PPT-03609211-4- Thermal Power Plant.pptx

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1. Basic Thermodynamics ( 0360 9211 )

2. Thermal Power Plant CHAPTER- 4

3. Types of Thermal Power Plant Thermal power plants generate electricity by converting heat energy into electrical energy. Here are some common types of thermal power plants : Coal-fired power plants Natural gas-fired power plants Oil-fired power plants Combined Cycle Power Plants Nuclear Power Plants Geothermal Power Plants

4. Thermal Power Plant Layout

5. Component of Power Plant Boiler or Reactor Turbine Generator: Condenser : Cooling Tower : Fuel Storage and Handling System Control Room and Instrumentation : Transformer and Switchyard: Ash Handling System (in coal-fired plants ) Emission Control Systems:

6. Rankine Cycle

7. Rankine cycle is a thermodynamic cycle derived from Carnot vapour power cycle for overcoming its limitations. In earlier discussion it has been explained that Carnot cycle cannot be used in practice due to certain limitations. Rankine cycle has the following thermodynamic processes. 1 – 2 = Isobaric heat addition (in boiler) 2 – 3 = Adiabatic expansion (in turbine) 3 – 4 = Isobaric heat release (in condenser) 4 – 1 = Adiabatic pumping (in pump)

8. REHEAT CYCLE

9. Here steam generated in boiler is supplied to high pressure steam turbine at state 2 and is expanded upto state 3. This steam is sent to boiler for being reheated so that its temperature gets increased, normally this temperature after reheating may be equal to temperature at inlet of high pressure steam turbine. Steam after reheating is supplied to subsequent turbine at state 4, say to low pressure steam turbine. Steam is now expanded upto the exhaust pressure say state ‘5’. Expanded steam is subsequently sent to condenser and condensate at state ‘6’ is pumped back to the boiler employing feed pump at state ‘1’.

10. Thus, it is possible to take advantage of high steam pressure at inlet to steam turbine as the problem of steam becoming excessively wet with increasing steam pressure could be regulated by reheating during the expansion. Expansion occurs in two stages one begining at high pressure and other occurring at low pressure with reheating in between. The principal advantage of reheat is to increase the quality of steam at turbine exhaust Secondary advantage of reheating is marginal improvement in thermal efficiency when steam pressure is above 100 bar.

11. Thermodynamic analysis of reheat cycle as shown on T–S diagram may be carried out for estimation of different parameters as below, Total turbine work output = WHPST + WLPST Net work, Wnet = (Total turbine work output) – (Pump work) Wnet = WHPST + WLPST – W p

12. where different works for ms mass of steam are , HP steam turbine, WHPST = ms · (h2 –h3 ) LP steam turbine, WLPST = ms · (h4 –h5) Feed Pump, W p = (h1 –h6) · ms Wnet = {(h2 – h3) + (h4 – h5) – (h1 – h6)} · ms Heat supplied for ms mass of steam; Qadd = (h2 – h1) · ms + ms · (h4 – h3 )

13. Cycle thermal efficiency, ηReheat = Wnet / Qadd

14. BINARY VAPOUR CYCLE Image source : Google In the vapour power cycles most commonly used working fluid is water. But at high temperatures to get the high efficiency of vapour power cycle, some other working fluids are used. At high temperatures a few working fluids are used, which are mercury, sodium, potassium and sodium-potassium mixtures. Among these, only mercury has been used in practice.

15. For the best performance, the working fluid should have the following characteristics : High Critical temperature and safe maximum pressure, Low triple point temperature, Condenser pressure which is not too low, High enthalpy of vaporization, Good heat transfer characteristics, and Inert, easy availability at low cost.

16. Image source : Google In this diagram it consist of mercury cycle and steam cycle. The mercury leaves the condenser as saturated liquid and steam leaves as the saturated vapour . The mercury cycle 1-2- 2 ¢ -3-4-1 is named as topping cycle and steam cycle 5-6-6 ¢ -7-8-5 as bottoming cycle.

17. ERICSSON CYCLE From earlier discussions, we have seen that the thermal efficiency of gas turbine power plant may be increased by regeneration, reheat and intercooling. But there exists limit to the number of stages practically. If a large number of multistages of compression with intercooling and large number of multistages of expansion with reheating and regeneration are employed then the cycle is called Ericsson cycle . The Ericsson cycle is an altered version of the Carnot cycle in which the two isentropic processes featured in the Carnot cycle are replaced by two isothermal regeneration processes.

18. Atkinson Cycle Image source : Google The point 1 represents that the cylinder is full of air with volume V1, pressure p1, and absolute temperature T1. a) Process 1-2: This process represents the isentropic compression of air from state-1 to state-2. b) Process 2-3: Heat is supplied to the compressed air at constant volume from an external source. The pressure rises and the ratio α=p3/p2 is called the explosion ratio . Process 3-4: The increased high pressure exerts a greater amount of force on the piston and pushes it forward. Expansion of working fluid takes place isentropically up to the lowest pressure P1-p4 of the cycle, and work is done by the system. Process 4-1: This process represents the rejection of heat by air at constant pressure. Hence volume and temperature of air decreases to initial value. Therefore, a cycle is completed.

19. Image source : Google Calculation of air standard efficiency Consider 'm' kg of air in the cycle. Heat supplied at constant volume , Qs= mC (T-T12) Heat rejected at constant pressure, QR = MC, (T-T1) Net work done, Wnet = Heat supplied - Heat rejected = mCv ( T3-T2 )- mCp ( T4-T1)

20. Image source : Google

21. Image source : Google

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