A Practical Approach to Chemical Engineering for Non-Chemical Engineers

By Moe Toghraei

A Practical Approach to Chemical Engineering for Non-Chemical Engineers is aimed at people who are dealing with chemical engineers or those who are involved in chemical processing plants. The book demystifies complicated chemical engineering concepts through daily life examples and analogies. It contains many illustrations and tables that facilitate quick and in-depth understanding of the concepts handled in the book. By studying this book, practicing engineers (non-chemical), professionals, technicians and other skilled workers will gain a deeper understanding of what chemical engineers say and ask for.

The book is also useful for engineering students who plan to get into chemical engineering and want to know more on the topic and any related jargon.

• Provides numerous graphs, images, sketches, tables, help better understanding of concepts in a visual way
• Describes complicated chemical engineering concepts by daily life examples and analogies, rather than by formula
• Includes a virtual tour of an imaginary process plant
• Explains the majority of units in chemical engineering

• Language: English
• Publisher: Elsevier Science
• Release date: Sep 19, 2021
• ISBN: 9780128242155

Moe Toghraei

Moe Toghraei, M.Sc., P.Eng. is Process Engineer who has more than 25 years' experience in chemical engineering, and more than 20 years' experience in teaching. He has in-depth knowledge in project management skills including, man-hour estimation, budgeting, scheduling, and planning. Currently he is an independent Project/Process Engineer. Up to 2011 he was Lead Engineer with CH2M and Jacobs, Calgary, Alberta, Lead Process Specialist with Worley Parsons; Calgary, Alberta. He authored the book “Piping and instrumentation diagram development” published with Wiley-AIChE in 2019. He developed and instructed in-class training courses on “Water treatment in the oil industry”, “De-Oiling: Oil Removal From Water”, “P&ID: Reading & Interpretation”, “Practical Process Control: A P&ID Approach”, “Pressure Safety Valves”, and online training courses on “Process Engineering for Control Practitioners", “Process Engineering for Control Practitioners", “Chemical Engineering for non-chemical engineers”.

Book preview

Preface

This book gives you a wealth of information about chemical engineering. This book is mainly written for individuals who are not studying chemical engineering in universities but for some reason need to have some knowledge about it. The information contained herein could also be beneficial for young chemical engineers. I will try to give you information about chemical engineering not only at the elementary level, but also at a very high level and using very down-to-Earth language. Experienced chemical engineers because this book uses a specific angle of view to chemical engineering, which is different than the angle of view used by universities and colleges.

The book is written based on the required knowledge of a working chemical engineer.

The skeleton of this book has four parts as below.

Part 1: Components of Chemical Process Industries

This part is basically a virtual tour inside a chemical process plant.

Part 2: Behind the Scenes of Chemical Process Plants

In this part, we see a process plant with deeper insight.

Part 3: Unit Operations and Process Units

In this part, we will discuss the heart of chemical engineering, which is conversions.

Part 4: Chemical Process Plants and Society

In the last part, the relationship and interactions between process plants and society will be discussed.

Introduction

Chemical engineering is about materials, systems, and their relationships. Materials are something chemists also know about, but with a deeper approach. Systems here means equipment, control systems, and utilities. In this book, we will talk about both of these items.

The heart of chemical engineering is making the conversion of materials happen. There are two types of conversion: physical conversion and chemical conversion. Fig. 1 shows one example of a physical change in a kitchen (left-hand picture) and another of a chemical change in a kitchen (right-hand picture).

Figure 1 Physical change and chemical change in a kitchen.

Based on the above example, you may say, chemical conversion allows us to make more products than physical conversion. You are right, chemical conversion provides more products for us, but the bad news is that chemical conversion is more difficult to perform and control.

A conversion is a change. When we talk about change, two parameters should be considered:

1. the possibility of change and

2. the speed of the change.

For a change, both these parameters are important. As an example, coal (carbon) has a natural tendency to be converted to diamond. Yes, really! But do not run to the store to buy some coal, because this process takes about a million years. Therefore speed is also important; sometimes it is more important than the possibility.

