The Economic Analysis Of The BOG Reliquefaction On LNG Carrier

Nature gas is considered as a kind of new first-advocated energy sources at the twenty-first century for its characteristic of high quality and pollution-free to the environment. The physical volume of the nature gas is only 1/625 for the original volume after been liquefied at low temperature. It is very convenient for transportation and storage. With Chinese economy developing rapidly, the requirement of the natual gas is increasing day by day. Domestic nature gas can't satisfy what the market's need, liquefied natural gas has to be imported in great quantities annually. Because of the high economical efficiency and flexibility to store and transfer natural gas in liquid, LNG carriers play a great important role in the natural gas market all over the world.At present most of LNG Carriers have no reliquefaction plant for liquid cargo. So the BOG from cabin can not be reliquefied and wasted. At the same time the thermal efficiency of LNG carriers steam drive Plant is very low, maybe 30%, then the operation expenses increase. Reliquefaction technology for BOG is studied in theory method in this article, and also the research on economical efficiency of LNG carriers that installed reliquefied plant is carried on.Firstly, the study situation of reliquefaction technology and development situation of LNG carriers all over the world now are introduced, reliquefaction plant is discussed from the views of technology, energy and economical efficiency, and the feasibility of reliquefaction plant is also discussed.Reliquefaction tecnology relates to low temperature refrigeration principle, reverse brayton principle, liquefaction methods, principle on the land and LNG carriers are analyzed. Equipments that maybe used in reliquefaction plant, such as compressor, cryogenic heat exchanger, separator, expander and throttle valve are imitated in thermodynamic way. Secondly, model of reliquefaction principle in the given carrier is made, and the total cargo capacity, refrigeration compressor power, cargo flux, nitrogen compressor power, nitrogen cycle flux are caculated according to the given experiment parameters and relative formulas. Saving fee yearly, investment cycle of reliquefaction plant, saving fee of propulsion plant, increasing transfer capacity and etc are obtained by comparing the fuel fee, LNG comsume fee, repairment and maintainment fee and the investment of the steam power plant of the carriers with reliquefaction plant and that without it. Moreover, the reliability, safety of reliquefaction plant are studied in the thesis.