Medical Products News

However, as the fibers are recycled, they get shorter and weaker which results in a lower grade product with less final sheet strength. Synthetic additives to enhance product strength have often been prohibitively expensive in a marketplace where profit margins have been ravaged by declining paper prices.

Now, a cost-effective starch spray solution has emerged in the United States that is designed to boost paper strength (up to 100% in IGT, 25% in Concora, and 20% in CFC and Mullen) while cutting fiber use by replacing much of the fiber with starch. Essentially, special spray nozzles apply an unmodified starch suspension to the fiber web of paper products to increase their internal strength and improve their surface properties. The starch stays internally on formed sheets and gelatinizes while drying.

Starch supplier Corn Products recently introduced the technology to the US after adapting it from one widely used in Europe and Latin America, where sources of virgin fiber have been scarce for decades. In its starch spraying system, process water mixes with starch to create slurry that flows into a run tank, which is sprayed onto the sheet former.

Filtering closed mill systems.
One key to making the starch spraying system work was proper filtering. This was all the more important since many paper mills now run closed systems in response to environmental regulations limiting water discharge and requiring process water re-use instead of adding fresh water.

"Getting the filtering right was critical, especially for closed systems where process water contains a lot of suspended trash," said a Corn Products representative. "Dirt, grit, metal shavings, anything on the floor of a paper mill that goes into the drain ends 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 $10,000 to replace."

Initially, Corn Products used two disposable basket-screen filters at a commercial trial location, mixing fresh water with process water in a 50:50 ratio.

"We couldn't keep the basket filters clean," said the representative. "Their surface area was too small and their throughput too low. Every 30-minutes a basket strainer plugged. We would have to tear it apart, clean it, and reassemble it. By that time, the other basket filter was plugged up. Since there was no way to sustain operation with the basket filters not performing, we stopped the trial."

A self-cleaning filter solution.
In the search for starch spraying filtration solution, the starch manufacturer turned to RPA Process Technologies (formerly Ronningen-Petter). RPA has installed thousands of industrial filtration systems worldwide in over 10,000 distinct applications.

A number of criteria for the proper filtration system were determined by collaboration between the two manufacturers. 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, which could disrupt paper formation.

Based on these criteria, Corn Products installed two Ronningen-Petter DCF-1600 filters on each starch spraying system, one for primary water filtration, and another for secondary starch slurry filtration.

With the DCF self-cleaning filter, process water enters the top inlet and passes through the screen. The screen holds any particles over 50-microns while cleaned water leaves through the bottom outlet. A cleaning disc moves up and down the filter screen, removing debris. With the aid of the downward fluid flow and the disc movement, the debris is deposited in a holding chamber at the bottom of the filter housing and regularly purged through a valve at the bottom of the chamber.

"The DCF self-cleaning filters are a night and day improvement over labor-intensive disposable filters," said the Corn Products representative. "The DCF 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."

For questions about industrial filtration, please visit the Ask Filter Man forum at http://www.rpaprocess.com/Ask-Filter-Man-Blog.asp.

If you would like to discuss this filtration solution with one of RPA Process Technologies highly-trained Applications Specialists, please visit http://www.rpaprocess.com/ContactUs/Contact-Us.asp.