Patent Application
20240110254
The present disclosure relates generally to an eco-friendly method for producing iron with zero-CO2 emission. More specifically, the present disclosure describes methods for producing iron with zero CO2 emission using hydrogen plasma and/or hydrogen with rotary kiln furnace, and a hydrogen-plasma rotary kiln furnace used therein.
Conventional steel manufacturing is not an environmentally friendly process. Globally, the steel industry emits more than 3.3 billion tons of carbon dioxide (“CO2”) annually, which accounts for 30% of the global industrial and 8% of the global total CO2 emissions. Of various steps in the steel manufacturing process, the blast furnace process for reducing iron ore to metallic iron accounts for about one-third of the total CO2 emissions.
Specifically, during the blast furnace process, iron ore is reduced using coke and limestone at temperatures above 2,000° C. to create molten pig iron. Pig iron has a high carbon content, approximately 4-5%, which makes it brittle. To reduce the carbon content, pig iron is processed in the basic oxygen furnace by treating it with pure oxygen using a water-cooled lance, which then removes the carbon as CO2, yielding a crude steel product. Additional processing may further be utilized to produce a high-grade steel product.
However, conventional steel manufacturing processes operate close to their thermodynamics limit, making it difficult to meet the goals set in the Paris Agreement adopted on Dec. 12, 2015. Furthermore, conventional steel manufacturing process requires high energy consumption. Conventional blast furnace process requires operation of the furnace at a temperature above 1550° C. A substantial amount of energy is lost in the sensible heat of the high temperature iron and slag.
Many have attempted to solve the issues addressed above with new processes, including direct reduced iron (“DRI”) processes, which offer the advantages of lower capital cost, complexity in design, operation compared to conventional blast furnace processes. Currently, about 100 million tons of steel are produced annually by various DRI processes.
As an example, the MIDREX DRI process uses a shaft furnace as the reactor and pellets or lump ore as the raw material. The DRI shaft furnace requires that the iron ore be fed into the reactor in pellet form. While the MIDREX DRI process allows a lower carbon footprint compared to the traditional blast furnace process, further reductions in the required energy and resulting carbon footprint are desired. In addition, the MIDREX DRI has disadvantages in that pelletizing the iron ore adds additional cost and produces about 200 kg of CO2 per ton of steel. Furthermore, shaft furnaces cannot match the production rate of blast furnaces due to sticking, fusion of particles, and pellet disintegration.
Another DRI process studied is directed to producing sponge iron using a rotary kiln furnace. However, the DRI-rotary kiln furnace process uses coal as the reducing agent. The process burns coal with air to obtain heat for the iron ore reduction, and because of the high nitrogen content in air, the flue gas contains a substantial amount of nitrogen that carries a lot of heat out of the reactor. That is, the DRI-rotary kiln furnace process does not provide efficiency advantages compared to the blast furnace technology.
Iron reduction by hydrogen plasma has also been studied. Hydrogen plasma provides advantages thermodynamically and kinetically for reducing iron oxide compared to thermal processes utilizing hydrogen, because the plasma can generate monoatomic (H·), ionic (H+) species, and energetic rotationally- and vibrationally-excited molecular hydrogen states (H2*). The energy carried by these species is released at the reduction interface leading to localized heating. Thus, a hydrogen plasma does not require volumetric heating as is required with thermal processes, which reduces heat loss from the reactor and subsequently reduces cost. The reduction of Fe2O3 to Fe3O4 and Fe3O4 to FeO by molecular H2 are thermodynamically favorable at temperatures above 900 K (627° C.). However, the reduction of FeO to Fe with molecular H2 is thermodynamically unfavorable. All three reduction processes become favorable in a hydrogen plasma due to the presence of plasma-generated monoatomic (H·) and ionic (H+) hydrogen that can be generated at relatively low temperatures.
The above described iron reduction by hydrogen plasma is not free of disadvantages. For example, ionizing hydrogen to plasma requires a lot of energy, and after the hydrogen plasma reduces iron ore, a lot of heat is released. Previous studies have not considered recovering the heat after the hydrogen plasma reaction with iron ore. Therefore, the energy efficiency of the previous studies of the hydrogen plasma process is low.
