2020thth INTERNATIONAL CONFERENCE INTERNATIONAL CONFERENCE ON FLUIDIZED BED COMBUSTIONON FLUIDIZED BED COMBUSTION
58th IEA_CFB meeting
Update of CFB research and Update of CFB research and development in Chinadevelopment in China
G. X. Yue
Thermal Engineering Department, Tsinghua University
Marketing of CFB in China
1980 1985 1990 1995 2000 2005 2010 20150
200
400
600
800
CFB
Boi
ler L
oad,
MW
e
Year
capacity developing of Chinese CFB
Total capacity: 63000MWe, occupying over 10% of coal fire power in China.
Total number of operating CFB boilers: around 3000.
During the Eleventh Five Year Plan (2007-2011), 50 units of 300MWe CFB boilers are to be built and more CFB boilers burning coal waste with total capacity of 2000MWe are under approval.
<50 50 100-150 200 3001
10
100
1000
6
13
250
150
Uni
ts
Boiler load, MWe
2581
Unit number of CFB boiler in China
Performance of CFB in China
Operating performance is improving
0
100
200
300
400
2004 2005 2006 2007年份
最长
连续
运行
时间
( 天)
Statistic of continue operating
time for 135MWe CFB boiler
SOx and NOx emission for 135MWe CFB
Statistic of fuel consumption of power generation for 135MWe CFB
Research Activities and Results
Frame of researchGas –solid two phase flow in circulating fluidized bed
Combustion in CFB
Heat transfer in CFB furnace
State Specification Design Theory of CFB boiler
Gas –solid two phase flow in CFB(1) Material balance in CFB loop
Confirm a combined bubble bed with fast bed in CFB furnace. For fast bed, multi status corresponding to one gas velocity.Suggest the concept of multi size particle balance in the open
circulating fluidized system. The balance only be depending on so called overall particle collection efficiency and input fuel ash size formation character that can be measured in lab. Test.
(2) Multi cyclone loop character of large CFB
0
500
1000
1500
2000
2500
3000
-1000 -500 0 500 1000 1500 2000
l oops eal
l e f t mi ddl e r i ght
pr es s ur e , Pa
heig
ht a
bove
dis
trib
utor
,mm
c as e 1-2ex i t o f c y c l one
The results confirmed the polymorphism of flow pattern in multi cyclones.
Experimental investigation was done to simulate the fluid dynamics in the 300MWe and 600MWe CFB boilers with multiple cyclones.
In the furnace the lateral difference of the axial pressure profiles corresponding to the cyclone location is little, indicating that the transverse material concentration distribution in the furnace is unbiased.
However, the solid flow rate and the material distribution in one loop could be remarkable different from the others.
Under present experimental condition, the circulating rate in the middle loop is about 10% larger than that in the side loops.
Experimental facility
Pressure balance in CFB loop
Suggest the concept of one dimension heat release distribution along the height of furnace and develop a test system for measurement. Determine the impact of fuel size and character on the one dimension heat releasing.
Confirm the the combustion in dense bed is an reduced condition but with rich O2 because of the gas diffusion between bubble phase and emulsion phase in dense bed.
Secondary air Secondary air
Lean Oxygen Core
Combustion in CFB furnace
Find the reduce condition at the upper part of CFB furnace. Suggest the momentum of second air injection 。
Investigation on the post combustion in cyclone
Heat transfer in CFB furnace
0.0 0.2 0.4 0.6 0.8 1.00.0
0.3
0.6
0.9
1.2
Dim
ensi
onle
ss h
eat f
lux
Dimensionless distance from the left to the right wall
between side wall and wing wall between wing wall
Following the idea by Prof. Leckner that the main mechanism of heat transfer in CFB furnace is particle convection and radiation . Develop tools to measure heat transfer coefficient in CFB furnace.
Set up model and standard for heat transfer coefficient calculation in furnace.
On site measure of two dimension heat transfer coefficient for thermal –hydro prediction of supercritical CFB design.
0.0 0.1 0.2 0.3 0.4 0.5
0.96
0.98
1.00
1.02
1.04
1.06
1.08
1.10
Norm
aliz
ed H
eat T
rans
fer C
oeffi
cien
t, α
/αce
nter
Dimensionless Distance from Side Wall Center, d/Dbed
Distance from Distributor h=12m Distance from Distributor h=18.5m Distance from Distributor h=23m
`
Front Wall RightSide Wall
Left SideWall
6.6
13.13.3
14
L1
22.2
2638
L2
L3
SecondaryAir
1218
.523
Unit: m
10 20 30 40 50 60 125
175
225
275
325
1-模型(2)计算结果 800℃
2-商业化模型结果 800℃
换热
系数
αW
/ (m
2 K)
物料浓度 ρ kg/m3
1
2
tools on site measure
Heat transfer model
Heat transfer coefficient along horizontal
State Specification Design Theory of CFB boilerThe CFB boiler with fast bed in the upper
furnace can be operated at multiple states and each state is “specified” by Ug and Gs
it is suggested that during the design of a CFB boiler, the state in fast bed regime is pre-selected. When the state is fixed, the heat transfer coefficient profile along the furnace height is also fixed.
The operator should keep the CFB boiler operating around the pre-selected state by controlling the bed inventory. CFB boiler fluidization status map
A CFB boiler status selection map is developed for the design engineer.The map already be used to design CFB for Chinese coal, also used to
relocate the status of some foreign CFB technologies to improve their performance.
Challenges and Near-future Developments
If CFB want to stand up in utility world, it has to be competitive in three aspects:
(1) Power generation efficiency
(2) De-SOx effectiveness,
(3) Availability.
