The Advantages of Using Ambient Air

Vaporizers Throughout the Entire LNG Market

Introduction approve the process. The general public is now intimately involved which
brings a number of beliefs and attitudes to this process ranging from “not
Is it possible to accomplish the regasification of LNG using no fuel, no in my back yard” to “is it safe for my family and neighborhood” to “what
power and no moving parts? What would be the implications of doing are the associated carbon emissions”.
so? What are the benefits to the environment? Regasification of LNG
is something that is rarely understood completely and seems to be No reasonable person would argue that a 1970’s vintage vehicle could
shrouded in mystery in the minds of some. LNG vaporizers are quite be the answer to the perennial ‘fuel crises’ that seem to recur with each
commonplace, just follow any liquid supply chain, from a 10,000 gallon new generation. Similarly, the conventional methods for regasification
ISO container to a 70 million gallon LNG carrier, at the end of the chain of LNG have been pressured to improve, and newer methods are receiv-
you will find vaporizers that can take a variety of forms. ing serious consideration. Some of the strongest influences pressuring
the adoption of alternative regasification methods include concerns over
It takes energy to achieve regasification, and where that energy comes CO2, SOx, NOx and CO emissions. Also, the unknowns associated with
from is the key distinction between the various types of vaporizers. En- using large quantities of seawater for regasification, have increased the
ergy comes in all forms, but some of the more popular sources for re- rejection of or objection to the old ‘tried and true’ technologies. Be-
gasification include ambient air, seawater, cooling tower water, steam, cause of these and other legitimate concerns, numerous ‘hurdles’ have
electricity or even combustion of the natural gas itself. Significant inter- been added to the success equation for regasification of LNG. Since the
est has been devoted to using ambient air as an energy source due to its original LNG advancement efforts 40 years ago, concerns about pollut-
infinite free supply, zero environmental impact and lack of operational ant emissions, climate change and environmental impact have become
complexity. It is this technology that Cryoquip has specialized in for considerably more politicized issues.
decades, and is the highlight of this article as we explore some of the in-
dustry background, operational explanation and modern day examples Background
of ambient vaporizer installations.
With regard to the current public and political awareness of LNG, it is
What makes the regasification of LNG such a topic of interest in recent from this context that we approach the topic of the simplest form of re-
years, and why has it become such a complicated issue? In a chang- gasifying cryogens, that is direct contact ambient air vaporizers known
ing world, public awareness of heretofore uninteresting chemical and in the industry as AAV’s and forced draft fan ambient vaporizers, or
hydrocarbon-based processes has become a significant item of focus. FAV’s. One of the many questions asked about ambient vaporizers is
What was once a relatively mundane topic, has become sensationalized. “why have they not been used for regasifying LNG for 40 years like some
One need not look very far to find news reports and documentary pre- of the other alternatives?” Although ambient vaporizers have been used
sentations discussing the potential issues surrounding LNG as a supple- to regasify cryogens, including LNG, for more than 50 years, they were
ment for the world’s energy demand. not available until recently, in a configuration suitable for the high flow
rates associated with modern day LNG user applications. More than 50
LNG represents the world’s largest cryogenic regasification energy de- years ago, industrial gas suppliers working with Cryoquip, determined
mand simply because the majority of suppliers and end-users are sepa- ambient vaporizers were the simplest, safest, cleanest and most reliable
rated by oceans and continents. Therefore regasification is no small device for regasification of cryogens from CO2 through argon, oxygen,
matter and there are many considerations when evaluating the various nitrogen, hydrogen, helium and a variety of other cryogens.
technologies associated with LNG vaporizers. No longer is the meth-
odology for regasifying LNG relegated to a few agencies authorized to The air separation companies have made a significant effort over the years
to maximize the size and application of ambient vaporizers around the
world. It is conservatively estimated that more than 50,000 such units
are employed currently around the world in a multitude of applications.

As the air separation industry designed and built ever larger plants and
this progression resulted in and the demand for much larger capacity
ambient vaporizers. Today, it is commonplace for Cryoquip to supply
the industrial gas companies with hundreds of ambient vaporizers each
year for deployment all around the globe. These ambient vaporizers can
accommodate flow rates 10 – 20 times higher than their predecessors
20 years ago. The ambient air technology has come a long way since its
infancy half a century ago.

