How to choose a solvent evaporator

Solvent concentrator: is a type of device used to concentrate samples or remove solvents.

There are many different methods such as rotary vacuum evaporator, and multi-position solvent evaporators….

Multi-position model with HT Series3i Genevac centrifuge

Multi-position model with HT Series3i Genevac centrifuge

Multi-position centrifuge EZ-2 4 Genevac

Multi-position centrifuge EZ-2 4 Genevac

Basic issues in choosing the solvent evaporator

Evaluate product characteristics and process requirements to choose from different evaporator designs.

Evaporators are used in a wide range of processes, including pharmaceuticals, food and beverage, pulp and paper, chemicals, polymers and plastics, inorganic salts, acids, bases, and many other materials. There are many types and variations of evaporators, and the best type for a particular application depends on the product characteristics and desired results.

This article first explains the process requirements that an evaporator must meet, and discusses important product and operational characteristics and their influence on evaporator selection. It then reviews different types of evaporator designs, their modes of operation, features, advantages and limitations, and provides guidance on how to select an evaporator for a particular application.

  • Evaporation is an operation used to concentrate a solution of a nonvolatile solute and a volatile solvent, in many cases water. Part of the solvent is evaporated to produce a concentrated solution, a slurry, or a thick, viscous liquid.
  • Evaporation differs from drying in that the residue is a flowable liquid rather than a solid. Evaporation differs from distillation in that there is no attempt to separate the vapor into its individual components.
  • Either vapor or concentrate, or both, may be the desired product (1). Therefore, the evaporator must be designed to clearly separate the vapor from the condensate and feed water.
  • The evaporator consists of a heat exchanger or hot water tank, valves, manifolds, controls, pumps, and a condenser. The most common designs are the shell-and-tube heat exchanger, the plate-and-frame heat exchanger, and the stirred-film evaporator.

SELECTING A SOLVENT CONCENTRATOR BASED ON FACTORS:

  • Designed to transfer heat efficiently at high speeds with minimal surface area to save costs on installation, operation and maintenance
  • Efficient separation of vapor from concentrated liquid
  • Meet the conditions required by the product being processed
  • Create products that meet the required quality
  • Save energy, where possible, using steam efficiently with multi-effect evaporation or steam compression
  • Minimizes fouling of heat transfer surfaces
  • Built with suitable materials to minimize corrosion
  • Important product and operational features

The critical product and operating characteristics of the evaporating solution have a major influence on the selection of the most suitable evaporator type for the application.

Heidolph industrial vacuum rotary

Heidolph industrial vacuum rotary

Heidolph industrial vacuum rotary

Heidolph industrial vacuum rotary

Thermal sensitivity

Many foods, pharmaceuticals, chemicals and plastics are heat or temperature sensitive and require low heating temperatures or short residence times exposed to heat or both. This can be accomplished by a combination of minimizing the volume of product in the evaporator at any one time, minimizing the time in the evaporator and reducing the bulk boiling point of the product by operating the evaporator at a reduced pressure. Reducing the internal operating pressure can also allow operation at lower heating temperatures while maintaining reasonable heat transfer forces (the temperature difference between the boiling point of the bulk product and the temperature of the heating medium).

Dirty

Fouling of heat transfer surfaces is usually caused by solids in the feed, solids precipitation in the concentrate, or product degradation. The slow formation of a film on the heat transfer surface will gradually reduce the overall heat transfer coefficient. Ultimately, this will require stopping the process and cleaning the heat transfer surfaces, resulting in production downtime and additional maintenance costs.

Foaming

Foaming during evaporation is common. It can range from a small amount of unstable, fragile foam to very stable, difficult-to-break foam that tends to fill the entire headspace of the evaporation system. Foaming can often be minimized by special designs of the feed inlet (separating the feed from the steam stream) and the vapor/liquid separation area (specially designed separator). Additionally, reducing the boiling point of the liquid at the heat transfer surface (by operating at lower temperatures or higher pressures) and reducing the velocity of the vapor in the tubes can significantly reduce the potential for foaming. When product purity specifications permit, applying an antifoaming agent can solve or significantly reduce the problem.

Solid

The properties of the concentrate can change as the solids concentration increases. Solids can clog tubes, causing loss of heat transfer surface, resulting in reduced heat transfer rates and the need for

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