Certain embodiments described herein relate generally to a hydrogen-plasma rotary kiln furnace reactor. The reactor comprises a rotary kiln furnace and a hydrogen-plasma generator.
Certain embodiments described herein relate generally to a method of reducing iron using a hydrogen-plasma rotary kiln furnace reactor. The reactor comprises a rotary kiln furnace and a hydrogen-plasma generator.
Certain embodiments described herein relate generally to a method of reducing iron. The method comprises feeding iron ore and/or iron ore concentrate to a rotary kiln furnace, and reducing iron ores to iron using hydrogen gas and a hydrogen plasma.
It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the subject matter disclosed herein.
The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several implementations in accordance with the disclosure and are not, therefore, to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.
Reference is made to the accompanying drawings throughout the following detailed description. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative implementations described in the detailed description, drawings, and claims are not meant to be limiting. Other implementations may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and made part of this disclosure.
As used herein “room temperature” shall mean temperatures within 15 to 40° C.
As used herein, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, the term “a member” is intended to mean a single member or a combination of members, “a material” is intended to mean one or more materials, or a combination thereof.
As used herein, the terms “about” and “approximately” generally mean plus or minus 10% of the stated value. For example, about 0.5 would include 0.45 and 0.55, about 10 would include 9 to 11, about 1000 would include 900 to 1100.
It should be noted that the term “exemplary” as used herein to describe various embodiments is intended to indicate that such embodiments are possible examples, representations, and/or illustrations of possible embodiments (and such term is not intended to connote that such embodiments are necessarily extraordinary or superlative examples).
The terms “coupled,” “connected,” and the like as used herein mean the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another.
The majority of processes attempting to reduce the carbon footprint of the iron ore reduction step use molecular hydrogen along with varying amounts of some form of carbon (e.g. coke, coal, natural gas, or carbon monoxide). The method of reducing iron ore disclosed herein provides a carbon-free reduction of iron ore using a combination of direct hydrogen gas reduction of iron ore in a rotary kiln furnace with a low temperature hydrogen plasma reduction process.
Reduction of iron ore or iron ore concentrate generally follows successive reaction steps. For instance, hematite from iron ore is reduced to magnetite (3Fe2O3+CO/H2→2Fe3O4+CO2/H2O), magnetite is then reduced to ferrous oxide (Fe3O4+CO/H2→2FeO+CO2/H2O), and ferrous oxide is reduced to iron in carbon monoxide or hydrogen (FeO+CO/H2→Fe+CO2/H2O). The hydrogen plasma, with its high concentration of highly reactive atomic and ionic hydrogen, provides favorable thermodynamics and kinetics in the reduction of ferrous oxide to iron (that is, the reduction of FeO to Fe). The hydrogen plasma further provides improved kinetics for prior reduction steps including the reduction of Fe2O3 to Fe3O4 and of Fe3O4 to FeO. Further, the hydrogen plasma also provides thermal energy. More specifically, the plasma provides local heating to the ore, thus reduces heating demands compared to traditional approaches that require volumetric heating. In other words, compared to conventional techniques, using a hydrogen plasma is advantageous for its lower operating temperature while serving as an excellent heat source, providing increased reaction rates, and more favorable thermodynamic driving forces.
On the other hand, the rotary kiln furnace allows collection and utilization of the thermal energy in the plasma for the initial stages of iron ore reduction by molecular hydrogen. The rotation of the rotary kiln provides mixing that exposes new particle surfaces at the plasma-particle interface, thereby improving the overall reaction rate. Advantages of using a rotary kiln furnace include elimination of the need for pelletizing the iron ore, efficient recovery of plasma waste energy, better mixing of the ore to improve solid-gas contact and reduce reaction times, and better control over the ore flow rate and residence time.
The method and reactor disclosed herein combines the advantages of hydrogen plasma and rotary kiln furnace, and improves energy efficiency compared to conventionally available techniques such as blast furnace processes or DRI processes. The improved energy efficiency compared to the conventionally available techniques allows use of the smaller sized reactor, thereby also reducing the capital cost associated with using the invention.
In one embodiment, iron ore is reduced to iron in a hydrogen-plasma rotary kiln furnace reactor, which will be described further below.
