Field of the invention

The invention relates to a method and a device for raceway depth measurement in a blast furnace, and the use thereof in a control system.

Background of the invention

Blast furnaces have been known for several hundred years. More than 1.1 billion tonnes of iron were produced globally in 2016 via the blast furnace (BF) route. Although the overall process and the chemical reactions inside a BF are well understood, it still remains a kind of black box when it comes to local flow conditions and the movement of solid particles, gas, and liquids inside. The conditions inside a blast furnace are hostile, inaccessible and therefore largely unknown. Measurements are complicated, especially in the bottom part of the blast furnace, if possible at all. For iron makers operational know-how and experience, to end up with hot iron having the desirable characteristics, is of significant importance. Measurements in the bottom part can only occur on or near the outer edge of the blast furnace. In the top part the conditions are, in general, more favourable.

In the lower part of the BF, preheated air and reducing agents (gas, oil or pulverized coal) are often injected through tuyeres into a bed of coke particles, forming a void zone, called a "raceway", in which the injected reducing agent and some of the coke descending from the top of the BF are converted into a gaseous reducing agent. A very important process parameter is the size of the raceway, mainly the depth, which is formed largely by the flow of hot blast (oxygen enriched air) through the tuyeres. The raceway depth is linked to the combustion of gas and injection coal in the bottom part of the blast furnace and thus far could not be measured accurately. In the past, temperature and pressure sensors have been installed in the wall of the blast furnace, but the measurements were not representative for the conditions in the bottom part of the blast furnace. Further, the hot blast and coal distribution over the different tuyeres and the effect on the inner state of the bottom part of the blast furnace are largely unknown. As blast furnace stability and homogeneity is very important to produce a constant quality at a good speed, iron makers are keen on better control of the processes in the blast furnace.

The shape and size of the raceway greatly affect the combustion of the coke and the injected reducing agents in the BF, and therefore these raceways are crucial to the operation of a BF. Unfortunately, raceway blockages are a regular occurrence in blast furnace operation. These blockages mainly occur due to erratic movements in the burden. Another undesired phenomenon is channelling which happens when the ascending gases in the furnace do not properly get uniformly distributed both radially and circumferentially in the furnace and find a passage of least resistance. This diversion of the gases upsets the preheat of the materials and the reduction process. Early detection of these blockages and channelling events is important to avoid tuyere damages, to avoid pulverized coal being blown into the bustle pipe and to trigger operational reactions like, e.g., the shutdown of pulverized coal injection (PCI) branches.

It is known that the raceway depth depends on the coal injection rate, conversion, charging profiles (the way of loading the blast furnace), gas flow, cohesive zone characteristics, dead man characteristics, tapping practice and coal I hot blast flow mixture. It is also believed that raceways "collapse" at certain points in time and are built up after that. This is a cyclical movement but it seems to be an unpredictable process.

Small raceway sizes, having relatively shallow depths and frequent collapses are an indication of a low gas flow leaving the specific raceway and rising up into the bottom part and further into the shaft of the blast furnace. Increasing the gas flow through the tuyere will increase the kinetic energy against the coke bed, thereby forming a deeper raceway. Measuring the raceway's dimensions is therefore deemed to be important to improve process control of the BF.

CN106191350A describes the use of a radar system to measure the raceway depth according to measurements over a long period of time. The measurements are performed at individual tuyeres to fill the model with data. However, the method proposed is not accurate enough for process control. Radar measurement systems as such are available from local suppliers on the market.

W02020108987-A1 discloses a method for raceway depth control in a blast furnace by means of radar sensor measurements which are compared by the control system with a predetermined raceway depth.

EP3029160A1 discloses an abnormality detection method and a blast furnace operation method of detecting abnormality of a blast furnace from a tuyere image shot by a camera installed in the vicinity of a tuyere of the blast furnace using brightness information of a raceway portion.

Objectives of the invention

It is an object of the invention to provide an improved system for raceway depth measurement and raceway observation.

It is a further object to provide an improved method for raceway depth control.

It is a further object to provide a method to simultaneously observe the raceway with different sensors.

It is a further object to improve the blast furnace process by a better process control and a better stability of the iron making process in the blast furnace. Description of the invention

To promote the objectives of the invention, a method, a device and the use thereof is proposed in accordance with the features of one or more of the appended independent claims. Preferable embodiments are proposed in the dependent claims.

