Exergy and Reference Environment

Industrial Coal Gasification Technolo es Covering Baseline and High-Ash Coal, First Edition. 

the exergetic process efficiency rj in percent, which is interpreted in the sense of a degree of quality, is calculated from the sum of the exergy flows ( in MW) passing the boundary of the system that are assigned to be an effort or benefit 

Exergy flows are identical to power in the case of the change of potential, kinetic, or electric energies. To evaluate the flow i of a fluid mixture, specific exergies e, in kj/kg for every mass flow w, in kg/s must be calculated. 

A distinction can be made between thermomechanical exergy due to temperature and pressure, chemical exergy ei,chem due to the reaction potential compared to the pure environmental components, and concentration exergy Ci conc due to composition differences with the environment [1]. 

The last term in Equation (8.3) is not applied for most of the evaluated streams, as the concentration potential is not usable. However, the concentration exergy represents the minimal necessary reversible separation energy for the concentrated oxygen (in gasifying agents) and nitrogen flows (e.g., for dry feeding from the air separation unit. Therefore, it is included in these streams. 

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