What is a Rotary vacuum dryer (RVD) | Types

What is a Rotary vacuum dryer (RVD) ?

Rotary vacuum dryer is a cylindrical or cone vessel integrated with jacketed or limpet coil and rotated by a hollow shaft. Basically this is used for a batch operation plant. The complete drying of the product is done by combination process of under vacuum, stirring / agitation and consistent heating is through a jacket. It is an efficient method that offers a drying of the slurry product with quality. Generally this dryer is designed to remove moisture content from product materials under consistent heat and heat and vacuum.

Function of a Rotary vacuum dryer

RVD is also used for changing a material’s molecular and physical properties of materials in specialized operations, including chemical reactions for the chemical and pharmaceutical industries. RVD does rapid drying at low temperatures of press cake, filter cake and slurry materials but that is also required subsequently stirring / agitation.

There are two types of agitators used in this system these are paddle types and blade types and the clearance between blade and inside shell is very close. The main purpose of agitators is to distribute product materials over inside vessels. RVD rotates with shafts on both ends supported by high performance bearing and driven by electric motor and reduction gear box. RVD, Gearbox, and motor may be connected with direct couple or by belts systems.

Rotary vacuum dryer types
Rotary vacuum dryer

The cooling and heating is provided through jackets or limpet systems as per installation with the vessel and main purpose for this is protection of contact between product and heating and cooling media. The drying completion time is not fixed because it depends on the quantity of solvents present in product materials.

  • Technical details Operational Temperature: 0-200°C  and Heating Temperature: 30°C to 300°C.
  • Capacity: 200 – 10,000 liters but for vacuum paddle dryer 100 –  25000 liters depends on the size of the vessel.
  • Atmospheric to Full Vacuum: Up to 0.6 torr it is dependent on product specification requirements. The requirement of vacuum is to increase the boiling point of product solvents.
  • Rotary vacuum dryer is efficient to dry many types of processed materials like slurries to solid shapes, granular, crystalline or fibrous solids such as centrifuged solids, Pharmaceuticals, Pigments and Synthetic rubber.

Parts of  Rotary vacuum dryer (RVD)

Some important parts of RVD are drive unit motor and gearbox, agitator, vacuum equipment like pump, condenser, dust catcher, material charging door, solvent receiver, discharge nozzle, sealing element like mechanical seal etc. 

How many types of Rotary vacuum dryer (RVD) ?

Basically (RVD) is classified and customized in many categories depending on the requirements and function. Here explain the types of construction and drive arrangement.

  • Vacuum Paddle Dryer
  • Cone type with Limpet coil and (direct couple or belt drive with reduction gearbox).
  • Cone type with Limpet coil and (direct couple or belt drive with reduction gearbox).
  • Horizontal cylindrical type with jacket and (direct couple or belt drive with reduction gearbox).
    Horizontal cylindrical type with Limpet coil and (direct couple or belt drive with reduction gearbox).

Advantage of Rotary vacuum dryer

  • Efficiently heat transfer 
  • Uniform drying process
  • Good solvent recovery capacity
  • Less time cycle time for one batch process.
  • It is power consumption and useful for cost reduction.
  • Less hazards at the workplace because of the closed system process.
  • Low pressure and temperature drying processing of highly toxic materials
  • No degradation of dry product due to over-exposure, more temperature and time.
  • Automated discharge of product with condenser of moisture and recovery of solvents.

Disadvantage of a vacuum rotary dryer

  • More complex system arrangement 
  • Mechanical seal is a expensive part of the system 
  • Specialization required for design, process and operation
  • Leakage of steam is a big issue due to rotating and static parts
  • Vacuum build up and agitation in running condition is a critical task

Working principle of rotary vacuum dryer

RVD (Rotary vacuum dryer is mechanical equipment which is used to remove moisture from products under vacuum by providing additional heat sources like steam, hot water and other. 

  • Take batch of product for dry in dryer as designed and requirements and close the door
  • Create vacuum as per product nature and boiling point.
  • Provided heat source by steam or hot water as availability and requirements.
  • Start rotating the dryer by the help of drive equipment like motor and gearbox at very slow speed.
  • Agitator is also an integral part of the dryer so it also works accordingly to distribute product material equally.
  • And finally get the product as desired at the completion of the process after some time.

Rotary vacuum dryer diagram

Rotary cone vacuum dryer diagram
Rotary cone vacuum dryer diagram

Feature and combination  of RVD

  • Available with Direct drive and belt drive and Available with Mechanical seal arrangement
  • Available  Pulse jet dust filter arrangement and Sampling valve and Breaker bars arrangement
  • Product temperature and vacuum probe arrangement and Rotor Types: Helical Ribbon, Paddles, and Special. 
  • Heating Surfaces: Shell, End Covers, and Shaft and Heating Media: Steam, Hot Water/Oil, Thermic Fluid.
  • Suitable for drying heat sensitive material, as low temperature for drying can be maintained by high vacuum.
  • Higher Thermal Efficiency.Almost 100% recovery of solvents.
  •  Heating Temp.: From 30°C to 300°C.
  • Limpet coil could be provided instead of jacket if the heating media is fluid.
  • The Evaporation Rate 4-12 Kg/H/Sq.m approx of heating surface area of water at heating temperature of 100°C.
  • Nitrogen purging arrangements provided for bag cleaning done with pulsation by nitrogen jet injector.

Materials selection for RVD

The selection totally depends on product nature which has to dry. But some of the most commonly used materials are CS, SS 316, 304, SS316L, SS304L, Monel, Inconel, Titanium, Hastelloy etc.

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