New compact compressor solution

The Explorer floating storage and regasification unit (FSRU) upgrade in the Dubai dry dock included several advanced features to improve the services on the vessel, such as new high-pressure vaporisers and a dual-fuel diesel generator power module to provide more fuel-efficient power generation and the world’s first LNG bunker port installed in an FSRU which enables small scale LNG users to take LNG directly. A new state-of-the-art compressor from Neuman & Esser (NEA) increased the maximum regasification send-out capacity from 690 million ft³/d to 1.0 billion ft³/d – an unprecedented milestone for an FSRU.

Upgrading to higher send-out rates

In 1975, the city of Dubai had 183 000 inhabitants; 20 years later, in 1995, it had 674 000 inhabitants. Today, it is the most populous city in the United Arab Emirates (UAE) and its infrastructure must regularly be adapted and extended in accordance with this development.

With 2.5 million inhabitants and an annual influx of up to 14 million foreign tourists, Dubai has a huge hunger for energy, including the desalination of seawater and air conditioning.

The Dubai Supply Authority (DUSUP) is responsible for supplying energy to the Emirate. It ensures the energy supply of the Emirate using natural gas pipelines from Abu Dhabi and Qatar. In the long-term, however, DUSUP is looking for new energy sources. In this context, DUSUP completed the construction of an LNG import terminal in the port of Jebel Ali in 2010, enabling the import of LNG via an FSRU. The FSRU is a converted LNG tanker which is permanently moored, providing natural gas for power generation and other industrial use. Jebel Ali, located 35 km southwest of the city of Dubai, is the world’s largest man-made harbour and the largest and busiest port in the Middle East.

The advantage of LNG is its low volume, which simplifies storage and transport. LNG has only about six hundredths of the volume of gaseous natural gas. The liquefied, -160°C gas is heated in the FSRU and subsequently transported onshore in a gaseous status. The benefit of an FSRU is the significantly lower investment costs than a land-based terminal. In addition, the floating solution can be implemented within one to three years. In comparison, a land-based terminal typically takes four to six years to develop. A dockside or offshore regasification facility requires less land use than a land-based terminal, thus minimising environmental impact on the surrounding environment.

In order to meet the increasing demand for natural gas in the Emirate, DUSUP entered into a long-term agreement with US company Excelerate Energy in 2014 for a larger and more efficient FSRU to replace its existing regasification vessel. Excelerate’s existing FSRU Explorer was not only upgraded to achieve send-out rates as high as 1.0 billion ft³/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 docks.

The 290 m long and almost 45 m wide ship has an LNG storage capacity of 151 000 m³. The Explorer covers its own energy requirements with a dual-fuel generator power module, which provides more fuel-efficient power generation for regasification services.

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 exhaust standards in the ports are becoming more stringent worldwide. The upgraded Explorer can therefore also fuel these ships.

Combination of a centrifugal and reciprocating compressor

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 their longstanding partner NEA. Atlas Copco Gas and Process also provided the supervisory control system.

The suction condition from the LNG tanks for the upstream turbo centrifugal compressor GT026T2K2 from Atlas Copco is approximately 1 bar abs. at -140°C. The first two compressor stages permanently compress 5500 kg gas to 6.5 bar with 650 kW drive power every hour. Centrifugal compressors are not designed to produce high pressures; however, they can supply large volumes even at very low temperatures, with no wear. The centrifugal compressor therefore operates permanently.

From there, approximately 1000 kg natural gas reaches the dual-fuel generators for producing electricity or reliquefying gas in the recondenser per hour. In the next step, the two-stage so-called send-out compressor 2TDS130 from NEA supplies approximately 4500 kg of the meanwhile 40°C natural gas at 70 bar each hour. The 700 kW reciprocating compressor runs 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 efficiently 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.

Reciprocating compressors are popular for the highly variable application range. NEA LNG reciprocating compressors cover the major applications for handling LNG, as well as for offshore and onshore plants within the LNG chain.

