Fundamental of Power Plant And its thermodynamic cycles
A power plant is assembly of systems or subsystems to generate electricity, i.e., power with
economy and requirements. The power plant itself must be useful economically and environmental
friendly to the society.
CLASSIFICATION OF POWER PLANTS
a flow of mechanical or electrical energy. The main equipment for the generation of electric power is
generator. When coupling it to a prime mover runs the generator, the electricity is generated. The type of prime move determines, the type of power plants. The major power plants,
1. Steam power plant
2. Diesel power plant
3. Gas turbine power plant
4. Nuclear power plant
5. Hydro electric power plant
The Steam Power Plant, Diesel Power Plant, Gas Turbine Power Plant and Nuclear Power Plants
are called THERMAL POWER PLANT, because these convert heat into electric energy
TYPES OF ENERGY
There are various types of energy which, they include nuclear, electrical, thermal, chemical, and
radiant energy. In addition, gravitational potential energy and kinetic energy that combines to produce mechanical energy.
Nuclear energy produces heat by fission on nuclei, which is generated by heat engines. Nuclear
energy is the world’s largest source of emission-free energy. There are two processes in Nuclear energy fission and fusion. In fission, the nuclei of uranium or plutonium atoms are split with the release of energy. In fusion, energy is released when small nuclei combine or fuse. The fission process is used in all present nuclear power plants, because fusion cannot be controlled. Nuclear energy is used to heat steam engines. A Nuclear power plant is a steam engine using uranium as its fuel, and it suffers from low efficiency.
Electricity powers most factories and homes in our world. Some things like flashlights and Game
Boys use electricity that is stored in batteries as chemical energy. Other items use electricity that comes from an electrical plug in a wall socket. Electricity is the conduction or transfer of energy from one place to another. The electricity is the flow of energy. Atoms have electrons circling then, some being loosely attached. When electrons move among the atoms of matter, a current of electricity is created.
Thermal energy is kinetic and potential energy, but it is associated with the random motion of
atoms in an object. The kinetic and potential energy associated with this random microscopic motion is called thermal energy. A great amount of thermal energy (heat) is stored in the world’s oceans. Each day, the oceans absorb enough heat from the sun to equal the energy contained in 250 billion barrels of oil (Ocean Thermal Energy Conversion Systems).
Chemical energy is a form of energy that comes from chemical reactions, in which the chemical
reaction is a process of oxidation. Potential energy is released when a chemical reaction occurs, which is called chemical energy. A car battery is a good example, because the chemical reaction produces voltage and current to start the car. When a plant goes through a process of photosynthesis, what the plant is left with more chemical energy than the water and carbon dioxide. Chemical energy is used in science labs to make medicine and to product power from gas.
Radiant energy exists in a range of wavelengths that extends from radio waves that many be
thousands of meters long to gamma rays with wavelengths as short as a million-millionth (10– 12) of a meter. Radiant energy is converted to chemical energy by the process of photosynthesis.
The next two types of energy go hand and hand, gravitational potential energy and kinetic
energy. The term energy is motivated by the fact that potential energy and kinetic energy are different
aspects of the same thing, mechanical energy.
Potential energy exists whenever an object which has mass has a position within a force field.
The potential energy of an object in this case is given by the relation
PE = mgh,
where : PE is energy in joules, m is the mass of the object,
g is the gravitational acceleration,
h is the height of the object goes.
Kinetic energy is the energy of motion. An object in motion, whether it be vertical or horizontal
motion, has kinetic energy. There are different forms of kinetic energy vibrational, which is the energy due to vibrational motion, rotational, which is the energy due to rotational motion, and transnational, which is the energy due to motion from one location to the other. The equation for kinetic energy is
KE = ½ mv²
m is the mass and
v is the velocity.
This equation shows that the kinetic energy of an object is directly proportional to the square of its speed.
