Spray drying tower is a device that can complete drying and granulation at the same time, is a very common equipment in the field of biopesticides, pharmaceuticals, food microorganisms and other fields.

Today for you to introduce in detail the working principle of spray drying tower, characteristics, operating procedures, common failure repair methods and operational considerations, so that partners have a short period of time on the spray drying tower have a deep understanding!

Main functions

The solution state of the material can be sprayed into the spray drying tower, the material is dried solid powder state out of the material, according to the process requirements can be adjusted to the liquid pump pressure, flow, the size of the spray hole, to get the desired proportion of the size of the spherical particles according to a certain size. Mostly used in biological pesticides, pharmaceuticals, food microorganisms drying.

Principle of action

The air is filtered and heated, and enters into the air distributor at the top of the dryer, and the hot air enters into the drying chamber uniformly in spiral shape.

The material liquid is sprayed into very fine mist liquid beads by the high-speed centrifugal atomizer or high-pressure atomizer at the top of the tower, which can be dried into finished products in a very short time by contacting with the air in parallel flow.

The finished products are continuously output from the bottom of the drying tower and the cyclone separator, the fine dust material is collected by the pulse bag collector, and the exhaust gas is exhausted by the fan.

Features of spray drying tower

1、Fast drying speed, completion takes only a few seconds;.

2、Suitable for drying heat-sensitive materials.

3, the use of a wide range: according to the characteristics of the material, can be used for hot air drying, centrifugal granulation and cold air granulation, most of the characteristics of the products are very different from the production of this machine;.

4、Because the drying process is completed in an instant, the finished particles can basically keep the droplets approximate spherical, the product has good dispersion, fluidity and solubility.

5、The production process is simplified and the operation control is convenient. Spray drying is usually used for solid content of 60% or less of the solution, after drying, do not need to be crushed and screened, reducing the production process, simplify the production process. For the product particle size, bulk density, moisture, within a certain range, can change the operating conditions for adjustment, control, management are very convenient;.

6, in order to make the material is not contaminated and prolong the life of the equipment, all contact with the material part, can be made of stainless steel.

Main types

1. Centrifugal spray

High-speed centrifugal spray drying is the most widely used process in the liquid process forming and drying industry.

It is most suitable for generating powdery and granular solid products from solutions, emulsions, suspensions and pasty liquid raw materials. Therefore, when the particle size distribution, residual moisture content, bulk density and particle shape of the finished product must meet precise standards, spray drying is a very ideal process.

Performance characteristics:
(1) fast drying speed, the material is atomized by the surface area greatly increased in the hot air stream, the instant can be evaporated 95% -98% of the water, the completion of the drying time in just a few seconds, especially suitable for heat-sensitive materials drying.
(2) The product has good uniformity, fluidity and solubility, high purity and good quality.
3）The production process is simplified and the operation control is convenient. For the moisture content of 40-60% (special materials up to 90%) of the liquid can be dried into powder products at one time, control and management are very convenient.

Applicable materials:

• Chemical industry: sodium(potassium) fluoride, alkaline dyestuff and pigment, dyestuff intermediate, compound fertilizer, formaldehyde silicic acid, catalyst, sulfuric acid agent, amino acid, white carbon black, etc.
• Plastic resin: AB, ABS emulsion, urea-formaldehyde resin, phenol-formaldehyde resin, mastic (urea) formaldehyde resin, polyethylene, polyvinyl chloride and so on.
• Food industry: enriched milk powder, tickle prion, cocoa milk powder, milk replacer powder, hunting blood powder, egg white (yolk) and so on.
• Food and plant: oats, chicken juice, coffee, instant tea, flavored spices meat, protein, soybean, peanut protein, hydrolysis, etc.
• Sugar: corn syrup, corn starch, glucose, pectin, maltose, potassium sorbate, etc.
• Ceramics: aluminum oxide, tile materials, magnesium oxide, talcum powder, etc.

2.Pressure spraying

The working process of this unit is that the material liquid is input by diaphragm pump at high pressure, spraying mist droplets, and then drop with the hot air, most of the powder particles are collected by the discharge port at the bottom of the tower, and the exhaust gas and its tiny powder are separated by the cyclone separator, the exhaust gas is discharged by the exhaust fan, and the powder is collected by the powdering cylinder located at the lower end of the cyclone separator, and the outlet of the fan can be equipped with the second level of dust removing device, with the recovery rate of 96-98% or more. The recovery rate is above 96-98%.

