sid_galt said:
1) What is the efficiency of converting the heat energy generated by a power plant due to combustion/fusion to electric energy?
Nuclear (fission) plants have technical safety limits imposed on temperature and pressure which limit the efficiency. Current US plants obtain thermal to electrical efficiencies around 31-33%. Framatome claims the new EPR with greatly improved steam turbines may realize about 37% efficiency. All nuclear plants use steam (Rankine) cycle for thermal to mechanical conversion.
Back in the 1970's there were plans for at least 8 advanced High-Temperature Gas Cooled Reactors in the US, and the efficiencies of those plants was targeted in the range 39-42%, due to high temperatures of the He-cooled, graphite-moderated core. None of the plants were built, and the only gas cooled reactor in commercial operation - Ft. St. Vrain (Colorado) had significant technical problems (
http://fsv.homestead.com/FSVHistory.html).
Coal/oil plants can operate at much higher temperatures and pressure (superheat), and so their efficiencies can be in the mid-to-upper 30's%.
The most efficient plants to date are combined-cycle plants which operate with an aero-derivative gas-fired turbine (Brayton cycle) with a steam cycle using the exhaust heat of the gas turbine. The gas turbine efficiency is about 42-45%, and the steam cycle gets about 30-33% of the exhaust for a total efficiency of about 62%.
For additional info on congen plants - see http://www.poweronsite.org/Tutorial/Cogeneration.htm
Some basics on thermodynamic cycles -
https://wrc.navair-rdte.navy.mil/warfighter_enc/SHIPS/shipeng/Thermo/thermo.htm
sid_galt said:
2) What are the major ways in which energy is lost while converting it?
Plant efficiency is primarily determined by the maximum temperature of the working fluid (steam in most cases, or combustion temperature in a combustion turbine). Think of Carnot efficiency. In the case of steam, it must be condensed and pumped back to the steam generator (boiler).
sid_galt said:
3) Is there any way to improve the efficiency?
Efficiency can be improved by raising the temperature and pressure of the steam, but that comes with a trade off with respect to corrosion and erosion of the metals (alloys) in the boiler and steam generator. Corrosion in nuclear plants is complicated by the fact that corrosion products from the core and in the primary coolant circuit are radioactive, and must be collected by a filter system and ultimately disposed as radwaste.
Improvements have been made in steam turbine blade design - see the Olkiluoto-3 (EPR) thread - which enable more efficient thermal to mechanical conversion without increasing T
hot. Similarly, the manufacturers of aeroderivative turbines (e.g. GE, Siemens, Alsthom) have greatly improved efficiencies of compressors and gas turbines, so system efficiencies have also improved.
http://www.gepower.com/prod_serv/products/plant_perf_software/en/gatecycle/library.htm
Siemens bought the Westinghouse gas turbine business, IIRC, and ABB may have sold their turbine business as well.
http://www.siemenswestinghouse.com/en/gasturbinesitem/index.cfm
sid_galt said:
4) Are their efficient methods to increase the temp. difference so as to increase the Carnot efficiency and therefore the operating efficiency?
New alloys have been developed that may enable higher temperatures. I believe fossil plants may be maxed out, but there are several designs for advanced (Gen-IV) nuclear plants that may allow higher temperatures and therefore higher efficiencies. However, the advanced plants are still in design phase.
