Pump Design Final.docx

6.1 Pumps 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. A pump is a device used to raise, compress, or transfer fluids. The motors that power most pumps can be the focus of many best practices. It is common to model the operation of pumps via pump and system curves. Pump curves offer the horsepower, head, and flow rate figures for a specific pump at a constant rpm. System curves describe the capacity and head required by a pump system. Pump Types Various types of pumps are used in the chemical industry, including centrifugal, reciprocating, and helical rotor pumps. Centrifugal Pump Centrifugal pumps operate by applying a centrifugal force to fluids, many times with the assistance of impellers. These pumps are typically used in moderate to high flow applications with low-pressure head, and are very common in chemical process industries. There are three types of centrifugal pumps—radial, mixed, and axial flow pumps. In the radial pumps, pressure is developed completely through a centrifugal force, while in axial pumps pressure is developed by lift generated by the impeller. Mixed flow pumps develop flow through a centrifugal force and the impeller. Reciprocating Pump Reciprocating pumps compress liquid in small chambers via pistons or diaphragms. These pumps are typically used in low-flow and high-head applications. Piston pumps may have single or multiple stages and are generally not suitable for transferring toxic or explosive material. Diaphragm pumps are more commonly used for toxic or explosive materials. Helical Rotor Pump Helical rotor pumps use a rotor within a helical cavity to develop pressure. These pumps are useful for submersible and waste applications.

Selection Criteria of Pumps 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.

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The properties of the fluid.

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The increase in presence of the fluid due to work input of the pump.

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Types of the flow distributions.

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Types of the power supply.

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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 cheap.

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Fluid is delivered at uniform pressure without shocks or pulsation.

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They are no valves involved in pump operation.

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They operate at high speed (up to 4000 rpm) therefore they can be coupled directly to an electric motor.

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The discharge line may be partly shut off or completely closed off without changing the pump.

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They are much smaller than other pumps of equal capacity.

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Maintenance costs are lower than other types of pumps.

Pump (P-1) Pump Selection Pump type is selected from the below graph: Capacity = 61372.4 kg/hr = 370.02 gpm of Selexol P(g) Head = 𝑠𝑝.𝑔𝑟∗0.4367 Head = 39 ft

Figure : Selection of pump

Hence, the Pump Selected is Centrifugal Pump. Pump Sizing Calculation Steps  Locate the process equipment  Estimate z1 and z2.  Estimate Frictional pressure losses ED and ES  Calculate Pump Work.  Calculate Pump shaft horsepower & estimate its Efficiency.  Calculate electric-motor horsepower & estimate its Efficiency.  Select a standard electric-motor horsepower.  Calculate NPSH Pump Calculation Define the inlet and outlet pressures: The inlet pressure is = P1 = 1.2 bar The outlet pressure is = P2 = 30 bar Locate the process equipment: Locate the process equipment according to the rule of thumb listed in following table…

Figure : Selection of pump head

As we need to pump the liquid in to the absorber so our process equipment is absorber which is supported by a skirt having skirt height of about 3.5 ft or 1.069 m. Estimation of z1 & z2: Z1 with respect to pump = 0 Z2 = skirt height + height of column Z2 = 1.069 + 16.5 Z2 = 17.57m Z2 = 57.64 ft Estimation Frictional pressure losses ED and ES

Figure : Flow system component pressure drop

So, ES & ED is equal to 0.35 Calculate the pump work: 𝒈 𝑷 𝟏 − 𝑷𝟐 (𝒛𝟏 − 𝒛𝟐 ) + 𝑾= − (𝑬𝑺 − 𝑬𝑫 ) 𝒈𝑪 ʃ 𝑊=

9.8 (1.2 ∗ 105 − 3.0 ∗ 106 ) (0.35 + 0.35) ∗ 105 (0 − 57.64) + − 32 1009 1009

𝑁𝑚 𝐾𝑔 Calculate the pump shaft horsepower: Pump efficiency is calculated as… 𝑚𝑊 𝑃= ɳ 𝑊 = −2941

𝑃=

61372.4 ∗ 2941 0.7

P = 2.57*108 J/hr P = 71625.48 J/s P = 96.05 hp Figure: Efficiency of Pump Calculate Electric-Motor Horsepower & Estimate its Efficiency:

Figure: Efficiency of Electric motor On the basis of horsepower the selected motor is squirrel cage Induction motor having power range of 1 to 5,000 hp. Efficiency of motor is selected to be = 0.91 The power of motor is calculated as = PE = 𝑃𝐸 =

𝑃𝑃

96 𝑃𝐸 = 0.91 PE = 105.5 hp Select a Standard Electric Motor Horsepower:

ɳ

Figure: Horsepower Selection Hence the selected motor is of 125 hp. Net Positive Suction Head NPSH: 1 𝑃𝑎 − 𝑃𝑣 𝑁𝑃𝑆𝐻 = ( − ℎ𝑓𝑠 ) − 𝑍𝑎 𝑔 ʃ Absolute pressure at the surface of reservoir = Pa = 1.2 bar = 1.2*105 Pa Vapor pressure of Selexol = Pv = bar = 1000Pa Friction losses in suction line = hfs = 0 Za = 0 1 1.2 ∗ 105 − 1000 𝑁𝑃𝑆𝐻 = ( − 0) − 0 9.8 1009 NPSH = 11.79 m

Specification Sheet Identification Item Item No.

Pump P-1

No. Required

1

Type

Centrifugal Function

To increase pressure from 1.2 bar to 30 bar Feed Flow Rate Inlet Pressure

61372.4 kg/hr 1.2 bar

Outlet Pressure

30 bar

Power of pump

96.05 hp

Power of electric motor

105.5 hp

NPSH

11.8 m

1. Silla, Harry. Chemical Process Engineering Design and Economics. USA 2. Jennifer Dyment , Suphat Watanasiri. Acid Gas Cleanin using DEPG Physical Solvents