METHODE D'ADDITION D'UN AGENT MALODORANT AUX GAZ

METHOD OF ADDING A MALODORANT TO GASES

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
The disclosure relates to a method of adding a malodorant to
a consumer gas which is distributed to a consumer point, in order
to render the surroundings aware of the existence of a risk of
accident if consumer gas were to leak out into the air, employing
such a process using a concentrated gas, master gas, that the
malodorant does not condense during transport and storage of the
master gas at low temperatures. The malodorant, in the form of an
organic sulphur or other compound, is dissolved in liquid carbon
dioxide or other condensable gas in a pressure vessel, in which
there is obtained a solution which essentially comprises a gaseous
phase and a liquid phase. The solution, the master gas, is
withdrawn from the liquid phase, vaporized and added to the
consumer gas which is distributed to the consumer.

Revendications

WHAT WE CLAIM AND DESIRE TO SECURE BY LETTERS PATENT IS:
1. A method of adding a malodorant to a consumer gas
distributed to a consumption point, such as, for example, oxygen,
natural gas, propane, town gas or other combustion gas, odorless
toxic gas or more or less inert gas, in order to draw the
attention of the surroundings to the existence of a risk of fire,
explosion, poisoning, suffocation or other danger if, as a result
of leakage, carelessness or by other means, the consumer gas is
allowed into the atmosphere, concentrated gas containing a
malodorant, master gas, being mixed with the consumer gas,
characterized in that the malodorant, in the form of an organic
sulphur compound such as, for example, dimethyl sulphide,
tetrahydrothiophene or methyl mercaptan, is dissolved in a
condensed gas in a pressure vessel, suitably carbon dioxide,
propane, butane, sulphur hexafluoride or dinitrogen oxide, there
being obtained a solution, master gas, essentially comprising a
liquid phase and a gas phase; and that said solution is withdrawn
from the liquid phase, is vaporized and is supplied to the
consumer gas which is distributed to the consumer.
2. The method as claimed in Claim 1, characterized in that
the malodorant in the master gas consists of dimethyl sulphide;
and that its concentration in the master gas lies between 1 and
15%.
3. The method as claimed in Claim 2, characterized in that
the master gas is added in such an amount that the concentration
of dimethyl sulphide in the consumer gas lies in the range of
between 5 and 50 ppm.
4. The method as claimed in Claims 2 and 3, in which the
consumer gas is distributed to the consumer through a pipe system
at relatively low pressure, characterized in that the vaporized
dimethyl sulphide is, via a per se known type of gas mixer,
supplied to the consumer gas before the consumer gas is led out
into the pipe system.
5. The method as claimed in Claim 3, in which the consumer
gas is distributed to the consumer in containers under high

pressure, characterized in that the master gas is fed to the
container before the compressed comsumer gas is filled into the
container.

Description

4 2 ~
The mixture of the solution, the master gas, consisting of
malodorant dissolved in, for example, liquid carbon dioxide, into
that gas which is to be distributed to the consumer, proceeds such
that the liquid phase of the solution is withdrawn from the
pressure vessel in which the solution is stored, is vapourized and
mixed with the consumer gas in such proportions that the
concentration of malodorant in the gas will lie between 5 and
50 ppm~ preferably approx. 20 ppm.
In the event that the solution with malodorant is to be
supplied to a gas which is distributed to different points of
consumption by means of a pipe network or a central gas supply
system, a gas mixer of more or less conventional type is coupled
in upstream of the inlet to the pipe network. In this mixer, the
consumer gas and the vaporized solution are mixed to the desired
proportion.
In the event that the consumer gas is distributed to the
consumer in gas containers at high pressure, the vaporized
solution is first fed into the container in such a volume that,
when the consumer gas is thereafter filled to the desired
pressure, the concentration of malodorant is at the desired
level.
Hence, the consumer gas which is supplied with malodorant in
accordance with the method described in the foregoing will
include, in addition to the odoury vector, an insignificant
concentration of the major component of the master gas, for
example carbon dioxide. If the master gas has a malodorant
concentration of, for example, 5% and admixture is effected with
one part master gas to 2,500 parts consumer gas, the concentration
of malodorant will be 20 ppm and the concentraticn of carbon
dioxide 0.04 per cent. This is of no consequence whatever in cases
involving combustion gases. For employment of oxygen in various
industrial flame processes, such as welding, cutting and heating
work, this concentration of carbon dioxide will not have any
injurious effect either. The purity of the oxygen which is
produced today often lies above the requirements in, for example,
gas cutting, by a few tenths of a percentage units.

