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Vapor and Advanced Power Cycles
Published in Kavati Venkateswarlu, Engineering Thermodynamics, 2020
Regeneration is another method of improving the thermal efficiency of the Rankine cycle by raising the mean temperature of the heat addition. It is the process of heating the feedwater to raise its temperature before it enters the boiler so that the mean temperature of the heat addition can be increased. One practice to raise the temperature of feedwater is to install a heat exchanger built into a turbine and extracting the heat from expanding steam. This method, however, is not practical since designing such a heat exchanger is not that easy, and moreover, it creates additional problems of increased moisture in the exhaust. The other method of raising the temperature of feedwater is by extracting steam at different locations of the turbine and using this heat to heat the feedwater. The device used for heating the feedwater is termed feedwater heater or regenerator. There are two types of feedwater heaters: open feedwater heaters and closed feedwater heaters. In open feedwaters also known as direct contact heat exchangers, both the steam and feedwater mix with each other so that there is heat transfer from steam to water while in closed feedwater heaters, and both the fluid steams don’t mix with each other.
Containment Buildings and Their Function
Published in Robert E. Masterson, Nuclear Reactor Thermal Hydraulics, 2019
For reasons that we will subsequently discuss, the thermal efficiency of a power plant can be increased even further if we choose to reheat the feedwater before it is sent back to the steam-producing side of the NSSS. The best way to do this is to withdraw some spent steam from an intermediate stage of the power turbines. Although this may seem like a rather lame thing to do, this extra step turns out to be well worth the expense because it increases the thermal efficiency of the plant. The actual heating takes place in a unit that is known as a feedwater heater. A feedwater heater can be thought of as another “black box” with a cluster of pipes coming into it and going out of it. A picture of a typical feedwater heater is shown in Figure 32.15. The inlet pipes take depleted steam from one of the turbines and use it to reheat the feedwater. It is usually best to take the steam from an intermediate stage of the power turbines, but this does not always have to be the case. So, in a sense, a feedwater heater is just a big heat exchanger that uses depleted steam as its power source. The water enters the feedwater heater with a defined energy content (or enthalpy hIN) and then leaves the feedwater heater with a different energy content (or enthalpy hOUT). The total amount of heat added to the water can be determined from a simple energy balance, which in turn requires us to specify the mass flow rates.
Containment Buildings and the Nuclear Steam Supply System
Published in Robert E. Masterson, Nuclear Engineering Fundamentals, 2017
For reasons that we will subsequently discuss, the thermal efficiency of a power plant can be increased even further if we choose to reheat the feedwater before it is sent back to the steam-producing side of the NSSS. The best way to do this is to withdraw some spent steam from an intermediate stage of the power turbines. Although this may seem like a rather lame thing to do, this extra step turns out to be well worth the expense because it increases the thermal efficiency of the plant. The actual heating takes place in a unit that is known as a feedwater heater. A feedwater heater can be thought of as another “black box” with a cluster of pipes coming into it and going out of it. A picture of a typical feedwater heater is shown in Figure 16.15. The inlet pipes take depleted steam from one of the turbines and use it to reheat the feedwater. It is usually best to take the steam from an intermediate stage of the power turbines, but this does not always have to be the case. So in a sense, a feedwater heater is just a big heat exchanger that uses depleted steam as its power source. The water enters the feedwater heater with a defined energy content (or enthalpy hIN) and then leaves the feedwater heater with a different energy content (or enthalpy hOUT). The total amount of heat added to the water can be determined from a simple energy balance, which in turn requires us to specify the mass flow rates.
Identification of Working Conditions in Secondary Loop of Nuclear Power Plant Based on Improved Multiple PCA Modeling
Published in Nuclear Science and Engineering, 2020
Yunfeng Zhang, Xiangshun Li, Lin Cai
In the secondary loop, the hot steam in the SG goes into the main steam pipe. The hot steam from the main steam pipe is distributed to high steam turbines and drives the rotors to rotate. The rotor then drives the shaft of the propeller to rotate. Heat energy is converted into mechanical energy. The hot steam from the high steam turbine goes into a moisture separator reheater to remove the water vapor to avoid corroding the blades in the low steam turbine. Then the hot steam goes into the low steam turbine to drive the rotor to rotate. The exhausted steam is condensed in the condenser by sea water. The condensed water is pumped to the low-pressure feedwater heater by the condenser pump and is heated by the hot steam coming from the low steam turbine. Then the water goes into a deaerator and is heated by the hot steam coming from the main steam pipe and high steam turbine. At the same time, oxygen is removed to avoid the corrosion of the SG. The heated water is pumped by the feedwater pump to the high-pressure feedwater heater to be heated by the hot steam coming from the main steam pipe and high steam turbine. Finally, the water goes into the SG and absorbs heat to produce steam. The above process constitutes the cycle of the secondary loop of an NPP.
Heat Recovery from the Incineration of Polychlorinated Biphenyls Waste in Rotary Kilns
Published in Energy Engineering, 2019
Ehab Hussein Bani-Hani, Ahmad Sedaghat, Zabihollah Najafian Ashrafi
The heat recovery systems utilizing heat exchangers have improved the overall efficiency of traditional steam power plants significantly, from 0.29 to 0.35. This is equivalent to the improvement in the efficiency of steam power plants using feedwater heaters, between 6 and 10% by only installing one or two heat recovery units. The advantages of heat recovery units are not limited to efficiency improvements but also in energy savings. It is estimated that about 2.0 million USD can be saved annually. This study is useful for countries with high cost fuels used in cement industry, where rotary kilns are used, and/or steam power plants where heat recovery units can provide efficiency increases and energy savings. The value of energy saved in this case is 89.2 kJ/kg, which can be used to determine savings that can be obtained using different types of fuels.
Exergy Analysis and Thermodynamic Optimization of a steam power plant- Based Rankine cycle system Using Intelligent Optimization Algorithms
Published in Australian Journal of Mechanical Engineering, 2022
Samad Elahifar, Ehsanolah Assareh, Rahim Moltames
In order to study the exergy and to optimise the process, a 60-megawatt power plant in Kerman province was selected. This power plant is a steam type with Rankine cycle that uses two similar units with the same capacity. The flow diagram of the power plant has been shown in Figure 1. Water after passing through the hot tubes of boiler converts to superheated high-pressure steam and exits from the boiler and enters into the turbine. The turbine of the power plant is extraction turbine. In the extraction turbines, steam exits from the turbine in the several stages and they are used to send the feedwater heaters to improve the overall efficiency of the system. There are two types of the feedwater heaters in these power plants, one of them is open type another one is closed type. Warming up the feed water before entering the boiler increases the efficiency of this cycle. This heating is performed by extracting small amounts of steam passed through the turbine in the same heat exchangers, which are called as fed water recover. In a cycle with the recover or heater, a part of the heat is recovered in the cycle and the amount of heat released to the environment through the condenser is reduced and increases the thermodynamic cycle efficiency. The presence of heater and its suitable performance in increasing the temperature of water entering into the boiler and in decreasing the consumption of fuel in the boiler and in reducing the volume of demanded air and as a result in reducing the speed of combustion products in the furnace and will cause less damage to the furnace. Each of Kerman power plant uses four feedwater heaters. The steam after power generation in the turbine in the last extraction enters into the turbine condenser where it is converted to saturated liquid. Then, it entered into the feedwater heater by pump and enters into the boiler again.