Cold facts about a hot commodity: LNG

Development of liquefied natural gas includes Nobel Prize, anxiety about US air defense, disaster that destroyed part of Cleveland

Bill White

Researcher/writer for the Office of the Federal Coordinator

Liquefied natural gas is an odorless, colorless, non-toxic, non-corrosive and non-flammable form of methane. As fuels go, it’s pretty cool.

Actually, LNG is colder than Antarctica on winter solstice. Methane is chilled to about minus 260 degrees — a temperature that transforms it from a vapor to a liquid, compressing its volume 600 times to make it more economical to store for later use or to ship long distances from countries endowed with natural gas to those starved for the fuel.

That’s the broad story of LNG — a case of Adam Smith capitalism at work.

But in the details, the LNG story is a tale of brilliant physicists, savvy government engineers and entrepreneurial risk takers. LNG’s back story includes a Nobel Prize, anxiety about U.S. air defense and a disaster that destroyed part of Cleveland.

LNG touches only a small portion of the world’s gas supply, but it’s the fastest-growing portion. Since 2000, global demand for LNG has grown 140 percent and now accounts for roughly 10 percent of the methane consumed worldwide. The rest moves to market by pipeline.

LNG is exported from 19 countries, including from one U.S. plant in Nikiski, Alaska.

Since 2006, Norway, Russia, Yemen, Peru, Angola and Equatorial Guinea all have started making LNG, while Qatar, Nigeria, Australia, Oman and Indonesia have expanded production.

Qatar’s expansion was an act of sheer audacity. Qatar tripled its LNG production capacity to over 80 million metric tons a year — about 11 billion cubic feet a day — leaping past Malaysia and Indonesia as the world’s largest LNG maker. Last year Qatari plants exported almost one-third of the LNG traded across the globe. In the mid-2000s, with construction under way, Qatari officials thought they’d be selling much of their LNG to the United States. The Lower 48 shale-gas boom blew apart that plan. But last year, as Japan idled nuclear power production after the Fukushima disaster, Qatari exports to Japan soared 56 percent over their 2010 level, according to the BP Statistical Review of World Energy. That dulled Qatar’s pain of losing the U.S. market.

Meanwhile, more countries are clamoring for LNG to quench their growing energy appetite.

Since 2006, China, Brazil, Chile, Dubai, Kuwait, the Netherlands and even Canada and Mexico all became first-time importers of LNG. They joined the mainstay LNG consumers of Japan, South Korea and Taiwan, according to the International Group of Liquefied Natural Gas Importers.

In all, 25 countries took LNG shipments last year, the gas importers group said.

As the world’s demand for LNG grows, more locations are mulling entry into the production game. Export projects in Western Canada, Eastern Africa, Russia and the U.S. Gulf Coast are under consideration.

One other possible contender: Export of LNG made from Alaska North Slope gas. The main North Slope producers — ExxonMobil, ConocoPhillips and BP — jointly are at an early stage of considering such a project.

How it works

And for decades LNG tankers — essentially massive thermos bottles that keep the gas cold and liquid — have sailed the oceans safely.

Like many great inventions, liquefied natural gas emerged as an industry via a progression of events over many years, responding to both commercial and geopolitical pressures.

A key development was learning methane’s “boiling point,” a temperature below which methane is a liquid and above which it’s a vapor.

Most people likely are familiar with the boiling point of water: 212 degrees. Heat water above that temperature and the liquid becomes a vapor.

Methane’s boiling point is about minus 260 degrees. Above that frigid temperature it’s a vapor. Below it and you have a liquid.

But liquefying natural gas involves more than superchilling it and maintaining the temperature.

That’s because a natural gas stream rising out of the ground contains more than just methane, although methane usually is the main component. The ethane, propane, butane, pentane, carbon dioxide, water and other components each have separate boiling points.

Ethane liquefies at minus 127, propane at minus 44, butane at plus 31 degrees, and so on. Like water at 32 degrees, these gases also have “melting points,” a temperature below which they become solid. (Dry ice is nothing more than solid carbon dioxide, whose melting point is minus 109.)

These gases have different boiling and melting points because although they’re all hydrocarbons — composed of hydrogen and carbon atoms — the number of atoms differs. The more carbon atoms a molecule contains, the heavier it is. That weight determines the temperatures and pressures that make the gas a vapor or liquid.

Methane has the fewest carbon atoms — one — so it has the coldest boiling point of these gases. If the entire produced natural gas stream were liquefied, some components — such as butane with its four carbon atoms and pentane with its five — would freeze solid before the methane vapors got cold enough to become liquid.

