Claims:ABSTRACT
A SYSTEM AND METHOD FOR SINTERING OF IRON ORE TO IMPROVE PHYSICAL PROPERTIES OF SINTER

The present subject matter discloses a system and method for producing a sintered metal ore from a sintering material is disclosed. The system (100) comprises a conveyor (104) carrying a sinter bed (102) of the sintering material, an ignition mechanism (106) to fire a top layer (102a) of the sintering material, a suction mechanism (108) to allow passage of air from the top layer (102a) to a bottom layer (102c) of the sintered material and a valve (110) to control the air flow created by the suction mechanism (108). The valve (110) is configured to generate pulses of air flow by controlled opening or closing of a damper (112). The physical properties of sintered ore such as tumbler index, abrasion index and reducing sinter return fines and sintering time are improved. The method and system also helps in improving high temperature properties of sinter such as reduction degradation index (RDI) and reducibility index (RI).
[To be published with Figure 2]
, Description:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENT RULES, 2003

COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

Title of the subject matter:
A SYSTEM AND METHOD FOR SINTERING OF IRON ORE TO IMPROVE PHYSICAL PROPERTIES OF SINTER

Name and Address of the Applicant:
TATA STEEL LIMITED, Jamshedpur – 831 001, Jharkhand, India;

Nationality: India

The following specification describes the subject matter and the manner in which it is to be performed.
CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY
[001] The present application does not claim priority from any patent application.
TECHNICAL FIELD
[001] The present subject matter described herein generally relates to a system and method for sintering of iron ore to improve physical properties of sinter and more specifically to a process and system to improve a method of downdraft suction of sintering machine.
BACKGROUND
[002] Sintering is a process in a sinter machine for agglomeration of iron ore and other raw material fines into a compact porous mass, i.e., sinter, used in Blast Furnaces as an iron bearing input charge material for hot metal production. ‘Permeability’ of sinter-bed on the sinter machine i.e., the porosity in sinter-bed of charged materials, facilitates passage of atmospheric air from the top to bottom across the depth of sinter-bed. A suction is created from the bottom of the sinter-bed, for efficient heat transfer from top to bottom of the sinter-bed for complete burning of charged materials and it controls the productivity of the sinter machine.
[003] In conventional sintering process, there is a ‘heat deficiency’ at the top portion of sinter bed, due to the insufficient fuel materials which causes generation of weak sinter fines leading to reduction in ‘yield’ of sinter production. The heat pattern in the sintering bed of an actual sintering machine is not uniform in the vertical direction of the bed (within the pallet), and there is a general tendency that the maximum temperature reached in the bed increases with increasing depth and that the temperature-fall speed slows down accordingly.
[004] During sintering process, the upper portion of the sintering material layer is lower in the bulk temperature and besides shorter in the length of time for exposure to elevated temperature than the intermediate and lower portions. This leaves the problem that a sintered ore formed in the upper portion is low in melt bonding and hence poor in mechanical strength with reduced sintering yield. When the flame front travel beneath the sinter bed the top layer of sinter experiences the maximum amount of thermal shock. The temperature of top layer drops in higher magnitude compare to middle and bottom layer. Further the partial pressure of oxygen is also high at top portion and hence the coke burns at faster rate in top layer as compare to middle and bottom layer. The excess available oxygen in top layer results in conversion of mot form wustite into hematite, and so the top layer is so porous and fragile. Around 20-30% of the total sinter bed is unusable owing to its fragile nature and hence it is always reported as return sinter fines (-5mm), which result in poor yield of the sinter plant.

Prior Arts
[005] Japanese Patent Publication No. 61-223136 discloses, a sintering material layer to be formed on a pallet should be reduced in its density by means of a screen constituted with a plurality of wire materials extending along a flow of Sintering material being loaded on the pallet, and at the same time, the Sintering material should be segregated with fine particles held in an upper layer and with coarse particles held in intermediate and lower layers So as to make the upper layer highly permeable to air with eventual improvement of yield and productivity of a sintered ore. This prior art method, however, has the problem that since a sintering material of 7% or so in water content is prone to get adhered to the wire materials, the resultant Sintering material layer is difficult to stably retain in a Segregated State as originally desired.
