GB2037960A - Methods of monitoring a blast furnace - Google Patents

Abstract

A method of monitoring the operation of a blast furnace. The distance x, y to the surface of the glowing mass located in the raceway 12 formed in front of a tuyere 6 is measured by a distance meter 13 placed at an inspection window 11 located in or near the tuyere 6. The distance is measured for a plurality of the tuyeres of the furnace, and if any of the measured distances deviates more than a predetermined value from the mean value for the measured distances, the deviation indicates a fault in the furnace process and that a correction is required. <IMAGE>

Description

SPECIFICATION Methods of monitoring a blast furnace The present invention relates to methods of monitoring the operation of a blast furnace.

The operation of a blast furnace is extremely complex and is dependent upon, inter alia, the composition of the iron ore charged thereto, the particle size and the type of reduction coke used, and the pressure and temperature of the air injected into said furnace. It is extremely important that all these parameters are adjusted to one another in an adequate manner. It is also essential that the furnace operates as symmetrically as possible about its central axis in a manner such that the hottest part of the furnace lies as close as possible to said central axis. If the furnace is heated unevenly, the furnace wall will also be heated unevenly, and in extreme cases part of the furnace wall can be heated to such an extent as to cause said part to fracture. Consequently, many methods of monitoring the state of the furnace have been proposed.One of these methods proposes that the surface temperature of the charge is continuously monitored by means of equipment which provides an infrared image of the surface of the charge. Although good control of the furnace can be had by checking the surface distribution or the temperature of the charged surface, it has been found necessary to complement this particular form of investigation with other, different investigations concerning the state of the furnace charged lower down in the furnace, In most cases it is of particular interest that the raceways located in front of the tuyeres in the furnace are maintained of equal size as far as possible. However, the furnace in itself may not be quite symmetrical and if that is the case it is essential to have the size of the raceways individually set to be within predetermined limits.

To this end the tuyere nozzles are arranged in a manner such as to enable the diameter thereof to be changed. The problem in this respect is the difficulty in obtaining correct information as to the size of the raceways. The most common method today in this respect is to physically peer into the raceway through an observation window located in the tuyere system, said window comprising a suitable heat-resistance material, such as quartz.

Normally, this window is so small that the person looking through the window is only able to peer into the tuyere system with one eye, and consequently is unable to use stereoscopic vision to assess the depth of the raceway. Thus, it requires a person of great experience to make an even approximate assessment, and it is only natural that this assessment is highly subjective.

In order to improve this situation, a number of furnaces have been provided with viewing windows on each side of the tuyere instead of in the tuyere itself, through which windows the raceway in front of the tuyere can be observed.

These windows have been made to such a width, i.e. about 2 mm, as to enable a person peering into the furnace to observe the interior of the furnace with both e.yes. Although the provision of two windows has improved the possibility of assessing the size of a raceway, the accuracy of the assessment is still dependent upon the relatively subjective judgement of an observer.

According to one aspect of the invention, there is provided a method of monitoring the operation of a blast furnace in which an observation window is provided allowing observation of the raceway associated with a tuyere and of the surface of the glowing mass bounding the raceway, said surface being monitored in a measuring operation by a distance meter via said window and the distance of said surface from a reference position being thereby determined.

Preferably, a said observation window is provided in respect of each of at least three tuyeres and said measuring operation is carried out in respect of each said window to provide a group of measurements.

Preferably, said windows are disposed symmetrically about the circumference of the furnace.

In one method, said measuring operation is carried out in respect of a plurality of said tuyeres simultaneously to provide a group of measurements.

In another method, a sequence of said measuring operations is carried out.

According to a further aspect of the invention, there is provided a blast furnace provided with a distance measuring means arranged to measure the distance from a reference~position to the surface of the glowing mass bounding a raceway when the furnace is in operation.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example to the accompanying drawings in which: Figure 1 is a side view of a blast furnace, partly in section, with a distance meter placed adjacent a tuyere; Figure 2 illustrates at a larger scale a distance meter placed adjacent a tuyere; Figure 3 illustrates how distnce meters can be placed around a blast furnace during a measuring sequence, the view in Figure 3 being at the same scale as that in Figure 1; Figure 4 illustrates an alternative method of positioning distance meters; and Figures 5 and 6 illustrate two different methods of positioning distance meters adjacent an inspection panel present in a tuyere.

Figure 1 illustrates a blast furnace 1 having a hearth in which tuyere systems 2, 3 are connected to a circular drum 4 extending around the furnace.

Pre-heated furnace air is fed to the drum 4 and distributed through the drum and blown into the furnace through the tuyeres 2, 3.

