AU650849B2 - Adding a malodorant to a gas and liquid gas mixture - Google Patents

Description

ADDING A MALODORANT TO A GAS AND LIQUID GAS MIXTURE The present invention relates to a method of adding a malodorant to a consumer gas which is distributed to a consumer station, so that persons present in the surroundings of the distribution system will be warned that the surrounding atmosphere contains more than the lowest permitted concentration of gas, therewith constituting the risk of explosion, suffocation, toxicity and some other risk. An example of gases which can be odorized in this way is oxygen, which can cause extremely comprehensive fire and explosion damage if it leaks into the surroundings ambient of the distribution system and/or the consumer station and therewith enriches the ambient air or atmosphere. Another example includes combustible gases, such as natural gas, propane gas, town gas, etc., which when admixed with atmospheric oxygen can give rise to fires and explosions. Another example includes odorless, toxic gases or more or less inert gases. If these latter gases escape into the ambient surrounds, they are able to displace the oxygen in the air, thereby creating suffocation conditions.

A prior art method of adding a malodorant to oxygen gas had been developed so that if the air becomes enriched with oxygen, individuals in the near vicinity are warned that there is an imminent risk of explosion. This method eliminates the need of handling toxic malodorants by the consumer, thereby avoiding the risk of explosion created by the addition of such malodorants. In a space or chamber provided for this purpose, there is produced a gaseous mixture or malodorant and a carrier gas, in this case oxygen, a so-called master gas, by adding to the oxygen gas a malodorant in a concentration of 1,000- 10,000 ppm. In a separate space or chamber, isolated from the aforesaid space, the master gas is admixed with oxygen gas distributed to the consumer in an amount such that the malodorant has a concentration of 5-50 ppm in the :consumer gas.

ii". However, when the master gas contains solely oxygen and malodorant, 1-.30 for example dimethyl sulphide, DMS, problems can occur when filing the master gas container. For instance, it is unavoidable to lie in a concentration range during part of the filling procedure in which the mixture is combustible, at least in a part of the container. There is thus a risk of ignition and explosion.

One method of avoiding this risk is a method of producing a master gas consisting of oxygen and a malodorant, in this case dimethyl sulphide.

According to this method, the master gas container is first filled with a mixture of dimethyl sulphide and nitrogen or helium gas. The dimethyl sulphide is present in a concentration of 0.5-2.5 mole per cent. Oxygen gas is then introduced until a desired working pressure, e.g. 200 bars, is obtained in the container.

One drawback with the master gas produced in with this described method, however, is that during transportation and storage, the master gas must not be subjected to temperatures which are so low as to condense the malodorant. For example, in the case of a master gas which consists of 0.2 mole per cent dimethyl sulphide, 9.8 mole percent helium or nitrogen and 90 per cent oxygen at 200 bars, dimethyl sulphide will condense when the temperature falls beneath 13 0 When the master gas container is subsequently heated to a temperature above 13 0 C, a very long time elapses before the condensed dimethyl sulphide has again turned to a gaseous state.

The object of the present invention is to provide a method for producing master gas for admixture with a consumer gas, preferably natural gas and other combustible gases, such as town gas and propane gas, and oxygen and which avoids the aforesaid drawbacks.

The method is characterized by dissolving a malodorant in the form of an organic sulphur compound or a mixture of two or more organic sulphur compounds, said compounds comprising tetrahydrothiophene, methyl mercaptan, ethyl mercaptan, propyl mercaptan, butyl mercaptan, dimethyl S*i e WO 91/17817 PCT/SE90/00340 3 sulphide, diethyl sulphide and methylethyl sulphide, in condensed carbon dioxide, sulphur hexafluoride or dinitrogen oxide in a pressure vessel, thereby obtaining in the pressure vessel a liquid phase, consisting of a solution of the malodorant in the condensed gas, and a gas phase; and by removing the liquid phase from the vessel, vaporizing said liquid phase and adding the vapor phase to the consumer gas distributed to the consumer. According to one preferred embodiment, the malodorant has a concentration of 0.5-10 mole per cent in the master gas. It is also preferred to add the master gas to the consumer gas in a quantity such that the malodorant concentration in said consumer gas is 1-20 ppm.

Other advantageous embodiments of the inventive method will be evident from the dependent Claims 4-8.

The invention also relates to a gaseous mixture consisting of liquid carbon dioxide, sulphur hexafluoride or dinitrogen oxide containing a dissolved malodorant of the aforesaid kind.

The malodorant, which is an ill-smelling organic compound or a mixture of two or more such compounds, is introduced into the carrier gas, i.e. the condensed gas, as nitrous gas (laughing gas), sulphur hexafluoride or preferably carbon dioxide, in an amount of 0.5-10 mole per cent, calculated on the total quantity of gas. The aforesaid illsmelling substances, methyl mercaptan, ethyl mercaptan, propyl mercaptan, butyl mercaptan, tetrahydrothiophene, dimethyl sulphide, diethyl sulphide and methyl ethyl sulphide, are soluble in the condensed gases in quantities sufficient to enable the method to be applied in practice. The pressure in the resultant gas phase will vary when the gas mixture is stored at differing temperatures. The malodorant content of the condensed gas is only affected to a negligible extent at temperatures within the range of -40 0 C to +50 0

C.

