In the production process of quartz sand, the drying equipment (especially
the roller drier) undertakes the key task of removing the moisture of the
material. The moisture content of the finished sand directly affects the
subsequent magnetic separation, screening, storage and transportation. If the
moisture content exceeds the standard (for example, the actual moisture content
of the quartz sand ≤ 0.5% is more than 2%), the material caking and blocking
during the magnetic separation will be caused, the material will become mildewed
and metamorphic during storage, and the weight cost will be increased during
transportation; However, low drying efficiency will slow down the whole
production line and increase energy consumption and time cost. As a professional
manufacturer focusing on R&D and manufacturing of quartz sand drying
equipment, we combined with a large number of project practices to find out the
core causes of low drying efficiency and substandard water content and
systematic solutions to help enterprises quickly break through the production
bottleneck.
Clarify "problem judgment": scientifically define abnormal drying effect
Before troubleshooting, it is necessary to determine whether the drying
equipment really has efficiency and moisture content problems through accurate
detection to avoid wasting energy due to detection error or standard
confusion:
Moisture content detection: use a fast moisture meter to continuously sample
3-5 times (100g for each time) from the outlet of the dryer, and detect the
moisture content after the mixing is even. If the results of multiple tests are
higher than the production requirements (such as PV sand requirements ≤ 0.3% and
building sand requirements ≤ 1%), it can be determined that the moisture content
is unqualified;
Efficiency judgment: record the feed quantity and finished product quantity
of the dryer per unit time, calculate the actual drying capacity (e.g. the rated
capacity of the equipment is 20t/h, only 15t/h in fact), and count the energy
consumption of the unit product (e.g. the drying of 1t quartz sand requires more
than 8m ³ of natural gas, far exceeding the normal range of 6-7m ³). If the
capacity is 20% lower than the rated value or the energy consumption is 30%
higher than the standard, the drying efficiency can be judged as low;
Observation of material state: if the material appears "caking and caking",
"local overheating and discoloration" or "uneven drying and wetting" (some
materials are dry and some are still wet) after drying, it also belongs to
abnormal drying effect and needs further investigation.
Step 1: Troubleshoot the heat supply system - "insufficient heat" is the core
cause
The drying efficiency and moisture content control of the roller drier mainly
depend on the stable and sufficient heat source. The insufficient heat source
temperature, supply or heat utilization rate is the most common cause of the
problem.
Low heat source temperature or unstable supply
Problem performance: the temperature at the feed inlet of the dryer or inside
the roller is far lower than the design value (such as the rated hot air
temperature of the natural gas heated dryer is 600-800 ℃, only 400 ℃ in fact).
After drying, the moisture content of the material exceeds the standard, and
fluctuates with the temperature of the heat source, and the moisture content
fluctuates from high to low; If the coal-fired hot-blast furnace is used, the
flame may be unstable due to poor coal quality and insufficient air supply, and
the heat supply is intermittent.
Cause analysis: first, burner failure (such as nozzle blockage of natural gas
burner, improper air valve adjustment), insufficient fuel combustion and
insufficient heat output; Second, the heat exchange efficiency of hot-blast
furnace is reduced (such as furnace liner scaling and flue blockage), and the
heat cannot be effectively transferred to the hot-blast furnace; Third, the fuel
quality is not up to the standard (such as low purity of natural gas and coal
heating value less than 5000kcal/kg), and sufficient heat cannot be
generated.
Solution: first check the state of the burner, clean the blockage of the
natural gas nozzle, adjust the opening of the air valve (ensure the ratio of air
to fuel is about 10:1 to achieve full combustion). If the burner is aged,
replace the high efficiency burner with the same power (select the brand with
thermal efficiency ≥ 90%); Remove dust and scale from the hot-blast furnace,
wash the furnace liner with a high-pressure water gun, and dredge the flue
blockage (it is recommended to clean it quarterly); Replace high-quality fuel,
select LNG with purity ≥ 95% for natural gas and anthracite with calorific value
≥ 5500kcal/kg for coal to ensure stable output of heat source; A temperature
sensor is installed in the hot air pipe to monitor the hot air temperature in
real time, form linkage control with the burner, and automatically increase the
fuel supply when the temperature is lower than the set value.
