Method and system for increasing the carbon content of direct reduced iron in a reduction furnace

Abstract

A method for producing direct reduced iron with increased carbon content, comprising: providing a carbon monoxide-rich gas stream and dividing the carbon monoxide-rich gas stream into at least two separate carbon monoxide-rich gas streams; providing a hydrocarbon-rich gas stream and dividing the hydrocarbon-rich gas stream into at least two separate hydrocarbon-rich gas streams; blending one of the carbon monoxide-rich gas streams with one of the hydrocarbon-rich gas streams to form a mixed carburizing gas stream; blending another of the at least two separate carbon monoxide-rich gas streams with another of the at least two separate hydrocarbon-rich gas streams to form a different mixed carburizing gas stream; conveying each of the mixed carburizing gas streams with different compositions to a transition zone of a direct reduction furnace, and exposing partially or fully reduced iron oxides to the mixed carburizing gas streams to increase the carbon content of the resulting direct reduced iron to greater than 4.5 weight percent.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present invention claims priority to co-pending U.S. Provisional Patent Application No. 62 / 993,771, filed on March 24, 2020, and entitled “MIDREX PROCESS UTILIZING EXTENDED ADJUSTABLE CARBON TECHNOLOGY,” the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present invention relates generally to the fields of direct reduced iron (DRI) and steelmaking. More specifically, the present disclosure relates to methods and systems for increasing the carbon content of DRI in a direct reduction (DR) facility, and more particularly to direct reduction (DR) methods and systems capable of producing carbon in excess of about 4.5 wt. % DRI. Background Art

[0004] Direct reduced iron (DRI), commonly referred to as sponge iron, is typically produced by the reaction of iron ore in a moving bed or vertical reactor in a reactive gas stream containing a reducing agent such as H2 and CO. In addition to iron-containing waste and pig iron in steel production, such DRI products can also be used as a source of low residual iron, mainly through electric arc furnaces (EAFs) in steelmaking facilities. EAFs utilize electric arcs to melt the charged material, typically accompanied by oxygen injection to burn impurity carbon and Fe3C (if present). When oxygen is injected into the EAF, the partial or complete combustion of carbon using oxygen provides a uniform internal energy source for the EAF. In addition, the conversion of Fe3C to iron and carbon is an exothermic reaction, which improves the thermal efficiency of the EAF. Therefore, the carbon content of DRI can be interpreted as an energy source, and this energy is ultimately utilized in the EAF when the DRI is melted.

[0005] Current electric arc furnace (EAF) technology relies on scrap metal or direct reduction (DR) grade ore supply to minimize the production loss to slag. With the potential ore supply reduction, DR grade ore may be limited in the future. The EAF of the state of the art produces steel with low carbon content, typically below 0.35% by weight in carbon steel. This means that some DR devices (DR plants, DR plants) do not have to produce high carbon. If a lower grade iron source is used, the increased slag amount leads to a higher iron loss to the slag, which may adversely affect the overall economy and benefits of the process. In the future, it may be necessary to limit the iron loss to the slag by changing the process conditions in the melter. One way to achieve this is to have a higher reducing environment in the melter by adding more carbon to DRI. Today's steelmakers are always looking for high carbon iron units such as pig iron or molten iron (hot metal liquid, hot metal) from blast furnaces to provide them with the carbon they need to compensate for their power consumption. The carbon in the iron raw material to the melter can be converted using the oxygen blowing practice in steelmaking to release heat energy in the melting step. This energy release forms CO and some CO2. By controlling the oxygen injection, the steelmaker can control the CO / CO2 ratio in the atmosphere above the molten bath to keep it reducing for iron. Steelmakers use this energy and chemical composition in the melter to reduce the electrical input required to melt iron without carbon (as is the case with steel scrap). Melters that melt steel scrap require carbon units to maintain a reducing atmosphere in the melter and provide additional energy for melting. High carbon iron units are the most desirable because they provide the greatest carbon gain per unit of high carbon iron material. It allows EAF steelmakers to maximize the use of steel scrap in the melter charge. With this growing demand from steelmakers for higher and higher carbon iron units, there is a need to achieve greater carbon in the DRI from the DR unit.

[0006] Carbon can be added to DRI in the DR process by a carburizing reaction or a combination of carburizing reactions in a countercurrent DR reactor. The carburizing reactions that can be utilized in the DR process are:

[0007] (1) Boudouard reaction

[0008] (2) Water-Carbon Reaction

[0009] (3) Hydrocarbon Cracking

[0010] And each of these carburization reactions is catalyzed in the presence of metallic iron. In each of the carburization reactions (1)-(3), the resulting carbon form can be graphite carbon or cementite Fe3C as shown in these equations. Both carbon forms are present in the DRI product from the DR reactor.

[0011] As detailed in prior U.S. Patent No. 10,508,314, also to Midrex Technologies, Inc., and entitled "METHODS AND SYSTEMS FOR INCREASING THE CARBON CONTENT OF SPONGE IRON IN A REDUCTION FURNACE," the contents of which are incorporated herein by reference, the current practice of adding carbon to DRI in a reduction reactor is via the cracking of hydrocarbons by reaction (3) in a region of the reactor known as the transition zone. This region is located just below the bustle area where the primary reducing gas stream is introduced, and extends downward to the top of the discharge or cooling zone of the DR reactor. The system proposed in the above-mentioned patent makes the transition zone more carburized by adding a CO-rich gas to be mixed with a hydrocarbon gas (typically natural gas), thereby resulting in a single mixed gas stream entering the transition zone to create a more carburizing and less endothermic reaction environment, thereby increasing the carbon content in the DRI while retaining heat energy within the descending reactor charge.

[0012] The transition zone in a cold discharge direct reduced iron (CDRI) unit has a large carburizing potential due to the large amount of thermal energy stored in the DRI that must be removed before the DRI can be discharged to the atmosphere. In a CDRI unit, there is 130-140 kcal / kg of DRI energy to be removed before discharge. Much of this energy can be used to fuel the cracking reactions that are typically used to carburize the DRI via injection of natural gas into the transition zone.

