BACKGROUND

[0001] This invention relates generally to a method for the recovery of iron. More particularly , the invention relates to a process for the recovery of iron from iron ore fines using hydrogen.

[0002] The beneficiation of iron ore fines is becoming increasingly important. Various methods for the recovery of iron from iron ore fines have been proposed; however, these methods typically make use of calibrated fines which are not readily available and are expensive to produce. One such method, known in the art as the IMBS process, involves the use of carbon as a reducing agent in a rotary kiln in order to produce a direct reduced iron (DRI) product. Due to the nature of the reductant used, carbon dioxide is produced as by-product, which has a negative impact on the environment.

[0003] Due to the need to control greenhouse gas emissions, the use of hydrogen as a reductant for fines has been proposed. One method, known in the art as FINMET®, is a direct reduction process that produces hot briquetted iron (HBI). The process is based on natural gas as the energy source, and steam reforming technology is applied for the production of the reducing gas. A series of fluidized bed reactors is used wherein the solid iron fines flow downward under gravity action from an upper to a lowermost reactor, while H ₂ -rich reducing gas flows upwards in a counter-current fashion. [0004] Another solution, known in the art as Circored™, is a hydrogen-based process for the direct reduction of fine ore. The Circored™ process applies a two-stage reactor configuration with a circulating fluidized bed followed by a bubbling fluidized bed downstream. This process failed when scaled up and the only industrial plant built was dismantled.

[0005] These hydrogen solutions typically use fluidized bed reactors. In these solutions, the reduction can only be realized when carried out in stages which are dependent on the specific degree of reduction required for each ore. There must also be a match in a close range between the gas velocity in the reactor and the particle size of the iron ore fines.

[0006] An object of the present invention is to provide an alternative method of processing iron ore fines using hydrogen to address, at least to some extent, the aforementioned problems.

SUMMARY OF THE INVENTION

[0007] The invention provides a method of recovering iron ore from iron ore fines using hydrogen, the method including the steps of: a) feeding iron ore fines with a particle size distribution of up to 3mm and hydrogen reducing gas into a rotary kiln furnace; and b) contacting the iron ore fines with the hydrogen reducing gas in the rotary kiln furnace at a temperature of up to 1450°C to produce a hot direct reduced iron ore product. [0008] The rotary kiln furnace may be a carbon steel kiln with a refractory lining.

Alternatively, the rotary kiln furnace may be a metallic alloy kiln.

[0009] The method may optionally include a first preliminary step of heating hydrogen gas in a process gas heater to a temperature of between 750°C to 900°C to provide a heated hydrogen gas stream.

[0010] The method may include a second preliminary step of partially combusting the heated hydrogen gas stream in the presence of oxygen to increase the temperature of the stream to up to 1450°C, thereby to produce a hydrogen rich reducing gas.

[0011] Preferably the oxygen and hydrogen are obtained from the hydrolysis of water.

[0012] The hydrogen rich reducing gas from the second preliminary step may be fed into the rotary kiln furnace such that it flows in a direction counter-current to the iron ore fines.

[0013] If the first preliminary step is not carried out, the temperature of the kiln may be maintained at temperatures of up to 1000°C through external heating of the kiln using suitable burners. In this instance, the hydrogen rich reducing gas from the second preliminary step may be fed into the rotary kiln furnace such that it flows in a direction co- current to the iron ore fines to ensure a high temperature is maintained in a FeO reduction zone of the furnace.

[0014] Reacted top gas, produced in the rotary kiln furnace, may be cleaned and quenched and returned to the first preliminary step or to the second preliminary step. Make-up hydrogen gas may be added as required. [0015] Iron ore fines which are not reduced in the rotary kiln furnace, and which are carried out by the reacted top gas, may be separated in a cyclone and recycled to the rotary kiln in step (a).

[0016] Preferably, the iron ore fines have a particle size distribution in the range of 500 micron to 3 mm.

