Gas-Power.
Steam as motive power finds its most formidable rival in cheap gases, whose familiar varieties have been long used for illumination. A simple experiment shows with what ease gas can be made, which, duly cooled, may be carried long distances without the condensation which subtracts from the value of steam. Take a narrow tube of metal or Jena glass, open at both ends: put one end near the wick of a burning candle, at the other end apply a lighted match, and at once a flame bursts forth. Here is a miniature gas-works; close to the wick inflammable gases are generated by the heat, before they have time to burn they are conveyed through the tube to a point a foot distant where, on ignition, they yield a brilliant flame. Enlarge this operation so that instead of an ounce of wax you distill tons of coal from hundreds of big retorts; set up a gas-holder as huge as the dome of the Capitol at Washington; instead of short tube lay miles of pipe through the avenues and streets of a city, and a trivial experiment widens into lighting a hundred thousand homes. So much for dividing combustion in halves, by conducting gasification in one place on a vast scale, and burning the produced gas whenever and wherever you please. One supreme advantage of the process is that coal, wood and other sources of gas much cheaper than wax or oil can be employed. Alongside the retorts which gasify coal or wood are built scrubbers which remove substances undesired in the gas,—tar, sulphur, and so on,—all salable at good prices. It was in 1792 that William Murdock, an assistant to James Watt at the Soho Works near Birmingham, there originated gas-lighting. His enterprise was a seed-plot for a variety of industries which have reached commanding importance, and are to-day expanding faster than ever before. Illuminating gas from its first introduction has on occasion wrought disaster; when it leaks through a joint into a room it rapidly unites with air; instantly on the intrusion of a flame there is a violent explosion, that is, an abrupt output of enormous energy set free under circumstances which do only harm. Can the energy, as in the case of blasting, be usefully directed?
Combustible gas from a candle is taken through a tube to a distance and there burnt.
Yes, as long ago as 1794, Robert Street designed a pump driven by the explosion of turpentine vapor below the motor piston. He was followed by inventors who used illuminating gas as their propelling agent; among these, in 1860, was Lenoir of Paris, who built a double-acting engine with a jump-spark electric igniter such as to-day is in general use. His engine consumed 95 feet of gas per hour for each horse-power, which meant that commercially the engine was a failure. Lenoir’s design has been so much improved that now large gas engines yield in motive power one fifth of the whole value of their fuel, an efficiency twice that of the best steam engines or turbines, and five-fold better than that of Lenoir’s apparatus.
Producer Gas.
How this remarkable result has been attained we shall consider a little further on, as we briefly examine the construction of a typical [gas engine]. At this point let us note how a gas, suitable for an engine, is manufactured at least cost, the outlay being much less than in the case of illuminating gas which represents but one third of the coal placed in the distilling retorts. Instead of this process of distillation, “producer” gas is due to a modified combustion which gasifies all the fuel. In a producer of standard type, atmospheric oxygen comes into contact with the glowing carbon of the coal or wood, forming carbon dioxide, CO². The heat generated by this union is taken up by the carbon dioxide and the nitrogen of the supplied air. These gases as they rise through the fuel bring it to incandescence so that the carbon dioxide takes up another atom of carbon, becoming carbon monoxide, CO, a highly combustible gas. Were there no impurities in the fuel, were the entering air quite free from moisture, the gases would be in volume 34.7 per cent. carbon monoxide and 65.3 per cent. nitrogen, with a heating value per cubic foot of about 118 British thermal units, a unit being the heat needed to raise a pound of water to 40° Fahr. from 39°, where its density is at the maximum. Gas thus produced is intensely hot; and as usually it contains sulphur, dust, dirt, and other admixtures, their removal by water in a scrubber would involve a waste of about 30 per cent. of the fuel heat. This loss is much diminished by sending into the producer not only air but steam, to be decomposed into oxygen and hydrogen; the oxygen combines with carbon to form more carbon monoxide, while the hydrogen is the most valuable heating ingredient in the emitted stream of gases. Were only air sent through the producer, the outflowing gases would contain nitrogen to the extent of 65 per cent.; with a charge in part air and in part steam, this percentage falls to 52; as nitrogen is useless and wastefully absorbs heat, this reduction of its quantity is gainful. By a duly regulated admission of steam, a producer is kept at a temperature high enough to decompose steam, but not so high as to send forth gases unduly hot to the purifier.
For water-gas the method is to blow steam into the fuel until decomposition ceases; the steam is then shut off, the fire allowed to recover intense heat, when more steam is injected, and so on intermittently.
