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Baghouse Tips with Dr. Vent Goode

Are your system’s ventilation hoods effective?

Vent hoods are the point where gasses are suctioned into your ventilation system.  They are a very important component in the performance of your baghouse and discharge system, yet designers often pay little attention to their design and location.

To understand hooding design, first we need to understand the purpose of your ventilation system.  Or more precisely, what it’s not supposed to do.  With a few exceptions in process equipment, the ventilation system is NOT intended to suction dust.  Its purpose is just to keep your process equipment or your enclosure under negative pressure.  Some dust will inevitably end up in the baghouse, but it’s not intended to act like a vacuum cleaner.

Hoods have two basic functions:  They should minimize material carryover and they should minimize pressure losses at the pick-up points.  These two objectives can be accomplished with proper hooding design.

In a nutshell, the larger the hood, the lower the amount of dust suctioned.  And the more tapered, the lower resistance to flow.  There is obviously a physical and cost limitation, so rule-of-thumb guidelines are presented in design manuals to make them reasonably sized.  The typical recommendation is to form a square box as wide as the enclosure allows before tapering to the round ductwork.

hoodVent

Hooding position is also important to minimize material carryover.  Even a properly designed hood will end up suctioning excess material if it’s placed at the wrong location.  In general, hoods must be placed away from the source of dusting, as shown below.

hoodVent2

Properly designed and properly positioned hoods can make a big difference in your systems’ performance to reduce wear on filter bags and discharge system overload.

Call us to discuss your application with one of our engineers today!

Air Quality Workshop

WORKSHOP SCHEDULE

8:00 – Registration & Breakfast

8:30 – Keynote Speaker

9:00 – Block Andrews, Burns & McDonnell – “Compliance Strategies for the 21st Century”

9:45 – Jon Norman, UCC – “Case Study: Using Trona & SBC for High Level SO2 Removal”

10:30 – Break

10:45 – Steve Baloga, Novinda – “Amended Silicates™ for Hg Control”

11:30 – Mike Atwell, Solvair – “Trona: a viable solution for SO2, SO3, HCl, and HF”

12:15 – Lunch sponsored by Lhoist

1:00 – Rafic Minkara, Headwaters – “Flyash in a changing Air Emissions Market”

1:45 – Joe Wong, ADA Carbon Solutions – “Advanced Activated Carbons for MATS Compliance”

2:30 – Break

2:45 – Melissa Sewell, Lhoist – ““Dry Sorbent Injection with Enhanced Hydrated Lime”

3:30 – Art Dean, Pine – “To be Determined”

4:15 – Break

4:30 – Panel Discussion

5:00 – Cocktail Hour sponsored by United Conveyor Corporation.

There is no charge to attend this event. Please register online at http://airqualityworkshop.com/locations/houston-tx-nov-3rd/

View the testimonials from the 2014 Air Quality Workshop airqualityworkshop.com/testimonials

Air Quality Workshop

WORKSHOP SCHEDULE

8:00 – Registration & Breakfast

8:30 – Keynote Speaker

9:00 – Block Andrews, Burns & McDonnell – “Compliance Strategies for the 21st Century”

9:45 – Jon Norman, UCC – “Case Study: Using Trona & SBC for High Level SO2 Removal”

10:30 – Break

10:45 – Steve Baloga, Novinda – “Amended Silicates™ for Hg Control”

11:30 – Mike Atwell, Solvair – “Trona: a viable solution for SO2, SO3, HCl, and HF”

12:15 – Lunch sponsored by Lhoist

1:00 – Rafic Minkara, Headwaters – “Flyash in a changing Air Emissions Market”

1:45 – Joe Wong, ADA Carbon Solutions – “Advanced Activated Carbons for MATS Compliance”

2:30 – Break

2:45 -Melissa Sewell, Lhoist – ““Dry Sorbent Injection with Enhanced Hydrated Lime”

3:30 – Pramodh Nijhawan, IAC – “Novel Recirculation Scrubber”

4:15 – Break

4:30 – Panel Discussion

5:00 – Cocktail Hour sponsored by United Conveyor Corporation.

