FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See section 10, rule 13)
“SYSTEM FOR PRODUCING DIRECT REDUCED IRON AND A PROCESS FOR THE SAME”
Dharmendra Gupta of Indian nationality of C/o, Mrs. Vandana Gupta, B-1,1501 Green Acres, Phase-3, Waghbill, Ghodbunder Road, Thane (West)-400607,Maharashtra, India.
The following specification particularly describes the invention and the manner in which it is to be performed.

TECHNICAL FIELD
The present disclosure relates to a system for producing direct reduced iron (DRI) and a process for the same.
BACKGROUND
Direct reduced iron (DRI) or sponge iron is obtained after the reduction of ores containing oxides of iron. Though, sponge iron as such has a limited area of direct application, the end products obtained after processing of the sponge iron have a major role to play in the manufacturing industry. Almost every industrial sector requires an iron-based product or its alloy as the base or starting material. Therefore, owing to its ever increasing demand, it has become the need of the hour to produce DRI or sponge iron with high purity and efficiency.
DRI or sponge iron production is an energy intensive process as it requires very high temperatures to reduce the oxides of iron. This energy can be supplied by means of a reducing gas having high calorific value. Such gases can be a mixture of carbon monoxide, hydrogen, carbon-di-oxide, etc. Midrex and HYL-III are commercially available gas-based processes. Apart from this, there are several coal-based processes also existing in the market, examples of such processes include rotary kiln or SL/RN process, Hoganas process, Kinglor Metor (KM) process, etc.
The tunnel kiln or furnace employing the Hoganas process is a very popular technique currently being used in China for producing DRI. In this process, the raw material passes through different temperature zones namely heating, reducing and cooling zones. The Hoganas process tunnel furnace is a long tunnel, provided with a

means for moving cylindrical structures called saggers. The saggers are made of silicon carbide and are loaded on bogies, which travel inside the tunnel. The feed material comprising oxide of iron, carbon source and limestone are fed inside the saggers and heated using a suitable means. Typical retention time of this process is 72 to 80hrs. The product quality obtained is of good quality.
In Kinglor Metor process, oxides of iron and coal are charged in a vertical retort furnace, which is heated externally by solid or gaseous fuel. Unlike the tunnel furnace of the Hoganas process, the furnace of Kinglor Metor process extends vertically. The height of this furnace depends on various factors such as amount of feed to be reduced, the extent of reduction desired, etc. The process results in good quality reduced iron.
Rotary kiln process employs a continuously rotating furnace which is inclined at certain angle for ease in flow of the feed material. A mixture of oxide of iron, coal and dolomite is sent into the first half of the kiln, known as the pre-heating zone. In the other half of the kiln, the actual reduction takes place and metallic iron is produced. The heated gas flows counter currently through the kiln.
Although, the above existing processes produce a good quality reduced iron, the amount of capital expenditure and requirement of energy is tremendously high. Moreover, the tunnel furnace of the Hoganas process face frequent jamming of bogies/trollies inside the tunnel and frequent breakage of silicon carbide saggers apart from a very long retention time. However, the vertical retort furnace of the Kinglor Metor process overcome the above drawbacks as they are tall and have a shorter length. Nevertheless, the vertical retorts frequently lead to jamming of the charge mix inside the retort. The retention time is also high and the thermal

efficiency is sufficiently low. All these factors eventually lead to a high cost of DRI production.
Therefore, in order to overcome the limitations of the above discussed system and the associated process for producing DRI, there exists a need to develop a system and a method for producing DRI which is economical and energy efficient.
SUMMARY
The present disclosure provides a system for producing direct reduced iron. The present system for producing direct reduced iron comprises a tunnel furnace, means for collecting the reduced iron and means for removing flue gases produced in the furnace. The tunnel furnace comprises a plurality of stationary saggers disposed inside the tunnel furnace, means for charging a particulate mixture into the plurality of stationary saggers and means for heating the tunnel furnace.
In an embodiment of the disclosure, the tunnel furnace is elevated above the ground by means of a plurality of pillars.
In an embodiment of the disclosure, the means for charging the furnace with the particulate mixture is disposed on side wall of the furnace and comprises a primary hopper to collect and store the particulate mixture, a conveyor belt to transport the particulate mixture from a point of supply to the primary hopper and a plurality of secondary hopper mounted in first trolley over the tunnel furnace to discharge the particulate mixture into the plurality of stationary saggers.
In an embodiment of the disclosure, the particulate mixture comprises an iron oxide source, a carbon source and an additive.

