Cyclone & Bag Filter

Cyclones are highly effective at removal larger particulates (> 5 μm) but less so for particulates smaller than these. While bag filters can remove larger particulates, they clog very easily; larger particulates with sharp edges may also damage them. For this reason larger particulates are first removed by a cyclone, then the air is passed to a bag filter to remove smaller particulates.

One big reason is the reclamation of heat during winter these units would remove a lot of heat from the building. To balance the pressure in the building. A hazard to have the doors slam shut do to the vacuum some big units would provide in a close sealed building. One other reason in your area there maybe regulations about expelling exhaust gases outside with out a scrubber which would increase the cost. It also forces you to maintain the equipment. Most companies would not worry about expelling fine dust into the air because of poorly maintain equipment. They would ignore the explosion sensors on the exhaust. But if you are dumping it back into your work environment then you will.

There is one Raymond mill & cyclone & Bagfilter in closed room . And Fan Is given at the outlet of bag Filter to suck material from mill . my question is why cyclone discharge is given to bag Filter instead of giving outlet of cyclone.

Outlet ( Air containing some fine particles) of cyclone is given to again Mill Why?

There shouldn't be much going back to the mill after going through a cyclone and a bag-house your bag-house should be about 98% efficient. What type of mill is it? I working with non-coal non-metallic mineral crushing plants and asphalt plants The exhaust from both are released into the air.

GA Frank

I'd have to agree with your interpretation, although that situation seems so unlikely, it boggles the mind. By discharge, he apparently means the bottom of the cyclone, because he clearly says the "air -fine particle outlet from cyclone is returned to mill". He further says that in the general case (meaning usually, as seen everywhere else) "the cyclone air outlet is given to bag filter," meaning that he understands the way things should work.

Good complete answer.

One wonders how this could possibly happen...

Good answer considering the confusing posts by OP. Either the OP does not understand his system and the cyclone design and terminology (gas inlet vs. gas outlet vs. dust outlet), or, as you stated, someone is an idiot and connected things backward. However, I would add one important comment. OP stated the fan was on the outlet side of the bag filter. If, in fact, the mill was connected to the cyclone inlet, the cyclone "air" outlet from the top vents only to the mill, and the cyclone bottom discharge (dust discharge) is connected to the bag filter, then the cyclone would, essentially be non-functioning. The fan will draw air from the point of lowest resistance. I would be thinking that the path from the mill to the cyclone air outlet, straight down through the cyclone and to the bag filter would be that path, so the system would vent the mill by using the cyclone as an elaborate piece of ductwork only. The connection of the cyclone inlet to the mill would be non-functional, or, at best, a secondary path for air flow to the bag filter. In any event, the cyclone would not function as a cyclonic dust removal device. From this standpoint, the cyclone could be removed without disruption to the system and if the bag filter discharge to atmosphere meets current code requirements, then no harm/no foul. I just don't understand how the system would operate well considering the choke point created at the bottom of the cyclone.

I agree. The cyclone would function as a very costly piping Y, with slightly less restriction in the straight shot from (usual) air/fines outlet (now serving as one inlet) than from the longer and less direct path from the tangential inlet to the dust discharge.

The OP could check the airflow direction at the end of the duct that he thinks returns air to the mill. It should be toward the cyclone, not away from it, if the system is really as he has described it.

Pictures or a diagram would really help from OP.

Although I agreed with you initially, I think that Guest 1947 probably describes the situation correctly. The Raymond mills are powder mills (I found out upon searching), with the output product being powder. So as Guest 1947 says, there can be several configurations for collection, depending upon the desired output, which could include fines, course stuff, or both separately. In the OP description, the fines seem to be going back to be re-milled, which seems strange.

Here's a pic of a Raymond mill installation. (From: http://www.grindingmills.biz/raymond-mill-output-problem.html )

I tend to think of dust as being the "bad" stuff (especially now, with asbestos exposure showing up on my chest Xrays). But in this case, I think the dust is the product. A little more description from the OP would be helpful, of course.

Kudos to you, kudos to guest 1947.

I can not speak as to the cyclone it's self, but the reason the exhaust air is returned to the building is replace the air that is being pulled out. The in and out needs to balance. If you are exhausting 120,000 CFM from the extraction system, then you have to make it up or you will have a severe negative pressure problem in the work area. The other option which allows for better air quality is to exhaust it out side and use a properly sized Make up air unit interlocked with the cyclone controls.

The recirculation method is the cheaper way to go and the replacement air method is the better, bu more expensive.

Cyclones is before a Bagfilter and its purpose is to arrest coarser particles by centrifugal action inside the Cyclone. The coarser particle in your case is going back to mill as the final quality is based on Bag filter output. There are cases both Cyclone and Bag filter out puts are taken as final product. It depends on desired Apparent Density of the product. There are cases where the products goes to Bag filter straight and there is no cyclone. As Cyclone takes care of coarser particle , which are not desired in final product ,so in your case it is going back to Mill.

Cyclone takes care of coarser particle , which are not desired in final product ,so in your case it is going back to Mill.

However, that is not what he has described. He wrote that the cyclone discharge (the larger particles) goes to the bag filter, and that the cyclone air outlet (the finer particles) goes back to the mill.

It is not clear from his description that the final product comes from the bag filter -- although you are right, it could. His description seems more in line with the standard dust collection situation, in which the both small and fine particles are considered an air pollutant, if they are not captured. (But the system is strangely plumbed, prompting his question here.) Nothing makes a great deal of sense to me.

Maybe a picture would help.

He seems to describe this, with the fan on the exhaust end, making the cyclone effecticely a Y:

Although he describes the cyclone air outlet going to the mill, the airflow direction would have to be away from the mill, unless there is another fan somewhere.

But perhaps, as you say, the contents of the bag filter are the final product.

Thanks for your valuable reply. I wll contact you if any further clarification regarding this.