Revitalizing Today's Dust Collectors To Meet Tomorrow's Needs
The problem is that all this new equipment has added maintenance issues and production constraints to many manufacturing facilities. Additionally, “new” equipment that was installed 10 years ago to comply with regulations may no longer be adequate as new regulations are put in place. Does this mean that more new equipment will be needed?
Not necessarily. New filter elements are emerging that can help companies cost-effectively retrofit existing equipment to meet increasingly stringent emissions standards. When specified and used correctly, these elements can also help reduce energy use and maintenance requirements while increasing operational efficiencies, making them a worthwhile consideration in any ceramic manufacturing facility.
Optimizing Baghouse CollectorsHistorically, filter bags constructed from 16-oz polyester felt have been the primary media used in baghouse systems for filtering process dust in temperatures up to 275F. However, polyester felt bags were designed to meet less stringent regulations, and, as a result, may not meet future emissions standards set by the EPA and other government organizations. Additionally, due to the abrasive nature of many ceramic materials, the bags have to be changed rather frequently—every six months is common—and they often limit the actual cubic feet per minute (ACFM) airflow of the collector, making it difficult for manufacturers to achieve their material handling and production goals.
In many cases, these filter bags can be replaced with 100% non-woven, spun-bond, pleated filter elements* to produce greater dust collection efficiencies. In side-by-side stack efficiency testing, the pleated filters were 58% more efficient than 16-oz polyester felt bags in reducing emissions (see Table 1).
How the Non-Woven Elements WorkThe non-woven, spun bond polyester elements are composed of a fine-denier (tightly spun), renewable media that combines high efficiency, good release characteristics and moisture tolerance to ensure high volume and a long element life. Unlike earlier models of pleated elements, which were often difficult to clean and tended to fall apart during operation, the non-woven, spun bond pleated elements are designed to be both user-friendly and durable. They are constructed of an all-metal design with a 68% open area helix core, which facilitates cleaning, and their interfaces are both mechanical and adhesive to prevent any part of the elements from separating. Additionally, the pleat retainers are pleat-anchored and have a riveted overlap to ensure that they cannot fall into the product.
Unlike many conventional filter elements, the pleated elements do not require a filter cake to reach their efficiency, which leaves more of the product in the process. The elements are also typically 60 in. shorter than the conventional filter bags they replace, which increases the drop-out box by 60 to 90 in. Depending on the product’s weight per cubic foot and the collector’s opening parameters, manufacturers can expect to see from 28 to 41% fewer particles reaching the element due to their shorter design. This type of load reduction provides longer element life—since the elements don’t have to be pulsed as frequently, lower compressed air usage is needed.
The elements also feature wider pleat spacing and shallower pleats than conventional cartridges, allowing them to be cleaned more easily and eliminating bridging in the baghouse system.
Choosing the Right Element TypeThe non-woven, spun-bond polyester elements can be used in both conventional pulse-jet and high-volume, low-pressure (rotary arm) baghouse dust collectors to reach up to 99.999% efficiency at 0.1 micron. Elements are typically specified based on the collector’s maximum operating temperature and other parameters, as well as the dust size, weight and loading. Since every application varies, manufacturers should consult with their filter element supplier to determine the right element for their needs. However, a wide variety of surface treatments and designs enables the elements to suit a range of applications.
Surface TreatmentsSurface treatments can enable the pleated elements to meet challenging filtration requirements. For example, for applications that must meet NFPA 77 regulations, the base material can be vacuum metallized with aluminum or impregnated with conductive carbon particles to make an anti-static element design.
For applications with light moisture or oil contaminants, a hydro and oleophobic surface treatment can be used to repel the water or oil. For difficult filtration problems, a polytetrafluoroethylene (PTFE) membrane can be laminated to the basic spun-bond polyester media to produce a filter with high release characteristics and high efficiencies for fine particles. And for submicron particles and/or the release of sticky, agglomerating material, the elements can be both carbon-impregnated to minimize the electrostatic charge and laminated with a PTFE membrane for greater collection efficiency. Elements treated with a PTFE membrane can reach up to 99.999% efficiency at 0.3 micron.
