PREHEATING SYSTEM IN GLASS MELTING FURNACE

Abstract

PREHEATING SYSTEM IN A GLASS MELTING FURNACE The system (10) for preheating batch material in a glass melting furnace (12) includes a preheater (16) having an outlet (84) from which fluid is discharged and an inlet (82) receiving fluid discharged from the furnace and recirculated from the preheater outlet. In one embodiment, the cyclone separator (20) has an inlet (92) in communication with the preheater outlet and an outlet (96) in communication with the fan (30). The controller (70) controls the fan speed in response to the pressure drop between the inlet and outlet of the separator and the temperature at the outlet of the separator.In other embodiments, the controller (76, 77) controls valves (34, 40, 44) that (i) control the amount of fluid discharged from the preheater that is sent to the flue (100) and recirculated to the preheater or (ii) control the amount of fluid diverted to the charger (18) for the furnace, in response to the temperature in a line coupled to the inlet of the preheater.

Description

Description PREHEATING SYSTEM IN GLASS MELTING FURNACE Technical Field of Invention The present invention relates to a system for preheating batch material prior to its introduction into a glass melting furnace. Specifically, the disclosure relates to a system for preheating batch material wherein the mass flow and / or temperature of the exhaust fluid through the preheater and / or furnace charge is controlled to maximize energy transfer to the batch material while protecting the ductwork leading to and from the preheater and other components. Background of the Invention In glass melting furnace systems, preheaters are often used to heat the batch material, which is then fed to the glass melting furnace along with other unheated batch material. The heat in the preheater is generated, at least in part, by directing at least a portion of the exhaust fluid from the furnace to the preheater through ductwork. It is desirable to maximize the energy transfer from the exhaust fluid to the batch material while simultaneously protecting the ductwork leading to and from the preheater and other components from excessive temperatures. Careful control is necessary to achieve this goal because changes in the quality (e.g., moisture content and / or size) of the batch material (especially the cullet) can substantially alter the amount of heat transfer to the batch material and, consequently, the temperature of the exhaust fluid. The inventors herein have recognized the need for a furnace system that will minimize and / or eliminate one or more of the above-mentioned shortcomings. Brief Description of the Invention This disclosure relates to a system for preheating batch material in a glass melting furnace. Specifically, the disclosure relates to a system for preheating batch material wherein the mass flow and / or temperature of the discharge fluid through the preheater is controlled to maximize energy transfer to the batch material and protect the ductwork leading to and from the preheater and other components. The batch material may comprise raw materials such as silica sand, limestone, soda ash, or other raw materials, as well as recycled glass (e.g., slag) or a mixture thereof. A system for preheating batch material prior to delivery to a glass melting furnace according to one embodiment of the present invention includes a preheater configured to receive unheated batch material and to deliver heated batch material. The preheater includes a main outlet configured to exhaust fluid from the preheater and a main inlet configured to receive exhaust fluid from the glass melting furnace and recirculated exhaust fluid from the main outlet of the preheater. The system further includes a cyclonic separator having an inlet in fluid communication with the main outlet of the preheater and an outlet configured to exhaust fluid from the cyclone separator. The system further includes a fan in fluid communication with the outlet of the cyclone separator.The system further includes a pressure sensor configured to generate a pressure signal indicating a pressure drop between the inlet and outlet of the cyclone separator and a temperature sensor configured to generate a temperature signal indicating a temperature at the outlet of the cyclone separator. The system further includes a cyclone flow controller configured to control a fan speed responsive to the pressure signal and the temperature signal. A system for preheating batch material prior to delivery to a glass melting furnace according to another embodiment of the present teachings includes a preheater configured to receive unheated batch material and to deliver heated batch material. The preheater includes a main outlet configured for exhaust fluid from the preheater and a main inlet configured to receive exhaust fluid from the glass melting furnace and recirculated exhaust fluid from the main outlet of the preheater. The system further includes a first valve configured to control a first amount of exhaust fluid from the preheater sent to a flue for combination with exhaust fluid from the glass melting furnace and a second valve configured to control a second amount of exhaust fluid from the preheater recirculated to the inlet of the preheater.The system further includes a temperature sensor configured to generate a temperature signal indicating the temperature of a fluid within a line coupled to the preheater inlet and an inlet temperature controller configured to control a first valve and a second valve responsive to the temperature. A system for preheating batch material prior to delivery to a glass melting furnace according to another embodiment of the present teachings includes a preheater configured to receive unheated batch material and to deliver heated batch material. The preheater includes a main outlet configured for exhaust fluid from the preheater and a main inlet configured to receive exhaust fluid from the glass melting furnace and recirculated exhaust fluid from the main outlet of the preheater. The system further includes a charger configured to receive heated batch material from the preheater and feed the heated batch material to the glass melting furnace.The first recirculation line provides exhaust fluid from the charger to a second recirculation line coupled to the preheater inlet and carrying exhaust fluid from the glass melting furnace and the exhaust fluid is recirculated from the main outlet of the preheater. The system