Systems and Methods for Preheating Metal-Containing Pellets

Abstract

A direct flame impingement system for preheating metal pellets before charging into a melting furnace, wherein the pellets are transported by a conveyor belt to a chute discharging into the melting furnace, including a refractory-lined preheater hood including a chute hood covering the chute and a conveyor hood covering at least a portion of the conveyor belt, the preheater hood having an entrance end through which pellets enter and an exit end through which pellets exit toward the melting furnace, and at least one bank of burners each containing at least one burner disposed in the hood positioned to direct flames into contact with the pellets being transported to preheat the pellets prior to discharge into the melting furnace.

1 . A direct flame impingement system for preheating metal pellets before charging into a melting furnace, wherein the pellets are transported by a conveyor belt to a chute discharging into the melting furnace, comprising:
 a refractory-lined preheater hood including a chute hood covering the chute and a conveyor hood covering at least a portion of the conveyor belt, the preheater hood having an entrance end through which pellets enter and an exit end through which pellets exit toward the melting furnace; and   at least one bank of burners each containing at least one burner disposed in the hood positioned to direct flames into contact with the pellets being transported to preheat the pellets prior to discharge into the melting furnace.   
     
     
         2 . The direct flame impingement system of  claim 1 , wherein the at least one bank of burners includes a chute bank of burners disposed in the chute hood containing at least one burner positioned to direct flames into contact with the pellets being transported through the chute. 
     
     
         3 . The direct flame impingement system of  claim 1  or  2 , wherein the at least one bank of burners includes a first conveyor bank of burners disposed in the conveyor hood containing at least one burner positioned to direct flames into contact with pellets being transported on a first section of the conveyor belt. 
     
     
         4 . The direct flame impingement system of  claim 3 , wherein the at least one bank of burners further includes a second conveyor bank of burners containing at least one burner disposed in the conveyor hood positioned to direct flames into contact with the pellets on a second section the conveyor belt. 
     
     
         5 . The direct flame impingement system of  claim 4 ,
 wherein at any particular time, one of the first and second banks of conveyor burners is controlled to be fuel-rich so as to create a reducing zone and the other of the first and second banks of conveyor burners is controlled to be oxygen-rich so as to create an oxidizing zone; and   wherein the reducing zone is near the exit end of the conveyor cover and the oxidizing zone is near the entrance end of the conveyor cover.   
     
     
         6 . The direct flame impingement system of any one of  claims 1 - 5 , further comprising a bank of inert fluid nozzles positioned along the conveyor cover for injecting inert fluid toward the conveyor to enable rapid cooling and/or fire suppression of the pellets, wherein the inert fluid is selected from the group consisting of an inert gas, an inert liquid, and a combination of an inert gas and an inert liquid. 
     
     
         7 . The direct flame impingement system of any one of claims  claim 1 - 6 , further comprising a flue at the entrance end of the preheater hood to induct hot flue gases to flow from the melting furnace, under the preheater hood and over the pellets in the chute and on the conveyor, to enhance convective heat transfer to the pellets. 
     
     
         8 . The direct flame impingement system of any one of  claims 1 - 7 , further comprising one or more ploughs along the conveyor belt to mix the pellets for enhanced contact of the flames with the pellets. 
     
     
         9 . The direct flame impingement system of any one of  claims 1 - 8 , wherein the burners combust fuel with one or more of air, oxygen-enriched air having greater than 23% molecular O2, and industrial-grade oxygen having at least 70% molecular O2. 
     
     
         10 . The direct flame impingement system of any one of  claims 1 - 9 , further comprising:
 at least one sensor to detect a process condition; and   a controller programmed to operate the burners based on the process condition;   wherein when the at least one sensor is a flue gas sensor positioned at the entrance end of the preheater hood to measure the concentration of one or more gases in the flue gas, the controller is programmed to adjust operation of the burners based on a measure concentration of one or more gases in the flue gas;   wherein when the at least one sensor is a temperature sensor positioned in the conveyor hood for measuring one or more of gas temperature, pellet temperature, and belt temperature the controller is programmed to adjust operation of the burners based on one or more of a measured gas temperature, a measured pellet temperature, and a measured belt temperature; and   wherein when the at least one sensor is configured and arranged to detect a safety condition, the controller is programmed to shut down the burners in the event a safety condition is detected.   
     
     
         11 . A method of preheating metal pellets upstream of a melting furnace, wherein the pellets transported by a conveyor belt and to a chute discharging into the melting furnace, comprising:
 operating at least one bank of burners each containing at least one burner to direct flames into contact with the pellets being transported to preheat the pellets prior to discharge into the melting furnace.   
     
     
         12 . A preheating system for preheating metal-containing pellets before charging into a melting furnace, comprising:
 a refractory-lined preheater furnace having an inlet end wall, an exit end wall opposite the inlet end wall, and a substantially cylindrical side wall defined by an axis of the furnace and extending from the inlet end wall to the exit end wall, the inlet end wall having a door or opening for receiving unheated pellets, the exit end wall having a door or opening for discharging heated pellets toward the melting furnace;   at least one burner for firing into the preheater furnace to impart heat to the pellets; and   a flue for exhausting combustion gases produced by the burner from the preheater furnace;   wherein the preheater furnace rotatable and is arranged to rotate about its axis.   
     
     
         13 . The preheater system of  claim 12 , further comprising:
 a controller programmed to control operation of the at least one burner so as to produce a non-oxidizing atmosphere over the pellets to inhibit oxidation of the pellets.   
     
     
         14 . The preheater system of  claim 12 , further comprising a mechanism in the furnace configured and arranged urge the pellets to move from the inlet end to the exit end.