Performance characteristics:
(1) fast drying speed, the material is atomized by the surface area is greatly increased, in the hot air stream, can instantly evaporate 95% -98% of the water, the completion of the drying time is only a dozen or so seconds to dozens of seconds, especially suitable for heat-sensitive materials drying.

(2) All products are spherical particles, uniform particle size, good fluidity, good solubility, high purity and good quality.

(3) Wide range of use, according to the characteristics of the material, can use hot air drying, can also use cold air granulation, strong adaptability to the material.

4）Simple and stable operation, convenient control, easy to realize automatic operation.

Adaptable materials:

Spray drying granule:

• Chemical industry: catalysts, resins, synthetic laundry detergent, oil and grease, ammonium sulfate, dyes, dye intermediates, silica, graphite, ammonium phosphate and so on.
• Foodstuffs: amino acids and analogues, flavorings, proteins, starch, dairy products, coffee extracts, fish meal, meat extracts, etc.
• Pharmaceuticals: proprietary Chinese medicines, pesticides, antibiotics, pharmaceutical preparations, etc.
• Ceramics: magnesium oxide, china clay, various metal oxides, dolomite, etc.

Spray granulation: all kinds of fertilizer, alumina, ceramic powder, pharmaceuticals, heavy metal super-hard steel, fertilizer, granular laundry detergent, proprietary Chinese medicine.
Spray cooling granulation: amine-based fatty acids, paraffin, glycerin, tallow, etc.
Spray crystallization, spray concentration, spray reaction is often used.

3.Chinese medicine spraying

The machine adopts fully closed form, all parts are made of stainless steel, equipped with three-stage purification device, filtered air up to 100,000 grade requirements. The cylinder and the top are equipped with cold wall device to make the wall temperature <80℃, and the drying tower is equipped with air brush sweeping tower device.

After the drying of Chinese medicine extract powder by this machine, there will be no coking and deterioration phenomenon, greatly increasing the powder rate (more than 95%), and will not produce the phenomenon of mixing and sticking wall phenomenon.

Working Principle:
High-speed centrifugal spray device for Chinese medicine extract is the application of centrifugal spray drying technology in specific material drying, and also the use of high-speed centrifugal atomizers to make the material dispersed into a mist, and the full contact with the hot air, to complete the instantaneous drying, the formation of powdered finished products of the drying device.

Performance characteristics:
(1) The tower body has a cold air jacket;
(2) The tower is equipped with automatic vibration device;
(3) The tower and pipeline are equipped with quick-opening cleaning holes and sewage holes;
4 ） Can be equipped with automatic control of constant temperature charging tank;
5 ） It can be equipped with manual high-pressure washing tower random accessories;
(6) the part in contact with the material is made of stainless steel; (or all stainless steel manufacturing)
(7) The material collection adopts bipolar cyclone dust collector, or primary cyclone dust collector and wet dust collector;
8 ） Inlet air temperature realizes automatic control and continuous device.
9 ） It can be equipped with air sweeping device

4. Airflow spray

Mainly air or water vapor through the high speed from the nozzle spray, relying on friction to make the material liquid separation into fine droplets, so that it is in complete contact with the hot air to form a heat exchange, the whole process is less than half a minute. The effect is very good for the viscous material, which is incomparable with other spray dryers. And it is easy to operate.

Product application:
The main applications are chemical industry: latex, dyes, resins, etc.; food industry with maltose, dextrin, starch, etc.; dairy industry, building materials industry is also often used.

Operation Procedure

The operation procedure of the spray drying system is as follows: clarifying the technical characteristics of the equipment → equipment inspection and confirmation → production operation → parking operation → cleaning system. Specific procedures are as follows:

1. Define the technical characteristics of the equipment (spray drying tower)

Liquid handling capacity: 270-400kg/h; evaporated water: 170-250kg/h; finished product output: 100-150kg/h;
Inlet air temperature ≥ 185-240 ℃; air temperature ≤ 95 ℃.

