nox emission study - presentation 2011-12-19

8/13/2019 Nox Emission Study - Presentation 2011-12-19

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© Metso

Method of analysis

• Data analysis in this report is based on the process data collected

from the boiler plants listed in the section 3.3. The process data has

been collected as validated hourly averages.

• For improving confidence of the data analysis, all data from each

boiler has been screened to exclude time periods when

- Boiler output steam flow is zero (boiler is off)- Boiler output steam flow measurements are outside 99 % confidence range

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© Metso

Studied boiler plants

• None of the six studied boiler plants are base-load plants but all of

them supply heat to industrial processes and to district heat network.

• Plants are located in different parts of Finland.

Plant [MWfuel] Boiler

type

Main fuels SNCR Year of

start-up

Kaukaan Voima 410 CFB CHP Biomass and peat Yes 2009

Kymin Voima 294 BFB CHP Biomass, peat and sludge No 2002

Porin

Prosessivoima

206 CFB CHP Biomass, peat and REF Yes 2009

Rauman Voima 120 BFB CHP Biomass, peat, REF and

sludge

Yes 2006

Stora EnsoVeitsiluoto

280 BFB CHP Biomass, peat and sludge No 1996

Tornion Voima 143 CFB CHP Peat, biomass and CO gas Yes 2007

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Fuel mixtures

• The average fuel N-content calculated on a monthly basis

• N-content reflects the fuel mix changes which are due to the season,fuel availability and boiler operational reasons

• Nitrogen content is expressed by weight percent in dry matter

4

1 2 3 4 5 60

0.5

1

1.5

2

2.5

3

Nitrogen content of fuel mix

N i t r o g e n - %

Month

BFB boiler 1

BFB boiler 2

BFB boiler 3

1 2 3 4 5 60

0.5

1

1.5

2

2.5

3

Nitrogen content of fuel mix

N i t r o g e n - %

Month

CFB boiler 1

CFB boiler 2

CFB boiler 3



© Metso

Effect of peat on the fuel mix nitrogen content

• Nitrogen content of

peat itself depends

on the geographical

location of the peat

field

5

0 50 1000

1

2

3

Nitrogen share in fuel mix vs. Peat share

N i t r o g e n %

Peat %

BFB boiler 1

0 50 1000

1

2

3

N i t r o g e n %

Peat %

BFB boiler 2

0 50 1000

1

2

3

N i

t r o g e n %

Peat %

BFB boiler 3

0 50 1000

1

2

3

Nitrogen share in fuel mix vs. Peat share

N i t r o g e n %

Peat %

CFB boiler 1

0 50 1000

1

2

3

N i t r o g e n %

Peat %

CFB boiler 2

0 50 1000

1

2

3

N i

t r o g e n %

Peat %

CFB boiler 3



© Metso

Effect of fuel N on NOx in BFB:s 1 and 3

• Illustration of correlation between SO2 and NOx emissions. It is liableto assume that higher SO2 emission reflect higher fuel’s nitrogen

content at that particular time.

6

0 100 200 300 400 5000

200

400

N O x - m g / N m 3

NOx - SO2 fit

BFB boiler 1

0 50 100 150 2000

200

400

N O x - m g / N m 3

SO2 - mg/Nm3

BFB boiler 3

Typical N

% (dry

matter)

TypicalS

% (dry

matter)

Biomass

from wood

0,1 – 0,5 0,05

Peat 1,3 – 3,0 0,2 – 0,4

Emission expressed in mg/Nm3 6 % O2 in

dry gas



© Metso

Annual boiler load variations

Measure BFB 1 BFB 2 BFB 3 Average of

BFB 1-3

%

Max 106 112 99 106

High 99% limit 100 105 91 99

Mean 69 56 50 58

Low 99% limit 47 37 26 37

Min 24 27 26 26

7

Measure CFB 1 CFB 2 CFB 3 Average of

CFB 1-3

%

Max 100 109 106 105

High 99% limit 96 108 101 102

Mean 68 79 82 76

Low 99% limit 38 35 48 40

Min 11 17 38 22

0 50 1000

5

Breakdown of boiler load

%

BFB boiler 1

0 50 1000

5

%

BFB boiler 2

0 50 1000

5 %

Boiler load (%)

BFB boiler 3

0 50 1000

5

Breakdown of boiler load

%

CFB boiler 1

0 50 1000

5

%

CFB boiler 2

0 50 1000

5 %

Boiler load (%)

