Piping system:

Piping system is an essential part of a steam power plant. It is employed to transmit water, steam, air, oil and vapor from one position to others.

Types of piping system:

A power uses many fluids like water, air, oil, steam, gas etc during its operation. This requires a variety of integrated piping system mentioned below:

1.      Water piping: Raw water, feed water, condensate and condenser cooling water.

2.      Steam piping: Main, reheat, bleed exhaust steam.

3.      Blow of piping: Boiler, evaporator, feed treatment.

4.      Miscellaneous piping: Water treatment, service water, lubricating oil, drains compressed air etc.

                                                Figure:  Steam piping system

Materials for pipes:

Ø      Cast iron: Cast iron pipes are used underground for water and drainage system and in order to place where problem of corrosion is excessive. Cast iron pipes are used for water service up to a pressure of 15 kg/cm².

Ø      Wrought iron: Wrought iron pipes are used for condensate, feed water and blow of lines. Such pipes are used for low and medium pressure range and should not be used when pressure is more than 250 psi.

Ø      Wrought steel: Most of the pipes used in power station are made of wrought steel. It is cheaper than others.

Ø      Alloys steel: For high temperature flow pipes are made of alloys steel. Chromium steel pipes are used for the temperature higher than 525⁰C. For temperature between 400⁰C-525⁰C carbons molybdenum steel may be used.

Ø      Copper and brass: Pipes made up of copper and brass are costly and are mostly used for oil lines. Brass pipe are used up to pressure 20 kg/cm².

Gas turbine:

A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. Gas turbine may also refer to just the turbine component. Energy is added to the gas stream in the combustor, where fuel is mixed with air and ignited. In the high pressure environment of the combustor, combustion of the fuel increases the temperature. The products of the combustion are forced into the turbine section. There, the high velocity and volume of the gas flow is directed through a nozzle over the turbine's blades, spinning the turbine which powers the compressor and, for some turbines, drives their mechanical output. The energy given up to the turbine comes from the reduction in the temperature of the exhaust gas.

                                                Figure: Gas turbine chamber.

Gas turbine works on the basis of Bray ton cycle. Brayton cycle is called the backbone of the gas turbine. Here the T-S and P-V diagram is shown in below:

All four processes of the Brayton cycle are executed in steady flow devices so they should be analyzed as steady-flow processes.

When the changes in kinetic and potential energies are neglected, the energy balance for a steady-flow process can be express, on a unit-mass basis, as −

                       

                                                                                               

           Figure: 1^st stage blade of GT

                                        Figure: T-S and P-V diagram of Brayton cycle.

(Q _in –Q _out) + (W_in –W _out) = H _exit – H _inlet

Therefore, heat transfers to and form the working fluid are

                        Q _in = H₃ – H₂ = C_p (T₃- T₂)

            And, Q _out = H₄ – H₁ = C_p (T₄ – T₁)

Then the thermal efficiency of the ideal Brayton cycle is-

 Brayton efficiency = 1 – (Q _out / Q _in).

           

                       

Turbine blades:

The energy conversion takes place through the turbine blades. A turbine consists of alternate rows of blades. This blades convert the chemical or thermal energy of working fluid into kinetic energy and then from kinetic energy to mechanical energy as rotation of the shaft.

 There are two types of blade, fixed and moving blade. Moving blade is also two types.

One is impulse blade and another reaction blade.

Fixed blade:

A fixed blade assembly is very important for turbine blading. It is also known as diaphragm. The shape of the blade is the key to the energy conversion process. Since the fixed blades have a conversing nozzle shape, it is also called nozzles. When steam is passed over the fixed blades, they increase the velocity of steam as an operation of nozzles. Here blades are converted the thermal energy of steam into kinetic energy by causing the steam to speed up and gain velocity.

                                                                                          

Moving blade:

Moving blade can be shaped in either of two ways: reaction shaped or impulse shaped. The shape of the blade determines how the energy is actually converted. Either type of moving blades or a combination of both can be attached to the shaft of the rotor on dices, called wheels as shown in the figure. Along the outer rim of the blades is a metal band, called shrouding which ties the blades together. The moving blades convert the kinetic energy in the moving speed into the mechanical energy as rotor rotation.

                      

Steam turbine:

Steam turbine is such type of turbine where steam is used as working fluid. When steam is injected over the blades it rotates at a certain speed. Since steam is used for rotation it is called steam turbine. Generally it is used at steam turbine power station.

In most power station, steam turbines are used for steam turbine units. All the turbines are manufactured by BBC (Germany).

                                                 Figure: Steam turbine (case opened).

Main parts of steam turbine:                

Ø      Rotor

Ø      Blades (fixed and moving)

Ø      Bearings (thrust and journal)

Ø      Turbine casing

Ø      Valves (main stop valve, control valve etc).

  

Turbine:

A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work. The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and impart rotational energy to the rotor.

Types of turbine:

1.      Steam turbine

2.      Gas turbine

3.      Water turbine

4.      Wind turbine

5.      Transonic turbine

6.      Ceramic turbine

Pumps:

Pumps are such a device, which transfer liquid from one place to another place by pressure difference.

Types of pump:

1.      Centrifugal pump

2.       Reciprocating pump

Centrifugal pump:

                        The pump which raises water or a liquid from a lower level to a higher level by the action of centrifugal force is known as centrifugal pump. A centrifugal pump is a rot dynamic pump that uses a rotating impeller to increase the pressure of a fluid. Centrifugal pumps are commonly used to move liquids through a piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing racially outward into a diffuser or volute chamber, from where it exits into the downstream piping system. Centrifugal pumps are used for large discharge through smaller heads.

Working principle: 

A centrifugal pump works by converting kinetic energy into potential energy measurable as static fluid pressure at the outlet of the pump. This action is described by Bernoulli's principle. With the mechanical action of an electric motor or similar, the rotation of the pump impeller imparts kinetic energy to the fluid through centrifugal force. The fluid is drawn from the inlet piping into the impeller intake eye and is accelerated outwards through the impeller vanes to the volute and outlet piping.