The mini spray dryer machine process (spray drying) is a common drying technique used to quickly convert liquid substances into powder form. It is applicable to many fields, including food, medicine, chemical industry and so on. The basic principle of spray drying is to spray liquid into small particles, and then contact with hot air to evaporate water in an instant to form solid particles. The whole process can be divided into three main steps of spraying, drying and collecting.
Working Principle Of Spray Dryer
Spray dryer process
The spray dryer process is composed of three parts, the first part is to atomize the material liquid, the second part is to make the atomized material liquid contact with the air, and the third part is to separate the dried powder from the air .
The material liquid in the batching tank is sent to the high-speed centrifugal atomizer by the feeding pump, and the liquid is atomized into fine mist particles in the drying tower. The air at normal temperature is filtered by the blower through the primary and medium effect filters, and then heated to about 14o ℃ (pressure 6kgf/cm2) by the steam heater, and then heated by the electric heater to the set air inlet temperature of 220 ℃. After the first-stage filter (old equipment is not installed), it flows through the volute and the hot air distributor, and evenly enters the tower.
Fine mist droplets contact with high-temperature hot air, dry instantly, and continuously dry the residual water during the falling process. Most of the dry powder is discharged from the bottom of the tower, and some fine powder enters the secondary cyclone separator along with the air from the air duct to separate and fall into the the pipeline of the lower dehumidification air delivery system, the dehumidification cold air sends the dry powder into the clean room of the clean area, and the small cyclone separates the receiving material
Packing into bags. The dehumidified wind from the small cyclone is sent back to the drying tower to ensure that the tail powder is not discharged. The tail gas separated from the large cyclone is sent into the pipeline by the induced draft fan (most of the new equipment has been humidified and filtered for dust removal) to be emptied.
Characteristics Of Spray Drying
Compared with other drying technologies, the spray dryer process mainly has the following advantages:
① Fast drying speed:
After the material liquid is atomized by the atomizer, the volume increases thousands of times, and the evaporation of more than 90% to 95% of the water can be completed in an instant during the contact between the fine mist droplets and the hot air. According to the difference of different types of equipment, the drying time can be controlled within 5-30 s, the drying process is very fast.
②Suitable for drying heat-sensitive materials
During the spray drying process, the material is in direct contact with the hot air, but most of the heat is used to evaporate the moisture in the material liquid. The temperature of the material will not exceed the wet bulb temperature of the high-temperature air, and the quality of the material will not be affected by the high-temperature air.
The spray dryer process is very suitable for drying materials with a liquid-solid content of 0-60%. By changing the parameters of the spray dryer process, it is possible to produce powders that meet the requirements of particle size and shape, density, dispersibility, polymorphism and complex powders with precise powder properties such as flow properties.
④ Convenient operation and control
Low-temperature spray drying is usually used to deal with solutions with a moisture content of 40%-60%. Special materials can be dried into powder products at one time without concentration even if the moisture content is as high as 90%. Most of the products do not need to be destroyed and screened after drying, which reduces the production procedures and simplifies the spray dryer process. In addition, the particle size, bulk density and water content of the product can be adjusted by changing the operating conditions within a certain range, and the control and management are very convenient.
⑤Good product quality
During the drying process of the spray dryer, the temperature of the droplets is not high, and the product quality is better. According to the industry, the temperature range used for spray drying is very wide (80-800 degrees). In the early stage of drying, the temperature of the material does not exceed the wet bulb humidity of the surrounding hot air. The dry product is of better quality. For example, defects such as protein modification, vitamin loss, and oxidation are not easy to occur, and the quality of heat-sensitive materials, organisms, and drugs can basically be close to the standard of drying under vacuum.
Case Of Spray Drying In The Food Industry
Instant tea beverage:
Instant tea beverages usually require a tea concentrate to be extracted from the tea leaves. First, tea leaves are steeped in water to form a tea infusion. The tea extract is then filtered and clarified to remove solid particles and impurities. The extract is transformed into tea concentrate powder by spray drying technology. The extract is sprayed into tiny droplets, and the water evaporates quickly after contact with hot air to form a tea concentrate powder. The temperature and speed of spray drying can be adjusted according to product requirements to ensure the quality and solubility of tea concentrate powder.
Through spray drying technology, tea extract can be efficiently converted into tea concentrated powder, which facilitates the manufacture of instant tea beverages. Spray drying can quickly dry the liquid, avoiding the adverse effects of long-term high-temperature exposure on tea quality. This technology increases production efficiency while maintaining product flavor and quality.
Because certain food additives are easily affected by factors such as light, oxygen, temperature, and moisture in the environment, and the odor, odor, and spicy taste of food additives themselves have bad odors, which seriously affect their application in food and hinder the food industry. Development of.
With the birth of microcapsule technology in the 20th century, these problems were all solved, and the key of microcapsule technology is spray drying. Nglaytze et al. Studied the effects of different maltodextrin concentrations and spray-drying inlet temperature on the content of betatin in dragon fruit. The optimal spray-drying conditions obtained were the inlet temperature of 155°c and the concentration of maltodextrin of 20%.
Common Problems And Improvements
Fault 1: Wet powder adheres to the inner wall of the main tower.
(1) the amount of feed is too large to fully evaporate;
(2) insufficient heating of the drying chamber before spraying starts;
(3) when spraying starts, the discharge flow rate is adjusted to too large;
(4) the feed liquid added is unstable.
Appropriately reduce the amount of feed; appropriately increase the inlet and outlet temperatures of hot air; at the beginning of spraying, the flow rate should be small, gradually increase, and adjust until appropriate; check whether the pipeline is blocked, adjust the solid content of the material, and ensure the flow of the material liquid sex.
Fault 2: The phenomenon of powder running out is serious, and the recovery rate of the product is low.
If there is a problem with the cyclone separator, or the dust removal performance is low, powder running is easy to occur. In response to this phenomenon, the solution to the former is to check the cyclone separator to see if there is a gap and whether the airtightness is intact; the solution to the latter is to appropriately increase the secondary dust removal.
Fault 3: High moisture content.
Generally, the exhaust air temperature is too low. Properly reduce the amount of feed to increase the temperature of the exhaust air.
Fault 4: The powder is too fine and the solid content is too low or the feed amount is too small.
Increase the solid content of the feed liquid, increase the amount of feed, and increase the temperature of the inlet air.
Fault 5: The nozzle speed is low and the centrifugal nozzle component is faulty.
Check the printhead internals.