Patent Publication Number: US-9417322-B2

Title: Measurement of charge bank level in a metallurgical furnace

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional application 61/328,023, filed on Apr. 26, 2010, which is incorporated herein by reference. 
    
    
     FIELD 
     The described embodiments relate to the measurement of a level of material contained in a metallurgical furnace and a related furnace control system. 
     BACKGROUND 
     Metallurgical furnaces are used to process feed material to separate metals and other materials in the feed materials to matte and slag. Various factors, including the rate at which feed material is introduced into a furnace, the rate at which matte and slag materials are drawn from the furnace, the operation of electrodes and control systems for melting equipment may be varied to control the process of converting feed material into matte and slag. It can be desirable to monitor amount of feed material in the metallurgical furnace to control some of these factors and other factors in the operation of a metallurgical furnace. 
     SUMMARY 
     In a first aspect, some embodiments of the invention provide a system for monitoring a level of a feed material layer contained in a metallurgical furnace including at least one non-contact sensor to sense a distance between the feed material layer and a reference position. The at least one sensor is positioned above the feed material layer. The system also includes a process controller communicably linked to the at least one sensor to output a control signal based on the sensed distance. 
     In some examples, the at least one sensor includes at least one transmitter positioned above the feed material. The sensor has an unobstructed line of sight to the feed material layer contained in the furnace. The at least one transmitter is configured to project an electromagnetic signal toward the feed material layer. The sensor also includes at least one receiver positioned to receive a reflection of the electromagnetic signal from a surface of the feed material layer. The sensor is operable to determine the sensed distance. 
     In some examples, at least one sensor is fixedly mounted relative to the furnace. 
     In some examples, the furnace comprises a plurality of feed ports and at least one sensor is positioned proximate to at least one of the plurality feed ports. 
     In some examples, the furnace comprises a plurality of electrode ports and at least one sensor is positioned proximate to at least one of the plurality of electrode ports. 
     In some examples, the at least one sensor comprises a plurality of sensors each generating at least one corresponding sensed distance and the process controller is configured to generate the control signal based on a plurality of sensed distances. 
     In some examples, the process controller is configured to process the plurality sensed distances to provide a surface topography of a surface of the feed material layer. 
     In some examples, the system also includes a display communicably linked to the controller to display at least one of any one of the plurality of sensed distances and the surface topography. 
     In some examples, the display is remote from the furnace. 
     In some examples, the process controller is configured to compare the surface topography to a pre-determined surface topography and to provide a surface output signal based on the comparison. 
     In some examples, the process controller is configured to output a plurality of control signals, each control signal being based on a corresponding one of the plurality of sensed distances. 
     In some examples, each sensor comprises a radar sensor. 
     In some examples, the system also includes a protective housing surrounding each sensor. 
     In some examples, each protective housing comprises a Faraday cage to provide electromagnetic shielding. 
     In some examples, the system also includes a thermal radiation shield between each sensor and the feed material layer to inhibit heat transfer between the sensor and the feed material layer. 
     In some examples, the thermal radiation shield is substantially transparent to the electromagnetic signal and the reflection. 
     In some examples, each sensor is position above a corresponding opening in a roof of the furnace, the opening providing the unobstructed line of sight to the feed material layer. 
     In some examples, the reference position is a known mounting location of the sensor. 
     In some examples, the controller is operable generate the control signal in real-time. 
     In some examples, the process controller is communicably linked to a feed actuator and is configured to generate a feed control signal to automatically regulate a feed rate of the feed material based on feed control signal. 
     In some examples, the process controller is communicably linked to an electrode actuator and is configured to generate an electrode control signal to automatically move an electrode from a first position to a second position based on the electrode control signal. 
     In some examples, the process controller is communicably linked to an electrode power supply regulator and is configured to generate an electrode control signal to automatically regulate the power supplied to an electrode based on the electrode control signal. 
     In some examples, the at least one sensor is moveably supported to enable the at least one sensor to sense a first sensed distance when the sensor is in a first position and to sense a second sensed distance when the sensor is in a second position. 
     In some examples, the at least one sensor is operable to sense a plurality of sensed distances corresponding to a plurality of locations on a surface of the feed material layer. 
     In some examples, the process controller is configured to receive and process data from at least one thermal sensor. 
     In some examples, the at least one sensor is positionable to sense a second sensed distance between a second material layer and the reference position. 
     In some examples, the at least one sensor includes a first sensor positioned for sensing the sensed distance and a second sensor positioned to sense a second sensed distance between a second material layer and the reference position. 
     In some examples, the at least one receiver comprises at least two receivers and the at least one transmitter is communicably linked to each of the at least two receivers. 
     According to a second aspect, some embodiments of the invention provide a method of monitoring a feed material layer in a metallurgical furnace including the steps of a) providing at least one non-contact sensor positioned above the feed material layer contained in the furnace while the furnace is in use; b) sensing a sensed distance between a surface of the feed material layer and a reference position using the sensor; c) providing a process controller communicably linked to the sensor to generate a control signal based on the sensed distance; and d) outputting the control signal. 
     In some examples, step a) comprises providing at least one transmitter in a fixed position above the feed material layer and providing at least one receiver above the feed material layer; and step b) comprises projecting an electromagnetic signal from the transmitter toward a surface of the feed material layer, collecting a reflection of the electromagnetic signal off a surface of the feed material layer using the receiver and comparing the electromagnetic signal to the reflection. 
     In some examples, the method also includes the step of using the process controller to control at least one of a feed material supply rate, an electrode position and an electrode power supply based on the control signal. 
     In some examples, the step of controlling at least one of the feed material supply rate, the electrode position and the electrode power supply based on the control signal is carried out automatically by the process controller without user intervention. 
     In some examples, at least the steps of comparing the electromagnetic signal to the reflection and outputting the control signal are preformed by the controller in real-time. 
     In some examples, the method also includes the step of providing a display and generating a display output based on the control signal. 
     In some examples, step a) comprises providing a plurality of transmitters above the feed material layer, step b) comprises providing a corresponding plurality of receivers above the feed material layer, and determining one sensed distance corresponding to each transmitter. 
     In some examples, step c) comprises providing a plurality of control signals, each control signal based on one sensed distance. 
     In some examples, step c) comprises generating a surface topography based on the plurality of sensed distances and generating a surface control signal based on the surface topography. 
     In some examples, the surface is an upper surface of a feed material layer contained in the furnace. 
     In some examples, the method also includes the step of positioning the at least one sensor in a second position to sense a second sensed distance between a second location on the surface and the reference position. 
     In some examples, the method also includes the step of positioning the at least one sensor in a second position to sense a second sensed distance between a second material layer and the reference position. 
