Method for operating a direct reduction system

Abstract

The invention relates to a method for operating a direct reduction system according to claim 1.

Description

[0001] Method for operating a direct reduction plant

[0002] The invention relates to a method for operating a direct reduction plant.

[0003] In the direct reduction process, a heterogeneous reaction takes place between the iron ore carriers and the reducing gas, during which oxygen is removed from the iron ore. The reaction takes place below the melting point of the iron ore, so that the external shape of the ore remains unchanged. Since the removal of oxygen results in a weight reduction of approximately 1 / 4 to 1 / 3, the reaction product has a honeycomb-like microstructure (solid, porous iron with many air-filled spaces). For this reason, directly reduced iron is often also referred to as sponge iron. The direct reduction process traditionally uses a shaft furnace as a reactor with a reduction zone through which the iron ore carrier passes against the flow of the reducing gas. In a special variant of the process, the reduction zone is arranged above a cooling zone in the shaft furnace, with a cooling gas flowing through the cooling zone.The iron ore carrier then passes through the shaft furnace in a vertical direction from top to bottom. Such shaft furnaces allow for good circulation of reducing gas and optional cooling gas through the iron ore carrier due to the underlying chimney effect. In particular, the reducing gas flows through the reduction zone against the direction of movement of the iron ore carrier. Accordingly, the cooling gas also flows through the cooling zone against the direction of movement of the produced sponge iron. The countercurrent principle is therefore used in both the reduction zone and the optional cooling zone to achieve an efficient reaction between the gases and the solids.

[0004] Carbon monoxide or hydrogen, or a mixed gas comprising carbon monoxide and hydrogen, is used as the reducing gas. This reducing gas (or mixture) is fed hot to the direct reduction plant, where iron ore carriers are reduced.

[0005] The use of high-quality / lumpy iron ore carriers, especially with increasing degrees of metallization, tends to lead to so-called "sticking" or "plating." Sticking or plating is the uncontrolled caking and agglomeration of the iron ore carriers without or under mechanical pressure, respectively. This can lead to disruptions with increasing reduction gas temperatures and also with increasing hydrogen contents, see the article "Sticking of iron ore pellets in direct reduction with hydrogen and carbon monoxide: Behavior and prevention," DOI: 10.1007 / S11771-014-1968-6. It also proposes coating the iron ore carrier to reduce sticking / plating in the reduction process, which, however, slows the reduction and produces additional slag during the smelting process.

[0006] If sticking / plating occurs, this can be observed with a delay due to reduced sponge iron removal and poorer permeability, meaning that countermeasures may be initiated too late. Early detection of sticking is therefore desirable.

[0007] The object of the present invention is to ensure optimal operation and / or to detect possible sticking / plating in good time in order to essentially avoid resulting malfunctions.

[0008] This object is achieved by a method having the features of claim 1 and by a direct reduction plant having the features of claim 10.

[0009] The first teaching thus relates to a method for operating a direct reduction plant in which iron ore carriers are heated and reduced to sponge iron using a hot reducing gas. At least one parameter is recorded which, if a predefined threshold is exceeded or not reached, indicates the occurrence of sticking and / or a deviation from the target process specifications.

[0010] According to a second teaching, the invention relates to a direct reduction plant with a shaft furnace for the direct reduction of iron ore carrier to sponge iron and means for feeding hot reducing gas. At least one means for recording parameters is provided, which indicates the occurrence or occurrence of sticking and / or a deviation from the target process specifications when a predefined threshold value is exceeded or undershot.

[0011] In order to be able to detect irregularities during ongoing operations and thus deviations from target process specifications and / or the occurrence or onset of sticking / plating early and in a timely manner, the inventors have discovered that at least one parameter can be recorded which can provide information about adverse conditions and thus about potential undesirable malfunctions by ensuring that a predefined threshold value is not exceeded or undershot. A direct reduction plant is adjusted for economic efficiency, particularly after commissioning and ramp-up. Every change, for example, the temperature of the reducing gas, the composition of the reducing gas, the quality / composition of the iron ore carriers, to name just three possible criteria influencing the process, should be adjusted for optimal operation.If the process target specifications remain constant, a corresponding operating profile can be derived and, along with it, parameters that are optimal in a certain process window. If a predefined threshold is exceeded or undershot, countermeasures should be initiated in order to bring the operating mode back into the optimal range and / or to reduce or avoid sticking / plating.

