Abstract:
A system  100  of monitoring mass in a furnace is described having a number of hanger rods  110  used to support at least a portion of the furnace. The system has at least one pressure sensor  111  that may be a load washer  111  operatively engaging a hanger rod  110  that provides a signal indicative of an amount of tension on the hanger rod  110 . A pivoting unit  107, 109  distributes the force over the surface of the pressure sensor  111 . A processor  200  monitors the signals from the pressure sensors  111  to set alarms when there is a mass overload, or adjust the operation of the furnace. The processor  200  may also predict when an overload will occur by extrapolating pressure sensor  111  readings forward into the future.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional application entitled “Method And System Of Monitoring Mass In A Pulverized Coal Fired Furnace” having Ser. No. 61/300,265, filed Feb. 1, 2010, which is entirely incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to pulverized coal fired furnaces, and more specifically, to a method and system of monitoring mass in a pulverized coal fired furnace. 
     BACKGROUND 
     During normal, recommended unit operation of a utility style steam generator, coal ash is continuously being created and continuously being removed from the bottom of the furnace. Unusual conditions may arise that can prevent continuous ash removal. During these conditions, ash may accumulate and increase the mass of the furnace. Since most furnaces are partially or wholly suspended from above, a large increase in mass can potentially create an overload condition that will rip seams, deform supports or structures, or result in tubing failure within the furnace. 
     Large ash clumps have been created and fallen down within furnaces causing damage to the furnace. Therefore, it is very desirable to monitor the rate of accumulation of ash and relative increase in suspended mass. 
     Traditional furnace support systems do not provide a means to let operators know if there is a change in suspended mass. Existing systems employ a visual method where the operator observes ash build-up in a furnace through an observation hole or an observation door. This is only useful where there is a direct line of sight from the observation point to the ash accumulation inside of the furnace. 
     Currently, there is a need for an accurate method of monitoring the accumulation of ash in a furnace. 
     SUMMARY 
     The present invention may be embodied as a mass sensor assembly  105  for monitoring mass in a pulverized coal fired furnace, the mass sensor  105  having 
     a pressure sensor  111  operatively engaging a hanger rod  110  used to support at least a portion of the furnace; and 
     a fastener  115  and pivoting unit  107 ,  109  that maintain the hanger  110  in operative engagement with the pressure sensor  111 . 
     The present invention may also be embodied as a system  100  for monitoring mass in a pulverized coal fired furnace having a plurality of hanger rods  110  used to support at least a portion of the furnace, the system having 
     at least one hanger rod  110  operatively engaging a pressure sensor  111  and providing a signal indicative of an amount of load on the hanger rod  111 ; 
     a fastener  115  and pivoting unit  107 ,  109  that maintain the hanger rod  110  is in operative engagement with the pressure sensor  111 ; and 
     a processor  200  coupled to at least one of the pressure sensors  111  to receive their signals, calculate a mass measurement and provides an action in response to the calculated mass measurement. 
     The present invention may be embodied as a mass sensor assembly  105  for monitoring mass in a furnace hanging from hanger rods  110  supported by an upper surface of beams  11 ,  13 , the mass sensor assembly  105  having 
     a fastener  115  having a substantially planar lower surface attaching to an upper end of the hanger rod  110 ; 
     a pivoting unit  107 ,  109  for receiving the hanger rod  110 , the pivoting unit  107 ,  109  being located between the fastener  115  and beams  11 ,  13 , the pivoting unit having a top surface being parallel to a bottom surface of the fastener  115  so as to fit flush against the fastener  115  and a bottom surface being in a parallel plane with the top surface of the beams  11 ,  13  so as to fit flush against the beams  11 ,  13 , the pivoting unit  107 ,  109  functioning to distribute force provided by the fastener  105  to its top surface through the pivoting unit  107 , 109  over the lower surface of pivoting unit  107 ,  109 ; 
     a pressure sensor  111  pressed flush between the bottom surface of the pivoting unit  107 ,  109  and the upper surface of the beams  11 ,  13  to receive force distributed to its top surface and to create a signal indicative of the force that it is receiving. 