The possibility of a change is studied in the topic of Thermodynamics. In the case of chemical conversion, the thermodynamics at play are chemical thermodynamics, which is studied as a separate topic.

The speed of a change is studied in Kinetics (for chemical conversions), or in Mass Transfer (for physical conversions).

Thermodynamics, mass transfer, and kinetics are the heart of subjects in chemical engineering programs in universities (Fig. 2).

Figure 2 Topics in a typical chemical engineering program.

These three topics in chemical engineering are shown in a box in Fig. 2.

If we want to step back toward the more theoretical aspect (going toward the left), we can see deep theoretic topics.

The basic theory of possibility of change can be found in Physical Chemistry, which is a topic in the science of chemistry.

The basic theory of speed of change falls within the topic of Transport Phenomena, which is taught in some undergraduate chemical engineering programs, but it is more common at the graduate level.

If we take several steps toward reality and toward practical concepts (going to the right), then we can see the topics about the fundamentals of equipment. There are two types of equipment or units available in chemical engineering: units for physical conversions and units for chemical conversions. The topic in chemical engineering programs in universities that deals with the fundamentals of units for physical changes is called Unit Operations.

Reactor Design is the topic that deals with the fundamentals of units for chemical conversion. In chemical engineering, each container in which a chemical conversion or chemical reaction occurs is called a reactor.

Chemical conversions (chemical reactions) are more complicated. Generally, at the undergraduate level, one topic is offered as Kinetics and Reactor Design, which covers both chemical reactions and their applications.

Taking one step closer toward reality (going further toward the right), we will have a topic on design and economics. This topic could be covered within one subject (e.g., Process Design and Economy) or two separate ones (e.g., Process Design and Engineering Economics).

In the last step, universities develop and offer different topics, which are more industry-oriented than academic. These are topics such as Fundamentals of Environmental Engineering, Petroleum Engineering, Water and Wastewater Treatment, Air Pollution Engineering, and Polymer Processing.

There is one (and possibly only one) topic in undergraduate chemical engineering programs on the control of process plants, and the name of this topic is Process Dynamics and Control. The reason we need this topic is because we live in a world full of changes (the only constant thing in this world is change), so we need control. Process plants are no different than other things in this world; they need control too.

People generally underestimate the concept of control, simply because there are many topics on design in universities, but possibly only one topic on control. However, a successful plant results from good design AND good control (Fig. 3).

Figure 3 Components of a successful plant.

One other topic that is not in the table is Fluid mechanics; this is one of the fundamental topics in chemical engineering. Why is it fundamental? A process plant could be thought of as a string of conversion boxes, with the fluid passing through them, from one box to the next. This material transfer is done using an understanding of fluid mechanics.

Part 1

Components of chemical process industries

Outline

Part 1 Components of chemical process industries

Chapter 1 Equipment and pipes (applications)

Chapter 2 Utilities

Chapter 3 Instrumentation and control

Part 1

Components of chemical process industries

Chemical engineering was born based on the need in process plants. In the olden days, there were engineers (mainly mechanical engineers) who worked in process plants. After a while, people realized that those engineers needed some specific knowledge about the chemical processes, thus was born chemical engineering.

Therefore studying process plants could be considered as a logical and easy way to learn chemical engineering. This is the approach I took to write this book.

You may consider this part of the book as a set of information that I provide for you when you are walking through a process plant. Some of the topics in this part of the book will be discussed in greater detail in the next parts of this book.

In general, all process industries have three main elements: equipment, utility generation and network, and instrumentation/control (I&C) system.

The first element is the string of equipment used to convert raw materials into products.

In each plant, pieces of equipment are tied together to convert raw material(s) to product(s). This equipment could include vessels, tanks, pumps, etc. However, these pieces of equipment usually need external help, or utilities, for their daily operation. For example, a pump needs electricity to operate, so in this case, electricity is considered a utility. A heat exchanger may need a heat stream, such as steam, to change the temperature of a process stream. In this example, steam is a utility.

