The airflow classifier is a key equipment for achieving fine classification
in large-scale quartz sand production lines (daily processing capacity ≥ 3000
tons), especially suitable for the classification requirements of photovoltaic
and semiconductor grade high-purity quartz sand (SiO ₂ purity ≥ 99.995%)
(requiring classification accuracy deviation ≤ 5%, fine powder recovery rate
above 400 mesh ≥ 85%), directly determining the quality of finished sand grading
and its adaptability to high-end applications. If there is poor grading accuracy
(deviation exceeding 10%) and low recovery rate of fine powder (less than 70%),
it will lead to disorder of finished product grading, obstruction of high-end
market access, and exacerbation of raw material waste. Based on the lightweight
and highly dispersed characteristics of high-purity quartz sand particles, a
three-step optimization plan is summarized to improve classification efficiency
and accuracy.
Step 1: Optimize the airflow system configuration and strengthen the graded
core power
Insufficient airflow velocity, imbalanced airflow, or uneven airflow
distribution are the core reasons for poor classification accuracy, and targeted
optimization of airflow parameters and flow structures is needed.
Airflow parameters and power adaptation: ordinary centrifugal fans are
selected, with air pressure below 12kPa, and insufficient airflow penetration to
drive fine powder classification; The air volume fluctuates by more than 15%,
and the graded cutting particle size is unstable; If the airflow speed is below
18m/s, the fine powder cannot be effectively separated. Replace the
high-pressure Roots blower (with a wind pressure of 15-18kPa) and equip it with
a variable frequency speed control system to stabilize the airflow velocity at
22-26m/s; Accurately adjust the air volume according to the standard of
"800-1000m ³ per ton of sand", and dynamically adjust it based on the target
particle size. When grading fine powder with 400 mesh, the upper limit of air
volume is taken, and when grading medium sand with 200 mesh, the lower limit is
taken.
Optimization of airflow distribution and circulation: A single air inlet
leads to airflow deviation, resulting in "blind spots" in the classification
chamber and ineffective sorting of local particles; The deviation of the guide
plate angle exceeds 3 °, and the airflow trajectory is disordered. Install an
annular homogenizer to evenly distribute the airflow along the circumference of
the grading chamber; Calibrate the angle of the deflector to 15-18 ° and
optimize the airflow rotation trajectory; Install an airflow stabilizer in the
intake duct to reduce air volume fluctuations and ensure stable classification
environment.
Step 2: Calibrate the grading structure parameters to improve grading
accuracy
Improper speed of the grading wheel, wear or poor sealing of the grading
chamber structure can cause fluctuations in the grading effect, requiring
precise regulation and maintenance.
Optimization of grading wheel speed and structure: If the speed is below
2800r/min, it cannot effectively cut fine particles, and coarse powder is mixed
into fine powder products; Above 4200r/min, the centrifugal force is too high,
and some qualified fine powders are mistakenly judged as coarse powders and
discharged; The wear of the grading wheel blades exceeds 2mm, and the efficiency
of airflow cutting decreases. Stabilize the speed at 3200-3800r/min through a
frequency conversion system, with the upper limit set for fine powder grading
and the lower limit set for medium sand grading; Replace the high hardness
wear-resistant steel blades, and ensure that the end face runout deviation after
blade installation is ≤ 0.2mm to ensure even airflow cutting.
Classification chamber sealing and inner wall protection: The classification
chamber sealing components are aging, and the external air infiltration rate
exceeds 8%, which damages the stability of the airflow; The inner wall lacks
wear-resistant coating, and quartz sand erosion causes deformation of the cavity
wall and deviation of the airflow trajectory. Replace the fluororubber seal and
install a sealing pressure ring to control the air infiltration rate within 3%;
Spray ceramic wear-resistant coating (thickness 3-5mm) on the inner wall of the
cavity to reduce wear and deformation, ensuring the stability of the size of the
graded cavity structure.
Step 3: Optimize feed control and pretreatment to ensure grading
stability
Overloading of feed volume, particle agglomeration, or insufficient
pre-treatment of raw materials can exacerbate fluctuations in grading
efficiency, and front-end control is necessary.
Control of feeding quantity and feeding method: If the feeding quantity
exceeds the rated value (such as rated 150t/h, actual 180t/h), the particle
concentration in the classification chamber is too high, and the airflow cannot
penetrate, resulting in "entrainment classification"; The lack of a dispersing
device at the feed inlet resulted in incomplete classification due to particle
agglomeration. Strictly control the amount with an electronic belt scale to
maintain the feed rate at 85% -95% of the rated value; Install an
electromagnetic vibration disperser, combined with high-pressure airflow pre
dispersion, to control the particle agglomeration rate below 5%.
Raw material pretreatment and impurity control: Coarse particles with a
particle size exceeding 5mm are mixed into the raw material, which can easily
collide with the grading wheel and cause structural damage; Excessive dust
content pollutes the airflow system and affects grading accuracy. Install a
high-precision pre screening machine (with a mesh size of 100) before the
classifier to remove coarse particles and impurities; Equipped with a pulse bag
filter to control the dust content of the feed below 10mg/m ³; After drying, the
moisture content of the raw materials should be ≤ 0.5% to avoid particle
agglomeration caused by moisture.
Daily maintenance should pay attention to: checking the airflow speed,
grading accuracy, and fine powder recovery rate every day; Clean up residual
dust in the grading chamber every week and check the integrity of the seals;
Calibrate the speed and airflow parameters of the grading wheel every month, and
check the wear of the blades; Conduct comprehensive maintenance on fans and dust
collectors every quarter. By implementing the above measures, the classification
accuracy deviation can be stabilized within 4%, the recovery rate of 400 mesh
fine powder can be increased to over 90%, ensuring that the quality of
photovoltaic/semiconductor grade high-purity quartz sand meets the standards and
is suitable for the fine classification needs of large-scale production
lines.