According to a first aspect a method is provided for raceway depth (R) measurement in a blast furnace provided with a plurality of tuyeres for injecting hot blast and powder coal into the blast furnace, comprising carrying out a simultaneous raceway depth measurement (RM) and a recording of the EM-spectrum with a wavelength of 280 nm up to 5.50 pm emitted or reflected from within the raceway through a tuyere, wherein the raceway depth is measured by means of a radar sensor capable of emitting a radar beam and receiving a reflected radar beam, and wherein the emitted EM-spectrum is recorded by EM-spectrum recording means, wherein a first spectral divider is placed in the optical path between the EM-spectrum recording means and the raceway and in the optical path between the radar sensor and the raceway, wherein

(i) the first spectral divider is at least partly transparent for the emitted EM-spectrum and at least partly reflective for the reflected radar beam, or

(ii) wherein the first spectral divider is at least partly reflective for the emitted EM- spectrum and at least partly transparent for the reflected radar beam, and wherein the radar sensor is positioned such that the optical paths of the reflected radar beam and the emitted EM-spectrum converge on the spectral divider and wherein the optical paths of the EM-spectrum and the reflected radar beam between the first spectral divider and the raceway coincide, and wherein the reflected radar beam is received by the radar sensor and the emitted EM-spectrum is recorded by the EM- spectrum recording means.

In the context of this invention the term "coinciding optical paths" is deemed to include "parallel optical paths".

This method allows the simultaneous measurement of the raceway depth (RM) through a tuyere and allows an observation of the raceway in the UV, visual and IR spectrum. This means that the same spot of the raceway is observed simultaneously. This provides information about the process temperatures and changes therein, allows for a visual inspection to detect raceway collapse, blockage and the like, and allows the process control model or operator to act upon these occurrences, e.g. by changing the amount of injected hot blast or powder coal through the tuyere. W02020108987-A1, discloses a method for raceway depth control in a blast furnace by means of radar sensor measurements of the raceway only, which are combinable with top gas temperatures, infrared and I or visual light images, spectrometric measurements, CO and I or CO2 amounts, wall temperatures and pressure measurements. However, it does not disclose the method of performing a simultaneous observation of the same spot with radar sensor and EM-spectrum recording means, nor does it solve the problem of the sensor and the recording means being in each other's optical paths.

The first spectral divider may consist of a wire mesh, preferably a woven mesh, preferably wherein the warp and the shute wires are perpendicular, which is at least partly transparent for the emitted EM-spectrum and at least partly reflective for the reflected radar beam. Alternatively the first spectral divider may be a beam splitter which is at least partly reflective for the emitted EM-spectrum and at least partly transparent for the reflected radar beam. The optical paths of the reflected radar beam and the EM-spectrum coincide between the raceway and the first spectral divider. Depending on the type of divider either the EM-spectrum continues along its original optical path and the reflected radar beam is diverted to the radar sensor or the reflected radar beam continues along its original optical path and the EM-spectrum is diverted to the EM-spectrum recording means. This is achieved by placing the first spectral divider under an angle in the optical path of the reflected radar beam and the emitted EM- spectrum.

The method according to the invention may be carried out through one tuyere, but it is preferable that a method is carried out through a plurality of tuyeres, preferably divided over the circumference of the blast furnace. For each tuyere a device according to the invention will be needed, each device comprising at least a radar sensor, an EM- spectrum recording means and a first spectral divider. It is not necessary to equip all tuyeres of the BF with a device according to the invention, but it is possible.

In an embodiment the angle between the optical path of the emitted radar beam and the optical path of the observing EM-spectrum recording means has a value of 13, and wherein the first spectral divider is positioned under an angle of Vi 13 with respect to the optical path of the visible light.

In an embodiment the EM-spectrum recording means comprises one or more of an IR-detector, an UV-detector and a visible light camera. By means of a proper selection of one or more of these recording means a more or less elaborate observation of the raceway can be made. In an embodiment a peephole window is provided in the optical path for the visible part of the EM-spectrum to allow a simple visual observation of the raceway. The peephole window consists of glasses made of regular glass or fused- silica or sapphire. Peephole made of regular glass and do not transmit long-wave and mid-wave infrared light. The fused silica and sapphire transmit longer wavelength infrared and will allow for simultaneous thermo-vision measurements.

