Turbines, steam Rankine cycle

Rankine steam-turbine cycle The most widely used in various power plants usually for solid, gaseous, and liquid fuels, but other energy sources can also be used (eg, geothermal, solar, etc.). 

Combined-cycle power plant (combination of Brayton gas-turbine cycle [fuel = natural gas or liquefied natural gas combustion product parameters at the gas-turbine inlet Tin 1650°C] and Rankine steam turbine cycle [steam parameters at the turbine inlet = 620°C (r = 374°C ]). Up to 62... 

This appendix provides additional materials (schematics, layouts, T—s diagrams, basic parameters, and photos) on advanced thermal (combined cycle and supercritical pressure Rankine steam turbine cycle) power plants and nuclear power plants with modern nuclear power reactors [pressurized water reactors (PWRs), boiling water reactors (BWRs), pressurized heavy water reactors (PHWRs), advanced gas-cooled reactors (AGRs), gas-cooled reactors (OCRs), light water-cooled graphitemoderated reactors (LGRs) (RBMKs and EGPs), and liquid metal fast-breeder reactors (LMFBRs) (BN-600 and BN-800)]. 

It should be noted that in aU NPPs with PWRs, ABWRs, BWRs, PHWRs, and LGRs, subcritical-pressure Rankine steam turbine cycle is used. Primary steam is a saturated steam at the corresponding pressure. For the reheat, the primary saturated steam is used. Therefore, the reheat temperature is lower than the primary steam temperature. In general, the primary steam and secondary steam parameters at NPPs are significantly lower than those at thermal power plants. Due to this, thermal efficiencies of these NPPs equipped with water-cooled reactors are lower than those of NPPs equipped with AGRs and LMFBRs (sodium-cooled fast reactors, SFRs), and... 

Figure A1.9 Simplified T—s diagram for Tom -Usinsk thermal power plant supercritical-pressure Rankine steam turbine cycle.

In addition, supercritical carbon dioxide (Pioro and Duffey, 2007) was considered as a modeling fluid instead of water due to significantly lower critical parameters. Also, in the 2000s, supercritical carbon dioxide Brayton gas turbine cycle became quite attractive in some coimtries, including the US as an alternative power conversion cycle compared to subcritical and supercritical pressure Rankine steam turbine cycle for a number of Generation IV nuclear reactor concepts. 

Thermodynamic cycle Indirect steam turbine Rankine cycle Indirect steam turbine cycle... 

Concentrated solar thermal power plants with heliostats, solar receiver (heat exchanger) on a tower, and molten salt heat storage system (for details, see Fig. 1.10). Molten salt maximum temperature is 565°C. Rankine steam turbine power cycle used. Up to 20... 

Natural gas is considered as a clean fossil fuel compared to coal and oil, but still, due to the combustion process, emits a lot of carbon dioxide when it used for electrical generation. The most efficient modem thermal power plants with thermal efficiencies within a range of 50—60% (up to 62%) are, so-called combined cycle power plants (combination of Brayton gas turbine and Rankine steam turbine power cycles) (see Figs. Al.l—A1.4, and Tables Al.l and A1.2), which use mainly natural gas as a fuel. 

Figure A1.18 Simplified iayout of typicai BWR NPP (courtesy of US NRC) geneiai basic features (1) thermal neutron spectrum (2) UO2 fuel (3) fuel enrichment about 3% (4) direct cycie with steam separator (steam generator and pressurizer are eiiminated), ie, singie-flow circuit (singie loop) (5) RPV with verticai fuel rods (elements) assembled in bundle strings cooled with upward flow of fight water (water and water—steam mixture) (6) reactor coolant, moderator, and power cycle working fluid are the same fluid (7) reactor cooiant outlet parameters pressure about 7 MPa and samration temperature at this pressure is about 286°C and (8) power cycle subcritical-pressure regenerative Rankine steam turbine cycie with steam reheat.

Fossil Fuel-Fired Plants. In modem, fossil fuel-fired power plants, the Rankine cycle typically operates as a closed loop. In describing the steam—water cycle of a modem Rankine cycle plant, it is easiest to start with the condensate system (see Fig. 1). Condensate is the water that remains after the steam employed by the plant s steam turbines exhausts into the plant s condenser, where it is collected for reuse in the cycle. Many modem power plants employ a series of heat exchangers to boost efficiency. As a first step, the condensate is heated in a series of heat exchangers, usually sheU-and-tube heat exchangers, by steam extracted from strategic locations on the plant s steam turbines (see HeaT-EXCHANGETECHNOLOGy). 

