Home > Articles

This chapter is from the book

19.2 Fluid Flow Equipment

The basic characteristics of fluid flow equipment are introduced in this section. The performance of pumps and compressors is dictated by their characteristic curves and, for pumps, the net positive suction head curve. The performance of these pieces of equipment is discussed in Section 19.5.

19.2.1 Pipes

Pipes and their associated fittings that are used to transport fluid through a chemical plant are usually made of metal. For noncorrosive fluids under conditions that are not of special concern, carbon steel is typical. For more extreme conditions, such as higher pressure, higher temperature, or corrosive fluids, stainless steel or other alloy steels may be needed. It may even be necessary, for very-high-temperature service such as for the flow of molten metals, to use refractory-lined pipes.

Pipes are sized using a nominal diameter and a schedule number. The higher the schedule number, the thicker the pipe walls, making pipes with a higher schedule number more suitable for higher-pressure operations. The nominal diameter is a number such as 2 in; however, there is no dimension of the pipe that is actually 2 in until the diameter reaches 14 in. For pipes with a diameter of 14 in or larger, the nominal diameter is the outside diameter. Pipes typically have integer nominal diameters; however, for smaller diameters, they can be in increments of 0.25 in. At larger diameters, the nominal diameters may only be even integer values. Table 19.1 shows the dimensions of some schedules of standard pipe.

Table 19.1 Dimensions of Standard Steel Pipe

Nominal Size (in)

