Ministry of Higher Education and Scientific Research

University of Technology

Chemical Engineering Department

PROJECT Fourth Year

By

Dr. Riyadh Sadeq Al Muktar

Reference

1. Sinnott R. and Towler C; 2009 " chemical Engineering Design"

5th edition Butterworth-Heinemann

2. Coke,A.K ;2007"Ludwig s Applied Process Design of Chemical

and petrochemical Plant" vol. 1 4th edition Gulf professional

Publisher

3. Branan C. 2005 " rules of Thumbs for Chemical

Engineers"4th edition Gulf professional

Publisher

4. Couper ,J.;Penny, W R ;Fair J and Walas 2010

"Chemical Process Equipment" 2nd edition

5. Peters,M; timmerhause k.D;and West R. 2003 "

plant Design and economics for Chemical

Engineers '5th edition McGraw-Hill

6. Perry R and Green D; 1997 " Perry s Chemical

Engineers Handbook " 7th edition MaGraw –hill

Design Information and Data

Information on manufacturing processes, equipment parameters, materials of construction, costs and the physical properties of process materials are needed at all stages of design; from the initial screening of possible processes, to the plant start-up and production When a project is largely a repeat of a previous project, the data and information required for the design will be available in the Company's process files, if proper detailed records are kept. For a new project or process, the design data will have to be obtained from the literature, or by experiment (research laboratory and pilot plant), or purchased from other companies. The information on manufacturing processes available in the general literature can be of use in the initial stages of process design, for screening potential process; but is usually mainly descriptive, and too superficial to be of much use for detailed design and evaluation. SOURCES OF INFORMATION ON MANUFACTURING PROCESSES The chemical process industries are competitive, and the information that is published on commercial processes is restricted. The articles on particular processes published in the technical literature and in textbooks invariably give only a superficial account of the chemistry and unit operations used. They lack the detailed information needed on reaction kinetics, process conditions, equipment parameters, and physical properties needed for process design. The information that can be found in the general literature is, however, useful in the early stages of a project, when searching for possible process routes. It is often sufficient for a flow-sheet of the process to be drawn up and a rough estimate of the capital and production costs made. The most comprehensive collection of information on manufacturing processes is probably the Encyclopedia of Chemical Technology edited by Kirk and Othmer (1978, 1991 If), which covers the whole range of chemical and associated products. Another encyclopedia covering manufacturing processes is that edited by McKetta (1977). Several books have also been published which give brief summaries of the production processes used for the commercial chemicals and chemical products. The most well known of these is probably Shreve's book on the chemical process industries, now updated by Austin, Austin (1984). Others worth consulting are those by Faith et al, (1965), Groggins (1958),

Stephenson (1966) and Weissermal and Arpe (1978). Cornyns (1993) lists named chemical manufacturing processes, with references. The extensive German reference work on industrial processes, Ullman's Encyclopedia of Industrial Technology, is now available in an English translation, Ullman (1984). Specialised texts have been published on some of the more important bulk industrial chemicals, such as that by Miller (1969) on ethylene and its derivatives; these are too numerous to list but should be available in the larger reference libraries and can be found by reference to the library catalogue Books quickly become outdated, and many of the processes described are obsolete, or at best obsolescent. More up-to-date descriptions of the processes in current use can be found in the technical journals. The journal Hydrocarbon Processing publishes an annual review of petrochemical processes, which was entitled Petrochemical Developments and is now called Petrochemicals Notebook', this gives flow-diagrams and brief process descriptions of new process developments. Patents are a useful source of information; but it should be remembered that the patentee will try to write the patent in a way that protects his invention, whilst disclosing the least amount of useful information to his competitors. The examples given in a patent to support the claims often give an indication of the process conditions used; though they are frequently examples of laboratory preparations, rather than of the full-scale manufacturing processes. Several short guides have been written to help engineers understand the use of patents for the protection of inventions, and as sources of information; such as those by Capsey (1963), Lieberry (1972) and HMSO (1970, 1971). World Wide Web It is worthwhile searching the Internet for information on processes, equipment and products. Many manufacturers and government departments maintain web sites. In particular, up-to-date information can be obtained on the health and environmental effects of products. GENERAL SOURCES OF PHYSICAL PROPERTIES

International Critical Tables (1933) is still probably the most comprehensive compilation of physical properties, and is available in most reference libraries. Though it was first published in 1933, physical properties do not change, except in as much as experimental techniques improve, and

ICT is still a useful source of engineering data. Tables and graphs of physical properties are given in many handbooks and textbooks on Chemical Engineering and related subjects. Many of the data given are duplicated from book to book, but the various handbooks do provide quick, easy access to data on the more commonly used substances. An extensive compilation of thermophysical data has been published by Plenum Press, Touloukian (1970-77). This multiple-volume work covers conductivity, specific heat, thermal expansion, viscosity and radiative properties (emittance, reflectance, absorptance and transmittance), Elsevier have published a series of volumes on physical property and thermodynamic data. The Engineering Sciences Data Unit (ESDU) was set up to provide authenticated data for engineering design. Its publications include some physical property data, and other design data and methods of interest to chemical engineering designers. They also cover data and methods of use in the mechanical design of equipment. Caution should be exercised when taking data from the literature, as typographical errors often occur. If a value looks doubtful it should be cross-checked in an independent reference, or by estimation. The values of some properties will be dependent on the method of measurement; for example, surface tension and flash point, and the method used should be checked, by reference to the original paper if necessary, if an accurate value is required. The results of research work on physical properties are reported in the general engineering and scientific literature. The Journal of Chemical Engineering Data specialises in publishing physical property data for use in chemical engineering design. A quick search of the literature for data can be made by using the abstracting journals; such as Chemical Abstracts (American Chemical Society) and Engineering Index (Engineering Index Inc., New York). Computerised physical property data banks have been set up by various organizations to provide a service to the design engineer. They can be incorporated into computer aided design programs and are increasingly being used to provide reliable, authenticated, design data. An example of such a data bank is the Physical Property Data Service (PPDS) available from the National Engineering Laboratory (NEL).