further includes a first temperature sensor configured to generate a first temperature signal indicative of a temperature of the first fluid in the second recirculation line and a second temperature sensor configured to generate a second temperature signal indicative of a second temperature of the fluid in the second recirculation line at a location upstream of the line where the first temperature is obtained. The system further includes a valve configured to control an amount of fluid in the second recirculation line diverted to the charger and a charger temperature controller configured to control the valve responsive to the first and second temperatures. The system for preheating batch material offers advantages over conventional systems. Specifically, the inventive system allows for efficient energy transfer from the discharge fluid to the batch material within the preheater while protecting the ductwork leading to and from the preheater from excessive temperatures. The foregoing and other aspects, features, details, benefits and advantages of the disclosed system will be illustrated from the detailed description and claims that follow, and also from the accompanying drawings that illustrate the features in this system as examples. Short Description of Image Figure 1 is a schematic view of a furnace system incorporating a system for preheating the culet in accordance with one embodiment of the present invention. Figure 2 is a graph illustrating a separate distance control profile of target flow rate and valve position in accordance with one embodiment of the present invention. Figure 3 is a graph illustrating a separate distance control profile of a valve position in accordance with one embodiment of the present invention. Complete Description of the Invention The present invention refers to the drawings wherein such reference numerals are used to identify identical components in various views, Figure 1 illustrates a furnace system 10 in accordance with one embodiment of the present invention. System 10 is provided for melting raw materials for use in forming articles or products. System 10 may comprise, for example, a glass melting furnace system for use in melting silica sand, soda ash (sodium carbonate), limestone and other batch materials such as slag (recycled broken glass) into molten glass. System 10 may include a furnace 12, a batch screw feeder 14, a batch material preheater 16, a charger 18, a cyclone separator 20, a duct system 22, a plurality of fans 24, 26, 28, 30, a plurality of valves 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, pressure sensors 60, 62 temperature sensors 64, 66, 68 and various controllers 70, 72, 74, 76, 77. Furnace 12 is provided for melting raw materials. Furnace 12 may comprise a glass melting furnace that melts batch materials including silica sand, soda ash, limestone, and slag into molten glass. Furnace 12 may have an operating temperature of approximately 1565 degrees Celsius (2850 degrees Fahrenheit). Furnace 12 may generate heat using natural gas and preheated combustion air. Furnace 12 may also supplement heat using an electric booster system. Excess heat may be removed from furnace 12 through duct system 22. A batch screw feeder 14 is provided for directing raw materials (e.g., silica sand, soda ash and limestone) to the charger 18. Although the screw feeder 14 is shown in the illustrated embodiment, it should be understood that various mechanisms including chutes, conveyors and other structures may be used in addition to, or as an alternative to, the screw feeder 14 to convey batch material from one or more silos (not shown) to the charger 18. The screw feeder 14 and / or other components of the batch delivery system may be controlled using conventional electromechanical controls that regulate the amount of batch material delivered to the charger 18 based on feedback signals from sensors used to monitor various conditions of the furnace 10, charger 18, or other structures in the system 10. A preheater 16 is provided to preheat the material before it is fed into the furnace 12 to improve the operating efficiency of the furnace 12. In the glass melting furnace system referenced above, the preheater 16 comprises a batch material preheater configured to receive unheated batch material and preheat the batch material before delivering the heated batch material to the furnace 12. The batch material preheater 16 may comprise a direct contact rain flow counterflow preheater wherein the unheated batch material is fed into one end of the preheater 16 and travels through the preheater 16 under gravity while heat is fed into the opposite end of the preheater 16 and flows in the opposite direction to the batch material. However, it should be understood that other conventional forms of preheater 16, for culet, raw batch material, or the like may be used alternatively in the glass melting furnace system.Batch material may be fed into the preheater 16 via a batch material inlet 78 from one or more silos (not shown) and may exit the opposite end of the preheater 16 via a batch material outlet 80 and be fed to the charger 18. In between, the batch material flows through the preheater 16 around a baffle plate. Heat, in the form of waste fluid from the furnace 12, preheater 16 and charger 18 may be fed into the preheater 16 via a main inlet 82 and discharged via a main outlet 84. As discussed below, waste fluid may also be fed into the preheater 16 from the furnace 12, preheater 16 and charger 18 via a bypass inlet 86 disposed between the main inlet 82 and the main outlet 84 relative to the direction of flow of the batch material in the preheater 16. A feeder 18 is provided for feeding a mixture of raw batch material and culet into the furnace 12. The feeder 18 may include a Hopper 88 and a feed chamber 90. The Hopper 88 is provided for combining the raw material streams from the batch screw feeder 14 and the batch material from the preheater 16 and for directing the combined streams to the feed chamber 90. The feed chamber 90 has an inlet end coupled to the outlet end of Hopper 88. The inlet end is configured to receive the combined streams of raw batch material and heated batch material from Hopper 88. The feed chamber 90 also has an outlet end where the mixture of raw batch material and heated batch material is discharged from the feed chamber 90 into a molten bath in the furnace 12 using, for example, a vibratory motion or a reciprocating pushing motion. A cyclone separator 20 is provided for