Heat recovery from melted blast furnace slag Control of .... Shimizu heat... · – Control of clinker size by particle ... Phase change from liquid to solid by cooling. Accumulation

Heat recovery from melted blast

furnace slag

– Control of clinker size by particle

spraying into falling melted slag –

Kouta Suzuki, Tadaaki Shimizu

Niigata University, Japan

72nd IEA-FBC, Budapest, Hungary, Apr.28-29, 2016

Blast furnace slag production in Japan

Production of blast furnace slag

290 kg-slag/1000 kg iron

Annual production of slag is 24 Mt.

For one large scale blast furnace, production rate of

melted slag (at about 1500℃) is 100 – 150t/hour.

Solidified by natural cooling in atmosphere or rapid

cooling by water. Heat recovery has not yet been

done.

Potential of melted slag as heat source

Melted slag at 1500℃ has sensible and latent heat

of about 400 – 500 cal/g.

If half of the heat of melted slag is to be recovered

in Japan, the total heat recovery will be equivalent

to about 1 million tonnes of coal.

=0.5％ of annual coal import of Japan

=1.1％ of coking coal consumption of Japan

Problems with heat recovery from melted slag

Phase change from liquid to solid by cooling.

Accumulation of solid slag on to heat transfer

surface if solidified.

Insufficient heat recovery if heat removal in from

only liquid phase (sensible heat of liquid) is to

be done.

Heat recovery after solidifying (cooling) reduces

temperature difference

Need to new technology to heat recovery

Fluidized bed heat recovery system • Melted slag is

dropped into the bed

↓

• Solidification in bed

and heat transfer to

immersed boiler

tubes

↓

• Removal of solidified

slag from the bottom

↓

• Crushing a part of the

solidified slag and

use as bed material

Importance of size control of slag droplets

• If the size of slag

droplets is too big,

they sedimentation

velocity will be too

fast.

• Insufficient heat

recovery, too hot

materials in the

bottom, difficulty in

withdrawal.

• Control of size is

necessary.

Control of size (1) Agitation of FB

Screw transporter

Fluidized bed

Motor

Fluidizing air

Fluidizing

air

Agitator

M

M

Agitation of bed

•Mechanical force to

shear droplets during

solidification

•Control is easy (by

rotation rate).

•Heat-resistant metal is

necessary.

•Erosion problem.

Control of size (2) Solid injection

Injection of solid-gas

flow to melted wax

• Rapid cooling and

covering slag by

particles (“dry”

surface)

• Application of CFB

technology.

• High rate of solid

transportation is

necessary.

WAX

AIR

Fluidized

Bed

Down-

comer Riser

B

A

AIR

AIR AIR

Melted slag

This work

Objective of this work

Injection of solid-gas two-phase flow using cold model.

●Measurement of solid transportation rate to

find out suitable design of transportation

system

●Control of solid size using simulated melted

slag (wax)

Experimental

Cold model

FB main body

Bed material

Silica balloon

Dp.: 0.37 mm

Dens.：870kg/m3

Slag (wax)

1-Hexadecanol

M.P. 49 ℃

Dens.： 800 kg/m3

Wax

Down-

comer

Air

Riser 0.51g/s

80℃

Height ：60 cm

Cross sec.：16 cm sq

Gas vel: 0.076m/s

Air

247mm

447mm

Small FB

Different

height of

downcomer

Cold model (transportation system)

Small-FB

Height：70mm

Length：90mm

Width：A:20mm, B:30mm,

C:40mm, D:60mm,

E:90mm

Downcomer

ID：20mm

height：247mm,447mm

Riser

ID ：9mm

Length：600mm,800mm

Air

Down-

comer

Riser

Small Fluidized Bed

FB

Measurement of transportation rate

Down-

comer

Air

Air

Riser

●Solid sampling at

the exit of riser

●Effect of design

parameters and gas

feed rate on solid

transportation rate Air

Injection of solid-gas to falling wax

Down-

comer

Air

Air

Riser

Wax 0.51g/s, 80℃ ●Melted wax (simulated

slag) was continuously

fed to fluidized bed

●Solid-gas flow was

injected to wax above

the bed

●Clinkers were sampled

after the experiment.

Size distribution was

measured by sieving.

Solid transportation rate

Width of Small-FB = 20 mm

There existed optimal gas feed rate condition to

maximize solid transportation rate.

70mm

20mm

90mm

20mm

FB

Riser

Downcommer

>Ut

Max flow >Umf

2Ut


70mm

40mm

90mm

40mm

FB

Riser

Downcommer

Optimal gas feed: Riser gas vel. = 2Ut;

Fluidizing velocity =1.5 Umf

1.5Umf


2Ut

Max flow


70mm

90mm

90mm

90mm

FB

Riser

Downcommer

When the bottom fluidized bed was too big, solid

transportation did not occur even when gas velocity

in riser was higher than Ut.

