Calculated exergy losses

Fig. 5.10. Calculated exergy losses as fractions of fuel exergy for the General Electric LM 2500 CBT plant, for varying combustion temperatures (K) (after Ref. [13 ).

Subsequently, we refer briefly to other comparable studies, including the calculations of exergy losses and rational efficiency. Finally, we show the real gas exergy calculations for two practical plants—[CBT]i and [CBTX]i. 

Once the state points are known round a cycle in a computer calculation of performance, the local values of availability and/or exergy may be obtained. The procedure for e.stimating exergy losses or irreversibilities was outlined in Chapter 2. Here we. show such calculations made by Manfrida et al. [13] which were also presented in Ref. [14]. 

In this way, the exergy loss of each subsystem can be calculated. The overall exergy efficiency r e of the process is defined here in the following way ... 

Use exergy balance or exergy loss calculations to evaluate the utilization of energy and as a guide for process... 

In the natural environment, however, there are components of states differing in their composition or thermal parameters from thermodynamic equilibrium state. These components can undergo thermal and chemical processes. Therefore, they are natural resources with positive exergy. Only for commonly appearing components can a zero value of exergy be accepted. A correct definition of the reference level is essential for the calculation of external exergy losses. The most probable chemical interaction between the waste products and the environment occurs with the common components of the environment. 

Combustion reactions often cause extensive exergy loss. Exeigy calculations show that the entropy production can cause the loss of considerable potential work due to a reaction. An electrochemical membrane reactor or a fuel cell could reduce exergy loss considerably. 

The constituent exergy losses are calculated from the coefficients. I nm... 

Local gross exergy loss 8external exergy losses in the used technology for the major product and byproduct, and it can be calculated from the following steady-state exergy balance ... 

This equation reveals the real cost sources in the fcth component, which are the capital cost Z , the exergy destraction within the component as expressed by Cp.k, the operating and maintenance costs, and the exergy loss. Among these sources the first two are the most significant ones and are used for calculating the exergoeconomic factor. 

Exergy is an extensive property and a thermodynamic potential. In contrast to energy, exergy is not conserved and decreases in irreversible processes. If we discharge the waste product of the process into the environment, external exergy loss occurs due to the deviation of thermal parameters and the chemical composition between the product and the components of the environment. The thermal state and chemical composition of the natural environment represent a reference level (dead state) for the calculation of exergy. 

Liu ef al. (2008) can be used to calculate the exergy losses, but some assumptions of these authors have been removed as their validity appears to be questionable for example, that the vapor pressure at the sublimation interface is equal to the chamber pressure. The exergy losses due to heat transfer during primary drying h) calculated from the temperature profile in the dried layer (see Fig. 5.1) ... 

Calculation of Internal Exergy Loss in a Heat Exchanger... 

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