separating fine particulates, including glass fine particles, from the exhaust fluid produced by the preheater 16. The cyclone separator 20 defines an inlet 92 configured to receive the exhaust fluid from the main outlet 84 of the preheater 16. The cyclone separator 20 further defines outlets 94, 96, at opposite ends of a cylindrical container 98 configured to discharge the particulates and the cleaned exhaust fluid, respectively. The configuration of the inlet 92 and the shape of the container 98 establish a high-speed rotating air stream within the container 98 that causes the particulates in the exhaust fluid to be removed from the air stream and drop to the bottom of the container where they can be discharged through the outlet 94 while the clean air is discharged from the outlet 96. The particles exiting the outlet 94 can be directed to the inlet for the batch screw feeder 14 for mixing with the raw batch material. A duct system 22 is provided for routing fluid between the furnace 12, preheater 16, charger 18 and other components (not shown) of the system 10 as well as the atmosphere (for air intake and byproduct removal). The duct system 22 is constructed of material sufficient to withstand the anticipated operating temperatures in the components of the system 10 and may be constructed of steel in some embodiments. Fans, including fans 24, 26, 28, 30 may be used to introduce fluid into channels in the duct system 22 or to move fluid within the duct system 22. Mechanically or electrically controlled valves, including valves 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58 may be disposed into the duct system 22 to control the amount of fluid flowing to and from the various components of the furnace system 10.In the illustrated embodiment, the duct system 22 includes an exhaust duct 100, a furnace exhaust duct 102, an air intake duct 104, a preheater exhaust duct 106, a cyclone separator exhaust duct 108, a charger exhaust duct 110, 112, recirculation ducts 114, 116, 118, 120, 122, 124 and bypass ducts 126, 128. However, it should be understood that additional ducts may be part of the duct system 22. The flue duct 100 is provided to capture flue gases from the furnace 12 and preheater 16. The flue duct 100 recycles a portion of the flue gases for use in portions of the system 10 such as in preheating batch material in the preheater 16 or material in the charger 18. The flue duct 100 also provides a means for cooling the flue gases prior to reuse in the system 10 and / or treatment by downstream filters, scrubbers and other energy recovery and pollution control equipment prior to discharging the remaining liquid to the atmosphere. Furnace exhaust duct 102 is provided to transport exhaust fluid from furnace 10 to exhaust duct 100. The duct 102 is connected to exhaust duct 100 near one end of exhaust duct 100. Exhaust duct 102 may have a different composition in terms of material composition, shape (e.g., thickness), or other characteristics relative to other ducts in the duct system 22 to adequately handle the relatively high temperature exhaust fluid discharged from furnace 12. An air inlet duct 104 is provided for introducing ambient air or other fluid into the exhaust duct 100 for mixing with the furnace flue gas to cool the flue gas. In the illustrated embodiment, the air inlet duct 104 is connected to, and receives fluid from, the recirculation duct 114 and therefore may provide ambient air, recirculation fluid, or a mixture of both depending on the position of valves 32, 34. The preheater exhaust duct 106 and the cyclone separator exhaust duct 108 are provided for the exhaust fluid of the preheater 16 and the cyclonic separator 20 respectively. The duct 106 extends between the main outlet 84 of the preheater 16 and the inlet 92 of the cyclone separator 20. The duct 108 extends between the outlet 96 of the cyclone separator 20 and the fan 30. The charger exhaust ducts 110, 112 are provided for the exhaust fluid from Hopper 88 and feed chamber 90, respectively, from the charger 18. The duct 110, extends from Hopper 88 to fan 28. The duct 112 extends from feed chamber 90 and intersects the duct 110 between Hopper 88 and fan 28. Recirculation channels 114, 116, 118, 120, 122, 124 are provided to recirculate the exhaust fluid from the furnace 12, preheater 16, charger 18 and cyclone separator 20 in the system 10. Recirculation channel 114 transmits a portion of the exhaust fluid from the preheater 16 (via the cyclone separator 20) to the exhaust duct 100 via the air inlet duct 104. Recirculation channel 116 transmits another portion of the exhaust fluid from the preheater 16 (via the cyclone separator 20) to the recirculation channel 120. Recirculation channel 118 again transmits another portion of the exhaust fluid from the preheater 16 (via the separator 20) directly to the preheater 16 and extends from the fan 30 to the inlet bypass 86 of the preheater 16. Recirculation channel 120 transmits a portion of the mixed exhaust gas of the furnace 12 and preheater 16 (together with ambient air) for use in preheater 16 and charger 18.A channel 120 extends from the exhaust outlet 100 to the main inlet 82 of the preheater 16. A recirculation channel 122 intersects a channel 120 between the exhaust outlet and the main inlet 82 of the preheater 16 and directs a portion of the fluid mixture in the recirculation channel 120 to the feed chamber 90 of the charger 18. Finally, the recirculation line 124 also bypasses the line 120 between the exhaust outlet and the inlet preheater main line 82 and directs the effluent from the Hopper 88 and the mixing chamber 90 of the charger 18 to the line 120. Bypass lines 126, 128 are provided to redirect portions of the fluid from the recirculation lines 122, 120, respectively, for specific uses. Bypass duct 128 extends between recirculation ducts 118, 120 and directs a portion of the fluid mixture in recirculation duct 120 to recirculation duct 118. Bypass duct 128 is connected to recirculation duct 120 between exhaust duct outlet and main inlet 82 of preheater 16 and is connected to recirculation duct 118 between fan 30 and bypass inlet 86 of preheater 16. Bypass duct 126 extends between recirculation duct 122 and charger discharge duct 112 and directs a portion of the fluid mixture in recirculation duct 122 to charger discharge duct 112 respectively to maintain the temperature within charger discharge ducts 110, 112 at a predetermined level to avoid condensation within ducts 110, 112. Fans 24, 