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IV th International Conference on Advances in Energy ResearchIndian Institute of Technology Bombay, Mumbai

 D.H. Kokate, D. M. Kale, V. S. Korpale, Y. H. Shinde, S.P. Deshmukh,S.V. Panse, A. B. Pandit*

Institute of Chemical Technology, Mumbai-19E-mail: dr.pandit@gmail.com

Conservation of Energy through Solar Energy Assisted Dryer for Plastic Processing Industry

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Contents

☼ Introduction☼ Construction of ISC based Solar dryer ☼ Development of mathematical model for solar

collector ☼ Drying kinetics of Nylon-6 and modeling of

drying process☼ Economic evaluation of solar dryer☼ Conclusion ☼ References

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India’s Per Capita Consumption Is Just one fifth of the World Average !We need to Enhance our HDI by rapid mfg of Plastic Goods with sustainable Development.

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1.1 Indian Plastic Industry

The Plastic Industry has growing 1.5 times of GDP ( 1995- 2005)  with GDP @ 9% , the expected domestic demand of Polymer to Reach at 9.5 MMT. Increased Demand in Polymer will Increase the Energy Wastages ( If EC measures are not        adopted/ neglected) 

1995-96 2005-06 2011-120123456789

10

Year

Poly

mer

dem

end,

MM

T

9%

13%

5

The boosting Demand will reach to 12.8 MMT. The Growth Drivers are need to be closely monitored and policies need to integrated with EC Act 01 & RE Sources to promote the EC. Managing the Energy Demand to meet the Polymer demand @ 19 % is a challenge . Energy Management of using alternative energy sources will be a IMP tool to meet the above challenge.

1.1 Indian Plastic Industry

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Energy

Distribution Blending

Rejects Process

Granulation Drying

Dispatch

Energy

Energy

Energy

Energy

0%

1%

2%

3%

4%

Use of energy for drying in various processes

1.2 Energy in plastic processing

•Total enthalpy of the drying process:

Where,HGG = Enthalpy of Humid gasHGW = Enthalpy of moistureHGM = Residual enthalpy for mixing        

and other effectsY = Absolute humidity of gas

1.3 Low temp. Application in plastic processing for Solar Chimney / Dryer

 Drying of  hygroscopic Polymers & preheating of Polymeric materials up to 70 °C easily achieved by solar Chimney / Dryer 

Common name Specific gravityMax. operating

temp. (°C) Solar Thermal ProcessAcrylic 1.18 55 Preheating up to 40°C

Acrylo Nitrile Butadiene Styrene (high impact)

1.04 70

LDPE 0.92 80PVC (flexible) 1.3 50PVC (rigid) 1.4 90 Preheating up to 50°C

Polycarbonate 1.15 115

Epoxies 1.2 130 Preheating up to 70°CPolyester 1.8 130PTFE 2.1 180

Silicones 1.4 240Nylon 6 1.14 220 De-humidification & 

Preheating up to 70 °C 

1.4 Scope for Solar Thermal in Plastic Processing

Solar Thermal Implementation measure Energy Reduction (expected)

Preconditioning of Polymeric Material. - Heating & Drying before processing. 7 – 10 %

Heating during Processing ( partially) 8- 12 % Effluent Treatment 5- 10 % Shop floor & Industry Lighting by Solar PV Panel

3- 5 %

Total 23 – 37 %

About 20 % cost reduction, in required energy is possible by using only Solar Thermal application that will reduce the cost of manufacturing / maximize the profit.

2.1 Concept of Solar Dryer

Temperatures of absorber plate

T1 T2

T3 T4

T5

T7

T9

T11

T13

T14

T6

T8

T10

T12

Temp. of drying tray

Temp. of drying MaterialTemperatures of air

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Different design:•Basic ISC design•Absorber lining inside the drying chamber•Some part Top cover was replaced by absorber cover from above

2.2 Solar Dryer Model

Drying material Properties:Good strength, stiffness, chemical and impact resistance, as well good frictional characteristics. Its diffusion characteristics show very different nature compared with other plastic materials.

Aperture factor,

Solar radiant energy falling on absorberConvection heat transfer coefficient between absorber plate and air

Convection heat transfer coefficient between

transparent cover and air Convection heat transfer coefficient of re-radiation from absorber plate to air through transparent cover Top loss coefficient Bottom loss coefficient

Mean temperature of absorber Mean temperature of cover Temperature of Ambient air Mean width of trapezoidal collectorLength of absorber plate

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3.1 Development of mathematical model for solar collector

𝐶𝑐=(1− 𝐴𝑒𝑛𝑐𝑙𝑜𝑠𝑢𝑟𝑒

𝐴𝑝)

Assumptions:

- bulk mean temperature of air rises from Tf to Tf +dTf

flowing through the distance dx

- The air mass flow rate md

- The mean temperature of absorber plate and cover are

Tpm and Tc respectively.

- Bottom and side losses are neglected.

