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"DRY" NATURAL GAS.
Some natural gas contains only methane as the combustible constituent and according to the above classification may be considered the driest of natural gases. This kind of gas is rare in the oil fields, but is common in gas fields, or in marshy districts unassociated with oil. The Hogshooter pool of Oklahoma, according to tests made by the bureau, produces a natural gas that contains methane as the only combustible constituent.
This kind of gas is found in States or districts in which oil has never been found. Incidentally it might be mentioned that the occurrence of such gas naturally escaping from the surface of the earth affords some proof of the nonexistence of oil. However, the indication is not infallible, because some natural gas that contains only methane as the combustible constituent is found in the oil fields. This gas comes from sands that do not bear oil.
The next grade in the transition of "dry" to "wet" gas may be considered that at present obtained from the Appalachian oil fields and used in Pittsburgh, Pa., and other cities. This natural gas issues under considerable pressure from wells in or near the oil fields. It has varied little in composition from the figures given on page 24 for the three years that the Bureau of Mines has been testing it. Air has never been detected in the samples tested. Many wells are abandoned yearly by the company that furnishes the city the supply, and new wells are drawn upon, the wells being abandoned when the rock pressure becomes so low as to be insufficient to assist in forcing the gas to Pittsburgh and other points of consumption, or when the yield becomes too small even with the gas pumps that are used. In composition this gas is typical of the natural gas supplied to many cities. All of the ingredients present are gases at ordinary temperatures. Traces of butane and even of higher paraffin hydrocarbons are present-enough because of the many thousands of cubic feet of gas transported daily, especially in the winter time, to cause some condensation of vapors or drip, in the pipe lines. This gas has been said to pass at the rate of a mile a minute through mains connecting the wells to Pittsburgh. The drip is not sufficient to indicate that the gas is of value for gasoline extraction.
As to the so-called "wet" gas, or that from which gasoline can be extracted in quantity sufficient to warrant the installation of a plant, the proper testing of such gas in order to determine its gasoline content is of much importance. In the early days of the gasoline industry some failures of plants to fulfill expectations were due to inadequate testing of the gas before the construction of the plant had begun.
METHODS AND EQUIPMENT USED IN TESTS.
At present, tests have become better standardized, and there is scarcely any excuse for the failure of a plant because of inadequate preliminary tests. By itself, the ordinary eudiometric analysis is of little value for determining the gasoline content of natural gas. Moreover, it is extremely difficult to make, and the authors are safe in saying that a gas analyst must have had experience in refined analytical methods before he can make a satisfactory analysis of natural gas, especially of "wet" gas. In addition, the ordinary gasanalysis determination informs one only of the two predominating paraffins present but gives slight knowledge of the quantity of gasoline vapors. Early in the history of the industry, gas analysts turned their attention to other more easily conducted and more definite tests. Those laboratory methods adopted and at present in chief use have to do with solubility and specific-gravity tests.
Natural gases are soluble in various solvents, such as alcohol, claroline oil, olive oil, kerosene, sperm oil, and rape-seed oil, in proportions depending upon the amount of higher paraffin hydrocarbons present in the gas mixture. All of the solvents mentioned have been used. F. P. Peterson, of Tulsa, Okla., informed the authors that he found it expedient to use claroline oil.
USE OF CLAROLINE OIL.
The Bureau of Mines methods of testing are described in Bulletin 42a of the bureau. In using claroline oil the following procedure is adopted: 35 c. c. of the oil is placed over mercury in an ordinary Hempel gas pipette, and 100 c. c. of the natural gas to be tested is shaken with the oil until no further absorption of the gas mixture occurs. It was found that many natural gases from which gasoline is at present commercially obtained were soluble in the oil to the extent of 30 to 86 per cent of their volume.