     According to a third aspect, some embodiments of the present invention provide a feed control system for a metallurgical furnace containing a feed material layer, the feed control system includes at least one non-contact sensor to sense a distance between a surface of the feed material layer and a reference position. The sensor is positioned above the feed material layer. The system also includes a process controller communicably linked to the at least one sensor and configured to output a control signal based on the distance. The system also includes at least one feed supply actuator communicably linked to the controller to automatically regulate a flow of feed material into the furnace based on the control signal. 
     In some examples, the at least one sensor includes at least one transmitter fixedly positioned above the feed material layer and having an unobstructed line of sight to the feed material layer. The at least one transmitter is configured to project an electromagnetic signal toward the feed material layer. The sensor also includes at least one receiver fixedly positioned to receive a reflection of the electromagnetic signal from a surface of the feed material layer. 
     According to a fourth aspect, some embodiments of the present invention provide a metallurgical furnace including a reactor vessel for containing a feed material layer and at least one non-contact sensor mounted to the reactor vessel. The sensor is positioned to have an unobstructed line of sight to the feed material layer contained in the furnace. The sensor is operable to sense a sensed distance between a surface of the feed material layer and the sensor. 
     In some examples, the furnace also includes a process controller communicably linked to the at least one sensor. The process controller is operable to generate and output a control signal based on the sensed distance. 
     In some examples, the furnace also includes at least one feed port and at least one feed supply actuator to regulate a flow of feed material through the at least one feed port. The at least one feed supply actuator is communicably linked to the process controller to automatically regulate a flow of feed material into the furnace based on the control signal. 
     In some examples, the furnace also includes at least one electrode movably received within a corresponding electrode port and at least one electrode actuator operable to translate the electrode relative to the reactor vessel. Each electrode actuator is communicably linked to the process controller to translate the at least one electrode based on the control signal. 
     According to a fifth aspect, some embodiments of the present invention provide a system for monitoring a level of a material layer contained in a metallurgical furnace including at least one non-contact sensor to sense a distance between the material layer and a reference position. The at least one sensor is positioned above the material layer. The system also includes a process controller communicably linked to the at least one sensor to output a control signal based on the sensed distance. 
     According to a sixth aspect, some embodiments of the present invention provide a method of controlling a feed rate at which feed material is supplied to a metallurgical furnace. The method includes the steps of: a) obtaining a charge bank level; b) obtaining a slag level; c) comparing the charge bank level and the slag level to determine a charge bank height; d) comparing the charge bank height to a plurality of pre-determined acceptable height values; and e) adjusting at least one of the feed rate and an electrode power based on the comparison of step d). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the present invention will now be described in detail with reference to the drawings, in which: 
         FIG. 1  is a schematic representation of an example of a metallurgical furnace; 
         FIG. 2  is a schematic representation of another example of a metallurgical furnace; 
         FIG. 3  is a schematic representation of another example of a metallurgical furnace; 
         FIG. 4  is an isometric view of an example of a metallurgical furnace; 
         FIG. 5  is a partial section view of a portion of a roof of a metallurgical furnace with a sensor mounted to the roof; 
         FIG. 6  is a schematic representation of an example of a metallurgical furnace; 
         FIG. 7  is a schematic representation of an example of a metallurgical furnace; 
         FIG. 8  is a schematic representation of an example of a metallurgical furnace; 
         FIG. 9  is a diagram of a control system for a metallurgical furnace; 
         FIG. 10  is a schematic representation of an example of a metallurgical furnace and a control system for the furnace; 
         FIG. 11  is a flow chart illustrating an example of a method of operating a control system for a metallurgical furnace; 
         FIG. 12  is a flow chart illustrating another example of a method of operating a control system for a metallurgical furnace; 
         FIG. 13  is a flow chart illustrating another example of a method of operating a control system for a metallurgical furnace; and 
         FIG. 14  is a diagram of another example of a control system for a metallurgical furnace. 
     
    
    
     For simplicity and clarity of illustration, elements shown in the figures have not been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Various apparatuses or processes will be described below to provide example of embodiments of each claimed invention. The described embodiments do not limit any claimed invention and any claimed invention may cover processes or apparatuses that are not described below. The claimed inventions are not limited to apparatuses or processes having all of the features of any one apparatus or process described below or to features common to multiple or all of the apparatuses described below. It is possible that an apparatus or process described below is not an embodiment of any claimed invention. Any invention disclosed in an apparatus or process described below that is not claimed in this document may be the subject matter of another protective instrument, for example, a continuing patent application, and the applicants, inventors or owners do not intend to abandon, disclaim or dedicate to the public any such invention by its disclosure in this document. 
     Reference is first made to  FIG. 1 , which is a schematic representation of a metallurgical furnace, for example furnace  100 , having a bottom surface, at least one side surface and a top surface that cooperate to define a furnace or reactor vessel  108  to contain material being melted in the furnace. The furnace  100  includes a sensor  110  that is used to determine the position or level of the material in the furnace, relative to the sensor  110 . Based on the level of the material in the furnace, one or more operating parameters of the furnace can be modified, including, for example the rate at which additional material is introduced into the reactor vessel and the rate at which material is drawn from the reactor vessel. Optionally, the sensor  110  can be communicably connected to any suitable instruments, actuators and controllers so that the operating parameters can be automatically adjusted based on the level of the material, without requiring intervention or input from a human operator. 
     In the examples described herein, the sensors  110  are permanently or fixedly connected to furnace  100  in their operating positions so that the sensors  110  can conduct ongoing measurements while the furnace is in use, as opposed to being only temporarily positioned over the furnace for a one-time measurement. Accordingly, the sensors  110  are configured to withstand the expected operating conditions of the furnace. While any given sensor may be moveable or positionable relative to the furnace  100  (i.e. pivotable, rotatable, translatable), the sensors  110  are fixedly connected to the furnace so that the sensors remain in their operating position while the furnace is in use. It is understood that even permanently mounted sensors can be temporarily removed or detached for inspection, maintenance and replacement. 
     In  FIG. 1 , the bottom surface of the reactor  100  is provided by hearth  102 , the side surface is provided by the sidewalls  104  and the top surface is provided by the reactor roof  106 . Together, these elements define the reactor vessel  108 . The reactor roof  106  includes at least one feed port  112  through which material to be melted, or feed material, can be introduced into the reactor vessel  108 . The flow or supply of feed material into the reactor vessel  108  is represented schematically in the Figures by the plurality of arrows  114 . The feed material can be any suitable material to be melted in the furnace  100 , including for example, ore, metal and the like. 