     The above described and other features are exemplified by the following figures and detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike: 
         FIG. 1  is a perspective view of a support employing hanger rods to support a furnace, in accordance with the present invention; and 
         FIG. 2  is a cross sectional side elevational view of the support of  FIG. 1 . 
         FIG. 3  is a cross sectional side elevational view of system  100  of monitoring mass according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An increase in mass is an indication of undesired ash accumulation. Monitoring changes in furnace mass provides an advantage over not measuring changes at all. The present invention allows personnel to understand the operation of the furnace with more certainty allowing them to make informed decisions with respect to the operation of the furnace. 
     Since most of the mass of a furnace is constant, an increase in mass is usually due to the buildup of ash. The coal fuel is constantly being added to the furnace and is burned into gases, water vapor, flyash and bottom ash. The ash created typically falls to the bottom of the furnace and is removed. As stated above, the ash creates large clumps that stick to the walls or other structures of the furnace. This accumulation creates additional mass that can stress structures designed to support the furnace. 
     This problem is more pronounced in larger furnaces. The ash mass may conceivably reach 1700 metric tons. This can cause bending, tearing and breakage of structures within the furnace. Therefore, the mass must be monitored. 
     Since the mass of the furnace remains constant and most of the mass gain is due to the ash accumulation, monitoring the furnace and ash will indicate the buildup of ash. 
       FIG. 1  shows a conventional support  10  that employs hanger rods  110  that attach to the furnace and support the furnace from above. These hanger rods  110  are typically suspended from beams  11 ,  13 . A fastener  115 , washers  107  and  109 , and a washer plate  113  suspend the hanger rod  110  from the beams  11 ,  13 . 
       FIG. 2  shows a cross sectional view of a conventional boiler support  10  employing a fastener  115 , washer  112  and a washer plate  113 . At times, hanger rods  110  may become slanted and be pulled by the furnace mass downward at an angle as shown. Since fastener  115  does not press equally on washer  112 , there are locations of concentrated force. Here the force vector is shown as arrow “A”. 
     Sometimes it is important to measure the force on each hanger rod  110 . If washer  112  were replaced with a pressure sensor, such as a load washer ( 111  of  FIG. 3 ) that monitors force applied to it and creates an electric signal indicating the force it is experiencing, it would give inaccurate readings since the force is unevenly distributed. Therefore, a device for distributing the mass experienced by the load washer  111  will be important. 
       FIG. 3  shows an elevational view of a mass sensor assembly  105  of the present invention  100 . It employs a hanger rod  110  that supports the furnace and experiences a large force. A fastener  115  holds the end of the hanger rod  110 . 
     A washer plate  113  fits flat on the upper surface of the beams  11 ,  13 . 
     A load washer  111  rests flat on the upper surface of washer plate  113 . 
     A spherical washer  107  has a through hole that receives the hangar rod  110 . It also has a flat upper surface that fits flush against the fastener  115  (or intermediate washer), and a lower convex surface  117 . 
     A cup  109  has a bottom surface that fits flush against the load washer  111  below it. Cup  109  has a concave upper surface  119  designed to receive the convex lower surface  117  of spherical washer  107  allowing spherical washer  107  to pivot about various axes with respect to cup  109 . The spherical washer  107  and the cup  109  together may be referred to as a pivoting unit  107 ,  109 . For small angular movements, such as those common to the motion of hanger rods  110 , convex surface  117  will remain in contact with concave surface  119 . This distributes the force through the spherical washer  107  and cup  109  along the surfaces as indicated by force vectors “B”. 
     The function of the spherical washer  107  and cup  109  is to provide a true flat surface for load washer  111 . This spherical washer  107  is capable of pivoting ±4° within cup  109  from the normal vertical axis while still transferring its full load evenly. 