2. Equipment inspection confirmation

• Check whether the production water, electricity and steam are normal or not; check whether the voltage and current meter signals are normal.
• Check the oil level of the stirrer in the middle tank and add lubricating oil in time; tighten the stirring paddle in time if it has fallen off; start the stirrer and observe whether it rotates normally and whether there are no noises.
• Whether the pipeline connection is loaded with good sealing material, and then connect it to ensure that no unheated air is allowed to enter the drying chamber.
• Before driving operation, the drying room, material pipeline, intermediate tank, receiving cylinder and other devices and parts in contact with the material should be cleaned, in line with the health requirements of product quality. (Wash the tank and high pressure pipe with 90℃ hot water before driving)
• Add lubricant to each lubrication point of the equipment as required.
• Check whether each transmission equipment is running flexibly and whether the steering is correct by pointing.
• Close the observation window, put on the receiving cylinder, and check whether the sealing condition of the pipeline joints and valves is good.
• Whether the process parameters and operating procedures are clear.
• Thoroughly drain the steam condensate from the sub-cylinder and pipeline, and slowly open the steam valve.

3. Production operation

(1) first open the blower → open the exhaust fan to open the electric heating to taste → open the atomizer → maintain negative pressure 100-200 Pa, exhaust the steam condensate in the steam cylinder and steam pipe, slowly open the steam valve, preheat the drying tower 0.5-1 hours or so (air ducts, towers, etc., condensate is all turned into steam discharged before you open the material pump feed).

(2) Normal negative pressure after feeding to maintain 50-150Pa, adjust the amount of material, control tower temperature 75-90 ℃, moisture less than 5%; drying process at any time to pay attention to the material level in the material tank.

(3) Finished product packaging: spray-dried and cooled to room temperature of the seasoning (powder) products in accordance with the standard inspection, according to the quality requirements of the bag weighing, into the inspection certificate, sealing and sewing package into the warehouse (warehouse requirements to maintain good ventilation and dry).

4.Parking operation

(1) each batch of material drying is completed, add the middle tank of hot water switch to open, in order to clean the atomizer, atomization disk, material pipe, pumps and so on.

(2) the parking order is to stop steam → feed pump → electric heater → atomizer (adjust the air temperature, so that the feed speed between 15-20, the air temperature down to 150 ℃, off the atomizer) → close the vibration → drying exhaust fan → air supply organs (air temperature down to 110 ℃) → closed power.

5. Cleaning system

1) In order to ensure that the drying tower body and its pipeline and all the parts in contact with the finished product clean, get first-class products, there are rules for cleaning equipment is very necessary.

2) When the product replacement, or equipment has been stopped for more than 24 hours without cleaning, should be made a comprehensive and thorough cleaning.

Dry cleaning: sweeping with brush, broom, vacuum cleaner. Wet cleaning: Clean with hot water at 60-80℃.

Acid washing: formulate nitric acid (HNO3) into a solution of 1-2% concentration and heat it at a temperature not exceeding 95℃ for washing, and then wash it with water.

Alkali washing: sodium hydroxide (NaOH) is prepared into a 0.5-1% concentration solution, heated to 60-80 ℃ for washing, and then cleaned with water.

(3) When wet washing and chemical washing are carried out, the equipment and parts should be installed and sterilized at high temperature for 15-30 minutes.

4) When this equipment is cleaned, it should be noted that it cannot be washed with chlorine and its compounds.

(5) The cleaning of the air filter should be according to the surrounding environmental conditions, that is, the high and low dust content in the air, generally high content of 3-6 weeks to clean once, low dust content of 6-8 weeks to clean once.

Common failure repair methods

1. Sticky wall phenomenon

(1) the feed amount is too large, can not be fully evaporated.
(2) spray before the start of the drying chamber heating is insufficient; (3) the start of the drying chamber heating is insufficient; (4) the drying chamber heating is insufficient.
(3) Start spraying, the lower material flow rate is adjusted too large; (4) Add the material to the drying chamber, the drying chamber is not heated enough.
(4) The added material is not stable.

Repair method:

• Appropriately reduce the amount of feed material.
• Appropriately increase the inlet and outlet temperature of the hot air.
• At the beginning of spraying, the flow rate should be small, gradually increase, adjusted to the appropriate time until;.
• Check whether the pipeline is blocked, adjust the material solids content, to ensure the fluidity of the material.

