How does a Baghouse Work?
What is a Baghouse?
A Baghouse, commonly mentioned as a fabric filter, is a dust collection device that houses filter bags, also referred to as filter media, which removes particulate matter/dust from process gases.
Baghouse are utilized in many industrial applications to capture particulate that is produced by a facility before it’s emitted into the environment.
How does a baghouse Works?
The industrial waste gas stream enters the baghouse either via an inlet air plenum or directly into the hopper. Upon entry, the larger particulate drops directly into the hopper below, thanks to a decrease in conveying velocity. Because the gas flows upward into the bag mass, the finer particles attach to the surface of the filter bags, allowing only the clean air to undergo the filter media, into the clean air plenum, then released into the environment.
Once a layer of dust cake is made on the surface of the filter bags, bag cleaning takes place to regenerate the permeability of the filter media. The dust cake being built actually adds to the filtration efficiency of the system, but eventually, this will begin to figure against the system and supply an excessive amount of resistance to the flow. The buildup of the dust cake on the filter bag increases the differential pressure measured over the baghouse which then prompts the cleaning process.
When a baghouse dust collector is best?
Choosing between a baghouse system and a cartridge system is primarily application-based, though it are often a case-by-case situation. There are many factors that play into this.
Advantages of baghouse dust collectors.
High Temperature
Baghouse dust collectors can withstand higher temperatures than cartridge dust collectors. If your application requires temperatures above 250 degrees Fahrenheit, it’s often best to choose a baghouse system.
Sticky Materials
Sticky or adhesive particulates are better collected during a baghouse dust collection system. A bag filter is best fitted to the discharge of the sticky particulate than a cartridge filter. Therefore, a dust collector baghouse is best for adhesive applications than a cartridge dust collection system.
Heavy Dust Load
The more dust you’re collecting, the more likely you’re to wish a baghouse dust collector. Although not as efficient as a cartridge, baghouse dust collection systems are great for particulates within the five micron-plus range and are great with heavy dust loads.
Durability
Some foremost challenging and heavy loading applications enjoy the utilization of baghouse dust collectors. The bag filters are durable, flexible and typically have an extended service life than cartridges, reducing the frequency of filter replacements.
How many types of bag filters are there?
How the dust is collected and the way the baghouse is cleaned depends on the sort of baghouse. The three commonest baghouse cleaning systems are pulse-jet, shaker, and reverse-air styles. The most differences between these sorts of baghouse are described below.
Pulse Jet Baghouse
The pulse-jet or reverse-pulse filter baghouse is ubiquitous in industrial dust collection. These industry workhorses boast no moving parts in their basic configurations and permit collection efficiencies greater than 99.9%. Within the pulse jet dust collector, the dusty air stream usually enters from below the bags or filters and is pulled upwards through the filters where dust is captured on the outside surface and clean gas passes through to the clean air plenum side for exhaust.
When fabric filters are used, the bags are supported by internal wire cages. The pulse-jet cleaning cycle is controlled by a solid-state timer which sequentially pilots “pulses” of compressed gas within the reverse direction of filtering, into blow pipes mounted above each row of filters. When activated, the reverse pulse air pulses travel down the length of every bag within the given row, causing a ripple effect, dislodging and releasing the caked dust into the hopper at the bottom.
A main advantage of the pulse jet baghouse is that it doesn’t need to be taken off-line to wash the filters. With the dust removal programmed for normal or on-demand intervals, the system offers more complete cleaning and reconditioning of the filter bags than the opposite systems. Operating costs are minimal outside the value for compressed gas for cleaning.
Shaker Baghouse
A shaker baghouse, as the name suggests, mechanically disposes of collected dust by shaking it out of the bags into a collection hopper at the bottom of the baghouse. During a shaker baghouse, filter bags are hung and tensioned from the highest of the filter housing and attached with rock bottom open, to the tube sheet. No internal cages are used for shaker bags. The air stream enters from below the bags and is pulled upwards through the inside of the bags, where the dust collects.
The air stream passes through the filter bags, trapping the contaminants on the dusty side. Clean gas is exhausted near the highest of the collector. To clean a shaker baghouse, which normally uses woven filter bags, the airflow through the system must be periodically shut down, also mentioned as being taken off-line, while mechanical shake-cleaning is used. After the dust cake is released from the bags, it falls into a hopper at the bottom of the baghouse for removal.
Shaker style baghouse are generally uncomplicated and are commonly employed where compressed gas isn’t available. However, limitations exist for the appliance of shaker baghouses therein they can’t operate and clean continuously without periodic shut-down. Also, particle collection efficiencies are generally less than other sorts of baghouses that use felted or pleated filter media.
Reverse Air Baghouse
There are two sorts of reverse air baghouses. More common nowadays, especially with fibrous dusts like those from grain or wood processing, may be a round reverse air collector style wherein dust collects on the outside of the filter bags or filters. For cleaning, reverse air generated by the equipment fan or medium pressure blower is directed by a rotating arm over the filter bags, blowing reverse air into them to get rid of dust.
This sort of reverse air baghouse generates a lower cleaning atmospheric pressure than the compressed gas pulses of a pulse-jet. It’s referred to as a low-pressure high-volume cleaning system and cleans while on-line. This gentler cleaning method decreases wear and tear on the bags and saves on the value of compressed gas. The trade-off for the value of compressed gas, however, is that of the horsepower requirements and maintenance costs of the reverse air blower and moving parts.
An older sort of baghouse filters, also known within the industry as reverse air, is usually seen with an oblong housing and multi-compartments. Sort of a shaker unit, during this style, dust collects on the inside of the filter bags because the airflow rises. These sorts of reverse air baghouses need to be taken offline for cleaning, thus are often divided into compartments, so one section at a time are often cleaned.
Generally, a whole compartment is pressurized with a system fan within the reverse direction of filtration. Once activated, the pressure from the reverse airflow causes the filter bags to slightly collapse. These sorts of reverse airbags have sewn-in rigid rings that allow them to flex but not collapse completely or “pancake” during the cleaning cycle. Thanks to the off-line cleaning requirement, this sort of reverse air baghouse must be oversized to account for some of it to be off-line during cleaning, making this style less cost-effective than a pulse-jet.