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Cold climate could give Alaska LNG edge Project could require less powerful liquefaction equipment, but facilities would also have to be weatherproofed because of cold Stan Jones Researcher/writer for the Office of the Federal Coordinator
Colder and colder
At Nikiski, the gas would be chilled by passing it through a chain of several coolants, each colder than the one before. The final coolant is so good at its job that the natural gas liquefies as it passes through.
And how are the coolants kept cool?
The coolant refrigeration cycle starts with each coolant in a relatively warm gaseous state. It’s compressed to a fraction of its original volume, which heats it further. Next, the hot, pressurized gaseous coolant passes through a condenser - or heat exchanger - here heat is transferred away and the coolant becomes a high-pressure liquid. The coolant is then allowed to expand, which further reduces its temperature.
Now a cooler low-pressure liquid, it passes through an evaporator - another type of heat exchanger - where it absorbs heat from the natural gas and then evaporates back to its original relatively warm gaseous state, ready to start the cycle over.
It’s similar to the refrigeration cycle of the coolant - Freon, usually - inside your kitchen fridge. It, too, starts out as a relatively warm gas. Then it’s compressed and run through a condenser - that assembly of fins and tubing on the back of the refrigerator. There, it cools and condenses into a pressurized liquid and gives up its heat to the air within your house.
Then it’s run back into the refrigerator and through an expansion valve, which cools it to a low-pressure liquid. Then it’s circulated through a heat exchanger as the refrigerator’s warm interior air - warmer than the Freon, at any rate - is blown through the heat exchanger. The interior air cools off to keep that lettuce crisp, the Freon heats up and evaporates back to a gaseous state inside the tubing, and the cycle beings anew.
In a multi-coolant LNG plant, all coolants may not be treated alike. In many installations, only the condenser for the first coolant transfers heat to the outside air. For subsequent coolants in the chain, the heat exchangers are inside the reservoir of that first coolant. In such cases, the first coolant is the sole medium for transfer of heat from natural gas to outside air - the essence of the liquefaction process.
After the natural gas leaves the final coolant reservoir in the desired liquid state, it is pumped into storage tanks to await shipment to market on LNG carriers.
Most of the efficiency benefit in this complex and interlooping process comes as the initial coolant passes from the compressor to its air-cooled condenser. The colder outside air means less pressure in the line to the condenser, and that means the turbine-driven compressor doesn’t have to work as hard to push against it.
With ambient air at 36, rather than 80, the Alaska plant’s 44-degree advantage comes into play not just on the first pass, but also during each subsequent loop the initial coolant makes through the system.
Finally, there are efficiencies connected with the huge, insulated LNG storage tanks. Because no insulation system is perfect, the liquefied gas absorbs some heat from the surrounding environment and as a result part of it evaporates. This gas is called boil-off gas.
If, as at Nikiski, the surrounding environment is colder, less of the gas boils off.
What gas does boil off must be reliquefied so that it can be returned to the tanks. And reliquefaction of boil-off gas, as with incoming gas, is more efficient at lower air temperatures.
Ultimately, the higher output of gas turbines, the higher effectiveness of the air-cooled condensers, and the fuel gas savings that all result from Alaska’s colder ambient temperatures produce lower costs and improved energy efficiency.
More advantages for Alaska project There are some savings on capital expenditures because less-powerful equipment can be used in some places in the production chain, though that is offset at least to some extent by the higher cost of building and running things in cold climates.
For example, some of the plant’s equipment would need to be toughened and specially designed to work in very cold temperatures. And any space where people need to work must be enclosed, insulated and heated; in the Middle East and other warm regions, some of that same work can take place in open-air sheds.
Moreover, some aspects of an LNG plant’s construction and operation don’t much depend on temperature. A storage tank big enough to hold a given amount of LNG must be the same size, whether in Nikiski or the Middle East. And the sizes of pumps and pipes big enough to move a given amount of LNG per day from liquefaction to storage or from storage to tanker don’t change with temperature.
Even though colder temperatures don’t reduce costs for every piece of the project and its construction, it’s one of the quantifiable advantages for Alaska LNG.
The project has another big advantage, as well. The liquefaction site is closer to Asian markets than much of the competition.
Nikiski is about 3,800 miles from Yokohama, a major port in central Honshu, Japan’s main island, and home to Tokyo and several LNG import terminals. The proposed Kitimat project in British Columbia is almost 4,500 miles from Yokohama, and Russia’s huge Yamal project in the Arctic is not only about 7,800 miles away from Yokohama but also ice-locked for much of the year.
On the other side of the ledger are the disadvantages of the cost and difficulty of building and running facilities in a cold, remote locale like Alaska. Another issue is the fact that the Alaska project - unlike many of its competitors around the world - would need an 800-mile pipeline to get gas from the fields to the liquefaction plant.
Calculating the financial implications of those advantages and disadvantages will go a long way toward helping the North Slope producers - ExxonMobil, BP and ConocoPhillips - determine if they have a project that can compete on price per million Btu of delivered gas.
Long road ahead The sponsors of the $45 billion to $65 billion Alaska LNG project will take a few years for engineering, design, environmental work and all the other tasks that come with such an enormous undertaking.
First, a lengthy process of engineering and design has to take place, as does a complicated permitting process with federal and state agencies. The project would then be ready for a final investment decision, after which, if the sponsors proceed, construction could begin. The earliest LNG deliveries could start would be 2023-2024.
But if that day does come, it could mean billions of new dollars for the state of Alaska, a longer life for the North Slope oil fields, and a major bump in oil-industry employment in the state.
And, for once, the fact that Alaska is colder than most of the rest of the world could actually help a little.
Part 1 of this story ran in the July 27 issue.
Editor’s note: This is a reprint from the Office of the Federal Coordinator, Alaska Natural Gas Transportation Projects, online at www.arcticgas.gov/alaska-frigid-climate-could-give-state-edge-lng-market
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