The condensate represented by test 2 (Table 7) was obtained when the pressure on the natural gas was 210 pounds per square inch. The liquid did not boil when withdrawn from the tank, although a bubble of gas would occasionally issue during the first hour of exposure. Hence the condensate probably contained only a small quantity of liquid butane. Likewise the proportion of pentane must have been smaller than in the condensates obtained from plant A.

The condensates represented in Tables 7 and 8 were obtained from different plants than those represented in Table 6. The pressures employed were practically the same, yet the character of the condensates differed. For instance, all of the condensates obtained in the tests conducted at plant A would boil more or less at first, owing to escaping gas. Those obtained at plants B and C bubbled only a little. This difference was largely due to differences in the composition of the natural gases used at the plants.

In Table 9 are shown the results of blending natural-gas condensate (specific gravity 48° B.) from plant A (Table 1) with naphtha having a specific gravity of 57° B. The percentages of losses are calculated to percentage losses of the natural-gas condensate and not of the mixture.

The conditions under which these tests were conducted would not warrant definite conclusions regarding the decrease of evaporation rate to be effected by blending. However, the losses after blending were still large.

If the evaporation loss were to be calculated to the percentage loss of the mixture of condensate and naphtha the percentage of losses on the blends would be much reduced, but the figures so obtained would not show the true loss of condensate. Some experimenters have probably done this and misled themselves into believing that the percentage so calculated represented the actual loss of condensate. The authors calculated the blending losses by throwing the loss wholly on the condensate. They determined by experiment that the evaporation loss of the refinery naphtha used in making the blends was so small as to be inappreciable as compared to condensate losses.

RESULTS OF EVAPORATION TESTS IN WEST VIRGINIA.

Table 10, following, shows the evaporation losses when natural-gas condensates from a different plant than those mentioned previously had been exposed to the atmosphere. The evaporation losses shown in the preceding tables occurred at plants along the Allegheny River near the New York State line. The tests represented in the table following were made at a plant in West Virginia. Plant operations were so conducted as regards pressures that condensates of different specific gravities were obtained. The condensates were allowed to evaporate in graduated glass cylinders of the same form as those used in the tests covered by Tables 6 to 9.

TABLE 10.-Evaporation losses of condensates from the same plant, but of different specific

gravities.

Gravity.

Loss.

hours.

hours.

Loss.

Table 11, following, shows results obtained when mixtures of naturalgas condensate and refinery naphtha were exposed to the air and allowed to evaporate. The tests were made at the same plant as the tests covered by Table 10, and with the same condensates.

TABLE 11.-Evaporation losses of mixtures of natural-gas condensates and refinery

naphthas.

a Test conducted in a shallow pan, 8 inches in diameter and 1 inch deep.

TABLE 11.-Evaporation losses of mixtures of natural-gas condensates and refinery naphthas-Continued.

Proportions

Specific

in mixture. gravity

of

End of 6

hours.

End of 7

End of 8

End of 24
hours.

hours.

hours.

Temperature of at

mosphere.

gravity.

Loss.

Specific
gravity.

Loss.

Specific

gravity.

Loss.

a Test conducted in a shallow pan, 8 inches in diameter and 1 inch deep.

DISCUSSION OF RESULTS SHOWN IN TABLES 8 TO 11.

As shown in Table 10 the losses when condensates of gravities. between 79° and 98° B. were exposed to the atmosphere were as follows: One hour, 0 to 19 per cent; 2 hours, 0 to 26 per cent; 3 hours, 1 to 34 per cent; 4 hours, 2 to 38 per cent; 5 hours, 2 to 42 per cent; 6 hours, 3 to 45 per cent; 7 hours, 4 to 48 per cent; 8 hours, 4 to 46 per cent; and for 24 hours, 10 to 65 per cent. At the end of 24 hours. the temperatures of the condensates were practically the same as the temperature of the atmosphere.

