Abstract:
A heating apparatus for charge material includes a preheater having a housing with a combustion chamber therein constructed and arranged to receive the charge material, at least one oxy-fuel burner mounted to the housing for providing a combustion flame to the combustion chamber wherein a combustion atmosphere is created to provide heat sufficient to increase a temperature of the charge material, a fuel supply and an oxidant supply connected to the at least one oxy-fuel burner, an exhaust in communication with the combustion chamber for removing a portion of the combustion atmosphere from the combustion chamber; and a melter separate from the preheater for coaction therewith to receive the heated charge material for being melted in the melter.

Description:
[0001]    The present embodiments relate to apparatus and methods for preheating charge materials to be subjected to a heating or melting operation. 
         [0002]    In a melting or reheating furnace, a lower and more uniform flame temperature will reduce the likelihood of overheating the charge material, reduce the formation of oxides of nitrogen (NO x ) and the formation of metal oxides (scale or dross), increase furnace throughout, and reduce furnace fuel consumption, due to an improved heat transfer mechanism. 
         [0003]    Fossil fuel melting furnaces for aluminum and copper utilize energy released from a flame to raise the temperature of the charge material and the furnace superstructure (which consists of a refractory lining and steel structure). Air-fuel fired furnaces are fairly inefficient, with only about 20-30% of the gross energy released going to the charge material during the melt portion of the furnace cycle. The remainder of the gross energy is used to heat the superstructure, or lost through to the furnace exhaust. 
         [0004]    Air-fuel systems that utilize preheated combustion air offer a significant improvement over “cold” air systems. Preheating the combustion air can result in furnace efficiencies of approximately 30-40%. The primary drawbacks to preheated air-fuel systems are equipment cost, footprint and ongoing equipment maintenance. 
         [0005]    Oxy-fuel fired furnaces are a significant improvement over conventional air-fuel furnaces as described above. Due to the elimination of nitrogen in the oxy-fuel process, the amount of energy lost to the furnace exhaust is significantly reduced. As a result, with an oxy-fuel based melting furnace, approximately 35-50% of the gross energy input is used to heat the charge material. 
         [0006]      FIG. 1  shows a known melting operation wherein the charge material is, for example, in one or more of the forms or structures indicated, and is provided to a furnace, such as a reverberatory furnace, for melting to produce a cast or molten product for subsequent use or application. 
       SUMMARY OF THE INVENTION 
       [0007]    The flameless impingement preheating furnace embodiment (“preheater”) is used in conjunction with melting furnaces. The preheater is a relatively small stand alone furnace that utilizes oxy-fuel. The furnace heats the charge material (sow, t-bar, bundled ingots, etc. of various sizes and shapes) to a temperature that is below its solid-to-liquid transition point. Once heated to the desired temperature, the charge material is transferred to the melting furnace where the remainder of the melting process is carried out. 
         [0008]    The preheater embodiment heats material more efficiently than a conventional air-fuel or oxy-fuel furnace. Specifically, the preheater will raise the material temperature more quickly and utilize less energy than conventional cold and hot air-fuel or conventional oxy-fuel processes. The preheater operated in combination with a conventional melting furnace will result in greater net furnace efficiency, and also offers greater melting operation flexibility. 
         [0009]    From a safety perspective, the preheater furnace embodiment will thoroughly dry the charge material prior to it being charged to the melting furnace. Moisture present in any porous section of the charge material may increase the risk of a steam bubble(s) submerged in molten metal within, for example, a reverberatory furnace. Steam trapped below the molten surface is a common cause of explosions that result in injury and equipment damage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    For a more complete understanding of the present embodiments, reference may be had to the following drawing figures taken in conjunction with the description of the embodiments, of which: 
           [0011]      FIG. 1  is a flow chart of a known melting operation. 
           [0012]      FIG. 2  is a flow chart of a melting operation using a flameless impingement preheating furnace embodiment of the present invention. 
           [0013]      FIG. 3  is a schematic view in partial cross-section of the flameless impingement preheating furnace embodiment of the present invention. 
           [0014]      FIG. 4  is a schematic view in cross-section taken along line  4 - 4  of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    Referring to  FIG. 2 , the preheater furnace embodiment of the present invention shown generally at  10  is added to or used in conjunction with a known melter. The preheater  10 , when combined with a conventional melting furnace, provides production flexibility in terms of a) the ability/option to heat the scrap in the preheater rather than in the melting furnace, and b) the ability to heat charge material in the preheater while at the same time heating material in the conventional melting furnace, thereby increasing the production capacity of the facility (in other words, expanding the operating window). 
         [0016]    Now referring to  FIGS. 3 and 4 , the preheater furnace embodiment  10  is shown for use with conventional melting furnaces (not shown). The preheater  10  includes a housing  12  which may have a plurality of side walls  14  depending upon the shape of the housing  12 . A top  16  or crown and a bottom  18  or floor is provided for the housing  12 . One of the side walls  12  is provided with a door  20  which is moveable to permit charge material, such as for example aluminium ingots or aluminium sows, to be introduced into a combustion chamber  22  of the preheater  10 . The sidewalls  14 , top  16  and bottom  18  define the combustion chamber  22  within the housing  12 . 
         [0017]    Disposed within the combustion chamber  22  is at least one or a plurality of support members  24  such as for example stanchions to support charge material  15 , such as an ingot or sow, in the combustion chamber  22  for heating thereof. An exhaust  26  or a plurality of exhausts is/are in communication with the combustion chamber  22  of the preheater  12 , the exhaust  26  including a damper  28  disposed at an interior of the exhaust  26  to control pressure of the preheater  12 . 
