The single drum dryer is responsible for the final dehydration task in the
quartz sand production line, and stable discharge moisture is a prerequisite for
the qualified finished product. But many customers have found that the moisture
content of the discharged material from the dryer fluctuates during operation.
Some materials in the same batch are thoroughly dried, while others still carry
moisture, with moisture content fluctuating back and forth between 0.5% and 3%.
The temperature of the hot air and the rotational speed of the cylinder seem to
be normal, but the problem often lies in more hidden systemic links.
Unstable feeding is the source of moisture fluctuations. The control accuracy
of the front-end feeding equipment is insufficient, and there is a continuous
deviation in the flow rate of materials entering the cylinder per unit time.
Under the premise of a constant total heating supply, the effective heat
allocated per unit mass of materials changes accordingly, and the moisture
content of the discharged material cannot be stabilized naturally. At the same
time, if there is a significant difference in the initial moisture content of
the incoming materials between batches, even if the dryer operating conditions
are completely stable, the moisture content of the discharged materials will
fluctuate accordingly. Suggest adding a buffer bin in front of the dryer and
matching it with a variable frequency feeder to control the fluctuation of the
feeding amount within ± 5%. Sample and test the moisture content of the incoming
materials every shift, and adjust the front-end dehydration process in a timely
manner when the fluctuation exceeds 3 percentage points.
Thermal system imbalance is the core cause of water instability. The fuel
supply or combustion state of the burner fluctuates, and the temperature of the
hot air entering the cylinder changes accordingly. The total evaporation heat
obtained by the material continues to shift, and the water evaporation
efficiency cannot be stabilized. Leakage of air in pipelines or accumulation of
ash and slag in heat exchange components can also weaken effective heat
conduction and exacerbate the oscillation of the thermal environment inside the
cylinder. Check the flame color of the burner. If it turns yellow or red, it
indicates insufficient combustion. Clean the nozzle and adjust the air damper.
At the same time, check the sealing of the inlet and outlet ends of the
cylinder. When the air leakage rate is high, a large amount of heat is lost, and
the thermal efficiency will drop from over 80% to the range of 60%.
The imbalance of negative pressure in induced draft can cause the wet steam
to "regain moisture". When the moisture discharge air volume and the negative
pressure inside the cylinder continue to fluctuate, some high humidity steam
cannot be discharged from the cylinder in time and comes into contact with the
material again, causing the moisture content of the discharged material to
fluctuate rapidly and completely deviate from the preset control range. Check if
the frequency of the induced draft fan is stable. When the negative pressure
gauge reading fluctuates greatly, check if there is any air leakage or blockage
in the pipeline. In addition, when the residence time of coarse particles and
fine powder in the quartz sand cylinder is the same, there will be coarse sand
entrapment and fine powder over drying, which will also exacerbate moisture
fluctuations. At the feeding end, the plate can be appropriately encrypted to
allow fine powder to pass faster and coarse particles to have a longer residence
time.
Unstable moisture in the discharge is rarely caused by a single fault point.
Systematic troubleshooting in the order of "checking the stability of the feed
first, then checking the thermal system, and finally checking the negative
pressure of the induced draft" is more effective than repeatedly adjusting a
single parameter. Encountering problems during equipment operation, welcome to
contact the technical team of Shandong Heavy Industry for communication: Manager
Zhang 13583776655 (same as WeChat).