[0013] In a hot discharge direct reduced iron HDRI or hot briquetted iron HBI unit, the minimum temperature that must be maintained in the hot product to support downstream processing is significantly greater than in a CDRI unit. These significantly higher discharge temperature requirements reduce the available heat that can be used to support carburization in the transition zone to a range of about 13.5-18.5 kcal / kg DRI. This is almost a tenth the energy reduction compared to a CDRI unit. This is an important reason why the carbon content from HDRI and HBI units is much lower than that of a CDRI unit, and the demand from steelmakers is to produce higher carbon products to more efficiently support downstream steelmaking operations.

[0014] Thus, while prior teachings can provide for increasing the carbon content in DRI to as high as 3.5 wt%, there are limitations, such as thermal limitations and equilibrium limitations. In order to achieve higher carbon levels approaching and even exceeding about 4.5 wt%, which is a significant advantage, new methods and systems are needed. Thus, regardless, what is still needed in the art is a direct reduction (DR) method and system that is capable of producing carbon in DRI in excess of about 4.5 wt%. Summary of the invention

[0015] Embodiments of the present invention improve upon existing methods and practices for carburizing DRI, especially in HDRI or HBI units. The challenges mentioned previously focus on the full use of available heat within the transition zone of a nearly adiabatic system. Only heat losses through the walls of the shaft furnace prevent it from being completely adiabatic, and these heat losses are relatively insignificant as they fall within the range of <1% of the thermal energy in the transition zone.

[0016] This prior practice, while beneficial, can only do so much in terms of optimizing and utilizing the carburizing potential within the transition zone. Embodiments of the present invention advantageously provide even greater carburizing potential by increasing the potential gas flow that can be handled within the transition zone and increasing both the gas-solid contact area and gas chemical composition distribution at higher temperatures for enhanced DRI carburizing.

[0017]

[0013] Thus, according to embodiments, provided herein are direct reduction (DR) methods and systems that are advantageously capable of producing carbon in excess of about 4.5 wt. % in DRI.

[0018] According to an embodiment, the present invention provides a method for producing direct reduced iron with increased carbon content. The method includes: providing a carbon monoxide-rich gas stream and dividing the carbon monoxide-rich gas stream into at least two separate carbon monoxide-rich gas streams; providing a hydrocarbon-rich gas stream and dividing the hydrocarbon-rich gas stream into at least two separate hydrocarbon-rich gas streams; blending one of the carbon monoxide-rich gas streams with one of the hydrocarbon-rich gas streams to form a mixed carburizing gas stream; blending another of the at least two separate carbon monoxide-rich gas streams with another of the at least two separate hydrocarbon-rich gas streams to form a different mixed carburizing gas stream; transporting each of the mixed carburizing gas streams with different compositions to a transition zone of a direct reduction furnace, and exposing partially or fully reduced iron oxides to the mixed carburizing gas stream to increase the carbon content of the resulting direct reduced iron to greater than about 4.5 weight %. The method may also include: dividing the carbon monoxide-rich gas stream into a first carbon monoxide-rich gas stream, a second carbon monoxide-rich gas stream, and a third carbon monoxide-rich gas stream; dividing the hydrocarbon-rich gas stream into a first hydrocarbon-rich gas stream, a second hydrocarbon-rich gas stream, and a third hydrocarbon-rich gas stream; mixing the first carbon monoxide-rich gas stream with the first hydrocarbon-rich gas stream in a first mixer to form a first mixed carburizing gas stream; mixing the second carbon monoxide-rich gas stream with the second hydrocarbon-rich gas stream in a second mixer to form a second mixed carburizing gas stream; mixing the third carbon monoxide-rich gas stream with the third hydrocarbon-rich gas stream in a third mixer to form a third mixed carburizing gas stream; each of the first mixed carburizing gas stream, the second mixed carburizing gas stream, and the third mixed carburizing gas stream having different compositions is transported to a transition zone of a direct reduction furnace, and partially or fully reduced iron oxides are exposed to the first mixed carburizing gas stream, the second mixed carburizing gas stream, and the third mixed carburizing gas stream to increase the carbon content of the resulting direct reduced iron to greater than about 4.5 weight percent. Providing a carbon monoxide rich gas stream may include initially providing one of the reformed gas streams from the reformer, and the carbon monoxide rich gas stream is directed from a carbon monoxide recovery unit, the carbon monoxide recovery unit forming a portion of the carbon monoxide rich gas stream and the H2 rich exhaust gas stream. The transition zone may include a plurality of tiers of equal height within the transition zone, and each tier includes a set of nozzles, and wherein each of the mixed carburizing gas streams is introduced into a separate tier of the transition zone via the set of nozzles at each tier. The nozzles at each tier for introducing the mixed carburizing gas stream may be arranged in a circumferential ring of the same number of nozzles at the bottom of each tier.The peripheral ring may include about 16 to 28 nozzles. The nozzle may be single valve controlled or manifold valve controlled, wherein each manifold has no more than 4 nozzles. The nozzle may be closed or opened and coordinated to maximize the contact area with the hottest DRI. For each layer, a separate mixer may be used to introduce each of the mixed carburizing gas streams into a separate layer of the transition zone with a different composition for each layer. For each layer, a separate preheater may be used to preheat each of the mixed carburizing gas streams to a different temperature. The preheating temperature may be in the range of ambient temperature to 400° C. Each of the mixed carburizing gas streams may have a different composition. The transition zone may include multiple layers stacked vertically, and each of the mixed carburizing gas streams may be introduced into a separate layer. The total height of the transition zone, typically in the range of 1.0 m-3.0 m, will increase by more than 0.5 m, for example, reaching a height of 1.5 m-3.5 m, to allow for sufficient volume for the effective implementation of the layer arrangement.

