(568d) Utilizing the "Cool" in Lng

Liquefied natural gas (LNG) is commonly transported by sea in large specially designed tankers and then unloaded into a thermally insulated cryogenic storage tank at slightly above atmospheric pressure. Conventionally, the liquid from the ship and/or the storage vessel at approximately 110oK is converted into gas at the pipeline pressure by (1) vaporizing the liquid at atmospheric pressure in an exchanger using sea water, ambient air, or the hot products of combustion of a small portion of the LNG as a heating fluid, and then compressing the gas to the pipeline pressure, which may be 1200 psia or 500 psia for a long-distance or short-distance one, respectively, or (2) pumping the liquid to the pipeline pressure, and then vaporizing it directly into the pipeline using one or more of the same three sources of heat. In the proposed new process the cold liquid is pumped to 1200 psia as in (2), but is then vaporized by heat exchange with a working fluid (a commercial refrigerant), and then heated up to the ambient temperature by exchange with a stream of aqueous solution of ethylene glycol. The working fluid, after heat exchange with the LNG, compression as a liquid, and vaporization by heat exchange with aqueous ethylene glycol, passes through two turbines in series (with intermediate cooling by aqueous ethylene glycol) to generate electricity, and thereafter recycles back as a vapor to the LNG vaporizer where it is condensed in the first pass and then pumped as a liquid through the second pass. The refrigerating capacity of the combined streams of chilled aqueous ethylene glycol is sold in the form of a recycling stream to nearby industrial plants. In the event that some or all of the natural gas is delivered to a short-distance pipeline, that fraction is expanded through a turbine to generate additional electricity and then reheated to the ambient temperature with the solution of ethylene glycol.