     When the furnace  100  is in use, the feed material melts to form a generally molten fluid or slurry that can include a variety of different components. It is understood that relative differences in the density of such components can result in a predictable stratification or layering of the material in the reactor vessel  108 . In the illustrated example, the material in the reactor vessel  108  contains a layer of molten product material, that is the desired end product of the smelting operation. Depending on the nature of the feed material supplied to the furnace  100 , the molten product material is commonly referred to as being a metal phase or a matte phase. It is understood that the sensors and control systems described can be used on furnaces that contain either a molten metal phase or a molten matte phase. For simplicity, the examples described herein refer to a molten matte phase that forms a matte layer  116 , but it is understood that alternatively a molten metal phase could be present in any of the examples described herein. The matte layer  116  defines a measurable, matte layer depth or thickness  117 . 
     Floating above the matte layer  116  is a slag layer  118 . The slag layer  118  is formed from material defining a slag phase, that can include a combination of impurities, lighter molten elements (possibly comprising different metal compositions) and other by-products produced when the feed material is melted. In some examples, the slag layer  118  contains generally unwanted or undesirable compounds and is withdrawn from the reaction vessel  108  separately from the matte phase. The slag layer  118  defines a slag layer depth  119 . 
     Over time, in some embodiments, portions of the matte phase in matte layer  116  can solidify, or freeze, and form solid matte particles that are denser than the matte phase, and therefore tend to settle to the bottom of the vessel  108 . Such solid matte particles can collect at the bottom of the vessel  108  and may form a build-layer  122 , having a build-up layer depth  123 . 
     While the interfaces between each of these levels is schematically illustrated as a straight line for convenience and clarity, it is understood that such interfaces may not be defined by a single, flat plane, but instead may vary across the surface of the vessel  108  and can define interface sub-layers that include a mixture of adjacent phases (for example a mixture of slag and matte phases between slag layer  118  and matte layer  116 ). These interface sub-layers typically have a measurable thickness. 
     When the furnace  100  is in use, incoming feed material  114  can be added to a reaction vessel  108  that already contains a combination of molten matte material and slag material. As the feed material is exposed to the operating temperatures of the furnace, for example in some furnaces that temperature can be between 1500-1700 degrees Celsius, the feed material can be consumed to produce additional matte and slag material. If the rate at which feed material is introduced into the reactor vessel  108  exceeds the rate at which feed material contained in the reactor vessel  108  is consumed (i.e. transformed into matte and slag material) a layer of feed material, illustrated schematically as feed material layer  120 , can accumulate in an unmelted condition above the slag layer  118 . The accumulated feed material layer is also described as a charge bank  120 , and the distance between the feed material-slag phase interface, or feed/slag interface  124  and the upper or exposed surface of the feed material layer  126  defines a feed material layer depth or charge bank height  121 . The distance between the feed/slag interface  124  and the furnace roof  106  (or other reference position that is used to determine the charge bank level  128 , described below) defines a slag level  125 . 
     The distance between the upper surface  126  of the charge bank  120  and a pre-determined point or reference point on the reactor  100 , for example a point on the roof  106 , defines a charge bank level  128 , also referred to herein as a freeboard height. 
     To determine the level or total depth  130  of material contained in the reactor vessel  108  and/or the charge bank level  128 , a sensor  110  can be positioned above the material in the furnace  100  to measure or sense a distance between the upper surface  126  of the charge bank  120  and the sensor  110 , represented in  FIG. 1  as sensed distance  132 . 
     In some examples, the charge bank level  128  can be calculated based on the sensed distance  132 . For example, the sensor  110  can be mounted to the roof  106  in a known location so that the position of the sensor  110  relative to the walls of the reactor vessel  108  is known. In this example, the charge bank level  128  can be calculated by comparing or combining the sensed distance  132  with the known position of the sensor  110  relative to the vessel  108 . Optionally, the sensors  110  can be position so that the sensed distance  132  is greater than or less than the charge bank level  128 , see  FIG. 3 . 
     In other examples, as exemplified in  FIG. 2 , the sensor  110  can be positioned at one of the reference points of the furnace  100 , so that the sensed distance  132  coincides with the charge bank level  128 , so that additional calculations may not be necessary to determine the charge bank level  128 . 
     The sensor  110  is communicably linked to a controller, for example process controller  138 . The link between the sensor  110  and process controller  138  can be a one-way link (allowing data to be sent from the sensor  110  to the process controller  138 ) or a two-way link (allowing data to be sent from the sensor  110  to the process controller  138  and from the process controller  138  to the sensor  110 ). Optionally the process controller  138  can be configured to control the operation of the sensor  110  and receive information, including the sensed distance  132 , from the sensor  110 . The process controller  138  can then generate one or more output or control signals that can be used to provide user feedback so that an operator can take an appropriate action (i.e. as an open-loop control system) or automatically control one or more other aspects or operating parameters of the reactor, as explained in detail below (i.e. as a closed-loop control system). The process controller  138  can be connected to the sensor  110  using any suitable cable or connector that can withstand the expected operating conditions of the furnace  100 . 
     Referring to  FIG. 2 , an example of a furnace  100 , an electric arc furnace, includes a reactor vessel  108  containing a matte layer  116 , a slag layer  118  and a charge bank  120 . The roof  106  of the furnace  100  includes a pair of feed ports  112  for receiving a supply of feed material  114  and an electrode port  140  for receiving a corresponding electrode  142 . The electrode  142  can be any suitable electrode known in the art, and can be movably received within the electrode port  140  so that the vertical position of the electrode  142  can be adjusted, for example based on the amount of material in the reactor vessel  108 , using any suitable electrode actuator, schematically represented as electrode actuator module  144 . 
     Each feed port  112  can be supplied with feed material using any suitable feed material conduit, for example conduit  146 , known in the art. In the illustrated example, the feed material conduit  146  includes a feed supply regulator for controlling or regulating the flow of feed material into the reactor vessel  108 . As schematically illustrated in  FIG. 2 , one example of a feed supply regulator includes a feed gate  150  that is driven by gate actuator  152  that is used to physically constrict, and optionally completely block, feed conduit  146 . 
     As feed material is added through feed ports  112 , it may tend to accumulate beneath the feed ports  112  and then disperse to the other portions of the reactor vessel  108  as additional feed material is added. In  FIG. 2 , the upper surface  126  of the charge bank  120  is illustrated as having a sloping or generally cone or pyramid like shape, having a thickness or charge bank height  121  below the feed port  112  that is greater than the charge bank height  121  at other locations, for example proximate the electrode  142  as illustrated. 