There is no charge to attend this event. Please register online at http://airqualityworkshop.com/locations/orlando-fl-october-7th/

View the testimonials from the 2014 Air Quality Workshop airqualityworkshop.com/testimonials

Air Quality Workshop

WORKSHOP SCHEDULE

8:00 – Registration & Breakfast

8:30 – Keynote Speaker

9:00 – Block Andrews, Burns & McDonnell – “Compliance Strategies for the 21st Century”

9:45 – Jon Norman, UCC – “Case Study: Using Trona & SBC for High Level SO2 Removal”

10:30 – Break

10:45 – Steve Baloga, Novinda – “Amended Silicates™ for Hg Control”

11:30 – Mike Atwell, Solvair – “Trona: a viable solution for SO2, SO3, HCl, and HF”

12:15 – Lunch sponsored by Lhoist

1:00 – Rafic Minkara, Headwaters – “Flyash in a changing Air Emissions Market”

1:45 – Joe Wong, ADA Carbon Solutions – “Advanced Activated Carbons for MATS Compliance”

2:30 – Break

2:45 – Melissa Sewell, Lhoist – ““Dry Sorbent Injection with Enhanced Hydrated Lime”

3:30 – Art Dean, Pine – “To be Determined”

4:15 – Break

4:30 – Panel Discussion

5:00 – Cocktail Hour sponsored by United Conveyor Corporation.

There is no charge to attend this event. Please register online at http://airqualityworkshop.com/locations/chicago-il-sept-9th/

View the testimonials from the 2014 Air Quality Workshop airqualityworkshop.com/testimonials

 

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Value of IAC’s TTG ePTFE Membranes

IAC’s Hi-Tech TTG ePTFE (expanded PTFE membrane) provides state of the art filtration efficiency in dust particle capture, air flow permeability, and is rated top level in performance of all membranes by the EPA sponsored ETV/VDI testing. IAC’s TTG ePTFE operates at ranges of 2.0” to 2.5” water column lower than other membranes manufactured in the U.S. capable of being laminated to almost all filter media; the IAC TTG membrane helps ensure maximum dust collection efficiency without restricting airflow. With the new more restrictive particulate emission regulation, why settle for anything but the best?

TTG’s production facility in Higginsville, MO, uses state-of-the-art equipment to produce ePTFE membranes of exceptional quality. The equipment is computer controlled and automated to ensure repeatability and adherence to specifications, including pore size, thickness, bubble point, air permeability, water extrusion pressure and moisture vapor transmission rate.

TTG produces ePTFE membrane and laminates for a variety of filtration applications. Their products are used to filter air and liquids through the following properties of ePTFE.

  • Filtration Efficiency – All TTG products will capture 99.99% of material 1 micron and larger, and many of our products are HEPA rated.
  • Cleanability – Our products can be re-used since they do not blind or foul like traditional filtration fabrics. We use surface filtration to keep the particulate on the surface of TTG membranes.
  • Pressure Drop – Over time our membranes maintain their low pressure drop since their surface remains clean and un-blinded.
  • Chemical and Thermal Resistance – TTG ePTFE membranes are rated to temperatures up to 500°F, and since they are produced from polytetrafluoroethylene, they are chemically resistant to acids, alkalis, solvents, and other chemicals.

IAC is committed to bringing you the best in filtration quality and our TTG ePTFE is an example of providing our customers the best in class products and services.

Helpful links:

Membranes.  http://ttgtech.net/products/membranes/

Filtration.  http://ttgtech.net/products/filtration/

weekly blog

Startup & Shutdown Procedures for a Baghouse

Start-Up Procedures

Proper start-up procedures are not only beneficial to the life of filter media in dust collector applications, but to your baghouse system as a whole. Proper “start-Up” procedures are actually designed to prevent potentially harmful dew point excursions and help establish the formulation of dust cakes across the filter bags prior to full activation of the system. Think of the dust cake as a protective layer surrounding the bag itself.  Contrary to what many think, it is this layer that actually filters the air/dust stream while the bag simply supports the “dustcake.”  By using a pre-coat to create this initial “dustcake,” a porous and efficient layer is created prior to the system starting up.  This is due to the various sizes of particulates found within the pre-coat, as opposed to a more uniform particulate size often found in process applications.  The porous cake allows air to make its way through the tiny crevices, but the dust particulate and sticky/tacky substances cannot.