[006] Japanese Patent Publication (Kokoku) No. 55-19299 which discloses the following technique. "There is provided a first half hood section of negative pressure in the first half of the upper portion of the strand. There is also provided a second half hood section of positive pressure in the second half of the upper portion of the strand. When exhaust gas in the second half hood section is circulated by the positive pressure in the second half section and the negative pressure in the first half section, it is possible to decrease a volume of exhaust gas and also it is possible to decrease the electric power rate and further it is possible to prevent the deterioration of productivity." However, according to the above method, the second half section, in which sintering is conducted by the atmosphere, is covered with the hood for positive pressure, and a blower successively connected to a wind box in the second half section is removed so as to decrease the equipment cost as small as possible. It is an object of this apparatus that the equipment cost is decreased as small as possible when a volume of exhaust gas is decreased by the exhaust gas circulating apparatus described above. In the above patent, there are no description of enhancing the productivity by positively increasing a shifting speed of the combustion and melting zone on the raw mixture bed. From the composition of exhaust gas, the exhaust gas characteristic and the drawings, which are disclosed in the above patent publication, it can be presumed that the completion of sintering in this method is in the beginning of the second half hood section, and cooling is conducted on the strand in the residual range of the second half hood section. This method is not a method in which the firing completion point is made to approach as close as possible to the ore discharging section so that the entire strand can be utilized to enhance the productivity to the maximum.
[007] Above cited inventions either mentioned new design incorporation in sinter plant for production increase, by reducing the sinter fines and increasing the permeability of sinter bed. Such methods demand the modification in sinter plants which is not economical. Hence the present subject matter describes an improved method for sintering of iron ore to improve physical properties of sinter.
SUMMARY
[002] Before the present subject of a system and method for sintering of iron ore to improve physical properties of sinter is described, it is to be understood that this application is not limited to a particular type of system and method for sintering of iron ore to improve physical properties of sinter, as there may be multiple possible embodiments, which are not expressly illustrated in the present disclosures. It is also to be understood that the terminology used in the description is for the purpose of describing the particular implementations, versions, or embodiments only, and is not intended to limit the scope of the present application. This summary is provided to introduce aspects related to a system and method for sintering of iron ore to improve physical properties of sinter. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.
[003] In one embodiment, a system for producing a sintered metal ore from a sintering material is disclosed. The system comprises a conveyor carrying a flat bed of the sintering material, an ignition mechanism to fire a top layer of the sintering material, a suction mechanism to allow passage of air from the top layer to a bottom layer of the sintered material and a valve to control the air flow created by the suction mechanism. The valve is configured to generate pulses of air flow by controlled opening or closing of a damper.
[004] In another embodiment, a method for producing a sintered metal ore from a sintering material is disclosed. The method comprises steps of: firing a top layer of the sintering material by means of an ignition mechanism, allowing suction of air from the top layer to a bottom layer of the sintering material by means of a suction mechanism and controlling the air flow created by the suction mechanism by means of a valve.
BRIEF DESCRIPTION OF DRAWINGS
[005] The foregoing detailed description of embodiments is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present subject matter, an example of construction of the present subject matter is provided as figures; however, the present subject matter is not limited to the specific system and method for sintering of iron ore to improve physical properties of sinter disclosed in the document and the figures.
[006] The present subject matter is described in detail with reference to the accompanying figures along with reference numbers. The same reference numbers are used throughout the figures to refer various features of the present subject matter.
[007] Figure 1 illustrates a view of conventional system for sintering of iron ore, in accordance with an embodiment of the present subject matter.
[008] Figure 2 illustrates another view of conventional system for sintering of iron ore, in accordance with an embodiment of the present subject matter.
[009] Figure 3 illustrates a temperature distribution graph for conventional system for sintering of iron ore, in accordance with an embodiment of the present subject matter.
[0010] Figure 4 illustrates a proposed system for sintering of iron ore, in accordance with an embodiment of the present subject matter.
