The generator for the manufacture of what is known as "crude oil water gas" is very similar to that used for ordinary water gas ; in fact, under one system the old apparatus is converted to the new use by con structing checker work in the generator proper and placing the oil burners at the top instead of at the bot tom. But the greatest success is obtained where the apparatus is specially constructed for the purpose. In this apparatus, the generator, instead of a bed of fuel, has a fire brick checker, which is heated by means of oil burners, carbon being at the same time deposited on the brick. The proper heat in the generator and superheater being attained, the air supply is shut off, and the steam and oil introduced, as in making ordi-. nary water gas. The steam combines with the carbon on the checkers, forming water gas, while the oil is decomposed to form oil gas, which is fixed in the usual manner. The apparatus, like the usual water gas sets, is intermittent in its action.
The making of crude water gas does not require any special grade of oil. It is made from the heavy Californian and Mexican oils as well as from the lighter grades of Texas oils, and either the crude oil from the wells, or its distillates or residuums may be used. The amount of oil required per 1000 cubic feet depends upon the grade of gas, but general it requires about 8 gallons per 1000 cubic feet in large plants, and about 12 gallons per 1000 cubic feet in small plants.
In the past ten years great progress has been made in the making of gas from crude oil. For years the one feature which has prevented oil from being an ideal material for gas manufacture has been the large percentage of the rich hydro-carbons which are dissociated, only the hydrogen portion of which ap pears in the gas, the carbon being a by-product. The severe treatment of the oil with extremely high heats was the cause of the production of lampblack in the early oil gas, and the proportionately poor quality of the gas. It was not alone the extreme temperature but, the lack of uniformity of temperature. The high temperature is what is called "false" or "surface heat" ; that is, the actual temperature existed, but its capacity for doing work in the breaking up of the oil was lack ing. The extreme temperature existed only during the beginning of a run or gas making period and in the lat ter part of the run, the temperatures were far below any now utilized for gas making. If this had not been the case the efficiency of the early gas would have been extremely high, only the quality of the gas being low ; and if uniform heats had been used, the early gas man would have encountered no scrubbing troubles other than the removal of lampblack ; tar would have been unknown.
It was not unusual to have from 30 to 35 lb. of lampblack from each 1000 cubic feet of gas made, and in a large gas plant manufacturing 6,000,000 cubic feet of gas daily this was a very important item. The lamp black as it was removed from the separators contained from 50 to 60 per cent water, and it was necessary to drain off this water, until it was reduced to about 30 per cent, before it could be used as a fuel. Only a certain amount of this lampblack could be used under the boilers, so it became necessary to find a market for the balance' The lampblack was made into briquettes and sold for domestic use ; these made an ideal fuel for use in open grates, as may be seen from the following analysis, which was made of a briquette that had been stored for nearly one year : Tests have been made at various times during the process of oil gas manufacture and the following gives the results of a typical run : To determine the part played by the steam in mak ing gas the following runs were made first, in the ordi nary way ; second, with oil injected under its own pres sure without steam ; third, by steam without the use of any oil. In each case the test was made after the generator had been heated ready to make gas : Ordinary run—Same pressure as combined oil and steam runs, 17 inch pressure inside machine, 47 gal lons a minute.
All oil run-18 lb. to 19 lb. pressure, on primary, 25 to 27 lb. oil pressure on secondary ; 21 inch pressure . inside machine ; 51 gallons a minute.
All steam run-25 lb. pressure on heat burners ; 26 lb. pressure on primary make burners ; 32 lb. pres sure on secondary make burners ; 10 to 11 inch pres sure inside machine.
The run made with all steam cannot be directly compared with the other two runs, as very little gas was produced ; barely enough to enable the taking of a sample at the wash box. The generator at this period was at the same temperature as during ordinary runs ; that is, it was at a temperature high enough to decom pose steam in the presence of incandescent carbon, and only 10.6 per cent of carbonic oxide was produced. Had there been much carbon deposited on the checker brick, this generator would have been in ideal condi tion for the manufacture of blue water gas.