In Chapter 1, Equipment and Pipes (Applications), we will cover pipes, containers, and equipment.

The second element of the process industry is the utility generation plant, along with the utility distribution and collection network.

There may be different types of utilities in each process plant, including electricity, steam, utility water, instrument air, utility air, cooling water, etc.

All of these utilities need to be generated in an auxiliary plant near the main process plant. Such a plant can be named the utilities plant. In some cases, the used utility needs to be collected to save some money by recycling it and converting it to a fresh utility. In such cases, a collection network is also needed.

Chapter 2, Utilities, covers the utilities and their distribution/collection within chemical process plants.

The third element of the process plant is the instrumentation and control system. This element works like the nervous system in the human body in that it monitors different locations of the plant and controls their operation.

Chapter 3, Instrumentation and Control, talks about instruments and control systems in chemical process plants.

Do you think it is strange to classify process plants into equipment, utility generation and network, and I&C system? We can also study our body using this classification. Our body consists of organs like the heart, lungs, kidneys, etc., which are basically the equipment. Our body has some utility networks, like veins, which convey blood to organs. We also a have nervous system, which controls our body’s actions.

Still not sure? We can use the same classification when studying cars. In a car, there are three main groups of items that work together: equipment (motor, radiator, etc.); utilities (cooling water system, lubricating oil system, etc.); and the instrument and control system (including all the items on the dashboard). So, we can see all living systems have these three components.

Chapter 1

Equipment and pipes (applications)

Abstract

This section talks about pipes, containers, and equipment.

Keywords

Pipe; tank; vessel; pump; fan; compressor; blower

As was mentioned in the introduction section of this book, the main objective of process plants is conversion, and this is done in unit operations and process units. So, can we say that the only units we need in process plants are equipment in unit operation equipment and/or process? The answer, surprisingly, is no! Actually, in a process plant, only 10% of the equipment (number-wise and not price-wise) may be unit operations or process units. So, what are the other pieces of equipment? They are the ones that prepare process materials for the conversion.

What do we need to have outside of conversion units?

The first things are the equipment which bring process materials into the conversion units. fluid conductors (e.g., pipes) and fluid movers (e.g., pumps) do this duty. We also most probably need some types of containers to store a variety of materials during operation.

The other things we may need to do is prepare process materials to be ready to initiate conversion inside of conversion units. There are three main parameters that may need to be changed: material temperature, material pressure, and material volume (they will be discussed in more detail in Chapter 5: Concepts of Materials). Temperature can be changed by heat exchangers and/or fired heaters. Pressure change is mainly applicable to gas/vapor phases of materials. Pressure change can be achieved with blowers and compressors. Volume change, again, mainly applies to gases and vapors.

Therefore, we can summarize all equipment in process plants as follows:

1. Fluid conductors: pipes, tubes, ducts, channels;

2. Fluid movers: pumps, compressors, etc.;

3. Containers: tanks, vessels;

4. Heat transfer equipment: heat exchangers, furnaces; and

5. Unit operations and unit processes: reactors, separators, etc.

We will talk about these items in this chapter without going through the scientific bases of them. In Chapter 6, Concepts of Process Equipment, we will discuss the detail of them.

There are hundreds of different types of equipment in the different process industries. The types of equipment in an edible oil processing plant may be different from the equipment in an oil refinery; the equipment in a mineral processing plant may be different from the equipment in a wastewater treatment plant. However, the above five main groups of equipment are common in almost all process plants.

We have almost the same elements in our daily life too! In the below table you can see items in a city that are analogous to items in a process plant (Table 1.1).

Table 1.1

In the rest of this chapter, we introduce each of the above pieces of equipment. We will do it by introducing features of each of them. In the chemical engineering world we name these features as their specifications or, in brief, specs. Understanding these specs are very important when buying the equipment and making sure we are buying exactly what we are looking for it (Fig. 1.1).

I was asked to go and buy a gallon of milk; my wife gave me this note. It can be considered as a spec. sheet of milk I have to buy.

