Thermodynamic cost

For any process or subsystem the specific cost of exergy c in US per kW per unit time for a stream is 

The ratio (Exf/Exiu ) 1 due to inevitable exergy loss is in the boiler, and hence cHP cF. Similarly, the cost rate balance for the turbine (control volume 2) is 

As Tjt 1, the specific cost of electricity (product) will be higher than that of high-pressure steam. 

Example 5.1 Cost of power generation A turbine produces 30 MW of electricity per year. The average cost of the steam is US 0.017/(kW h) of exergy (fuel). The total cost of the unit (fixed capital investment and operating costs) is US 1.1 X 105. If the turbine exergetic efficiency increases from 84% to 89%, after an increase of 2% in the total cost of the unit, evaluate the change of the unit cost of electricity. 

Assume that heat transfer effects between the turbine and surroundings are negligible. Also, kinetic and potential energy effects are disregarded. 

---

It is for this reason that orthoesters and acetals are (comparatively) stable in the absence of an acid. Alternatively, one can have an uncatalyzed mechanism involving preliminary tautomerization to a zwitterion, but the thermodynamic cost of this imposes a considerable barrier to reaction. 

Finally, we want to point out that the concept of the endoreversible engine is a simplification that leads to a quick and clear insight into the role and thermodynamic cost of transfer processes in reducing the Carnot efficiency into smaller and more realistic values. But for finding the real optimum conditions, the concept of endoreversibility has to be sacrificed. This will complicate the matter to some extent but will allow for including all contributions to the lost work ... 

Thermodynamic cost analysis relates the thermodynamic limits of separation systems to finite rate processes, and considers the environmental impact through the depletion of natural resources within the exergy loss concept. Still, economic analysis and thermodynamic analysis approaches may not be parallel. For example, it is estimated that a diabatic column has a lower exergy loss (39%) than that of adiabatic distillation however, this may not lead to a gain in the economic sense, yet it is certainly a gain in the thermodynamic sense. The minimization of entropy production is not always an economic criterion sometimes, existing separation equipment may be modified for an even distribution of forces or an even distribution of entropy production. Thermodynamic analysis requires careful interpretation and application. 

The results of thermodynamic analysis may be in line with those of economic analysis when the thermodynamic cost optimum, not the maximum thermodynamic efficiency, is considered with process specifications. Figure 5.3 shows pinch technology in terms of optimum hot and cold utilities by accounting for the investment costs and exergy cost. With an optimum approach temperature ATmin, the total cost may be optimized. 

The above reactions are at ambient temperature, so that an associated Carnot cycle (Chapter 1) is not needed, as would have been the case at high temperature. As the electrolytes are repeatedly reused, the question of the economic or thermodynamic cost of their manufacture is... 

Density fimctional theory (DFT) calculations show that this mechanistic hypothesis is energetically reasonable. The generation of the HO-Fe =0 oxidant from the [(TPA)Fe -OOH(OH2)] intermediate was found to have a thermodynamic cost of only 5 kcal/mol and a kinetic barrier of 20 kcal / mol (Fig. 18.5) [52]. Furthermore, the HO-Fe =0 oxidant could carry out either epoxidation or cis-dihydroxylation of the olefin, depending on which oxygen atom of the oxidant initiated attack of the substrate [53]. Thus, epoxidation occurs by 0x0 attack on the olefin, forming the first C-O bond and an intermediate carbon-based radical, which then reboimds to form the second C-O bond. On the other hand, czs-dihydroxylation is initiated by hydroxo attack to form the first C-O bond and an intermediate carbon-based radical, followed by reboimd with the 0x0 group to form the second C-O bond. 

Summary The recurring theme in the above examples is that a minor delocalizing interaction can be inactive at the most stable ground state geometry defined by an alternative stronger interaction that moves the system perpendicularly to the desired reaction coordinate. The stereoelectronic readjustment requires a conformational change and comes with a thermodynamic cost. When such readjustment is unnecessary, the role of stereoelectronic effects is revealed clearly and their accelerating power is ntihzed fully. 

Aryl radical intermediates were also snccessfnlly nsed for the preparation of the strained polyarene cavicularin (60) from aryl iodide 58 (Eq. 9.13). In this transformation, the key step involved the generation of the a-complex 59 with a sp carbon that was able to alleviate the strain of the macrocycle and the cyclization proceeded withont any significant distortion of arene A. The thermodynamic cost of bending the arene A was compensated by the rearomatization of arene D from the intermediate 59 [48] ... 

---