Jonathan
Top Load vs Bottom Load Baghouses – Pros and Cons
- The Application.
- How big is the baghouse?
- The location on the baghouse?
- Physical constraints on the size of baghouse, in particular, height constraints.
A good Sales Engineer will review with you the factors that make a Top Load or a Bottom Load system a better choice but in general, Top Load and Bottom Load systems have specific Pros and Cons. This Tech Note lists Pros and Cons of each system to help you make a better informed decision on which style is right for your company and application.
Top Load Baghouse
Top Load Baghouse Advantages
- Bag inspection and change-out is on the clean top side of the system
- The employees do not have to enter the dirty side of the baghouse which addresses health and safety concerns.
- Filters can be inspected and changed out in all types of weather with a walk-in plenum design (Hatch access requires good weather)
- Baghouse leak detection powder can be used with ease as there is easy access to the clean air side of the baghouse. Operators look down into the filters to see if any of the fluorescent powder entered any of the filters. This is not easy with the bottom load system as there is Limited to No Access to the clean air plenum.
- Replacement of a single bad filter is quick and easy.
- There is no need for plywood or other temporary floor, ladder or elevated catwalks inside the collector to reach the clamps for filters longer than 7’ long (filters 87” or longer).
- Plenum can be outfitted with lighting and ventilation doors.
- With a top-load, maintenance people walk on the tubesheet and regardless of the size of the person, they can get to the filter holes in the tubesheet to replace filters.
- In a top load, the filters snap into place using a snap band collar. Very easy.
- Spent filters can be unsnapped and dropped down into the hopper for removal thru hopper access door keeping the clean side of baghouse cleaner.
- For a Top Load with a Hatch Access System, there is no need for employee training and certification for confined space operation. No OSHA permits required. No Attendant is required. (Note: A Walk-In-Plenum may or may not be considered a Confined Space. With adequate lighting and ventilation, a walk-in plenum does not meet the requirements of a Confined Space.)
- Costs –Top Load with Hatches $$$ < Top Load with Walk-In-Plenum $$$ < Bottom Load $$$ for system with identical air to cloth ratio, filter size and number of filters.
Top Load Baghouse Disadvantages
- Top load system are usually not a great choice for a silo/bin filter application. Silos are tall enough. Climbing a ladder on top of the silo to reach the top load access takes a fearless maintenance operator. But, there are easy to maintain Top Load systems that are an ideal solution for a silo/bin vent application.
- Top Load Systems with hatch access to the filters cannot be maintain in inclement weather.
- Additional height needed to remove cages which limits indoor use. Overall height and loading of filter cages may be restricted by building interior structure.
Bottom Load Baghouse
Bottom Load Baghouse Advantages
- Small bottom load systems where the filters can be reached without entering the baghouse are versatile, easy to maintain, can be used with a hopper and support steel or as a silo/bin vent.
- Better fit when there is a height restriction.
- Filter Access Door allow visual inspection of the interior of the baghouse enabling direct inspection of the filter exterior and dust cake as well as the opportunity to check for bridging problems.
- The hopper is visible through the Filter Access Door enabling visual inspection and some accessibility to knock dust off the walls with a bar/stick.
Bottom Load Baghouse Disadvantages
- There are many issues with accessing the filter/cage/thimble/clamp assembly depending on the length of the filter. 7’ long filters are an ideal size as many people can reach the tube sheet. 6’ filters and short can be difficult for taller operators to walk around inside as the tubesheet is at approximately 6.5 feet. For filters longer than 7 feet, the tube sheet is at 8.5’ and higher. Most people will not be able to reach the filter/cage/thimble/clamp assembly. Ladders or catwalks are required.Filter changes typically require two maintenance operators. One to hold the filter/cage to the thimble. The other to align and tighten the clamp.
- Properly attaching the filters/cages with clamps to the tubesheet thimbles is a tedious task, especially for long filters. If not done right, filters/cages can fall off during operation.
- It is not easy to properly align and clamp the filter to the tubesheet. In a top load, the filters snap into place using a snap band collar. Very easy.
- Varying degrees of personal protective equipment (PPE)is needed when entering the baghouse house including respirators and protective clothing
- Baghouse needs to be outfitted with lighting and ventilation when performing maintenance and inspection
- Good weather is a required during filter changes as going in and out of the dusty, dirty baghouse with wet clothing will result in more dust accumulating on the person and the person becoming covered in dust mud
- Baghouse leak detection powders cannot be used to detect leaks as there is Limited to No Access to the clean air plenum.