[0019] In addition, according to an embodiment, a direct reduction shaft furnace includes: a reduction zone; a transition zone, wherein the transition zone has a plurality of vertically stacked layers, and each layer is configured to receive a separate flow of a mixed carburizing gas flow; and a cooling zone located below the transition zone, wherein the reduced iron is partially or completely exposed to the mixed carburizing gas flow to increase the carbon content of the obtained direct reduced iron to greater than about 4.5% by weight. The transition zone may include multiple layers of equal height within the transition zone, and each layer includes a set of nozzles (an arrangement of nozzles), and wherein the furnace is configured to receive each of the mixed carburizing gas flows in the individual layers of the transition zone via the set of nozzles at each layer. The nozzles at each layer may be configured in a peripheral ring of the same number of nozzles at the bottom of each layer. The peripheral ring may include about 16 to 28 nozzles. The nozzles may be single valve controlled or manifold valve controlled, wherein each manifold does not exceed 4 nozzles. The furnace may be configured to receive each of the mixed carburizing gas flows introduced into the individual layers of the transition zone with different compositions. Each layer may comprise a different composition and typically the total height of the transition zone, which is in the range of 1.0m-3.0m in height, will increase by more than 0.5m, for example to a height of 1.5m-3.5m, to allow sufficient volume for efficient implementation of the layer arrangement. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention is illustrated and described herein with reference to the several drawings, wherein like reference numerals are used to refer to like systems / components / method steps where appropriate, and wherein:

[0021] Figure 1 is a schematic diagram showing an exemplary embodiment of the direct reduction (DR) process of the present invention for increasing the carbon content of DRI, wherein a formulated carburizing gas mixture is introduced into a direct reduction shaft furnace via a three-mixer, three-layer peripheral gas injection system in an extended transition zone region;

[0022] Figure 2 is a schematic diagram showing another exemplary embodiment of the direct reduction (DR) process of the present invention for increasing the carbon content of DRI, wherein a formulated carburizing gas mixture is introduced into a direct reduction shaft furnace via a three-mixer, three-preheater, three-layer peripheral gas injection system in the extended transition zone region;

[0023] Figure 3 is a schematic diagram showing yet another exemplary embodiment of the direct reduction (DR) process of the present invention for increasing the carbon content of DRI, wherein a formulated carburizing gas mixture is introduced into a direct reduction shaft furnace in the extended transition zone region via a two-mixer, two-layer peripheral gas injection system; and

[0024] Figure 4 is a schematic diagram showing another exemplary embodiment of the direct reduction (DR) process of the present invention for increasing the carbon content of DRI, wherein a formulated carburizing gas mixture is introduced into a direct reduction shaft furnace in the extended transition zone region via a two-mixer, two-preheater, two-layer peripheral gas injection system. DETAILED DESCRIPTION

[0025] Embodiments of the present invention advantageously improve existing methods and systems for increasing the carbon content of direct reduced iron (DRI). For example, in some prior art, in the case of a single peripheral injection system for introducing all carburizing gas mixtures at the bottom of the transition zone, the carburizing gas passes quickly from the outer wall of the reactor and merges to produce a single column flowing upward in the center of the reactor. Although this geometry / process disclosed in the above teaching of U.S. Patent No. 10,508,314 and now also generally referred to as adjustable carbon technology (Adjustable Carbon Technology, ACT) is beneficial, it can be improved, especially with respect to the reaction system, because the gas has a limited heat transfer contact area and metal carburizing surface area. A practice in the transition zone injection is to introduce hydrocarbon gas through a minimum number (~8) of paired grouped nozzles (positioned at 90 ° intervals). These nozzles supply a very small portion of the total area of ​​the zone that actually contacts the gas. This may cause some local supercooling, which may inhibit the kinetics of the carburizing reaction in this injection stream.

[0026] It has been determined herein that it is impractical to increase the number of nozzles on the periphery only. The transition zone gas is introduced into the DR reactor by the tuyere passing through the refractory wall of the reactor. These tuyere are in contact with or exposed to the thermal radiation from the charge itself of about 700-860°C. The system is limited by the requirement for keeping most of the heat energy already present in the charge in terms of how much total gas flow can be injected into the reactor. However, increasing the number of nozzles on the periphery to increase the contact area will require one of two adjustments (either of which is impractical). The first is to increase the number of nozzles in the same size. This will produce a significant decrease in the mass velocity in each nozzle, thereby causing the nozzle to become hotter. Hotter nozzle tips cause premature activation of the carburizing reaction in the nozzle, thereby causing nozzle clogging. Second, increasing the number of nozzles and reducing their diameter to maintain sufficient cooling speed in the nozzle causes the nozzle diameter to be too small, and whenever the nozzle does not need to work and the reactor is blocked by metallized iron fines when running.

[0027] Thus, embodiments of the present invention advantageously improve upon existing methods and practices for carburizing DRI, particularly in HDRI or HBI plants. The challenges previously mentioned focus on the full use of available heat within the transition zone of a nearly adiabatic system. Only heat losses through the walls of the shaft furnace prevent it from being completely adiabatic, and these heat losses are relatively insignificant as they fall within the range of <1% of the thermal energy in the transition zone.

[0028] This prior practice, while beneficial, can only do so much in terms of optimizing and utilizing the carburizing potential within the transition zone. Embodiments of the present invention advantageously provide even greater carburizing potential by increasing the potential gas flow that can be handled within the transition zone and increasing both the gas-solid contact area at higher temperatures and the gas chemical composition distribution for enhanced DRI carburizing.

[0029] For example, and as further explained below, embodiments of the present invention advantageously provide an elongated / extended transition zone that is longer than the length of the furnace below the furnace belly by > about 0.5 m; the height of the transition zone, which is typically in the range of 1.0 m-3.0 m in height, will be increased by more than 0.5 m to provide the additional volume required to support the multi-layer gas injection system to enhance carburization. The CO-rich gas from the ACT unit is delivered to at least two or three layers of the gas mixer. Therefore, according to an embodiment, the above-mentioned adjustable carbon technology (ACT), i.e., a process for producing a CO-rich stream and mixing it with, for example, natural gas, is partially improved to adopt multiple injection points into the extended transition zone. The above-mentioned mixer is ratio-controlled to provide a blended mixing ratio of CO-rich gas and hydrocarbon gas. Each layer has an optimized gas mixture ratio. The upper layer is richer in hydrocarbons because the temperature distribution there is hotter and hydrocarbon cracking is more promoted in the higher temperature range (about 800-850°C). The lower layer is a significantly more CO-rich gas mixture because the exothermic nature of the CO carburizing reactions makes them more favorable at a lower temperature range (about 700-750°C). The middle layer is optimized for a more balanced ratio between CO and cracking reactions because it operates in a temperature zone between the other two (about 750-800°C). The layered gas injection system with independent mixers allows the distribution of gas chemistry to be applied to match the temperature distribution.

