Tips for Operation and Maintenance of Dust Collection Systems
"In addition to the on-going challenge of combustible dust, Pennsylvania feed and grain mills have been under increasing pressure by the FDA regulations to meet human food standards in the production of animal feed."
Grain Mill Dust: The Basics
Dust is produced from a variety of processes in the grain and feed industry, as well as many other manufacturing applications. Anytime the material (corn, wheat, soy, etc.) is modified, reduced, or mixed dust is produced as a by-product. This dust is commonly referred to as fugitive grain dust.
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Dust collectors of all types from cyclones to cartridge filters and fabric filters are applied in the milling process to capture dust. In some cases the dust is returned to the process, and in others it is removed from the process as completely as possible - as in manufacturing for example. Make no mistake, dust collectors are not a set and forget animal. These systems have a personality that can change abruptly if you introduce something irregular such as wet compressed air or a change in the process it serves.
In the case of grain milling, grain is fed into a milling machine from above while the reduced or modified material is dispensed into a material transfer system below for further disposition.
Dust collection is applied to the milling common area where the milled product moves to the next portion of the operation: be it bagging, mixing or storage.
How to Collect the Dust, and What to Avoid
Let’s assume a bag filter or fabric filter is applied to remove the grain dust prior to venting the air to atmosphere. Modern filtration equipment is employed to keep the milling machine interior under a negative atmosphere or a slight vacuum to avoid blowing combustible dust into the facility. A slight vacuum is several inches of water column. Full vacuum would be 29.92 inches of mercury.
To accomplish this, the filtration system must be properly sized. If undersized,
the milling machine enclosure begins to spout dust. If over-sized, no harm is done to the process, only to the pocketbook in initial acquisition as well as maintenance and operating expenses.
Filter cleaning for dust collectors can be timer based (most expensive to operate, but least expensive to purchase) or pressure based (least expensive to operate, but more expensive to purchase).
To begin with, the filter cleaning system must be supplied with compressed air at all times. The air should be instrument quality for all systems mounted outdoors. Air compressors typically deliver air at a 37 degree dew point temperature. Think dry material, dry air and dry filters. If any one of the three are wet, you will increase your energy and O&M costs significantly.
Air pressure should initially be set to the lowest pressure recommended by the dust collector manufacturer. A pressure of 110 PSI is typically too high for cleaning a fabric filter dust collector. Many recommend 80 to 85 PSIG. Over cleaning the filters due to excessive air pressure will shorten the filter life and other parts of the system as well as potentially create fugitive dust in or around the process.
Filter Cleaning in Bag or Fabric Filter Dust Collectors.
Recently, we visited a milling operation where the bag type dust collector was supplied with compressed air (filter cleaning air) at 115 PSIG. A bag filter constructed of polyester felt at a weight of 16 oz. per square yard is referred to as depth loading media. It is possible to over clean these types of filters.
Depth loading media is a matrix of media fibers that create a hazardous path for the incoming particle. As material or dust accumulates on the filter exterior, the dust itself becomes the filter. The dust accumulation on the filter exterior becomes the “dust cake”.
The dust cake is desirable as it can increase the filter media efficiency. The way to maintain a healthy dust cake is to manage the filter cleaning interval as well as the filter cleaning pressure.
The filter cleaning pressure required is a function of the design of the cleaning system. It is determined from the airflow through the system, the size of the system and space, and number of filters in the system. Use this information to calculate the pressure required. Once established, the filter cleaning air pressure and volume requirements should not change.
Maintaining Your Dust Collector: Do’s and Don’ts
Replace the diaphragm valves and springs on a yearly basis for timed filter applications and eighteen months for pressure based applications. Alter these as required based on how the valves sound and perform (from new) when they pulse. A functioning system should of loud concussive sounds. A deteriorating system will have a reed-like noise.
Be prepared to replace the electrical solenoids at the two-year mark for timed applications, and three years for pressure based applications.
When purchasing a dust collection system access to the electronics used to initiate the filter cleaning cycle should be located at chest height in the area of the collector, at platform level. Preferably, this enclosure should be located in a non-electrically classified area. Savings for the electrical enclosure itself can range in the many thousands of dollars for a non-classified electrical enclosure!
If one of the filter/cage assemblies fall off during operation, the top or clean side of the dust collector will have to be accessed and cleaned spotless. If organic material finds its way in this area of the system it could spell contamination trouble in food applications.
Replace the filters on a regular basis as recommended by the manufacturer. Typical applications for fabric filter bags are replaced at one year intervals.
Finally, if the product has made its way into the clean air section for the dust collector, the fan wheel blades will have been affected. Lock out and tag out the fan motor and wipe the fan wheel blades with a rag. A small build-up can have a large effect on system performance.
If you'd like to learn more, please click here to view our Dust Collector Page and view feature sheets and case studies about our various dust collection installations and options.