In an embodiment of the disclosure, the iron oxide source is selected from a group comprising mill scale green pellet, magnetite green pellet, hematite green pellet or a combination thereof.
In an embodiment of the disclosure, the carbon source is selected from a group comprising coal fine, coke fine, charcoal fine, sawdust or a combination thereof.
In an embodiment of the disclosure, the additive is at least one selected from a group comprising dolomite, limestone, marble fines, lime, bentonite, molasses or a combination thereof.
In an embodiment of the disclosure, the stationary saggers are made of stainless steel.
In an embodiment of the disclosure, the stationary saggers are provided with refractory lined cap at the top to avoid heat loss and emission of gases.
In an embodiment of the disclosure, the stationary saggers are provided with slide gate at the bottom to discharge the reduced iron.
In an embodiment of the disclosure, each stationary sagger is provided with an opening near the top to release the gases formed therein into the tunnel.
In an embodiment of the disclosure, the means for heating the furnace comprises a plurality of burners disposed on the side wall of the tunnel furnace in the longitudinal direction between the plurality of stationary sagger.
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In an embodiment of the disclosure, the plurality of burners is disposed on opposite side walls of the tunnel furnace in longitudinal direction and on each side wall of the tunnel furnace in the longitudinal direction the plurality of burners is disposed equidistantly.
In an embodiment of the disclosure, the means for collecting the reduced iron from the tunnel furnace comprises a trough for receiving the reduced iron and provided with a plurality of nozzle to quench the reduced iron by water jet, and a plurality of second trolleys for collecting the quenched reduced iron from the trough.
In an embodiment of the disclosure, the trough is disposed below the stationary saggers on the side walls of the tunnel furnace in the longitudinal direction.
In an embodiment of the disclosure, the means for removing the flue gases is a chimney disposed on the side wall at the outlet of the tunnel furnace.
The present disclosure also provides a process for producing direct reduced iron, comprising the steps of:
(a) charging a particulate mixture into a plurality of stationary saggers disposed inside a tunnel furnace,
(b) heating the tunnel furnace to a temperature in the range of 1100-1200°C for a retention time of 12-20 hours,

