Learning the right way to start up your dust collector or bag house will optimize performance, help initial blinding, and extend the life of your dust collector’s new filters. Let’s review the proper start-up procedures for new dust collectors and for those with new filter bags installed.
Keep in mind that the following information is just a rough guideline. Afterward you may want to contact your baghouse OEM, as they may suggest some variations unique to their equipment.
Before beginning start-up procedures, be sure to inspect your unit for correct installation of the filter bags and operation of related auxiliary equipment. On critical emission installations, you should also perform a dye test to check for any mechanical leaks from worn gaskets or improperly-installed filter bags. For more information on this, see our video on how to perform a dye test at slyinc.com.
Also be sure to turn the power off when inspecting the equipment and also to perform any lockout, tagout, or other safety procedures as required on rotary valves, screw conveyors and fans. This will help ensure you're working in a safe environment.
Season Your Filter Bags:
Start-up procedures are used to develop an initial protective dust cake on the filter bags. This is also referred to as pre-coat, seasoning or conditioning the media, and can be done with the dust you're collecting, or preferably with agricultural lime, diatomaceous earth, or one of several specifically-developed products available. Seasoning your collector’s filter bags is one of the most important things you can do to ensure your dust collector will perform at its optimal level over the life of the filter media.
In a fabric-filtered dust collector, the filter media is used to store the dust cake. The initial dust cake is a coarse layer of collected particulate that develops during the conditioning period of new filter bags.
Pre-Coat Your Bags to Avoid Blinding:
During start-up, you should pre-coat your filter bags to protect them from damage caused by dust impacting the new bags at a high velocity, becoming lodged deep in the fibers. This lodged dust will likely be retained permanently, causing an increased pressure drop for the life of the media. In fact, some oily and/or sticky dusts absolutely require this protection beforehand, or the media will clog and will not clean down from the onset—this is called blinding. In extreme cases, blinding during start-up can immediately ruin your filter bags, costing you time and money.
However, a needle felt filter bag will not reach its highest collection efficiency until an adequate dust cake is developed on the filter media. Because of this, you may be required to bring your new filters up to a desired level of collection efficiency by pre-coating them with a conditioning agent before you can start your process.
Choose a Good Conditioning Agent:
You can use various conditioning agents to pre-coat your filters, such as diatomaceous earth and agricultural limestone., Sly recommends a conditioning agent marketed under the name of PreKote and available through Sly. PreKote forms a uniform three-dimensional porous dust cake which is ideal for efficient and effective baghouse operation. You’ll also use much less PreKote than any other type of conditioning agent, saving on cost.
Note: We recommend you avoid using un-hydrated lime, pebble, quicklime, fly ash, and any material that is hydroscopic, non-agglomerating or spherical in particle shape.
Procedures When Using a Pre-Coat Agent:
Ensure that you have enough conditioning agent on hand. To calculate how much you need when using PreKote conditioning agent, take the total square foot of filtered media in the baghouse and divide by 0.042. This number is the total pounds of conditioning agent your baghouse will require, or just over one pound for each 40 square feet of media.
For diatomaceous earth, use 1 lb for 20 square feet of media, and agricultural limestone will require 1 lb for every 5 square feet of media.
If you don't know how many square feet of media your filter bags have, you'll need to take measurements. If the filter is tubular-bagged, simply take the bag diameter, multiply it by pi (3.1416), then multiply that by the bag length in inches, then divide by 144, and the result is the square feet for one bag. Multiply this number by the number of filters in the unit, and you’ll know the total square feet of filter media in your dust collector.
To start pre-coating the new media, first be sure to turn the post-cleaning system off. You can now start the exhaust fan with the damper closed to 50 to 60% of design volume. Then introduce the pre-coat material into your collector. You can do this through an access door in your duct work or a hopper. You may need to install a small two- to three-inch diameter takeoff with a blast gate in your inlet duct work.
The rate of feet for the pre-coat should not exceed 10 lbs per minute maximum on units designed up to 25 thousand CFM; 25 lbs per minute on units designed for 25 to 50 thousand CFM; 45 lbs per minute for units between 50 and 75 thousand CFM; 60 lbs per minute for 75 to 100 thousand CFM; and 100 lbs per minute for units between 100 and 200 thousand CFM.
Maintain this flow of pre-coat until the baghouse differential pressure stabilizes, anywhere from one to three inches in water gauge. Once the differential pressure stabilizes, you can be sure of an even layer of dust cake on your filters. Now move the damper or blast gate to full open or previous full operation set point and begin collecting dust from your process.
When the differential pressure reaches four to five inches of water, initiate one complete cleaning cycle. Pressure drop should then go down to one to two inches of water. Now when the differential pressure returns to four to six inches, you can start your automatic cleaning system.
Monitor Pressure Drop to Spot Issues
Now that the filters are seasoned and you have resumed production, monitor pressure drop and adjust the amount of cleaning to achieve a stable condition. This will require adjusting the duration of your on-time and off-time pulse-cleaning timer settings.
Be sure to monitor your dust collector's pressure drop over time; best practice is to record differential pressure each day. This will allow you the ability to spot developing issues with your dust collector.
Optional: Preheating in Dryer or Dryer Cooler Applications:
If your baghouse is installed on a dryer or dryer cooler application, you'll need to use a slightly- different start-up procedure. You may also need to perform startup without using a pre-coating agent. Watch our YouTube video which covers startup in these cases.
The Dust Collection Experts
This should give you a rough framework to properly perform dust collector start-up procedures. However, please always remember to follow your company’s safety procedures when working on any equipment at your facility.
To learn more, watch our full video at https://www.youtube.com/watch?v=8zQtfWqtYAk&t=37s.
For further assistance, just give us a call at 800-334-2957, or visit our website at slyinc.com.