Economic optimization

Figure 10.7 shows that the tradeoff between separation and net raw materials cost gives an economically optimal recovery. It is possible that significant changes in the degree of recovery can have a significant effect on costs other than those shown in Fig. 10.7 (e.g., reactor costs). If this is the case, then these also must be included in the tradeoffs. 

Economic Aspects. Several pubUcations probe the various areas of electroorganic process cost. CeUs (90), overaU process costs (41,91—93), economic optimization (94,95), and a comparison between the chemical and electrochemical methods (91,96) are aU discussed. 

Fig. 13. Economic optimization of conversion costs for a plate and frame cell where A is total divided cell, B is electricity, C is capital, and D is membranes,...

Fig. 14. Economic optimization compatison. Total cost of A, plate and frame, and B, stack cells.

Cake filters are used when the desired product of the operation is the solids, the filtrate, or both. When the filtrate is the product, the degree of removal from the cake by washing or blowing with air or gas becomes an economic optimization. When the cake is the desired produc t, the incentive is to obtain the desired degree of cake purity by washing, blowing, and sometimes mechanical expression oi residu liquid. 

Economics It is ironic that a great virtue of membranes, their versatility, makes economic optimization of a membrane process veiy difficult. Designs can be tailored to veiy specific applications, but each design requires a sophisticated computer program to optimize its costs. Spillman [in Noble and Stern (eds)., op. cit., pp. 589-667] provides an overall review and numerous specific examples including circa 1989 economics. 

There are no general rules allowing selection of the correct y value. The correct selection is a result of technico-economical optimization however, for a first guess y can be set to y = 1.02. 

Market prices of energy often diverge from the true cost to society of consuming that energy. Two of the most common reasons for that divergence are external costs and subsidies, both of which make consumers think that energy is less expensive to society than it really is, and hence lead to more consumption of energy than would be economically optimal. 

Adler, L., and Goodson, R., An Economic Optimization of a Kraft Pulping Process, Laboratory for Applied Industrial Control, Report 48. Purdue University, West Lafayette, IN, 1972. 

Finally, optimization means dealing with time and other improvements spanning the overall process. Optimizing the speed of the analysis is obvious, but optimizing resolution can improve the process as well (as we will see later). An economic optimization of individual analyses will result in time improvements throughout the process because it will liberate resources for other tasks. 

The critical load concept is intended to achieve the maximum economic benefit from the reduction of pollutant emissions since it takes into account the estimates of differing sensitivity of various ecosystems to acid deposition. Thus, this concept is considered to be an alternative to the more expensive BAT (Best Available Technologies) concept (Posch et al., 1996). Critical load calculations and mapping allow the creation of ecological-economic optimization models with a corresponding assessment of minimum financial investments for achieving maximum environmental protection. 

Compare with actual load. The amount by which critical loads are exceeded and the area in which they are exceeded (using a GIS) can be also included in the calculation when the actual loads (for example, atmospheric deposition data in case of forest) are known. Furthermore, these exceedance values are used for ecological-economic optimization scenario of emission reduction. 

Bauer, M. H. and J. Stichlmair. Design and Economic Optimization of Azeotropic Distillation Process Using Mixed-Integer Nonlinear Programming. Comput Chem Eng 22 1271-1286 (1998). 

Costs of energy and raw materials for a reactor as a function of yield and selectivity [Adapted and modified from R LeGoff, The Energetic and Economic Optimization of Heterogeneous Reactors, Chem Eng Sci 35 2089 (1980)]. 

Guntem, C. A. H. Keller and K. Hungerbiihler. Economic Optimization of an Industrial Semi-batch Reactor Applying Dynamic Programming. Ind Eng Chem Res 37(10) 4017-4022 (1998). 

Marlin and Hrymak (1997) reviewed a number of industrial applications of RTO, mostly in the petrochemical area. They reported that in practice a maximum change in plant operating variables is allowable with each RTO step. If the computed optimum falls outside these limits, you must implement any changes over several steps, each one using an RTO cycle. Typically, more manipulated variables than controlled variables exist, so some degrees of freedom exist to carry out both economic optimization as well as establish priorities in adjusting manipulated variables while simultaneously carrying out feedback control. 

In Chapter 3 we discussed the formulation of objective functions without going into much detail about how the terms in an objective function are obtained in practice. The purpose of this appendix is to provide some brief information that can be used to obtain the coefficients in objective functions in economic optimization problems. Various methods and sources of information are outlined that help establish values for the revenues and costs involved in practical problems in design and operations. After we describe ways of estimating capital costs, operating costs, and revenues, we look at the matter of project evaluation and discuss the many contributions that make up the net income from a project, including interest, depreciation, and taxes. Cash flow is distinguished from income. Finally, some examples illustrate the application of the basic principles. 

The problem posed by an operator advisor, to give expert diagnosis of plant condition and to recommend emergency actions or economic optimization adjustments, illustrates these real-time requirements. Some of the plant conditions which can occur include ... 

The more we know about what is occurring during reaction, what the reacting materials are, and how they react, the more assurance we have for proper design. This is the incentive to find out as much as we can about the factors influencing a reaction within the limitations of time and effort set by the economic optimization of the process. 

Figure 18. Economic optimization of desulfurization plus sulfide shape control, using mischmetal at 50% recovery, by ladle addition for critical applications...

In a chemical plant the capital investment in process piping is in the range of 25-40% of the total plant investment, and the power consumption for pumping, which depends on the line size, is a substantial fraction of the total cost of utilities. Accordingly, economic optimization of pipe size is a necessary aspect of plant design. As the diameter of a line increases, its cost goes up but is accompanied by decreases in consumption of utilities and costs of pumps and drivers because of reduced friction. Somewhere there is an optimum balance between operating cost and annual capital cost. 

Provides abstracts of worldwide research on design and performance of mechanical draft and natural draft wet, dry, and dry-wet combination cooling towers. Abstracts cover studies on size reduction, corrosion protection, and economic optimization of cooling towers primarily used with nuclear power plants and fossil fuel power plants. Also covered are abstracts which pertain to cooling towers used in waste-water treatment. It contains 305 abstracts, 65 of which are new entries to the previous edition. 

Research on the synthesis of economically optimal heat exchanger networks (HENs) has been performed for over 15 years (Nishida et al., 1981). As a result of this research, two general conclusions have emerged (1) the optimum network generally features minimum or close to minimum utility consumption, and (2) the optimum network generally has a mini-... 

Control is the manipulation of a degree of freedom (e.g., heater, cooler or exchanger load, stream split fraction) in order to make a process feasible and/or economically optimal in the steady state. In this chapter, control is used in a static sense only process dynamics are not considered. 

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