Before starting up a baghouse system, it’s vital to ensure you’re following the correct startup procedures.  Below is a step-by-step startup process made easy:

  1. For applications dealing with extreme temperatures (above 250°F), and auxiliary heat sources and gases, preheating your baghouse to prevent moisture condensation is a crucial, yet overlooked step. This should be carried out once a measurement of the temperature within the baghouse states that it is appropriate to continue. This minimizes the potential of moisture condensation or passing through the dew point at start up where one could potentially activate chemically harmful particulates or cause dust agglomeration that could plug the filter media.
  2. Activate the dust removal system. This might include rotary airlocks, pneumatic conveying equipment or discharge devices. This will help ensure any residual dust is removed prior to full system activation.
  3. Activate main fan.
  4. Insert pre-coat powder.
  5. Activate the bag house cleaning mechanism (make sure the cleaning system is set to pulse only when the operation/OEM recommends).
  6. Begin dust-collection/system process.

Shut Down Procedures

The fan should run for a short time span after the heat source and dust collection pick-up points are shut off, until the internal temperatures and conditions stabilize to the appropriate levels. This helps the “stagnant” gas stream to be expelled from the system as fast as possible, again minimizing dew point excursions.  Below is a step-by-step process on how to properly shutdown your baghouse system.

  1. Shut down the operation or process where dust is being collected.
  2. Continue operation of dust-removal conveyor and cleaning of bags for 10 to 20 minutes to ensure good removal of collected dust.
  3. Shut down the main system fan.
  4. Shut down the bag house cleaning system.
  5. Shut down the dust removal system that’s transferring particulates/powders into the hopper.
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Pneumatic Conveying- Dilute vs Dense Phase

Pneumatic Conveying Systems

A pneumatic conveying system transfers powders, particulates, and dry bulk materials through an enclosed conveying line. The primary force during this transfer phase comes from a combination of differential pressure and the flow of air through the use of a fan. By controlling the pressure (push phase) and vacuum (pull phase) airflow forces inside the conveying line, the system will successfully convey materials.

Pneumatic conveying is utilized in one of two forms: through a dilute or dense phase of transportation.  However, each phase is unique and is applicable for different purposes – namely sizes and types of materials that are to be conveyed.

Dilute Phase  dilute-phase

 

The Basics:                         

The “Dilute Phase method” conveys material in a continuous manner, transporting materials at low pressures with a high velocity. Particulates remain suspended in the air, preventing accumulation on the bottom of the conveying line.

Dilute Phase Vacuum Conveying:

Dilute phase vacuum conveying is appropriate for conveying materials that tend to compress under pressure, such as lightweight grain particles. This pneumatic method is used to convey materials over short distances at low capacities, often referred to as “slug intervals.”

Dilute Phase Pressure Conveying:

Dilute phase pressure conveying is a widely used conveying method for lightweight powders and particulates. At the start of the dilute pressure conveying phase, a high volume of low-pressure air is processed into the system. This “push” method requires the airstream’s velocity to keep the material being handled suspended mid-air along pipeline(s).  This application is utilized with non-abrasive and non-fragile materials such as: sugar, starch, plastic granules, sodium bicarbonate, hydrated lime, activated carbon, and zinc oxide.

Dilute Phase is best suited for conveying material where degradation is not a major issue.

Pros:

  • Nearly any material can be conveyed
  • Far less maintenance required
  • Economically cost-friendly

Cons:

  • Degradation to “abrasively-prone” materials and particulates
  • A higher power output = increased expenditures

Dense Phase dense-phase

The Basics:      

The “Dense Phase Method” conveys material through low velocity, high pressure surges through the pneumatic conveying system, with the particulates/materials accumulating along the bottom of the conveying line, as opposed to being suspended in air like the dilute phase. The material being transported through this means of pneumatic conveying are actually dragged or pushed along, and many times flow in timed periodic surges.

Dense phase conveying is the best choice when you want to minimize damage to the material you are transporting pneumatically.

Dense Phase Vacuum Conveying:

Dense phase vacuum conveying is recommended when transporting abrasive or potentially fragile materials over short distances (typically under a 300’ distance). This application is most commonly used to transfer bulk powders and particulates at low rates (25tph or less) via railcar or truck transportation.

