The spray granulation dryer is an important equipment in the PFA production process. The equipment is expensive, complex in composition, and difficult to use and maintain. The good operation of the equipment can not only ensure the normal production of PFA, but also extend the service life of the equipment and reduce the production cost. Therefore, it is necessary to operate the equipment correctly and strengthen the maintenance.

1. Principle and composition of spray granulation dryer

Granulation is a very important process in the production of PFA, and the quality of pellets directly affects the appearance, mechanical properties and resistance-temperature characteristics of PFA. Granulation refers to the addition of a certain amount of binder to the ground powder, uniform and after the formation of PFA granular powder, this powder has good fluidity and calendering, so that in the tabletting process can be obtained with good strength, not easy to delamination cracking of the film. Spray drying granulation is used in industrial production. The basic principle is to spray the powder with adhesive into the granulation tower for atomization. The mist droplets in the tower are dried into PFA granular powder by hot air in the tower, and then discharged from the bottom of the drying tower.

The pressure spray granulation dryer used in PFA processing plant 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 barrel, a filter, a diaphragm pump and a spray gun. The ball-milled secondary slurry is transferred from the ball mill to the stirring tank, pumped by the diaphragm pump through the filter and transferred, and then enters the drying tower through the spray gun.

The slurry from the spray gun nozzle into the drying tower to start the spray granulation drying process, the specific process is divided into three stages:

(1) slurry atomization. The slurry is pressed into the drying tower from the nozzle with a certain pressure by the diaphragm pump in the feeding system, and the energy of the pressure is converted into kinetic energy. The slurry is sprayed from the nozzle from bottom to top to form a layer of high-speed liquid film, which is then split into droplets. The droplet size produced by atomization is inversely proportional to the pressure, and the productivity of the nozzle is proportional to the square of the pressure.

(2) fog particles dry into a ball. Mist particles and hot air work in the form of mixed flow. The hot air enters the tower through the hot air distributor on the top cover. The hot air distributor generates a downward streamline air flow, and the mist droplets are sprayed into the hot air flow from bottom to top. The droplets form a spherical shape due to surface tension, and because the droplets have a large surface area, the water evaporates rapidly and dries, and eventually shrinks to form a dry spherical shape.PFA GranulesPowder.

(3)PFA particle powder discharge. The formed spherical PFA particle powder gradually settles in the drying tower and is separated from the hot air. The funnel cavity at the lower part of the tower collects the PFA particle powder and discharges it from the discharge port. The finer PFA particles are drawn together with the drying air by the suction fan connected to the funnel-shaped upper part into the dust removal system. The blower, the drying tower and the exhaust fan for conveying hot air to the drying tower form the drying system.

The dust removal system consists of a high-efficiency cyclone separator, a bag filter, and a centrifugal fan. The suction fan sends the finer PFA particles together with the dry air into the high-efficiency cyclone separator. After effective separation, the finer PFA particles enter the collection cylinder at the bottom of the separator for recovery, and the remaining waste gas containing a very small amount of fine PFA particles is sucked into the bag filter by the centrifugal fan and collected again through dust removal, thus realizing the harmless treatment of the waste gas, and the final waste gas is discharged from the chimney.

In addition, a heating system consisting of an electric heater and a gas engine hot blast stove provides hot air for the drying tower. Electrical control cabinet and installed in the air inlet and outlet to monitor the temperature of the field sensors and other components of the electrical system of the spray granulation dryer to monitor and control the main links to ensure the normal operation of the entire equipment.

2. Daily operation and matters needing attention

In the daily production process, the necessary preparations should be made before starting the equipment. First of all, check whether the connection between the bearing and the sealing part of each device is loose, the lubricating oil condition of each mechanical part and whether the valve ports of each water, air and slurry pipe are in the required position. Then turn on the power supply to check whether the voltage and instrument are normal, and finally check the amount and concentration of slurry in the slurry mixing barrel. If there is any problem, it should be eliminated in time.

Then turn on the blower and exhaust fan in turn, and then turn on the heating switch to start heating up. When the outlet temperature reaches the set temperature (generally about 130 ℃), start the material pump and dust removal system. When the pump pressure reached 2MPa, open the spray gun to start granulation. After the equipment is in operation, the atomization situation and the working condition of the material pump shall be observed in time. If the gun is blocked, the nozzle shall be cleaned or replaced immediately. After the normal operation of the equipment, it is also necessary to regularly receive materials, regularly check the operation of each system, record each process parameter, and pay attention to cleaning the vibrating filter screen.

At the end of granulation, the heating device should be shut down first to stop the operation of the gas engine. Then close the gun valve, replace the gun, unscrew the nozzle and flush it. When the inlet temperature is reduced to below 100 ℃, the operation of the blower and exhaust fan can be stopped. Then clean up the residual material in the drying tower and dust collector, close the dust collector and air hammer, and finally close the total power supply to complete the production operation.

In case of emergency, the equipment must be shut down immediately, and the blower and material pump should be shut down first. In case of sudden power failure, pull out the gas engine to cool down the tower naturally, then open the blowdown valve to drain the slurry in the slurry pipeline and clean the equipment.

3. Maintenance and Maintenance

Granulation is an important part of the PFA production process, and maintaining the normal operation of the equipment is a necessary condition to ensure the stability of PFA production. Regular cleaning, maintenance and maintenance help to find problems in time, solve potential failures, reduce downtime, and ensure normal and stable production.

If the equipment runs for a long time or due to improper operation, aggregates will appear in some equipment, which will affect the normal operation. At this time, the work needs to be stopped for cleaning. For the cleaning of aggregate in the drying tower, the cleaning door should be opened, the aggregate at the bottom of the funnel should be swept with a long broom, the discharge valve should be opened, and the tower should be flushed with tap water. For the removal of dust collected in the cyclone separator, it is also necessary to open the cyclone separator, clean the aggregate with a broom, and flush with water if necessary. For the cleaning of the bag filter, turn on the control switch, knock continuously, then open the cleaning door, knock on the bag filter, and finally replace the filter bag. For the cleaning of the slurry pipeline system, the drain valve of the two-way filter should be opened to clean the filter screen and pipeline, then the material pump should be opened to replace the material with water, and the pump pipe, pressure stabilizing bag and pipeline should be cleaned. After a period of operation (generally about 600h), it is necessary to carry out the necessary inspection and maintenance of the spray granulation dryer. For the feeding system, check the filters, pipes, valves, nozzles, etc. to see if there is any blockage, clean them regularly, and check the nozzle wear so as to replace them in time. Check whether the material pump leaks oil, whether the pressure is normal, whether the oil level is normal, etc. For fans, check whether the shaft and bearings are short of oil and heat, vibration and noise, etc., and clean the blades and balance and check the blades if necessary. For the heater, check whether the heat pipe is normal, and clean the filter screen of the oil pipe, oil pump and oil nozzle if necessary. In addition, attention should also be paid to the presence of heat, vibration, abnormal sound, etc. of each motor, and whether the instruments and electrical appliances of the control cabinet work normally. In addition, during the operation of the equipment for about 2400h (generally during the period of shutdown), the maintenance personnel shall carry out partial disassembly and maintenance of the equipment.

This article comes from:www.tflpfa.com

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