본 논문에서는 선박에서 배출되는 CO2 배출을 최소화하기 위한 노력의 일환으로 선박에서 배출되는 열에너지를 회수하고 재활용하여 극대화 시킬 수 있는 방안들을 조사하고 버려지는 열에너지를 이용하여 ORC(Organic Rankine Cycle) 발전장치를 구동함으로써 선박의 에너지 효율을 높이고 온실가스 배출을 최소화할 수 있는 방안들을 연구하였다. 선박에서 배출되는 배기가스의 폐열을 열원으로 하는 유기냉매 랭킨사이클을 구성하는 방안과 열에너지 비중은 높지만 상대적으로 낮은 온도인 해수냉각 시스템으로 배출되는 열에너지를 재활용하여 터빈 발전기를 구동하는 ORC 발전시스템을 설계하고 시뮬레이션 하였다. 시스템 해석 결과 배기가스에서는 1,000㎾급, 해수 냉각 시스템에서는 650㎾급 발전 출력을 얻을 수 있었고, 다양한 친환경 유기냉매를 이용하여 온도와 유량 조건에 따른 열 해석을 실시하여 시스템의 효율과 출력을 비교하였다. As a result of the worldwide increased consumption of fossil fuel energy, global warming is currently greatest challenges to human. Greenhouse Gas(GHG) emissions from ocean-going shipping are currently main issue in the international maritime society. As a matter of fact, the International Maritime Organization (IMO) is studying the GHG emission reduction system including mandatory fuel-efficiency indices and voluntary guidelines on efficient operation.
In this study, for the purpose of reduction of CO2 gas emission and to increase recovery of waste heat from ships, the ORC(Organic Rankine Cycle) is investigated and offered for the conversion of temperature heat to electricity from waste heat energy from ships. Simulation was performed with waste heat from the exhaust gas which is relatively high temperature and cooling sea water which is relatively low temperature from ships. The result shows that 1,000㎾ power generation is available from exhaust gases and 600㎾ power generation is available from sea water cooling system. Different variable fluid is used for simulation of the ORC system with variable temperature and flow condition and efficiency of system and output power is compared.
As a result of the waste gas ORC power generating system, efficiency of TFEA is highest with heat source of high temperature above 140℃ and efficiency of SES36 was high from 110℃ to 140℃. Also, The mass flow rate of TFEA is lowest and obtained 1,897㎾ maximum output power at 170℃.
As a result of the sea water cooling ORC power generating system, efficiency of the working fluid with R717 is highest as a 2.86% and the next working fluid is R152a, R134a, R143a and R125a. The system with working fluid R717 is obtained 289,869㎏/h of Mass flow rate among the various working fluid.
On the sea water cooling ORC power generating system, output of net power is below 0 under system temperature 42℃ because cooling water pump driving power is increased by consumption of cooling water on the condenser. To overcome this problem, scoop cooling piping system will be one of alternative solution to get cooling water from a ship because cooling water can obtained by ship's propulsion power.
To optimize ship's waste heat ORC generating system, it is suggested that system utilize of cooling water waste heat and exhaust gas waste heat in one ORC system with re-heater. Cooling water waste heat was used for a heating medium of pre-heater and exhaust gas waste heat was used for a heating medium of heater. To increase efficiency of system the pre-heated working fluid is re-heated by re-heater installed between turbine and condenser. The system with TFEA as a working fluid obtained output of 2,400㎾ at the turbine.
In many ways, ORC(Organic Rankine Cycle) is a promising method for the conversion of low temperature heat to electricity. Different and new fluid can be used in the cycle for the re-utilization of waste heat.
A study and operation result on the ship's cooling water ORC generating system will contribute to development and practical use of OTEC(Ocean Thermal Energy Conversion) system since it's similarly principle with working temperature and pressure.