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By Richard Juskowiak, Donaldson Process Filtration
Steam is prevalent in food and beverage processing. While the high temperatures of steam generally prevent bacterial growth, other kinds of contamination can occur. Particles, rust and scale can be present in system equipment, and these pose a greater risk when steam is recirculated. Filtration is essential on steam lines, and the choice of filtration methods is critical, especially in high-pressure, high-temperature applications.
The traditional filtration media for steam has long been carbon, an option in use since the 1950s. Carbon can be suitable in temperatures up to 260° C / 500° F and pressures to 27.5 bar / 400 pounds per square inch gauge (psig).
However, with a sandpaper-like texture, some granulated carbon tubes can shed carbon particles during use. By contrast, high-grade stainless steel tolerates high pressure and is rated for use up to 371° C / 700° F. Stainless steel filters can also be ultrasonically cleaned up to six times before replacement.
These properties make stainless steel better in three instances:
A common challenge in steam equipment is controlling water hammer. This phenomenon occurs when a cooled system is reheated too quickly, propelling the accumulated condensate through the system. The force can damage valves, joints, and filters along the way. Water hammer can also occur due to sudden pressure or velocity changes, as well.
Several large dairy processors recently discovered carbon particles downstream in their product following a water hammer event. They contacted Donaldson process engineers looking for an alternative that could fit into their existing filter housings. The recommendation was to use stainless steel because of its greater resistance to cracking, chipping, or shattering.
Dairy processors are governed by the Pasteurized Milk Ordinance (PMO), which requires filtration on steam lines. The ordinance, drafted in the 1950s, specifies a particular brand of carbon filter prevalent in the market decades ago. However, the ordinance also allows processors to use an “equivalent” filter with similar capture properties.
Prompted by requests from the dairy industry and the instances of carbon shedding mentioned earlier, Donaldson expanded its P-GSL N filter line to serve this need. This pleated stainless steel alternative meets PMO regulations and is sized to drop into most legacy carbon tube housings. Since filter housings are connected to the larger steam system, the compatibility of the P-GSL N elements allows facilities to upgrade to PMO-compliant steel elements without expensive remodeling.
In processes where steam is injected into food products or used to clean and sterilize food processing equipment, it is required to be culinary-grade. 3-A, the premier standards organization for food processing, defines culinary-grade as steam filtered to remove 95% of particulates 2 microns and larger. P-GSL N filters are 99.9% efficient in that range, exceeding 3-A requirements.
The standard also requires stainless steel filtration, because the media is non-fiber releasing and is fabricated without binders, adhesive, additives, or surface-acting agents that can leach into the process. Typically, two sets of steam filters are recommended on a culinary-grade steam line: Pre-filtration to remove particulates 25 microns or larger, followed by the 2-micron point-of-use filters.
Finally, P-GSL N stainless steel filters help reduce energy costs. The more restrictive an element is, the more energy it takes to push steam through the media. Compared to carbon, the pleated construction of P-GSL N filters improves filtration surface area, which reduces differential pressure by a factor of eight over comparable carbon tube filters, based on laboratory testing.
If your steam system has a regulatory challenge or the risk of water hammer damage, it pays to consider stainless steel steam filters. They are durable, standards-compliant, can be regenerated, and deliver energy savings. While carbon tube filters have a lower initial cost, the return on investment for stainless steel P-GSL N filters can be significant.