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Blog: Imperial Systems Approach to Dust Collection

BagHouses: How They Work

Baghouses and Dust Collectors are often used as synonyms. The baghouse is a system in which air is filtered by bags made of various materials, which are periodically cleaned to remove the accumulated dust. Today, cartridge dust collectors are increasingly popular in many industries, and for good reason: cartridge filters can pack a lot of surface area into a small space and can filter very small (sub-micron) particulate very efficiently. For some industries this is essential, particularly for industries such as metalworking that generate smoke and fumes that contain potentially toxic materials.

The baghouse, however, has been a workhorse industrial dust control for many years, and continues to serve its role today. While the basic concept remains the same, new filter materials and new ways to solve problems make them more adaptable than ever. Not every industry produces dust that’s fine enough to need the high efficiency of a cartridge collector.baghouses

Generally, all baghouses have a tube sheet to which the bags are attached, an inlet for dirty air and an outlet for clean air, and an opening at the bottom for collected dust to drop out. The location of these features depends on the type of baghouse. The main differences between types of baghouses is how the bags are kept clean.

In a shaker baghouse, the bags are cleaned by mechanically shaking them. The bags usually hang from the top of the unit and are attached to the tube sheet at the bottom. In this type of system, air typically enters from the bottom.  It is then pulled through to collect on the inside of the bags. Air then exits at the top as clean air while the dust is collected on the inside of the bags. To clean the bags, the airflow must be shut off and the hanging mechanism shakes the bags to get rid of the dust, which drops out the bottom. These are not the most efficient types of baghouses and can be high-maintenance.  Yes, the design is simple and does not require compressed air or complicated supports for the bags, however damage to the bags can occur from the mechanical shaking mechanism.

In a reverse air baghouse like our BRF, dirty air enters the collector and dust collects on the outside of the bags, which are supported by a metal cage to keep the air pressure from collapsing them. Steady air circulation continuously pulls air through the filter bags. For cleaning, a fan rotates over the bags, blowing reverse air into them to remove dust. This type of reverse air baghouse generates a lower pressure than the compressed air pulses of a pulse jet, which can decrease wear and tear on the bags and save on the cost of compressed air. They are usually very cost-efficient and if used within the parameters for which they were designed, they are very effective.

Also, this type of reverse air baghouse can continue running while cleaning occurs. An older type of baghouse also sometimes referred to as reverse air may collect dust on the inside of the bags and then cut off the inflow of dirty air and use a reverse flow of clean air to partially collapse the bags, which also removes the dust. These types of bags have rigid rings that allow them to flex but not collapse completely, or “pancake”. These types of reverse air baghouses have to be taken off line for cleaning or are divided into compartments so one section at a time can be cleaned.

A pulse jet baghouse is somewhat similar. The bags are supported by metal cages and hang from a tube sheet at the top of the baghouse. Dust and air enter and dust collects on the outside surface of the bags, not the inside. The bags are cleaned by bursts or pulses of compressed air that travel down the length of the bag and dislodge the dust. Because the pulse of air travels very quickly down the bags, this type of baghouse can be cleaned without taking it offline. This allows them to operate more efficiently since dust is removed from the bags at more regular intervals. The downside to these types of collectors is the higher pressure and expense of compressed air, which adds to operating costs.

The EPA provides information (link: https://www3.epa.gov/ttncatc1/dir1/cs6ch1.pdf) to help you make a general calculation of the capital costs of a baghouse dust control system. Their calculations include the cost of the collector, the bags (and cages if necessary), measurement instruments, installation costs, and the annual operating costs (electricity, compressed air, labor, and materials). These costs will obviously vary widely. A pulse jet baghouse requires compressed air, which is not needed for the other types of baghouses, but may require fewer filters since they are more efficient.

One thing that is a major headache for owners of any type of baghouse: replacing the bags. This is usually a dirty, messy, time-consuming job that requires the collector to be off-line for a considerable period of time. It often involves working in an enclosed space. Mechanisms for attaching the bags to the tube sheets vary widely, but especially when cages are involved it can be a very involved process. Some companies installing new dust control equipment choose a cartridge filter collector because vertical collectors like our CMAXXTM are easy to change and do not involve issues with confined spaces. For existing baghouses that need frequent bag changes, a pleated filter bag (link to our page) is an option that should be considered. These have a much larger surface area and last much longer than traditional bags, which means less frequent changes. Also, pleated filter bags do not require cages, which greatly simplifies the changing process.

To learn more about Imperial Systems’ Baghouses, call us today at 800-918-3013.  Our helpful, knowledgeable team members can answer any questions you may have about all types of dust collection solutions.