ANALYSIS OF USING EXHAUST FLUE GAS FOR POWER …

ANALYSIS OF USING EXHAUST FLUE GAS FOR POWER

GENERATION IN THERMAL POWER PLANT

1M.Hariprabhu, K. Sundararaju, K.Arnold Wilson

Department of Electrical and Electronics Engineering, M. Kumarasamy College of Engineering, Karur-

639113, India. 1Corresponding author mail id: [email protected]

ABSTRACT

Normally the thermal power plant will generate electricity by burning the coal. The water

will be converted in to steam by using the heat generated by burning coal. During this process flue

gas is obtained as the waste product. That will be taken into many process and at last will be

emitted into at atmosphere. This project is to utilize the flue gas for any protective purpose. That the

heat of the flue gas is used in this project to heat the feed water of the boiler. That the heat of the

flue gas is used in the condensate system. That one of the low pressure heater (LPH) is replaced by

the flue gas heater. So the efficiency of the thermal power plant will be improved and the energy

used by the power plant will be reduced.

KEYWORDS: Flue gas, Reuse, Waste Heat, Low Pressure Heater

1.INTRODUCTION

The thermal power stations are used to generate electricity for a long time. This uses the heat

energy to convert liquid into gas and by using this electricity will be generated. In most of the place

the water is used for this process. Then the fossil fuels are used to generate the heat which is needed

to heat the water. The fossil fuels are fuels which are created by natural process, such as

decomposition of buried organisms in absence of oxygen. The fossil fuels are mostly made up of

carbon and some percentages of other materials. During the burning process the fuel will emit heat

energy and light energy. Then there also some other by-products also will be obtained[1]. They are

ash and exhaust gas. The exhaust gas consists of carbon-dioxide(CO2), water vapor and other

pollutants. The exhaust flue gas will be emitted to the atmosphere. But we can use the heat energy

of the waste gas to improve the efficiency of the thermal power plant. But if the temperature of the

exhaust gas drops low will lead to the formation of the acids which will reduce the efficiency of the

boiler[2,3]. There are many heat exchanging type but mostly shell-in-tube design gives more

International Journal of Pure and Applied MathematicsVolume 118 No. 20 2018, 2161-2171ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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benefits on the process[4]. The flue gas is used in air pre-heater to increase the temperature of the

water before it reaches the boiler [5]. The heat obtained by the flue gas will be around 150ºC which

will be suitable for the low pressure heater [6]. The flue gas will condense generate acids when it is

condensed it is the drawback [7]. The LP Heater is used to improve the efficiency of the power

plant by increasing the heat of the water before it reaches the boiler [8]. As the heat of the flue gas

also can be used to increase the heat of the water for the economic purpose [9].The flue gas

temperature is the main cause of the global warming so by using the flue gas for the heating

purpose the temperature of the exhaust flue gas will be reduced and the environment can be

protected [10-16].

Fig 2.1 Schematic view of Solar Chimney power plant

The Solar Chimney Power plant (SCPP) which works on the principle of three methodologies

such as greenhouse, chimney and turbine methods. The major problem of facing the SCPP is its

efficiency is very low. The total efficiency of SCPP is the multiplication of three main

methodologies efficiencies.

ŋtotal = ŋchimney * ŋcollector * ŋturbine

Because of the collector and the chimney it gets the lower efficiency. The collector invests 50% of

the investment cost and 50% of overall cost losses and overall system losses. Improving the

performance of collector and chimney will gives very high strength to make the cost of SCPP

through commercial power generation in electrical sector.

The Solar-Flue Gas is the new methods of the Solar Chimney Power plant. It gives waste heat as

source to use heat transfer in the solar radiation.

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2. EXISTING SYSTEM

This is the existing condensate system in thermal power plant. The condensate system is used to

collect the water which was obtained due to the cooling of the steam which leaves the turbine. Then

the water obtained due to the condensation of the steam is taken in to the series of heaters to

improve the efficiency of the power plant. Because when the pre-heated water is send into the boiler

then the lesser heating of the water is required and the time required to heat the water will also be

reduced. So the efficiency of the thermal power plant will be increased.

Fig 2.1 Block diagram of the condensate system

If the pre-heating is not done in the condensation system then the low pressure, low temperature

water will be straightly fed into the boiler which will reduce both the heat of the boiler and the

water which is already present in the boiler. Due to this the boiler efficiency will be reduced and the

life span of the boiler also will be reduced due to the repeated cooling and heating. The time taken

to heat the water will also be increased. This is the reason of the need of the condensate system in

the thermal power plant.


