Chemical Engineering for Non-Chemical Engineers

Jack Hipple

• Publisher: Wiley-AIChE
• Year: 2017
• ISBN:
  9781119309659
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

Outlines the concepts of chemical engineering so that non-chemical engineers can interface with and understand basic chemical engineering concepts

• Overviews the difference between laboratory and industrial scale practice of chemistry, consequences of mistakes, and approaches needed to scale a lab reaction process to an operating scale
• Covers basics of chemical reaction eningeering, mass, energy, and fluid energy balances, how economics are scaled, and the nature of various types of flow sheets and how they are developed vs. time of a project
• Details the basics of fluid flow and transport, how fluid flow is characterized and explains the difference between positive displacement and centrifugal pumps along with their limitations and safety aspects of these differences
• Reviews the importance and approaches to controlling chemical processes and the safety aspects of controlling chemical processes,
• Reviews the important chemical engineering design aspects of unit operations including distillation, absorption and stripping, adsorption, evaporation and crystallization, drying and solids handling, polymer manufacture, and the basics of tank and agitation system design

1
What Is Chemical Engineering?

There are no doubt numerous dictionary definitions of chemical engineering that exist. Any of these could be unique to the environment being discussed, but all of them will involve the following in some way:

1. Technology and skills needed to produce a material on a commercially useful scale that involves the use of chemistry either directly or indirectly. This implies that chemistry is being used at a scale that produces materials used in commercial quantities. This definition would include not only the traditional oil, petrochemical, and bulk or specialty chemicals but also the manufacture of such things as vaccines and nuclear materials, which in many cases may be produced in large quantities, but by a government entity without a profit motive, but one based on the welfare of the general public.
2. Technology and skills needed to study how chemical systems interact with the environment and ecological systems. Chemical engineers serve key roles in government agencies regulating the environment as well as our energy systems. They may also serve in an advisory capacity to government officials regarding energy, environmental, transportation, materials, and consumer policies.
3. The analysis of natural and biological systems, in part to produce artificial organs. From a chemical engineering standpoint, a heart is a pump, a kidney is a filter, and arteries and veins are pipes. In many schools, the combination of chemical engineering principles with aspects of biology is known as biochemical or biomedical engineering.

The curriculum in all college‐level chemical engineering schools is not necessarily the same, but they would all include these topics in varying degrees of depth:

1. Thermodynamics. This topic relates to the energy release or consumption during a chemical reaction as well as the basic laws of thermodynamics that are universally studied across all fields of science and engineering. It also involves the study and analysis of the stability of chemical systems and the amount of energy contained within them and the energy released in the formation or decomposition of materials and the conditions under which these changes may occur.
2. Transport Processes. How fast do fluids flow? Under what conditions? What kind of equipment is required to move gases and liquids? How much energy is used? How fast does heat move from a hot fluid to a cold fluid inside a heat exchanger? What properties of the liquids and gases affect this rate? What affects the rate at which different materials mix, equilibrate, and transfer between phases? What gas, liquid, and solid properties are important? How much energy is required? Materials do not equilibrate by themselves. There is always a driving force such as a pressure difference, a temperature difference, or a concentration difference. Chemical engineers study these processes, their rates, and what affects them.
3. Reaction Engineering and Reactive Chemicals. Chemical reaction rates vary a great deal. Some occur almost instantaneously (acid/base reactions), while others may take hours or days (curing of plastic resin systems or curing of concrete). A chemical reaction run in a laboratory beaker may be where things start, but in order to be commercially useful, materials must be produced on a larger scale, frequently in a continuous manner, using commercially available raw materials. These industrially used materials may have different quality and physical characteristics than their laboratory cousins. Since most chemical reactions either involve the generation of heat or require the input of heat, the practical means to do this must be chosen from many possible options, but for an industrial operation with the potential of release of hazardous materials, the backup utility system must be clearly defined. In addition, chemical reaction rates are typically logarithmic, not linear (e.g., as is the case with heat transfer), providing the possibility for runaway chemical reaction. Chemical engineers must design operations and equipment for such conditions.
4. Safety. There is no basic difference in the hazards or properties of a substance such as chlorine gas on any scale. Its odor, color, boiling point, and toxicity do not change from a small laboratory canister or cylinder to a 10 000 gallon tank car or bulk cylinders used in municipal drinking water disinfection. However, the release of such a material from large‐volume processes and tanks can have disastrous consequences to surrounding communities and the people living around them. Any large chemical complex has the same concern about the materials it uses, handles, and produces to ensure that its operations have minimal negative effects on the surrounding community and its customers. The incorporation of formal safety and reactive chemicals education within the college chemical engineering curriculum is a fairly recent and positive development. Chemical engineers are heavily involved not only in designing and communicating emergency plans for their operations but also in assisting the surrounding communities’ emergency response systems and procedures, including ensuring that the hazardous nature of materials used and processes are well understood.
5. Unit Operations. This is a unique chemical engineering term relating to the generic types of equipment and processes used in scaling up laboratory chemistry and the practice of chemical engineering. Heat transfer would be an example of such a unit operation. The need to cool, heat, condense, and vaporize materials is universal in chemical and material processing. The equations used to estimate the rate at which heat transfer occurs can be generalized into a simple equation such that Q (amount of energy transferred) is proportional to the temperature difference (ΔT) as well as the physical characteristics of the system in which the heat transfer is occurring (mixing, physical property differences such as density and viscosity). This would be expressed mathematically as Q = UAΔT. The amount of energy transferred and the temperature difference may be known, but the “coefficient” (frequently represented by the letter U) relating the two may vary considerably. However, this basic equation can be applied to any heat transfer situation. The same thoughts apply to many separation unit operations such as distillation, membrane transport, reverse osmosis membranes, chromatography, and other “mass transfer” unit operations. The rate of mass transfer is proportional to a concentration difference and an empirical constant, which will be affected by physical properties, diffusion rates, and agitation. In many chemical plant operations, there is an overlap in these areas. For example, a distillation column will involve both heat and mass transfer. The same is true for an industrial cooling tower. The last of these general topics is fluid flow. Though there are many types of pumps and compressors, they all operate on the same basic principle that says that the rate of flow is proportional to the pressure differential, the energy supplied, and the physical properties of the liquid or gas. Again, there is an overlap, as any equipment of this type is also using energy and heating up the liquid or gas it is moving. The heat transfer, as well as the fluid transfer, must be considered.
6. Process Design, Economics, and Optimization. There are numerous ways of scaling up a chemical production system. The choice of particular separation processes, transport systems, storage systems, heat transfer equipment, mixing vessels, and their agitation systems can be done in various combinations, which will impact reliability, cost, the way the process is controlled, and the uniformity of the output of the process. “Design optimization” is a term frequently used. The “optimum” design will not be the same for all companies making the same product as their raw materials base, customer requirements, energy costs, geographic location, cost of labor, and other company unique variables will affect the decision as to what is optimum. Our ability to computerize chemical engineering design calculations has greatly enabled chemical engineers’ capabilities to evaluate a large number of options.
7. Process Control. In a laboratory environment where small quantities of materials are made, the control system may be rather rudimentary (i.e., an agitated flask and on/off heating jacket). However, when this same reaction is “scaled up” orders of magnitude and possibly from batch to continuous, the nature of the process control changes dramatically. The continuous production of specification material around the clock has special challenges in that the raw materials (now coming from an industrial supplier and not a reagent chemical bottle) will not be uniform, the parameters of utilities needed to heat and cool will not be uniform, and the external environment will constantly change. Chemical engineers must design a control system that will not only have to react to such changes but also ensure that there are minimal effects on the product quality, the outside environment, and the safety of its employees.