[0030] In addition, according to an embodiment, each layer of gas injection is then composed of a full perimeter group of nozzles (optimally, 16-28 nozzles per layer) that penetrate the shaft furnace wall to introduce gas into the transition zone. Each nozzle ring is located at the bottom of the section of the transition zone it serves. The countercurrent nature of the operation of the shaft furnace makes this the optimal location for each nozzle ring for each layer of reaction. The nozzles on each ring are either single valve controlled or controlled via sub-manifold valves, with each manifold serving no more than 4 nozzles. This allows gas injected at any level to be selectively introduced at a specified area on the periphery of the transition zone or to the entire periphery if desired. Selectively adding gas at a specified area of ​​the transition zone can provide additional temperature profile control for the reaction, as well as more refined control of the discharge temperature from the transition zone to meet the operating objectives of the device.

[0031] Therefore, according to the embodiment, a method for producing direct reduced iron is realized, which uses a unique and adjusted arrangement of a CO-rich gas stream and a hydrocarbon-rich gas stream with a specified gas composition and temperature distribution to produce direct reduced iron with a carbon content of >4.5% by weight. For example, according to the embodiment, using an extended transition zone and a multi-layer carburizing gas injection system, the reaction conditions along the length of the transition zone can be controlled to optimize the desired carburizing reaction. Each of these layers can have a peripheral, independently valve-controlled or sub-manifold valve-controlled nozzle arrangement to further optimize the contact area and temperature distribution of the transition zone. According to the embodiment, such a method and system provide a three-dimensional control scheme designed to provide operational and optimization flexibility.

[0032] Thus, one objective of embodiments of the present invention, namely controlling gas and temperature profiles to enhance carburizing potential, is advantageously achieved while not violating the minimum discharge temperature requirements inherent in HDRI and HBI DR units.

[0033] Now refer specifically to Figure 1 In an exemplary embodiment, the method 20 of the present invention comprises passing a syngas or reformed gas stream 1 through an ACT unit C for the purpose of separating CO from the remainder of the syngas / reformed gas. It is noted that the reformed gas stream 1 is derived from a reformer unit (not shown) of any design at near ambient temperature, such as a catalytic reformer (e.g., a tubular reformer), a non-catalytic reformer (e.g., a partial oxidation reactor), or even a combined reformer (e.g., an auto-thermal reformer or a two-stage reformer), or any other reducing gas generating unit capable of producing a CO-containing gas having a relatively high CO / CO2 ratio). As further described below, an optional cooler / quencher (not shown) may also be employed. Preferably, the reformed gas stream 1 contains at least 20.0 mol% CO.

[0034] like Figure 1As further shown, the reformed gas stream 1 enters the ACT unit C. As mentioned above, the U.S. Patent Application No. 10,508,314 mentioned above (the contents of which are incorporated herein by reference) discloses adjustable carbon technology (ACT) geometry / processing, and as described herein, the embodiments of the present invention improve this technology. Therefore, the characteristics of the ACT unit C will be briefly described below. Generally, the ACT unit C can adopt the cooler / quencher mentioned above. The cooler / quencher can utilize direct contact cooling, indirect contact cooling, refrigeration cooling, etc. During cooling, the reformed gas may lose a portion of its water content, which in turn improves the carburization potential of the reformed gas. The cold / dry reformed gas optionally flows through a compressor that can increase its pressure (e.g., to 15 barg) because most separation / adsorption methods work best at higher pressures. During compression, the gas loses even more water, resulting in even further improved carburization potential. After optional temperature adjustment, the compressed gas flows to the system of the membrane module for CO recovery. Any other kind of CO recovery unit / mechanism such as PSA / VPSA / TSA, refrigeration, etc. may also be employed.

[0035] The H2-rich stream 13 (rejected gas from the CO recovery unit of the ACT unit C) can be sent back, for example, as a recycle to be used elsewhere in the process loop, such as as fuel, cooling gas, synthesis gas or process gas in different parts of the DR unit, or it can be exported to another facility.

[0036] like Figure 1 As shown and as further described below, the CO-rich stream 2 leaving the ACT unit C arrives at a meeting point 15, which divides the stream into a first CO-rich stream 7, a second CO-rich stream 8 and a third CO-rich stream 9, and allows them to enter three separate gas mixers, namely a first gas mixer D, a second gas mixer E and a third gas mixer F, respectively.

[0037] like Figure 1 As shown, high hydrocarbon gas (hydrocarbon-rich gas, such as natural gas) is introduced through a hydrocarbon-rich gas stream 3, which is divided into three independently controlled streams, namely a first hydrocarbon-rich gas stream 4, a second hydrocarbon-rich gas stream 5 and a third hydrocarbon-rich gas stream 6, which also enter gas mixers D, E and F respectively.

[0038] Note also that, optionally, if the hydrocarbon-rich gas stream 3 is wet, one or more dehumidification units (not shown) may be used to dry the gas to inhibit decarbonization reactions. Optionally, if the hydrocarbon-rich gas stream 3 contains significant amounts of sulfur compounds, a desulfurization unit (not shown) may be used to reduce and control the total sulfur content, for example, to less than 100 ppm.

[0039] The first hydrocarbon-rich gas stream 4 , the second hydrocarbon-rich gas stream 5 and the third hydrocarbon-rich gas stream 6 are blended with the first CO-rich stream 7 , the second CO-rich stream 8 and the third CO-rich stream 9 , respectively, and then introduced into the DR furnace A.

[0040] The resulting mixed carburizing gas streams, each having a formulated composition based on the ratio control of the gas mixer steps, exit gas mixers D, E and F as first mixed carburizing gas stream 12, second mixed carburizing gas stream 11 and third mixed carburizing gas stream 10, respectively.