(c) collecting the reduced iron discharged from the stationary saggers,
(d) quenching the reduced iron obtained in step (c) by means of a water jet,
(e) collecting the quenched reduced iron obtained in step (d) in second trolley.
BRIEF DESCRIPTION OF FIGURES
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The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
Figure 1 illustrates the schematic view of a system of the present disclosure.
Figure 2a illustrates the top view of a tunnel furnace. Figure 2b shows the side view of the tunnel furnace shown in Figure 2a.
Figure 3a illustrates a sagger. Figure 3b shows the side view of the sagger shown in Figure 3a.
Figure 4 illustrates the feeding arrangement of sagger shown in Figure 3a, inside the tunnel furnace of Figures 2a & 2b.
Figure 5 illustrates the means for collecting the reduced iron from the system shown in Figure 1.
Figure 6 illustrates a process flow diagram of the process of the present disclosure.
DETAILED DESCRIPTION
While the embodiments in the disclosure are subject to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the figures and will be described below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
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It is to be noted that a person skilled in the art would be motivated from the present disclosure and modify various constructions of the system and its components for producing direct reduced iron, which may vary from system to system. However, such modification should be construed within the scope and spirit of the disclosure. Accordingly, the drawings show only those specific details that are pertinent to understand the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.
The terms “comprises”, “comprising”, or any other variations thereof used in the disclosure, are intended to cover a non-exclusive inclusion, such that an apparatus, system, assembly, mechanism that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such system, or assembly, or apparatus. In other words, one or more elements in a system or device proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system.
The following paragraphs describe the system of the present disclosure with reference to Figures 1 to 5. In the Figures, the same element or elements which have same functions are indicated by the same reference signs.
The terms such as upward, downward, vertical, horizontal, lower and upper used in the description are referred with respect to particular orientation of the system as shown in the figures of the present disclosure. Hence, such words should not be construed as limitation to the present disclosure, as the same may be varied depending on the orientation of the system.
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Figure 1 illustrates the schematic view of a system of the present disclosure. The system comprises a tunnel furnace (2) for producing sponge iron, means for collecting the sponge iron and means for removing flue gases produced in the tunnel furnace (2).
In an embodiment, the tunnel furnace (2) is of rectangular cross section and comprises a plurality of stationary sagger (8), means for charging a particulate mixture into the plurality of stationary saggers (8) and means for heating (9) the tunnel furnace (2). Referring to Figures 1, 2a and 2b, the tunnel furnace (2) extends primarily in the longitudinal direction. The plurality of stationary saggers (8) is disposed inside the tunnel of the furnace (2). The tunnel furnace (2) is elevated above the ground by means of a plurality of pillars (5) to provide an ease in discharging the products.
The stationary saggers (8) may be made up of oxidation resistant stainless steel such as but not exclusively of SS310 or SS310S or HK40. The material for saggers (8) is chosen such that it undergoes minimum physical deformation and can withstand the high reducing temperatures. Though, the thermal conductivity of the already existing silicon carbide saggers is higher than stainless steel, the chances of their breakage at high reducing temperatures are very high.
In an embodiment, the saggers (8) may have, but not limited to, a rectangular cross section. The rectangular saggers, as shown in Figures 3a and 3b, extend primarily in the vertical direction and are hollow from inside to accommodate a particulate mixture (14). Each sagger (8) has two opposing surfaces, an upper surface and a lower surface. The upper surfaces of the saggers (8) are provided with refractory lined cap to feed the particulate mixture (14). The lower surfaces of the saggers (8) are provided with slide gate to collect the reduced iron.
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In an embodiment, the particulate mixture (14) comprises an iron oxide source, a carbon containing source and an additive. The iron oxide source is an iron bearing pellet obtained after primary size reduction operation of iron ores. Such primary size reduction methods are well known to a person skilled in the art and can be chosen from a wide variety such as crushing, grinding, milling etc.
The iron oxide source may be selected from but not limited to mill scale green pellet, magnetite green pellet or hematite green pellet or a combination thereof. In an embodiment, the iron oxide source may be either pelletized to 5-20mm in size or briquetted. Lump ore of size 5-20mm can also be used for producing sponge iron.
The carbon containing source may be selected from but not limited to coal fine, coke fine, charcoal fine, sawdust or a combination thereof. In an embodiment, the carbon source is kept below 3mm size for better reaction kinetics. The additive may be selected from a group comprising dolomite, limestone, marble fines, molasses, bentonite or a combination thereof. The additives are used for desulphurization and to avoid sticking of DRI with sagger (8). The additives further facilitate smooth discharge of reduced iron from the saggers (8). The ratio of the iron oxide source to the carbon source is kept in the ratio ranging 1:1 to 1:1.5 by weight and depends on the fixed carbon of the carbon source.
In an embodiment, the stationary saggers (8) are provided with an opening (16) near the upper surface for outlet of gases produced due to reduction of iron containing source. The opening (16) can be of, but not limited to, circular, rectangular or any other shape. In an embodiment, the opening (16) is circular in shape and prevents choking of the stationary saggers (8) due to the gases formed inside, thereby preventing any pressure build-up resulting therefrom.
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The tunnel furnace (2) has two opposing side surfaces, first side surface and second side surface. In an embodiment, the means for charging the particulate mixture into the plurality of stationary saggers (8) is disposed on the first side surface. The said means for charging comprises a primary hopper (10), a conveyor belt (4) and a plurality of secondary hopper (11). As shown in Figure 1, the primary hopper (10) is disposed on the first side surface to collect and store the particulate mixture (14). The particulate mixture (14) is supplied to the primary hopper (10) by the conveyor belt (4) from the point of supply (1).
The means for heating (9) the tunnel furnace (2) comprises a plurality of burners. The tunnel furnace (2) has two opposing longitudinal side walls, first side wall and second side wall. As shown in figures 2a and 2b, the plurality of burner is disposed equidistantly on first and second side walls of the tunnel furnace (2). In an embodiment, the plurality of stationary saggers (8) is arranged in, but not exclusively, five horizontal rows and four vertical columns to form a matrix of plurality of stationary saggers (8) inside the tunnel of the furnace (2). Six such matrices are placed equidistantly inside the tunnel of the furnace (2) along the longitudinal direction. Each matrix of the plurality of stationary saggers (8) is placed between two burners on first and second side walls such that the flame does not hit the saggers (8) directly.
