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Research & Development and Its Application of Circulating Fluidized Bed Boiler Technology in China
Junfu LYU, Hairui YANG, Guangxi YUETsinghua University, Beijing, PRC
20171023
Content
1. General introduction on CFB technology and its application in China
2. Supercritical CFB boiler design and operation in China
2.1 Gas-solid two-phase flow of large riser
2.2 Heat flux in a CFB boiler
2.3 Heat transfer of the supercritical water
2.4 Practices of supercritical CFB boiler
3. Ultra-low emission CFB boiler research and application
3.1 SO2 controlled by limestone injection
3.2 NOx controlled by low NOx combustion
4. Conclusion
1. Circulating fluidized bed (CFB) for electric power generation in China
Coal is the dominate fuel in China
Coal is dirty, its utility produces pollution emission
Washing coal is an effective way to control the coal pollution
Coal washing by-products a large number of low heating value fuel
It should be used cleanly
The unique advantages of CFB is high fuel flexibility and low cost emission control.
CFB boiler is one of the best way to deal with low grade coal.
CFB is very important for the countries in which coal is major energy resource
CFB boiler is playing an important role of electric power generation in China.
Circulating fluidized bed boiler
Washed coal High efficiency PC boiler
Washery rejects, slurry
Washed coal for powerUtility
waste
Raw coal
For coal washing Coal
washing
1. Circulating fluidized bed (CFB) for electric power generation in China
low heating value coal
The scaling of CFB boiler in China
It is in 1960s that China started the R&D on bubbling bed boiler (BFB). By 1980, over3000 BFBs of capacity ranging from 4 to 130t/h were operating in China.
Then Chinese started to investigate CFB to avoid the shortage of BFB.
It costs 10 years to understand CFB combustion process and to improve the CFBboiler design theory and finalized their own understanding on the CFB boiler.
1. Circulating fluidized bed (CFB) for electric power generation in China
1980 1990 2000 20100
200
400
600
800
Uni
t cap
acity
of C
FB b
oile
r Year
2020
The design theory now are widely accepted in China to develop series capacities CFB
boilers from small one of 35t/h to the world biggest one
6-15MW
Medium temperature
Medium pressure
1980-1989Learning
125~200MW
Over high pressure Once reheat
15-25MW
Medium temperature
Medium pressure
25-100MW
High temperatureHigh pressure
SC 600MW
Supercritical
300MW
Subcritical
SC 350MW
Supercritical
1990-1994Understanding
1995-2000Improving
2005-presentDeveloping2000-2005
Scaling-up
including 300MW subcritical CFB boilers, 350MW & 600MW supercritical CFB
boilers which dominates Chinese CFB market. Now, the ultra-super critical CFB
boiler with capacity of 660MW is being developed.
1
10
100
1000
10000
<50 ~50 100~150 ~200 ~300Boiler capacity MW
Boi
lern
umbe
rn
~350 ~600
Commercial operationUnder construction
Availability of CFB power plant in China
1995 2000 2005 201080
85
90
95
100
Avai
labi
lity
inde
x, %
Year2015
Maximum continuous running time
Max
con
tinuo
us ru
nnin
g tim
e, d
ays
1995 2000 2005 2010
150
300
450
600
Year2015
0 0.01
0.1
1
10
100
1990 1995 2000 2005Year
Tota
l cap
acity
of C
FB u
nitG
W
2010 2015
Total capacity of CFB Boiler unit
Number of CFB boiler in China
And CFB boilers are widely used in China. The CFB boiler number increases every year,
by the end of two thousand fifteen, there are about two thousand and eight hundred unit
were in commercial operation, and more than three hundreds were under construction.
In the same time, the availability of CFB power plant increases also.
as well as the maximum continuous running time. The CFB boiler plays a essential role
in Chinese power generation, the total capacity of CFB unit is more than 100 GW.
1. Circulating fluidized bed (CFB) for electric power generation in China
China could supplied varies capacity CFB boiler with varies parameter and varieskinds of fuel: varies kinds of coal, biomass, petroleum coke, and RDF.
There are many boiler workers devotes themselves for CFB, such as:
The CFB boiler performance becomes better and better even better than PC boiler in China. This is due to the technical progress. Here, I would like to take some time to shown two major examples. The first one is:
1. Circulating fluidized bed (CFB) for electric power generation in China
Harbin Boiler Workers co., LTD. Dongfang Boiler Group co., LTD. Shanghai boiler Workers co., LTD. Taiyuan Boiler Group co., LTD. Wuxi Huaguang boiler co., LTD. Jinan boiler group co., LTD.
