Title of Invention

A METHOD FOR ONLINE DETERMINATION OF HEARTH WEAR PROFILE OF BLAST FURNACES

Abstract

A method for estimating wear profile of refractory lining of a blast furnace hearth, comprising the steps of providing a plurality of probes at various locations circumferentially around the blast furnace hearth, adjusting the conductivity of the elements in specified regions for matching the calculated temperature with the average temperature measured over a period of time; adjusting the boundary temperatures of nodes at hot metal interface for matching the calculated temperature with the instantaneous measured temperature; and analyzing the measured temperatures from said plurality of probes to estimate the solidification isotherm utilizing numerical methods for obtaining solidus contour periodically thereby wear contour in the hearth region.

Full Text

FIELD OF INVENTION The present invention relates to a method for online determination of hearth wear profile of blast furnaces. The purpose is to determine the state of the refractory lining, using temperatures measured from the thermocouples embedded in the hearth refractory lining. The method is applicable to any blast furnace, as a tool to determine the campaign life as well as a basis for taking corrective action in the case of detection of large wears. Temperature sensing probes like thermocouples (US Patent 4,412,090), are inserted into the body of the refractory lining at the time relining. These probes are placed circumferentially all around the blast furnace. They are concentrated in the regions, subject to the maximum wear, guided by experience from previous relining. Layers of such thermocouples are mounted at various levels of the hearth. In this method, the hearth is broken up into a number of angular sectors, typically 6. The temperature readings of the thermocouples in each sector are used to carry out a two dimensional axis symmetric finite element analysis. The temperature readings of thermocouples at the same elevation in a sector are averaged. The geometry of the finite element mesh is so constructed that the location of the thermocouples maps to a nodal coordinate of the mesh. In addition the mesh is so configured, as to follow the geometry of the Blast Furnace. Boundaries between different refractory materials are accurately mapped on the mesh edges. A number of mesh elements are identified around a node representing a temperature sensor. These are so selected as to have the greatest bearing on the heat flow into the node. The conductivity of these mesh elements is manipulated. The initial value corresponds to the material property of the refractory. During operation of the blast furnace, the refractory properties degrade due to the generation of cracks and chemical processes. In situ measurement of the conductivity is not feasible. Instead, the conductivity values are altered in steps, till the calculated temperature matches the average measured temperature. A 3-months long average is taken, as the refractory properties are assumed to change slowly. Since the conductivity of one element affects the heat flow in the entire body, an exact match for all the thermocouples is not attained. Instead, the process minimizes the root mean square of the deviation between the calculated and the measured values. BACKGROUND ART Iron is mostly made through the blast furnace route. The blast furnace comprises of a steel shell, which is internally lined with refractory bricks. A hot blast of air flows from an annual pipe known as the bustle main and is directed through tuyeres into the blast furnace. The iron ore mixed with coke is charged into the furnace from the top, and is gradually reduced to iron. The temperature of the liquid iron in blast furnaces approaches 1450° C. The refractory lining serves to hold the hot metal and prevent direct contact with the steel shell. This is essential, failing which the hot metal is liable to melt the steel shell, and gush out fatal consequences. During service, the refractory lining gradually wears out. The wear occurs mostly in the hearth region. This is because the temperatures are highest in there. The wear occurs due to thermo-mechanical and thermo-chemical stresses on the refractory lining and due to viscous flow of the hot-metal or dirty hearth. In addition, if water seeps into the refractory from the cooling staves, then the refractory bricks become friable and wear out. Maximum wear accours near the taphole from where the hot metal is tapped. There are other mechanisms for the hearth wear. Due to unequal thermal expansion, openings are formed between the refractory bricks and the shell. These opening might become filled with air and serve to decrease the heat transfer. The refractory bricks on the hot side adjacent to such gaps serve under a double disadvantage, namely higher temperatures and lack of mechanical support that is broken by the gap. The openings in the refractories might also become filled with hot metal that gradually seeps in through the interstitial cracks. This would lead to the formation of a local hot spot on the steel shell. The wear of the refractory brick lining must be closely monitored during the life of the blast furnace. Localized wear at a few places can generally be patched with special techniques. In order to do this, the location and extent of the damage has to be quantified. When the refractories have become generally debilitated, a decision must be taken to shut down the blast furnace, and schedule the installation of a new