Dust Collection Guide

May, 2009
Tire Recycling plant, Dunnville, Ontario
Equipment; Baghouse Dust collector collecting from hammer mills
Dust; rubber, synthetic fibers, steel wire, carbon

Occasionally, the filters in a shaker or pulse cleaning dust collector will lose their efficacy because of moisture or other liquids entering the collector.
1) The base filter media will be coated with moisture. In general if the media does not absorb moisture the filter elements can be recovered if the pressure drop has not reached levels over 15-29 inches depending on dust characteristics. The load of dust must be then stopped and the flow through the collector is reduced to between 20% to 50% of the normal gas flow. These conditions should continue until the moisture is evaporated. The media cake will have been restored enough to allow reverse air to flow through the media and increase the permeability. Repeated cleanings will restore the media in the cleaning process so that it will be able to support an effective filter cake. This normally requires 10 to 40 cleaning cycles. The pressure drop should be monitored as it is possible to over clean the bags so that dust may come out the clean side and cause problems if the exhaust air is re-circulated to a work area. This procedure is effective if the media has not been physically or chemically attacked, (cellulose media will swell and lose its permeability when subject to repeated wet and dry cycles). Chemical or solvent attack presents more complex problems where the section of the media becomes critical. If the pressure drop is too high before the above process has begun, there is good possibility the dust can have imbedded itself in the fibers where the cleaning system can not restore the permeability enough to recover the filter elements.
2) The next possibility of blinding is due to a “painting” phenomenon. In that case the dust reaches the cleaning element surface in a paste or liquid paint form. It does not form a permeable cake. Usually there will be some powdered granulated dust that will be mixed with the paste. The ratio of liquid to powdered or granulated powder is critical. If the ratio of dust is very high, the collector will operate normally. Many processes do have occasional loads of liquid dust such as when dew points are high. The pressure drop rises and falls temporarily but the operations are satisfactory.
Our examination and testing of the bags revealed that in this process in which automotive tires were recycled to recover the metal and the rubber through hammer mills there was a dust/paste mixture reaching our continuous cleaning pulse jet collector that had a high proportion of liquid paste compared to the granulated powder. The bags were completely blinded. We sent them through normal fabric laundering process that removed a lot of the dust but were still badly blinded. We concluded chemical attack but the base fabric was as strong as a brand new bag.

We then subjected the bag to some deep cleaning procedures that are used to clean grease and sludge from some commercial and industrial processes. It was a last ditch effort to investigate the problem. We were applied our technology from related fields to develop a procedure to clean the bags and restore the media to virgin conditions. Cleaning the bags is challenging and can be somewhat messy. In addition it has some other hazards notably those involving the risk of fire and toxicity when inhaled. To address all these concerns we are proposing a three step cleaning process which addresses these concerns. These we shall refer to as coarse cleaning, medium cleaning and fine cleaning.

These are listed below.
1) Coarse cleaning is meant to remove the most of the dirt (by weight) clinging on the bags. Our first step was to separate the bags into groups of five and lay them on a concrete floor with three inches between the bags when they are laid side by side. The worker starts at the open top of each bag with his feet standing on the bags with about a foot between his shoes to brush the dirt into the space between the bags until he comes to the closed end.
2) This procedure is repeated for all five bags in the set. The dust is then swept with a hand brush and dust pan to be disposed of or recycled to the process.
3) The bags are turned over and the same procedure applied again.
4) Medium cleaning is meant to remove much of the remaining dust. Tie the open ends of the bags with a cord and put them in a laundry tub with clothes washing detergent. Swish them around in the tub and then rinse.
5) Final cleaning will get out the hardened paste by dissolving the hardened paste {latex type paint} it also can be used to strip latex paint from a piece of canvas. We use a surfactant compound that we use in cleaning grease in commercial [restaurant grills.] and high speed industrial machining to collect submicron smoke and oil mist. We use these in our other product lines. The surfactant powder can be ordered from our lab facility in Charlotte, NC.
6) After the bags are rinsed in step 4 above they are again put in a laundry tub with one cup of the surfactant powder in each tub, if multiple tubs are used. They are swished around and rinsed as in the medium wash.
7) Finally, they are hung up to dry.
We can check one of the cleaned bags to be sure that they have recovered enough to use. You can send the bag to our office in Waterloo to test permeability.
9) Give one pint of Canadian whisky to each of the workers who cleaned the bloody bags.

Retrofit and Dust Collector Consulting