According to a second aspect the invention is also embodied in a device for raceway depth measurement in a blast furnace comprising a radar sensor for emitting and receiving a radar beam through a tuyere, and EM-spectrum recording means for a simultaneous recording of an EM-spectrum with a wavelength of 280 nm up to 5.5 pm which is, in use, emitted from the raceway through the tuyere, wherein a first spectral divider is provided in the optical path between the EM-spectrum recording means and the raceway and in the optical path between the radar sensor and the raceway, wherein

(i) the first spectral divider is at least partly transparent for the emitted EM-spectrum and at least partly reflective for the reflected radar beam, or

(ii) wherein the first spectral divider is at least partly reflective for the emitted EM- spectrum and at least partly transparent for the reflected radar beam, and wherein the radar sensor is positioned such that the optical paths of the reflected radar beam and the emitted EM-spectrum converge on the spectral divider and wherein the optical paths of the EM-spectrum and the reflected radar beam between the first spectral divider and the raceway coincide, and wherein in use, the reflected radar beam can be received by the radar sensor and the emitted EM-spectrum can be recorded by the EM-spectrum recording means.

In an embodiment the EM-spectrum recording means comprises one or more of an IR-detector, an UV-detector and a visible light camera. By means of a proper selection of one or more of these recording means a more or less elaborate observation of the raceway can be made. In an embodiment a peephole is provided in the optical path for the visible part of the EM-spectrum to allow a simple visual observation of the raceway.

In an embodiment the angle between the optical path of the emitted radar beam and the optical path of the observing EM-spectrum recording means has a value of 13, and wherein the first spectral divider is positioned under an angle of Vi 13 with respect to the optical path of the visible light. Preferably the angle 13 is between 80 and 100° and more preferable is an angle 13 of 90°, in which case the first spectral divider is positioned in the optical path under an angle of 45°.

The first spectral divider may consist of a wire mesh which is at least partly transparent for the emitted EM-spectrum and at least partly reflective for the reflected radar beam, or the first spectral divider may be a beam splitter which is at least partly reflective for the emitted EM-spectrum and at least partly transparent for the reflected radar beam.

In an embodiment the wire mesh consists of an electrically conductive wire with a distance between subsequent threads of the mesh of about 75/1000th and 125/1000th of the wavelength of the radar beam.

In a preferable embodiment the wire mesh is disposed onto a transparent carrier, to support and flatten the wire mesh. Of course the carrier material must be transparent for the radar beam and the EM-spectrum of interest. Preferably the transparent carrier consists of transparent polymer material, glass, fused silica or sapphire. Instead of the preferable use of a wire mesh it is also possible to use an ITO transparent substrate, such as a plastic or glass substrate. ITO (Indium tin oxide) is a ternary composition of indium, tin and oxygen in varying proportions. ITO is, when the layer is sufficiently thin, transparent to visible light and UV, but not to IR, and it reflects radar beams.

In an embodiment a second spectral divider (13a) is present in the optical path of the EM-spectrum and wherein the second spectral divider (13a) redirects part of the EM-spectrum to a detector for the IR-, visible and/or EM spectrum (12a), and wherein the unredirected remainder of the EM-spectrum passes the first spectral divider (13) towards a visible light camera (12) and/or the peephole. This embodiment allows the simultaneous observation by three different means (see e.g. figure 6).

According to a third aspect the invention is also embodied in the use of the method and the device according to the invention in a control system for controlling the hot blast flow through the plurality of tuyeres by comparing the raceway depth measurement with the predetermined raceway depth for the plurality of tuyeres in order to achieve a uniform raceway depth over the circumference of the blast furnace. Controlling the hot blast flow though the plurality of tuyeres has the advantage that control takes place in a synchronised manner. The individual differences over the plurality of tuyeres between the raceway depth measurement and the predetermined raceway depth can thus be controlled. Hot blast flow as well as powder coal injection (PCI) over the circumference of the blast furnace can be independently controlled by the control system by valves positioned at the tuyeres. The valves can be opened or closed in a manner known per se. The predetermined raceway depth is a depth that is set according to historical measurements and the results of these measurements can change over time, under specific circumstances and is relative to a specific blast furnace as well.

Preferably the control system carries out the raceway depth measurement through a plurality of tuyeres by means of a plurality of devices according to the invention divided over the circumference of the blast furnace. Measurements of the raceway depth with radar sensors through different tuyeres have revealed that raceway depths differ largely over the circumference of the blast furnace. For a stable process it is believed that a uniform raceway depth over the circumference of the blast furnace is preferred. Since a blast furnace is equipped with a plurality of tuyeres divided over the circumference of the blast furnace, a plurality of radar sensors divided over the circumference of the blast furnace enables a more consistent control of the hot blast flow through the plurality of tuyeres.