Figure 1. Sample illustration of the heat transfer

mechanism using a 12-fin extrusion. continued
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 progression is that surrounding ambi-
ent air begins to cool while giving up its
sensible heat to the LNG. As this occurs,
the air becomes denser and begins to fall
under gravity’s control. As the ambient air
continues to chill, the velocity increases as
does the external heat transfer coefficient.
In essence, the reverse effect of a chimney
is being created. When air is heated in a
fireplace or other device, the heated air be-
comes lighter and rises. This effect can be
rather dramatic, especially as the height of
a chimney increases, increasing the draft,
hence the very large slender stacks seen at
power plants and smelters. Exactly the op-
posite effect occurs when cooling air with
LNG. In addition, a fan can be mounted
on the top of an ambient vaporizer to of-
Figure 2. Send-out ambient vaporizer train at Cheniere’s Sabine Pass LNG terminal. fer further performance enhancement.
Something to keep in mind, is that there is
Technical Discussion no climate on Earth that is too cold to vaporize LNG, therefore, direct
contact ambient vaporizers will always be capable of regasification no
What makes an ambient vaporizer greener than other regasification matter where they are installed.
processes? First, it uses a completely renewable energy source, which
is heat generated by the sun every day and carried in the ambient air As the air cools, it reaches the saturation point and the moisture within
we all breathe. There are no fuel or power requirements with ambient the air begins to condense. This creates a significant benefit because
vaporizers, which makes it a truly unique technology. In addition, the the heat of vaporization of the water is relatively high. As the moist air
only environmental impact created by operating ambient vaporizers continues to cool, the temperature drops to the point where ice as crys-
is the removal of moisture from the ambient air. As the air reduces in talline frost begins to form on the external surfaces of the extrusion.
temperature to heat the cryogen inside the heat exchanger, moisture is This supplies additional energy from the heat of fusion. Because of
deposited onto the external surfaces. this freezing process, design consideration needs to be given to the ac-
cumulation of this frost which attaches to the extrusions. Frost forma-
One of the most significant beneficial characteristics of this direct contact tion has led Cryoquip to develop extrusions which can accommodate
ambient system is that it relies upon a single approach temperature. This is various amounts of frost with significant heat transfer performance still
not always the case with some indirect ambient systems where multiple ap- being achieved. Each type of fin and spacing has a characteristic perfor-
proach temperatures are required. In general, more intermediate degrees mance curve in ambient air. Years of research and testing have resulted
of separation between the air and LNG result in decreased
thermal efficiency and more operational complexity.

The pressurized LNG is passed on the tube side through

the internal section of the finned heat exchange element,
known in the industry as extrusions. Nature, not liking a
thermal imbalance, immediately begins to warm the very
cold fluid. Enhancing this process, the stainless steel tube
carrying the LNG is metallically bonded to a set of alu-
minum fins directed radially outward. This allows heat to
pass more easily between the ambient air and the LNG be-
ing heated. Proper design of the internal section assists in
maximizing heat transfer to the LNG being heated. These
finned sections are connected together to create large ar-
rays and are firmly held in place in a honeycomb type at-
tachment. This arrangement allows for easy scaling of
additional extrusions for a wide range of LNG flow rates.
Also, there are a large number of possible tube side con-
figurations, allowing flexibility in the number of parallel
and series passes.

Part of the popularity of ambient vaporizers is due to the Figure 3. Cryoquip ambient vaporizer installation at
simplicity of the process. The natural thermodynamic Shenzhen Gas’ LNG peak shaving plant.

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in a design program that predicts the performance of the various sizes, Ambient vaporizers lack any moving parts and their energy source is
types and configurations of extrusions for a wide range of cryogens. always available, even on the coldest day of winter. This makes ambient
vaporizers very reliable and an excellent choice in critical performance
After a reasonable period of time, usually several hours, the frost situations where a gas supply outage is highly troublesome.
builds to the point where it begins to reduce the heat transfer below a
predetermined level. At this point, the unit is taken out of service and Moving further down the size scale, ambient vaporizers can also be used
allowed to defrost, while another ambient vaporizer is activated. The for industrial heat and power generation, otherwise known as virtual
ces are so efficient, this happens quickly in comparison to the online pipeline or satellite LNG installations. These typically are retrofit con-
time, and vaporizers can be quickly returned to service. versions of boilers, burners, kilns and generators from diesel or LPG
to natural gas. Cryoquip recently completed a number of these types of
Applications projects in the Northeastern U.S., the Caribbean and Australia using
ambient vaporizers with great success which produced significant daily
In the ever expanding LNG market, applications for ambient vaporizers fuel expense savings for the industrial users. In the very near future, the
are always growing. As previously mentioned, any liquid supply chain that LNG conversion wave will reach islands around the world, where power
you follow will terminate in a vaporizer in one form or another. Ambi- costs are extraordinarily high compared to the mainland.
ent vaporizers are very flexible by nature due to their modular construc-
tion making them fit for any flow rate or pressure. In addition, extrusions Ambient vaporizers are routinely installed at LNG fueling stations for
can be manufactured in lengths up to 40ft. which means relatively large trucks and vehicles. In particular they are used as LNG warmers for
equipment can be shipped in 45ft containers for transport cost savings. saturating the fuel before dispensing in ‘warm’ fuel stations. In addi-
Cryoquip has manufactured the largest ambient vaporizers ever pro- tion, they are combined with a high pressure pump for the production
duced, which are installed for send-out regasification purposes at Che- of CNG from LNG when the fueling station lacks a compressor.
niere’s Sabine Pass LNG terminal. Given the immense scale of this termi-
nal, correspondingly the vaporizers are 12ft (L) x 12ft (W) x 50ft (H) and Not surprisingly ambient vaporizers have found their way into nearly
were transported as special permitted loads from California to Louisiana. every corner of the LNG market, as many LNG users have discovered
Furthermore, ambient vaporizers are used on the export liquefaction side the same advantages that the industrial gas companies recognized many
of the Sabine Pass terminal for flaring purposes. When the liquefaction decades ago.
train runs into an ‘upset’ condition, the off-product from the cold boxes
is vaporized and sent to the flare. For further information, visit to www.cryoquip.com.

In addition to the large regasification terminals, ambient vaporizers Originally appeared in LNGIndustry March 2015. www.lngindustry.com
are also used in many peak shaving facilities, most notably in China.
Figure 4. Satellite LNG ambientvaporizer system for industrial
heat and power in the Northeastern U.S.