The baghouse or bag filter is a device to filter air in asphalt mixing plant. It is the best pollution control device for asphalt plants. It uses number of bags in a chamber to filter air. The air is made to pass through the bags and as a result all the dust will get stuck to the bags.
Most bag filters will have elongated cylindrical bags for dust collection. These bags will be placed inside cages for support. The gases will pass from the outer end of the bag to the inside. This process will make the dust stick on the outer end of the bag filter. Woven or felted fabric is used as a filter medium.
Baghouses, have been doing dust control in asphalt plant for many years, and they continue their work even today. The basic concept is the same, new filter materials and new ways to solve problems make them more adaptable than before.
Use of bag filter in asphalt plant:
Bag filter for asphalt plant is used for pollution control. It will help eliminate dist and harmful gases. Dust is produced from aggregates and most of the time we don’t want additional dust to get into the final product as it will spoil the final product. Harmful gases are emitted as a result of the burner that fires the drum. These gases along with the dust is made to pass through the filter bags for cleaning.
Bag filters act as secondary pollution control device. The primary dust collectors are cyclone separators. These primary separators trap heavier dust by sucking and creating cyclone inside the chamber. The lighter dust and harmful gases however will not be trapped by this. This is where the importance of bag filters for asphalt mixing plants comes into existence. The gas after escaping from the cyclone separator will move towards the main chamber. All bag houses will have a tube sheet or frame on which the bags are hanging. There are baffle plates on the inside. These baffle plates will keep the heavy dust away and not allow them to damage the filters. As the bag filter will be continuously used, the dust passing through it will be slowly and steadily stuck on top of the filter media. This will create a rise in pressure and the cleaning mechanism will help clean the bags regularly.
For cleaning the bags the rotating system of fan on top of the filter allows cleaning of only 8 bags at a time. This is good as less number of bags get good air pressure and hence cleaning process is very efficient. The air pulse emitted by the fan on top will help in expelling the dust cake that will be formed on outside of the bags. There is an inlet for dirty air and outlet for clean air. At the bottom the bag house will have an opening to throw the dust collected.
This process allows us to use the bags continuously without any problem. It is very cost effective and effective.
Maintenance of filter bags of asphalt plants
Filter bags in asphalt mixers are used exposed to extreme temperatures and aggressive corrosive gases. There are some factory that put strain on the filter bags these are frequent fluctuations in the temperature, start up and shutting down the equipment, switching different fuels. Sometimes harsh environment and high dust and moisture content also put a lot of pressure on the filter materials.
The pressure inside the bag filter chamber has to be maintained so that bags keep working smoothly. However in most of the cases customers want to use the equipment even if it is raining and this can prove to be disastrous. There are cases where bag fuel has caused severe damage to the bag filters and they required to be replaced immediately.
Replacing the bags is a time consuming and tedious job that requires the plant to be shut down and is a dirty job. All the bags have to be removed from the top of the bag filter and then new bags have to be replaced in the existing cage. When cages are involved, the job is tedious.
When you have the right type of bag filter fitted with your equipment you are assured of tension free performance. Do discuss with us if you want us to fit bag filters in any of your existing asphalt plants.