An invisible gremlin is poised to invade homes and business across America and tinker with their gas appliances. The gremlin is liquefied natural gas (LNG), and its tool for tinkering is the unpredictable stew of hydrocarbons it contains.

More than 160 million gas appliances are installed in residential and commercial buildings in the U.S. Some are recent purchases. Some are decades old. Still more purchases will occur in the days, weeks and years ahead. All are designed with certain expectations about the fuel that will power them. And all are built according to the appliance industry’s established standards for safety and reliability. But, what if these appliances were to break down prematurely, or cause safety issues, and not because of faulty design or manufacture, but because of the gas that powers them?

That is a potential scenario over the next couple decades as more appliances encounter LNG, with more and more of it being imported, and with no federal standards in place as to gas composition. LNG supplies can vary in their chemical content, and there is concern about the ability of gas appliances being able to handle the different contents, an issue known as LNG interchangeability. The percentage of LNG in the supply chain is low and has little effect on gas appliances so far, but that is likely to change.

The problem is that imported LNG generally has a higher heat content than domestic gas, which may cause problems for gas appliances. The higher the energy content, the hotter the flame, leading to the firing of an appliance at a higher rate than for which it was designed. Frank Stanonik, chief technical advisor for the Gas Appliance Manufacturers Association, says introducing LNG with “certain extreme characteristics” can cause failure in gas burners, ignition systems and the safety components designed to detect over firing conditions.

Basic burner operation concerns include incomplete combustion, yellow tipping, flame lifting, flashback, higher emissions of NOx, and increased production of carbon monoxide. Durability and reliability concerns include premature failure of components because of overheating or excess stressing.

From a safety standpoint, Stanonik says that there is concern about proper ignition sequence and timing and overheating issues because of the gases that burn hotter. The extent of the danger, up to and including explosions, is not completely understood and additional research is needed.

Indeed, the U.S. Federal Energy Regulatory Commission says that appliances designed for domestic gas supply are not interchangeable with imported gas. A 2005 study of natural gas interchangeability by the NGC+ Interchangeability Work Group, reported that a number of interchangeability issues that could occur.

In appliances, imported gas can result in soot formation, elevated levels of carbon monoxide and pollutant emissions, and yellow tipping. It can also shorten heat exchanger life, and cause nuisance shutdowns from extinguished pilots or tripping of safety switches. Flame stability issues such as lifting are also a concern.

In commercial boilers, furnaces and heaters, it can result in degraded performance, damage to heat transfer equipment and noncompliance with emission requirements.

Imported gas can also negatively affect other gas powered equipment, such as natural gas engines and turbines.

Expected growth

More LNG will be imported in the future.

The U.S. demand for natural gas exceeds supply and has for more than a decade. While natural gas usage is increasing, U.S. production is falling. According to the U.S. Energy Information Administration, the U.S. could face a gap in supply of natural gas of about 5 trillion cu. ft. (tcf) by 2020. The EIA predicts that natural gas production will grow from 19.1 tcf in 2000 and 28.5 tcf in 2020. However, demand is expected to grow from 22.8 tcf to about 33.8 tcf in that timeframe. (EIA's numbers are slightly higher than GAMA, which predicts LNG demand to grow to 31.4 Tcf by 2020.)

That gap means more imports, including imports of LNG. In the grand scheme of things, natural gas and LNG usage are small. Natural gas accounts for about 25 percent of all energy consumed in the U.S., and LNG represents only 1 percent of natural gas use. However, LNG usage is expected to grow, and by 2025 LNG may account for about 14 percent to 17 percent of the U.S. natural gas supply, according to the Department of Energy.

Domestic natural gas is primarily methane, but the LNG’s exact composition differs depending on its source. LNG may have other compounds such as ethane, propane and heavier liquid hydrocarbons, according to the Center for Energy Economics, and the quantities will determine how the gas burns. Suppliers could standardize the content based on standards for the particular market, but the U.S. does yet not have a uniform standard that addresses natural gas quality.

No crisis, yet

Enlarge this picture Fig. 1. The consumption of natural gas in 2003. Source: GAMA

Stanonik says that appliances can handle the LNG that is currently distributed, but is not as certain in the future as imports grow. Currently, LNG is mixed with natural gas, especially usually during peak period.