Figure 1.1 Typical spec. sheet in daily life.

There are two types of specifications defined for each piece of equipment: duty-based and geometric-based. Does it look strange? No, we have two types of specifications for individuals too! Table 1.2 is an example list of duty-based and geometric-based specifications for an individual. As can be seen, duty-based specs are the ones that outline the role and duty of the individual, while geometric-based specs talk about the features of an individual that are more tangible and easier to measure.

Table 1.2

It is good to note that chemical engineers are generally more interested in duty-based specs, while other engineers are more interested in geometric-based specs (Fig. 1.2).

For a food, the duty-based spec is its nutrition information and its geometric-based spec is its ingredients.

Figure 1.2 Specifications of a bottle of chocolate milk.

In the following sections, we will cover the equipment mentioned above, but in Chapter 6, Concepts of Process Equipment, we will talk about the concepts behind each of these equipment.

1.1 Fluid conductors: pipes, tubes, ducts

Why do we need fluid conductors? For the same reason that we need roads and streets.

Table 1.3 shows this analogy.

Table 1.3

Valves together with fittings are discussed in the next section (Section 1.2) rather than this section because they are a big group.

There are quite a few types of fluid conductors; pipes, channels, tubes, and ducts are the most common ones.

Fig. 1.3 shows pipes and channels.

Figure 1.3 Shapes of pipes and channels.

For low-pressure water streams, channels are the conductor of choice. For high-pressure flows, like on the outlet (discharge) side of pumps, the choice is generally pipes. The liquids flowing through channels are exposed to the environment so if the flowing liquid is flammable, hazardous, or toxic, a pipe should be used instead. The features and applications of different fluid conductors are summarized in Table 1.4.

Table 1.4

Here, we concentrate on pipes which are the most common type of fluid conductor.

For pipes, again, we can define two types of specifications.

It is tempting to say that duty-based specification of pipes are defined by their carrying flowrate or simply flowrate. But it is not right! The concept of flowrate will be discussed in Chapter 5, Concepts of Materials, but as examples the flowrate of Bow river in Canada could be 120 m³/s or the flowrate of a stream could be 20 m³/h. We cannot say this pipe with this specific size can carry 10 m³/h. In theory you can force each pipe to carry whatever flowrate you want as long as you put enough pressure on its back. You may ask, can I force my drinking straw to carry the flow of Bow river? The answer is yes, as long as you can place a pump to pressurize it to very high pressure and the wall of your drinking straw is robust enough to not explode because of that pressure. Thus, in brief, flowrate is NOT a specification of a pipe and we would not talk about a 4′′ pipe as a 30 m³/h pipe!

Geometric-based specification of pipes can be defined as their diameter (pipe size) and the pipe wall’s thickness. However, it could be more complicated and it is discussed in Section 1.1.1.

1.1.1 Pipe specifications

To specify a pipe based on its geometry, two parameters need to be mentioned: pipe diameter [inside diameter (ID) or outside diameter (OD)] and pipe thickness.

Pipes are built to different standards, but the two most common are the American Standard (ASME/API), which is in Imperial units (e.g., inches), and the ISO Standard (or European Standard, which is based on DIN, for example), which uses metric units (e.g., millimeters).

In the American Standard, the nominal pipe size (NPS) and schedule are mentioned. NPS is an indicative value of the diameter of the pipe, but it does not correspond to the ID, nor to the OD (with some exceptions). NPS starts at less than 1′′ and goes up to more than 36 inches.

Schedule is an indicative number of the thickness of the pipe. The bigger the schedule number is, the thicker the pipe. Schedule number starts at Sch. 10 (Schedule 10) and goes up to 160. There are also three alphabetic schedules: STD (Standard), XH or XS (extra heavy or extra strong), and XXH or XXS (double extra heavy or double extra strong).

The schedule of pipes in our houses are generally Sch. 40. (or std.). In industrial facilities, the schedule pipes generally start with Sch. 80 and go higher depends on the fluid pressure.

