Band Pass Filter

Band pass filter is terminology which is used in telecommunication. Filter is device which passes or stops specific things.

 Filter:  Filter is as like net used to catch fishes or birds or beasts etc. Filter is also used for water purification. Here terminology used for filter, is for telecommunication. This filter is electronics circuit which passes or stops the specific frequency.

Band: As written up, here things are discussed are about the telecommunication. Band is range of frequencies. as like from 2 hz to 10 hz. this is called band.

Band Pass Filter: Band pass filter is electronics circuit which pass specific range of frequencies. These filters blocks the specific range frequencies or allow to pass the range of frequencies. When there is modulated signal then for transmission, one of bands or both bands are transmitted. After receiving the signal, for demodulation we have to separate the signal from carrier frequency. Here Band pass or Band stop filters are used. Mostly these filters are used in telecommunication system. Communication system can be of Radio, television, telephone etc

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What is actual Rankin Cycle?

Actual Rankin Cycle:


In actual Rankin cycle, the processes are deviated from those of Ideal Rankin cycle.
Solid lines are showing ideal processes and dotted lines are showing actual processes.
 





1’-2’: Actual adiabatic expansion of superheated steam in the turbine. Turbine is surrounded by insulating material such as fiber glass or asbestos to prevent heat loss.

2’-3’: Actual process of condensation.

3’-4’: Adiabatic rise in pressure in the pump.

S’2 is higher than S2 and S4 is higher than S4, showing that entropy is generated in these processes.

Isentropic Efficiency = Actual work/ Ideal work when expansion is isentropic.

Unfortunately, the entropy is generated in cases, the expansion and the compression.


4’-5’: Heating in the economizer. 

5’-6’: Actual process of heating in the boiler.

6’-1’: Super-heating process in the super heater.

It must be mentioned here that all the process in the Rankin Cycle are control volume as mass is entering and leaving and also the heat and work.

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What is Ideal Rankin Cycle?

Ideal Rankin Cycle:

Ideal Rankin Cycle is a Cycle in which all the thermodynamic processes go ideally without losses and there is no entropy generation during any of the process.

In the figure below, the actual Rankin cycle is shown on the T-S diagram.

 

1-2: Isentropic expansion of superheated steam in the turbine.

2-3: Condensation in the condenser which converts steam into water. It is the constant pressure and constant
temperature heat rejection from steam which causes condensation. The volume is reduced about 1000 time in the condenser, thus saving huge amount of mechanical work.

3-4: Constant entropy pressure rise in the pump.

4-5: There is constant pressure heat supply in the economizer or with feed water heating.

5-6: Heat supply at constant temperature and pressure in the Boiler.

6-1: The steam is superheated at constant pressure.

4-5-6-1 ; This is the line of constant pressure.

5-6: Is the line of constant Temperature.

After expansion inside the turbine, the dryness fraction is kept more than 0.85, as high water content causes damage like rust etc.

To reduce mechanical work for pumping, we cool until saturated liquid is obtained and no steam content remains.

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What is steam Turbine Power Plant?

Steam Turbine Power plant.

A steam turbine power plant converts the energy of the fuel into the shaft work continuously and ultimately from the shaft work, electricity is produced.  In the boiler, there is combustion of fuel (fossil fuel) like oil, natural gas, and coal or fissile fuel such as Uranium or Thorium to produce steam.

In the combustion process, heat generated is supplied to the boiler which is a heat exchanger. Boiler is a tube separating two fluids by a walls and thermal conductivity of this wall is very high. In the Nuclear Power plant, the furnace is replaced by Nuclear reactor.

The steam is produced at very high temperature and pressure which expands in steam turbine to produce Mechanical energy and the electrical energy.

Where
Mf     = Mass of fuel

C.V   = Calorific value

Wp    = Work of  the Pump

Q1     = Heat Supplied

Q2     = Heat rejected

Wt is the shaft work, which is form of mechanical energy.  Steam coming from the turbine is fed to the condenser where condensation of the steam takes place. Here heat is extracted from steam to convert it into liquid. Steam emitted from the turbine has both liquid and vapour phases.

River or see water can be used to extract heat from steam and there is change of phase from vapour to liquid. If no river or see is present in nearby area, cooling tower is needed to supply cold water to condenser. The pressure inside the condenser is 10% of the atmospheric pressure. So, a pump is used to raise the pressure from condenser pressure to boiler pressure.  Therefore steam turbine power plant work in a sequence.

B -----> T -------> C ------> P  ------> B

And the cycle is going on repeatedly.

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What is Co-generation?

Co-Generation:

The production of electric power and heat in a single unit is called co-generation. Co-generation is applicable to the industries like paper, Textile, sugar, chemical, cement etc.

