Example of a dust collection system layout for a woodworking shop.

We continue from our last article where we reviewed the 4 key design variables of airflow (in CFM), static pressure/resistance, air velocity and air to cloth ratio. Now we can begin calculating these variables for our new dust collection system. When we are finished we will know exactly how large of a baghouse we will need (including how much filter area required) along with our fan output (x airflow @ y static pressure).

The sizing and design process can be divided into two stages. The first stage involves sizing your duct work for adequate volume (CFM) and velocity (ft/m) for the type of dust you will be handling. Then in the second phase you calculate the static pressure (SP) of your system to determine the size of your baghouse (how many filters and what size) and power of your system fan. If you already have a ductwork system and want simply to replace an existing baghouse/fan combo, you still need to calculate the CFM and static resistance from the existing ductwork system to properly size the baghouse and/or fan.

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Step 1 – Find the Minimum Conveying Velocity (ft/m) of Your Product

Determine from a reputable source the minimum conveying velocity for the material the system will handle. The box on the right lists several common materials and their recommend conveying velocities. Most materials require between 3,500 ft/m to 5,000 ft/m. A more extensive list can be found on Baghouse.com

Step 2 – Identify Total Number of Primary and Secondary Sources

Sizing your system requires you to determine how many much airflow you need at each location. Begin by making a list of all the equipment you plan to vent with the dust collection system. Identify your primary and secondary sources that you will connect to the system.

Primary Sources need constant venting whenever system is running. Some facilities may have only one large source to vent (e.g. a single boiler, furnace, etc.). Others may have many different systems but each one requires its own system as the different equipment cannot be connected for some reason (e.g. gypsum plants, cement plants, process applications)

Secondary Sources do not always run concurrently without primary sources and sometimes shutdown completely. Secondary sources are common in wood/metal milling, fabrication and manufacturing shops. For example, a woodworking shop uses several different pieces of equipment such as saws, lathes and sanders requiring dust collection. While the large saw and lathe run continuously everyday (primary), a small specialty-use sander and a planner are only used once or twice a week (secondary) and never at the same time as each other. In this example, you would size your system to handle the two primary sources (saw and lathe) and only one of the two secondary sources (sander and planer) as they will never run at the same time. Plan with the objective of defining the heaviest use scenario so you can size your system to meet it. Incorporating pickup points that see limited or infrequent use may result in an oversized the system, which increases its total cost to purchase, operate and maintain. Plan wisely, as increasing capacity post installation is nearly impossible. A good rule of thumb is to oversize the system by roughly 10% to ensure proper operation and accommodate any future expansions.

Primary or Secondary Source?

  • Take care to correctly classify each piece of equipment
  • Classifying all sources as primary sources will result in an unnecessarily large system, increasing initial installation costs and making it more costly to operate in the long run.
  • Classifying too many sources as secondary sources will result in an undersized system, resulting in insufficient capacity for normal operations. This will produce production bottlenecks or inadequate venting leading to health/safety hazards.[/box]

Step 3 – Calculate Total CFM Required for Each Branch

In the next step, determine how much CFM you need at each branch of your system. If your source equipment has a built in collar or port identify the diameter (if rectangular calculate the total cross sectional of the duct and convert to round equivalent). On larger sources such as kilns, furnaces or process equipment or for sources with custom-designed venting determine CFM required by consulting with the equipment OEM or by using industry-best practice methods. (Consult a dust collection expert experienced in the specific application for advice.) Finally, using the chart in this section find your duct size and match to column with the required conveying velocity to find the needed CFM for each branch.

Determining CFM for Each Branch in Our Example System – To illustrate we have prepared a sample system layout for consideration of this design step (See illustration below. We will continue to use this same example throughout the following 3 sections.)

Here we have a woodworking shop with a total of (5) pickup points. We have a sander, backdraft table, planer and two floor pickups. Next we determine the CFM required for each branch by duct diameter and then matching it to the appropriate conveying velocity required for wood (see chart in previous section)

  • (1) Sander = 4” OD @ 4,000 ft/m = 350 CFM (rounded)
  • (1)Planer = 5” OD @ 4,000 ft/m = 550 CFM (rounded)
  • (1)Backdraft table = 6” OD @ 4,000 ft/m = 780 CFM (rounded)
  • (2) Floor pickups = 4” OD @ 4,500 ft/m = 400 CFM (For reference only, secondary sources are not counted towards final total.)

Baghouse.com Expert Tips Many types of equipment come with built-in connections for dust collection. These ports are sized by the manufacturer to provide sufficient ventilation while operating the equipment. Simply confirm the diameter of the port to calculate the required CFM (using chart in this section) for the unit.