[0011] Figure 5 illustrates a proposed method for sintering of iron ore, in accordance with an embodiment of the present subject matter.
[0012] Figure 6a illustrates the distribution of temperature in the sintering process where a valve is closed to 30% of total opening, in accordance with an embodiment of the present subject matter.
[0013] Figure 6b illustrates the distribution of temperature in the sintering process where a valve is closed to 60% of total opening, in accordance with an embodiment of the present subject matter.
[0014] Figure 6c illustrates the distribution of temperature in the sintering process where a valve is closed to 100% of total opening, in accordance with an embodiment of the present subject matter.
[0015] Figure 7 illustrates the comparison of tumbler index of sintering material for different closed positions of the valve, in accordance with an embodiment of the present subject matter.
[0016] Figure 8 illustrates the comparison of abrasion index of sintering material for different closed positions of the valve, in accordance with an embodiment of the present subject matter.
[0017] Figure 9 illustrates the comparison of return sinter fines of sintering material for different closed positions of the valve, in accordance with an embodiment of the present subject matter.
[0018] Figure 10 illustrates the comparison of sintering time in the sintering process for different closed positions of the valve, in accordance with an embodiment of the present subject matter.
[0019] Figure 11 illustrates the comparison of sinter bed shrinkage during the sintering process for different closed positions of the valve, in accordance with an embodiment of the present subject matter.
[0020] Figure 12a illustrates a microstructure of sinter in normal sintering condition, in accordance with an embodiment of the present subject matter.
[0021] Figure 12b illustrates a microstructure of sinter produced by the proposed pulse sintering process, in accordance with an embodiment of the present subject matter.
DETAILED DESCRIPTION
[0022] Some embodiments of this disclosure, illustrating all its features, will now be discussed in detail. The words "comprising," "having," "containing," and "including," and other forms thereof, are intended to be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. It must also be noted that as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Although any system and method for sintering of iron ore to improve physical properties of sinter and, similar or equivalent to those described herein may be used in the practice or testing of embodiments of the present disclosure, the exemplary, system and method for sintering of iron ore to improve physical properties of sinter is now described.
[0023] Various modifications to the embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. However, one of ordinary skill in the art will readily recognize that the present disclosure is not intended to be limited to the embodiments described, but is to be accorded the widest scope consist in this regard, in a generic sense.
[0024] A conventional sintering process of iron ore, in which the combustion starts by burning the top layer of sinter mix on subsequent suction which is mainly 600-700 mm water column and make the process autogenous. This means the suction flow of the air takes care of burning of coke which is added as fuel in the sinter mix. The flame which decent down on suction (negative pressure) by the blower connected to the sinter machine control the flame front nature (narrower or broad).
[0025] The combustion process does not happen simultaneously in the whole thickness of the bed. On the contrary, the combustion happens as a horizontal layer that moves vertically through the bed. The thickness of this layer is a small fraction of the bed. Permeability is a quality requirement for the load, and for that reason the granulation process was previously used (permeability is improved during granulation). In the region above the combustion zone, very hot sintered product heats the air that passes through this layer. In this way, pre-heated air arrives to the combustion area. The heat of the air/gases previously heated is absorbed in these cold sections, causing preheating of the load and evaporation of the water. In this context, high temperatures that cause partial melting are reached, and the sintering process takes place. This high thermal efficiency is caused by heat accumulation in a partial layer of the load called sintering zone or flame front. The flame front progresses at 10-30 mm/min (23.9-27.7 mm/min, towards the sintering grate. In a bed height of 500-600 mm the process would take 25 minutes).
