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Chapter IX ENERGY CONVERSION WITH HEAT ENGINES Chapter IX.— ENERGY CONVERSION WITH HEAT ENGINES Page Page Background . 329. Noise . ......................388 Thermodynamics. .. 330 WaterUse in SteamCycles . .............389 Cogeneration. .......................332 Sodium and Potassium Vapor . ...........389 The RankineCycle. ....................333 Cycle Performance . ..................336 Turbine Efficiency . ..............338 PerformanceWith Heat Recovery. ...340 PerformanceWith Backup PowerSources343 LIST OF TABLES State of the Art. ....................345 Table System Costs... ....................352 No. Page Costs of Organic RankineSystems. .. ...354 I. Organic Power-CycleWorking Fluids Used in SystemTesting or in The BraytonCycle. ....................354 Development . ...................339 System Efficiency. ..................360 2. Efficiency of Steam Rankine Devices OperationWith Fossil Backup. .........365 Operated From Storage at Reduced System Costs... ....................365 Temperature . .. ...................345 TheStirlingand Ericsson Cycles.. .......366 3. Ratio of EnergyRequired for Boiling Priniciples of Operation . ..............366 to Total EnergySenttoTurbine . .........345 Design Alternatives. ..............368 4. Small Steam RankineTurbines . .........346 Performance . ...............376 5. Design and Performance Parameters of PerformanceWithWaste Heat. .........378 Current and Projected RankineAutomotive SystemCosts. ....................379 PowerSystems . ......................347 State of the Art. ....................381 6. ExperimentalOrganic RankineTurbines in the UnitedStates. ..................348 Other Heat-Engine Designs . .............383 7. Brayton Cycle Efficiencies. ............363 The Thermionic Converter . ............383 8. Stirling Engine Characteristics . .........378 ThermoelectricConversion . ...........385 9. Performance of Free-Piston Stirling The Nitinol Engine. ..................385 Engine Designs of EnergyResearch and Osmotic-Pressure Engine. ............386 Generation, inc.. .....................379 EnvironmentalandSafetyProblems. .......387 10. Performance of SunPower Free-Piston Fluorocarbons . ..................387 Devices . ......................379 LIST OF FIGURES Figure No. Page 21. 50 MWe Closed-CycleGas Turbine .......359 Figure No, Page 22. Section Through a Combined Gasand 1. Cycle Efficiencies of Heat Engines . .. 331 SteamTurbine Powerplant. ............361 2. System Performance (Ratio of Electric 23. Artists’sRendering of Proposed Solar- and Thermal Energy Produced to Energy HeatedAirTurbineGenerating Facility ...362 Entering the System). ................333 24. Temperature Dependence of Optimum 3. Rankine-Cycle Devices With Heat Cycle Efficiencies. ...................363 Extraction . .....................335 25. The Effect of Waste-Heat Extraction 4. Temperature Dependence of Rankine- on the Performance of Gas Turbines . 364 Cycle Devices . .......................337 26. Closed Regenerated-Cycle GasTurbine. ..364 5. Rankine-Cycle Expander Efficiencies. ....338 27. installed Costs of Open-Cycie 6. Efficiency of Backpressure Steam BraytonTurbines. ....................365 RankineDevices . .....................340 28. ldealStirlingand Ericsson Cycles.. .. ....367 7. Schematic Diagram of the SolarTotal 29. Calculated Performance of a 225-HP Energy System lnstalled at Sandia Stiriing Engine as a Function of the Laboratories in Aibuquerque, N.Mex. ....341 Specific PowerandWorking Gas . .......369 8. Electric and Thermal Performance of a 30. Phiiips Rhombic-DriveStirling Engine ....37O 12.5 MWe Generai Electric Extraction 31. Swashplate Stirling Engine . ............371 Turbine . ....................342 32. Calculated Performance of a Philips 9. Designs for Providing Backup Power Rhombic-DriveStirling Engine . .371 for Solar Rankine-CycleSystems . .......344 33. Free-PistonStirlingand Ericsson 10.TheSunstrand 100kW Organic Rankine Cycle Designs.. .....................372 Turbine . .....................348 34. SunpowerSystems Free-Piston Stirling 11. Components of the Solar Heated, Rankine- and Ericsson Cycle Design Approach. ....374 Cycle Electric Power/3-Ton Air-Conditioning 35. Free-PistonTotal EnergySystem . .......375 System . .....................349 36. Free-PistonTotal EnergySystem . .......376 12. Flow Diagram of the Soiar Heated, 37. The Philips Design for a Stiriing Rankine-Cycle Electric Power/3-Ton EngineTotal EnergySystem . ...........377 Air-ConditioningSystem . ..............350 38. Heat Balance for the Stirling and 13. United Technologies Design for Diesel Engine... .....................379 Rankine CycleAir-Conditioner . .........351 39. ElectricandThermal Output of a 14. Sun PowerSystemsFlow Diagram for Stirling Engine.. .....................380 5HP, Rankine CycleAir-Conditioner. .. ...352 40. Weight-to-PowerRatios of EnginesWith 15. Experimental Expander at General lnternal Combustion and of Stirl`ing Electric . .....................353 Engines . .. .381 16. installed Costs of Steam Rankine 41. Cost of Diesel Engines . .........381 Turbines . .....................354 42. 