Step 4 – Create a System Layout and Size Your Main Trunk

Now we need to create a layout of the ductwork system, deciding where it will connect to each machine and where we will place the dust collector. This will determine what size ducts we need including our main trunk line. To help illustrate these concepts we will continue to refer to our sample system first described in the previous section.

Steps to Layout Your System and Size Your Main Trunk

  1. Make rough floor plan showing the location of each piece of equipment
  2. Sketch layout of ductwork connecting each piece of equipment together and running all the way back to the dust collector
  3. Where two primary branches meet combine the CFM require by each branch (using figures from previous step) and calculate the duct size needed to provide sufficient CFM for both branches at the required air velocity (where needed round up to next largest duct size)

Example of a dust collection system layout for a woodworking shop.

Make Floor Plan of Equipment – Take your primary and secondary sources and make a rough floor plan of every piece of equipment. Once you have every source in its approximate location map out the ductwork connection each piece back to the collector. Try to locate your dust collector in a central, convenient location. Safety regulations covering applications involving combustible dusts (e.g. wood, metals, grains, etc.) may mandate placing the baghouse outside or on an exterior wall (along with explosion venting to the outside).

Create Rough Layout of Ductwork System – Now each piece of equipment needs to be connected together and run back to the baghouse. Start at the source farthest away from your collector. Using the CFM requirements you calculated for each branch in the previous step, note the diameter of the duct required and map it out running towards the collector to the point where the next branch connects. Additionally, note the length of each run of duct (important for next step).

Where the next branch connects add the CFM of both lines together and determine what size duct you need for that amount of CFM at the required velocity in ft/m. Increase the size of the duct accordingly and continue mapping the trunk forward. Repeat the process and increase the duct size only at each spot where a primary source connects to the main trunk. Continuing mapping your main trunk (making sure to connect to all primary and secondary sources) until you reach the collector.

Example of a dust collection system layout for a woodworking shop.

Sample shop layout – Notice our calculations for the required CFM, air velocity and the total static resistance generated by the system. Now you can determine the required filter area (i.e. number of filters in the collector) and the fan power. 

Determining Duct Size for Each Branch and Main Trunk in Our Example System – First, we begin with the farthest source the sander. Its built in connection port is 4”, so we begin with a 4” duct leading out of it. Then we continue running it where it connects with the 5” duct coming from the planer. (NOTE We do not increase the size where it meets the Floor Pickup, as this is a secondary source.) By combining 4” duct requiring 350 CFM and the 5” duct requiring 550 CFM, we get 900 CFM +/- at 4,000 ft/m (see previous section for more details). Where these two combine we need a duct to handle at least 900 CFM@ 4,000 ft/m. According to our chart, this falls between a 6” and 7” duct. Per best practice, we will move up and oversize the duct slightly to ensure sufficient airflow and allow for possible expansion later.

Continuing on the 7” duct next combines with the 6” duct running from the backdraft table. The 6” duct requires 780 CFM +/- and the 7” duct requires 1068 CFM. Again, the total combined CFM falls in between the 9” and 10” OD duct, so we size up to 10”. Finally, with all the primary sources connected, the system requires at least 1,680 CFM @ 4,000 ft/m.

Now we have sufficient CFM for all of our primary branches. We also have a safe amount of oversizing to ensure adequate operation and provide a cushion for any possible future expansion. To accommodate the other secondary branches we can install blast gates on all the branches and close off other lines.

Baghouse.com Expert Tips:

  1.  Try to keep the largest equipment closest to where you will place your dust collector.
  2. Try to run your ductwork in the shortest possible route.
  3. Always size up if the required CFM falls between two duct sizes. This allows for future expansion.
  4. Only increase the duct size when a primary source branch connects, but do not forget to run trunk so that all the secondary sources can connect as well.
  5. Consult fire/safety regulations may require the dust collector be located on an external wall or outside.[/box]

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Step 5 – Calculate The Static Pressure (i.e. Static Resistance) of Your System

Static pressure or static resistance (measured in inches of water w.g.) refers to the amount of resistance to airflow created friction and channeling of air through the ductwork. For the system to work the system fan must overcome the resistance created by the ductwork and the baghouse. Accurately calculating the static pressure or SP of the system is crucial for the system to function correctly. To determine the total SP of your system you must add the SP generated by following three elements together:

  • The branch with the great SP (also known as the Worst Branch)
  • The SP of the main trunk line, including any fire protection/prevention devices
  • The resistance created by the dust collector(s). This would include any precleaners (cyclones, knockout chambers, etc.) as well as the filters within the baghouse.