For example, a 4′′ pipe with a schedule of 80 could be specified; to determine the diameter and thickness of this pipe, we need to consult the relevant table. An excerpt from one such table is shown in Table 1.5. Complete tables can be found in different pipe standards.

Table 1.5

Here, the table shows that a 4′′ pipe with a schedule of 80 has the following characteristics:

Outside diameter: 4.5′′

Inside diameter: 3.826′′

The table also shows some interesting facts:

1. For pipes with an NPS larger than 12′′, the NPS is the same as the OD.

2. For pipes with an NPS equal to or smaller than 12′′, in most cases, the NPS falls somewhere between the ID and the OD.

These two facts can be seen in Table 1.6.

Table 1.6

3. As schedule number increases, pipe thickness also increases while the OD remains constant. In other words, schedule number only causes a variation in the ID. This can be seen in Table 1.7.

Table 1.7

Demonstrates that the schedule number only causes a variation in the ID, and not the OD.

A higher pipe schedule needs to be used when the fluid to be transferred has a higher temperature and/or pressure.

In the European system, pipe size is specified using nominal diameter (DN). DN has the same numerical value as NPS but is expressed in millimeters and is rounded. For example, an NPS of 1′′ would be equivalent to 25 mm.

1.2 Pipe appurtenances: fittings and valves

Pipe appurtenances are the items which are installed on or are in the way of fluid conductors including pipes. There are two main groups of appurtenances: fittings and valves.

Fittings are passive tools that are used to cause a permanent change to the flow and/or the pipe’s routing. One very common fitting is an elbow.

Valves are active tools that are used to cause a temporary change in flow. A gate valve is a type of valve.

When you want to drive from point A to point B, you will come across bends in the road or changes in street width. These bends, narrows, and widenings may be inevitable and may have been implemented when the road was built. You will also see some traffic lights along your route, which are installed to control the flow of cars for the purposes of keeping peace in the city.

Fittings and valves are discussed in Sections 1.2.1 and 1.2.2.

1.2.1 Fittings

There are many fittings available for pipes. Table 1.8 shows an arbitrary classification of the most common fittings. There are also a bunch of other fittings that are in essence a combination of two or more basic fittings.

Table 1.8

Fig. 1.4 shows a real shape of flanges.

Figure 1.4 Flanges.

1.2.2 Valves

There are many types of valves used in chemical industries. Some of them are globe valves, gate valves, ball valves, and butterfly valves. Globe valves (Fig. 1.5) got their name from the ball-like shape of their bodies.

Figure 1.5 Globe valve.

Valves have two main components: the valve operator and the valve plug (Fig. 1.6).

Figure 1.6 Main components of a valve.

The valve operator is the part that takes orders from an external source to take some action on the fluid flow.

The valve’s plug is the part of the valve which is in contact with the flowing fluid.

The valve operator is connected to the valve plug by a piece of rod named the stem. The stem can have an up-and-down movement or a quarter turn movement, depending on the type of valve.

There are many different types of valves: globe valves, butterfly valves, gate valves, etc. But all of them can be grouped based on their different types of operators and also their different types of plug (by the way, plug valve is a specific type of valve too!).

Based on plug type of valves there are four types: throttling, blocking, diverting, and special valves. The above different roles of valves are achieved because different types of plugs are installed inside of valve bodies. These types of valves are discussed in Sections 1.2.2.1–1.2.2.4.

Based on the operator type, there two main types of valves: manual valves and automatic valves. There are two types of remotely operated valves: control valves and switching valves, and both will be discussed in Section 1.2.2.5.

1.2.2.1 Throttling valves

Throttling valves can adjust the flow anywhere from 0% (no flow) to 100% of flow (when the valve is fully open). The role of throttling valves is to adjust a flow.

In Fig. 1.7, I tried to adjust the flow from a hose by adjusting my thumb’s location on the hose opening. This is how a throttling valve adjust the flowrate.

Figure 1.7 Adjusting flow by my thumb.