- Proper maintenance is less likely to be performed if personnel need to climb in to the dirty air section.
- Inspection and replacement of the filters is difficult in larger baghouses without access walkways. It requires a lot of work to replace one or more failed bags in the middle of the array as often many good filters need to be removed to get to the defective filter.
- There is no need for plywood or other temporary floor, ladder or elevated catwalks inside the collector to reach the clamps for filters longer than 7’ long (filters 87” or longer).
- With a bottom-load, if there is a broken filter in the middle of the baghouse, there is no easy access without walkways. Often, good filters need to be removed to access the broken filter.
- Costs –Bottom Load $$$ > Top Load with Walk-In-Plenum $$$ > Top Load with Hatches $$$ for system with identical air to cloth ratio, filter size and number of filters.
Mike Ryan
VP & GM
Griffin Filters
110 Bi-County Bvd, Ste 124, Farmingdale, NY 11735
Main Number - 315-451-5300
Sales Engineering – 315-444-2908
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Dust Collector Maintenance Schedule
Daily Maintenance Checks
- Monitor gas flow and dust collection pick-up point(s); make sure dust is removed as needed. Ensure there is adequate flow and dust is being removed.
- Monitor discharge system (airlock, rotary gate, hopper high limit switch, etc.); make sure dust is removed as needed.
- Walk around baghouse to check for normal or abnormal visual and audible conditions.
- Observe stack outlet visually or with a continuous monitor (opacity meter, broken bag detector, etc.).
- Check pressure drop.
- Monitor cleaning cycle, pilot lights, or meters on control panel.
- Check compressed air on pulse-jet baghouses.
Weekly Maintenance Checks
- Check all moving parts on the discharge system including screw-conveyor bearings.
- Check damper operation; bypass, isolation, etc.
- Check compressed air lines including filters.
- Verify temperature-indicating equipment.
- Check bag-cleaning sequence to see that all valves are seating properly.
- Check drive components on fan.
Monthly Maintenance Checks
- Spot check bag-seating condition.
- Spot check for bag leaks and holes.
- Spot check bag tensioning for reverse-air and shaker bags.
- Check all moving parts on shaker baghouses.
- Check fan for corrosion and blade wear.
- Check all hoses and clamps.
- Inspect baghouse housing for corrosion (inside and out).
- Check gas flow rate. Ensure it is correct (pitot tube, thermal flow meter, etc.).
Quarterly Maintenance Checks
- Thoroughly inspect bags.
- Check duct for dust buildup.
- Observe damper valves for proper seating.
- Check gaskets on all doors.
- Calibrate opacity monitor.
Semi Annual and Annual Maintenance Checks
- Check all welds and bolts.
- Check hopper for wear.
- Inspect inlet baffle plate for wear.
- Replace high-wear parts on cleaning system.
- Inspect paint on baghouse.
Baseline System Operation - Take Measurements – Keep Notes
Know The Normal Operation Parameters of Your System
Adapted from: Reigel and Applewhite 1980; McKenna and Greiner 1982.
Baghouse Differential Pressure
The Differential Pressure reading between the “dirty” side and the “clean” side of the baghouse can provide a great deal of information regarding how well your baghouse is working and the health of your filters.
Click Here to Buy Dwyer 2010 Magnehelic® Differential Pressure Gauge "Huge Discount"
It is always a good idea to monitor differential pressure and develop a baseline differential profile for your baghouse. Future readings within the baseline pressure reading profile will be a good indication the baghouse is operating properly.
The differential pressure readings are also useful in monitoring the condition of the filters. As the differential pressure rises above the clean filter baseline after a cleaning, you know the filter material is starting to become clogged with dust. As the pressure rises to 8” WG or higher, the filters are considered blinded and it is time to replace the bags.
The differential pressure can also indicate a catastrophic filter failure or the presence of worn and torn filters. If differential pressure readings drop below the clean filter baseline pressure reading and starts heading towards Zero, you can suspect there is a system failure. It is time to check for a filter which has fallen out of place or for filters with holes and tears or a complete blowout.
At Griffin Filters, we recommend operating between 2” WG and 6” WG. This considered the normal operating range.
