Tr 00087

IDL - International Digital Library Of Technology & Research Volume 1, Issue 5, May 2017

Available at: www.dbpublications.org

International e-Journal For Technology And Research-2017

An approach to reduce cooling water consumption in thermal power plant by vapor absorption refrigeration plant using Taguchi L9 orthogonal analysis AsimMahapatra1,Bishal Dey2 1

Asst. Professor, Department of Mechanical Engineering, Jalpaiguri Govt. Engineering College Post Graduate Scholar, Department of Mechanical Engineering, Jalpaiguri Govt. Engineering College Jalpaiguri, India 1 bishaldey92@gmail.com

2

Abstract:

Low water levels in feeder canals of thermal power plants causes shut down of power generations for a few days in the last few years. Apart from that the „Central Electricity Authority‟ produced a report on minimizing the overall water requirement of coal based thermal power stations, and as the report tells that a major proportion of the total water requirement of the power stations is the cooling water used.In this paper we made an attempt to perform a thermodynamic study and analysis of a 250 MW thermal power plant, to reduce the mass flow of cooling water by decreasing its temperature with the help of solar powered refrigeration system. So, here we are going to study an analytical mathematical model of a vapor absorption refrigeration system, and we will try to optimize it‟s control parameters using Taguchi L9 orthogonal array. where the cooling water coming from the cooling tower enters into a solar refrigeration system before entering to the condenser of the power plant. , and we will try to optimize it‟s control parameters using Taguchi L9 orthogonal array.

As the temperature of the cooling water drops down because of the refrigeration system, the overall requirement of cooling water reduces. A mathematical model of amount of cooling water flow per second is made in this paper using Taguchi analysis.

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Keywords: Cooling Water, Thermal Power plant, Solar refrigeration, Vapor absorption refrigeration, power generation, Taguchi L9 analysis.

1. INTRODUCTION A thermal power station is a power plant in which heat energy is converted to electric power. In most of the places in the world, as well as in India the turbine is steam-driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle. Now this is a big deal to condense the steam (working fluid), because this needs a large amount of cooling water to take away that large amount of heat from steam. But the cooling water is recycled through Cooling Tower. Cooling towers are a very important part of many chemical plants. The primary task of a cooling tower is to reject heat into the atmosphere. They represent a relatively inexpensive and dependable means of removing lowgrade heat from cooling water. The make-up water source is used to replenish water lost to evaporation.

Hot water from condenser is sent to the cooling tower.

The water exits the cooling tower and is sent back to the condenser for further cooling. Now, the amount of Copyright@IDL-2017

IDL - International Digital Library Of Technology & Research Volume 1, Issue 5, May 2017

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International e-Journal For Technology And Research-2017 make-up water is also very large, though its 2-5% of the total cooling water, it is not available now-a-days through-out the year. So this is time to think about reducing the consumption of cooling water.

So, in this context we are proposing to set a refrigeration system in order to cool down the cooling water further before entering the condenser. But to avoid environmental hazards and energy crisis we would like to run the refrigeration system with the help of solar energy.

Now as our prime focus is to design and set up a solar powered refrigeration system, which can cool a large amount of water, we have to be specific on large scale solar refrigeration system. Before that we limit our research into the two main kind of refrigeration system (a) Vapour compression refrigeration system and (b) Vapour absorption refrigeration system.

And in this paper we will focus on the second one or the vapour absorption refrigeration system and the effect of some guiding parameters to optimise the system.

internet. Now if we consider that there is no heat loss, then we can assume that the Cooling water temperature at cooling tower inlet is equals to the cooling water temp. at high temperature leaving the condenser. As well as the cooling water temperature at cooling tower outlet is equals to the temperature of low temperature cooling water going to power plant condenser.

So, here we take some of these values, likeMass flow rate of cooling water (m) = 3632 đ?‘š3 /hr. = 1.01Ă— đ?&#x;?đ?&#x;Žđ?&#x;‘ đ?’Œđ?’ˆ/đ?’” Temperature of cooling water going to condenser = 29.4℃ Temperature of cooling water coming out from condenser = 46.1℃ So, heat extracted from the condenser,

2.

OBJECTIVES

In this context we are proposing to set a refrigeration system in order to cool down the cooling water further before entering the condenser. But to avoid environmental hazards and energy crisis we would like to run the refrigeration system with the help of solar energy.

Now as our prime focus is to design and set up a solar powered refrigeration system, which can cool a large amount of water, we have to be specific on large scale solar refrigeration system. Before that we limit our research into the two main kind of refrigeration system (a) Vapour compression refrigeration system and (b) Vapour absorption refrigeration system.

Q = m.cp.dT cooling water

,

where, m = mass flow rate of

Cp = Specific heat of water at constant pressure, for water = 4.184 KJ/Kg-K dT = Temperature difference in Kelvin (K) So, Q = 1.01Ă— 103 Ă— 4.184 Ă— (319.1 − 302.4) KJ/s =70571.528 KJ/s or KW (= 60.3 Million Kcal/hr ) So, we have got the amount of heat the cooling water extracts from the condenser.