[0041] like Figure 1 As further shown, the first mixed carburizing gas stream 12, the second mixed carburizing gas stream 11 and the third mixed carburizing gas stream 10 are then introduced into the transition zone B of the furnace A through a set of peripheral nozzles located at the bottom of each layer of the transition zone B, as shown in FIG. Figure 1 As shown, the transition zone B includes a first layer, a second layer and a third layer, which are layers B-1, B-2 and B-3, respectively. The nozzles are individually valve-controlled, or valve-controlled in a sub-manifold arrangement (each sub-manifold is preferably grouped with no more than 4 nozzles). This provides chemical composition and thermal distribution control, which can achieve the carburizing potential of the transition zone B from the maximum 3.5 wt. % carbon in the DRI taught by conventional ACT to > 4.5 wt. % carbon in the DRI. More particularly, according to an embodiment, each layer of gas injection is composed of all peripheral nozzle groups (rings) 30, 32, 34 (optimally, 16-28 nozzles per layer), which pass through the vertical furnace wall to introduce gas into the transition zone B. Each nozzle ring 30, 32, 34 is located at the bottom of the section of the transition zone B it serves. The countercurrent characteristics of the operation of the vertical furnace A make this the best position for each nozzle ring 30, 32, 34 for each layer of reaction. The nozzles on each ring are either individually valve controlled or controlled via sub-manifold valves, with each manifold serving no more than 4 nozzles. This allows gas injected at any level to be selectively introduced at specified areas on the circumference of transition zone B or to the entire circumference if desired. Selective addition of gas at specified areas of transition zone B can provide additional temperature profile control for the reaction, as well as finer control of the discharge temperature from transition zone B to meet the operating goals of the unit.

[0042] Now refer to Figure 2In another exemplary embodiment, the method 22 of the present invention includes passing the synthesis gas or reformed gas stream 1 through an ACT unit C for the purpose of separating CO from the rest of the synthesis gas / reformed gas. It is noted that the reformed gas stream 1 comes from a reformer unit (not shown) of any design at near ambient temperature, such as a catalytic reformer (e.g., a tubular reformer), a non-catalytic reformer (e.g., a partial oxidation reactor) or even a combined reformer (e.g., an auto-thermal reformer or a two-stage reformer), or any other reducing gas generating unit capable of producing a CO-containing gas with a relatively high CO / CO2 ratio). As further described below, an optional cooler / quencher (not shown) may also be employed. Preferably, the reformed gas stream 1 contains at least 20.0 mol% CO.

[0043] like Figure 2 As further shown, the reformed gas stream 1 enters the ACT unit C. As mentioned above, the adjustable carbon technology (ACT) geometry / processing is disclosed in the aforementioned U.S. Patent Application No. 10,508,314, and as described herein, the embodiments of the present invention improve this technology. Therefore, the features of the ACT unit C will be briefly described below. Typically, the ACT unit C can adopt the aforementioned cooler / quencher. The cooler / quencher can utilize direct contact cooling, indirect contact cooling, refrigeration cooling, etc. During cooling, the reformed gas may lose a portion of its water content, which in turn improves the carburization potential of the reformed gas. The cold / dry reformed gas optionally flows through a compressor that can increase its pressure (e.g., to 15 barg) because most separation / adsorption methods work best at higher pressures. During compression, the gas loses even more water, resulting in even further improved carburization potential. After optional temperature adjustment, the compressed gas flows to a system of membrane modules for CO recovery. Any other type of CO recovery unit / mechanism, such as PSA / VPSA / TSA, refrigeration, etc., can also be adopted.

[0044] The H2-rich stream 13 (exhaust gas from the CO recovery unit of ACT unit C) can be sent back, for example, as a recycle to be used elsewhere in the process loop, such as as fuel, cooling gas, synthesis gas or process gas in different parts of the DR unit, or it can be exported to another facility.

[0045] like Figure 2 As shown and as further described below, the CO-rich stream 2 leaving the ACT unit C arrives at a meeting point 15, which divides the stream into a first CO-rich stream 7, a second CO-rich stream 8 and a third CO-rich stream 9, and allows them to enter three separate gas mixers, namely a first gas mixer D, a second gas mixer E and a third gas mixer F, respectively.

[0046] like Figure 2 As shown, high hydrocarbon gas (hydrocarbon-rich gas, such as natural gas) is introduced through a hydrocarbon-rich gas stream 3, which is divided into three independently controlled streams, namely a first hydrocarbon-rich gas stream 4, a second hydrocarbon-rich gas stream 5 and a third hydrocarbon-rich gas stream 6, which also enter gas mixers D, E and F respectively.

[0047] It should also be noted that, optionally, if the hydrocarbon-rich gas stream 3 is wet, one or more dehumidification units (not shown) may be used to dry the gas to inhibit decarbonization reactions. Optionally, if the hydrocarbon-rich gas stream 3 contains significant amounts of sulfur compounds, a desulfurization unit (not shown) may be used to reduce and control the total sulfur content, for example, to less than 100 ppm.

[0048] The first hydrocarbon-rich gas stream 4 , the second hydrocarbon-rich gas stream 5 and the third hydrocarbon-rich gas stream 6 are blended with the first CO-rich stream 7 , the second CO-rich stream 8 and the third CO-rich stream 9 , respectively, and then introduced into the DR furnace A.

[0049] The resulting mixed carburizing gas streams, each having a formulated composition based on the ratio control of the gas mixer steps, exit gas mixers D, E and F as first mixed carburizing gas stream 12, second mixed carburizing gas stream 11 and third mixed carburizing gas stream 10, respectively.

[0050] like Figure 2 As further shown, the first mixed carburizing gas stream 12, the second mixed carburizing gas stream 11 and the third mixed carburizing gas stream 10 are then introduced into the transition zone B of the furnace A through a set of peripheral nozzles located at the bottom of each layer of the transition zone B, as shown in FIG. Figure 2As shown, the transition zone B includes a first layer, a second layer and a third layer, which are layers B-1, B-2 and B-3, respectively. The nozzles are individually valve-controlled, or valve-controlled in a sub-manifold arrangement (each sub-manifold is preferably grouped with no more than 4 nozzles). This provides chemical and thermal distribution control, which enables the carburizing potential of the transition zone B to be increased from a maximum of 3.5 wt. % carbon in the DRI taught by conventional ACT to > 4.5 wt. % carbon in the DRI. More particularly, according to an embodiment, each layer of gas injection is composed of all peripheral nozzle groups (rings) 30, 32, 34 (optimally, 16-28 nozzles per layer), which pass through the vertical furnace wall to introduce gas into the transition zone B. Each nozzle ring 30, 32, 34 is located at the bottom of the section of the transition zone B it serves. The countercurrent characteristics of the operation of the vertical furnace A make this the best position for each nozzle ring 30, 32, 34 for each layer of reaction. The nozzles on each ring are either individually valve controlled or controlled via sub-manifold valves, with each manifold serving no more than 4 nozzles. This allows gas injected at any level to be selectively introduced at specified areas on the circumference of transition zone B or to the entire circumference if desired. Selective addition of gas at specified areas of transition zone B can provide additional temperature profile control for the reaction, as well as finer control of the discharge temperature from transition zone B to meet the operating goals of the unit.

