INTRODUCTION TO THE INVENTION This invention relates to a preheating apparatus. More specifically, but not exclusively, the invention relates to an apparatus for preheating material before it enters a furnace.

BACKGROUND TO THE INVENTION

Heating and melting furnaces, and in particular electric arc furnaces, are used to heat or melt various materials. Electric arc furnaces pass an electric arc (current) through ferrous metallic, non-ferrous metallic, and non-metallic scrap or other feed stock in order to melt the furnace feed material.

During this production process, large quantities of very hot particulate-laden gases are generated. These gases create a problem, in that they are very hot, abrasive, difficult to handle, and they cannot be vented directly into the environment, due to the particulate material in them. These gases are usually drawn out of the furnace through a hole in the furnace roof.

The gases are cooled, usually by passing through water- or air-cooled ductwork, and are filtered through a bag house, scrubber, precipitator, or other device with the function of collecting the particulate matter prior to discharge of the gas into the atmosphere.

If these off-gases can be used to preheat material to be charged into the furnace, several problems can be solved at once. First, the amount of time and energy required to melt the materials in the furnace can be reduced, resulting in considerable cost savings in the production process. Second, since in some cases the off-gases are cooled as they are passing through the gas cleaning equipment, the cooling systems can be eliminated or reduced, saving considerable capital and operating expense. Third, some of the particulate matter becomes trapped in the furnace feed material, thus reducing the waste material to be disposed from the dust collection device. Fourthly the calorific value of the gas can be used to preheat the furnace raw material feed, which will also lead to a saving in energy. Fifthly any other combustible gas or material can be used to preheat the gasses to be used for the preheating of the furnace feed material.

There are several systems in use or proposed which are intended to use the off- gases to preheat the material to be charged into the furnace, and there are problems with all the existing systems. Some systems for using the off-gas to preheat require a complete redesign of the production process and equipment. Some other systems are simply not compatible with normal furnace operations, because they do not permit good operating practices or for other reasons. Most of the existing systems are very maintenance-intensive and/or have high operating expenses. In many designs, only part of the gases pass through the material to be preheated, sharply reducing the efficiency of the system. In some designs, the preheater cannot be bypassed if maintenance problems occur, which is clearly an undesirable situation. Some systems require additional processing of materials prior to use, or are limited to certain specific types or sizes of material.

Some systems preheat the charging bucket containing the furnace feed material each time the furnace feed material is preheated. Because the bucket has a significant weight relative to the contents, much energy is wasted in heating the bucket. This heating of the bucket is also damaging to the bucket, increasing maintenance costs.

Because of the space required for the preheat system, it typically is not located in the immediate vicinity of the melting furnace. When the preheat station is located at some distance from the furnace, several problems result. First, the heated vessel must be moved by crane or other device through the operating area to the furnace, resulting in a loss of preheat temperature and the escape of irritating or toxic fumes into the air. Second, in order to transport the vessel to the furnace area in time to quickly charge the furnace when the furnace is shut off, the vessel must be removed from the preheat station prematurely, thus resulting in a loss of, efficiency in the preheat process. Third, this movement of the vessel to the furnace by crane or other means is a double handling of the charging material, compromising normal operations. Fourth, due to the distance between the furnace and the vessel, much of the energy in the off-gas, pre-reduced or heated material is lost before the gases and or furnace feed material reach the furnace, resulting in a loss of efficiency. Fifth, because the system is not near the furnace, great distances are required to transport the gases and heated material to the furnace, wasting energy and creating a large capital and maintenance expense. OBJECT OF THE INVENTION

It is therefore an object of the present invention to provide a preheating apparatus, with which the aforesaid disadvantages can be overcome or at least minimised and/or which provides a useful alternative to known methods and/or systems.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a preheating apparatus for preheating material before it enters a furnace, the apparatus comprising a cavity for receiving the material and said cavity being defined at least partially by permeable side walls through which gas can pass from a gas inlet, through the material in the cavity and out of the apparatus via a gas outlet.

The gas that passes into the apparatus may be relatively very hot gas, so that as the gas passes through the material in the cavity, the material is heated, where after the cooled gas passes out of the apparatus. A feed bin may be provided, which may have a bin outlet which may be in communication with the cavity via a cavity inlet defined by an upper end of the apparatus, for allowing the material to pass from the bin to the cavity. The feed bin outlet may also serve as a seal to seal the open upper end of the apparatus.