A famous type of throttling valve is the globe valve.

The important thing is that the throttling valves are not good in the role of blocking and if you try to block a flow by a throttling valve, the flow may pass by (internally leaking).

1.2.2.2 Blocking valves

Blocking valves, in contrast, allow only for full flow or no flow at all. Therefore, the stem of the valve will be completely up (for the fully open case), or completely down (for the fully closed case).

The role of blocking valves is stopping or continuing a flow.

Gate valves and ball valves are two common types of blocking valves. Fig. 1.8 shows the inside of a ball valve. You can see the ball in the middle of the ball valve which is partially opened.

Figure 1.8 A ball valve.

It is important to know that using blocking valves in the duties of a throttling valve is wrong. This means it is not advised to use a blocking valve—like a globe valve—to adjust a flow by partially opening it. The life of blocking valves will be shortened when you always keep them partially open.

1.2.2.3 Diverting valves

Diverting valves neither block nor throttle flows; they simply divert flow from destination A to destination B. In theory, you can avoid using any diverting valve by using two or more blocking valves. Fig. 1.9 shows a schematic diagram of a diverting valve and also a corresponding arrangement without use of a diverting valve.

Figure 1.9 Diverting valve.

Now, it could be recognized that the application of a diverting valve is mainly to save money and space. Diverting valves are seen a lot in compact systems. They are generally not available in large sizes (say more than 6′′), because larger sizes are needed for larger equipment, and if a plant has large equipment, it generally does not have tight space or a tight budget!

1.2.2.4 Special valves

All the other valves that could not be categorized into the above classes could be called special valves. Two important types of special valves are check valves and pressure safety valves.

Check valves

Check valves, also known as non-return valves (NRV), are a very common type of valve in piping systems. They function very similar to a wrong way sign (see Fig. 1.10). A wrong way sign on a street shows that cars can go in one specific direction, and not in the opposite direction. By placing a check valve on a pipe, we sort of guarantee that a fluid, liquid, or gas only goes in one direction though the pipe, and not the opposite way.

Figure 1.10 A wrong way sign is similar to a check valve.

The most common type of check valve is a swing check valve (Fig. 1.11). However, there are also other types of check valves available on the market. For example, if the pipe size is very small, say, less than 3′′, a swing check valve may not be economical; instead, a ball or piston-type check valve would be used.

Figure 1.11 Swing check valves.

One easy way to recognize a check valve in a process plant is the arrow on their body. All check valves have an arrow engraved onto their body, showing the direction of flow they are trying to maintain.

Pressure safety valves

Have you seen pressure safely valve (PSV) in your daily life? See a picture of a pressure cooker in Fig. 1.12.

Figure 1.12 A pressure cooker.

What is the item pointed to by the arrow? It is a PSV. It is a special valve that opens when the pressure inside of the cooker goes beyond a specific limit to protect it from bursting (Fig. 1.13).

Figure 1.13 Safety valve.

We have the same device in process plants for the same reason as on a pressure cooker. In a pressure cooker, the lid is closed and sealed. Therefore, during the cooking period, some water turns into vapor and pressurizes the pressure cooker. We like this higher pressure because it helps us to cook our food quicker. However, the pressure should not go too high, because the pressure cooker could burst and explode. The PSV on the top limits the internal pressure to a specific predetermined value; this value is called the PSV set pressure. Without such a safety device on the pressure cooker, the pressure could increase beyond the structural limitations of the vessel, and it may explode.

The earliest type of pressure device was the one used for steam engines in the 1900s. It was basically a plug that exerted force using a hanging weight to close the pressure-releasing hole (orifice), thus keeping it closed up to a point that the pressure exceeded a specific value. The value of the pressure at which the device was intended to start to opening, or the set pressure, could be adjusted by sliding the weight along the lever (Fig. 1.14).

Figure 1.14 Early type of pressure relief valve.