Calculate the SP of all your branches and identify the one with the greatest amount of resistance in w.g. (Likely the branch farthest from the unit with have the highest SP, but not always.) Only figure the SP of the worse branch into your calculations for the entire system’s SP. Next, move on to the main trunk line. Calculate the resistance created by the duct diameter and the length of each section, along with any elbows, splits, or other connections. Finally, identify the SP generated by the dust collector(s), which in most cases will be only a baghouse. For most baghouses plan on a maximum of 5”-7” of resistance (most baghouses should run between 3”-5” differential pressure, but sizing slightly above this figure is conservative and allows for some flexibility).

Steps to Calculate System Static Pressure (i.e. Static Resistance)

  1. Identify the branch with the highest static pressure (Worst Branch)
  2. Calculate the SP of the main trunk line
  3. Determine SP of dust collector

Determining Static Pressure for Each Branch, Main Trunk and The Baghouse in Our Example System

Step 1 – Find the Branch with the Highest SP – Starting at each piece of equipment work back through to the main trunk and determine the total SP of each branch. In our example, the sander branch has the great resistance.

  • Entry loss at equipment adaptor of 1.5” (constant)
  • 10’ of 4”OD duct
    • Reference Table 2-3 shows 100’ of 4” OD duct @ 4,000 ft/m = 7.03”
    • 10’ = 7.03 x .1 (for 10’ feet out of 100’) = 0.70” SP
  • (1) 90° elbow
    • Reference Table 2-4 shows (1) 90° elbow of 4” OD is equivalent of 6’ of straight pipe
    • 6’ of 4 OD = 0.28” SP
  • 25’ of 4” OD duct
    • Reference Table 2-3 shows 100’ of 4” OD duct @ 4,000 ft/m = 7.03”
    • 25’ = 7.03 x .25 (for 25’ feet out of 100’) = 1.76” SP
    • 1.5” + 0.70” + 0.28” + 1.76” = 4.24” Total SP for sander branch

Step 2 – Calculate SP of Main Trunk Line – In our example our ductwork has 50’ of 7” OD duct, followed by 30’ of 10” OD duct at 4,000 ft/m.

  • 50’ of 7” OD duct
    • Reference Table 2-3 shows 100’ of 7” OD duct @ 4,000 ft/m = 3.55”
    • 50’ = 3.55 x .5 (for 50’ feet out of 100’) = 1.78” SP
  • 30’ of 10” OD duct
    • Reference Table 2-3 shows 100’ of 10” OD duct @ 4,000 ft/m = 2.30”
    • 30’ = 2.30 x .3 (for 30’ feet out of 100’) = 0.69” SP
  • 1.78” + 0.69” = 2.47” SP Total SP for main trunk line

Step 3 – Calculate SP for Dust Collector – Each type of dust collectors generates different SP. For this figure, it is best to consult with an experienced baghouse OEM such as Baghouse.com. For our example we will assume a SP of 6” for a baghouse dust collector. Note: Baghouses are normally designed to operate between 3” – 5” of differential pressure. Baghouse.com recommends being conservative with this estimate and designing in extra capacity to provide a cushion for normal operational ups and downs.

  • 6” Total SP for baghouse

Total SP for our example system:

  • 4.24” for worst branch
  • 2.47” for main trunk line
  • 6” for baghouse
  • = 12.71” total system SP

Now we have all the data needed for completing our system. The dust collection system must provide a minimum airflow of 1,680 CFM through a 10” trunk duct at air velocity 4,000 ft/m with a static pressure of at least 12.71” w.g.

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Next Section – Part 4 – Additional Considerations for Dust Collection System Design

 Baghouse Design Guide Overview

Baghouse.com dust collector technical Drawings - S-TA 9-144 Models

For a dust collection system to function adequately engineers must design and operate the system to maintain the (4) key design parameters of airflow (measured in CFM), airflow velocity (measured in FPM), Static Pressure/Static Resistance and Air to Cloth Ratio (or A/C). Changes to any of these key system parameters will result in systemwide performance issues. All four of these parameters are fluid and directly affect the others. Maintaining all at proper levels requires careful engineering, operation and maintenance. Lets review these four parameters one by one.

Airflow in CFM (Cubic Feet per Minute)

CFM – What Is it? – How much air the system moves is measured in Cubic Feet per Minute or CFM. (Related terms include ACFM for Actual Cubic Feet per Minute and SCFM for Standard Cubic Feet per Minute). Most often baghouses are sized and categorized according to CFM. In general, the larger the space being vented or the greater the number of pickup points in the system the more CFM required. The CFM generated by the system fan can be fixed or adjusted (Variable Frequency Drive or VFD Fans). However, total CFM generated by a fan can be affected changes in altitude, ductwork restrictions and sizing as well as resistance to flow created by the system (ductwork + filters).

