Saturated steam cycles, thermal efficiencies

In studies of homogeneous reactors, saturated steam cycles are assumed in which 12% moisture is permitted in the last stages of the turbine. Thermal efficiencies of such plants are shown in Fig. 9-1 as a function of the steam temperature at the turbine throttle [2]. 

An ideal Rankine cycle uses water as a working fluid, which circulates at a rate of 80kg/sec. The boiler pressure is 6 MPa, and the condenser pressure is lOkPa. The steam is superheated and enters the turbine at 600°C and leaves the condenser as a saturated liquid. Determine (1) the power required to operate the pump, (2) the heat transfer added to the water in the boiler, (3) the power developed by the turbine, (4) the heat transfer removed from the condenser, (5) the quality of steam at the exit of the turbine, and (6) the thermal efficiency of the cycle. 

The basic cycle for a steam power plant is shown by Fig. 8.1. Suppose that the turbine operates adiabatically with inlet steam at 6,500 kPa and 525°C and that the exhaust steam enters the condenser at 100°C with a quality of 0.98. Saturated liquid water leaves the condenser, and is pumped to the boiler. Neglecting pump work, and kinetic- and potential-energy changes, determine the thermal efficiency of the cycle and the turbine efficiency. 

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. 

The thermal efficiency of this cycle is that of a Carnot engine, given by (5.8). As a reversible cycle, it could serve as a standard of comparison for actui steam power plants. However, severe practical difficulties attend the operatk of equipment intended to carry out steps 2 3 and 4 1. Turbines that take i saturated steam produce an exhaust with high liquid content, which causes sevel erosion problems, t Even more difficult is the design of a pump that takes in mixture of liquid and vapor (point 4) and discharges a saturated liquid (poll 1). For these reasons, an alternative model cycle is taken as the standard, at lei for fossil-fuel-buming power plants. It is called the Rankine cycle, and diSei from the cycle of Fig. 8.2 in two major respects. First, the heating step 1 2 ... 

The heat utilisation system will be different, in function of the specific scope of the plant, and will be able to reach - as highest performance limits and with reference to the core characteristics above described - the following performances a) the production of saturated steam at 17 bar b) the production of sub-cooled water at about 210°C. Should steam be used for the production of electric power through a turbine-alternator group, a thermal cycle efficiency of 28% could be achieved, with the production of about 170 electric MW. 

These data correspond to a conservative variant of SVBR-75/100 using available SGs and saturated steam turbine, with the maximum temperatures of fuel element claddings not exceeding 600°C. Currently, the work to increase the temperature of the fuel element cladding up to 650 C is being conducted that would make it possible to increase the reactor thermal power by -15% and enhance the possibility of a transfer to a superheated steam turbine cycle that worrld resrrlt in the increase of the thermodynamic cycle efficiency by -15%. In calcrrlations of the preserrted technical and economic parameters, an additional margin of 17% over the normative parameter values has been introduced, which corresponds to 60% of the reactor installation eqrripment cost. 

One way of reducing the average temperature difference is by superheating of the saturated steam, as shown by the line CD in the right portion of Fig. 6.21. This not only increases the thermal efficiency of the cycle, but has... 

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... 

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. 

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