     In the illustrated example, the charge bank  120  is shown as having a desired charge bank height  121 . In this state the upper surface  126  is shown as being in a desired position relative to the top of the slag layer  118 , the feed/slag interface  124 . Illustrated using dashed lines on the right side of  FIG. 2 , upper surface  126 ′ represents an over fed condition (in which the charge bank  120  has built up to an undesired height  121 ′ as a result of feed material being fed into the furnace  100  faster than it can be consumed). As the feed material continues to accumulate, the surface  126 ′ can rise above a desired operating position within the reactor vessel  108 , which results in a sensed distance  132 ′ that is less than a desired charge bank level  128 . In some furnaces, a charge bank having an increased charge bank height  121  acts as a thermal insulator that reduces the heat transfer from the slag and matte phases into the freeboard region (the region between the charge bank surface  126  and the furnace roof). This decrease in heat transfer can result in overheating of the material in the furnace, which may lead to crusting of the charge bank surface  126  and may reduce smelting efficiency. As explained in greater detail below, the process controller  138  can be linked to both the sensors  110  and the gate actuator  152 , so that when the sensors  110  detect an over fed condition, i.e. when the charge bank height  121  has increased beyond a pre-determined threshold, the flow of feed material into the furnace can be automatically restricted, without requiring operator input. 
     Also in  FIG. 2 , upper surface  126 ″ represents an under fed condition (in which the charge bank height  121  has decreased to an undesired height as a result of feed material being fed into the furnace  100  more slowly than it can be consumed). A thinner than desired charge bank height  121 , as occurs when the reactor is under fed, can result in hot spots on the furnace roof  106  and reduced smelting efficiency as a result of higher than expected heat loss (due to the absence of the insulating effect of the charge bank  120 ). In this example a sensed distance between the sensor  110  and the upper surface  126 ″ would exceed the desired or expected distance  132 . 
     In addition to variations in the feed rate, the position of surface  126  relative to the sensor  110 , i.e. the sensed distance  132 , can vary based on other furnace operations. For example, the distance between surface  126  and the sensor  110  may increase (i.e. the charge bank level  128  can increase) when the furnace is being tapped because the overall quantity of material in the furnace is reduced. In other instances, the charge bank level  128  can decrease (i.e. the surface  126  can move toward the sensor  110 ) if the furnace is over filled. If the surface  126  reaches a pre-determined location within the furnace, for example within 1 m of the roof  106 , the sensed distance  132  may decrease below a pre-determined alarm threshold condition and the process controller  138  can generate an alarm condition and/or a control signal based on the alarm condition. Optionally, the process controller  138  can be configured to automatically shut down the furnace. 
     In either example, when the actual sensed distance  132  differs from an expected or desired distance  128 , or if the charge bank height  121  differs from a desired range of heights, the process controller  138  can be operable to control the gate actuator  152  to automatically adjust the feed material supply rate in an appropriate manner, for example increasing the supply rate when the reactor  100  is under fed, and decreasing the supply rate when the reactor  100  is over fed or is approaching or past an alarm threshold. 
     Referring to  FIGS. 2, 6, 7 and 8 , one example of a sensor  110  that is suitable for use in combination with the furnace  100  is a radar sensor  110  that emits and receives electromagnetic signals. Radar sensors, and the operating principles of existing radar sensors are known in the art and will be only briefly explained below. 
     When configured as a radar sensor  110 , each sensor  110  includes at least one transmitter portion for generating and projecting an electromagnetic signal (for example a microwave pulse or a continuous microwave signal) and at least one corresponding receiver portion for receiving incoming electromagnetic signals. 
     Outgoing electromagnetic signals (or EM signals) generated by the sensors  110  are projected toward the material in the reactor  100 , for example toward upper surface  126 . The signals travel at a known rate and have other known properties (including signal frequency and signal magnitude). In the present examples, outgoing electromagnetic signals are illustrated using a plurality of arrows  154 . When the outgoing EM signals  154  contact an opposing object, such as upper surface  126 , at least a portion of the outgoing signals  154  is reflected off the upper surface  126  and forms an incoming or reflected EM signal, illustrated herein using a plurality of wavy arrows  156 . The magnitude or emission power of the EM signals  154  can be selected based on a variety of factors, including, for example, plant operating conditions and applicable safety regulations. 
     Referring to  FIG. 2 , each sensor  110  can project an outgoing EM signal  154  toward a portion of the charge bank  120  that underlies the sensors  110 . The information received from each sensor  110  is relayed to a suitable controller in the furnace control system, for example process controller  138 , where it can be compared to predetermined furnace operating parameters, including for example, acceptable charge bank heights, charge bank level alarm threshold conditions, desired or optimal sensed distances, a range of acceptable sensed distances, and one or more alarm criteria that are stored in a system memory or database. Based on the results of the comparison (or query), the process controller  138  can generate one or more appropriate output or control signals. 
     Optionally, the sensors  110  can be configured to emit EM signals in a generally conical pattern, represented by dashed lines  158 , that increases in diameter as it approaches the charge bank  120 . Projecting EM signals in this manner can allow each sensor  110  to determine the position of upper surface  126  across a larger area (i.e. across a larger proportion of the total surface area of the material held in the vessel  108 ). Sensing distances across a larger area may allow the sensor  110  to measure multiple distances  132  for the portion of the surface  126  within the conical projection  158 . After collecting each distance  132 , the process controller  138  can optionally be configured to calculate the average of all of the distances  132  and/or determine a plurality of separate sensed distance  132  values (for example a maximum and a minimum sensed distance  132  within a given measurement area). 
     By comparing the distances  132  with the position of the feed/slag interface  124 , the process controller  138  can determine a plurality of charge bank heights  121 , including a maximum height, a minimum height and an average height. The process controller  138  can generate a control signal based on the minimum, maximum and average distance  132 , the minimum, maximum and average charge bank height  121  or any combination or sub-combination thereof. 
     Referring to  FIG. 6 , in some examples of the furnace  100 , a sensor  110  can be movably mounted to the furnace  100 , for example to furnace roof  106 , using any suitable moveable mounting apparatus, including for example, a gimbal  158 . Using a gimbal  158 , the sensor  110  can be pivoted and/or rotated relative to the furnace  100 , allowing each sensor  110  to take multiple measurements at multiple locations. In some examples the gimbal can be controllable by any suitable controller, for example the process controller  138 , and can be programmed to sweep the sensor  110  in a pre-determined (or possibly random or pseudo-random) pattern to measure and record a plurality of sensed distances  132  at different locations on the upper surface  126  of the charge bank  126 . As described above, the plurality of sensed distances  132  recorded using the moveable sensor  110  can be processed to obtain a variety of different information regarding the contours or topography of the upper surface  126  (e.g. average charge bank height  121 , max or minimum charge bank height, etc.). 