Element DesignsThe elements can also be specified in four different designs to meet a variety of filtration needs. Top-load pleated bags can be built to fit tubesheet holes ranging from 4.625 to 8 in. in diameter and can handle temperatures up to 500∞F. Bottom-load pleated bags come in sizes to fit 4.625 and 5.75-in. elements and are constructed to meet temperatures to 200F. In both the top- and bottom-load designs, a sonic-welded seam, combined with open helix cores, facilitates cleaning and helps ensure element integrity.
For applications that require multiple tubesheet fits from a single element, all-urethane top-load pleated bags with heavy-duty construction can be specified. These elements can be used in temperatures up to 200F. At the end of their useful life, the elements can be completely incinerated. This design offers operators of older collectors a cost- and labor-efficient way to meet increasingly stringent collection efficiency requirements.
Finally, for bottom-load filters operating in temperatures from 200 to 500F, an all-metal design bottom-load unit can be specified. The seal at the interface with the bag cup is better than flexible tops or conventional bags because it can be securely tightened without the worry of cracking or fabric impingement. The elements’ all-metal construction is combined with a 65% open helix core and mechanical interlocked bottom. The pleat retainers have riveted overlaps and are pleat-anchored, virtually eliminating band separation.
Fiber ConstructionThe type of fiber used in the element also provides application flexibility. For applications up to 375F that require high strength, abrasion resistance, dimensional stability and superior dust-release properties, aramid fibers can be specified. The aramid fibers can also be combined with the efficiency of a PTFE membrane for extremely fine particle filtration applications at temperatures up to 375F.
For alkaline, mineral and organic acid or solvent applications at temperatures up to 375F, a polyphenylene sulfide (PS) fiber with superior dust-release properties can be used. When combined with the efficiency of a PTFE membrane, PS can provide excellent filtration in high-temperature chemical applications.
For high-temperature applications (up to 500F), fiberglass elements can be used. These elements, which are currently in field-testing, are also designed to provide chemical resistance and low moisture absorbency.
Avoiding PitfallsNon-woven, spun bond pleated filter elements can provide improvements over bag filters in most baghouse collectors. In some cases, however, manufacturers who have installed the pleated element have not achieved the additional performance they were seeking. Typically, this is because the elements have an imbalance between cleaning and loading—i.e., either the loading is too high for the cleaning, or the cleaning is insufficient for the loading. Many manufacturers get stuck on the air-to-cloth ratio of filter elements. While an element’s square footage can be increased from 12 to 80 square feet, the pulse valve cannot support this kind of increase in the cleaning requirement.
Additionally, manufacturers should not expect to achieve both an increase in airflow and energy savings. If greater throughput is a priority, the pleated elements can help manufacturers increase throughput while maintaining their energy use. Alternatively, if the overriding goal is energy savings, the pleated elements can significantly lower energy use while maintaining the previous level of airflow and material throughput. However, if both increased throughput and energy savings are desired, a new collection system may be the best solution.
Working closely with the element supplier can help manufacturers avoid these and other pitfalls.
Reaping the BenefitsRegulations on emissions will undoubtedly become even more stringent over the next several years, and limitations on dust collection equipment may make it difficult for manufacturers to comply. In many cases, however, simply changing to pleated filter elements can make a big difference in collection efficiency, throughput or energy efficiency in existing collectors.
For More InformationFor more information about 100% non-woven, spun bond pleated filter elements, contact TDC Filter Mfg., Inc., 1331 S. 55th Ct., Cicero, IL 60804; (800) 424-1910; fax (708) 863-4472; e-mail firstname.lastname@example.org; or visit www.tdcfilter.com.
*Pleat+PlusTM filter elements, supplied by TDC Filter Manufacturing, Inc.
**The delta P is the level of resistance that is in a system, measured in inches.