Thermal efficiency ideal power plants

Another important point that should be made is this it is misleading to imply that the value of a fuel lies in its heating value. The true measure of a fuel s potential to cause useful change for us is its content of available energy. This fact leads to interesting "discrepancies." For instance, if an ideal power plant were used in the boiler problem, so that the available energy in it were turned completely into electricity, that plant s "thermal efficiency" (nj) would be... 

Consider a combined power plant made up of two cyclic plants (H, L) in series (Fig. 7.1). In this ideal plant, heat that is rejected from the higher (topping) plant, of thermal efficiency tjh, is used to supply the lower (bottoming) plant, of thermal efficiency tjl, with no intermediate heat loss and supplementary heating. 

In a Rankine power plant, the steam temperature and pressure at the turbine inlet are 1000°F and 2000 psia. The temperature of the condensing steam in the condenser is maintained at 60° F. The power generated by the turbine is 30,000 hp. Assuming all processes to be ideal, determine (1) the pump power required (hp), (2) the mass flow rate, (3) the heat transfer added in the boiler (Btu/hr), (4) the heat transfer removed from the condenser (Btu/hr), and (5) the cycle thermal efficiency (%). 

Water circulates at a rate of 80kg/sec in an ideal Rankine power plant. The boiler pressure is 6 MPa and the condenser pressure is lOkPa. The steam enters the turbine at 600°C and water leaves the condenser as a saturated liquid. Find (1) the power required to operate the pump, (2) the heat transfer added to the boiler, (3) the power developed by the turbine, (4) the thermal efficiency of the cycle. 

Steam is generated in the boiler of a steam power plant operating on an ideal Rankine cycle at 10 MPa and 500° C at a steady rate of 80 kg/sec. The steam expands in the turbine to a pressure of 7.5 kPa. Determine (1) the quality of the steam at the turbine exit, (2) rate of heat rejection in the condenser, (3) the power delivered by the turbine, and (4) the cycle thermal efficiency (%). 

Consider a steam power plant operating on the ideal regenerating Rankine cycle 1 kg/sec of steam flow enters the turbine at 15 MPa and 600°C and is condensed in the condenser at lOkPa. Some steam leaves the high-pressure turbine at 1.2 MPa and enters the open feed-water heater. If the steam at the exit of the open feed-water heater is saturated liquid, determine (1) the fraction of steam not extracted from the high-pressure turbine, (2) the rate of heat added to the boiler, (3) the rate of heat removed from the condenser, (4) the turbine power produced by the high-pressure turbine, (5) the turbine power produced by the low-pressure turbine, (6) the power required by the low-pressure pump, (7) the power required by the high-pressure pump, and (8) the thermal cycle efficiency. 

The maximum and minimum temperatures and pressures of a 40 MW turbine shaft output power ideal air Brayton power plant are 1200 K (Ta), 0.38 MPa (P3), 290 K (TO, and 0.095 MPa (Pi), respectively. Determine the temperature at the exit of the compressor Tj), the temperature at the exit of the turbine (P4), the compressor work, the turbine work, the heat added, the mass rate of flow of air, the back-work ratio (the ratio of compressor work to the turbine work), and the thermal efficiency of the cycle. 

Irreversibilities in the compressor and turbine greatly reduce the thermal, efficiency of the power plant, because the net work is the difference between the work required by the compressor and the work produced by the turbine. The temperature of the air entering the compressor TA and the temperature of the air entering the turbine, the specified maximum for Tc, are the same as for the ideal cycle. However, the temperature after irreversible compression in the compressor Ts is higher than the temperature after isentropic compression T B, and the temperature after i never - ible expansion in the turbine TD is higher than the temperature after isentropic expansion T d. 

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 steam power plant is using an ideal regenerative Rankine cycle. Steam enters the high-pressure turbine at 8600 kPa and 773.15 K, and the condenser operates at 30 kPa. The steam is extracted from the turbine at 3 50 kPa to heat the feedwater in an open heater. The water is a saturated liquid after leaving the feedwater heater. The work output of the turbine is 75 MW. Determine the thermal efficiency and the work loss at each unit. 

As alluded to in Chapter 8, the ideal biomass feedstock for thermal conversion, whether it be combustion, gasification, or a combination of both, is one that contains low or zero levels of elements such as nitrogen, sulfur, or chlorine, which can form undesirable pollutants and acids that cause corrosion, and no mineral elements that can form inorganic ash and particulates. Ash formation, especially from alkali metals such as potassium and sodium, can lead to fouling of heat exchange surfaces and erosion of turbine blades, in the case of power production systems that use gas turbines, and cause efficiency losses and plant upsets. In addition to undesirable emissions that form acids (SOx), sulfur can... 

A power plant is operating on an ideal Brayton cycle with a pressure ratio of Vp = 9. The fresh air temperature is 300 K at the compressor inlet and 1200 K at the end of the compressor and at the inlet of the turbine. Using the standard-air assumptions, determine the thermal efficiency of the cycle. 

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