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Short Path Evaporator

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Short path evaporation / distillation is a thermal separation technique that provides minimal pressure drop, permitting deep vacuum operation down to 0.001 mbar. Short path evaporation is also called molecular distillation while a short path evaporator is sometimes known as an SPE or SPDU (short path distillation unit).

Short path evaporation is excellent for gently processing heat sensitive, high boiling products. Short path evaporation perfectly complements LCI's thin film evaporation technology program, allowing us even greater capability to provide the right solution for your separation problems.

How It Works

In a short path evaporator, the rotor cage assembly (top view illustrated below) surrounds an internal condenser and revolves at moderate speeds. Feed enters through a nozzle at the top of the unit and is spread into a thin film on the inside surface of the shell via the rotor blades.

The rotor blades gently agitate the process liquid as it travels down the heated surface in a very short time while vapors are generated on the heating surface. These vapors flow through the rotor cage and entrainment separator before condensing on the internally-located condenser.

The cage-type construction and location of the internal condenser create a short vapor flow path or “short path”, extending the operating pressure capability from 1 mbar to 0.001 mbar compared to a standard thin-film evaporator. Typical heating media temperatures are 300°F to 650°F (149°C to 343°C).

The distillate and the remaining liquid concentrate drain out through separate outlets at the bottom of the unit.

short path evaporator rotor illustration
Top View
Short Path Evaporator side view


Design Principles

LCI offers short path evaporators with the following design configurations.

Rotor Designs

Short Path Evaporator Rotor Designs
  • Wiped Film/Hinged Blade for materials with very high fouling tendencies or vaporization ratios
  • Transported Flow provides positive transport for viscous materials which do not flow by gravity—usually those of 50,000 cp or more

Rotor Orientation

  • Vertical is used for all short path applications. The vertical configuration provides reliable, efficient processing of viscous and fouling fluids. Units are designed with no bottom bearing.

Vapor Flow

  • The vapor flows radially from the liquid/concentrate stream along the thermal surface through the internal entrainment separator to the internal condenser where it is condensed to liquid. Non-condensibles exit through the vacuum nozzle. A freeze trap/coldd finger is used frequently to capture uncondensed volatiles before the vacuum system.



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