A plurality of secondary hopper (11) mounted in first trolley (12) over the tunnel furnace (2) discharge the particulate mixture (14) into the plurality of stationary saggers (8) from the primary hopper (10). As shown in Figure 4, five stationary saggers (8) of a matrix are filled with the particulate mixture (14) at once. Similarly, other stationary saggers (8) are charged with the particulate mixture (14).
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The carbonaceous fuel for the plurality of burners (9) can be but not limited to coal, gas oil, natural gas, etc. The choice of fuel may depend on different parameters such as ease of availability, calorific value, etc. In an embodiment, the carbonaceous fuel is coal. Before supplying the coal to the plurality of burners (9), it is stored temporarily in a coal hopper (7) fixed to the ground near the tunnel furnace. Preheated air and coal are charged to the plurality of burners (9) by means of an air blower. The burners (9) heat the tunnel furnace (2) to a temperature in the range of 900-1200°C, suitable for reducing the iron oxide source.
The stationary saggers (8) inside the tunnel furnace (2) get heated up and at temperature closer to 1200°C, the carbon from the carbon containing source reduces the iron oxide source to reduced iron. The reduction reaction occurs inside the stationary saggers (8) and results in byproduct gases such as but not limited to CO, CO2, etc. The byproduct gases continuously build inside the saggers (8) and fill the vacant space between the particulate mixture (14). This results in pressure built-up inside the sagger (8). In order to avoid this additional pressure built up, an opening (16) is provided near the upper surface of the saggers (8). The byproduct gases leaving the plurality of stationary saggers (8) from the opening now enter the tunnel and exit the furnace (2).
Referring to Figure 5, a means for collecting the reduced iron from the tunnel furnace (2) is provided. In an embodiment, the means comprises a trough (13) and a plurality of second trolleys (19). The trough (13) is disposed on the surface of the tunnel furnace (2) extending outwardly towards the ground. The trough (13) extends across the width of the tunnel furnace (2) and is slightly inclined towards the ground subtending a very small angle with the ground to allow the reduced iron to flow down. The reduced iron from the plurality of stationary saggers (8) is withdrawn
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from the lower surface of saggers (8) using the slide gate by means of a single screw mechanism, once the retention time of 12-20 hours has elapsed.
In an embodiment, the reduced iron exiting from the stationary saggers (8) is at temperature in the range of 1100-1200°C. This reduced iron is quenched to atmospheric temperature by means of a plurality of nozzles disposed equidistantly on the trough (13) in the longitudinal direction. The plurality of nozzle emits water jets which quench the reduced iron to atmospheric temperature. The water is supplied to the nozzle by means of a pump (18).
As shown in Figure 5, the reduced iron from the trough (13) is finally collected in the plurality of second trolleys (19). In an embodiment, the plurality of second trolley (19) run over rails disposed on the ground immediately below the inclined trough (13). The quenched iron collected in the plurality of second trolleys (19) is sent for further processing.
Large amount of flue gases are generated inside the tunnel furnace (2) due to burning of carbonaceous fuel and from the plurality of stationary sagger (8). Since these gases have very less or almost no calorific value, it is necessary to dispose of these gases. In an embodiment, the system of the present disclosure comprises a means for removing flue gases. The means for removing flue gases comprises a chimney (3). Referring to Figure 1, the chimney (3) is disposed on the second side surface of the tunnel furnace (2). Natural draft convection drives the flue gases from first side surface to the second side surface of the tunnel furnace (2). The natural draft accounts for the unidirectional flow of the flue gases inside the tunnel furnace (2).
It is evident from the above description that the present disclosure provides an economic system and a process for production of DRI or sponge iron. The
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effectiveness of reduction by the present disclosure can be illustrated by means of examples discussed below. The effectiveness of the system is illustrated by degree of metallization. The degree of metallization is defined below as:
From the above, it can be observed that higher the content of metallic iron in DRI, higher will be the degree of metallization. Thus, the degree of metallization gives an extent of reduction of the iron containing source. The present disclosure is capable of providing degree of metallization in the range of 95-99%.
EXAMPLES
The following examples are given by way of illustrations of the present invention and therefore should not be construed to limit the scope of the present invention.
Example 1:
Stainless steel sagger (SS310S) filled with mill scale green pellet having 5% internal coal and carbon source containing 50% coke and remaining 50% as coal with particle size below 3 mm in the ratio of 1:1 by volume was taken. About 10% dolomite fine was added along with mix carbon source. The stainless steel sagger is place inside the furnace and heated to a temperature of 1150°C. After the retention time of 15 hours, hot DRI was discharged directly on the trough, where it was quenched to atmospheric temperature. After drying and separation from char, DRI sample analysis was carried out for estimating the degree of metallization and metallic Fe.
The DRI produced above had a total content of Fe as 84.74% by weight, metallic Fe as 81.16% and a degree of metallization of 96%.
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Example 2:
Stainless steel sagger filled with Hematite green pellet and coal having particle size less than 3mm in the ratio of 1:1 by volume was taken. 5% by weight of limestone fine was added to the above mixture. The stainless steel sagger filled with the particulate mixture was placed inside the tunnel furnace and provided a retention time of 12 hours at an elevated temperature of 1200°C.
Once the above retention time elapsed, DRI was discharged over the trough where it was quenched to lower the temperature of the reduced iron to atmospheric condition. The quenched DRI was collected by means of second trolley and analyzed for degree of metallization.
The DRI produced above had a total content of Fe as 87.10% by weight, metallic Fe as 85.42% and a degree of metallization of 98%.
It is evident from the above examples that better degree of metallization is obtained using stationary saggers inside the tunnel furnace. This results in a better quality of DRI at low retention time. Moreover, it is also evident that the process of the present disclosure is capable of providing an effective reduction of iron to produce DRI or sponge iron. The present system and process require a shorter installation and commissioning time. The requirement of low maintenance cost, production cost and capital cost make the present disclosure highly economic.
LIST OF NUMERALS