lining. In case of localized wear, corrective action is undertaken, by mixing additives such as titanium-carbon-nitride (ileminite) with the blast furnace charge. These form a coating of titanium precipitate on the refractory material and prevent further refractory wear. Alternatively, the damaged regions may be repaired by injecting a paste of high conductivity material between the refractory brick and the metal shell to close the openings, which form between the refractory bricks. The prime requisite for such repair jobs is that the location of such damaged regions has to be reliably determined. The decision as to whether a blast furnace is fit to be kept in operation, is critical for a steel mill. Cost and safely are two conflicting goals that have to be judiciously balanced. Relining a blast furnace is an expensive proposition, because apart from the expensive refractory bricks, the loss of production for the duration affects the economics of the steel mill. A longer campaign life spreads the relining cost over a greater period, and increases the productivity achieved from the furnace. The state of the hearth determines the life of the blast furnace, as most of the refractory wear occurs in this region. The blast furnace may be kept in operation only if the remaining hearth refractory lining is of sufficient width. Otherwise accidents, known as Breakout can occur, where the hot metal in the belly of the furnace spouts through an opening the refractories, punctures the steel shell and causes fatalities among the workers. Direct measurement of the refractory erosion is generally carried out by positioning detection devices in the refractory lining of metallurgical vessels, such as ladles. The device comprises metal or ceramic rods positioned in the upper or outer portions of the refractory bodies with their inner ends spaced from the opposite surfaces of the refractory body. The molten metal introduced into the metallurgical vessels erodes the refractory bodies and the rod simultaneously. The complete erosion and absence of the metal rods indicates a predetermined safety level thickness of the remaining refractory bodies and signals the need of replacement of the lining. A refractory erosion indicator gauge for use in blast furnaces and other equipment is also available. The erosion indicator comprises a structural plate member having a preferably triangular configuration. The member is welded within the refractory lining of the equipment in which it is employed. These gauges must be introduced at the time of relining itself. The plate members are welded to the blast furnace shell before the refractory lining is installed or alternatively, it may be integrated within the refractory lining per se and secured to the shell with the refractory. As the new refractory surface wears or erosion takes place, the exposed portion of the triangle is determinative of the remaining actual thickness of the refractory lining or the amount of lining eroded away, depending on the orientation of the plate. This permits determination of the remaining refractory life. Thus, the time for replacement of the refractory can be determined by visible observation of the indicators in the internal lining of the equipment. The problem is that all such direct measurement devices, require a clear view into the belly of the furnace through specially designed peepholes. Alternatively, the wear of the bar and the lining may be detected ultrasonically by generating ultrasonic pulses in the bar and detecting the reflection of the pulses from the worn inner end of the bar (US Patent No. 4,510,793). All these methods comprise time consuming and laborious tasks and are rarely practical. To obtain the state of wear, indirect measurement are used as there is no convenient method to directly monitor the left out thickness of the refractories, on a continuing basis. An indirect measure of the state of the worn profile, can be obtained from temperature measurements. A high value of the temperature at a location, indicates proximity to the hot metal and corresponds to larger refractory wear. This provides a qualitative understanding of the state of the refractory profile. Also, a high temperature difference from the cooling plates is representative of hearth wear. But the state of the furnace can only be guessed on the basis of above information. Quantitative estimates of the refractory wear can be made from "dual thermocouples", as practiced in Japanese steel companies [Nippon Steel]. However these require a multiplicity of thermocouples, where 2 or 3 thermocouples are placed "in line". In such installations, several thermocouples are placed at the same radial and elevation locations, but a different insertion depths. Typically one in the refractory lining, another following in the same bore but at a smaller insertion depth and a third also placed inline but located in the outer steel shell (JP 1290709). A group of such thermocouples are placed in the vicinity of the tap hole. A second group of thermocouples in placed vertically above the first group, at an elevation above the top surface of the hearth pad. A third group of thermocouples is placed in the same common vertical section as the first two groups, but at the corner junction of hearth sidewall and the hearth pad. Heat transfer calculations are used to calculate the refractory temperature distributions and then later compared with the measured temperatures to estimate the remaining refractory and skull thickness. It will be appreciated that such extensive