US3186830A - Melting process - Google Patents

Description

June 1, 1965 w. H. MOORE ETAL MELTING PROCESS 2 Sheets-Sheet 1 Filed May 20, 1963 FIG.

\? OX/D/Z/IVG COMBUSTION ZONE 3* REDUCING ZONE (SUPER/ EATING ZONE h d l w x INVENTORS WILL/AM h. MOORE HARRY H KESSLER June 1, 1965 w. H. MOORE ETAL 3,186,830

MELTING PROCESS Filed May 20, 1963 2 Sheets-Sheet 2 FIG. 3

PREHEATING ZONE 3/ IGNITION ZONE OXIDIZING 2 COMBUSTION zone a J REDUCING ZONE 3/ SUPERHEATING zous 1 m 13/ j w: F 4

7 I 32 INVENTORS.

WILLIAM H. MOORE Y HARRY H. KESSLER United States Patent 3,186,830 MELTTNG PRGCESS William H. Moore, 19 Viiia Road, Larchmont, N.Y., and Harry H. Kessler, 7 Dromara Road, Ciayton, Mo. Filed May 20, 1963, Ser. No. 295,259 4 Claims. (Cl. 75-43) This application is a continuation-in-part of SN. 139,- 312, filed September 19, 1961, and now abandoned.

This invention relates to metallurgical furnaces for the melting of metals and, more particularly, to a cupola or shaft type furnace for the production of cast iron and other metals conventionally melted by being brought into contact with incandescent coke and air.

An object of this invention is to provide a means of melting cast iron from a charge comprising in part reducible oxides and metal chips and shavings.

A further object is to provide a means of superheating and refining the molten metal after it has been melted.

Another object is to provide a means of utilizing all the products of combustion resulting from contact of air and coke, so as to increase fuel efficiency and decrease melting costs. A further object is to provide a furnace which can both oxidize and reduce the metallic charge so as to provide positive control on the chemistry of the molten metal.

A further object is to provide a furnace free from harmful smoke and air pollution.

A further object is to provide a means of reducing the phosphorus content of the metal during the melting operation.

Another object of this invention is to provide a means for preheating the furnace charge and a further object of this invention is to provide a means for raising the fuel portion of the charge to a temperature above its ignition temperature.

Still further objects of this invention will be apparen from the specifications and drawings which describe this invention in its preferred form and in which:

FIGURE 1 is a side elevation of one form of the apparatus of this invention;

FIGURE 2 is a side elevation of the apparatus showing diagrammatically the various zones that exist in the furnace;

FIGURE 3 is a side elevation of another form of the apparatus of this invention; and,

FIGURE 4 is a side elevation of this form showing diagrammatically the various zones that exist.

The apparatus or furnace of FIGURES 1 and 2 comprises a vertical shaft 1 having upper and lower end portions 13 and 19 respectively with a refractory or water cooled inner wall 13. A first ignition burner, coke ignition torch, or fuel ignition means 7 is located in the shaft and a generally horizontally disposed elongated receiver or forehearth 2 with an arch roof is located adjacent and in communication with the lower end portion of the shaft through the throat 2% of the furnace. A blower and a heat exchanger 4 are provided and are connected together by means of first conduit means 21 which also connects the blower to an air tuyere 8 to introduce air under pressure into the upper portion 18 of the shaft 1.

A double bell charger 3 is located at the upper end portion 18 of the shaft 1 and includes an upper bell 15 and a lower bell 16 with a chamber 14 formed therebetween. A second ignition burner or torch 6 is provided in the receiver 2 as well as tap out and slag out spouts 9 and 10 respectively for the removal of metal and slag. Second conduit means or exhaust 11 lead from the receiver 2 through the heat exchanger 1 and to the atmosphere and this servesto preheat material in the first conduit means '21. The apparatus also has a furnace bottom 12 and a door 17.

