Filtration & Separation
Industry Will Remain Vibrant and Grow
By Wu Chen, Ph.D., Dow Chemical,
Freeport, Texas, U.S.A.
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Filtration technology is used in all industries and households and is an important part of human life. The filtration and separation industry provides services and devices to meet these filtration needs. Since it covers such a wide applications spectrum, it is natural that this industry is very diversified, segmented and not well understood. Most of the work and industry analyses are focusing on certain market segments or technology. It is very difficult and seldom attempted to have a sensible analysis of the whole filtration and separation industry. The Bigger Picture When discussing the filtration industry, one needs to be aware of what is really in the so-called filtration world, and this needs to be discussed from three different aspects; technology, market segments and value chain.
Evaluation of Industry There are two key filtration mechanisms,
direct sieving and indirect interceptions. In direct sieving, the
particles are larger than the openings of the filter medium and
get filtered out. The more commonly encountered filtration mechanism
in gas filtration is indirect interception where the particles are
collected by the filter media by inertial impaction, diffusion (Brownian
motion), interception, and electrostatic effects. In addition to
filtration, there are also separation methods without filter media.
These methods utilize inertia, electrostatic or centrifugal forces
to achieve solid/gas separation. The simplest filtration mechanism is straining where particles are caught on the medium by direct sieving. Particles larger than the medium openings are filtered out. The second mechanism is cake filtration where the number of particles is high enough to form a particle bed called the filter cake. This cake becomes the primary filter septum and the original filter medium is not as important in the particle capture. Sometimes the filter media are thick so the particles are caught inside the filter media. This type of filtration is called depth filtration. Very fine particles tend to form a dense cake and retard the filtration rate, in these cases cross flow filtrations are commonly used to keep the particles from forming a cake. This technique is used by most membrane filters since they are used to separate very fine particles. Beside filtration, solid/liquid separation can also be accomplished by gravitational or centrifugal forces where the particles are separated due to their density differences from the liquid phase. Different equipment and design considerations are used for these two mechanisms. Flotation, also utilizes gravitational force but the particles are made lighter than the liquid phase so they float to the top and are separated. There are other field-forces like magnetic and electrostatic forces used for separating particles from liquid streams. Unlike solid/gas separtion, the mechanisms of filtration and separation are equally used and none of the applications dominate solid/liquid separation. Therefore, the commonly used term of "liquid filtration" is not a good representative term for solid/liquid separation. The above brief discussion provides high lever overview of technologies used in the filtration and separation industry today. It can be seen that this industry covers a broad technology spectrum. Therefore, it is very difficult for any participant to engage in more than one technology area. Almost all of the companies in this industry focus on one or part of one technology area. In North America, very few companies are able to participate in multiple technology areas. One example is Pall, which is strong in straining type of liquid filtration technology but also participate in businesses involving cake filtration, cross flow filtration and gas filtration technologies. The trend will continue as large companies like Pall continue to expand their technology envelope. There will also be smaller companies who focus on part of a technology area and excel in that specific market. An example is the Oberlin Filter Company who focuses on one type of cake filters. Evaluation by Market Segments
The applications above are predominantly accomplished through filter media. Therefore, filter media plays the key role in the solid/gas separation arena. Although each segment has its own opportunity and development trend, the emphasis on filter media is universal among all segments. The common needs are to increase efficiency in particle removal, reduce pressure drop, and in the meantime, lower the cost. This trend has been in the past and will continue in the future. The use of membrane media is a major approach
toward high efficiency filters. New material (like PTFE) gradually
finds its place in the media market with its better performance
in pore size control and chemical compatibility. Due to the high
cost of membranes, meltblown technology is continually being improved
to provide low-cost high efficiency media. The use of nano fibers
are now on the rise and this may provide a proper middle point between
meltblown and membrane media in terms of cost and filtration efficiency.
