ONLINE ELECTRICAL ENGINEERING STUDY SITE

Rankine Cycle

Ideal Rankine Cycle

Principles of thermodynamics are useful for power cycle for of electrical power generation (i.e net power output) and to study refrigeration & heat pump which requires input of net power. Classification of thermodynamics power cycles can be done into two types:
  • Vapor cycle working fluid exists in liquid phase during one part of the cycle (i.e from condenser outlet to Boiler) and mixed phase wit in the steam boiler and in vapor phase at the Boiler outlet.
  • Gas cycle working fluid during the cycle remains in gas phase.
Steam power generation units run on vapor power cycle using water as the working fluid. Under this section attempt is made to familiarize the readers with the concepts of ideal vapor cycle called Rankine cycle.

Typical Power Plant Cycle

Electrical power is generated by using vapor cycle power plants by using Coal, Lignite, Diesel, Heavy furnace oil as fuel depending upon the availability and cost. The flow scheme of the vapor power cycle is given below: rankine cycle The entire power plant can be broken down into following sub-systems.
  • Sub-system A: Classified as main-components of power plant (Turbine, Condenser, Pump, Boiler) for power generation.
  • Sub-system B: Classified as stack/chimney, from where the waste gases are exhausted to atmosphere.
  • Sub-system C: Classified as electric generator for converting the mechanical energy to electrical energy.
  • Sub-system D: Classified as Cooling water system for absorbing the heat of the rejected steam in the condenser and helping in changing the phase of the steam to liquid (condensate).
The focus is to study sub-system a which deals Rankine cycle. Many of the practical limitations related with the Carnot cycle can be conveniently overcome in Rankine cycle.

Typical Ideal Rankine Cycle

In a vapor cycle if the working fluid in a vapor cycle passes through various components of the power plant without irreversibility and frictional pressure drop, then the cycle is called as Ideal Rankine Cycle. The Rankine cycle is the basic operating cycle for all power plants where an working fluid is continuously changing its phase from liquid to vapour and vice-versa. rankine cycle The (p-h) and (T-s) diagrams are useful in understanding the working of Rankine cycle along with the description given below: rankine cycle 1-2-3 Isobaric Heat Transfer or Constant pressure heat addition in a boiler Boiler is a large heat exchanger where heat liberating fuel like coal, lignite or oil transfers the heat indirectly to water at constant pressure. Water enters the steam boiler from boiler feed pump as a compressed liquid at state-1 and is heated to the saturation temperature as shown in the T-s diagram as state-3. The energy balance in the boiler is or energy added in steam generator, qin= h3-h1 3-4 Isentropic Expansion or Isentropic expansion in a turbine Vapor from the boiler outlet enters the turbine at state 3, where it expands isentropically over the turbine fixed and moving blade to produce work done in the form of mechanical rotation of the turbine shaft which in turn is connected to the electrical generator.

Work delivered by turbine, (Neglecting heat transfer with the surroundings) Wturbine out= h3-h4 4-5 Isobaric Heat Rejection or Constant pressure heat rejection in a condenser At state-4 vapor enters the condenser and the change of phase occurs as vapor is condensed to liquid at constant-pressure in the condenser by transferring the heat of the steam to the circulating water flow through the tubes of the condenser. Change of phase occurs in condenser and the working fluid leaving the condenser is in liquid state and marked as point 5. Energy rejected in the condenser, qout= h4-h5 5-1 Isentropic Compression or Isentropic compression in a pump Water exits the condenser at state 5 and enters the pump. This pump raises the pressure of the water by imparting work during the processes. In units of smaller size and because of low specific volume this small work can be neglected when compared to work-output of steam turbine. Work done on pump, per kg of water, W51= h5-h1 The thermal efficiency of the Rankine cycle is given by, OR

Closely Related Articles Engineering Thermodynamics Part 1Science of Engineering Thermodynamics Part 2Basic Law of Conservation and First Law of Thermodynamics Carnot Cycle and Reversed Carnot CycleEnthalpy Entropy and Second Law of ThermodynamicsRankine Cycle and Regenerative Feed HeatingRankine Cycle for Closed Feed Water Heaters and Rankine Cycle CogenerationIdeal Verses Actual Rankine CycleRankine Cycle Efficiency Improvement TechniquesMore Related Articles Steam Boiler | Working principle and Types of BoilerMethods of Firing Steam BoilerFire Tube Boiler | Operation and Types of Fire Tube BoilerWater Tube Boiler | Operation and Types of Water Tube BoilerSteam Boiler Furnace Grate Firebox Combustion Chamber of FurnaceFeed Water and Steam Circuit of BoilerBoiler Feed Water Treatment Demineralization Reverse Osmosis Plant DeaeratorCoal Combustion TheoryFluidized Bed Combustion | Types and Advantages of Fluidized Bed CombustionSteam Condenser of TurbineJet Condenser | Low Level High Level Ejector Jet CondenserSurface Steam Condenser Economics of Power GenerationCooling Tower Useful Terms and Cooling Tower PerformanceCooling Tower Material and Main ComponentsPower Plant Fire Protection SystemHydrant System for Power Plant Fire ProtectionMedium Velocity Water Spray or MVWS System for Fire ProtectionFoam Fire Protection SystemFire Detection and Alarm SystemGas Extinguishing SystemElectric Power GenerationPower Plants and Types of Power PlantThermal Power Generation Plant or Thermal Power StationHydro Power Plant | Construction Working and History of Hydro power plantNuclear Power Station or Nuclear Power PlantDiesel Power StationWhy Supply Frequency is 50 Hz or 60 Hz?Economiser in Thermal Power Plant | EconomiserMHD Generation or Magneto Hydro Dynamic Power Generation Cogeneration | Combined Heat and PowerThermoelectric Power Generators or Seebeck Power GenerationCost of Electrical EnergyGas Turbine Power PlantNuclear ReactorSolar ElectricitySolar Energy System | History of Solar EnergyTypes of Solar Power StationComponents of a Solar Electric Generating SystemWhat is photovoltaic effect?Staebler Wronski EffectWorking Principle of Photovoltaic Cell or Solar CellSolar CellCharacteristics of a Solar Cell and Parameters of a Solar CellSolar Cell Manufacturing TechnologyWhat is a Solar PV Module?What is Standalone Solar Electric System?Solar LanternSteamSteam Dryness FractionSuperheated Steam and Steam Phase DiagramVapour Properties Mollier Chart Heat CapacitiesWhat is Steam Flashing?How to Calculate Steam Consumption During Plant Start Up Effective Steam Distribution SystemWhat is Water Hammer?Wind Energy Electricity GenerationTheory of Wind Turbine Wind Turbine | Working and Types of Wind TurbineBasic Construction of Wind TurbineNew Articles Water MeterAir MeterDigital PotentiometersBasic Construction of Wind TurbineCharacteristics of Sensors