3,186,83d Patented June 1, 1965 "ice In operation, a coke bed is built up in the refractory lined shaft directly on the furnace bottom 12. The burner 7, which is self-igniting and may use gas, oil or any combustible fuel, is started and the blower 5 is also started. The burner 6 is also started, in order to ignite gases traveling from the furnace shaft into the forehearth 2. As the coke is raised above its ignition temperature the coke bed burns under the action of air supplied by the blower S and the temperature of the coke bed is raised while the products of combustion pass into the forehearth and from there, after ignition by the torch 6, they pass out through the heat exchanger or blast preheater 4, and the exhaust 11.

When the fuel bed and the forehearth have been raised to a sufiiciently high temperature, the metallic charge to be melted is charged through the upper bell 15 into the upper chamber 14 and then through the lower bell 16, while the upper bell 15 is in the closed position. This keeps the inside of the furnace under positive pressure at all times. Sufiicient coke to melt the metallic charge is charged along with the charge and a series of charges is fed into the furnace as melting proceeds. The charge and coke level is kept above the burner 7 so that the coke may be raised above its ignition temperature by the burner.

As the charge melts, molten metal and slag fall through the coke bed and run into the forehearth through the throat 2% where it collects and where the metal and the slag may be removed intermittently or continuously through the spouts 9 and 19. The metal is heated to pouring temperature by the burner 6 which ignites the combustible gases from the fuel bed. The hot exhaust gases passing through the heat exchanger 4 heat the incoming air from the blower 5, which then passes into the furnace through the tuyere opening 8.

At the end of the melt, charging is stopped and melting is continued until the fuel bed is exhausted. Any charge or bed left in the furnace is then dropped through the door 17 located at the bottom of the shaft. The roof of the forehearth is movable and can be opened for direct access to the forehearth when desired.

The conventional foundry cupola has always been subject to a number of drawbacks, despite its simplicity of operation and its widespread industrial use over the years. In the conventional cupola the fuel or coke is combusted in a bed immediately above the air-entry ports, or tuyeres. The products of combustion pass upwards through the cupola where they preheat and melt the descending metallic charge and raise the descending fuel charge to a temperature above its ignition point. 7

It has been shown metallurgically, that the distribution of air in the cupola can be modified by many factors, particularly tuyeres and windbelts and over the years many Letters Patent relating to these phases of cupola design have been issued.

As the products of combustion ascend up the shaft a great deal of the heat produced is wasted by exhaust in the upper portions of the shaft. Some attempts have been made, with limited success, to utilize the wasted heat by using it to preheat the blast, but under the best circumstances a cupola furnace is not more than 50% eflicient.

A great deal of latent heat in the form of combustible CO gas and actual sensible heat is lost from the cupola gases that escape to the atmosphere.

In the ordinary cupola, as distinct from the blast furnace, it is not possible to accomplish any major reduction of metallic oxides contained in the furnace charge. This is because the need for efficient operation and high tapped metal temperatures precludes a sufficient quantity of carbon-monoxide in the products of combustion to allow reduction. 7

Furthermore, immediately after melting the molten droplets fall down through the coke bed and pass into an oxidizing zone where oxidation of the metallics occurs to a greater or lesser extent, depending upon the height of penetration of free oxygen in the fuel bed.

In the furnace of this invention combustion is accomplished in a different manner. Oxygen in the air enters at a point above or in theupper region of the fuel bed and metallic charge and when it reaches the coke which has been raised to above its ignition temperature by the burner 7, it causes combustion. The products of combustion pass downwards through the fuel bed. The metallic charge melts in a zone where free, oxygen occurs and some oxidation takes place, but the molten droplets then pass down through a reducing zone where all metallic oxides have the opportunity of being reduced.

The molten charge and the products of combustion then pass through the throat 20 of the furnace into the forehearth. At this point the second burner 6 ignites carbon-monoxide in the exhaust gases, thereby providing heat units for superheating the metal in the forehearth. This results in a degree of efi'iciency of combustion not possible in conventional cupola furnaces.

