US2322617A - Method and apparatus for odorizing liquefied gas - Google Patents

Description

June 22, 1943. I w. c. DAYHUFF 2,322,517

METHOD AND APPARATUS FOR ODOROZING LIQUEFIED GAS File'd Sept. 24, 1941 I00 I50 200 I00 4 A NORMALLY. ODORIZED LIQUEFIED HYDROCARBON I- GASES NO ADSORBENT IN OUTLET coNDuIT Z IL. I

\ \L B ODORANT CONCENTRATION IN LIQUEFIED GAS AgguT Io PERCEN OF THAT IN CURVE A WITH ADSORBEN'T' 1 IN QUTLETICQNDUITI I I SAFETY FACTOR WHEN GAS CONCENTRATION IN ROOM RESULTS IN DEGREE? ODORIZATION FIG.2

[NVIE'NTOR Wa/fcr C. Dag huf I Patented June 22, 1943 METHOD AND APPARA 'IU S FOR OI JORIZING LIQUEFIED GAS Walter C. Dayhufl', Whittier, Calif" assignor to Standard Oil Company of California, San Francisco, Calif., a corporation of Delaware Application September 24. 1941, Serial No. 412,138

Claims.

This invention relates to a method and apparatus for controlling the odorization of liquefied gas which is stored under pressure and then vaporized to gaseous form for use, and particularly to such a method and apparatus for a system to which are connected successive containers of liquefied hydrocarbon gas which has been odorized with a material less volatile than the particular hydrocarbons present.

Because of the so-called differential vaporization of the lighter fractions in a mixture, of lique fled gas and an odorant which is less volatile than t the liquefied gas, the usual procedure of evaporating the mixture from a liquid surface and permitting it to pass freely out of the tank or-cylin-. der outlet results in considerable variation in odorant intensity of the gas. This is due to the well-known tendency of the lighter fractions or components to evaporate from the liquid surface at a greater rate than the heavier components, the latter including the less volatile odorant. Effective odorization of gas representing the first few per cent of such. a liquid mixture withdrawn from a tank or cylinder can usually be accomplished only by having present in the liquid such a high concentration of the less volatile odorizing medium that the gas representing the last few per cent of the liquid mixture in the tank or cylinder is considerably over-odorizeda This results in anodor nuisance that is well recognized in this art.

The United States Bureau of Mines has exten- Ysively invest gated gas odorization and has-substantially standardized an odor intensity scale which is related to the degree of explosibility of a mixture of gas and air in a roorr In the United States Bureau of Mines Reportv of Investigations R. I. 2979, Odor Intensity and Symptoms Produced by Commercial Propane, Butane, Pentane, Hexane, and Heptane Vapor, a scale of odor isgiven which is quoted below: I

Intensity lTescrlption I No odor l-o detectable odor.

Veryi int Minimum but posithely perceptible.

2 Faint 'eek odor, readily perceptible. 3 Easily noticeable Moderate inteusitv.

4 Strong U; Cogent, forcible odor.

5 Very strong Intense ollcct, tray bite or irritote.

or vapor are considered adequate from a practical standpoint if the gas possesses odor intensity degree 2 (faint but readily perceptible) when present in a concentration equal to one-fifth its lower inflammable limit. A safety factor of fiv used in conjunction with degree 2 permits detection well in advance of a dangerous situation, and at thesame time insures a-much higher degree of to the gas user, particularly at safety factors of over 100.

This invention comprehends broadly a method and apparatus for increasing the odorization during the first part of the withdrawalof gas from the liquid mixture of odorant and liquefied hydrocarbon gas, for example, in a closed container, and decreasing the degree of odorization during the last part and particularly the gas representing the last 1 or 2 per cent of the liquid that may be withdrawn from such a container. For con-.

-venience, the penultimate. 1 per cent or that with drawn when the liquid content of the tank falls from 2 to 1 per cent of the original amount has been chosen to define the nature of this invention, as will be further apparent below.

It is anobject of this invention to provide a method and means for obtaining a more uniform odorization of the vapors withdrawn from a closed container of liquefied hydrocarbons, for example propane, butane and the like, which not only prevents under-odorization at the beginning of the withdrawal periodand over-odorization at the end of such period but also permits the safe use of a far smaller proportion of odorant in the mixture of liquefied hydrocarbons than has been possible heretofore.