[0026] Flame-front speed has a large influence on sinter quality, productivity and sintering time. The flame-front is the region where coke particles are combusting, having two borders, where coke begins to combust in the initial one and is burned out in the opposite. However, the temperature at which coke particle starts to combust depends on size, oxygen partial pressure, volatile content and component types in the coke. The temperature-time profiles are measured by means of thermocouples embedded in the sintering bed. In some cases it is suggested that the flame-front is the area where coke did not reach the combustion temperature, defining a border between combusted zone and initial mix of raw materials. Flame front speed influences the mineralogy and microstructure of the formed sinter. A molten (mainly of Fe2O3 and CaO) is generated in the sinter bed when the sintering process is carried out at 1200°C. Iron oxide and fine particles are incorporated in the molten. When the molten penetrates the hematite grain, interfacial breakdown takes place and primary hematite (un-melted) is left. This primary hematite is considered beneficial for sintering because it improves the Reducibility Index (RI). When CaO and Al2O3 are assimilated to the molten, this reacts with the iron oxide and generates acicular calcium ferrite (< 10 µm) with Al2O3 and SiO2 as solid dissolutions. This compound is known as silico-ferrites of Calcium and Aluminium (SFCA), and is considered beneficial for the sinter structure (good reducibility, improves shatter index (SI) and Tumbler index (TI)). SFCA in iron ore sinter can be divided into two types according to its composition, structure and morphology: SFCA and SFCA-I. SFCA is a low-Fe form that exhibits a prismatic or columnar morphology, while SFCA-I is a high-Fe and low-Si form.
[0027] The intersecting microplates morphology of SFCA-I is beneficial for sinter strength and reducibility (sinters with significant amount of SFCA-I are considered of high quality). When sintering is performed at temperatures lower than 1300°C, magnetite formation decreases (less FeO) and improves the RI and the Reducibility Degradability Index (RDI). Moreover, the optimum structure for sinter reducibility in the blast furnace is achieved, wherein the hematite nuclei (un-melted) is surrounded by an acicular ferrite network. When sintering is performed at temperatures higher than 1300°C, a fraction of the ferrite dissolves and melts to convert into hematite or magnetite and into gangue components.
[0028] During the cooling period, the molten forms new phases as large acicular ferrite, and secondary hematite, which deteriorates the RDI. The best results are reached among 1225°C and 1275°C, e.g. maximum percentage of ferrites, high primary hematite, low secondary hematite, good porosity and good quality indices (FeO, Reduction Degradation Index, Reducibility Index and Shatter Index).
[0029] The sintering process is based on treating a mix (mineral fines, return fines, fluxes, etc.) layer in presence of coke dust with the action of a burner placed in a surface of the layer. In this way, heating takes place from the upper to the lower sections. The mix layer rests over a strand system and an exhausting system allows the whole thickness to reach the suitable temperature for the partial melting of the mix, and the subsequent agglomeration. In the Dwight-Lloyd system, the sintering grate is a continuous chain of large length and width, formed by the union of a series of pallet cars that make the sintering strand. As shown in figure 1 the overall sinter strand attached with the blower where commonly suction takes place at the pressure of 1200-1400 mm water column. Figure 1 shows the normal sintering operation, in a conventional sintering method. At initial stage of ignition, air is allowed to pass through the sintering material layer from its ignited surface to its bottom upon suction at a lower part of the pallet.
[0030] In a conventional or normal sintering method as shown in figure 1, the basic raw materials are transported to proportioning unit wherein raw material are weighed and proportioned as per the required material balance iron ore fines, limestone fines and solid fuel (anthracite coal/coke fines, dolomite/ pyroxenite fine and sinter return fines are conveyed to mixing and granulation unit where water and lime fines are added and wet granulated mixture is formed. The granulated mixture is then transported to feeding hopper of sinter plant straight grate furnace. Feeding hopper feeds the material on endless pallet car of a sintering machine. Before feeding the material on the pallet cars, sinter of size (10-25 mm) are layered as hearth layer using hearth layer sinter bins. This bed of un-sintered mix having hearth layer at bottom and granules over it moves forward with the movement of endless car in forward direction. When the bed comes under the ignition furnace, top layer gets ignited and due to suction from bottom, flame front proceeds downwards and sintering occurs.
[0031] At the end of the sintering process, the sinter machine is tilted and sinter cake falls on spike crusher and crushed sinter is transported to sinter cooler. Cooled sinter, thereafter, screened into three fractions, minus 5 mm which goes to a granulation unit for recycling, plus 5 mm which goes to blast furnace stock house.