CFB boiler 3



© Metso

NOx emissions

8

0 1 2 3 4 50

200

400

NOx trend

m g / N m 3

Month

BFB boiler 1

0 1 2 3 4 50

200

400

m g / N m 3

Month

BFB boiler 2

0 1 2 3 4 50

200

400

m g / N m 3

Month

BFB boiler 3

0 1 2 3 4 50

200

400

NOx trend

m g / N m 3

Month

CFB boiler 1

0 1 2 3 4 50

200

400

m g / N m

3

Month

CFB boiler 2

0 1 2 3 4 50

200

400

m g / N m 3

Month

CFB boiler 3

Not calendar monthsEmission expressed in mg/Nm3 6 % O2 in dry gas



© Metso

99 % confidence regions for NOx emissions

9

BFB 1 BFB 2 BFB 3

0

100

200

300

400

500

80

171126

260 258290

401353

438

NOx 99% confidence range

m g / N m 3

CFB 1 CFB 2 CFB 3

0

100

200

300

400

500

1359

86

133 134 144

240 250216

NOx 99% confidence range

m g / N m 3

• High 99 % limit, mean and low

99 % limit values are plotted



© Metso

NOx emission statistics

10

Measure BFB 1 BFB 2 BFB 3

mg/Nm3 % mg/Nm3 % mg/Nm3 %

Max 437 168 478 185 1038 357.5

High 99% limit 401 154 353 137 438 151

Mean 260 100 258 100 290 100

Low 99 % limit 80 31 171 66 126 43

Min 53 20 56 22 65 22

Std 55 21 37 14 48 17

COV 21 % 14 % 17 %

Measure CFB 1 CFB 2 CFB 3

mg/Nm3 % mg/Nm3 % mg/Nm3 %

Max 342 257 286 214 306 212

High 99% limit 240 180 250 187 216 150

Mean 133 100 134 100 144 100

Low 99 % limit 13 95 59 44 86 60

Min 0.003 0.02 34 25 31 21

Std 5 21 37 27 25 17

COV 21 % 27 % 17 %

Emission expressed in mg/Nm3 6 % O2 in dry gas



© Metso

Monthly averages of NOx emission

11

1 2 3 4 50

50

100

150

200

250

300

350

400

NOx averages

m g / N m 3

Month

BFB boiler 1

BFB boiler 2

BFB boiler 3

1 2 3 4 50

50

100

150

200

250

300

350

400

NOx averages

m g / N m 3

Month

CFB boiler 1

CFB boiler 2

CFB boiler 3

Not calendar monthsEmission expressed in mg/Nm3 6 % O2 in dry gas



© Metso

Breakdowns of NOx emission

12

0 50 100 150 200 250 300 350 4000

1

2

3

4

Breakdown of NOx

%

NOx (mg/Nm3)

BFB boiler 1

0 50 100 150 200 250 300 350 4000

1

2

3

4

%

NOx (mg/Nm3)

BFB boiler 2

0 50 100 150 200 250 300 350 4000

1

2

3

4

%

NOx (mg/Nm3)

BFB boiler 3

0 50 100 150 200 250 300 350 4000

5

10

Breakdown of NOx

%

mg/Nm3

CFB boiler 1

0 50 100 150 200 250 300 350 4000

5

10

%

mg/Nm3

CFB boiler 2

0 50 100 150 200 250 300 350 4000

5

10

%

mg/Nm3

CFB boiler 3

Vertical-axis shows % disperse of NOx emissions




© Metso

Combustion circumstances affecting NOxemissions - background

• The degree of explanation between the NOx emission and eachcombustion variable are shown at following tables. The explanation

degree for perfect match is 100 % whereas 0 % explanation degree

indicates that there does not exist explanation between two

variables.

• For estimating impact of fuel nitrogen content to the NOx

emissions,

the fuel nitrogen content is indirectly represented by the SO2

emission which in the case of peat and wood biomass burning

correlates in BFB boilers with fuel N and NOx emissions. Some

factors e.g. SNCR, other sulphur containing fuels and SO2 control

methods can weaken the correlation

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© Metso

NOx emissions and boiler load

15

0 50 1000

200

400

m g / N m 3

NOx - Boiler load fit

BFB boiler 1

0 50 1000

200

400

m g / N m 3

NOx - Boiler load fit

CFB boiler 1

20 40 60 80 1000

200

400

m g / N m

3

BFB boiler 2

20 40 60 80 1000

200

400

m g / N m

3

CFB boiler 2

20 40 60 80 1000

200

400

m g / N m 3

Boiler load (%)

BFB boiler 3

20 40 60 80 1000

200

400

m g / N m 3

Boiler load (%)

CFB boiler 3

• NOx emission of the BFBboilers does not stay constant

at different boiler loads but,

instead, it heavily tends to

increase at low loads below 35

% - 50 % and also at the high

load over 70 % for the BFB

boiler 2

• For CFB boilers, the NOx

emission has a minimum

typically with in load range of

60 - 80 %. The emission

increases at low and high end

boiler loads. Use of SNCRsystem evens out the variation.




