Pictures of the Future      Spring 2008

A hook the size of a sumo wrestler glides silently down from the factory roof. Bearing the legend "50 t," it is strong enough to pick up a tank. A worker with a remote-control unit guides the hook until it hangs above a steel contraption that’s about as big as a tractor. The mechanism looks something like a tuba, complete with mouthpiece, which has somehow become too large and angular in shape. Once the hook has been securely fastened, the colossus is gently lifted and swung over a steel frame as big as a house. This is the test bed where the oversized tuba—in reality a gigantic industrial compressor—is to be put through its paces.

Everyone is familiar with the hum of the compressor in the refrigerator at home, and some people have small compressors in their garages for pumping up car tires. However, the unit being built and tested here at the Compressor Works of the Siemens Oil & Gas Division in Duisburg, Germany—in the vicinity of the blast furnaces of the Rhineland steel industry—is on a completely different scale. Inside the compressor, person-sized impellers suck in cubic meters of air or gas and compress it to 50 bars or more—the kind of pressure found at depths of 500 meters underwater.

Many industrial sectors, including the chemicals industry, manufacturers of plastics and fertilizers, and, above all, the oil and gas industry, need compressed air and gases, including air separation plants the size of factories.  Each compressor from Siemens’ Duisburg plant is a unique example of engineering design. The compressors are precisely tailored to the industrial process in question, its operating temperatures and pressures, the corrosive properties of the gases used, and the required volume flows.

Liquefied Gas. "We’re able to select from a wide range of components and can thus put together exactly the right product," says Dr. Thomas Mönk, director of Product Development and Technical Coordination at Siemens Oil & Gas in Duisburg. Responsible for industrial gas and steam turbines as well as compressors, Mönk is referring to the immense fund of knowledge that Siemens has accumulated in this sector over the years. This includes the use of different compressor types and impellers featuring a wide range of geometries and materials such as corrosion-resistant metals and many kinds of special alloys.

Siemens’ compressors also benefit from unique software and design tools with which specialists bring them to life in the virtual world long before they leave the Duisburg facility.

Recently, Mönk and his colleagues have focused on one industrial process in particular: the compression and liquefaction of natural gas to make LNG—liquefied natural gas. Thanks to extremely rapid growth in demand for energy over the last few years, LNG has become an energy carrier worth taking seriously. LNG is nothing other than natural gas that has been liquefied to turn it into a manageable volume for transport purposes. This involves cooling the gas to a temperature of -163 °C, a process that reduces its volume by a factor of 600.

Construction of a liquefied natural gas plant is an interesting proposition for all natural gas fields in remote regions—places such as Nigeria, Venezuela, Qatar, Indonesia, and Australia, for example. As a rule, pipelines are unprofitable at lengths upward of 3,000 km. At that point it becomes cheaper to convert gas into LNG and ship it to the consumer in huge tankers.

According to the International Energy Agency (IEA) in Paris, global demand for natural gas is set to increase by about 3.5 % a year until 2020. By then, natural gas will cover one-quarter of the world’s energy needs, compared to around 20 % at present. Although the non-liquefied variety still accounts for the lion’s share of gas sales, LNG is making steady inroads and, according to the IEA, is destined to increase its share of the world’s natural gas market from the current figure of 7 % to 10 % by 2010. What’s more, liquefaction and transport of LNG are also energy-efficient.

North of the Arctic Circle. On the face of it, liquefied natural gas production is breathtakingly simple. The gas is first cooled and then transported in liquid form. Yet the dimensions of liquefaction facilities are gigantic. Norwegian energy company StatoilHydro is currently commissioning the first LNG plant north of the Arctic Circle, on the island of Melkøya, near the port of Hammerfest.