[0032] The figure 2 illustrates any conventional sintering machine wherein the sintering material (sinter bed) is layered upon the conveyor. The sintering material comprises of three layers; top, middle and bottom. These three layers may be distributed comprising an equal height of the sinter bed i.e. 200mm for each layer. A thermocouple is placed in each of the three layers to sense temperature of the respective layer during the sintering process. A fourth thermocouple is also placed at lower portion of the sinter bed to detect the temperature of the air being sucked by the blower.
[0033] The figure 3 shows the distribution of temperature as measured by the four thermocouples. The arrangement of thermocouple in sinter bed at different heights is shown in figure 2. From the figure 3, it can be seen that the bed temperature 1 represents the temperature of the top layer which gets increased from room temperature to 1185 ºC within 10 minutes and drop to almost 200-150 ºC, at time interval of 5-5.5 minutes. The bed temp 2 represents the temperature of the bottom layer, which increases to 1250 ºC, at time interval of 14 minutes and drop to 200-150 ºC after 16-18 minutes, similarly the bed temperature 3 represents the temperature of the middle layer of the sinter bed that faces the maximum time of sintering process and its temperature increases to 1340-1360 ºC. The total sintering time estimated is 26 minutes. The off gas represents the temperature of the air being sucked by the blower as detected by the fourth thermocouple. Hence from the graph shown in figure 3, it is evident that the top layer of the Sintering material layer is lower in the bulk temperature and besides shorter in the length of time for exposure to elevated temperature as compared to the middle and bottom layer.
[0034] Now referring to figure 4, an improved system 100 for sintering of iron ore is illustrated. The system 100 comprises a conveyor 104, an ignition mechanism 106, a suction mechanism 108 and a valve 110. The conveyor 104 is loaded with the sintering material in the form of a sinter bed 102 which comprises three layers; a top layer 102a, a middle layer 102b, and a bottom layer 102c. A hearth layer 103 is layered below the sinter bed 102 wherein the hearth layer 103 is generally made of sinter material of size 10-25mm. The ignition mechanism 106 is placed over the top layer 102a and as the sinter bed 102 over the conveyor 104 passes below the ignition mechanism 106, it ignites the top layer 102a. Further the suction mechanism 108 is provided to create a negative pressure below the bottom layer 102c by sucking the air from the sinter bed 102 and then blowing this air out of the system 100. The valve 110 is placed in the path of air being sucked by the suction mechanism 108. The valve 110 is configured to control the flow of air or pressure in the air path by rotating the damper 112 based on the command from a control unit 120. A pair of pressure sensors 114a and 114b may be placed at upstream and downstream of the valve 110 to sense the upstream and the downstream air pressure respectively.
[0035] In an embodiment, the ignition mechanism 106 may be an igniter hood or an ignition furnace. The suction mechanism 108 may be a blower or a pump. Further the valve 110 may be selected from the set of a globe valve, a butterfly valve or an electrically driven solenoidal valve.
[0036] A plurality of thermocouples 116 may be placed in the layers of the sinter bed 102. The thermocouples 116a, 116b and 116c are placed in the top layer 102a, the middle layer 102b and the bottom layer 102c respectively to measure the temperature of respective layers of the sinter bed 102. A thermocouple 118 is placed in the air path and below the bottom layer 102c to sense the temperature of the air being sucked from the sinter bed 102. The control unit 120 is configured to receive the data from the thermocouples (116a, 116b, 116c, 118) and the pressure sensors (114a, 114b) to control the operation of the valve 110.
[0037] The valve 110 is configured to generate a pulse by controlling the opening or closing or partial opening of the damper 112. During the initial stage of sintering process the valve 110 is kept in fully open position to work as a normal sintering process. In an embodiment of the present subject matter, after 2 minutes of start of ignition of the top layer 102a, a pulse may be generated by closing the valve 110 as per the requirement of sintering process and various strategies may be used to receive different outputs from the sintering process.
[0038] Referring to figure 5, a method 200 for producing a sintered metal ore from a sintering material is illustrated. At step 202, the top layer 102a of the sintering material may be fired by the ignition mechanism 106. At step 204, the suction mechanism 108 may allow suction of air from the top layer 102a to a bottom layer 102c of the sintering material. At step 206, the air flow created by the suction mechanism 108 may be controlled by a valve 110. Further the operation of the valve 110 may be controlled by a control unit 120 by implementing a number of control strategies as per the desired physical properties of the sintered metal ore.
