RU2782579C1 - Method for direct reduction in a fluidised bed - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: group of inventions relates to direct reduction of iron oxide-containing particles into a reduction product in a fluidised bed wherein a reducing gas containing 30 to 100% mol. hydrogen H₂ passes through said layer in counter-flow. According to the method, direct reduction of iron oxide-containing particles (2) into a reduction product (9) is performed in a fluidised bed (4) wherein a reducing gas (8) containing 30 to 100 mol.% hydrogen H₂ passes through said layer in counter-flow. At least 90 wt.% of the iron oxide-containing particles (2) supplied to the fluidised bed (4) have a fineness less than or equal to 200 mcm. The fictitious speed U of the reducing gas (9) passing through the fluidised bed (4) is set between 0.05 m/s and 1 m/s so that for a fineness d equal to d₃₀ of the iron oxide-containing particles (2) supplied to the fluidised bed (4), the speed exceeds the theoretical speed of transition to the suspended state U_t and is less than or equal to U_max.

EFFECT: possibility of reducing iron-containing particles without prior agglomeration, and lowering the building and operating costs of the set for the implementation of the method.

14 cl, 3 dwg

Description

Technical field

The present invention relates to a process for the direct reduction of iron oxide-containing particles into a fluidized bed reduction product through which a reducing gas containing 30-100 mol % hydrogen H ₂ flows in countercurrent.

State of the art

Various methods are known for the direct reduction of iron oxide-containing particles, such as iron ore, in a fluidized bed, also called a fluidized bed, through which a reducing gas passes. For commercial purposes, for example, FIOR, FINMET, FINEX, CIRCORED have been used so far.

For the purposes of this application, the term "iron ore" refers to both ore that is immediately submitted for recovery after mining in a mine, and ore that is only submitted for recovery after preparation steps or other post-mining pre-treatments. In any case, they contain oxidized iron.

In fluidized bed processes used to reduce iron ore, the reducing gas passes through solid particles, ie iron oxide-containing particles, for example iron ore in the form of bulk material, against the direction of gravity. Due to this, the particles of the solid matter pass into a fluidized state, i.e. into suspension, and practically acquire the property of liquid fluidity, which is also called fluidization. Fluidization is also used for the transport of solids, for example in the case of air ducts with countercurrent movement of solids and gases.

The state of the fluidized bed, depending on the degree of fluidization, can be divided into various stages, for example, minimal/stable/bubbly/turbulent. The initial state is a fixed or stationary bed, in which the reducing gas passes through the bulk material without causing fluidization. As the gas velocity increases, fluidization begins in the minimum fluidization state, and then, with a further increase in gas velocity, a transition occurs to a stable fluidization state. Fluidization in the pre-fluidized bed stage depends on the velocity, density and viscosity of the gas, as well as on the mass and density of the particles, the shape, volume of the particles and the particle size distribution of the solids used. The term "fluidized bed" is identical to the term "fluidized bed", and both terms are used in this application interchangeably. At the point of fluidization, there is a transition from a fixed bed to a fluidized bed.

In principle, relatively large mass and heat transfer coefficients are achieved in a fluidized bed due to the presence of large interaction surfaces between the solid and the gas. Accordingly, high specific conversions are achieved in the reduction reaction.

The technically and economically achievable degree of metallization of the reduction products depends on many factors.

In order to reduce iron oxide to metallic iron, it is necessary to obtain at least the stoichiometric amount of reducing gas required for the reduction reaction. The volume of reducing gas actually passed through the solid is determined by the thermodynamic equilibrium between the various oxidation states of the ore and the reducing gas. This balance can be affected by temperature.

In the mode of operation at elevated pressure, the mass flow of the reducing gas can be increased, however, the disadvantages are higher design and safety requirements for the reduction unit.

At high temperatures, there is also a disadvantage that the solid particles tend to agglomerate, also called agglomeration, which adversely affects the fluidized bed behavior, for example, stopping fluidization.

In the mode of operation with increased gas velocity, the mass flow of the reducing gas can be increased.

For the purposes of this application, the term "gas velocity" means the fictitious velocity in terms of the total cross section.

In the case of some bulk materials consisting of particles of solid matter, the maximum practically acceptable gas velocity - and thus the maximum amount of gas per unit area per unit time, passed through the fluidized bed - follows from such a gas velocity at which the fluidized bed during technological process carries away a negligible fraction of solid particles.

The state where the gas velocity matches the sedimentation velocity of the solid particles is called the blow-off point. The rate of the reducing gas at the point of entrainment is equal to the rate of settling of the solid particles and is taken as the rate of suspension. With a further increase in the gas velocity, solid particles are entrained by the gas and are carried away from the fluidized bed against the direction of gravity. The solid particles carried away from the fluidized bed no longer react in the fluidized bed, whereby the efficiency of the reduction method based on the fluidized bed is reduced.

