1 Principle and composition of spray granulation dryer
Granulation is an important process in the production of PTC thermal ceramic sheets. The quality of pellets directly affects the appearance, mechanical properties and temperature resistance of PTC ceramic sheets. Granulation refers to the addition of a certain amount of binder to the ground powder, which is uniformly blended to form a granulated powder. The powder has good fluidity and calendering properties, so that it can be used in the tableting process. A sheet having better strength and less delamination cracking can be obtained. In the industrial production, the spray drying method is used for granulation. The basic principle is that the powder with binder is sprayed into the granulation tower by atomizer for atomization, and the droplets in the tower are dried by the hot gas in the tower to form granules. The powder is then discharged from the bottom of the drying tower.
The pressure spray granulation dryer used by the company mainly consists of a feeding system, a drying equipment system, a dust removal system, a heating system and an electrical system, and each system includes some related equipment.
The feeding system consists of a mixing tank, a filter, a diaphragm pump and a spray gun. The ball-milled secondary slurry is transferred from the ball mill to the mixing drum, pumped by a diaphragm pump and conveyed, and then passed through a spray gun into the drying tower.
The slurry enters the drying tower from the nozzle of the spray gun and begins the spray granulation drying process. The specific process is divided into three stages:
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(1) slurry atomization. The slurry is pressed into the drying tower from the nozzle by a diaphragm pump in the feeding system, and the energy of the pressure is converted into kinetic energy. The slurry is ejected from the nozzle from the bottom to the top to form a high-speed liquid film, and the liquid film is then split into Droplet. The droplet size produced by atomization is inversely proportional to the pressure, and the throughput of the nozzle is proportional to the square of the pressure.
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(2) The mist particles are dried into balls. The mist particles and the hot air work in a mixed flow manner. The hot air enters the tower through the hot air distributor on the top cover, and the hot air distributor generates a downward flow of the stream air, and the mist is sprayed from the bottom to the top. Air flow. The droplets form a spherical shape due to the surface tension, and at the same time, since the droplets have a large surface area, the moisture rapidly evaporates and dries, and eventually shrinks to form a dry spherical particle powder.
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(3) The granule powder is discharged. The formed spherical particulate powder gradually settles in the drying tower and is separated from the hot air, and the funnel cavity in the lower portion of the tower collects the particulate material and discharges it from the discharge port. The finer pellets are drawn together with the dry air by an extractor connected to the funnel-shaped upper portion into the dedusting system. A blower, a drying tower, and an exhaust fan that transport hot air to the drying tower constitute a drying system.
The dust removal system is composed of a high efficiency cyclone separator, a bag filter, and a centrifugal fan. The blower feeds the finer pellets together with the dry air into the high efficiency cyclone. After effective separation, the finer particulate material is collected into the collecting cylinder at the bottom of the separator, and the remaining exhaust gas containing a very small amount of fine particulate material is collected by the centrifugal fan and then collected by the dust collector to be dedusted and collected, thereby realizing the harmless treatment of the exhaust gas. The exhaust gas is discharged from the chimney.
In addition, a heating system composed of an electric heater and a gas engine hot blast stove provides hot air to the drying tower. The electrical control system consisting of the electrical control cabinet and the on-site sensors installed at the air inlet and the discharge port monitors and controls 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. First check the joints of the bearing and sealing parts of each device for looseness, the condition of the lubricating oil of each mechanical component and whether the water, wind and slurry valve ports are in the required position. Then turn on the power to check whether the voltage and the meter are normal. Finally, check the amount and concentration of the slurry in the slurry mixing tank. If there is any problem, it should be eliminated in time.
Then, the blower and the exhaust fan are sequentially turned on, and then the heating switch is turned on to start the temperature rise. When the outlet temperature reaches the set temperature (generally around 130 °C), the material pump and dust removal system are activated. When the pump pressure reaches 2 MPa, the spray gun is turned on to start granulation. After the equipment is running, the atomization and the working condition of the pump should be observed in time. If there is a gun blocking phenomenon, the nozzle should be cleaned or replaced immediately. After the equipment is in normal operation, it should also be timed to receive materials, check the operation of each system regularly, record the process parameters, and pay attention to clean the vibration filter screen.
At the end of the granulation, the heating device should be shut down first to stop the gas engine operation. Then close the gun valve, replace the gun, unscrew the nozzle and rinse. When the inlet temperature is reduced below 100 °C, the operation of the blower and the blower can be stopped. Then clean the remaining materials in the drying tower and the precipitator, turn off the dust collector and the air hammer, and finally turn off the main power supply to complete the production operation.
In case of emergency, the equipment must be shut down immediately. The blower and feed pump should be shut down first. If there is a sudden power outage, the gas engine should be pulled out to cool the tower naturally, then the drain valve is opened, the slurry in the slurry pipeline is drained, and the equipment is cleaned.
3 Maintenance and maintenance
Granulation is an important part of the PTC production process. Maintaining the normal operation of the equipment is a necessary condition to ensure the stability of PTC production. Regular cleaning, maintenance and maintenance help to identify problems in a timely manner, resolve potential failures, reduce downtime, and ensure normal production stability.
If the equipment is operated for a long time or due to improper operation, aggregates will appear in some equipments and affect normal operation. At this time, it is necessary to stop working for cleaning. For the cleaning of the aggregate in the drying tower, open the cleaning door, sweep the funnel-shaped bottom aggregate with a long broom, open the discharge valve, and rinse the tower with tap water. To remove the dust in the cyclone, it is also necessary to open the cyclone, sweep the aggregate with a broom, and rinse with water if necessary. For the cleaning of the bag filter, open the control switch, tap continuously, then open the cleaning door, hit the bag filter, and finally replace the filter bag. For the cleaning of the slurry pipeline system, the sewage valve of the two-way filter should be opened, the filter screen and the pipeline should be cleaned, and then the material pump should be opened to replace the pump tube, the pressure regulation package and the pipeline with water. After a period of operation (about 600 hours), the spray granulation dryer needs to be inspected and cured as necessary. For the feeding system, check the filter, pipe, valve, nozzle, etc. to see if there is any blockage, regular cleaning, check the nozzle wear condition for timely replacement. The material pump should be checked for oil leakage, whether the pressure is normal, and whether the oil level is normal. For the fan, check whether the shaft and the bearing are short of oil and heat, whether there is vibration or noise, etc. If necessary, clean the blades and balance the blades. For the heater, check whether the heat pipe is normal, and if necessary, clean the filter of the oil pipe, oil pump and grease nipple. In addition, you should also pay attention to whether the motor has heat, vibration, abnormal sound, etc., whether the instrument and electrical appliances of the control cabinet work normally.
In addition, the equipment needs to be partially disassembled and repaired by the maintenance personnel when the equipment is running for about 2400 hours (generally during the shutdown).
Huayi Foodstuff Co., Ltd. , http://www.ln-foods.com