FIGURE 2 illustrates generally the metallurgical zones that are important in one form of this furnace. The ignition zone represents the zone of influence of the burner 7 which heats the coke to above its'ignition temperature. Below this is the oxidizing zone where free oxygen exists and where combustion takes place. The extent of this'varies according to the amount and velocity of the air delivered through the upper tuyeres and according to the combustion characteristics and size characteristics of the coke in the burner. The reducing zone below the oxidizing zone is a function of height and coke reacticity and may be varied by adjusting the initial position of the pre-ignition burner. The superheating zone is in the forehearth where extra heating is supplied by means of the burner 6, or electrical or other means if desired.

In. general, normal operation of this furnace tends to give an extremely high carbon pickup and a higher than normal silicon and manganese loss. The silicon and manganese that is oxidized during initial melting in the oxidizing zone may be reduced back to metallics by having a sufiiciently extensive reducing zone in the lower half of the furnace. The relative amount of oxidation and reduction can be controlled by varying the position of the coke ignition burner. As little or no ignition takes place above this burner, lowering it produces a confined reducing zone. This will lower carbon pickup, but will tend to increase silicon and manganese loss. Raising the position of this burner will give a broaderreducing zone, will tend to give increased carbon pickup and less silicon and manganese loss. By having the reducing zone sufiiciently broad, it is possible to charge a proportion of iron, manganese and chromium and/or chromium oxides or ore into the charge and effectively convert them to molten metal-thus, the furnace of this invention may be used, in part, like a blast furnace.

The apparatus or furnace of the present invention illustrated in FIGURES 3 and 4 comprises a vertical shaft 31 having upper and lower end portions 48 and. 49 respeotively, with a refractory or water cooled inner wall .43. A generally horizontally disposed elongated receiver or forehearth 32,;with an arch roof,.is located adjacent and in communication with the lower end portion of the shaft through the throat 50 of the furnace; A blower 35 and a heat exchanger 34 are provided and are connected together by means of first conduit means I51 which also connects the blower to an air windbelt 37 and a plu-. 'rality of tuyere openings 38 arranged at various heights and with each tuyere opening individually controllable by valves 54 to introduce air under pressure into different portions of what may still be referred to as the upper portion of the shaft even though not located atthe ex: trerne upperend, In otherwords, theylaare located at some point above the bottom or throat of the shaft so that the downdraft principle is employed.

A second conduit means 52 fitted with a control valve 53 allows some of the air from a tuyere 38 to pass upward through the furnace charge and then by way of the conduit to the elongated forehearth 32.

A double bell charger 33 is located at the upper end portion 48 of the shaft 31 and includes an upper bell and a lower bell 46 with a chamber 44 formed therebetween. An ignition burner or torch 36 is provided in the receiver 32 as well as tap out and slag out spouts 39 and 40 respectively for the removal of metal and slag. Third conduit means or exhaust 41 lead from the receiver 32 through the heat exchanger 34 and to the atmosphere and this serves to preheat material in the first conduit means 51. The apparatus also has a furnace bottom 42 and a door 47.

The operation of the furnace of FIGURE 3 is quite similar to FIGURE 1, however, it will be described. A coke bed is built up in the refractory lined shaft directly on the furnace bottom 4-2. The fuel bed is ignited in the area of the tuyeres by convenient means (not shown) such as a burner like 7 in FIGURE 1, and the blower 35 is started. The burner 36 is started in order to ignite gases traveling from the furnace shaft into the forehearth 32. As the coke is raised above its ignition temperature by air which flows upwards through the charge and conduit 52 thecoke bed burns under the action of air supplied by -the blower 35 and the temperature of the coke bed is raised while the products of combustion pass into the forehearth and from there they pass out through the heat exchanger or blast preheater 34 and the exhaust 41.

