Abstract:
A rotary aluminum kiln temperature regulation system comprising a temperature sensing device in the kiln that is configured to take temperature readings in an area of the kiln in proximity to the temperature sensing device. The system including a wireless transmitter operatively associated with the temperature sensing device and a receiver wirelessly associated with the transmitter, such that the transmitter and receiver wirelessly transmit the temperature readings taken by the temperature sensing device from the transmitter to the receiver. The system also including a control unit operatively connected to the receiver that is configured to receive the transmitted temperature readings and determine when the transmitted temperature readings exceed a predefined temperature setpoint. The control unit is operatively connected to a heat flow control device that can adjust heat flow inside the kiln in proximity to the temperature sensing device, such that the control unit regulates the heat flow control device to maintain a desired level of heat flow in the kiln in proximity to the temperature sensing device in response to the temperature readings transmitted from the temperature sensing device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application derives and claims priority from U.S. provisional application 61/346,199 filed 19 May 2010, which application is incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    This invention relates principally to a metal furnace or kiln, and more particularly to a temperature sensing and control system for rotary aluminum delacquering kilns using wireless thermocouples or comparable temperature sensing devices. 
         [0004]    It has for some time been a standard practice to recycle scrap metals, and in particular scrap aluminum. Various furnace and kiln systems exist that are designed to recycle and recover aluminum from various sources of scrap, such as used beverage cans (“UBC”), siding, windows and door frames, etc. One of the first steps in these processes is to use a rotary kiln to remove the paints, oils, and other surface materials on the scrap aluminum (i.e. “feed material”). This is commonly known in the industry as “delacquering.” Delacquering is typically performed in an atmosphere with reduced oxygen levels and temperatures in excess of 900 degrees Fahrenheit. The temperature at which the paints and oils and other surface materials are released from the aluminum scrap in the form of unburned volatile gases is known as the “volatilization point.” One such typical aluminum recycling system utilizes a rotary kiln to delacquer the aluminum. Many of these systems utilize a recirculating heat apparatus comprising a burner with a blower to direct heat into the kiln, and a recovery device that collects exhaust heat from the kiln and recirculates the recovered heat into the heat flow for the kiln. 
         [0005]    Due to the difficulties in accessing the rotating material during operation, the temperatures in traditional rotary aluminum kilns are not regularly monitored. Sensing devices external of the kiln are sometimes used as a temperature testing method. This requires manual intervention and is not particularly accurate. Unfortunately, failure to consistently and accurately monitor the conditions in the kiln can lead to fires. These fires result when the feed material reaches the volatilization point too rapidly and the feed material begins to rapidly oxidize and generate its own heat, leading to a high temperature excursion (i.e. “overtemp event”). Applicants have learned through tests, utilizing wireless high temperature thermocouples placed in the kiln, that certain temperature profiles occur in the feed material that can be used as precursors to predict such high temperature excursions or overtemp events, and that such events can arise in as little as 10 minutes of operation and can arise in different locations within the kiln. Further, applicants have learned through testing that controlling the heat flow into the kiln can regulate and prevent such overtemp events. These overtemp events can occur at different positions along the length of the feed material in the kiln, and may be affected by such variables as the size of the feed material put into the kiln, the moisture content of the feed material, the volume of the feed material and the feed rate, the composition of the feed material, and the cleanliness of feed material. A fire in a rotary aluminum kiln can require a costly shut-down, will likely destroy the feed material, and can damage the kiln and other associated equipment. 
         [0006]    One example of a condition that can lead to an overtemp event concerns the presence of magnesium in aluminum feed material. Most aluminum cans (e.g. UBC&#39;s) have lids or tops that comprise a higher percentage of magnesium than the body of the can. Magnesium melts at a lower temperature than aluminum, and is very combustive. When placed in a rotary aluminum kiln, the aluminum can lids can separate from the aluminum can body. This is known in the industry as “lid fracturing”. This lid fracturing reduces the lids to particles of aluminum and magnesium as small as a grain of sand. Oxidation of these particles in the kiln occurs very rapidly, resulting in highly combustible partially oxidized aluminum and magnesium. The amount of heat in the kiln must be reduced or the partially oxidized aluminum and magnesium can accelerate in temperature and ignite in the kiln. Like other overtemp events, such UBC lids fracture events can be localized to one or more zones within the kiln. However, once ignition occurs the fire can flash rapidly throughout the kiln. 