Why Important? – Without sufficient CFM the sources will not be vented adequately. Poor venting directly causes damage to equipment, high emissions, loss of reclaimed product and hazardous environment (especially of concern in facilities handling combustible dusts or hazardous materials). Low CFM can also negatively affect air velocity, air to cloth ratio, and vacuum pressure, other key design parameters.

Vacuum Pressure (Suction) & Static Pressure (Static Resistance)

What Are Static Pressure and Static Resistance? – Vacuum pressure or suction is measured in inches of water gauge, w.g. and is the basis of a properly functioning dust collection system. The system fan must supply enough suction to pull the materials from the collection point(s) all the way through the ductwork to the baghouse and then through the filters and out to exhaust. To do that it must overcome the resistance to flow created by the filters and the ductwork. Conversely, static pressure or static resistance is a measurement of resistance generated by the ductwork and the filters in baghouse. This also is measured in inches of water gauge.

Why Important? – Without sufficient CFM the sources will not be vented adequately. Poor venting directly causes damage to equipment, high emissions, loss of reclaimed product and hazardous environment (especially of concern in facilities handling combustible dusts or hazardous materials). Low CFM can also negatively affect air velocity, air to cloth ratio, and vacuum pressure, other key design parameters.

Air Velocity and Minimum Conveying Velocity

What are Air Velocity and Minimum Conveying Velocity? – Air velocity within the system is measured in feet per minute, or ft/m. The system must be carefully engineered to keep the air speed within an acceptable range to prevent two major issues. Air speed is related to CFM as follows: ft/m = CFM ÷ cross sectional of duct (i.e. size of duct).

Dust builds up within the ductwork when the air velocity is too low causing blockages and affecting airflow and performance.

Dust builds up within the ductwork when the air velocity is too low causing blockages and affecting airflow and performance.

Why Important? – High air velocity can quickly wear holes the ductwork by means of abrasion (especially abrasive dusts like metals, ceramics, etc.) or can break up delicate conveyed products such as processed foods (cereals), pharmaceuticals, and others. Of greater concern is low air velocity, which can cause dust buildup within the ductwork and lead to poor dust capture at inlets. For a dust to travel suspended in air it must most at or above the minimum conveying velocity for that product. If it drops below that minimum speed at any point in the ductwork the dust will begin to settle or dropout of the airstream, which then accumulate into large piles that eventually choke off the duct. These accumulations of dust within the ductwork create major safety hazards. When combined with an ignition source (such as a spark or ember) they provide ample fuel for a combustible dust fire or explosion, which then can propagate throughout the entire system, being continually fed by dust accumulations further downstream until it reaches the dust collector. Additionally, these accumulations can eventually become so large that the duct collapses under the added weight.

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Air to Cloth Ratio

What is Dust Collector Air to Cloth Ratio? – The ratio of gas volume (ACFM) to total cloth area (sq. ft.) of the baghouse. First calculate the total cloth area of your collector by calculating the total filter area of each filter (bag diameter x 3.14 x length ÷ 144 [for number of inches in a square foot] = filter cloth area) and then multiply that figure by the total number of bags in the collector. Take the CFM of the system and divide it by the total filter cloth area to get your air to cloth ratio.

Why Important? – For the baghouse to capture the dust from the airstream the unit must have a sufficient number of filters. As you push more air through the same amount of filter material the collection efficiency goes down. Maintaining an adequate air to cloth ratio enables the baghouse to operate at peak efficiencies, collecting more than 99.9% all dust particles that pass through it. For most applications, anything less than near peak efficiency will result in excessive emissions, violating pollution regulations and creating hazardous environment for workers and neighbors.

Putting All 4 Variables Together and Designing Your System

Now that we have discussed the 4 key design considerations, we will now see how to design a baghouse dust collection system so as to maintain all 4 of these parameters within acceptable ranges to ensure proper operation. Our next section is titled: Design Process for Your Baghouse Dust Collection System

Next Section – Part 3 – Design Process for Your Baghouse Dust Collection System

 Baghouse Design Guide Overview

Baghouse.com dust collector design and sizing

Dust collection systems play a vital role in many commercial and industrial facilities. Whether part of a system process, used to capture harmful pollutants from furnaces/boilers, to convey dry bulk product or to maintain a clean and safe work environment, dust collection systems need to function at near constant peak efficiency for facilities to operate safely and productively. While maintenance and proper operation play a large role in keeping these systems running properly, many facilities face challenges due to improper system design and engineering.

