Most Important Power Plant Fundamentals – Part -1
Before discussing boilers and power plants in detail, it’s important to understand some basic mechanical engineering principles. These fundamental concepts are essential for boiler operation engineers in their daily tasks.
LAW OF CONSERVATION OF ENERGY
The law of conservation of energy states that energy cannot be created or destroyed, only transformed from one form to another. Energy is defined as the capacity to do work, and it exists in various forms, such as mechanical, electrical, chemical, heat, light, kinetic, and potential energy.
In a boiler system, chemical energy in fuel is transformed into heat energy through combustion. This heat energy is then used to convert water into steam. The heat energy in steam is transformed into kinetic energy, which then powers a steam turbine, converting kinetic energy into mechanical energy. This mechanical energy drives a generator to produce electricity, transforming mechanical energy into electrical energy.
TEMPERATURE
Temperature measures the average energy of an object’s molecules, which move faster as they gain energy. In practical terms, temperature is the sensation of warmth or coldness we feel upon contact with an object and is measured quantitatively with a thermometer.
Most materials expand when heated, with some, like mercury, expanding consistently with temperature. Various principles are commonly used to measure temperature:
Change in length: e.g., the length of a mercury column
Change in volume: e.g., the volume of a fixed mass of gas at constant pressure
Change in pressure: e.g., the pressure of a fixed mass of gas at a constant volume
Change in electric resistance: as seen in thermistors
Electric flow (Seebeck effect): used in thermocouples
Radiation: used in radiation pyrometers
These methods allow us to measure temperature accurately across a range of conditions.
TEMPERATURE SCALES
There are three primary scales used to measure temperature:
Celsius (Centigrade) Scale
- Developed by Anders Celsius (1701–1744), the Celsius scale divides the temperature difference between water’s Icing and boiling points into 100 units.
- 0 °C is defined as the Icing point of water under standard atmospheric pressure, and 100 °C is the boiling point.
- Each unit is called a degree Celsius (°C). Engineers worldwide, including in India, use this scale.
Fahrenheit Scale
- This scale, created by Daniel Gabriel Fahrenheit (1686–1736) in 1724, sets water’s Icing point at 32 °F and its boiling point at 212 °F.
- The interval between these points is divided into 180 equal units, each known as degree Fahrenheit (°F).
- The Fahrenheit scale is commonly used in the United States, and the normal human body temperature is approximately 98.6 °F on this scale.
Kelvin Scale
- The Kelvin scale, based on absolute zero, was introduced by Lord William Kelvin (1824–1907) in 1854.
- Absolute zero (0 K or -273.15 °C) is the theoretical temperature at which all molecular movement stops, representing the lowest possible energy state.
- The Icing point of water is 273.15 K, and the boiling point is 373.15 K.
- Unlike Celsius and Fahrenheit, the Kelvin scale does not use the term “degree” or the symbol (°). Each unit is called Kelvin (K). This scale, which has no negative values, is ideal for measuring extremely low temperatures in scientific research.
Each scale has applications depending on regional preferences or scientific and industrial research requirements.
The absolute pressure of a system is obtained by adding the gauge pressure to the atmospheric pressure. At sea level, atmospheric pressure is approximately 1.0332 kg/cm² or 1.0132 bar absolute. If the measurement location is above sea level, atmospheric pressure decreases.
At sea level, a mercury column has a height of 760 mm and a density of 13.5951 g/cm³. This is commonly used as a standard reference for atmospheric pressure.