NOVELTY - The system comprises a heat exchanger (11) to liquefy a portion of components having high heating values by cooling natural gas, a gas-liquid separator (15) to separate the liquefied component from the natural gas, and a mechanism to add nitrogen to remaining non-liquefied components of the natural gas. The heat exchanger employs cold heat generated upon regasification of liquefied natural gas (LNG) to liquefy the portion of the components having the high heating values. The system further comprises an additional heat exchanger (13) to cool and liquefy the remaining non-liquefied components.    USE - The system is useful for reducing a heating value of natural gas in a liquefied natural gas regasification vessel (LNG RV) or an LNG floating storage and regasification unit (FSRU), which regasifies LNG at sea (claimed).    ADVANTAGE - The system can prevent an excessive increase of the ratio of nitrogen in natural gas components, can reduce operating costs even at sea where satisfactory supply of nitrogen cannot be obtained, eliminates a separate storage tank and other associated devices for storing components e.g. ethane in a liquid state, thus preventing an increase in overall size of the system.    DETAILED DESCRIPTION - The system comprises a heat exchanger (11) to liquefy a portion of components having high heating values by cooling natural gas, a gas-liquid separator (15) to separate the liquefied component from the natural gas, and a mechanism to add nitrogen to remaining non-liquefied components of the natural gas. The heat exchanger employs cold heat generated upon regasification of liquefied natural gas (LNG) to liquefy the portion of the components having the high heating values. The system further comprises an additional heat exchanger (13) to cool and liquefy the remaining non-liquefied components of the natural gas after the gas-liquid separator separates the liquefied component from the natural gas, and a generator, which uses the liquefied component as fuel separated by the gas-liquid separator. The additional heat exchanger employs cold heat generated upon regasification of LNG to liquefy the remaining non-liquefied components of the natural gas. The gas-liquid separator comprises a separator separating a gas and a liquid from each other. The heat exchanger and the gas-liquid separator are integrated into a single module. The nitrogen adding mechanism comprises a nitrogen injector to inject nitrogen gas into LNG and a nitrogen valve to adjust an amount of nitrogen gas injected into the LNG. The nitrogen adding mechanism comprises a nitrogen mixer to mix liquid nitrogen with LNG and a nitrogen valve to adjust an amount of liquid nitrogen mixed with the LNG. An INDEPENDENT CLAIM is included for a method for reducing a heating value of natural gas in a floating marine structure with LNG regasification equipment and a generator.    DESCRIPTION OF DRAWING(S) - The diagram shows a conceptual view of a system for reducing a heating value of natural gas.    Low pressure pump (1, 5)    Vaporizer (3, 7)    Heat exchanger (11)    Additional heat exchanger (13)    Gas-liquid separator. (15)