Vapour Power Systems

Vapour Power Systems Learning Objectives: Demonstrate an understanding of the basic principles of vapor power plants. Develop and analyze thermodynamic models of vapor power plants based on the Rankine cycle and its modifications, including: sketching schematic and accompanying T-s diagrams. evaluating property data at principal states in the cycle. applying mass, energy, and entropy balances for the basic processes. determining cycle performance, thermal efficiency, net power output, and mass flow rates. Explain the effects on Rankine cycle performance of varying key parameters. Vapour Power Systems

Two important areas of application of Thermodynamics POWER CYCLES: Two important areas of application of Thermodynamics Vapour Power Systems

Geo-Thermal Power Hydel Power Plant Thermal Power Plant Wave Power POWER PLANTS: Geo-Thermal Power Hydel Power Plant Thermal Power Plant Wave Power Nuclear Power Plant Wind Power Solar Power Plant Vapour Power Systems

Vapour Power Systems POWER PLANTS - % contribution: Today we are heavily dependent on Thermal Power. Coal, natural gas, and nuclear will continue to play important roles in years ahead. Contributions from wind power, solar power, and other renewable sources are expected to be increasingly significant up to mid-century at least Vapour Power Systems

1. 3. 2. Vapour Power - vs - Gas Power Internal Combustion - vs - THERMAL POWER - classification: 1. Vapour Power - vs - Gas Power 3. Internal Combustion - vs - External Combustion 2. Open Cycle - vs - Closed Cycle Vapour Power Systems

Introducing Vapour Power Cycle: In a vapor power plant, a working fluid is alternately vaporized and condensed. A key difference among the plants is the origin of the energy required to vaporize the working fluid. There are four alternative vapor power plant configurations Fossil-fueled vapor power plants. Pressurized-water reactor nuclear vapor power plants. Concentrating solar thermal vapor power plants. Geothermal vapor power plants. In geothermal plants, the energy required for vaporization originates in hot water and/or steam drawn from below the earth’s surface. In solar plants, the energy required for vaporization originates in collected and concentrated solar radiation. In fossil-fueled plants, the energy required for vaporization originates in combustion of the fuel. In nuclear plants, the energy required for vaporization originates in a controlled nuclear reaction. Vapour Power Systems

Vapour Power Systems POWER PLANTS – Thermodynamic Cycles:  Let’s see which of the power plants are working using Thermodynamic Cycles? Vapour Power Systems

A Vapour Power Station: a bird’s eye view Vapour Power Systems

Vapour Power Systems A Vapour Power Station: inner details ..\..\video\Coal Power Plant.wmv

Vapour Power Systems POWER CYCLES: scope of our syllabus Each unit of mass of water periodically undergoes a thermodynamic cycle as it circulates through the components of subsystem B. In subsystem C, power developed by the turbine drives an electric generator. The overall plant is broken into four major subsystems identified by A, B, C, and D. Water is the working fluid. Subsystem D removes energy by heat transfer arising from steam condensing in subsystem B. In subsystem B, the water vapor expands through the turbine, developing power. The water then condenses and returns to the boiler. Subsystem A provides the heat transfer of energy needed to vaporize water circulating in subsystem B. In fossil-fueled plants this heat transfer has its origin in the combustion of the fuel. Vapour Power Systems

Vapour Power Systems POWER CYCLES: There are four principal control volumes involving components: Turbine Condenser Pump Boiler All energy transfers by work and heat are taken as positive in the directions of the arrows on the schematic and energy balances are written accordingly. Vapour Power Systems

The processes are: Vapour Power Systems VAPOUR POWER CYCLE: Process~1-2: vapor expands through the turbine developing work Process~2-3: vapor condenses to liquid through heat transfer to cooling water Process~3-4: liquid is pumped into the boiler requiring work input Process~4-1: liquid is heated to saturation and evaporated in the boiler through heat transfer from the energy source Vapour Power Systems

IDEALIZATION: Born: 1 June 1796, in Palais du Petit-Luxembourg, Paris, France Died: 24 August, 1832 (age 36) Paris, France Nationality: French Fields: Physicist and engineer Vapour Power Systems

