The Chemical Processing Industries

The chemical processing industries produce many different and unrelated products and serve a myriad of different markets. Some authors define the CPI to include all industries in which a chemical reaction takes place. Using such an approach, the CPI would also include wineries, paper mills, steel mills, tanneries, petroleum refineries, sugar refineries, and petrochemical plants. Chemical Engineering takes this broad approach (Table 1.1). 

An attempt to cover in detail a group of such diverse activities as those found in Table 1.1 would require many volumes. In this text we shall concentrate our efforts on Standard Industrial Classification (SIC) group 28 (chemicals and allied products) and group 29 (petroleum refining and related industries) (1). 

Bureau of the Budget publishes the SIC code and updates it about every 5 years. It defines SIC 28 as follows  

Vegetable oil mills except cottonseed and soybean mills 2076 

Animal and marine fats and oils including grease and tallow 2077 

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DILLON Materials Selection for the Chemical Process Industries freeman Hazardous Waste Minimization... 

Flocculating agents differ from other materials used in the chemical process industries in that their effect not only depends on the amount added, but also on the concentration of the solution and the point at which it is added. The process streams to which flocculants are added often vary in composition over relatively short time periods. This presents special problems in process control. 

Chemical Applications. The chemical processing industry uses large amounts of granular and fine powder PTFE. Soft packing appHcations are manufactured from dispersions, and hard packings are molded or machined from stocks and shapes made from granular resin. 

Chemical Properties. A combination of excellent chemical and mechanical properties at elevated temperatures result in high performance service in the chemical processing industry. Teflon PEA resins have been exposed to a variety of organic and inorganic compounds commonly encountered in chemical service (26). They are not attacked by inorganic acids, bases, halogens, metal salt solutions, organic acids, and anhydrides. Aromatic and ahphatic hydrocarbons, alcohols, aldehydes, ketones, ethers, amines, esters, chlorinated compounds, and other polymer solvents have Httle effect. However, like other perfluorinated polymers,they react with alkah metals and elemental fluorine. 

Induction heating is used to heat steel reactor vessels in the chemical process industry (5). The heat produced in the walls is conducted to the material within. Multisectioned cods are used to provide controlled heat input to the process material as it passes through the reactor. Figure 6 illustrates a cross section of such a typical installation. 

The purpose of hazard analysis and risk assessment ia the chemical process industry is to (/) characterize the hazards associated with a chemical facihty (2) determine how these hazards can result in an accident, and (J) determine the risk, ie, the probabiUty and the consequence of these hazards. The complete procedure is shown in Figure 1 (see also Industrial hygiene Plant safety). 

Coal, considered a soHd hydrocarbon with a generic formula of CHq g, was explored by numerous workers (24—31) as a feedstock for the production of acetylene. Initially, the motivation for this work was to expand the market for the use of coal in the chemical process industry, and later when it was projected that the cost of ethylene would increase appreciably if pretroleum resources were depleted or constrained. 

In the United States, the acetylene production exceeded 450, 000 t/yr between 1963 and 1970, but then declined until it hit a minimum production level below 150, 000 t/yr in 1982. Of this production, about 40,000 t were dedicated to industrial use, ie, welding, etc. Thus only slightly more than 100,000 t were produced for the chemical process industry. Figure 14 illustrates the 17-year decline in acetylene production and indicates the reduced derivative demand to which the accumulated decline is attributed (37). 

Table 1. Exposure Sources in the Chemical Process Industry...

Chemical-grade limestone is a pure type of high calcium or dolomitic limestone used by the chemical-process industry or where exacting chemical requirements ate necessary. It contains a minimum of 95% total carbonate. In a few areas of the United States this minimum may be extended to 97 or 98%. 

Such low capacities result ia a formal way of designating capacity specification in the pumping industry, ie, using capacity per hour, rather than minutes. Common uses are for metering and for controUed-volume process services in the chemical process industries. 

Zirconium is used as a containment material for the uranium oxide fuel pellets in nuclear power reactors (see Nuclearreactors). Zirconium is particularly usehil for this appHcation because of its ready availabiUty, good ductiUty, resistance to radiation damage, low thermal-neutron absorption cross section 18 x 10 ° ra (0.18 bams), and excellent corrosion resistance in pressurized hot water up to 350°C. Zirconium is used as an alloy strengthening agent in aluminum and magnesium, and as the burning component in flash bulbs. It is employed as a corrosion-resistant metal in the chemical process industry, and as pressure-vessel material of constmction in the ASME Boiler and Pressure Vessel Codes. 