With new filters in the baghouse, reading can be less than 2” WG but once conditioned and a dust cake is formed, the readings on a clean bag should be around 2” WG. Dust cake is a good thing. A filter with a good dust cake is more efficient in capturing dust than a brand new clean filter. The layer of dust prevents new dust entering the baghouse from migrating through the filter material and out of the baghouse on the “clean” side.
At 6” WG, Griffin Filters recommends running the cleaning cycle. Continuing to operate the baghouse at 6” WG and higher forces dust into the filter material. This causes the bags to “blind-over”. The filter material becomes clogged with dust and no longer allows air to pass through the filter material properly.
Monitoring the differential pressure after a cleaning is important. Pressure readings that rise above 6” and towards 8” WG after a cleaning is a strong indication that the filters are reaching the end of their useful life and the baghouse will require maintenance in terms of filter replacement or filter reconditioning. At differential pressure reading between 6” and 8” WG, your system will be running hard. Energy consumption will go up as the fan will be working harder to pull air through the high resistance caused by the blinded filters and the frequency of the cleaning cycles will increase to the point of continuous cleaning. Sooner, the better applies here. The sooner the filters are replaced when the differential pressure of the system is at 6” WG or higher, the better it is for protecting your baghouse from additional component failure.
DIFFERENTIAL PRESSURE
A magnehelic gauge is provided to monitor the static differential pressure across the bags.
- <2" W.G. new bags
- 2"- 6" W.G. normal range
- >6" W.G. dirty bags - (Ideal time to replace filters)
- >8" W.G. blinded bags - time to recondition or replace (Must replace filters as damage to system components can occur)
Note: Differential pressure will vary with application. During the initial start-up, the differential pressure could be lower than normal, as the filter media is new and quite porous. The high initial porosity could also be evidenced by visual emissions at the exhaust stack until dust cake is formed on the bags.
Application Engineering
Griffin Filters
106 Metropolitan Park Drive
Liverpool, NY 13088
Main Number - 315-451-5300
Sales Engineering – 315-444-2908
This email address is being protected from spambots. You need JavaScript enabled to view it.
Griffin at The Biomass Conference
We are proud to announce that we will be exhibiting at the 2015 International Biomass Conference & Expo, the largest gathering of biomass professionals in North America. Visit us April 20 – 22, 2015 at booth 730 to discuss our latest biomass dust collection projects, designs and everything else dust related.
We look forward to seeing you there!
International Biomass Conference & Expo
Minneapolis Convention Center
Minneapolis, MN
April 20-22, 2015
Booth 730
Cartridge Collectors or Baghouses?
Tips for determining the best dust filtration method for your application.
Which is better—a Baghouse or a Cartridge Dust Collector? There are many strong opinions and compelling arguments, largely driven by the success or failure of installed projects. As one would expect, the answer boils down to good applied application knowledge as both technologies have pros and cons. While every application can have its own list of unique or special challenges, we recommend the following guidelines be considered:
Know your application
Knowledge of your application is paramount to providing an optimal filtration system. If the collected particulate is sticky, tacky or has any agglomeration characteristics which allows it to adhere to itself, a cartridge collector will operate very poorly. When the pulse cleaning mechanism engages a cartridge, the pleated “peaks & valleys” do not expand like a filter bag. Instead, they collapse in on themselves. When this occurs with a very sticky application, the collected particulate will be pressed into the internal valley of the cartridge pleat. If this material does not release and drop out, that portion of the filter area is effectively blinded over which puts more demand on the remaining effective filter area. Under these conditions, the differential pressure of the system will increase, resulting in either higher power consumption of the system fan or fan overload and failure.
Material Entry
Should the unit incorporate an inlet located in the hopper or elevated near the top of the dirty air plenum as a high entry inlet? Surprisingly, the location of dirty inlet on a cartridge collector does have an impact on the effective operation of the unit. Consider the following:
A cartridge collector will incorporate a smaller vessel. This is a trademark advantage of this style of unit; optimal filtration in a smaller and more compact package. However, the internal velocities play a significant role in the effective operation of the filtration process. There are two terms for the measured velocity inside a baghouse: Can velocity is the upward air velocity below the bottom of the filters. Interstitial velocity is the upward air velocity between the filters. If the interstitial velocity is too high, the dust will stay in suspension and not drop into the hopper. If the dust stays in suspension, it will gravitate to the filters and ultimately penetrate and blind them over, causing a high differential upset condition which can only be corrected by changing the filters.