When the fuel bed and the forehearth have been raised to a sufliciently high temperature, the metallic charge to be melted is charged through the upper bell 45 into the upper chamber 44 and then through the lower bell 46 while the upper bell 45 is in the closed position. This keeps the inside of the furnace under positive pressure at all times. Suflicient coke to melt the metallic charge is charged along with the charge and a series of charges is fed into the furnace as melting proceeds. The charge and coke level is kept above the tuyeres 38 so that the coke may be raised above its ignition temperature by the proportion of air that flows upwards.

As the charge melts, molten metal and slag fall through the coke bed and run into the forehearth through the throat where it collects and where the metal and the slag may be removed intermittently or continuously through the spouts 39 and ii). The metal is heated to pouring temperature by the burner 36 which ignites the combustible gases from the fuel bed. The hot exhaust gases passing through the heat exchanger 34 heat the incoming air from the blower 35 which then passes into the furnace through the tuyere opening 38.

At the end of the melt, charging is stopped and melting is continued until the fuel bed is exhausted; Any charge or bed left in the furnace is then dropped through the door 47 located at the bottom of the shaft. The roof of the forehearth is movable and can be opened for direct access to the forehearth when desired.

As noted, one of the main differences in the operation of the furnace of FIGURE 3 over FIGURE 1 is the manner in which the combustion of the solid fuel is achieved at the desired point.

The downdraft cupola described in this invention works on a different principle, in that melting occurs at the point of contact between the air and the fuel, as distinct from the conventional cupola, where melting occurs at a point well above the point of entry of air into the coke bed.

In the downdraft cupola, therefore, melting takes place in an area rich with free oxygen and the molten metal droplets subsequently pass through a zone where reducing conditions are prevalent.

'Itjhas been found that the furnace: of, this invention is particularly useful for the melting of charges containing small material such as borings and clippings which are normally too light to be melted in conventional cupolas, unless they are briquetted. In the furnace of this invention it is not necessary to briquet materials of this type, because they are blown down through the fuel bed where they effectively melt. Both steel turnings and cast iron borings can be melted and may constitute as much as 100% of the charge.

The forehearth used in the furnace of this invention provides a suitable opportunity not only for superheating the metal to a suitable casting temperature, but for adjusting the composition for special purposes. Thus, alloys such as copper, chrome, manganese, silicon, and the like, may be added through a suitable port opening in the forehearth or through an injection tube under the surface of the bath. This makes the melting of special compositions of all types possible. Where desired, electric are or induction means may be utilized in the superheating zone. 7 The slag composition in the cupola and in the forehearth may be varied at will so as to provide basic, neutral or acidic melting. This enables the bath to be cleansed of sulphur, phosphorous, or other impurities, if it is so desired. It is also possible to perform special treatments such as the addition of magnesium for nodularizing in the forehearth. As the atmosphere in the forehearth may be varied at will, excessive losses of volatile additives may be effectively prevented.

The furnace of this invention has allowed extremely efiicient melting with coke ratios that are quite impossible in normal cupola operation. This eificiency is the result of direct contact of the metallic charge with the products of combustion and of the additional preheating of the blast by the exhaust gases.

The revolutionary concept utilized in the furnace of this invention has allowed the use of cheaper and more abundant raw materials which cannot be used in conventional cupolas and furnaces and has allowed the production of metal to a degree of superheating not heretofore possible in conventional cupolas.

One of the difiiculties of a downdraft type of operation is maintaining the combustion at a point where the air enters the cupola. In the conventional cupola, where the draft proceeds upwards in a vertical direction, the products of combustion and the hot gases preheat the descending charges and the descending coke used for fuel. Thus, by the time the coke arrives at a zone where free oxygen is present, it is heated well above its ignition temperature. Most cokes will ignite in oxygen at a temperature which ranges from approximately 900 F. to about 1200" F. In a downdraft cupola, therefore, it is necessary to supply some means of heating the coke above its ignition temperature, so that when it reaches the tuyere area, where oxygen is introduced into the furnace, it is in a position to ignite immediately.

