ES307311A1 - Method of handling natural gas - Google Patents

Abstract

A plurality of containers 10a . . . 10n, Fig. 2 (not shown), are charged sequentially with pressurized hydrocarbon cargo gas by first forcing a cushion fluid at about the pressure of said hydrocarbon gas into the container 10a, then expelling the cushion fluid from container 10a and transferring it to the next container 10b by forcing cargo gas into container 10a and thereafter forcing cushion fluid from container 10b into container 10c by passage of cargo gas into container 10b and so on until cushion fluid is expelled from the last container 10n. The containers are arranged in the hold of a ship in series-connected batteries 11a ... 11n, the containers of each battery being connected in parallel with first access ducts 12a ... 12n connected to sub-headers 17a. . . 17n having valued connections to first and second main headers 20, 22. Second access ducts 13a . . . 13n are connected to sub-headers 18a ... 18n, having valved connections to a third main header 25. In operation compressed cushion gas, e.g. lean natural gas or nitrogen at ambient temperature is transferred from a shore header 43, a valve 49 in a by-pass 48, a flexible duct 36 to main header 22 through an open valve 23a into sub-header 17a and serves to pressurize containers 10a. Valves 23a, 49 are now closed and valves 21a, 23b, 26a are opened whereon liquid cargo gas passes from a shore header 41 through a valved flexible duct 35, main header 20, sub-header 17a into containers 10a whilst cushion gas is expelled therefrom through subheader 18a, open valve 26a, main header 25, a heat exchanger 52 in a by-pass 51 back to header 22 and through open valve 23b to the sub-header 17b and into containers 10b to effect pressurization thereof. Immediately containers 10a are filled with cargo gas, a device 28a responsive to the interface between cushion gas and liquid cargo gas automatically closes, valves 21a, 26a opens valve 21b to direct cargo gas into the next containers 10b, closes valve 23b to shut off cushion gas from containers 10b and opens valves 23c, 26c of battery 11c and valve 26b of battery 11b thereby allowing containers 10b to be charged with cargo gas and containers 10c to be pressurized with cushion gas which when leaving the last container 10n passes through sub-header 18n, main header 25 and shore header 43, by-pass 48 and header 42. Unloading is effected by coupling shore headers 59 ... 61, Fig. 24 (not shown), to main headers 20, 22, 25 and directing high-pressure displacement gas, e.g. lean natural gas or nitrogen through headers 61, 25 an open valve 26a and sub-header 18a thereby forcing cargo gas from containers 10a through sub-header 17a, open valve 21a and headers 20, 59. When containers 10a are emptied of cargo gas an interfaceresponsive device 27a automatically closes valves 21a, 26a and opens valve 21b to allow emptying of containers 10b of battery 11b. Also valve 23a is opened to allow displacement gas to expand from containers 10a through sub-header 17a, valve 23a and headers 22, 60 to a desired low pressure for the return voyage. In a modification, cushioning during loading is effected by liquid naphtha which also serves as the displacement fluid during unloading and the naphtha is itself displaced by a scavenging gas.