Chilling the entire gas stream to minus 260 to liquefy methane thus could produce a slushy slurry of product that would muck up the machinery. This is why the heavier hydrocarbons mostly are stripped from the gas stream before liquefaction.

The process

Step one: Clean the natural gas stream so that mostly methane is being processed. The residual ethane and other components left behind after processing are in quantities too small to matter.

Sometimes this cleansing occurs before the gas reaches the liquefaction plant. More typically cleansing occurs at the plant.

Buyers in Japan and Europe typically like their LNG to be spiked with a little ethane or other carbon-rich gases because their mainstream gas burns hotter than mainstream gas in North America. Ethane, propane, butane, etc., have higher Btu contents than methane and serve as the spiking agents.

Step two: Superchill the methane.

A variety of techniques will liquefy methane. A Pennsylvania company called Air Products licenses the technology that dominates the industry.

Air Products uses several variations on the same process. Essentially, it starts by using propane to precool the methane. Propane is compressed and condensed, then its pressure is eased in steps to provide refrigeration that cools the methane. (Gas warms as it is compressed and then cools as the compression eases. This principle is applied throughout a typical liquefaction process, similar to an air conditioner where warm air passes over coiled tubing filled with a cold gas.)

Next, the cooled methane enters the main stage, a heat exchanger where the gas comes in contact with a blend of refrigerants that transforms the methane vapor into a liquid. Air conditioners work in a similar way: warm air passes over coiled tubing filled with a cold gas.

A new variation uses nitrogen as a final superchilling refrigerant. This allowed much bigger LNG plants to get built, and it partly explains how Qatar could construct so much capacity in recent years.

A technology that’s a distant second in the market to Air Products’ is licensed by ConocoPhillips. The company’s Nikiski, Alaska, plant as well as plants in Trinidad and Tobago, Egypt, Angola, Equatorial Guinea and one site in Australia use it.

ConocoPhillips routes cleansed methane first into a propane heat exchanger to initially drop the temperature. Ethylene is used to drop the temperature more (you can make ethane colder than propane before it boils into a vapor). Then the gas enters a methane cold box connected to mighty compressors to cool the gas to near a liquid state. A final “flash blast” finishes the job.

Most LNG plants have on site more than one processing unit — called trains. The trains operate independent of each other, running in parallel to liquefy methane. Qatar hosts the world’s largest trains — the biggest can handle about 1 billion cubic feet of natural gas per day. Qatar’s most massive plant, at the Ras Laffan complex, features two such trains plus four smaller ones that together can process about 5 bcf a day. That’s about twice the volume as has been discussed for an LNG plant that could process Alaska North Slope gas. Alaska’s Nikiski plant is relatively small, with capacity to handle about 200 million cubic feet a day.

One final point about liquefying methane: About 10 to 15 percent of the gas gets consumed during the process. Much of it to run the plant’s turbines, compressors and other machinery.

Step three: Store the LNG until it’s shipped to market. Special insulated metal tanks keep the gas liquid. A small fraction will “boil off” — warm into a vapor — and this gas can be reliquefied or used to power the plant.

Storage tank dimensions vary widely, depending on whether the LNG is stored for truck fueling, peak shaving or import-export. The largest storage tanks stand as tall as a 14-story building (about 170 feet tall), are nearly as wide as a football-field length (280 feet in diameter) and can hold up to 200,000 cubic meters of LNG — the equivalent of roughly 4 billion cubic feet of vaporous methane, or about one-15th of daily U.S. gas production last year. In short: They can be big.

Step four: Ship the gas. Special tankers with insulated chambers keep the gas below minus 260. Again, a small volume of liquid methane vaporizes on the trip to market; this gas typically is used to power the ship or is reliquefied.

At the end of 2011, 360 ships comprised the global LNG fleet, according to the International Gas Union. Ships typically get built in tandem with LNG plants and get contracted to sail between the plant and its customers. Just as the capacity to make LNG has skyrocketed in recent years, so has the tanker capacity, growing 150 percent since 2006, the IGU said.

The average tanker capacity is about 3.1 bcf of gas (after the liquid gets converted back into a vapor). South Korea is the big builder of tankers. An average one can cost at least $150 million. The largest tankers were built for the Qatar expansion. They can carry about 5.5 bcf, but the tankers are too big for some LNG receiving ports.

Step five: Convert the liquid back into a vapor, called regasification.

This happens in the LNG destination port. LNG is offloaded into storage tanks. The LNG then is warmed into vapor as needed before entering the local gas pipeline system.

Part 2 of this story will run in the Nov. 4 issue of Petroleum News. Editor’s note: This is a reprint from the Office of the Federal Coordinator, Alaska Natural Gas Transportation Projects, online at www.arcticgas.gov/lng-cold-facts-about-hot-commodity.