Many users rely on outside vendors or so-called “experts” with little to no actual dust collection experience to design and engineer a system for them. Other times vendors may purposefully undersize a system in order to undercut other potential suppliers regardless of how it actually performs in the end for their customer. Still others design their own system in-house thinking it an easy process that just any engineer can accomplish with little to no outside guidance. These cases frequently end with an inadequate dust collection system that cannot meet the needs of the process, resulting in high emissions, lowered productivity, hazardous work environments or all three! So what can facilities do to ensure they do not encounter these same issues?

Need Help Designing Your Baghouse?

Looking for help designing your dust collection system? Let our us use our 40+ years of expertise to help you select the right system for your application.

In our experience, an educated user benefits the most and becomes best customer. With that in mind, we have prepared this guide (broken into 4 major sections) to assist users in designing and properly sizing a dust collection system. By following the direction in this guide closely, you can effectively estimate what kind of system you require and then use this information as a basis for gathering quotes and additional assistance.

This guide is NOT an exhaustive course on dust collector design. Each system presents unique circumstances that affect the general operation of a baghouse system. As such, the guidelines present in this guide should be used only to estimate the sizing of your system. A qualified, and experienced dust collection system OEM should be consulted before purchasing any equipment or making design changes.

Now let’s get right into it! First we start with the four key dust collector design variables.

Next Section – Part 2 – The Four Key Baghouse System Design Variables

 Baghouse Design Guide Overview

Key Points to This Guide

  • Many So-called “Baghouse Experts” know little about proper dust collection design and operation OEMs and sales reps frequently undersize systems to win contracts leaving customers with a system that does not work
  • Educated clients can determine the general size they need and use it as a basis to compare quotes from multiple sources
  • Understanding principles of dust collection system design enables facilities to make better decisions regarding baghouse maintenance, operation and safety
  • Designing a baghouse with the correct variables CFM, air velocity, static/vacuum pressure/resistance, number of pickups

    How large of a baghouse do you need? How do you determine how many filters you need? What air to cloth ratio meets your needs? How much vacuum pressure (static pressure) do you need in the system fan? How much CFM do you need?

    These are just some of the questions that may arise when working with dust collection systems are your facility. When designing a new system plant engineers need to decide how large of a system they require before they begin getting quotes from vendors.

    A danger exists when facilities ask outside vendors to design a system for them. Many so-called “dust collection experts” are really just sales rep organizations that have little technical background or engineering experience with these systems. As such, they will often sell whatever product lines they have with little regard for making sure it is the best fit for your specific application. Others vendors purposefully recommend undersized systems in order to undercut other vendors on pricing, regardless of how the end system performs for the customer.

    Plant personnel can easily avoid being sold an undersized dust collection system by conducting research in advance to get a general idea of what size system they need. Then they can use this estimated sizing information as a basis for getting quotes from multiple vendors.
    For this reason, Baghouse.com has prepared a detailed series of articles to help educate users on how to properly size their baghouse system. Each article in this series will cover a different step in the process of determining your dust collection needs for your system. This article series will primarily be of use to plant personnel looking to install new baghouses and ductwork systems. However, the information can also be used when troubleshooting existing systems (where capacity may not be sufficient) or when looking to expand capacity on existing systems.

    Click here to download the complete eBook: How To Size a Baghouse Dust Collection System.


    Next Section – Part 1 – Why You Need to Properly Size Your Baghouse System

     Baghouse Design Guide Overview

    A entry level triboelectric broken bag detection system - Courtesy of http://auburnsys.com/

    By Dominick DalSanto

    Quickly finding and replacing leaking filters is crucial for keeping a baghouse operating at peak efficiency. The longer you take to replace the leaking filter the more likely you will have to report the event to your air quality control regulatory agency (reportable event) and the more abatement costs you will incur.

    How Broken Bag Detectors Work

    How Triboelectric Dust Detection Systems Work

    How triboelectric bag leak detection systems work – Courtesy of http://auburnsys.com/

    Triboelectric broken bag detectors measure the amount of static electricity generated by dust particles in an airstream. Dust particles generate an electrical current when they encounter the insulated metal probe in the ductwork. A dust particle directly impacting the probe creates a DC signal while a particle passing near to the probe generates an AC signal. The latest generation of triboelectric detectors (such as the Auburn Systems’ TRIBO series) unify both signals and then output a measurement of particle concentration to a nearby control panel or transmit it to a PLC.

    Using a Triboelectric Broken Bag Detector as Early Warning

    Most leaking baghouse filters begin as small holes or rips that overtime become worse and worse. Catching a leak quickly is crucial. The longer a leak persists the worse it becomes, often quickly causing a plant to exceed its maximum PM 2.5 emissions limits set out in its air permit. Additionally, abatement requirements quickly increase as a leak continues over time.

