EFFECT OF FIRING TEMPERATURE AND TIME ON ... - ethesis

This confirms that the thesis entitled “Effect of firing temperature and time on the swelling behavior of reduced iron ore pellets”, submitted by Mr. Sponge Iron of DRI, is obtained from the direct reduction of iron ore and has an iron content between 84 and 84. 95 percent. In the existing blast furnace, a production increase of at least 25 to 35% can be achieved by using pre-reduced iron ore.

Also, most of the fines generated in the course of handling, mining, transportation, etc. are exported at a pass-through price to be utilized in the production of iron ore pellets for the production of sponge iron. In the present project work, an attempt has been made to study the reduction behavior and kinetics of burnt iron ore pellets. Third chapter deals with selection of raw materials, preparation of samples, production of iron ore pellets, experimental procedure.

4.10-4.11 Porosity versus firing temperature plots for fired BPJ and DR Pattnaik hematite iron ore pellets. 4.12-4.14 Crushing strength versus firing temperature plots for fired BPJ and DR Pattnaik hematite iron ore pellets.

Introduction

Coal based

Total Gas based Coal based

Total

Production, consumption, export and surplus availability of iron ore lumps and fines in India

Table 1.2 clearly shows that the ratios between fines and total exports are increasing year after year. So it is very clear that the fines generated do not find a market in India. Moreover, about 84% of fines are exported abroad at a throwaway price, causing huge economic losses to our countries.

Future of DRI-EAF route of Steel making in India

Aims & objectives of the project

CHAPTER-2 LITERATURE

Literature survey

Details of iron ore reserves in India
Definition of pellets
Mechanism of pellet formation
Advantages of pellets
Swelling of iron-ore pellets
Industrial significance
Mechanism of swelling
Thermodynamics and kinetics of iron ore reduction

India has the sixth largest reserves of iron ore in the world and these are of high quality. Iron ore deposits in India are mainly located in eastern India (especially in Odisha and Jharkhand) or in central India (Chattisgarh and Madhya Pradesh). Most of the iron ore deposits in India occur in the form of hills that protrude above the ground.

The fine particles are first used to increase the iron content to over 65%, as the common gas in iron ore is concentrated in the "fines" fraction. Pellets are approximately spherical lumps formed by agglomeration of the crushed iron ore in the presence of moisture and binder, with subsequent hardening at 1300°C. However, swelling increases the rate of iron oxide reduction due to the formation of highly porous reduction products.

Whisker growth can be considered an extreme case of preferential nucleation that occurs when the relative rates of iron ion diffusion and oxygen removal are relatively high, i.e., when gas reduction potential is low and mineral diffusion of high iron. A schematic diagram of the reduction modes of iron oxide before the formation of the Metallic Layer.

Table 2.1 Typical properties of pellets suitable for use in blast furnace

CHAPTER-3

Experimental

R Pattnaik

Experimental procedure
Determination of cold crushing strength: The crushing strength of fired pellets and some of reduced pellets (size 15mm) have been determined by employing a
Determination of apparent porosity: The apparent porosity values of iron ore pellets were determined by using kerosene oil as a medium in accordance with the
Determination of degree of reduction: The degree of reduction was calculated by using the following formula
Determination of percentage swelling: Swelling is a volumetric expansion of the agglomerate during reduction of iron oxide. The diameters of pellets before and

The pellets were kept in an oven at 110 °C for drying and removal of moisture for 2 hours. The pellets were taken out and stored in separately marked bags according to the binder percentage and firing temperature. Crushing strength: The crushing strength of fired pellets (approx. size 15 mm) was determined using a cold uniaxial hydraulic press (capacity 20 tons).

Degree of reduction: Reduction studies of baked pellets were carried out in a stainless steel container (80 mm height x 40 mm diameter). The diameter (mm) of the fired pellet of required quality was taken and the weight (g) was measured and then placed centrally on this coal bed and the remaining part of the stainless steel container was filled with coal to fire the pellet completely. Pellet weight losses were recorded by an electronic balance and final diameter measurements were made using a caliper.

Where σc is the crushing strength in kg.cm-2; W maximum load at break in kg;. Where Vf = final volume of reduced pellets; Vi = initial volume of burned pellets. Swelling up to 20% is generally accepted as "normal", while higher values are called "abnormal swelling" or even "catastrophic swelling".