In process plants, we have flowing fluids inside pipes and vessel, and there could be certain scenarios that could cause these items to be overpressurized. The term overpressurized is used here to refer to a pressure inside an enclosure which is beyond its structural limitations. In such cases, we need to install a PSV. An enclosure could be a pipe, a tank, a vessel, or even the casing of a piece of equipment.

A schematic diagram of a PSV is shown in Fig. 1.15.

Figure 1.15 PSV internals when closed and when relieving. PSV, Pressure safely valve.

PSVs will be discussed in more detail in Chapter 18, Safety Requirements of Plants.

1.2.2.5 Remotely operated valves

In manual valves (Fig. 1.16), the situation of the plug inside of valve body can be changed by manual rotating of the operator (handwheel). But in an automatic valve it is done by an actuator which adjusts the plug of a valve. As actuators can be activated remotely these valves are named remotely operated valves.

Figure 1.16 A manual valve.

The actuator of remotely operated valves can be activated by an order from the control room, or by an order derived from an event. Here, event means a change in a parameter in the process plant. Examples of events are a change in pressure or a change in temperature. These events will be discussed in detail in Chapter 3, Instrumentation and Control.

As we have two types of plugs, throttling and blocking, we can say we will have four different types of valves (Table 1.9).

Table 1.9

A control valve is a type of automatic valve where its plug functions as a throttling valve.

A switching valves is a type of automatic valve where its plug functions as a blocking valve (Fig. 1.17).

Figure 1.17 A switching valve.

1.3 Fluid movers: pumps and compressors

Here, the phrase fluid movers is used as a collective term for pumps, fans, blowers, and compressors. Note that this name is not an industry term; it is only used here for educational purposes.

Fluid movers could be liquid movers (pumps), or gas movers (compressors, fans, and blowers).

All fluid movers have a suction side and a discharge side (Fig. 1.18). The suction side is where the fluid enters the fluid mover, and the discharge side is where the fluid comes out.

Figure 1.18 Suction side and discharge side of a pump.

There are two possible reasons for using a fluid mover: transfer (or mobilization) and pressurization.

Liquid movers (pumps) are only used for transferring liquids, while gas movers could be used for mobilization only, or for both mobilization AND pressurization.

Compressors are gas movers that are used for gas mobilization AND pressurization. Fans, on the other hand, are used only for gas mobilization. Blowers could also be considered as gas movers that have the combined duties of mobilization and pressurization.

For gases and vapors, there are three main types of movers: fans, blowers, and compressors. The first two (fans and blowers) are basically only for transfer or mobilization of the gas or vapor, while the third type, the compressor, is used for mobilization AND pressurization of the gas or vapor. If the only purpose is transferring a gas from point A to point B and there is no need to have pressure in the pipe, then a fan or a blower is enough. However, if, in addition to transferring gas from point A to point B, the gas needs to be pressurized for the purposes of a downstream unit of operation or process, then a compressor needs to be used (Table 1.10).

Table 1.10

It is important to note that when using a pump, the fluid should be only liquid; pumps have a very low tolerance for the presence of gas bubbles in the liquids. In the case of compressors, the fluid should be gas; compressors have a very low tolerance for the presence of liquid droplets in gas streams. That is why when a liquid is near its boiling point, a specific control system must be implemented to make sure that no vapor will be formed and get into the pump. Similarly, in the case of compressors, if there is a chance that the vapor stream may contain liquid droplets, these must be removed upstream of the compressor.

Fluid movers move fluids with mechanisms similar to moving solids in our daily lives; by passing along and by throwing out. Fluid movers are designed based on these two main mechanisms, and are called dynamic-type and positive displacement (PD)-type fluid movers.

In the dynamic type, movement of fluid is achieved by throwing out the fluid, while in the PD type, movement of fluid is done by passing along pockets of fluid. This concept is shown in Table 1.11.

Table 1.11

Dynamic-type fluid movers could be either axial type or centrifugal type, and PD-type fluid movers could be either rotary type or reciprocating type.

