In selecting an industrial dust collector for a specific environment, the characteristic of the specific dust that is going to be collected should be considered. Things that are to be considered are like the size of the dust, if it is extremely small, or is the size of the dust is a mix of sizes, or if the dust is abrasive or is it hygroscopic, or moisture absorbing, or does the dust agglomerate easily or even not at all, or is the dust explosive or combustible, or is it from a corrosive or toxic or unstable substance.
All of these things are necessary considerations when it comes to choosing an industrial dust collector. The equipment must relate to the dust being collected, however, the dust is not the only factor that needs to be considered.
It is also important that when it comes to choosing an industrial dust collector, the conditions of the gas stream that is entering and passing through the industrial dust collector should also be factored into the choice of an industrial dust collector.
The gas stream characteristics have a significant if not greater impact when it comes to industrial dust collector selection than just the dust characteristics. The combination of the dust and the gas stream are characteristics that can make the selection of the equipment challenging.
Common Gas Stream Characteristics and Their Impact on Industrial Dust Collector Selection
As mentioned, it is important that the common gas stream characteristics and their impacts must be looked at because this will give an impact on the selection of the appropriate industrial collector equipment.
The following are the gas stream characteristics that need to be considered:
- The gas stream temperature
The temperature, more specifically high temperature, affects not only the selection of filter media but also the construction materials of the collector and the filter style either bags or cartridges.
The temperature can also affect the method of the filter reconditioning or cleaning and the total required filter area. The required filter area is the outcome that is driven by the air volume requirement and the reasonable filtration velocity which is commonly referred to as the Air-to-Media Ratio. A higher temperature condition is usually going to require more conservative filtration velocities.
There are a lot of different filter media that is available with known characteristics. Selecting the filer media may seem relatively simple by the process of elimination, and, it can even be simpler if you know the other characteristics of the gas stream.
But, of course, not all of the media are suitable for all types of collectors or conditions. Setting fiberglass as an example, fiberglass is not generally considered suitable for envelope-shaped pulse jet collector bag, this holds true with spunbond polyester which is not generally considered suitable for shaker style collectors.
Thus, the operating temperature and available media for temperature can affect the industrial dust collector that is being considered.
As said in the earlier parts, the temperature can also affect the materials of construction that are to be used for the industrial dust collector. This will include the type of metals, gaskets, or paint also with the special requirements for insulation for both of the moisture and acid consideration control or personnel safety.
Furthermore, it is also important to remember that filtration velocity is impacted by the changes in the density of the gas stream. The increases in temperature and the total volume of the filtered air will increase with the temperature, thus, the temperature will affect the size of the industrial dust collector.
- The gas stream moisture
When it comes to high moisture levels, it can have both negative and positive effects on the performance of an industrial dust collector. When the moisture levels are higher, there must be precautions that must be taken into consideration in order to prevent condensation on not only the filter media but also on the interior sidewalls of the body of the industrial dust collector and hopper in order to avoid an obvious effect of moisture interacting with the dust-mud.
When removing the mud form a filter media by normal pulsing or shaking, it is often difficult if not impossible. And it is even more difficult in trying to get any air movement through the mud, therefore, there is value in maintaining an interior temperature in the collector above the moisture and acid dew.
The impact of dust from the filters being pulse cleaned, and falling into the wet hopper must be considered. The result here is dust not going to slide smoothly down the hopper walls as intended, but when it comes to sticky dust, this will eventually bridge across the discharge opening, thereby effectively shutting down the operation just as if mud were performed on the bags themselves.
Through preventative action, this will keep these issues from developing that is going to take form of insulation of the housing or additional heating elements on the exterior of the hoppers. There are some environments that even require the heating of the compressed air that is being used in pulse cleaning to prevent the collector from passing through a dew point due to the chilling effect from expanding the compressed are that is being released during each of the pulse.
Although condensation is an extreme moisture condition, problems may arise form increased moisture levels without condensation from actually occurring. The hygroscopic dust like sugars, salts, and lime that actively absorb moisture from a gas stream and it can become very difficult to dislodge from filter media.
Generally, an industrial dust collector can perform best if the relative humidity of an air stream that is containing hygroscopic dust that is kept at less than 40% RH.
The challenges that are being associated with the high moisture level is relatively well-known and predictable. But with low moisture levels with high temperatures including bags of dust-like metallic salts that can become even more challenging. With high temperatures and low moisture levels, metallic salts, including other specks of dust with similar characteristics, will behave as if each of the dust particles has the same electrical charge. The particles will then repel each other and agglomeration of small particles into large particles can become negligible.
Because dust particles must be agglomerate for the collected dust on the media that is to be dislodged and migrated to the hopper, if dust is not going to agglomerate, the particle size of the dust will stay the same and the air currents will just transport with disturbed dust back to the media to be re-deposited. This implies that dust will never migrate into the hopper. So with some dust, this effect is going to be severe enough that it can be actually advantageous to introduce moisture into the air stream.
- The gas stream moisture
Chemistry is a broad term that encompasses a multitude of contaminants. The most common are acid gases but this also includes condensable compounds, hydrocarbons, Volatile Organic Compounds (VOC), and others. The acid-forming compounds like Sulfur Oxide and Chlorine which are the common byproducts of combustion which are included in this grouping.
These compounds when it is being combined with moisture, these will have the potential to form acids when the temperatures in the system drop that is below their acid dew points. Each of these items presents challenges in materials of construction, surface coatings, insulation, and filter media selection.
The gas streams with mixtures of a number of these contaminants represent with even more challenge and are going to require a thorough review of the process and performance personalities.
As a conclusion, each of these gas stream characteristics is offering common challenges in the selection and operation of the dust collection equipment. However, gas streams with combinations of these factors can cause great challenges.
The answer for on process may not be the right one for what would appear with even a similar gas stream. To illustrate, polyphenylene sulfide media may be a great selection when it comes to a hot SOx-laden gas stream from a coal-fired boiler.
But, this may not be a good choice when it comes to hot Sox-laden gas from a coal-fired kiln when a kiln brings significant amounts of excess air, with therefore produces higher oxygen content than the coal-fired boiler.
With a hot moist flue gas environment, Ryton media can be subjected to a loss of physical strength which is caused by oxidation as oxygen levels surpass 8%. These boiler flue gases are rarely above that level, but the extra air from the kiln can drive oxygen levels that are well above the level.
The overall point here is that in order to make the proper equipment selections in terms of challenging gas streams, the full characteristics of the gas stream must be known.
Thus, when an inquisitive salesman or engineer of an industrial dust collector is starting to grill you about your process, you should be able to trust his intention. The main reason here is for the prevention of surprises during the commission and operation that might happen because something was left unknown when it comes to the planning phase.