[0039] The figure 6a shows the distribution of temperature in the sintering process where the valve 110 is closed to 30% of total opening. The time of closing of valve 110 to 30% is maximum up to 20 seconds. The temperature of the top layer 102a, as detected by thermocouple 116a, is increased from room temperature to 1230-1240 ºC with 18 minutes and drops to almost 200-150 ºC, at time interval of 6-7 minutes. The temperature of the bottom layer 102c, as detected by thermocouple 116c increases to 1260 ºC, at time interval of 14 minutes and drops to 200-150 ºC after 18-19 minutes. Similarly the temperature of the middle layer 102b of the sinter bed 102, as detected by thermocouple 116b, which faces the maximum time of sintering process and it increases to 1340-1360 ºC. The total sintering time estimated is 24 minutes.
[0040] The figure 6b represent the temperature distribution when the control unit 120 close the valve 110 to 60% for the time interval of 20 seconds whereas figure 6c represent the temperature distribution when the control unit 120 closed the valve 110 fully to 100% for 20 seconds.
[0041] As compare to results found in 30% damper closing /pulse generating, the time at which the sinter bed retain at temperature more than 1200ºC, is more in 60% valve closed and found to be highest when valve is closed to 100% for 20 seconds of time interval, similarly the sintering time is also lower.
[0042] The important phenomena seen in figure 6b and figure 6c is that the all three sinter bed layers attain the temperature of 1200 ºC within a shorter period of time and stay there for more than 3-5 minutes and slowly cooled down to 150-200 ºC. The burn through temperature (temperature of air as detected by the thermocouple 118) found to be higher in last 2 cases which is the indication of better sinter kinetic rates and reaction across the sinter bed 102.
[0043] Table no 1 shows the time interval at which the layers of the sinter bed 102 withstands at temperature of more than 1200 ºC, and cooled to 150-200 ºC at the end of sintering process.
Table No: -1
Time above 1200 ºC, minutes
Process Top Layer Bottom Layer Middle Layer Total time
Normal sintering not reach the temp 2 7 9
Sintering with 30% valve Closed 2 4 4 10
Sintering with 60% valve Closed 3 5 5 13
Sintering with 100% valve Closed 4 5 5 14
[0044] From the table 1 it is clear that during the normal sintering process, the top layer 102a did not attain the demanded sintering temperature and hence generate poor quality as compare to sinter in middle and bottom layer. However, when the pulse is generated in the sintering process, the time at which all the layers remains for more than 1200 ºC even at lower sintering time of 2minutes. This shows that the sinter remains at temperature of 1200-1300 ºC which is the beneficial temperature zone for good sinter and cooled at lower rate compare to normal sinter.
Table No:-2
% Area Above 1200 ºC
Process Top Layer Bottom Layer Middle Layer
Normal sintering not reach the temp 12.45 31.45
Sintering with 30% valve Closed pulse 16.23 24.22 30.22
Sintering with 60% valve Closed pulse 18.56 27.62 34.52
Sintering with 100% valve Closed pulse 24.55 32.42 37.29

[0045] From table 2 the positive effect of pulse on sintering process is clearly estimated where it was found that in last case at 100% valve closed and open pulse give maximum area coverage above 1200 ºC at different height of sinter bed. This distribution of temperature and more area coverage at higher temperature result in better microstructure and phase transformation in sinter also the temperature gradient also lowered down from top bed to the bottom bed of the sinter. As seen in normal sinter process the area coverage at higher temperature is much lower than in remaining three cases.
Case Study:
[0046] In this work, four sets of sinter pot test were made to simulate the conventional sintering method as well as method proposed in the present subject matter. Effect of proposed method of pulse sintering by generating pulses in suction flow in sinter making (reducing and increasing the suction flow of desired magnitude) on sinter process parameters and physical properties was also established.
