UNDERGROUND STORAGE OF NATURAL GAS
CONTEXT DELHI
Compressed Natural Gas ( CNG) is an environment friendly alternative for diesel. In view of this the need is being felt to have uninterrupted supply of gas and its easy availability within the city.The reliable supply
Can only be ensured by having some backup storage to tide over some disruption of gas through a long pipeline. Natural gas can be stored in depleted oil fields and freshly excavated caverns under pressure or under refrigeration.In the context of Delhi only the storage in excavated caverns can be considered feasible.
Lined Underground Cavern
Excellent Aravalirocks are exposed in about 40% of Delhi area. These rocks are most suitable for safe and economical construction ofcaverns/ tunnels.These rocks extend south –southwest and may be nearer to the path of gas pipeline.These tunnels may be parallel to each other and may be as wide as 7 to 10 metres. (See Fig 1) These tunnels are to be linedby reinforced cement concrete and to be made leakproof by cladding the surface of lining by plastics or steel.The depth of these tunnelsmay be about 100 metresand the lining should be capable of with standing a pressure of 150 kg. Per cm. Sq.It is possible to plan, design and construct an appropriate system of gas storage, which may be safe and economicalbesides being tapped in emergencies.
Liquid Natural Gas (LNG)
Natural gas liquefies at –162 degrees centigrade and can bestored at normal atmospheric pressure. The refrigerated storage can be in caverns or in inground tanks.There are a number of refrigerated underground storages in Scandinaviancountrycountries.The inground tanks are normal concrete tanks sunk in ground with their top lid flushing with ground surface (see Fig. 2)It is also possible to bury the tank top below the ground toensure energy efficient operation over a long period of time. Such inground tanks are very common in Japan where the gas serves 10% energy needs of the nation single tank can have a capacity of 120,000 cu. Metres. It is possible to plan, design and construct such tanks in rocky areas of Delhi.
The storages can be dispersed in the city and can be interconnected by tunnels for ease of operation.The entire canbe designed to suite the intended need.It may be cautioned here that only storages larger the 50,000 cu. Metre of capacity are economical as compared to their surface counterparts
It is not necessary to construct them in the city premises, as they can be located near the pipelinebefore Delhi is approached, if suitable rock is available.