The drum is located above the tuyeres and is connected to each tuyere through a respective pipe 5 (see Figure 2) which extends obliquely down towards the furnace. Each tuyere 3 comprises a straight pipe 6 which extends through the centre of a substantially conical tuyere stock 8 with the base of said stock facing the outer periphery of the furnace wall 7. The pipe 6 is wedged in a tuyere nozzle 9 which opens into the furnace and the diameter of which can be changed by inserting the pipe into the nozzle 9 to a greater or lesser extent, by means of an adjusting wheel 10. The pipe 6 is provided at its other end with a viewing window 11 made of quartz or some other suitable, heat-resistant and transparent material All of the aforedescribed elements are standard elements in a blast furnace.

As previously mentioned, it has previously bene difficult to assess the size of a raceway formed before the tuyere nozzle 9 in the furnace. The size of the raceway has previously been assessed by an observer peering through the pipe 6, which requires a great deal of skill and a high level of judgement. The raceway section is a vital part of a blast furnace, since it constitutes a heat source in a gigantic reactor. At the same time this section serves as a reduction source for the furnace. Coke in the furnace-charge is consumed very rapidly in the raceway. The appearance or form of the raceway is very dependent upon the quality and the type of coke used. Particularly difficult problems occur when the coke contains a large quantity of fine coke, since the pressure in the raceways then tends to rise.This results in a pressure imbalance adjacent the raceways, which affects the form of the raceways so that they become unstable. On the other hand, coke containing only a small percentage of fine coke results in raceways of relatively constant size. It is expensive and troublesome to produce coke of uniform particle size and if a method can be devised whereby the size of the raceways can be monitored in a practical and accurate manner, a poorer quality of coke can be used, i.e. coke having a higher percentage of fine coke than was previously possible, since a compensation therefore can be made.

Anpther serious problem encountered with large blast furnaces used today is one of changes in temperature-distribution adjacent the tuyere systems, as a result of the diameter of the hearth being too large. This in turn has led to increased efforts to find a practical method of continually monitoring the furnace, and in particular a method of by which the size of the raceways can be assessed in a practical and objective manner. In the methods described herein, the distnce from a reference point to the glowing mass in the furnace is measured through the tuyere systems with a distance meter 13 of a suitable type such as described in German Patent Specification No.

2 551 965.

The distance meter 1 3 is arranged adjacent the window 11 on the tuyere system through which the measurement is to be taken. The distance to the orifice of the tuyere nozzle 9 can be assessed by measuring the distance of the distnce meter 13 from the furnace wall 7 mechanically and adding thereto the known thickness of the furnace wall and the dimensions of the tuyere nozzle. It is also possible to align the distance meter with the outlet orifice of the tuyere nozzles and to take a measurement directly thereto, prior to making the actual distance measurement to the glowing mass. A further method is to place a measuring prism 14 at a suitable location in the tuyere system as illustrated in Figure 2.As illustrated in Figure 2, the prism 14 can be mounted on the wall of the inside of the tuyere system at a location where the downwardly extending pipe 5 connects to the pipe 6, in a manner such that the flow of gas to the tuyere system is obstructed by the prism 14, since the forward surface thereof merges with the pipe wall. The prism 14 may be placed at other locations in the passage 6, although in this case it must be expected that the prism will have some affect on the flow of gas through the pipe. A reference measurement can also be made to the outer part of the tuyere facing the distance meter adjacent the window 11, although this measurement must be corrected in respect of the retarding affect of the window 11 on the phase velocity of the light to the meter 13 to effect measurement.In Figure 2, are illustrated two different forms of raceways and it can be clearly seen that different forms give different distances between the outlet orifice of the tuyere nozzle and the surface of the glowing mass. The distance y is obtained with relatively high furnaceair pressure. The distance x is obtained with a lower pressure. It is desirable that the distance is held constant within certain limits, and this is achieved by regulating the diameter of the tuyere nozzle to a suitable value, by means of the wheel 10.

Figure 3 illustrates schematically how a measuring sequence may be made. In one such measuring sequence, a plurality of distance meters are arranged sequentially adjacent a plurality of mutually spaced tuyere systems a1, b1, . . . 1, and the raceway distance therethrough is measured. The mean value of the measurements is calculated to serve as a reference value, and the individual deviations from this mean value are assessed. If the distance measured by one of the distance measurements, e.g. taken with the distance meter 1 3 placed in position F in front of the tuyere system f1, deviates by more than a predetermined amount from said mean value, the size of the tuyere nozzle of this tuyere system is regulated accordingly. In addition, a measurement is made through one or both of the tuyere systems g', g", lying adjacent the tuyere system fin order to determined whether or not the.deviating distance measured through tuyere system fis an indication that something is radically wrong in the furnace process. In such a case, the measurements taken through tuyere system g' and g" will, of course, also show a deviation from said mean value, and steps to counteract this must quickly be taken.