The smaller the particle size of the solid, the lower the rate of transfer to a suspended state. From the low gas velocity follows the need for a large area of the reactor to ensure a given performance in the case of small particle size. However, increasing the area of the reactor has disadvantages such as high manufacturing costs, high production costs, higher susceptibility to malfunctions. The use of large reactor areas in current technologies, for example due to costly safety and operational measures, is counteracted by, for example, a significant increase in pressure, a turbulent fluidized bed regime, including recirculation of entrained solids.

Therefore, when processing particles containing iron oxide with a large proportion of particles of small size, problems of a slightly variable gas velocity appear, thereby associated with the need for reactors of large areas.

As a measure to increase the entrainment rate, the small solid particles are often agglomerated prior to being fed to the fluidized bed reduction.

Brief description of the invention

Technical task

The object of the present invention is to provide a method and apparatus which, with relatively mild safety requirements and low building and manufacturing costs, allows the use of iron oxide containing particles, of which at least 90 mass% have a particle size of less than or equal to 200 micrometers, for direct reduction in a fluidized bed without a previous agglomeration step.

Technical solution

This problem is solved by a method for the direct reduction of particles containing iron oxide into a reduction product in a fluidized bed, through which a reducing gas containing 30-100 mol.% hydrogen H ₂ passes countercurrently, characterized in that the particles containing iron oxide fed into the fluidized bed are at least 90 mass % have a particle size less than or equal to 200 micrometers, and the fictitious velocity U of the reducing gas passing through the fluidized bed is set between 0.05 m/s and 1 m/s so that for a particle size d equal to d ₃₀ supplied to the fluidized bed containing oxide iron particles, exceeds the theoretical rate of translation into a suspended state U _t and less than or equal to U _max .

The value of d ₃₀ in relation to particle size, also referred to in this application as the size of the supplied iron oxide particles, indicates that ₃₀ wt.

The theoretically predicted value of U _t for size d is obtained from the formula:

and U _max is obtained from the empirically found relationship between the particle size and the rate of transfer to a suspended state of particles with a particle size d equal to d ₃₀ :

U _max \u003d (40000 * d) ^2.78 ,

where

U _t is the theoretical speed of transfer to a suspended state, m/s;

U _max - maximum fictitious speed for d=d ₃₀ , m/s;

^ρp is the particle density, kg/m3;

ρg is the density of the reducing gas, kg/m ³ , in the operating mode;

d—particle size, m;

g - free fall acceleration, m/s ² ;

µ – dynamic viscosity, kg/(m s);

c _w is the drag coefficient;

Re is the Reynolds number.

The theory, in accordance with accepted scientific ideas, according to the previously indicated dependence for U _t , would make it possible to expect that, given a fictitious velocity U, exceeding the theoretical one, in the case of particle size d ₃₀ supplied to the fluidized bed containing iron oxide particles, with the actual transfer rate to a suspension state U _t carryover will be more than 30 mass%.

Surprisingly, in the case of fluidized-bed particles containing iron oxide, of which at least 90 mass% have a particle size less than or equal to 200 micrometers, it was found that in an embodiment of the method according to the invention, the entrainment is less, although U _t for particle size d equal to d ₃₀ is exceeded as long as the fictitious speed U is less than or equal to U _max for d equal to d ₃₀ . Accordingly, it is possible, for a given maximum acceptable entrainment, to operate at a higher gas velocity than expected from theory. The fictitious velocity U is preferably set so that the entrainment is at most 30 wt%, i.e. U _max for d=d ₃₀ , more preferably at most 25 wt%, particularly preferably at most 20 wt% and most preferably at most 15 wt%.

The reducing gas according to the invention passes through the fluidized bed at a speed of more than 0.05 m/s, preferably more than 0.1 m/s. With the parameters selected according to the invention, the iron oxide-containing particles in the resulting fluidized bed, through which a reducing gas is passed in countercurrent, show a different behavior than that predicted according to accepted scientific ideas, according to the previously indicated dependence for U _t . At a speed of less than 0.05 m/s, maintaining a fluidized bed is difficult to control, and the ratio of the costs of the implementation of the method and the performance achieved is hardly acceptable. The excess of the actually selected speed over 0.05 m/s, and preferably over 0.1 m/s, depends on the degree of entrainment from the fluidized bed allowed by the operating conditions. On the one hand, a higher speed is desirable since, as a result, the area of the reactor required to provide the required productivity may be smaller. On the other hand, entrainment increases with increasing speed, and entrainment of particles from the fluidized bed reduces the possible productivity. Therefore, the upper limit of the fictitious speed is 1 m/s.

It is more preferable to carry out the process in the speed range from 0.05 m/s to 0.5 m/s, since in this case the productivity and entrainment are in a favorable ratio.

According to the invention, the fluidized bed is used in the state of fluidization in the region of the minimum; in this case, a circulating fluidized bed is not used.

