PUMPS USED IN CHEMICAL PLANT

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Introduction
Pump is a device that imparts momentum and mechanical energy to the process fluid. Pumps are used to transfer fluid from one location to other.
Main Types Of Pumps
·         Reciprocating pump
·         Centrifugal pump

Reciprocating Pump:
Reciprocating pumps delivered energy to a flowing fluid by means of a piston acting through a cylinder. Although steam is often employed as a source of power for this type of pumps, the piston can be activated by other means, such as o rotating crankshaft operated by an electric motor. Thus reciprocating piston pumps can be classified as
·         Steam pumps
·         Power pumps
They can also be classified as single acting or double acting depending on weather energy is delivered to the fluid on both the forward and backward strokes of the piston. Reciprocating pumps, in general, have an advantage of being able to deliver fluids against high pressure and operate with good efficiency over a wide range of operating conditions. a major disadvantage of piston and plunger pumps is that they cannot be used with fluids, which contain abrasive solids. Reciprocating diagram pumps, however, are satisfactory for handling fluids with large amount of suspended solids at low heads.

Centrifugal Pumps
The centrifugal pumps are most commonly used type in the chemical industry. it can be constructed in a wide range of corrosion resistance materials or lighted with rubber or plastic. It is infact, used for almost all pumping operations other then those where a large head or a positive displacement is required.
In centrifugal pumps, the mechanical energy of the liquid is increased by centrifugal action. The liquid enters through a suction connection concentric with the excess of a high speed rotary element, called the impeller. The impellers carried radial vanes integrally case in it. liquids flow outwards in the space between the vanes and leave the impeller, at a considerable greater velocity with respect to the ground than at the entrance to the impeller. In properly functioning pump, the space between the vanes is completely filled with a liquid flowing without cavitations. The liquid leaving the outer periphery of the impeller is collected in a spiral casing, called the volute and leaves the pumps through a tangential discharge connection. In the volute, the velocity head of the liquid from the impeller is converted into pressure head. Centrifugal pumps may be single stage or multi stage, propeller, mixed flow and peripheral.

Selection Criteria:
Many different factors can influence the final choice of the pump for a particular operation. The following list indicates the major factors that govern the pump selection:
·         The amount of liquid that must be pumped out.
·         The properties of the fluid
·         The increase in pressure of the fluid due to work input of the pump
·         Types of the flow distributions
·         Types of the power supply
·         Cost and mechanical efficiency of the pump.
    
We have selected centrifugal pumps for a process because of the following outstanding advantages:
·         They are simple in operation and cheep
·         Fluid is delivered at uniform pressure without shocks or pulsation
·         They are no valves involved in pump operation
·         They operate at high speed(up to 4000 rpm) therefore they can be coupled directly to an electric motor
·         The discharge line may be partly shut off or completely closed off without changing the pump
·         Maintenance costs are lower then other types of pumps.


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