A vision and experiment for 30 years, the mercury-vapor turbine is now finally developed to a point where it may yield the 50% or more increase in power-producing efficiency which has long been hoped from it. For three General Electric engineers (in papers recently published by the American Society of Mechanical Engineers) report that the known faults of mercury-vapor engines have at last been conquered.
The most efficient steam turbine in the U.S. (TIME, Nov. 24) converts about 33% of its fuel's heat into energy. Reason: most of the heat must always be transferred not to the turbine's whirling rotors as force but to the water which cools and condenses the steam for re-use in the boiler. Much of this wasted heat is conserved in a mercury-vapor turbine operating with a secondary steam turbine. The mercury vaporized at 975° F., blasts through the rotors and then, while condensing, boils the water which cools it. This creates steam for a second turbine. Some heat is still wasted, of course, when the steam in turn is condensed. But in effect, two turbines are operated with the heat wastage of one.
The mercury turbine was first conceived about 1912 by the late William LeRoy Emmett. He tinkered with small-scale machines in G.E. laboratories until 1922, when the progressive Hartford (Conn.) Electric Light Co. volunteered to install a 1,800-kilowatt mercury plant for commercial power production. It was not a thumping success, nor were two 20,000-kw. plants built for the New Jersey's Public Service Electric & Gas Co. at Kearny and for G.E. at Schenectady.
Trouble was that the mercury 1) dissolved a lot of rust from the steel tubes it moved through, 2) did not heat uniformly, so that it flowed poorly, overheating certain boiler pipes. A corps of chemists, metallurgists, engineers finally figured out the reason. Mercury—with its well-known tendency to hug itself in little globules—was not "wetting" the steel heating tubes in intimate contact. Hence oxygen crept between the two metals and rusted the steel, and the uneven contact led to uneven heating. What was needed was a wetting agent for the mercury. Scientists found it by putting traces of magnesium and titanium in the mercury. Now the mercury covers the tubes as evenly as water. Boiler design was also revised.
The Kearny plant was rebuilt in 1940, run for over a year under all conditions. Its efficiency averages over 37%, reports Engineer Harold N. Hackett. It uses 1,300 fewer B.T.U. (fuel heat units) to produce a kilowatt-hour than any steam plant in historya saving of about 12%. "Future applications of the [mercury with steam] cycle may exceed 50% thermal efficiency," predicts Hackett.
In ships such a saving may be doubly important, for they must not only buy but haul their fuel. Cargo capacity of merchant ships, cruising range of warships can be upped by a 25 to 40% economy of fuel. (A mercury-powered ship was planned in 1938 by Sun Shipbuilding & Dry Dock Co., then postponed until mercury's problems were overcome.)
The 20,000-kw. Kearny turbine uses 310,000 Ib. of mercury (normal value: about $250.000). Widespread use of mercury in turbines, engineers are sure, will not be hindered by inadequate supplies in a peacetime world. But today all mercury in the Western Hemisphere funnels into U.S. war industries.