[0012] The hot reducing gas is heated to a temperature between 500 and 1100 °C. The temperature of the hot reducing gas can be, in particular, 600 °C, preferably at least 700 °C, more preferably at least 800 °C. When feeding in (essentially 100%) hydrogen, this can be done without additional exposure and thus post-combustion with oxygen, meaning that this ensures the complete utilization of the hydrogen for the reduction of the iron ore carrier and thus the process can be operated more economically. Very high hydrogen contents do not need to be heated to such high temperatures, since the reduction of the iron ore (cf. Baur-Glässner diagram) can take place at low temperatures. The temperature can be reduced, in particular, to a maximum of 1050 °C, preferably to a maximum of 1000 °C, more preferably to a maximum of 950 °C.

[0013] When iron ore carrier is reduced to sponge iron, the elemental iron increases and can be described by the degree of metallization: Degree of metallization [%] = 100 * elemental Fe [%] / total Fe [%]■ Due to the contact of the iron ore carrier surface with the hot reducing gas, the reaction processes and ultimately metallization begin from the outside in. Complete reduction, i.e. a degree of metallization of 100%, is theoretically possible, but in practice economics plays an important role and thus the time required for reduction, so a degree of metallization of up to 100%, in particular up to 98%, is aimed for. The higher the degree of metallization, the greater the tendency towards sticking. A degree of metallization of at least 70%, in particular 75%, preferably at least 80%, more preferably at least 85% and particularly preferably 90% is aimed for in the direct reduction process.Iron ore carriers can be provided in the form of sinter, pelites and / or iron lump ore.

[0014] According to one embodiment, the at least one parameter can be recorded in the form of a vibration. The at least one means for recording the parameters comprises at least one vibration sensor. Every plant in operation or currently in operation, including a direct reduction plant, generates vibrations that can be measured, for example, using vibration sensors or structure-borne sound sensors. During optimal or normal operation, a direct reduction plant also "oscillates" in a specific frequency range that is typical for the plant. In particular, the vibration sensor(s) used should not have a resonance frequency in the "typical" frequency range of the direct reduction plant. The vibration sensors can be installed, for example, in the reduction zone of the shaft furnace and / or at other locations where the information can be acquired. This can be determined by trial and error.A deviation from the typical frequency range, i.e., exceeding or falling below a predefined threshold, especially for an extended period, can be an indication of an incipient problem in the direct reduction plant. The operating principle of vibration or structure-borne sound measurement is well known in the field.

[0015] According to an alternative or additional embodiment, the at least one parameter can be recorded in the form of sound. The at least one means for recording the parameters comprises at least one sound pressure sensor. Every plant that is in operation or currently in operation, including a direct reduction plant, generates sound in addition to vibrations, which can be measured, for example, using sound pressure sensors. During optimal or normal operation, a direct reduction plant also generates a specific sound pressure that is typical for the plant. The sound pressure sensors can, for example, be provided in the reduction zone of the shaft furnace and / or at other locations where the information can be acquired. This can be determined by trial and error.A deviation from the typical sound pressure, i.e., a value that exceeds or falls below a predefined threshold, especially for an extended period, can indicate an incipient problem in the direct reduction system. The functional principle of a sound pressure measurement is well known in the field.