instrumentation is a costly affair. US Patent No. 5,975,754 documents the use of one and two dimensional finite element models, based on the thermocouple readings on a vertical plane to determine, solidified metal skull lining thickness as well as the brick thickness. But in all such previous descriptions, they have made use of inline [dual] thermocouples installed at definite locations (JP 1290709). The present method also uses thermocouple temperatures to determine skull thickness as well as worn refractory lining but the locations for thermocouples are not so stringent. It is preferable to have more thermocouples installed in a region of larger wear, but there is no constraint that a set thermocouples must be placed inline. In the prior art, the temperature differences between a set of inline thermocouples, is used in a one dimensional finite element model to derive the location of the solidification line [1050° C] and the boundary condition on the hot metal side is accordingly modified. This modified boundary condition is then used in a two dimensional finite element model. SUMMARY OF THE INVENTION The proposed method circumvents the difficulty of requiring numerous thermocouples. Instead, it works with the data from the thermocouples already installed. Naturally, providing additional inputs from more probes will enhance the accuracy of predictions, but it can still provide meaningful results from the currently installed thermocouples. The present invention also relates to a two-stage process. But it uses a two dimensional finite element analysis in both stages. In the first stage, the conductivities of selected elements are modified and in the following stage the boundary temperatures on the hot metal side are modified, to obtain the best RMS fit with the measured temperatures. Because of this process, the maximum difference between the calculated and measured temperatures can be constrained within 10° C and provide reliable estimates of the worn refractory lining profile. A further advantage is that, since a one-dimensional finite element analysis is not resorted to, there is no requirement of inline thermocouples. The systems in the prior art were constrained by the necessity of inline thermocouples, which formed the starting point of the analysis. Retro fitting of inline thermocouples in an operating blast furnace is troublesome and expensive. And even in new relinings, installation of multiple thermocouples in the same borehole, adds substantially to the expenses. There is the additional problem, that if either thermocouple of the pair burns out, the data from the other cannot be used. The proposed method makes use of all the data from the available sensors, even from the one functioning sensor of a pair of inline thermocouples where the other of the pair has been damaged. It works with the data from already installed sensors, and does not call for the installation of new sets of thermocouples at particular locations, which might be inaccessible because of problems of fouling with other equipment. A further advantage is that, the readings form thermocouples tend to fluctuate because of instrument errors. Since the proposed method uses a two- dimensional finite element analysis consistently, the measured temperatures in the vicinity guide the calculated heat flow pattern at any point. In this way, random instrument errors are automatically compensated, since all the measured values are simultaneously considered while arriving at the predicted heat flow at all the nodes of the mesh. This invention provides a method of estimating the remaining refractory lining of a blast furnace hearth by analyzing the temperatures of embedded thermocouples. The temperature probes do not need to be in any particular alignment (as in in-line thermocouples). The temperature probes may be embedded at convenient locations circumferentially around the blast furnace hearth, at suitable elevations and insertion depths. Although this method can work with a few thermocouples, the larger the number of sensors the greater is the fidelity of the estimate of refractory wear. The measured temperatures are used to determine the average temperature readings [3-month average]. In the first stage the conductivity's of elements in the vicinity of the temperature recorders are modified, and a finite element analysis using a 2-Dimensional model is carried out to calculate the temperature filed. The calculated temperatures at the locations of the recorders are compared with the measured average values. This is an iterative procedure, and terminates with a close match between the calculated and the measured average values. The conductivity adjustments are performed with a gradient search method. The termination criteria are respect to the maximum number of iterations as well as a specified maximum limit on the RMS deviation between calculated and measured values. In the second stage, proceeding from the modified conductivities, the temperatures at the hot metal interface are progressively altered. This again is an iterative procedure similar to the one outlined above, except that it is the boundary temperatures, which are now being adjusted. The objective is to match the calculated values of the temperature field at the sensor locations with the current measured temperatures. The process terminates when the RMS deviation with the measured current temperatures decreases below a preset threshold, or after a specified maximum number of iterations. This 2 stage iterative procedure ensures a good match