Power Principles - Key Notes

Power Principles

  • Power Plant Basics Series

Plant Cycle

  • Unit 1: Water/Steam Properties

  • Unit 2: Applications

  • Unit 3: The Steam Tables

  • Unit 4: Plant Performance

Copyright Information

  • Copyright 1982 by NUS Training Corporation

  • Revised May 31, 1986

  • Revised June 30, 1993

Table of Contents

  • Water/Steam Properties (Section 1.0)

    • Energy Flow Path and Plant Cycle (1.1): 1.1-1

    • Definition of Terms (1.2): 1.2-1

      • Pressure: 1.2-1

      • Temperature: 1.2-2

      • Specific Heat: 1.2-5

      • Specific Volume: 1.2-6

      • Enthalpy: 1.2-6

    • Subcooled Water (1.3): 1.3-1

      • Temperature and Specific Heat: 1.3-1

      • Specific Volume: 1.3-2

      • Enthalpy: 1.3-3

    • Steam/Water Mixture (1.4): 1.4-1

      • Latent Heat of Vaporization: 1.4-2

      • Specific Heat, Specific Volume, and Enthalpy of Saturated Steam: 1.4-3

      • Moisture Content and Quality of the Steam/Water Mixture: 1.4-4

    • Superheated Steam (1.5): 1.5-1

      • Superheated Steam and Specific Heat: 1.5-1

      • Specific Volume and Enthalpy of Superheated Steam: 1.5-2

    • Pressure (1.6): 1.6-1

      • Specific Heat, Specific Volume, and Pressure: 1.6-5

      • Enthalpy, Moisture Content, Quality, and Pressure: 1.6-5

  • Applications (Section 2.0)

    • Additional Components in the Plant Cycle (2.1):. 2.1-2

      • Condensate Pump: 2.1-4

      • Low Pressure Feedwater Heater: 2.1-5

      • Condensate Booster Pump and Feedwater Pump: 2.1-6

      • High Pressure Feedwater Heater: 2.1-7

      • Boiler, Cross-Compound Turbine, and Condenser: 2.1-7

    • The Saturation Curve and the Properties of Water/Steam (2.2): 2.2-1

      • Condensate Pump Outlet Conditions: 2.2-3

      • Low Pressure Feedwater Heater Outlet Conditions: 2.2-4

      • Condensate Booster Pump and Feedwater Pump Outlet Conditions: 2.2-5

      • High Pressure Feedwater Heater Outlet Conditions: 2.2-6

      • Boiler Superheater Outlet Conditions: 2.2-7

      • Turbine Outlet Conditions: 2.2-9

      • Condenser Outlet Conditions: 2.2-12

    • Effects of Pressure and Temperature, Part 1 (2.3): 2.3-1

      • Water Hammer: 2.3-1

      • Flashing: 2.3-6

    • Effects of Pressure and Temperature, Part 2 (2.4): 2.4-1

      • Effects of Changes in Temperature and Volume: 2.4-1

      • Shrink and Swell: 2.4-2

      • Effects of Increases in Temperature and Pressure: 2.4-3

      • Design of a Feedwater Heater: 2.4-5

      • Removing a Feedwater Heater from Service: 2.4-6

    • Avoiding Pressure and Temperature Problems (2.5): 2.5-1

      • Preparing for Removing a Feedwater Heater from Service: 2.5-2

      • Isolating the Steam Side: 2.5-2

      • Isolating the Water Side: 2.5-2

  • The Steam Tables (Section 3.0): 3.1-1

    • Introduction to the Steam Tables (3.1): 3.1-1

      • Organization of Table 1, "Saturated Steam: Temperature Table": 3.1-2

      • Organization of Table 2, "Saturated Steam: Pressure Table": 3.1-4

    • Using the Saturation Tables (3.2): 3.2-1

      • Subcooled Conditions and the Saturation Tables: 3.2-1

      • The Saturation Tables and Boiler Drum Outlet Conditions: 3.2-4

    • The Superheated Steam Table (3.3): 3.3-1

      • Organization of "Table 3. Superheated Steam": 3.3-1

      • Using "Table 3. Superheated Steam" to Find the Properties of Superheated Steam: 3.3-3

    • Superheated Steam Table and Conversion Factors (3.4): 3.4-1

      • Using "Table 3. Superheated Steam" to Calculate Enthalpy at a Reheater Outlet: 3.4-1