As the field of chemical engineering has expanded, many curricula will also contain specialty courses in such areas as materials science, environmental chemistry, and biological sciences. However, even when these specialty applications are “scaled” to commercial size, the aforementioned basics will always be needed and considered.

What Do Chemical Engineers Do?

With this type of training, a unique combination of chemistry, mechanical engineering, and physics, chemical engineers find their skills used in a variety of ways. The following is certainly not an all‐inclusive list but represents a majority of careers and assignments of most chemical engineers:

1. The scale‐up of new and modified chemical processes to make new materials or lower cost/less environmentally impactful routes to existing materials. This is most often described as “pilot plants,” which typically is a middle step between laboratory chemistry and full‐scale production. In some cases this can involve multiple levels of scale‐up (10/1, 100/1, etc.) depending upon the risk factor and the knowledge that exists. A newly proposed process that has operating issues or causes safety releases in a laboratory environment is a serious issue. If that same problem occurs on a much larger scale, the consequences can be far more severe, simply due to the amount and scale of materials being inventoried and processed. These consequences can easily include severe injuries and death, large property damage, and exposure of the surrounding community to toxic materials.
2. Design of Processes and Process Equipment. It is rare that the equipment used in a full‐scale plant is identical in type to that used in the laboratory or possibly even in the pilot plant. The piping size; the number and type of trays in a distillation tower; the configuration of coils, tubes, and baffles in a heat exchanger; the shape and size of an agitator system; the shape and geometry of a solids hopper; the shape and configuration of a chemical reactor; and the depth of packing in a tower are all examples of such detailed design calculations. In the commercial world, there may be limitations of certain speeds, voltages, and piping specifications that may not match exactly with what may...

Table of contents

• Cover
• Title Page
• Table of Contents
• Preface
• Acknowledgments
• 1 What Is Chemical Engineering?
• 2 Safety and Health
• 3 The Concept of Balances
• 4 Stoichiometry, Thermodynamics, Kinetics, Equilibrium, and Reaction Engineering
• 5 Flow Sheets, Diagrams, and Materials of Construction
• 6 Economics and Chemical Engineering
• 7 Fluid Flow, Pumps, and Liquid Handling and Gas Handling
• 8 Heat Transfer and Heat Exchangers
• 9 Reactive Chemicals Concepts
• 10 Distillation
• 11 Other Separation Processes
• 12 Evaporation and Crystallization
• 13 Liquid–Solids Separation
• 14 Drying
• 15 Solids Handling
• 16 Tanks, Vessels, and Special Reaction Systems
• 17 Chemical Engineering in Polymer Manufacture and Processing
• 18 Process Control
• 19 Beer Brewing Revisited
• Appendix I: Future Challenges for Chemical Engineers and Chemical Engineering
• Appendix II: Additional Downloadable Resources
• Appendix III: Answers to Chapter Review Questions
• Index
• End User License Agreement