CHAPTER-4 RESULTS &

DISCUSSIONS

Results and Discussions

Effects of firing condition on the crushing strength and porosity of the pellets
Effects of firing temperature on the extent of reduction and swelling of fired haematite iron ore pellets
Effect of reduction temperature on the degree of reduction and extent of swelling of fired haematite iron ore pellets
Effect of reduction time on degree of reduction and extent of swelling of fired haematite iron ore pellets
Effect of firing temperature on drop number, of fired haematite iron ore pellets
Scanning electron micrographic study of the reduced pellets

D.R Pattnaik 3%
D.RPattnaik3%
D.RPattnaik6%
B.P.J 3% binder (fired-1100 o C)

As shown in Figure 5.14, the crushing strength of fired pellets increased with increasing firing temperature. This appears to be due to the increased extent of slag binding in the pellets[4]. This appears to be due to slag formation and pore filling at a firing temperature of 1300 oC.

As shown in Figure 4.9, a decrease in the degree of reduction was observed as the baking temperature increased. This appears to be due to the lower porosity of the pellets fired at higher temperatures. As shown in Figures 4.1 to 4.7, the degree of reduction increases as the reduction temperature increases.

As shown in fig and 4.23, the degree of swelling first increases a little with increase in reduction temperature, then it decreases with increase in reduction temperature. The initial increase may be due to high temperature, high degree of reduction and high diffusion rate of gases. The decrease in the swelling after with an increase in reduction temperature is more likely due to sintering of iron whiskers at higher temperature.

As shown in fig. 4.1-4.7, the degree of reduction increases with the increase of time at a certain reduction temperature. As shown in fig. 4.18, the extent of swelling increases with increasing reduction time at a specific reduction temperature and specific firing temperature. This is believed to be due to fibrous growth of iron hairs in the pellet matrix without any limitation in growth, but pellets fired at higher temperature showed a decrease in the extent of swelling with increasing reduction time.

This increase in slump number values is due to greater densification during firing at higher temperatures and the resultant decrease in porosity. As shown in fig 4.30 to 4.33 cracks have developed in iron ore pellets due to swelling, the cracks are more pronounced at 900oC compared to 850oC. As shown in Figs 4.26 to 4.29, the excessive swelling of the iron ore pellet is due to the fibrous growth of iron whiskers in the pellet matrix[3].

Physical properties of fired BPJ iron ore pellets

Physical properties of fired D.R Pattnaik Iron ore pellets

Degree of reduction and swelling values of fired BPJ haematite iron ore pellets reduced in Basundhara non-coking coal

Reduction rate and swelling values of BPJ iron ore hematite calcined pellets are reduced in non-coking Basundhara coal. Reduction rate and swelling values of calcined DR Pattnaik hematite iron ore pellets are reduced in non-coking Basundhara coal.

Degree of reduction and swelling values of fired DR Pattnaik haematite iron ore pellets reduced in Basundhara non-coking coal

Degree of reduction and swelling values of fired DR pattnaik haematite iron ore pellets reduced in Basundhara non-coking coal

Degree of reduction and swelling values of fired BPJ hematite iron ore pellets reduced in Basundhara non-coking coal: A comparison for the.

Degree of reduction and swelling values of fired BPJ haematite iron ore pellets reduced in Basundhara non-coking coal: A comparison for the

CHAPTER-5

CONCLUSIONS

Conclusions

The effect of firing temperature on the Crushing Strength is more pronounced at firing temperature of 1300oC. The degree of swelling increases with increase in reduction time at a given reduction temperature and given firing temperature. However, the pellets fired at higher temperature showed a decrease in the degree of swelling with an increase in reduction time.

The use of concentrated sugar cane juice as a binder is useful in providing good binding properties so that we can mix the lost +100# fines (-25+36#) together with the -100# fines to form pellets. The reduction behavior of these blended pellets was found to be similar to pellets produced only from -100# fines. Thus the use of concentrated sugarcane juice as a binder provides a way to utilize waste fines thus avoiding the disposal problem and saving large amounts of energy.

CHAPTER-6

FUTURE WORK

Suggestions for future work

Similar studies can be carried out with other non-coking coals of Orissa, Jharkhand, Chattisgarh and nearby areas. This work can be extended for study on reduction and swelling behavior of iron ore lumps. Detailed studies on the carbon uptake in the reduced products, under different parameters, can be carried out.

The addition of other possible binders for the chemical and physical properties of the iron ore pellets can also be carried out.

CHAPTER-7 REFERENCES

7.References

Kumar M.; Patel S K.,Characte ristics of Indian Non-coking Coals and Iron ore reduction by their Chars for directly re duced Iron production,

Longbottom Raymond; Kolbeinsen Leiv, Iron ore Reduction with CO and H2 Gas Mixtures – Thermodynamic and Kinetic Modelling, Proceedings of