Natural gas stores are essential for reliability of supply with flexible inbound and outbound storage transfer needed to balance the varying demand between summer and winter months.
During the summer when consumption is low, excess volumes from the gas fields, which deliver at a preferably uniform rate, can be stored. During high consumption in winter months, storage caverns quickly provide large additional amounts of natural gas. The proximity of the storage capacity to the consumers is an important prerequisite for high availability.
Growing demand requires enlargement of storage capacity
The Empelde natural gas store with its three caverns has helped ensure reliability of supply for almost three decades. It is part of the gas management infrastructure in northern Germany and is integrated into the transport network of Erdgas Münster Transport and the distribution grid of the enercity grid company.
To meet the growing demand for storage capacities, Gasspeicher Hannover has been upgrading and expanding the plants in Empelde since 2003. Three caverns are currently in use, with expansion to four being planned.
Approximately 100 million cubic metres of natural gas can be stored per cavern at a depth of 1300 to 1700 metres in a salt dome.
Solution mining of a new cavern
Solution mining of a new cavern takes roughly two and a half years and the filling with natural gas half a year. Deep drilling is done in the first step. In the subsequent process fresh water is pumped into the borehole, the salt dissolves and a cavern is created. The generated salt solution is used to flood a disused potassium mine.
The salt solution is transported via a steel pipeline roughly 50 km long. Depending on the solution mining process, the transport rates vary between 250 and 450 cbm/h. To prevent oxygen corrosion in the steel pipeline a 40% sodium hydrogen sulphite solution is added before entry into the pipeline.
The dosing point is located in the connecting line from the brine settling tank to the suction manifold of the brine transport pumps. A sera dosing system CVD2-550.1- C409.2-75e withdraws the medium from a horizontally installed outdoor cylindrical storage tank with a capacity of 20 cbm.
Magnetic flowmeters record the flow rates of the brine and the oxygen-binding sodium hydrogen sulphite. The regulation of the electronically controlled sera dosing pumps takes place proportionally to the volume. A metering device for the measurement of the free oxygen monitors the proper function of the dosing system.
Once the cavern has reached its planned capacity, natural gas is pumped into the cavern and the salt solution is completely displaced from the cavity. The cavern is now available for storage operation.
Technical benefits
The CVD2 dosing system from sera is already designed for the upcoming expansion of the storage capacities in Empelde. Apart from its technical values and the Profibus connection, it stands as the right choice thanks to its modular design, ease of expansion, the defined interfaces and the variety of optional accessories. The CVD2 is a technically advanced solution that combines maximum application flexibility and adaptability with the economic advantages of a standardised series product.
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