    Older optical emissions monitors (i.e. opacity meters) and optical bag leak detectors can only detect a filter leaking so badly damaged that the increase in emissions exceeds 10% opacity (often greater than the maximum permissible levels for many air permits).

    Triboelectric systems are sensitive enough to detect even the smallest of increases in dust emissions such as when a bag first begins leaking. Operators can then examine the realtime trending emissions data to see whether it was a sudden spike indicates a damaged bag (such as from quickly worn hole) or slow rise indicating wearing filters.


    Using Broken Bag Detector to Pinpoint Which Filters Are Leaking

    An added advantage of triboelectric bag leak detectors is they can enable operators and maintenance technicians to pinpoint exactly which bags are leaking and need to be replaced.

    Personnel should carefully monitoring emissions while cleaning system runs. When emissions spike during one cleaning cycle it means that leaking filters are present. Using this method, maintenance personnel can trace the leaking filters down to a specific baghouse, compartment and even row (pulse jet only) of bags. This saves time and money over traditional dye leak testing.

    However, on older units, or when first beginning to troubleshoot a unit dye leak testing should still form part of your maintenance schedule. Dye leak testing can pinpoint multiple leaks at once, and in structural components as well as filters.

    By quickly pinpointing leaking filters maintenance staff also reduce the amount of abatement required after the leak is fixed.

    Below is the sample data from a test conducted to determine the differences in performance between a triboelectric leak detection system and a typical optical system (opacity meter). Notice the huge difference in response time and abatement required.

    Leak Test ResultsTriboelectric Bag Leak DetectorOptical System
    Estimated Time to:
    Detect LeakLess than 1 Hour2-3 days
    Locate Leaking Filter(s)Less than 1 Minute2-3 Man Hours (dye leak test)
    Clean Up LeakLess than 1 Man-Hour8-10 Man Hours
    Estimated Size of:
    Hole Detected1/4”8”
    Dust Accumulation2.6 cubic feet60 cubic feet
    Dust Clean Up ToolShopvacShovels

    Source: https://cdn2.hubspot.net/hubfs/354686/BrandBuilder%20Solutions/Case%20Studies/Aluminum_Case_Study.pdf

    Reduce Baghouse System Downtime

    When a baghouse goes down it often brings much down with it, from specific equipment to entire production lines to even entire plants due to emissions or health and safety issues. Preventing unscheduled baghouse shutdowns directly impacts the bottom line. In some facilities, losses from just one down day can add up to tens of thousands of dollars in lost production, fines and other costs. Therefore, investing in the maintenance and upkeep of these baghouse systems is well worth the initial capital costs.

    Triboelectric dust monitoring system often prove one of the most cost-effect ways to improve dust collector maintenance and operation. With the ability to monitor emissions in realtime and trends over time, operators can better assess the condition and operation of their baghouses than those who rely solely on differential pressure.

    For example, by carefully analyzing the triboelectric data trends maintenance planners can accurately predict when filters will no longer achieve their require collection efficiency and need a changeout. Further, they can begin preparations for the changeout in advance, sourcing filters and cages, obtaining contract labor for the changeout and scheduling the changeout for the next most convenient time (e.g. yearly maintenance shutdown). Compare this with the added costs and stress involved when a changeout is done at the last minute!

    Additionally, as mentioned above, triboelectric bag leak detectors also prevent downtime by quickly alerting plant personnel to any leaks as soon as they begin to form. By catching leaks before they become serious plants can avoid stoppages for abatement, repair and any possible fines or sanctions from air quality regulators.

    Recap of the Key Points

    • Triboelectric bag leak detectors directly impact the bottom line of your baghouse by improving maintenance efficiency, reducing downtime
    • Increased detection range means finding leaks quicker, before they become reportable events
    • See when filters first begin to fail allows predictive maintenance planning to reduce inconvenient shutdowns
    • Find leaking filter bags quicker, pinpoint down to specific unit, compartment and row without a dye leak test
    • Comply with MACT standards that require triboelectric broken bag detectors over opacity meters

    Interested in a Triboelectric Broken Bag Detection System?

    If you would like to know more about our line of triboelectric broken bag detectors  and how they can benefit your facility contact us today for a free consultation and quote!

    Baghouse maintenance from Baghouse.com personnel
    Dust build up inside a duct connected to a dust collector

    Question: What is “normal” differential pressure in a baghouse?

    Answer: In most applications a baghouse dust collector should run between between 3″ to 6″ w.g. under normal use. Once levels rise above 6″ (roughly) and the cleaning system cannot return it any lower (even when turned to continuous cleaning or “Test” mode) it is a sign that the filters are beginning to be blinded and likely need to be changed. It is not advisable to run a baghouse with a DP higher than 6″ for any length of time as this will have an impact on the function of the entire system. Running at such a high DP will lead to a number of problems including vacuum loss at the pickup points of the system (loss of suction), lower air speeds in the ductwork, higher emissions, and higher energy usage.