26, 28, 30 are provided to draw fluid from one location and direct that fluid to another location within the system 10. Fans 24, 26, are provided to introduce ambient air from the atmosphere into the air intake duct 104 for mixing with furnace exhaust fluid in the exhaust duct 100. Fan 28 is provided to take exhaust fluid from Hopper 88 and feed chamber 90 of the charger 18 and send that fluid to the recirculation duct 124 for mixing with other exhaust fluid from furnace 10 and preheater 16 used in preheating batch material in the preheater 16. Fan 30 is provided to take exhaust fluid from the preheater 16 (via a separator 20) and direct that fluid to the recirculation ducts 114, 116, 118. In accordance with one aspect of the present disclosure discussed below, the speed of fan 30 may be controlled to control the mass flow of exhaust fluid and temperature in the system 10. Valves 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58 are provided to control the fluid flow within the duct system 22. Valves 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58 may comprise butterfly valves and the position of each valve may be changed using conventional electromechanical controls under the direction of controllers such as controllers 70, 72, 74, 76, 77. Valve 32 is provided to control the amount of ambient air admitted to the air intake duct 104 (and ultimately to the exhaust duct 100). Valve 34 is provided to control the amount of liquid discharged from the preheater 16 (via the cyclone separator 20) that is fed from the recirculation line 114 to the air intake line 104 (and ultimately the exhaust line 100). Valve 36 is provided to control the amount of liquid discharged from the air intake line 104 to the exhaust line 100.A valve 38 is provided to control the amount of fluid introduced from the discharge line 100 into the recirculation line 120. A valve 40 is provided to control the amount of fluid discharged from the preheater 16 (via the cyclone separator 20) introduced from the recirculation line 116 to the recirculation line 120. A valve 42 is provided to control the amount of fluid introduced into the recirculation line 120 from the discharge line 100 and the recirculation line 116 that is conveyed downstream to devices such as the preheater 16 and the charger 18. A valve 44 is provided to control the amount of fluid transmitted from the recirculation line 120 downstream through the recirculation line 122 to the charger 18. Valves 46, 48 are provided to control the amount of fluid transmitted from the recirculation line 122 to the feed chamber 90 of the charger 18 and through the bypass line 126 to the recirculation line 112.Valves 50, 52 are provided to control the amount of exhaust fluid fed from Hopper 88 and feed chamber 90, respectively, of the charger 18 to the recirculation line 110. Valve 54 is provided to control the amount of exhaust fluid fed from the recirculation line 124 to the recirculation line 120. Valve 56 is provided to control the fluid flow from the fan 30 to the bypass inlet 86 of the preheater 16 and, in particular, the amount of exhaust fluid from the preheater 16 (via the cyclone separator 20) that is fed to the bypass inlet 86 of the preheater 16. Finally, valve 58 is provided to control the amount of exhaust fluid mixture in the recirculation line 120 that is diverted from the main inlet 82 of the preheater 16 to the inlet 86 of the preheater 16. In accordance with various aspects of the present disclosure discussed below, the positions of one or more valves 34, 40, 44, 56, and 58 may be controlled to control the flow of mass of exhaust fluid and temperature in system 10. Pressure sensor 60 comprises a differential pressure sensor and is provided to measure the pressure drop between the inlet 92 and outlet 96 of the separator 20. Pressure sensor 62 is provided to measure the pressure in the recirculation line 114. Sensors 60, 62 may comprise any of a variety of conventional pressure sensors including piezoresistive, piezoelectric, capacitive, resonant or other sensors. Pressure sensor 60 generates a pressure signal indicative of the pressure drop between the inlet 92 and outlet 96 of the cyclone separator 20 and provides that signal to controller 70. Pressure sensor 62 generates a pressure signal indicative of the pressure in line 114 and provides that signal to controller 76. Although the illustrated embodiments show selected pressure sensors relevant to the present disclosure, it should be understood that other pressure sensors may be located throughout the system 10 and used in various control processes.Temperature sensors 64, 66, 68 are provided to measure fluid temperatures at various locations in the duct system 22. Sensors 64, 66, 68 may comprise various types of conventional temperature sensors including thermistors or thermocouples. Sensor 64 measures the fluid temperature of the exhaust fluid immediately downstream of the outlet 96 of the cyclone separator 20. Sensor 64 generates a temperature signal indicative of the temperature at the outlet 96 of the cyclone separator 20 and provides such signal to controllers 70, 72, 74. Temperature sensors 66, 68 are provided to measure fluid temperatures at two locations in the recirculation duct 120. Temperature sensor 66 measures the fluid temperature in duct 120 at a location upstream of temperature sensor 68. Temperature sensors 66, 68 generate a temperature signal indicative of the fluid temperature in duct 120 and provide such signal to controllers 76, 77.Although the illustrated embodiments show selected temperature sensors relevant to the present disclosure, it should be further understood that other temperature sensors may be disposed throughout the system 10 and used in various control processes. Controllers 70, 72, 74, 76, 77 are configured to control various components in system 10. In the illustrated embodiments, certain controllers will be described for use in controlling fan 30 and valves 34, 40, 44, 56, 58. It should be understood, however, that additional controllers may be used in system 10 to control other system components. Furthermore, although controllers 70, 72, 74, 76, 77 are illustrated as separate controllers in the illustrated embodiments, it should be understood that one or more controllers 70, 72, 74, 76, 77 may be integrated into a single controller and that one or more of the controllers 70, 72, 74, 76, 77 may be subdivided into additional controllers responsible for subsets of tasks associated with a particular