The Combined (Brayton-Rankine) Cycle The 1990s has seen the rebirth of the combined cycle, the combination of gas turbine technologies with the steam turbine. This has been a major shift for the utility industry, which was heavily steam-tnrbine-oriented with the use of the gas turbine for peaking power. In this combined cycle, the hot gases from the turbine exhaust are used in a heat recoveiy steam generator or in some cases in a snpplementaiy fired boiler to produce superheated steam. 

The most effective cycle is the Brayton-Rankine cycle. This cycle has tremendous potential in power plants and in the process industries where steam turbines are in use in many areas. The initial cost of this system is high however, in most cases where steam turbines are being used this initial cost can be greatly reduced. 

The basic steam cycle for a steam turbine installation is called a Rankine cycle (named after Scottish engineer and physicist William John Macquorn Rankine). This cycle consists of a compression of liquid water, heating and evaporation in the heat source (a steam boiler or nuclear reactor), expansion of the... 

The combination of the Brayton (gas turbine) and Rankine (steam) cycle is known as the combined cycle. A typical gas turbine in combined cycle is shown diagram-matically in Figure 15.10. 

Combined Brayton-Rankine Cycle The combined Brayton-Rankine cycle. Figure 9-14, again shows the gas turbine compressor for the air flow to the cell. This flow passes through a heat exchanger in direct contact with the cell it removes the heat produced in cell operation and maintains cell operation at constant temperature. The air and fuel streams then pass into the cathode and anode compartments of the fuel cell. The separate streams leaving the cell enter the combustor and then the gas turbine. The turbine exhaust flows to the heat recovery steam generator and then to the stack. The steam produced drives the steam turbine. It is then condensed and pumped back to the steam generator. 

The performance of a SOFC system with a Brayton-Rankine bottoming cycle for heat and fuel recovery has been calculated. Gas turbine compressor and expander efficiencies of 83% and 89% and a steam turbine efficiency of 90% have been assumed. 

Determine the power required by the compressor, power required by pumps 1 and 2, power produced by turbines 1, 2, and 3, rate of heat added by the nuclear reactor, net power produced by the Brayton gas turbine plant, net power produced by the Rankine plant, rate of heat removed by coolers 1 and 2, rate of heat exchanged in the heat exchanger, rate of heat added in the gas burner, mass rate flow of helium in the Brayton cycle, mass rate flow of steam extracted to the feed-water heater (mixing chamber), cycle efficiency of the Brayton plant, cycle efficiency of the Rankine plant, and cycle efficiency of the combined Brayton-Rankine plant. 

A Rankine/Rankine combined cycle is shown in Fig. 5.16. The exhaust from the top steam turbine (TURl) is hot enough to generate freon vapor in a waste-heat boiler. The freon vapor generated can power a freon turbine, thus increasing the total work produced. The Rankine/Rankine combined cycle has a thermal efficiency greater than either a steam or freon cycle may have by itself. The power plant occupies less area, and the fuel requirements are less. 

Rankine Cycle. The sleam-Rankine cycle employing steam turbines has been the mainstay of utility thermal electric power generation for many years. The cycle, as developed over the years, is sophisticated and efficient. The equipment is dependable and readily available. A typical cycle (Fig. 21) uses superheat, reheat, and regeneration. Heat exchange between flue gas and inlet air adds several percentage points to boiler efficiency in fossil-fueled plants. Modern steam Rankine systems operate at a cycle top temperature of about 800 K with efficiencies of about 40%. All characteristics of this cycle are well suited to use in solar plants. 

In a combined-cycle power plant, electricity is produced by two turbines, a gas and a steam turbine. The term combined cycle comes from the fact that the combustion gas turbine operates according to the Brayton cycle and the steam system operates according to the Rankine cycle. As shown in Figure 2.115, the dual-shaft combined-cycle plant consists of a gas turbine (GT)... 

In addition to the pyrolysis and gasification cases, a conventional Rankine cycle case was analyzed for comparison. In this case the same amount of bagasse was combusted in a modem boiler with a steam turbine power cycle. The overall efficiency for this case is 25 percent. 

A Rankine power generation cycle using steam operates at a temperature of 100 C in the condenser, a pressure of 3.0 MPa in the evaporator, and a ma,ximum temperature of 600°C. Assuming the pump and turbine operate reversibly, plot the cycle on a 7-S diagram for steam, and compute the efficiency of the cycle. 

A Rankine power generation cycle is operated with water as the working fluid. It is found that 100 MW. of power is produced in the turbine by 89 kg/s of steam that enters the turbine at 700°C and 5 MPa and leaves at 0.10135 MPa. Saturated liqnid water exits the condenser and is pumped back to 5 MPa and fed to the boiler, which operates isobarically. 

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