Airflow screening is the core grading equipment for fracturing sand
production, responsible for screening products with precise particle size ranges
such as 20-40 mesh and 40-70 mesh (requiring a particle size qualification rate
of ≥ 98%), which directly affects the fracturing construction effect of oil and
gas wells. If the screening accuracy is low (with a pass rate of less than 90%)
and the screen mesh is frequently clogged (cleaned more than twice per hour), it
will lead to product degradation and a sharp drop in production efficiency.
Based on the high hardness and strong fluidity of fracturing sand (quartz
sand/ceramic sand), a three-step investigation method is summarized to quickly
restore screening performance.
Step 1: Optimize the airflow system and air pressure control - airflow
stability is the foundation of screening
Abnormal wind pressure, air volume, and airflow distribution are the main
reasons for low accuracy.
Insufficient or fluctuating wind pressure: When the working wind pressure is
below 0.3MPa, the airflow cannot effectively blow up fine powder, and the sieve
mesh is blocked; The wind pressure fluctuation exceeds 0.05MPa, the grading
threshold is unstable, and the coarse powder is mixed with qualified products.
Adjust the parameters of the Roots blower to stabilize the air pressure at
0.35-0.45MPa, and install a stabilizing tank to buffer pressure fluctuations;
Optimize the air duct through the airflow distribution plate to ensure uniform
airflow on the screen surface (wind speed deviation ≤ 0.2m/s), and avoid local
airflow from forcefully blowing away qualified sand particles.
Improper airflow direction or nozzle angle: The nozzle is facing vertically
towards the sieve, which can easily push coarse particles into the sieve holes
and cause blockage; The oblique blowing angle of the airflow exceeds 30 °,
making it difficult to separate fine powder. Adjust the nozzle angle to 15 ° -20
° and arrange it in a "spiral" pattern, blowing away fine powder without
impacting the sieve mesh; Install a blowback device (with a wind pressure of
0.2MPa) under the sieve, blow back every 5 minutes to prevent hole blockage.
Step 2: Calibrate the sieve structure and screening parameters - the core
components determine the accuracy
Improper mesh specifications and speed settings can exacerbate screening
problems.
Mismatched mesh material or mesh size: Ordinary stainless steel mesh has poor
wear resistance (service life<50 hours), and mesh deformation can easily lead
to particle size deviation; The deviation of the mesh size exceeds 5% (if 40
mesh is required, actually 38 mesh), and the qualified range is out of control.
Replace the polyurethane composite screen mesh (with 4 times higher wear
resistance than stainless steel), accurately match the mesh size according to
the target particle size (20 mesh corresponds to 850 μ m, 40 mesh corresponds to
425 μ m), and calibrate the mesh tension with a tension meter during
installation (maintain 15-20N/cm) to avoid mesh relaxation and deformation.
The rotation speed of the screening cylinder is too fast or too slow: when
the rotation speed exceeds 60r/min, the material stays in the screening cylinder
for less than 3 seconds, resulting in insufficient screening; Below 40r/min, the
material accumulates on the screen surface, and the risk of hole blockage
increases dramatically. Use a tachometer to detect and adjust to 45-55r/min, and
achieve stepless speed regulation through a frequency converter; Adapt according
to the type of fracturing sand: choose high speed (50-55 r/min) for quartz sand
and low speed (45-50 r/min) for ceramic sand, balancing screening efficiency and
accuracy.
Step 3: Adapt to the characteristics and pretreatment of fracturing sand -
avoid faults at the source
Material impurities, humidity, and insufficient pretreatment can affect
screening stability.
The material contains impurities or exceeds the humidity limit: the mud
content exceeds 3%, and the fine mud binds to the sieve; Moisture content
exceeding 2%, sand particles clumping and blocking the mesh. Before screening,
add a drying process (reducing moisture to below 1%) and install a mud removal
drum screen (with a diameter of 1mm) to remove mud lumps and large impurities;
Install a dispersing device (with a speed of 300r/min) at the feed inlet to
crush agglomerated particles (with a particle size exceeding 8mm) that are prone
to clumping.
Overloading or uneven feed rate: Exceeding the rated processing capacity
(such as rated 80t/h, actual 100t/h), material filling rate in the screening
cylinder exceeds 60%, and the screening channel is blocked; The feed fluctuates
frequently, and the screen load fluctuates greatly. Use an electronic belt scale
to control the quantity and maintain it at 85% -90% of the rated value. Install
a spiral feeder to achieve uniform feeding; Install a splitter plate at the feed
inlet to evenly distribute the material along the axial direction of the sieve
cylinder, avoiding local overload.
Daily maintenance should pay attention to: cleaning the residual sand
particles on the surface of the sieve every day and checking the smoothness of
the nozzle; Calibrate wind pressure, speed, and mesh size on a weekly basis, and
replace worn-out nozzles; Monthly inspection of screen cylinder wear and
tightening of bearing seat bolts (torque 80-100N · m). By taking these measures,
the qualified rate of fracturing sand particle size can be increased to over
99%, and the number of screen clogging times can be reduced to less than once a
day, ensuring stable sand quality for fracturing construction. If there are
still problems, it is recommended to contact the manufacturer to optimize the
compatibility between the gas flow field and the sieve, and match the screening
requirements of specific particle size fracturing sand.