Detailed P & I diagram for pressure control loop

MAIN STEAM AND WATER CIRCUITS OF BOILER - TURBINE UNIT

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 source
T2 = Temperature of receiver

RANKINE CYCLE

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 in Figure below

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

The cycle is represented on Pressure Volume P-V and S-T diagram as shown in Figure below respectively.

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. The various advantages of reheating are as follows:

• It increases dryness fraction of steam at exhaust so that blade erosion due to impact of water particles is reduced.
• It increases thermal efficiency.
• It increases the work done per kg of steam and this results in reduced size of boiler.

The disadvantages of reheating are as follows:

• Cost of plant is increased due to the reheater and its long connections.
• It increases condenser capacity due to increased dryness fraction.

Figure bvelow shows flow diagram of reheat cycle. First turbine is high-pressure turbine and second turbine is low pressure (L.P.) turbine.

This cycle is shown on T-S (Temperature entropy) diagram (Figure below).

If,
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
Efficiency = {(H1 – H2) + (H3 – H4)}/{H1 + (H3 – H2) – Hw4}

BINARY VAPOUR CYCLE

In this cycle two working fluids are used. Figure below shows Elements of Binary vapour power plant. 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.

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. The arrangement of bleeding the steam at two stages is shown in Figure below

Let,

m2 = Weight of bled steam at a per kg of feed water heated

m2 = Weight of bled steam at a per kg of feed water heated

H1 = Enthalpies of steam and water in boiler

Hw1 = Enthalpies of steam and water in boiler

H2, H3 = Enthalpies of steam at points a and b

t2, t3 = Temperatures of steam at points a and b

H4, Hw4 = Enthalpy of steam and water exhausted to hot well.

Work done in turbine per kg of feed water between entrance and a

= H1 – H2

Work done between a and b = (1 – m2)(H2 – H3)

Work done between b and exhaust = (1 – m2 – m3)(H3 – H4)

Total heat supplied per kg of feed water = H1 – Hw2

Efficiency (η) = Total work done/Total heat supplied

= {(H1 – H2) + (1 – m2)(H2 – H3) + (1 – m2 – m3)(H3 – H4)}/(H1 – Hw2)

REHEAT-REGENERATIVE CYCLE

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. Figure below shows the flow diagram of reheat regenerative cycle. This cycle is commonly used to produce high pressure steam (90 kg/cm2) to increase the cycle efficiency.

THERMODYNAMICS CYCLES RELATED TO POWER PLANTS

Thermodynamics is the science of many processes involved in one form of energy being changed into another. It is a set of book keeping 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. Equilibrium implies the existence of a situation in which the system undergoes no net charge, and there is no net transfer of heat between the bodies.

The first law of thermodynamics says that energy can’t be destroyed or created. When one energy form is converted into another, the total amount of energy remains constant. An example of this law is a gasoline engine. The chemical energy in the fuel is converted into various forms including kinetic energy of motion, potential energy, chemical energy in the carbon dioxide, and water of the exhaust gas.

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. This means that no transformation of energy resource can ever be 100% efficient. The second law declares that the material economy necessarily and unavoidably degrades the resources that sustain it. Entropy is a measure of disorder or chaos, when entropy increases disorder increases.

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. It’s unattainable because it is the lowest temperature that can possibly exist and can only be approached but not actually reached. This law is not needed for most thermodynamic work, but is a reminder that like the efficiency of an ideal engine, there are absolute limits in physics.

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 et al.

Power

Power is the rate doing work, which equals energy per time. Energy is thus required to produce power. We need energy to run power plants to generate electricity. We need power to run our appliances, and heat our homes. Without energy we would not have electricity. The units of power are watts, joules per second, and horsepower, where;

1 Watt	=	1 joule per second
1 Kilowatt	=	1,000 Watts
1 Megawatt	=	1,000 kilowatts
	=	1 horsepower

Electricity is the most convenient and versatile form of energy. Demand for it, therefore, has been growing at a rate faster than other forms of energy. Power industry too has recorded a phenomenal rate of growth both in terms of its volume and technological sophistication over the last few decades. Electricity plays a crucial role in both industrial and agricultural sectors and, therefore, consumption of electricity in the country is an indicator of productivity and growth. In view of this, power development has been given high-priority in development programme.

The last universal key to open the door to illumination:

• Mankind assumes that a supreme creator exists.

• This supreme creator has supposedly given mankind reason from his own pure "essence".

• If you believe in that, then this pure essence must be pure reason excluding everything irrational.

• Likewise the reason given to mankind should also exclude everything which is irrational.

• Therefore reason excludes anything irrational.

• If we go by the assumption that the "donor's intention in giving "reason" to mankind is keeping its "creation" pure, and if reason excludes everything irrational, then the exclusion principle dictates that there should be nothing irrational in creation or in existence.

• So the existence of an irrational supreme creator is contrary to reason, and no supreme creator could give orders contrary to reason.

• Consequently if what is called the divine word contradicts reason, either it is not the word of the supreme creator or the supreme creator itself is irrational.

• Being irrational, this supreme creator is also subject to the exclusion principle.

• In other words, reason and the supreme creator cannot coexist.

LIGHT RAIL VEHICLE DESIGN CHARACTERISTICS - Vehicle Mass

As an example of what crash energy management (CEM) principles can mean to carbody mass, it is useful to compare the 70% low-floor LRVs built for New Jersey Transit with those delivered to Santa Clara County (San Jose), California. The latter were constructed to the 2-g criterion under California PUC regulation 143-B while the former were designed around crash energy management (CEM) principles. The same carbuilder produced both cars, and they have the same overall dimensions, performance, and capacity.

The California car has a maximum wheel load at AW2 loading that is 540 pounds [245 kg] greater than that of the New Jersey LRV, a difference of 3.2 tons [2.9 metric tonnes] per car. The difference will result in appreciable propulsion energy cost savings over the life cycle of the New Jersey Transit car as well as less loading and wear and tear on the track.