Recent Progress of CFB in China

Yang Hairui

Dept. of Thermal Engineering, Tsinghua Univ.

Dec. 06-07, 2016, Japan

73rd IEA-FBC ExCo Meeting

1: Update of CFB technology in China and the

challenges

2: the feasible solutions

1. SC/USC CFB boiler

2. Energy-saving CFB technology

3. Low emission technology

3: summary

Features of CFB and its importance

◆Longer Residence time in

Furnace

◆ Even Bed Temperature

（850～900℃）

◆ Fuel flexibility

Features

◆ In-Situ De-SOx and Low

NOx emission

Kind ＲＰＦ* Paper Sludge Waste Tire

Aspect

Feature

(1)Heating value

(LHV=23.3MJ/kg)

(2)Chlorine

（Max. 0.3wt%）

(1)Heating value

(LHV=2.6MJ/kg)

(2)High Moisture

（64wt%）

(1)Heating value

(LHV=32.4MJ/kg)

(2)Steel wire

(approx.10wt%）

*ＲＰＦ : Refuse Paper & Plastic Fuel(Pellet fuel of mixture of waste paper and waste plastics)

２-１ Waste fuels

The progress of CFB in China

2013, total power generation 1247380 MW, while, 1850MW in

1949，more than 674 times increasing

CFB in power generation starts with 100MW in 1996, and SC

CFB in 2013.

Huangzhong, etal， 2015

Large scale CFB distribution map

Over 92 cities

own >100MW CFB

boilers,

total capacity

over 61675MW,

>350 units

In. M., Shanxi, Shandong, Guangdong

Huangzhong eral, 2015

History of CFB in China

35-75t/h,

75-130t/h

100MW-300MWe

SC 600MW

Heat and power Power Generation

New challenges for energy saving and low emission

To improve the competence of CFB boiler in electricity

market ( net coal consumption rate 310g/kWh.)

Higher combustion efficiency

lower auxiliary power consumption

higher availability

Emission control

lower emission : SO2 and NOx < 100mg/m3 (2011)

Ultra-low “50355”: NOx(50mg/m3 ), SO2(35mg/m3 ),

Dust( 5mg/m3 )

2 The possible solutions

1. Higher parameters and larger capacity CFB

Super/ ultra-super critical CFB boiler （660MW）

2. Low/ ultra-low emission technology

Solution 1

Higher parameters and larger

capacity

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

Mid temp. mid

pressure

450℃/3.82MPa

High pressure

540℃/9.8MPa

Super high pressure

reheat

540℃/13.7MPa

Sub-critical reheat

555℃/16.7MPa

SC pressure

540℃/23.7MPa Steam Parameters Increase

Te

mp

er

at

ur

e

Pr

es

su

re

Sub-critical reheat

540℃/17.5MPa

Year

GO LARGE – In steam parameters

2005

USC pressure

605℃/28MPa

SBWL

Remember: SC by IHI in 1970!

Advantages of combining SC/USC and CFB technology

50% lower than that of the PC boiler, the

highest mainly in the taped section

covered with anti erosion layer

The flow rate can be lower as 500－800

kg/m2·s, much lower than that of PC boiler

of >1800 kg/m2·s

Lower flow rate has the feature of nature

circulation for Benson straight tube, i.e.

flow rate increases with higher heat flux

The temperature deviations decreases

Smooth tube can be used rifled tube

smooth tube

The advantage of supercritical parameters with

CFB boiler

CFB combustion and supercritical steam cycle

30

35

40

45

50

5 10 15 20 25 30

Steam pressure MPa

Eff

icie

ncy

%

tem. 500oC

Efficiency VS steam parameters

Tem. 600oC

CFB with

subcritical

This

600MW

• High generation Efficiency

• SCCFB as a technical route 10th five year plan （continue）：

solve the feasibility study

“863”：

solve the Technical scheme and key

parameter-heat flow density

11th five year plan：

key technology and project

2000 2010

10th year plan “11th five year

plan

863

• Develops at the same pace with

FW and independently

The largest 600MW SCFB boiler pass the 168h test

• 8am,2013-4-14,the 600MW SCCFB

boiler developed with TH technology

passed the 168h test

• Shenhua Baima

During 168h test

350MW SCFB boilers

Boiler company Order Operation

Dongfang Boiler 40 8

Shanghai Boiler 18 2

Harbin Boiler 14 0

Summary of the 350MW boiler operation

Boiler operation parameters meet the design value;

metal temperature deviation in water wall and partition wall

< 30 ℃(20℃), and the metal temperature is safety;

Operation bed pressure in the furnace is about 7～8kPa

NOx emission is lower than 300MW subcritical CFB boiler.

The reasons of this phenomenon

Bed temperature is lower;

The level of the secondary air is higher;

Problems in boiler operation

bed temperature deviation along lateral > 60 ℃;

Pressure drop of the air grid is not enough;

Inlet arrangement of primary air.

