Nova Patents
US2984080A

Method and means for the transportation of liquefied natural gas

Abstract

This record has no abstract on file.

Term

Term ended

Expired 16 May 1978, 48.4 years ago.

  1. Priority and filed
  2. Granted
  3. Expired
  4. Today

4 claims: 4 independent, 0 dependent

  1. 1
    I claim:1. In the storage and transportation of natural gas in a tank in a liquefied state at extremely low temperature, the method of minimizing the loss of natural gas by vaporization comprising admixing with the liquefied natural gas a liquefied nitrogen gas in an amount to last substantially throughout the period of time that the liquefied natural gas in the tanks, said liquefied nitrogen being present in an amount up to 20 percent by weight of the liquid in the storage tank.
  2. 2
    In the storage and transportation of a natural gas in a liquefied state housed in a tank at extremely low temperature for transportation from a source of plentiful supply to an area where a deficiency exists, the method of minimizing loss of natural gas by vaporization and maintaining an inert atmosphere within the tank comprising admixing with the liquefied natural gas another inert gas in a liquefied state having a vapor pressure substantially higher than the vapor pressure of the liquefied natural gas at the temperature conditions existing and present in an amount to last substantially throughout the time that he tank is filled at the source of supply until discharged at the area where the deficiency exists, said other liquefied inert gas being present in an amount up to 20 percent by weight of the liquid in the tank.
  3. 3
    In the storage and transportation of a natural gas in a liquefied state housed in a tank at extremely low temperature for transportation from a source of plentiful supply to an area where a deficiency exists, the method of retaining the refrigeration in the emptied tank during transportation from the area where the deficiency exists back to the area of plentiful supply for refilling the tank, comprising introducing into the tank following discharge of the natural gas at the area where a deficiency exists another liquefied inert gas in an amount less than 20 percent of the volume of the empty tank, said other liquefied gas having a vapor pressure substantially higher than the vapor pressure of the liquefied natural gas at the temperature conditions existing.
  4. 4
    In the storage and transportation of natural gas in a liquefied state housed in a tank at extremely low temperature for transportation from a source of plentiful supply to an area where a deficiency exists, the method of 3 feet the economics of the entire process. The excessive vaporization of the natural gas will further tax the devices for handling such vapors to the end that an expense would be involved in additional material-handling equipment and excessive losses would occur in the desir- 5 able product, namely, the natural gas. When the lower boiling liquefied gas is embodied in desirable amounts in the tank for return, it is unnecessary to leave a substantial portion of the liquefied natural gas in the tank for purposes of maintaining the tank at the 10 desired low temperature during the return voyage. Further, the lower boiling liquefied gas will be able to retain the tank at a temperature lower than that of the liquefied natural gas so that cool-down can be eliminated or at least greatly minimized and vaporization of the natural 15 gas upon loading can be greatly reduced. Thus, excessive losses of natural gas vapors will be avoided and it will be unnecessary to make use of additional materialhandling and processing equipment. Of considerable importance is the protection made avail- 20 able by the use of an inert liquefied gas in the tanks during such return voyage. The vapors released will fill the available space in and about the tanks to provide a safe and inert atmosphere. It will also eliminate the necessity to purge the tanks for removal of air, oxygen 25 and the like materials which might form a combustible mixture with natural gas vapors. While it is desirable to make use of an amount of the lower boiling liquefied gas calculated to last for the entire return voyage from the source of supply to the source 30 of use, the amount introduced into the tank for the return voyage is not so critical since the residual lower boiling liquefied gas remaining in the tank can be admixed with the new load of liquefied natural gas introduced to refill the tank. In fact, where such lower boiling lique- 35 fled gas can be made available at lower cost by utilization of refrigeration available in large amounts in the liquefied natural gas at the point of use, it would be feasible to introduce an amount of such liquefied gas calculated to be sufficient for the complete voyage to the source 40 of plentiful supply and back. Liquefied nitrogen may be taken as representative of a gas preferred for use in the practice of this invention. Nitrogen is a relatively inert gas which, in the liquefied state, has a lower critical boiling point than liquefied 45 natural gas at atmospheric pressure. It is capable of admixture with liquefied natural gas to provide a system wherein preferential vaporization of nitrogen occurs at a temperature below the critical vaporization temperature of liquefied natural gas. Further, nitrogen is freely avail- 50 able in unlimited quantities in air, and it can be procured rather inexpensively by the liquefaction of air and the subsequent separation of nitrogen from oxygen by fractionation, utilizing the large amount of refrigeration available from the liquefied natural gas upon reconversion to 55 the gaseous state. It will be understood that other liquefiable, lower boiling gases may be used as represented by helium, argon and the like. For this application, it would be undesirable to make use of gases capable of forming a combiistible mixture with the hydrocarbon vapors, such 50 as oxygen or air. In practice, the liquefied natural gas introduced into the storage tanks for transportation would contain about 10% by weight of liquefied nitrogen when experience indicates loss by vaporization of about 0.5% per day, and 65 a period of about 20 days from the time that the tanks are filled at the source of plentiful supply until the tanks are emptied at the point of discharge or use. For the return voyage, an equivalent amount of liquefied nitrogen would be introduced into the emptied tanks 70 for maintaining the cold temperature in the tanks during the return voyage and for providing an inert atmosphere. In the event that the liquefied nitrogen is more readily available or available at lower cost at the point of use of the natural gas, twice the amount of liquefied nitrogen 75 3,984,080 ;. . 5 minimizing the loss of natural gas by vaporization during transportation from the source of plentiful supply to the area where a deficiency exists and minimizing the loss of refrigeration from the tank during transportation from the area where the deficiency exists back to the area of supply for refilling of the tank comprising introducing into the tank following discharge of the liquefied natural gas at the area where a deficiency exists another liquefied inert gas in an amount up to 20 percent by volume of the tank, said other liquefied gas having a vapor pressure substantially higher than the vapor pressure of the liquefied natural gas at the temperature conditions existing. References Cited in the file of this patent UNITED STATES PATENTS
Independent claims4