The 64th IEA Fluidized Bed Conversion Meeting

3rd, June 2012 Naples, Italy

The influence of the new emission standard on the CFB boiler in China and

the solutions

Hairui Yang, Hai Zhang Lv Junfu Guangxi Yue

Dept. of Thermal EngineeringTshinghua University

P.R. China

Content

Up to date of CFB boilers in China

The new emission standard

The challenges and the solutions

Dust

SO2

NOx

Technical measures

1 Up to date of CFB boilers in China

Key position of CFB combustion in the clean coal technologies

Among CFB, IGCC, PFBC, PC+FGD, CFB and PC+FGD are the most applicable

Over 3000 units of CFB boilers in operation in China; 112 units of 300MWe CFB

30 units of Alstom technology; 42 units of domestic technology; Other 40 units under construction

0

10

20

30

40

50

60

70

80

t ot al oper at i on al st om domest i c

Unit

Num

ber

Dongf angShanghaiHaer bi n

600MWe SCCFB in construction

2 New emission standards (21st, Sept, 2011)

Emission limits of different pollutions （mgm-3）

Pollutions Boiler limits

dust total 30

SO2Newly build 100(200*)

Existing 200(400*)

NOx（base on NO2 ） total 100(200**)

Mercury and other total 0.03

*

Note: ** W flame PC boiler and existing CFB boiler, the units under construction before 1st , Jan. 2012

0

50

100

150

200

250

Chi na USA JPN Eur o

Emis

sion

, mg

/Nm3

dust NOx SO2

3 the gap and the solutions

Dust emission survey of 300MWe CFBs

For coal with high ash content, the separation efficiency is required as high as 99.85%.

Bag house dust collector (BH)

Electric bag dust collector (EB)

0 10 20 30 40 50 600

20

40

60

80

100

dust

dust

em

mis

ion,

mg/

Nm

3

ash content, %

New standard

China Electricity Council, 2011

Comparison of BH and EB for 300MW CFB

BH EH (2E+B)

Gas rate, m3/h 1 074 400 1 074 400

Design efficiency, % 99.92 99.92

Resistance, Pa <1500 <1000

No. of electric fields / 2Area of bag 29470 25613

Service life, year 3 4

Investment cost ,% 100 129

Operation cost, % 100 118

maintain cost ,% 100 60

Performance of emission from CFBs

SO2 emission survey of 300MWe CFBs

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

100

200

300

400

500

SO2

SO

2 em

issi

on, m

g/N

m3

sulfer content, %

New Standard

0

2

4

6

8

10

Ca/S

Ca/

S

China Electricity Council, 2011

SOx

排放

/mg

Nm

3 (6%

O2)

Low quality coal with high S content?

Solutions for desufurizaiton

Coal with low S content <1.5%

Furnace limestone injection

Optimization, >90%

Limestone size

Injection points optimization

More and quick contact with oxygen

Temperature

Ruzhou 150MW CFB, S= 1.0%, limestone consumption 40 tone/day

Solutions for desufurizaiton

Coal with high S content:

FGD------disadvantage

High efficiency, low limestone cost , high investment cost, high desufurization cost

Seriously decreasing the competition of CFB boiler

or Flash dyer absorber (FDA)

Alstom flash dyer absorber

Counteraction between DeSOx and DeNOx

FDA Decreasing the limestone comsuption

increase in boiler efficiency

decrease in CO2 emission

decrease in ash flow

A few percent decrease in ammonia consumption

SO2

NOx

Ruzhou 150MW CFB

Effect of CaO on NO

CaO （CaCO3 ,CaSO4) catalyze the oxidation and reduction of NH3

Pure furnace limestone Injection is not enough

Low NOx emission feature of CFB boilers

Low combustion temperature

No thermal NOX

Mainly fuel NOx

High carbon content

Reducing atmosphere : air staging

N2 O should be considered in the future

Volatile influence

For low volatile coals, anthracite, lean coal, coke, can meet the new emission standard with furnace temperature <900oC

0

200

400

600

800

1000

0 10 20 30 40 50

Volatile Dry ash free basis, Vdaf /%

NO

x/m

g.N

m3

CFB boilerPC boilerNew standard 200mg/Nm3

0 10 20 30 40 50 600

50

100

150

200

250

300 NOx

NO

x em

issi

on, m

g/N

m3

Volatile content, Vdaf, %

0

2

4

6

8

10

12

carbon content

Car

bon

cont

ent i

n fly

ash

, %

NOx emission survey of 300MWe CFBs

For high volatile coals, DeNOx is needed

SCR: is too expensive and decreasing the advantage of CFB comparing with PC boiler

SNCR is more feasible and more economic

Lower investment

Simple and compact

Suitable for the relative low emission of NOx from CFB

Benefit for the desufurizaiton efficiency

M.C.Stewart, Fuel 2012

Key factors for SNCR with ammonia or urea

Temperature:800- 900oC

Good mixing

temperature

mixing

800~900℃, optimum temperature for  SNCR

Longer residence time（1.5~2.5s

Turbulence 

3 2 2 2

3 2 2 2 2

2 2 2 2 2 2

4NH + 4NO+O = 4N +6H O

4NH +2NO +O = 3N +6H O

2CO(NH ) + 4NO+O = 4N +2CO + 4H O

Optimization of the injection points

DG480/13.7-Ⅱ2 CFB

Technical measures to meet new standard

coals Low volatile <12% High volatile

Low S content<1.5%

Furnace limestone injection

Furnace limestone injection + SNCR

High S content

Furnace limestone injection + FDA

Furnace limestone injection + SNCR+ FDAor never used in CFB

More challenges and more opportunities