In some embodiments, in accordance with the elongated furnace body 250, the hydrogen-plasma generator 230 may also be elongated. In other embodiments, the hydrogen-plasma generator 230 may be disposed in an elongated tube. More specifically, as shown in
The shell, liner, and thermal insulators may be selected from any materials considered suitable by a person of ordinary skill in the art. For example, commercially available furnace shells are often made of various metals such as carbon steel, stainless steel, aluminized steel, aluminum, etc. In one embodiment, the shell may be a steel shell.
The thermal insulator and liner should inhibit heat transfer to the external environment, but there may be additional requirements such as thermal-shock resistance, resistance to corrosion, physical strength, and/or flexibility. Commonly used thermal insulator materials and liners include refractory ceramic fibers, alkaline earth silicate fibers, polycrystalline fibers, high-temperature fibers with firebricks, or any combinations thereof. Depending on desired properties, any materials may be chosen as considered suitable by a person of ordinary skill in the art. In one embodiment, the liner may be a ceramic liner.
Referring back to
The reactor may further include a feeder 210, a sponge iron cooler 220, a water-hydrogen separator 224, and an exhaust gas outlet 226. In one embodiment, the feeder 210 connected to the end cap 211 and is configured to feed iron ore or iron ore concentrate into the furnace body 250. The sponge iron cooler 220, which is configured to cool the sponge iron, may be connected to the kiln hood 240. In one embodiment, the reactor 200 may further include an exhaust gas outlet 226, which is configured form a passageway for exhaust gas to exit the furnace body and to connect the first end of the furnace body 250 and a water-hydrogen separator 224. The water-hydrogen separator 224 connected to the exhaust gas outlet 226 condenses steam from exhaust gas.
The hydrogen-plasma generator 230 may include a plurality of jet nozzles 232 configured to discharge hydrogen plasma jets. The plurality of jet nozzles may be disposed along the body of the hydrogen-plasma generator 230 at a distance from each other. While
In one embodiment, hydrogen plasma is generated along only a portion of the furnace body 250. Because hydrogen plasma is not generated throughout the entirety of the furnace body 250, different processes may occur within the furnace body. For the purposes of description herein, Zone 1 is defined as a region of the furnace body 250 from the second end that is connected to the kiln hood 240 to an end of the hydrogen-plasma generator 230 that is the closest to the second end of the furnace body 250. Zone 2 is defined as a region of the furnace body 250 in which the hydrogen-plasma generator 230 is disposed. Zone 3 is defined as a region of the furnace body 250 from the first end that is connected to the feeder 210 to an end of the hydrogen-plasma generator 230 that is the closest to the first end of the furnace body 250.
In one embodiment, in Zone 3, iron ore is fed into the furnace body 250 and exchanges heat with exhaust gas consisting of hydrogen and steam. Further in Zone 3, initial stages of reduction, including reduction of hematite to magnetite and reduction of magnetite to ferrous oxide, of the ore with molecular hydrogen occur. As discussed above, the furnace body 250 is inclined at an angle, generally between approximately 1° and 15°. Due to the inclination of the furnace body 250, iron ore powder can move from Zone 3 toward Zone 1 slowly. By controlling the incline and the rotation rate, the ore flow rate can be controlled. The ore subsequently moves from Zone 3 to Zone 2.
In Zone 2, iron ore is reduced to sponge iron by using hydrogen plasma, and hydrogen is oxidized to steam. During the operation, the temperature of the kiln furnace in Zone 2 may be heated up to 1550° C. at approximately 1 atm. Compared to conventional processes that use molecular hydrogen, a hydrogen plasma allows processing at a lower temperature range because hydrogen species in plasma status are much more active than regular hydrogen molecules. The reduction using a hydrogen plasma generates excess heat, which can be used to supply thermal energy required to carry out the chemical reduction process. Absent the excess heat generated by a hydrogen plasma, additional energy is required to keep the reaction at the required temperature in the reactor at approximately 1 atm.
Finally, the reduced sponge iron flows from Zone 2 to Zone 1 and into the sponge iron cooler 220, where it is cooled by hydrogen gas near the inlet of the hydrogen-plasma generator 230.