Evaporation Loss (m3/hr) = 0.00085 x 1.8 x circulation rate (m3/hr) x (T1-T2)

And in this paper we will focus on the second one or the vapour absorption refrigeration system and the effect of some guiding parameters to optimise the system.

T1-T2 = Temp. difference between inlet and outlet water

3. METHODOLOGY For a general cooling tower of a 250 MW thermal power plant, we have collected some data from the

For circulation rate= 1010 Kg/s and Temperature difference between inlet and outlet temperature = (319.1 − 302.4)K

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IDL - International Digital Library Of Technology & Research Volume 1, Issue 5, May 2017

Available at: www.dbpublications.org

International e-Journal For Technology And Research-2017 Evaporation Loss = 25.82 Kg/s ;which is 2.56% of the circulating water.

Now, as we are going to set up a refrigeration plant which will cool down the cooling water temperature further after coming from cooling tower, so, if the temperature can further decreased by 1K, the cooling water mass flow rate becomes-

Refriger ating Effect or load (RE) in (KW)

3985.

176

7547.

68

10746 .89

13636.

995

1626 0.7

Now, we are going to focus on the refrigeration plant to be used.

m = 952.48 Kg/s So, the mass flow rate decreases by = 57.52 Kg/s or 5.7% (đ?’‚đ?’‘đ?’‘đ?’“đ?’?đ?’™) Now, for reducing the temperature of 952.5Kg/s cooling water by 1K, the Refrigerating Effect or Load is 3985.176KJ/s or KW Like the same way, for decreasing the cooling water temperature further by 2K, 3K, 4K and 5K, where the mass flow rate without refrigeration is 1010 Kg/s, we get – Table: Reduction of mass flow of cooling water with decreasing temperature1K

2K

3K

4K

5K

Mass flow rate(m) in(Kg/s)

952.4 8

901.9 7

856.1 9

814.83

777.2 8

Reductio n of mass flow rate(Kg/s )

57.52

108.0 3

153.8 1

195.17

232.7 2

% reduct ion of mass flow rate

For this operation we have chosen “LiBr-H2O�

VaporAbsorption Refrigeration System where H2O as refrigerant and LiBr as absorbent.

The parameters which are kept constants are, Mass flow rate 1.01Ă—103Kg/s

of cooling water

(Mw)

=

Cp of water= đ?&#x;’. đ?&#x;?đ?&#x;–đ?&#x;’đ?‘˛đ?‘ą/đ?‘˛đ?’ˆđ?‘˛ Condenser Temperature (Tc) = 313K REGRESSION ANALYSIS Regression analysis is a statistical tool toprovides relationship between response and predictor variables.

By regression analysis we can determine how response variable changes with change of the predictor variables. Now, Simple regression equation is Y= a+bX. But we have to consider more than one predictor variables, so we are not going to use simple regression analysis. In this problem we apply polynomial multiple regression analysis to obtain the mathematical model.

Polynomial multiple regression analysis(Second order or more )i.e.-

5.7

10.7

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15.23

19.32

23.1

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Y= đ?›˝0 + đ?›˝1 X1 + đ?›˝2 X2+đ?›˝3 X3 + đ?›˝4X1∗X1+đ?›˝5X2∗X2+đ?›˝6X3∗ X3+đ?›˝7X1∗X2+đ?›˝8X2∗X3+ đ?›˝9(X3∗X1) This equation is second order polynomial equation with three variables i.e. X1, X2, X3; Y is the response variable and β is the coefficients. In our project we Copyright@IDL-2017

IDL - International Digital Library Of Technology & Research Volume 1, Issue 5, May 2017

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International e-Journal For Technology And Research-2017 have used this equation to form the mathematical model. Temperature drop from the inlet to outlet of the refrigerator (dT),Generator temperature (Tg)&Evaporator Temperature (Te) are control factors, final equation looks like – Qg= đ?œˇđ?&#x;Ž + đ?œˇđ?&#x;? dT + đ?œˇđ?&#x;? Tg + đ?œˇđ?&#x;‘ Te + đ?œˇđ?&#x;’ (dT*dT) +đ?œˇđ?&#x;” (Tg*Tg) + đ?œˇđ?&#x;” (Te*Te) + đ?œˇđ?&#x;• (dT*Tg) + đ?œˇđ?&#x;– (Tg*Te) + đ?œˇđ?&#x;— (Te*dT) This equation is solved by following matrix method – [β] = [Y]*INV[X], Where, [β] = Coefficients matrix; [Y] = Response variable matrix; INV[X]= inverse of control variables matrix; In this problem three variables are there with three different range or level, so Taguchi L9DOA matrix table is used to do the theoretical experiment. But L9 Orthogonal table gives us nine equations and number of unknown coefficients are ten (i.e. - [X] = [10*9]).

To solve this we did one extra experiment taken from L18 Orthogonal array. Now number of equations is equal to know of unknown co-efficient (i.e. [X] = [10*10]).

