TECHNICAL FIELD

The present disclosure generally relates to condition monitoring in metallurgical furnaces, namely shaft and blast furnaces. The present disclosure relates in particular to condition monitoring of cooling elements after abrasion of the protective layer in front of the cooling elements.

BACKGROUND

As it is well known, a shaft furnace works as a countercurrent reactor, wherein the downward flow of charge material is in contact with an upflow of hot, carbon monoxide-rich combustion gases. The solid burden materials consisting of ferrous materials (iron ore, sinter, and pellets), coke, and fluxing materials are gravitally charged into the top of the furnace, while air normally enriched with O2, and sometimes with auxiliary fuels is fed through the tuyeres near the bottom of the furnace. The liquid hot metal and liquid slag are tapped at regular intervals through a number of tapholes situated at the bottom of the furnace.

Shaft furnaces, and particularly blast furnaces (BF), are desirably operated with high productivity and low fuel rate in a flexible, stable and efficient manner, while having a long campaign life.

The blast furnace has often been referred to as ‘black box’. One reason seems to be due to the difficulty of observing or monitoring what is happening inside the furnace. Indeed, in a BF three phases of gas, solid, and liquid coexist; reactions proceed non-uniformly in radial direction, the process is accompanied by a time dependent variation, and the parameters to be measured are always moving in a high temperature, high pressure, and dust containing atmosphere.

This being said, the probes and measuring devices of the BF have made a great advancement over the last decades on the basis of developments on electronics, optics and computer technology. With the use of computers, it has now become possible to monitor the different parameters of the blast furnace in a better way since computers allows not only displaying of the variables but also uses established models, compares different variables, and builds up data bases to store the variables and their evolution during the process.

The main process monitoring sensors are:Pressure taps, which are located in the bustle pipe to monitor the blast pressure as well as at different heights in the BF to monitor the permeability of the burden and the location of the cohesive zone.Thermocouples installed in the refractory lining at various locations (hearth and shaft) to monitor the condition of the refractory and local heat variationsFixed-above burden probes to measure gas temperatures and determine gas patterns through the burden.Below-burden probe inserted for monitoring the temperature and composition of the gas inside the shaft of the furnace.Trajectory probe measures the trajectory of the burden falling from the distribution chute during the charging process.Radial profile meter at the top measures the stockline surface profile of the burden material.Stock movement sensors for monitoring the descent of the burden.

Hence, today, the use of sophisticated probes and measuring devices provides to the BF operator useful information on the state of the process. For the reliable operation of the BF, it is essential to collect various operating parameters by using these different sensing devices so that the BF process becomes transparent to the operator.

A modern blast furnace is thus equipped with a large number of probes, instruments and measuring devices that provide process data in continuous regime to the BF control center.

In addition to process parameters, it is required to monitor condition parameters, which reflect e.g. the wear state of furnace proper components. This is done by inspection and by means of sensors. For example, it is known to monitor the condition of cooling elements by means of ultrasound probes.

In this connection, the heart of the furnace undergoes high temperatures and a rough environment. Also, in order to protect the furnace walls and to limit heat evacuation through these walls, the furnace interior wall is equipped with a lining of refractory material. In modern furnaces, the refractory material is mounted on cooling elements referred to as cooling staves.

Originally, such cooling elements have been cast iron plates with cooling pipes cast therein. As an alternative to cast iron staves, copper staves have been developed. Nowadays, cooling elements for a metallurgical furnace are thus also made of copper, a copper alloy or, more recently, of steel.

The refractory brick lining, the refractory igniting material or the process generated accretion layer forms a protective layer arranged in front of the hot face of the panel-like body. This protecting layer is useful in protecting the cooling element from deterioration caused by the harsh environment reigning inside the furnace.

Depending on the conditions of operation of the BF by the operator, the protective layer may wear out mainly due to rubbing of the descending burden (coke, ore, etc.). In practice, the furnace is however also occasionally operated without this protective layer, resulting in erosion of the lamellar ribs of the hot face.

To anticipate a maintenance operation it is therefore useful to monitor the condition, i.e. the wear, of the cooling elements. Due to the harsh conditions described above, it is not yet conceivable to mount a sophisticated device inside the furnace. For the same reason and because there is constantly material inside the furnace, it may not be possible to visually check the state of the cooling elements.

