Filter Cleaning - Pulsing
Poor filter cleaning can be the result of undersized or restricted cleaning system components. It is important to make sure that there are not any restrictions starting from the compressor all the way to the reservoir. Also, ensure that your header tank size matches your cleaning requirements.
Ensure better cleaning with tanks that are kept free of moisture and debris as they can substantially impact the ability to clean the filters. The pulsing frequency can never be any faster than the reservoir can recover to full pulsing pressure.
The pulse sequence should be adjusted to ensure that newly cleaned filters do not take in dust from the neighbouring filter being pulsed. Staggering the firing order helps reduce cross contamination.
Make sure your pulse pipes are aligned properly over filters to prevent velocity damage and loss of cleaning effectiveness. Pulse pipes can be knocked out of position during installation of replacement filters, during routine maintenance, or even when pipes were initially installed. Any of these errors could result in internal velocity abrasion and premature failure.
Venturi generates more efficient pulse cleaning by diverting more air into the filter during pulse cleaning
Suitable for: all dust types
- Diverts more air into the filter during pulse cleaning
- Optimises energy use resulting in more efficient cleaning
- Less air consumption
- Minimises energy cost
- Various dimensions to fit your system
- Horizontal or vertical installation
Re-entrainment is the term used for dust particles that are constantly returned to the filtration surface, resulting in high-pressure drop across the filters.
This is generally associated with finer particulate collection and has several root causes.
- Too high an upwards velocity at the bottom of the filters
- Particulate being pulled back on to the filters after pulsing (too high a filtration velocity)
- Air jetting from the exit point of the collector, which does not permit finer particles to leave the filter
- Particulate pulsed from one bag to another ( bad spacing, high velocity)
- Inlet not baffled correctly, causing high velocity to pick up dust from the bottom of the hopper
The upward velocity may need to be calculated when the entry point to the collector is located at the bottom. Firstly by calculating the surface area of the filter bottom and deducting this figure from the total square area of the dust collector at this point. This shall equal the free area of the unit up which the total volume of air must pass before starting to percolate through the filer to perform the filtration process.
All filer units, irrespective of type, shakers, reverse air, pulse jet, etc are manufactured to each particular manufacturers design, with little or no consideration per application as to the properties of the dust type and ho the dust will arrive at the point of removal.
If we look at the average filter unit, a high percentage of the dust would not fall to the point of removal and therefore the degree of slope given to a hopper is most critical. It would not be practical for all dusts to reach the point of removal immediately on clean down, because as the hopper necks slope to a narrow exit point the dust tends to compact and, bridging can and does occur. As a result, nothing is removed through the valve.
The angle or slope would of course not permit dust to slide to the point of removal if it were too slight. Problems associated with the angle can be generally detected. You will find that operators have damaged the hopper with heavy objects to create movement to dislodge the cake.
Condensation also causes problems in some hoppers, creating solid cake to the hopper walls thus greatly reducing the slip value. This can be created from a number of sources but in the main form of un-insulted systems.
We can see that there are many factors involved in getting the dust to the point of removal without even looking at a wide variety of dust types and their individual characteristics. Having reached the removal point, many more serious considerations are apparent.
The purpose of the screw, rotary valve is to remove the dust and keep air out, for if the air is allowed in at this point fine particulate would never leave the filter.
Screws and rotary valves rotate at a fixed rate and have a limited capacity. Be sure that the amount of dust presented to the valve can be removed, if not measures should be taken to have the speed increased.
The drop out box/ baffle plate is designed to allow for the heavier dust particles to be dropped from the airflow before contacting the filter surface area. The drop out box/ baffle plate removes the filter from the abrasion zone.
Operating a dust collection system with leaking filter bags /cartridges defeats its sole intended purpose. A few leaking filter bags/ cartridges or even one within a collector/system can result in a substantial emissions increase. Causing dust bypass to adjacent filters increase pressure drop. Leak testing of your dust collector needs to be a regular part of any maintenance program to ensure system efficiency, and maintain compliance with emissions/safety regulations and avoid the fines and/or safety hazards that come with it.
All filters will eventually wear all out and need to be replaced. Dust collector maintenance programs should include periodic leak testing to ensure a few or even one faulty bag does not reduce the operating efficiency of the entire system. On occasion, a defective filter will fail early and need to be replaced. In other instances, there may be a temporary or unanticipated event that can cause premature failure of Baghouse filter bags. Once identified these should be investigated to ensure the incident does not occur again and determine the extent of the damage done to the system. Examples may include; abrasion, thermal durability, and chemical attack.
To perform a standard leak test several things need to be done before the actual test can take place. First, since testing requires temporary isolation from the facility process, and shutdown, you must determine the best time for each unit and/or compartment to be tested. Second, safety measures for plant personnel must be taken into account when estimating total down time. Units must be given sufficient time for cooling, atmospheric testing to check for harmful gases, and personnel assigned to perform both the test and fulfil any and all safety regulations regarding confined space entry. Once the preliminary steps have been taken, the actual testing can begin.
First, florescent leak detection powder is added upstream of the unit such as at a maintenance access in the ductwork. Then after sufficient time has past for the powder to work its way through the system, the unit is shutdown. Once it is possible, a technician will enter into the unit with a UV light source i.e. a black light to examine the filter bags/ cartridges for leaks. The powder fluoresces under the UV light, thereby making it easy for the technician to see even the smallest of holes. The technician makes note of any faulty filters, which can then be replaced. If there is a larger section of filters need replaced, then a full change should be considered due to a section of new filters potentially causing premature blinding as this area would have the least line of resistance.