         [0018]    The charge material  15  is subjected to the circulatory combustion atmosphere represented generally by arrows  30 . 
         [0019]    The preheater includes one or a plurality of the burners  32  mounted to the top  16  of the preheater  12 , such as for example an oxy-fuel burner  32 . The burner  32  is in communication with the combustion chamber  22  to provide a flameless impingement heat source  25  for heating the charge material  15 . The heat source  25  provides a flame envelope  27  which includes the atmosphere and combustion products circulating in the combustion chamber  22 . Oxygen as an oxidant for the burner  32  is provided from a pipe  34  which is at one end connected to the burner  32  and at distal end ultimately in communication with a liquid or gaseous oxygen source  36  such as a tank, vessel or oxygen generating machine. The burner  32  or burners may also be disposed in the sidewall  14  for communication with the combustion chamber for combustion therein. 
         [0020]    Tracing the line  34  from the source  36 , the line  34  passes through a vaporizer  38 , after which a pressure relief valve  40  is interposed at the line  34 . 
         [0021]    While the preheater  10  may be disposed in its own separate lot or building for use with a melter such as a reverberatory furnace, the source  36 , vaporizer  38  and valve  40  will probably be disposed external to the building in which the preheater  10  is arranged and therefore, a wall represented generally at  42  is provided with a port or aperture  44  through which the line  34  may pass to be connected to a control system  46  having valves and meters for control and metering of the liquid oxygen to the burner. 
         [0022]    A fuel line  48  is also provided having one end in communication with the burner  32  and a distal end in communication with a fuel source  50 . The line  48  connecting the fuel source  50  with the burner  32  is also connected to the controller  46  for the necessary valving and metering with respect to the fuel control to the burner  32 . A port or aperture  52  is also provided in the wall  42  to accommodate the fuel line  48 , as the fuel source  50  will be remote from the preheater  10 . The fuel from the fuel source  50  can be selected from natural gas, propane and oil, for example. 
         [0023]    A control panel  54  is connected to the burner  32  by line  56 , and to the control system  46  by line  58 . 
         [0024]    The preheater  10  may be operated above 300° F. (149° C.), and with aluminium and other metals from 700° to 800° F. (371° to 427° C.). The preheater  10  is not used to actually melt the charge material, but rather to elevate the temperature of the charge material  15  such that it is more receptive and closer to its melting temperature in the melting furnace. 
         [0025]    The charge material  15  is loaded into the preheater  10  through the door  20  by for example a forklift. It is common for the charge material  15  to be constructed such that it is readily accessible by a forklift or other mechanical conveying means. After the charge material  15  has reached the necessary preheating temperature in the preheater  10 , the forklift will remove or extract the material  15  through the door  20  from the combustion chamber  22  and deposit same in the melting furnace. 
         [0026]    Aluminium for example will become molten when it reaches a temperature just over 1,200° F. (649° C.). Therefore, heating the aluminium charge material  15  to a temperature between 700 to 800° F. (371° to 427° C.) will substantially reduce the residence time of the charge material  15  in the melting furnace. This will also lead to a reduction in the use of fuel and oxidant that the melting furnace would otherwise have to use to elevate the aluminium charge material  15  to reach its molten state. 
         [0027]    By way of example only, the preheater  10  may have dimensions of approximately 6 feet (1.8 meters) in length, 4 feet (1.2 meters) in width and 5 feet (1.5 meters) in height. 
         [0028]    The preheater  10  is oriented such that when fired the flame envelope  27  is in contact with the surface of the material to be preheated. The direct contact of the flame envelope results in effective heat/energy transfer. 
         [0029]    The small, refractory lined preheater  10  provides the top for the burner flame  25 . The unoccupied interior furnace volume (combustion chamber  22  volume minus charge material  15  volume) is relatively small. The small volume and the atmosphere circulation  30  in the combustion chamber  22  create combustion atmosphere velocities that produce convective heat transfer to the surfaces of the charge material  15  not being directly impinged upon by the flame  25 . 
         [0030]    The products of combustion present in the unoccupied combustion chamber  22  volume (or furnace interior volume minus the charge material  15  volume) are recirculated into the flame envelope  27 . 
         [0031]    The preheater operates  10  in a semi-flameless mode, wherein the flame is still visible (hot) to a combustion system UV detector, but flameless (cool) enough to maintain a flame temperature that is low enough not to cause melting of the charge material  15  surface. 
         [0032]    The heat transfer effect of the preheater  10  results in the ability to more quickly raise the temperature of the charge material  15  which results in faster melting processes and improved overall manufacturing efficiencies (increased throughput, reduced specific labor cost, reduced specific overhead cost, etc.). 
         [0033]    The flameless direct flame impingement, along with the compact preheater  10  dimensions results in reduced fuel consumption when compared to currently available technologies. Specific fuel consumption pertains to the amount of energy consumed to raise a prescribed amount of material to a given temperature. 
         [0034]    The preheater  10  is a relatively low cost solution to incrementally increase the production capacity of a given melter facility. In other words, having reached a production limit on a given melter furnace, the furnace operator may elect to build a new melting or holding furnace, but the justification for such a large investment is often challenging and may result in a significant level of risk. The preheating  10  requires a lower capital investment and offers a more manageable level of risk. 
         [0035]    Steel, aluminum and copper for example can be heated by the preheater  10 . 
         [0036]    It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.