Vapour Power Systems CARNOT CYCLE: Turbine: Isentropic Expansion Four Processes in CARNOT cycle: Turbine: Isentropic Expansion Condenser: Isothermal Heat Rejection Pump: Isentropic Compression Boiler: Isothermal Heat Addition Vapour Power Systems

CARNOT CYCLE: Four Processes in CARNOT cycle: Vapour Power Systems

Vapour Power Systems CARNOT CYCLE: TH TL Four Processes in CARNOT cycle: TH TL Vapour Power Systems

CARNOT CYCLE: why is this impractical? Vapour Power Systems

Vapour Power Systems The Practical Cycle for Vapour Power Plans: Born: 5 July 1820, Edinburgh Died: 24 December 1872 (aged 52), Glasgow Nationality: Scottish Fields: Physics, Engineering Vapour Power Systems

Vapour Power Systems Ideal RANKINE CYCLE: Processes in RANKINE cycle: 1 2 3 4 Processes in RANKINE cycle: Turbine: Isentropic Condenser: Isobaric Pump: Isentropic Boiler: Isobaric Vapour Power Systems

Wnet = Qin – Qout Vapour Power Systems Ideal RANKINE CYCLE: 1 2 3 4 Energy Analysis: Wnet = Qin – Qout 1 2 3 4 Vapour Power Systems

Each component is analyzed as a control volume at steady state. IDEALIZATION: Engineering model: Each component is analyzed as a control volume at steady state. The turbine and pump operate adiabatically. Kinetic and potential energy changes are ignored. Vapour Power Systems

Vapour Power Systems Ideal RANKINE CYCLE: Energy Analysis ¬ Component wise: 1 2 3 4 Vapour Power Systems

Draw h-s representation of simple Rankine Cycle Ideal RANKINE CYCLE: Draw h-s representation of simple Rankine Cycle Vapour Power Systems

Vapour Power Systems Ideal RANKINE CYCLE: Performance Parameters: Net Power output: WT - WP Thermal Efficiency: 1 – QR/QA Heat Rate: Steam Rate: Back-Work Ratio:  Back work ratio is characteristically low for vapor power plants. For instance, the power required by the pump may even be less than 1% of the power developed by the turbine. Vapour Power Systems

Class Assignments // Vapour Power Cycle Problem No.: 01 In a steam turbine installation running on ideal Rankine cycle steam leaves the boiler at 10 MPa and 700ºC and leaves turbine at 0.005 MPa. For the 50 MW output of the plant and cooling water entering and leaving condenser at 15ºC and 30ºC respectively determine (a) the mass flow rate of steam in kg/s (b) the mass flow rate of condenser cooling water in kg/s (c) the thermal efficiency of cycle (d) the ratio of heat supplied and rejected (in boiler and condenser respectively). Neglet K.E. and P.E. changes. Vapour Power Systems

Vapour Power Systems RANKINE CYCLE with irreversibilities: Irreversibility associated with subsystem B are called internal. They include: The expansion of steam through the turbine The effects of friction in flow through the pump, boiler, and condenser. The most significant internal irreversibility associated with subsystem B is expansion through the turbine. Vapour Power Systems

Principal Irreversibilities Isentropic turbine efficiency, accounts for the effects of irreversibilities within the turbine in terms of actual and isentropic turbine work, each per unit of mass flowing through the turbine. work developed in the actual expansion from turbine inlet state to the turbine exit pressure work developed in an isentropic expansion from turbine inlet state to exit pressure

Vapour Power Systems Ideal RANKINE CYCLE: Problem No.: 01/A Repeat the Problem No.: 01 assuming an isentropic efficiency of 85 percent for both the turbine and the pump. Show the cycle on a h-s diagram. Vapour Power Systems

Tmean = An imaginary temperature heat transfer at which is equal to QH Ideal RANKINE CYCLE: Improvement of Performance : 5 TM 6 Tmean = An imaginary temperature heat transfer at which is equal to QH Vapour Power Systems

