Theoretical analysis of cogeneration system for ships Wen-Kuo Tien a , Rong-Hua Yeh b, * , Jen-Ming Hong c a Department of Merchant Marine, National Taiwan Ocean University, 2, Pei Ning Road, Keelung 202, Taiwan b Department of Marine Engineering, National Taiwan Ocean University, 2, Pei Ning Road, Keelung 202, Taiwan c Department of Power Mechanical Engineering, Army Academy, 113, Sec. 4, Chongshan E. Rd., Chongli 320, Taiwan Received 17 October 2005; received in revised form 10 July 2006; accepted 30 January 2007 Available online 26 March 2007 Abstract A methodology of assessing a cogeneration system on a ship is proposed. Given the mass flow rate of exhaust gas and cooling sea- water and the inlet temperatures of the gas and seawater, the net power of this system can be obtained through an iterative method. The parameters of mass flow rate of exhaust gas, heat transfer area of boiler and condenser and outlet temperature of the gas from the boiler are considered. In the heating process, the boiler tubes contain superheated, saturated and subcooled sections. It is shown that the dimen- sionless saturated area of the boiler increases with exhaust mass flow rate, whereas the superheated region tends to decrease on increasing the mass flow rate of flue gas at a fixed exhaust temperature. As for the subcooled portion, no significant change is observed. The power consumption of the working fluid circulating pump increases as the exit exhaust temperature from the boiler decreases. In addition, the more net work the turbine produces, the lower is the outlet temperature of the working fluid in the condenser for a fixed mass flow rate of exhaust gas. The net output of the cogeneration system is larger for a larger mass flow rate and a smaller exit temperature of the exhaust. Finally, an experiment is conducted to validate the proposed model. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Cogeneration; Ship; Superheated; Saturated; Subcooled 1. Introduction Growing transportation requirements, combined with declining oil production, have led to burgeoning oil imports of most developing countries in the world. Rising oil prices are having an adverse impact on the economy of these countries. Apparently, oil will become more expen- sive and less available. This will be painful in the industri- alized countries that have become totally dependent upon oil and in the less developed countries where oil use is extremely sensitive to price escalation. Cogeneration, also known as combined heat and power (CHP) and total energy, is an efficient, clean and reliable approach to generating power and thermal energy from a single fuel source. Namely, cogeneration uses heat that is otherwise discarded from conventional power generation to produce thermal energy. This energy is used to provide cooling or heating for certain devices on ships. By recycling this waste heat, cogeneration plants achieve a dramatic improvement in the system’s efficiency. In addition, the higher efficiencies of cogeneration reduce air emissions of nitrous oxides, sulfur dioxide, mercury, particulate matter and carbon dioxide, which are the leading greenhouse gases associated with climate change. Because of competitive pressures to cut costs and reduce emissions of air pollutants and greenhouse gasses, owners and operators of commercial vessels are actively looking for ways to use energy more efficiently. Cogeneration is the simultaneous production of electricity and useful heat from the same fuel or energy. Facilities with cogeneration systems use them to produce their own electricity and use the unused excess (waste) heat for process steam, hot water heating, space heating and other thermal needs. They may also use excess process heat to produce steam for electricity 0196-8904/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2007.01.032 * Corresponding author. Tel.: +886 2 24622192x7107; fax: +886 2 24633765. E-mail address: RHYeh@mail.ntou.edu.tw (R.-H. Yeh). www.elsevier.com/locate/enconman Energy Conversion and Management 48 (2007) 1965–1974