1. Process Design CEN 574 Spring 2004
Chemical Engineering and Materials Science
Syracuse University
Piping and Pumping
Process Design
CEN 574
Spring 2004

2. Outline NPSH and cavitation Regulation of flow
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

3. 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.

4. 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 P&ID.
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.

5. References
Appendix III.3 (pg ) 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.

6. 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.

7. Plan View piping chase reactor steam header feed tank 40 ft 60 ft

8. Layout View: Looking Down
steam header
40 ft
feed
tank
piping chase
45 ft
30 ft
reactor
10 ft
reactor
50 ft
35 ft

9. Plan View piping chase reactor = out = in steam header feed tank 40 ft

10. Layout View steam header feed tank reactor 85 ft 30 ft 20 ft 35 ft

11. 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.

12. Size the Pump Determine optimum pipe size.
Determine pressure drop through pipe run.
200 ft
globe valve
check valve
150 ft
100 gpm

13. 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 .

14. Optimum Pipe Diameter Total Cost Optimum Annualized Capital Cost
Pumping Power Cost

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

17. 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 = in.
Select standard size, nominal 3 in. pipe.

18. 3.3 in optimum diameter 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.
3.3 in optimum diameter

19. 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) = ft2
0.033 ft2 = 3.14d2/4
d = 2.47 in

20. 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.

21. Calculating the Pressure Drop through a Pipe Run
Use the article Estimating pipeline head loss from Chemical Processing (pg 9-12).
P = (/144)(Z+[v22-v12]/2g+hL)
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

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

23. Loss Due to Fittings K= 0.5 entrance K = 1.0 exit
K=f(L/d)=(0.018)(20) flow through tee
K=3[(0.018)(14)] elbows
K=0.018(340) globe
K=0.018(600) check valve
Sum K = 19.5

24. hLsum=7.2 + 5.7 ft of liquid head loss Using Bernoulli Equation
hL due to fittings = c3Ksumq2/d4 = 5.7 ft of liquid head loss due to fittings.
hLsum= ft of liquid head loss
Using Bernoulli Equation
P = (/144)(Z+[v22-v12]/2g+hLsum)
P = ( /144)( )= 70.1 psi due mostly to elevation. Use P to size pump.
elevation velocity friction and fittings

25. Find the Pressure Drop check valve 400 gpm water 4 in pipe 400 ft

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

27. Note: not 2003 $
$/linear ft

28. Pumps – Moving Liquids Centrifugal Positive displacement
Reciprocating: fluid chamber stationary, check valves
Rotary: fluid chamber moves

29. Centrifugal Pumps

31. Centrifugal Pump Impeller

32. 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

33. Positive Displacement: Reciprocating (plunger)

34. Positive Displacement: Rotary
Gear, lobe, screw, cam, vane
For viscous fluids up to 200 atm
Very close tolerances

35. Positive Displacement: Rotary

36. 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

37. 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

38. Centrifugal Pumps Advantages Disadvantages 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

39. Moving Gases Compression ratio = Pout/Pin
Fans: large volumes, small discharge pressure
Blowers: compression ratio 3-4, usually not cooled
Compressors: compression ratio >10, usually cooled.
Centrifugal (often multistage)
Positive displacement

40. Fan Impellers

41. Two-lobe Blower

42. Reciprocating Compressor

43. Centrifugal Pump Symbols

44. 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.

45. Pump Curve - used to determine which pump to purchase
Pump Curve - used to determine which pump to purchase. - provided by the manufacturer.

46. Pump Curve Low flow at high head Pressure increases with diameter
Head sensitive to flow at high flow rates

47. 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).

48. Pressure Profile in the Pump

49. 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

50. What if NPSHactual < 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)

51. 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.

52. Typical Installation
operator set-point FT FC FV

53. 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).

54. 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.