in this topic , Marc A. Rosen had concluded that
"The relations between environmental impact and exergy in general and the chemical exergy of waste emissions in particular, suggest that exergy could be a meaningful and useful indicator of the potential for environmental impact. An exergy-based indicator could contribute to the development of simple, rational and objective procedures for assessing the harmful effects on the environment and predicting the potential for environmental impact for a substance. This view is primarily based on the general premise that a substance has exergy due to its disequilibrium with respect to a reference environment, and therefore the exergy of unrestricted waste emissions has the potential to impact on the environment. The potential usefulness of exergy analysis in addressing and solving environmental problems is significant, but further work is needed if utilizable, objective exergy-based indicators of the potential of a substance to impact on the environment are to be developed "
Dear Ali ,
Since you have been reading Marc A. Rosen studies, you already know that exergy is a part of thermodynamic system energy that can be converted into useful work (we may say that exergy is a measure of energy form quality). It represents the maximum work of an open thermodynamic system that can be achieved by matter or energy flow with defined reference environment (described by its temperature, pressure, chemical composition and concentration), during the process which direction is the direction of establishing equilibrium. Therefore, exergy is not a simple thermodynamic concept as it relates to the system and to the environment, i. e. it does not only depend on the state of a system and an energy transformation, but also on the state of the environment.
The one of colleagues has already stated that "the higher the exergy efficiency, the less the environmental impact" (the more sustainable development).
It is necessary to consider energy consumption and depletion of natural resources, i. e. the efficiency of the processes, the assessment of emission and reduction of its effects to the environment, as well as the development of new and less harmful technologies and sustainable energy resources use. Exergy efficiency is proposed as an indicator of environmental characteristic which includes the aspects of energy efficiency and environmental impact of the energy conversion processes, e. g. reduction of harmful impacts and environment degradation.
Regarding some process, you should take into account that study of a different energy forms transformation processes, based on exergy, could be used in order to estimate the effect of these processes on the environment. This approach gives more realistic picture than energy, allows detection of critical points of processes, and contributes to efficiency increasing, rational use of natural resources, development of green technologies and sustainable energy sources. Exergy analysis can determine which part of available energy could be converted into work, reaching a working substance in balance with the environment in a reversible manner.
Exergy efficiency is a measure of entropy generation or exergy destruction by the system, i. e. a measure of irreversibility and it might indicate how close the actual process approaches the ideal case (reversible process).
Many environmental problems are caused by, or are directly related to transformation and use of energy. For example, the relatively low cost of fossil fuels had made modern mankind to increasingly depend on them and caused significant pollution, endangering many biological systems. An important implication of the above assumption is that sustainable development requires not only the ability to use energy resources, but also their efficient use. Since the exergy methods are essential in assessing and improving energy (exergy) efficiency, they could be very useful in the sustainable development.
All other things being equal, the higher the exergy efficiency, the less the environmental impact. All other things being equal, maximizing exergy efficiency means getting the most from the least. But sometimes all other things may not be equal. For example, thermoelectric generation via thermocouples is usually less exergy-efficient than turboelectric generation. But thermocouples have no moving parts and if made of noncorroding materials can last almost indefinitely without maintenance. So thermoelectric generators may or may not have less environmental impact than turboelectric generators, depending on the circumstances.
Dear Ali
As explained Jack Denur, the emissions increases with the reduction of the exergy efficiency, the main cause of the reduction in the exergy efficiency is the large difference between the temperature of the system and the temperature of the environment. So the environmental impact is in inversely proportional with the exergy efficiency of a process.
Dear Heydar and Jack. I'm thankfull for your answer and your Wanderfull E xplainations. However I want to if it's possible the depentance between exergy efficiency of process and it's sustainability.
