Utilization of LNG Cold Energy in the Petrochemical Industry

Abstract

Depending on its mode of use, LNG possesses great value as a source of cold energy. The application of the cold energy of LNG to the petrochemical industry is explained hereunder.Facilities actually constructed and in operation which utilize the cold energy of LNG to separate the heavy components contained in the LNG are those at the Barcelona Terminal in Spain and the La Spezia Terminal in Italy.A method of using the cold energy of LNG for separation purposes and for the ethylene production unit itself, wherely ethane separated from LNG containing heavy components in used as feed for ethylene production, is described in the literature released by Air Products Ltd. in “LNG-1”.There is a process, in the patent stage, by which heavy components are separated from LNG containing such comporents and high-pressure methane gas is produced. This method does not require the use of the compressor for which a patent application has been lodged by Air Liquid.The methane is liquefied using the cold energy of LNG and vaporized after being pressurized with a pump.Similarly, Conch Methane Service has announced its patented method which utilizes the cold energy of LNG to separate refinery tail-gas into its individual components.A scrubbing method using LNG and propane chilled by means of liquefied nitrogen to remove trace quantities of impurities from hydrogen, is adopted.The use of the cold energy of LNG in an ethylene production plant, taking the case of an ethylene production rate of 300, 000 tons per year, is described briefly.In this case, 1, 380, 000 tons per year of LNG will be required if all necessary refrigeration is to be carried out by the sole use of LNG.Trial calculations were per formed on the basis of using LNG for the ethylene refrigeration around the demethanizer only. These calculations evaluate the cost of one kilogram of LNG at 1.59 yen.The use of the cold energy of LNG, especially in ethylene production units, will probably be realized with the establishment of stable supply and increased imports of LNG.