United States Patent 0 "
C6
3,324,670
Patented June 13, 1967
1
liquid air, liquid nitrogen or liquid ammonia. These sub
3,324,670
METHGD 0F TRAN SPORTKNG METHANE
0R NATURAL GAS
stances, which are gaseous at normal temperature and
pressure, have, however, drawbacks which make them
Alfred L. Van Kleef, The Hague, Netherlands, assignor
less suitable for use as refrigerants.
to Shell Oil Company, New York, N.Y., a corporation Cl
Liquid nitrogen, for example, has the disadvantage of
of Delaware
being relatively dif?cult to obtain, while it also has the
N0 Drawing. Filed Nov. 3, 1965, Ser. No. 506,264
drawback of having an atmospheric boiling point of ap
Claims priority, application Netherlands, Nov. 9, 1964,
proximately ~196° C. In order, therefore, to transport
6,413,015
nitrogen in the liquid state at atmospheric pressure in
22 Claims. (Cl. 62—55)
10 reservoirs from the consumption point to the production
methane or natural gas is transported to a consumption
point it is necessary to cool the nitrogen to considerably
below the atmospheric boiling point of methane or nat
ural gas, for which purpose a relatively large amount of
energy is required. Another drawback of nitrogen is that
its atmospheric boiling point lies very far below the am
bient temperature so that when giving oft" its cold to the
methane or natural gas the liquid nitrogen will pass into
the gaseous state. Since gaseous nitrogen has relatively
few applications, it has to be discharged into the atmos~
point in substantially atmospheric pressure containers
phere, and this must be regarded as a loss.
ABSTRACT OF THE DISCLOSURE
Methane or natural gas is lique?ed at a production point
for transport in atmospheric pressure containers by heat
exchange with a cold liquid refrigerant which sustains
its liquid state after heat exchange with the methane or
natural gas. The heated liquid refrigerant along with the
where the lique?ed methane or natural gas is heat ex
Liquid oxygen, like nitrogen, has the drawback of being
changed with the liquid refrigerant to heat the methane
or natural gas to a gaseous state and cool the liquid re
_ difficult to obtain. Another disadvantage arising from the
use of liquid oxygen as refrigerant is that it is not really
frigerant. The cool liquid refrigerant is then transported
back to the production point in substantially atmospheric
possible to transport the liquid oxygen from the con
sumption point to the production point in the same reser
pressure containers where it is heat exchanged with meth
voirs as are used for conveying the liquid methane or
ane or natural gas as in the beginning.
natural gas from the production point to the consump
tion point. The reason why this is not really possible is
that oxygen can form explosive mixtures with methane
or natural gas. Since the atmospheric boiling point of
The invention relates to a method of transporting meth- “
ane or natural gas in the liquid state and preferably at
oxygen, like that of nitrogen, is very low, namely —183°
approximately atmospheric pressure.
C., the use of oxygen as refrigerant has also the same dis~
advantages as the use of nitrogen as refrigerant.‘ At the
It is known to liquefy methane or natural gas at a pro
duction point by cooling it deeply. Since the atmospheric
production point the liquid oxygen will pass into the gase
boiling point of methane or natural gas is approximately
-160° C. the amounts of energy required for the cooling
ous state and it is not always easy to ?nd useful applica
tions for these large quantities of gaseous oxygen. Dis~
are relatively large. Accordingly, the necessary capital
outlay in the cooling plant is also relatively high. It is
charging it into the atmosphere would, of course, mean
an economic loss.
therefore desirable to reduce the amount of energy re
quired to liquefy methane or natural gas at the produc
._
The use of liquid air as refrigerant in the. above method
O has approximately the same drawbacks as the use of
liquid oxygen as refrigerant.
'
tion point.
To achieve this object a method of transporting meth
Nor is ammonia really suited for use as a refrigerant
ane or natural gas has been proposed, comprising the fol
since its atmospheric freezing point lies relatively far
lowing stages:
above the atmospheric boiling point of methane or nat
ural gas, namely at —77° C. Moreover, ammonia has the
(a) At a production point methane or natural gas is
lique?ed by cooling and passed in the liquid state into
disadvantage of having an atmospheric boiling point which
a reservoir in which a pressure of preferably approxié
lies far below the ambient temperature, namely at —33°
mately 1 atmosphere is maintained,
C., so that when giving off cold to the methane or nat
(b) The reservoir thus ?lled is transported to a con- r
sumption point,
(c) At the consumption point the liquid methane or
natural gas is converted to the gaseous state by bringing
it into heat exchange with a refrigerant,
(d) The refrigerant, cooled off as a result of the stage
described under (c), is passed into a reservoir,
(e) The reservoir ?lled with the cooled refrigerant as
described in stage (d) is transported to production point,
(f) At the production point gaseous methane or nat
ural gas is cooled according to stage (a) by bringing it
"
ural gas to be lique?ed the liquid ammonia easily passes
into the gaseous state with the result that difficulties arise
at the production point with the storing of the gaseous
ammonia. Since gaseous ammonia is poisonous it cannot
be discharged into the atmosphere, but must be worked
up, for example, into fertilizers.