There are several solutions which can offset this upset condition:
- Increase the spacing of the filters will lower the interstitial velocity. However, this will increase the vessel size, effectively negating the most important advantage of this design approach.
- A better solution is to offer a high entry inlet. If designed properly, the airflow will enter the dirty air plenum and disburse with a downward flow pattern. This greatly reduces the interstitial velocity and protects against re-entrainment of the particulate.
Buying Used vs New Baghouses
The Advantages and Disadvantages of Buying Used Dust Collectors
With the closing of plants in the recent past and scaling back of manufacturing there is a lot of used pollution control equipment proliferating the industry. From a first look, buying used equipment looks like a great deal. Saving on capital expenditure along with a quick delivery to resolve an air pollution issue is very enticing. You may discover what appears to be a suitable baghouse for your application, BUT here are some questions that you need to take into consideration before you write the check and take delivery:
Is the equipment the proper design for your specific application?
- Can it handle the chemical and physical properties of the dust collected?
- Is there sufficient air-to-cloth ratio for the application?
- Is the filter media correct for the application?
- Is the interstitial velocity correct to allow for good filter cleaning?
- Does the equipment need to meet NFPA requirements for hazardous or explosive conditions?
- Do you know for sure if the dust collector will meet your EPA requirements?
- Do you know what product this existing unit was exposed to in the past? This is crucial as it is virtually impossible to completely clean the product contact surfaces of a baghouse system. Liability risks from chemical incompatibilities can range from contaminating your product to the creation of a hazardous environment.
- How old is this equipment? Is it in acceptable working order or has it been “in storage” for an extended period of time?
- Is this equipment rated for your design temperature condition?
- Is this equipment rated for your design pressure or vacuum condition?
If the answers to the above questions are satisfactory, then you may have discovered a cost effective solution for your application.
However, if the answers are not satisfactory with concerns the equipment being considered will not meet your application requirements, we submit the additional time, capital resources and logistics to bring this unit in compliance will almost certainly exceed the cost of a new system.
Additionally, if your application requires compliance with an EPA performance guaranty to meet a specific particle emission (PM) limit, this can only be provided by an original equipment manufacturer. Future fines/ court actions and legal fees can cost much more than the savings initially accrued.
Buying NEW just may be the better choice
When buying a new dust collector, the equipment is manufactured to your specifications and properly sized, yielding the maximum particulate collection at the lowest operating costs.
To arrive at the proper collector design, the proper sequence of steps should include:
Selecting the correct air-to-cloth ratio for the application is one key design factor.
- The analysis of physical and chemical properties of the dust is extremely important for selecting the correct materials of construction. Factors carefully considered include size, type, shape, and density of dust; average and maximum dust load concentrations; chemical interactions with materials of construction, explosiveness and flammability characteristics, and additional physical properties such as abrasiveness, electrostatic charge, and agglomeration tendencies.
- Proper Fabric features are then chosen. The designer must determine the following: woven or felt filters; filter thickness, fiber size, fiber density, filter treatments such as napping, resin and heat setting, and special coatings. With the determination of dust and gas stream properties, filter choice and special treatments of the filter can be properly made.
- Filter cleaning methods must be matched with the chosen media. The ratio of filtering time to cleaning time is the measure of the percent of time the filters are performing. If bags are cleaned too frequently, their functional life will be greatly reduced. If the bags are not cleaned often enough, higher pressure differential leading to greater operating costs will be incurred.
- Mechanical stress from cleaning and filtering should be minimized to extend bag life. The amount of flexing and creasing to the fabric must be matched with the cleaning mechanism and the A/C ratio; pulse-jet units place the most vigorous stress on the fabric.
- Bag spacing is very important for good operation and ease of maintenance. Spacing affects the velocity at which the gas moves through the baghouse compartment. If bags are spaced too close together, the interstitial gas velocity would be high because there is very little area between the bags for the gas stream to pass through. Settling of dust particles into the hopper below during bag cleaning would be negated by high upward velocities and re-entrainment would take place. It is preferable to space bags far enough apart to minimize this potential problem but not so far apart as to increase the size of the baghouse shell and associated costs. For pulse-jet baghouses, bag spacing is also important to prevent bag abrasion.