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3. PROPOSED SYSTEM

In this project we have to replace the low pressure electric heater (which is used to heat the

water from the condenser before it enters the boiler) by flue gas low pressure heater. In the existing

condensate system the low pressure electric heater is used. But the exhaust gas which is waste the

obtained due to the combustion of the fossil fuel can be used.

Table.3.1. Temperature of flue gas from different sources

FLUE GASES TEMP(ºC)

Flue gas form household gas water heater 110ºC-160ºC

Flue gas from gas boiler 90ºC-130ºC

Flue gas from Natural gas power plant 90ºC-150 ºC

Flue gas from Thermal power station 90ºC-140ºC

That there are numerous ways to heat the water, the waste exhaust flue gas can be used to heat it

and can be used to improve the overall efficiency of the power plant. The heat of the exhaust flue

gas is already used in the air pre-heater and economizer. During this process the heat of the exhaust

gas is around 300ºF.

This temperature can be used to heat the water in the condensate mechanism. The condensate

system has series of LP heater to improve the temperature. Each heater increases the temperature

for certain degree. Basically the temperatures of the low pressure heater increases gradually for

each of them if the first low pressure heater increase the heat from 45ºC to 75ºC .

Then the next will increase from 75ºC to 105ºC. Mostly the highest heat obtained from the low

pressure heater will be in the range of 140ºC – 160ºC. So the flue gas can be used in this process.

This is to improve the efficiency of the condensate system. Because if only one heater used the

energy and maintenance will be needed. So the suitable heater should be selected for the flue gas

heater according to the temperature.


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Fig 3.1 Block diagram of the proposed system

ADVANTAGES AND DISADVANTAGES

Advantages:

The energy required by the thermal power plant will be reduced.

The reuse of the exhaust flue gas efficiency improves.

The temperature of the exhaust flue gas will be reduced significantly, so the atmosphere will

be protected.

The energy which was used to pre-heat the water will be reduced and can be used for any

other purpose.

The cost which is used for the power of the heater will be reduced.

There will be no cost for the exhaust flue gas as it will be obtained in large quantities in

thermal power plant.

Disadvantages:

New setup should be created to implement the exhaust flue gas heater.

The exhaust flue gas may get deposited in the system or the tube.

Regular maintenance will be required.

Cooling of the exhaust flue gas gives rise to the formation of acids.


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Table 3.1 Generated Output power

SOURCE USED HEAT GENERATED OUTPUT POWER

ELECTRICITY 140º -160º C 210MW

FLUE GAS 120º -160º C 210MW

Fig 3.2 Generated Output power

Fig 3.3 Overall efficiency when flue gas is used

0

50

100

150

200

250

Electricity flue gas

Heat generated(◦C)

30

31

32

33

34

35

36

37

38

39

40

0 5 15 30

Flue gas

Flue gas


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Fig 3.4 Overall efficiency when electricity is used

Fig 3.5 N-Solar Mode Average Temperature Fig 3.6 Solar Irradiance on 3 different days

The temperature analysis of solar mode is the 3 different days with different solar

irradiance as shown in Figure below 3.7 and also indicates the waste gas temperature inlet is

used as a backup. In the normal mode (N- solar mode), after the rain drop on that day the

irradiance are increased after the rainfall time and the solar radiation is very low during rain drop

due to sky cloudy.

30

31

32

33

34

35

36

37

38

39

40

0 5 15 30

Electric heater

electric heater


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Fig 3.7 Temperature Difference (∆T) between the temperature of Ch-B Air and the Amb. Air

4. CONCLUSION

The condensate system is one of the important system in the thermal power plant. That uses the

electricity to pre-heat the water before it reaches the boiler. In this the heat developed by the

exhaust flue gas is used in the condensate system for the purpose of pre-heating. The output

obtained is same as that of the electric low pressure heater. That the heat of the exhaust gas and the

heat of the electric heater is same. So the heat of the flue gas can be used to pre-heat the water

before it enters the boiler. By this the electricity can be saved and the overall efficiency of the

power station will be improved. And due to the use of the exhaust flue gas in the pre-heater

temperature of the exhaust gas which will be emitted to the environment will be reduced. It will

help in the saving of both the electricity and the atmosphere.

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ANALYSIS OF USING EXHAUST FLUE GAS FOR POWER …