Friday, April 13, 2012

No. 485: Improving the quality of energy: the concept of exergy efficiency (April 13, 2012)

The idea to improve the quality of waste heat for repeated usage as energy is in progress. The part of energy usable for work is called exergy, and the ratio of exergy is called exergy ratio. Such fossil energies as oil, coal, and natural gas have a high exergy ratio, but they will be low quality energy once they are burnt to generate heat. It is impossible to increase the gross volume of energy because energy has the conservation law, but it is possible to improve the quality of energy.

Nippon Steel Engineering is working on the substantiative study of the self-heat generation that Tokyo University professor Atsushi Tsutsumi proposed about five years ago, by applying pressure to the steam in the process of decreasing the temperature. The high-temperature steam with high exergy does not need application of heat from outside. The self-heat generation method has a wide range of applications. As compared with the traditional energy-saving technology, it can reduce energy and fuel by more than 70% in naphtha desulfurization, carbon dioxide separation, and drying coals with a large amount of moisture.

Kyusyu University professor Tatsumi Ishihara proposed the technology to collect waste energy and regenerate exergy with the help of the solid oxide fuel cell (SOFC) method. The SOFC method does not need pure hydrogen as fuel, and it can generate electricity using methane of city gas as fuel. That is, it can change methane into such fuel gas with a high exergy ratio as hydrogen and carbon monoxide. The professor is developing the technology to collect waste heat and generate hydrogen simultaneously by running the system of a fuel cell in the opposite direction.

Exergy regeneration will bring lots of spin-off benefits to the industry. For example, it will be possible to reduce fuel consumption considerably by building additional equipment without modifying greatly the existing chemical plant and generation equipment. The energy-saving technology is advancing. 

The concept of exergy efficiency

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