[0016] According to an alternative or additional embodiment, the at least one parameter can be detected in the form of a current flow. The at least one means for detecting the parameters comprises at least two electrodes. In the direct reduction plant, using the example of a shaft furnace, the at least two electrodes are distributed around the circumference, in particular in the area of ​​the reduction zone, preferably in the area where the hot reducing gas is fed in or above, and have different polarities. They are in contact with the iron ore carriers, which are also in contact with one another. Due to the partially metallized iron ore carriers contacting each other (where the metallization can initially begin on the surface and progress inwards as described), an electrical circuit can be formed, and as a result, an electrical current flow can be generated, which can be detected by means of current measurement.The at least two electrodes can, for example, be arranged on the wall on the circumference within the shaft furnace, in particular integrated within or on a refractory lining, whereby contact should be maintained with the iron ore carrier passing through. The electrodes are preferably arranged partially protruding within the lining in the reduction zone. In order to withstand the harsh conditions, the electrodes can be made of steel plates or electrically conductive ceramics. During optimal or normal operation, a certain current flow or measurable electrical resistance prevails. If there is a deviation from the typical current flow or electrical resistance, i.e. if a predefined threshold value is exceeded or not reached, in particular for a longer period of time, this can be an indication of an incipient problem in the direct reduction plant. The principle of a current flow orResistance measurement is well known in the professional world.

[0017] If irregularities occur such that the parameters exceed or fall below a predefined threshold for a longer period of time, for example for at least 2 minutes, in particular for at least 3 minutes, preferably for at least 4 minutes, preferably for at least 5 minutes, at least one of the following countermeasures must be initiated in order to essentially avoid a particularly prolonged disruption, in the worst case a standstill:

[0018] - to reduce, at least temporarily, the temperature to which the reducing gas is heated;

[0019] - to increase the discharge quantity at least temporarily;

[0020] - to reduce the flow rate of the hot reducing gas, at least temporarily;

[0021] - to change the composition of the reducing gas, in particular by adding or omitting its carbonaceous components, at least temporarily; to change the composition (mixture) of the iron ore carriers, in particular by adding or omitting sinter and / or pelites and / or iron ore / lump ore, at least temporarily.

[0022] A temporary reduction in the temperature of the reducing gas, as well as a temporary reduction in the flow rate of the hot reducing gas, temporarily lowers or reduces the energy required to convert the iron ore carrier to sponge iron, thus also influencing the degree of metallization. A temporary increase in the sponge iron discharge can reduce (further) solid bonding between the individual iron ore carriers / sponge iron. The countermeasures can be maintained until the parameter(s) have returned to the normal range and thus essentially reach the optimal process window.

[0023] The invention is explained in more detail using the following embodiments in conjunction with the figures.

[0024] Figure 1 illustrates the invention using the example of a direct reduction plant comprising a shaft furnace (10). In the direct reduction plant, iron ore carrier (io) is heated and reduced to sponge iron (si) by means of a hot reducing gas (12). Iron ore carrier in the form of, for example, lump / iron ore (io) is introduced at the upper end of the shaft furnace (10). The sponge iron (si) produced is removed at the lower end of the shaft furnace (10). A reduction zone (11) and optionally a cooling zone (14) are arranged in the shaft furnace (10). The reduction zone (11) is arranged above the optional cooling zone (14).The cooling zone (14) is not absolutely necessary if hot use of the hot sponge iron (si) leaving the reduction zone (11) directly is possible, for example by melting the sponge iron (si) in a suitable melter (not shown) or feeding it to a briquetting plant (not shown) for the production of so-called and known "hot DRI". The reducing gas (12) as well as the optional cooling gas (15) flow through the iron ore carrier located in the reduction zone (11) and the sponge iron located in the optional cooling zone (14) in countercurrent, thus counter to a direction of movement of the iron ore carrier (io) or sponge iron. Before being fed into a heater / reformer (not shown), the reducing gas (12) is heated to a temperature of at least 500 and up to 1100 °C. The reducing gas (12) can have a high hydrogen content of up to 100% hydrogen.The process gas (13) discharged from the reduction zone (11) of the shaft furnace (10) may consist of, among other things, unused reduction gas and unavoidable impurities.

[0025] In order to be able to detect irregularities during operation and thus deviations from process target specifications and / or incipient or occurring sticking / plating early and in a timely manner, at least one parameter is recorded that can provide conclusions about the circumstances by ensuring that a predefined threshold value is not exceeded or undershot. The parameters can be recorded using means (17) that are arranged or provided, for example, in the reduction zone (11), in particular in the area or above the feed of the hot reduction gas (12). Other locations may also be considered and can be determined through appropriate tests.