      • Conversion Factors: 3.4-2

    • Introduction to the Mollier Diagram (3.5): 3.5-1

      • The Organization of the Mollier Diagram: 3.5-2

    • Using the Mollier Diagram (3.6): 3.6-1

      • Energy Transfer to High Pressure Section of the Turbine: 3.6-1

      • Energy Transfer to the Remainder of the Turbine: 3.6-4

  • Plant Performance (Section 4.0): 4.1-1

    • Efficiency and Heat Rate (4.1): 4.1-1

    • Heat Rate (4.2): 4.2-1

      • Calculating Heat Rate: 4.2-2

      • Factors Affecting Heat Rate: 4.2-4

    • Heat Rate and Plant Cycle Components (4.3): 4.3-1

    • Superheated Steam Temperature (4.4): 4.4-1

      • Control of Superheated Steam Temperature: 4.4-3

      • Effect of a Decrease in Superheated Steam Temperature: 4.4-5

    • Condenser Vacuum (4.5): 4.5-1

      • Measurement of Condenser Vacuum: 4.5-2

      • Effect of a Decrease in Condenser Vacuum: 4.5-4

      • Operator Checks on Condenser Vacuum: 4.5-5

    • Feedwater Temperature (4.6): 4.6-1

      • Effect of a Decrease in Feedwater Temperature: 4.6-1

      • Effect of an Increase in Feedwater Temperature: 4.6-3

      • Operator Checks: 4.6-4

Water/Steam Properties

  • Energy conversion is a crucial aspect of power plant operation.

  • Energy Flow Path: Chemical energy in fuel -> Thermal energy -> Mechanical energy -> Electrical energy.

  • Plant cycle is integral to the energy flow path.

  • Objectives:

    • Understand the plant cycle.

    • Know five properties of water.

    • Understand how these properties change when water turns to steam.

    • Understand the effects of pressure changes on water properties.

The Energy Flow Path and Plant Cycle

  • Operators control energy flow within the plant.

  • Energy Flow Path:

    • Fuel (coal, gas, oil) is ignited in the boiler: Chemical energy -> Thermal energy.

    • Thermal energy produces steam.

    • Steam moves to the turbine: Thermal energy -> Mechanical energy (turbine rotor turns).

    • Generator: Mechanical energy -> Electrical energy.

  • Plant Cycle:

    • Thermal energy is transferred to water in boiler tubes.

    • Water boils and vaporizes into steam.

    • Steam flows to the turbine.

    • Thermal energy in steam -> Mechanical energy.

    • Rotor drives the generator.

    • Mechanical energy -> Electrical energy.

    • Steam is exhausted to the condenser and cooled back into water (condensate).

    • Condensate is pumped back to the boiler.

    • The plant cycle is a closed loop.

Definition of Terms

  • Properties of Water: Pressure, Temperature, Specific Heat, Specific Volume, Enthalpy.

  • Pressure:

    • Force per unit area.

    • Units: pounds per square inch (psi).

    • Symbol: P.

    • Scales: Absolute (psia) and Gauge (psig).

    • Absolute Scale: Zero reference is a complete vacuum (0 psia).

    • Gauge Scale: Zero reference is atmospheric pressure.

    • Conversion: psia=psig+AtmosphericPressurepsia = psig + Atmospheric Pressure

  • Temperature:

    • Measurement of warmth or coolness.

    • Scales: Fahrenheit (°F) and Celsius (°C).

    • Symbol: T.

    • °C=(°F−32)mes59°C = (°F - 32) mes \frac{5}{9}

    • °F=(95mes°C)+32°F = (\frac{9}{5} mes °C) + 32

    • British Thermal Unit (BTU): Heat to raise 1 lb of water 1°F.

  • Specific Heat:

    • Heat to raise 1 lb of a substance 1°F.

    • Units: BTU/lb-°F.

    • Symbol: c.

    • Water: Approximately 1 BTU/lb-°F.

  • Specific Volume:

    • Space occupied by 1 lb of a substance.

    • Units: cubic feet per pound (ft³/lb).

    • Symbol: v.

    • Water: Approximately 0.016 ft³/lb.

  • Enthalpy:

    • Heat content or thermal energy in 1 lb of a substance.

    • Units: BTU/lb.

    • Symbol: h.

    • Water at 32°F: 0 BTU/lb.

    • Increase approximately 1 BTU/lb per 1°F increase.

Subcooled Water

  • Water exists as solid (ice), liquid, or vapor (steam).

