PRODUCTION OF POWER FROM HEAT

The kinetic energy associated with atmospheric winds is used in afew favorable locations to produce power by large windmills. The potential energy of tides is another possible source of power, but production from these sources remains insignificant in comparison with world demands for energy. 

In a conventional power plant the molecular energy of fuel is released by a combustion process. The function of the work-producingdevice is to convert part of the heat of combustion 

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Smith, J.M., van Ness, H.C. and Abbot, M.M. (2001) Production of Power from Heat, in Introduction to Chemical Engineering Thermodynamics, 6th edn, McGraw Hill, New York, NY, Chapter 8. 

The question of possible limits on the production of work from heat engines was taken up brilliantly by a young French military engineer, Sadi Carnot (Sidebar 4.1). Carnot s monograph of 1824, Reflections on the Motive Power of Fire, pointed to the answers to these questions in a remarkably bold and incisive (if abstract) way. Carnot introduces the question of the motive power (ability to cause movement) of fire (heat) in its most general terms ... 

The second law does not prohibit the production of work from heat, but does place a limit oq. the fraction of the heat that may be converted to work i any cyclic process. The partial conversion of heat into work is the basis for nearly all commercial production of power (water power is an exception). The develop ment of a quantitative expression for the efficiency of this conversion is the nex step in the treatment of the second law. 

Real power plants operate differently from the Carnot cycle but the big picture is the same An energy source at high temperature is used to supply heat to a process, whose net result is to produce an amount of work. In industrial production of power the heat source is either a fossil fuel such as coal or a nuclear fuel. In either case a chemical or nuclear reaction releases heat at an elevated temperature, which acts as the high-temperature reservoir. Invariably, part of this heat must be rejected to the surroundings but at a lower temperature. As a result, only a fraction of the heat released by the fuel is converted into work. The Carnot efficiency gives the maximum possible fraction of work that can be extracted, given the... 

It has been proposed [616, 617] to recover heat, not by converting water to steam, but by evaporating liquid ammonia at high pressure. This could take place inside the ammonia converter, since it does not involve the safety risks involved in the evaporation of water in such equipment. The hot, high pressure ammonia would be used for power production by expansion in a turbine in a way similar to the production of power from high pressure steam. The proposed system has, however, not been used in industrial practice. 

Alkali metal thermo-electric converters (AMTEC) are high-efficiency (>35%) cells for the production of electricity from heat(7). A key component of this cell, as well as of Na/S batteries, is a nonporous, P"-alumina ceramic electrolyte that conducts Na ions when either system is operating ( 800 C for AMTEC, 400 C for Na/S). Despite the high performance ratings for both power sources, their widespread use is limited by a very high cost of production. The manufacture of high quality P"-alumina tubes contributes to this high cost. 

Municipal solid waste (MS W) represents a significant resource for energy recovery operations. Energy from waste (EfW) conversion process is considered one of the most efficient commercially available technologies for the production of power, combined heat and power, and liquid biofuels via the Fischer—Tropsch reaction (Howes and Warren, 2013). 

Ekstrom, C. et al., Technologies and Costs in Sweden for Capture and Storage of C02 from Combustion of Fossil Fuels for Production of Power, Heat, and/or Transportation Fuels, Vattenfall Utveckling AB, Stockholm, 1997. 

Robertson, R. C. 1980. Waste heat rejection from geothermal power plants. In Kestin, J. (ed) Sourcebook on the Production of Electricity from Geothermal Energy. US Department of Energy, Washington DC, 997 p. 

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