Capacity Scaling up for Efficiency Improvement
The successful of Alstom 300MW subcritical CFB gave Chinese power sector confidence for subcritical CFB(17.5MPa,540/540) which gain 5% generation efficiency improve compare with 200MW reheat CFB(12.7MPa, 535/535) .
China developed his own 300MW subcritical CFB for big market. Besides, a simplify process of 300MW CFB with single furnace and without EHE was practiced , that save more auxiliary power. It was welcomed and got more than 40 contracts.
Supercritical CFB
Research on supercritical CFB was started in 2003. A demonstration of 600MWe supercritical CFB was initiating in 2006 supported by government.
The first demonstration in Baima was approved in 2008, that shall be commissioned in 2011
Steam T: 571℃/569℃Steam P : 25.4MPaSteam Flow: 1900t/h,Boiler efficiency: 92%SO2 : <300mg/Nm3,NOx: <200mg/Nm3,Generation efficiency: 42%
Schematic of boiler
Feature:Benson vertical tube water membrane,
mass flow 800kg/M2 S Twin furnace (with total cross section
15x28m2 and 55 m height) divided by a partition water wall .
Six cyclones with inner diameter 9m. six external heat exchanger (EHE). In furnace superheater panels The LT SH and LT RH in second passThe HT RH , the MT SH located in
EHEs. There are two options for the cyclone
selection – steam cooled and insulated . Water jacketed rotary ash cooler is used
bed ash 2011.
Schematic of boiler
SO2 Removal in CFB Boiler
The new SO2 emission regulation for coal fire power are becoming more stricter ( <400mg/Nm3)
Chinese CFB has never equipped qualify de-SOx system and no more experience on in-furnace de-SOx
Recent efforts got satisfied results. CFB de-SOx cost: ¥0.008/kWh FGD de-Sox cost: ¥0.025/kWh.
The compensation for de-SOx from Power Grid is ¥0.015/KWh.
SO2 emission record for a 135MW CFB boiler in Huasheng Power after retrofitting. The average SOxemission over one month operation was 104mg/Nm3 when Ca/S=2.2, burning a coal with sulfur content of
2.11%.
Energy Saving CFB Process
0
10
20
30
40
0 100 200 300
总 悬 浮 浓 度 , kg/m3
炉膛
高度
,m
=
二 次 风
0 100 200 300
粗 颗 粒 浓 度 , kg/m3
+
0 100 200 300
细 颗 粒 浓 度 , kg/m3
Based on the State Specification Design Theory, Tsinghua University proposed a novel CFB technology by reconstructing the fluidization state in the furnace by adjusting the bed quality so as to decrease the bed inventory.
It is expected to decrease the draft fan power and erosion in furnace.
auxi l i ar y power t ot al 8. 303%
1. 373
1. 529
2. 022
0. 906
0. 867
0. 2170. 0770. 019
1. 293
pumpI D f andr af t f ansecond ai r f ancompr ess ai r ash t r anspot at i on coal cr usherl i mest one cr ushert r ansf or mer
First practice for energy saving CFB processThe first test was done in a 75T/h CFB
burning coal washing waste with heating value 3500Kcal/Kg. cyclone and loop seal were carefully designed for quality of material balance.
Bed inventory was selected from 3.2-7.5KPa for full load operation.
Schematic of tested boiler
0 2000 4000 6000 80000
20
40
60
80
100
75t/h, 3220Pa 75t/h, 3830Pa 75t/h, 5680Pa 75t/h, 7330Pa 50t/h, 3540Pa s i z e of as h
f or mat i on
Accu
mula
tive
mas
s fr
acti
on,
%
Coal s i z e, µm
Overview of the tested boiler
Size distribution of feeding coal
0 20 40 600
4
8
12
16
20
-200 0 200 400 600 800 10000
4
8
12
16
20
75t/h, 3220Pa 75t/h, 3830Pa 75t/h, 5680Pa 75t/h, 7330Pa
Heig
ht a
bove
dis
trib
utor
,m
Sus pens i on dens i t y , kg/m3
0
4
8
12
16
20
870 900 930
75t/h, 3220Pa 75t/h, 3830Pa 75t/h, 5680Pa 75t/h, 7330Pa
Bed Temperature/oC
Dis
tanc
e fro
m D
istri
buto
r/m
ResultsThe boiler could reach full load even bed
inventory was just 3.22KPa.As decreasing bed inventory, the dense bed was
shrinking From bed inventory 7.5KPa to 3.22Pa, furnace
temperature increased 170C. Clearly, the impact of suspension density on heat
transfer is less. ( need 5% heating surface more)One year operation for three units boilers save 5M
KWh electricity, and no obvious erosion in furnace Technology already used for tens of CFB covering
15-50MWe and burning lignite ,bituminous and anthracite. Process patent is approved.
Hope energy saving CFB process can compete with PC + FGD
Biomass coal co-combustion
Demonstration of biomass CFB was initiated 5 years ago.Steam parameter is 400-450CTwo types of superheater EHE or in second pass
Oxygen fuel CFB
Southeast University is leading the research The pilot was built in the laboratory
Chemical Looping
Chemical loop is in the stage of fundamental.Many researchers are getting funding from the State Science Foundation.No pilot or demonstration is built.
Conclusion
CFB boilers already dominate co-generation and entering utility in China.
Chinese researchers and engineers accumulate more and more experience on the design theory, manufacturing and maintenance of CFB boiler.
However, challenges and problems still remain, such as availability, power generation efficiency, and SO2 capture.
Continues efforts are making to improve the CFB technology . Besides the new topics are initiating, such as Oxgen-fuel and biomass .
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