Another object is to provide a method and means of odorizing a gas system towhich'successive containers of'liquefied hydrocarbon gas, for example propane, butane and the like, are connected by the steps of adding less than the customary amount of liquid odorant to the liquefied gas in said containers, imparting added odorant to about the first 20 per cent of gas vaporized into said system from the liquid in a given container, and abstracting odorant from about the last 20 per cent of gas vaporized from the liquid in said container, the odorant so abstracted being available to be imparted to gas initially withdrawn from the next container of liquefied gas to be connected to the gas system. 7 3

Another object is to improve the eificiency of the odorant which is added to a body of liquefied hydrocarbon gases, said odorant being less volatile than said hydrocarbons, so that a lesser amount of odorant is needed to reach a certain degree of odorization of the vapor withdrawn from the mixture by reducing the pressure on said mixture.

These and other objects and advantages of the invention will be further apparent from the following description and from the drawing which illustrates a preferred embodiment of the invention as it is applied to a tank of liquefied hydrocarbon gases.

In the drawing:

Figure 1 is a diagrammatic part sectionalview of one form of this invention applied to a system supplied from. a tank or bottle of liquefied petroleum gas.

Figure 2 is a chart showing two curves comparing normal odorizing behaviour of liquefied hydrocarbon'gas and the effect of this invention upon a quantity of gas to which has been added only about 10 per cent'of the normal odorant quantity.

This invention comprehends broadly the use of means in the gas stream or a conduit for the same adapted to withdraw vaporized liquefied hydrocarbons from a succession of closed containers for the latter to which asmall proportion of less volatile odorant has been added, these means serving to add or impart odorant to the gas that is firstwithdrawn from a full tank of the mixture and, more particularly, to Withdraw or abstract,

odorant from the gas which is withdrawn from the last few per cent of the liquid in the almost emptytank. In this example a body of finely divided charcoal or other absorbent or adsorbent material, such as silica gel, activated alumina or the-like, is placed in the outlet conduit system from'such a container. In this specification the word adsorbent is used to designate the function and properties of this material, which are not completely understood, and may include absorption, adsorption, or even chemical change. Desirably, but not necessarily, this body is placed in a low pressure zone of the system such as is found between the pressure reducing. means or regulator and the gas disposal means, although it is operable in the high pressure zone between-the regulator-and the closed tank. It is also desirable that the body of adsorbent material be kept in a dry condition, that is, not saturated or wet with the, liquefied hydrocarbon in liquid form.

Referring to the drawing and particularly to Figure 1, reference numeral designates a closed tank or container of liquefied hydrocarbons II which may be withdrawn through the outlet l2 by opening the valve l3 which may include a pressureregulating means. A conduit l4 leads from the valve l3 through a closed container l5 fitted with retaining meansor filters I6 which serve to confine a body of finely divided charcoal or other adsorbent material l1. Liquefied hydrocarbons II have previously been odorized by the addition of a small proportion of an odorant material such as the concentrated odorizing mathe liquid odorant material. are allowed to evaporate freely leaving the odor .terial prepared from petroleum hydrocarbons and sold by Standard Oil Company of California under the trade-mark Calodorant. Other types of odorant, so long as they are less volatile than the hydrocarbons H, may be utilized. To obtain the best results the adsorbent material I! in container I5 is precharged with the odorant material. This may be done by withdrawing a quantity of odorized gas through the new material I! or by saturating that material with a small quantity of liquefied hydrocarbons to which has been added The hydrocarbons ant material adsorbent or atleast retained in the material II.

Referring to Figure 2, it will be noted that the effect on odor intensity by withdrawal of gases from a mixture of liquefied propane with a small proportion of butane and containing the normal or usual proportion of odorant required by these liquefied hydrocarbons without using this invention is represented by curve A. In the test illustrated the normal proportion of odorant in liquefied hydrocarbons was used, that concentration being required to obtain an initial safety factor of 5 as defined by the United States Bureau of Mines R. I. 2979 quoted above. from this curve that the degree of odorization increased steadily from the beginning of the withdrawal period. It will be noted further that the gas representing about the last 20 per cent of liquid, and particularly the penultimate 1 per cent, was extremely over-odorized as evidenced by the high safety factor attained.

Curve B represent the relationship between the amount of liquid withdrawn as gas and the safety factor to attain degree 2 odorization when gas was withdrawn from a closed container of liquefied hydrocarbons containing only about 10 per cent of the amount of Calodorant represented by curve A and using this invention. It will be noted that when this invention was used the safety factor at notime fell appreciably below 25, which indicates that an even smaller proportion of liquefied odorant could have been used without falling below the recommended minimum safety factor of 5. Curve B also shows that during the withdrawal of gas representing about the first 20 per cent of the liquid evaporated, odorant was added to the gas by the precharged adsorbent material in l the gas line.

During the withdrawal of gas representing about the last 20 per cent of liquid and particularly the penultimate 1 per cent, the safety factor, did not rise above about 60 to 100, the average being about 72, which indicates the advantage of this invention over the prior art.