between the calculated and measured values [typically a maximum deviation of 6°C]. Finally, the modified conductivities and the modified boundary temperature at the hot metal interface, are used to locate the solidification isotherm [1150° C]. This is considered to represent the hearth wear profile. Thus the application provides a method for estimating wear profile of refractory lining of a blast furnace hearth, comprising the steps of providing a plurality of probes at various locations circumferentially around the blast furnace hearth, adjusting the conductivity of the elements in specified regions for matching the calculated temperature with the average temperature measured over a period of time, adjusting the boundary temperatures of nodes at hot metal interface for matching the calculated temperature with the instantaneous measured temperature; and analyzing the measured temperatures from said plurality of probes to estimate the solidification isotherm utilizing numerical methods for obtaining solidus contour periodically thereby wear contour in the hearth region. The method operates in two stages. First, the conductivity of the elements in specified regions is adjusted, so that he calculated temperatures match the average measured temperatures, averaged over 3 months. The modified conductivity values provide an indication of the formation of openings in the refractories as well as documenting the degradation of the refractory qualities in particular regions. Repair work can then be undertaken in those regions. In the following stage, the boundary temperatures of nodes at the hot metal interface are adjusted so that the calculated temperatures match the instantaneous measured temperatures. The1150° C temperature contour, with these adjusted conductivity's and boundary temperatures, is taken to represent the wear profile inclusive of the skull. By substituting the instantaneous temperatures with the maximum temperatures than have been recorded during the operation of the blast furnace, the refractory wear profile can be estimated. The radial difference between these two wear lines indicates the depth of skull formation. BRIEF DESCRIPTION OF THE ACCOMYING DRAWINGS Figure 1 shows a composite view of the arrangement of thermocouples in the hearth of a typical blast furnace. 3 orthogonal views and one isometric view are shown. The lengths indicate the insertion depth from the shell into the refractory. Figure 2 shows a composite view of the finite element meshes in the hearth of a typical blast furnace. 3 orthogonal views and one isometric view are shown. The Furnace is radically divided into 6 axis symmetric sectors. Figure 3 shows a cross-section of a blast furnace hearth corresponding to a pair of diametrically opposite sectors. Showing the arrangement of the finite element mesh as well as the location of thermocouples that are considered as belonging to that pair of sectors. 3 orthogonal views and one isometric view are shown. Figure 4 shows a cross-section of a blast furnace hearth corresponding to a pair of diametrically opposite sectors. Showing the elements of the finite element mesh that are taken for Conductivity Adjust for a specified node with thermocouples. In the right half 4 elements are taken, while in the left half 8 elements are taken. These elements are shown in a different colour, as well as being isolated in 2 separate windows. Figure 5 shows a cross-section of a blast furnace hearth corresponding to a pair of diametrically opposite sectors. Showing the boundary nodes that are taken for Temperature Adjust for a specified node with thermocouples. In the right half 2 boundary nodes at the hot metal interface are taken, while in the left half a single node is taken. The node numbers are marked, as well as being isolated in 2 separate windows. Figure 6 shows a cross-section of a blast furnace hearth corresponding to a pair of diametrically opposite sectors. The Inner line is obtained from the current thermocouple readings and represents the line at the skull. The outer line is obtained with the maximum temperatures and indicates the refractory line. The arrows are scaled representations of the temperatures measured at those locations. Figure 7 shows an isometric view of a blast furnace hearth showing the lines that represent the skull formation. These are drawn for 6 sectors. The dimensions to the skull line are also indicated. The outer dimension indicates the distance the steel shell, while the inner dimension provides the wear from the original refractory surface. These are indicated at 2 elevations. Rgure 8 shows a cross-section of a blast furnace hearth corresponding to a pair of diametrically opposite sectors. The inner window shows a contour map of the thermal conductivity of the elements as estimated by this method. The outer window shows the line representing a specified conductivity value. This provides information pertaining to the degradation of the refractories and indicates regions where corrective action is required. DETAILED DESCRIPTION OF THE INVENTION The standard finite element technique, uses a known geometry, element properties and specified boundary conditions (nodes with known temperature / heat flux), and solves for the unknown temperatures and heat fluxes. This is done through standard numerical techniques. In the case of this problem, the predicted temperatures from finite element analysis will differ from the measured thermocouples temperature readings. This is because, the boundary conditions are altered by the lining wear. By using the steepest descent method, the conductivities of selected elements and the temperature of selected boundary nodes are adjusted. The finite element analysis is repeated iteratively. This continues till convergence with all the measured temperatures and the current wear profile is estimated. The objective of this invention is to determine the solidification isotherm, at 1150° C, on a continuing basis using temperatures from the hearth thermocouples [Fig.1.]