If tests 1 and 2, Table 10, be excepted, the largest losses occurred during the first hour and the rate of evaporation gradually decreased. This is to be expected. Most of the material that first evaporated was liquid butane. Liquid butane boils at 1° C. (34° F.); hence it would evaporate rapidly. The rate of evaporation of the pentanes and hexanes is, of course, much slower. The curves shown elsewhere clearly illustrate these points.

Table 11 shows the evaporation losses when the natural-gas condensates were mixed with refinery naphthas and allowed to evaporate. The rate of evaporation for tests 1 and 2 (Table 11) are almost the same, but slightly slower than of test 9 (Table 10), which represents the evaporation loss when the condensate alone was allowed to evaporate. The difference is especially noticeable at the end of the second hour, being 19 per cent as against 12 and 13 per cent. The rates are not widely different for the remaining period, but still noticeable. Tests 3, 4, 5, 7, and 9, Table 11,

may be compared to tests 4, 5, 6, 7, and 8, Table 10. In the former when condensates alone were allowed to evaporate the losses for the first hour ranged from 13 to 19 per cent. When condensates of approximately the same specific gravity were mixed with naphtha and allowed to evaporate, the losses for the first hour ranged from 4 to 14 per cent.

DIFFERENCE IN EVAPORATION RATES OF MIXTURES.

The difference in the evaporation rates, shown for the mixtures, is marked all through the tests. The following tabulation clearly brings out this variation:

Evaporation losses of condensates and "blends" for periods ranging from 1 to 24 hours.

In the tests represented in the foregoing table for all of the "blends," condensates with specific gravities of 94° to 98° B. were used. However, Table 11 shows that in preparing the "blends," different amounts of the condensate were used for different tests. In some of the tests the "blends" were prepared by mixing the condensates and naphtha in equal proportions. In others, the proportions were 70 per cent of condensate and 30 per cent of naphtha; in others, 60 and 40. Table 11 shows that the evaporation rates were slower when the smaller quantities of condensate were used, as was to be expected.

COMPARATIVE EVAPORATION LOSSES OF MIXTURES AND CONDENSATES.

Table 12 shows the evaporation losses when the condensates alone were exposed to the atmosphere and when the condensates were mixed in various proportions with the naphtha. This table was compiled from the results of tests 1, 2, 3, 4, 5, 9, 10, and 12, Table 11, and tests 3, 4, 5, 7, 8, and 9, Table 10.

TABLE 12.-Comparative evaporation losses of blends prepared by mixing different proportions of condensate and naphtha and of condensate alone.

The slower rates of evaporation of the mixtures of condensates and naphtha as compared to those of the condensates alone follow from the fact that if two liquids dissolve each other in all proportions, and if they have widely different vapor pressures and boiling points, the vapor pressure of the mixture frequently falls between the vapor pressures of the components, and the boiling point of the mixture falls between the boiling points of the components. The more volatile liquid evaporates principally, at first, during the distillation, the less volatile liquid remaining behind, so that by a repetition of the process the two may be more or less completely separated. As evaporation continues a mixture is finally left that contains components whose boiling points and vapor pressures lie near together.

FACTORS AFFECTING RATE OF EVAPORATION.

Attention should be called to the higher evaporation rates of tests 3 and 4, Table 9, as compared to tests 1 and 2, Table 9. Tests 3 and 4 were conducted in shallow pans, whereas tests 1 and 2 were conducted in tall narrow cylinders. For a given temperature, other things being equal, the rate of evaporation is almost proportional to the area of the surface of the liquid.

In actual operation different evaporation losses will be sustained than those mentioned above, depending upon the shape of the container that is used for holding the liquid when the latter is exposed to the air. If the mixture be placed in a drum such as is ordinarily used for transporting natural-gas gasoline, and the bunghole left open there will occur a much slower rate of evaporation than if the entire surface of the liquid be exposed to the air by means of an opening, say, as large as the area of the liquid.