Numeral Reference
1 Point of supply
2 Tunnel furnace
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3 Chimney
4 Conveyor belt
5 Pillar
6 Air blower
7 Coal hopper
8 Sagger
9 Means for heating
10 Primary hopper
11 Secondary hopper
12 First trolley
13 Trough
14 Particulate mixture
15 Refractory lined cap
16 Opening
17 Slide gate
18 Pump
19 Second trolley
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We Claim:
1. A system for producing direct reduced iron, comprising:
(a) a tunnel furnace, comprising:
(i) a plurality of stationary saggers disposed inside the tunnel furnace,
(ii) means for charging a particulate mixture into the plurality of stationary saggers, and
(iii) means for heating the tunnel furnace
(b) means for collecting the reduced iron, and
(c) means for removing flue gases produced in the furnace.

2. The system as claimed in claim 1, wherein the tunnel furnace is elevated above the ground by means of a plurality of pillars.
3. The system as claimed in claim 1, wherein the means for charging the furnace with the particulate mixture is disposed on side wall:

(a) a primary hopper to collect and store the particulate mixture,
(b) a conveyor belt to transport the particulate mixture from a point of supply to the primary hopper, and
(c) a plurality of secondary hoppers mounted in first trolley over the tunnel furnace to discharge the particulate mixture into the plurality of stationary saggers.

4. The system as claimed in claim 1, wherein the particulate mixture comprises an iron oxide source, a carbon source and an additive.
5. The system as claimed in claim 4, wherein the iron oxide source is selected from a group comprising mill scale green pellet, magnetite green pellet, hematite green pellet or a combination thereof.

6. The system as claimed in claim 4, wherein the carbon source is selected from a group comprising coal fine, coke fine, charcoal fine, sawdust or a combination thereof.
7. The system as claimed in claim 4, wherein the additive is at least one selected from a group comprising dolomite, limestone, marble fines, lime, bentonite, molasses or a combination thereof.
8. The system as claimed in claim 1, wherein the stationary saggers are made of stainless steel.
9. The system as claimed in claim 8, wherein the stationary saggers are provided with refractory lined cap at the top to avoid heat loss and emission of gases.
10. The system as claimed in claim 8, wherein the stationary saggers are provided with slide gate at the bottom to discharge the reduced iron.
11. The system as claimed in claim 8, wherein each stationary sagger is provided with an opening near the top to release the gases formed therein into the tunnel.
12. The system as claimed in claim 1, wherein the means for heating the furnace comprises a plurality of burners disposed on the side wall of the tunnel furnace in the longitudinal direction between the plurality of stationary saggers.
13. The system as claimed in claim 12, wherein the plurality of burners is disposed on opposite side walls of the tunnel furnace in longitudinal direction and on each side wall of the tunnel furnace in the longitudinal direction the plurality of burners is disposed equidistantly.
14. The system as claimed in claim 1, wherein the means for collecting the reduced iron from the tunnel furnace comprises:
(a) a trough for receiving the reduced iron and provided with a plurality of nozzles to quench the hot reduced iron by water jet, and

(b) a plurality of second trolleys for collecting the quenched reduced iron from the trough.
15. The system as claimed in claim 14, wherein the trough is disposed below the stationary saggers on the side walls of the tunnel furnace in the longitudinal direction.
16. The system as claimed in claim 1, wherein the means for removing the flue gases is a chimney disposed on the side wall at the outlet of the tunnel furnace.
17. A process for producing direct reduced iron, comprising the steps of:

(a) charging a particulate mixture into a plurality of stationary saggers disposed inside a tunnel furnace,
(b) heating the tunnel furnace to a temperature in the range of 1100-1200°C for a retention time of 12-20 hours,
(c) collecting the reduced iron discharged from the stationary saggers,
(d) quenching the reduced iron obtained in step (c) by means of a water jet,
(e) collecting the quenched reduced iron obtained in step (d) in second trolley;