Climbing Film Evaporator

 Climbing Film Evaporator

The climbing film evaporator has a advantages of high heat transfer coefficient and short residence time for the liquid to be evaporated. The temperature difference in rising film evaporators should be high between the heating chest and boiling chamber for proper circulation and formation of a climbing film.

Principle

In climbing film evaporator, steam is supplied to the external surface of tubes. The pre-heated feed is introduced from the bottom which flows up through the heated tubes. The overall heat transfer coefficient of the pre-heated feed is high due to which the liquid heats of rapidly. The liquid near the wall vaporises forming small bubbles which combine in to larger bubbles. Theses bubbles travel up in the tubes along with the slug entrapped. The liquid films blown up from the top of the tubes strike the entrainment separator (deflector) above. As a result, the liquid concentrate is thrown down in the lower part for its collection.

Construction

Climbing film evaporator consist of a heating unit with steam jacketed tubes which are long and narrow, and held between two plates. At the top of the vapour head, a deflector/entrainment separator is present. The evaporator carries an inlet for steam, two outlets for vent, and a condensate. The feed inlet and product outlet is at the bottom of the steam compartment.

Working

The pre-heated liquid feed to be evaporated is introduced through the inlet provided at the bottom. The height of the liquid column is kept 0.6m or 1.2m above the bottom tube sheet. Steam introduced through the inlet enters the spaces outside the tubes. Heat from the steam gets transferred through the walls of the tubes to the liquid which vaporises forming small bubbles. Theses bubbles fuse to form larger bubbles (of the width of tubs), which while moving up the tubes trap a part of the liquid known as slug. This slug is blown up in the tubes with the formation of more vapours. As a result, the liquid spreads over the walls of the tube forming a film undergoing rapid vaporisation. The liquid concentrate and vapour mixture ejects from the top of the tubes at high velocity. The entrainment separator prevents entrainment and also brakes the foam. The vapour escapes from the vapour outlet at the top, and the concentrated product is collected from the bottom outlet.

Uses

Climbing film evaporator has the following uses:

1) It is used for concentrating thermolabile substances such as insulin, Liver extracts, and vitamins.

2) It can also be used for evaporating clear, foamy, and corrosive liquids.

Merits

Climbing film evaporator has the following merits:

1)It consist of long and narrow tubes which provide a large area for heat transfer.

2) It is also suitable for evaporating large quantities of clear liquids and corrosive solutions.

3) It can be used for foam-forming liquids as the entrainment separator also acts as a foam breaker.

4) It requires a small floor space.

Demerits

Climbing film evaporator has the following demerits:

1) It is expensive with a complicated construction.

2) It is cleanliness and maintenance is difficult.

3) It requires a large head space.

4) It is not suitable for vary viscous, salting, and scaling liquids.