© Metso

NOx emissions and boiler load

16

0 20 40 60 80 100 1200

100

200

300

400

500

NOx vs. Boiler load

m g / N m 3

Boiler load (%)

BFB boiler 1

BFB boiler 2

BFB boiler 3

0 20 40 60 80 100 1200

100

200

300

400

500

m g / N m 3

Boiler load (%)

CFB boiler 1

CFB boiler 2

CFB boiler 3




© Metso

NOx emissions and air staging

18

10 20 30 40 50 60 700

100

200

300

400

500

NOx vs. OFA/Total air

m g / N m 3

OFA/Total air ratio (%)

BFB boiler 1

BFB boiler 2

BFB boiler 3

10 20 30 40 50 60 700

100

200

300

400

500

m g / N m 3

OFA/Total air ratio (%)

CFB boiler 1

CFB boiler 2

CFB boiler 3




© Metso

NOx emissions and flue gas oxygen

• The NOx emission of bothBFB and CFB boilers

increases proportional to

flue gas oxygen level

19

0 2 4 6 80

200

400

m g / N m 3

NOx vs. residual oxygen

BFB boiler 1

0 2 4 6 80

200

400

m g / N m 3

NOx - Residual oxygen fit

CFB boiler 1

0 2 4 6 80

200

400

m g / N m

3BFB boiler 2

0 2 4 6 80

200

400

m g / N m

3CFB boiler 2

0 2 4 6 80

200

400

m g / N m 3

Residual oxygen (%)

BFB boiler 3

0 2 4 6 80

200

400

m g / N m 3

Residual oxygen (%)

CFB boiler 3




© Metso

NOx emissions and CO emissions

• The NOx emissionsdecrease when the

CO emissions increase

21

0 100 200 300 400 5000

200

400

m g / N m 3

NOx - CO fit

BFB boiler 1

0 50 1000

200

400

m g / N m 3

NOx - CO fit

CFB boiler 1

0 50 1000

200

400

m g / N m

3

BFB boiler 2

0 50 1000

200

400

m g / N m

3

CFB boiler 2

0 50 1000

200

400

m

g / N m 3

CO (mg/Nm3)

BFB boiler 3

0 50 1000

200

400

m

g / N m 3

CO (mg/Nm3)

CFB boiler 3




© Metso

NOx emissions and CO emissions

22

0 50 100 150 2000

100

200

300

400

500

NOx vs. CO

m g / N m 3

Flue gas CO (mg/Nm3)

BFB boiler 1

BFB boiler 2

BFB boiler 3

0 50 100 150 2000

100

200

300

400

500

m g / N m 3

Flue gas CO (mg/Nm3)

CFB boiler 1

CFB boiler 2

CFB boiler 3




© Metso

Conclusions

• Six fluidized bed boilers located in Finland were analyzed based onprocess data retrieved from the boilers for a 5-6 month operation

period. The data was collected during the normal operation without

any specific tests on the boilers. Based on the data analysis, the

following conclusions can be drawn:

- Boiler load, fuel’s nitrogen content, flue gas oxygen level in furnace and

combustion air staging are the most important variables on NOx emission- Fuel nitrogen content and NOx emission have a strong correlation. As the

nitrogen content of the fuel increases the NOx emission increases especially in

BFB boilers.

- At low boiler loads NOx emissions increase. Depending on the boiler

dimensioning, emissions can also increase at high boiler load.

- Flue gas oxygen level correlates with NOx emission level. The higher the flue gas

oxygen level is the higher the NOx emission.- The effects of different variables on NOx emissions cannot always be generalized

because all boilers are unique (design, fuel etc.)

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© Metso

Conclusions

• Based on different features in combustion technologies of BFB andCFB, the NOx emissions, when using only primary methods are

higher in BFB compared to CFB boilers. Both technologies, BFB and

CFB, have their own benefits and optimum areas concerning fuel

palette used in the boiler, targeted emission limits and economic

aspects. Selection is being done case by case after evaluating these

factors.

• For new boilers the emission requirements can be taken into account

by boiler design and applicable secondary methods. The

performance of an existing boiler depends on the design. The lowest

reachable NOx

level and the cost of the required investment must be

studied case specifically.

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nox emission study - presentation 2011-12-19

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