LNG Project in Dubai
With 2.5 million inhabitants and an annual influx of up to 14 million foreign tourists Dubai has a huge hunger for energy, among other things for desalination of sea water and air conditioning.
The company DUSUP is responsible for energy supply to the Emirate. In 2010, DUSUP built a terminal, which enables the import of liquefied natural gas (LNG) via a Floating Storage Regasification Unit (FSRU). The FSRU is a converted LNG tanker which is permanently moored. The liquefied, -160°C cold LNG is heated here and transported onshore in a gaseous status.
Due to the increased energy demand in Dubai, DUSUP hired Excelerate Energy to provide a larger and more efficient FSRU. Excelerate’s existing FSRU Explorer was not only upgraded to achieve send out rates as high as 1.0 Bcf/d, but it also received additional upgrades. The FSRU now includes an LNG bunker port to service small-scale LNG offtakers, and can also provide gas-up and cool-down services to LNG vessels leaving dry dock.
The 290-meter-long (950ft) and almost 45-meter-wide (150ft) ship has an LNG storage capacity of 151,000 cubic meters. The Explorer covers its own energy requirements with dual fuel generator sets. Engines which can use two fuels such as clean natural gas and cheap diesel are defined as dual fuel engines. This system is currently being implemented in shipbuilding because the exhaust standards in the ports are becoming more stringent worldwide. The upgraded Explorer can therefore also tank dual fuel ships.
Combination of Centrifugal Compressor and Recip
In order to be able to feed the natural gas into the national grid, it must be adapted to the network operator’s requirements. The feeding system for the local pipeline network consists of a combined centrifugal compressor and reciprocating compressor, a joint project by Atlas Copco Gas and Process together with longstanding partner NEUMAN & ESSER (NEA). Furthermore, Atlas Copco Gas and Process, the leading, internationally active industrial company with many years’ experience in the LNG business, provided the supervisory control system.
The suction condition from the LNG tanks for the upstream turbo centrifugal compressor from Atlas Copco is about 1 bar abs. at -140°C (-220°F). The first two compressor stages permanently compress 5,500 kg/h gas to 6.5 bar.
From there, some 1,000 kg/h reach the generators for producing electricity or reliquefying gas in the recondenser. In the next step, the two stage so called send out compressor from NEA supplies some 4,500 kg/h of the 40°C (104°F) natural gas at 70 bar. The recip is running in during energy requirement peaks, loading processes as well as the entire winter period.
The NEA compressor offers the high flexibility of this particularly compact solution. It also works highly efficient under variable operating conditions; its effectiveness hardly changes. Therefore, this combined system consisting of two different compressor principles is ideal for large throughput quantities and non-continuous conditions.
Successful Integration of Two Technologies
As for all offshore machines, this system also requires marine classification. NEUMAN & ESSER definitively has exceptional experience in marine classification. The NEA compressor on the floating liquefied natural gas platform Prelude, the largest swimming factory ever constructed, had to meet the requirements of Marine Class 1A from Lloyd’s Register of Shipping. For this purpose, the compressor had to prove that it can withstand wind gust speeds of up to 330 km/h (205 mph) as well as a maximum wave height of 27.5 m (90ft).
For NEA Project Manager Karl-Heinz Hammes, the challenge was greater than merely the technical aspects of the FSRU project: “Coordination with Atlas Copco Gas and Process was collaborative and at eye level. Nonetheless, it is not easy to integrate both different systems, a centrifugal compressor and a recip, into one configuration. That requires a lot of agreement and communication between everyone involved.” The fact that Karl-Heinz Hammes and his team mastered this task with flying colors can even be seen in the meantime because the system has already been running in the Gulf of Dubai without any problems for several weeks (location of the vessel).
For a new LNG market order, the NEA recips will be found on the cold side this time around. Installation will take place at an LNG terminal in Russia, close to St. Petersburg. NEUMAN & ESSER will deliver two recips at suction temperature of -160°C (-256°F).