     In some instances, the rate of feed material consumption in the furnace  100  increases in the portions of the charge bank  120  that surround the electrode(s)  142  in the furnace  100 . In such instances, the charge bank height  121  proximate the electrodes  142  can be smaller than the charge bank height  121  at other locations within the furnace  100 . 
     In some examples, as illustrated in  FIG. 6 , the feed material surrounding the electrodes  142  can be completely consumed, creating a feed bank height of zero, while other locations in the vessel  108  can still have an accumulation of feed material providing a measurable charge bank  120 . Where the feed material has been completely consumed, the upper surface  176  of the slag layer  118  can be exposed to the freeboard and can be within the line of sight of the sensor  110 . 
     In these examples, the sensor  110  can be used to determine the charge bank height by measuring the position of the upper surface  126  of the charge bank  120 , and to determine the level of the slag layer  118  by measuring the distance between the exposed surface  176  of the slag layer  118  and the sensor  110  (or other reference position). The measurements of both the upper surface  126  and slag upper surface  176  can be sent to the process controller  138  for further processing as described herein. 
     Referring to  FIG. 3 , a furnace  100  is illustrated showing examples of possible sensor  110  mounting locations. As illustrated on the left side of  FIG. 3 , a sensor  110  can be mounted above the furnace, for example above roof  106 , and need not be directly coupled to any portion of the furnace  100 . In this example, the sensor  110  can be mounted on an external support bracket  162  that extends from, and/or is coupled to, an external support structure that is located adjacent the furnace  100 , for example a ceiling of a building or other furnace enclosure, or a freestanding support structure. 
     The sensor  110  can be positioned in any desired location above the roof  106 , and at any height above the roof  106  provided that the sensor  110  is aligned with a corresponding hole or aperture  164  in the roof  106  or other furnace fixture (in this case the aperture is shown as being formed in a portion of the feed supply conduit  142 , optionally in a the portion of the conduit  142  that houses the feed gate  150 ). Aligning the sensor  110  with an aperture  164  in the furnace  100  ensures that the sensor  110  has an unobstructed line of sight to the material contained in the furnace  100 , for example the charge bank  120 . Providing an unobstructed line of sight means that the path between the sensor  110  and material in the furnace  100  (i.e. the charge bank  120 ) is substantially free from obstacles or objects that would materially interfere with the desired operation of the sensor  110 . 
     The sensor  110  mounted above the furnace  100  can be moveably mounted, for example using a gimbal as described herein, to record distance measurements at multiple locations on the upper surface  126 . Alternatively, or in addition, the sensor  110  can be movable between a plurality of positions that correspond to a plurality of apertures  164  in the furnace  100 , enabling the sensor  110  to take distance measurements through each of the plurality of apertures  164 . Sensors  110  mounted above the furnace  100  will measure a sensed distance  132  that is greater than the charge bank level  128 . To determine the charge bank level  128 , the sensed distance  132  can be compared to the known configuration of the furnace  100 , including the relative distance between the sensor  110  and the roof  106  or other reference position. 
     Referring to the right side of  FIG. 3 , a sensor  110  positioned within the internal volume or interior of the reactor vessel  108  and is supported using an internal support bracket  166 . The sensor  110  can be movably mounted to the internal support bracket  116  using a gimbal as described herein or any other suitable apparatus that allows pivoting and or rotation of the sensor relative to the internal support bracket  166 . Alternatively, or in addition, the internal support bracket  166  can be moveably mounted to the vessel  108 , for example on a rail or track system (not shown) so that the internal support bracket  166  can translate vertically, as indicated by arrows  168 , and horizontally (i.e. into the page as viewed in  FIG. 3 ). The internal support bracket  166  can also be configured to extend and contract, for example by telescoping, as illustrated by arrows  170 . 
     In examples where the physical location of the sensor  110  and internal support bracket  166  can change (as opposed to simply pivoting or rotating in place) either the sensor  110 , process controller or other suitable module can be configured to automatically account for the physical location of the sensor  110  relative to the vessel  108  when determining the sensed distance  132 . For example by comparing the vertical position of the internal support bracket  166  to the known reference position to determine a baseline position and then comparing the sensed distance  132  to the baseline position to determine the charge bank level  128  relative to the reference position. 
     Alternatively, or in addition, the sensed distances from a plurality of sensors  110  (either fixed or moveable sensors) can be compiled or composited by any suitable computer or controller, for example process controller  138 , to provide information regarding the overall topography of substantially the entire upper surface  126  (or at least the portions of the upper surface  126  that can be measured by one or more sensor  110 ).  FIG. 4  illustrates an example of a furnace  100  having a plurality of sensors  110  mounted on the furnace roof  106 . In this example, a sensor  110  is provided proximate each feed port  112 , to monitor the charge bank height beneath each feed port  112 , and a second plurality of sensors  110  position proximate each electrode port  140 , to monitor the charge bank height around each electrode that extends into the furnace  100 . 
     Each of the sensors  110  in this example can be connected to a single process controller  138  that can receive and process the signals from each sensor  110 . Alternatively, or in addition, one or more sub-controllers  160  (illustrated using dashed lines) can be provided to collect the data from a portion of the sensors  110 , for example the plurality of sensors proximate the feed ports  112 , and then relay the collected information, or an output signal based on the collected information, to the primary process controller  138 . While illustrated to include four feed ports  112  and four electrode ports  140 , it is understood that the furnace  100  of  FIG. 4  could have any desired number of feed ports  112  and electrode ports  140  (if necessary). It is also understood that additional sensors  110  can be placed at additional locations throughout the furnace  100  if desired, or a greater or fewer number of sensors  110  could be used (so that there is not a 1:1, port  112 ,  140  to sensor  110  ratio. 
     Referring to  FIG. 7 , in some examples each sensor  110  can include separate transmitter and receiver components. The transmitter components can be any suitable transmitter or antenna, including horn, parabolic, rod and other types of antennas. 
     As exemplified, the sensor  110  includes a transmitter  172  and a pair of space apart receivers  174 . In this configuration, the outgoing EM signal  154  from the transmitter  172  can produce a plurality of reflected EM signals  156 , and each receiver  174  can receive a different reflected signal  156 , which enables each receiver  174  to sense a different distance  132 . Optionally, the transmitter  172  can be movable and can emit a series of pluses or outgoing signals  154  in order to produce a desired number of reflected signals  156 . 
     The transmitter  172  and receivers  174  are communicably linked to each other and to the process controller  138 . 
     In any of the examples described herein, the transmitters (and optionally receivers), for example transmitter  172  or the transmitter portion of integrated sensors  110 , can include antenna array and any other suitable components, including wave guides, filters and signal processors. 
