The Importance of Air Separation in Hulling
After a rice huller completes paddy dehusking, the discharge is a mixture of brown rice, husks, and a small amount of unhulled grains. Efficiently separating these three components directly affects rice yield, quality, and production environment. Air separation (pneumatic separation) is currently the most common and efficient method.
Basic Principles of Air Separation
Air separation utilizes the specific gravity difference and suspension velocity difference between husks and brown rice:
- Husks: Light specific gravity (approx. 100-150 kg/m³), suspension velocity 2-3 m/s
- Brown Rice: Heavy specific gravity (approx. 800 kg/m³), suspension velocity 8-12 m/s
- Unhulled Paddy: Intermediate specific gravity, suspension velocity 6-8 m/s
By controlling airflow velocity between the suspension velocities of husks and brown rice, light husks are blown away while heavy brown rice and unhulled grains settle, achieving separation.
Air Volume Calculation and Fan Selection
Air Volume Calculation
Required air volume for the hulling section can be estimated using:
Q = q × G
Where:
- Q = Total air volume (m³/h)
- q = Air volume per ton of paddy, typically 150-250 m³/ton
- G = Huller hourly processing capacity (tons/hour)
Example: A huller with 5 tons/hour capacity
- Taking q = 200 m³/ton
- Q = 200 × 5 = 1000 m³/h
Air Pressure Calculation
Air network system resistance includes:
- Pipeline friction resistance
- Local resistance from elbows, reducers, etc.
- Separator (settling chamber or cyclone) resistance
- Dust collector resistance
Total resistance is generally 1500-2500 Pa. Fan selection should include 15%-20% margin.
Fan Selection Recommendations
| Huller Capacity | Air Volume Range | Pressure Range | Recommended Fan Power | |-----------------|------------------|----------------|----------------------| | 1-3 t/h | 400-800 m³/h | 1500-2000 Pa | 3-5.5 kW | | 4-6 t/h | 800-1500 m³/h | 1800-2200 Pa | 5.5-11 kW | | 8-12 t/h | 1500-2500 m³/h | 2000-2500 Pa | 11-18.5 kW |
Core Airflow Adjustment Techniques
Technique 1: Adjust by Rice Variety
Different rice varieties have different specific gravity differences between husk and brown rice:
- Japonica: Lighter husks, slightly reduce airflow
- Indica: Heavier husks with stronger adhesion, need slightly higher airflow
- Glutinous: Tight husk-brown rice bond, increase airflow with vibrating separation
Technique 2: Adjust by Season and Moisture
Paddy moisture significantly affects air separation:
| Moisture Range | Separation Characteristics | Adjustment Recommendation | |----------------|---------------------------|---------------------------| | < 13% | Husks become brittle, produce fine dust | Slightly reduce airflow, increase dust collection | | 13%-15% | Ideal range, good separation | Run at standard airflow | | > 16% | Husks become tough, harder to blow away | Increase airflow, check fan speed |
Technique 3: Real-Time Observation-Based Adjustment
Operators should learn to judge airflow appropriateness through observation:
Signs of Excessive Airflow:
- Husks blown out with brown rice at discharge
- Increased impurity in brown rice
- High fan current
- Excessive pipeline wear from high velocity
Signs of Insufficient Airflow:
- Excessive brown rice in husk discharge (high grain content)
- Material accumulation in separator
- Low fan current
- Dust-filled workshop
Signs of Proper Airflow:
- Husks fully blown away, discharged in fluffy state
- Essentially no husks in brown rice discharge
- Grain content in husk < 0.5%
- No material accumulation in separator
Technique 4: Fine Damper Adjustment
Most huller air separation systems have adjustable dampers:
- Inlet damper: Controls total airflow, typically 70%-90% open
- Supplemental damper: Adjusts airflow distribution in separation chamber
- Exhaust damper: Coordinates with dust collector to regulate system negative pressure
Adjustment Principles:
- First adjust total airflow for overall separation near target
- Then adjust distribution dampers to optimize chamber flow field
- Each adjustment should be moderate; observe for 5-10 minutes before continuing
- Keep records and establish optimal parameter profiles for different varieties
Separation Effect Optimization Solutions
Solution 1: Optimize Separator Structure
Traditional settling chambers have limited efficiency. Consider upgrades:
- Add deflectors: More uniform airflow distribution, reduce short-circuiting and dead zones
- Install flow equalizers: Perforated plates at inlet to balance velocity
- Expand separation cross-section: Lower airflow velocity, increase separation time
- Use cyclone separators: For 5+ t/h capacity, cyclones offer higher efficiency
Solution 2: Air Network System Optimization
- Shorten pipelines: Shorter ducts mean less resistance and airflow loss
- Reduce elbows: Each 90° elbow adds approximately 50-100 Pa resistance
- Use smooth pipes: Galvanized steel or PVC has less resistance than rough concrete ducts
- Properly position suction inlets: Inlets should be where husks most easily become airborne
Solution 3: Combined Use with Vibrating Screens
For fine mixtures difficult to completely separate by air alone, add vibrating screens:
- Paddy-brown rice separator: Separates unhulled grains from brown rice
- Bran-broken rice separator: Separates bran from broken rice
- Air-screen combination: First remove most husks by air, then fine separation by screening
Common Air Separation Problems and Solutions
| Problem | Cause | Solution | |---------|-------|----------| | Excessive grain in husk | Insufficient airflow, duct blockage | Clear blockage, open damper wider | | Excessive husk in brown rice | Excessive airflow, poor separator design | Reduce damper, modify deflectors | | Excessive fan vibration | Impeller dust buildup, bearing wear | Clean impeller, replace bearings | | Pipeline blockage | Low velocity, excessive moisture | Increase velocity, enhance dehumidification | | Excessive workshop dust | Air leaks, poor dust collection | Seal leaks, check dust collector |
Air Separation System Maintenance
Daily:
- Check fan operation for smoothness
- Observe separation effect, record abnormalities
- Clean fan inlet filter screens
Weekly:
- Check ducts for damage or air leaks
- Clean accumulated bran powder in ducts
- Check fan belt tension
Monthly:
- Check fan impeller for wear or dust buildup
- Check if dust collector filter bags need replacement
- Measure and record velocities at various points
Zhejiang Lianggong's Air Separation Solutions
Zhejiang Lianggong Machinery's rice hullers are equipped with efficient air separation systems:
- Optimized duct design: CFD simulation optimized for uniform airflow distribution
- High-efficiency fans: Dedicated centrifugal fans with high efficiency and low noise
- Intelligent adjustment: Pneumatic hullers automatically adjust airflow for different conditions
- Low-loss separation: Grain content in husk stably controlled below 0.5%
For detailed technical parameters of air separation systems, please call 0575-87335525.