ACCURACY REQUIRED OF ENGINEERING DATA

The accuracy needed depends on the use to which the data will be put. Before spending time and money searching for the most accurate value, or arranging for special measurements to be made, the designer must decide what accuracy is required; this will depend on several factors: 1. The level of design; less accuracy is obviously needed for rough scouting calculations, made to sort out possible alternative designs, than in the final stages of design; when money will be committed to purchase equipment, and for construction, 2. The reliability of the design methods; if there is some uncertainty in the techniques to be used, it is clearly a waste of time to search out highly accurate physical property data that will add little or nothing to the reliability of the final design. 3. The sensitivity to the particular property: how much will a small error in the property affect the design calculation. For example, it was shown in Chapter 4 that the estimation of the optimum pipe diameter is insensitive to viscosity. The sensitivity of a design method to errors in physical properties, and other data, can be checked by repeating the calculation using slightly altered values.

PREDICTION OF PHYSICAL PROPERTIES

Whenever possible, experimentally determined values of physical properties should be used. If reliable values cannot be found in the literature and if time, or facilities, are not available for their determination, then in order to proceed with the design the designer must resort to estimation. Techniques are available for the prediction of most physical properties with sufficient accuracy for use in process and equipment design. A detailed review of all the different methods available is beyond the scope of this book; selected methods are given for the more commonly needed properties. The criterion used for selecting a particular method for presentation in this chapter was to choose the most easily used, simplest, method that had sufficient accuracy for general use. If highly accurate values are required, then specialised texts on physical property estimation should be consulted; such as those by: Reid et al (1987), Bretsznajder (1971) and Sterbacek et al. (1979), and AIChemE (1983) (1985). DENSITY Liquids

Values for the density of pure liquids can usually be found in the handbooks. It should be noted that the density of most organic liquids, other than those containing a halogen or other "heavy atom", usually lies between 800 and 1000 kg/m3 An approximate estimate of the density at the normal boiling point can be obtained from the molar volume

where, = density, kg/m3, M = molecular mass, Vm = molar volume, m3/kmol. For mixtures, it is usually sufficient to take the specific volume of the components as additive; even for non-ideal solutions,

Gas and vapour density (specific volume) For general engineering purposes it is often sufficient to consider that real gases, and vapours, behave ideally, and to use the gas law: PV=nRT

VISCOSITY Viscosity values will be needed for any design calculations involving the transport of fluids or heat. Values for pure substances can usually be found in the literature.. Methods for the estimation of viscosity are given below. Liquids A rough estimate of the viscosity of a pure liquid at its boiling point can be obtained from the modified Arrhenius equation:

Where — viscosity, mNs/, pb — density at boiling point, kg/m3. A more accurate value can be obtained if reliable values of density are available, or can be estimated with sufficient accuracy, from Souders' equation, Souders (1938):

Gases Reliable methods for the prediction of gas viscosities, and the effect of temperature and pressure, are given by Bretsznajder (1971) and Reid et al. (1987). Where an estimate of the viscosity is needed to calculate Prandtl numbers (see Volume 1, Chapter 1) the methods developed for the direct estimation of Prandtl numbers should be used. For gases at low pressure Bromley (1952) has suggested the following values: Prandtl number Monatomic gases (e.g. Ar, He) 0.67 ± 5 per cent Non-polar, linear molecules (e.g. C>2, C^) 0.73 ± 15 per cent Non-polar, non-linear molecules (e.g. CH4, CeHe) 0.79 ± 15 per cent Strongly polar molecules (e.g. CH3OH, SO2, HC1) 0.86 ± 8 per cent The Prandtl number for gases varies only slightly with temperature.

THERMAL CONDUCTIVITY The experimental methods used for the determination of thermal conductivity are described by Tsederberg (1965), who also lists values for many substances. Ho et al. (1972) give values for the thermal conductivity of the elements. Solids The thermal conductivity of a solid is determined by its form and structure, as well as composition. Values for the commonly used engineering materials are given in various handbooks. 8.8.2. Liquids The data available in the literature up to 1973 have been reviewed by Jamieson et al, (1975). The Weber equation (Weber, 1880) can be used to make a rough estimate of the thermal conductivity of organic liquids, for use in heat-transfer calculations.

Gases Approximate values for the thermal conductivity of pure gases, up to moderate pressures, can be estimated from values of the gas viscosity, using Eucken's equation, Eucken (1911):

SPECIFIC HEAT CAPACITY The specific heats of the most common organic and inorganic materials can usually be found in the handbooks. . Solids and liquids Approximate values can be calculated for solids, and liquids, by using a modified form of Kopp's law, which is given by Werner (1941). The heat capacity of a compound is taken as the sum of the heat capacities of the individual elements of which it is composed. The values attributed to each element, for liquids and solids, at room temperature,

Gases For a gas in the ideal state the specific heat capacity at constant pressure is given by: C°p = a + bT + cT2 + dT3 (equation 3.19) Values for the constants in this equation for the more common gases can be found in the handbooks. Several group contribution methods have been developed for the estimation of the constants, such as that by Rihani and Doraiswamy (1965) for organic compounds. Their values for each molecular group are given in Table 8.4,