     In some examples, the sensor  110  can be configured to measure the distance to multiple surfaces or layers defined in the material in the furnace  100 . As exemplified in  FIG. 8 , the sensor  110  can be configured to emit an outgoing EM signal  154  that is specifically calibrated or modulated to produce predictable, partial reflections  156   a - c  as the EM signal passes through multiple layers of material. In the illustrated example a first reflection  156   a  is created when the EM signal  154  contacts the upper surface  126  of the charge bank  120 . This reflection  156   a  can be used by the sensor  110  and/or process controller to determine the charge bank height. 
     A second partial reflection  156   b  is created when the EM signal  154  contacts the upper surface  176  of the slag layer  118 , defined at the interface between the charge bank  120  and the slag layer  118 . The second partial reflection  156   b  can be used to calculate the level of the interface  176  (relative to the sensor  110  or a reference point) and to calculate the thickness of the charge bank  120 . 
     A third partial reflection  156   c  is created when the EM signal  154  contacts the interface  178  between the slag layer  118  and the matte layer  116 . The third partial reflection  156   c  can be used to calculate the level of the interface  178  (relative to the sensor  110  or a reference point) and to calculate the thickness of the slag layer  118 . 
     The sensor  110  can include multiple receivers to collect the partial reflections  156   a - c , or a single receiver that is configured to collect and decipher each reflection  156   a - c . The partial reflections  156   a - c  can be isolated based on a number of factors including frequency and attenuation using known methods. 
     In any of the examples described herein, the compiled information from any plurality of sensors  100 , optionally in combination with inputs from other furnace instrumentation, can be used to create a surface topography map or profile (i.e. a graphical representation of the shape of the upper surface  126 ) which can then be compared to one or more preferred or desired surface topography stored in a database, memory or other suitable system component. 
     Optionally, as exemplified in  FIGS. 1, 2 and 5 , the sensor  110  can be encased in a housing  134  that can optionally protect the sensor  110  from dirt, dust, ash and other particulate contamination as well as provide a desired degree of thermal and electromagnetic shielding. The housing  134  can be provided with additional utilities and monitoring equipment to protect and monitor the sensor  110 . For example, the interior of the housing  134  can be flushed with a cooling gas, for example air, via nozzle  184  that is connected with hose  186  to a gas supply system (not shown). Flushing filtered cooling gas into the housing  134  can help cool the sensor  110  and can reduce the accumulation of dust and other debris within the housing  134 . Optionally, the housing  134  can be configured to withstand the expected pressure loads that can be exerted on the housing  134  during normal operation of the furnace  100  (for example when the reactor vessel  108  is operated under slight vacuum conditions, or when relatively high pressure gases are emitted from the material in the furnace). 
     The housing  134  can also be equipped with any suitable temperature sensor  188  (for example a thermocouple or RTD) to allow for remote monitoring of the internal temperature of the housing  134 . Optionally, information from the temperature sensor  188  can be provided to the process controller  138 . 
     In some furnaces  100 , for example electric-arc furnaces, the sensor  110  mounted to the reactor vessel  108  can be exposed to high levels of electromagnetic energy or signals that can interfere with the operation of the sensor and its associated electronic components. In such examples, as exemplified in  FIG. 5 , the housing  134  can include electromagnetic shielding components, including for example a Faraday shield or Faraday cage  180 , to attenuate the magnitude of the electromagnetic signals that reach the sensor  110 . Optionally, such electromagnetic shielding can be configured to filter or screen electromagnetic signals in a first or selected spectrum, while allowing electromagnetic signals in a second spectrum to pass relatively uninhibited through the housing  134 . 
     Alternatively or in addition, the housing  134  can include one or more thermal radiation shielding elements to protect the sensor  110  from thermal radiation emitted by the material contained in the reactor vessel  108 . Optionally, the thermal radiation shielding elements can be positioned between the sensor  110  and the upper surface of the  126  of the charge bank  120 . In such examples, the thermal radiation shield can be formed from a material that provides a desired level of thermal isolation while still allowing the desired operation of the sensor (i.e. the thermal radiation shielding is substantially transparent to the sensor  110  so that it does not interfere with the operation of the sensor  110 ). The radiation shield can be any suitable material, including refractory cloth. In the illustrated examples, the thermal radiation shield is provided as a removable cassette containing refractory cloth  136 . 
     Providing the refractory cloth  136  as a removable cassette allows for the refractory cloth  136  to be removed for inspection, repair and maintenance and then re-inserted to provide the desired shielding. The use of removable cassettes can also enable a user to replace or substitute the refractory cloth  136  shield with a different material to accommodate different sensors  110  and different furnace operating conditions. In other examples, the radiation shield may be integrally formed with the sensor  110 , or provided as a fixed component attached to the housing  134 , reactor vessel  108  or any other suitable support. 
     The housing  134  can be removable to allow inspection and maintenance of the sensor  110 , and can include a handle  182  to enable removal of the housing  134 . 
     It is understood that the furnace can be any suitable type of metallurgical furnace (including electric and non-electric furnaces) and the method of adding feed material into the furnace can be any suitable method, including for example, a continuous, semi-continuous or batch feeding regime. 
     While described as a radar sensor in the above examples, the sensor can be any suitable type of sensor, including, for example, a laser sensor, an automated sounding sensor (including digital image processing or optical sensing), an optical sensor, a Muon particle sensor, an acoustic sensor, a pulsed or frequency modulated electromagnetic sensor, an ultrasound sensor and a yo-yo sensor. Shielding materials and other control components can be selected based on the particular requirements of any given sensor. 
     While illustrated as simple schematic figures, it is understood that any furnace described herein can include any suitable features known in the art, including tap blocks, refractory linings and condition monitoring instruments, displays and control panels. The reactors can also include redundant control mechanisms allowing a human operator to override any of the automated features described above, either directly (manually controlling an actuator) or indirectly (using a supplemental or override control system). 
     Referring to  FIGS. 9 and 14 , an example of a system for monitoring the level of material contained within a metallurgical furnace includes a plurality of sensors  110  that are communicably linked to a central process controller  138 . It is understood that each sensor  110  can also include its own sub-controllers for performing basic calculations and generating sensor output data, including, for example, sensed distances  132 . 
     The process control  138  is also connected to a suitable power source  190  and can optionally be configured to receive any suitable number of additional or auxiliary input signals  192  from other furnace instruments and sensors (including RTD, thermocouples, pressure sensors and any other type of sensor), and to generate and output any suitable number of auxiliary control signals  193  for controlling other furnace equipment, instruments or processes. 
     When used in combination with the examples described above, the process controller  138  is configured to output feed control signals  222  to the gate actuators  152 , for controlling the feed supply, and electrode control signals  218  to the electrode actuator  144 , for controlling the movement of the electrode  142  and to the electrode power supply regulator  194  for controlling the electrode power, and any other suitable furnace control actuators. 
