4 Things To Know About Dust Cake
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4 Things To Know About Dust Cake
Not all dust cakes are created equal, and therefore they each have a specific impact on a dust collection systems performance. Below are four characteristics of dust cakes that influence Baghouse operations. I discuss these independently but they all occur at the same time and influence each other.
? Particle Size Distribution Matters
Comparing two particle size distributions with the 50% passing point at the same size. The curve that is wider will have smaller void spacing, and create a “tighter” dust cake. While the narrow curve, smaller delta from the min and max particle size, will have a larger void spacing. This directly impacts the differential pressure of the Baghouse.
System Impact
A “tighter” dust cake will have a lower air permeability and thus a higher differently across the bag. The dust collector will likely clean more frequently to maintain the target dp for the system. The increased cleaning will reduce the dust cake thickness to increase air permeability. This reduced dust cake could lead to accelerated bag blinding or bleed-through due to the fabric doing more filtration, as compared to a system with a thicker dust cake.
? Particle Shape Matters
The shape of the particle will impact how well it floats or falls. Let me explain. Spherical particles are more easily fluidized and lifted by an upward gas stream, than a more cubical or multi-faced particle. The farther from “round” the more energy required to lift the particle, all material characteristics the same.
System Impact
When the filter bag is cleaned, the dust cake is broken and the dust at the bottom of the bag “should” all fall into the hopper. If the dust particles are round, as compared to cubic particles, more dust will be picked up due to the velocity (can velocity) in this area. This is why a low can velocity (<200 FPM, ~1.0m/s) should be used in Baghouse design to minimize the particle shape impact. (Minimizing the can velocity will help get a dust cake into the hopper).
? Dust Cake Density Matters
A dust cake that has a low density will be highly impacted by the can velocity with regard to dust re-entrainment. When dust is pulse cleaned off the filter and then picked up by the gas stream to be delivered back onto the filter bag. This is dust re-entrainment in a nut shell. And it all has to do with gravity. The only force that is moving, or pulling if that term makes more sense, the dust down to the hopper. Two particles identical in all ways but density, will react differently when passing the cage can’s and interacting with the can velocity.
System Impact
Using the same Baghouse design that works for one material product, may not work for a different material product. Understanding what is being collected is just as important as having the correct air-to-cloth ratio.
? Dust Cake Agglomeration Matters
The tendency for a dust to agglomerate, basically stick to other particles and things, will impact the cakes release. Dust agglomeration can create a particle that is larger, and therefore heavier, so it can pass the can velocity but could cause a high dp due to the thicker dust cake. Electrostatic charge and moisture are common causes for agglomeration of dust. Making the dust cake potential dense or even difficult to release from the filter bag. Now if the agglomeration happens before reaching the bag, the dust may go directly to the hopper if the “drop out” zone of the Baghouse is of sufficient size.
System Impact
The tendency for a dust to agglomerate may impact the angle needed on the hopper walls to prevent build up. It may also determine if a specific bag surface treatment or finish is required to allow the dust cake to release properly.
sales and solutions provider for the pollution control system likes bag filter system for steel cement and other process industry.
5 年How to calculate can velocity ,?? Plz mail me [email protected]
Building Materials Industry Expert
5 年BWF is a great company in the world looking forward to more business in MEA region Matt Devitt
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6 年Supposed your setting up new plant, what is allowable dust cake and how you will know if dust cake thickness is enough.
Founder at UAB Sortus
6 年When designing right dust collector can velocity is directly related to dust density. Of course same material in same baghouse in certain situations can have various densities but normally if we talk about bulk density then selected right can velocity can go easily lower than 0,36m/s if bulk density is for example 0,1 t/m3. But happens that for example bulk density of stone wool dust is 0,05 when in the same time particle density is over 1,8!!! So whats then :)? Only answer is - experience :).
Ash Grove Mississauga Plant Manager (CRH Company)
6 年Very good information!