research & development and its application of circulating ... lyu.pdf · supercritical cfb...

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


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.


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.


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:


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










4. Conclusion


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.


Once through for supercriticalNature circulation

P11


The safety of the water wall in a SC boiler depends on the heat flux


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.


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


2.4 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



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.


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


The performance test data are well matching with the design


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


With the research and technologies, 350MW are then developed.

More than 70 are ordered (3 for oversea). 16 boilers are in operation.


Content










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.


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



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,



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.


Coalparticle

NColatile-N

Volatile

Fuel-N

char

Char-N

N

N2

N2

NO

N


~ 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



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.



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.



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.



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 .



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.



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










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!

research & development and its application of circulating ... lyu.pdf · supercritical cfb...

Documents