controller. The controllers 70, 72, 74, 76, 77 may comprise a programmable microprocessor or an application-specific integrated circuit (ASIC). The controllers 70, 72, 74, 76, 77 may include central processing unit (CPU) and input / output (I / O) interfaces to which the controllers 70, 72, 74, 76, 77 may receive input signals including signals generated by sensors 60, 62, 64, 66, 68 and generate output signals including those used to control fan 30 and valves 34, 40, 44, 56, 58. In accordance with the teachings disclosed herein, controllers 70, 72, 74, 76, 77 may be configured (coded) with a set of instructions executable from a computer program (i.e., software) to perform methods for controlling the mass flow and temperature of the exhaust fluid in the system portion 10 and, in particular, for controlling fan 30 and valves 34, 40, 44, 56, 58 to achieve mass flow and temperature control. A cyclone flow controller 70 is provided to control a fan 30 and, in particular, the speed of the fan 30 to control the mass flow of exhaust fluid through the preheater 16 and the cyclone separator 20. The controller 70 is configured to receive input signals from a pressure sensor 60, a temperature sensor 64 and a temperature controller 72. The controller 70 is further configured to generate output signals used to control the fan 30 that are responsive to the pressure signal from the pressure sensor 60 and the temperature signal from the temperature sensor 64. In particular, the controller 70 is configured to determine the actual flow rate through the cyclone separator 20 that is responsive to the pressure signal (indicating a decrease in pressure across the cyclone separator 20) and the temperature signal (where an increase in temperature indicates an increase in mass flow). The controller 70 is further configured to receive a target flow rate signal from the temperature controller 72 that indicates the desired fluid flow rate through the cyclone separator 20.The target flow rate signal is intended to reflect the batch material throughput rate (the furnace draw rate multiplied by the rinse material ratio) and the batch material quality (e.g., size and moisture content). The target flow rate may be set by the operator of system 10. However, the temperature controller 72 may also be configured to set the target flow rate based on one or more variables in system 10. The controller 70 is further configured to adjust the fan speed 30 if the actual flow rate meets predetermined conditions relative to the target flow rate. For example, if the actual flow rate exceeds the target flow rate, the controller 70 may generate a control signal configured to decrease the fan speed 30. If the actual flow rate is less than the target flow rate, the controller 70 may generate a control signal configured to increase the fan speed 30.Controller 70 may implement a proportional-integral-dependent (PID) control algorithm for this purpose. Finally, controller 70 may be configured to establish a predetermined speed for fan 30 during predetermined events including startup and shutdown of system 10 and during emergencies. A temperature controller 72 is provided to control the temperature of the discharge fluid through ducts 106, 108 to protect the ductwork, cyclone separator 20 and fan 30 and to optimize energy transfer to the batch material in the preheater 16. The controller 72 is configured to receive signal input from a temperature sensor 64 (the controller 72 may also receive operator input indicating a desired target flow rate). The controller 72 is configured to generate output signals in the form of a target flow rate signal indicating the desired target flow rate and a valve control signal indicating the commanded position for valve 56. As set forth above, under certain circumstances the target flow rate signal may be responsive to operator input selected based on factors including the batch material yield rate and the batch material quality.However, controller 72 also has an operating mode configured to generate a target flow rate responsive to the temperature measured by sensor 64 near the outlet 96 of the cyclone separator 20. Controller 72 may be configured to implement a mode where the target flow rate signal is generated responsive to the temperature measured from sensor 64 - as opposed to using operator input under various circumstances including, for example, if the measured temperature varies from the desired temperature by more than a predetermined amount or shows signs of rapid change over time. Controller 72 is also configured to generate a valve control signal to control the position of valve 56 responsive to the temperature signal. Valve 56 may be used to control the temperature in lines 106, 108 by controlling the amount of exhaust fluid from the preheater 16 that is recirculated to pass through the inlet 86 of the preheater 16.Since fan 30 controls the flow rate through the preheater 16 and the flow is constant at a constant fan speed, changing the position of valve 56 to increase or decrease the flow through the bypass inlet 86 of the preheater 16 causes a corresponding decrease or increase, respectively, in the amount of exhaust gas drawn into the preheater 16 from the recirculation line 120. In this way, opening valve 56 to increase the flow through line 118 to bypass the inlet 86 of the preheater 16 reduces the flow from line 120 to the inlet 82 and the temperature of the exhaust fluid leaving the outlet 84 of the preheater 16. Conversely, shutting valve 56 decreasing the flow through line 118 to bypass the inlet 86 of the preheater 16 increases the flow from line 120 to the inlet 82 and the temperature of the exhaust fluid leaving the outlet 84 of the preheater 16.In an alternative embodiment, controller 72 may be configured to control a valve (not shown) that directs ambient air to the mass flow entering, within, or leaving the preheater 16 to control the temperature. Referring to Figure 2, in accordance with some embodiments, controller 72 may be configured to generate a target flow rate signal and a valve control signal according to predetermined separate distance control profiles. The use of separate distance control profiles allows for smooth and uneven transfer of manipulation of the target flow rate and valve position by establishing a mathematical relationship between the two values. In the illustrated profile, valve 56 moves from a fully open position to a closed position depending on the desired rate of temperature rise in the ducts 106, 