(E)


Max flow

2Umf

Effect of design on transportation rate

There was an

optimal width of

bottom small-FB

to maximize solid

transportation.

Width： A:20mm

B:30mm

C:40mm

D:60mm

E:90mm

Resistance of solid horizontal flow

12 L/min

For designs A-C (narrower fluidized beds at the bottom),

solid flow rate differed among designs. Pressure drop in

the horizontal direction was measured.

Solid flow

Downcomer Riser

⊿P

Horizontal pressure drop in small FB

Reverse

direction

For narrow small FB in the bottom, pressure gradient

in reverse direction was observed. Resistance

Pressure difference at

a gas flow of 12 L/min

12 L/min

装置幅20mm

装置幅30mm

装置幅40mm

Effect of gas feed rate on horizontal

pressure difference

Narrow bedWide bed

Design of solid transportation

Higher downcomer is favorable to provide

head for solid transportation.

Riser gas velocity : about 2Ut

Fluidization in bottom small FB at about 1.5Umf

Appropriate width of bottom small-FB

Solid injection into falling melted wax

Reduction of coarse clinkers Size control possible.

Type C system, gas feed rate =12 L/min (Optimum

condition to maximize solid transportation rate

Conclusion

As a measure to control solidified clinker size for

a fluidized bed heat recovery system, injection of

solid-gas two-phase flow was proposed

There was an oprimum design and operation

condition to maximize solid transportation for

solid-gas injection.

Size of clinkers can be controlled by injecting

solid-gas two phase flow to falling melted wax in

the freeboard.

吹き付け量測定

Fig.5 Concept of the present process

ある点を過ぎると吹き付け量が低下する。

→下降管に空気の逆流が発生。

層内への空気流量の増加により、上昇管内の圧力損失が大きくなったからだと考えられる。

吹き付け量測定

• 下降管が長い方が吹き付け量が多くなった。

下降管の延長により、下降管と上昇管との圧力差が大きくなったため。

流動化速度に対する吹き付け量

装置幅20mm

装置幅30mm

装置幅40mm

装置幅60mm

装置幅90mm

最小流動化速度

流動化速度に対する圧損

装置幅20mm

装置幅30mm

装置幅40mm

上昇管圧力(装置C)

上昇管と下降管の圧力差(装置C)

結果と考察

0

2

4

6

8

10

12

0.00 0.02 0.04 0.06 0.08

流動化ガス速度 [m/s]

粒子

質量

速度

[g/

s]

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

上昇

管ガ

ス速

度 [

m/s

]

粒子質量速度(下降管247mm)粒子質量流速（下降管447mm)最小流動化速度終端速度上昇管ガス速度

気固２相流質量流量

最大流量

最小流動化速度以上で、上昇管ガス速度が終端速度を超えるように設計できた。

0

2

4

6

8

10

12

0.00 0.02 0.04 0.06 0.08


粒子

質量

速度

[g/

s]

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

上昇

管ガ

ス速

度 [

m/s

]



流動化ガス速度、上昇管ガス速度の関係を変えて検討。

粒子がうまく上昇しなかった

0

2

4

6

8

10

12

0.00 0.02 0.04 0.06 0.08


粒子

質量

速度

[g/

s]

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

上昇

管ガ

ス速

度 [

m/s

]



下降管が長いほうが吹きつけ量が多くなった。吹きつけ駆動力となる粒子ヘッドが増加したため。

下降管447mm

下降管247mm

0

2

4

6

8

10

12

0.00 0.02 0.04 0.06 0.08


粒子

質量

速度

[g/

s]

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

上昇

管ガ

ス速

度 [

m/s

]



流動化ガス速度の増加に伴い吹きつけ量が減少。流量の増加に伴い、圧損が大きくなるため。

吹きつけによるせん断効果

0

10

20

30

40

50

60

70

80

90

100

＜3.36mm 3.36～6mm 6mm～10mm 10mm＜Clinker size

Mas

s fr

action

[%]

吹きつけなし吹きつけあり(下降管247mm)吹きつけあり(下降管447mm)

吹きつけにより粗大クリンカーの発生を抑制

結言

●流動媒体の吹きつけ量を測定し、吹きつけ量と流動化速度、上昇管速度との関係を示した。

●連続的に滴下される溶融ワックスに気固２相流を吹きつけることによりワックスを細かくせん断することができた。

●吹きつけに必要な空気量は総空気量の約10%

でプロセス運転にかかるコストとして問題ないと思われる。

Heat recovery from melted blast furnace slag Control of .... Shimizu heat... · – Control of clinker size by particle ... Phase change from liquid to solid by cooling. Accumulation

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