Vapour Power Systems Ideal RANKINE CYCLE: Improvement of Performance : RANKINE cycle efficiency can be expressed as follows: Vapour Power Systems

Vapour Power Systems Ideal RANKINE CYCLE: Improvement of Performance : How to increase mean temperature of heat addition? Vapour Power Systems

Ideal RANKINE CYCLE: Improvement of Performance : Vapour Power Systems

Ideal RANKINE CYCLE: Improvement of Performance : Vapour Power Systems

Ideal REHEAT - RANKINE CYCLE: Vapour Power Systems

Reheat - RANKINE CYCLE: Vapour Power Systems

Vapour Power Systems Ideal REHEAT - RANKINE CYCLE: The average temperature during the reheat process can be increased by increasing the number of expansion and reheat stages. As the number of stages is increased, the expansion and reheat processes approach an isothermal process at the maximum temperature. Vapour Power Systems

Ideal REHEAT - RANKINE CYCLE: Practicability of REHEATING: The use of more than two reheat stages is not practical. The theoretical improvement in efficiency from the second reheat is about half of that which results from a single reheat. Double reheat is used only on supercritical-pressure (P 22.06 MPa) power plants. If the turbine inlet pressure is not high enough, double reheat would result in superheated exhaust. The addition of extra reheat will not be justified if the gain becomes too small compared to the added cost & complexity. Vapour Power Systems

Class Assignments // Vapour Power Cycle Problem No.: 02 A steam power plant running on Rankine cycle has steam entering HP turbine at 20 MPa, 500ºC and leaving LP turbine at 90% dryness. Considering condenser pressure of 0.005 MPa and reheating occurring upto the temperature of 500ºC determine, (a) the pressure at which steam leaves HP turbine (b) the thermal efficiency Vapour Power Systems

Class Assignments // Vapour Power Cycle Draw h-s plot of Reheat Rankine Cycle Vapour Power Systems

Efficiency: 1 – (TL/TM) Vapour Power Systems Ideal RANKINE CYCLE: Improvement of Performance : Efficiency: 1 – (TL/TM) Vapour Power Systems

Ideal RANKINE CYCLE: Improvement of Performance : Vapour Power Systems

Ideal RANKINE CYCLE: Improvement of Performance : Vapour Power Systems

Vapour Power Systems Ideal RANKINE CYCLE: actual REGENERATIVE RANKINE CYCLE: Vapour Power Systems

Vapour Power Systems actual REGENERATIVE RANKINE CYCLE Thermodynamic Analysis: Vapour Power Systems

REGENERATIVE RANKINE CYCLE with two OFWHs Vapour Power Systems

(a) there is no feed water heater Ideal RANKINE CYCLE: Class Assignment: o4 A regenerative Rankine cycle has steam entering turbine at 200 bar, 650ºC and leaving at 0.05 bar. Considering feed water heaters to be of open type determine thermal efficiency for the following conditions; (a) there is no feed water heater (b) there is only one feed water heater working at 8 bar (c) there are two feed water heaters working at 40 bar and 4 bar respectively. Also give layout and T-s representation for each of the case described above. Vapour Power Systems

Ideal RANKINE CYCLE: Draw flow chart of a Reheat Regenerative RANKINE CYCLE With one reheat and three regenerations (one in HPT, TWO other in LPT) Vapour Power Systems

Ideal RANKINE CYCLE: Draw flow chart of a Reheat Regenerative RANKINE CYCLE With one reheat and three regenerations (one in HPT, TWO other in LPT) Vapour Power Systems

? Vapour Power Systems Ideal RANKINE CYCLE: Improvement of Performance : 1 2 3 4 Vapour Power Systems

heat, called process heat. Isothermal Heating in Chemical Industry Paper Industry Oil Refinery Food Processing Industry Texlile Industry  Process heat in these industries (Rubber, Sugar, Dying) is usually supplied by steam at 5 to 7 atm and 150 to 200°C (300 to 400°F).  Energy is usually transferred to the steam by burning coal, oil, natural gas, or another fuel in a furnace. Many systems or devices, in industry, require energy input in the form of heat, called process heat. Vapour Power Systems