108.At a certain point, the profile sets a minimum open position (approximately 20% open) despite the desire for further temperature rise so that some fluid always flows through channel 118 to prevent condensation within channel 118. The target flow rate assumes a predetermined minimum value (set to create the airflow required to separate particulates in the cyclone separator 20) until the commanded temperature rise exceeds the predetermined value at which point the target flow rate increases incrementally depending on the desired temperature rise up to a predetermined maximum flow rate. In the illustrated profile, the target flow rate begins to increase from its minimum flow rate at the same point that valve 56 reaches its minimum open position.However, it should be understood that the profile may vary so that the target flow rate and valve position change simultaneously over a range of temperature values. Finally, controller 72 may be configured to establish a predetermined position for valve 56 during predetermined events including starting and stopping of system 10 and during emergencies. A bypass valve controller 74 is provided to increase the heat in the lines in the line system 22 including lines 106, 108 during the start-up of the preheater 16 to protect the line work from exposure to condensation. The controller 74 is configured to receive an input signal from a temperature sensor 64. The controller 74 is further configured to generate an output signal that is used to control a valve 58 that is responsive to the signal from the temperature sensor 64. The valve 58 is configured to control the flow of fluid from the recirculation line 120, which carries exhaust fluid from the glass melting furnace sent through exhaust line 100, to pass through the inlet 86 of the preheater 16. By directing this exhaust fluid to pass through the inlet 86, the fluid bypasses some of the batch material and the heat is instead diverted directly through the outlet 84 of the preheater 16 instead of being transferred to the batch material.In this way, various channels in the channel system 22, including channels 106, 108, will heat up faster. Thus, when the temperature at outlet 96 indicated by temperature sensor 64 is relatively low, bypass controller 74 is configured to open valve 58. As the temperature increases, valve 58 can move to the closed position or remain fully open depending on the control strategy employed. However, once the temperature reaches a predetermined threshold, controller 74 is configured to generate a control signal for valve 58 that closes valve 58. This threshold temperature may be less than the temperature at which temperature controller 72 performs target flow rate control and valve 58. For example, bypass valve controller 74 may operate valve 58 for temperatures below 120 degrees Celsius while temperature controller 72 starts operating when the temperature exceeds 150 degrees Celsius.Controller 74 may be further configured to establish predetermined positions for valve 58 during predetermined events including start-up and stoppage of system 10 and during emergencies. An inlet temperature controller 76 is provided to control the temperature of the fluid mixture in the recirculation line 120 leading to the inlet 82 of the preheater 16 to optimize the energy transfer from the fluid to the batch material in the preheater 16 and to protect the line 120. The inlet temperature controller 76 is configured to receive input signals from temperature sensors 66, 68 and to generate output signals used in controller valves 34, 40. Valve 34 controls the amount of effluent fluid from the preheater 16 sent to the exhaust line 100 for mixing with the exhaust fluid from the furnace 12 to control the temperature of the mixture in the exhaust line 100 and protect downstream energy recovery and emission reduction equipment. Valve 40 controls the amount of effluent fluid from the preheater 16 fed to the recirculation line 120 to control the temperature of the fluid mixture in the line 120.Referring to Figure 3, in accordance with one aspect of the present disclosure, controller 76 may generate valve control signals for valves 34, 40 according to a predetermined split-range control profile. The use of the split-range control profile establishes a mathematical relationship between the positions of the two valves 34, 40 that prevents the movement of one valve 34, 40 from affecting the position of the other valve 34, 40 and makes the split flow of exhaust gas in ducts 114, 116 independent of the plenum pressure downstream of fan 30. In the illustrated profile, as the measured temperature changes, controller 76 will output a control signal to increase the opening of one of the valves 34, 40, while decreasing the opening of the other valve 34, 40. Increasing the opening of valve 40 will direct a greater portion of the exhaust fluid from the preheater 16 into the recirculation duct 120 as opposed to the exhaust duct 100.Since the exhaust fluid from the preheater 16 is cooler than the exhaust fluid exiting the exhaust port 100, this action will decrease the temperature of the fluid mixture in the recirculation port 120 and at the inlet port 82 to the preheater 16. Conversely, increasing the opening of Valve 34 will direct a greater portion of the exhaust fluid from the preheater 16 to the exhaust port 100 compared to the recirculation port 120. This action will increase the temperature of the fluid mixture in the recirculation port 120 and at the inlet port 82 to the preheater 16. Thus, in the illustrated profile, once the measured temperature exceeds a predetermined threshold, any further increase will cause a proportional increase in the opening of the valve 40 from the minimum opening position to the fully open position. Conversely, if the temperature increases, the opening of the valve 34 decreases proportionally from the fully open position until it reaches the minimum opening position.Each valve 34, 40 has a minimum opening position (i.e., never fully closed) so that there is always at least some exhaust fluid flow through the recirculation lines 114, 116 to prevent undesirable cooling and condensation in the lines 114, 116. It should be understood that the illustrated profiles are exemplary only and that the minimum and maximum opening positions, the rate of rise / fall and the position of the valves 34, 40 relative to each other may vary. The controller 76 may also be configured to establish predetermined positions for the valves 34, 40 during