The plurality of devices according to the invention gather the data from the raceway depth and the data is sent to the control system. Then the data is processed by the control system. The predetermined raceway depth could be set as a raceway depth range, by defining a minimum and a maximum raceway depth between which values the raceway depth is believed to have an optimal value. It is further believed to be beneficial that the raceway depth is uniform over the circumference of the blast furnace so as to achieve maximum stability, yield, speed and product quality.

In a preferred embodiment the control system changes the hot blast flow and/or PCI through one or more tuyeres when the raceway depth measurement has a deviating value from the target raceway depth. The pre-set raceway depth is the ideal situation set for an optimal process inside the blast furnace.

Preferably the plurality of devices according to the invention send the raceway depth measurements to the control system in a continuous manner. It is preferred to control the hot blast flow through every tuyere individually, but also continuously. Controlling every tuyere individually guarantees that every single tuyere can be set to a hot blast flow value and PCI-rate independently of the other tuyeres. Since modern blast furnaces are producing iron in a continuous manner, this means it is preferred that the measurements are also done in a continuous manner to maintain the raceway depth at its pre-set value.

Example

In figure 9b a result of a raceway measurement (RM) is indicated. The end of the tuyere is about 3.2 m, and the peak between the dashed vertical lines is the raceway measurement. The shape of the peak is indicative for the shape and depth of the raceway and these results and the changes therein can be used in an appropriate control system. The signal between 0 and 3.2 m are reflections that extinguish to a stable value of about 30-40 dB. These measurements were performed through tuyere 11 of Blast Furnace 6 in the IJmuiden integrated steel works. Figure 9a shows the schematic setup. 1. The spectral divider consisted of a woven square "100 Mesh Copper .0012” Wire Dia" with 79% open area supplied by TWP Inc. The mesh has wire diameters of 0.03 mm (0.0012 inch) and openings of 0.224mm. The mesh reflects reflect radar and transmits light.

The radar transmitter and receiver is a Vegapuls 64 working at 80 GHz. The sensor has a dynamic range of 120dB and has been originally designed to measure liquid levels in tanks. The sensor has an accuracy of +/- 1mm and can measure up to a distance of 30 meter at process conditions up to 200°C and a pressure of 25 bar. The frequency of 80 GHz allows for good focussing of the signal with a beam angle of 8° . It should be noted that the radar-beam is not circular but elliptical. The orientation of the radar around the axis will therefore likely have some influence on the signal strength (amplitude). The depth of blast furnace raceways is measured as follows: a radar signal is sent into the blast furnace via a tuyere peephole and the travel time of the signal reflection from the back of the raceway is determined. The tuyeres of the blast furnace are also equipped with EM-spectrum recording means (in this example visible light cameras) to check for tuyere blockages. To simultaneously measure the raceway depth with radar and monitor the raceway with a camera, the radar signal and light are separated. A conductive wire mesh about with gaps of about l/10th the radar wavelength (0.375mm) can be used to reflect the radar signal while transmitting light of shorter wavelength. A wire mesh with thin wires and large open area can be selected for efficient separation.

Brief description of the drawings

The invention will hereinafter be further elucidated with reference to the drawing of an exemplary embodiment according to the invention that is not limited as to the appended claims.

Figure 1 shows a section view of a blast furnace;

Figure 2 shows a part of the section of figure 1 in enlarged view;

Figure 3 shows the system when in operation;

Figure 4 shows the two main embodiments of the device according to the invention;

Figure 5 shows a preferred embodiment of the device according to the invention;

Figure 6 shows an embodiment with two spectral dividers, two EM-spectrum recording means and a radar sensor;

Figure 7 and 8 shows the principle of the coinciding optical paths between raceway and first spectral divider.

Figure 9 shows an example of a raceway measurement.

Figure 10 shows the flow chart of the control system.

Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

Figure 1 shows a schematic section view of a blast furnace (1) having a shaft (2), a cohesive zone (3), a dripping zone (4) and a dead man zone (5). In the dripping zone

(4) a raceway (6) is shown having a raceway depth (R).