Admixture of the master gas, i.e. the carrier gas diluted with the malodorant, with the consumer gas is effected by first removing the liquid mixture of carrier gas and malodorant from the pressure vessel in which the mixture is stored, and vaporizing the liquid phase and then introduc- WO 91/17817 PCT/SE90/00340 4 ing the gaseous mixture into the consumer gas in quantities such that the concentration of malodorant in the consumer gas will lie within the range of 1-50 ppm (1.0001-0.0050 mole per cent), preferably within the range of 1-20 ppm.

When the master gas, i.e. the gas mixture consisting of malodorant and carrier gas, is to be admixed with a consumer gas which is distributed to various consumer stations through a pipe network or a through a central gas system, a gas mixer of more or less conventional kind is connected to the system upstream of the inlet to the pipe network. The consumer gas and the master gas are mixed in desired proportions in this mixer. The gas mixer includes a control system by means of which the ratio between the flow of master gas and the flow of consumer gas can be constantly maintained at a constant level. For example, if the master gas contains 2 mole per cent malouorant and the consumer gas shall contain 4 ppm malodorat, the aforesaid ratio shall be 1:5000.

When the consumer gas is distributed to the consumer in a high pressure container, the vaporized mixture, the master gas, is first introduced into the container in a quantity such that the desired proportion of malodorant is obtained when subsequently introducing the consumer gas into the container to the desired container pressure.

The consumer gas containing the malodorant added thereto in accordance with the invention will therefore contain a given amount of carrier gas in addition to the malodorant.

When the carrier-gas content of the master gas is, for instance, 95 mole per cent, i.e. the master gas contains mole per cent malodorant, an admixture has been effected with one part of master gas to 5000 parcs of consumer gas, the malodorant content will be 10 ppm and the carrier gas content, e.g. carbon dioxide, will be 0.02 mole per cent.

This proportion of non-combustible carrier gas is insignificant with regard to combustible gases. Neither will this carrier gas conteit have any noticeable negative effect when using oxygen which contains a malodorant for different industrial flame processes, such as welding, cutting and heating work. The purity of oxygen produced industrially

Claims (12)

1. A method of adding a malodorant to a consumer gas, such as oxygen, natural gas, propane gas, town gas or some other combustible gas, an odorless, toxic gas or a more or less inert gas distributed to a consumer station for the purpose of warning individuals in the surroundings that there is a risk of fire, explosion, suffocation, toxicity or some other risk due to the presence of consumer gas in the surrounding atmosphere as a result of leakage, negligence or some other reason, said method including the step of mixing a master gas, i.e. a carrier gas diluted with malodorant, with the consumer gas, c h a r a c t e r i z ed by the further steps of dissolving the malodorant in the form of an organic sulphur compound or a mixture of two or more organic sulphur compounds, these compounds comprising tetrahydrothiophene, methyl mercaptan, ethyl mercaptan, propyl mercaptan, butyl mercaptan, dimethyl sulphide, diethyl sulphide and methyl- ethyl sulphide, in condensed carbon dioxide, sulphur hexaflu- oride or dinitrogen oxide in a pressure vessel, thereby obtaining in the pressure vessel a liquid phase, consisting of a solution of malodorant in the condensed gas, and a gas phase; and removing the liquid phase from the vessel, vaporizing said liquid phase and supplying the resultant vapor phase to the consumer gas, which is distributed to the consumer.

2. A method according to Claim 1, c h a r a c t e r i z e d in that the concentration of the malodorant in the master gas is 0.5-10 mole per cent.

3. A method according to Claim 1 or 2, c h a r a c t e r i z e d by adding the master aas to the consumer gas in an amount such that the concentration of malodorant in the consumer gas is 1-20 ppm.

4. A method according to\one ei=ee of Claims 1-3, where the consumer gas is distributed to the consumer through a conduit system at relatively low overpressure, c h a r a c t e r i z e d by supplying the vaporized gas mixture to the consumer gas via a gas mixer of known kind prior to intro- 'WO 91/17817 PCT/SE90/00340 today is often some tens of per cent units above the degree of purity required for gas cutting work, for example. WrO 91/17817 PCT/SE90/00340 7 ducing the consumer gas into the conduit system.

A method according to Claim 3, where the consumer gas is distributed to the consumer in a high pressure container, c h a r a c t e r i z e d by introducing the vaporized gas mixture into said container prior to introducing the com- pressed, pure consumer gas into said container.

6. A method according to\one Er amr of Claims c h a r a c t e r i z e d in that the malodorant is tetra- hydrothiophene, and in that the consumer gas is natural gas.