In order to eliminate the above~mentioned drawbacks
it is proposed according to the invention to use a liquid
refrigerant having an atmospheric freezing point below
or slightly above the atmospheric boiling point of meth—
ane or natural gas, and having an atmospheric boiling
point above or slightly below the ambient temperature.
The atmospheric freezing point of the refrigerant ac
cording to the invention is at most approximately 20° C.
above the atmospheric boiling point of methane or nat~
the place where the natural gas or methane is lique?ed
ural gas, but is preferably lower than this maximum value.
for dispatch, while by consumption point is meant the 65 If the atmospheric freezing point of the refrigerant were
place where the liquid natural gas or methane is con
to be higher than said maximum value the refrigerant
into heat exchange with the refrigerant supplied accord,
ing to stage (c).
It should be noted that by production point is meant
verted, on arrival, to the gaseous state.
It should be further be noted that the above-mentioned
reservoir can be arranged on a vehicle or built into a
tanker.
It has been proposed to use as refrigerant liquid oxygen,
could not very Well be used since it would then solidify
and consequently could no longer be pumped, at a tem
perature which is considerably higher than the atmos
pheric boiling point of methane or natural gas. This means
that the methane or natural gas could not be cooled tr
3,324,670
3
4
latter is gasi?ed by passing it in heat-exchange with the
a su?icient extent with the refrigerant alone, thus making
warm isopentane. The cooled down isopentane is then
stored until a period of small demand for natural gas or
methane arrives again. Then the cold isopentane is used
for liquefying a quantity of methane or natural gas which
an extra cooling plant necessary.
The atmospheric boiling point of the refrigerant accord
ing to the invention is at most approximately 30° C.
below the ambient temperature, but is preferably higher
is stored until the demand for natural gas or methane _
than this value.
A refrigerant which is very suitable for use with the
method of the invention is isopentane, which has an
atmospheric freezing point of —160° C. and an atmos
rises again.
I claim as my invention:
1. A method of transporting a gas comprising the fol
stages:
pheric boiling point of +28° C. and which is moreover 10 lowing
(a) a ?rst quantity of gas is lique?ed at a production
readily available in large quantities at a reasonable price.
point by cooling and is passed in the liquid state into
Another substance which could be used as refrigerant,
a reservoir in which a pressure of at least approxi
but which has less advantageous physical properties than
mately one atmosphere is maintained;
isopentane, is isobutane which has an atmospheric freez
(b)
the reservoir containing the liquid gas is tran
ing point of —160° C. and an atmospheric boiling point
ported to a consumption point;
of —l2° C. A drawback of this substance is, however,
(e) at the consumption point the liquid gas is con
that the atmospheric boiling point is rather on the low
side.
Other substances which are in principle suitable are,
for example, hexyne with an atmospheric freezing point
verted to the gaseous state by bringing it into heat
exchange with a liquid refrigerant having an atmos
20
of —~l50° C. and an atmospheric boiling point of
+71° 0, methyl ether with an atmospheric freezing
point of —138° C. and an atmospheric boiling point of
—8° C., or 2-methyl pentane with an atmospheric freez
ing point of \-—154° C. and an atmospheric boiling point
of +60° C. A drawback of methyl ether is, however, that
the atmospheric freezing point is rather on the high side,
while the atmospheric boiling point is rather on the low
of said gas to further cool said refrigerant within
the liquid phase range;
(d) the cooled liquid refrigerant is passed into an
insulated reservoir in which a pressure of approxi
side.
Instead of pure substances as refrigerants, use may also 30
be made of mixtures having both an atmospheric freezing
point and an atmospheric boiling point within the said
ranges. Examples of such mixtures are mixtures of iso
pentane or isobutane. Further examples are mixtures of
isopentane and isohexane or mixtures of isopentane and 35
normal pentane. Particularly suitable is a mixture con
tainer 75% isopentane and 25% isohexane which remains
a liquid to minus 170° C., that is 10° C. lower than for
pure isopentane. Since methane lique?es under atmos
pheric pressure at minus 160° C. the use of this type of
refrigerant makes it possible to install all refrigeration
capacity at the gas consumption p'oint. Suitable mixtures
may furthermore, for example, also be those which have
an eutectic point in the freezing point.
Other mixtures which may be considered for use are,
for example, hydrocarbon fractions with a boiling range
below approximately 100° C., preferably between 35° C.
and 75° C., obtained by distillation of crude petroleum
or of a petroleum fraction which has been subjected to
a cracking process. These mixtures consist substantially
of paraf?nic and ole?nic hydrocarbons having 5 and 6
carbon atoms.
The refrigerant, having been cooled at the consump
tion point, is preferably transported to the production
point in the tanks which have been used for conveying
the liquid methane or natural gas from the production
point to the consumption point. This procedure has the
advantage that the tanks are invariably maintained at a
pheric pressure boiling temperature above or slightly
below the ambient temperature and an atmospheric
pressure freezing temperature below or slightly
above the atmospheric pressure boiling temperature
mately one atmosphere is maintained;
(e) the insulated reservoir ?lled with said cooled liquid
refrigerant is transferred to the gas production point,
said refrigerant being preserved in the liquid phase
at approximately one atmosphere pressure by the in
sulation of said reservoir;
(f) at said gas production point a second quantity of
gaseous gas is cooled according to stage (a), at least
some of the heat of vaporization of said gas being
transferred in heat exchange with said liquid
refrigerant.
