Patent Publication Number: US-3875504-A

Title: Apparatus for continuously determining the moisture content of a moving ore bed

Description:
United States Patent rm Bodycomb, Jr. et a1.  
 1 1 APPARATUS FOR CONTINUOUSLY DETERMINING THE MOISTURE CONTENT OF A MOVING ORE BED [75] Inventors: Frederick Mercer Bodycomb, .Ir..  
 Flemington; James Julius Barna, Somerville. both of NJ.  
 [73] Assignee: Johns-Manville Corporation, New  
 York. NY.  
  221 Filed: Feb. 11. 1972 211 Appl. No.: 227.088  
 152] US. Cl. 324/65 R, 191/591 1511 lnt.Cl ..G01r 27/02 [581 Field of Search 324/65 R. 65 P; 191/29. 191/591. 49&#39;. 73/421 R [56] References Cited UNITED STATES PATENTS 354.203 12/1886 McDcrmott 73/421 R 764.211 7/1904 Slater 191/49 946.744 1/1910 Van Mater 73/421 R 949.284 2/1910 McConc .1 73/421 R 1.586.221 5/1926 Schwurzcnhaucr 191/49 X 1.589.450 6/1926 Wilson ct alt 324/65 R X 1.915.028 6/1933 Maycr-Jngcnbcrg.......... 324/65 R X 2.003.077 5/1935 Hcppcnstall 324/65 R 2.892.904 6/1959 Sicrk 191/49 2.942.248 6/1960 Huggins 324/65 R UX 3.035.226 5/1962 Strindberg... 324/65 R 3.042.861 7/1962 Br)s 324/65 R one FEED RATE FUEL CONTROL CONTROL CONTROLLER 1 51 Apr. 1, 1975 Prinmry Examiner-Stanley T. Krawczewicz Auorney. Agent. or Firm-Robert M. Krone; John H. Miller 1571 ABSTRACT The disclosure relates to a method for controlling the moisture content of ore exiting from a drier and an apparatus for effecting the measurement of the moisture content. A portion of the ore exiting from the drier is diverted onto a conveyor to form a moving ore bed sample. The moisture content of this sample is measured by an apparatus which comprises a conductivity meter provided with a pair of electrodes having convex surfaces in contact with the moving surface of the ore sample. The electrodes are maintained a fixed relative distance apart to insure a constant amount of ore therebetween and thus an arcuute relative measurement of the moisture content for different positions of the ore bed as the ore passes by the electrodes. The measurements are converted to signals which actuate control apparatus to effect any necessary adjustments in the drying process to maintain the moisture content of the ore within specified limits.  
 2 Claims. 3 Drawing Figures ORE FEED FUEL CONTROL /CONTROLLER RATE  APPARATUS FOR CONTINUOUSLY DETERMINING THE MOISTURE CONTENT OF A MOVING ORE BED BACKGROUND OF THE INVENTION This invention relates to a method of controlling the moisture content of ore exiting from a drier and the apparatus for effecting an accurate measurement of the moisture content.  
  After asbestos ore is removed from a mine, it is initially crushed and then dried in large driers. Depending on the part of the mine from which the ore is taken and other factors, the ore entering the driers contains variable amounts of moisture. In the past, to assure that the wettest ore was dried to an optimum degree of 2 to 2%. percent water by weight, the ore containing lesser amounts of moisture was overdried. This resulted in wasted fuel, inefficient use of equipment. and possible damage to the overdried asbestos fiber due to calcination. Since changes in the moisture content of the ore entering the driers occur fairly rapidly. there is a need to continuously determine the moisture content of the asbestos ore leaving the driers and effect the necessary changes in the driers to maintain the moisture content of the exiting ore within specified limits.  
  It is the object of the present invention to provide a rapid continuous determination of the moisture content of asbestos ore by an electrical conductivity measurement. This measurement is utilized to determine the ore feed rate through the driers or the rate of the burner fuel consumption within the drier. Thus, all of the ore can be dried to the optimum degree without using the equipment inefficiently, wasting fuel, or damaging any portions of the ore.  
 SUMMARY OF THE INVENTION Accordingly, the present invention provides an apparatus for measuring the moisture content of a moving ore bed. The apparatus comprises a conductivity meter which is provided with first and second electrodes having curved contact portions with convex surfaces of the contact portions riding on the surface of the moving ore bed. The curved contact portions of the electrodes are maintained in fixed relative positions to maintain a constant amount of ore therebetween.  
  The invention also provides a method of controlling the moisture content of ore exiting from a drier wherein a portion of the ore exiting from the drier is diverted onto a conveyor to form a moving ore bed sample. The moisture content of the sample is measured with the moisture measuring apparatus of the present invention, and the drying process in the driers is adjusted in accordance with the measurement to maintain the moisture content of the ore within specified limits.  
