Piping and Pumping

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Piping and Pumping
Chemical Engineering and Materials
Science Syracuse University

• Process Design
• CEN 574
• Spring 2004

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Outline

• Pipe routing
• Optimum pipe diameter
• Pressure drop through piping
• Piping costs
• Pump types and characteristics
• Pump curves
• NPSH and cavitation
• Regulation of flow
• Pump installation design

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Piping and Pumping Learning Objectives

• At the end of this section, you should be able
  to
• Draw a three dimensional pipe routing with layout
  and plan views.
• Calculate the optimum pipe diameter for an
  application.
• Calculate the pressure drop through a length of
  pipe with associated valves.
• Estimate the cost of a piping run including
  installation, insulation, and hangars.

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• List the types of pumps, their characteristics,
  and select an appropriate type for a specified
  application.
• Draw the typical flow control loop for a
  centrifugal pump on a PID.
• Describe the features of a pump curve.
• Use a pump curve to select an appropriate pump
  and impellor size for an application.
• Predict the outcome from a pump impellor change.
• Define cavitation and the pressure profile within
  a centrifugal pump.
• Calculate the required NPSH for a given pump
  installation.
• Identify the appropriate steps to design a pump
  installation.

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References

• Appendix III.3 (pg 642-46) in Seider et al.,
  Process Design Principals (our text for this
  class).
• Chapter 12 in Turton et al., Analysis, Synthesis,
  and Design of Chemical Processes.
• Chapter 13 in Peters and Timmerhaus, Plant Design
  and Economics for Chemical Engineers.
• Chapter 8 in McCabe, Smith and Harriott, Unit
  Operations of Chemical Engineering.

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Pipe Routing

• The following figures show a layout (looking from
  the top) and plan (looking from the side) view of
  vessels.
• We want to rout pipe from the feed tank to the
  reactor.

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Plan View
piping chase
reactor
steam header
40 ft
feed tank
60 ft
35 ft
50 ft
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Layout View Looking Down
steam header
40 ft
feed tank
piping chase
45 ft
30 ft
reactor
10 ft
reactor
35 ft
50 ft
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Plan View
piping chase
reactor
out in
steam header
40 ft
feed tank
60 ft
35 ft
50 ft
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Layout View
steam header
85 ft
30 ft
feed tank
20 ft
35 ft
60 ft
10 ft
10 ft
reactor
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Pipe Routing Exercise

• Form groups of two.
• Draw a three dimensional routing for pipe from
  the steam header to the feed tank on both the
  plan view and the layout view.

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Size the Pump

1. Determine optimum pipe size.
2. Determine pressure drop through pipe run.

200 ft
globe valve
check valve
150 ft
100 gpm
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Optimum Pipe Diameter

• The optimum pipe diameter gives the least total
  cost for annual pumping power and fixed costs.
  As D , fixed costs , but pumping power costs
  .
•  

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Optimum Pipe Diameter
Total Cost
Annualized Capital Cost
Pumping Power Cost
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Example

• Two methods to determine the optimum diameter
• Velocity guidelines and Nomograph.
• Example What is the optimum pipe diameter for
  100 gpm water.

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Using Velocity Guidelines

• Velocity 3-10 ft/s flow rate/area
• Given a flow rate (100 gpm), solve for area.
• Area (?/4)D2, solve for optimum D.
• Optimum pipe diameter 2.6-3.6 in.
• Select standard size, nominal 3 in. pipe.

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Nomograph -Convert gpm to cfm ? 13.4 cfm. -Find
cfm on left axis. -Find density (62 lb/ft3) on
right axis. -Draw a line between points. -Read
optimum diameter from middle axis.
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Practice Problem

• Find the optimum pipe diameter for 100 ft3 of air
  at 40 psig/min.

• A (s/50ft)(min/60 s)(100 ft3/min) 0.033 ft2
• 0.033 ft2 3.14d2/4
• d 2.47 in

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Piping Guidelines

• Slope to drains.
• Add cleanouts (Ts at elbows) frequently.
• Add flanges around valves for maintenance.
• Use screwed fitting only for 1.5 in or less
  piping.
• Schedule 40 most common.

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Calculating the Pressure Drop through a Pipe Run

• Use the article Estimating pipeline head loss
  from Chemical Processing (pg 9-12).
• ?P (?/144)(?Zv22-v12/2ghL)
• Typically neglect velocity differences for
  subsonic velocities.
• hL head loss due to 1) friction in pipe, and 2)
  valves and fittings.
• hL(friction) c1fLq2/d5

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• c1 conversion constant from Table 1 0.0311.
• f friction factor from Table 6 0.018.
• L length of pipe 200 ft 150 ft 350 ft.
• q flow rate 100 gpm.
• d actual pipe diameter of 3 nominal from Table
  8 3.068 in .
• hL due to friction 7.2 ft of liquid head

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Loss Due to Fittings

• K 0.5 entrance
• K 1.0 exit
• Kf(L/d)(0.018)(20) flow through tee
• K3(0.018)(14) elbows
• K0.018(340) globe
• K0.018(600) check valve
• Sum K 19.5

