ESP:Breathing New Life into Dust Collection Filters
Anyone who maintains baghouse dust collectors understands the significant costs that are often associated with replacing the filters. Aside from new filters, retainers (cages) and the labor to remove the old filters and install new filters, there are also other cost-related issues involved. For process-related industries, the most important issue is down time—in most cases, when the baghouse is down, so is the process. Another consideration is the safety and environmental exposure risk that takes place while people are working inside the baghouse. Let’s face it: baghouse filter replacement is a dirty, labor-intensive and time-consuming job.
One of the more common reasons manufacturers replace baghouse filters is due to increased baghouse differential pressure, which creates air restriction on the process side and causes reduced production. The assumption is that once the filters can no longer properly permeate, the filter life is over. However, for many filters, this is no longer the case. Through a new high-efficiency cleaning method, “dead” filters are now being revitalized to “as new” condition.
Turning Old into NewReconditioning used filters bags is not an original concept. Over the years, a number of companies have tried unsuccessfully to clean filters using direct cleaning methods and tools such as air cannons that send an undetermined amount of air mass into the filter bags. Other methods—such as laundering filters in industrial washing machines, using air lances to clean filters from the inside and outside, and the “old beat down” method of sending employees into the baghouse to whack the filters with broomsticks—have also been attempted without success.
The concept of using air is the right approach, but there is a scientific method of understanding compressed air (mass) and cleaning velocity as it relates to static pressure of the dirty filter. In other words, you must know how much air to use when using a dedicated cleaning source to clean a filter that is impinged with dust particles. Using too much air will destroy the integrity of the filter’s construction and, in some cases, cause injury to the person handling the equipment, while using too little air will not accomplish anything except wasting time and money.
A successful high-efficiency cleaning method was developed in Germany and has been used at hundreds of sites since 1996. In 2001, this proprietary filter cleaning technique* was introduced in North America and has already been successfully implemented in several North American process-related industries as a proven method of removing dust particles within filter media and improving airflow levels back to the filter’s original design (see Figure 1).
Where, When and HowThe standard measurement to determine airflow restriction is differential pressure, which is the difference between the clean and dirty sides of the filter. Most plants that operate a baghouse system are required to monitor and routinely record differential pressure to determine the productivity of the baghouse and its associated filters. When the differential pressure is determined to be “too high” because it causes flow restriction problems, the filters must either be discarded or cleaned.
Many pulse-jet baghouses use compressed air to regularly self-clean the filters. The compressed air is transferred from a reservoir tank through a valve connection that sends a predetermined amount of air through a piping device, known as the blow pipe, which is above a row of filters. The air (energy) travels through the pipe and is directed through small orifices and into the filters that are below the pipe. The compressed air causes a pulse or energy source that extends down the length of the filter and knocks off dust particles. All of this occurs while dirty air is continuously sent to the filters for capture.
In the majority of pulse-jet baghouses, the bags are filtering and being cleaned simultaneously. This can cause a problem known as dust re-entrainment, in which dust that is being cleaned from the filter returns to the filters. The cleaning energy is shared by several filters per blow pipe, and as filters age and become impregnated with dust particles, the effectiveness of the cleaning is slowly negated. The dust on and inside them becomes harder to remove, and the filter requires more energy than the baghouse cleaning equipment can provide. Filters are typically replaced once conventional cleaning is not capable of properly removing the dust from the filters.
High-efficiency cleaning can prolong the life of these filters by using dedicated compressed air energy to effectively remove dust particles that have penetrated the filter media. The cleaning technique is performed off-line, which prevents dust re-entrainment, and filter removal is not required. In most cases, the cost to perform the cleaning is equal to the cost associated with the labor of removing and replacing filters.
The cleaning service is designed for pulse-jet/plenum pulse baghouses with top-entry access. The service will work with all filter media—including polyester, aramid, acrylic, fiberglass, spun-bond and other high performance media, such as membrane technology—applied to any substrate, and it does not structurally damage the filters.
Before high-efficiency cleaning is conducted on the baghouse system, a sample filter is used to accurately predict the success of the cleaning method in a testing chamber by mirroring the baghouse parameters. A monitoring unit measures the fabric condition, the ability of the filter to be cleaned and the approximate level of recovery the cleaning will provide. Based on this information, a pressure-versus-airflow measurement is created that illustrates the effectiveness of the cleaning. Finally, the high-efficiency cleaning equipment independently cleans each filter with a predetermined amount of dedicated compressed air, removing embedded dust particles and prolonging the filter’s life.