Economic Basis

2 Set Reflux Ratio to 1.2 Times Minimum Reflux Ratio 

The other conunon distillation economic heuristic is to select a reflux ratio that is 20% larger than the minimum reflux ratio. The minimum reflux ratio found in Chapter 3 from the simulation was 2.9. Multiplying this by 1.2 gives an actual reflux ratio of 3.48. This is very close to the reflux ratio (3.49) we found was necessary in Chapter 3 for a 32-stage column. 

It is interesting to compare the minimum reflux ratio found in the rigorous simulation with the approximate prediction from the Underwood equations. These equations are derived assuming constant relative volatilities. As we have seen in Section 4.1.1, the relative volatility between propane and isobutane is almost constant. It varies from 1.85 to 1.76. Therefore, the Underwood equations should predict the minimum reflux ratio quite well. 

As discussed in Chapter 2, there are two equations. The first is solved for a parameter 6 that is one of the roots of this equation. 

Applying this to the binary propane/isobutane system for saturated liquid feed with composition of 40 mol% propane and using the average relative volatihty of 1.8076 for propane and 1 for isobutane give 

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Ethers, such as MTBE and methyl / fZ-amyl ether (TAME) are made by a catalytic process from methanol (qv) and the corresponding isomeric olefin. These ethers have excellent octane values and compete on an economic basis with alkylation for inclusion in gasoline. Another ether, ethyl tert-huty ether (ETBE) is made from ethanol (qv) and isobutylene (see Butylenes). The cost and economic driving forces to use ETBE vs MTBE or TAME ate a function of the raw material costs and any tax incentives that may be provided because of the ethanol that is used to produce it. 

Because of the broad differences between ultrafilttation equipment, the performance of one device cannot be used to predict the performance of another. Comparisons can only be made on an economic basis and only when the performance of each is known. 

While process design and equipment specification are usually performed prior to the implementation of the process, optimization of operating conditions is carried out monthly, weekly, daily, hourly, or even eveiy minute. Optimization of plant operations determines the set points for each unit at the temperatures, pressures, and flow rates that are the best in some sense. For example, the selection of the percentage of excess air in a process heater is quite critical and involves a balance on the fuel-air ratio to assure complete combustion and at the same time make the maximum use of the Heating potential of the fuel. Typical day-to-day optimization in a plant minimizes steam consumption or cooling water consumption, optimizes the reflux ratio in a distillation column, or allocates raw materials on an economic basis [Latour, Hydro Proc., 58(6), 73, 1979, and Hydro. Proc., 58(7), 219, 1979]. 

Approach temperature differences between the oudet process fluid temperature and the ambient air temperamre are generally in the range of 10 to 15 K. Normally, water cooled heat exchangers can be designed for closer approaches of 3 to 5 °K. Of course, closer approaches for air cooled heat exchangers can be designed, but generally these are not justified on an economic basis. 

For gas-fired shell boilers it is difficult to justify these trim controllers on an economic basis. Equally important, the position to control based on CO in such a boiler is ideally in the reversal chamber and not the flue. However, the temperature and stratification of flue products here make it impracticable. 

Are alternative processes available that would further reduce environmental impact on a technical and economic basis Identify potential opportunities. Identify the risk category. 

For waste treatment rather than fermentation for product formation, again few examples of process economics exist in the literature. Those that do, favor fluidization. Badot et al. (1994) described an industrial prototype fluidized bed reactor that competed favorably on an economical basis with activated sludge processes for treating carbon pollution and was estimated to be economically comparable to fixed bed processes for denitrification. Schneeberg (1994) described the successful and economically-sound implementation of fluidization as an upgrade to an existing wastewater treatment plant. The restricted space available for extension of the wastewater plant made fluidization particularly advantageous in this case. 

Supporters claim that CERCLA and the court rulings promote economic efficiency because they internalize externalities they make "polluters" pay. Such reasoning has an economic basis only when companies did not practice due care (i.e., utilize disposal practices whose benefits exceeded costs at the time of disposal). Economic efficiency is about the present and the future, not about the past. What should be done about sunk costs or past behavior is not an economic question except insofar as those policies that pay for sunk costs might affect current and future decisions. 

