Hot gases and dust leaving the dryer drum are drawn by the exhaust fan through the baghouse filter. The dust collection line matters not only for environmental regulations but for the plant itself: the draught balance determines how the burner burns, and the fine material captured in the filter is recovered as filler in most plants. This page covers the basics of baghouse and exhaust fan automation.
Parts of the dust collection line
- Exhaust fan: creates draught through the drum and filter. It is the heart of the line; if the fan stops, the burner must stop too.
- Exhaust damper: adjusts the draught. Too open and heat escapes through the stack; too closed and pressure builds up in the drum.
- Fresh-air damper: if gas temperature rises above what the filter bags can withstand, it dilutes the gas with outside air to protect the bags.
- Baghouse and jet-pulse cleaning: dust collecting on the bag surface is knocked off row by row with pulses of compressed air and falls into the hoppers below.
Why the draught balance matters so much
The burner burns steadily in a drum where combustion air and gases are drawn out properly. With too little draught, flame and dust blow out of the drum inlet; with too much, heat is thrown out of the stack before it reaches the aggregate and fuel consumption rises. The damper position has to be considered together with the burner output. The automation’s job is to let the operator make this adjustment within safe limits and never allow the burner to ignite before the fan runs.
Jet-pulse cleaning and bag life
As the bags get dirty, flow through the filter becomes harder, differential pressure rises and draught drops. Jet-pulse cleaning blows compressed air into the bag rows at set intervals to remove the dirt. Too infrequent and draught falls; too frequent and the bags wear out needlessly and compressed air is wasted. A properly configured cleaning sequence and interval directly affects bag life.
Temperature protection
Filter bags have an upper temperature limit. If the burner setting runs away or too little material enters the drum, gas temperature rises quickly. Opening the fresh-air damper in time — and reducing or stopping the burner if necessary — keeps the bags from burning. This protection should not be left to the operator’s attention.
How DKT APlants handles the dust collection line
DKT APlants controls the exhaust fan, exhaust damper, fresh-air damper and jet-pulse cleaning valves from the software. The filter cleaning carriage and robot fan are on the same screen. Thanks to the machine priority system the burner cannot ignite before the fan runs; if there is a thermal fault on the fan or filter equipment, the related chain stops and the fault is shown on screen.
Frequently asked questions
What happens if the exhaust fan stops in an asphalt plant?
Draught from the drum is lost and flame and hot gases can blow back. The burner must therefore stop safely when the exhaust fan stops; the automation enforces this dependency through the priority sequence.
How often should the baghouse be cleaned?
The cleaning interval is set according to dust load and differential pressure. The goal is to clean often enough not to lose draught, but not so often that the bags wear out needlessly.
What is the fresh-air damper for?
When the gas temperature reaching the filter approaches the bags’ limit, it lets outside air in to cool the gas and protect the bags.
What happens to the dust captured in the filter?
In most plants the fine material captured in the filter is recovered as filler and fed back into the mix in a controlled way.
Related pages
- Asphalt plant control software (DKT APlants)
- Burner and dryer drum control
- Asphalt plant cold feed and dosing
- Plant automation retrofit
Send us your plant’s IO list
The plant’s input/output list and PLC model are enough. We check compatibility together, set up DKT APlants for your plant and show it running in simulation. WhatsApp: +90 547 909 99 90