Trading off costs

Some of the problems that concern the proper methods for consideration of several different objectives in reservoir planning are discussed. Classical systems analysis approach to decision making for multiple objective problems is outlined and the inherent difficulties associated with multiple objectives and subjective estimates are identified. Techniques used in reservoir design and operation are reviewed. An alternate technique for considering noncommensurate, objectives, which relates the objectives in terms of real trade-off costs and eliminates the need for a priori estimates of objective worth is presented. The method is illustrated with three examples, including a reservoir operation problem and a cooling tower design problem. 31 refs, cited. 

Generally the effects of trade-offs are assessed in two ways from the point of view of their impact on total costs and their impact on sales revenue. For example, it may be possible to trade off costs in such a way that total costs increase, yet because of the better service now being offered, sales revenue also increases. If the difference between revenue and costs is greater than before, the trade-off may be regarded as leading to an improvement in cost effectiveness. However, without an adequate logistics-oriented cost accounting system it is extremely difficult to identify the extent to which a particular trade-off is cost-beneficial. 

Increasing the chosen value of process energy consumption also increases all temperature differences available for heat recovery and hence decreases the necessary heat exchanger surface area (see Fig. 6.6). The network area can be distributed over the targeted number of units or shells to obtain a capital cost using Eq. (7.21). This capital cost can be annualized as detailed in App. A. The annualized capital cost can be traded off against the annual utility cost as shown in Fig. 6.6. The total cost shows a minimum at the optimal energy consumption. 

Reducing waste from feed impurities which undergo reaction. If feed impurities undergo reaction, this causes waste of feed material, products, or both. Avoiding such waste is most readily achieved by purifying the feed. Thus increased feed purification costs are traded off against reduced raw materials, product separation, and waste disposal costs (Fig. 10.2). 

Figure 10.7 Effluent treatment costs should be included with raw materials costs when traded off against separation costs to obtain the optimal recovery. (From Smith and Petela, Chem. Eng., 513 24, 1991 reproduced by permission of the Institution of Chemical Engineers.)...

Ahmad, S., Heat Exchanger Networks Cost Trade-ofFs in Energy and Capital, Ph.D. thesis, UMIST, U.K., 1985. 

Increasingly, maintenance engineers think in terms of the performance and maintenance of equipment over the whole life of the field. This is often at the centre of the decision on capex-opex trade-offs for example spending higher capex on a more reliable piece of equipment in anticipation of less maintenance costs later in the life of the equipment. 

Useful materials incorporating fire-retardant additives are not always straightforward to produce. Loadings of 10% are common, and far higher levels of flame retardants are used in some formulations. These concentrations can have a negative effect on the properties and functions for which the materials were originally intended. Product-specific trade-offs are generally necessary between functionaUty, processibiUty, fire resistance, and cost. 

Potassium fluoride [7789-23-3], KF, is the most frequently used of the alkaU metal fluorides, although reactivity of the alkaU fluorides is in the order CsF > RbF > KF > NaF > LiF (6). The preference for KF is based on cost and availabiUty traded off against relative reactivity. In its anhydrous form it can be used to convert alkyl haUdes and sulfonyl haUdes to the fluorides. The versatility makes it suitable for halogen exchange in various functional organic compounds like alcohols, acids and esters (7). For example, 2,2-difluoroethanol [359-13-7] can be made as shown in equation 9 and methyl difluoroacetate [433-53 ] as in equation 10. 

Increased heat utilization does not always mean a trade-off, and many studies have shown a reduction in energy consumption as well as capital cost which in itself is a remarkable recommendation for a systematic approach to network design. 

Stand-alone computer systems, usually based on a personal computer (PC) or programmable logic controller (PLC), provide a separate computer system for each pilot plant. This allows for economical expansion for new units, separates pilot plants completely for maintenance and troubleshooting, and often has the lowest initial cost. Standardization can be a problem and software control, data gathering, and storage packages can be limited in size, scope, and capabiUty these are usually acceptable trade-offs. 

Alloy selection is not made fiom only consideration of strength and conductivity. For example, the cupronickels have about the same strength as do copper—2inc brasses, and also have much lower conductivity. However, the corrosion resistance of the cupronickels far exceeds that of brass and is worth the higher cost if needed in the appHcation. Similar trade-offs exist between these properties and formabiUty, softening resistance, and other properties. 

An important part of planning an experimental program is the identification of the variables that affect the response and deciding what to do about them. The decision as to how to deal with each of the candidate variables can be made jointiy by the experimenter and the statistician. However, identifying the variables is the experimenter s responsibiUty. Controllable or independent variables in a statistical experiment can be dealt with in four different ways. The assignment of a particular variable to a category often involves a trade-off among information, cost, and time. 

Two main benefits accrue from a systems approach to materials handling and packaging. First, a trade-off of investment and operating costs is made possible nigher costs in some parts of a system become permissible in return for much lower costs in other parts. The net result is usually the lowest overall cost. If this is not the case, the reasons for incurring the higher costs can be identified and justified. The second benefit is that customers are not offended by ill-conceived packages, delivery vehicles, or product characteristics. 

Factors that enter into any economic analysis of handhng-warehousing systems are (1) expected mechanical and economic life of the system (2) annual maintenance cost (3) capital requirements and expected return on investment (4) building-construction cost and land v ue (5) detailed analysis of each work position (to determine trade-offs of labor and equipment expected future costs and availability of labor are important) (6) relation of system control and personnel used in system (trade-offs of people versus mechanical control) (7) type of information system (computerized or manual) and (8) expected changed in product, container, unit pallet loads, and customer preferences during the life of the system. 

FIG. 22-55 Typical capital-cost schematic for membrane equipment showing trade-off for membrane area and mechanical equipment. Lines shown are from families for parallel hues showing hmiting costs for membrane and for ancillary equipment. Abscissa Relative membrane area installed in a typical membrane process. Minimum capital cost is at 1.0. Ordinate Relative cost. Line with positive slope is total membrane cost. Line with negative slope is total ancillary equipment cost. Curve is total capital cost. Minimum cost is at 1.0. 

UF and MF use energy to depolarize membranes so as to increase flux. As is shown in Fig. 22-55, membranes and mechanical equipment are traded off to achieve an overall economic minimum. Three things can drive a design toward the use of more membranes and less mechanical equipment cheaper membranes, veiy high flux, and veiy low flux. The availability of lower-cost membranes is easiest to understand. In the five years ending in 1995, the cost of both membrane area and membrane housings was driven down by competition. 

Trade-offs in basic core cost, final transformer cost, and RFI are the primary considerations. 

After each issue outlined in the evaluation criteria has been developed for each corrective measure, the selection of the most appropriate alternative can be made. Trade-offs among health risks, environmental effects and other pertinent technical, environmental and human health factors enter into this decisionmaking process. In the RCRA context, cost is not a factor in the selection process except when two or more corrective measure alternatives are determined by EPA to provide similarly adequate levels of protection of human health and the environment. 

Fl urf 2.13 Using mass transfer driving force to trade off fixed cost versus operating cost. 

As discussed in Section 2.5, the minimum allowable composition differences can be used to trade off fixed versus operating costs. TVpically, an increase in j leads to an increase in the MOC of the network (see Figs. 3.12 and 3.14) and a decrease in the fixed cost of the system. Hence, the minimum allowable composition differences can be iteratively varied until the total annualized cost of the system is attained (see Fig. 2.13). 

The other common approach for trading off fixed costs against operating costs is mixing of waste streams. In some cases, the plant operation and the... 

Trading off Rxed versus operating costs using mass-load paths... 

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