SLIDE 1 Conference on Modelling Fluid Flow (CMFF’03)
- T. LAJOS, G. KRISTÓF, J. M. SUDA
Department of Fluid Mechanics Budapest University of Technology and Economics
DUNAFERR Danube Iron and Steel Corporation
EXPERIMENTAL AND NUMERICAL MODELLING OF SECONDARY EMISSION CONTROL SYSTEM OF BOF (BASIC OXYGEN FURNACE)
SLIDE 2 Secondary emission of BOF technology
The most serious air pollution of steel production occurs when hot iron is charged from a ladle into the converter vessel filled partly with scrap (mass of solid pollutants is 10−20 kg/cycle, concentration: 1- 2 g/m3). The space available for the hood capture system is limited by the
Aim of investigation was to find appropriate hood capture system and to predict its capture efficiency.
SLIDE 3 Solution of the problem: combined application of model experiment and CFD
Flow characteristics: temperature of hot gases is
- appr. 1000°C. Gas velocity in
the opening of the vessel of D=2.6 m diameter is about 8 −10 m/s. Hot gas jet flow is strongly influenced by buoyancy force. High temperature exhaust gas escaping the converter was modelled with hot air in a 1:20 scale model.
1 2 3 4 5 11 12 6 7 8 13
NYM1 NYM3 NYM2 SM2 SM3 NYM3 HM5 TM1 HM1 SM1 HM4 HM2
9 14
NYM4 HM3 TM2
10
SLIDE 4
Experimental setup
SLIDE 5 Considerations of modelling
a) Flow similarity: the buoyancy forces influence the shape
b) Evaluation of capture efficiency: simple and reliable method for evaluating different hood and exhaust variations c) Flow visualisation
SLIDE 6 a) Flow similarity
inertia/buoyancy forces at full scale and model should be identical ⇒ model discharge velocity can be determined from full scale discharge velocity, model scale and temperature ratio
b) Evaluation of capture efficiency
At measuring heat flux entering the capture hood thermal stratification of air removed by the hood should be considered : a) either by measuring velocity and temperature distribution or b) by mixing of air layers of different temperatures
FrM=Fr
T T D D ∆ ∆ =
M M M
v v
( ) ,
g ρ ρ D v ρ Fr
g a 2 g 2
− =
⇒
vessel converter the from discharged flux heat hood capture the entering flux heat CE =
SLIDE 7
Mixing of stratified flow
Numerical simulation of the flow in a labyrinth (FLUENT 5.5)
c) Flow visualisation by transilluminating the hot gas flow
SLIDE 8 Numerical simulation of flow in hood capture system model
a) The geometry of simulation model was scaled after the experimental setup. Outlet air velocity and temperature have been taken from the laboratory scale model. b) Symmetry assumption with respect to the mid-plane of the facility was
- employed. The grid consisted of
approximately 250,000 tetrahedral cells. c) Hot gas was introduced to the computational domain through a velocity inlet, and pressure outlets were applied on the remaining boundary surfaces. d) Air density was computed from the incompressible ideal gas model as a function of local temperature. e) Time dependent simulation was applied and turbulent transport was computed with Renormalisation Group k−e model.
SLIDE 9 Calculated flow field of hot gas jet (FLUENT 5.5)
Velocity vectors and pathlines are coloured by velocity
- magnitude. Temperature distribution belongs to a given phase
- f the charging process.
SLIDE 10
Influence of relationship of mass flows
qm,out[kg/s] = 14,5 14,5 7,25 qm,exh[kg/s] = 136 68 68 qm,out/qm,exh = 0,107 0,213 0,107 CE [%] = 86 57 100 The simulation results prove the significance of similarity requirement: Frm=Fr
SLIDE 11
Analyses of the charging process
a) Capture efficiency was mostly affected by the position of charging ladle. b) When using the hood of optimized geometry CE=0.87 was measured without charging ladle. In the first phase of the charging process, when ladle approaches the jet, the capture efficiency decreases to CEmin=0.54 because of interaction between the jet and ladle. c) At the end of the charging when the open-cross section of the ladle approaches the vertical, the capture efficiency increases rapidly and reaches 100%. d) So the average capture efficiency (estimated to 75−85%) depends also on the pace of the charging determined by the crane operator. To improve the capture efficiency, the construction of the charging vessel should be changed in order to avoid the “adherence” of the jet to the charging ladle.
SLIDE 12 Conclusions
- Experimental investigations on a scale model are reliable
tools for development of air pollution control systems in metallurgy, removing in general hot gases. In order to ensure flow similarity, the Froude number for model and prototype should be identical.
- Measurement and comparison of exhaust and discharge
heat fluxes proved to be a suitable method for determining the capture efficiency of the pollution control system.
- Interaction between the jet and charging ladle influences
the capture efficiency significantly.
- The results of the 3D numerical simulation agreed well with
the results of measurements, so CFD can efficiently be used in solving similar air pollution control problems in metallurgy.
