What is a spray dryer?
Spray dryer is one of the most widely used types of dryers, which is used to dry a wide range of chemical, industrial, and food solutions and slurries.
How spray dryer works?
In the spray dryer, the desired solution or slurry is pumped by high pressure piston pumps to the special nozzles or atomizer of the device, and the solution is exposed to hot air after being sprayed into the cylindrical tank of the spray dryer. Due to the increase of the surface of the solution to its volume, the evaporation of the solution water is done easily and quickly, and the dissolved material or slurry injected into the device evaporates as soon as it dries, and the material falls solid down into the funnel. Most of the produced solids fall into the funnel of the machine and some of it is drawn to the cyclone and filter bag together with the steam and hot air produced by the aerator, and in this way the solution containing dried materials and solids It is isolated.
Uses and applications
- Drying all kinds of chemicals such as iron sulfate, zinc sulfate, manganese sulfate, magnesium sulfate, etc.
- Drying of tile glaze grouts and ceramic manufacturing industry
- Production of powdered milk and drying of edible materials such as maltodextrin
- Whey drying
- Drying egg whites and yolks
The main components and parts
Spray dryers are usually made of a cylindrical body that is placed vertically and a funnel with a slope of more than 60 degrees is placed in its lower part. Some spray dryers (especially in the food industry) are made in the form of cubic tanks for ease of construction and to reduce construction costs, as well as to simplify the division and direction of hot air flow.
Spray dryer air generator or hot air furnace: It is used to supply hot air and its burner may be of a gun or stove type. It is better for the spray dryer burner to have a command system, electrical panel and modular damper to automatically keep the temperature inside the device constant.
Centrifugal suction fan: to draw the flow of hot air produced by the burner, create a regular flow of air and remove the water vapor produced inside the spray dryer nozzle. It is better to have blades
Cyclone dust collector: separation of produced solid particles that have passed through the main nozzle of the spray dryer and its separation from air and steam coming out of the device.
High pressure pump: Due to the need for high pressure for effective atomization of the solution, high pressure pumps (100-200 bar) should be used. The most used spray dryer pumps are piston pumps. Like the pumps used in the car wash.
Nozzle or atomizer device: The nozzle is used to spray the solution into the inner space of the device until the size of the solution drops reaches the desired minimum and the ratio of the solution surface to its volume reaches the maximum possible value. In the spray dryer, wear-resistant nozzles (due to the high pressure of the flow) are used for powder spraying of the solution. The type of nozzles is different depending on the type of passing solution. Steel 316 and tungsten carbide are the most important alloys in the manufacture of spray dryer nozzles. It is also possible to use a disk atomizer to spray the solution into the tank of the spray dryer. The advantage of the atomizer compared to the nozzle is much less consumption and better atomization power of the solution. Of course, the cost of installing an atomizer is much higher than a nozzle.
Bag filter: In some cases, the bag filter is used to completely purify the air coming out of the spray dryer. Of course, the presence of hot steam in the exhaust air of the bag filter may cause vapor condensation and clogging of the bag filter bags. The rapid decay of the filter bag due to the presence of hot steam also makes it difficult to use it in a spray dryer.
Exhaust: The exhaust pipe is installed to remove the exhaust steam of the spray dryer from the surrounding environment. Of course, by installing a condenser, most of the output vapors can be condensed and the water used can be recovered.
Advantages and disadvantages
Pros of Spray Dryer:
It includes drying, pulverizing, and packing operations at the same time, which are done separately in other dryers. Better drying quality and high efficiency of evaporation and less consumption of thermal energy and fuel compared to other dryers are the advantages of spray dryers.
Cons of Spray Dryer:
High cost of construction and investment, complexities used, and the need for experienced workers. Of course, the use of advanced automation and the installation of the HMI board can make it easier to use and minimize operator error.
Important and effective factors in design
- Soluble density
- The viscosity of the solution
- Spray dryer tank height
- Suitable temperature for
- drying the solution
- Tank temperature (the temperature is adjusted
- depending on the relevant materials, for example, a temperature of less than 65 degrees is suitable for drying maltodextrin, and a temperature of 250 degrees is suitable for drying manganese sulfate)
- Type of solution spray
