Heat recovery from melted blast furnace slag using fluidized bed

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1 1 Heat recovery from melted blast furnace slag using fluidized bed Tadaaki Shimizu, Daisuke Haga, Go Mikami, Takayuki Takahashi, Kenji Horinouchi Niigata University, Japan

2 2 Blast furnace slag production in Japan roduction 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 t/hour. Solidified by natural cooling in atmosphere or rapid cooling by water. Heat recovery has not yet been done.

For one large scale blast furnace, production rate of melted slag (at about 1500 ) is

3 3 otential of melted slag as heat source Melted slag at 1500 has sensible and latent heat of about 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 Mt of coal. =0.5% of annual coal import of Japan =1.1% of coking coal consumption of Japan

If half of the heat of melted slag is to be recovered in Japan, the total heat

4 4 roblem with heat recovery from melted slag hase 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

Insufficient heat recovery if heat removal in from only liquid phase (sensible heat of liquid)

5 Melted slag droplets are fed into fluidized bed consist of crushed solid slag. Heat of phase change is recovered through boiler tubes. roposed concept Crushing No direct contact between liquid slag and boiler tube. FB Slag droplets Boiler tube Removal of solidified slag from the bottom. Use as material Gas Slag (solid) 5

roposed concept Crushing No direct contact between liquid slag and boiler tube.

6 6 rocess conceptual design Feasibility of steam recovery is discussed. Target: Steam of 550, 150atm (for power generation) Temperature-Enthalpy diagram Required heat transfer surface area.

7 7 Feasibility of steam recovery At a bed temperature of 750, steam recovery is possible at 550, 150atm. For a slag feed rate of 100t/h and 52% recovery, heat recovery rate is 27MW(11MWe). T [oc] Heat source Steam H [kcal/s]

For a slag feed rate of 100t/h and 52% recovery, heat recovery rate

8 8 Arrangement of heat transfer surface To provide necessary heat transfer area, a bed of 3 m in bed height and a horizontal cross sectional area of 27 m 2 is required. The volume of bed in which heat transfer tubes are immersed is 50m 3. For slag sedimentation, additional 30m 3 is required. ractical size. Area 27m 2 Top view Height 3m Side view

The volume of bed in which heat transfer tubes are immersed is 50m 3.

9 9 Basic study using FB cold model Experiments to feed simulated melted slag (melted wax) were carried out. Continuous feed of melted was and withdrawal of solidified slag. Detection of solid accumulation in the bottom.

Continuous feed of melted was and withdrawal of

10 10 Apparatus Wax feeder 1-hexadecanol (m.p.49, density Heat transfer media (water) TR Valve open/close control 800kg/m 3 ) Wax reservoir Feed rate: 0.04g/s Diameter of a Heater Valve system droplet was about 5mm. Capillary

11 11 BFB Cold model Cross sectional area: 10cm 6cm Height: 40cm Feed of BM (light solid) from top. Withdrawal of coarse material from bottom. Gas vel.:12.5cm/s Bed material feed Fluidizing air H=0cm Screw transporter Wax droplets Fluidized bed ressure transducers Fluidizing air M Motor

12 12 Experimental procedures Withdrawal from bottom: two different procedures Continuous withdrawal at a rate of 6g/min Intermittent withdrawal: 4 minutes wax feed followed by withdrawal at a rate of 24g/min without wax feed Effect of withdrawal procedure on removal of bed material with coarse particles.

minutes wax feed followed by withdrawal at a rate of 24g/min without wax

13 13 Results Removal of BM with wax: Continuous withdrawal: 280g/100g-coarse Intermittent withdrawal: 80g /100g-coarse Bottom part worked as a classifier when operated under intermittent mode. Excess accumulation in the bottom Defluidization Detection of solid accumulation in the bottom

worked as a classifier when operated under intermittent mode.

14 14 Experiments Measurement and analysis of pressure fluctuation in the bed with coarse solids accumulation in the bottom by Fourier transformation. Bed material feed Fluidizing air H=0cm Screw transporter Wax droplets Fluidized bed ressure transducers Fluidizing air M Motor

15 15 Without acclumuation Spectrum peak of 2~3Hz at height >8.5cm Bubble スペクトルパワー cm 8.5cm 14.5cm 周波数 [Hz]

16 16 スペクトルパワー Accumulation of 50g eaks decreased due to the change in the place of bubble formation. 2.5cm 8.5cm 14.5cm 良好状態周波数 [Hz] 基準位置

17 17 スペクトルパワー Accumulation of 100g eak disappeared with the formation of channeling through accumulated coarse solids. 2.5cm 8.5cm 14.5cm 良好状態周波数 [Hz] 基準位置

18 18 スペクトルパワー Accumulation of 150g Complete defluidization. eak at 7Hz appeared. Solid fluidization in fixed bed. 2.5cm 8.5cm 14.5cm 良好状態周波数 [Hz] 基準位置

19 19 Summary If half of heat of blast-furnace slag is to be recovered in Japan, the heat will be equivalent to about 1 million tonnes of coal annually. The bed size to recover heat is estimated to be 6m 4.5m(cross sectional area) x 3 m height for 100tslag/hour. Cold model experiments were carried out to remove solidified material from the bottom. Observation of frequency pressure fluctuation is considered to be an effective method to detect defluidization.

5m(cross sectional area) x 3 m height for 100tslag/hour.

20 20 Acknowledgement T.Shimizu expresses his thanks to The Ministry of Education, Culture, Sports, Science and Technology for Grant-in-Aids (No ).

FXA 2008. Candidates should be able to : Define and apply the concept of specific heat capacity. Select and apply the equation : E = mcδθ

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