An effective dust extraction system must capture dust close to the point where it is generated, transport it safely through the duct network, separate it from the airflow and discharge the collected material without interrupting production.
The design should not begin with the fan or collector alone. The hood, airflow, ducting, filtration, fan, hopper and control system must function as one integrated arrangement.
Design sequence:
Dust-source assessment → hood design → airflow calculation → duct design → filtration → fan selection → dust discharge → controls → commissioning
1. Identify Every Dust Source
Begin by locating all points where dust becomes airborne.
Typical sources:
- Conveyor transfer points
- Crushers and screens
- Bag-dumping stations
- Mixer charging
- Grinding and cutting machines
- Silo filling
- Packing operations
- Truck or hopper loading
Record for each source:
- Material type
- Dust characteristics
- Operating temperature
- Moisture conditions
- Operating duration
- Open or enclosed condition
- Simultaneous operation
- Available space
The system airflow should be based on actual operating conditions rather than summing all equipment.
2. Contain the Dust Where Possible
Containment reduces airflow requirement and improves system efficiency.
- Conveyor skirt boards
- Flexible curtains
- Machine covers
- Bag-dump enclosures
- Mixer covers
- Partial enclosures
A partially enclosed system is easier to control than an open process.
3. Position the Extraction Hood Correctly
- Close to dust source
- Aligned with dust movement
- Away from cross-drafts
- Protect operator breathing zone
- Avoid excessive material pickup
Poor hood design cannot be corrected by increasing fan size.
4. Calculate the Required Airflow
Basic formula:
Q = A × V
- Q = airflow
- A = hood area
- V = air velocity
Also consider:
- Hood design
- Leakage
- Dust behavior
- Cross drafts
- Thermal effects
- Dust surges
The goal is effective dust capture with minimum airflow.
5. Define Simultaneous Operation
Identify which dust points operate together.
- Continuous vs intermittent operation
- Use of dampers
- Use of VFD for airflow control
Avoid airflow reduction that may cause dust settling.
6. Design the Duct Network
The duct system must transport dust efficiently.
Avoid:
- Sharp bends
- Sudden size changes
- Long flat runs
- Poor branch entry
- Excess flexible ducts
Duct velocity considerations:
Low velocity causes:
- Dust settling
- Blockage
- Weak suction
High velocity causes:
- High pressure loss
- Fan power increase
- Abrasion
- Noise
7. Calculate Total Pressure Loss
The fan must overcome total system resistance.
- Hoods
- Ducts
- Elbows
- Dampers
- Filters
- Exhaust
Include clean and dirty filter conditions in calculation.
8. Select Collector and Filter Media
- Pulse-jet bag filters
- Cartridge collectors
- Cyclone + filter systems
- Compact collectors
Selection factors:
- Dust concentration
- Particle size
- Temperature
- Moisture
- Chemical properties
- Abrasiveness
- Combustibility
Air-to-cloth ratio:
Airflow ÷ Filter area
9. Select the Fan
- Airflow requirement
- Total pressure
- Efficiency
- Motor rating
- Speed control
A larger motor alone does not improve system performance.
10. Hopper and Dust Discharge
- Rotary airlock
- Screw conveyor
- Slide gate
- Dust bins or bags
The system must maintain an air seal during discharge.
11. Monitoring and Controls
- Differential pressure sensor
- Pulse controller
- Level sensors
- Motor protection
- Temperature monitoring
- Alarms and interlocks
12. Maintenance Access
- Filter replacement access
- Fan servicing
- Hopper cleaning
- Duct inspection
Proper access improves maintenance quality and reduces downtime.
Commissioning the System
Before start-up:
- Check duct installation
- Confirm filter placement
- Verify fan rotation
- Check dampers
- Test discharge system
Measure during commissioning:
- Airflow
- Pressure
- Fan current
- Filter pressure
Record baseline values for maintenance reference.
Design Checklist
- All dust sources identified
- Enclosures provided
- Hoods correctly positioned
- Airflow calculated
- Duct velocity suitable
- Pressure loss calculated
- Filter selected correctly
- Fan selected properly
- Discharge system adequate
- Maintenance access available
FAQs
What is the first step?
Identify all dust-generation points and understand dust behavior.
How is airflow calculated?
Based on hood area and velocity, adjusted for real conditions.
Why enclosure is important?
It reduces dust escape and airflow requirement.
How is duct size selected?
Based on airflow and required transport velocity.
How is the fan selected?
Based on airflow and total system pressure.
Should system be tested?
Yes, commissioning ensures correct performance.