A study to assess the energy savings potential in the ocean going trawler 'Roxana Bank'

Abstract

Increasing fuel prices have forced marine engineers and diesel engine manufacturers to look at methods of. reducing fuel consumption without a loss in output power. Engineers are always Investigating the following points: (1) decreasing the specific fuel consumption (2) enabling engines to use worse fuels ... (3) extending part load capability (4) using as much waste heat as possible. The sources of heat loss are investigated and the design of an efficient heat recovery system has been evaluated for Ideal temperature and heat conditions. after taking lnto consideration the various methods of heat recovery that are possible on the fishing trawler MFV Roxana Bank. Sources of heat loss identified by engine manufacturers are found primarily in engine cooling water and exhaust systems. These methods are investigated and extra heat transfer systems have become apparent. The use of exhaust gas boilers in diesel engine installations has become widespread as there is always a demand for heating services regardless of vessel type. The predominant form of heat transfer on the Roxana Bank is by forced convection and fluids must always remain in a turbulent state when passing through heat exchange apparatus. The introduction to heat exchangers shows that a high degree of turbulence in both primary and secondary fluids will the overall heat transfer coefficient and also reduce fouling. The design parameters of the heat recovery systems discussed as suitable for the Roxana Bank require the existing cooling water system to be scrapped and a fresh water system with one central cooler to be designed with a high temperature and a low temperature circuit together with a variable speed pump arrangement. should be fitted with such central cooling systems for a number of reasons. The central cooler system Is discussed In detail and it is shown that existing ships and/or new buildings The heat recovery system requires a certain degree of automation to prevent undercooling of the main engine systems and to maintain set Inlet and outlet temperatures to makers specifications. After attending the Roxana Bank on the 09/10 November 1989, the monitored operati~g parameters show a marked deviation to the Ideal temperatures, particularly In the cylinder cooling water circuit ... temperatures. The adverse effects these deviations have on the heat recovery and combined engine load fluctuations found on the Roxana Bank show that steady state heat recovery Is difficult to achieve on this particular type of vessel. Through calculation it Is shown that the envisaged steam turbine alternator is not practical due to the combination of low feed water inlet temperatures to the boiler and insufficient driving steam. The consequence of the reduction in electrical load on the power take off alternators have on the exhaust gas mass flow rates due to reduced engine load are also discussed. A brief mention is also made of organic fluid and thermal oil systems as a form heat recovery and possibilities for efficient heat transfer using these systems. ii Recommendations are made to Irvin and Johnson with regards to a centralised cooling system and the benefits that can be realised with regard to more efficient heat exchanger operations, but that heat recovery on the Roxana Bank from the proposed sources is not a viable proposition.