         [0007]    As will become evident in this disclosure, the present invention provides benefits over the existing art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The illustrative embodiments of the present invention are shown in the following drawings which form a part of the specification: 
           [0009]      FIG. 1  is a schematic of an aluminum rotary kiln delacquring system incorporating one embodiment of the present invention; 
       
    
    
       [0010]    Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0011]    In referring to the drawings, a schematic embodiment of the novel wireless temperature sensing and control system for metal kiln  10  of the present invention is shown generally in  FIG. 1 , where the present invention is depicted by way of example as integrated into a representative mass flow delacquering system X with a rotary aluminum kiln  12  having a delacquering zone  13  within the kiln  12 . As can be seen, a set of four independent high temperature thermocouples  14 ,  16 ,  18  and  20 , are positioned along the length of the kiln  12 . In practice, the thermocouples  14 ,  16 ,  18  and  20  are positioned with at least the temperature sensing portion of the thermocouple exposed to the delacquering zone  13  within the rotary kiln  12 . All of the thermocouples  14 ,  16 ,  18  and  20  are configured to detect temperature readings in the kiln  12 , including temperature readings in excess of the melting point of aluminum, and are further configured to transmit the temperature readings they sense inside of the kiln  12  via radio signals to a receiving device or receiver  22  that is external of the kiln  12 . Alternately, the thermocouples  14 ,  16 ,  18  and  20  could be operatively connected to a wireless transmitter (not shown) that would transmit the temperature readings to the receiving device or receiver  22 . 
         [0012]    Aluminum feed material  26 , which is ready for the delaquering process, is supplied to the kiln  12  through a feed material control chute  11 , which regulates the rate at which the feed material is supplied to the kiln  12 . The material then travels through the kiln  12  as the kiln  12  rotates about its central axis, and the material  26  is then discharged through a discharge chute  15 , which regulates the rate at which feed material is discharged from the kiln  12 . In order to reach and maintain temperatures sufficient to delacquer aluminum feed material  26  in the depicted system X, the kiln  12  receives heated air from a burner  30  and a burner bypass pipe  32 . The burner  30  receives ambient temperature air, at a temperature of approximately 70 degrees F., from a combustion blower  34  and recirculated gases, at a temperature of approximately 500 degrees F., from a variable speed recirculation blower  36  which in turn receives the recirculated heated gases that have passed through the kiln  12 . Combustion gases are controllably supplied to the burner  30  through a mass flow controller  31 . The combustion blower  34  also drives the ambient temperature air into an afterburner  35  attached to the burner  30 . Oxygen can be controllably injected as desired directly into the afterburner  35  through a mass flow controller  37 . A thermocouple  39  positioned near the exit for the afterburner  35  takes temperature readings of the gases as they exit the afterburner. The thermocouple  39  connects to the combustion gas mass flow controller  31  and a mass flow controller  41 , positioned between the combustion blower  34  and the burner  30 , such that the mass flow controllers  31  and  41  regulate the flow of combustion gases and air, respectively, in response to the temperature readings from the thermocouple  39 , so as to automatically control the burner operation to control the temperature of the gases supplied through a supply pipe  114 . 
         [0013]    Because the recirculation blower  36  simultaneously supplies preheated air to the burner  30  and the kiln  12 , the volume of heated air supplied to the kiln  12  in system X can be predictably controlled by varying the speed of the blower  36 . Because the volume of heated air supplied to the kiln  12  in turn affects the amount of heat injected into the kiln  12  and thereby to the feed material  26  in the delacquering zone  13  within the kiln  12 , varying the speed of the blower  36  has a and controllable predictable impact on the amount of heat applied to the feed material  26  in the delacquering zone  13 . 
         [0014]    The receiver  22  is operatively connected to a programmable control unit  24 , although in other configurations the control unit  24  can comprise the receiver  22 . Of course, wires or wireless devices may alternatively be used to operatively connect components positioned outside the kiln  12  or outside the gas and material flow components of the system X. Hence, for example, the receiver  22  may be wired to or wirelessly connected to the control unit  24 . The kiln temperatures transmitted from the thermocouples  14 ,  16 ,  18  and  20  to the receiver  22  are communicated to the control unit  24 . In traditional configurations, an automated feedback loop adjusts the speed of the blower  36  in response to the quantity and rate of feed material directed into the kiln  12 . In the present configuration of  FIG. 1 , the control unit  24  is operatively connected to and controls a mass flow controller  40  that regulates the speed of the recirculation blower  36 , and thereby the heat applied to the feed material  26  in the delacquering zone  13  within the kiln  12 . The control unit  24  may be wired to or wirelessly connected to the mass flow controller  40 . The control unit  24  automatically controls the speed of the blower  36 , using commands to the mass flow controller  40 , based upon a predetermined process loop control algorithm programmed into the control unit  24 . 