[0051] Advantageously, in this exemplary embodiment and as Figure 2 As further shown, each of the carburizing gas mixtures, namely the first mixed carburizing gas flow 12, the second mixed carburizing gas flow 11 and the third mixed carburizing gas flow 10, is passed through independently controlled preheaters, such as the first preheater G, the second preheater H and the third preheater I (such as Figure 2 As shown) to preheat to the appropriate and desired temperature as needed to further enhance the temperature distribution control for transition zone B. This provides the flexibility to add gas at the appropriate temperature to the appropriate layer within the carburizing gas injection system.

[0052] Now refer to Figure 3In another exemplary embodiment, the method 24 of the present invention comprises passing the synthesis gas or reformed gas stream 1 through an ACT unit C for the purpose of separating CO from the rest of the synthesis gas / reformed gas. It should be noted that the reformed gas stream 1 comes from a reformer unit (not shown) of any design at near ambient temperature, such as a catalytic reformer (e.g., a tubular reformer), a non-catalytic reformer (e.g., a partial oxidation reactor), or even a combined reformer (e.g., an auto-thermal reformer or a two-stage reformer), or any other reducing gas generating unit capable of producing a CO-containing gas with a higher CO / CO2 ratio). As further described below, an optional cooler / quencher (not shown) may also be employed. Preferably, the reformed gas stream 1 contains at least 20.0 mol% CO.

[0053] like Figure 3 As further shown, the reformed gas stream 1 enters the ACT unit C. As mentioned above, the adjustable carbon technology (ACT) geometry / processing is disclosed in the aforementioned U.S. Patent Application No. 10,508,314, and as described herein, the embodiments of the present invention improve this technology. Therefore, the features of the ACT unit C will be briefly described below. Typically, the ACT unit C can adopt the aforementioned cooler / quencher. The cooler / quencher can utilize direct contact cooling, indirect contact cooling, refrigeration cooling, etc. During cooling, the reformed gas may lose a portion of its water content, which in turn improves the carburization potential of the reformed gas. The cold / dry reformed gas optionally flows through a compressor that can increase its pressure (e.g., to 15 barg) because most separation / adsorption methods work best at higher pressures. During compression, the gas loses even more water, resulting in even further improved carburization potential. After optional temperature adjustment, the compressed gas flows high in the system of the membrane module for CO recovery. Any other type of CO recovery unit / mechanism, such as PSA / VPSA / TSA, refrigeration, etc., can also be adopted.

[0054] The H2-rich stream 13 (exhaust gas from the CO recovery unit of ACT unit C) can be sent back, for example, as a recycle to be used elsewhere in the process loop, such as as fuel, cooling gas, synthesis gas or process gas in different parts of the DR unit, or it can be exported to another facility.

[0055] like Figure 3 As shown and as further described below, the CO-rich stream 2 leaving the ACT unit C reaches a junction 15 which divides the stream into a first CO-rich stream 7 and a third CO-rich stream 9 and allows them to enter two separate gas mixers, namely a first gas mixer D and a third gas mixer F, respectively.

[0056] like Figure 3As shown, high hydrocarbon gas (hydrocarbon-rich gas, such as natural gas) is introduced through a hydrocarbon-rich gas stream 3, which is divided into two independently controlled streams, namely a first hydrocarbon-rich gas stream 4 and a third hydrocarbon-rich gas stream 6, which also enter gas mixers D and F respectively.

[0057] It should also be noted that, optionally, if the hydrocarbon-rich gas stream 3 is wet, one or more dehumidification units (not shown) may be used to dry the gas to inhibit decarbonization reactions. Optionally, if the hydrocarbon-rich gas stream 3 contains significant amounts of sulfur compounds, a desulfurization unit (not shown) may be used to reduce and control the total sulfur content, for example, to less than 100 ppm.

[0058] The first hydrocarbon-rich gas stream 4 and the third hydrocarbon-rich gas stream 6 are blended with the first CO-rich stream 7 and the third CO-rich stream 9, respectively, and then introduced into the DR furnace A.

[0059] The resulting mixed carburizing gas streams, each having a formulated composition based on the ratio control of the gas mixer steps, exit gas mixers D and F as first mixed carburizing gas stream 12 and third mixed carburizing gas stream 10, respectively.

[0060] like Figure 3 As further shown, the first mixed carburizing gas stream 12 and the third mixed carburizing gas stream 10 are then introduced into the transition zone B of the furnace A through a set of peripheral nozzles located at the bottom of each layer of the transition zone B, as shown in FIG. Figure 3 As shown, the transition zone B includes two layers, namely, layer B-1' and B-2'. The nozzles are individually valve-controlled, or valve-controlled in a sub-manifold arrangement (each sub-manifold is preferably grouped with no more than 4 nozzles). This provides chemical composition and thermal distribution control, which can achieve an increase in the carburizing potential of the transition zone B from a maximum of 3.5 wt. % carbon in the DRI taught by conventional ACT to >4.5 wt. % carbon in the DRI. More particularly, according to an embodiment, each layer of gas injection is composed of all peripheral nozzle groups (rings) 30', 34' (optimally, 16-28 nozzles per layer), which pass through the vertical furnace wall to introduce gas into the transition zone B. Each nozzle ring 30', 34' is located at the bottom of the section of the transition zone B it serves. The countercurrent characteristics of the operation of the vertical furnace A make this the best position for each nozzle ring 30', 34' for each layer of reaction. The nozzles on each ring are either individually valve controlled or controlled via sub-manifold valves, with each manifold serving no more than 4 nozzles. This allows gas injected at any level to be selectively introduced at specified areas on the circumference of transition zone B or to the entire circumference if desired. Selective addition of gas at specified areas of transition zone B can provide additional temperature profile control for the reaction, as well as finer control of the discharge temperature from transition zone B to meet the operating objectives of the plant.