The entrained amount refers to the time interval from the moment the iron oxide-containing particles are fed into the fluidized bed until the reaction product formed therefrom is withdrawn, that is, the residence time of the particles in the fluidized bed.

With regard to the general circumstances of recovery in any fluidized bed or in any fluidized bed, the introductory part of the application refers to the prior art. "Any" should be understood in the sense of the ambiguity in the expression "in any fluidized bed".

The iron oxide-containing particles may be iron ore or other suitable fine-grained material containing iron oxides, such as flue dust, agglomerated dust, pelletized dust, or other waste from a metallurgical or steel plant; they can also be a mixture of them. The term "iron ore" according to the invention should be understood to mean both ore supplied immediately after mining in the mine for reduction, and ore that is supplied for reduction only after preparation stages, for example after flotation, or after other types of pre-treatment carried out after mining. In any case, they contain oxidized iron.

The particle size range and particle size distribution is provided in the process of large-scale industrial production of the starting material. These characteristics are determined by sieve analysis. Material containing iron oxide particles, of which at least 90 wt.% have a particle size less than or equal to 200 micrometers, and, as a rule, with more than 50 wt.% less than 50 micrometers, is, for example, pellets. The accepted method for analysis is ISO 13320 as of March 2019.

The reducing gas may consist of hydrogen H ₂ or be a mixture of hydrogen with one or more other gases. For example, commercially pure hydrogen can be used. Thus, the reducing agent may be at least hydrogen H ₂ . Other gases can themselves also have a reducing effect on the particles containing oxide iron, that is, in addition to hydrogen, H ₂ are other reducing agents. The other gas may be, for example, carbon monoxide CO. Hydrogen can be produced, for example, by electrolysis, preferably from clean energy or from natural gas reforming.

The kinetics of reduction of iron oxides with hydrogen H ₂ is fundamentally, and especially at lower temperatures, more favorable than in the case of other gases, for example, in comparison with carbon monoxide CO. Therefore, the reducing gas according to the invention must contain at least 30 mole % of hydrogen H ₂ in order to provide economically acceptable reduction kinetics in the preferred temperature range according to the invention due to the risk of sticking. Compared to a reducing gas with a lower hydrogen content, therefore, less fresh reducing gas must be used to achieve a certain degree of metallization. Compared to a reducing gas with a lower hydrogen content, therefore, if necessary, the exhausted reducing gas leaving the fluidized bed must be recycled after treatment in order to use the unreacted reducing agent contained therein.

The reducing gas is fed through the fluidized bed from bottom to top, against the direction of gravity. According to the invention, the method is carried out in countercurrent. The movement of particles - containing iron oxide particles, an intermediate product, a reduction product - in a fluidized bed is carried out so that a counterflow of reducing gas and particles occurs. During the process, iron oxide-containing particles are fed into the fluidized bed, and the reduction product is removed from the fluidized bed. The movement from the point of supply to the point of outlet in countercurrent with respect to the reducing gas flowing against the direction of gravity takes place essentially horizontally.

In the case of a fluidized bed in countercurrent - realized, for example, in a channel with a fluidized bed - direct reduction is carried out - preferably in an almost horizontal position - along the length of the fluidized bed from the place of supply to the place of output. Thus, along the length of the fluidized bed, the quality of the iron oxides contained varies, for example, the proportions of the iron oxides of magnetite, hematite or wustite, or the porosity of the particles. Back mixing, as can occur in the case of a fluidized bed until homogeneity at all points, is undesirable, because as a result, for example, material with a low degree of reduction could pass from the point of entry to the point of exit or the residence time of the particles would be unstable .

The reduction product - for example, sponge iron DRI with a metallization degree greater than 90% - has a higher metallization degree than those containing iron oxide particles. The degree of metallization is defined as the ratio of the mass fractions of metallic iron contained to the total iron contained in the reduction product:

degree of metallization=mass fraction (metal Fe)/mass fraction (total Fe).

Depending on the embodiment of the method, the degree of metallization of the reduction product may be different. Depending on the purpose (end use) of the reduction product, a higher or lower degree of metallization may be required - for example, when using the method according to the invention for pre-reduction for further final reduction, it can also be less than the degree of metallization of DRI sponge iron, for example, about 60%.