         [0015]    As seen in  FIG. 1 , in a representative mass flow delacquering system X, gases exiting the kiln  12  travel through an exit pipe  100 , where a bypass pipe  102  joins the exit pipe  100 . The temperature of the gases traveling in this area of the system X is approximately 500 degrees F. The gases are then directed into a cyclone  104 , through an inlet pipe  106  into the recirculating blower  36 . The blower  36  both draws the gases from the cyclone  104  and pushes the gases into supply pipe  108 . A diverter valve  110  is positioned at a junction along the pipe  108  to direct the gas flow into an afterburner  35  or through the burner bypass pipe  32 . Gases directed into the afterburner  35  are subjected to the heat generated by the burner  30 , where the gas temperature is raised to approximately 1500 degrees F. The gases are then directed out of the afterburner  35  and directed along the supply pipe  114  to the kiln  12 . 
         [0016]    Near the afterburner  35 , the bypass pipe  102  is connected to the supply pipe  114 , where a portion of the gases are diverted to the exit pipe  100 . The amount of gas that is allowed to exit through the bypass pipe  102  is controlled by a bypass valve  116 . The bypass valve  116  is, in turn, connected to a thermocouple  118  in the exit pipe  100 , and the valve  116  opens and closes in response to the temperature readings supplied by the thermocouple  118 . 
         [0017]    Downstream from the junction of the bypass pipe  102  and the supply pipe  114 , a vent pipe  120  joins the supply pipe  114 . The vent line connects to a pressure control damper  122  and, through which the gas pressure in the system X can be controlled. In addition, an emergency vent stack  124 , that is triggered by temperature readings supplied from a thermocouple  126  in the supply pipe  114  near the exit for the afterburner, connects to the vent pipe to provide for a safety pressure relief for the system X. 
         [0018]    Before entering the kiln  12 , the supply pipe  114  is joined by the burner bypass pipe  32 . By utilizing the diverter valve  110  to controllably combining the higher temperature gases supplied by the afterburner with the lower temperature gases supplied by the bypass  32 , the user can regulate the temperature of the gases supplied to the kiln  12 . A nominal target temperature for a typical delaquering operation is approximately 1100 degrees F. The diverter valve  110  is connected to a thermocouple  128  in the supply pipe  114  near the entrance to the kiln  12 , and the valve  110  rotates to control the ratio of gases directed into the afterburner  35  as opposed to the bypass  32 , in response to the temperature readings supplied by the thermocouple  128 . 
         [0019]    A thermocouple  130  near the junction of the kiln  12  and the exit pipe  100  takes temperature readings of the gases as they exit the kiln  12 . This temperature data provides an additional source of information to alternatively control the mass flow controller  40 . The temperature readings from thermocouple  130  may be used separate from or in conjunction with the operation of the control unit  24 . 
         [0020]    A pressure sensor  132  is positioned in the supply pipe  114  near the entrance to the kiln  12 . The pressure sensor  132  is connected to and controls the pressure control damper  122  in the vent stack  120 . 
         [0021]    Upon initial setup, the wireless thermocouples  14 ,  16 ,  18  and  20  can be used to profile the temperatures along the inner length of the kiln  12 . This profile is then programmed into the control unit  24  as a baseline from which overtemp events are detected and to which a response is performed. During operation of the system X, the control unit  24  constantly and automatically monitors the kiln  12  via the temperatures received from each of the wireless thermocouples  14 ,  16 ,  18  and  20 . The algorithm in the control unit  24  is programmed to use the baseline profile to monitor for spikes or unacceptable increases in temperature in the feed material  26  in the delacquering zone  13  within the kiln  12 , and automatically control the heat supplied to the kiln  12  to prevent fires in the kiln  12  and otherwise maintain a proper operational delacquering profile within the kiln  12 . 
         [0022]    In a simple form, and by way of example, should any one or more of the thermocouples  14 ,  16 ,  18  and  20 , detect a temperature that exceeds a predetermined high limit setpoint for a period of time that exceeds a predetermined duration, or should one or more of the thermocouples  14 ,  16 ,  18  and  20 , detect an abnormal temperature pattern in the kiln  12  such as a rapid rise in temperature, the control unit  24  then automatically instructs the mass flow controller  40  to decrease the speed of the blower  36  a predetermined amount based upon the anticipated reduction in heat that is necessary to avoid a fire in the kiln  12 , as formulated from tests and calculations. Should the temperatures in the kiln  12  drop below a lower limit setpoint for a period of time that exceeds a duration setpoint, the control unit  24  then automatically instructs the mass flow controller  40  to increase the speed of the blower  36  a predetermined amount based upon the anticipated increase in heat that is necessary to properly operate the kiln  12 , also as formulated from tests and calculations. Of course, one skilled in the art will recognize that much more complex algorithms may be incorporated in the control unit  24  to enable refined control of the temperature profile of the feed material  13  and the and the efficiency of the kiln  12 . 
