Sunday, 30 December 2012

Heart of any CHEMICAL Plant - it's Utilities

Plant Utilities

1) Any Chemical Plant requires raw materials in order to produce final products.

2) It also requires various other services called Utilities for smoothly carrying out the processes.

3) Utility is neither a reactant nor a product, But Utilities are required for maintaining adequate conditions of a manufacturing unit.

4) Utility area is an important area of a Chemical Plant.

5) This may house various Boilers, Large Compressors, Refrigeration systems, Air Conditioning systems, Water Treatment Plants, Cooling Towers etc.

6) Utilities also include Electric Power, so Power Plants are also considered as a part of Utilities.

7) Utilities are situated outside Battery limits should not give any wrong impression that utilities are any less important than the main process,because it is the Efficient Management of Utilities that generate Profits.

8) On the other hand bad management of utilities can make even the most profitable processes unprofitable.

9) The utilities help to maintain proper process conditions like pressure,temperature etc., without which it will be impossible to carry out the process.

10) Now a days most of the Engineering practices are aimed at reducing the consumption of utilities, Because the production of utilities whether it is compressed air,steam etc., requires energy and energy is becoming costlier day by day.

11) Efficient Utility Management doesn't end at cost cutting, If utilities supply is not proper the equipments may not last their full life.

12) For eg :-
If Steam at higher temperature than desired enters Heat Exchangers,the Exchangers may get damaged.

13) Air,Water,Steam etc., are the common utilities used in Chemical Plants.

14) Some Properties of utilities :-
a) They are generally Reusable.
b) Their Composition do not change.
c) They cannot be stocked, So regular supply is must.

15) The aim of an Chemical Engineer should be to provide Utilities & other services in required quantities and of quality as required by the users.

Tuesday, 25 December 2012

CentriFugal Pump - Overview

CentriFugal Pump

What is a Centrifugal Pump ?

If Mechanical energy is converted into Pressure energy by means of a Centrifugal force acting on the fluid then this type of hydraulic machine is called as Centrifugal Pump.

Construction & Various parts of the Centrifugal Pump :-

A Centrifugal Pump essentially consists of the following main parts :-

1) Impeller :- It is the rotating part of the centrifugal pump which consists of a number of blades,either open or shrouded ,mounted on a shaft that projects outside the casing.

2) Casings  :- There are 3 general types of casings ,but each consists of a chamber in which the impeller rotates,provided with inlet and exit for the liquid being pumped.
a) Circular casing
b) Volute casing
c) Diffuser-type / Guide vanes

3) Suction Pipe :- A pipe whose one end is connected to the inlet of the pump and other end dips into the liquid in a sump is known as suction pipe. A foot valve / Non-return valve is fitted at the lower end of the suction pipe.

4) Delivery Pipe :- A pipe whose one end is connected to the outlet of the pump and other end delivers the liquid at the required height is known as delivery pipe.

Working of a Centrifugal Pump :-

1) In the operation of a centrifugal pump before the pump is started, PRIMING of the pump is done.

2) In the Priming operation ,the suction pipe,pump casing and the portion of the delivery pipe up to delivery valve are completely filled with the liquid to be pumped so that all the air,gas or vapours from this portion of the pump is expelled and no air pocket is left.

3) Without Priming if the impeller is made to rotate in the presence of air, negligible pressure would be produced so that no liquid will be lifted in the pump.

4) After the pump is Primed properly ,the delivery valve is kept close and power from outside source is applied to the shaft.

5) The delivery valve is kept close in order to reduce the starting torque for the motor.

6) The impeller then rotates within the stationary casing.

7) The rotation of the impeller produces a force which imparts a centrifugal head to the liquid and thus results in an increase in the pressure thoughout the liquid mass.

8) As long as the delivery valve is closed and impeller is rotated there will be just churning of liquid within the casing.

9) When the delivery valve is opened,the liquid is made to flow outward thereby leaving the impeller vanes with high velocity and pressure.

10) Due to centrifugal action, a partial vaccum is created at the edge of the impeller which causes the liquid from the reservoir to rush through the suction pipe to the impeller.

Advantages of a Centrifugal Pump :-

1) It is Simple in construction.
2) It operates at high speed and therefore,can be coupled directly to an electric motor.
3) It gives a steady delivery.
4) Maintainance costs are lower than any other pump.
5) No damage is done to the pump if the delivery line becomes blocked.
6) It is much smaller than other pumps of equal capacity.
7) Quiet in operation.

Disadvantages of a Centrifugal Pump :-

1) The single stage pump will not develop a high pressure.
2) It is not usually self priming.
3) If a non-return valve is not incorporated in the delivery or suction line ,the liquid will run back into the suction tank as soon as the pump stops.

4) Very viscous liquids cannot be handled efficiently.

Sedimentation or Dorn Effect

Sedimentation or Dorn Effect

1) We know that the dispersed phase remains suspended in Dispersion medium.

2) It is a two phase system and very stable.

3) But even though these colloidal dispersions are fairly stable, the particles slowly settle down under the influence of gravity when kept undisturbed for a longer period of time.

4) It is a very slow process and is just like falling of a spherical body in highly viscous medium.

5) While settling the heavy particles settle first at the bottom and the light particles at the top.

6) Such settling of the colloidal particles under the influence of an gravity is called as Sedimentation or Dorn Effect.

7) In 1880, DORN observed this phenomenon first ,hence it is known as DORN effect.

8) The Potential developed due to this is called as Sedimentation Potential.

9) Sedimentation Potential can be measured by placing the electrodes at different levels in the falling stream of the colloidal particles.

10) It is just reverse of Electrophoresis i.e in Electrophoresis there is movement of colloidal particles due to an applied potential while in Dorn effect the potential is developed due to movement of colloidal particles.

Electro-Osmosis - An Electro Kinetic Phenomenon


Electroosmosis was first observed by a Russian scientist F.F. Reuss in 1809.

1) We know that a COLLOID is a substance which is microscopically dispersed (widely spread) evenly throughout another substance.

2) The Colloidal particles form Dispersed phase and the medium used for this is called as Dispersion medium.

3) Also we all know that Electrophoresis is a phenomenon in which the colloidal particles move under the influence of an electric field.

4) But,Suppose if it happens that, the colloidal particles are not allowed to move under the influence of an electric field, then What Will Happen...?

Nothing but.....
The dispersion medium itself will begin to move under the influence of the electric field.

5) This movement of the dispersion medium under the influence of an electric field is called as "Electroosmosis" .

6) The pressure required to counter the Electro osmotic flow is called as Electroosmotic pressure.

7) To study the Phenomenon of Electroosmosis consider the experimental setup as shown in the figure below:-

8) The colloidal solution(sol) is taken in X-compartment whereas the Y and Z compartments are filled with Dispersed medium,here water is taken as dispersion medium

9) The X compartment is seperated from Y and Z compartments by a semipermeable membrane or a porous partition.

10) A positive and a negative  electrode is immersed in the Y and Z compartments as shown in the figure.

11) When a potential is applied at the electrodes the dispersion medium will move from one side to other which can be observed on the basis of the movement of the boundries in the side tubes.

12) The direction of the movement of dispersion medium will be opposite to the direction of flow of the colloidal particles ,i.e., if colloidal particles are positively charged then the dispersion medium moves towards the negative electrode and vice versa.

13) The Zeta Potential developed due to electroosmosis is given by :-
                                     Pπr2 /2DE
P = Electroosmotic pressure in N/m2
r = radius of side tube in cm
E = Potential applied
D = Dielectric constant of medium