2. The method as claimed in claim 1, characterized in
that said liquid refrigerant, heated as described in stage
(f) is passed, in the liquid phase, into a reservoir and
carried back to the consumption point.
3. The method as claimed in claim 1, characterized
in that said liquid refrigerant, cooled as described in stage
(a) is transported from the consumption point to the pro
duction point in the same reservoir as has been used to
transport the liquid methane from the production point
to the consumption point.
4. The method as claimed in claim 1, characterized
in that the atmospheric freezing point of the refrigerant
is at most approximately 20 degrees above the atmos
pheric boiling point of lique?ed gas.
5. The method as claimed in claim 1, characterized
in that the atmospheric boiling point of the refrigerant is
55 at most approximately 30° C. below the ambient tem
perature.
6. The method as claimed in claim 1, characterized in
that the refrigerant is a mixture of liquids, both the
atmospheric freezing point and the atmospheric boiling
low temperature so that heating and cooling of the tanks 60
point of the mixture being within the said ranges.
do not occur.
7. The method as claimed in claim 1, characterized
The refrigerant having been heated at the production
in
that the refrigerant is isopentane.
point, can if desired be used up on the spot, as fuel for
8. The method as claimed in claim 1, characterized
example, or if desired, it can be transported to the con
in that the refrigerant is isobutane.
sumption point to be there brought into heat exchange
9. The method as claimed in claim 6, characterized
with an amount of liquid methane or natural gas which
in that the refrigerant is a mixture of isopentane and
has to be converted into the gaseous state.
isohexane.
It is remarked that the refrigerants mentioned may also
10. The method as claimed in claim 9, characterized
be used in storage of methane or natural gas for peak
in that the mixture contains 75% isopentane and 25%
shaving purposes. During periods of small demand for
isohexane.
,
natural gas or methane this can be lique?ed by passing
11. The method as claimed in claim 6, characterized
it in heat exchange with the cold refrigerant, for example,
in that the refrigerant is a mixture of‘isop‘entane and
cold isopentane. The methane or natural gas thus lique
normal pentane.
‘
?ed can then be stored in suitable reservoirs and in
12. The method as described in claim 1, characterized,
periods of large demand for natural gas or methane the 75
5
8,324,670
6
in that said liquid refrigerant remains in the liquid state
throughout all stages of said method.
13. The method as described in claim 1 wherein said
in that the refrigerant is a mixture of liquids, both the
atmospheric freezing point and the atmospheric boiling
point of the mixture being within the said ranges.
gas is natural gas.
20. The method as claimed in claim 19, characterized
14. The method as described in claim 1 wherein said
in that the refrigerant is a mixture of isopentane and iso
gas is methane.
hexane.
15. A method of liquefying a gas selected from the
21. The method as claimed in claim 20, characterized
group consisting of ‘methane and natural gas at superat
in that the mixture contains 75% isopentane and 25% iso
mospheric production pressure by cooling through bring
hexane.
ing it into heat exchange with a cooled liquid refrigerant,
22. The method as claimed in claim 19, characterized
10
having an atmospheric freezing point not substantially
in that the refrigerant is a mixture of isopentane and
greater than 20 degrees C. above the atmospheric boiling
normal pentane.
point of said gas, and having an atmospheric boiling point
References Cited
not substantially greater than 30 degrees C. below the
UNITED STATES PATENTS
ambient temperature.
15
16. A method of converting liquid methane to the gase
2,682,154
6/ 1954 Wilkinson __________ __ 62—54
ous state by bringing it into heat exchange with a liquid
2,784,560
3/1957 Johnson ____________ __ 62—54
refrigerant which is cooled off thereby, said liquid refrig
2,799,997
7/1957 Morrison ___________ __ 62—54
erant having an atmospheric freezing point not substan
2,959,020 11/1960 Knapp _____________ __ 62-54
tially greater than 20 degrees C. above the atmospheric 20 2,975,604 3/1961 McMahon __________ __ 62—55
boiling point of methane, and having an atmospheric
3,018,632
1/1962 Keith ______________ _.. 62—52
boiling point not substantially greater than 30 degrees C.
3,034,309
5/1962 Muck ______________ __ 62—55
below the ambient temperature.
3,077,082
2/ 1963 Adams et al. ________ __ 62—52
17. The method as claimed in claim 15, characterized
in that the refrigerant is isopentane.
18. The method as claimed in claim 15, characterized
25
3,108,447
3,195,316
3,246,480
11/1963
7/1965
4/1966
Maher et al. _______ __ 62—54
Maher et al. _______ __ 62—54
Rigby _____________ __ 62—48
in that the refrigerant is isobutane.
19. The method as claimed in claim 15, characterized
LLOYD L. KING, Primary Examiner.