Exergy utilization efficiency

The efficiency of exergy utilization in an open system (chemical reactor) is then defined by Eq. 11.4 ... 

The values of efficiencies help in assessing the effectiveness of exergy usage, as the value of (1 -17) is directly related to the exergy loss. They can be used to compare the performance of columns with each other. Smaller exergy losses mean the utilization of a higher portion of available energy, and hence fewer thermodynamic imperfections in a column. 

Table 4.17 shows that column 2 operates with efficiency as low as 4.1%, while the efficiency of column 1 is 50.6%. The exergy values for the whole separation system of two columns are also low and need to be improved. The individual values of PI show that it is possible to reduce by 13.1% the total loss of 0.834 MW in column 1 and by 19.1% the total loss of 27.813 MW in column 2. Despite the heat integration, the separation section of the methanol plant performs poorly in utilizing the exergy in the distillation columns. 

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. 

For the optimal efficiency to occur at steady state, oxidative phosphorylation progresses with a load. Such a load. /L is an ATP-utilizing process in the cell, such as the transport of substrates. A load, which will make the steady state the optimal efficiency state, can be identified through the total exergy loss T,c... 

Exergy analysis can be used to compare FP-FC systems with rechargeable batteries and combustion engines. Other important aspects, in addition to exergetic efficiency, are environmental impact, safety and life cycle cost. Efficient fuel utilization is particularly important for larger FP-FC systems. For small systems, the energy... 

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