What this amount of steam can accomplish in combination with the mercury turbine in existing power plants is shown by the table below: Case A represents the best development of modern plants with 35o lb. pressure, high superheat and the most effective auxiliary and feed heating arrangements. Case B represents a station that was considered very good a short time ago with about 200 lb. steam pressure, less perfect firing and auxiliary arrangements and less superheat. Case C represents a station in which conditions of size, load factor or efficiency are even less favourable. Case D represents what might be done in a good non-condensing station. The ratios here shown are not much affected by the usual causes of relative inefficiency such as load factor, turbine efficiency or condensing facilities.
The mercury cycle lends itself particularly to the increasing of station capacity of existing plants. By burning approximately 20% more fuel, the same amount of steam as before can be produced, the power from the mercury turbine will be almost equal that produced by the steam turbines, the fuel rate of the mercury turbine will be at approximately 4,000 B.T.U. per kilo watt hour, and the fuel rate of the steam turbine will remain as before. If this rate was 17,00o B.T.U. per kilowatt hour, the combined rate would be at about 10,500 B.T.U.—a gain of 38%.
Heating Plants.—From the figures that have been given, it
will be seen that the gain in economy is incident to the production of steam by a method which gives a valuable by-product in the form of power. A very striking case of profitable use is found in a city heating plant. If, in such a plant, this unit were used in connection with a suitable steam turbine unit which would take steam at 35o lb. gauge pressure, superheated and exhausted into the street mains at Ioo lb. per square inch and saturated, the results with the best coal burned efficiently would be about as fol lows : Fuel burned per hour, 14,500 lb. ; steam delivered per hour, 125,000 lb.; power produced by mercury turbine, io,000 kw.; power produced by steam, 3,400 kw. ; total power produced, 13,400 kilowatts. From these figures it will be seen that the power is produced at a rate of about 16,000 B.T.U. in fuel per kilowatt hour, which is comparable with very good condensing steam stations, and that all this ioo lb. heating steam is produced in addition.
A careful investigation in regard to the probable mercury supply of the world indicates that it is sufficient to take care of this process for practically an indefinite time. The present mercury mines in operation could easily double their output which would take care of i,000,000 kw. per year, in addition to the present uses of mercury.