선박폐열회수(WHRS) 및 해양온도차 (OTEC)발전용 유기랭킨사이클(ORC)의 효율향상을 위한 연구

Abstract

Waste heat recovery system is one of ORC applied technologies. Waste heat recovery system refers to the technology that generates power by withdrawing waste heat of industrial use or vessel and applying ORC. In case of vessels, this technology can generate 1MW of power with only 10% of waste heat withdrawal. In addition, since ORC cycle shows 10~12% efficiency in waste heat withdrawal generation, if applied to industrial waste heat withdrawal, considerable amount of power can be generated.

Ocean thermal energy conversion was first suggested by France J.D'Arsonval in 1881. The basic idea is that warm surface seawater is used to generate steam, and this steam again rotates turbine to generate power. He also designed technology that condensed steam to a liquid by drawing up deep cold water to surface. This is called "closed cycle". Open cycle is the opposite concept with closed cycle, and for this to work, warm sea water itself is evaporated by spray flash in low pressure, and produces steam. This steam rotates turbine and generate power. If it is condensed wit deep water, there is the advantage of producing additional plain water. However, since lots of water is required to generate meaningful scale of power and technical feasibility is not met, focus is only on closed cycle yet.

Distinction of these two ORC properties is a different temperature scope. Waste heat power generation uses about 160~200 degree of heat source, and makes about 130~170 degree of temperature difference to condensate water. Ocean thermal energy conversion makes about 20 degree of difference. Cycle efficiency according to this is currently showing about 10~12%, 4%. Common ground of these two technology is the use of ORC, and most of all, it is required to have technology that can increase cycle efficiency.

Selecting working fluid is important to increase cycle efficiency. Currently used working fluid includes ammonia, R22, R134a, R245fa, and recently known refrigerants are R1234yf, and R1234ze(E). According to this working fluid, proper working fluid selection through specific interpretation is important. To enhance regeneration cycle from existing closed cycle, currently there are Kalina cycle, and Uehara cycle. Also, turbine design technology, and heat exchanger design technology are among the important elements.

For the purpose of this thesis, through ORC cycle efficiency enhancement, generation efficiency can be improved. To increase generation efficiency, comparison analysis was performed in terms of various specific interpretations of ORC based on working fluid, specific interpretation of ORC based on operation cycle, and specific interpretation when applying medium temperature ORC and low temperature ORC.

For this, interpretation through simulation was performed. This is done by comparing with experiment result. to ensure the reliability of simulation result.