THERMODYNAMICS CYCLES RELATED TO POWER PLANTS
Thermodynamics is the science of many processes involved in one form of energy being changed
into another we should keep in mind principles that enable us to understand and follow energy as it
transformed from one form or state to the other
-The zeroth law of thermodynamics was enunciated after the first law. It states that if two bodies
are each in thermal equilibrium with a third they must also be in thermal equilibrium with each other
-The first law of thermodynamics says that energy can’t be destroyed or created. When one energy
form is converted into another
-The second law of thermodynamics is the entropy law, which says that all physical processes
proceed in such a way that the availability of the energy involved decreases
-The third law of thermodynamics is the law of unattainability of absolute zero temperature, which
says that entropy of an ideal crystal at zero degrees Kelvin is zero.
The steam power plants works on modified rankine cycle in the case of steam engines and isentropic cycle concerned in the case of impulse and reaction steam turbines. In the case of I.C. Engines (Diesel Power Plant) it works on Otto cycle, diesel cycle or dual cycle and in the case of gas turbine it works on Brayton cycle, in the case of nuclear power plants it works on Einstein equation, as well as on the basic principle of fission or fusion. However in the case of non-conventional energy generation it is complicated and depends upon the type of the system viz., thermo electric or thermionic basic principles and theories
CLASSIFICATION OF POWER PLANT CYCLE
Power plants cycle generally divided in to the following groups,
(1) Vapour Power Cycle (Carnot cycle, Rankine cycle, Regenerative cycle, Reheat cycle, Binary vapour cycle)
(2) Gas Power Cycles (Otto cycle, Diesel cycle, Dual combustion cycle, Gas turbine cycle.)
CARNOT CYCLE
This cycle is of great value to heat power theory although it has not been possible to construct a
practical plant on this cycle. It has high thermodynamics efficiency.
It is a standard of comparison for all other cycles. The thermal efficiency (η) of Carnot cycle is as
follows:
η = (T1 – T2)/T1
where, T1 = Temperature of heat sourceT2 = Temperature of receiver
Steam engine and steam turbines in which steam is used as working medium follow Rankine
cycle. This cycle can be carried out in four pieces of equipment joint by pipes for conveying working
medium as shown. The cycle is represented on Pressure Volume P-V and S-T diagram
Efficiency of Rankine cycle = (H1 – H2)/ (H1 – Hw2)
where,Hl = Total heat of steam at entry pressure
H2 = Total heat of steam at condenser pressure (exhaust pressure)
Hw2= Total heat of water at exhaust pressure
REHEAT CYCLE
In this cycle steam is extracted from a suitable point in the turbine and reheated generally to
the original temperature by flue gases. Reheating is generally used when the pressure is high say above 100 kg/cm².
where
H1 = Total heat of steam at 1
H2 = Total heat of steam at 2
H3 = Total heat of steam at 3
H4 = Total heat of steam at 4
Hw4 = Total heat of water at 4
REGENERATIVE CYCLE (FEED WATER HEATING)
The process of extracting steam from the turbine at certain points during its expansion and using
this steam for heating for feed water is known as Regeneration or Bleeding of steam
In this cycle two working fluids are used. The mercury boiler heats the mercury into mercury vapours in a dry and saturated state.
These mercury vapours expand in the mercury turbine and then flow through heat exchanger where they transfer the heat to the feed water, convert it into steam. The steam is passed through the steam super heater where the steam is super-heated by the hot flue gases. The steam then expands in the steam turbine.
In steam power plants using high steam pressure reheat regenerative cycle is used. The thermal
efficiency of this cycle is higher than only reheat or regenerative cycle. This cycle is commonly used to produce high pressure steam (90 kg/cm2) to increase the cycle efficiency.
1. Rankine efficiency = (H1 – H2)/(H1 – Hw2)
2. Efficiency ratio or Relative efficiency =
Indicated or Brake thermal efficiency/Rankine efficiency
3. Thermal efficiency = 3600/m(H1 – Hw2), m = steam flow/kw hr
4. Carnot efficiency = (T1 – T2)/T1
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https://mechasource.blogspot.com/2018/04/thermodynamic-principles-of-electricity.html
https://mechasource.blogspot.com/2018/04/thermodynamic-process.html
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