Practical minimum-energy requirements

Practical minimum-energy requirements (PME) set reference values for the intensive-energy steps and suggests energy-reduction strategies. 

The metrics can be integrated with other analysis tools, such as practical minimum-energy requirements, lifecycle inventories and total cost assessment (TCA), to develop integrated decision-support tools that can provide guidance for decisionmakers [8]. 

An example of a recent CWRT project is the use of their previously developed Sustainability Metrics to establish a methodology for determining practical minimum energy requirements for chemical processes. 

The appearance energy (formerly known as appearance potential) is a widely used concept in threshold mass spectrometry experiments, which involve measuring the minimum energy required to cause a certain process. However, there are a number of theoretical and practical problems associated with the determination of reliable values of H o(A+/AB). In the following paragraphs we summarize the discussion of this subject made by the groups of Traeger for photoionization [64,65] and Holmes for electron impact [66]. 

The minimum energy requirement, unattainable in practice, is 1543 kWhr/T Cl2. This... 

The minimum energy requirement for a brackish water (say 4000 p.p.m. of salt) will be much less than for sea water, but it is doubtful if the practical requirement will be very different, because this will be determined largely by the irreversible effects which will not be very different for the two cases. Operating data on small household units published by Hickman et al. (21) show only minor differences in energy requirement between tap water of 170-p.p.m. solids and sea water. 

In practice, the energy requirement for separation will be many times greater than this minimum value W j. Different t) s of separation processes exist and each requires a different amount of energy. Thus, the production of fresh water from the sea, which is a very practical problem, can be performed by several commercially available separation... 

We shall see in Chapter 6 that energy consumption during industrial synthesis increases in importance with the decrease of the unit price of a particular product. In this section we shall address the fundamental concepts of thermodynamics to the calculation of minimum energy requirements and open-cell voltages. We shall consider energy balances and heat transfer requirements, since both can be an essential part of practical reactor design. 

Section 6.3.3.3 studies RO in bulk flow parallel to the force configuration and describes various membrane transport considerations and flux expressions. Practical RO membranes are employed in devices with bulk feed flow perpendicular to the force configuration, as illustrated in Section 7.2.I.2. A simplified solution for a spiral-wound RO membrane is developed analytical expressions for the water flux as well as for salt rejection are obtained and illustrated through example problem solving. A total of sbt worked example problems have been provided up to Chapter 7. Chapter 9 (Figure 9.1.5) shows a RO cascade in a tapered configuration. Section 10.1.2 calculates the minimum energy required in reverse osmosis based desalination and compares it with that in evaporation. Section 11.2 covers the sequence of separation steps in a water treatment process for both desalination and ultrapure water production. The very important role played by RO in such plants is clearly illustrated. 

The minimum energy requirement, unattainable in practice, is 1543kWh/T CI2. This corresponds to 100 percent current efficiency (685.8 kAh/T CI2) and 100 percent voltage efficiency (i.e., no IR drops and zero overvoltage at both electrodes, so that the voltage is the thermodynamic potential, or 2.17 volts). The energy efficiency of a typical diaphragm cell is easily expressed as ... 

At low gas velocities, the bed of particles is practically a packed bed, and the pressure drop is proportional to the superficial velocity. As the gas velocity is increased, a point is reached at which the bed behavior changes from fixed particles to suspended particles. The superficial velocity required to first suspend the bed particles is known as minimum fluidization velocity (umf). The minimum fluidization velocity sets the lower limit of possible operating velocities and the approximate pressure drop can be used to approximate pumping energy requirements. For agglomeration process in the fluid-bed processor, air velocity required is normally five to six times the minimum fluidization velocity. 

In general, it is desirable to choose operating conditions requiring minimum energy potential of the air utilized. However, in practice it is not possible to... 

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