. This can be done by solving a heat transfer problem. The finite element technique, which can be used for such a solution, is a standard method, and commercial programs are available for the purpose. However the solution methodology for this problem, requires an iterative search with modification of the boundary conditions at each iteration. No commercial program exists for this purpose. This necessitated the development of an independent finite element analysis software, which incorporates the requisite additional features. A finite element model for the hearth is constructed and the mesh is drawn such that the nodes coincide with the thermocouples [Fig.2]. The temperature data is taken from the thermocouples embedded in the refractory at various locations in radial directions and across the thickness of the refractory lining of the hearth. These probes need not be in a fixed plane or at stipulated locations. Hence this method can be applied using existent hearth thermocouples, without the need for enhancing the instrumentation. The hearth geometry is modeled as a set of independent vertical sections. For this purpose, the hearth zone is divided into a number of sectors, as per the need of sensitivity. Typically 6 sectors have been found to be sufficient, but additional sectors may be configured (Fig.3.). A zero line on the periphery is selected to identify these sections distinctly as per their angular distance from the zero-line on the periphery. Typically this zero-line is taken as the centerline between tapholes of the furnace. The data from thermocouples in a particular section is considered to determine the wear for that section. The data is captured through a TDC and fed into the analysis package through a pre-processor software. Although the heat flow is really a 3 Dimensional solid body problem, it is assumed that temperature values in one sector are predicated on the wear in that sector, and have no influence on an adjacent sector. The existing thermocouples are grouped into a number of sectors [say 6], and all thermocouples in a specific sector [say between 330 and 30 deg], are assumed to provide temperatures of the central vertical section in the sector [in this case at 0 deg]. In case there are more than one thermocouple at the same elevation and insertion depth in a sector, the arithmetic average of these thermocouple readings, is taken as representative of a point in the sector, at elevation and insertion depth [Fig.3.]. The output comprises of an estimate of the thickness of the left out lining [including the skull]. During actual furnace operation, the estimate of the distance between the wear line and the inner surface of the blast furnace metal shell, provides a key input regarding the condition of the blast furnace. The life of the refractory lining of the furnace hearth may be extended by maintaing a sufficient thickness of the protective layer of solidified metal skull during operation of the furnace. The input data that is required for such analysis is captured in two phases. First the average temperatures recorded by each temperature probe over the past 3 months period are considered. The history of temperature readings of ail the thermocouples is stored in a computer database. This is accessed and the average temperature values are extracted. These values are required in order to adjust the conductivities and tune the model and is performed in a process called Conductivity Adjust. In the second phase, the current temperature data is taken for adjusting the boundary nodal temperatures. This process is called Temperature Adjust. Finally the soildication isotherm is estimated and this gives the wear profile for the time period under consideration. CONDUCTIVITY ADJUST The hearth of the method comprises the estimation of the conductivities of selected elements [Fig.4]. Starting from the known thermal conductivity properties of the several refractories comprising the lining, the conductivities of selected elements close to the outer steel shell of the blast furnace are iteratively adjust. This results in calculated temperatures at the thermocouples locations, which is close to the measured averages. The logic of this operation is that the heat flow from the interior of the blast furnace outwards to the steel shell and thence to the cooling water can become impeded because of flaws developing in the refractories. These flaws can take of gaps forming at the interface between the outer surface of the refractories and the inner surface of the blast furnace steel shell. Or there might be impediments in the flow of the cooling water contacting the outer surface of the blast furnace steel shell. In both these cases, as the heat flow is impeded, the measured thermocouple temperatures will tend to rise. Alternatively, the gaps might become filled with solidified hot metal, seeping into these spaces from the interior of the furnace, and subsequently solidifying. In such cases, the measured temperatures will tend to be higher, as the solidified metal will conduct heat more quickly, out to the steel