Furnace for heating particles

Abstract

A bottom-up cocurrent combustion furnace for the production of synthetic microspheres by thermal expansion of glass particles is provided having improved characteristics with regard to anti-fouling, process efficiency, and yield. The disclosed furnace uses preheated combustion air to preheat the feed material and to convey the feed material in a dilute phase transport regime to a burner. The combustion air, fuel, and feed material are premixed prior to being injected though the burner. The feed material rapidly expands as it is ejected through the burner and through a flame and then rapidly cools to solidify the microspheres. Additional features are provided to prevent the furnace from fouling by keeping the feed material away from the furnace walls, removing feed material that adheres to the furnace walls, and collecting feed material that agglomerates or does not expand.

1 . A furnace, comprising:
 a body, the body comprising one or more walls defining a combustion chamber therein;   a delivery system having one or more conduits configured to convey fuel and feed material to the body, and further configured to convey feed material in a dilute phase transport regime such that the solids content is less than about 1% by volume;   a burner assembly positioned within the combustion chamber, the burner assembly having one or more injectors in communication with the delivery system, the injectors configured to inject the fuel and feed material into the combustion chamber;   a cooling system in communication with the one or more walls and configured to maintain the walls below a pre-selected temperature; and   an anti-fouling system configured to keep feed material from adhering to the walls and to remove feed material that contacts the walls, a portion of the anti-fouling system comprising a vibrator configured to impart a vibration to the body at variable frequencies to dislodge particles adhered thereto.   
   
   
       2 . The apparatus of  claim 1 , wherein the walls are constructed of a non-refractory material. 
   
   
       3 . The apparatus of  claim 1 , wherein the delivery system is configured to mix the fuel and feed material prior to injection into the combustion chamber. 
   
   
       4 . The apparatus of  claim 3 , further comprising a combustion gas delivery conduit in communication with the delivery system and configured to mix fuel, feed material, and combustion gas prior to injection into the combustion chamber. 
   
   
       5 . The apparatus of  claim 4 , wherein the combustion gas has been preheated. 
   
   
       6 . The apparatus of  claim 1 , wherein the burner assembly further comprises a diverging expansion cone extending away from the burner such that the combustion gasses are allowed to expand to fill the increasing volume provided within the expansion cone. 
   
   
       7 . The apparatus of  claim 1 , further comprising a second wall surrounding and generally concentric with, the body and spaced therefrom such that an annular chamber is formed between the second wall and the body, and wherein the cooling system comprises circulated media delivered to the annular chamber to withdraw heat from the body. 
   
   
       8 . The apparatus of  claim 7 , wherein the circulated media is heated within the annular chamber and is then diverted to the delivery system and used as combustion gas. 
   
   
       9 . The apparatus of  claim 1 , wherein the pre-selected temperature is below the softening temperature of the feed material. 
   
   
       10 . The apparatus of  claim 1 , further comprising a second vibrator configured to cooperate with the first vibrator to apply one or more selectable vibration modalities to the body. 
   
   
       11 . The apparatus of  claim 10 , wherein one vibration modality is mode  1  simple harmonic vibration. 
   
   
       12 . The apparatus of  claim 10 , wherein the vibrators are configured to operate out of phase with one another to apply a circular vibration modality. 
   
   
       13 . The apparatus of  claim 1 , further comprising a slag trap configured to capture material at the bottom of the body. 
   
   
       14 . The apparatus of  claim 1 , further comprising an additive conduit configured to deliver an additive to the delivery system such that the additive is mixed with the fuel and feed material prior to injection into the combustion chamber. 
   
   
       15 . The apparatus of  claim 1 , wherein the additive is provided to coat the feed material to inhibit the feed material from adhering to the body. 
   
   
       16 . The apparatus of  claim 1 , further comprising expansion means configured to allow the body to expand axially to accommodate thermal expansion. 
   
   
       17 . A furnace, comprising:
 a body comprising an inner cylinder defining a combustion chamber therein, and a coaxial outer cylinder spaced apart from the inner cylinder to define an annular chamber therebetween;   a delivery system in communication with the combustion chamber comprising one or more conduits configured to deliver feed material, fuel, air, and an anti-fouling additive to the combustion chamber; and   a burner assembly disposed within the combustion chamber and in communication with the delivery system and configured to inject the feed material, fuel, air; and the anti-fouling additive into the combustion chamber, wherein the anti-fouling additive is selected to inhibit the feed material from adhering to the inner cylinder.   
   
   
       18 . The furnace of  claim 17 , wherein the anti-fouling material is significantly smaller than the feed material. 
   
   
       19 . The furnace of  claim 17 , wherein the anti-fouling material is a mixture of two or more materials. 
   
   
       20 . The furnace of  claim 17 , wherein the anti-fouling material is a mixture of kaolin and at least one other material.