The residence time of the particles in the fluidized bed before being converted into the desired reduction product, called the residence time of the particles, depends on the kinetics of the ongoing reduction reaction. This in turn depends on a variety of factors such as the composition of the reducing gas, the speed of the reducing gas, the type of particles containing iron oxide - for example, depending on whether magnetite, hematite or wustite are reduced - the porosity of the particles being reduced. The residence time of the particles corresponds to the time it takes for the particles to move from the place of supply to the place of output, while the particles are fed in the form of particles containing iron oxide, and output in the form of particles of the reduction product. The value of the residence time of the particles depends, for example, on the distance between the feed point and the output point and on the height of the fluidized bed. When carrying out the method according to the invention in countercurrent, which is carried out, for example, in a substantially horizontal fluidized bed, with preferably continuous supply of particles containing iron oxide and with preferably continuous withdrawal of the reduction product, the residence time of the particles can be simply controlled by the height of the layer, given, for example, by overflow thresholds. In this case, the residence time of the particles can also be controlled by choosing the distance between the feed point and the output point. A substantially horizontal position is up to 10° off the horizontal, preferably up to 5° off the horizontal, and more preferably up to 2° off the horizontal. If the deviation from the horizontal is too large, the height of the layer in the fluidized bed along the length of the fluidized bed from the place of supply to the place of output becomes unequal, which has a negative effect on the controllability of the residence time of the particles.

The residence time of the gas refers to the reducing gas in the fluidized bed. If the residence time of the gas is too short to establish an approximate equilibrium of the reduction reaction, then relatively much unreacted reducing agent leaves the fluidized bed. The proportion of unreacted reducing agent in the gas leaving the fluidized bed, referred to as spent reducing gas, can be influenced by the height of the bed. The implementation of the process in countercurrent makes it easy to reconcile the requirements regarding the residence time of the particles and the residence time of the gas.

Positive effects of the invention

With the method according to the invention it is possible to economically recover iron-containing particles without prior agglomeration. Compared to known methods, it is also possible to reduce the construction and operating costs of the installation for carrying out the method, since at least the temperature, and if necessary also the pressure, is relatively low (low). It also means that there will be less investment in terms of safety.

The increase in pressure manifests itself in an increased mass flow of the reducing gas as a possible increase in productivity for the same reactor area or a possible decrease in reactor area for the same productivity. At the same time, with the expected high pressure, higher requirements may be imposed on the design and safety of the reduction unit.

The method according to the invention is preferably carried out at a temperature between the limit values of 773 K and 1173 K, and with the inclusion of these limit values. This reduces the risk of particle sticking in the fluidized bed to an undesirable extent, which at higher temperatures would create problems. Below 773 K, for thermodynamic and kinetic reasons, recovery does not occur to the extent that would be satisfactory for an economically acceptable implementation of the process.

For example, particles containing iron oxide are preheated and injected into the fluidized bed at temperatures up to 1173 K, and the reducing gas is fed into the fluidized bed at temperatures up to 1023 K. Reduction with hydrogen H ₂ proceeds endothermically, so that the reduction product is obtained at a lower temperature, for example about 853 K.

Instead of preheating outside the fluidized bed or in addition to it, it would also be possible to set the ratio of exothermically reacting reducing components, such as, for example, carbon monoxide CO, and endothermically reacting reducing components, such as, for example, hydrogen H ₂ , in the reducing gas so that to bring to the fluidized bed in situ heat in the required amount.

The method according to the invention is preferably carried out at a slight excess pressure relative to the environment. With a slight excess pressure, on the one hand, depending on the design of the apparatus and the safety requirements, additional costs are still not required compared to the implementation of the method without excess pressure, and, on the other hand, the risk of ambient air entering the reactors is reduced. The overpressure is preferably up to 200,000 Pascal, including this value.

According to a preferred embodiment, the value of d ₃₀ supplied to the fluidized bed containing iron oxide particles is less than or equal to 110 micrometers. In this range, the fluidized bed can be handled particularly easily, since the entrainment of the fine iron oxide-containing particles is not very high, and the fluidization of the bed is not hampered by the large particle size.

According to a preferred variant, the process according to the invention is carried out in such a way that the iron oxide-containing particles fed into the fluidized bed are in the range of at least 50 mass % between 15 micrometers and 100 micrometers, including the boundary values.

In this range, the fluidized bed can be handled particularly easily, since the entrainment of the fine iron oxide-containing particles is not very high, and the fluidization of the bed is not hindered by the large particle size.

According to another preferred variant, the process according to the invention is carried out in such a way that the iron oxide-containing particles fed into the fluidized bed have a particle size of at least 50 mass % greater than or equal to 15 micrometers. In this range, it is particularly easy to work with a fluidized bed, since the entrainment of fine iron oxide containing particles is not very high.

The finer the iron oxide-containing particles are, the greater the costs for dedusting the spent reducing gas become necessary due to increased dust entrainment. In addition, the fluidized bed itself may become less stable and more difficult to control as the size of the iron-containing particles decreases. Preferably, particles containing iron oxide with a proportion of at most 30 mass% have a particle size of less than 10 micrometers. At least up to this fineness of the iron oxide particles, good process control is ensured.