Solutions have already been proposed in the art. For example, document JPS61264110 discloses a cooling stave comprising a condition monitoring system using an ultrasonic probe in contact with the rear face of the stave body to detect erosion thereof. This appears as a cumbersome technique to be implemented in the blast furnace environment.

Another document WO 2016/023838 discloses a cooling stave comprising a condition monitoring system. The stave comprises a plurality of closed pressure chambers distributed at different locations within the stave body. A pressure sensor is associated with each pressure chamber in order to detect a deviation from a reference pressure when a pressure becomes open due to wear out of the body portion. While the solution described in this document is technically satisfactory, it requires some workshop preparation, which may add on costs.

WO 2013/009824 discloses a stave/brick construction wherein wear monitors and/or thermocouples are disposed through or adjacent to the stave and/or one or more of the bricks. Data transmitting cables are attached to the thermocouple and the wear monitor system ends for transmission to a control center so that data readings can be continuously transmitted “real time” during furnace operation. The wear monitoring technology is rather complex as it relies on time-domain reflectometry.

Also disclosed in WO 2013/009824 is a laser scanning and mapping system to automatically scan and map the interior of the furnace and track the internal condition of staves and refractory bricks. The mapping system uses energy waves such as laser light waves from a emitter/receiver unit. In order to perform such mapping, it will be understood that such specific equipment can be used in the blast furnace in the rare situation where the blast furnace is shut down and the charge has been lowered.

U.S. Pat. No. 3,532,797 discloses the use of conductive loops to detect wear of refractory lining. Each loop is accommodated in a respective tube of aluminum oxide and the tubes are bundled into a generally cylindrical bundle, in a staggered manner. The conductor loops are formed of a wire having a melting point in the neighborhood of the furnace lining, so that the loops melt when the lining liquefies or melt. The staggered arrangement of the conductive loops allows detecting wear at several depths. However, the sensor design and installation is rather experimental and cumbersome.

SUMMARY

The present disclosure improves the condition monitoring in shaft furnaces.

The disclosure improves the condition monitoring of cooling elements, namely their wear condition.

The present disclosure is derived from considerations regarding shaft and blast furnace condition monitoring. As discussed above, a number of sensors and probes are arranged in the BF to monitor process parameters such as pressures, temperatures, burden distribution. These provide process data in continuous regime to the BF control center, which are required for efficient and reliable running of the blast furnace.

The installation of these process monitoring probes and sensors is time consuming and represents a substantial amount of work. Since the sensors are required to provide continuous data for the BF operation, it is not only required to install the sensors inside the furnace, but also to run cables through the furnace outer shell up to the control center.

Wiring is again at issue during maintenance shut-down of the BF, in particular when restoring the refractory layer or replacing cooling staves.

In the context of condition monitoring, the present inventors propose the use of wireless transmission of sensor data, instead of wired transmission. The use of wireless transmission in the context of the shaft furnaces may at first sight seem inappropriate: there are many metal structures surrounding the wireless module and the operating conditions are harsh (temperature/dust/barrier of the furnace shell). Also, the replacement of batteries during furnace operation may be an issue.

However, the use of wireless transmission does make sense for transmitting data from condition monitoring sensors. Contrary to process parameters that are continuously required for the furnace operation, condition parameters such as e.g. the wear status of the refractory lining or of cooling elements, do not require such continuous monitoring. Condition parameters can be checked selectively, or periodically on a time basis ranging between several hours to several days. In practice, condition parameters may be checked every few hours or once a day. This short daily operating time preserves battery time and allows for weeks/months of service, so that battery replacement is likely to be not required between shut-down periods.

Last but not least, the use of wireless modules for transmitting the data of condition monitoring sensors and probes will avoid time-consuming and cumbersome wiring operations, and hence significantly reduce the shaft furnace shut-down time.

According to a first aspect, the present disclosure proposes a shaft furnace, in particular a shaft furnace, comprising:

a metal jacket defining the furnace outer wall;

a protective layer protecting (at least partially) the inner surface of said outer wall;

at least one condition monitoring probe arranged inside said outer wall and within the protective layer to monitor the latter;

wherein the at least one condition monitoring probe is connected to a detection module (34) operatively connected to a wireless module, which are battery powered and arranged outside the outer wall to transmit condition monitoring data;

wherein said outer wall comprises an aperture for wired connection between condition monitoring probe(s) and the wireless module, a casing being mounted to the outer surface of said metal jacket in a gas-tight manner to cover the aperture.