shell. These effects are simulated in the s/w by adjusting [decreasing or increasing] the thermal conductivity coefficients of the mesh blocks in the vicinity of the thermocouples which have a different temperature as compared to the steady state temperatures predicted from the known thermal conductivities of the refractories. Internal cracks in the refractories, present another problem. Such cracks would become filled with hot metal from the interior of the blast furnace and would result in substantially raising the temperatures of the thermocouples tailing such fissures. The mapping of the finite element mesh blocks with the appropriate thermocouples has to be specified in a separate data file. The entries into this data file have to be manually specified, based on an understanding of the process of heat flow [Fig. 4]. When the mapping has been done satisfactorily, the software-adjusted conductivities will result in a temperature filed that matches the measured average values. Since such flaws in the refractories have long lasting consequences, they are derived from average measured temperatures, averaged over a reasonably long time span [3-months]. The following notations are defined: VALUE= Measured value from the thermocouple at that node VALJNL= Calculated temperature of a node with thermocouples ELMTEM= Calculated temperature of an element, by averaging the nodal temperatures VAL12=Specified conductivity of the element VALRSL= Modified conductivity of the element FACTOR= Ratio of VALRSL/VAL12 Two situations can arise. If the element is not contiguous with the thermocouple node, then the element conductivity is modified by the factor FACTOR==VALUE/VALJNL; when ELMTEM.GT.VALJNL And FACTOR=VALJNL/VALUE; when ELMTEM.LE.VALJNL If the element is contiguous with the thermocouple node, then the element conductivity is modified by a factor that considers the influence of all the nodes of element. The following terms are defined: TMS[3,3]= Influence matrix of the nodes of the element. In case of quadrilateral elements, the element is broken into the constituent triangles and the operation is executed for the individual triangles in sequential passes. SUMHTF= Heat transfer factor for the node in question SUMRQD= Required heat transfer factor to match the measured temperature. Certain minimum (MNCNAD) and maximum [MXCNAD] conductivity check values are also defined. If the calculated value is outside these limits, the modified value is constrained to the limit. IF (VALRSL.GT.MXCNAD)VALRSL=MXCNAD IF (VALRSL.LT.MNCNAD)VALRSL=MNCNAD After calculating the adjusted conductivity's at each location, they may be used for further decision-making, such as to indicate the presence of a gap between the shell and the hearth brickwork [Fig 8). Corrective action may then be taken to fill the gap e.g. with a high conductivity grout material to re-establish contact with the cooled shell. Since the s/w modifies the conductivities of the mapped blocks iteratively, the conductivity values lie in a continuous spectrum. These values would result in the best match of the measured average temperatures. The adjusted conductivities are written to a file, and may also be graphically displayed as contours of the conductivities. Sharp changes in the adjusted conductivities are displayed as a band of dense closed contours and indicate locations where repair work should be targeted [e.g. carbon paste injection]. Maintaing a protective layer implies an adequate heat transfer form the refractory hearth walls to the metal shell of the furnace hearth and from the metal shell to the cooling water applied to the metal shell. Maintaining adequate heat transfer would imply the thermal conductivity's lying in a suitable band from the initial refractory conductivities. Conductivities lower than a specified minimum value can be used to determine if a gap has formed between the refectory and the metal shell. The preset limit typically may be selected from within a range of [-50% to -100%]. Conductivities higher than a specified maximum [+50%+100%] may be compared to determine if a build-up on the shell has occurred. The presence of a build-up on the furnace shell would result in turbulent water cooling on the shell, and would be indicated by low average temperatures of the thermocouples, which would be manipulated by the s/w to indicate higher conductivities in the associated mapped blocks. Once the problem areas are identified, corrective action may be concentrated in such regions. This might comprise sand blasting the surface of the shell in the specified location to remove incipient build up. Alternatively problems in the water flow system may be pinpointed such as increase temperature of the feed water or choking of the flow, once the region has been identified. Next the boundary temperatures in the interior of the blast furnace are considered. These are initially considered to be at 1500° C. The temperatures at the nodes of this internal boundary are then altered in successive iterations [Figs.5]. The temperature field is evaluated after every iteration by using a 2 dimensional finite element model, and the RMS of the divergence with the measured values is calculated. The moving boundary calculation is terminated when the RMS of the divergence after having reduced in stages, commences to increase. The following notations are defined: VALI2= Measured value from the thermocouples at that node VALJNL= Calculated temperature of a node with thermocouples VALUE= Temperature at the boundary node as modified in the previous