200-Watt,SunpowerStirling Engine, 17. installed Costs of Organic Rankine Mounted in ConcentratingCollector .. ...383 Turbines . .....................355 43. identification of Thermionic 18. installed Costs of Field-Erected ConverterComponents . ...............384 Boilers . .............................356 44. Effect of ColiectorTemperature 19. Four Brayton-CycleSystems Compatible on Thermionic Efficiency . ..............385 With SolarApplications . ...............357 45. The Nitinol Engine. ...................386 20. Components of a 500kW GasTurbine. ....358 Chapter IX Energy Conversion With Heat Engines BACKGROUND The basic resource of solar energy is a constant temperature thermal source at approximately 10,000° F.* If this resource is to be used for anything other than lighting, the energy received must be converted into a more useful form. This paper examines three separate technologies for ac- complishing this conversion: 1. Thermal devices which use sunlight to heat a fluid and direct this heated fluid either directly for applications requiring heat (such as space-heating or industrial processes) or to operate heat engines; 2. Photovoltaic devices which convert light directly into electricity; and 3. Photochemical devices which use light directly to drive chemical react ions. This chapter compares the costs and performance of a number of specific heat-engine devices. Photovoltaic and photochemical processes are dis- cussed in chapter X. A large number of devices for converting thermal energy into mechanical energy and electricity have been developed over the years, and many of these could be converted for use with solar power. The only energy conversion cycles with which direct solar power would not be easily compatible are those requiring internal combustion— diesel engines, for example, would be cliff i cult to convert to a direct-solar application. The following cycles are considered in overall cycle efficiency is relatively low (5 to some detail: 20 percent) because of the low theoretical maximum efficiency of low-temperature Rankine-cycle systems using organic working heat engines, Low-temperature engines can, fluids such as Freon show the greatest prom- however, be operated from fluids produced ise for producing useful mechanical work by simple nontracking collectors and track- from solar-heated fluids with temperatures ing collectors with low-concentration ratios in the range of 650 to 3700 C (1490 to 6980 and can use relatively inexpensive storage. F). The technology is reasonably well-devel- oped and prototype devices are currently Steam Rankine devices are probably the available in sizes ranging from kilowatts to most attractive contemporary heat-engine many megawatts. An Israeli manufacturer designs for temperatures in the range of has been selling small units for nearly a 3700 to 550“C (6980 to 1,0220 F). (Recip- decade, and devices are now available from rocating steam engines and saturated steam U.S. manufacturers. Small organic Rankine devices can also operate at lower tempera- devices are similar to air-conditioners work- tures. ) A variety of devices are available and ing in reverse and should be able to exhibit the technology is mature, although the mar- the reliability, simplicity, and low cost en- ket for small steam turbines has, until joyed by refrigeration equipment. Organic recently, been quite small and designs are Rankine devices are able to make efficient somewhat outdated. Rankine-cycle devices use of the temperatures available, but the operating with steam or other working fIuids *This is the effective “blackbody” radiation tem- at temperatures higher than 600“C (1,1100 F) perature of the Sun, not its actual surface tempera are possible, but the equipment must be ture made from special materials. 329 Ji,{. , $J ( ) - 2’2 330 ● So/ar Technology to Today’s Energy Needs One difficuIty with Rankine devices oper- sol id-electrolyte devices (systems have been ating in conventional temperature regimes is tested which operate in the temperature that their generating efficiency falls sharply range of 7500 to 1,5000 F, but research is in if waste heat is recovered. a very early stage). Brayton-cycle (gas-turbine) engines operate The overall system efficiency of these at temperatures of 900“C (1 ,6520 F). Com- cycles is illustrated in figure IX-I. The tem- mercial devices are available in a variety of perature ranges which can be produced by sizes, although
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