[0047] Iron ore, Lime stones fines, Pyroxenite, dolomite, and coke breeze of mentioned chemistry in table 1 was used for preparing sinter base mix. The chemistry of mill scale is also mentioned in the table 3.
Table 3: - Chemistry of raw materials
MATERIAL T. Fe CaO SiO2 MgO Al2O3 FeO LOI
JODA Iron ore 62.93 0.00 0.08 0.01 2.58 2.77 3.36
Pyroxenite 5.26 0.00 39.43 50.12 1.25 0.65 1.57
Lime Fines 0.17 68.90 2.12 0.56 1.31 0.56 27.54
Limestone 0.00 45.25 5.62 7.49 2.12 -- 48.25
Dolomite 0.83 36.35 2.14 18.62 4.00 0.67 43.65
Coke breeze -- 12.5 0.24 5.2 -- 79.22

[0048] Iron ore used for sinter base mix preparation was first screened at -10 mm fraction. The mill scale having size range as shown in table3.
[0049] These materials were then mixed with preferred proportion in such a way that the basicity (CaO/SiO2) achieved around 2.6. The material is mixed in the granulating drum along with moisture ~6-7%. The green mix was produced having mean particle size of 2-3mm. Four sets of pot grate sintering test were taken wherein in base case the normal sinter was made without giving any pulse in downward suction (negative suction) during sintering.
[0050] The sinter was made with target chemistry i.e the basicity (CaO/SiO2) of 2.3 and MgO at 1.9 %. The Coke rate in all set of trials was kept constant at 6.5 %. The bulk density of green bed of sinter in 600 mm pot maintained around 1.8 to 2 g/cc while in normal sintering it is in the range of 2.2-2.4 g/cc
[0051] The sinter raw mix of 100 kg was mixed in mixer drum and moisture was also added to convert the fines into micro ball having mean particle size of 2. 5mm. The Green sinter mix was then transferred to pot sinter. In all set of trials, the initial suction rate and the ignition flame temperature for firing the sinter in sintering process was kept constant (1200 mm of water column) and at 11000 C respectively.
[0052] The three set of experiments are carried out in a sequence of closing of the valve/damper based on the command from the control unit. The sequence of pulse generator is done in three ways:
1. The valve of pulse generator is closed to 30% for 20 secs and again opened to 100% for 2 minutes.
2. The valve of pulse generator is closed to 60% for 20 secs and again opened to 100% for 2 minutes.
3. The valve closed to 100% (zero suction) and again opened to 100% normal suction in negative downdraft suction in sintering machine.
[0053] During sintering process, the time to complete the sintering process was noted i.e after achieving the burn through temperature of sinter bed (maximum temperature of waste gas). The fired sinter was then removed from the pot and stabilized by dropping the whole mass of sinter for 4 times from 2-meter height. After dropping, minus 5 mm fraction of sinter fines was removed and weighed and the remaining sinter was further screened in size range -40 mm to +10 mm for tumbler test. The sinter is then tested for microstructural analysis. During sintering process, the temperature of the top layer of the sinter bed was measured to note the thermal behavior.
[0054] As shown in figure 7, it was found out that pulse sintering process helps in increasing the tumbler index of sinter to 5-6 points with increases the magnitude of pulse generator. The pulse in suction helps in maintaining the flame front temperature and speed and the flame front covers the entire section of sinter smoothly at lower time. This helps the strong sinter produce at top bed of the sinter (around 300-400 mm of total bed of 600 mm).
[0055] The retention of sinter at higher temperature for more than 5-6 minutes as explain before allowing the formation of SFCA/SFCA-I and primary hematite phase which is beneficial for increasing the tumbler strength of the iron ore sinter and so the abrasion index of sinter also get improved as shown in figure 8.