Generator temperature (Tg)

358K

363K

368K

Evaporator Temperature (Te)

278K

279K

280K

In this study, values of control parameters or factors (dT, Tg, Te) were put and correspondingon heat given to the refrigerant in generator(Qg) was calculated from the equation, đ?‘¸đ?’ˆ =

đ?‘ťđ?’† đ?‘ťđ?’ˆâˆ’đ?‘ťđ?’„ [ ] đ?‘ťđ?’„ đ?‘ťđ?’„−đ?‘ťđ?’†

where,đ?‘Şđ?’‘ = Specific heat

at constant pressure of Water= 4.184 KJ/Kg-K. Nine experiment were done according to the L9 Orthogonal array and one according to L18 Orthogonal array.

Then these ten sets of equation are solved in MATLAB by matrix method and got the required values of co-efficient. ∴The proposed mathematical model from theoretical experiment: Qg= −đ?&#x;’. đ?&#x;?đ?&#x;Žđ?&#x;“đ?&#x;” + đ?&#x;Ž. đ?&#x;Žđ?&#x;“đ?&#x;Žđ?&#x;Ž dT −đ?&#x;Ž. đ?&#x;Žđ?&#x;Žđ?&#x;Žđ?&#x;• Tg + đ?&#x;Ž. đ?&#x;Žđ?&#x;‘đ?&#x;Žđ?&#x;‘ Te + đ?&#x;Ž. đ?&#x;Žđ?&#x;Ž (dT*dT) + đ?&#x;Ž. đ?&#x;Žđ?&#x;Ž (Tg*Tg) – 0.0001(Te*Te) –0.0001(dT*Tg) + 0.00(Tg*Te) +0.0001 (Te*dT)

Control Factors & their rangesThree control factors and their range or level are shown in belowCONTROL

LEVEL

FACTORS

LOW(1)

MEDIUM(2)

HIGH(3)

Temperature drop from the inlet to outlet of the refrigerator(dT)

1

2

3

 4.

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đ?‘´đ?’˜âˆ—đ?‘Şđ?’‘∗đ?’…đ?‘ť

OUTCOMES

Above regression equation was simulated in computer to find out the effect of control factors (dT, Tg, Te) on change inHeat given to the refrigerant in generator (Qg) within the considered range or levels. A computer C-Programming gives the responses for each input and this is done by varying one parameter within the considered range while keeping other two parameters constant.

Effect of Control Factors on mass flow rate of cooling water (m):

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IDL - International Digital Library Of Technology & Research Volume 1, Issue 5, May 2017

Available at: www.dbpublications.org

International e-Journal For Technology And Research-2017 1.

Variation of Heat given to the refrigerant in generator (Qg) on temperature drop(dT) while other two parameters, Generator temperature (Tg)&Evaporator temperature (Te) were kept constant at 363K &279K respectively

Qg

Qg Te

dT

2.

Variation of Heat given to the refrigerant in generator (Qg) on Generator temperature (Tg) while other two parameters, temperature drop (dT) & Evaporator temperature (Te) were kept constant at 2& 279K respectively

We, also used Taguchi method to analyze the guiding parameters for “smaller the better� criteria. The S/N ratio forheat given to the refrigerant in generator (Qg) is calculated by using MINITAB 17 software:

Qg

Tg

3.

Variation of Heat given to the refrigerant in generator (Qg) on Evaporator temperature (Te) while other two parameters, temperature drop (dT) &Generator temperature (Tg) were kept constant at 2&363K respectively

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CONCLUSION In this study Taguchi methods of Design of Experiment (DOE) was used to examine how heat given to the refrigerant in generator (Qg) in an steady flow refrigeration process of a VARS vary with Copyright@IDL-2017

IDL - International Digital Library Of Technology & Research Volume 1, Issue 5, May 2017

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International e-Journal For Technology And Research-2017 temperature drop, Generator temperature&Evaporator temperature. Conclusion can be made from the analysis of results obtained from the mathematical model is that we came to know What are the optimum values of the control factors to decrease the heat given to the refrigerant in generator and by lowering this we can make the refrigeration less costly and affordable and that is how we will be able to decrease mass flow rate of cooling water. And this can be a one-time investment process, even the maintenance cost is very low. But the Main thing is that power generation will not get hampered due to scarcity of cooling water, besides when there water much available we can use this system to produce additional electricity.

[8]. Design of Solar Powered Vapour Absorption SystemByV.K.Bajpai

REFERENCES [1].http://www.thehindubusinessline.com/companies/fi veunitsinntpcfarakkaplantshutdownduetolackofwater/a rticle8346477.ece [2].

Bureau of Energy Efficiency (https://www.beeindia.gov.in/sites/default/files/3Ch7.p df) [3]. Saving Water With Cooling Towers, By Frank Morrison, Member ASHRAE [4]. A textbook of Refrigeration and Air Conditioning,

By R. S. Khurmi and J. K. Gupta [5]. A solar refrigeration system to reduce cooling water consumption in a thermal power plant. By AsimMahapatra and BishalDey [6]. Report on Minimization of Water Requirement in Coal Based Thermal Power Stations, From Central Electricity Authority, New Delhi- 110066 [7].Performance of a Single Effect Solar Absorption Cooling System (Libr-H2O) By Omar Ketfia,b*, Mustapha Merzouka, NachidaKasbadjiMerzoukb, Said El Metenanb

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