The invention relates to a method for raceway depth control in a blast furnace, comprising controlling a hot blast flow through a tuyere by means of a control system, the control system carrying out a raceway depth measurement through the tuyere by means of a radar sensor, the radar sensor sending the raceway depth measurement to the control system and the control system comparing the raceway depth measurement with a predetermined raceway depth. It further relates to a system for raceway depth control.

Blast furnaces have been known for several hundred years. However, the conditions inside a blastfurnace 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.

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.

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 / 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. 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.

It is an object of the invention to provide a better measurement method and system for raceway depth control. It is a further object to improve the process in the blast furnace by a better process control and a better stability of the iron making process in the blast furnace. A further object is to improve the blast furnace productivity. Another object is to increase the yield of the iron making process.

To promote the objectives of the invention, a method and a system is proposed in accordance with the features of one or more of the appended claims.

Accordingly the method of the invention further comprises the control system carrying out the raceway depth measurement through a plurality of tuyeres by means of a plurality of radar sensors 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 make a better control of the hot blast flow through the plurality of tuyeres possible. Each radar sensor could be dedicated to a specific tuyere, but more radar sensors dedicated to one tuyere are possible to increase the stability and accuracy.

In a preferred embodiment the control system is 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 over the circumference of the blast furnace is 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.

In the method a plurality of radar sensors, preferably having a small opening angle, are placed such that the radar sensors measure through the one or more tuyeres divided over the circumference of the blast furnace. The radar sensors 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 and speed.

In a preferred embodiment the control system is decreasing the hot blast flow through one or more tuyeres when the raceway depth measurement has a higher value than the predetermined raceway depth and increasing the hot blast flow through the one or more tuyeres when the raceway depth measurement has a lower value than the predetermined raceway depth. In general terms, the higher the flow of the hot blast, the deeper the raceway depth will be. Therefore, the hot blast flow is directly related to the raceway depth. The predetermined raceway depth is the ideal situation set for an optimal process inside the blast furnace.

In a further preferred embodiment the control system is controlling the hot blast flow through the one or more tuyeres combining the raceway depth measurement with at least one other blast furnace control measurement sent to the control system, selected from the group comprising top gas temperatures, top gas compositions, infrared and / or visual light images, spectrometric measurements, CO and / or CO2 amounts, wall temperatures and pressure measurements. It is preferred to combine at least one other measurement sent to the control system with the raceway depth measurement. In this way a more thorough control of the processing conditions inside the blast furnace can be made. The control system is constantly gathering data from a number of sensors. By combining the measurements a more optimised blast furnace operation can be established based on the combination of the data.

In a further preferred embodiment the control system is controlling the hot blast flow via one or more groups of two or more tuyeres. It is preferred to group at least two tuyeres to create a greater effect on the process inside the blast furnace. Every single tuyere has some effect on the other tuyeres as well and in this way control can be further increased. The groups can be chosen according to the measured raceway depths. It may be required that a group of at least two tuyeres is formed by two or more tuyeres adjacent to each other. But it may also be required to group at least two tuyeres opposite to each other. This depends on the specific processing conditions inside the blast furnace and the control system can set a desired combination according to the measurements of the different raceway depths over the circumference of the blast furnace. As will be clear, there are an almost infinite number of combinations of groups of tuyeres, since a group of tuyeres can consist of two, three, four, or even more tuyeres and this group can be adjacently, oppositely or via another pattern be placed aver the circumference of the blast furnace relative to one another.

In a further preferred embodiment the control system is providing a visualisation of the raceway depths over the circumference of the blast furnace. In this manner the process operator is given an immediate visual overview of the raceway depths over the circumference of the blast furnace. It is known that visualisation has the benefit over a list of data since it is far easier to interpret. It will then be immediately apparent for the process operator where the hot blast flow needs to be increased or decreased if necessary, should the system not control this automatically. The visualisation will be shown on a process control screen.

In a further preferred embodiment the plurality of sensors are sending 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 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 keep close to the predetermined raceway depth. This also means that the measurements are done in real time and immediate control and homogeneity is guaranteed, without delay. In this way also rapid changes in the raceway depth can be measured,. Naturally, time intervals could be set as well, depending on the necessity and the stability of the conditions inside the blast furnace. This gives the method and system a greater flexibility.

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.

In the drawing:

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 a top view of the system in operation Figure 5 shows a diagram of measurements of raceway depths over the circumference of the blast furnace in a sub-optimal condition

Figure 6 shows a diagram of measurements of raceway depths over the circumference of the blast furnace in an optimal condition

- Figure 7 shows a flow chart of the process.

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

Figure 1 shows a section view of a blast furnace (1 ) having a shaft (2), a cohesive zone (3), a drippling zone (4) and a dead man zone (5). In the drippling zone (4) a raceway (6) is shown having a raceway depth (R), more clearly indicated in Figure 2.

Figure 2 shows the raceway depth (R) of a raceway (6). Raceways are formed in the blast furnace coke bed in front of the birds nest (7) by a hot blast flow (8) through a tuyere (9). 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 birds nest (7) of the drippling 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 (1 1 ) 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 (RM) to the control system (16), more clearly shown diagrammatically in Figure 7.

Figure 4 shows an example of a top view of a radar sensor (15) installed at a tuyere (9). For clarity purposes only three radar sensor (15) are displayed, but more radar sensors (15) could be installed at a plurality of tuyeres (9) divided over the circumference of the blast furnace (1 ). The raceways (6) having a raceway depth (R) are clearly shown. Depending on the design of the blast furnace (1 ) other configurations of radar sensors (15) can be chosen. For clarity purposes the wall (14) is also indicated

Figure 5 shows a visualisation (17) of the raceway depth (R) at a plurality of tuyeres (9) divided over the circumference of the blast furnace (1 ). Every dot represents a raceway depth (R) and in this visualisation 30 tuyeres (9) having 30 raceways depths (R) are shown. This is an example of what a plot could look like in a sub-optimal blast furnace process. As is shown, several raceway depths (R) exist over the circumference of the blast furnace (1 ), there is no uniform distribution of raceway depths (R) over the circumference of the blast furnace (1 ).

In Figure 6 an optimal situation is plotted. All raceway depths (R) - as in Figure 5 also 30 tuyeres (9) having 30 raceway depths (R) - formed by the hot blast flow (8) through the tuyeres (9) have the same value and therefore a uniform raceway depth (R) over the circumference of the blast furnace (1 ) is achieved.

Figure 7 shows a flow chart of the method. A plurality of radar sensors (15) 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) by the radar sensor

(15). The control system is controlling the processes of the blast furnace (1 ) by controlling the hot blast flow (8) through the plurality of tuyeres (9). The control system

(16) compares the at least one raceway depth measurement (RM) with a predetermined raceway depth (RP). This can be set at desired values and is mainly based on historical data stored in the control system. The control system controls the hot blast flow (8) through the a 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 adjusted to gather data from a number of other sensors, like top gas temperatures, top gas compositions, infrared and / or visual light imaging, spectrometric measurements, CO and / or C02 amounts, 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. Indicated is also the possibility to provide a visualisation of the raceway depth (R) on a process control screen (17) in order for the process operator to get a quick and informative view of the raceway depth (R) inside the blast furnace (1 ). These visualisations are more clearly shown in Figures 5 and 6.

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 which can be varied in many ways without departing from the invention. The discussed exemplary embodiments shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiments are merely intended to explain the wording of the appended claims without intent to limit the claims to these exemplary embodiments. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using these exemplary embodiments.