As apparent from the above-cited prior art, the common wisdom in the art is to use wired wear monitoring sensors and process monitoring sensors (thermocouples). The present disclosure thus overcomes a technical prejudice by using wireless modules for condition monitoring probes.

The disclosure resides in the insight that battery operated wireless modules are viable to transmit data from condition/wear sensors, because the measurement frequency is low compared to process monitoring sensors, and since their readings are not required for production purposes.

The use of wears probes combined with wireless modules greatly simplifies the installation of wear sensors, and in particular when retrofitting existing Blast Furnaces. As it will be understood, it is sufficient to take advantage of an aperture in the furnace shell to draw the sensor wire outside and connect to the detection/wireless module.

The use of wireless modules for transmitting the data of condition monitoring sensors and probes will avoid time-consuming, cumbersome and cost-intensive wiring operations, and hence significantly reduce the shaft furnace shut-down time. In embodiments, the detection module is configured to evaluate the condition by means of said the condition monitoring probe(s) at predetermined time intervals but no more than once or twice a day.

Advantageously, the wireless module, detection module and battery are located inside the casing. For improved communication, the antenna of the wireless module may extend outside the casing. The detection—wireless module is thus protected from harsh environment of the BF, but accessible from time to time by opening the casing. Despite the fact that the detection—wireless module is located in a closed metallic casing, the wireless transmission is enabled since the antenna is guided outside the casing.

In embodiments, the casing comprises a steel pipe piece, one end of which is positioned to surround the aperture in the metal jacket and is welded to the outer surface of said metal jacket; the opposite end of the pipe piece being tightly closed by a cover.

In general, the protective layer may comprise cooling elements and/or refractory lining. The condition monitoring probes can be embedded within the cooling elements and/or the refractory lining. The term “cooling element” is used herein to encompass any cooling device that may be used in a shaft or blast furnace proper, including the well-known cooling plates and cooling staves.

Condition monitoring of the cooling elements is advantageously achieved by means of the design recited in the claims. The condition monitoring probe includes one or more conductive loops positioned at predetermined depths below the front face of the cooling plate body, each loop being connected to a pair of terminals on the rear face of the body, so that wear of the conductive loops the can be detected by a change of an electrical characteristic of the loop(s) due to abrasion. This design of condition monitoring probe may also be referred to as wear detection probe.

A condition monitoring probe with such conductive loops can be evaluated by a detection module connected to the terminals based on a variety of electrical principles: change of voltage, current or resistance.

Preferably the detection module is configured to evaluate an electrical closed circuit condition of each conductive loop. Such evaluation can be easily implemented since it does not require prior calibration and is not subject to temperature variations.

The above and other embodiments are recited in the claims.

According to another aspect, the present disclosure concerns a cooling plate for a metallurgical furnace or shaft furnace as recited in the claims. It comprises a body with a front face and an opposite rear face, wherein in use said front face is turned towards the furnace interior. The body includes at least one coolant channel therein, for circulating a coolant fluid, e.g. water. The front side preferably comprises alternating ribs and grooves.

It shall be appreciated that at least one wear detection probe is embedded in the body to detect wear thereof. The wear detection probe includes a plurality of conductive loops positioned at predetermined depths below the front face of said body and are electrically insulated therefrom, each loop being connected to a pair of terminals on the rear face of the body, so that wear of the body can be detected by a change of an electrical characteristic of a the loop(s) due to abrasion. The cooling plate is further characterized in that:

The conductive loops are formed as conductive lines on a board;

each conductive loop describes a generally U-shape, and the loops are nested within one another;

The conductive loops generally extend from the rear side in a thickness direction of the body so that an end section, forming a wearable section, of each loop is located at the predetermined distance (d1, d2, d3) from the front face;

the probe is arranged in a through bore or blind bore in said body;

the probe comprises a cylindrical housing surrounding said board with the conductive loops, the cylindrical housing having a shape matching the shape of the bore; and

the cylindrical housing is made from the same material as the cooling plate body.

Other embodiments of this cooling plate are recited in the claims.

According to a further aspect, the disclosure concerns a wear detection probe as recited in the claims.