[0026] The at least one parameter can be recorded, for example, in the form of a vibration. The at least one means (17) for recording the parameters comprises at least one vibration sensor (20). Alternatively or additionally, the at least one parameter can be recorded, for example, in the form of a sound. The at least one means for recording the parameters comprises at least one sound pressure sensor (19), see Figure 2, which shows an enlarged, schematic representation of the means (17) from Figure 1. During operation, a specific frequency range or one typical for the direct reduction plant oscillates and / or generates a specific sound pressure that is typical for the direct reduction plant, which is / are processed by suitable means (not shown) into signals that can be displayed, for example, in the control center for monitoring and / or made available to an automated system for monitoring.A deviation from the typical frequency range and / or sound pressure, i.e. an exceedance or undershoot of a predefined threshold, especially for a longer period of time, can be an indication of an incipient problem in the direct reduction plant.

[0027] Alternatively or additionally, the at least one parameter can be recorded, for example, in the form of a current flow / resistance. The at least one means for recording the parameters comprises at least two electrodes (18), see Figure 3, which shows an enlarged, schematic representation of the means (17) from Figure 1. The at least two electrodes (18) are in contact with the already partially metallized iron ore carriers passing through, so that an electrical current flow / resistance can be measured. If the typical current flow / resistance deviates by exceeding or falling below a predefined threshold value, especially for a longer period of time, this can be an indication of an incipient problem in the direct reduction plant.

[0028] If these deficiencies occur for a period of at least 2 minutes, appropriate countermeasures must be taken by initiating at least one of the following countermeasures: - at least temporarily reducing the temperature at which the reducing gas (12) is heated; - at least temporarily increasing the discharge quantity of the sponge iron (si); - at least temporarily reducing the flow rate of the hot reducing gas (12); - at least temporarily changing the composition of the reducing gas (12) by adding or omitting carbon-containing components; - at least temporarily changing the composition (mixture) of the iron ore carriers, for example by adding or omitting sinter and / or pelites and / or iron ore / lump ore.

[0029] With the above-mentioned operating mode, sticking / plating and / or defects in the reduction process (unsteady operation) can be detected early or in a timely manner.

Claims

Patent claims 1. A method for operating a direct reduction plant in which iron ore carriers are heated and reduced to sponge iron by means of a hot reducing gas, characterized in that at least one parameter is recorded which, when a predefined threshold value is exceeded or fallen below, indicates an incipient or occurring sticking / plating and / or a deviation from the target process specifications.

2. The method according to claim 1, wherein the parameter is detected in the form of a vibration.

3. The method according to claim 1, wherein the parameter is detected in the form of a sound.

4. The method according to claim 1, wherein the parameter is detected in the form of a current flow / resistance.

5. Method according to one of the preceding claims, wherein the temperature at which the reducing gas is heated is at least temporarily reduced by falling below or exceeding the predefined threshold value.

6. Method according to one of the preceding claims, wherein the discharge quantity is at least temporarily increased by falling below or exceeding the predefined threshold value.

7. Method according to one of the preceding claims, wherein the flow rate of the hot reducing gas is at least temporarily reduced by falling below or exceeding the predefined threshold value.

8. Method according to one of the preceding claims, wherein the composition of the reducing gas is changed at least temporarily by falling below or exceeding the predefined threshold value.

9. Method according to one of the preceding claims, wherein the composition of the iron ore carriers is changed at least temporarily by falling below or exceeding the predefined threshold value.

10. Direct reduction plant with a shaft furnace (10) for the direct reduction of iron ore carrier (io) to sponge iron (si) and means for feeding in hot reducing gas (12), characterized in that at least one means (17) is provided for detecting parameters with which, when a predefined threshold value is exceeded or undershot, an indication is given of an occurring or occurring sticking / plating and / or a deviation from the target process specifications.

11. Direct reduction plant according to claim 10, wherein the means (17) comprises at least one vibration sensor (20).

12. Direct reduction plant according to claim 10, wherein the means (17) comprises at least one sound pressure sensor (19).

13. Direct reduction plant according to claim 10, wherein the means (17) comprises at least two electrodes (18).

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