Tube damage of reheat surface

4 m width ;

Temperature deviation among tubes, >100℃ .

Flow regimes in ultrahigh riser

Key technologies

Key

points

for

SCCFB

boiler

Technical scheme

Basic researches facing application

Maldistributon among multi cyclones

Stability of ultra-large bed

Hydrodynamic of low mass flow

Dynamic model of boiler

SCFB simulator

Key auxiliaries

Basic and applied

basic research

combination of

theory and

Practice

Solution 2

Low emission technology

New emission standards (21st, Sept, 2011)

Emission limits of different pollutions

（mgm-3）

Pollutions Boiler limits

dust total 30

SO2 Newly 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

China USA JPN Euro

Emission, mg/Nm3

dust NOx SO2

Key factors on in-Situ Desulphurization

Furnace temperature

0

20

40

60

80

100

750 800 850 900 950

温度 /oC

脱硫

效率

/%

Key factors on in-Situ Desulphurization

Reactivity and size of limestone

d50 = 120～150μm (after fragment)

reactivity fragment attrition

Key points on in-Situ Desulphurization

Inject points location- avoiding the reducing zone

10 100 1000 10000

10

100

1000

800oC

900oC

CaO

CaS

SO

2 (

pp

mv

)

CO (ppmv)

CaSO4

feeding

return

Reducin

g zone

Optimization of the convey pipelines for limestone

23

Multi-Particle-Size In-Situ Desulphurization

The Advantages of Multi-Particle-Size In-Situ Desulphurization

1 Sufficient residence time

2 Uniform distribution of turbulent desulphurizer

3 Oxidizing atmosphere

1 2 3 4 5 6 7 8

0

5

10

15

20

25

30

石灰石粉 石灰石颗粒 脱硫效率

测试数据编号

石灰石投入量

(t/

h)

60

70

80

90

100

脱硫效率

(%

)

Test Data No.

Desu

lph

uri

za

tio

n E

ffic

ien

cy, %

Lim

esto

ne

Con

su

mp

tio

n, t/

h

Fine limestone powder

Coarse limestone particles

Desulphurization efficiency

1 10 100 10000

2

4

6

体积份额

(%

)

煅烧前 煅烧后

粒度 (m)Particle Size, μm

Volu

me P

erc

enta

ge,

%

Before calcination

After calcination

Low NOx emission feature of CFB boilers

0

200

400

600

800

1000

0 10 20 30 40 50 Volatile Dry ash free basis, Vdaf /%

NO

x

/mg

.Nm

3

CFB boiler

PC boiler

New standard

200mg/Nm3

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

temperature <900oC

Strategies of De-NOx in CFB furnace

Low temperature operation

More heating surfaces in furnace

Higher Gs

Reconstruction of atmosphere

Ratio of P/S air

Location of secondary air points

80

100

120

140

160

180

200

220

240

860 880 900 920 940

NO

x浓度

(mg/

Nm

3 )

床温 (℃)

80 120 160 200 240 2800

2

4

6

8

距布

风板

高度

(m)

NOx (ppm)

二次风份额0.4

二次风份额0.2

Influence of bed inventory on De-NOx and De-SOx

Material size decreasing

Dense bed

combustion in dense bed

becomes more reducing

NOx SO2

In freeboard

more cluster formation, solids in

cluster tends more reducing.

NOx SO2

Utilization of limestone particles

increases due to high cyclone

efficiency SO2

.

Mass transfer

Heat transfer

Bubble phase

Emulsion

phase

Fuel particle(Mainly char)

Fuel particle(Mainly char)

Main stream

Cluster

Mass transfer

Heat transfer

Heatin

g su

rface

Field tests

Load plant Vdaf Tb /oC

Pressure drop of

dilute

/kPa

Nox

/mg∙m-3 Carbon /%

260 t/h Zibo, TG 16 870 1.5 27.2 2.50

560 t/h Liwen, TG 38 850 1.7 18.5 1.82

1000 t/h Guofeng, TG 24 890 1.6 59 2.82

Something new：

1：high efficiency cyclone (inlet, diameter, votex finder)

2：loopseal design

3：higher location of secondary air

4：air distributor and inlet layout

5：heating coefficient adjustment

The preconditions for low emission

1. Normal operation ! ! !

2. Avoiding the over temperature in furnace！

3. Reliable convey system of limestone

4. Optimal locations of limestone injecting points

5. Optimal SNCR system for load changing process

Under normal operation, optimizing the atmosphere and

combustion by adjusting primary/secondary air is

recommend to reduce the SO2 and NOx in furnace.

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+ Semi-dry FGD

or never used in CFB

Summary

1. CFB combustion technology has important role in power generation in China

2. SC/USC is the developing direction

3. Furnace temperature is the precondition for low emission.

4. Feeding coal size, cyclone efficiency and loopseal design are

key points for controlling furnace temperature.

5. The atmosphere adjustment is key to Nox emission.