[0017] The axial gas velocity of the hydrogen reducing gas in the furnace may be below the saltation velocity. The gas velocity may be in the range of 0.5 to 6 meters per second.

[0018] The rotary kiln furnace may include one or more lifters. The lifters may be of any suitable kind. The lifters lift the iron ore fines thereby to increase the heat and mass transfer between the iron ore fines and the reducing gases. The lifters cause the solids to move along a length of the rotary kiln furnace in a direction counter-current to the flow of the hydrogen rich reducing gas.

[0019] The invention further provides an installation for reducing iron ore fines having a particle size distribution of up to 3 mm in the presence of hydrogen reducing gas at a temperature of up to 1450°C, the installation including: a) a combustion chamber for combusting at least a portion of the hydrogen reducing gas in the presence of oxygen to provide a heated hydrogen rich reducing gas; b) a rotary kiln furnace having a housing with a first end and a second end, the housing being configured to rotate, a gas inlet to the housing at the first end and a gas outlet from the housing at the second end, an ore feed at a second end of the housing for receiving the iron ore fines and a discharge port at the first end of the housing for discharging directly reduced iron; c) a cleaning and quenching unit for treating reacted top gases removed from the housing; and d) a gas blower for recycling the cleaned and quenched hydrogen rich gases into the process gas heater and on to the combustion chamber.

[0020] A process gas heater may be provided for heating the hydrogen reducing gas prior to entering the combustion chamber to produce a pre-heated hydrogen gas stream. At least a portion of the preheated hydrogen gas stream may then be combusted in the combustion chamber. Alternatively, one or more burners may be provided for externally heating the housing of the furnace.

[0021] The housing of the rotary kiln furnace may include one or more lifters.

[0022] The rotary kiln furnace may be a carbon steel kiln with a refractory lining. Alternatively, the rotary kiln furnace may be a metallic alloy kiln. [0023] A cyclone may be used to separate the reacted top gases from unreacted iron ore fines carried out by the top gas from the housing.

[0024] The hot direct reduced iron ore fines may be sent to a melting furnace or may be converted to hot briquetted iron (HBI). [0025] In use of the installation, the heated hydrogen rich reducing gas is passed into the housing through the gas inlet and the iron ore fines are passed into the housing through the ore feed such that the hydrogen gas moves through the housing thereby to cause the reduction of the iron ore fines by the hydrogen reducing gas to produce a direct reduced iron ore product.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The invention is further described by way of examples with reference to the accompanying drawings in which:

Figure 1 is a schematic side view of a rotary kiln furnace used in a method of the invention according to one embodiment of the invention;

Figure 2 is a schematic side view of a rotary kiln furnace used in the method of the invention according to another embodiment of the invention;

Figure 3 is a schematic side view of a rotary kiln furnace used in the method of the invention according to yet another embodiment of the invention;

Figure 4 shows in block diagram form an installation used for recovering iron from iron ore fines according to a method of the invention;

Figure 5 shows in a block diagram form an installation used for recovering iron from iron ore fines according to a different embodiment of a method of the invention; and

Figure 6 is a cross-sectional view of the furnace in Figure 1 illustrating the movement of iron ore fines in the furnace. DESCRIPTION OF PREFERRED EMBODIMENTS

[0027] Figure 1 is a side view of a rotary kiln furnace 10 used in the method of the invention. The furnace 10 includes a housing 12 formed from carbon steel with a refractory lining 14 which encloses a reaction chamber 16. The housing has a first end 18 and a second end 20. A gas inlet 22 is provided at the first end 18 and a gas outlet 24 is provided at the second end 20.

[0028] An ore feed 26 is provided at the second end 20 of the housing 12 to feed iron ore fines into the reaction chamber 16. One or more lifters 28A, 28B, 28C...28N are provided in the reaction chamber 16 and are spaced circumferentially around an inner wall of the housing 12. A discharge port 30 is provided for discharging direct reduced iron (DRI) from the reaction chamber 16.

