Yang Hairui Tsinghua University

66th

IEA-FBC meeting

Optimal Design and Operation of SNCR System for a 150t/h CFB Boiler and

Discussion on the Measurement of Flue Gas Components

18-20, March, 2013 Brno, Czech Republic

Content

1 Background

2 Design and Operation

of the SNCR System

2.1 Introduction of the 150t/h CFB Boiler

2.2 Design of the SNCR system

2.3 Performance of the SNCR system

3 Discussion on the

Measurement of Flue Gas Components

3.1 Problems in the Previous Measuring Methods

3.2 Suggested Measuring Method

4 Summary

The total NOx emission of China in 2010 is 1.8524×107

ton

The NOx emission from coal-fired power plants is about 79.1% in 2010.

For NOx emission, the new National Emission Regulation (NER) of China is 100mg/Nm3

(dry base, 6%O2

), which is more stringent than other countries & regions.

NOx emissions of China in recent years[The Chinese Ministry of Environmental Protection, 2012] NOx emission regulation of several countries & regions 

[Q. Sheng, 2011]

Background

· 1 ·

SCR is not fit for

CFB boilers

Catalyst

Space

Cost

The dust conc. of flue gas is harmful to the catalyst. Especially, the catalyst will be poisoned by the residual CaO from in-situ

desulphurization.

The space under economizer is not enough to place the SCR reactor.

The cost of SCR is about 3~5 times more than SNCR, which will greatly weaken the advantage of CFB boilers.

Considering the CFB’s feature of low initial NOx emission, SNCR is preferable with the advantages of moderate deNOx efficiency, low cost, simplexes of installation and operation etc.

The CFB cyclone is regard as a satisfying region for SNCR reaction due to the proper temperature, strong turbulence and mixing effect.

4NH3

+4NO+O2

=4N2

+6H2

O ( NH3

as reductant )

2CO(NH2

)2＋4NO＋O2

=4N2＋2CO2＋4H2

O (Urea as reductant )

Background

· 2 ·

Basic parameters of 5#

CFB boiler of Shengzhou thermal 

power plant

No. Item Unit Value & Description

1 Manufacturer — Taiyuan Boiler Company, China

2 Location — Shengzhou, Zhejiang Province

3 Time in operation — Feb, 2012

2 BMCR t/h 150

3 Rated steam temperature oC 540

4 Rated steam pressure MPa 13.73

5 Feed water temperature oC 256

6 Exit flue gas temperature oC 145

7 Fuel consumption t/h 16.1

8 Boiler

heat efficiency % 91.2

Design and Operation of the SNCR SystemIntroduction of the 150t/h CFB

Boiler

Introduction of the 150t/h CFB Boiler

Simplified drawing of 5#

CFB boiler of 

Shengzhou thermal power plant

· 3 ·

PSD of the fuel  PSD of the bottom ash  PSD of the fly ash（d50

=22.271μm，d90

=67.823μm）

Proximate and ultimate analysis of the fuel

0 2000 4000 6000 8000 10000 120000.0

0.2

0.4

0.6

0.8

1.0

Cum

ulat

ive

mas

s fra

ctio

n

Particle size (μm)

Fuel of 5# boiler

0 2000 4000 6000 8000 10000 120000.0

0.2

0.4

0.6

0.8

1.0

Cum

ulat

ive

mas

s fra

ctio

n

Particle size (μm)

Slag of 5# boiler

Design and Operation of the SNCR SystemIntroduction of the 150t/h CFB

Boiler

Introduction of the 150t/h CFB Boiler

· 4 ·

100

200

300

400

500

NO

x��

��

(mg/

Nm

3 )

NOx� � � �

� � (h)

6.2

6.4

6.6

6.8

7.0 � � � � -� � � � � � � � � � -� � � �

��

��

(kPa

)

0.1

0.2

0.3

0.4

��

��

(kPa

)

900

930

960

� � � � � � � � � � � � �

��

��

��

(�)

810

840

870

��

��

��

� (�

)

0.0 0.5 1.0 1.5 2.0 2.5 3.080

100

120

140

��

��

(t/h

) � � � �

NOx

Fuel consumption

Time

Fuel

co

nsum

ptio

nT

of fu

rnac

e bo

ttom

Tof

cyc

lone

ou

tlet

Furnace bottomCyclone outlet

Bot

tom

p

drop

Upp

er p

dr

op

BottomUpper

NO

xco

nc.

0.0 0.5 1.0 1.5 2.0 2.5 3.0100

120

140

160

��

(t/h

)

� � (h)

� �

4

6

8

10

� � O2� � � � O2� �

��

O2�

� (%

)

2

4

6

��

O2�

� (%

)

100

200

300

400

500

NO

x��

��

(mg/

Nm

3 )

NOx� � � �

50000

55000

60000

65000 � � � � � � � �

��

��

(Nm

3 /h)

35000

40000

45000

50000

55000

��

��

(Nm

3 /h)

Time

Boiler load

Primary airSecondary air

Sampling point

Furnace

NOx

NO

xco

nc.

Load

O2

conc

. of

sam

plin

g po

int

O2

conc

. of

furn

ace

Flow

of

prim

ary

air

Flow

of

seco

ndar

y ai

r

The NOx emission conc. in this case is greatly influenced by the

O2

conc. of the combustion zone.

It is significant to decrease the initial NOx emission by combustion adjustment to reduce the burden of SNCR system.

The relationship of NOx and several other parameters

Design and Operation of the SNCR SystemIntroduction of the 150t/h CFB

Boiler

Introduction of the 150t/h CFB Boiler

· 5 ·

Risk

DeNOx efficiency Ammonia solution of low conc. Urea solution

Ammonia solution of low conc. Ammonia solution of high conc.