 BRIEF DESCRIPTION OF THE DRAWINGS The above objects ofthe invention will become more apparent and other objects of the invention will become apparent from the following detailed description of a preferred embodiment of the invention and the accompanying drawings wherein:  
  FIG. I is a schematic representation of a process employing the method and apparatus of the present invention:  
  FIG. 2 is an elevational view in section of the electrode assembly of the present invention along lines 2-2 of FIG. 3 showing the electrodes in their lowermost positions (solid line) and normal operating position (phantom line); and  
  FIG. 3 is a plan view partially in section of the electrode assembly of the present invention along lines 3-3 of FIG. 2.  
 DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, FIG. I illustrates a drier 20 provided with an input conveyor 22 and an output conveyor 24. An ore sample conveyor 26 is alsoo illustrated together with a moisture measuring apparatus 28 and a control system 30 for regulating the drying process.  
  The input conveyor 22 carries crushed, wet ore from the mine and deposits the ore within the drier 20. The ore is dried within the drier by hot air which is heated by means of burners 31 and passed through the drier 20. The major portion of the ore exiting from the drier 20 is discharged onto output conveyor 24 which conveys the ore to a dry rock storage area. However, a sample portion of the exiting ore is diverted to the vibrating conveyor 26 where the moisture content of the sample is measured to determine the moisture content of the exiting ore at that moment. From the vibrating conveyor 26 the sample portion of ore passes to the output conveyor 24 which then takes the ore directly to the dry rock storage area.  
  The moisture measuring apparatus 28 utilizes the correlation between ore moisture content and ore electrical conductivity. The conductivity of the ore increases as the moisture content of the ore increases, and conversely the conductivity of the ore decreases as the moisture content of the ore decreases. Thus the moisture measuring apparatus 28 comprises a conventional conductivity meter 32 provided with a chart recorder 34 to maintain a record of the conductivity readings and an electrode assembly 36.  
  The electrode assembly 36 is connected to the input terminals of the conductivity meter 32. The chart recorder 34 and a conventional controller 38 of control system 30 are connected to the output terminals of the conductivity meter 32. Thus an input signal which is indicative of the conductivity of the material between the electrodes is fed from the electrode assembly 36 to the conductivity meter 32 where it is measured. Due to the correlation between the conductivity and moisture content of the material, the output signal from the conductivity meter 32, produced by this measurement, is indicative of the moisture content of the ore sample. This output signal is fed to the chart recorder 34 and the controller 38 of the control system.  
  The chart recorder 34 provides a visual record of the moisture content of the ore exiting from the drier 20 thereby enabling the operator to easily ascertain whether the system has been or is operating normally. The output signal fed to the controller 38 causes the controller to initiate any required changes in the drying process. The controller 38 can actuate the fuel control 40 (e.g., a valve control) to adjust the fuel consumption of the burners 31 and thereby alter the temperature of the air within the drier. The controller 38 can also actuate the ore feed rate control 42 (e.g.. bin gate control) to adjust the rate of flow of ore into and through the drier 20. Thus the drying process can be controlled through the fuel control 40. the ore feed rate control 42. or a combination ofthe two to maintain the moisture content ofthe ore exiting from the drier within specified limits.  
  The electrode assembly 36 comprises a housing 44 plus a pair of electrodes 46 and 48. The housing is dust proof and at least the lower supporting plate 50 which carries the electrodes 46 and 48 is made from a nonconducting material. The support plate 50 is provided with a pair of apertures 52 and 54. Shafts 56 and 58 bridge the apertures 52 and 54, are affixed to the support plate 50, and support the electrodes 46 and 48. The apertures 52, 54 are laterally and longitudinally spaced with respect to each other (see FIG. 3) to offset the electrodes 46, 48 and prevent ore lumps from being wedged between the electrodes. The clearcnce between the sidewalls of apertures 52 and 54 and the electrodes 46 and 48 is minimized to prevent dust from entering the housing through the apertures.  
  Since electrodes 46 and 48 are identical in construction, only electrode 46 will be discussed in detail to prevent unnecessary repetition. Electrode 46 comprises an upper section 60, a coupling collar 62, and a replaceable lower section 64. The upper and lower sections 60 and 64 have been made of three-eighths of an inch diameter metal rod with the complementary metal collar 62 joining the upper and lower sections. However, elec trodes of different sizes and lengths can be used.  
