Evaporation for Steam Jacketed Kettle notes

Steam Jacketed Kettle

Steam jacketed kettle is very large having deep kettles mounted on the platform standing on the floor. Two-third portion of the kettle bottom is shielded by a metal jacket. The shallow kettles are fully - jacketed.

Principle

The evaporation pan or the jacketed kettle containing aqueous extract is subjected to steam which provides heat to the pan. This heat gets transferred to the aqueous extract by conduction and convection. As a result , extract temperature rises and the tendency of the solvent molecules to convert into vapour increases. Vaporisation of the solvent molecules can be enhanced by stirring the extract.

Construction

Steam jacketed kettle is a hemispheric structure with an inner pan called kettle enclosed with in an outer pan, called jacket. These two pans join together to enclose an air space in to which steam is applied to pass to the extract placed in the kettle.

For small scale use (when small quantities are to be evaporated), the kettle heat transfer is made of a single metal sheet. For large scale use (when large quantities are to be evaporated), the kettle is made by welding several metal sheets together. The best metal of choice for this purpose is copper because of its good conductivity.

But copper may dissolve on evaporating acidic material. Thus , tinned copper is suitably used for such preparation. Iron because of its minimum conductivity can also be used as a material of construction for jacket. However , its inner surface is either tinned or enamelled for preventing the rusting of jacket.

Working

The aqueous extract to be evaporated is placed in the pan and steam is interduced through the inlet. Condensation occurs on the outer surface of the pan and the condensation exists through the outlet. Steam supply heat to the contents of the pan. when the content are in small quantities, the should be manually stirred, while for large quantities a mechanical stirred should be used absorbing heat.

Thus, the pan is equipped with fans for removing vapour and preventing condensation in the room . The fan also accelerated the evaporation rate by removing the saturated air from the liquid surface.

The kettle is either kept fixed or is tiled while collecting the products. The capacity of kettles is up to 90 liters ; but if the kettle are above this capacity , it becomes difficult to tilt them because of the weight of the pan and its contents. In this case, the outlet present at the base of the kettle is used for collecting the product.

Use

Steam jacketed kettle is used for concentrating aqueous and thermo-stable liquors, e.g., liquorice extract.

Merits

Steam jacket kettle has the following merits;

1) It is suitable for small scale, as well as for large scale operations.

2) Its construction and operation is simple.

3) Its installation and maintenance cost is low.

4) Its allows easy removal of the products.

Demerits

Steam jacketed kettle has the following demerits

1) Its heat economy is less, thus per unit material production cost is more.

2) It is not suitable for thermolabile material due to long exposure time.