Content
1. General introduction on CFB technology and its application in China
2. Supercritical CFB boiler design and operation in China
2.1 Gas-solid two-phase flow of large riser
2.2 Heat flux in a CFB boiler
2.3 Heat transfer of the supercritical water
2.4 Practices of supercritical CFB boiler
3. Ultra-low emission CFB boiler research and application
3.1 SO2 controlled by limestone injection
3.2 NOx controlled by low NOx combustion
4. Conclusion
2. Supercritical CFB boiler design and operation in China
CFB performs very well in fuel flexibility but is not very efficient in power generation
Increasing steam parameter to supercritical is the way to improve the power generation efficiency
Milestone of SU CFB in China
2000—technology feasibility study of SC CFB
2003—the classification of key questions of SC CFB
2006—research program on SC CFB
2007—600MW SC CFB demon. approval
2011—approval of invest.
2012 end— erection
2013.4—commissioning and full load test
2014.7: performance test
It was realized the CFB future is supercritical
From then a series of investigation on supercritical CFB were conducted including two phase flow, combustion and heat transfer in a larger furnace that never be
2.1 Gas-solid flow of large riser
The height of a 600MW CFB is 15 m higher than that of a 300MW. The gas- solid two-phase flow was studied
Comparison of solid suspension density distribution between measurement
and model prediction
A 55m height CFB test facility was built to investigate the fluidization in such high riser. Based on the systematic measurements in this rig and many other real CFB boilers, a model predicting solid density is suggested. It seems that the model is reasonable by comparison between model and test.
2. Supercritical CFB boiler design and operation in China
Once through for supercriticalNature circulation
P11
2.2 Heat flux in a CFB boiler
The safety of the water wall in a SC boiler depends on the heat flux
2. Supercritical CFB boiler design and operation in China
Heat flux in a CFB boiler is unknown The flux distribution model is suggested
50 70 90 110 130 15050
70
90
110
130
150
-10%
+10%
-25%
25% error 10% error
Mea
sure
d he
at fl
ux (k
W/m
2 )
Predicted heat flux (kW/m2)
+25%
Heat transfer coefficients vs particle density and temperature Heat flux model accuracy
This model is the combination of the local heat transfer model and solid density distribution model. The heat flux distribution model prediction agrees very well with the measurement.
2.3 Heat transfer of the supercritical water
With the heat flux model
The hydrodynamic of the water wall was calculated
The prediction agrees well with the real boiler operation
Prediction Operation
Tube location(the tube number from the wall corner) n
to+0
to+20
to+15
Stea
m te
mpe
ratu
re a
t th
e ou
tlet o
f No.
n ℃
150
to+20
50 10 0 200 1
to+10
Comparison between model prediction and operation on the water tube outlet temperature
2. Supercritical CFB boiler design and operation in China
2.4 Practices of SC CFB boiler
Based on the clear understanding of supercritical CFB boiler principle A series of patent are invented A new thermal process is created System integration technologies including control are developed The world’s first 600MW SC CFB boiler was built in Baima Power Plant
2. Supercritical CFB boiler design and operation in China
2.4 Practices of SC CFB boiler
Item Unite Value
Mar % 7.58
Aar % 43.82
Vdaf % 14.74
Qnet,ar MJ/kg 15.17
Sar % 3.3
Coal in Baima
The 600MW SC CFB was successfully demonstrated in Baima Power Plant. It was put into commercial operation in April 2014. it runs very well.
2. Supercritical CFB boiler design and operation in China
item unit design test Power load MW 600 601
Living Steam pressure MPa 25.39 24.81 Living Steam temperature 571 569.88Reheat steam pressure MPa 4.149 4.04
Reheat steam temperature 569 566.96Total attemperation flow t/h 142 109.2
Furnace temperature 890 ~890Boiler efficiency % >91.01 91.52SO2 emission mg/m3 <380 192.04
Calcium/Sulfur mol. ratio mol/mol 2.1 2.07De-SO2 efficiency % 96.7 97.12
NOx emission mg/m3 <200 111.94Particulate emission mg/m3 30 9.34
2.4 Practices of SC CFB boiler
The performance test data are well matching with the design
2. Supercritical CFB boiler design and operation in China
Beside Baima project, there are also other three 600MW SC CFB boiler are ordered.
P16350MW SC CFB boilers for oversea
350MW SC CFB boilers in Hequ Power Plant 350MW SC CFB boilers in Guojin Power Plant
350MW SC CFB boilers in Datuhe Power Plant
2.4 Practices of SC CFB boiler
With the research and technologies, 350MW are then developed.
More than 70 are ordered (3 for oversea). 16 boilers are in operation.
