Unit operation chapter

Study of unit operations. If the reader has had courses in the transport processes of momentum, heat, and mass. Chapters 2 through 7 can be omitted and only the unit operations chapters in Part 2 studied in a one-semester or two-quarter course. This plan could be used by chemical and certain other engineers. 

This book covers all four disciplines chemical aspects in Chapter 2, thermal and mechanical unit operations (Chapter 3), reaction engineering (Chapter 4), and general chemical technology (Chapter 5). In addition, 20 industrial processes are inspected in detail (Chapter 6). 

This section describes the use of separation processes which utilize membranes. Placement in this chapter is in recognition of the recent ascendency of industrial-scale rnernbrane-based separations, but it also reflects the iew that within a decade, many of these separation processes will be mainstream unit operations. Some approach that status already. Figure 22-46 shows the relath e size of things important in membrane separations. 

The chapters are developed by design function and not in accordance with previously suggested standards for unit operations. In fact, some of the chapters use the same principles, but require different interpretations that take into account the process and the function the equipment performs in the process. 

A small amount of nickel in the FCC feed has a significant influence on the unit operation. In a clean gas oil operation, the hydrogen yield is about 40 standard cubic feet (scf) per barrel of feed (0.07 wi /r ). This is a manageable rate that most units can handle. If the nickel level increases to 1.5 ppm, the hydrogen yield increases up to 100 scf per barrel (0.17 wt%). Note that in a 50,000 barrel/day unit, this corresponds to a mere 16 pounds per day of nickel. Unless the catalyst addition rate is increased or the nickel in the feed is passivated (see Chapter 3), the feed rate or conversion may need to be reduced. The wet gas will become lean and may limit the pumping capacity of the wet gas compressor. 

The heat balance exercise provides a tool for in-depth analysis of the unit operation. Heat balance surveys determine catalyst circulation rate, delta coke, and heat of reaction. The procedures described in this chapter can be easily programmed into a spreadsheet program to calculate the balances on a routine basis. 

This chapter assumes isothermal operation. The scaleup methods presented here treat relatively simple issues such as pressure drop and in-process inventory. The methods of this chapter are usually adequate if the heat of reaction is negligible or if the pilot unit operates adiabatically. Although included in the examples that follow, laminar flow, even isothermal laminar flow, presents special scaleup problems that are treated in more detail in Chapter 8. The problem of controlling a reaction exotherm upon scaleup is discussed in Chapter 5... 

Sources of data on costs were discussed in Chapter 6 and materials of construction in Chapter 7. This chapter covers sources of information on manufacturing processes and physical properties and the estimation of physical property data. Information on the types of equipment (unit operations) used in chemical process plants is given in Volume 2, and in the Chapters concerned with equipment selection and design in this Volume, Chapters 10, 11 and 12. 

Separation of two liquid phases, immiscible or partially miscible liquids, is a common requirement in the process industries. For example, in the unit operation of liquid-liquid extraction the liquid contacting step must be followed by a separation stage (Chapter 11, Section 11.16). It is also frequently necessary to separate small quantities of entrained water from process streams. The simplest form of equipment used to separate liquid phases is the gravity settling tank, the decanter. Various proprietary equipment is also used to promote coalescence and improve separation in difficult systems, or where emulsions are likely to form. Centrifugal separators are also used. 

A 6,750 gal reactor will be specified. Its dimensions will be 8.33 ft in diameter and 16.67 ft high. These dimensions were chosen because it is generally cheaper to install and operate a smaller number of large units than a large number of small units (see Chapter 9). This philosophy will be followed throughout the design of the plant. 

Each chapter presents several detailed studies illustrating the application of various optimization techniques. The following matrix shows the classification of the examples with respect to specific techniques. Truly optimal design of process plants cannot be performed by considering each unit operation separately. Hence, in Chapter 15 we discuss the optimization of large-scale plants, including those represented by flowsheet simulators. 

Presentation of each optimization technique is followed by examples to illustrate an application. We also have included many practically oriented homework problems. In university courses, this book could be used at the upper-division or the first-year graduate levels, either in a course focused on optimization or on process design. The book contains more than enough material for a 15-week course on optimization. Because of its emphasis on applications and short case studies in Chapters 11-16, it may also serve as one of the supplementary texts in a senior unit operations or design course. 

The complexity and vastness of the scientific field that has been reviewed in this chapter bring forth, as a natural consequence, the parallel need for further in-depth studies into some key research areas. Knowledge of the process, as a unit operation, has jumped forward due to the fruitful work of the EU-FAIR Concerted Action CT96-1118 improvement of overall food quality by application of osmotic treatments in conventional and new processes and could already support the application of the technique at the industrial level as a prestep in innovative combined processes. The decisive challenge for a completely successful process control and optimization has to be focused on the following problematic aspects. 

Specific objectives and results of propellant grinding tests performed in support of the EDS II program for the Eco Logic technology package are discussed in detail in Chapter 4. The description of the tests and the committee s evaluation of the results presented in Chapter 4 are also applicable to the use of this unit operation in the SILVER II technology package. 

The previous chapters have demonstrated that liquid-liquid extraction is a mass transfer unit operation involving two liquid phases, the raffinate and the extract phase, which have very small mutual solubihty. Let us assume that the raffinate phase is wastewater from a coke plant polluted with phenol. To separate the phenol from the water, there must be close contact with the extract phase, toluene in this case. Water and toluene are not mutually soluble, but toluene is a better solvent for phenol and can extract it from water. Thus, toluene and phenol together are the extract phase. If the solvent reacts with the extracted substance during the extraction, the whole process is called reactive extraction. The reaction is usually used to alter the properties of inorganic cations and anions so they can be extracted from an aqueous solution into the nonpolar organic phase. The mechanisms for these reactions involve ion pah-formation, solvation of an ionic compound, or formation of covalent metal-extractant complexes (see Chapters 3 and 4). Often formation of these new species is a slow process and, in many cases, it is not possible to use columns for this type of extraction mixer-settlers are used instead (Chapter 8). 

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