Vacuum drying

Vacuum drying is the mass transfer operation in which the moisture present in a substance usually wet solid is removed by means of creating vacuum. In chemical process industries like food, pharmaceutical, agricultural, textile, paper & pulp etc. drying is an essential unit operation to remove the moisture from various substances to get a solid finished product .Vacuum drying is generally used for the drying of those substances which are hygroscopic and heat sensitive and is based on the principle of creating vacuum. With the help of vacuum the pressure is reduced around the substance to be dried and boiling point of water inside that product decreases and rate of evaporation of water increases significantly thus increasing drying rate.[1] The pressure maintained in vacuum drying is generally 0.0296 –0.059 atm and the boiling point of water is 25-30 ◦C .The vacuum drying is a batch operation and at reduced pressures the relative humidity is also lower and that is why the drying occurs faster.[2]

Vacuum Dryer

Vacuum dryer is the equipment with the help of which vacuum drying is carried out. In the pharmaceutical industry vacuum dryer is known by a common name called vacuum oven. Vacuum dryers are made up of cast iron so that they can bear the high vacuum pressure without any kind of deformation .The oven is divided into hollow trays which increases the surface area for heat conduction .The oven door is locked air tight and is connected to vacuum pump to reduce the pressure.

Working

The materials to be dried are kept on the trays inside the vacuum dryer and pressure is reduced by means of vacuum pump. The dryer door is tightly shut and steam is passed through the space between trays and jacket so that the heat transfer occurs by conduction .Water vapors from the feed is sent into the condenser and after drying vacuum pump is disconnected and the dried product is collected from the trays.

Applications

  1. Vacuum dyer can be used to dry heat sensitive hygroscopic and toxic materials.
  2. If the feed for drying is a solution it can be dried using vacuum dryer as the solvent can be recovered by condensation.
  3. Drying of the materials which are difficult to handle in other dryers because of convenient tray arrangement inside the dryer.

References

  1. ↑ "Vacuum dryer by Saraswathi.B". www.pharmainfo.net. Retrieved 2016-04-05.
  2. ↑ David Mills , Pneumatic Conveying Design Guide

[1]

  1. ↑ "Vacuum dryer by Saraswathi.B". www.pharmainfo.net. Retrieved 2016-04-05.
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