The gas inlet may be provided at a first inlet side of the apparatus and the gas outlet may be provided at on opposite second outlet side.

The permeable side walls may include a first permeable side wall at the first inlet side of the apparatus and a second permeable side wall at a second outlet side of the apparatus, the arrangement may be such that the gas flows from the gas inlet at the first inlet side, through the first permeable wall, through the cavity, which is filled with material, through the second permeable wall and out of the apparatus via the gas outlet at the second side.

The permeable walls may each include a plurality of planar bodies located adjacent one another and being at least partially spaced apart from one another.

The bodies may be arranged substantially parallel relative to one another. The hot gas provided to the apparatus to pass through the material in the cavity may be heated to the applicable temperature for the process for which the preheating apparatus is used. The hot gas may be provided to the apparatus from any known energy source or directly as heated gas from the furnace.

The material to be heated and provided to the apparatus within the cavity may be furnace charge consisting of any suitably required material.

According to a second aspect of the invention there is provided an arrangement of multiple preheating apparatuses according to the first aspect of the invention for receiving material to be preheated. BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described further by way of a non-limiting example with reference to the accompanying drawing, which is a schematic sectional side view a preheating apparatus according to a preferred embodiment of the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Referring to the drawing, a preheating apparatus according to a preferred embodiment of the invention is generally designated by reference numeral 10. The preheating apparatus 10 is suitable for preheating material (not shown) before it enters a furnace (also not shown). The apparatus defines a cavity 12 therein for receiving the material to be preheated. The cavity 12 is defined by two opposing permeable side walls, a first permeable side wall 14 and a second permeable side wall 16 through which gas can pass from a gas inlet 18, through the material in the cavity 12 and out of the apparatus 10 via a gas outlet 20. The gas inlet 18 is provided at a first inlet side 30 of the apparatus 10 and the gas outlet 20 is provided at on opposite second outlet side 32 of the apparatus 10.

A feed bin 22 is also provided having a bin outlet 24 which is in communication with the cavity 12 via a cavity inlet 26 defined by an upper end 28 of the apparatus 10, for allowing the material to pass from the bin 22 to the cavity 12. The feed bin outlet 24 also serves as a seal to seal the open upper end 28 of the apparatus 10, so that gas being passed into and through the apparatus 10 cannot escape from the open upper end of the apparatus 10, but is forced to pass out of the apparatus via the gas outlet 20.

The first permeable side walls 14 is located at the first inlet side 30 of the apparatus 10 and the second permeable side wall 16 is located at the second outlet side 32 of the apparatus 10. The arrangement is such that the gas flows from the gas inlet 18 at the first inlet side 30, through the first permeable wall 14, through the cavity 12, which is filled with material, through the second permeable wall 16 and out of the apparatus 10 via the gas outlet 20 at the second side 32 (as indicated by the arrows shown in the drawing). While the hot gas flows through the material in the cavity 12, the material is heated.

The permeable walls 14 and 16 each include a plurality of planar bodies 34 located adjacent one another and being at least partially spaced apart from one another. The bodies 34 are arranged substantially parallel relative to one another.

The material to be heated and provided to the apparatus 10 within the cavity 12 is furnace charge (feed) consisting of any suitably required material.

The gas that passes into the apparatus 10 is relatively very hot gas, so that as the gas passes through the material in the cavity 12, the material is heated, where after the cooled gas passes out of the apparatus 10. This hot gas is heated to the applicable temperature for the process and material for which the preheating apparatus 10 is used. A typical example is 600°C, however, it could be much higher and even lower, depending on the application. The hot gas may be provided to the apparatus 10 from any known energy source. However, it is foreseen that since a closed submerged arc furnace (SAF) produces a furnace gas containing CO and H2 of approximately 80%, this gas can be used (or flared) as a fuel for plant heating and electrical power generation. The chemical energy in a portion of this gas, about one third, can be used to pre-heat the raw material feed to the SAF in the preheating apparatus of the invention, integrated into the SAF feed system. Using the preheating apparatus the raw material feed to the SAF can be heated to approximately 550°C or whatever temperature is required. The preheating eliminates all moisture from the feed as well as some of the volatiles contained in the feed materials. Depending on the feed and alloy chemistry by pre-heating the SAF power consumption can be reduced in the furnace.

It will be appreciated that variations in detail are possible with a preheating apparatus according to the invention without departing from the scope of the appended claims.