Storage tank for liquefied gas having bottom insulation gas shielding

Claim 1

In an enclosed liquefied gas storage tank having a bottom, side wall and roof, the improvement comprising: a chamber positioned in insulation beneath the tank bottom and extending over substantially the entire area of the tank bottom, a vapor supply conduit extending from, and communicating with, a vapor space above the design maximum liquid level storage capacity of the tank to, and in communication with, the chamber, and a vapor removal conduit communicating with the chamber for withdrawing vapor from the chamber after circulating therethrough, said chamber having a central hollow cylindrical section with a plurality of hollow ring-like sections of increasing size in series extending outwardly therefrom with the inner most ring spaced below and in c0mmunication with the central hollow cylindrical section, and each ring out therefrom is spaced below the next adjacent inner ring, said vapor supply conduit communicating with the central hollow cylindrical section and the vapor removal conduit communicates with the outer-most ring-like section.