No. Item Unit Value

1 Rated flow of the flue gas Nm3/h 140000

2 NSR — 1.4

3 Initial NOx emission conc. mg/Nm3 300

4 Target NOx emission conc. mg/Nm3 80

5 Mass fraction of ammonia solution — 20%

6 Consumption of ammonia solution  L/h 70

Calculation of ammonia solution consumption

0 8 16 24200

250

300

NO

x em

issi

on c

onc.

(mg/

Nm

3 )Time (h)

24h NOxaverage value

24h monitoring data of initial NOx emission conc. 

Ammonia solution is used as the reductant in the Shengzhou SNCR project.

Considering the general NOx emission conc., the SNCR deNOx efficiency should be at least 70% to meet the regulation.

Design and Operation of the SNCR SystemDesign of the SNCR

System

Design of the SNCR System

Comparison of low conc. ammonia solution and other reductant

· 6 ·

Flow chart of the Shengzhou SNCR system

Design and Operation of the SNCR SystemDesign of the SNCR

System

Design of the SNCR System

The consumption of ammonia solution is controlled by the NOx emission conc. and the consumption of dilution water is adjusted to maintain the optimal atomization effect of nozzles.

· 7 ·

Viewing from the results of CFD simulation, though the reductant

conc. in the upper zone of cyclone is rather high, the mixing effect in the flue benefits for the SNCR reaction.

Ammonia distribution in the cyclone

(2 nozzles)

Nozzles

Design and Operation of the SNCR SystemDesign of the SNCR

System

Design of the SNCR System

Simplified drawing of the spray lance

No. Item Unit Value & Description

1 Nozzle number of each cyclone — 2

2 Nozzle position — Top of the cyclone 

inlet

3 Nozzle type — Air atomizing nozzle

4 Spray speed m/s 45

5 Spray angle ° 40 (=2α)

6 Average atomized size μm 50

Basic parameters of nozzles

Compressed air

Ammonia solution

· 8 ·

Design and Operation of the SNCR SystemDesign of the SNCR

System

Design of the SNCR System

Ammonia solution tank

Dilution water tank

Pumps

Flow distributor

Compressed air tubes

Injection points (Cyclone inlet)

Injection points Nozzles

· 9 ·

0 20 40 60 80 1000

100

200

300

400

Stop

NO

x em

issi

on c

onc.

(mg/

Nm

3 )

Time (h)

Start

0 40 80 1200

20

40

60

80

100

N O x

N H 3

N H 3溶 液 用 量 ( L/h )

NO

x(mg/

m3 )

0

5

10

15

20

NH

3 (ppm)

Ammonia solution consumption (L/h)

The SNCR deNOx efficiency could reach 80% with the NOx emission conc. of less than 80mg/Nm3

and NH3

slip of less than 10ppm.

With the increase of NSR, the maximum SNCR deNOx efficiency could be over 90%, while the NH3

slip increases sharply.

72h continuous running test of the Shengzhou SNCR system

DeNOx effect test of the Shengzhou SNCR system

Design and Operation of the SNCR System

Performance of the SNCR SystemPerformance of the SNCR System

· 10 ·

New SNCR design in 2*300MWe CFB boilers

Midong 300MWe CFB boiler, Xiangjiang ProvenceFlue gas flow rate: 1133792 Nm3/h (O2,6%) Nox initial con. 400mg/Nm3,

Reductant : Ammonia solution, 20%, 2640kg/hdeNox efficiency: >80%Comssioning: Nov. 2013

Discussion on the Measurement of Flue Gas Components

Problems in the Previous Measuring MethodsProblems in the Previous Measuring Methods

Schematic diagram of the previous measuring method

Some water-soluble components, such as NO2

, NH3

and SO2

, may be absorbed during water removal process.

Water

Ash

Some components, such as NO, N2

O, may be catalytically reduced by the ash which blocks the filter, especially in the high-temperature cases (e.g. T>1000K). [I. Aarna, et al., 1997; Z. Zhao

et al., 2002]

2 21NO+CO N +CO2

2 2 2N O+CO N +CO 2 22NO+C N +CO

· 12 ·

Prepositive filter

Stainless steel tube

PumpWater removal equipment

Flue gas analyzer

Discussion on the Measurement of Flue Gas Components

Suggested Measuring Method

Suggested Measuring Method

Schematic diagram of the suggested measuring method

Most of the particles will be entrained into the cyclone so that

much less particles will block the porous ceramics filter and react with the flue gas components.

The high-temperature infrared analyzer( Fӧdisch MCA04-M is employed to eliminate the errors caused by the water removal process.

· 15 ·

Summary

· 16 ·

Ammonia solution is used as the reductant in the Shengzhou SNCR system. The SNCR deNOx efficiency could reach 80% with the NOx emission conc. of less than 80mg/Nm3

and NH3

slip of less than 10ppm.

With the increase of NSR, the maximum SNCR deNOx efficiency could be over 90%, while the NH3

slip increases sharply.

It is recommended to decrease the initial NOx emission conc. by combustion adjustment to reduce the burden of SNCR system.

There is no obvious relationship between deNOx and SO2

emission found during shutting down the SNCR system.

Design and Operation of the SNCR System in 150t/h CFB boiler

Discussion on the Measurement of Flue Gas Components

Considering the influence of water and ash, there exists some problems in the previous measuring methods of flue gas components.

With the high-temperature infrared analyzer and gas-solid separator, a suggested measuring method is proposed, which may solve the problems mentioned above.