Dense Phase Pressure:

Dense phase pressure conveying is recommended when transporting abrasive, potentially fragile and super lightweight particulates over long distances (typically more than 300’). Some examples of materials applicable to this process include: silica sand (frack sand), feldspar, fly ash, glass cullet, alumina, glass batch mix, carbon black and dextrose. Dense phase systems convey materials at low speeds to prevent material wear, abrasion along pipelines and bends.

Pros:

  • Since the velocity is much lower during this method of pneumatic conveying, there is far less wear and abrasion to worry about in regards to the material being transported. This process is much more energy-efficient when compared to the dilute phase.

Cons:

  • Air pressure must be high, or a conveying distance fairly short for the system to be ideal.
  • Additional fittings may be needed for certain customized dense conveying – resulting in increased installation, maintenance, and overhead costs.

 

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5 Helpful Baghouse Maintenance Tips

1 Ensuring a Proper Bag-to-Cage Fit

The fit between the bag and the cage is critical for filters to perform properly.  Filters that are too lose or too tight will have severely limited collection efficiency and may fail prematurely. There are many different types of media, each with a different pinch “size” to look for when ensuring your pinch isn’t too loose or too tight.  For instance, when inspecting a filter bag made of felt, a proper “pinch” should only be about .025”-0.5,” whereas a bag filter made of fiberglass or a ePTFE membrane would require a much tighter pinch (ranging from .0625”-0.375”).

To learn more about the specific details and bag-to-cage fits, along with the proper “pinch,” visit IAC’s website at http://www.iac-intl.com/catalog/bag-to-cage-fit/ which covers all media types, their respective bag-to-cage fit, and the necessary “pinch” you should be utilizing for the filters your company plans to integrate.

2 Which Type of Filter Bag Would Be Most Applicable For Your Baghouse?

Choosing the correct filtration material for your process and dust collection needs is obviously a crucial element in terms of maximizing operational performance.  There are several key criteria that one must consider to ensure you have the right filter for your application:

Maximum Inlet Operating Temperature

Always consider what would be the highest inlet temperature into the baghouse.  This will immediately narrow your choices to the synthetic fibers that can withstand and operate in those ranges.

Inlet Grain Loading

An often overlooked factor is the amount of dust the system will see. Knowing your inlet grain loading/cfm will help a bag manufacturer determine the possible needs for durability and the type of fiber and possibly the weight of the filter bag.

Particle Size/Distribution by BOTH Volume and Count

Understanding the distribution size of material collected is critical in establishing the right filter media.  Years ago, only particle size by weight was considered, and while that’s an important factor to consider, one must not overlook the importance of getting the distribution by size as well. For example, if you had 100 grains/acfm, and 99 of them were <1 micron and only 1 was very large, you obviously need to develop and choose a media (and possibly a finish such as membrane) to handle the very fine particles. If that one “large” particle weighed 100 X’s the total weight of the other 99, the weight analysis only would’ve directed you to use a completely different style media, with potentially dire emission circumstances.

Gas Stream Chemistry

It’s obviously important to understand whether the baghouse will be filtering particulate and gases that are chemically active (whether acidic or alkaline). Certain fibers are more resistant to each of these.

Gas Stream Moisture Level

Every bit as important as “gas stream chemistry” is understanding the amount of moisture in the gas stream, and the propensity to go through dew point during start up and shut down periods. This could not only have an effect on chemically activating the particulate, but also affect the ability of the filter properly being able to remove dust during pulsing (moisture will cause agglomeration of the particulate onto the bag causing a crust like surface that blocks air flow paths, and if severe enough, will require the use of treatments to the filter surface such as laminating with TTG ePTFE) to provide the best possible release characteristics.

3 Timely Cage Inspections

A thorough inspection of the cage is highly recommended each time new bags are installed.  Some of the most frequent and common problems to look for when inspecting a cage include: bent and damaged wires, rusting and pitting, and sharp edges along the bottom of the cage pan.