predetermined events including starting and stopping the system 10, and during emergencies. In accordance with one aspect of temperature control in conduit 120, controller 76 may generate control signals for valves 34, 40 that are responsive to temperature signals generated by one of temperature sensors 66, 68. Temperature sensor 68 measures the temperature of the fluid mixture in conduit 120 nearest the inlet 82 of the preheater 16 and controller 76 will typically generate control signals for valves 34, 40 responsive to the measured temperature indicated by temperature sensor 68 to optimize energy transfer to the batch material in the preheater 16. Temperature sensor 66 measures the temperature of the fluid mixture in conduit 120 at a position upstream of temperature sensor 68 and closer to the point of inlet of the exhaust fluid from the exhaust conduit 100 to conduit 120. Controller 76 may be configured to generate control signals for valves 34, 40 that are responsive to the measured temperature from sensor 66 when the measured temperature indicates a relatively high temperature within the pan critical to damage to conduit 120 and the valve nearby.Controller 76 may be configured to select one of the temperature signals from sensors 66, 68 for use in establishing a control signal for valves 34, 40 based on various control strategies. In accordance with one embodiment, controller 76 generates a control signal for valves 34, 40, responsive to the temperature signal from sensor 68 unless the temperature indicated by sensor 66 satisfies a predetermined condition. Specifically, controller 76 generates a control signal for valves 34, 40, responsive to the temperature signal from sensor 68 unless the temperature indicated by sensor 66 exceeds the temperature indicated by sensor 68 by more than a predetermined amount.Since the temperature measured by sensor 66 must always be higher than the temperature measured by sensor 68 (based on the relative location of the sensors in the discharge fluid stream), controller 76 may compare the temperatures measured by sensors 66, 68 using a predetermined offset and base control of valves 34, 40 on the temperature measured by sensor 68 unless the temperature at sensor 66 exceeds the temperature at sensor 68 by more than the offset. After controller 76 selects the temperature signals from sensors 66, 68 for use in controller valves 34, 40, controller 76 may be configured to apply a PID controller to compare the measured temperatures to the desired temperatures and generate a value indicating the difference that may be used in generating control signals for valves 34, 40, according to the predetermined profiles referenced above. In accordance with another aspect of the present teaching, the inlet temperature controller 76 may be configured to control the pressure in the recirculation line 114 by controlling the minimum opening position of the valves 34, 40. As set forth above, each of the valves 34, 40, preferably has a minimum opening position to allow some exhaust fluid flow through each of the lines 114, 116 to maintain the temperature within the line above a predetermined level to prevent condensation in the lines 114, 116. In one embodiment, each of the valves 34, 40 may have a minimum opening of at least twenty percent (20%) relative to the fully open position. The controller 76 may be configured to adjust the minimum opening position of the valves 34, 40, responsive to a pressure signal from the pressure sensor 62 to increase or decrease the fluid flow through the lines 114, 116.In one embodiment, controller 76 may be configured to compare the pressure in conduit 114 indicated by pressure sensor 62 with a predetermined threshold pressure and to increase the minimum opening of each of the valves 34, 40 if the pressure in conduit 114 satisfies a predetermined condition relative to the predetermined threshold pressure (e.g., if the pressure in conduit 114 exceeds the predetermined threshold pressure). A charger temperature controller 77 is provided to control the temperature in the charger 18 and charger discharge line 112 to prevent condensation in the charger 18 and discharge line 112. The charger temperature controller 77 is configured to receive input signals from temperature sensors 66, 68 and to generate output signals used in controlling valve 44. Valve 44 controls the amount of exhaust fluid from the furnace 12 and preheater 16 that is diverted from the recirculation line 120 to the recirculation line 122 for the purpose of controlling the temperature of the charger 18 and charger discharge line 112.Because temperature sensor 66 measures the temperature of the fluid mixture in channel 120 upstream of the location where recirculation channel 124 joins recirculation channel 120 and temperature sensor 68 measures the temperature of the fluid mixture in channel 120 downstream of the location where channel 124 joins channel 120 (i.e., after the entry of the discharge fluid from Hopper 88 and feed chamber 90 of charger 18 through channel 124), the temperature difference measured by sensors 66, 68 indicates the temperature of the discharge fluid from Hopper 88 and feed chamber 90 of charger 18 and, therefore, the temperature of charger 18. Controller 77 may be configured to control the position of valve 44 responsive to temperature readings from sensors 66, 68 to control the temperature in charger 18 and in the discharge channel of charger 112 (e.g., to maintain the temperature of charger 18 and / or channel 112 above a predetermined temperature to prevent condensation within charger 18 and / or channel 112). 112). The system for preheating batch material according to the present invention has advantages over conventional systems. Specifically, the inventive system allows for efficient energy transfer from the exhaust fluid to the batch material within the preheater 16 while protecting the ducts in the duct system 22 leading to and from the preheater 16 and other components from excessive temperatures. The disclosure has been presented in connection with several illustrative embodiments, modifications, and additional variations. Such modifications and variations will readily suggest to those skilled in the art the preceding discussion. For example, the subject matter of each embodiment is incorporated by reference into each of the other embodiments, for convenience. This disclosure is intended to cover all modifications and variations that are well suited to the broad scope of the appended claims.