The Wobbe Index is the main indicator of the interchangeability of gases (see sidebar). If two fuels have the same Wobbe Index, it will theoretically burn the same. Variations up to about 4 percent are not noticeable, but outside of that upper and lower control limit problems can occur.

Historically, natural gas in the U.S. had a Wobbe number in the range of 1,200 to 1,400, with an average of about 1,345 and a heating value of 1,035 BTU per cu. ft., says Stanonik. He says that recent studies have shown BTU ranges from as low as 970 BTUs per cu. ft. and up to about 1,080 BTUs, or a spread of about 100 BTUs per cu. ft. (a higher Wobbe number equates to a higher BTU value).

As an example, if a water heater is set to fire at 1,000 BTUs per cu. ft., the firing range is maybe about 40,000 BTUs per hour. However, if the gas has a heating value of 1,100 BTUs per cu. ft., the appliance will continue to burn at the same rate, not knowing the difference. As a result, it will burn 44,000 BTUs per hour instead of the expected 40,000 BTUs.

Currently, there are more than 100 LNG facilities in the U.S., most of them built between 1965 and 1975 to serve the needs of local utilities that set their own guidelines.

For instance, Stanonik points to the Washington Gas Light Co. facility in suburban Washington D.C. The utility researched the needs of its customers and now specifies the composition of its LNG.

FERC says that additional facilities may be built. Plans for 40 LNG terminals are either before FERC or under discussion by industry executives. FERC suggests that the number of terminals that will actually be built varies, with potentially only 12 of the proposed terminals getting built. With fewer terminals, more pipelines will be needed. Pipelines are limited in their ability to mix higher BTU LNG with lower BTU LNG.

Stanonik says that the fear down the road is that the offshore LNG will be brought in the country and distributed through transmission lines that ferry the gas across the country. While before LNG was specific to one region and geared to that region’s historical uses, future LNG may end up anywhere in the U.S.

Design issues

Enlarge this picture Fig. 2. Use of both natural gas and LNG is expected to continue rising over the next two decades. Source: GAMA

The LNG issue poses a dilemma for the appliance industry. Knowing what lies ahead, some might argue that appliance design engineers should start designing gas products that can handle hotter firing. But even if they did, that would not solve the problem about what to do with the millions of gas appliances already in the field. Even if it were practical to retrofit all gas appliances already in place, the concept raises two important questions. Retrofit to what BTU content? Without standards, the BTU content of LNG might change again. The other, more important question is who would pay for the retrofit.

GAMA’s position on that issue is quite clear. “You don’t fix the appliance,” says Stanonik. Instead, he says the answer is don’t put that gas in the pipeline to begin with.

LNG composition needs to be standardized along the supply chain, before it gets to the appliance.

Currently, there are no U.S. standards regulating LNG content. Other countries, most notably Japan, have standards that gas suppliers must meet. GAMA and other groups have lobbied FERC and the DOE to develop the standards based on historical usage, but neither body has developed national specifications so far.

FERC has been studying the issue, but has declined to establish nationwide LNG specifications. In July, FERC issued a policy statement that lets each interstate gas pipeline and its customers work out quality standards for gas the pipeline will transport, establishing a case-by-case approach to the issue.

GAMA disagrees with this approach and is working to launch research projects to look at the various compositions of gases and what can happen when an out-of-range gas situation occurs. (The Association of Home Appliance Manufacturers agrees with GAMA on that issue. For more on AHAM’s views, see the Association Report on page 56.)

In the interim, Stanonik says that appliance manufacturers need to become more vocal. “It would be useful to have more end users making known their views and their needs in terms of future gas supplies so that everyone understands what happens at the end of the line.”



For more information email GAMA at info@gamanet.org

SIDEBAR: Wobbe Index Example

A Wobbe calculation divides the heat content (BTU per standard cu. ft. or scf) by the square root of the specific gravity of the gas stream. The result is expressed in BTU per scf. Pure methane, for example, has a BTU content of 1,009.7 BTU/scf and a specific gravity of 0.55. The Wobbe Index for methane is 1,357 BTU/scf. A pipeline gas stream rated at 1,075 BTU per scf and with specific gravity of 0.65 (a general rule-of thumb for pipeline gas), would have a Wobbe Index of 1,333 BTU/scf.

Source: FERC, excerpted from BP America Production Company and BP Energy Company, Post-Conference Comments on Gas Quality and Interchangeability Issues