    If you are seeing levels below 3″ after having run the baghouse for sometime you liking are getting false DP readings. When brand new bags are installed in a dust collector they should provide approximately 1″ of resistance alone. Once they begin to load dust that number will rise to between 2″ – 3″ no matter how much you clean them.

    A clean on demand baghouse controller (i.e. clean on pressure) is the best way to keep a dust collector running in the recommended DP range. (see article: 3 Cheap Ways to Increase Efficiency in Dust Collection Systems)

    Dust build up inside a duct connected to a dust collector

    Maintaining the minimum conveying velocity in the dust collection system prevents dust drop out and build up inside the ductwork

    Question: What is minimum conveying velocity in my baghouse and why is it important

    Answer: The minimum airspeed required to keep dust particles suspended in the conveying system (i.e. dust collection system). When the air in any part of the dust collection system slows below the minimum conveying velocity the dust will begin to drop out of airstream and settle to the bottom of the ductwork (known as product drop out).

    Maintaining the airspeed throughout the system above the minimum conveying velocity is required to prevent the accumulation of dust in the ductwork. Overtime, dust can accumulate into large piles, eventually blocking off part of the ductwork and reducing suction downstream in the system, further compounding the problem. Blockages can also cause the passing airstream to accelerate (forcing same air through a smaller space) that can lead to abrasion issues and eventually wear holes into the ductwork. Large accumulations of dust can eventually collapse sections of the ductwork due to the added weight.

    Preventing product drop out is even more serious in applications involving combustible dust. Any accumulations of dust within the ductwork provide a potential fuel source for any ignition source that may find its way into the ductwork such as sparks. Additionally, if a fire starts in one part of the system it could continue to propagate throughout the rest of the system being fed by the accumulations in the ductwork. Further, if the system is operating below capacity due to blockages, dust may accumulate elsewhere in the facility including on elevates spaces that can then become fuel for both primary and secondary dust fires and explosions.

    Question: Why are my baghouse filters so expensive to replace?

    Answer: Many simply buy their replacement filters from the OEM or sales rep that supplied their baghouse. Often times, manufacturers and sales rep organizations deliberately sell their units cheaper and then make convince their customers that they are locked into using a proprietary filter design that only they can supply and thus they charge outrageously high prices for them. Other times, they convince their customers to use an outdated or rarely-used technology so hard to find form other manufacturers that it nearly guarantees them your repeat business for replacement parts. This is common with many cartridge collector OEMs, whereby they win the initial unit sale by undercutting other manufacturers (often by recommending a undersized dust collection system) and then plan on making their profit on the expensive replacement filters later on. This marketing technique is commonly called the “razor blade” system, for its well-known use by makers of disposable razors and cartridges.

    Need New Filters?

    We offer replacement baghouse filters, cartridges, and pleated filters for all makes and models of dust collectors, including the most popular brands Farr, Donaldson / Torrit, Wheelabrator, and more. Often we can offer significantly better prices than buying from the original dust collector manufacture, sometimes as much as 50% less! If you do not believe us, give us a try and let us give you a quote for your next set of replacement baghouse filters.

    Question: How long will my baghouse filters last?

    Answer: Baghouse filters have an average service life of 1-3 years in most applications. Some can go beyond that without major increases emissions, while others may last less than a year in more difficult applications. The main reason to replace baghouse filters is because when old they begin to leak and thus the system is no longer collecting particulates as its designed to do. Filters can also be damaged prematurely by sparks/embers that can cause fires or even explosions. Upset conditions in the process may cause a spike in temperature (beyond the maximum for the filter fabric) or may create an acid flash or similar chemical attack on the bags. Finally, bags may be damaged during maintenance or by other external forces.

    The main signs that your filters need to be replaced are that they are can no longer be cleaned effectively by the baghouse and/or they start leaking.

    Baghouse filters that are blinded

    Blinded filters must be replaced.

    Question: What does it mean when my baghouse filters are “blinded”?

    Answer: Blinded filters means the filters are so loaded with dust that they can no longer be cleaned by the baghouse cleaning system and must be replaced.

    During normal operation dust particles accumulate on the surface of the filters and form a dust cake, which is then cleaned by the pulses of compressed air during the cleaning cycle. Overtime, some dust particles pass through the surface layer and become embedded deep within the fibers of the filter fabric where it cannot be removed by the cleaning pulses. Eventually, the fabric becomes so filled with dust particles that it severely restricts the movement of air through the filter. When this occurs the filter is said to be “blinded”.

