Specific exergy chemicals

The objective of this work is to develop a set of group contributions for estimating the specific chemical enthalpy, 8, and the specific chemical exergy, e, which are essential in carrying out the thermodynamic analysis and synthesis of a process system. This set of group contributions can be employed not only for known organic compounds, but also for new organic compounds which are yet to be synthesized or discovered. 

The values of availability (exergy) and energy (enthalpy relative to the dead state) of all materials that are in complete, stable equilibrium with the dead state are zero. The datum level materials and their concentrations that age used in this work to compute the specific chemical enthalpy, 8, and the specific chemical exergy, e, are listed in Table I. 

Specific Chemical Exergies of Gaseous and Liquid Chemicals, t ... 

Exergy is a property of a material system, which measures the maximum work obtainable when the system proceeds from its given state to the dead state while interacting only with the environment (1,8.14). The specific chemical exergy is defined as... 

In the present scheme, the specific chemical exergy, e , is computed as... 

As flow processes are common in industry, exergy of the mass flow crossing the system boundary is important. In an open system, excluding the chemical exergy, specific flow exergy exfis... 

We can determine the specific enthalpies and the specific entropies from the temperature, pressure, and composition of the environment. Once we specify the environmental conditions, all enthalpy and entropy terms are fully defined regardless of the process within the control volume. The term 7 0Chemical exergy, Exch, is... 

The most stable end products of reactions involving the resource under consideration are chosen as reference chemical species rs in the environment (air, ocean, or earth cmst). These reference species are not in thermodynamic equilibrium, as the biosphere is not a thermodynamic equilibrium system. Reference species are assigned a specific free energy (exergy) b s due to their molar fraction in the environment by means of the formula = —RT Inz s, where the reference species are assmned to form an ideal mixture or solution. 

The total chemical exergy of the resomce is finally calculated as boh,res = Abf+ X ch,i+ X rs- In so doing, tables of exergies per unit mass or per mole (specific exergy) can be constracted for each resource. 

The standard molar chemical exergy of any substance not present in the environment can be determined using the change in the specific Gibbs function Ag for the reaction of this substance with substances present in the environment (Bejan, Tsatsaronis, and Moran, 1996 Moran and Shapiro 1998) ... 

Physical exergy results from the deviation of temperature and pressure from the environmental values. Chemical exergy results from the deviation of the composition of a component in a system from the composition of the same component in the environment. Chemical exergy of a stream of matter can be defined as the maximum work (useful energy) that can be obtained from it in taking it to chemical equilibrium (of composition) with the environment. In an open system, the specific flow exergy exf is expressed by... 

---