PROCESS HEAT Let us now examine a process-heating plant closely: Process heating may seem like a perfect operation with practically no waste of energy!!! Vapour Power Systems

PROCESS HEAT Let us now examine a process-heating plant closely: # The temperature in furnaces  Around 1400°C # The temperature of steam produced  About 200°C or below Vapour Power Systems

COGENERATION: PROCESS HEAT Industry also needs power to drive various machines, for lights, fans and for other purposes. What if we make integrated systems that simultaneously yield two valuable products, electricity and steam (or hot water) from a single fuel input? It will be cost saving system relative to producing power and steam (or hot water) in separate systems. Vapour Power Systems

Vapour Power Systems COGENERATION: The plant that produces electricity while meeting the process-heat requirements of certain industrial processes. Such a plant is called a cogeneration plant. Also known as ‘Back Pressure Turbine’ Or, By-Product Power Cycle Vapour Power Systems

COGENERATION: Utilization Factor: Vapour Power Systems

Vapour Power Systems COGENERATION: A cogeneration plant with Pass out Turbine: Vapour Power Systems

Vapour Power Systems COGENERATION: Consider the cogeneration plant where steam enters the turbine at 7 MPa and 500°C. Some steam is extracted from the turbine at 500 kPa for process heating. The remaining steam continues to expand to 5 kPa. Steam is then condensed at constant pressure and pumped to the boiler pressure of 7 MPa. The extraction fractions are adjusted so that steam leaves the process heater as a saturated liquid at 500 kPa. It is subsequently pumped to 7 MPa. The mass flow rate of steam through the boiler is 15 kg/s. Disregarding any pressure drops and heat losses in the piping and assuming the turbine and the pump to be isentropic, determine the rate of process heat supply when 70 percent of the steam is extracted from the turbine at 500 kPa for process heating and hence the utilization factor. Vapour Power Systems

COGENERATION: Vapour Power Systems

No Single fluid can meet all the requirements as mentioned above!!! The continued quest for higher thermal efficiencies… Desirable Properties of working substance in a vapour power cycle: No Single fluid can meet all the requirements as mentioned above!!! High Critical Temperature @ safe max pressure Saturation Pressure of heat rejection should be above condenser pressure Saturated vapour line in T-S plot should be steep (an inverted U saturation dome). Freezing point should be low. A high enthalpy of vaporization T-s diagram of an ideal working substance Vapour Power Systems

….@ 12 bar pressure Substance H2O Al2Br6 Hg Tsat 187 482.5 560 The continued quest for higher thermal efficiencies… ….@ 12 bar pressure Substance H2O Al2Br6 Hg Tsat 187 482.5 560 At 320C saturation pressure is : 0.0000007 bar At 2370C saturation pressure is : 7 bar Critical Properties of Hg Pcr (bar) Tcr (oC) 1080 1460 Vapour Power Systems

BINARY (Two Fluid) VAPOUR CYCLE BINARY (Two Fluid) VAPOUR CYCLE The Solution is… BINARY (Two Fluid) VAPOUR CYCLE BINARY (Two Fluid) VAPOUR CYCLE Vapour Power Systems

BINARY (Two Fluid) VAPOUR CYCLE Vapour Power Systems

In a binary vapour cycle working on mercury and steam, the mercury vapour is generated dry saturated at 8.45 bar and expanded upto 0.07 bar in mercury turbine. The condenser or mercury cycle is used for generating steam at 40 bar, 0.98 dry. The steam is superheated separately upto 450ºC and then supplied into steam turbine for being expanded upto 0.075 bar. Determine the steam generation rate per kg of mercury and efficiency of cycle. The enthalpies of mercury may be taken as, enthalpy of dry saturated vapour at 8.45 bar = 349 kJ/kg enthalpy after isentropic expansion to 0.07 bar = 234.5 kJ/kg enthalpy of saturated liquid at 0.07 bar = 35 kJ/kg Neglect pump work for getting efficiency. Vapour Power Systems