Claims

1. A system (10) for preheating batch material before it is fed into a glass melting furnace (12), comprising: a preheater (16) configured to receive unheated batch material and to deliver heated batch material, the preheater including a main outlet (84) configured to discharge liquid from the preheater and a main inlet (82) configured to receive waste liquid from the glass melting furnace and recirculated waste from the main outlet of the preheater; a cyclone separator (20) having an inlet (92) in fluid communication with the main outlet of the preheater and an outlet (96) configured to discharge liquid from the cyclone separator; a fan (30) in fluid communication with the outlet of the cyclone separator;a pressure sensor (60) configured to generate a pressure signal indicating a pressure drop between the inlet and outlet of the cyclone separator; a temperature sensor (64) configured to generate a temperature signal indicating a temperature at the outlet of the cyclone separator; and, a cyclone flow controller (70) configured to control a fan speed responsive to a pressure signal indicating a pressure drop between the inlet and outlet of the cyclone separator and responsive to a temperature signal indicating a temperature at the outlet of the separator, for efficient energy transfer from the exhaust fluid to the batch material in the preheater while protecting the ductwork leading to and from the preheater.; 2. The system according to claim 1, wherein the cyclone flow controller is further configured, in controlling the fan speed, to: receive a target flow rate signal indicating a desired fluid flow rate through the cyclone separator; determine an actual flow rate through the cyclone separator responsive to the pressure signal and the temperature signal; and, adjust the fan speed if the actual flow rate satisfies a predetermined condition relative to the target flow rate.

3. The system according to claim 2, further comprising a temperature controller (72) configured to generate a target flow rate signal responsive to a temperature signal.

4. The system according to claim 3, further comprising a valve (56) configured to control the flow of fluid from the fan to the bypass inlet (86) of the preheater.

5. The system according to claim 4, wherein the temperature controller is further configured to transmit a valve control signal to control the valve position responsive to the temperature signal.

6. The system according to claim 5, wherein the target flow rate signal and the valve control signal are generated in response to the temperature signal according to a predetermined separate range control profile.

7. The system according to claim 1, further comprising: a valve (56) configured to control the flow of fluid to a bypass inlet (86) of the preheater from a flue (100) carrying exhaust fluid from a glass melting furnace; and, a bypass valve controller (74) configured to transmit a valve control signal to control the position of the valve responsive to a temperature signal.

8. The system according to claim 1, further comprising: a valve (56) configured to control fluid flow from a fan to a bypass inlet (86) of a preheater; and, a temperature controller (72) configured to transmit a valve control signal to control the valve position responsive to the temperature signal.

9. The system according to claim 1, further comprising: a first valve (34) configured to control a first quantity of exhaust fluid from the preheater sent to the flue (100) for combination with exhaust fluid from the glass melting furnace; a second valve (40) configured to control a second quantity of exhaust fluid from the preheater recirculated to the inlet of the preheater; a first temperature sensor (68) configured to generate a first temperature signal indicating a temperature of the first fluid in the first conduit (120) coupled to the inlet of the preheater; and, an inlet temperature controller (76) configured to control the first valve and a second valve responding to the first temperature.

10. The system according to claim 9, further comprising a second temperature sensor (66) configured to generate a second temperature signal indicating a second temperature of the fluid in a first line coupled to the preheater inlet at a location in the upstream line where the first temperature is obtained and wherein the inlet temperature controller is configured to control a first valve and a second valve responsive to one of the first and second temperatures.

11. The system according to claim 10, wherein the inlet temperature controller is configured to control the first valve and the second valve is responsive to the second temperature if the second temperature meets predetermined conditions.

12. The system according to claim 11, wherein the defined condition comprises whether the second temperature exceeds the first temperature by more than a predetermined amount.

13. The system according to claim 10, wherein the inlet temperature controller controls the first and second valves responsive to a single temperature according to predetermined separate range control profiles.

14. The system according to claim 9, wherein the inlet temperature controller controls first and second valves responsive to the first temperature according to predetermined separate range control profiles.

15. The system according to claim 9, wherein the inlet temperature controller is configured to keep both the first and second valves at least partially open at all times.

16. The system according to claim 9, further comprising a pressure sensor (62) configured to generate a pressure signal indicating the pressure in a second line (114) conveying exhaust fluid from the preheater to the flue and an inlet temperature controller further configured, in controlling the first valve and the second valve, to adjust the minimum opening of each of the first and second valves responsive to the pressure signal.

17. The system according to claim 16, wherein the inlet temperature controller is further configured, in adjusting the minimum opening of each of the first and second valves, to: compare the pressure in the second line with a predetermined threshold pressure; and, increase the minimum opening of each of the first and second valves if the pressure in the second line satisfies a predetermined condition relative to the predetermined threshold pressure.

18. The system according to claim 1, further comprising: a charger (18) configured to receive heated batch material from the preheater and feed the heated batch material to a glass melting furnace, a first recirculation line (124) providing exhaust fluid from the charger to a second recirculation line (120) coupled to the inlet of the preheater and carrying exhaust fluid from the glass melting furnace and the exhaust fluid being recirculated from the main outlet of the preheater; a first temperature sensor (68) configured to generate a first temperature signal indicating a temperature of a first fluid in the second recirculation line; a second temperature sensor (66) configured to generate a second temperature signal indicating a second temperature of a fluid in the second recirculation line at a location upstream of the line from which the first temperature is obtained; a valve (44) configured to control an amount of fluid in the second recirculation line that is diverted to the charger;and, the charger temperature controller (77) is configured to control valves responsive to the first and second temperatures.; 19. The system according to claim 18, wherein the first temperature is obtained at a location downstream of the location where the first recirculation channel joins the second recirculation channel and the second temperature is obtained at a location upstream of the location where the first recirculation channel joins the second recirculation channel.

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