filling operation. His goals: to produce as much finished product as possible, using the least wasteful, most environmentally friendly methods available.

In consultation with RPA Process, PPG replaced their vibrating screen, accumulating vessel, and diaphragm pump with a DCF-800, mechanically-cleaned filter. Removing the vibrating screen eliminated the need for the accumulating vessel, associated piping and controls, as well as the second diaphragm and its compressed air components and controls.

The DCF filter has virtually eliminated operator involvement in the operation, and removing the vibrating screen and second diaphragm pump has dramatically reduced noise levels. The DCF filter purges residual paint and debris into the plant recycling system, where the solids are separated and the paint is reused.

According to Story, there has been a significant reduction in product waste.

"Post installation cost for the first year was under $10 (USD)," says Story. "Payback was achieved in four months, and this analysis does not include the savings generated in utility costs for the vibrating screen, its maintenance, or additional operator time. The DCF filter has contributed to our paint and stain production efficiency, and exceeded the objectives set at the beginning of the project. It also provides our workers with a quieter, more environmentally friendly workplace."

Self-cleaning filter starch spray system boosts paper product strength

Corn Products International, Inc. based in Westchester, Ill., a major starch supplier to the corrugating and paper industries, recently introduced a technology in the U.S. that is a cost-effective starch spray solution that dramatically boosts paper strength while cutting fiber use by replacing much of the fiber with starch. In the starch spraying system, process water mixes with starch to create slurry that flows into a run tank, which is sprayed onto a sheet former.

One key to making the starch spraying system work, however, was implementing the proper filtering system.

"Getting the filtering right was critical, especially for closed systems where process water contains a lot of suspended trash," said Doc Kinney, Corn Products International's technical director for its U.S. business. "Dirt, grit, metal shavings, anything on the floor of a paper mill that goes into the drain winds up in process water and needs to be filtered. Otherwise, it will plug up the spray nozzles, and could degrade paper quality, destroy sheets traveling at 4,000 ft./min., or even the paper forming wire that can cost upwards of $100,000 to replace."

Initially Corn Products used two basket screen disposable filters at a commercial trial location, where fresh water was mixed with process water in a 50/50 ratio. The basket filters didn't have the surface area to contend with the amount of trash in the water and required near continuous manual cleaning.

"We couldn't keep the basket filters clean," said Kinney. "Their surface area was too small and their throughput too low. Every thirty minutes a basket strainer plugged."

In his search for a starch spraying filtration solution, Kinney turned to RPA Process Technologies. After discussing Corn Products' process goals, Kinney - along with RPA Process - determined a number of criteria for the proper filtration system. The filters would have to be self-cleaning, self-contained, maintenance free, operated by PLC, and able to handle 150 gpm throughput as well as filter out any foreign material greater than 50 microns.

Based on these criteria, Kinney implemented two RPA Process DCF 1600 filters on each starch spraying system, one for primary filtering of water and another for secondary starch slurry filtration.

"The DCF self-cleaning filters are a night-and-day improvement over labor-intensive disposable filters," said Kinney. "The filters have a much higher throughput, a larger surface area, and automated PLC-programmable clean and purge cycles that can be tailored to specific water configurations at each paper mill. They are worry-free and virtually maintenance-free so there's no lost production, and no need to have staff on hand to watch over them. That's particularly important at low margin paper mills that need to operate efficiently 24/7 year-round."

For more information on self-cleaning filter technology, write to RPA Process Technologies, Inc. at 9151 Shaver Road, Portage, Mich. 49024-6798; call 866-867-2893 toll free; fax 269-323-2403; or visit .

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