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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.