Principle, Construction, Working, Uses, Merits and Demerits of Climbing Film Evaporator

Climbing Film Evaporator

Principle

As liquid and vapour flow upwards in parallel during the boiling process, the ascending force of the steam is responsible for the climbing film evaporator. Additionally, the vapour production increases, and the vapour produces a thin film on the walls of the tubes, which causes the liquid to rise upwards. The upward co-current creates a high degree of turbulence in the liquid as a result of this upward movement against gravity.

Construction

RFEs are vertical shell and tube heat exchangers that have a vapour liquid separation system mounted on top, as shown in figure. In the cylindrical evaporator chamber, the steam is transported internally through vertical tubes. Boiling tubes typically have a maximum length of 23 feet (7 meters). Calandria evaporators are known as Roberts evaporators in Europe, while Roberts evaporators are known as Roberts evaporators in the U.S.

Working

Into the heated tube bundle at the bottom is delivered the liquid to be concentrated. Heat is transferred from the feed to the shell when steam condenses on the outside of the tube. Upon boiling, steam and vapour form within the tube, resulting in a rising temperature. The liquid is circulated using natural convection. As a result, the vapour pushes the feed upward as an upward force is created by the liquid against the tube walls. A thin layer of vapor forms above the calandria as vapor generation increases the tube's center of velocity and forces the remaining liquid against the wall. Due to the high velocities generated by the vapour lift, it provides good thermal performance. Items that clog the heating surface or are excessively viscous or sticky can be evaporated using this technique. To transport the liquid and to produce the rising film, a high temperature difference is typically needed between the heating and boiling sides of the evaporator. A vapour-liquid separator separates the vapour from the balance liquid.

Uses

Desalination of seawater by thermal means.
Consolidation of multiple dilute solutions, like plant extracts.
The distillation column is reboiler for this unit.
A moderate vacuum can be achieved with this economical alternative to falling film evaporators.
The effluent is treated with climbing films.
Producing polymers and concentrating juice and processing food are its applications.
Seawater can be desalinated by using it.
It is also used as a solvent recovery device in the pharmaceutical industry.
Reboilers for distillation columns are also made of this material.
To remove volatile components prior to stripping, it is used as a pre-concentrator, a flash evaporator, or a preheater.

Merits

• Rising film evaporators have the advantage in comparison to other evaporators that the liquid feed stays inside for a short time.
• It has a relatively high heat transfer coefficient, which in turn reduces the heat transfer area needed to cool the evaporator, lowering the cost of the evaporator.
• The tubes can be cleaned more easily.
• And without an external pump for circulation, it has a relatively low capital cost.
• The feed can tolerate trace amounts of suspended particles.
• A reasonable vacuum can be achieved.
• Steam economy is achieved through multiple effects.
• Quite an affordable evaporator.

Demerits

• The machine is heavy and requires a lot of space.
• When temperature differences are small, it transfers heat poorly.
• Materials that are thermolabile should not be used.
• During evaporation, low viscosity products evaporate and have minimal fouling potential.

Get subject wise printable pdf documentsView Here

Share

Tweet

Share

Pin it

Share