Uneven distribution of hot air or excessive heat loss
Problem performance: the local temperature in the dryer roller is too high
(causing discoloration of materials), the local temperature is too low
(materials are wet), and the materials are not dry and wet evenly after drying;
Or the heat dissipation of the hot air pipe and roller shell is serious, and the
temperature of the outer wall of the pipe is over 60 ℃ when touched by hand,
resulting in serious heat waste.
Cause analysis: First, the design of hot air inlet is not reasonable, and the
hot air is only concentrated at one end of the roller and cannot be diffused
evenly; Second, the internal plate of the roller is worn, deformed or
insufficient, and the materials cannot be fully lifted to contact with the hot
air; Third, the equipment insulation measures are not in place, the pipe and
roller shell are not insulated or the insulation layer is aging and damaged.
Solution: Transform the structure of hot air inlet and install deflector or
diffuser to make the hot air uniformly enter the roller and distribute along the
axial direction; Check the internal plate of the roller, and replace the plate
with excessive wear (select 16Mn wear-resistant steel material). If the number
of plate is insufficient, add 8-12 pieces per meter of roller to ensure that the
material can be fully lifted; Heat preservation treatment shall be carried out
for hot air pipe and roller shell, rock wool or aluminum silicate heat
preservation cotton (thickness: 50-80mm) shall be selected, and galvanized iron
sheet shall be wrapped on the outer layer to reduce heat loss (temperature of
outer wall of pipe after heat preservation shall be ≤ 40 ℃).
Step 2: analyze equipment structure and operating parameters - "insufficient
adaptability" slowing down efficiency
The rotating speed, inclination, feeding amount and other parameters of the
roller drier, and whether the equipment structure is suitable for the
characteristics of quartz sand directly affect the drying effect, and the
deviation between the parameters and the structure will lead to the efficiency
reduction.
The roller speed is too fast or too slow
Problem performance: when the rotating speed is too fast, the retention time
of materials in the roller is too short (less than 5 minutes), the contact with
hot air is not sufficient, and the moisture content exceeds the standard; When
the rotating speed is too slow, the materials accumulate at the bottom of the
roller, which is easy to cause "pasting cylinder" (the materials are stuck on
the cylinder wall for burning), and the production capacity is reduced, and the
drying efficiency is low.
Troubleshooting method: measure the actual rotating speed of the roller with
a tachometer and compare it with the "adaptive rotating speed" recommended in
the equipment specification (such as rotating speed of 3-5r/min for the roller
drier with a diameter of 1.5m and a length of 10m when handling quartz sand) to
judge whether it deviates from the reasonable range.
Solution: adjust the motor frequency converter parameters or replace the
transmission gear (change the transmission ratio), adjust the rotating speed to
the appropriate range - appropriately reduce the rotating speed (3-4r/min) and
extend the retention time when dealing with quartz sand with high water content
(>15%); When dealing with quartz sand with low water content (<8%), rotate
speed (4-5r/min) can be increased to increase productivity; The water content of
3 batches of finished products shall be inspected continuously after adjustment
to ensure the stability and compliance.
Unreasonable inclination of roller
Problem performance: when the dip angle is too large (more than 5 °), the
material slides too fast in the roller, the retention time is short and the
drying is not sufficient; When the dip angle is too small (less than 2 °), the
material flow is slow, easy to accumulate and block, even the "material pouring"
(the material cannot move to the outlet), and the capacity drops sharply.
Troubleshooting method: measure the angle between the roller axis and the
horizontal plane with a protractor, and compare it with the standard inclination
(generally 3-4 °) marked in the equipment specification.
Solution: adjust the adjusting bolt on the base of the drying machine, insert
the oblique iron to change the tilt angle of the roller, adjust 0.5 ° each time,
and observe the flow state of the materials in the roller until the materials
can move evenly and the retention time meets the requirements (generally 8-12
minutes); If the adjustment range of the base is insufficient, the manufacturer
can be contacted to modify the base structure and increase the adjustment stroke
to ensure that the dip angle can adapt to quartz sand with different water
content.
