Commodity available energy

A quantity of energy can be assigned a value only when certain conditions are known. Since the enthalpy does not pertain to the quality of energy, the available energy (exergy) should be used to measure the value of a commodity for operating and sustaining a process system (l). 

This paper gives a simple, comprehensible presentation of (a) the first and second laws of thermodynamics (b) their associated basic concepts of energy and available-energy, respectively and, (c) their practical implications on the performance of processes and equipment. It will be seen that is is available energy, not energy, which is the commodity of value and, hence, the proper measure for assessing inefficiencies and wastes. 

The charge current is represented by Ig and IE = energy current. Furthermore PA = [ - 4>o]lq the current of the commodity called available-energy, is the useful power or available power. 

When the transport rates of independent commodities are known (given or determined from kinetic relations), then the available energy transport terms can be evaluated using the aforementioned relations. (The application of these transport relations, which will now be set forth, requires the use of the thermostatic property relations.) Once the transport term values are known, the balance can be used to evaluate the available energy destruction, Aj. 

As a consequence, the conclusion can be drawn, from the second law, that "the available energy is the maximum shaft work obtainable." This statement is usually used to define available energy. Unfortunately such a definition gives the impressions (i) that available energy is relevant only to "work processes," and (ii) that work is the ultimate commodity of value. Actually,... 

Evaluation of Available Energy Transport Expressions. Available energy transport relations are seen to be products of thermostatic properties with commodity currents. Given the commodity currents, the available energy transports can then be evaluated by determining the thermostatic properties, using traditional thermochemical property evaluation techniques. References (6) and (7) present convenient relationships for practical evaluation of available energy flows for several important cases. 

In the theoretical limit, available energy contained in any commodity can be completely transferred to any other commodity (12,13). In the case of real transformations, the degree to which this perfection is approached is measured by the second law efficiency (often called the "effectiveness" (8,9,10,11) ... 

The purpose of this article is to provide appropriate criteria for the practical selection of reference datums for the calculation of available energy. The selection of a reference datum generally depends on the commodity whose available energy is being evaluated, upon the particular process (or device) being analyzed, upon the complex of processes (devices) with which the particular process interacts, and upon the ambient environment of the complex. 

The cost of process steam is then obtained from a money balance on the turbine. Nevertheless, the commodity of value is available energy—any method which assigns costs on any other basis such as energy or mass is usually invalid. Furthermore, only with available-energy costing can co-generating power plants be analyzed by other methods—equality, extraction, by-product steam— discussed in the preceding paper (2). 

VINYL CHLORIDE. Vinyl chlonde, [CAS 75-01-4] CH2=CHC1, by virtue of the wide range of application for its polymers in both flexible and rigid forms, is a major commodity chemical in the U.S. and an important item of international commerce. Growth in vinyl chlonde production is directly related to demand for its polymers and, on an eneigy-equivalent basis, rigid polyi vinyl chlonde) (PVC) is one of the most energy-efficient construction materials available. 

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