The MSDTM (Multi-Stage Dryer)/ FSDTM (Fluidized Spray Dryer)
A MSDTM (Multi-Stage Dryer) or FSDTM (Fluidized Spray Dryer) is a dryer that combines spray drying and fluid bed drying technologies. Through the process it produces coarse, agglomerated, free-flowing dustless powder. This drying principle was first introduced in the early 70'es by using the VIBRO-FLUIDIZER® for the final drying.
A new dryer concept
GEA Niro has always focused on developing dryers with improved energy efficiency and final product quality, and in order to improve the dryer efficiency even further, without deposit problems in the chamber, a completely new spray dryer concept - named MSDTM (Multi-Stage Dryer) - was developed around 1980. Since then GEA Niro has delivered more than 300 plants with the MSDTM/FSDTM concept.
Drying in more stages
The first necessary step to reach the concept of the MSDTM was spray drying in two stages. The MSDTM/FSDTM operates with three drying stages, each adapted to the moisture content prevailing during the drying process. In the preliminary drying stage the concentrate is atomized by co-current nozzles placed in the hot drying air duct.
The air enters the dryer vertically through the air disperser at high velocity, ensuring optimal mixing of the atomized droplets with the drying air. The evaporation at this stage takes place instan-taneously during the passage vertically down through the specially designed drying chamber. In this primary drying stage the particles reach a moisture content of 6-15 %, all depending upon the type of product.
Second-stage drying
At such high moisture content the powder will exhibit high thermo plasticity and becomes very sticky. But the design and air flow pattern in the MSDTM plant is created in a way, that prevents the particles from sticking to the drying chamber, but be led directly into the integrated static fluid bed for the second-stage drying.
The integrated static fluid bed is supplied with air at a sufficient velocity and temperature for the second stage drying. The drying air from the preliminary drying stage and the subsequent second-stage drying leaves the chamber from the top.
VIBRO-FLUIDIZER®- final drying and cooling
When the powder has reached a certain moisture content, it is discharged via a rotary valve into a VIBRO-FLUIDIZER® for the final drying and subsequent cooling. The drying/cooling air from the chamber and VIBRO-FLUIDIZER® is passed through a cyclone, separating the powder contained in the air. The fine powder is returned back to the atomization device, the chamber cone (static bed), or the VIBRO-FLUIDIZER®, depending on the requirements to the final powder bulk density. On today's modern dryers the cyclone(s) are replaced by a CIP-able bag filter.
The high velocity air inlet for the primary drying is creating a venturi effect, the vacuum of which will suck surrounding air - with entrained fines particles - into the wet atomizer cloud. This will result in a "spontaneous agglomeration"
The powder will therefore exhibit a coarse powder structure originating from this agglomeration in the atomizer cloud. Further there is a continuous supply of dry fines particles from the cyclones/bagfilter that will stick to the semi-dry particles enhanching the agglomeration. For non-agglomerated powders all fines from the cyclone/bag filter are returned
to the
VIBRO-FLUI DIZER®.
It has been possible to operate this plant at a very high primary drying air temperature (220-275 C) and an extremely short residence time, still maintaining a good solubility of the powder. The physical dimensions of this type of plant are small, and thus the requirements to the size of the building are limited.
This together with the improved drying economy (10-15 % less compared to conventional two-stage drying), due to the high primary drying air temperature, makes it a very attractive solution, and is today the preferred dryer for top quality products like cold-water instant
whole milk powder and
infant milk formulas/baby foods.