For large capacity freeze dryers GEA Niro offers our ATLAS CONRAD™ Continuous Radiation Freeze Drying plant.

What is freeze drying?
Freeze drying is drying of an already deep frozen product in a vacuum below the triple point. Here water can only be present in two phases: ice and vapor. The ice will in a sublimation process pass through the water phase directly into vapor. This ensures that the product retains most of its original shape, color, taste and nutritients. If energy is applied the sublimation process will proceed faster.

The CONRAD™ plant is fully automatic and requires minimal staff for the continuous operation. Every movement and process parameter is carefully controlled, monitored and tagged through the most modern PLC/PC system. The CONRAD™ plant consist of four main sections:

- The cabinet, which is a long cylindrical chamber desgined to operate under vacuum. At the front-end – inside the cabinet – there is an elevator for stacking the trays with the frozen product. Each tray is entering the cabinet through an uniquely designed airlock system that allows the trays to enter without breaking the vacuum, which would otherwise have a negative impact on the sublimation process. When the elevator has made a full stack, the entire stack is pushed forward into the first drying zone, where the temperature on the heating plates is adjusted to the actual product type, composition and water content.

More stacks are filled and they are pushed in turn through the various and subsequent drying zones in the cabinet. The conditions in each zone is adjusted to provide the optimal drying characteristics. When the trays on the stack arrives at the dryer exit, an elevator will unload the trays and discharge them again through an airlock. The dried product is emptied from the trays and conveyed to the packing room.

- In order to apply energy to the freeze drying process a number of heating plates made of anodized aluminum are placed inside the cabinet. Hot water is circulated through the system to secure an efficient heat transfer by radiation to the product to be freeze dried. The water temperature can be regulated during the freeze drying process to achieve the optimal evaporation laps and avoid overheating of the products.

By correct loading into the cabinet the product trays are placed between the heating plates for optimal heat transfer. Direct contact between the product trays and heating plates must be avoided as heat damage of the product will be the result.

- To condense the sublimated water vapor, the cabinet is equipped with a number of vapor condensers for Continuous De-Icing (CDI). When one of the vapor condensers has to be de-iced (typically after one hour operations the section is sealed off while the other takes over the condensation function. To melt the accumulated ice, water vapor (vacuum steam) at 25 ̊ C is led into the room.

The water vapor will now condense on the cold icy surface of the condenser and thus melt the ice. In order to restore the de-iced condenser to operating conditions any remaining vapor in the condenser chamber must be condensed by cooling it down until operating temperature and vacuum is reached. A direct switch over when the next de-icing cycle is needed can now be done without loss of operating vacuum.

- Via an external combined elevator and convey system the empty trays are conveyred back to the cold store for refilling with frozen product.

 The CONRAD™ benefits:

- Continuous production
- Economical operation
- 98 % or more efficiency
- Low maintenance costs

Capacity examples for Atlas CONRAD™ - Continuous freeze drying plants

Type CONRAD™	300	400	500	2x500
Beef with 38% dry matter
Capacity input kg/h	415	550	690	1380
Capacity output kg/h	160	215	270	540
Output kg/24 h	3900	5200	6500	13,000
Extracts with 25% dry matter
Capacity input kg/h	469	625	781	1,563
Capacity output kg/h	121	161	201	403
Output kg/24h	2,900	3,867	4,833	9,667
Raspberry with 15% dry matter
Capacity input kg/h	256	341	426	852
Capacity output kg/h	40	53	66	152
Output kg/24h	948	1,264	1,580	3,161

The ATLAS secret
The internal vapor condenser with built-in de-icing system, is the unique feature of all Atlas freeze dryers. The benefits: it saves space, it is more reliable, it does not cause the loss of product and it uses less power compared with traditional external systems.

Space saving
The special vapor condensers are optimized and built into the side of the drying chamber.

More reliable
The condenser system does not rely on large external vacuum valves with pressure drops that are difficult to secure. Using the internal system, de-icing is performed under vacuum avoiding the need to seal the chamber against large pressure differentials.

Low product loss
Nor product abrasion and low vapor velocities within the dryer guarantee as little as 0.1 % loss during the process.

Low power consumption.
De-icing under vacuum rather than at atmospheric pressure, eliminates the need to re-establish vaccum. This, combined with optimal vapor flow conditions, reduces power consumption by up to 40 % compared with ordinary freeze drying technology.