Baghouse – Typically removes dust from the drier that passes the No. 200 sieve, utilizing a principle similar to a giant vacuum cleaner. Exhaust fans pull dust laden air through 100 or more long metal cages, covered with cloth bags to catch
sections are collecting dust; others are using reverse air, a shaker system or a pulse cleaning system to release dust from the outside of the bags. Dust then falls to the floor of the baghouse and travels by auger or conveyor to a central point outside of the system. Caltrans allows two options for the collected dust at this point in the process. The collected dust can either be rejected into a waste pond or returned to the pugmill as described in the following section, “Baghouse Dust Return”. If any of the
collected fines stored in a silo
from the baghouse are to be used in the completed mix, they then metered by mass (weight) as a portion of the dry aggregate.
must be The AC
inspector must be sure that is equipped with an auger
baghouse fines are or pipe connecting
returned to the hot elevator. If a baghouse to the hot elevator, an
inline inspection gate must remain open during all hours baghouse dust is not being returned to the hot elevator.
A few other items the plant inspector should be aware of when a baghouse dust collection system is in use at the AC plant (batch or continuous mix).
1. If the aggregate entering the drier drum has a high moisture content, the fines will have a tendency to cake onto the outside of the bags, reducing the overall efficiency of the dust collection system.
If incomplete combustion of the burner fuel is occurring, an oily film will permeate the bags, reducing the overall efficiency of the dust collection system. The oily bags may need to be removed and cleaned by a professional service or replaced.
If the aggregate drying temperature is too high, damage to the bags will occur from overheating. The bags may become singed or develop holes, compromising the efficiency of the dust collection system and possibly creating air quality issues. If the bags are damaged in this manner, a light sensitive powder can be introduced into the baghouse air system. Then a monochromatic light (blacklight) is used on each bag to find the ones containing holes.
4. The plant inspector should verify that dust return is at a uniform rate, surges in dust return should be brought to the plant operator’s attention and corrected as soon as possible. Caltrans Standard Specifications and contract special provision prohibit surges in the dust return system.