- Emission regulations for grain-loading and opacity requirements will ultimately play an important role in the final design decisions. Baghouses usually have a collection efficiency of greater than 99.99%. Many emission regulations (and permit limits) require that industrial facilities meet opacity limits of less than 10% for six minutes, thus requiring the baghouse to operate continuously at optimum performance.
Key Takeaways for New Equipment
Equipment properly designed for the specific application.
Equipment guaranteed to meet regulations.
Full factory warranty.
Maintenance cost and potential downtime are minimal because you are starting with all new components.
Growth in Frac Sand Requires More Air Filters
LIVERPOOL, N.Y., Oct. 1, 2014 -- Griffin Filters, a subsidiary of Cemtrex Inc., announced today that they have seen a growing demand for industrial air filtration directly attributable to the oil and gas boom currently taking place in the United States due to hydraulic fracturing technologies.
Some studies estimate that the Hydraulic Fracturing proppants industry will continue to grow at 8-9% per year. According to a Morningstar report, the United States is still by far the largest supplier of premium sand with 30 million tons currently used per year and 3.5 million tons in Canada with the market expecting double-digit growth in 2014. The growing demand for silica sand and proppants has resulted in supply shortages and logistical challenges.
The processing of the frac sand results in air pollution, including post wash drying of the sand, screening, loading and unloading of railcars, barges and trucks. The silica and fugitive dust particulate emissions are controlled by the high efficiency proprietary baghouse filters which Griffin Filters provides for maximum control. Griffin bag filters decrease safety concerns for the operators of the frac sand trucks through elimination of dusty, hazardous breathing conditions. Griffin Filters has seen that the frac sand mining industry along with the logistics trans-load points as a major growth area for its baghouse filters.
CEO of Griffin Filters, Saagar Govil, commented, "After receiving several significant orders and now with increasing inquiries in this market we see this as a strong market for the next few years as the oil & gas boom continues in the US. With strong relationships with many customers in this space and a considerable history of providing durable, efficient industrial air filtration systems we are confident we can grow in this space."
Safe Harbor Statement
This press release contains forward-looking statements. Actual results could differ materially from those projected in the forward-looking statements as a result of a number of risks and uncertainties. Statements made herein are as of the date of this press release and should not be relied upon as of any subsequent date.
For further information, please contact:
Griffin Filters
Contact: Saagar Govil
Phone: 631-756-9116
Business information: This email address is being protected from spambots. You need JavaScript enabled to view it.
Investor Information: This email address is being protected from spambots. You need JavaScript enabled to view it.
Another Griffin Success Story!
One of our customers needed a new baghouse system to replace a 30-year-old undersized unit for their Calciner (rotary kiln) operation.
To suit our customer's needs, Griffin's application engineers designed an insulated multi-module baghouse system, including (5) of our model JA-272-E baghouse modules. The baghouse system includes:
- Inlet / Outlet interconnecting ductwork
- Walkway and service mezzanine
- Hopper Discharge valves
- Screw Conveyor with an automatic product discharge valve.
Read the case study for more information.
OSHA's Proposed Silica Rule
Last year, OSHA proposed to toughen the rules against Crystalline Silica dusts in the workplace. According to OSHA's, crystalline silica exposure puts workers at greater risk for several deseases, including silicosis, chronic obstructive pulmonary disease and kidney disease. The proposed ruling would require businesses to implement tougher measurements against respirable silica dust in the workplace.
The ruling will have an large impact on many companies, including those in both the construction and metalcasting industries. At Griffin, we are keeping a close eye on this proposed rule's progress to ensure our customers will be ready if it passes.
Let us know if you have any questions about your current dust collection systems and how the rule will affect your operation.
Further Reading:
OSHA's Proposed Crystalline Silica Rule: Overview
OSHA's Rulemaking on Crystalline Silica
OSHA's Proposed Rule: Construction Industry
Crystalline Silica Resource Page (American Foundry Society)
Griffin Exhibiting at PTXi May 2014
We're proud to announce that we will be exhibiting at the 2014 Powder & Bulk Solids Conference & Exhibition, a premier tradeshow for the process industry's finest products and companies. Visit us May 6-8, 2014 at booth 2844 to discuss our latest projects, designs, and everything else dust related.
We'll see you there!
International Powder & Bulk Solids Conference & Exhibition
Donald E. Stephens Convention Center
Rosemont, IL
May 6 – 8
Booth 2844
See the full sized map here.
