SPECIAL CONSIDERATION ON THE DESIGN OF AN LNG HARBOR

Abstract

One of the primary considerations in the design of an LNG harbor is safety, requiring berths to be separated by large distance and well protected from the outside wave agitation. Therefore, LNG harbors require expensive structures established as close as possible to the liquefaction plant (while crude tankers may be served by relatively much cheaper, single point mooring servers in deeper water). The cost of waiting time for the very expensive LNG ships has to be weighted against the cost of the additional berths and structures. (A 125, 000 m-^ LNG ships costs $2000/hour. ) The present paper describes the results of a study in which the optimum solution has been obtained by comparing these costs. The number of options is characterized by the number of berths. The cost to be added to the cost of construction of the berths includes an additional length of breakwater and additional dredging, plus the costs of financing during construction and the cost of maintenance. The waiting time for the LNG ship is generally determined, based on the classical Erlang formula for quelng theory. It is recalled that this formula is developed for an open loop. A closed loop theory has been specially developed for the present problem (since LNG ships will most probably operate between two well-defined harbors). The waiting times are 15 to 20% smaller than given by the closed loop theory. A comparison between single berth and double berth is examined. The effect of the rate of filling which is a function of the cryogenic pump capacity (or size of ship depending upon the dominating controlling factor) is analyzed. Finally, the sensitivity of the recommended solution as a function of the interest rates--examined in view of current economic uncertainties--is also investigated. The final recommendation for the design of the harbor, based on the prevailing factors, is the optimum economic solution.