INDUSTRY FOCUS OIL & GAS
CONSTRUCTION SITE: GAS STORAGE CAVERNS
Rösberg Engineering has assisted astora in the safe filling of natural gas storage caverns
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any years generally elapse from the initial permission for a natural gas
storage cavern, the planning and construction, to the first filling. In this complex project, the focus is always on safety – the safety of the people operating the plant, the people living nearby, the environment, and the safety of the plant itself. Thus external experts are required who can reliably plan and implement automation solutions for the individual project stages. Natural gas is an ideal “buffer partner”
for the fluctuating performance of renewable energies. It can also go some way towards compensating the differences in energy consumption between summer and winter. However, it does require storage possibilities. To store natural gas, either naturally- occurring porous reservoirs or specially- made storage caverns are used. These are formed by creating artificial cavities in subterranean salt domes using leaching (solution mining). Salt domes provide a gas-impermeable barrier and thus ensure that the caverns are naturally sealed. With a working gas volume of more than 900 million cubic meters, the cavern storage facility in Jemgum, Lower Saxony, is one of the biggest natural gas storage sites in Germany. It can store enough gas to cover the annual consumption of around 700,000
detached family homes. The storage facility is operated by
astora (Company Box 1) and VNG Gasspeicher, with astora marketing a good 80 percent of the total storage capacity. It has been a long haul from the initial test drilling in the 1980s, to the first drilling at the collection point in 2009/2010, to the operating storage facility of today. The automation experts from Rösberg
have supported this process at many stages. It all began with transporting the fresh water supply and shaping the first caverns. To do this, water from the nearby river Ems was introduced through a borehole to a depth of approx. 1500 m, and the cavern was leached over about two years. During this time the pipe string was steadily retracted upwards, so that the cavern “grew” in a cylindrical shape. The water dissolved the salt, and the resulting brine (salt mixed with water) was directed into a settling basin, cleaned and then released into the sea near Rysum. In this way ten caverns, each 400 meters high and filled with brine, have been formed over years. For comparison: the 368-meter-tall Berlin television tower would fit comfortably into one of them (Figure. 1). The first filling of a storage cavern with
gas is also a complex project, taking somewhere between 100 and 120 days.
Figure 3a: Modified plant used for the first gas filling. (Copyright: Rösberg)
Figure 2: Klaus Kerner, process control technology project manager at Rösberg Engineering (Copyright: Rösberg)
Klaus Kerner (Figure. 2) is process control technology project manager at Rösberg Engineering (Company Box 2) and has been concerned with the Jemgum project right from the start. He said: “The filling of the first two caverns with gas was taken on by astora themselves. But as the equipment they leased for this was very expensive, they decided on purchasing the equipment for the other filling and emptying manoeuvres – because removing the brine and filling with gas are processes that go hand in hand. This is where we came in again.” Three used plants were purchased. Each complex consisted of three cabinets (control cabinet, compressor cabinet and electrical distribution cabinet with frequency converter) a degassing tank, measuring instruments and valves, a pump and various pipes for connection to the brine plant (Figure. 3a/b). “We were able to re-use most of the
Figure 1: The ten caverns in the Jemgum natural gas storage facility are each approximately 400 meters high. The 368-meter-tall Berlin television tower would easily fit into one. (Copyright: Niki Hüttner)
24 APRIL 2020 | PROCESS & CONTROL
mechanical components. However, the necessary I&C technology had to be redesigned and purchased. It was also our task to perform the installation and fitting of the instrumentation and control devices and the wiring of the automation components,” Kerner explained. Of course, in this safety-critical environment the control engineering had to take account of the relevant requirements for explosion protection and functional safety. The automation experts developed a completely new concept for the control system of the plant and the safety system. A PCS7 was used for control, and of course it had to
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