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• hL due to fittings c3Ksumq2/d4 5.7 ft of
  liquid head loss due to fittings.
• hLsum7.2 5.7 ft of liquid head loss
• Using Bernoulli Equation
• ?P (?/144)(?Zv22-v12/2ghLsum)
• ?P (? /144)(150012.9) 70.1 psi due mostly to
  elevation. Use ?P to size pump.

elevation velocity friction and
fittings
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Find the Pressure Drop
400 ft
50 ft
check valve
400 gpm water 4 in pipe
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Estimating Pipe Costs

• Use charts from Peters and Timmerhaus.
• Pipe
• Fittings (T, elbow, etc.)
• Valves
• Insulation
• Hangars
• Installation

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Note not 2003
/linear ft
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Pumps Moving Liquids

• Centrifugal
• Positive displacement
• Reciprocating fluid chamber stationary, check
  valves
• Rotary fluid chamber moves

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Centrifugal Pumps
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Centrifugal Pump Impeller
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Positive Displacement Reciprocating

• Piston up to 50 atm
• Plunger up to 1,500 atm
• Diaphragm up to 100 atm, ideal for corrosive
  fluids
• Efficiency 40-50 for small pumps, 70-90 for
  large pumps

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Positive Displacement Reciprocating (plunger)
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Positive Displacement Rotary

• Gear, lobe, screw, cam, vane
• For viscous fluids up to 200 atm
• Very close tolerances

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Positive Displacement Rotary
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Comparisons Centrifugal

• larger flow rates
• not self priming
• discharge dependent of downstream pressure drop
• down stream discharge can be closed without
  damage
• uniform pressure without pulsation
• direct motor drive
• less maintenance
• wide variety of fluids

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Comparisons Positive Displacement

• smaller flow rates
• higher pressures
• self priming
• discharge flow rate independent of pressure
  utilized for metering of fluids
• down stream discharge cannot be closed without
  damage bypass with relief valve required
• pulsating flow
• gear box required (lower speeds)
• higher maintenance

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Centrifugal Pumps

• Advantages
• simple and cheap
• uniform pressure, without shock or pulsation
• direct coupling to motor
• discharge line may be closed
• can handle liquid with large amounts of solids
• no close metal-to-metal fits
• no valves involved in pump operation
• maintenance costs are lower

• Disadvantages
• cannot be operated at high discharge pressures
• must be primed
• maximum efficiency holds for a narrow range of
  operating conditions
• cannot handle viscous fluids efficiently

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Moving Gases

• Compression ratio Pout/Pin
• Fans large volumes, small discharge pressure
• Blowers compression ratio 3-4, usually not
  cooled
• Compressors compression ratio gt10, usually
  cooled.
• Centrifugal (often multistage)
• Positive displacement

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Fan Impellers
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Two-lobe Blower
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Reciprocating Compressor
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Centrifugal Pump Symbols
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Pump Curves

• For a given pump
• The pressure produced at a given flow rate
  increases with increasing impeller diameter.
• Low flow rates at high head, high flow rates at
  high head.
• Head is sensitive to flow rate at high flow
  rates.
• Head insensitive to flow rate at lower flow
  rates.

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Pump Curve- used to determine which pump to
purchase.- provided by the manufacturer.
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Pump Curve
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NPSH and Cavitation

• NPSH Net Positive Suction Head
• Frictional losses at the entrance to the pump
  cause the liquid pressure to drop upon entering
  the pump.
• If the the feed is saturated, a reduction in
  pressure will result in vaporization of the
  liquid.
• Vaporization bubbles, large volume changes,
  damage to the pump (noise and corrosion).

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Pressure Profile in the Pump
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NPSH

• To install a pump, the actual NPSH must be equal
  to or greater than the required NPSH, which is
  supplied by the manufacturer.
• Typically, NPSH required for small pumps is 2-4
  psi, and for large pumps is 22 psi.
• To calculate actual NPSH
• NPSHactual Pinlet-P (vapor pressure)
• Pinlet P(top of tank, atmospheric) ?gh -
  2?fLeqV2/D

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What if NPSHactual lt NPSHrequired?

• INCREASE NPSHactual
• cool liquid at pump inlet (T decreases, P
  decreases)
• increase static head (height of liquid in feed
  tank)
• increase feed diameter (reduces velocity, reduces
  frictional losses) (standard practice)

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Regulating Flow from Centrifugal Pumps

• Usually speed controlled motors are not provided
  on centrifugal pumps, the flow rate is changed by
  adjusting the downstream pressure drop (see pump
  curve).
• Typical installation includes a flow meter, flow
  control valve (pneumatic), and a control loop.

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Typical Installation
operator set-point
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Designing Pump Installations

• use existing pump vendor, note spare parts the
  plant already stocks.
• select desired operating flow rate, maximum flow
  rate.
• calculate pressure drop through discharge piping,
  fittings, instrumentation (note if flow control
  is desired need to use pressure drop with control
  valve 50 open).

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• add safety factor to calculated head 10 psig
  spec pump for 20 psig, 150 psig spec pump for 200
  psig.
• using head and flow rate, select impeller that
  gives efficient operation in region of operating
  flow rate.
• vertical location of pump compared to level of
  influent tank (NPSH).
• if want to control flow rate spec and order
  flow meter and flow control valve also.