Thanks a lot again
Dear Ali ,
Since you have been reading Marc A. Rosen studies, you already know that exergy is a part of thermodynamic system energy that can be converted into useful work (we may say that exergy is a measure of energy form quality). It represents the maximum work of an open thermodynamic system that can be achieved by matter or energy flow with defined reference environment (described by its temperature, pressure, chemical composition and concentration), during the process which direction is the direction of establishing equilibrium. Therefore, exergy is not a simple thermodynamic concept as it relates to the system and to the environment, i. e. it does not only depend on the state of a system and an energy transformation, but also on the state of the environment.
The one of colleagues has already stated that "the higher the exergy efficiency, the less the environmental impact" (the more sustainable development).
It is necessary to consider energy consumption and depletion of natural resources, i. e. the efficiency of the processes, the assessment of emission and reduction of its effects to the environment, as well as the development of new and less harmful technologies and sustainable energy resources use. Exergy efficiency is proposed as an indicator of environmental characteristic which includes the aspects of energy efficiency and environmental impact of the energy conversion processes, e. g. reduction of harmful impacts and environment degradation.
Regarding some process, you should take into account that study of a different energy forms transformation processes, based on exergy, could be used in order to estimate the effect of these processes on the environment. This approach gives more realistic picture than energy, allows detection of critical points of processes, and contributes to efficiency increasing, rational use of natural resources, development of green technologies and sustainable energy sources. Exergy analysis can determine which part of available energy could be converted into work, reaching a working substance in balance with the environment in a reversible manner.
Exergy efficiency is a measure of entropy generation or exergy destruction by the system, i. e. a measure of irreversibility and it might indicate how close the actual process approaches the ideal case (reversible process).
Many environmental problems are caused by, or are directly related to transformation and use of energy. For example, the relatively low cost of fossil fuels had made modern mankind to increasingly depend on them and caused significant pollution, endangering many biological systems. An important implication of the above assumption is that sustainable development requires not only the ability to use energy resources, but also their efficient use. Since the exergy methods are essential in assessing and improving energy (exergy) efficiency, they could be very useful in the sustainable development.
Though the question is very valid would it not be better to expand it a little and think about this matter not in terms of energy efficiency bit rather in terms of resource efficiency? At one level all the energy that is incoming from the sun is available to be harvested or sequestrated and the balance that allows the current global environment to exist is just the niche that we humans can exploit to exist as we do. How resilient and stable is the balance? Or have I gone of topic?
Dear Bernard,
This is a very excellent point of view - exergy efficiency also applies to all resources (raw materials, biomass etc.) as well as energy source.
Note: Almost all energy comes to us from the sun, but don't forget the energy from the Earth - geothermal energy (heat released in the Earth's core in natural exothermic reactions of radioactive decay of elements in the Earth's core or crust) or high and low tide which predominantly appears by impact of moon gravity (and by sun gravity, too, but it's very low according to the moons') e.g. And our resources were not all created by sunlight influence...
But let's get back to the subject. The Exergy efficiency is a standard term, as well as the exergy analysis, so we have to look through the definitions and laws given by these terms. Especially because they explain in the simply way the second law of thermodynamics.
However, I agree that things should be looked in a wide context when it comes to sustainable development.
If we deal with some process and study their exergy efficiency, we have to be strict in our calculations, especially when we are trying to find an inefficient part of the process, e.g. the loss of heat energy in steam boilers of thermal power plants, which results in the loss of some other raw material - in this case it might be coal for example...
I don't know what is Alis' study, but I recommend an open mind and a lot of literature consultations...
Thanks dears Ivana and Bernard.
I'm very satisfied by your analysis of concept and your great explanations. as it's indicates above you are giving the essential. I agree with Dr. Bernard for his suggestion if we asking about resource efficiency? I'm asking this question because I need to defined how can I optimized a thermal process from its exery analysis. I find that I should defined the exergitic losses that it's in relation with the environment. In addition How an optimization can be sustainable. I'm thankful if we continue together this benefited conversation.
Kind Regards
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