Daily maintenance and use of spray dryers

Spray drying is a method
of systematic technology applied to material drying.

After the dilute material is atomized in the drying chamber, in contact with hot air, the moisture vaporizes rapidly, that is, the dried product
is obtained.

This method can directly dry the solution and emulsion into powdered or granular products, which can eliminate evaporation, crushing and other processes
.

Spray granulation dryer is an important equipment in the production process of PTC thermal ceramics, the equipment is relatively expensive, the composition is complex, and it is difficult to use and maintain
.

The good operation of the equipment can not only ensure the normal production of PTC thermal ceramics, but also appropriately extend the service life of the equipment and reduce the production cost, so the correct operation of the equipment and the need to strengthen maintenance are necessary
.

1 Principle and composition of spray granulation dryer Granulation is an important process in the production process of PTC thermal ceramic sheet, and the quality of the pellet directly affects the appearance, mechanical properties and temperature resistance characteristics
of PTC ceramic sheet.

Granulation refers to the amount of adhesive added to the grinding powder, uniformly blended to form a granular powder, this powder has good fluidity and calenderability, so that in the tableting process can be obtained with good strength, not easy to layer cracking pieces
.

In industrial production, the spray drying method is used for granulation, the basic principle is to spray the powder with adhesive into the granulation tower with a sprayer for atomization, and the droplets in the tower are dried into granular powder by the hot air flow in the tower, and then discharged
from the bottom of the drying tower.

The pressure spray granulation dryer adopted by the company is mainly composed of feeding system, drying system, dust removal system, heating system and electrical system, and each system includes some related equipment
.

The feeding system consists
of a mixing bucket, a filter, a diaphragm pump and an spray gun.

The ball-milled secondary slurry is transferred from the ball mill to the mixing bucket, extracted and transferred by the diaphragm pump through the filter, and then enters the drying tower through the
spray gun.

The slurry enters the drying tower from the spray gun nozzle to start the spray granulation drying process, which is divided into three stages: (1) slurry atomization
.

The slurry is pressed from the nozzle into the drying tower by the diaphragm pump in the feeding system at pressure, the energy of the pressure is converted into kinetic energy, and the slurry is sprayed from the nozzle from the bottom up to form a high-speed liquid film, and the liquid film immediately splits into droplets
.

The size of the droplets produced by atomization is inversely proportional to the pressure, and the production capacity of the nozzle is proportional to
the square of the pressure.

(2) The fog particles are dried into balls
.

The fog particles and hot air work in a mixed stream, and the hot air enters the tower through the hot air distributor on the top cover, which produces a downward streamlined air flow, and the droplets spray hot air from the bottom up
.

The droplets form a spherical shape due to surface tension, and because the droplets have a large surface area, the moisture quickly evaporates and dries, and finally shrinks to form a dry spherical particle powder
.

(3) Granular powder unloading
.

The resulting spherical granular powder gradually settles in the drying tower and separates from the hot air, and the funnel cavity in the lower part of the tower collects and unloads the pellet from the
outlet.

The finer granules are extracted together with the dry air by a fan connected to the upper part of the funnel shape and enter the dust collection system
.

The drying system is formed by the supply blower, the drying tower and the exhaust fan that deliver hot air to the drying tower
.

The dust removal system is composed
of high-efficiency cyclone separator, bag dust collector, centrifugal fan and so on.

The exhaust fan feeds the finer pellets together with the dry air into the high-efficiency cyclone separator
.

After effective separation, the finer particles enter the collection cylinder at the bottom of the separator for recovery, and the remaining exhaust gas containing a very small amount of fine particles is sucked into the bag dust collector by the centrifugal fan and collected again by dust removal, realizing the harmless treatment of the exhaust gas, and the exhaust gas is discharged
from the chimney.

In addition, a heating system consisting of an electric heater and a gas turbine hot blast furnace provides hot air
to the drying tower.

The electrical control cabinet and the field sensors installed in the air inlet and outlet to monitor the temperature of the electrical system monitor and control the main links of the entire spray granulation dryer to ensure the normal operation of
the entire equipment.