The fluidized bed may also have different zones with different bed heights. As a rule, in the case of particles containing oxide iron, due to the presence of iron with different oxidation states, reduction occurs in several stages through intermediate products - for example, magnetite through hematite to wustite. The optimal values of the particle residence time and the gas residence time for different stages and intermediate products differ for morphological, thermodynamic, and kinetic reasons. Different intermediate products in the case of an embodiment of the method according to the invention in countercurrent are contained in different zones of the fluidized bed with different concentrations. In this context, fluidized bed zones are understood to mean areas along the direction from the feed point to the output point. Therefore, it is preferable to have different bed heights in different zones of the fluidized bed. Thus, the particle residence time and the gas residence time for different zones can be appropriately adapted by adjusting the bed height. For example, the fluidized bed can be limited by weirs or different partitioned zones of the reactor space.

The height of the bed in the fluidized bed is preferably 0.1-0.5 m, more preferably 0.3-0.4 m. In the case of an embodiment of the process according to the invention, sufficient gas residence times can be achieved by reducing iron oxide particles. and residence time of the particles. The proportion of unreacted reductant in the spent reducing gas is within economically acceptable ranges when the fluidized bed height is between 0.1-0.5 meters, with 0.1 and 0.5 included in the range.

The residence time of the reducing gas in the fluidized bed is preferably 0.1 second to 10 seconds, more preferably 1 to 2 seconds. When the reducing gas is in the fluidized bed between 1 and 2 seconds, and with the values 1 and 2 included in the interval, the elimination of oxygen can already approach equilibrium, and the proportion of unreacted reducing agent in the spent reducing gas is in this case within particularly economically acceptable limits.

The aim is precisely to consume as much reducing agent as possible during the passage of the fluidized bed. The less reducing agent is consumed, the more reducing gas must be supplied for a given amount of iron oxide-containing particles in the fluidized bed, and the greater will be the cost of recycling the unreacted reducing agent.

When implementing the method according to the invention with regard to bed height and/or gas residence time, it has also surprisingly been found that an increased pressure of the reducing gas causes a slight increase in the conversion of substances and can lead to an increase in the proportion of unreacted reducing agent in the spent reducing gas. In the case of atmospheric pressure or a slight overpressure, it is possible to work accordingly with an advantage in terms of resource saving and safety without sacrificing a significant increase in the conversion of substances.

The spent reducing gas leaving the fluidized bed is preferably recycled as a component of the reducing gas into the fluidized bed after treatment. This makes the method more economical. Hydrogen as a component of the reducing gas makes the recirculation in the reduction of iron oxide particles very simple, because in addition to the need to separate the dust, only the H ₂ O water as a reaction product has to be separated.

According to a preferred embodiment, the same reducing gas is fed into the fluidized bed throughout its length; it applies equally to composition, or to temperature, or to pressure, or to two or all three of these parameters. This makes process control simple and reduces equipment costs.

According to another preferred embodiment, different reducing gases are fed into the different zones of the fluidized bed - for example, mixtures of several components in different ratios, ie the reducing gas has a different composition in each case; it can also be a reducing gas at different temperatures, or a reducing gas at different pressures, or reducing gases that differ in two or all three of the above parameters. It is also possible for the fluidized bed to have different zones. Thus, it is possible to react with different reactive reducing gases so that different reactive intermediates are present in different zones.

The device for carrying out the method according to the invention can be made as described below. It contains a fluidized bed reactor suitable for supplying particles and reducing gas in countercurrent somewhere in the reactor space with a distribution plate to form a fluidized bed. The reactor space has at least one opening for feeding particles containing oxide iron and at least one opening for withdrawing the reaction product from the reactor space. The device also includes at least one reducing gas supply line for supplying reducing gas to the distribution plate and at least one reducing gas outlet line for removing exhausted reducing gas from the reactor space.

"Somewhere" should be understood in the sense of the ambiguity in the expression "anywhere in the reactor space".

The reactor space can be divided into several zones along the direction from the inlet to the outlet. This can be done, for example, preferably by movable overflow weirs, which block the radial mixing of particles - from the inlet to the outlet - from adjacent zones, and also allow targeted adjustment of zones with different layer heights. This can be realized in such a way that the fluidized bed reactor comprises several sub-reactors, with the spaces of the sub-reactors forming separate zones. In sum, the partial reactors form a fluidized bed reactor and the spaces of the partial reactors form a fluidized bed reactor space. The spaces of partial reactors can also be divided into several zones.

According to one embodiment, the individual zones may have different horizontal and/or vertical dimensions, so that the fluidized bed may have different widths or different maximum bed heights; thus, with the same performance, different layer heights in different zones can be realized.

According to one variant, the fluidized bed reactor - and, if necessary, partial reactors - contains (at) several identical modules. This enables the construction of an affordable plant with prefabricated modules as well as an easy adaptation to different performance requirements.

Preferably, the fluidized bed reactor contains several sub-reactors. They may be arranged in series and/or in parallel. They are preferably connected to each other via transmission devices. For example, when operating, particles from any partial reactor in the direction from the feed port to the output port along the fluidized bed reactor are transferred by transfer devices to the adjacent partial reactor. The transfer devices are suitable for transferring particles without air entering the partial reactors or gas leakage.