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Similar to air filtration, the major development area in the liquid filtration arena is the media. The opportunities and trends are very similar to those in air filtration. One of the key differences between solid/liquid separation and solid/gas separation is that equipment and mechanical design are much more emphasized in solid/liquid separation arena. For example, in the biopharmaceutical and food & beverage industries, CIP (clean-in-place) is a must and effort is spent in improving that capability. This trend will continue. In membrane filtration, not only the membrane itself is the subject of improvement, but the module design to increase surface area, the vessel design to improve the controllability of crossflow and transmembrane pressure, and the seal design for different chemicals all present challenges and opportunities.
Evaluation by Value Chain The value chain starts with material supplies. This alone is a very large industry, which includes plastics (polypropylene, polyester, nylon, PTFE, etc.), metals (steel, stainless steel or other metals), adhesives (epoxy, polyurethane, etc.), and more. The filtration industry has not been putting a lot of effort into the improvement in this area since it may be quite involved to introduce a new material to the manufacturing process or market. It can also be due to a lack of awareness of the advances and opportunities in raw materials. With today's progress in the chemical industry, there are great opportunities in plastic materials alone. There are technologies that allow plastics to have improved properties like higher temperature resistance, better chemical resistance, higher tensile strength, better removal efficiency for special substances like fine particles or allergens and lower melt viscosity to allow for order of magnitude faster speed in the media manufacturing. The next step in the value chain is the media producers, filter component producers or equipment parts producers. These are all essential parts of a filter or a separator. In the filtration and separation industry, the attention has been in the media production as it is considered the core of the filtration. The industry for filter media itself has many segments and it takes a book to discuss them individually. Besides the general trend of developing higher efficiency, lower pressure drop and lower cost media, custom tailored media for specific applications to catch a niche market is also on the rise. One example is multifunctional media which can remove volatile organic compounds and odor as well as particulates. This kind of medium is especially useful in the automotive cabin air filter segment. Filter fabricators and equipment fabricators take the filter media and make the filter. While filters with different configurations can be made from the same media, the drive is to maximize the filtration area within the space constrain but maintain filtration efficiencies and operation capability. Frequently used approaches include the use of pleated media, multi-layer media, graded depth media structure and other innovative designs. For improving filtration efficiency, finer fibers or surface treatments are the general direction. For equipment fabricators (either for filters or separators), improvement in equipment design is focusing on material handling (like cake discharge, leak-by prevention) as well as better separation efficiency (higher electrostatic charge, longer lived electrostatic charge, higher centrifugal force, lower turbulences, etc.). Another important driver for more efficient filter media is government regulations. In the U.S., regulation has tightened the emission specifications from PM10 to PM2.5 (Particulate Matter smaller than 10 or 2.5 microns). This has impacted the emission filter design for power generation and created challenges and opportunities for filter bag suppliers. System integrators put ancillaries (pump, pipe, valves, controllers, etc.) together so the filter can function. In many applications, the "standard" system is provided. With the increasing demand in the market, especially in the solid/liquid separation market, suppliers need to be able to respond quickly and design systems for new or specific applications. Distributors play an important role between the end user and suppliers. Traditionally, they just distribute or sell but the trend in the past decade and for sure in the future is that the distributors will have a larger role as the field support for the filter suppliers and VOC (voice of customers) for the customers. They can even influence or control the trend of future development. Good examples are Walmart and Home Depot, with their high sales volumes; they set the standard and are influential in the Test Method definition. The end users are the actual consumers of the filter or separators. There are industrial users who normally place orders in large dollar amounts. There are also household users. Although the individual purchased quantity is small, the total number of domestic users outweighs any industrial users. None of the filters last forever and sooner or later they need to be replaced. The disposal of spent filter or related materials was seldom considered in the value chain since it is mixed with other waste/trash. With the growing awareness of environmental protection globally, there is a need to address the waste from spent filters or separators. This is already true in the industrial filtration processes. One of the major drives in the filtration industry today is to design longer life filters but there will still be plenty of waste to be disposed. Businesses relating to spent filter disposal will have opportunities in the future. On the Horizon
These subjects may not be all inclusive but definitely provide a good view of the industrial trend in people's mind. Conclusion
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