Energy consumption

Energy consumption increases as Y, the loading of product in the stream leaving the extractor, decreases. This is due to the greater mass of solvent which must be recirculated for a given amount of product. 

The term AH may in principle be reduced (with a corresponding reduction in Ec) by reducing the pressure drop AP required for product recovery. 

In practice, values of APi substantially in excess of those given by equation (10.4) will be required to give a realistic temperature driving force across the condenser/reboiler tubes and hence an acceptable heat exchanger area. 

As AP is reduced, the temperature driving force falls and the area required increases leading to an increase in capital cost. The actual value of AP used must take account not only of energy costs, which are favoured by a reduction in AP, but also amortisation costs on the heat exchanger. 

In addition to the energy required to operate the recirculation compressor, energy is also consumed when recovering solvent from the product stream and from the extracted materials. The energy consumption involved in these operations is much less than that consumed by the main compressor [1]. 

Energy consumption has always been an issue for the aluminum business since primary production is an energy-intensive process. The specific energy consumption for aluminum is given by  

As one can see from the equation, both CE and f/ceu must have been improved over the years. 

In the late nineteenth century cells were operating as high as 50-70 kWh/kg Al. Since then the specific energy consumption has dropped steadily, but over the last decade it has leveled out between 13 and 14kWh/kg Al. The best cells reported [4] today operate close to 12.5kWh/kg Al, and the question is really how low it is possible to reach. 

The actual consumption of energy exceeds the theoretical amount because the operating voltage varies from 1.9 to 2.6 V, depending on the design of the electrolytic cell. This entails a rise in energy consumption from 4.5 to 6.2 kw-hr. which corresponds to an energy efficiency of 65 to 48 per cent. 

According to the number of operations carried out on a refinery site, some 7 to 10% of the fuel value of crude oil introduced is consumed in the separation and interconversion of product streams. If we momentarily take naphtha as a reference point, energy is required for the catalytic reforming process to provide higher octane gasoline. The subsequent separations of individual aromatic 

In later sections, the author has assigned a fuel value to naphtha. However, even this material requires the production, transportation and distillation of crude oil at the very least. Thus, any strict assessment of energy utilization for a particular product should ultimately include inputs to bring the raw material out of the ground and for all subsequent operations. 

Energy is mainly used in the form of steam (for heating dryers and reactors, for stripping, etc.) and electrical power (to drive refrigeration units, pumps, stirrers, compressors). In some processes, natural gas is used to heat up dryers, but the typical consumption data shown below (1999 data) assume that no natural gas is used. Typical energy consumption of both S-PVC and E-PVC processes is shown in Table 5.9. 

Thrust bearings absorb the thrust force exerted by the screw as it turns 

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However, there are many other factors to be considered in the choice of reaction path. Some are commercial, such as uncertainties regarding future prices of raw materials and b3q)roducts. Others are technical, such as safety and energy consumption. 

Consider a three-product separation as in Fig. 5.11a in which the lightest and heaviest components are chosen to be the key separation in the first column. Two further columns are required to produce pure products (see Fig. 5.11a). However, note from Fig. 5.11a that the bottoms and overheads of the second and third columns are both pure B. Hence the second and third columns could simply be connected and product B taken as a sidestream (see Fig. 5.116). The arrangement in Fig. 5.116 is known as a prefractionator arrangement. Note that the first column in Fig. 5.116, the prefractionator, has a partial condenser to reduce the overall energy consumption. Comparing the prefractionator arrangement in Fig. 5.116 with the conventional... 

Both the side-rectifier and side-stripper arrangements have been shown to reduce the energy consumption compared with simple two-column arrangements. This results from reduced mixing losses in the first (main) column. As with the first column of the simple sequence, a peak in composition occurs with the middle product. Now, however, advantage of the peak is taken by transferring material to the side-rectifier or side-stripper. 

Kaibel, G., Distillation Column Arrangements with Low Energy Consumption, IChemE Symp. Ser., 109 43, 1988. 

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. 

Starting irom the original flowsheet, LinnhofT and Parker have shown that it is possible by a combination of distillation modifications and network improvements to reduce the energy consumption of this process by approximately 60 percent. 

If the network is optimized at fixed energy consumption, then only loops and stream splits are used. When energy consumption is allowed to vary, utility paths also must he included. As the network energy consumption increases, the overall capital cost decreases. 

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. 

Thermodynamic principles govern all air conditioning processes (see Heat exchange technology, heat transfer). Of particular importance are specific thermodynamic appHcations both to equipment performance which influences the energy consumption of a system and to the properties of moist air which determine air conditioning capacity. The concentration of moist air defines a system s load. 

However, the iadustry s popular terminology is the energy consumption expressed ia terms of kilowatt hours per ton of (Pq[) oi of NaOH An estimate of this value requires a knowledge of cell voltage, current efficiency, and the efficiency of the rectifier used to convert a-c power to d-c. The energy consumption for producing a ton of is... 

Fig. 16. Performance data obtained ia laboratory cells using Nafion NX-961, DSA anode, activated cathode, narrow gap, at 90°C. Energy consumption is...

Table 25. Energy Consumption of Operating Cells, Kilowatt-Hours per Ton of Chlorine...

Natural gas is by far the preferred source of hydrogen. It has been cheap, and its use is more energy efficient than that of other hydrocarbons. The reforming process that is used to produce hydrogen from natural gas is highly developed, environmental controls are simple, and the capital investment is lower than that for any other method. Comparisons of the total energy consumption (fuel and synthesis gas), based on advanced technologies, have been discussed elsewhere (102). 

World resources of sulfur have been summarized (110,111). Sources, ie, elemental deposits, natural gas, petroleum, pyrites, and nonferrous sulfides are expected to last only to the end of the twenty-first century at the world consumption rate of 55.6 x 10 t/yr of the 1990s. However, vast additional resources of sulfur, in the form of gypsum, could provide much further extension but would require high energy consumption for processing. 

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