Siemens is involved in the project. Following the growing pains so often encountered in a pilot project of this magnitude, the Melkøya plant commenced operation in January of this year and is scheduled to reach full capacity in 2009. In the plant—which is known as Snøvhit, or Snow White—natural gas is pumped into a so-called cold box, a 40-m heat exchange tower. Here, the natural gas is cooled in a step-by-step process and finally liquefied.

Cooling is provided by a refrigerant that flows through the heat exchangers in separate cycles driven by huge compressors. This functions in much the same way as does a refrigerator. The refrigerant is compressed, releasing its warmth to the environment. In subsequent steps, as it expands again, its temperature falls, and the refrigerant extracts more and more of the heat from the natural gas.

Impellers for carbon dioxide and liquefied natural gas compressors (above) are tested at Siemens’ Duisburg plant (below left). Below right, a complete compressor

Yet before the gas is liquefied, any impurities must be removed—especially sulfur compounds—that would interfere with the liquefaction process. This takes place by means of adsorption, using large surfaces of special materials, and absorption in chemical solutions. Natural gas also contains as much as 10 % carbon dioxide, which has to be removed from the liquefaction cycle, because it would otherwise disrupt the cooling process.

Siemens Oil & Gas in Duisburg has supplied a compressor that squeezes the carbon dioxide to around 200 bar in a separate cycle, allowing it to be sequestered. This will mean a reduction of around one million tons of the greenhouse gas emitted to the atmosphere every year once the plant has begun to operate at full capacity.

Another aspect of the LNG process is the recapture of so-called boil-off gases. The refrigerated LNG is stored in large insulated tanks until it is ready for shipment in tankers. As in a thermos bottle, there is a minimal temperature exchange between the liquefied natural gas and its surroundings. Heat gets into the tank and causes a small amount of the LNG to vaporize. This so-called boil-off gas is fed back into the cooling cycle or burned as fuel to power the gas turbines. Once again, the compressor for this part of the process is supplied by Siemens Oil & Gas, the market leader for boil-off compressors.

StatoilHydro plans to ship six billion cubic meters of LNG a year around the world—primarily to the U.S., but also to Spain and France. Once at its target destination, the liquefied natural gas is converted back into natural gas—a process that simply involves warming and expanding it—and then fed into the national supply network.

Today, 12 countries around the globe operate liquefied natural gas facilities, the largest of which is situated on the Persian Gulf, where around one-third of the world’s natural gas reserves are located. To date, all of these facilities have used gas turbines to power the huge refrigeration equipment. As is the case in a gas-fired power plant, these turbines are powered by natural gas. They are then connected to huge compressors, which drive the actual liquefaction process in the cold box. On the island of Melkøya, however, StatoilHydro and Siemens have opted for an alternative system: an all-electric ("E-LNG") train.

^{Snøvhit, the world’s first all-electric LNG plant, was shipped from Spain to northern Norway. The liquefaction facility features gigantic CO₂ compressors and electric motors (pictured below)}

Hammerfest Colossus. On Melkøya, the compressors for the principal cooling cycle are powered not by gas turbines but rather by huge electric motors from Siemens. One of the motors has an output of 32 MW and two have an output of 65 MW, making them the largest electric motors ever built (Pictures of the Future, Spring 2006, Electric Machines – Trends). Several motors are required, because in an LNG plant a number of drive and compressor trains operate in parallel in order to keep the cooling steps on track.

The motors, which are the size of a locomotive, were produced in Siemens’ Berlin Dynamo Works. "There are big advantages to an all-electric LNG train," explains project manager Klaus Ahrens. "Traditional gas turbines can only operate at fixed rotational speeds, are heavily dependent on the ambient temperature, and can’t really be regulated. They thus determine the performance of the compressor, which means you can only control the output of LNG to a limited extent." That makes it difficult to respond flexibly to changes in production volumes of natural gas or market demand for LNG. "Electric motors, on the other hand, are simple to regulate and can also be water-cooled, which makes them largely independent of ambient temperatures," adds Ahrens.

