Cryogenic In-Ground Storage
Authors: Proctor R.C. 
Published: December 2007

Introduction

Demand for gases storable as liquids at low temperature and pressure was relatively small in the past, and the storage of these gases as liquids was accomplished in above-ground double-wall insulated tanks. Recently there have been several large installations of above-ground single-wall insulated tanks erected for the storage of propane, butane and anhydrous ammonia. Refrigerated storage of LPG and anhydrous ammonia is not considered cryogenic storage because these gases are liquefied at atmospheric pressure at temperatures substantially higher than those associated with cryogenic work. When industries, like the natural gas industry, begin to think of storage in volumes of a billion cu ft of gas stored as a liquid, such as Transco's installation, and then multiples of this volume, the project then justifies an intensive study and evaluation of all possible methods of storage. This design is the result of years of research and study following the disastrous fire resulting from the rupture of the Cleveland above-ground tanks. Certain lessons and subsequently fire tests after Cleveland pointed to the following:1. LNG must he contained where it cannot run into occupied areas.2. The intensity of an LNG fire is not as severe as those of gasoline or propane.3. The intensity of fires from LNG or propane increases rapidly as the material is allowed to spill out on warm ground, which increases the vaporization rate. It is evident that any refrigerated storage should be contained in the minimum surface area. This means dikes must he as high as possible with minimum surface exposure, the ultimate being in-ground.4. Spillage or overflow from tanks must be contained.

This is a serious problem on above-ground tanks, and just a diked area is not an adequate solution. On the Arzew project, the initial above-ground ship-loading tanks are connected to overflow into the in-ground storage. The cryogenic in-ground storage tank offers a solution to these problems. Its level is maintained below ground where it cannot run out over the surface. Rather than a large diked area for rapid vaporization in case of an accident, only the top of the hole could be exposed. The ground containing the LNG is frozen to −260F storage temperature with an ice ring over 30 ft thick making a vast cold pool. Any variation boiloff as a result of a fire would be a small per cent of what could be expected above ground. The concept of prefreezing a ring of frozen earth and then excavating within this frozen ring a cryogenic in-ground storage unit, developed by Conch International Methane Ltd., was demonstrated for the first time in Oct., 1961, at Lake Charles, La. This has been one of the outstanding developments from the standpoint of both investment and safety. On the Transco job, double-walled above-ground tanks together with their foundations and dikes were evaluated with in-ground prestressed concrete tanks and cryogenic in-ground storage. This evaluation showed savings, by using cryogenic in-ground storage, of approximately $1 million when compared to above-ground storage, and $500,000 when compared to in-ground prestressed concrete tanks. Cryogenic in-ground storage is no panacea for storage of LNG, but the geology at the Transco site and the properties of the frozen earth at this location were particularly favorable to this type of storage. This paper presents the design and construction features of the storage unit for the Transcontinental Gas Pipeline Co. that is now under construction in the New Jersey Meadows near Carlstadt, N. J.

JPT

P. 393ˆ