    When a baghouse can no longer clean itself down to a lower DP range (e.g. below 6” of DP) even with constant cleaning (i.e. continuous cleaning mode or test mode) it is likely that the filters are blinded and must be replaced.

    a baghouse dust collector control board
    a baghouse dust collector control board

    With Clean on Demand Controllers  the “On-Time” setting  must be set correctly or else bag cleaning will suffer. On on Turbo baghouse controllers (and on many others) you need to first find the preset that corresponds to the on-time setting (here shown as F1), push select, and then enter the proper value (.1-.15 ms)

    Question: What does the “On-Time” setting on my baghouse control board do?

    Answer: On-Time determines how long the pulse valve is open for during a cleaning cycle. This setting is VERY important for proper cleaning of the baghouse filters on a pulse jet dust collector. If set too long then the air pulses will be weak and waste compressed air, lower pressure in the air header (causing delays while it builds back up or weakening the following pulses) or even damage the filters. If set too short not enough air volume will be released to clean the entire bag. It will also cause uneven dust loading on the bags, which in turn can cause a long list of problems in the collector.

    Question: What should I set as the “On-Time” on my baghouse control board?

    Answer: As a general rule, this should be set to between .01 – .015 ms (milliseconds). For certain specific applications (such as pleated filters, or certain “sticky” dusts) your dust collector OEM might provide you with a slightly different setting.

    Question: What is clean-on-demand and why should I use it instead of just setting a timer?

    Answer: Clean on demand (or clean on pressure) is a means of controlling a pulse jet baghouse cleaning system. It is the most effective way to operate your dust collector and it can lead to considerable savings in several areas.

    Using a clean on demand baghouse controller, operators set high and low differential pressure points (usually 5.5″ and 3″ respectively). When the DP reading hits the high point the control board begins firing the pulse valve(s). It will continue firing them in order until the DP drops below the low point.

    In contrast to a simple timer board, a clean on demand controller only cleans the bags only when necessary to maintain stable operation. This prevents over cleaning (which increases wear and produces higher emissions), reduces compressed air use (costly in most plants), and reduces wear on the diaphragm valves. Additionally, clean on demand controllers are able to adapt to changes in dust loads (common in most applications) something timers cannot do.

    PTFE membrane on a baghouse filter under a microscope

    Yes, there is a difference between the two. One is used to increase collection efficiency and one is used primarily for protecting the filter bags from chemical attack.

    What Are PTFE Membrane Filter Bags?

    PTFE membrane is semi-porous layer of PTFE bonded to the surface of a filter. This membrane acts at a permanent dustcake, capturing incoming dust particles (i.e. particulate matter or PM 2.5) on the surface of the filter (surface filtration) as opposed to normal filters that require a thick layer of dust buildup (dustcake) to actually reach peak efficiency. This means that PTFE membrane bags can operate at peak collection efficiency from the moment they are installed, and do not need to be precoated. Overtime, the membrane also works against the dust penetrating deep into the depth of the filter fabric, which is the cause of filter blinding. For this reason, PTFE membrane bags often last considerably longer than standard filter bags and have a more consistent differential pressure over time.

    PTFE membrane on a baghouse filter under a microscope

    PTFE membrane is a thin layer of PTFE laminated to the surface of a filter bag. It captures dust on the surface of the filter and easily releases the dust when pulsed.

    PTFE Baghouse filters with PTFE membrane have the highest collection efficiency of all filters in production today. Bags using membrane technology can collect particulate matter down to 2.5 microns in size at over 99.99% efficiency. (In laboratory testing one OEM’s PTFE filters had 0.00% detectable emissions in the test rig). For this reason, in the applications with very tight emissions requirements, PTFE membrane filters are the standard.

    Membrane bags are not recommended for a few limited applications, usually involving oils and hydrocarbons are these can close off the pores of the membrane and cause the filter to plug up.

    What Are Filter Bags with PTFE Finish or Treatment?

    In this use of PTFE, rather than creating a surface layer or membrane on top of the filter, the filter fabric is coated in a bath or spray of liquid polytetrafluoroethylene (PTFE) resin. This is done to protect the filter. The treatment improves the flex life, heat and chemical resistance and dust release from the fabric. This increases the service life and efficiency of the filters. PTFE finish is commonly used in applications with corrosive chemical compounds, sticky dusts, or high moisture contents.

    Would you like to learn how PTFE membrane filter bags can improve your dust collector operation and save you money? Contact us today to find out more!

    A Baghouse filter with PTFE (Teflon) Membrane

    PTFE membrane or PTFE finish can be applied to a baghouse filter made from any fabric, such as fiberglass, polyester, or aramid (Nomex). It can even be used with pleated filters or cartridges.