As emission controls of NOx, SOx, and CO2 have recently and gradually been tightened focusing on the seas of advanced countries, LNG(Liquefied Natural Gas), the environment-friendly fuel, is judged to be one of the most practical alternatives which satisfy global environment emission regulations. And the demand for LNG is expected to continue to increase. There are gas fuelled ships in the shipbuilding field and LNG-FSRU(LNG-Floating Storage and Regasification Unit) in the marine field as the representative method which applied this LNG. They have regasification systems, the core facilities, in common.
This paper is the study on characteristics according to variations of heating media in the regasification systems which are applied to gas fuelled ships and LNG-FSRU. It was composed based on the regasification system rules which are applied to gas-fuelled ships and LNG-FSRU by using HYSYS V8.0. And the following conclusion can be drawn according to the characteristics and vaporization methods to vaporize LNG.
(1) An analysis on the characteristics according to the mixing ratio of Eglycol water of regasification systems for gas fuelled ship
1) When pressure, temperature, and flux of natural gas(NG) which are supplied to DF engines are uniformly kept, the higher mixing ratio of Eglycol is, the lower mixing specific heat of Eglycol water. And the cycle flux and electric power were 1.65 and 1.54 times more required. respectively, than water was used as the heating medium.
2) When water was just used when adjusting the mixing ratio after fixing the size of the vaporizer, the temperature of natural gas which is supplied to an engine and Eglycol water in the outlet of the vaporizer were highest. And the changes that the temperature of natural gas gradually fell as enthalpy of Eglycol water which is supplied to a heat exchanger gets smaller because the higher mixing ratio of Eglycol is, the lower mixing specific heat of Eglycol water is.
3) Basic variables including mass flux according to the mixing ratio of Eglycol water, required electric power of operating fluid pumps, the temperature of natural gas which is supplied to the engine, and the heat exchanger’s capacity were drawn from the gotten results.
(2) An analysis on the characteristics according to changes of heat source temperatures and vaporization functions of regasification systems for LNG-FSRU
1) The seawater flow rate of 4,438ton per ton was, at least, required to regasify LNG of 200tons per hour with seawater of 25℃ in the vaporization method which uses it. In case of the vaporization method which uses Eglycol water, the seawater flow rate of 4,428tons per hour was, at least, required when the seawater temperature which is supplied is above 17.05℃. And steam was needed as an additional heat source in the seawater temperature which is lower than 17.05℃.
2) the seawater temperature supplied when vaporization performance is adjusted from 200 tons per hour to 150 and 100 tons can be vaporized with the seawater only in the temperatures of 17.05℃ , 14.2℃, and 11.3℃ according to vaporization performance. Boiler steam was required as an additional heat source when the seawater temperatures get to be lower than them. It has found that the quantity of boiler steam of 59.51, 44.51, and 29.44tons is required as steam is just used as the heat medium of Eglycol water when the seawater temperatures get to be lower than 5.5℃, the temperature of natural gas which is delivered to users in land.
3) the quantity of required steam and the seawater flow rate were calculated by dividing the vaporization method which uses Eglycol water into the case that the seawater flow rate is fixed so that LNG of maximum 200 tons per hour can be vaporized and the case that the seawater flow rate can be changed according to vaporization performance. the steam quantity of 62.3tons was required to vaporize LNG of 400 tons per hour. And if the seawater quantity can be changed according to vaporization performance, the seawater of 8,855tons and Eglycol water flow rate of 3,164ton per hour were needed when vaporization performance is 400 tons per hour in the same conditions.
4) Heat sources including changes of the seawater temperatures, changes of the temperatures of the inlets and outlets, and the steam quantity and the minimum flow rate of the seawater according to vaporization performance were calculated through the gotten results.
The above results in the study are judged to provide valuable basic data for the shipbuilding and marine fields in the future because there is no any study which drew system design variables according to changes of parameter values in Korea still now. And it is thought that better results can be gotten if studies which design, compare, and analyze systems based on the actual values of plant sites in the future.