     The process controller  138  also includes a memory  196  for storing a database of predetermined values for a variety of furnace operation parameters against which measured values can be compared. For example, the memory  196  can include a stored range of acceptable or desired charge bank levels  128  for a given furnace  100  (having a known geometry), an overfill or maximum fill threshold value, other alarm condition thresholds (maximum temperature, minimum temperature, etc), a range of acceptable charge bank heights  121  and corresponding over fed or under fed alarm thresholds (optionally warning thresholds can be included as well). A specific set of pre-determined furnace operation parameters can be provided for every furnace (for example if the value depends on the geometry of the furnace) and for each type of product produced or feed material that is introduced into the furnace (each of which may have unique requirements). 
     As illustrated in  FIG. 14 , each sensor  110  can include an antenna  230  connected to a transmitter  172  for emitting electromagnetic signals  154 , and a receiver  174  for receiving the reflected signals  156 . Optionally, the sensor  110  can include a sensor sub-controller  210  for processing the signals  154 ,  156  to determine the distance between the sensor  110  and the object being sensed (distance  132  in the examples above). The sensor  110  is configured to produce a sensor output signal  212  which can include data relating the distance  132  measured by the sensor  110 . In examples where the sensor  110  is positioned to measure the location of the upper surface  126  of the charge bank  120 , the sensor output signal  212  can be called a level signal or a charge bank level signal. 
     In some examples, the sensor  110  is not remotely controllable, and the system may only include a one-way communication link between the sensor  110  and the process controller  138 , e.g. for carrying the sensor output signal  212 . In other examples, the process controller  138  can be configured to control the sensor  110 , or some other related apparatus (for example the gimbal or inner support bracket). In such examples, the process controller  138  can be configured to output a sensor control signal  214  that can be sent to the sensor  110 . 
     In some examples, the electrode actuator  144  and electrode power supply regulator  194  described above can be contained within a single electrode control unit  216 . In this example the process controller  138  is configured to output an electrode control signal  218  that can be used to control the electrode actuator  144 , electrode power supply regulator  194  or both. In operation, the process controller  138  can also receive information and data from the electrode control unit  216  via electrode output signal  220 . 
     Similarly, the process controller  138  can be communicably linked to the feed gate actuator  150  (or any apparatus that is used to control the feed rate of feed material into the furnace) so that the process controller  138  can send a feed rate control signal  222  and receive a feed rate output signal  224 . The feed rate output signal  224  can include any suitable data, including current feed rate and feed gate  150  position. 
     A display control signal  226  can be sent from the process controller  138  to the display  200  and can contain any suitable display data or information. Optionally, a display output signal  228  can be sent from the display  200  to the process controller  138  to convey information from a display  200  that includes an input device to the process controller  138  for further processing (for example touch screen inputs from an operator). 
     Optionally, the process controller can be configured to receive one or more auxiliary output signals  192  from a variety of different furnace sensors and apparatus. For example, if a given furnace includes a plurality of thermocouples or RTDs for sensing a plurality of temperatures in the furnace, the corresponding process controller  138  can be configured to receive a plurality of temperature output signals  192  and to use the temperature data received for further processing. 
     In addition to receiving auxiliary output signals  192  (output signals  192  are output signals from the various furnace instruments and sensors mentioned above and serve as inputs to the process controller  138 ), the process controller  138  can be configured to generate any other suitable auxiliary control signal  193  that can be used to provide process controller output data, or to control any suitable system or apparatus. The nature of the auxiliary control signals  193  can be pre-determined when the process controller  138  is manufactured and installed, or the process controller  138  can be reconfigurable by an operator to provide different auxiliary control signals  193  based on the changing operating conditions of the furnace. 
     The process controller  138  also includes a processor  198  that can be configured using a suitable method, algorithm or software package to analyze the measured data. 
     Referring to  FIG. 11 , one example of a method begins at step  1100  with process controller  138  receiving at least one sensed distance from a sensor  110 . The sensed distance data can be accompanied by a plurality of other information that can be understood and processed by the process controller  138 , including, for example, location information for the sensor, time stamp information, raw outgoing EM signal data, and raw reflected EM signal data. 
     Having received the sensed distance from the sensor, at step  1102  the processor  198 , or any other suitable component of the process controller  138 , can receive the sensed distance  132  and derive a charge bank level  128  and compare against the calculated range of acceptable charge bank levels  128  for the given reactor  100 . 
     If the measured distance  132  is equal to an acceptable value, or falls within an acceptable range of values, the reactor  100  can be allowed to continue to operate without intervention, and the distance can be measured again by repeating step  1100  at any desired sampling rate (i.e. once a second, once a minute, etc.). 
     If the derived charge bank level  128  is not equal to the desired charge bank level  128 , the processor  198  can determine if the measured height is greater than the acceptable levels, at step  1104 . If the measured distance is greater than an acceptable level, the process controller  138  can generate a control signal, for example an under fed control signal at step  1106 , that is sent to the feed supply actuator, for example gate actuator  152 , causing the gate actuator  152  to increase the supply of feed material into the furnace. 
     If the measured distance is less than the acceptable level, the process controller  138  can output a control signal at step  1108 , for example an over fed control signal, that is sent to the feed supply actuator, for example gate actuator  152 , causing the gate actuator  152  to decrease the supply of feed material into the furnace. The nature and magnitude of appropriate changes to the feed material supply rate can be stored in, or calculated by, the feed rate module  202  and feed distribution module  204 . 
     The feed rate module  202  can provide instructions to the processor regarding how much the feed supply rate should be changed, and the feed distribution module  204  can provide instructions regarding how the feed material should be distributed within the furnace  100 . 
     For example, a process controller  138  connected to multiple sensors  110  may determine that, in a given furnace, the charge bank level in a first portion of the furnace is acceptable, the charge bank level in a second portion of the furnace is too high and the charge bank level in a third portion of the furnace is too low. Based on these inputs, the process controller  138  may individually controller three different gate actuators  152 , based on instructions from the feed rate module  202  and feed distribution module  204 , to maintain the current feed rate in the first portion, decrease the feed rate of the feed gate supplying the second portion and increase the feed rate of the feed gate supplying the third portion. 
     After completing either step  1106  or  1108 , the method returns to step  1100 , which can be conducted at any desired sampling rate (as described above). 
     Alternatively, or in addition to controlling the supply of feed material into the furnace  100 , control signals from the process controller  138  can be used to adjust the electrode position or electrode power. 
     Referring to  FIGS. 1 and 12 , another example of a control method  1200  can be a feed control system and can begin at step  1202  when the process controller  138  obtains a charge bank level  128  from sensors  110  and continues to step  1204  in which the process controller  138  also receives data relating to the slag level  125 . 