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so-called master gas, is produced by adding to pure oxygen gas a
malodorant in a concentration of between 1,000 and 10,000 ppm. In
a separate space discrete from the aforesaid compartment, the
master gas is added to the oxygen gas which is distributed to the
consumer in such a volume that the malodorant in the consumer gas
is present in a concentration of between S and 50 ppm.
However, if the master gas were to contain only oxygen and
the malodorant, for example dimethyl sulphide, DMS, problems may
occur in filling the master gas containers. It may then be
unavoidable that a certain part of the filling procedure will give
rise to a concentration region in which the mixture is
combustible, at least in a part of the gas container. The risk of
ignition and explosion may then be imminent.
One method of obviating this risk is described in Finnish
patent application 872278. This application thus discloses a
method of producing a concentrated 9dS, master 9dS, which
essentially consists of oxygen and a malodorant such as dimethyl
sulphide. According to the method disclosed in this application,
the container for the master gas is first filled with a mixture of
dimethyl sulphide and nitrogen or helium gas. The concentration of
the dimethyl sulphide then lies in the range of between 0.5 and
2.5%. Thereafter, pure oxygen gas is added until the desired
working pressure, for instance 200 bar, is obtained in the gas
container.
One drawback inherent in the master gas produced in
accordance with the above-described methods is, however, that it
may not be exposed during transport ~or storage to such low
temperature that the malodorant condenses. With a master gas
consisting of, for example, 0.2% dimeth~l sulphide, 9.8% helium or
nitrogen and 90% oxygen at a pressure of 200 bar, condensation of
the dimethyl sulphide will take place if the temperature falls
below approx. 13 C. When the gas container is subsequently warmed
to a temperature above 13 Cj a considerable time will elapse
before the condensed dimethyl sulphide has returned to its gaseous
form.

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OBJECT OF THE INVENTION
The object of the present invention is to realize a method of
production for master gas according to which the above-outlined
drawbacks are obviated and which may also be employed for
odorization of other gases than oxygen, such as natural gas, other
combusticn gases such as town gas and propane etc., toxic gases,
inert gases and othersA
SOLUTION
The methnd according to the present invention is essentially
characterized in that the malodorant in the form of an organic
sulphur or other compound, such as for example dimethyl sulphide,
tetrahydrothiophene or methyl mercaptan, is dissolved in carbon
dioxide, propane, butane, sulphur hexafluoride, dinitrogen oxide
or other condensable gas in a pressure vessel in which the
solution is present substantially in the liquid phase; and that
the solution, the master gas, is extracted from the liquid phase,
is vapourized and added to the gas intended for odorization which
is to be distributed to the consumer. The method according to the
present invention is further characterized in that when the
malodorant consists of dimethyl sulphide, this is employed in a
concentration of between 1 and 15%; and that such a volume of the
extracted vapourized solution is suppliecl to the consumer gas that
the malodorant is present in a concentration of between 5 and 50
ppm.
The liquid gas, for example carbon dioxide, in which the
malodorant is dissolved is stored at ambient temperature in a
pressure vessel in that the malodorant, for example dimethyl
sulphide, is also soluble in, for example, liquid carbon dioxide
at low temperatures. No separation of the substances will take
place even if the solution is cooled during transport and winter
storage to such extreme temperatures as -40 C. The reason for
this is that experiments have shown that the solubility of
dimethyl sulphide in liquid carbon dioxide is greater than 5 per
cent by volume throughout the entire temperature range of between
-40 C and +50 C.

4 ~ 7~L~i
The mixture of the solution, the master gas, consisting of
malodorant dissolved -in, for example, liquid carbon dioxide, into
that gas which is to be distributed to the consumer, proceeds such
that the liquid phase of the solution is withdrawn from the
pressure vessel in which the solution is stored, is vapourized and
mixed with the consumer gas in such proportions that the
concentration of malodorant in the gas will lie between 5 and
50 ppm, preferably approx. 20 ppm.
In the event that the solution with malodorant is to be
supplied to a gas which is distributed to different points of
consumption by means of a pipe network or a central gas supply
system, a gas mixer of more or less conventional type is coupled
in upstream of the inlet to the pipe network. In this mixer, the
consumer gas an~ the vaporized solution are mixed to the desired
proportion.
In the event that the consumer gas is distributed to the
consumer in gas containers at high pressure, the vaporized
solution is first fed into the container in such a volume that,
when the consumer gas is thereafter filled to the desired
pressure, the concentration of malodorant is at the desired
level.
Hence, the consumer gas which is supplied with malodorant in
accordance with the method described in the foregoing will
include, in addition to the odoury vector, an insignificant
concentration of the major component of the master gas, for
example carbon diox;de. If the master gas has a malodorant
concentration of, for example, 5% and admixture is effected with
one part master gas to 2,500 parts consumer gas, the concentration
of malodorant will be 20 ppm and the concentration of carbon
dioxide 0.0~ per cent. This is of no consequence whatever in cases
involving combustion gases. For employment of oxygen in various
industrial flame processes, such as welding, cutting and heating
work, this concentration of carbon dioxide will not have any
injurious effect either. The purity of the oxygen which is
produced today often lies above the requirements in, for example,
gas cutting, by a few tenths of a percentage units.

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Thus, the method described in the foregoing has realized a
master gas which includes a malodorant in the form of an organic
sulphur or other compound such as, for example, dimethyl sulphide
and which may also be stored and transported at low temperatures
without any risk of condensation of the malodorant.
The present invention should not be considered as restricted
to that described above, many modifications being conceivable
without departing from the spirit and scope of the appended
Claims.
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