[0061] Now refer to Figure 4 In yet another exemplary embodiment, the method 26 of the present invention comprises passing the syngas or reformate stream 1 through an ACT unit C for the purpose of separating CO from the remainder of the syngas / reformate gas. It should be noted that the reformate gas stream 1 is derived from a reformer unit (not shown) of any design at near ambient temperature, such as a catalytic reformer (e.g., a tubular reformer), a non-catalytic reformer (e.g., a partial oxidation reactor), or even a combined reformer (e.g., an auto-thermal reformer or a two-stage reformer), or any other reducing gas generating unit capable of producing a CO-containing gas having a relatively high CO / CO2 ratio). As further described below, an optional cooler / quencher (not shown) may also be employed. Preferably, the reformate gas stream 1 contains at least 20.0 mol% CO.

[0062] like Figure 4 As further shown, the reformed gas stream 1 enters the ACT unit C. As mentioned above, the adjustable carbon technology (ACT) geometry / processing is disclosed in the aforementioned U.S. Patent Application No. 10,508,314, and as described herein, the embodiments of the present invention improve this technology. Therefore, the features of the ACT unit C will be briefly described below. Typically, the ACT unit C can adopt the aforementioned cooler / quencher. The cooler / quencher can utilize direct contact cooling, indirect contact cooling, refrigeration cooling, etc. During cooling, the reformed gas may lose a portion of its water content, which in turn improves the carburization potential of the reformed gas. The cold / dry reformed gas optionally flows through a compressor that can increase its pressure (e.g., to 15 barg) because most separation / adsorption methods work best at higher pressures. During compression, the gas loses even more water, resulting in even further improved carburization potential. After optional temperature adjustment, the compressed gas flows to a system of membrane modules for CO recovery. Any other type of CO recovery unit / mechanism, such as PSA / VPSA / TSA, refrigeration, etc., can also be adopted.

[0063] The H2-rich stream 13 (exhaust gas from the CO recovery unit of ACT unit C) can be sent back, for example, as a recycle to be used elsewhere in the process loop, such as as fuel, cooling gas, synthesis gas or process gas in different parts of the DR unit, or it can be exported to another facility.

[0064] like Figure 4 As shown and as further described below, the CO-rich stream 2 leaving the ACT unit C reaches a junction 15 which divides the stream into a first CO-rich stream 7 and a third CO-rich stream 9 and allows them to enter two separate gas mixers, namely a first gas mixer D and a third gas mixer F, respectively.

[0065] like Figure 4 As shown, high hydrocarbon gas (hydrocarbon-rich gas, such as natural gas) is introduced through a hydrocarbon-rich gas stream 3, which is divided into two independently controlled streams, namely a first hydrocarbon-rich gas stream 4 and a third hydrocarbon-rich gas stream 6, which also enter gas mixers D and F respectively.

[0066] It should also be noted that, optionally, if the hydrocarbon-rich gas stream 3 is wet, one or more dehumidification units (not shown) may be used to dry the gas to inhibit decarbonization reactions. Optionally, if the hydrocarbon-rich gas stream 3 contains significant amounts of sulfur compounds, a desulfurization unit (not shown) may be used to reduce and control the total sulfur content, for example, to less than 100 ppm.

[0067] The first hydrocarbon-rich gas stream 4 and the third hydrocarbon-rich gas stream 6 are blended with the first CO-rich stream 7 and the third CO-rich stream 9, respectively, and then introduced into the DR furnace A.

[0068] The resulting mixed carburizing gas streams, each having a formulated composition based on the ratio control of the gas mixer steps, exit gas mixers D and F as first mixed carburizing gas stream 12 and third mixed carburizing gas stream 10, respectively.

[0069] like Figure 4 As further shown, the first mixed carburizing gas stream 12 and the third mixed carburizing gas stream 10 are then introduced into the transition zone B of the furnace A through a peripheral nozzle group (ring) located at the bottom of each layer of the transition zone B, as shown in FIG. Figure 4 As shown, the transition zone B includes two layers, namely, layer B-1' and B-2'. The nozzles are controlled by individual valves, or by valves arranged in a sub-manifold (each sub-manifold preferably does not exceed 4 nozzles for grouping). This provides chemical composition and thermal distribution control, which can achieve the carburizing potential of the transition zone B from the maximum 3.5 wt. % carbon in the DRI taught by conventional ACT to > 4.5 wt. % carbon in the DRI. More particularly, according to an embodiment, each layer of gas injection is composed of all peripheral nozzle groups 30', 34' (optimally, 16-28 nozzles per layer), which pass through the vertical furnace wall to introduce gas into the transition zone B. Each nozzle ring 30', 34' is located at the bottom of the section of the transition zone B it serves. The countercurrent characteristics of the operation of the vertical furnace A make this the best position for each nozzle ring 30', 34' for each layer of reaction. The nozzles on each ring are controlled by a single valve or via a sub-manifold valve, and each manifold serves no more than 4 nozzles. This allows gas injected at any level to be selectively introduced at specified areas on the circumference of transition zone B or to the entire circumference if desired. Selectively adding gas at specified areas of transition zone B can provide additional temperature profile control for the reaction, as well as finer control of the discharge temperature from transition zone B to meet the operating objectives of the unit.

[0070] Advantageously, in this exemplary embodiment and as Figure 4 As further shown, by passing each of the carburizing gas mixtures, namely the first mixed carburizing gas flow 12 and the third mixed carburizing gas flow 10, through independently controlled preheaters, such as the first preheater G and the third preheater I (such as Figure 4 As shown) to preheat to the appropriate and desired temperature as needed to further enhance the temperature distribution control of transition zone B. This provides the flexibility to add gas at the appropriate temperature to the appropriate layer within the carburizing gas injection system.

[0071] Advantageously, if Figure 1-4 As shown in each of the above, the iron oxides enter the top of furnace A. According to the embodiment, the partially or fully reduced iron oxides can thus be exposed to the above-mentioned CO-rich stream and hydrocarbon-rich stream.

[0072] like Figure 1-4 Each of the further advantageously illustrated, the main reduction zone / boshi zone 36, where most of the reactions occur, is shown in furnace A above transition zone B. Figure 1-4 As further shown, transition zone B extends from the main reduction zone / boshi zone 36 to the top of the cooling zone 38 (including vertically stacked layers) and is the location where the mixed gas is received and further reactions occur. As further explained above, transition zone B advantageously forms an extended transition zone in the furnace (extended length below the boshi zone). It should be noted that, according to embodiments, no mixed gas is received in the cooling zone 38. It should also be noted that, typically, prior to employing the vertically stacked multiple layers of transition zones B described above, the partially or fully reduced iron oxides in transition zone B and / or cooling zone 38 contain 0.0 wt. % to 3.0 wt. % bound carbon, while as Figure 1-4 As shown, carbon contents in the resulting DRI of greater than about 4.5 wt. % can be advantageously achieved.