Hydrogen flows counter-current to the sponge iron and ore flow. In one embodiment, in Zone 1, hydrogen gas exchanges heat with the sponge iron. More specifically, heat transfers from the sponge iron to hydrogen gas in Zone 1, cooling down the sponge iron while heating up hydrogen gas.
Furthermore, hydrogen is fed from two positions, from the sponge iron cooler 220 and from the inlet for the hydrogen-plasma generator 230. That is, at least some hydrogen gas introduced from Zone 1 is conducted to the Zone 2. The amount of hydrogen fed from two positions and thus the resulting balance of flow may be varied.
In the reduction process, hydrogen is consumed and steam (H2O) is formed. In one embodiment, the reduction reaction is carried out with excess H2, leaving residual hydrogen in the flow. The hydrogen fed from the sponge iron cooler 220 cools and collects residual thermal energy from the reduced iron, and is further used to reduce the iron ores. The hydrogen fed from the hydrogen-plasma generator 230 flows through the plasma jets and is converted to plasma in Zone 2. Further in Zone 2, the thermal energy from the hydrogen plasma is exchanged with the iron ores and with the hydrogen that was introduced from the sponge iron cooler 220. Such exchange of thermal energy provides energy for the reduction of iron oxide by molecular hydrogen.
In some embodiments, an additional gas without carbon substituents may be added to the hydrogen entering the plasma generator to adjust or alter plasma characteristics and stability. The additional gas may be a noble gas such as argon, and may be utilized for only a portion of the operational time, for example at the reactor startup, or for the duration of the process.
The gas flow exiting Zone 2 comprises of the residual hydrogen flow, combined of hydrogen fed from the sponge iron cooler 220 and hydrogen fed from the hydrogen-plasma generator 230, and steam formed during the reduction reaction. The steam and hydrogen flow that exited Zone 2 provide thermal energy to the iron ore entering Zone 3. Because hydrogen is consumed in the reactions in Zone 2, in Zone 3, steam is prevalent and only residual amounts of hydrogen remain. As discussed above, initial stages of reduction from the residual amounts of molecular hydrogen remaining will occur in Zone 3. However the amount of reduction will be limited by the steam present and the reduced hydrogen content. Exhaust gas exits the furnace body 250 and is transferred to the water hydrogen separator 224 through the exhaust gas outlet 226. Steam of the exhaust gas is condensed in the water-hydrogen separator 224, which is configured to transfer recycled hydrogen back to the sponge iron cooler 220.
In some embodiments, the reactor 200 may further include a drive assembly 246 configured to rotate the furnace body 250. For example, in some embodiments, the drive assembly 246 may be a gear drive. A drive gear includes a plurality of gears, including a gear wrapped around the furnace body 250. The gear wrapped around the furnace body 250 meshes with a small gear drive (not shown), which then drives rotation of the furnace body 250. While drive gear may be preferable because it is suitable for heavy-duty applications requiring high horsepower, other mechanisms may be used depending on desired operation scale. For example, other mechanisms may include chain and sprocket drive, friction drive, direct drive, and etc. In some embodiments, the reactor 200 may further include a plurality of tyres 242 attached to the furnace body 250. The tyres 242 are configured to transfer the gravity of the furnace body to supporting rollers (not shown) and allow the furnace body rotate smoothly on the supporting rollers.
The invention disclosed herein is advantageous in several aspects. For instance, the method disclosed herein only uses hydrogen gas as a reducing agent. Because the process does not use solid carbonaceous fuel as a reducing agent, the process is a zero-CO2 emission. Furthermore, use of plasma allows reduction of iron ores at a lower temperature compared to processes using molecular hydrogen, which is highly endothermic and thus requires high operating temperatures. Furthermore, the process does not require making iron ore pellets. Thus, less energy consumption is achieved, and the operating and capital costs may be reduced. The invention disclosed here in is estimated to reduce energy consumption by approximately 45% compared to the conventional blast furnace process and by approximately 15% compared to DRI process.
It is important to note that the construction and arrangement of the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present invention.
While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular implementations of particular inventions. Certain features described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
This invention was made with government support under Contract No. DE-AC02-06CH11357 awarded by the United States Department of Energy to UChicago Argonne, LLC, operator of Argonne National Laboratory. The government has certain rights in the invention.