Preferably, several partial reactors are placed one above the other. This reduces the space requirement for the device to carry out the method of the invention. Particles move under the action of gravity from the upper inlet to the lower outlet.

The distribution plate of the fluidized bed reactor is located essentially horizontally. In this case, the deviation from the horizontal is up to 10°, preferably a deviation of up to 5°, more preferably a deviation of up to 2°. If the deviation from the horizontal is too large, the height of the layer in the fluidized bed along the length of the fluidized bed from the place of supply to the place of output becomes unequal, which has a negative effect on the controllability of the residence time of the particles.

Preferably, the distribution plate of the fluidized bed reactor or at least one partial reactor is placed obliquely from the inlet to the downstream outlet. This arrangement simplifies the countercurrent flow of particles, as is known, for example, in the case of air supply channels.

In one embodiment, each zone contains a separate reducing gas supply line. According to one embodiment, each sub-reactor is provided with a separate reducing gas supply line. All of these reducing gas supply lines preferably exit from the central line. From the central pipeline, the reducing gas enters the reducing gas supply pipelines. The reducing gas fed through the central pipeline can be, for example, fresh reducing gas, i.e. reducing gas that has not passed through the fluidized bed, or a mixture of fresh reducing gas and recycled reducing gas, i.e. reducing gas obtained from a spent reducing agent treatment plant. gas.

According to one variant, each zone contains a separate pipeline for removing the reducing gas. According to one variant, a separate reducing gas vent line runs from each partial reactor. All reducing gas bleed lines preferably enter a bleed header which leads to the gas treatment unit. In the gas treatment plant, the spent reducing gas is, for example, dedusted and dried. Combining all spent reducing gas streams exiting the reactor space or zones and/or sub-reactors for the purpose of centralized treatment facilitates their recycling to the recovery process.

Another object of the present invention is a signal processing device with a computer readable program code, characterized in that it contains control instructions for implementing the method according to the invention. In the case of another object, we are talking about a signal processing device for implementing the method according to any one of paragraphs 1-12 of the claims.

Another object of the present invention is a computer-readable program code for a signal processing device, characterized in that the program code contains control instructions that the signal processing device issues to implement the method according to the invention. In the case of another object, we are talking about a computer program containing instructions for the signal processing device, which, when the program is executed, it issues to the signal processing device in order to carry out the method according to any one of claims 1-12 of the claims.

Another object of the present invention is an information carrier with the machine-readable program code of the invention recorded thereon. In the case of another object, we are talking about an information carrier with a computer program recorded on it for implementing the method according to any one of paragraphs 1-12 of the claims.

Brief description of the drawings

The present invention is described below by way of example using several schematic figures.

In FIG. 1 shows the implementation of the method according to the invention in a schematically shown space of the reactor in section.

In FIG. 2 schematically shows the arrangement of several sub-reactors.

In FIG. Figure 3 shows the theoretical dependence according to accepted scientific concepts and the dependence found by the authors between the fictitious speed U and particle size d.

Description of Embodiments

Examples

In FIG. 1 schematically shows the implementation of an embodiment of the method according to the invention. The method is carried out in a device 1. Particles 2 containing iron oxide, which have a particle size of at least 90 mass% less than or equal to 200 μm, are fed to the supply point A through the opening 3 for continuous supply to the fluidized bed 4 in the reactor space 5 reactor 6 with a fluidized bed, as shown by the arrows. In one embodiment, up to 30 wt % of the iron oxide containing particles may be smaller than 15 µm. The fluidized bed 4 in the reactor space 5 is formed due to the fact that the particles are lifted against the action of gravity by the reducing gas 8 coming from below through the distribution plate 7, shown by unshaded curly arrows. In the example shown, the same reducing gas 8 is supplied everywhere. The distributor plate 7 is indicated by openings in the lower part of the reactor space 5; for better clarity, not each of the openings is accompanied by a separate curly arrow and not all curly arrows are marked with the reference numeral 8. The iron oxides in the iron oxide-containing particles 2 are reduced by the reducing gas 8 into the reduction product 9 . The reducing gas 10 exhausted during the reduction of iron oxides in iron oxide-containing particles exits (shown by shaded curly arrows) upwards from the fluidized bed 4 . The reducing gas 8 consists, for example, of commercially pure hydrogen H ₂ ; accordingly, the spent reducing gas 10 contains, for example, water H ₂ O and hydrogen, since not all of the hydrogen coming from below is reacted. Particles carried upward by the exhaust reducing gas 10 from the fluidized bed are not shown separately. From the outlet B of the fluidized bed 4 in the reactor space 5, particles of the reduction product 9 are continuously removed, as shown by arrows. The reducing gas 8 flows through the fluidized bed 4 from the bottom upwards in a countercurrent flow at a speed greater than 0.05 m/s. The temperature of the supplied iron oxide particles 2 is, for example, 1173 K, and the temperature of the incoming reducing gas 8 is 1023 K everywhere. The reduction product 9 has, for example, a temperature of 853 K.