Choice of Utility - In this step, market knowledge is predominant. No one need test by a Model Test a product that is intended to supplant a presently abundant, inexpensive material. The advantages of the tested product have to be assessed clearly before it is considered as worthy of taking on such competition. We have noted frequently that experimental products are proposed as functionally useful, merely because their properties barely approach those of commonly accepted products. No attempt is made to justify their use on any economic basis. This is to be deplored. 

In each case the evaluation of a flowsheet is done very crudely, with such guidelines as minimum mass flow into separation tasics being used. Of course such crude evaluation is all that can be done in the preliminary stages because one is not able to evaluate on an economic basis until the process is fully synthesized and the equipment selected these programs stop short of selecting actual equipment. 

The ethical problems touch upon the interests not of the marketer but of the supplier industry. The economic basis of this industry rests upon profit margins sufficient to recover, within a reasonable time period, the expenses incurred in the development of fragrances. The practice of looking for lower-priced replacements from other suppliers denies such margins to the original supplier. 

For convenience in developing and illustrating the estimated variable operating costs of Table IV, the following arbitrary values for feed materials and energy were taken for mid-1979. Additional details of the economic basis are given in Table V. 

However, there does exist a relationship between emissions and electrolysis. Any pollution associated with electricity consumed by the electrolyzer needs to be taken into account. As stated previously, one fundamental appeal of electrolysis is that it creates a path for converting renewable power into fuel. But the low capacity factors of renewables (other than geothermal and hydro power) make an allrenewables case very difficult on an economic basis. Electricity from nuclear plants is also non-emitting on a greenhouse gas emissions basis, but the outlook for additional nuclear plants is uncertain at best. 

As suggested by several other chapters in this volume, the machinery of visuospatial reasoning may provide an economical basis for reasoning about transitive relations. Our visual systems are adept at computing spatial relations—such as above( ), larger-than( )—and many of these relations are transitive If object A is above object B and B is above C, then A will be above C. Importantly, the visual machinery that computes these relations from the information in a visual image must have this... 

Expenses, as outlined in Chap. 8, for various types of taxes and insurance can materially affect the economic situation for any industrial process. Because modem taxes may amount to a major portion of a manufacturing firm s net earnings, it is essential that the chemical engineer be conversant with the fundamentals of taxation. For example, income taxes apply differently to projects with different proportions of fixed and working capital. Profitability, therefore, should be based on income after taxes. Insurance costs, on the other hand, are normally only a small part of the total operational expenditure of an industrial enterprise however, before any operation can be carried out on a sound economic basis, it is necessary to determine the insurance requirements to provide adequate coverage against unpredictable emergencies or developments. 

The textbook relationship presented in Eq. (7) is seldom used in actual practice, because it places too much emphasis on the salvage value of the property and is certainly not applicable if the salvage value is zero. To overcome this disadvantage, the value of the fixed-percentage factor is often chosen arbitrarily using a sound economic basis. 

Related Calculations. The difference between the two internal rates of returns is so small that, on a purely economic basis, the projects are virtually indistinguishable. By contrast, the difference in the projects net present worths (see Example 18.5) is large enough to make the textile fibers expansion the clear choice for funding. As with the net present worth method, the internal rate of return procedure cannot be used unless the lifetimes of the competing projects are equal. 

Economics Basis 200,000-tpy cyclohexane complex, ISBL 2005 Gulf Coast location with PSA hydrogen is USS8 million. Catalyst cost is USS 1.2/metric ton of product. 

Economics Basis ISBL 2004 for a Gulf Coast location using 50,000 tpy of a raffinate-2 C4 cut containing 75% n-butenes. 

Economics Basis 50,000 mtpy GPPS, US Gulf Coast ... 

Economics Basis of 90,000 tpy butadiene from n-butane Estimated investment (Onsite, excluding extraction),... 

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