Gas Producers.—The substitution of gas for steam in the paper mill has not yet proved a success. The fact that heat is required for the drying cylinders of a paper machine, and that the heat is most cheaply and readily obtained in the form of exhaust steam from the engines driving the paper machine, militates considerably against economies which might otherwise be possible. The difficulties of heating such cylinders, or rather of properly controlling and regulating the temperature by any other means than steam, may easily be surmised.
Gas engines of over 200 h.-p. seem to give considerable trouble at present, but no doubt in course of time the required improvements will be effected.
It is generally supposed that gas producers can only be economical when utilised for the production of gas on a large scale, and for distribution to engines of smaller capacity than the main steam engine required in a paper mill. The peculiar conditions of the manufacture of paper do not appear to be favourable to the adoption of the gas producer system in its present form.
Motive Power.—The paper-maker has taken advantage of every modern improvement in steam engines for the purpose of reducing the cost of motive power. Amongst other alterations in this direction the use of a high speed enclosed engine and the employment of the modern steam turbine may be noted.
In the enclosed engine the working parts are boxed in by a casing fitted with oil-tight doors. The cranks and connecting rods splash into the oil, which is thus thrown about in all directions, so as to ensure sufficient lubrication. Another feature of this engine is the variable speed, and it is possible to run the paper machine at speeds varying from 100 to 500 ft. per minute without the use of change wheels.
Electrical Driving.—The application of electricity for motive power has made steady advances in the paper mill. At first it was limited to the driving of machinery in which variations of speed or load were not required to any large extent, but of recent years beating engines, calenders, and paper machines have all been fitted with electrical drives.
Fig. 56.—An “enclosed” Steam Engine.