In the fluidized bed reactor 6 shown schematically in FIG. 1, there is preferably a slight overpressure of 200,000 Pa relative to the environment.

The presented method can be, for example, carried out so that the height of the fluidized bed 4 is 0.1-0.5 m and/or the gas residence time is 0.1-10 s, and preferably 1-2 s.

The reducing gas 8 is fed through the reducing gas supply line 11 to the distribution plate 7. The reducing gas outlet line 12 is used to remove the exhausted reducing gas 10 from the reactor space 5.

In FIG. 2 schematically shows an embodiment in which the fluidized bed reactor 13 comprises several sub-reactors 14, 16, 18, 20. The sub-reactors are connected to each other in series; the partial reactor 14 is connected at its end 15 to the partial reactor 16, which, in turn, is connected to the partial reactor 18 at its end 17. The partial reactor 18 is connected to the partial reactor 20 at its end 19. The connections are made through the transfer devices 21a, 21b, 21c. The opening A for supplying iron oxide particles 22 is located at the beginning 23 of the partial reactor 14, and the opening B for withdrawing the reaction product 24 is located at the end 25 of the partial reactor 20. 21b, 21c are respectively fed from the partial reactor to the subsequent partial reactor, in the direction from the supply port A along the fluidized bed to the outlet port B. While the solid material in the fluidized bed (not shown separately), i.e. containing iron oxide particles, particles of intermediate products and particles of the reduction product, passes through successive, i.e. serially connected to each other partial reactors 14, 16 , 18, 20 from the supply port A to the output port B from the fluidized bed reactor 13, through which a reducing gas (not shown separately) flows countercurrently.

On the image in Fig. 2 partial reactors 14, 16, 18, 20 are placed vertically one above the other. They are made with slightly inclined bottoms. The various sub-reactors 14, 16, 18, 20 have separate reducing gas supply lines 26a, 26b, 26c, 26d, all of which exit the central line 27 (for reasons of clarity, their connections to the central line 27 are not shown separately). From the various sub-reactors 14, 16, 18, 20 separate reducing gas vent lines 28a, 26b, 26c, 26d all enter into a bleed manifold 29 (for reasons of clarity, their connections to the bleed manifold 29 are not shown separately). The exhaust manifold 29 leads to the gas treatment plant 30, where the spent reducing gas is, for example, dedusted and dried. Via the recirculation line 31, the processed product - in the case of the example of FIG. 1 dedusted and dried hydrogen - is fed into the central pipeline 27 and thus, together with fresh hydrogen H ₂ coming from another source, is recycled as a component of the reducing gas into the process.

The fluidized bed in the fluidized bed reactor 13 has several zones - one zone is located in each of the partial reactors 14, 16, 18, 20. Owing to the different sizes of the sub-reactors 14, 16, 18, 20 shown schematically in FIG. 2 with different heights, different bed heights are provided in different zones of the fluidized bed during continuous operation of the process.

According to one variant of the process according to the invention, different reducing gases could be supplied to different zones; this option is not shown separately.

A detailed image of the system for supplying and obtaining fresh hydrogen H ₂ from other sources is not shown for reasons of better clarity.

In general, the temperature, pressure and composition of the reducing gas affect the kinetics of the reaction, which results in requirements for gas residence time and particle residence time, as well as bed height. The speed of the reducing gas affects the degree of entrainment from the fluidized bed and the amount of circulating reducing gas. The reaction kinetics and the speed of the reducing gas, in turn, affect the required specific reaction surface.

In FIG. 3, the solid line shows the scientifically expected values of the theoretical suspension rate U _t for different sizes d of DRI/iron ore spherical particles at 1023 K with hydrogen H ₂ as the reducing gas and at an overpressure of 200,000 Pa:

The dashed line also shows the relationship actually found, which deviates from the accepted scientific ideas, between the fineness d and the rate of transfer to a suspended state U _max :

U _max \u003d (40000 * d) ^2.78 .

The above description of the preferred embodiments of the invention contains numerous features, which are partially given in separate dependent claims in several combined forms. However, these features can also be usefully considered individually and rationally generalized in other combinations. In particular, these features, individually and in any suitable combination, can be combined in the process of the invention.

When in the description or in the claims some terms are used in the singular or in combination with numerals, the scope of protection of the invention with respect to these terms is not limited to the singular or a specific numeral. The words "one" or "one" should be understood as an indication of uncertainty, and not as numerals.