Failure to ignite the coke at the right place will result in the combustion zone gradually going downwards in the furnace. In the downdraft cupola of this invention we have in the first firm (FIGURES l and 2) provided an additional burner for the purpose of igniting the coke. Such a burner has certain disadvantages, in that it requires an extra fuel supply and with the high velocity of air traveling inside of the cupola, it is often difficult to keep the burner ignited. Electrical means of igniting the coke are costly.

We have conceived the idea (illustrated in FIGURE 3) that the coke may be preheated to a temperature above its ignition temperature by keeping a quantity of coke above the tuyere inlet and allowing a certain quantity of the products of combustion to pass upwards through this coke, thereby raising its temperature, so that when it finally reaches the tuyere inlet it can cornbust immediately. It will thus be seen that although some means is initially used to ignite the fuel charge that combustion can proceed without this means or in conjunction with this means.

The amount of gas which is allowed to travel upward is a function of the height of the preheating zone between the tuyeres and the point of charging and also, the temperature of the incoming air which is supplied to the furnace. Thus, where this preheating zone is large, only a relatively small quantity of gas can be caused to flow upwards. Also, Where the temperature of the incoming air is at a point not too far removed from the ignition temperature of the coke, only a small quantity of gas may be allowed to pass upwards.

The portion of gas which is used for preheating the charge and the coke fuel is taken from the furnace by means of a suitable outlet and conduit and is then passed down into the forehearth, which is adapted for superheating the metal. The flow of this gas is controlled by means of a suitable valve (23 in FIGURE 3) and may be varied from a very small amount up to approximately 50% of the total air supplied to the cupola.

Any combustible gas, such as carbon monoxide, which is contained in this portion of gas which flows upwards through the charge, is ignited in the forehearth by the secondary air which is supplied to this forehearth.

We have found that this improved arrangement allows us to use fuels which are somewhat hard to burn and have a high ignition temperature. We refer to cokes of high ignition temperature which are very dense and hard to burn.

We usually prefer to keep at least two charges of metal and coke above the tuyere inlets, so as to give sufficient time and contact of hot gases to allow adequate preheating for ignition.

In the total air and gas flow system of the downdraft cupola the volume of gases which enter the cupola at the tuyeres is considerably increased, due to an increase in temperature. This means that the volume of exhaust gases which must leave the furnaces is considerably greater than the volume of air which enters the furnace. Because of this fact, we are able to bleed off a portion of these exhaust gases in our new and preferred arrangement, without materially altering the downward flow of air and gas within the furnace, necessary for melting under the downdraft principle.

In terms of the volume of air which enters the furnace at the tuyeres, we find We may bleed as much as 50% of the gases up through the charge and out by way of the upper conduit, although we seldom divert more than 25% of the total air supplied for the purpose of preheating. In any case, the amount is strictly controllable by means of the valve in the exhaust conduit. By opening and closing this valve, the amount of gas passing upwards through the char e may be varied in such a manner as to maintain suiiicient combustion in the tuyere area related to the type of fuel being used and the temperature of the inlet air.

By preheating the coke in this manner sufiiciently to raise it to the temperature of the incoming air, so that immediate combustion will take place, the height of the oxidizing and reducing zones shown in FIGURE 4 may be varied by varying the point at which the air for combustion enters the cupola. Thus, if a high tuyere is used, combustion takes place higher up and the subsequent reducing zone after combustion, which exists below the oxidizing zone, becomes more extended; conversely, by utilizing a lower tuyere opening the preheating zone is increased and the reducing Zone, which occurs below the oxidizing zone, is reduced. This gives extreme flexibility in the chemical control of the product.