[0056] When the flame front travels beneath the sinter bed, the top layer of sinter experiences the maximum amount of thermal shock. The temperature of top layer drops in higher magnitude compare to middle and bottom layer. Hence the top layer of sinter is fragile owing to results in sinter fine, this is more crucial as per the yield of sinter plant is considered. The partial pressure of oxygen is also high at top portion and hence the coke burns at faster rate in top layer as compare to middle and bottom layer. The excess available oxygen in top layer results in conversion of mot form wustite into hematite, and so the top layer is so porous and fragile. Around 20-30% of the total sinter bed is unusable owing to its fragile nature and hence it is always reported as return sinter fines (-5mm). In the proposed method, the percentage of return fines of sinter is largely reduced to 2-3% as shown in figure 9 and hence it helps in increasing the productivity.
[0057] As explained above that the flame front speed as well as flame front nature mainly (broaden up) is achieved while giving the pulses during suction in iron ore sintering process. Once the pulse is given to the suction air flow, the flame speed increases horizontally as well as vertically owing to which the time of sintering also get reduced to a larger extend. The time of sintering in normal case is 26 minutes while that for pulse sintering varies from 24-22 minutes based on magnitude of the valve/damper closing as shown in figure 10.
[0058] It was found that owing to higher rate of assimilation in top layer due to the presence of retention of top section of bed at temperature more than 1200 ºC for more time will cause the bed to shrink more as compare to conventional sintering process. The bed shrinkage of sinter in proposed method is found to be 87 mm against 70 mm in normal sintering process as shown in figure 11.
[0059] The figures 12a and 12b shows a comparison of microstructure of sinter in normal sintering condition and sinter produced by PULSE sintering process respectively. In normal sintering, the microstructure of normal sinter shows the columnar SFCA and some area covered with Acicular SFCA and minute amount of primary hematite. In pulse sintering process, the microstructure revels that the primary hematite is more in volume compare to sinter produce by normal sintering process. The hematite nuclei (un-melted) is surrounded by an acicular ferrite network. The porosity is also homogeneously distributed.
Table 4: Phases composition in normal and in pulse sintering process

[0060] Iron ore sintering process is the combination of oxidation and reduction process, hence in conventional sintering process owing to higher oxidation potential available at top of the sinter bed, the top layer gets oxidized rapidly and hence generation of porous fragile layer at the top is the indication of more fines generation in conventional sintering process. Similarly, the sinter retain at temperature of 1340-1350 ºC for more than 2-4 minutes results in more generation of non-beneficial secondary hematite and hence more glassy phases are formed owing to cooling suddenly from high temperature as shown in table 4.
Table 5: High Temperature properties in normal and in pulse sintering process
Process RDI, % RI,%
Normal sintering 24 74.25
Sintering with 30% valve Closed pulse 21 74.66
Sintering with 60% valve Closed pulse 21 75.62
Sintering with 100% valve Closed pulse 19 76.22

[0061] As shown in table 5, when sintering is performed at temperatures lower than 1300°C, magnetite formation decreases (less FeO) and improves the RI and the Reducibility Degradability Index (RDI). Moreover, the optimum structure for sinter reducibility in the blast furnace is achieved, hematite nuclei (un-melted) surrounded by an acicular ferrite network. When sintering is performed at temperatures higher than1300°C, a fraction of the ferrite dissolves and melts to convert into hematite or magnetite and into gangue components
[0062] Exemplary embodiments discussed above may provide certain advantages. Though not required to practice aspects of the disclosure, these advantages may include the following:
[0063] Some embodiments of the present subject matter disclose a method and system to improve physical properties of the sintered metal ore during a sintering process.
[0064] Some embodiments of the present subject matter disclose a method and system to generate pulses in the downward suction during a sintering process.
[0065] Some embodiments of the present subject matter disclose a control mechanism to apply a number of valve control strategies to generate pulses in the downward suction as per the desired sintered metal ore.
[0066] Some embodiments of the present subject matter disclose a method and system to produce a sintered material with having a uniform temperature distribution throughout the height of the sinter bed.
[0067] Some embodiments of the present subject matter disclose a method and system of pulse generating during downward suction and reduce the segregation of coke fines from top to the bottom layer of the sinter bed.
[0068] Although implementations for a system and method for producing a sintered metal ore from a sintering material have been described in language specific to structural features and/or systems, it is to be understood that the appended claims are not necessarily limited to the specific features or described. Rather, the specific features are disclosed as examples of implementations.