A Mercury vapour turbine is a form of heat engine

Heat engine

In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...

 that uses mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 to drive the thermal cycle. A mercury vapour turbine has been used in conjunction with a steam turbine

Steam turbine

A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....

  for generating electricity

Electrical generator

In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...

. This example of combined cycle

Combined cycle

In electric power generation a combined cycle is an assembly of heat engines that work in tandem off the same source of heat, converting it into mechanical energy, which in turn usually drives electrical generators...

 generation does not seem to have been widely adopted, probably because of high capital cost and the obvious toxic hazard

Poison

In the context of biology, poisons are substances that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism....

 if the mercury leaked into the environment.

The mercury cycle offers an efficiency increase compared to a steam-only cycle because energy can be injected into the Rankine Cycle

Rankine cycle

The Rankine cycle is a cycle that converts heat into work. The heat is supplied externally to a closed loop, which usually uses water. This cycle generates about 90% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants. It is...

at higher temperature. Metallurgical developments have allowed steam-only plants to increase in efficiency over time, making the mercury vapour turbine obsolete.

Historical example

The Electrical Year Book, 1937, contained the following description of a mercury vapour turbine operating in commercial use:

The advantage of operating a mercury-vapour turbine in conjunction with a steam power plant lies in the fact that the complete cycle can be worked over a very wide range of temperature without employing any abnormal pressure. The exhaust from the mercury turbine is used to raise steam for the steam turbine. The Hartford Electric Light Co. (U.S.A.) has a 10,000kW turbo-generator driven by mercury vapour, which reaches the turbine at 70 lb. per sq. in. (gauge), 880°F. The mercury vapour is condensed at 445°F and raises 129,000 lb. steam per hr. at 280 lb. per sq. in. pressure. The latter is superheated to 735°F and passed to the steam turbines. During 4 months continuous operation, this plant averaged about 0.715 lb. of coal per kWh of net output, about 43% of the output being from the mercury turbine generator and 57% from the steam plant. On maintained full-load the heat output averages 9800 B.Th.U. per net kWh. It is believed that maintenance costs will be lower than in ordinary steam plant. The back-pressure on the mercury turbine is fixed by the steam boiler pressure; only a small vacuum pump is needed, as there is no air or other gas in the mercury system.

External links

• Mercury as a Working Fluid
• Time magazine article 1929, Mercury into power'
• Time magazine article 1942 Power with Quicksilver
• "Mercury Turbine Now A Success drawing page 40
• "Cheaper Power From Quicksilver" Popular Science Monthly, September 1929