COMPARISON OF EXERGY OF EMISSIONS FROM 2 ENERGY-CONVERSION TECHNOLOGIES, CONSIDERING THE POTENTIAL FOR ENVIRONMENTAL-IMPACT

There is a reference state in which substances exist in a stable form in the environment (atmosphere, hydrosphere. lithosphere) for all elements. Substances which are out of equilibrium with the environmental reference state, either in terms of chemical composition, concentration, pressure or temperature represent an opportunity to do work as they pass through processes which bring them to the environmental reference state and hence into equilibrium with the environment. The degree to which a substance is out of equilibrium with the environment is represented by its exergy. For an unconstrained emission, the exergy, or potential to do work, of a substance is dissipated in the environment as the substance is brought to the reference state of the environment. Hence, exergy may be considered a measure of the potential of the substance to impact the environment. This paper examines emissions from two alternate automobile power trains: (i) methanol-fuelled spark ignition engines, and (ii) hydrogen-fuelled fuel cells. It is shown that the exergy of emissions from the methanol engine is high (and thus indicative of greater impact on the environment), whereas emissions from a hydrogen/air fuel cell are lower in exergy (thus indicating a system better synchronised with the environment). These results are as expected. Thus, the methodology presented for evaluation of potential for environmental impact, which is both general and quantitative, appears promising.