Overload or uneven feed
Problem performance: the feeding capacity exceeds the rated capacity of the
equipment (such as rated 20t/h, actual feeding 25t/h), the material accumulation
in the roller is too thick (more than 1/3 of the roller diameter), the hot air
cannot penetrate the material layer, and the drying is not thorough; The feeding
is variable (such as 10t/h feeding in certain period and 25t/h feeding in
certain period), which causes the material volume in the roller fluctuates, the
water content is variable and the efficiency is unstable.
Troubleshooting method: use an electronic belt scale to continuously monitor
the feed volume for 1 hour, record the peak value and valley value, calculate
the fluctuation amplitude (normally ≤ 10%), and observe the material flow at the
outlet of the roller. If there is "cutoff" or "surge", it indicates that the
feed is uneven.
Solution: Reduce the feeding speed of the feeder, control the feeding
quantity within 80% - 90% of the rated value of the equipment (e.g., rated
20t/h, actually controlled within 16-18t/h), and avoid overloading; Install the
material level sensor and the feeder to form a closed loop control. When the
material amount in the roller is too high, the feeding will be automatically
reduced, and when the material amount is too low, the feeding will be increased
to maintain the uniform feeding; Larger size dryers or additional drying lines
(operating in parallel) may be used instead of forced overloading if increased
capacity is required.
Step 3: Adapt material characteristics - "material difference" affects drying
effect
Due to different characteristics of quartz sand, such as grain size, initial
moisture content and impurity content, the requirements for drying conditions
are also different. If the equipment does not adapt to the material
characteristics, it is easy to have efficiency and moisture content
problems.
The initial moisture content of the material is too high
Problem performance: if the moisture content of raw material exceeds 20%
(such as quartz sand after ore washing), it is easy to agglomerate after
entering the dryer, block the roller plate, and the hot air cannot fully contact
with the material. After drying, the material still has "wet mass", the moisture
content exceeds the standard, and the drying time is prolonged, and the
efficiency is reduced.
Solution: Add the pre-dehydration process before drying, select the belt
filter press or centrifugal dehydrator to reduce the initial moisture content of
the material to below 12% (the filter press can reduce the moisture content to
15% - 18%, and the centrifugal dehydrator can reduce the moisture content to 10%
- 12%); If the pre-dehydration equipment is added unconditionally, a dispersing
device (such as high-speed rotating dispersing teeth) can be installed at the
feed inlet of the dryer to disperse the caked materials, and at the same time,
the feeding amount shall be reduced appropriately, and the hot air temperature
shall be increased (no more than 850 ℃ to avoid discoloration of the materials)
to extend the drying time.
Material particle size difference is too large
Problem performance: Coarse particles (>2mm) and fine particles
(<0.1mm) are mixed and dried, and fine particles are easy to be carried away
by hot air (causing dust loss), and too fast drying is easy to overheat; Coarse
particles have low drying efficiency due to small heating area, insufficient
drying, excessive moisture content.
Solution: add grading process before drying, use vibrating screen to divide
quartz sand into coarse particle size (>0.5mm) and fine particle size
(<0.5mm) according to particle size, and respectively enter into different
dryer or different areas of the same dryer (such as setting partition plate in
the drum) for treatment - the wind speed and temperature (500-600 ℃) of fine
particle size materials can be appropriately increased and reduced to avoid dust
loss; Reduce the wind speed and increase the temperature (700-800 ℃) of coarse
materials to ensure thorough drying; The drying efficiency after grading can be
increased by more than 20%, and the moisture content of the finished product is
more uniform.
Material contains too much impurities (such as clay and organic matter)
Problem performance: The material contains clay, organic matter and other
impurities. During drying, the impurities are easy to adhere to the roller wall
and the plate, forming a "scaling layer", affecting the heat transfer.
Meanwhile, the impurities may be carbonized after being heated and pollute the
quartz sand. In addition, the machine shall be shut down to further reduce the
efficiency.
Solution: add ore washing process before drying, use spiral sand washer or
wheel bucket sand washer to remove clay and other impurities, and reduce water
content by dewatering equipment after ore washing; If the impurity content is
small, a scraper device can be installed in the roller (the gap between the
scraper and the cylinder wall is 5-10mm) to clean the scaling on the cylinder
wall in real time to avoid accumulation; Regularly (every two weeks) shut down
the machine to disassemble the roller, and clean the scaling on the plate and
cylinder wall with a high pressure water gun to ensure that the inside of the
equipment is clean.
