- Title
- Characterisation of resistance to air flow in iron ore sintering by quantification of pressure drop
- Creator
- Singh, Tejbir
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The present study investigates the effect of various operating parameters i.e. total suction pressure, bed voidage etc. on resistance to air flow during sintering and attempts to examine the resistance of the flame front in greater detail. Sintering experiments were conducted in sinter pots at two scales i.e. pilot scale (314 mm x 600 mm) and laboratory scale (53 mm x 400 mm and 53 mm x 500 mm) for a range of coke rate and basicity and varied total suction pressure. The yield, productivity and mineralogy comparisons of the different scales showed that the lower half sinter product for the milli-pot at 5.5% – 8.0% coke rate were within ±10% of pilot scale sinter product at a corresponding coke rate of 3.5% – 5.5% in pilot scale. The air flow rate in the green bed was modelled using the modified Ergun equation and channel flow equation. The Ergun equation was sensitive to the packed bed voidage and needed modification for different systems whereas the channel flow equation predicted air flow within ±15% range for a wide range of voidage (0.32 to 0.41) and column diameter (53 mm, 100 mm and 300 mm). Similarly, in a fully sintered bed, the air flow rate was able to be predicted for suction pressure of 4 - 21 kPa, by the modified Sugiyama equation, where a flow fraction parameter (α) of 0.7 was used instead of the original value of 0.8. The simultaneously measured pressure and temperature profiles in milli-pot were analysed to examine the resistance to air flow in different zones during sintering. The maximum resistance to air flow in the bed was found to be in the region between the leading edge of the flame front at ~100 °C and the trailing edge of the flame front at ~1200 °C, defined as a region of maximum resistance (RMR). The main processes happening in this temperature range were de-humidification, goethite dehydroxylation, flux calcination, coke combustion and melting of granules. It was found that the RMR was responsible for 40% to 80% of the total pressure-drop, depending on its location in the bed. The pressure drop was mainly due to the changes in bed structure and the much greater gas volumetric flowrate at high gas temperature. The humidified bed (green bed with condensed moisture) contributed the next highest pressure drop where sintered bed have the lowest pressure drop contribution. The pressure drop per unit length (kPa/m) was 60 to 104 kPa/m, 35 to 44 kPa/m, and 3 to 5 kPa/m for RMR, humidified bed and the sintered bed respectively. It was found that the pressure-drop during granule melting (>1200 °C) was relatively low due presence of large flow channels in the region. X-Ray CT imaging was used to quantify the pore structure in different regions of a quenched sinter bed. Hence the sinter bed was divided into three new zones i.e. the humidified (green) bed, pre-melt reaction zone, and sintered bed zone (including the granule melting). To quantify the resistance of different zones, the pressure gradient in each zone (ΔP/L) was correlated with the specific kinetic energy of air (v2) for a range of suction pressures. The resistance of the individual process of RMR comprising (de-humidification zone, goethite dehydroxylation zone, flux calcination zone, combustion zone) was investigated collectively as pre-melt reaction zone (PMRZ). The resistance in PMRZ was found to be dependent on the green bed voidage and varying total suction pressure across the bed with higher resistance recorded for low suction and low voidage, vice versa. Based on preliminary results, the resistance of the individual process of PMRZ was quantified and it was found that the maximum contribution was from the goethite dehydroxylation zone followed by the de-humidification zone, coke combustion zone and flux calcination zone. The change in overall resistance of different zone was examined by conducting distinct experiments with no goethite, no flux and no coke blend where no goethite blend showed a maximum reduction in resistance. An equation was proposed to predict the ratio of PMRZ resistance to green bed resistance for total suction pressure and green bed voidage whereas the humidified bed resistance was related to green bed by a constant. The sintered bed resistance was calculated by using modified Sugiyama’s equation. The air flow rate was predicted by a proposed set of equations and the pressure balance across the bed for different suction pressure was within ±10% range at laboratory scale and pilot scale. In this study, an equation was proposed to estimate the yield of the sinter product as an exponential growth function for a given green feed +5mm fraction and temperature profile mainly for a given holding time over 1200 °C. The equation was validated with present experimental data and open literature data. The proposed yield prediction was satisfied by RMSD=0.05.
- Subject
- iron ore sintering; milli-pot sintering; air flow rate resistance; sinter productivity; sinter yield; sinter mineralogy; interrupted / quench sinter; pressure drop; flame front; region of maximum resistance; pre-melt reaction zone
- Identifier
- http://hdl.handle.net/1959.13/1508195
- Identifier
- uon:56104
- Rights
- Copyright 2022 Tejbir Singh
- Language
- eng
- Full Text
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