Electric motors have one more big advantage: they are virtually maintenance free. Gas turbines have to be shut down several days a year for routine maintenance, which has a significant impact on output at an LNG plant. "This can mean daily losses of millions of euros," says Ahrens. By contrast, electric motors can operate for as long as five years nonstop. In addition, Ahrens adds that whereas the efficiency of a gas turbine is generally around 35 %, an electric motor can manage up to 95 %. And once the efficiency of the power plant that is used to generate the electricity is also taken into account, the facility’s overall efficiency turns out to be around 52 %. This means reduced raw materials consumption and CO₂ emissions.

But electric motors are of little help in LNG areas that—as is often the case—are in areas too remote to have access to grid power. With this in mind, Siemens offers a standalone solution featuring a dedicated power plant to provide the requisite electricity. That may sound excessive, but according to Siemens, the costs of such a power plant are recouped within just a few years. What’s more, even conventional LNG plants require electricity, which in remote areas comes from generators powered by gas turbines.

In fact, the benefits of the stand-alone solution are substantial, not least because such a power plant operates in a combined cycle process, which is substantially more efficient than a solitary gas turbine in an LNG plant. Svein Nordhasli from StatoilHydro knows that the E-LNG plant has broken new ground. He’s therefore glad that Siemens technology was used in the project. "Siemens showed a great deal of commitment, particularly during the motor test phase," he says. "The company is very aware of its responsibilities, no matter whether we’re talking about individual components or complete systems."

All-Electric Solution. "The oil and gas industry is watching the Snøvhit project with       great interest," says Ahrens. "It’s a highly conservative sector as far as new technology is concerned. Mechanical solutions have been used for decades, but the fully electric system represents a sea change." Ahrens adds that the new technology will need to prove its reliability over a full year before other oil and gas companies climb on the bandwagon.

In spite of such industry hesitation, Siemens was recently awarded a contract for an E-LNG plant for Energy World Corporation on the Indonesian island of Sulawesi, where work is scheduled to commence next year. Siemens is to supply not only the main compressors for Energy World’s liquefaction plant and the powerful electric motors to drive them, but will also provide the entire power supply system, including the frequency converters, which help the power network to remain stable when the motors are switched on.

"When you flip a light switch, you know the fuse isn’t going to blow," says Ahrens. "But when you directly connect a 27-MW motor to the supply, it can bring down an entire network if you don’t have the right equipment in place." The Sulawesi plant will be supplied by a gas-fired power plant sited 40 km away.

Mobile Production Plants. All in all, Siemens is getting involved in the LNG market in a big way. Indeed, the company has an eye on more than just the major projects. Theodor Loscha, a leading LNG expert in Duisburg, is now looking at systems for smaller gas fields that, unlike Melkøya, will not be pumping gas for the next 30 years.

"It’s also possible to build an LNG plant on a floating platform—a barge—that can be towed to the next gas field as soon as the first goes dry," he explains. This reusability would make it commercially viable to tap smaller natural gas fields, since an LNG plant is a very expensive piece of technology. "Building an LNG plant is an incredibly complex project involving lots of partners working together over a long period," explains Loscha.

Small and flexible LNG plants are therefore an enticing prospect. That said, they need to be designed in such a way that they can be easily adapted to the requirements of a new location with, for example, different gas compositions or production volumes. "Whatever the solution here, an E-LNG-based concept would seem to be ideal for mobile LNG plants—although Siemens can always, if the client wishes, supply other types of drives, such as steam turbines," Loscha explains. This is because the entire process has to be accommodated in a very small area. On a single floating platform, electric motors are much easier and, in all likelihood, safer to integrate than gas turbines, with their fiery hearts. Yet irrespective of just how LNG plants will look in the future, Loscha is confident that Siemens, with its portfolio of powerful gas turbines, electric motors, electro-technology know-how, and, most of all, compressors, is ideally positioned to exploit this developing market.
                                                                                                                 Tim Schröder