4 Checking Pressure Drops (daily maintenance protocol)

Perhaps the most important indication of a dust collector’s performance is the differential pressure (resistance of air across the filters and clean air plenum). This measurement gives you an indication of whether your filters are operating correctly.  Based on your system(s), the collector(s) should have been designed to operate within a set range of resistance, (measured in inches of water column). The differential pressure reading will indicate whether there is an issue with too low of a differential pressure (typically meaning the filters are allowing too much air to pass through which usually means emissions as well), or too high of a delta P (meaning flow is being restricted and will lead to reduced system flow capabilities and ultimately lower manufacturing capacity).  Our experts and field specialists recommend a proactive maintenance program where you are monitoring and trending how differential pressure is performing.  In regards to critical process collectors, this should be done daily, and in regards to nuisance collection collectors – at least once a week. Upon seeing a negative trend, you can immediately start to evaluate potential problems with the process- are my cleaning systems operating properly? Are their leaks in the duct work causing outside air to be pulled in? Is material building up in the hopper causing erratic inlet flow distribution? Are my pick-up points balanced correctly to obtain the proper draft? Simply put, interpreting your pressure drop is like monitoring your blood pressure, and when done proactively, you can address potential problems before they cause serious plant production or emission issues

5 Check Cleaning Systems (daily/weekly maintenance protocol)

Ensuring your pulse jet dust collector cleaning system is operating properly is an imperative and proactive maintenance necessity. If you’re not getting proper cleaning due to a potential solenoid valve failure, diaphragm leakage or poor sealing,  or perhaps inadequate supply (or recovery) of compressed air for pulsing, the desired performance of your system could be potentially compromised . In regards to critical process collector systems, these components should be checked at least weekly, and in some cases daily. Simply monitoring the entire pulse sequence and compressed air usage will help ensure problems are addressed immediately. When any of these parts are not operating properly, you are most likely dramatically reducing the effective cloth area (and subjecting filters being pulsed properly to take on an undesired flow of air and dust) of the system which can quickly affect productivity as pressure drops will rise and pick up points will lose designed draft.

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4 Critical Baghouse Maintenance Issues to Consider

bluecrew man baghouse maintenance inspection

IAC acknowledges industries’ concerns when it comes to maintenance issues and provides knowledgeable, innovative solutions to your problem.

  1. Safety of Your Personnel

Baghouses, like many “work zones”, can be dangerous places. Only those personnel that should be in a work zone or hazardous area are those that have required training.  OSHA confined space entry regulations and first aid equipment and training are just a few of the many issues to be considered when providing a clean, safe, working environment.

  1. Inexperienced Staff and Time Limitation

Baghouse Maintenance staff should undergo regular system operations training.  When personnel or machinery is updated and/or replaced it is critical to have training repeated. The limitations of time and staff inexperience should never be an issue.

  1. Compliance Issues

Detailed documentation of all work performed for compliance reports should always be kept up to date. This documentation may also help with future compliance questions and provide recommendations for future improvements.

  1. Production Downtime

Routine scheduled maintenance can help prevent inadequate baghouse operation. Poor baghouse operation can have many negative results including but not limited to an increase in emission, a dirty, unsafe work environment, equipment wear and tear and an increase in energy usage.

The IAC Blue Crew Solution:  With a service project, scheduled inspection, preventative maintenance program or training seminar at your plant, IAC can help you keep your baghouse operating efficiently and your plant on-line and productive.

Baghouse Tips with Dr. Vent Goode

The difference between Gravimetric and Volumetric feed

A recent question came up for Dr. Vent Goode from a customer regarding Gravimetric/Volumetric.

Dr. Vent Goode,

I would appreciate your help on answering these questions.

  1. What is the difference between Gravimetric and Volumetric feed?
  2. What are the Pro’s and Con’s of each and what is the reason to go with one or the other?

dr vent goode illustration

 

 

 

 

 

 

 

Volumetric is a system that feeds material in cubic feet per hour, while gravimetric feeds in pounds per hour.  They would both be accurate if material density was constant, but it’s not.

Dry, powdered material density can vary greatly.  If it’s aerated (mixed with air) it is light and can flow like water.  If it’s packed, it is heavier.  An extreme case would be the same material pressed together, forming a heavy, solid rock.

On DSI systems, a certain amount of material (lbs) is required to reduce a certain contaminant.  If we feed volumetrically, we would get variations depending on the current density, which can vary depending on different factors, such as how much time the material has been sitting in the silo.

The gravimetric system actually weighs the material being fed, so it adjusts for density variation.  Bottom line, gravimetric is much more accurate and therefore more expensive.

We highly recommend the gravimetric when accurate material injection is important.  Significant savings can be obtained with volumetric feeding, but injection accuracy in lb/hr will vary as much as the material density.

Regards,

Dr. Vent Goode