Because carbon is difficult to machine, very tittle impervious carbon equipment is made. However, impervious graphite has been accepted as a standard material of constmction by the chemical process industry for the fabrication of process equipment, such as heat exchangers, pumps, valves, towers, pipe, and fittings (9,10). 

The second area, the implementation of a modem process monitoring and control system, is the most dramatic current appHcation of CAD/CAM technology to the chemical process industry. The state of the art is the use of computer graphics to display the process flow diagram for sections of the process, current operating conditions, and controUer-set points. The process operator can interact directly with the control algorithms through the... 

It is likely that there will always be a distinction between the way CAD/CAM is used in mechanical design and the way it is used in the chemical process industry. Most of the computations requited in mechanical design involve systems of linear or lineatizable equations, usually describing forces and positions. The calculations requited to model molecular motion or to describe the sequence of unit operations in a process flow sheet are often highly nonlinear and involve systems of mixed forms of equations. Since the natures of the computational problems are quite different, it is most likely that graphic techniques will continue to be used more to display results than to create them. 

Distillation Columns. Distillation is by far the most common separation technique in the chemical process industries. Tray and packed columns are employed as strippers, absorbers, and their combinations in a wide range of diverse appHcations. Although the components to be separated and distillation equipment may be different, the mathematical model of the material and energy balances and of the vapor—Hquid equiUbria are similar and equally appHcable to all distillation operations. Computation of multicomponent systems are extremely complex. Computers, right from their eadiest avadabihties, have been used for making plate-to-plate calculations. 

O. Axted and J. Robertson, Economic Evaluation in the Chemical Process Industries, Johis Wiley Sons, Inc., New York, 1986. 

R. L. Berglund and C. T. Lawson, "Pollution Prevention in the Chemical Process Industries," Chem. Eng. (Sept. 1991). 

J. R. Whiteley andj. F. Davis, "QuaHtative Interpretation of Sensor Patterns using a Similarity-Based Approach," paper presented at the IFAC Symposium on On-Eine Fault Detection and Supervision in the Chemical Process Industries, Newark, Del., Apr. 1992. 

Formulation of the Objective Function The formulation of objective functions is one of the crucial steps in the application of optimization to a practical problem. You must be able to translate the desired objective into mathematical terms. In the chemical process industries, the obective function often is expressed in units of currency (e.g., U.S. dollars) because the normal industrial goal is to minimize costs or maximize profits subject to a variety of constraints. 

Working capital may vaty from a very small fraction of the total capital cost to almost the whole of the invested capital, depending on the process and the industiy For example, in jewelry-store operations, the Fixed capital is veiy small in comparison with the working capital. On the other hand, in the chemical-process industries, the working capital is hkely to be in the region or 10 to 20 percent of the value of the fixed-capital investment. 

Since a fair allocation of costs requires considerable technical knowledge of operations in the chemical-process industries, a close liaison between the senior process engineers and the accountants in a company is desirable. Indeed, the success of a company depends on a combination of financial, technical, and managerial skills. 

Overheads in the chemical-process industries are commonly calculated as a percentage of (I) direct materials cost, (2) direct labor cost, or (3) prime or direct costs. Other methods of allocating overheads are on the basis of (I) plant area, (2) number of employees, (3) capital value, and (4) elec tric power. 

Ejfect of Raw-Materials Prices Raw materials for the chemical-process industries are subject to relatively wide variations in price. These effects on profits will now be considered. 

Heat pumps are particularly suitable for recycling heat energy in the chemical-process industries. For the outlay of an additional fixed-capital expenditure Cec on a heat-pump system, a considerable reduction in the annual heating cost can be effected. 

Rotameters The rotameter, an example of which is shown in Fig. 10-21, has become one of the most popular flowmeters in the chemical-process industries. It consists essentially of a plummet, or float, which is free to move up or down in a vertical, slightly tapered tube having its small end down. The fluid enters the lower end of the tube and causes the float to rise until the annular area between the float and the wall of the tube is such that the pressure drop across this constriction is just sufficient to support the float. Typically, the tapered tube is of glass and carries etched upon it a nearly linear scale on which the position of the float may be visually noted as an indication of the flow. 

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