7. A method according to one or more of Claims 1-6, c h a r a c t e r i z e d in that the malodorant is dis- solved in carbon dioxide.

8. A gas mixture containing a malodorant for addition to a consumer gas, for instance oxygen, natural gas, propane gas, town gas or some other combustible gas, an odorless toxic gas or a more or less inert gas, distributed to a consumer station, for the purpose of warning individuals in the surroundings that there is a risk of fire, explosion, suffocation, toxicity or some other risk due to the presence of consumer gas in the surrounding atmosphere as a result of leakage, negligence or some other reason, said method including the step of mixing a master gas, i.e. a carrier gas diluted with malodorant, with the consumer gas, c h a r a c t e r i z e d in that the malodorant has the form of an organic sulphur compound or a mixture of two or more organic sulphur compounds, said sulphur compounds consisting of methyl mercaptan, ethyl mercaptan, propyl mercaptan, butyl mercaptan, tetrahydrothiophene, dimethyl sulphide, diethyl sulphide and methyl sulphide dissolved in condensed carbon dioxide, sulphur hexafluoride or dinitrogen oxide in a pressure vessel.

9. A gas mixture according to Claim 8, c h a r a c t e r i z e d in that the malodorant is present in the condensed gas in an amount of 0.5-10 mole per cent.

10. A gas mixture according to Claim 8 or 9, c h a r a c t e r i z e d in that the malodorant is dis- '4 solved in liquid carbon dioxide. INTERNATIONAL SEARCH REPORT International Application No PCT/SE 90/00340 1. CLASSIFICATION OF SUBJECT MATTER (if several classification symbols apply, indicate all) 6 According to International Patent Classification (IPC) or to both National Classification and IPC IPCS: B 01 F 3/02, C 10 J 1/28 II. FIELDS SEARCHED Minimum Documentation Searched' Classification System Classification Symbols B 01 F; C 10 J; G 01 M Documentation Searched other than Minimum Documentation to the Extent that such Documents are Included in Fields Searched 8 SE,DK,FI,NO classes as above III. DOCUMENTS CONSIDERED TO BE RELEVANT 9 Category Citation of Document, 1 with indication, where appropriate, of the relevant passages 12 Relevant to Claim No. 1 3 E,X WO, Al, 9006170 (AGA AKTIEBOLAG) 1-10 14 June 1990, see the whole document A DE, A, 2259314 (PENNWALT CORP.)

11 October 1973, 1-10 see claims 1-7 A DE, B2, 2337782 (SAN DIEGO GAS ELECTRIC CO., ET 1-10 AL) 7 April 1977, see the whole document A DE, B2, 2347906 (SAN DIEGO GAS ELECTRIC CO., ET 1-10 AL) 26 May 1977, see the whole document SSpecial categories of cited documents: 10 later docunept published after he Iternational filing date A" document defining the eneral state of the art which is not or prlnry ose and not In conlct with the appi cat on but A ded e r ae the art which is not ited I nderstand the principle or theory underlying the considered to oe of particular relevance invention i E loarli cumen but publ l shed on or "afer Xth Internailonal document of patcular relevance, the claimed invention cannot be consid red novel or cannot be considered to doqugmnt which may throw doubts n riorlt clalm(a).or Involve an inventive step ci taton or o ther speciabl reason (as speci fed o ano l r document of psrticular relevance, the claimed Invention cannot be considered to involve an rinventive step w hen the "0 document referring to an oral disclosure, use, exhibition or dcument Is combin th one or moe other such sdoul her meanssUc combination being obviou, to a person skilled "P docqume n uble prior to ih e intlernational filing date but document member of the same patent family IV. CERTIFICATION Date of the Actual Completion of the International Search 11th December 1990 international Searching Authority Date of Mailing of this International Search Report 1990

-12- ANNEX TO THE INTERNATIONAL SEARCH REPORT ON INTERNATIONAL PATENT APPLICATION NO.PCT/SE 90/00340 This annex lists the patent family members relating to the patent documents cited in the above-mentioned international search report. The members are as contained in the Swedish Patent Office EDP file on 90-11-01 The Swedish Patent Office is in no way liable for these particulars which are merely given for the purpose of information. Patent document Publication Patent family Publication cited in search report date member(s) date WO-A1- 9006170 90-06-14 AU-D- 4656189 90-06-26 DE-A- 2259314 73-10-11 CA-A- 964061 75-03-11 FR-A-B- 2177675 73-11-09 JP-C- 1126672 82-12-14 JP-A- 49015701 74-02-12 JP-B- 57017039 82-04-08 NL-A- 7209754 73-10-01 US-A- 3826631 74-07-30 DE-B2- 2337782 77-04-07 NONE DE-B2- 2347906 77-05-26 AU-D- 6071773 75-03-27 CA-A- 1006353 77-03-08 FR-A- 2201424 74-04-26 GB-A- 1429954 76-03-31 JP-A- 49072302 74-07-12