2. High moisture content

Generally the exhaust air temperature is too low. Appropriately reduce the amount of feed to improve the exhaust air temperature.

3. Low purity

(1) poor air filtration.
(2) the accumulation of powder mixed into the finished product.
(3) The purity of raw materials is not high.
(4) equipment cleaning is not complete.

Repair method:

• Check whether the filtering material in the air filter is uniformly laid, whether the filter use time is too long, if so, it should be replaced immediately;.
• Check the hot air inlet coke powder situation, to overcome the eddy current.
• The material should be filtered before spraying; re-clean the equipment.

4. Powder is too fine

The solid content is too low or the feed amount is too small. Improve the solid content of the liquid material, increase the feed volume, increase the temperature of the air inlet.

5. Run powder phenomenon

The separation effect of cyclone separator is poor.
Repair methods:
(1) Check whether the cyclone separator is deformed due to knocking and collision; (2) Improve the separation effect of the cyclone separator.
(2) Improve the airtightness of the cyclone separator inlet and outlet; (3) Check whether the cyclone separator is deformed due to knocking and collision.
(3) Check whether the inner wall and the outlet are blocked with accumulated materials.

6. Low nozzle speed

The centrifugal nozzle parts are out of order. Check the internal parts of the nozzle.

7. Low evaporation

(1) The air volume of the whole system is reduced.
(2) Inlet temperature of hot air is low.
(3) There is air leakage in the equipment, and cold air enters the drying chamber.
Repair method:

(1) Check whether the speed of centrifuge is normal.
(2) Check whether the centrifuge regulating valve position is correct.
(3) Check whether the air filter and air heater pipe are blocked.
(4) Check whether the grid voltage is normal.
(5) Check whether the electric heater is working properly; (6) Check whether the components of the equipment are connected.
(6) Check whether the connection of each component of the equipment is sealed.

8. Nozzle vibration

Fault causes:

(1) improper cleaning and maintenance of the spray nozzle caused by the spray disk with residual substances or the spindle to produce bending and deformation.
(2) centrifugal disk dynamic balance is not good.

Repair method:
(1) check whether there is residual material in the spray disk, if so, should be cleaned in a timely manner.
(2) Replace the main shaft if there is any abnormality.
(3) Re-adjust or replace the dynamic balance of the centrifugal disk.

Precautions for operation

1、First turn on the centrifugal fan, then turn on the heater, and check whether there is air leakage, such as normal preheating can be carried out, because the preheating of the hot air determines the evaporation capacity of the drying equipment, under the premise of not affecting the quality of the material to be dried, the temperature of the incoming air should be increased as much as possible.

2、Pre-heating drying room top atomizer placed at the drying room and cyclone separator under the mouth must be sealed, so as to avoid cold air into the drying room, reduce the efficiency of preheating.

3, when the drying chamber inlet temperature reaches the set temperature, open the centrifugal nozzle, when the spray head reaches the highest speed, open the feed pump, add water spray for 10 minutes and then replace it with material, the amount of feed should be from small to large, otherwise it will produce the phenomenon of sticking to the wall, until adjusted to the appropriate requirements. The concentration of material liquid should be formulated according to the nature of material drying to ensure that the finished product has good fluidity after drying.

4, dry the temperature and humidity of the finished product, depending on the exhaust air temperature, in the process of operation, to maintain the exhaust air temperature is a constant is extremely important, which depends on the size of the feed volume, the amount of material under the stable, the exit temperature is relatively stable. If the solid content of the material and liquid flow changes in the export temperature will also change.

5, the product temperature is too high, you can reduce the amount of feed to improve the export temperature, the product temperature is too low, and vice versa. For the product temperature is low heat-sensitive materials can increase the amount of charging to reduce the exhaust temperature, but the temperature of the product will be increased accordingly.

6、Collection of finished products after drying. In the cyclone separator in the lower part of the pollination device, not filled before it should be replaced, in the replacement of pollination device, must first close the butterfly valve above can be carried out.

7, if the dried finished product has hygroscopicity, cyclone separator and its pipeline, pollinator parts should be adiabatic material wrapping, so as to avoid drying the finished product back moisture absorption.