Axial-type fluid movers are mainly used for low-pressure systems. PD-types are generally used for cases in which a high pressure is needed at the outlet of the fluid mover. However, PD-type fluid movers are not manufactured with a high flowrate capacity. If the flowrate is high, then centrifugal fluid movers should be selected.

In the table, the capacity and differential pressure of fluid movers are indicated using a scale system from 1 to 4, where 1 means the highest value for the parameter and 4 means the lowest.

The duty-base spec. of fluid movers is the capacity they can handle and the differential pressure they can generate (or differential head).

1.3.1 Axial pumps

Axial pumps are not very common in industry. Axial pumps are used when we deal with a huge amount of flowrate but we do not need to add much pressure to the stream.

1.3.2 Centrifugal pumps

Centrifugal pumps are the most common type of pump (Fig. 1.19).

Figure 1.19 An industrial centrifugal pump.

In a centrifugal pump, the fluid arrives at the suction nozzle as it flows through the suction piping. The fluid must be available to the pump with sufficient energy so that the pump can work with the fluid’s energy.

The geometric-based spec. of centrifugal pumps is based on their inlet flange size, outlet flange size, and impeller size. For example, a 8′′×6′′ ×11′′ centrifugal pump means a pump with suction flange size of 8′′, a discharge flange size of 6′′, and an impeller size of 11′′ (Fig. 1.20). The discharge size is always the smallest number, and the impeller size is always the largest number.

Figure 1.20 Geometric-based spec. of a typical pump.

There is one famous parameter related to centrifugal pumps. You definitely will hear the parameter of NPSH if you deal with centrifugal pumps in chemical plants. NPSH can be defined for other types of pumps too, but the most critical case is NPSH for centrifugal pumps. There are actually two parameters for NPSH, one is NPSHR and the other is NPSHA.

NPSH stands for Net positive suction head, and the R at the end represents required and the A at the end means available. However, we do not care a lot about these and we only want to learn the concept of the two parameters of NPSHR and NPSHA.

The fundamental fact about centrifugal pumps is that they cannot SUCK liquid from their suction sides, you need to bring the liquids and push them through their suction sides, and then they are able to pump the liquid. The level needed for pushed liquid in the suction side of a centrifugal pump is shown by NPSHR and the level of provided liquid in the suction is shown by NPSHA. This fact can mathematically be written in the form of: NPSHA should be higher than NPSHR.

NPSHA is something that we need to provide for a pump in our system, while NPSHR is a characteristic of a centrifugal pump.

NPSHR is like your appetite to food (required food) and NPSHA is available food. You go to a restaurant where the size of their portion of food (NPSHA) is not smaller than your need for food (NPSHR).

How does a centrifugal pump show its disappointment if NPSHA < NPSHR? The pump will cavitate. Cavitation is a phenomenon associated with vibration and also a sound from a pump like there is some sand in the suction side! Fig. 1.21 shows symbolically the concept of NPSH. If the suction side of the centrifugal pump needs a glass of water while we give it only a few droplets of water, the pump will definitely cavitate!

Figure 1.21 Symbolic concept of NPSH. NPSH, Net positive suction head.

1.3.3 Reciprocating pumps

A reciprocating pump are a type of PD pump that takes in the fluid at the suction nozzle and physically captures and contains the fluid in some kind of moveable enclosure within the pump. There are several designs of reciprocating pumps.

Old hand pumps are a type of reciprocating pump (Fig. 1.22).

Figure 1.22 Hand water pump.

One common application of PD pumps is as chemical injection pumps; these pumps need to inject chemicals at a very accurate flowrate. For example, when my baby needs to take some medicine in sirup form, I use a syringe to give her a very accurate amount. A syringe here is like a reciprocating pump, which works in the same role as a chemical pump.

1.3.4 Rotary pumps

Rotary pumps are a type of PD pump. In rotary pumps, moving enclosures of liquid are created between the teeth of rotating gears; there are many designs for this. The moveable enclosure expands and generates a low-pressure zone to take the fluid into the pump. Then, the captured fluid is physically transported through the pump from the suction nozzle to the discharge