The described features, features and advantages of the invention, as well as the means and methods by which they are achieved, can be more clearly and clearly understood in connection with the description of the example or examples of the invention, which are explained in more detail by the drawings. The example or examples of implementation serve to explain the invention and do not limit the invention either by the combinations of features indicated therein, or with respect to functional features. In addition, the features of each of the exemplary embodiments acceptable for this purpose can also be considered completely in isolation, apart from any exemplary embodiment, introduced into one of the other exemplary embodiments to complement it, and combined with one of any claims.

Although the invention has been explained and described in detail by one or more preferred embodiments, it is not limited to one or more of the disclosed examples, so that other variations can be developed without departing from the scope of the invention.

List of conventions

one Device for carrying out the method according to the invention 2 Particles containing iron oxide 3 Feed hole four fluidized bed 5 Reactor space 6 Fluidized bed reactor 7 distribution plate eight Reducing gas 9 Recovery product ten Waste reducing gas eleven Reducing gas pipeline 12 Reductant gas pipeline 13 Fluidized bed reactor fourteen partial reactor fifteen End 16 partial reactor 17 End eighteen partial reactor 19 End twenty partial reactor 21a, 21b, 21c Transfer devices 22 Iron-containing particles 23 Start 24 reaction product 25 End 26a, 26b, 26c, 26d Reducing gas pipelines 27 Central pipeline 28a, 28b, 28c, 28d Reducing gas pipelines 29 Outlet manifold thirty Gas treatment plant 31 Recirculation pipeline

Claims (31)

1. A method for direct reduction of iron oxide-containing particles (2) into a reduction product (9) in a fluidized bed (4), through which a reducing gas containing 30-100 mol.% hydrogen H ₂ passes countercurrently (8), characterized in that particles (2) containing iron oxide fed into the fluidized bed (4) have a fineness of at least 90 wt.% less than or equal to 200 micrometers, at the same time, the fictitious speed U of the reducing gas (8) passing through the fluidized bed (4) is set between 0.05 m/s and 1 m/s so that, for a fineness d equal to d ₃₀ , the oxide containing gas supplied to the fluidized bed (4) iron particles (2), exceeds the theoretical rate of translation into a suspended state U _t and less than or equal to U _max , and the value of d ₃₀ indicates that 30 wt.% containing oxide iron particles have a particle size of not more than d, moreover, the theoretically predicted value of U _t for size d is obtained from the equation:

and U _max is obtained from the empirically found relationship between the particle size and the rate of transfer to a suspended state of particles with a particle size d equal to d ₃₀ : U _max \u003d (40000 * d) ^2.78 , where U _t - theoretical speed of transfer to a suspended state, m/s; U _max - maximum fictitious speed for d=d ₃₀ , m/s; ρp - particle density, kg/m ³ ; ρg is the density of the reducing gas, kg/m ³ , in operating mode; d - particle size, m; g - free fall acceleration, m/s ² ; μ - dynamic viscosity, kg/(m s); C _W - drag coefficient; Re is the Reynolds number. 2. Method according to claim 1, characterized in that it is carried out at a temperature between 773 K and 1123 K. 3. The method according to any one of paragraphs. 1 or 2, characterized in that it is carried out at an excess pressure of 200,000 Pa relative to the environment. 4. The method according to any one of paragraphs. 1-3, characterized in that d ₃₀ is less than or equal to 110 micrometers for particles (2) containing iron oxide fed into the fluidized bed. 5. The method according to any one of paragraphs. 1-3, characterized in that the particles (2) containing iron oxide fed into the fluidized bed are at least 50 wt.% in the range between 15 micrometers and 100 micrometers. 6. The method according to any one of paragraphs. 1-5, characterized in that the iron oxide-containing particles (2) fed into the fluidized bed with a maximum fraction of 30 wt.% are less than 10 micrometers. 7. The method according to any one of paragraphs. 1-6, characterized in that the fluidized bed (4) has different zones with different bed heights. 8. The method according to any one of paragraphs. 1-7, characterized in that the bed height in the fluidized bed is 0.1-0.5 m, and more preferably 0.3-0.4 m. 9. The method according to any one of paragraphs. 1-7, characterized in that the residence time of the reducing gas (8) in the fluidized bed (4) is from 0.1 s to 10 s, more preferably 1-2 s. 10. The method according to any one of paragraphs. 1-9, characterized in that the spent reducing gas (10) leaving the fluidized bed (4) is recycled after treatment as a component of the reducing gas (8) into the fluidized bed (4). 11. The method according to any one of paragraphs. 1-10, characterized in that the same reducing gas (8) is supplied to the fluidized bed (4) everywhere. 12. The method according to any one of paragraphs. 7-10, characterized in that different reducing gas (8) is supplied to different zones of the fluidized bed (4). 13. A signal processing device with a computer-readable program code, characterized in that it contains control commands for implementing the method according to any one of paragraphs. 1-12. 14. A storage medium with a machine-readable program code recorded on it for a signal processing device, characterized in that the program code contains control commands that the signal processing device issues to implement the method according to any one of paragraphs. 1-12.

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