AS RUN BOILER PERFORMANCE AS RUN BOILER PERFORMANCE ASSESSMENT FOR ENERGY ASSESSMENT FOR ENERGY

EFFICIENCYEFFICIENCY

D PAWAN KUMARD PAWAN KUMAR

  Useful reference standardsUseful reference standards

British standard, BS845: 1987 This describes the methods and conditions under which a boiler should be tested. Boiler should be operated under steady load conditions (generally full load) for a period of one hour before taking reading

ASME Standard: PTC-4-1 _Power Test Code for Steam Generating Units        Part One: Direct method (also called as Input -output method)       Part Two: Indirect method (also called as Heat loss method)

 IS 8753: Indian Standard for Boiler Efficiency Testing

 All standards do not include blow down as a loss in the efficiency determination process.

Direct Method of as run Trials:Direct Method of as run Trials:

100 valuecalorific Gross x rate firing Fuel

enthalpy) water feed enthalpy (steam x rate flow SteamxEfficiencyBoiler

Indirect Method of as run Trials:Indirect Method of as run Trials:

Boiler Flue gas sample

Steam Output

Efficiency = 100 – (1+2+3+4+5+6+7+8) (by Indirect Method)

Air

Fuel Input, 100%

1. Dry Flue gas loss2. H2 loss3. Moisture in fuel4. Moisture in air5. CO loss

7. Fly ash loss

6. Surface loss

8. Bottom ash loss

Wat

er

Blow down

INSTRUMENTS REQUIRED:INSTRUMENTS REQUIRED:

Flue gas analysersFlue gas analysersPortable temperature indicatorPortable temperature indicator

On-line instruments of boiler control room.On-line instruments of boiler control room.Facilities of the chemistry lab or outside lab for Facilities of the chemistry lab or outside lab for

coal / ash / water analysis. (coal proximate or coal / ash / water analysis. (coal proximate or ultimate analysis, un-burnt in bottom and fly ultimate analysis, un-burnt in bottom and fly

ash, TDS, pH of feed water / blow-down / ash, TDS, pH of feed water / blow-down / condensate.condensate.

Power analyser for power measurement of ID fan, Power analyser for power measurement of ID fan, FD fan, ESP, crushers, BFP (boiler feed water FD fan, ESP, crushers, BFP (boiler feed water

pump) cool handling plant/ash handling plant, pump) cool handling plant/ash handling plant, etc.etc.

Fuel firing rate = 5599.17 kg/hr

Steam generation rate = 21937.5 kg/hr

Steam pressure = 43 kg/cm2(g)

Steam temperature = 377 oC

Feed water temperature = 96 oC

%CO2 in Flue gas = 14

%CO in flue gas = 0.55

Average flue gas temperature = 190 oC

Ambient temperature = 31 oC

Humidity in ambient air = 0.0204 kg / kg dry air

Surface temperature of boiler = 70 oC

Wind velocity around the boiler = 3.5 m/s

Total surface area of boiler = 90 m2

GCV of Bottom ash = 800 kCal/kg

GCV of fly ash = 452.5 kCal/kg

Ratio of bottom ash to fly ash = 90:10

Fuel Analysis (in %)

Ash content in fuel = 8.63

Moisture in coal = 31.6

Carbon content = 41.65

Hydrogen content = 2.0413

Nitrogen content = 1.6

Oxygen content = 14.48

GCV of Coal = 3501 kCal/kg

The illustrative data collected is for a boiler using coal as fuel.

Assessing the as run boiler

efficiency by indirect method.

S te p – 2 F in d th e o r e tic a l C O 2 % % C O 2 a t th e o re tic a l c o n d it io n ( C O 2 ) t

=

CofMolesNofMoles

CofMoles

2

W h e re , M o le s o f N 2

=

2

2

2

2

.. NofWtMol

fuelinNofWt

NofwtMol

airltheoriticainNofWt

M o le s o f N 2

=

1356.028

016.0

28

100/7791.4

x

W h e re m o le s o f C = 0 .4 1 6 5 /1 2 = 0 .0 3 4 7

( C O 2 ) t = 0347.01332.0

0347.0

( C O 2 ) t

=

2 0 .3 7 %

S t e p – 5 T o f i n d a c t u a l m a s s o f d r y f l u e g a s M a s s o f d r y f l u e g a s = M a s s o f C O 2 + M a s s o f N 2 c o n t e n t i n t h e f u e l + M a s s o f N 2 i n t h e

c o m b u s t i o n a i r s u p p l i e d + M a s s o f o x y g e n i n f l u e g a s M a s s o f d r y f l u e g a s

= 100

23)91.413.7(

100

7713.7016.0

12

444165.0 xxx

=

7 . 5 4 k g / k g o f c o a l

5 . % H e a t l o s s d u e t o p a r t i a l c o n v e r s i o n o f C t o C O ( L 5 )

= 100

5744

%%

%

2

xfuelofGCV

xCOCO

CxCO

=

1003501

5744

1455.0

4165.055.0xx

x

L 5

= 2 . 5 8 %

6 . H e a t l o s s d u e t o r a d i a t i o n a n d c o n v e c t i o n ( L 6 )

= 0 . 5 4 8 x [ ( 3 4 3 / 5 5 . 5 5 ) 4 – ( 3 0 4 / 5 5 . 5 5 ) 4 ] + 1 . 9 5 7 x

( 3 4 3 - 3 0 4 ) 1 . 2 5 x s q . r t o f [ ( 1 9 6 . 8 5 x 3 . 5 + 6 8 . 9 ) /

6 8 . 9 ]

= 6 3 3 . 3 w / m 2 = 6 3 3 . 3 x 0 . 8 6 = 5 4 4 . 6 4 k C a l / m 2 T o t a l r a d i a t i o n a n d c o n v e c t i o n l o s s p e r h o u r

= 5 4 4 . 6 4 x 9 0

= 4 9 0 1 7 . 6 k C a l % r a d i a t i o n a n d c o n v e c t i o n l o s s = 4 9 0 1 7 . 6 x 1 0 0

3 5 0 1 x 5 5 9 9 . 1 7

L 6 = 0 . 2 5 %

Summary of As run heat balance for Coal Fired Boiler

Good Practices in Boiler selection and O&M for Good Practices in Boiler selection and O&M for energy efficiency:energy efficiency:•Fuel shift Fuel shift

Drivers – cost, availability & CDMDrivers – cost, availability & CDM

•Technology shift to Fluidized bed combustion boilersTechnology shift to Fluidized bed combustion boilers

Drivers – compatibility with low grade and agro fuels, and cost economy and CDMDrivers – compatibility with low grade and agro fuels, and cost economy and CDM

•Adopting Burners with oxygen trim systems for excess air controlAdopting Burners with oxygen trim systems for excess air control

•Surface blow down control with blow down heat recovery systemsSurface blow down control with blow down heat recovery systems

•Adopting boiler house automation for draft & level control, for efficient operationAdopting boiler house automation for draft & level control, for efficient operation

•Optimizing Waste heat recovery (economizers and air pre-heaters)Optimizing Waste heat recovery (economizers and air pre-heaters)

•Adopting Saturated steam turbinesAdopting Saturated steam turbines

•Variable speed drives adoption for Boiler feed water pumps, FD/ID fans for capacity Variable speed drives adoption for Boiler feed water pumps, FD/ID fans for capacity controlcontrol

•Adopting Steam accumulators where feasibleAdopting Steam accumulators where feasible

•Good use of Energy Audit instrumentsGood use of Energy Audit instruments

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