         [0023]    In an even more simplified variant of the novel wireless temperature sensing and control system for metal kiln  10  of the present invention (not shown), there is no control loop to automatically control the heat supplied to the kiln  12 . Rather, when an overtemp event is identified by the control unit  24  from the wireless thermocouples  14 ,  16 ,  18  and  20 , such as for example when any one or more of the thermocouples  14 ,  16 ,  18  and  20 , detects a temperature that exceeds a predetermined high limit temperature setpoint for a period of time that exceeds a predetermined duration, or should one or more of the thermocouples  14 ,  16 ,  18  and  20 , otherwise detect an abnormal temperature pattern in the kiln  12  such as a rapid rise in temperature, the control unit  24  generates a notification. The notification can activate a notification apparatus, such as triggering an alarm (not shown) to alert the system X operators of a potential fire threat in the kiln  12 . The system X operators can then inspect the situation and make any manual or automated adjustments to the system X operation as they see fit. 
         [0024]    Of course, the programmable control unit  24  may be operatively connected to and control in response to the temperature readings from any one or more of the thermocouples  14 ,  16 ,  18  and  20 , any one or more of the heat flow control devices in the system X, which include for example and without limitation, the pressure control damper  122 , the combustion blower  34 , the combustion oxygen supply mass flow controller  37 , the combustion gas mass flow controller  31 , the combustion air mass flow controller  41 , the diverter valve  110 , the emergency vent  124 , the bypass valve  116 , the feed material control chute  13  and the feed material discharge chute  15 . 
         [0025]    While we have described in the detailed description two configurations that may be encompassed within the disclosed embodiments of this invention, numerous other alternative configurations, that would now be apparent to one of ordinary skill in the art, may be designed and constructed within the bounds of our invention as set forth in the claims. Moreover, both of the above-described novel wireless temperature sensing and control system for metal kiln  10  of the present invention can be arranged in a number of other and related varieties of configurations without expanding beyond the scope of our invention as set forth in the claims. 
         [0026]    For example, the system  10  is not necessarily required to be installed in a mass flow delacquering system X as depicted in  FIG. 1 , but may be installed or otherwise incorporated into a variety of configurations of metal recycling furnace and kiln systems. Further, the system  10  is not constrained to the use of four wireless thermocouples such as  14 ,  16 ,  18  and  20 . Rather, the system  10  may comprise any number of wireless thermocouples (or other temperature sensing devices), from as few as a single wireless thermocouple up to numerous more than four wireless thermocouples. Likewise, the system  10  is not restricted to a single receiver  22  or a single control unit  24 . Depending on the configuration of the recycle system and rotary kiln application, the system  10  may require or it may be desirable to utilize two or more receivers, such as the receiver  22 , or two or more control units, such as the control unit  24 . In addition, the system  10  is not restricted to using thermocouples, but may utilize any form of temperature sensing device that can be adapted for use in the furnace or kiln environment for which the system  10  is designed. 
         [0027]    By way of further example, depending on the configuration of the melt system, it may be necessary or otherwise desirable to include in the system  10  one or more mass flow controllers or other such heat flow control devices in the recycle system X that are capable of adjusting the heat flow in the kiln  12 . These other heat flow control devices may be positioned at various locations in the recycle system. Such heat flow control devices may include, for example, a cooling injection port, controllers for various gas supply lines to one or more burners in the melt system, and mechanical in-line dampers for gas flow. It would be recognized by one of ordinary skill in the art that any mechanism that can be manipulated to control the heat flow in the kiln  12  may potentially be incorporated into the system  10 . Each of these heat flow control devices can be operatively connected to the control unit  24  such that the control unit  24  regulates the heat flow control devices in response to the temperature readings transmitted to the control unit  24  from the thermocouples  14 ,  16 ,  18  and  20 . Further, the control unit  24  can be programmed to regulate the heat flow control devices in varying patterns depending on the profile of the temperature readings across the thermocouples  14 ,  16 ,  18  and  20 , and the durations of those temperature readings at or about any one or more predetermined temperature setpoints. 
         [0028]    Additional variations or modifications to the configuration of the novel wireless temperature sensing and control system for metal kiln  10  of the present invention may occur to those skilled in the art upon reviewing the subject matter of this invention. Such variations, if within the spirit of this disclosure, are intended to be encompassed within the scope of this invention. The description of the embodiments as set forth herein, and as shown in the drawings, is provided for illustrative purposes only and, unless otherwise expressly set forth, is not intended to limit the scope of the claims, which set forth the metes and bounds of our invention.