_Taylor gas-producing plant_ (Fig. 44).—The future of gas engines, especially large units, is intimately connected with production of poor gases at low cost, for they would be far from economical if coal gas were used at the price at which it is usually sold. For this reason many inventors have attempted to devise apparatus which should produce gases suitable for being used in a gas engine, by the decomposition of steam by red-hot carbon. The Taylor system is one of the best of those which have appeared in the last few years. It has been thoroughly tested in practice. The plant consists of a generator and boiler, a series of cleansing and washing towers, and a gasometer. The most important feature is the automatic manner of getting rid of the coke ash from the generator by a moving hearth, which enables it to be cleaned out without stopping the production of gas. By this system cheap coal can be used instead of anthracite, which is more expensive. The steam boiler is placed on the generator, and is heated by the gases coming from it. The steam passes first of all through a superheater consisting of a number of tubes round which circulate the gases from the generator. The high temperature of the mixture of steam and air ensures a good efficiency. The gases produced in the generator pass through vertical tubes, exposing them to a large cooling surface, where they are chilled; they then pass through scrubbers lined with coke and so into the gasometer. [Illustration: FIG. 44.—Taylor Gas-producing Plant.] The gaseous mixture, consisting of hydrogen, carbon monoxide, etc., produced in the generator has a heat of combustion of from 1400 to 1500 calories. The relative heating power compared with coal gas is therefore two-sevenths. A motor consuming 700 litres of coal gas would require 2500 litres of the poor gas produced by this system to develop the same power, and 550 grammes of anthracite would be consumed in the process. The cost per horse-power hour varies according to the price of materials. Supposing we have an eight horse-power motor consuming 25 cubic feet of coal gas per horse-power hour, at 2_s._ 6_d._ per 1000 cubic feet, and working for 10 hours, the cost per day would be 8 × 25 × 30 × 10_d._ ———————————————————— = 5_s._ or ¾_d._ 1000 per horse-power hour. If, on the other hand, it were supplied with poor gas generated from anthracite costing 25_s._ a ton, it would burn about 1¼ lbs. per horse-power hour, costing 16_d._, which is about one-fifth the cost, and using cheap coal this cost can be still further reduced. These figures clearly show how much cheaper it is to burn poor gases than coal gas.