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Pumps, Compressors, Fans, Ejectors and Expanders

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Pumps, Compressors, Fans, Ejectors and Expanders. Chapter 20. ChEN ... Ejector - advantage = large volumetric flow rate. Multi-Stage with interstage condensers ... – PowerPoint PPT presentation

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Title: Pumps, Compressors, Fans, Ejectors and Expanders


1
Pumps, Compressors, Fans, Ejectors and Expanders
  • Chapter 20
  • ChEN 4253 Design I
  • Terry A. Ring

2
Pumps
  • Moves Liquid, Creates Pressure
  • Vapor bubbles
  • Causes Cavitations
  • Erodes Impeller
  • Solids Erode Impeller
  • Pump Types
  • Centrifugal
  • Positive Displacement
  • Piston
  • diaphragm
  • Pump Power Q?P brake (delivered) (horse)
    power from motor

3
Centrifugal Pumps
  • Two Basic Requirements for Trouble-Free Operation
    of Centrifugal Pumps
  • no cavitation of the pump occurs throughout the
    broad operating range
  • a certain minimum continuous flow is always
    maintained during operation
  • Pump around loops

4
Reduced Flows
  • Unfavorable conditions which may occur separately
    or simultaneously when the pump is operated at
    reduced flows
  • Cases of heavy leakages from the casing, seal,
    and stuffing box
  • Deflection and shearing of shafts
  • Seizure of pump internals
  • Close tolerances erosion
  • Separation cavitation
  • Product quality degradation
  • Excessive hydraulic thrust
  • Premature bearing failures

5
Centrifugal Pump
Electric Motor
6
Centrifugal Pump
Electric Motor
7
Centrifugal Pump
  • Converts kinetic energy to pressure energy

8
Impellers
9
Converts Kinetic Energy to Pressure Energy
10
Different Types of Pump Head
  • Total Static Head -  Total head when the pump is
    not running
  • Total Dynamic Head (Total System Head) - Total
    head when the pump is running
  • Static Suction Head - Head on the suction side,
    with pump off, if the head is higher than the
    pump impeller
  • Static Suction Lift - Head on the suction side,
    with pump off, if the head is lower than the pump
    impeller
  • Static Discharge Head - Head on discharge side of
    pump with the pump off
  • Dynamic Suction Head/Lift - Head on suction side
    of pump with pump on
  • Dynamic Discharge Head - Head on discharge side
    of pump with pump on

11
Pump Head
  • The head of a pump in metric units can be
    expressed in metric units as
  • head (p2 - p1)/(?g) (v22- v12)/(2g)
    (z2-z1)      
  • where
  • h total head developed (m) 
  • p2 pressure at outlet (N/m2)
  • p1 pressure at inlet (N/m2)
  • ?   density of liquid (kg/m3)
  • g acceleratiosn of gravity (9.81)  m/s2
  • v2 velocity at the outlet (m/s)

12
Pump Efficiency
  • Centrifugal Pump

13
Pump Design Scaling
  • Pump Flow rate
  • Q2 Q1 x (D2xN2)/(D1xN1)
  • Pump Head
  • H2 H1 x (D2xN2)/(D1xN1)2
  • Pump Brake Horse Power
  • BHP2 BHP1 x (D2xN2)/(D1xN1)3
  • D Impeller Diameter
  • N specific speed

14
Pump Performance Curves
Resistance
15
Net Positive Suction Head-NPSH
  • Pumps can not pump vapors!
  • The satisfactory operation of a pump requires
    that vaporization of the liquid being pumped does
    not occur at any condition of operation.

16
Net Positive Suction Head Required, NPSHr
As the liquid passes from the pump suction to the
eye of the impeller, the velocity increases and
the pressure decreases. There are also pressure
losses due to shock and turbulence as the liquid
strikes the impeller. The centrifugal force of
the impeller vanes further increases the velocity
and decreases the pressure of the liquid. The
NPSH required is the positive head (absolute
pressure) required at the pump suction to
overcome these pressure drops in the pump and
maintain the liquid above its vapor pressure.
17
Net Positive Suction Head Available, NPSHa
Net Positive Suction Head Available is a function
of the system in which the pump operates. It is
the excess pressure of the liquid in feet
absolute over its vapor pressure as it arrives at
the pump suction, to be sure that the pump
selected does not cavitate.
Head to Feed Pump
Subcooling before Pump To overcome suction
head
HX
Head Designed into Installation
Cool a few Degrees To overcome suction head
18
Positive Displacement Pumps
  • Piston Pumps
  • Gear Pumps
  • Lobe Pumps
  • Diaphragm Pumps
  • The lower the speed of a PD pump, the lower the
    NPSHR.