[0073] Although the present invention is described and illustrated herein with reference to its specific preferred embodiments and specific examples, it will be apparent to those of ordinary skill in the art that other embodiments and examples can perform similar functions and / or achieve similar results. All such equivalent embodiments and examples are within the spirit and scope of the present invention and are therefore contemplated and are intended to be covered by the attached non-limiting claims. In addition, all features, elements, and embodiments described herein can be used in any combination.

Claims

1. A method for producing direct reduced iron with increased carbon content, the method comprising: providing a carbon monoxide rich gas stream, and dividing the carbon monoxide rich gas stream into at least two separate carbon monoxide rich gas streams; providing a hydrocarbon-rich gas stream, and dividing the hydrocarbon-rich gas stream into at least two separate hydrocarbon-rich gas streams; blending one of the carbon monoxide-rich gas streams with one of the hydrocarbon-rich gas streams to form a mixed carburizing gas stream; blending another of the at least two separate carbon monoxide-rich gas streams with another of the at least two separate hydrocarbon-rich gas streams to form a different mixed carburizing gas stream; Each of the mixed carburizing gas streams having different compositions is delivered to a transition zone of a direct reduction shaft furnace disposed below a reduction zone of the direct reduction shaft furnace, and partially or fully reduced iron oxides are exposed to the mixed carburizing gas streams to increase the carbon content of the resulting direct reduced iron to greater than 4.5% by weight. The transition zone has a plurality of vertically stacked layers, and each layer is configured to receive a separate flow of the mixed carburizing gas flow.

2. The method according to claim 1, further comprising: dividing the carbon monoxide-rich gas stream into a first carbon monoxide-rich gas stream, a second carbon monoxide-rich gas stream, and a third carbon monoxide-rich gas stream; dividing the hydrocarbon-rich gas stream into a first hydrocarbon-rich gas stream, a second hydrocarbon-rich gas stream, and a third hydrocarbon-rich gas stream; blending the first carbon monoxide-rich gas stream with the first hydrocarbon-rich gas stream in a first mixer to form a first mixed carburizing gas stream; blending the second carbon monoxide-rich gas stream with the second hydrocarbon-rich gas stream in a second mixer to form a second mixed carburizing gas stream; blending the third carbon monoxide-rich gas stream with the third hydrocarbon-rich gas stream in a third mixer to form a third mixed carburizing gas stream; Each of the first mixed carburizing gas stream, the second mixed carburizing gas stream, and the third mixed carburizing gas stream having different compositions is delivered to the transition zone of the direct reduction shaft furnace, and partially or fully reduced iron oxides are exposed to the first mixed carburizing gas stream, the second mixed carburizing gas stream, and the third mixed carburizing gas stream to increase the carbon content of the resulting direct reduced iron to greater than 4.5 wt%.

3. The method of claim 1 , wherein providing the carbon monoxide-rich gas stream comprises initially providing one of the reformed gas streams from a reformer, and the carbon monoxide-rich gas stream is directed from a carbon monoxide recovery unit, the carbon monoxide recovery unit forming a portion of the carbon monoxide-rich gas stream and the H2-rich exhaust gas stream.

4. The method of claim 1 , wherein the transition zone comprises a plurality of layers of equal height within the transition zone, and each layer comprises a set of nozzles, and wherein each of the mixed carburizing gas flows is introduced into a separate layer of the transition zone via the set of nozzles at each layer. 5 . The method according to claim 4 , wherein the nozzles at each layer that introduce the mixed carburizing gas flow are arranged in a peripheral ring of the same number of nozzles located at the bottom of each layer.

6. The method of claim 5, wherein the peripheral ring comprises 16 to 28 nozzles.

7. The method of claim 6, wherein the nozzles are individually valve controlled or manifold valve controlled with no more than 4 nozzles per manifold.

8. The method of claim 1 wherein each of the mixed carburizing gas flows is introduced into a separate layer of the transition zone with a different composition for each layer using a separate mixer for each layer.

9. The method of claim 1, wherein for each layer, each of the mixed carburizing gas flows may be preheated to a different temperature using a separate preheater, the preheating temperature may be in the range of ambient temperature to 400°C.

10. The method of claim 1, wherein each of the mixed carburizing gas streams has a different composition.

11. The method according to claim 1, wherein the total height of the transition zone is increased by > 0.5 m to a height of 1.5 m - 3.5 m.

12. A direct reduction shaft furnace, comprising: Restoration area; a transition zone below the reduction zone, wherein the transition zone has a plurality of vertically stacked layers and each layer is configured to receive a separate flow of the mixed carburizing gas flow; as well as A cooling zone below the transition zone wherein the reduced iron is partially or fully exposed to the mixed carburizing gas flow to increase the carbon content of the resulting direct reduced iron to greater than 4.5 wt%.

13. The direct reduction shaft furnace of claim 12, wherein the transition zone comprises a plurality of layers of equal height within the transition zone and each layer comprises a set of nozzles, and wherein the furnace is configured to receive each of the mixed carburizing gas flows in a separate layer of the transition zone via the set of nozzles at each layer.

14. The direct reduction shaft furnace according to claim 13, wherein the nozzles at each level are arranged in a peripheral ring of the same number of nozzles located at the bottom of each level.

15. The direct reduction shaft furnace according to claim 14, wherein the peripheral ring comprises 16 to 28 nozzles.

16. The direct reduction shaft furnace of claim 15, wherein the nozzles are individually valve controlled or header valve controlled with no more than 4 nozzles per header.

17. The direct reduction shaft furnace of claim 12, wherein the furnace is configured to receive each of the mixed carburizing gas flows introduced into separate layers of the transition zone at different compositions.

18. The direct reduction shaft furnace of claim 12, wherein each layer comprises a different composition.

19. The direct reduction shaft furnace according to claim 17, wherein the total height of the transition zone increases by > 0.5 m to a height of 1.5 m - 3.5 m.

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