2 Daily operation and precautions In the daily production process, the necessary preparations should be carried out before starting the equipment
.

Check whether the bearings and sealing parts of each device are loose, the lubricating oil condition of each mechanical component, and whether the water, wind, pulp pipe valve port, etc.
are in the required position
.

Then turn on the power supply to check whether the voltage and instrument are normal, and then check the amount and concentration of the slurry in the slurry mixing bucket, and if there is a problem, it should be eliminated
in time.

Then turn on the blower, exhaust fan, and then open the heating switch to start heating
.

When the outlet temperature reaches the set temperature (generally about 130 ° C), start the feed pump and dust collection system
.

When the pump pressure reaches 2MPa, open the spray gun and start pelletizing
.

After the equipment is running, the atomization situation and the working condition of the feed pump should be observed in time, and if there is a gun blockage, the nozzle
should be cleaned or replaced immediately.

After the normal operation of the equipment, it should also regularly receive materials, regularly check the operation of each system, record the process parameters, and pay attention to cleaning the vibrating filter
.

At the end of granulation, the heating device should be turned off and the gas engine should
be stopped.

Then close the gun valve, replace the spray gun, unscrew the nozzle and rinse it clean
.

When the inlet temperature is reduced to less than 100 ° C, the operation
of the supply and exhaust fans can be stopped.

Then clean the remaining material in the drying tower and the dust collector, turn off the dust collector and the air hammer, and then turn off the total power supply to complete the production operation
.

In case of emergency, shut down the equipment immediately, and shut down the blower and feed pump
.

If there is a sudden power outage, the gas engine should be pulled out to cool the tower body naturally, and then the sewage valve should be opened, the slurry in the slurry pipeline should be drained, and the equipment
should be cleaned.

3 maintenance and maintenance Granulation is an important part of the PTC production process, and maintaining the normal operation of the equipment is a necessary condition
to ensure the stability of PTC production.

Regular cleaning, maintenance and upkeep help to identify problems in a timely manner, solve potential failures, reduce downtime, and ensure normal and stable
production.

The equipment is running for a long time or due to improper operation, and the aggregate will appear in some equipment and affect the normal operation, and it is necessary to stop the work for cleaning
.

For the cleaning of the aggregate in the drying tower, the cleaning door should be opened, the funnel-shaped bottom aggregate should be swept away with a long broom, the discharge valve should be opened, and the
tower should be rinsed with tap water.

The removal of dust in the cyclone separator also requires opening the cyclone separator, cleaning the aggregate with a broom, and rinsing
with water if necessary.

For the cleaning of the bag filter, the control switch should be opened, continuously knocked, and then the cleaning door should be opened, the bag dust collector should be tapped, and the filter bag
should be replaced later.

For the cleaning of the slurry pipeline system, the sewage valve of the two-way filter should be opened, the filter screen and pipeline should be cleaned, and then the material pump should be opened to replace the material with water to clean the pump pipe, the pressure stabilization package and the pipeline
.

After a period of operation (generally about 600h), the necessary inspection and maintenance
of the spray granulation dryer is required.

For the feeding system, the filter, pipeline, valve, nozzle, etc.
should be checked to see if there is a blockage, regular cleaning, check the wear of the nozzle in time for timely replacement
.

It should be checked whether the pump leaks oil, whether the pressure is normal, whether the oil level is normal, etc.

。
For fans, it should be checked whether the shaft and bearings are lack of oil and heat, whether there is vibration, noise, etc.
, and if necessary, clean the wind blade and balance the wind blade to
calibrate.

For the heater, check whether the heat pipe is normal, and if necessary, clean the filter screen
of the tubing, the oil pump and the nozzle.

In addition, attention should also be paid to whether the motor has heating, vibration, abnormal sound, etc.
, and whether the instruments and electrical appliances of the control cabinet are working normally
.

In addition, when the equipment is running for about 2 400h (usually during the suspension period), the maintenance personnel need to partially disassemble and maintain
the equipment.