In figure 1 is shown a gas-analysis apparatus for determining the solubility of natural gas in claroline oil or alcohol. It consists of a measuring burette, e, having a capacity of 100 c. c., and an absorption pipette, c. It is provided at the top with a three-way T stopcock, d, so that communication can be made between the burette and outside air, or between the burette and the pipette. Water is used in the burette and mercury in the pipette. To begin an analysis, 35 c. c. of claroline oil or 50 c. c. of alcohol is placed in the pipette c over the
a Burrell, G. A., The sampling and examination of mine gases and natural gas, 1913, 116 pp., 2 pls.,
mercury. A 100-c. c. part of the gas sample is then drawn into the burette, measured, and forced into the pipette c. The pipette c is shaken for about three minutes to thoroughly mix the oil or alcohol and gas. The gas is then transferred to the burette and measured, and the loss in volume is noted. The gas is again passed into the pipette and the shaking operation repeated. Finally the gas is
FIGURE 1.-Apparatus for determining the gasoline content of natural gas.
measured again in the burette. The first and second readings should agree within 0.50 per cent. If they do not, the operation should be repeated until the burette readings become constant.
Below are given tables showing the solubility of natural gas and of methane and ethane in different oils. A 35-c. c. sample of the oil was shaken with 100 c. c. of the gas until absorption of gas by the oil ceased.
Solubility in different oils of the natural gas used at Pittsburgh.
Russian white (kerosene).
Kind of oil used as solvent.
Character of oil.
It was possible to check the above determinations within 0.50 per cent. Considerable uniformity as regards the solubility of the natural gas in the different oils will be noticed. The claroline oil used had the following characteristics, as determined by I. C. Allen, chemist of the bureau:
Solubility of pure methane in claroline and cottonseed oils.
Characteristics of claroline oil.
0.8667 at 15° C.
4. 4° Engler at 20° C.
152° C., Pensky-Martens closed test.
USE OF ALCOHOL AS A SOLVENT.
Solubility of gas.
Character of oil.
Solubility of methane.
The solubility of pure ethane in claroline oil, as determined by the authors, was 68.5 per cent.
The Bureau of Mines has used ethyl alcohol in much the same manner that claroline oil is used for testing natural gas. Instead of 35 c. c. of the claroline oil, 50 c. c. of ethyl alcohol may be used. The procedure otherwise is exactly the same. The results obtained with alcohol are similar to those with claroline oil.
ORSAT APPARATUS FOR DETERMINATION OF CARBON DIOXIDE AND OXYGEN.
In figure 2 is shown an Orsat apparatus for the determination of carbon dioxide and oxygen in natural gas. The Orsat apparatus is so well known that it needs little description. It is sufficient to say that the burette has a capacity of 100 c. c. The pipette b contains caustic potash solution for the removal of carbon dioxide, and the pipette a contains alkaline pyrogallate solution for the removal of oxygen. The figure (fig. 2) shows the level bottle of the burette, the water jacket, and a three-way stopcock, c. This apparatus may
be used to advantage for examining natural gases to determine whether air has leaked into mains, owing to the reduced pressures that are maintained in pipe lines at some gasoline plants.
Natural gas may vary in specific gravity from about 0.56 (air= 1) to as much as 1.65, or from a gas containing methane only as the paraffin hydrocarbon in proportions approaching 99 per cent or more of the total to an extremely "wet" gas, from which gasoline in quantities up to 4 or 5 gallons per 1,000 cubic feet can be obtained. Specific-gravity tests may be made either by weighing the gas in a small glass vessel or by means of Bunsen's effusion method. The weighing method is the more accurate. The following procedure is adopted by the Bureau of Mines:
A 100-c. c. glass globe, equipped with a stopcock, is exhausted of its contained air, thoroughly dried, and weighed. Natural gas is then introduced and a second weighing made. This weight as compared to that of an equal volume of air at the same temperature gives the specific gravity.
FIGURE 2.-Orsat apparatus for determining carbon dioxide and oxygen in natural gas.