[0029] Figure 2 is a side view of a different embodiment of a rotary kiln furnace 10A used in the method of the invention. The furnace 10A includes a housing 12A formed from a metallic alloy material which encloses a reaction chamber 16A. The housing has a first end 18A and a second end 20A. A gas inlet 22A is provided at the first end 18A and a gas outlet 24A is provided at the second end 20A.

[0030] An ore feed 26A is provided at the second end 20A of the housing 12A to feed iron ore fines into the reaction chamber 16A. A discharge port 30A is provided for discharging direct reduced iron (DRI) from the reaction chamber 16A. One or more burners 32A, 32B, 32C are provided for externally heating the housing 12A according to requirement. [0031] Figure 3 is a side view of a rotary kiln furnace 10B used according to a different embodiment of the method of the invention. The furnace 10B includes a housing 12B formed from a metallic alloy material which encloses a reaction chamber 16B. The housing has a first end 18B and a second end 20B. A gas inlet 22B is provided at the second end 20B and a gas outlet 24B is provided at the first end 20B.

[0032] An ore feed 26B is provided at the second end 20B of the housing 12B to feed iron ore fines into the reaction chamber 16B. A discharge port 30B is provided for discharging direct reduced iron (DR!) from the reaction chamber 16B. One or more burners 34A, 34B, 34C...34N are provided for externally heating the housing 12B according to requirement.

[0033] The method can be optimised according to the furnace (10, 10A, 10B) selected for use in the installation. Figure 4 illustrates an installation 100, using the furnace 10, for recovering iron from iron ore fines according to a method of the invention.

[0034] In a first preliminary step, hydrogen gas 102 is heated in a process gas heater 104 using a suitable fuel 106 to a temperature of between 750°C to 900°C, preferably

800°C to form a heated hydrogen gas stream. Tables 1A, 1B and 1C below illustrate the mass and energy balance for this step.

Table 1A: Gas entering the Process Gas Heater

Table 1B: Fuel to the Process Gas Heater

Table 1C: Gas at the Process Gas Heater Outlet [0035] In the second preliminary step, the heated hydrogen gas stream from the first preliminary step is partially combusted 108 in the presence of oxygen 110 and the resultant hydrogen rich reducing gas, comprising hydrogen and water, is fed into the furnace 10 through the gas inlet 22. The reducing gas reaches a temperature of up to 1450°C. Tables 2A, 2B and 2C illustrate the mass and energy balance for this step.

Table 2A: Hydrogen rich gas entering the combustion chamber

Table 2B: Oxygen used for partial combustion

Table 2C: Hot reducing gas after partial combustion

[0036] In a reducing step 112, the heated hydrogen rich reducing gas 102 is fed into the rotary kiln 10 through the gas inlet 22 at a first end 18 of the furnace 10. Iron ore fines 114 are fed into the rotary kiln furnace 10 through the ore feed 26 at a second end 20 of the furnace 10.

[0037] As shown in Figure 3, the lifters 28A, 28B, 28C...28N, together with the rotation of the furnace 10 in a direction shown by the arrow A, cause the iron ore fines 114 to move in a direction towards the first end 18 of the housing 12. The hydrogen reducing gas 102 moves in a direction towards the second end 20 of the furnace 10 i.e., in a direction counter-current to the iron ore fines 114. The iron ore fines 114 are reduced by the hydrogen reducing gas to produce a direct reduced iron product 118 which is discharged through the discharge port 30.

[0038] The rotational aspect of the kiln 10 can be varied in a controlled way to assist in optimizing the reduction process. [0039] The mass and energy balance for the reducing step is set out in Tables 3A, 3B, 3C and 3D below.