2. Supercritical CFB boiler design and operation in China
Content
1. General introduction on CFB technology and its application in China
2. Supercritical CFB boiler design and operation in China
2.1 Gas-solid two-phase flow of large riser
2.2 Heat flux in a CFB boiler
2.3 Heat transfer of the supercritical water
2.4 Practices of supercritical CFB boiler
3. Ultra-low emission CFB boiler research and application
3.1 SO2 controlled by limestone injection
3.2 NOx controlled by low NOx combustion
4. Conclusion
3. Ultra-low emission of CFB boiler research and application
One of the CFB boiler advantage is low cost emission control
CFB matches most regulation by limestone injection and low Nox combustion China Emission Limit for Coal-fired Power Plants is most strict
(GB 13223-2011) : NOx<100 mg/m3; SO2<100 mg/m3
careful design and operation of a CFB boiler is necessary
Upgrade action plan requires(2014):
NOx<50 mg/m3; SO2<35 mg/m3
CFB is facing great challenge in China
0
50
100
150
200
250
China USA JPN Euro
Emission, mg/Nm
3 (@6%) dust NOx SO2
Due to the pressure of fog
and haze Because of the large
number of coal
consumption
3.1 SO2 controlled by limestone
Factors that effect SO2 emission
so
11expr
CEA k
RT C
=
the final SO2 emission concentration C: ks, E: reactivityAr: surface area: residence timeT: temperatureCo: initial SO2 concentration
Cyclone collection efficiency
What we can do is to increase
Particle size
If the cyclone collection efficiency is better, the size of limestone could be finer for the same residence time. If the cyclone collection efficiency is not so good, the limestone has to be coarser.
3. Ultra-low emission of CFB boiler research and application
the effect of temperature
3 2CaCO CaO CO 煅烧
• Calcination reaction:750~900
• Desulphurization reaction:
2 2 41CaO + SO O CaSO2
800~950
4 2CaS 3CaSO 4CaO 4SO • Decomposition of desulfurization products:
>850
4 2 2CaSO CO CaO SO CO >880
The temperature should be balanced because the higher temperature causes higher SO2 capture reaction speed, however, the decomposition speed of desulfurization products is also increases. The temperature is optimized to around 850C.
700 750 800 850 900 950
脱硫
效率
S
/%
80
85
95
90
100
75
床层温度 tb/oC
The effect of temperature on desulphurization efficiency
3. Ultra-low emission of CFB boiler research and application
3.1 SO2 controlled by limestone
The cyclone collection efficiency should be improved:fly ash d<50 m, bottom ash <200 m
A new limestone size distribution:
The original SO2 emission could be less than 35 mg/m3
Recommended particle size distribution of limestone for higher efficiency SO2 capture
dlimestone particle size could be smaller
In the optimized temperature,
3. Ultra-low emission of CFB boiler research and application
3.1 SO2 controlled by limestone
In CFB combustion, most NOx is fuel NOx
挥发分 N
燃料 N
HCN
H NCO N
NH
NH2
NH3
O2, O
NO, NN2
NO
NH3
NO NH
N2
NO
O2,OH,O
NH
2,NH
,N
燃料 N
挥发分 N
OH
,H,O
O
H,H
,O
NH2
So the combustion atmosphere should be controlled carefully to reduce the formation of NOx from fuel Nitrogen.
3. Ultra-low emission of CFB boiler research and application
Coalparticle
NColatile-N
Volatile
Fuel-N
char
Char-N
N
N2
N2
NO
N
3.2 NOx controlled by low NOx combustion
~ 8504~6m/s
Flue gas~850
limestone
Air
Air
Fuel
The fuel particles are in emulsion phase. The gas pass through it at minimum velocity. This velocity depends on particle size.
The mass transfer in the emulsion phase is also depends on the particle size. The trend is same
The finer the particle, the less the gas velocity, the less the Oxygen, the more reduced the atmosphere.
In the dense bed of a CFB
3. Ultra-low emission of CFB boiler research and application
3.2 NOx controlled by low NOx combustion
The effect of particle size on NOx emission in dense bed is confirmed by experimental.
With the bed particle size decreasing, the NOx emission decreases.
