What Is a Spray Dryer?
Spray dryer [1] is a device that can complete drying and granulation at the same time. According to the requirements of the process, the pressure, flow rate, and nozzle size of the material liquid pump can be adjusted to obtain the required spherical particles in a certain size ratio. Spray dryer is a type of continuous atmospheric dryer. The liquid material is sprayed into a mist form by special equipment, and it is dried by contact with hot air. Used to dry some heat-sensitive liquids, suspensions and viscous liquids. It is also used to dry fuels, intermediates, soap powder and inorganic salts. Generally includes electric heating blast drying box, vacuum drying box, high-speed centrifugal spray dryer, aseptic spray dryer. The working principle, basic classification, characteristics, technical parameters, application range and operation process of spray dryer are introduced in detail.
- Spray dryer is a type of continuous atmospheric dryer [2]
- After filtering and heating, the air enters the air distributor at the top of the dryer, and the hot air enters the drying chamber uniformly in a spiral shape. The material liquid is sprayed into a very fine mist-like liquid bead through a high-speed centrifugal atomizer at the top of the tower body, and can be dried into a finished product in a very short time in contact with hot air in parallel. The finished product is continuously output from the bottom of the drying tower and the cyclone, and the exhaust gas is evacuated by the induced draft fan [3]
- The drying speed is fast, and the surface area of the material liquid is greatly increased after being atomized. In the hot air current, 95% -98% of water can be evaporated in an instant. The drying time is only a few seconds. It is especially suitable for drying heat-sensitive materials.
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- Material name, physical properties: solid content (or water content), viscosity, surface tension, PH value [3]
- * Chemical industry: battery raw materials, basic dye pigments, dye intermediates, compound fertilizers, formaldehyde silicic acid, catalysts, sulfuric acid agents, amino acids, white carbon, etc.
- Mainly suitable for spray drying of suspended liquids and high viscosity materials or solid content liquids [3]
Spray dryer preparation
- The material to be sprayed needs to be thoroughly emulsified and homogenized through a homogenizer and passed through an 80-mesh screen (to avoid clogging the atomizer and pipes), and placed in a stainless steel barrel for use. Another bucket of tap water is used to clean the atomizer and spray cavity. Install the peristaltic pump's material tube, clamp it tightly, cover it with 8 size nuts at the front of the inlet (to prevent air from floating up and suck in air), put it in the material tank for backup [6] .
Spray dryer inspection
Check whether the butterfly valves on the pipeline connecting the dehumidifier and the collecting bucket are all open. The damper on the spray tower should be fully open. The spray cabin door should be closed firmly. The quick-release clamps of each connecting pipeline should be installed correctly. The air outlet valve of the compressor should be opened, the exhaust valve closed, and the air pressure pipe connected well.
Spray dryer start-up procedure
Press the switch of the dehumidifier, close the air relay switch of the spray dryer, adjust the air pressure of the air compressor to 0.25Mpa (you can press the black button to adjust it and then press it), turn the red emergency stop button clockwise to open the LCD operation Screen, wait for 15S to automatically enter the operation interface, set the process parameters: set temperature 180 ° C, lower limit temperature 180 ° C, upper limit temperature 192 ° C, temperature between the set and lower limit, heating on time 10s, heating off time 3s, The vibrator is set to vibrate 2S and stop 2-10S (refer to the accumulation of materials on the wall). If the solid content of the water spray is very low, the set temperature should be adjusted to 185-190 ° C, and the lower limit is changed to 185 .
First turn on the induced draft fan, dehumidifier, and electric heating switch (the electric heating will turn on the automatic button, otherwise the temperature will not jump off when the temperature reaches the set temperature, and continue heating), preheat the system, the lighting can be always on, waiting for monitoring. When the temperature of the wind reaches the set temperature, the temperature of the output air reaches 80-90 degrees and the temperature is relatively stable, turn on the atomizer 30S, and then turn on the peristaltic pump switch in the interface, and adjust the speed to between 12-18 (depending on the material (Adjustment), start the peristaltic pump slowly in the early stage, do not introduce air into the material tube (high temperature of the atomizer, lack of new material cooling will quickly dry a small amount of liquid and block the atomizer), the direction arrow on the atomizer points "", press the Start key on the atomizer to start creep feeding. When the material enters the atomizer and starts spraying, turn on the vibrator (double air hammer) and observe the atomization and the temperature of the air outlet. If the air outlet temperature is higher than 90 degrees, you can slowly adjust the speed of the peristaltic pump (each time 0.5- 2) Continue to observe the temperature of the air outlet to see if it is stable. The temperature of the air outlet drops to 86-88 degrees and stabilizes. This is a normal spray flow rate (depending on factors such as material viscosity and solid content). Always observe the temperature of the air outlet and adjust it. The best material flow rate (empirical value is 17-18, hot pepper water is 32, chicken paste is dissolved with 1: 2 water is about 28).
Spray drying machine program
Immediately after all the materials have been sucked, put the feeding pipe head into the cleaning bucket, use water spray to clean the atomizer, adjust the speed of the peristaltic pump to about 15 (water has no solids, it is more difficult to spray dry), and observe the feeding pipeline after 5 minutes Whether it is cleaned with tap water, and then run for another 2-3 minutes until the atomizer is cleaned. Turn off the peristaltic pump and open the clamp on the pump to allow the water in it to flow back into the bucket. Wait for 3-5 minutes, after the atomizer sprays the remaining water, you can turn off the atomizer. When there is no fog, you can turn off the electric heating and vibrator, and wait for it to cool down naturally. When the inlet air temperature reaches below 150 ° C, you can open the hatch and use an air gun tip to blow down where there is material accumulation. Pay attention to each dead angle, aim at the bottom pipe elbow and let the material be recovered through the cyclone separator. After the powder is cleaned, close the door and blow the material. After 1 minute, turn off the induced draft fan and dehumidifier. Close the butterfly valve at the discharge port, remove the collector, and pour the powder out of the bag to prevent moisture.
Spray dryer cleaning spray tower
- Loosen the quick-release clamp on the official channel on the right side of the collector, and then remove the clamp at the bottom of the spray tower, you can rotate this section tube to the side, and put a large basin at the bottom of the spray tower to receive water. Turn on the atomizer and the peristaltic pump, put the feeding hose into the cleaning bucket to absorb water, press the Start button to start the peristaltic water absorption, and quickly adjust the speed to 100 after spraying. The maximum amount of water is used to clean the atomizer and the internal bulkhead. 3 -5min. According to the operation procedure, first turn off the peristaltic pump and let off the water in the material tube. After 2 minutes, turn off the atomizer, and then press the emergency stop button to shut down and turn off the relay in the control cabinet. Open the hatch and connect a water pipe to flush the dirty interior bulkhead. Be careful not to flush the water into the hole on the top of the atomizer (to prevent water from pouring into the heater) and rinse the inner wall thoroughly.
Spray dryer cleaning surrounding accessories
- Remove the 2 cutting pipes connected to the cyclone separator, the butterfly valve at the discharge port, the collector, the clamp, and the silicone gasket, clean them all and control the dry water. When cleaning the cyclone separator, first remove the peripheral connection accessories, and then be sure to close the outlet butterfly valve of the dehumidifier (to prevent water from being poured into the dehumidifier), flush the water at the inlet of the separator with a water pipe, and connect the outlet with a water basin. Water should not be splashed into the dehumidifier to burn the motor. Repeat the washing several times at multiple angles until the outflow of waste water is colorless and clear.