Spray dryer type MSD™ for agglomerated instant whole milk
Spray dryer type MSD™ for agglomerated instant whole milk

The GEA Niro MSD™ Multi-Stage Dryer combines spray drying and fluid bed drying technologies. Through the process, it produces coarse, agglomerated, free-flowing dustless powder.

A new dryer concept
GEA Process Engineering has always focused on developing spray dryers with improved energy efficiency and final product quality. In order to improve the dryer efficiency even further without encountering deposit problems in the chamber, a completely new spray dryer concept, named Multi-Stage Dryer MSD™, was developed around 1980. Since then, more than 300 plants with this spray drying concept have been delivered.

All flowsheets are available for download in the Animation Download area.

Product quality
Product quality, especially instant whole milk powder, from this type of spray dryer is used as a benchmark worldwide. However, other dairy products are also successfully spray dried in the MSD™ spray drying plant.

Drying in more stages
The first necessary step to reach the concept of the MSD™ was spray drying in two stages. However, the MSD™ operates with three drying stages, each of which is adapted to the moisture content prevailing during the spray 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 spray dryer vertically through the air disperser at a high velocity, ensuring optimal mixing of the atomized droplets with the drying air. At this stage, the evaporation takes place instantaneously during the passage vertically down through the specially designed drying chamber. In this primary spray 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 MSD™ plant is created in a way that prevents the particles from sticking to the drying chamber, but at the same time leading them 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 for fluidizing the product 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 for the final powder bulk density. In the modern dryers used today, the cyclone(s) are replaced by a CIP-able bag filter.

On request, the plant can be designed and delivered for a full manual and/or automatic CIP Cleaning In Place including CIP Kitchen with tanks, pumps, valves and instrumentation.

Powder structure
The high velocity air inlet for the primary spray drying creates 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". Therefore, the powder will exhibit a coarse powder structure originating from this agglomeration in the atomizer cloud. Further, a continuous supply of dry fines particles can be applied from the cyclones/bag filter. These fines particles will stick to the semi-dry particles enhancing the agglomeration. Additionally, for non-agglomerated powders, all fines from the cyclone/bag filter are returned to the VIBRO-FLUIDIZER™.

It is possible to operate this plant at a very high primary spray drying air temperature (220-275° C) and an extremely short residence time, whilst still maintaining a good solubility of the powder. The physical dimensions of this type of plant are small and thus the requirements for the size of the building are limited.

This, together with the improved drying economy (10-15 % less compared to conventional two-stage drying) caused by 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 food. To improve the drying economy further, a heat recovery system can be installed.

The Multi-Stage Dryer MSD™ forms the key element in a complete process line for food and dairy powders.

Safety aspects
All plants designed and supplied by GEA Process Engineering will enable the end user to obtain approvals put forward by the EU directive.