Table 3A

Table 3B

Table 3C

Table 3D

[0040] Iron ore fines 116 not reduced in the reaction chamber 16 and carried out of the chamber 16 by reacted top gas are recovered through the use of a cyclone 118 and are recycled back to the ore feed 26 to be used in the reducing step 112.

[0041] Exhausted top gases from the reaction chamber 16 flow from the gas outlet 24 and are subject to a cleaning and quenching step 120. The cleaned and quenched gases are fed into a gas blower 122. Make-up hydrogen gas 102 is added to the process as required and the gases are passed back into the process gas heater 104 in the first preliminary step.

[0042] The hot direct reduced iron 124 may be used directly in a melting furnace, or to make a hot briquetted iron (HBI) product.

[0043] Figure 5 illustrates an installation 100A, using the furnace 10A or 10B, for recovering iron from iron ore fines according to a method of the invention.

[0044] If the furnace 10A is used, in a first preliminary step, hydrogen gas 102A is heated in a process gas heater 104A using a suitable fuel 106A, derived from a pressure bleed from the installation to a temperature of between 750°C to 900°C, preferably 800°C to form a heated hydrogen gas stream.

[0045] In a second preliminary step, the heated hydrogen gas stream 102A from the first preliminary step is partially combusted 108A in the presence of oxygen 110A and the resultant hydrogen rich reducing gas, comprising hydrogen and water, is fed into the furnace 10A through the gas inlet 22A. The reducing gas reaches a temperature of up to 1450°C.

[0046] In a reducing step 112A, the heated hydrogen rich reducing gas 102A is fed into the rotary kiln 10A through the gas inlet 22A at a first end 18A of the furnace 10A. Iron ore fines 114A are fed into the rotary kiln furnace 10A through the ore feed 26A at a second end 20A of the furnace 10A. The rotation of the furnace 10A causes the iron ore fines 114A to move in a direction towards the first end 18A of the housing 12A. The hydrogen reducing gas 102A moves in a direction towards the second end 20A of the furnace 10A i.e., in a direction counter-current to the iron ore fines 114A. The reduction of the iron ore fines, particularly in the FeO zone, is facilitated through the external heating of the furnace 10A using one or more suitable burners 32A, 32B, 32C at the first end 18A to maintain the temperature at approximately 1000°C. The iron ore fines 114A are reduced by the hydrogen reducing gas to produce a direct reduced iron product 124A which is discharged through the discharge port 30A.

[0047] If the rotary kiln 10B is used, hydrogen gas 102A is partially combusted 108A in the presence of oxygen 110A and the resultant hydrogen rich reducing gas, comprising hydrogen and water, is fed into the furnace 10B through the gas inlet 22B at a second end 20B of the furnace 10B. The iron ore fines 114A are fed into the rotary kiln furnace 10B through the ore feed 26B at a respective second end 20B of the furnace 10B.

[0048] The rotation of the furnace 10B causes the iron ore fines 114A to move in a direction towards the first end 18B of the housing 12B. The hydrogen reducing gas 102A moves in a direction towards the first end 18B of the furnace 10B i.e., in a direction co- current to the iron ore fines 114A. The reduction of the iron ore fines is facilitated through the external heating of the furnace 10B using one or more suitable burners 34A, 34B, 34C...34N to maintain the temperature at approximately 1000°C. The iron ore fines 114A are reduced by the hydrogen reducing gas to produce a direct reduced iron product 124A which is discharged through the discharge port 30A. [0049] The use of a rotary kiln furnace in the method of the invention allows the reduction of iron ore fines to take place in a single step. The partial combustion of the hydrogen gas also allows high temperatures to be reached i.e., of the order of 1450°C, which increases the speed of the reaction and a shorter residence time in the reactor is therefore required. Due to the efficiency of the process, iron ore fines having a smaller particle distribution i.e., from 500 microns to 3mm can be used. The use of a renewable hydrogen energy source means that there are zero carbon emissions, and the method is therefore a sustainable solution for iron ore reduction.