The chemical industry has its share of tough filtration challenges. Most difficult are the three simultaneous requirements of high-temperature capabilities, chemical inertness and easy, rapid filter cleanability.
Individually, each need can be a challenge. However, when all three are needed at the same time, solutions are limited. This troika of capabilities is needed in many chemical processing, coal-fired power plant and other applications. It is a struggle for companies that design filtration systems to meet these challenges without the need for secondary or backup capability. A single stand-alone system continues to be the "holy grail" in these and other market segments.
To meet this challenge, one emerging technology ," the Thermapore technology ," appears particularly promising. This technology uses a filtration media from silicon carbide fibers that are 5 microns and/or 13 microns in diameter. The fibers either are wetlaid or otherwise made into a filtration medium with many possible designs, including a flat surface, pleated, spiral wrapped, rotary drum, through-wall or just about any conventional configuration required for use in a filter.
Shown here is a filter cartridge cleaning operation at 750C.
Photo courtesy of Industrial Ceramic Solutions.
Advantages of silicon carbide include its high temperature resistance and chemical inertness. When produced as a fiber and subsequent filter medium, filter and filtration system, silicon carbide appears to be a leading candidate and new disruptive technology worthy of in-depth investigation for potential wide use in demanding and stressful process environments.
Perhaps the best example of progress with silicon carbide filtration systems has been with diesel soot exhaust filters. Although many material candidates for this use have been explored, few, if any, fully meet all the requirements necessary to become a practical solution. Filters constructed of silicon carbide filtration media and support have been tested on dynamometers and through field trials and have been documented to remove 95 percent of 0.1-micron soot particles under a wide range of engine conditions, without adversely affecting the filter, the filtration system or vehicle performance.
Although these performance results are impressive, the most interesting part is that the filter has an associated magnetron (microwave device) that activates when the filter becomes contaminated with soot and reaches a predetermined differential pressure level. At this point, the magnetron is programmed to activate and heats the filter to a controlled temperature as high as 1,200C. At this temperature, the soot is vaporized instantly into a harmless exhaust plume, which is expelled to the atmosphere. The filter then is ready to collect more soot for another cycle. The entire purging cycle is performed in seconds.
Imagine the possibilities of rapidly eliminating large volumes of an unwanted organic substance in a chemical process in an environmentally beneficial manner. Of course, not every organic substance or circumstance will require a 1,200C burn-off to clean a filter. However, systems using silicon carbide Thermapore filters could be alternatives to widely available pressure and vacuum cake filtration devices, which typically use diatomaceous earth filter aids that often prove to be problematical in waste disposal.
Other new technologies
Other new and emerging filtration media technologies include:
Tensylon UHMWPE fabrics that have an extremely low elongation (2.8 percent) and creep (<5 percent with 20 percent load after almost a year). Tensylon has both a very high cut and abrasion resistance with tenacity at 17.0 grams per denier (gpd) and outstanding resistance to acids, bases and many other aggressive chemicals and fluids. The yarn has a surprising high temperature resistance for a polyethylene ," about 285F, a result of the long-chain molecules that make up the polymer. Filtration media from ultra-high strength Tensylon can be used as press cloths or belts under the most demanding applications.
MultiLobal micrometal fibers are metal filters made from stainless steel, nickel, titanium and other metals with fibers as fine as 1.5 microns in diameter. The media are capable of resisting heat as great as 500C, have high strength and modulus properties and are inert in most applications and through the pH range. When supported with wire cloth filter candles, cartridges or flat plates, they are rigid and capable of operating under high pressure.
EmmiTex PTFE yarns and fibers for filtration media are available as woven fabric and are emerging as wetlaid and hydroentangled nonwovens. PTFE has high surface release properties and temperature capabilities (to 250C) and is inert to most chemicals and through the pH range. These materials also are used as sewing threads in filter bags, belts and press cloths.
Halar ethylene-chlorotrifluoroethylene (E-CTFE) fluoropolymer filtration media are made into melt-blown fabrics. The media have very fine filtration capabilities, outstanding chemical properties and a wide range of pH capabilities. The media are emerging in demanding applications ," from coalescing and mist elimination to filtration of aggressive chemicals in cartridge and bag filter configurations.
New and emerging technologies ," disruptive filtration technologies ," will allow the chemical process industry to improve process applications and reduce costs. Disruptive filtration developments in the chemical process industry have not been a common occurrence. Disruptive technologies are not minor or incremental improvements, but wholesale developments that change the way products are produced and used.
Gregor is managing director of Edward C. Gregor & Associates LLC and is a co-founder of the American Filtration and Separations Society and Filtration Fellow. He is a consultant to the polymer, fiber and filtration industries and resides in Charlotte, N.C. Gregor can be contacted by e-mail at firstname.lastname@example.org or at (704) 442-1940.