Step 4: Inspect equipment maintenance and operation - "improper management"
aggravates the problem
Improper daily maintenance of the dryer and non-standard operation of the
operator will lead to equipment performance degradation and indirectly lead to
efficiency and moisture content problems.
Wear or blockage of equipment parts
Problem performance: the internal plate of the roller is worn and broken, and
the material cannot be lifted effectively, the contact area between the hot air
and the material is reduced, and the drying efficiency is reduced; Seals at the
feeding end (such as asbestos packing) are aged and damaged, cold air seeps into
the roller, hot air leaks and the temperature drops; The dust collector is
blocked, the air exhaust is not smooth, the negative pressure in the roller is
insufficient, the hot air cannot flow smoothly, and the drying effect is
poor.
Troubleshooting method: Open the roller access door after shutdown and check
the wear condition of the plate (replace the plate if the wear exceeds 1/2 of
the original thickness); Check whether the sealing elements at the feeding and
discharging ends are jointed or damaged; Check the differential pressure gauge
of the dust collector. If the differential pressure exceeds 1500Pa, it indicates
that the filter bag is blocked.
Solution: replace the worn plate and sealing parts. The plate shall be made
of wear-resistant materials (such as 16Mn), and the sealing parts shall be made
of high-temperature resistant fluorine rubber packing (3 times longer than the
service life of asbestos packing); Clean the filter bag of the dust collector,
purge the dust on the surface of the filter bag with compressed air (pressure
0.4MPa), and replace the damaged filter bag in time (select PPS high temperature
resistant filter bag, which can withstand high temperature above 200 ℃);
Establish equipment maintenance account, check the plate and sealing parts
weekly, and clean the dust collector monthly to ensure that the equipment parts
are in good condition.
Improper operation of operators
Problem performance: the operator fails to adjust the parameters according to
the procedures, such as randomly increasing or decreasing the hot air
temperature and rotating speed; Failure to clean the equipment blockage in time
causes the problem to expand; The production data (such as feed volume,
temperature and moisture content) are not recorded, the cause of the problem
cannot be traced, and the drying effect is unstable for a long time.
Solution: Formulate detailed Operating Specification for Drying Equipment,
specify parameter settings corresponding to different material characteristics
(such as quartz sand with water content of 15%, hot air temperature of 700 ℃,
rotating speed of 4r/min), train operators, and work after passing the
examination; The operator is required to record the feed volume, hot air
temperature, roller speed and finished product water content once an hour to
form a production report, and report in time in case of any abnormality;
Regularly organize operators to exchange experience, share parameter adjustment
skills and improve operation proficiency.
Preventive measures: 4. Guarantee stable and efficient operation of drying
equipment
Solidification and dynamic adjustment of parameters: for specific quartz sand
materials, determine the optimal parameters such as hot air temperature,
rotating speed and feeding volume through tests, input them into the equipment
control system for solidification, and conduct dynamic fine adjustment according
to the change of initial moisture content of materials (such as increase of
moisture content in rainy season) to ensure that the parameters are always
suitable;
Regular maintenance: establish the "daily inspection - weekly maintenance -
monthly maintenance" system, and check the temperature, pressure and sealing
parts every day; Clean the dust collector and check the plate; Disassemble the
roller every month to remove the dirt and replace the vulnerable parts to reduce
the faults from the source;
Energy optimization and recovery: A waste heat recovery device (such as a
heat exchanger) is installed at the outlet of the dryer tail gas to preheat the
cold air or raw materials with the tail gas heat, so as to reduce the fuel
consumption (15% - 20% energy can be saved);
Intelligent monitoring and early warning: the equipment is equipped with
intelligent control system to monitor the hot air temperature, roller speed and
finished product water content in real time. In case of abnormality, it will
automatically give an alarm and prompt the processing scheme to reduce manual
intervention error.
As a professional manufacturer of quartz sand drying equipment, we can
customize high-efficiency roller dryers according to the production capacity
demand (5-50t/h), material characteristics (moisture content, particle size) and
heat source types (natural gas, coal, biomass) of customers, and provide
full-cycle services from "process design - equipment manufacturing -
installation and commissioning - operation and maintenance training".