Baghouse Particulate Conglomeration Issue 1

[U.S. Air Filtration Inc.]

Greetings,

I have a customer who has a 20 year old baghouse. He does not have the money to replace it at this time, but they have ongoing issues that nobody seems to know the solution to. Our in-house engineers have made suggestions, but I wanted to reach out and see if we are on the same page. We hope to replace their equipment in the future, but for now, we are just trying to figure out a temporary solution.

The problem is they are getting material (PVC Dust) conglomerating in different locations inside the baghouse. It commonly occurs at the top, near the cell plate, on the bags, and even near the access door. They had several professionals/engineers come and look at it, but have only been advised to change bag styles, add ground wires to bags, ground the baghouse, and numerous other ideas that have not remedied the problem. After a brief phone conference with our engineer and their plant manager, we determined the air inlet was coming in below the bags (at hopper) and not allowing the particles to fall with gravity. The particles are then building up at various locations and sticking together, developing a honeycomb effect. We came up with three solutions.

1. Lower airflow with the damper and decrease airflow into the baghouse until the material can utilize gravity to fall.
2. Shut off the baghouse once a day and then pulse the bags to ensure no build-up.
3. Move the inlet closer (higher) to the cell plate (also adding a baffle so direct air doesn't damage bags).

Baghouse Information:

100 Poly Filters Bags (1257 Area)
4:1 Air to Cloth Ratio
5028 CFM
Dimensions (84" W 130" L)
Moisture Content: 0.03lb
Temperature Avg: 95F
Location: Outdoors
No Static
No Moisture
Good airflow at all times

Any other suggestions on this would be appreciated, or if I am missing something, please advise. Thank you in advance.



Michael Iverson
Equipment Manager

U.S. Air Filtration, Inc.
951-417-1745
mike@usairfiltration.com

 

[Compositepro]

Pictures would help a lot.

Are you sure that the compressed air for pulsing the bags is dry? Water in compressed air is a very common problem.

You might consider lowering your pulse rate. This will allow a thicker and denser filter cake to develop before each pulse, which is more likely to fall into the hopper.

 

[U.S. Air Filtration Inc.]

Thanks Compositepro for your input on this issue. Unfortunately I do not have photographs, just a description of the problem. We have requested this, but haven't received anything back. They mentioned moisture tests have been done, but the test results indicated little to no moisture inside, or outside, of the filter bags. As for filter cake, the build-up seldom appears on the bags themselves, but it occurs more often in the upper corners of the baghouse. The build-up usually starts at the wall and will build up to a point where it connects to the filters. I don't know if pulse frequency would be the issue since it is determined by negative and positive noncorrosive pressure fluctuations inside the baghouse. I will ask them more details on how often the bags are pulsed, and if they have the option to use a timer board vs. their Magnehelic pressure gauge.

Thanks again!

Michael Iverson
Equipment Manager

U.S. Air Filtration, Inc.
951-417-1745
mike@usairfiltration.com

 

[Compositepro]

Magnehelic control will usually give a lower pulse rate than a timed pulse unless it isn't set correctly or the fabric is plugged, leading to frequent pulsing. The point to allowing a filter cake to develop is to let fine particles to agglomerate into coarser ones before pulsing. Too frequent pulsing will re-disperse fines that cannot settle against the inlet air-flow, so they stay suspended until they stick somewhere other than the fabric or hopper. Then the pulsing will just compact the suspended powder against the walls.

Magnehelic control also implies that all of the bags are pulsed at once, which is not desirable. This results in all airflow through the baghouse coming to a momentary stop. The rush of air back though the bags after the pulse is done will tend to reattach the powder to the filter bag rather than allowing it drop. Zoned pulsing might help.

 

[U.S. Air Filtration Inc.]

I have talked to the Plant Manager several times about this issue. After reading your post, I called back to discuss pulse frequencies, but was transferred to a person in maintenance who has been hands on with the collector for the past 7 years. He stated the Plant Manager gave him all three solutions to try last week. He said when they lowered the airflow with the damper, they got less build-up. He said it still looked as if it still might build-up if they continued this process, but at a lower rate. He said they finally scheduled a shutdown time at night where they would shut off the fan and pulse the bags one time. He said they started this on Sunday, and they have not had any build-up at this point. He said since they know the direction of airflow is the problem, they will most likely move the ducting to the top of the baghouse to make sure the debris falls to the hopper. He said there goal is to not shut-down and spend less time on the dust collector and more time in operation.

I asked him about the pulse rate on the bags. He stated at one point, they were on a timer and each diaphragm valve would pulse for .01 seconds, in order, not all at one time. He understood filter cake and why it is important to have it. He said they moved to a Magnehelic control as one of their options over the timer board. He stated the valves are integral and use a control board that ensures they fire in zones, and not all at once. When we design our multi-channel boards, unless the customer requests it, pulse at intervals, and not all at one time.

You are very knowledgeable in this field, and I appreciate your feedback and assistance. I hope re-routing the inlet solves their problem, but if not, we may need to explore possible pulsing issues.

Michael Iverson
Equipment Manager

U.S. Air Filtration, Inc.
951-417-1745
mike@usairfiltration.com

 

[chicopee]

Certain coal fired plants use shakers in their baghouse.