Superheated steam drying
- How does it work?
- What can it be used for?
- What can it not be used for?
- Related Facilities
- Further Information
|Key words||superheated steam, low pressure, drying|
|Completed by||KU Leuven LFT|
How does it work?
|Primary objective||Drying of food products|
|Working principle|| This closed-system drying method is based on the vapourization of water in the product by contact with superheated steam. This water in its turn becomes part of the superheated steam. The superheated steam allows good heat transfer to the product that needs to be dried. (1,2).
Superheated steam is steam that has a temperature above the boiling point. Up to the boiling point, the term saturated steam is used, while above the boiling point, the steams is refered to as unsaturated or superheated. As long as the temperature remains higher than the saturation temperature (i.e. boiling point), a drop in temperature does not cause condensation of the steam (1,2).
The drying cycle using superheated steam consists of 3 periods (1,2):
To minimize the thermal damage to the product, superheated steam drying can be performed at reduced pressure. A lower pressure is accompanied by a lower saturation temperature. Although this also lowers the drying rates due to poorer convective heat transfer under reduced pressures, the products obtained are superior compared to conventional vacuum drying (4).
Superheated steam drying can also be performed at elevated pressures. This is mostly interesting for products that are not heat sensitive and when energy recovery is essential. The constant rate drying temperature then exceeds 100°C.
|Important process parameters||superheat of the steam, pressure (although for low-pressure superheated steam drying, the superheat is more important for the drying rate). Both affect the shape of the drying curve (4)|
|Important product parameters||thermal diffusivity, initial moisture content|
What can it be used for?
|Products||Sugar beet pulp, vegetables, noodles, wheat flour, meat, ….|
|Solutions for short comings||energy savings in drying (7)|
What can it NOT be used for?
|Products||Heat sensitive food products. In that case, low-pressure superheated steam drying needs to be applied.|
|Risks or hazards||not applicable|
|Maturity||Superheated steam drying is already in industry (both in food and other), although the number of different commercial equipments available and industrial applications is limited (2).|
|Modularity /Implementation||All dryer types (both continuous and batch) that are used for hot air drying can also be used for superheated steam drying. Pneumatic, flash and fluid bed dryers are the most common (2).|
|Consumer aspects||No issues expected|
|Legal aspects||No issues expected|
|Environmental aspects||Superheated steam drying is more environmentally friendly because of energy savings compared to hot air drying up to 50-80% (1).|
Facilities that might be interesting for you
|Institutes||TNO Institute, AgroParisTech, Karlstad University, University of Manitoba - DBE|
|Companies||GEA Barr-Rosin, Techniprocess, BMA Group, Eirich|
|References|| 1. Karimi, F. (2010) Applications of superheated steam for the drying of food products. Int. Agrophysics, 24, 195-204.
2. van Deventer, H.C. (2004) Industrial superheated steam drying. TNO-report R2004/239.
3. Ferreira da Costa, V.A., Neto da Silva, F., Rodrigues Ruivo, C. (2005) An Alternative Approach to the Inversion Temperature. Drying Technology, 9&11, 1783 – 1796.
4. Devahastin,S., Suvarnakuta,P., Soponronnarit, S., and Mujumdar, A. S. (2004) A Comparative Study of Low-Pressure Superheated Steam and Vacuum Drying of a Heat-Sensitive Material. Drying Technology, 22, 1845-1867.
5. Nygaard, H. & Hostmark, O. (2008) Microbial Inactivation during Superheated Steam Drying of Fish Meal. Drying Technology, 26, 222-230.
6. Head, D.S., Cenkowski, S., Holley, R. and Blank, G. (2008) Effects of superheated steam on Geobacillus stearothermophilus spore viability. Journal of applied microbiology, 104, 1213-1220.
7. Mujumdar, A.S. (2007) An overview of innovation in industrial drying: current status and R&D needs.Transp. Porous. Med. 66, 3-18.
8. Ezhil, C. (2010) Superheated steam drying of foods – a review. World Journal of Dairy and Food Sciences, 5, 214-217.
superheat of the steam, pressure (although for low-pressure superheated steam drying, the superheat is more important for the drying rate). Both affect the shape of the drying curve (4) thermal diffusivity, initial moisture content Dryers 2.2.2 physical stabilizing, conversion not applicable Web of science: superheated steam drying WikiSysop :Template:Review document :Template:Review status