Although a single example of this method and means for carrying out the invention has been described and illustrated, it will be obvious that it may be applied to other uses and also that numerous modifications and changes may be made without departing from its essential features. In consequence, all such changes that come within the scope of the appended claims are embraced thereby. l

I claim:

1. A method of improving the uniformity of odorant concentration in a stream of gas withdrawn from a container charged with .a predetermined quantity of liquefied hydrocarbons and a lessvolatile odorant, which hydrocarbons and odorant will be subject to differential vaporization during said withdrawal whereby the lighter components will be volatilized before the It will be noted let for adding to about the first 20% of gas disheavier components thereof, the quantity of said odorant in said container being sufficient to impart acceptable warning properties tosaid withdrawn gas under conditions which would evaporatesaid odorant at substantially the same rate as said hydrocarbons, comprising directing said gas stream from the container through a zone having means therein for adding to about the first 20% of gas discharged an amount of odorant suflicient to give acceptable warning properties thereto and for abstracting from about the last 20% of gas withdrawn an amount of odorant sufl'lcient to restore to said means substantially the amount of odorant previously abstracted therefrom by said first Withdrawn gas.

2. A method of improving the uniformity of odorant concentration in a stream of gas withdrawn from a container charged with a predetermined quantity of liquefied hydrocarbons and a less volatile odorant, which hydrocarbons and odorant will be subject to differential vaporization during said withdrawal whereby the lighter components will be volatilized before the heavier components thereof, the quantity of said odorant in said. container being suificient to impart acceptable warning properties to said withdrawn gas under conditions which would evaporate said odorant at substantially the same rate as said hydrocarbons, comprising contacting the gas from said container with a body of. solid adsorbent material which previously has been charged with odorant-whereby the first gas withdrawn from said container is odorized to a degree which is not below the acceptable value. and said adsorbent removes odorant from the last gas withdrawn so that the average safety factor atodor intensity 2 is not over about60 in the penultimate 1% of gas that can be withdrawn by vaporization from the liquid in said container. f

3. A method according to claim 2 in which the safety factor at odor intensity 2 in the penultimate 1% of gas that can be withdrawn by vaporization from the liquid in said container. is not materially greater than the minimum safetv factor attained during the preceding part of that withdrawal period.

4. A method according to claim 2 in which the safety factor at odor intensity 2 of the penultimate 1% of gas that can be withdrawn by vaporization from the liquid in said container is not over about three times the minimum safety factor attained during the preceding part of that withdrawal period. I

5. In combination, a container of liquefied hydrocarbons such as butane, propane and the like to which has been added a predetermined quan-- tity of a less volatile odorant, which hydrocarbons and odorant will begsubiect to differential vaporizationupon reduction of pressure within said container due to withdrawal of gas therefrom whereby the lighter components will be volatilized before the heavier components thereof, the quantity of said odorant in said container charged an amount of. odorant suilicient to give acceptable warning properties thereto and for abstracting from about the last of gas discharged an amount of odorant sufficient to restore to said means substantially the amount of odorant previously abstracted by said first within a dry state.

which the means in said outlet conduit combeing sufllcient to impart acceptable warning outlet forsaid container and means in said outprises a dry solid adsorbent selected from the group consisting of charcoal, silica gel and acti-' odorant at substantially the same rate as said.

hydrocarbons, comprising contacting the gas from said container with a body of solid adsorbent material which'previousiy has been charged with odorant whereby the-first gas withdrawn from said container is odorized to a degree which is not below the acceptable value, and said adsorbent removes odorant from the last gas withdrawn so that the average safety factor at od r intensity 2 is not over about in the penultimate 1% of gas that can be withdrawn by vaporization from theliquid in said container.

10. A method of improving the uniformity of odorant concentration in a stream of gas withdrawn from a container charged with a predetermined quantity of liquefied hydrocarbons and a less volatile odorant, which hydrocarbons and odorant will be subject to diiierentiai vaporization during-said withdrawal whereby the lighter components will be volatilized before the heavier components thereof, the quantity of said odorant in said container being suflicient to impart acceptable warning properties to said withdrawn gas under conditions which would evaporate said odorant-at substantially the same rate as said hydrocarbons, comprising contacting the g s from said container with a body of solid adsorbent material which previously has been charged with odorant whereby the first gas withdrawn from said container is odorized to a degree which is not below the acceptable value, and said adsorbent removes. odorantfrom the last gas withdrawn-so that the average safety factor at odor intensity 2 is not over about in the penultimate 1% of. gas that can be withdrawn by vaporization from the liquid in said container.

C. DAYHUFF.

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