Economics of chemical processes

Process economics is an essential element of a good design procedure. The objective of this appendix is to provide an overview of basic concepts in cost estimation and economics of chemical processes. For more details, the reacker is referred to Humphreys and Wellman (1996), Peters and Timmerhaus (1991), Garrett (1989) and Ulrich (1984). 

The purpose of chemical processes is not to make chemicals The purpose is to make money. However, the profit must he made as part of a sustainable industrial activity which retains the capacity of ecosystems to support industrial activity and life. This means that process waste must be taken to its practical and economic minimum. Relying on methods of waste treatment is usually not adequate, since waste treatment processes tend not so much to solve the waste problem but simply to move it from one place to another. Sustainable industrial activity also means that energy consumption must be taken to its practical and economic minimum. Chemical processes also must not present significant short-term or long-term hazards, either to the operating personnel or to the community. 

A. Chauvel and co-workers. Manual of Economic Analysis of Chemical Processes Feasibility Studies in Eefining and Petrochemical Processes, McGraw-Hid Book Co., Inc., New York, 1980. 

No single method or algorithm of optimization exists that can be apphed efficiently to all problems. The method chosen for any particular case will depend primarily on (I) the character of the objective function, (2) the nature of the constraints, and (3) the number of independent and dependent variables. Table 8-6 summarizes the six general steps for the analysis and solution of optimization problems (Edgar and Himmelblau, Optimization of Chemical Processes, McGraw-HiU, New York, 1988). You do not have to follow the cited order exac tly, but vou should cover all of the steps eventually. Shortcuts in the procedure are allowable, and the easy steps can be performed first. Steps I, 2, and 3 deal with the mathematical definition of the problem ideutificatiou of variables and specification of the objective function and statement of the constraints. If the process to be optimized is very complex, it may be necessaiy to reformulate the problem so that it can be solved with reasonable effort. Later in this section, we discuss the development of mathematical models for the process and the objec tive function (the economic model). 

Inherently safer design is a fundamentally different way of thinking about the design of chemical processes and plants. It focuses on the elimination or reduction of the hazards, rather than on management and control. This approach should result in safer and more robust processes, and it is likely that these inherently safer processes will also be more economical in the long run (Kletz, 1984, 1991b). 

Energy requirements of chemical processes should be recognised for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure. 

The purpose of chemical processes is to make money. An understanding of process economics is therefore critical in process design. Process economics has three basic roles in process design ... 

Chadwick, J. L. 1977. Economics of chemical refineries. Process Economic Program Report 107. Menlo Park SRI. 

Kuri, C. J. and A. B. Corripio. Two Computer Programs for Equipment Cost Estimation and Economic Evaluation of Chemical Processes. Chem Engr Educ pp. 14-17 (Winter, 1984). 

The key component in any process is the chemical reactor if it can handle impure raw materials or not produce impurities in the product, the savings in a process can be far greater than if we simply build better separation units. In typical chemical processes the capital and operating costs of the reactor may be only 10 to 25% of the total, with separation units dominating the size and cost of the process. Yet the performance of the chemical reactor totally controls the costs and modes of operation of these expensive separation units, and thus the chemical reactor largely controls the overall economics of most processes. Improvements in the reactor usually have enormous impact on upstream and downstream separation processes. 

The chemical industry typically involves much more high technology but smaller reactors because one usually desires to produce a single molecule as an intermediate to make a particular product. These molecules usually can be sold for a much greater price than gasoline so the extra value added in the petrochemical processing industry justifies the increased sophistication and cost of these reactors. The costs of separating the desired product from reactants and undesired products can dominate the economics of petrochemical processes. 

Three important economic drivers can also bring significant potential benefits for the environmental impact of chemical processes ... 

Applications. The kinds of motors that are being used successfully with particular kinds of. chemical process equipment are identified in Table 4.1. As many as five kinds of AC motors are shown in some instances. The choice may be influenced by economic considerations or local experience or personal preference. In this area, the process engineer is well advised to enlist help from electrical experts. A checklist of basic data that a supplier of a motor must know is in Table 4.2. The kind of enclosure may be specified on the last line, operating conditions. 

Purchase costs of pumps, motors and drives are taken from Manual of Economic Analysis of Chemical Processes, Institut Francois du Petrole (McGraw-Hill, New York, 1976). 

Precipitated CaCO. is produced in a number of chemical processes. Somclimcs it is economical In dry and calcine the byproduct to regenerate CaO or Cat OH) . Some precipitated CaCOt is made to specific particle size and shape, whiteness, and purity for use as functional filler for paper coatings, paint, and polymers. These products command a premium price as compared with pulverized limestone fillers. 

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