  The upper section 60 of the electrode has a loop 66 at its upper end which is pivotally retained on shaft 56. One of the two lead wires 68 connecting the electrodes 46 and 48 to the input terminals of the conductivity meter 32 is secured to the loop 66. The electrical con nection is formed by securing the lead wire 68 to the loop with a screw 69 or another conventional connec&#39; tion. The connection is located on the loop 66 where it will not contact the housing and interfere with pivotal movement of the electrode during operation.  
  the upper section 60, including loop 66, can be providcd with a tcflon coating 70 to help prevent mineral fibers from adhering to the section and working their way into the housing 44. In this way, a material buildup within the housing. which could form a conductive path between the electrodes, is prevented. The other end of the upper section 60 extends down beyond the support plate 50 and has a coupling collar 62 mounted thereon. The coupling collar 62 has a bore extending axially therethrough somewhat greater in diameter than sections 60 and 64 and is provided to rigidly connect the upper and lower sections 60 and 64 of the electrode. The collar 62 is affixed to the upper section 60 of the electrode by a pin 72 which passes diametrically through the collar 62 and a terminal portion of upper section 60 which is encased within the collar. An upper terminal portion of lower section 64 is also encased within collar 62. A pin 74 passes diametrically through the collar 62 and the terminal portion of section 64 to affix the lower section in the coupling.  
  The lower section of the electrode has a contact portion 76 which engages and rides on the upper surface of the ore bed. The contact portion 76 is curved with the lower end of the electrode trailing the upper end of the electrode in the direction of flow of the moving ore bed sample and the convex surface of the contact portion 76 riding on the upper surface of the ore bed. While in the preferred embodiment the convex surface of the curved contact portion 76 is a continuous curve in which the radius of curvature can change, it is to be understood that the convex surface can include flat portions as long as the overall configuration of the surface is convex. With this convex surface of the electrode 46 in contact with the ore bed, the electrode 46 can ride on top of the moving bed of ore with a minimum amount of abrasion and little or no buildup of asbestos material about the electrodes. Since a buildup of asbestos material on the electrodes could alter the conduction between the electrodes 46 and 48 and cause inaccurate measurements, it is important to minimize or eliminate such buildups of material.  
  Since the electrode 46 is pivotally mounted on shaft 56, the electrode is free to move up and down, As shown in FIG. 2, the pivotal mounting allows the electrode to ride on the ore sample bed regardless of the depth X of the bed. The pivotal mounting also allows the electrode to ride over lumps that are located on the upper surface of the ore bed. However, the pivotal movement of the electrode must be limited to prevent contact between the electrode 46 and the pan 78 of the vibrating conveyor 26 when no material is on the conveyor. To prevent the electrode 46 from contacting the conveyor pan the collar 62 is provided with a boss 80. Boss 80 abuts the underside of support plate 50 before contact is made between the contact portion 76 of the electrode and the conveyor pan 78 and assures that a minimum clearance Y is maintained between electrode 46 and pan 78.  
  If the electrodes were not held out of contact with the pan, the pan 78 of the conveyor 26 would form a conductive path between the electrodes when no ore was present and cause moisture measuring apparatus 28 to indicate a moist orc. Since the electrode is held out of contact with the pan 78, the conductivity measured is very low or negligible with no ore present (corresponding to very dry ore). Thus, the fuel rate is automatically minimized to conserve energy while the conveyor continues in operation to automatically feed ore to the drier 20 as soon as it is available.  
  In operation the contact portions 76 ofthe electrodes ride on the surface of the ore bed as shown in phantom line in PK]. 2. The contact portions 76 of the electrodes are maintained a set distance apart e.g., 6 inches with the electrodes easily riding over the rough surface of the ore bed due to their pivotal mounting and the convex surface of the contact portion. The weight of the electrodes 46 and 48 normally maintains them in contact with the surface of the ore bed. However, additional weight can be added to the electrodes 46 and 48 if they are not making adequate contact with the surface of the ore bed. Thus, a constant amount of ore is maintained between the electrodes 46, 48 and the electrodes are maintained in contact with the bed to assure that the conductivity readings of meter 32 give an accurate measurement of the moisture content as the ore sample bed passes by the electrodes.  
  The output signal from the conductivity meter 32 actuates the controller 38 which effects the necessary adjustments in the fuel consumption ofthe burners or the ore feed rate. Thus the conditions in the drier 20 are regulated to maintain the moisture content of the ore exiting from the drier with specified limits.  
 We claim:  
  I. An apparatus for measuring the moisture content of a moving mineral ore bed comprising a first conveyor means for moving the ore bed, a conductivity meter, first and second electrodes connected to said conductivity meter. said electrodes having surfaces for contacting the surface of a moving ore bed, said contact portions being a fixed relative distance apart, the improvement comprising diverter means to divert a small portion of the moving ore bed from said first conveyor means to form a moving ore bed on an ore sample conveyor. each of said electrodes having a convex surface portion of equal curvature. the electrodes being pivotally mounted at one end to enable the convex surfaces of said electrodes to ride on the surface of the moving ore bed on said ore sample conveyor. each electrode having an upper section which is pivotally mounted and a lower section with said convex surface electrodes are offset with respect to each other.