International Journal of Scientific & Engineering Research, Volume 5, Issue 7, July-2014 1247

ISSN 2229-5518

Chimney Height Optimisation in Thermal Power

Plants

K.K.Pandian , Tamil Nadu , Chennai, India, +919966529456

ABSTRACT: This proposal is based on my Experience on height optimization of chimney in thermal power plants without deviating from the stringent environmental norms laid out. It is the outcome of my exposure to projects, thermal power plants present status & analysis of reports. Outcome of above said confirms that chimney height reductions/ optimization is a viable option and directly proportionate to chimney cost as well.

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1.0.0 INTRODUCTION

This proposal based on our Engineering experience in Thermal power plant. It was realized during 1980’s to 1990’s to meet pollution control norms and Limitations, chimney heights were rapidly increased to
220meters and 275 meters ( 500 MW and
above) with ESP Outlet Dust Burden as
150mg/Nm3. The main purpose being pollution to be discharged at a considerable height such that dispersion take place over a wide area , their concentration on reaching the ground would satisfy the strict stipulations of pollution regulatory standards . Execution of work at considerable heights not only posed techno economic problems to the
contractors but also require modern sophisticated design tools and construction techniques (slipform). The present study is made to reduce chimney height considering all the pollution levels and reduced the construction cost and construction time . With the latest modern technology, pollution control equipment “ Electrostatic Precipitator ( with high Efficiency 99.9% “ has been developed to maintain outlet flue gas dust levels less than 50mg/Nm3 /hr. In most of the countries ESP have been designed and operational to maintain outlet dust burden less than 50 mg/Nm3 apart from this Flue gas de suphurization equipment also be installed to control SOx
levels .

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International Journal of Scientific & Engineering Research, Volume 5, Issue 7, July-2014 1248

ISSN 2229-5518

2.00.00 CHIMNEY HEIGHT CALCULATION

Height of the chimney

Formula for Height of Chimney (A*Q*F*K/CP)^0.5 x (N/VOL /∆ T)^1/6

Parameter

Unit

Value

Remarks

A

Constant

200

Q

mg/sec

29.25

dust leaving chimney ( 500 MW )

585 x 50/1000=29.25

F

Constant

2

if ESP eff > 90 %

K

Constant

0.9

Exit velocity 22-25m/sec

CP

GLC

0.05

Ground level concentration

N

No's

1

no of chimney

Vol

m3/sec

889.286

Volume of Flue Gases ( 500 MW)

@ worst coal firing

Nm3/sec

575.000

Volume of Flue Gases ( 500 MW)

@ worst coal firing

∆ T

92

( gas temp-ambient temp) ( 142-50)

ODB

mg/Nm3

50

Outlet Dust Burden

Calculated Height

mts

69.651

Flue gas Inlet Duct Height

mts

18

Boiler height

mts

80

Total Height of Chimney

mts

207.65

( 69.65+18+80*1.5=207.65)

@ ODB 50mg/Nm3

Total Height of Chimney

mts

259

@ODB 150mg/Nm3

It can be observed from the above calculations that same volume of flue gases and exit velocity with different ODB .The Height of Chimney for ODB =
150mg/Nm3/hr is 259mts with GLC = 0.05 as

guided /per standard practice and there is a considerable reduction in Chimney Height with ODB = 50mg/Nm3 is 207.65mts by maintaining same GLC of .05. The ODB can be achieved with high efficiency Electrostatic Precipitator (99.9%) which are in functional in various power plants and ESP Efficiency :

ESP Efficiency

proven technology to maintain ODB less than
50mg/Nm3/hr. Hence Chimney height can be reduced 275m to 207.65mts by maintaining the ODB and GLC .
Based on the stringent Pollution norms, It will also be remarkable to note that in most of the countries ESP manufacturers have designed ESP with high Efficiency (99.9 %) to maintain ODB less than
50mg/Nm3.

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International Journal of Scientific & Engineering Research, Volume 5, Issue 7, July-2014 1249

ISSN 2229-5518

Volume of Flue gasses in

Nm3/sec IDB in gm/Nm3

ODB in

mg/Nm3 ESP Efficiency

585 70.88 50 99.928

585 70.88 100 99.857

585 70.88 150 99.785

It can be observed from above table ESP Efficiency that for a given volume of flue gases and Ash Content and IDB, by increasing the efficiency of ESP
,ODB can be maintained as per the required

Chimney Draft :

pollution norms. Presently such ESP’s are in operational with high efficiency at various power plants with stated efficiencies.

Height of

Chimney Draft

Net Draft at Chimney

Chimney Draft Losses

Inlet

275 52.5 40.2 12.31

207 37.5 37.2 0.3

Civil Structure, RCC reduction :

The reduction in Civil quantities due to change in CHIMNEY Height is approximately 24.5% which will in turn reduce the Civil Quantities and leads to cascading effect on Construction Cost, time and Generation Cost.

CONCLUSIONS AND RECOMMENDATIONS :

Meeting the stringent Pollution norms of
50mg/Nm3 and GLC ( 0.05). The chimney height can be reduced by 68 from 275mts to 207mts. Thus reduction in Chimney Height is saving in terms of Construction time material and Cost of Thermal
Power Plant.

Reference :

1. Chimney sizing conditions limitation and concept is referred from S.N.Monohar “ Tall chimney construction-Design “

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