Outside Diameter

Schedule Number

Wall Thickness

Inside Diameter

Inside Cross-Sectional Area

in

mm

in

mm

in

mm

102ft2

104m2

1/8

0.405

10.29

40

0.068

1.73

0.269

6.83

0.040

0.3664

80

0.095

2.41

0.215

5.46

0.025

0.2341

1/4

0.540

13.72

40

0.088

2.24

0.364

9.25

0.072

0.6720

80

0.119

3.02

0.302

7.67

0.050

0.4620

3/8

0.675

17.15

40

0.091

2.31

0.493

12.52

0.133

1.231

80

0.126

3.20

0.423

10.74

0.098

0.9059

1/2

0.840

21.34

40

0.109

2.77

0.622

15.80

0.211

1.961

80

0.147

3.73

0.546

13.87

0.163

1.511

3/4

1.050

26.67

40

0.113

2.87

0.824

20.93

0.371

3.441

80

0.154

3.91

0.742

18.85

0.300

2.791

1

1.315

33.40

40

0.133

3.38

1.049

26.64

0.600

5.574

80

0.179

4.45

0.957

24.31

0.499

4.641

1 1/4

1.660

42.16

40

0.140

3.56

1.380

35.05

1.040

9.648

80

0.191

4.85

1.278

32.46

0.891

8.275

1 1/2

1.900

48.26

40

0.145

3.68

1.610

40.89

1.414

13.13

80

0.200

5.08

1.500

38.10

1.225

11.40

2

2.375

60.33

40

0.154

3.91

2.067

52.50

2.330

21.65

80

0.218

5.54

1.939

49.25

2.050

19.05

2 1/2

2.875

73.03

40

0.203

5.16

2.469

62.71

3.322

30.89

80

0.276

7.01

2.323

59.00

2.942

27.30

3

3.500

88.90

40

0.216

5.59

3.068

77.92

5.130

47.69

80

0.300

7.62

2.900

73.66

4.587

42.61

3 1/2

4.000

101.6

40

0.226

5.74

3.548

90.12

6.870

63.79

80

0.318

8.08

3.364

85.45

6.170

57.35

4

4.500

114.3

40

0.237

6.02

4.026

102.3

8.840

82.19

80

0.337

8.56

3.826

97.18

7.986

74.17

5

5.563

141.3

40

0.258

6.55

5.047

128.2

13.90

129.1

80

0.375

9.53

4.813

122.3

12.63

117.5

6

6.625

168.3

40

0.280

7.11

6.065

154.1

20.06

186.5

80

0.432

10.97

5.761

146.3

18.10

168.1

8

8.625

219.1

40

0.322

8.18

7.981

202.7

34.74

322.7

80

0.500

12.70

7.625

193.7

31.71

294.7

10

10.75

273.1

40

0.365

9.27

10.02

254.5

54.75

508.6

80

0.594

15.09

9.562

242.8

49.87

463.3

12

12.75

304.8

40

0.406

10.31

11.94

303.3

77.73

722.1

80

0.688

17.48

11.37

288.8

70.56

655.5

14

14

355.6

40

0.438

11.13

13.12

333.2

93.97

873.0

80

0.750

19.05

12.50

317.5

85.22

791.7

16

16

406.4

40

0.500

12.70

15.00

381.0

122.7

1140

80

0.844

21.44

14.31

363.5

111.7

1038

18

18

457.2

40

0.562

14.27

16.88

428.8

155.3

1443

80

0.938

23.83

16.12

409.4

141.8

1317

20

20

508.0

40

0.597

15.16

18.81

477.8

193.0

1793

80

1.031

26.19

17.94

455.7

175.5

1630

24

24

635.0

40

0.688

17.48

22.62

574.5

279.2

2594

80

1.219

30.96

21.56

547.6

253.6

2356

Source: Adapted from Geankoplis, C., Transport Processes and Separation Process Principles, 4th ed., Prentice Hall, Upper Saddle River, 2003 [1]; Perry, R. H., and D. Green, Perry’s Chemical Engineers’ Handbook, 6th ed., McGraw-Hill, New York, 1984, Section 5 [2].

Tubing is commonly used in heat exchangers. The dimensions and use of tubing are discussed in Chapter 20.

Pipes are typically connected by screw threads, flanges, or welds. Welds and flanges are more suitable for larger diameters and higher-pressure operation. Proper welds are stronger and do not leak, whereas screwed or flanged connections can leak, especially at higher pressures. Changes in direction are usually accomplished by elbows or tees, and those changes in direction are usually 90°.

19.2.2 Valves

Valves are found in piping systems. Valves are about the only way to regulate anything in a chemical process. Valves serve several functions. They are used to regulate flowrate, reduce pressure by adding resistance, or isolate (turn flow on/off) equipment.

Two common types of valves are gate valves and globe valves. Figure 19.3 shows illustrations of several common types of valves.

Figure 19.3

Figure 19.3 Common Types of Valves: (a) Gate, (b) Globe, (c) Swing Check (Reproduced by Permission from Couper, J. R. et al. Chemical Process Equipment: Selection and Design, 3rd ed. [New York, Elsevier, 2012] [3])

Gate valves are used for on/off control of fluid flow. The flow path through a gate valve is roughly straight, so when the valve is fully open, the pressure drop is very small. However, gate valves are not suitable for flowrate regulation because the flowrate does not change much until the “gate” is almost closed. There are also ball valves, in which a quarter turn opens a flow channel, and they can also be used for on/off regulation.

Globe valves are more suitable than gate valves for flowrate and pressure regulation. Because the flow path is not straight, globe valves have a higher pressure drop even when wide open. Globe valves are well suited for flowrate regulation because the flowrate is responsive to valve position. In a control system, the valve stem is raised or lowered pneumatically (by instrument air) or via an electric motor in response to a measured parameter, such as a flowrate. Pneumatic systems can be designed for the valve to fail open or closed, the choice depending on the service. Failure is defined as loss of instrument air pressure. For example, for a valve controlling the flowrate of a fluid removing heat from a reactor with a highly exothermic reaction, the valve would be designed to fail open so that the reactor cooling is not lost.

Check valves, such as the swing check valve, are used to ensure unidirectional flow. In Figure 19.3(c), if the flow is left to right, the swing is opened and flow proceeds. If the flow is right to left, the swing closes, and there is no flow in that direction. Such valves are often placed on the discharge side of pumps to ensure that there is no flow reversal through the pump.

19.2.3 Pumps

Pumps are used to transport liquids, and pumps can be damaged by the presence of vapor, a phenomenon discussed in Section 19.5.2. The two major classifications for pumps are positive displacement and centrifugal. For a more detailed summary of all types of pumps, see Couper et al. [3] or Green and Perry [4].

