Reusing dust / reducing carbonate levels in dust

(not verified)
Posted in: , on 11. Jul. 2003 - 17:14

Our current set-up involves a vacuum line that sucks dust off the punch of a press and sends it to a dust collector. The dust is dumped into sealed containers at the end of every run. We would like to be able to reuse 100% of this dust in our process, but we are not able to do that right now.

The problem is that carbonate levels in the dust shoot up when it is exposed to ambient air for too long (especially if the air is out of our temp/relative humidity specifications). We have tested the dust in the sealed containers, and we have found that the carbonate level doesn't increase while it is in the container. Therefore, the carbonation happens inside the dust collector.

There are only a couple of controls I can play around with to try to fix this problem. So far, I have added a temp/RH gauge to the dust collector so we can monitor conditions inside the collector, in hopes that maybe that is the source of the problem. Other things I know I can try are to change the flow rate of the vaccuum line, and to change the number of times the dust is dumped during a run.

Does anyone have any suggestions as to what else I can do? Am I looking at having to change the whole system, or it is just a small adjustment that I haven't thought of?

Thanks for all your feedback!

(not verified)

Possible Solution

Posted on 12. Jul. 2003 - 01:32


Without knowing more about your product and chemistry, I can only provide you with a possible factor. Assuming that your dust collector is of the pulse jet type (filters are cleaned using compressed air), this may be the source of your problem. There are several possibilites. One, the compressed air itself may be wet (ie., doesn't have a dryer or dryer isn't sufficent). The second possibility is even if the compressed air itself is dry enough, that the expansion cooling of the released gas is pushing the air in the dust collector down through the dew point (perhaps only in certain sections of the collector - in particular on the filter cake on the bags). Another issue is conditions in your collector when it isn't in use. You really shouldn't have material in the collector when off line but the reality is that everyone does. Depending upon the sensitivity of your material to temp / humidity, heat tracing the hopper or perhaps the entire collector may be in order. Finally, since it is likely that your system has the fan on the "clean side", your problems may be cause by leakage into the collector.

The solution to the first issue is self evident. Improve the quality of compressed air (ie., lower dew point). The second issue is more problematical. If the collected material is of sufficient value to make a system rework worthwhile, you might consider getting away from a pulse jet collector design. Shaker type collectors are still around although rarely used since they are considerably larger and more expensive but they don't use compressed air (they clean off line using mechanical shaking of the bags) and won't have the problem. An alternate, would be to put a mechanical collector (cyclone or multiclone) in front of your existing dust collector and capture the reusable material at that point and scrap whatever gets to the dust collector (mostly the smaller size particles). You may have to change fans (and make sure that your collector will handle the higher negative pressure) but it would be less expensive than going to a shaker. The last two possibilities are also self evident with respect to correction.

Hope this gives you some ideas.

Keith Simon