     The load washer  111  creates an electrical signal related to the load it is experiencing. The load washer  111  is designed to be slightly deformed by the load of the hanger rods  110  and act as a strain sensor. The load washer  111  is designed to create an electrical signal proportional to the strain and deformation that it is experiencing. These are directly related to the force/mass that it is experiencing. 
     A number of load washers  111  are positioned in the upper boiler support system  10 . In one embodiment, the load washers  111  are disposed on rows of hanger rods  110  along the front and rear wall support walls of the furnace. 
     Due to the number and proximity of the hanger rods  110  to one another in these rows, a select representative number of hanger rods  110  may be identified to be fitted with load washers  111 . The front and rear walls are selected in this embodiment because the majority of the load is transmitted through these walls with the side walls conveying a minority of the total load. 
     In alternative embodiments, load washers  111  may be placed at various other locations. 
     Each load washer  111  is coupled to a processor  200  within a plant control system to receive the signals from the load washers  111  for processing of the received signals. In embodiments in which there is an interest in localizing the sensed mass, the processor  200  is made aware of the location of each load washer  111 . 
     Signals received from the load washers  111  are used to determine a tare load. This setting is determined after the steam generator is erected, insulated and all appurtenances attached when the furnace is clean. As the load supported by a given hanger rod  110  increases it will be reflected in the signal from the appropriate load washer  111 . 
     The signals from the load washers  111  are provided to a processor  200 . The signals may be conditioned to filter out noise and otherwise remove extraneous interference signals from the signal received from the load washers  111 , converted to and amplified to a signal recognizable be control systems. 
     In its simplest embodiment, processor  200  monitors the load and produces a signal representing the load. In another embodiment, processor  200  sets off an alarm when at least one of the load washers  111  experiences a load above a predetermined threshold. 
     In another embodiment, processor  200  is provided with the locations of the load washers  111 . It also can differentiate between the input signals and identify which signals belong to which load washers  111 . It may then determine which locations may be overloading and provide and indication of this overloading. 
     Since the processor  200  receives information over time, it can produce and store information to determine rates of mass increase. This may be used to predict situations in which there will be an overload based upon the current mass increase rate. This may also be monitored by location so that a specific location can be identified which will be overloaded at a future time based upon its mass gain. 
     Similarly, by monitoring the mass over space and time, one may be able to identify short-term localized signal spikes that indicate an impact at a given location by a large chunk of falling ash. 
     Another phenomenon that could be identified would be a shift of the ash within the furnace. This would show a loss of mass in one location while an adjacent location would be gaining more rapidly than the remaining locations. 
     The processor  200  may provide its output signal to a distributed control system (DCS)  300  that controls the operation of the furnace. The DCS  300  includes a display that will show the relative loads of each load washer  111  compared to the normal conditions. Alarm thresholds are developed to trigger alarms or other actions. 
     In an alternative embodiment, the DCS  300  uses the information from the processor  200  to modify operation of the furnace. For example, the furnace could reduce its operation to a lower level that does not accumulate ash as quickly. In another embodiment, the DCS  300  may also shut down the furnace if the mass within the furnace exceeds at predetermined value. 
     In an alternative embodiment, there is no processor  200 . The signals from the load washers  111  are provided to the DCS  300 . The DCS is modified to perform the functions that the processor  200  performed as described above. 
     By integrating load washers  111  in the furnace upper support system  10 , a unique ability to monitor changes in the suspended mass of the furnace is presented. High capacity spherical washers are included to enhance the accuracy of the load washers by accommodating small angular movements of a hanger rod while maintaining flat mating surfaces between the washer plate, load washer, and lower half of the spherical washer. A unique graphic screen or set of screens will be employed to convey the information sensed by the load washers to the plant operators via control system displays. Further, the present invention contemplates that the strain signals from the load washers may control the operation of the furnace. 
     While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.