Positive-displacement pumps are often called constant-volume pumps because a fixed amount of liquid is taken into a chamber at a low pressure and pushed out of the chamber at a high pressure. The chamber has a fixed volume, hence the name. An example of a positive-displacement pump is a reciprocating pump, illustrated in Figure 19.4(a). Specifically, this is an example of a piston pump in which the piston moves in one direction to pull liquid into the chamber and then moves in the opposite direction to discharge liquid out of the chamber at a higher pressure. There are other variations of positive-displacement pumps, such as rotary pumps in which the chamber moves between the inlet and discharge points. In general, positive-displacement pumps can increase pressure more than centrifugal pumps and run at higher pressures overall. These characteristics define their applicability. Efficiencies tend to be between 50% and 80%. Positive-displacement pumps are preferred for higher pressures, higher viscosities, and anticipated viscosity variations.

Figure 19.4

Figure 19.4 (a) Inner Workings of Positive-Displacement Pump, (b) Inner Workings of Centrifugal Pump ([a] Reproduced by Permission from McCabe, W. L. et al., Unit Operations of Chemical Engineering, 5th ed. [New York, McGraw−Hill, 1993] [5]; [b] Reproduced by Permission from Couper, J. R. et al., Chemical Process Equipment: Selection and Design, 3rd ed. [New York, Elsevier, 2012] [3])

In centrifugal pumps, which are a common workhorse in the chemical industry, the pressure is increased by the centrifugal action of an impeller. An impeller is a rotating shaft with blades, and it might be tempting to call it a propeller because an impeller resembles a propeller. (While there might be a resemblance, the term propeller is reserved for rotating shafts with blades that move an object, such as a boat or airplane.) The blades of an impeller have small openings, known as vanes, that increase the kinetic energy of the liquid. The liquid is then discharged through a volute in which the kinetic energy is converted into pressure. Figure 19.4(b) shows a centrifugal pump. Centrifugal pumps often come with impellers of different diameters, which enable pumps to be used for different services (different pressure increases). Of course, shutdown is required to change the impeller. Although standard centrifugal pump impellers only spin at a constant rate, variable-speed centrifugal pumps also are available.

Centrifugal pumps can handle a wide range of capacities and pressures, and depending on the exact type of pump, the efficiencies can range from 20% to 90%.

19.2.4 Compressors

Devices that increase the pressure of gases fall into three categories: fans, blowers, and compressors. Figure 19.5 illustrates some of this equipment. For a more detailed summary of all types of pumps, see Couper et al. [3] or Green and Perry [4].

Figure 19.5

Figure 19.5 Inner Working of Compressors: (a) Centrifugal, (b) Axial, (c) Positive Displacement ([a] and [b] Reproduced by Permission from Couper, J. R. et al., Chemical Process Equipment: Selection and Design, 3rd ed. [New York: Elsevier, 2012]; [c] Reproduced by Permission from McCabe, W. L. et al., Unit Operations of Chemical Engineering, 5th ed. [New York: McGraw−Hill, 1993])

Fans provide very low-pressure increases (<1 psi [7 kPa]) for low volumes and are typically used to move air. Blowers are essentially mini-compressors, providing a maximum pressure of about 30 psi (200 kPa). Blowers can be either positive displacement or centrifugal, and while their general construction is similar to pumps, there are many internal differences. Compressors, which can also be either positive displacement or centrifugal, can provide outlet pressures of 1500 psi (10 MPa) and sometimes even 10 times that much.

In a centrifugal compressor, the impeller may spin at tens of thousands of revolutions per minute. If liquid droplets or solid particles are present in the gas, they hit the impeller blades at such high relative velocity that the impeller blades will erode rapidly and may cause bearings to become damaged, leading to mechanical failure. The compressor casing also may crack. Therefore, it is important to ensure that the gas in a centrifugal compressor does not contain solids and liquids. A filter can be used to keep particles out of a compressor, and a packed-bed adsorbent can also be used, for example, to remove water vapor from inlet air. Knockout drums are often provided between compressor stages with intercooling to allow the disengagement of any condensed drops of liquid and are covered in more detail in Chapter 23, Section 23.2. The seals on compressors are temperature sensitive, so a maximum temperature in one stage of a compressor is generally not exceeded, which is another reason for staged, intercooled compressor systems. It should also be noted that compressors are often large and expensive pieces of equipment that often have a large number of auxiliary systems associated with them. The coverage given in this text is very simplified but allows the estimate of the power required.

Positive-displacement compressors typically handle lower flowrates but can produce higher pressures compared to centrifugal compressors. Efficiencies for both types of compressor tend to be high, above 75%.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020