Meeting Tomorrow’s Efficiency Needs.Ever since the 1990 Clean Air Act amendments were passed into law, the cement industry has had to make a number of modifications to ensure that its manufacturing facilities comply with emissions regulations. And the regulations keep getting tougher. The Environmental Protection Agency’s (EPA) impending Maximum Achievable Control Technology (MACT), PM 10 and PM 2.5 standards will force companies with all kinds of emission sources that emit more than 10 tons per year (tpy) of a single hazardous air pollutant (as defined under the standards) or 25 tpy of combined HAPs to install additional controls. And the New Source Performance Standards regulations on particulate matter emissions are requiring new controls in a number of plant applications and transfer facilities. 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 manufacturing facility. Optimizing Baghouse Collectors Historically, 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 275°F. 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 some 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, spunbond, 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). The pleated elements can also increase the collector’s airflow by lowering the delta P across the filter (see Table 2).** Alternatively, for manufacturers who are looking to save energy, dropping the delta P by 3 or 4 in. can save approximately $9198 annually (operating 24 hours a day, seven days a week, 365 days a year @ $0.07 kw). Units with larger motors can save even more on energy costs (see Table 3). Additionally, the pleated elements are designed to resist wear from abrasive materials, enabling them to last two to three times longer than the felt bags in the same environment. They are also easier to change out than felt bags—change-out of pleated elements can be completed in just 25-35% of the time normally allocated for conventional bag and cage replacement. These lower maintenance requirements can enable manufacturers to significantly reduce their maintenance costs (see Table 4). Pleated elements can optimize both the operational efficiency and throughput of existing baghouse systems. In addition to helping manufacturers meet more stringent emission standards, the pleated filter elements can provide thousands of dollars in savings compared to bag filters (see Table 5). 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. Element Designs The 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 8.75 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 200°F. 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 200°F. 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 500°F, 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. Filters for High-Temperature Applications The type of fiber used in the element also provides application flexibility. For applications up to 375°F 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 375°F. For alkaline, mineral and organic acid or solvent applications at temperatures up to 375°F, 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 500°F), fiberglass elements can be used. These elements, which are currently in field-testing, are also designed to provide chemical resistance and low moisture absorbency. Table 1. Stack emission comparison16 oz. Polyester Felt Bags 100% Non-Woven Spun Bond Polyester Elements Dust size 5 microns 5 microns Air –to-cloth ratio 5:1 5:1 Grain Loading 30 g/acf 30 g/acf Temperature 275 ºF 275 ºF Emission .0060 .0025 Table 2. ACFM comparison* 16 oz. Polyester Felt Bags 100% Non-Woven Spun Bond Polyester Elements Filter elements 720 bags 720 40-inch elements ACFM 100,000 117,000 Air-to-cloth ratio 7.10:1 5.26:1 Unit square feet 14.14 26.39 Operating delta P 7.00 3.88 Motor 300 hp 300 hp System delta P @15 in. @11 in. Brake hp 291.50 291.50 *Based on a 100,000 ACFM baghouse using a backward inclined fan. Table 3. Energy comparison* 16 oz. Polyester Felt Bags 100% Non-Woven Spun Bond Polyester Elements Filter elements 720 bags 720 40-inch elements ACFM 100,000 100,000 Air-to-cloth ratio 7.10:1 5.26:1 Unit square feet 14.14 26.39 Operating delta P 7.00 3.88 Motor 300 hp 300 hp System delta P @15 in. @11 in. Brake hp 291.50 224.40 Total savings at $0.05kw= $19,732 per year *Based on a 100,000 ACFM baghouse using a backward inclined fan. Table 4. Maintenance comparison Change-out Time 720 re-bagging = 80 man hours 80 man hours @$45.00/hr = $3600.00 720 re-bagging to pleated filter elements = 20 man hours 20 man hours @ $45.00/hr - $900.00 Change-out labor savings = $2700.00 Table 4. Summary of total savings 3-year energy savings @ $19,732/yr $59,196.00 2-year change –out labor savings@ $3,600.00* $7,200.00 2 sets of bags @ $5,040.00* $10,080.00 1 set of cages @ $20.00* $14,400.00 Total Savings $90,916.00 *Assumes 1-year bag life versus 3-year pleated element life *Pleat+Plus™ filter elements, supplied by TDC Filter Manufacturing, Inc. **The delta P is the level of resistance that is in a system, measured in inches Written by For more information contact Tom Anderson at MIDWESCO/TDC, 800-805-5694, Fax: 503-977-0176, or ANDERSONT@tdcfilter.com
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