The cracking of the naphtha by the red hot coke is undoubtedly a great advantage, for, as I have pointed out, the cracking of rushing petroleum is an exothermic reaction, so that the coke at the top of the generator gets hotter and hotter, and it is no unusual thing to see the coke at the beginning of the make cherry red at the bottom and dull red at the top, while at the end of the make it is almost black at the bottom and cherry red at the top, in this way attaining the same advantage in working that the Springer and Loomis do by their down blast, that is, having the fuel at its hottest where the gas finally leaves it, so as to reduce the quantity of carbon dioxide, and so lessen the expense of purification.
It will be well now to turn for a few moments to the gas obtained by cracking the light petroleum oils by themselves. The Russian and American petroleum differ so widely in composition that it was necessary to see in what way the gases obtained from them differed; and to do this, equal quantities of American naphtha and a Russian naphtha were cracked, by passing through an iron tube filled with coke, and in each case heated to a cherry red heat, the gases being measured, and then analyzed, with the following results:
| American. | Russian. | |
|---|---|---|
| No. of cubic feet per gallon. | 72 | 104 |
| —— | —— | |
| Hydrogen | 26.0 | 45.3 |
| Methane | 41.6 | 22.3 |
| Ethane | 12.5 | 13.9 |
| Olefines | 14.1 | 11.6 |
| Carbon monoxide | 3.3 | 3.5 |
| Carbon dioxide | 1.7 | 2.3 |
| Oxygen | 0.8 | 1.1 |
| Nitrogen | Nil. | Nil. |
| —— | —— | |
| 100.0 | l00.0 |
Showing that, if the Russian oil is a little lower in illuminants, it quite makes up by extra volume, but it seemed to me to deposit a much larger proportion of carbon.
Taking 21/2 gallons of American naphtha, it would give roughly 180 cubic feet of gas of the above composition, while the remaining gas would be the ordinary water gas. Taking the analysis of this as given, and calculating from it what would be the composition of a mixture of it with the naphtha gas, we obtain:
| Calculated. | Actual. | |
|---|---|---|
| Hydrogen | 47.09 | 42.09 |
| Methane | 5.48 | 11.27 |
| Olefines | 2.53 | 7.59 |
| Ethane | 2.17 | 6.32 |
| Carbon monoxide | 30.07 | 18.65 |
| Carbon dioxide | 3.78 | 2.32 |
| Oxygen | 0.56 | 0.17 |
| Nitrogen | 7.17 | 8.25 |
| Sulphureted hydrogen | 1.15 | 2.84 |
| —— | —— | |
| 100.00 | 100.00 |
Showing how great the effect is of the diluents in the water gas in preventing the overcracking of the hydrocarbons, as shown by the increase in the percentage of them present in the finished gas; while the enormous reduction in the amount of carbon monoxide present is due to the interaction between it and the paraffin hydrocarbons in the presence of red-hot carbon, a point which makes the Van Steenbergh apparatus enormously superior to any of the superheater forms of plant.
After all said and done, however, the reactions taking place, although they have an intense fascination for the chemist, are not the factors which the gas manager deems the most important, the cost of any given process being the test by which it must stand or fall; and it will be well now to consider, as far as it is possible, the expense of enriching coal gas by the various methods I have brought before you.
In order to be well above the prescribed limit of illuminating power at all parts of an extended service, the gas at the works must be sent out at an illuminating power of 17.5 candles and we may, I think, fairly take it that 16 candle coal gas, as made by the big London companies, costs, as nearly as can be, 1s. per 1,000 cubic feet in the holder, and the question we have now to solve is the cost of enriching it from 16 to 17.5 candle power. When this is done by cannel, the cost is 2.6 pence per candle power, so that the extra 11/2 would cost 4d. per 1,000.
Carbureting by the vapors of gasoline by the Maxim-Clarke process costs 13/4d. per 1,000, so that the extra candle power would mean an expenditure of 2.62d. Unfortunately I have no figures upon which to calculate the cost of producing such a gas by the Dinsmore process, but with the three important water gas enrichers we can deal.