3. Ultra-low emission of CFB boiler research and application
3.2 NOx controlled by low NOx combustion
0 1000 2000 3000 40000
5
10
15
20
0.18-0.20 mm0.275-0.30 mm0.40-0.45 mm
NO排放浓度
(ppm
v)时间 (s)Resident time (s)
NO
x em
issi
on (
ppm
v)
150 300 450 600 7500
10
20
30
焦炭
氮向
NO转
化率
(%)
床料粒度 (m)
煤焦A 煤焦B 煤焦C
Bed particle size (m)
Con
vers
ion
rate
Cha
r-N to
NO
x (%
)
Char AChar BChar C
~850
4~6m/s
Flue gas~850
limestone
Air
Air
Fuel
The combustion behavior in free board is similar as that in dense bed. The cluster is enhanced and its density is higher by smaller particle size or higher circulating flow rate. The finer the particle and the bigger the circulating flow rate, the more reduced the atmosphere.
3. Ultra-low emission of CFB boiler research and application
3.2 NOx controlled by low NOx combustion
0.00 0.04 0.16 0.200.00
0.02
0.04
0.06颗粒
团中
的固含
率 s
c
截面平均固含率 sa0.08 0.12
sa=sc
Sectional solid concentration (sa)
Solid
con
cent
ratio
n in
clu
ster
(sc
)
800~900
4~6m/s
Flue gas800~900
limestone
Air
Air
Fuel
The reduction of NOx by CO and Char decreases NOx emission.
0
20
40
60
80
100
0 0.5 1.0 1.5 2.0 2.5
mole ratio of CO to NO
NO
red
uctio
n pe
rcen
tage
%Tb=860oCres=1.68s
CNO=220mg/Nm3
Over ash Over sand
0
20
40
60
80
100
750 800 850 900 950 1000
Temperature oC
NO
red
uctio
n pe
rcen
tage
%
res=2.1s
CNO=220mg/Nm3
Over char Mixed with ash Over char mixed with sand
NO CO
710
ash9.561 104.43 10 expk
RT
2 2 3 2 3ash SiO Al O CaO/MgO Fe O1.18 4.74 110.23X X X X
512 2.92
ashNO char2.063 104.41 10 expk
RT
2 2 3 2 3ash SiO Al O CaO/MgO Fe O1.18 4.74 110.23X X X X
The concentration of carbon monoxide in CFB is pretty high
There is a large number of char in bed material.
The ash from fuel combustion promotes the reduction reaction as a catalyst.
3. Ultra-low emission of CFB boiler research and application
3.2 NOx controlled by low NOx combustion
Technical routing of low NOx combustion
To increase performance of circulating system
To increase circulating flow rate
Reducing NOx emission
To increase bed quality
Reduced atmosphereAir distribution
Reducing gas from the combustion and unburnt carbon Reduction of NOx
Ultra low NOx emission
fly ash d<50 m, bottom ash <200 mdThus the key of Low-nitrogen combustion of CFB boiler is
This requires the better cyclone and loopseal performance. This is confirmed by real boilers. Practices shown that the better bed quality is necessary for low NOx emission .
3. Ultra-low emission of CFB boiler research and application
3.2 NOx controlled by low NOx combustion
Typical practices Lean coal, bituminous Only limestone injection into furnace and low NOx combustion Limestone promotes NOx emission
A 220t/h lean coal fired CFB boiler:The SO2 emission is controlled less than 10 mg/m3 only by limestone injection. NOxemission is less than 50mg/m3.
A bituminous coal fired CFB boiler:The SO2 emission is controlled less than 22 mg/m3 by only limestone injection. In the same time, the NOx is lees than 50mg/m3.
3. Ultra-low emission of CFB boiler research and application
3.2 NOx controlled by low NOx combustion
NOx emission
SO2 emissionconcentration De-SO2 efficiency %
Ca/S molar ratio
National inspection and measurement institute of China
NOx emission
SO2 emissionconcentration De-SO2 efficiency %
Ca/S molar ratio
NOx emission concentration
SO2 emission concentration
De-SO2 efficiency % Ca/S molar ratio
National inspection and measurement institute of China
Content
1. General introduction on CFB technology and its application in China
2. Supercritical CFB boiler design and operation in China
2.1 Gas-solid two-phase flow of large riser
2.2 Heat flux in a CFB boiler
2.3 Heat transfer of the supercritical water
2.4 Practices of supercritical CFB boiler
3. Ultra-low emission CFB boiler research and application
3.1 SO2 controlled by limestone injection
3.2 NOx controlled by low NOx combustion
4. Conclusion
4. Conclusion
• CFB is the best choice for low grade coal utilization for the countries where coal is major energy source.
• Chinese spend several decades to study CFB boiler. Now there are several boiler workers in China could supply CFB boilers.
• By the end of 2015, there are more than 2800 CFB boilers with total capacity of more than 100GW were in commercial operation in
China.
• The achievements of supercritical CFB and ultra-low emission CFB are successful, and this encourages the CFB boiler future in
China.
Thank you for your attention!