Rankine cycles simple

The Rankine cycle diagram placed adjacent the Brayton cycle in Figure 9-15 is indicated as a simple steam cycle with superheat, but no reheat and no multi-pressure steam generation. The thermodynamic advantage of the Rankine bottoming cycle is the lowered temperature of heat rejection, in the steam condenser, from the overall combined cycles. 

A simple Rankine cycle using water as the working fluid operates between a boiler pressure of 500 psia and a condenser pressure of 20 psia. The mass flow rate of the water is 31bm/sec. Determine (1) the quality of the steam at the exit of the turbine, (2) the net power of the cycle, and (3) the cycle efficiency. Then change the boiler pressure to 600 psia, and determine (4) the quality of the steam at the exit of the turbine and (5) the net power of the cycle. 

What is the quality of vapor at the inlet of the pump in a simple ideal Rankine cycle Why ... 

Is the efficiency of a reheat Rankine cycle always higher than the efficiency of a simple Rankine cycle operating between the same boiler pressure and condenser pressure ... 

Much of this chapter has been concerned with various modifications to the simple Rankine cycle at high temperature. In the following five sections, the Rankine cycle that makes possible use of energy sources at low temperature, such as solar, geothermal, ocean thermal, solar pond, and waste heat, will be discussed. Because of the small temperature range available, only a simple Rankine cycle can be used and the cycle efficiency will be low. This is not critical economically, because the fuel is free. 

The simple Rankine cycle is inherently efficient. Heat is added and rejected isothermally and, therefore, the ideal Rankine cycle can achieve a high percentage of Carnot cycle efficiency between the same temperatures. Pressure rise in the cycle is accomplished by pumping a liquid, which is an efficient process requiring small work input. The back-work ratio is large. 

Heat engines that are potential candidates for coupling a solar heat source include thermoelectric, thermionic, lliermochemical, magnelohydro-dynamic, Rankine, Brayton (simple or recuperated), and cascaded cycles. 

Example 4.12 Exergy analysis of a power plant A steam power plant operates on a simple ideal Rankine cycle (see Figure 4.18). The turbine receives steam at 698.15 K and 4200 kPa, while the discharged steam is at 40 kPa. The mass flow rate of steam is 3.0 kg/s. In the boiler, heat is transferred into the steam from a source at 1500 K. In the condenser, heat is discharged to the surroundings at 298 K. Determine the energy dissipated at each state. 

Example 4.13 Simple reheat Rankine cycle in a steam power plant A simple ideal reheat Rankine cycle is used in a steam power plant (see Figure 4.19). Steam enters the turbine at 9000kPa and 823.15 K and leaves at 4350kPa. The steam is reheated at constant pressure to 823.15K. The discharged steam from the low-pressure turbine is at 10 kPa. The net power output of the turbine is 65 MW. Determine the thermal efficiency and the work loss at each unit. 

A simple ideal Rankine cycle is used in a steam power plant. Steam enters the turbine at 6600 kPa and... 

A wood-fired power plant is included in the PEF system to produce electricity from the solid fuel produced on the dry-land Energy Plantation. Some of the various elements included in the power plant subsystem and the model are shown in Figure I. The power cycle modeled is a conventional steam Rankine cycle as is used in coal-fired and nuclear power plants, in keeping with the decision that the model should represent "state-of-the-art" equipment which would be readily available for a demonstration system. The system components are similar to those that would appear in a simple coal-fired power plant with the additional equipment to dry and screen the fuel before it enters the boiler. 

A steam power plant operates on a simple ideal Rankine cycle. The turbine receives the steam at... 

Such a thermal engine cycle is shown in Figure l3-9. Evaporation, expansion, condensation, and pressure rise are repeated in a simple Rankine cycle. In the simplest form, "waste heat" is applied to a boiler which provides saturated or superheated vapor to the expander, and the fluid passes on to a condenser, which provides liquid to the pump. The pump raises the pressure and resupplies fluid to the boiler, thereby completing the cycle. The working fluid condenser heat is rejected to a cooling fluid in the condenser, either cooling water or air. The expander shaft work is ultimately used as shaft power to drive compressors or pumps, or to drive a generator to produce electrical power. 

In other studies, another simple calculation method for thermal efficiency has also been used. First, thermal efficiencies of Carnot and Rankine cycles were calculated with the given steam conditions. Second, an averaged value between these efficiencies was obtained and a factor was calculated so that the thermal efficiency of the current BWR was correctly estimated by this method. If the core outlet temperature is given as 400°C, the thermal efficiencies obtained by the... 

A comparison of the effect of the various cycles on the overall thermal efficiency is shown in Fig. 29-40. The most effective cycle is the Brayton-Rankine (combined) 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 the combined cycle is between 800- 1200 per kW while that of a simple cycle is about 300- 600 per kW. Repowering of existing steam plants by adding gas turbines can improve tne overdl plant efficiency of an existing steam turbine plant by as much as 3 to 4 percentage points. 

A simple Rankine steam plant is shown in Figure 23.14. Steam is supplied to a turbine at 1000°F and 2000 psia, where it is expanded in a turbine with an isentropic efficiency of 85% to a pressure of 1 psia. The exhausfed sfeam is condensed and cooled to a subcooled liquid at 85°F. It is returned to the boiler with a pump that has an isentropic efficiency of 85%. The properties for each poinf in fhe cycle are calculated using computer generated steam tables and shown in Table 23.1. Points 2s and 4s represent conditions that would be achieved with an isentropic pump and turbine, respectively. In accordance with the state... 

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