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Energy balance for absorber plate:

Where

Energy balance for Cover:

Energy balance for air stream:

The final mathematical expression is,

0 1 2 3 4 5 6300

310

320

330

340

350

360

370

380Tfo(experimental)

Tfo(model)

Trials

Tfo

(K

)

Acceptable within 5 % variation

4.1 Temperature variation in natural Convection solar Chimney

10:00 11:00 12:00 13:00 14:00 15:00 16:0030

40

50

60

70

80

90

100

0

0.5

1

1.5

2

2.5

3Air temp & air velocity profile over the day

Air at in Air at 1 Air at 2 Air at 3 Air at out

outlet velocity inlet Velocity

Time, hr:min

Tem

p, o

C

Air

elo

city

, m/s

ec

 ∆T, achieved up to 40°C  & air velocity up to 2 m/sec

10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30280

290

300

310

320

330

340

350

360

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Pellet temperature and wind velocity

pellets temperature Wind velocity

Time, Hr:min

Tem

pera

ture

, K

Vel

ocity

, m/s

ec

4.2 Variation of pellet temperature and air velocity over a day

4.3 Thermal performance

Trial Tpm

(K)

md

(kg/s)Qi

(W)Qu

(W)ηth

%

E-11 339.4 0.117 6763 1630 24.1

E-21 340.8 0.132 9101 2215 24.3

E-31 336.3 0.115 5927 2043 35.7

Here is a scope to improve the Efficiency up to 40%

Trial Tpm

(K)

Tfo (exp.)

(K)

Pr Nu hfp

(W/m2 K)

hr

(W/m2 K)

E-11 339.4 331.5 0.72 5.95 1.66 5.67

E-21 340.8 331.8 0.72 5.38 1.47 5.71

E-31 336.3 328.6 0.72 5.30 1.73 5.62

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10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

E21 E31 E11

Time (Hr: min)

Dry

bas

is m

oist

ure

cont

ent (

%)

4.4 Drying Kinetics of Nylon-6 and modeling of Drying Process

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4.4 Drying Kinetics of Nylon-6 and modeling of Drying Process

Effective moisture diffusivity was calculated for all the trials, and found to be in the range of 4 - 6.5 X 10-9

cm2/s. is in good agreement with the value reported in the literature which is 5 X 10-9cm2/s.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.00005

0.0001

0.00015

0.0002

0.00025

0.0003

E21 E31 E11

Dry basis moisture content (%)

Dry

iing

rate

(g/g

. s)

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5.1 Dryer Sizing

Ms

(kg)Mw

(kg)Qe

(W)Qs

(W)Qd

(W)Qu

(W)Ap

(m2)

1 0.0162 10.73 1.99 12.72 33934 4.24

10 0.1628 107.3 19.93 176.75 33936 42.42

50 0.8140 536.6 99.66 176.75 11783 58.91

100 1.6281 298.1 199.33 353.50 23567 117.83

Assuming,1.5% drying efficiencyDry basis moisture content 9%Sample temp. 327KSolar Intensity 800W/m2

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5.2 Cost Analysis of solar dryer

The  simple  cost  analysis  approach  is  depicted  for    this  topic  and  it  shows  the 

total  cost  of  any  system  is  sum  of  cost  of  individual  components.  Solar  dryer 

consisting of collector and drying chamber.  

The roof of the collectors may be withstanding maximum temperatures up to 

80  0C,  thus  material  should  be  quite  stress  resistant  additional  to 

transparency. The collectors may be glass sheet, polycarbonate sheet or thin 

polyster sheet. 

Polyster sheet costs Rs. 72/m2 . Material cost for constructing the dryer is Rs. 

50/m2 of collector area.

Total cost of dryer = collector cost + drying chamber cost + fabrication cost

                                 = 72 + 50 + (72+50)

 = Rs. 244 /m2 of collector area

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6. Conclusion

Drying behavior of Nylon-6 was investigated using natural convection solar drying. 

Air  temperature  inside  the  dryer  is  found  to  be  in  the  range  of 55-70oC, which  is 

dependent  on  factors  such  as  solar  intensity,  outside  wind  velocity,  and  type  of 

absorber etc. 

Drying of Nylon-6 is found to be in the falling rate period. Nylon-6 took nearly 6 hrs 

to reach 0.15 % moisture content value. 

Value  of  effective  diffusivity  is  varied  from  4 - 6.5 X 10-9 cm2/sec.  The  results 

presented in this work suggest that solar dryer can be satisfactorily used for drying 

of Nylon-6. 

Economic analysis show simple payback period for solar dryer capable of drying 100

kg/hr is around 7 months.

 Solar Thermal Energy options can be quickly harnessed in plastic processing,

 e.g. Pre-conditioning , Drying , and Preheating of Polymers.  

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References

1. CRISIL Infrastrure Advisory. Indian Plastic Industry-Vision 2012. Delhi, 2006.2. Indian Plastic Industry. 1999-2013. (accessed 2013).3. Canadian Industry Program for Energy Conservation,Natural Resources Canada. 

Guide to energy efficiency opportunities in the canadian plastics processing industry. Ottawa ON K1A 0E4, 2007.

4. Tangram Technology. Energy efficiency in Plastic processing-Practical Worksheet for Industry. Tangram Technology Ltd.

5. D. M. Kale, R. G. Patil, A.B. Pandit, V. D. Deshpande, J. B. Joshi,  S.V. Panse, “Economic Optimization of Inclined Solar Chimney for Power Generation “ISWESD, Assam,2012

6. A.S.Jadhav, A.S.Gudekar, S.V.Panse, J.B.Joshi. (2011). Inclined solar chimney for power production, Energy Conversion and Management 52, 3096–3102

7. S.P.Sukhatme, J.K.nayak. Solar Energy-Principle of Thermal energy collection and storage. Delhi: Tata McGraw Hill Publishing Company Ltd., 2008.

8. Y.H. Shinde Development of natural convective solar drying. Mumbai: Institute of Chemical Technology, 2009.

9. Nelson W.E. Nylon Plastic Technology. Newnws-Butterworths, London: Butterworth and Co.(Publishers) Ltd., 1976.

10. Psychometric Analysis C.D.-Psychart-1,American Society of Heating, Refrigeration and Air conditioning Engineering Inc.,  Copyright 1992

Thank you

Drying model