  • Properties depend on state; Vary within states.

  • Constant pressure: 14.7 psia (atmospheric).

  • Saturation Temperature: the temperature at which water will begin to boil.

  • Temperature and Specific Heat:

    • Liquid state: 32-212°F at atmospheric pressure.

    • Saturation temperature at 14.7 psia: 212°F.

    • Subcooled water: Below boiling point.

    • Specific heat: Approximately 1 BTU/lb-°F.

  • Specific Volume:

    • Changes very little with heat.

    • At 32°F: Approximately 0.0160 ft³/lb.

    • At 212°F: Approximately 0.0167 ft³/lb.

  • Enthalpy:

    • Increases approximately 1 BTU/lb per 1°F.

    • At 32°F: 0 BTU/lb.

    • At 212°F: Approximately 180 BTU/lb.

Steam/Water Mixture

  • Heat is added to water at saturation temperature (14.7 psia).

  • Transition Zone: Water and steam coexist.

  • Temperature remains constant (212°F).

  • Distinction between saturated water (not boiling) and saturated steam (no water).

  • Latent Heat of Vaporization:

    • Heat to turn saturated water into saturated steam.

    • At atmospheric pressure: 970.3 BTU/lb.

    • No temperature change during boiling.

  • Specific Heat, Volume, and Enthalpy of Saturated Steam:

    • Specific heat is meaningless (no temperature change).

    • Specific volume changes substantially; increases approximately 1600 times.

    • Water at 212°F: Approximately 0.0167 ft³/lb.

    • Saturated steam: Approximately 26.8 ft³/lb.

    • Enthalpy of saturated steam: Enthalpy of saturated water + Latent heat of vaporization.

    • At 14.7 psia: 180.2 BTU/lb + 970.3 BTU/lb = 1150.5 BTU/lb

  • Moisture Content and Quality:

    • Moisture content: Percentage of water in the mixture.

    • Quality: Percentage of steam.

    • MoistureContent=Pounds:of:WaterPounds:of:Steam/Water:Mixturemes100Moisture Content = \frac{Pounds : of : Water}{Pounds : of : Steam/Water : Mixture} mes 100

    • Quality=Pounds:of:SteamPounds:of:Steam/Water:Mixturemes100Quality = \frac{Pounds : of : Steam}{Pounds : of : Steam/Water : Mixture} mes 100

    • Specific : Volume : of : Mixture = (Specific : Volume : of : Water \tmes Moisture) + (Specific : Volume : of : Steam \tmes Quality)

    • Enthalpy : of : Mixture = (Enthalpy : of : Water \tmes Moisture) + (Enthalpy : of : Steam \tmes Quality)

Superheated Steam

  • Steam heated above saturation temperature.

  • Plant cycle uses it to carry thermal energy from the boiler to the turbine.

  • Superheated Steam and Specific Heat:

    • Adding heat increases temperature.

    • Specific heat is lower than subcooled water.

    • Subcooled: 1 BTU/lb-°F; approximately 5 BTU/lb-°F


  • Specific Volume and Enthalpy:

    • At 14.7 psia increase temperature to 1000°F.

    • Specific volume increases to 59.1 ft³/lb.

    • Enthalpy increases to 1534.5 BTU/lb.

Pressure

  • Constant heat pressure affects water properties.

  • At 14.7 psia, heat is added to subcooled water and temperature increases up to the saturation temperature.

  • The temperature does not change by adding heat, because the Latent heat of vaporization turns water into steam.

  • After steam is saturated the steam enters the Superheated Zone.

  • At pressures lower than 14.7 psia:

    • Saturation temperature for water is lower.

    • Transition zone is larger.

  • At pressures higher than 14.7 psia:

    • Saturation temperature is higher.

    • Transition zone is smaller.

  • Latent Heat of Vaporization decreases as pressure increases.

  • Critical Point:

    • Pressure reaches 3208 psia at 705.47°F.

    • Latent heat of vaporization is zero.

    • No difference between water and steam.

  • Specific Heat, Specific Volume, and Pressure:

    • Specific heat of water doesn't change.

    • Specific heat of steam also changes very little.

    • The specific volume of water changes very little, regardless of pressure.

    • Steam decreasing the volume of the stream.

  • Enthalpy, Moisture Content, Quality, and Pressure:

    • Enthalpy does not change significantly as pressure changes.

    • Changes in moisture content, quality, and state of water/steam. can significantly affect power plant operation.