Figure 2 shows the raceway depth (R) of a raceway (6) in more (but still schematic) detail. Raceways are formed in the blast furnace coke bed in front of the so- called bird's nest (7) by a hot blast flow (8) through a tuyere (9). The bird's nest (7) has a bowl like shape and is located between the raceway (6) and the dead man zone

(5) The position of the tuyere (9) is indicated and is installed through an opening in a wall (14) of the blast furnace (1). The arrow in the figure shows the flow of hot blast (8) to pass through the tuyere (9) into the coke bed in front of the bird's nest (7) of the dripping zone (4) and thereby forms a raceway (6) having a raceway depth (R).

In Figure 3 is shown that a bustle pipe (10) is connected to a tuyere (9). The bustle pipe (10) runs around the circumference of the blast furnace and provides the tuyeres (9) with hot blast flow (8) via a valve (18). A coal injection lance (11) is also part of the configuration. Further a radar sensor (15) is shown which is configured to measure through a tuyere (9) of the blast furnace (1). The radar sensor (15) sends its signal through the tuyere (9) and measures the raceway depth (R) of the formed raceway (6). The radar sensor (15) then sends the raceway depth measurement to the control system.

In figure 4 the two main embodiments of the device according to the invention are depicted. Figure 4(i) depicts the embodiment where the first spectral divider (13) redirects the emitted and reflected radar to the tuyere and the raceway v.v. under an angle 13. By means of example the first spectral divider (13) may be a wire mesh that reflects the radar beam but is at least partly transparent for the EM-spectrum emitted by the raceway. Figure 4(ii) depicts the embodiment where the first spectral divider (13) redirects the emitted EM-spectrum under an angle 13 to the EM-spectrum recording means (12), whereas the emitted and reflected radar to the tuyere and the raceway v.v. goes in an uninterrupted straight line. By means of example the first spectral divider (13) may be a beam splitter that reflects the EM-spectrum but is at least partly transparent for the radar beam reflected by the raceway.

In both cases (i) and (ii) the optical paths of the EM waves and the radar beam coincide between the spectral divider (13) and the raceway (6) and are thus also parallel. This is further clarified in figure 5, where the angle 13 is a practical 90°. This angle makes aiming the radar beam easier.

Figure 6 shows a special embodiment of the device according to the invention where two spectral dividers are used. The first spectral divider (13) is a wire mesh that reflects the radar beam but is at least partly transparent for the EM-spectrum emitted by the raceway. The EM-spectrum that passes the second spectral divider (13a) where at least part of the visible light spectrum passes through the divider, but the UV and IR parts of the EM-spectrum are redirected to a second EM-spectrum recording means (12a), as well as some of the visible spectrum. This embodiment allows for a more detailed analysis of the EM-spectrum than the ones with only one spectral divider.

Figure 7 and 8 illustrates the feature of the invention of the parallel (figure 7) and the coinciding (figure 8) optical paths of the emitted and reflected radar beam and the emitted EM-spectrum between the raceway (RW) and the first spectral divider (13). In the context of this invention the term "coinciding optical paths" is deemed to include "parallel optical paths". Figure 9 a result of a raceway measurement (RM) is shown and described in more detail herein above in the example section.

Figure 10 shows a flow chart of a method according to the invention. A plurality of radar sensors (15) and EM-spectrum recording means (12) carry out a raceway depth measurement (RM) through a plurality of tuyeres (9) divided over the circumference of the blast furnace (1). The raceway depth measurement (RM) is the result of a signal from the raceway depth (R) of a specific raceway (6). This raceway depth measurement (RM) is then sent to the control system (16). The control system is controlling the processes of the blast furnace (1) by controlling the hot blast flow (8) and optionally the powder coal injection or gas injection over the circumference of the blast furnace can be independently controlled by the control system by valves positioned at the tuyeres. The control system (16) compares the raceway depth measurements (RM) with pre-set raceway depth (RP) values. These pre-set values and are mainly based on historical data stored in the control system. The control system controls the hot blast flow, PCI and/or gas injection through the plurality of tuyeres (9) according to the difference between the raceway depth measurement (RM) and the predetermined raceway depth (RP) in order to achieve a uniform raceway depth (R) over the circumference of the blast furnace (1). The control system (16) is also equipped to gather data from a number of other sensors, like top gas temperatures, top gas compositions, spectrometric measurements, wall temperatures and pressure measurements. These other measurements are indicated by (M). The control system (16) is adjusted to not only gather the other measurement data (M) but also to analyse them, combine them with the raceway depth measurements (RM) and then adjust the hot blast flow (8) through the tuyeres (9) accordingly.

Although the invention has been discussed in the foregoing with reference to exemplary embodiments of the invention, the invention is not restricted to these particular embodiments.