Analyzing the energy balance and optimizing the waste heat utilization on a passenger cruise ship
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Helsinki University of Technology |
Diplomityö
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Authors
Date
2007
Department
Major/Subject
Lämpötekniikka ja koneoppi
Mcode
Ene-39
Degree programme
Language
en
Pages
64
Series
Abstract
A large part of the waste heat, in form of steam, high temperature cooling water and low temperature cooling water, that is produced as a by-product of passenger cruise ships' main engines is currently dumped, or it is utilized in thermodynamically inefficient processes. In order to find the most promising targets for the waste heat utilization, the energy balance of a passenger cruise ship was analyzed by conducting an entropy generation analysis of the energy balance. Also, an index for describing the waste heat dumping that considered the qualities of the dumped heat was developed. Consequently, the waste heat would be utilized optimally when both the waste heat index and the entropy generation in the processes utilizing waste heat were minimal. The calculations conducted for a model passenger cruise ship showed that optimal waste heat utilization could save more than 4% of the total fuel consumed onboard the ship. The main engines onboard a model passenger cruise ship were identified as the largest cause of entropy generation in the entire system, and the next largest cause was steam production in the oil fired boilers for additional heat producing. However, if a part of the hot water could be used in some of the heating processes onboard, the utilization of the oil-fired boilers could be minimized, and also the efficiency of the main engines would be enhanced. This alone would have saved 2% of the yearly consumed fuel onboard the model passenger cruise ship. In addition to heating processes, the waste heat could also be utilized for electricity production in Organic Rankine Cycle that in theory could be able to utilize a portion of all waste heat streams. Utilizing the waste heat steam in this process clearly decreased the overall entropy generation in the ship, mainly because it also decreases the need for producing electricity with the main engines. Also, the availability of the hot water in every situation could be assured by installing heat pumps onboard the passenger cruise ship that could use the lowest temperature waste heat as their driving force. The entropy generation in both heating processes utilizing hot water and heat production in heat pumps was clearly smaller than heating processes that utilized steam, and steam production in oil fired boilers. The cooling onboard could be realized with absorption chillers that utilize steam or hot water as their driving force. This process was proven to minimize the overall entropy generation of the entire system, but only in situations when waste heat is available. Producing additional heat in heat pumps or in oil fired boilers for absorption chillers was not profitable according to calculations, but the option to use this might be useful in possible emergency circumstances. Fresh water production with reversed osmosis was discovered in calculations to be more profitable than production in evaporators, especially when steam is required for firing the evaporators. The real installations should be designed in a way that they can utilize the waste heat in all situations. This might require combining these different solutions that should be as thermodynamically efficient as possible, without making large tradeoffs with the economic aspects. This way can the waste heat be utilized optimally and the efficiency of the entire ship's energy system is enhanced.Description
Supervisor
Lampinen, MarkkuKeywords
entropy generation, waste heat utilization, passenger cruise ships