The three return drum dryer is a key equipment for drying finished products
in large-scale quartz sand production lines (with a daily processing capacity of
≥ 3000t). It is responsible for drying the filtered quartz sand (with a moisture
content of 18% -25%) to the standard state (requiring a moisture content of ≤
0.5% for finished products and ≤ 0.3% for photovoltaic/electronic grade quartz
sand), directly determining the storage stability of finished products and their
adaptability to high-end applications. If the drying efficiency is low (less
than 80t/h) and the moisture content of the finished product exceeds the
standard, it will cause clumping and deterioration, difficulty in subsequent
grading, and even affect the SiO ₂ purity compliance rate. Based on the thermal
conductivity characteristics of quartz sand and the continuous operation
requirements of large-scale production lines, summarize a three-step
optimization plan to improve drying efficiency and accuracy.
Step 1: Optimize the configuration of the hot air system and strengthen the
core heat source for drying
Insufficient hot air temperature, imbalanced air volume, or insufficient heat
exchange are the core reasons for low drying efficiency, and targeted
optimization of heat sources and heat exchange structures is needed.
Adaptation of heat source and hot air parameters: ordinary coal-fired hot air
stove is selected, with a thermal efficiency of less than 65% and large
fluctuations in hot air temperature (below 200 ℃), which cannot meet the
requirements of rapid drying; When the air volume is insufficient, the discharge
of humid and hot gases is obstructed, and the drying cycle is prolonged. Replace
the natural gas hot blast stove (thermal efficiency ≥ 75%) with a waste heat
recovery device to stabilize the hot air temperature at 280-320 ℃; By adjusting
the air volume through a variable frequency induced draft fan and setting it
according to the standard of "1200-1500m ³ per ton of sand", it ensures the
rapid discharge of humid and hot gases, and improves heat exchange efficiency by
more than 25%.
Optimization of hot air distribution and heat transfer structure: A single
air inlet leads to uneven distribution of hot air, resulting in local "drying
dead corners" inside the drum; The ash accumulation thickness of the heat
exchange tube exceeds 3mm, resulting in a decrease in thermal conductivity
efficiency. Install a circular air distributor to evenly distribute hot air
along the axial direction of the drum; Install a pulse dust cleaning device in
the hot air duct and regularly clean the accumulated dust in the heat exchange
tube; Optimize the angle of the inner plate of the drum, adopt a combination
design of "spiral plate+lifting plate", improve the contact area between quartz
sand and hot air, and enhance the heat exchange effect.
Step 2: Calibrate the drum structure parameters to improve drying
uniformity
Improper drum speed, poor sealing performance, or internal structural wear
can cause fluctuations in drying efficiency, requiring precise regulation and
maintenance.
Optimization of drum speed and inclination angle: When the speed is below
8r/min, the quartz sand stays in the drum for too long but does not flip enough,
resulting in local overheating and agglomeration; Above 15r/min, insufficient
residence time (less than 15min), and insufficient drying; The inclination angle
deviation of the drum exceeds 1 °, and the material pushing speed is unbalanced.
Stabilize the speed at 10-12r/min through a frequency converter; Use a spirit
level to calibrate the tilt angle of the drum to 3-5 °, ensuring that the
material pushing speed matches the drying cycle (20-25 minutes) and adapts to
the drying needs of quartz sand with different particle sizes.
Sealing and insulation optimization: The sealing components at both ends of
the drum are worn, the hot air leakage rate exceeds 15%, and the temperature
drops sharply; The outer wall of the cylinder has no insulation layer or the
insulation layer is damaged, resulting in significant heat loss. Replace the
graphite packing seal and install a sealing pressure ring to control the hot air
leakage rate within 5%; Wrap rock wool insulation layer (thickness 50mm) around
the outer wall of the cylinder, and install iron sheet protection on the outer
layer to reduce heat loss and ensure stable temperature inside the cylinder.
Step 3: Optimize feed control and pretreatment to ensure drying stability
Overloading of feed volume, uneven material layers, or insufficient
pre-treatment of raw materials can exacerbate fluctuations in drying efficiency,
requiring effective front-end control.
Feed quantity and layer control: If the feed quantity exceeds the rated value
(such as rated 100t/h, actual 130t/h), the thickness of the layer inside the
drum exceeds 120mm, the hot air flow cannot penetrate, and the drying is not
thorough; The fluctuation of feed quantity exceeds 10%, and the drying load is
unbalanced. Strictly control the amount with an electronic belt scale to
maintain the feed rate at 85% -95% of the rated value; Install a material layer
adjustment baffle to stabilize the thickness of the material layer inside the
drum at 80-100mm, ensuring sufficient contact between the hot air and quartz
sand.
Raw material pretreatment and optimization of feed uniformity: After pressure
filtration, quartz sand contains large clumps (particle size exceeding 5mm),
making it difficult for internal moisture to precipitate during drying; The
feeding port is not equipped with a dispersing device, resulting in concentrated
material accumulation and insufficient drying in some areas. Install a drum
disperser before feeding to break up large clumps; Equipped with a spiral feeder
to evenly distribute materials along the axial direction of the drum, avoiding
local overload; Pre screen the quartz sand before drying to remove impurities
and improve drying efficiency.
Daily maintenance should pay attention to: checking the hot air temperature,
finished product moisture content, and drying efficiency every day; Clean the
dust accumulation in the hot air duct and heat exchange tube every week, and
check the integrity of the seals; Calibrate the drum speed and tilt angle
monthly, and check the wear of the plate; Conduct comprehensive maintenance on
the hot blast stove and waste heat recovery device every quarter. By taking the
above measures, the drying efficiency can be improved to over 110t/h, the
moisture content of the finished product can be stabilized below 0.3%, ensuring
that the quality of photovoltaic/electronic grade quartz sand meets the
standards and is suitable for the continuous and efficient operation needs of
large-scale production lines.