iteration VALRSL= Modified temperature at the boundary node in the current iteration VALRSL=VALI2/VALJNL*VALUE Certain minimum [MNTMAD] and maximum [MXTNAD] temperature check values are also defined. If the calculated value is outside these limits, the modified value modified value is constrained to the limit. IF (VALRSL.GT.MXTMAD) VALRSL=MXTMAD IF (VALRSL.LT.MNTMAD) VALRSL=MNTMAD After having computed the modified element conductivities and the boundary temperatures, the contour representing the 1500° C solidification isotherm is derived. This is taken to represent the lining profile in the operating blast furnace [Fig 6+7]. The contour of the specification line provides valuable information. If the estimated left out refractory thickness decreases below a safe limit, remedial actions are required. This generally takes the form of increasing the formation of a protective skull over the worn refractory lining. The charging of ileminite together with the blast furnace charge encourages skull formation. If all else fails, the last option is to choke the hot blast flow in the tuyeres lying in that vertical section. This constrains the production, but the temperatures have to be reduced to avoid the chance of break out accidents. The procedure that has been outlined above is carried out with the current temperatures as measured by the embedded thermocouples. The solidification isotherm is interpreted as the wear profile including the skull formation at the hot metal interface. The temperature Adjust procedure is repeated with the maximum of the recorded temperatures. The temperature data from all the thermocouples is archived in a computer database. This archive is accessed to ascertain the maximum-recorded temperatures during the history of operation. When these maximum temperatures are used, the solidification isotherm is interpreted as the wear profile of the refractory lining [no skull formation]. Thus two distinct solidification lines are found, one of which is closer to the centerline representing the current skull and the other representing a hotter condition and being pushed further outwards, which represents the wear on the refractory lining. The distance between the two represents the thickness of the solidified skull. Skull formation is intrinsic to blast furnaces. They cause problems in the smooth decent of the burden and decrease the workings volume. But they have a beneficial aspect as well in that they protect the refractory lining and extend its life. During operation of blast furnaces, the skull formation cannot be directly viewed. The method outlined here provides a means of estimating the skull formation and provides an insight into the blast furnace. WE CLAIM: 1. A method for estimating wear profile of refractory lining of a blast furnace hearth, comprising the steps of: - providing a plurality of probes at various locations circumferentially around the blast furnace hearth; - adjusting the conductivity of the elements in specified regions for matching the calculated temperature with the average temperature measured over a period of three months; - adjusting the boundary temperatures of nodes at hot metal interface for matching the calculated temperature with the instantaneous measured temperature; and - analyzing the measured temperatures from said plurality of probes to estimate the solidification isotherm utilizing numerical methods for obtaining solidus contour periodically, thereby providing wear contour in the hearth region. 2. The method as claimed in claim 1, wherein with the adjusted conductivities and boundary temperatures the 1150°C temperature contour is taken to represent the wear profile comprising the skull. 3. The method as claimed in claim l,wherein refractory wear profile can be calculated by substituting the instantaneous temperatures with the maximum temperatures that have been recorded during the operation of the blast furnace. 4. The method as claimed in claims 2 and 3, wherein the radial difference between the two wear lines indicates the depth of skull formation. 5. A method for estimating the wear profile of refractory lining of a blast furnace substantially as herein described and illustrated in the accompanying drawings. A method for estimating wear profile of refractory lining of a blast furnace hearth, comprising the steps of providing a plurality of probes at various locations circumferentially around the blast furnace hearth, adjusting the conductivity of the elements in specified regions for matching the calculated temperature with the average temperature measured over a period of time; adjusting the boundary temperatures of nodes at hot metal interface for matching the calculated temperature with the instantaneous measured temperature; and analyzing the measured temperatures from said plurality of probes to estimate the solidification isotherm utilizing numerical methods for obtaining solidus contour periodically thereby wear contour in the hearth region.

Documents:

492-kol-2004-granted-abstract.pdf

492-kol-2004-granted-claims.pdf

492-kol-2004-granted-correspondence.pdf

492-kol-2004-granted-description (complete).pdf

492-kol-2004-granted-drawings.pdf

492-kol-2004-granted-examination report.pdf

492-kol-2004-granted-form 1.pdf

492-kol-2004-granted-form 13.pdf

492-kol-2004-granted-form 18.pdf

492-kol-2004-granted-form 2.pdf

492-kol-2004-granted-form 3.pdf

492-kol-2004-granted-form 5.pdf

492-kol-2004-granted-gpa.pdf

492-kol-2004-granted-reply to examination report.pdf

492-kol-2004-granted-specification.pdf