In order to maintain the critical conditions within LNG tanks, NEA’s boil-off gas (BOG) compressors are used to manage reliable and efficient boil-off of the LNG. Send-out compressors as applied in the upgraded Explorer constantly boost the vaporised LNG for all pipeline networks. The LNG fuelgas compressors from NEA deliver the suction pressure for injecting LNG boil-off for two-stroke and four-stroke engines. NEA LNG compressors provide solutions for a wide range of LNG applications.

Initial performance tests with the newly upgraded FSRU Explorer have demonstrated its improved send-out capacity from 690 million ft­³/d to 1.0 billion ft3/d – an unprecedented milestone for an FSRU. The increase in regasification capacity will allow DUSUP to import more LNG cargoes during the year providing greater flexibility to adapt to market conditions. “The increase in regasification capacity will allow DUSUP to import more LNG cargoes during the year providing greater flexibility for market conditions,” said the US-based company.

Successful integration of two technologies

As for all offshore machines, this system also requires marine classification. In this case, it was granted by Bureau Veritas without any objection. However, this was an easy task, compared to a previous project. The NEA compressor on the Prelude floating LNG (FLNG) platform, the largest swimming factory ever constructed, had to meet the requirements of Marine Class 1A from Lloyd’s Register of Shipping.

Compression from 8.5 to 89 bar is quite easy for an NEA compressor; no matter whether the medium is nitrogen, hydrogen or oxygen, a heavy hydrocarbon, or whether it is wet gas, where the condensate must be separated. A volume flow of 380 Nm³/hr is also effortless for an NEA compressor because the largest 500 series compressors can handle up to 100 000 Nm3/hr. However, for the deployment within the Prelude project, the compressor had to prove that it can withstand wind gust speeds of up to 330 km/hr as well as a maximum wave height of 27.5 m.

For NEA Project Manager Karl-Heinz Hammes, the challenge of closely linking two totally different compressor technologies was greater than merely the technical aspects of the FSRU project. “Coordination with Atlas Copco Gas and Process was collaborative and at eye level”, explains the experienced project manager. “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 colours can even be seen in the meantime: the system is already running in the Gulf of Dubai without any problems.

In collaboration with Atlas Copco Gas and Process and NEA, Excelerate Energy completed the gas-up operation at DUSUP’s Jebel Ali LNG Import Terminal via the FSRU on 31 August 2016. The FSRU gassed-up all five tanks in a 17-hour period due to the increased send-out capacity.

DUSUP’s ability to utilise the FSRU new services will allow LNG vessels departing from regional dry docks to avoid having to travel significant distances to perform this mandatory step in the LNG cargo cycle, making Dubai a full-service LNG hub.

“We are pleased to help in shaping this exciting project and contributing our knowledge and long-term experience,” explains Karl-Heinz Hammes. “Our compressor is only a small, but important part of the Explorer upgrade. However, merely the successful and smooth integration of all components offers DUSUP the outstanding characteristics and thus the ability to become a full-service LNG provider in the region. With the additional features of Explorer, the Jebel Ali LNG Terminal is more than just an import terminal.”

Growing LNG market in Russia

NEA reciprocating compressors for new LNG market orders can also be found on the cryogenic side. One such installation will be made at an LNG terminal in Russia, close to St. Petersburg, on the Baltic Sea. NEA will deliver two 3TVS300 reciprocating compressors with a drive power of 1200 kW at a suction temperature of -160°C.

This also applies to a compact V-type compressor 2TEV1 with 36 kW drive power and hourly more than 800 m³ volume flow that will soon be installed soon in Pskov close to the Estonian border. It will compress BOG from 1.15 to 7 bar abs. at a final temperature of -50°C. A vertical NEA BOG compressor provides the same pressure as the send-out unit in the Middle East, i.e. 6.5 bar abs. in Kaliningrad, the westernmost city in Russia, between Poland and Lithuania. With 21 kW, the smallest NEA compressor offers a little more than 550 m³ volume flow, while the -160°C cold BOG heats up to -10°C.

This article was originally published in LNG Industry magazine. To receive your free copy, click here.