Figure 3 illustrates a measuring sequence comprising six measuring operations, although it will be understood that this number is only given by way of example. The number of measuring operations in a measuring series can be chosen arbitrarily from three to the number of tuyere systems found on the furnace. The more measuring operations carried out, the better the result represents the furnace conditions, although the cost will increase with the number of measuring operations effected. Large blast furnaces may have up to thirty tuyere systems.In such case it may be preferable, instead, to carry out measuring sequences with relatively short time periods therebetween and with few measurements in each measuring sequence, and to carry out each measuring sequence either through tuyeres which lie some angular distance away from the preceding measuring sequence, or in accordance with a predetermined pattern of measuring sequences. In Figure 3, the measuring sequences are carried out in a manner such that a first measuring sequence is carried out through the tuyeres a1 -f1, and the next measuring sequence through the tuyeres a2-f2, and then through a3 - f3 and subsequently through a4 - f4.

Alternatively, instead of moving the same distance meter between different tuyeres, a multiplicity of distance metes A-F may be placed stationarily in front of respective ones of several tuyeres a1 - f1 distributed uniformly around the furnace, to carry out simultaneous measurements with said distance meters at predetermined time intervals. A mean value of the results can be made and a movable distance meter G can be placed adjacent a tuyere g' or g" located adjacent a tuyere f1 where a deviating distance value was obtained.By placing a plurality of distance meters at fixed positions around a furnace, operation of the furnace can be monitored from a remote location e.g. a control room and one person can monitor simultaneously a plurality of furnaces and summon personnel, for carrying out additional distance measurement and regulations of the size of rye tuyere nozzles, when necessary.

If the mean value obtained when carrying out a sequence of distance-measuring operations deviates from a normal means value by more than a predetermined amount, the various furnace parameters such as regulatIon of the flow of air to the furnace or charging of the furnace must be adjusted in order to return to normal conditions.

Figure 4 illustrates another method of carrying out measuring operations. In this case the furnace is assumed to be divided, for measurement purposes, into quadrants I, II, III, and IV with a plurality of tuyeres associated with each quadrant, the number in the illustrated example being seven.

In the illustrated example, a distance meter is placed at the central tuyere in each quadrant, such as distance meter A' at the centre of the first quadrant I, the distance meter B' adjacent the centre tuyere of the second quadrant II, the distance meter C' adjacent the centre tuyere of the third quadrant Ill and the distance meter D' adjacent the centre tuyere of the fourth quadrant IV. At each alternate or each third measuring operation or, on special occasions, at a predetermined time after e.g. charging of the furnace, additional measuring operations are carried out with a movable distance meter adjacent a tuyere remote from the centre tuyere of each quadrant, such as adjacent the tuyeres A"1 and A"2 in quadrant I.

If during a sequence of measuring operations it is found that the distance measured through the centre tuyere in one quadrant, e.g. D' in the fourth quadrant IV, deviates from the means value, an additional measuring operation must be made through the tuyeres located in the same quadrant as said centre tuyere. This additional measuring operation can be carried out symmetrically on both sides of the centre tuyere in the quadrant in question, such as through the tuyeres a1 and pt, in order to ascertain whether the deviation is distributed symmetrically in the quadrant.If it is not, the measuring operations are continued around the area where the deviation has been observed, such as by measuring through the tuyere p2 and p3 if the deviation is greater through the tuyere p1 than through the tuyere . If the deviation is greatly unevenly distributed, it is also suitable to carry out measuring operations in one or more of the tuyeres in an adjacent quadrant, such as through the tuyere y1.

Some blast furnaces are provided with observation windows placed on the sides of tuyeres, such windows being used, of course, when measuring the raceway formed in front of the tuyeres. An example of this is illustrated in Figures 5 and 6, in which pipes 15, 16 having windows 1 7 and 18 respectively are provided in the furnace wall adjacent the tuyere stock 8. Such pipes may, in some furnaces, be provided, instead, adjacent the tuyere in the tuyere stock itself. Such viewing pipes have a width such that a person is able to see through the pipe with both eyes, and thus use stereoscopic sight. It is also possible, through such viewing pipes, to see a larger part of the raceway in front of the tuyere than when viewing the raceway through the tuyere itself.The provision of such viewing pipes can be utilised in a manner such that a measurement can be taken to several locations on the bottom of the raceway through each viewing pipe, in order to assess the evenness of the bottom of said raceway.

Conveniently, instead of making just one distance measurement, (which could be an incorrect measurement owing to for example, an object such as a large piece of coke, slag or unmelted material, projecting up into the raceway) a series of measurements are taken at different measuring locations and the mean value of these measurements is taken as a basis for judging the state of the raceway. For this purpose, either the distance meter itself can be rotated to various positions for a plurality of measuring operations through the viewing pipe, or, as illustrated in Figure 5, a rotatable mirror 19 can be placed in the path of the beam from a fixediy positioned distance meter 20, which may then be placed in alignment with the furnace wall. Figure 6 illustrates another arrangement in which there is provided a scanning device comprising two prisms 21,22, which are rotated to different angular positions relative to one another and placed in front of a distance meter directed towards the pipe 15. It will be understood that the scanning device will be rotated before each measuring operation to a position which is particular to that measuring operation in question and is held stationary during the measurement process.