19
Piston Pumps
20
Gear Pumps
21
Lobe Pumps
  • food applications, because they handle solids
    without damaging the pump.
  • Particle size pumped can be much larger in these
    pumps than in other PD types

22
Screw Pump
23
Pump Costs
  • Cost based upon Size Factor
  • Centrifugal Pump
  • SQH1/2
  • Gear Pump
  • SQ
  • Piston Pump
  • S Power (brake)
  • Must cost Electric Motor
  • SPcPB/?M

24
Compressors
  • Types
  • Centrifugal
  • Positive Displacement
  • Piston
  • Lobed
  • Screw
  • Methods of Calculation in Simulators
  • Polytropic, PVk-1/k constant,
  • Isentropic, s(T1,P1)s(T2,isentropic,P2)
  • Theoretical Power
  • Powerisentropic f(h2,isentropic-h1)
  • Efficiency ?sPowerisentropic/Powerbrake
    (h2,isentropic-h1)/(h2-h1)
  • Cost of Compressors
  • Size Factor is Compressor Power

25
Positive Displacement Compressor
26
Positive Displacement Compressor
http//www.city-compressors.co.uk/
27
Centrifugal Compressors
  • Rotors
  • Stators
  • Jet Engine Design

28
Piston Compressor
29
Compressor Heuristic 36
  • Estimate the number of gas compression stages, N,
    assuming a maximum compression ratio of 4 for
    each stage. Assumes a specific heat ratio of 1.4
  • Optimal interstage pressures correspond to equal
    HP for each compressor. Use a pressure drop of 2
    psi for each intercooler.

30
Compressor System
31
Expander
  • Reverse of Compressor
  • Let flow produce shaft work
  • Types
  • Centrifugal
  • Positive Displacement
  • Piston
  • Lobed
  • Screw
  • Methods of Calculation in Simulators
  • Polytropic, PVk-1/k constant,
  • Isentropic, s(T1,P1)s(T2,isentropic,P2)
  • Theoretical Power
  • Powerisentropic f(h2,isentropic-h1)
  • Efficiency ?sPowerbrake/Powerisentropic (h2-h1)
    /(h2,isentropic-h1)
  • Cost
  • Size factor Power

http//www.city-compressors.co.uk/
32
Fans and Blowers
  • Types
  • Centrifugal (103-105 acfm, P1-40 in H2O)
  • Backward Curved
  • Straight radial
  • Vane Axial
  • Tube Axial
  • Cost of Fans and Blowers
  • Size factor Volumetric Flow Rate
  • Motor

33
Fan/Blower Heuristic 34
  • Use a fan to raise the pressure from atm to as
    high as 40 in water (g). Use a blower or
    compressor to raise the gas pressure to as high
    as 30 psig. Use a compressor for higher
    pressures.

34
Producing VacuumSteam Ejector
35
Producing Vacuum
  • Types
  • Ejector - advantage large volumetric flow rate
  • Multi-Stage with interstage condensers
  • Liquid (Oil) Ring Vacuum Pump
  • Dry Vacuum Pump (rotary screw, lobe) (advantage
    low pressure) Designs similar to Expanders
  • Design for
  • Flow Rate at suction plus
  • Air Leakage Rate
  • Function of pressure and Volume of vessel
  • Cost
  • Size factor Flow Rate at suction
  • Motor for pumps

36
Ejector
  • Produces Vacuum
  • Provides Low Pressures for Distillation Columns
  • Fluid (P Psat)
  • Steam
  • for suction pressure below 100 mbar absolute,
    more than one ejector will be used, with
    condensors between the ejector stages
  • Air
  • Water
  • Collects Particles in Gas Stream
  • Venturi Scrubber
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