Advantages of Co-generation:

Isothermal process is maintained by steam as it is the best fluid to maintain constant temperature.  The constant process is maintained by using its latent heat of vaporization.

Process is good for safety point of view. For example in inflammable environment, e.g in oil refinery, the direct heat can blow up the whole plant. Steam use for this process is safe.

Feasibility of the plant must be seen before choosing a co-generation plant.

There are two types of co-generation cycle.
A.    Topping cycle

B.    Bottoming cycle



Topping cycle:


It is cycle where main emphasis is on the production of electricity. High grade steam is used to generate power and then low grade steam is used in industial process. Topping cycle finds its application in process industry.

Bottoming Cycle:

Here the steam generated by the steam generator is mainly utilized in the Industrial process and then the steam from the discharge of industrial process is used to generate electricity.
In the cement industry, this type of cycle is applicable as the steam required there should be high grade. ( High temperature and pressure)

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What is Regenerative Cycle?

Regenerative Cycle:



Regenerative cycle is shown is the figure below.

To decrease the irreversibility of the process regenerative cycle is introduced. Less irreversibility mean greater efficiency.
Steam from the boiler enters the turbine and there is partial expansion of the turbine from pressure P1 to a pressure P2. At the state 2, some of the steam is extracted and fed to feed-water heater 1 for the purpose of heating water coming from the condenser. Further expansion of the steam takes place, and it reaches to a pressure P3. Some amount of water is also extracted for Feed water heater 2.
Complete expansion of the steam takes place up to pressure P4, i.e the condenser pressure. The purpose of heating water before it enters the boiler is to increase efficiency by decreasing irreversibility, and the phenomenon is called Regeneration.

Various processes are as explained below.

1-2: Isentropic Expansion of 1Kg of steam in turbine up to pressure P2.

2-3: (1-m1) Kg of steam expands in the turbine from pressure P2 to P3.

3-4: (1-m1 -m2) Kg of steam expands from P3 to condenser pressure P4 in the turbine.

4-5: Constant temperature and pressure condensation in the condenser.

5-6: Isentropic pressure rise in the Pump1.

6-7: Constant pressure heating in feed water heater 2.

7-8: Isentropic pressure rise in pump 2.

8-9: Constant pressure heating of feed water 1.

9-10: Isentropic pressure rise in the main pump.

10-1: Constant pressure heating in the Boiler.

Heat supplied in the Boiler = Q1 = h1 - h10

Work output of the turbine = Wt = (h1 -h2) +(1- m1)(h2 - h3) + (1-m1-m2)(h3 -h4)

Work input of the pump = Wp= (h10 - h9) +(1-m1)(h8 - h7)+(1-m1-m2)(h6 -h5)

Heat to condenser = Q2= (1- m1-m2)(h4-h5)

Thermal efficiency = (Wt- Wp)/Q1

We can see that heat lost in the condenser is reduced by an amount = (m1+m2)(h4-h5)

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What is Reheat Rankin Cycle?

Reheat Rankin Cycle:

The drawback of having high pressure in the boiler is the increase of water content at the blades steam turbine. To avoid this problem, reheat Rankin cycle is used.
The diagram for the Reheat Rankin cycle is shown.




We can enhance the thermal efficiency of the steam turbine power plant by reheating the steam coming from high pressure turbine, approximately to same temperature as the inlet of the first turbine and then passing it from an another turbine operating at low pressure, called low pressure turbine. By this arrangement, the dryness fraction at the exit of low pressure turbine is increase which is desirable to increase the thermal efficiency of the Plant.

The various processes in Reheat Rankin Cycle are:

1-2: Isentropic Expansion of superheated steam in the high pressure turbine.

2-3: Constant pressure reheating in the Re-heater.

3-4: Isentropic expansion in low pressure turbine.

4-5: Heat rejection in the condenser at constant temperature and pressure.

5-6: Isentropic pressure rise in the Pump.

6-7: Heating of sub-cooled liquid

7-1: Constant Pressure Reheating in the Boiler.

Heat supplied to the Boiler = h1 - h6 = Q1

Heat rejected to the condenser = h4 - h5 = Q2

Total Work output = Wt1 + Wt2 = Work done in low pressure turbine + Work done in high pressure turbine = (h1 - h2) + (h3 - h4)

Total Heat supplied = heat supplied in the Boiler + Heat supplied in the Re-heater = (h1 -h6) + (h3 - h2)

Thermal efficiency = Net work output/ Total heat supplied = {(h1 - h2) + (h3 - h4) – (h6 - h5)}/ {(h1 -h2) + (h3 - h2)}

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