In the foregoing it has been assumed that the furnace is symmetrical. This is not always the case, however, especially when the furnace has been working for a number of years. The effect of such symmetry may be compensated by altering the raceways so that at normal operation they have individual sizes. In order to be able to monitor the furnace in a case like this, each raceway is measured when the furnace is operating at optimal conditions. Measurements are made at several locations and the means value of these measurements for each of the tuyeres is used as an individual reference value, from which deviations are calculated when the check measurements are made in accordance with the methods described with reference to the Figures.

Claims (22)

1. A method of monitoring the operation of a blast furnace in which an observation window is provided allowing observation of the raceway associated with a tuyere and of the surface of the glowing mass bounding the raceway, said surface being monitored in a measuring operation by a distance meter via said window and the distance of said surface from a reference position being thereby determined.

2. A method according to claim 1 wherein a said observation window is provided in respect of each of at least three tuyeres and said measuring operation is carried out in respect of each said window to provide a group of measurements.

3. A method according to claim 2 wherein said windows are disposed symmetrically about the circumference of the furnace.

4. A method according to claim 2 or 3 wherein said measuring operation is carried out in respect of a plurality of said tuyeres simultaneously to provide a group of measurements.

5. A method according to claim 2 or 3 wherein a sequence of said measuring operations is carried out.

6. A method according to any one of claims 2 to 5 wherein when the distance obtained from at least one measuring operation in respect of a tuyere deviates by at least a predetermined amount from a reference value, an additional said measuring operation is undertaken in respect of at least one further tuyere in the vicinity of the tuyere in respect of which the deviating measurement was taken.

7. A method according to claim 6 wherein said reference value is a mean value of distances obtained in measuring operations in respect of a plurality of tuyeres.

8. A method according to claim 6 wherein said reference value is particular to the tuyere in respect of which the measuring operation is carried out.

9. A method according to claim 8 in which, to assess whether the distance deviates by said predetermined amount, the difference between said distance and said reference value is compared with a mean value of differences similarly computed in respect of further tuyeres.

10. A method according to any one of claims 2 to 9 in which for measuring purposes the furnace is regarded as divided into quadrants, and for each group of measurements a measurement is taken in respect of at least one tuyere in each quadrant.

11. A method according to any one of claims 2 to 10 in which a measuring operation is carried out in respect of a tuyere located at a predetermined angular distance from a tuyere in respect of which measurement was made during the immediately preceding measuring operation.

12. A method according to any one of the preceding claims in which a measuring operation is repeated in respect of a tuyere at a predetermined time and/or when any one of the process parameters such as temperature, gas analysis or temperature distribution on the upper side of the charge has changed significantly.

13. A method according to any one of the preceding claims, in which a calibration distance measurement is made to a reference position in the furnace wall, the distance to the surface of said glowing mass is measured, and the calibration distance measurement is subtracted from the measured distance of the glowing mass.

14. A method according to any one of the preceding claims in which said window is located in a tuyere.

1 5. A method according to any one of the preceding claims in which a said window is provided in an inspection panel adjacent a tuyere.

1 6. A method according to claim 1 5 in which when taking a distance measurement in respect of a tuyere a plurality of distance measurements are made sequentially at different angular positions through the inspection panel, and a mean value of the separate measurements is calculated to serve as the distance obtained for the measuring operation.

1 7. A method according to any one of the preceding claims, in which the mean value of the distance, obtained by measuring at a plurality of different tuyeres is recorded automatically and furnace parameters such as the flow of furnace air and charging of the furnace are regulated in a manner such that said mean value is maintained with given limits.

18. A method of monitoring the working function of a blast furnace, characterised by measuring, adjacent one or more tuyere systems of said furnace by means oi a distance meter through an inspection window, the distance to the surface of the glowing mass located in the raceway formed in front of a tuyere, said raceway being observable through said inspection window, said distance meter during an actual distance measuring operation from a given point to the glowing mass having a wall defined position in relation to the furnace and being of the type with which the distance to a glowing surface can be measured, a sequence of measuring operations being carried out simultaneously or in sequence through at least three tuyeres substantially uniformly distributed around the furnace.

19. A method of monitoring the operation of a blast furnace according to claim 1 and substantially as hereinbefore described.

20. A blast furnace provided with a distance measuring means arranged to measure the distance from a reference position to the surface of the glowing mass bounding a raceway when the furnace is in operation.

21. A blast furnace substantially as hereinbefore described with reference to the accompanying drawings.

22. Metal produced by the blast furnace of claim 20 or 21.