NAPHTHALENE IN COAL GAS 463
The following table has been compiled from the results and curves given by Thomas :—1
Naphthalene Saturation of Coal Gas
Temperature. Grains per 100 cubic feet. Pounds of naphthalene contained in a million cubic feet of dry gas.2
Cent. Fahr. Dry Gas.2 Wet Gas.2
0 32 1-85 0-55 2-64
5 41 3-26 111 4-66
10 50 5-59 1-98 7-99
15 59 9-39 4-02 13-4
20 68 15-5 7-93 22 1
25 77 25-2 14-2 36-0
30 86 40-3 34-5 57-6
40 104 98-5 101-9 141
50 122 227 252 324
60 140 497 552 710
The effect of water vapour upon the degree of Saturation will be observed from a comparison of the figures for wet and dry gas. Between 0° and 30° C. the Saturation vapour pressure of naphthalene in moist gas is less than that in dry gas. At about 40° C. the Saturation in both gases is identical, wliile above 40° C. the Saturation naphthalene content of wet gas is rather greater than that of dry gas. The difference has been ascribed to the condensation of a skin of water upon the naphtha-lene in the case of moist gas.
Neglecting the factor of supersaturation, the above table indicates that a million cubic feet of dry gas cooled in the mains from 20° C. (68° Fahr.) to 15° C. (59° Fahr.) may deposit 8-7 1b. of naphthalene; or if the same volume of gas was cooled from 20° C. to 10° C. the quantity deposited might be 14-1 1b.
It must be emphasized that the above figures should not be applied in Order to calculate the quantity of naphthalene which might be deposited for any definite temperature drop in the coal-gas condensers. The figures relate solely to the evaporation of naphthalene into coal gas, and the problem of naphthalene condensation mtroduces other factors which require entirely separate investigation. A point of considerable importance in gas engineering arises on account of the lower values of the Saturation naphthalene content of coal gas obtained by Thomas for temperatures up to 30° C. as compared with the values given by Allen; for on the basis of the latter’s figures no trouble should arise from naphthalene in the district mains so long as the gas as distributed contains less than 10 grains of naphthalene per 100 cubic feet. In point of faet, assuming that the lowest gas main temperature in et with is about 5° C. (40° Fahr.), the amount of naphthalene required to saturate
1 J. Soc. Chem. Industry, 1916, 506.
2 Measured at temperature of the experiment and pressure of 760 mm.