     At step  1206  the process controller  138  compares the charge bank level  128  to the slag level  125  to obtain the charge bank height  121 , which, in the examples illustrated, is the difference between the two levels  125 ,  128 . 
     Having calculated the charge bank height  121 , the process controller  138  can advance to step  1208 , in which the calculated charge bank height  121  is compared to one or more pre-determined desirable charge bank height values, or optionally a range of pre-determined desirable values, that are stored in the memory, or stored in a remote storage unit and retrieved by the processor. 
     Based on the comparison between the calculated charge bank height  121  and the plurality of pre-determined desirable heights, at step  1210  the process controller  138  determines if the calculated charge bank height  121  is acceptable, or is within an acceptable range. 
     If so, the process controller  138  need not take any immediate action or generate control signals, and the method  1200  can return to  1202  to obtain another charge bank level and continue the monitoring process. 
     If the charge bank height  121  is not acceptable or is not within an acceptable range, the method  1200  continues to step  1212 , at which the process controller  138  determines if the calculated charge bank height  121  is too large (i.e. greater than the desired values stored in the memory). If so, the method  1200  advances to step  1214  in which the process controller  138  generates a feed control signal and causes the rate at which feed material is being introduced into the furnace to be decreased, for example by controlling the gate actuators  152  to close the feed gates  150 . Once the feed rate has been decreased, the method  1200  returns to step  1202  and continues monitoring the furnace. 
     If the process controller  138  determines, at step  1212 , that the charge bank height is below the desirable range, then it can be inferred (or re-checked against the pre-determined values) that the charge bank height  121  is thinner than desired (or below the pre-determined desirable range). In this case, at step  1216 , the process controller  138  can increase the feed rate, thereby increasing the amount of feed material that is introduced into the furnace. Once the feed rate has been increased, the method returns to step  1202  to continue monitoring. 
     Referring to  FIG. 13 , another example of a control system  1300  can be an emergency stop or overfill monitoring system that begins at step  1302  when the process controller  138  obtains the charge bank level  128  from the sensors  110 . 
     At step  1304 , the measured charge bank level  128  is compared to one or more pre-determined warning and/or alarm and/or shutdown threshold values that are stored in the memory or other suitable location that can be accessed by the processor. 
     By comparing the calculated charge bank level  128  to the stored threshold values, the process controller  138  can determine if the charge bank level  128  is below a pre-determined alarm threshold. If not, the method  1300  returns to step  1302  and continues to monitor the charge bank level  128 . 
     If the charge bank level  128  is below an alarm threshold value, the process controller  138  can generate an alarm output (for example a siren, buzzer, flashing light, or on-screen warning message) and optionally, can output additional control signals to control other furnace operating parameters including, for example, reducing the feed rate. The process controller  138  can be configured to automatically take control of the furnace operating parameters, and/or it can prompt human operators to take corrective action. 
     Method  1300  then continues to step  1310  in which the process controller determines if the charge bank level  128  exceeds a pre-determined shut down threshold (i.e. if the distance between the upper surface  126  and furnace roof  106  is below a safe or desired limit). If not, the method  1300  can return to step  1302 . If so, the method advances to step  1314 , in which the process controller  138  can output an emergency or shut down control signal that can automatically shut down the furnace or transfer control of the furnace  100  to the human operators. 
     In some examples, shutting down a furnace  100  is a complicated, multi-step process and it may be desirable that the process controller  138  not be configured to automatically shutdown the furnace without operator intervention. However, it may still be desirable that the process controller  138  be operable to perform certain operations (either automatically or after receiving operator input), including, for example, pulling up the electrode, stopping the supply of feed material in to the furnace and suggesting tapping the matte and/or slag from the furnace. 
     In these examples, the process controller  138  can operate as a closed-loop controller that is capable of automatically adjusting furnace operating parameters (i.e. feed supply rate, electrode position, electrode power supply, emergency shutdown systems) without operator intervention. Such a system enables the process controller  138  to automatically balance the power use and feed supply/distribution delivered to the furnace  100  to allow the furnace to operate continuously at a desired steady state condition, for example to continuously maintain the charge bank level within an acceptable range. 
     The process controller  138  can be a separate, self contained unit that can be connected to an existing furnace control system (possibly including a separate furnace controller). Alternatively the process controller  138  can be integral to the furnace control system and can serve as the primary, an optionally only, controller that is used to control the plurality of reactor operations described above. 
     Optionally, the process controller  138  can be connected to a display apparatus, for example display  200 , that can be used to display a variety of data, including measured or sensed distances, feed supply rates and current charge bank levels, to a system operator in real-time. By watching the display  200 , an operator can ascertain the operating conditions of a given furnace. 
     The display  200  can be any suitable display known in the art, including a computer monitor, a television display, a light source, an audible alarm or other audio/visual device. 
     In addition to calculating charge bank levels and adjusting feed supply rates accordingly, the process controller  138  can be configured to generate an alarm signal by comparing any of the measured data against a database of pre-determined alarm threshold conditions stored in the memory  196 . When an alarm condition is detected (i.e. an alarm threshold is met or exceeded) the process controller  138  can generate an alarm output to notify a system operator, and/or automatically initiate an emergency protocol, including, for example, shutting down the furnace. 
     Referring to  FIG. 10 , an example of a furnace  100  includes a plurality of sensors  110 , as described above, and a plurality of thermal sensors, for example remote temperature diodes (RTD)  206  that are positioned on the sidewall of the furnace  100  to sense temperature variations in the material in the furnace and to located the interface planes (surfaces)  176 ,  178 ,  126  based on the difference in temperature recorded by each RTD. In this example, the process controller  138  is linked to each RTD as well as each sensor  110 . The process controller  138  can include any additional modules, for example an temperature measurement module  208 , to process the data received from the RTDs  206  and extrapolate the locations of surfaces  176 ,  178 ,  126 . This information can be combined with the charge bank level information and used to generate a suitable control signal that can be used to adjust the gate actuators  152 , electrode actuator  144 , electrode power supply regulator  194  and/or any other suitable furnace parameter. 
     Optionally, in some or all of the examples described herein, some or all of the material in the furnace (e.g. charge bank, slag phase and/or matte phase) can be seeded with detectable material to enhance the operation of the sensors. For example, in systems that use radar sensors, the material in the furnace can be seeded with particles of highly radar-reflective material to provide enhanced reflected signals. Optionally, only certain phases can be seeded, or each phase can be seeded with a different material to enhance the sensor&#39;s ability to distinguish between layers. 
     The present invention has been described here by way of example only. Various modification and variations may be made to these exemplary embodiments without departing from the spirit and scope of the invention.