As an example of how a change in the tuyere height location and consequently the location and extent of the oxidizing and reducing zones is varied, a melt was conducted in this furnace using the upper tuyere with the lower tuyeres cut off. A test bar was poured from this melt and shown to have the fol-lowing chemical analysis:

At some point during the heat the upper tuyere opening was closed and the lower tuyere opening was opened. This resulted in a reduced zone below the tuyeres and a second test bar was cast and analyzed. The results were as follows:

' Percent Total carbon 3.40

Silicon 1.50 Manganese .52 Sulphur .06 Phosphorus .12

This change in combustion zone had the effect of lowering the carbon content, slightly increasing the silicon loss, and very markedly influencing the phosphorus content of the metal. This is illustrative of the effect the point of ignition has on this type of operation and is one of the important features of this invention which in both forms depends on ignition at a defined point within the stack.

We have found that the secondary burner 6 in FIG- URE 1 and 36 in FIGURE 3 is desirable but by no means essential to this invention. This burner may be replaced by any air supply which is sufficient to combust the carbon monoxide in the exhaust gases that pass into the forehearth, either by means of the throat at the lower extremity of the stack, or by means of the conduit 53 in the second form of this invention.

It is desirable to have a secondary burner which can supply additional heat units only for purposes of extreme V heating of the metal, or else for heating up the furnace chamber or forehearth before operation, so that all combustible gases which subsequently enter the forehearth will become readily combusted.

In the actual running of this furnace we usually start off supplying additional fuel at the burners 6 and 36, but when once the furnace is in full operation, we often cut off the second supply and allow only additional air to enter the forehearth for the purpose of combustion and full utilization of the latent heat available in :the exhaust gases.

While this invention has been described in its preferred embodiment with a certain degree of particularly, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. The method of continuously producing cast iron in a substantially vertical shaft furnace having t'uyeres at the upper end portion and a conduit at the lower end portion leading to a metal receiver comprising the steps of introducing a bed of solid lump fuel to occupy the lower portion of the shaft furnace below said tuyeres, introducing air for combustion at said tuyeres, introducing a series of metal-solid lump fuel charges at said upper end portion of the shaft furnace, igniting said solid lump fuel at an upper portion of the shaft furnace and said air and said solid lump fuel producing a combustion zone at and below said tuyeres which produces hot gases substantially all of which pass downward through the shaft furnace, said combustion zone being rich in oxygen to produce an oxidizing zone and said downward how of gases producing a reducing zone containing substantially no free oxygen at a point in the shaft furnace below said combustion zone, said metal charge melting in said oxidizing zone and thereafter falling through said reducing zone and then passing through said conduit into said metal receiver.

2. The method as claimed in claim 1 wherein the relative extent of the oxidizing and reducing zones is varied by varying the height of the bed of solid lump fuel in the shaft furnace.

3. The method as claimed in claim 1 wherein the air introduced for combustion is preheated close to the ignition temperature of the charge.

4. The method as claimed in claim 1 wherein a portion of the hot gases are divertedupwardly through a metalsolid lump fuel charge approaching the combustion zone, to preheat the charge toward its ignition temperature.

References Cited by the Examiner UNITED STATES PATENTS 482,213 9/92 Wainwright 7 5-41 X 1,627,536 5/27 Vial 7543 1,751,185 3/30 Wust 7543 X 2,618,548 11/52 Drake 7543 2,788,964 4/57 Schnyder 26625 2,997,288 8/61 Schwecheimer 266-29 X 3,008,819 11/61 Schmid 7543 DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.

Claims (1)

1. THE METHOD OF CONTINUOUSLY PRODUCING CAST IRON IN A SUBSTANTIALLY VERTICAL SHAFT FURNACE HAVING TUYERES AT THE UPPER END PORTION AND A CONDUIT AT THE LOWER END PORTION LEADING TO A METAL RECEIVER COMPRISING THE STEPS OF INTRODUCING A BED OF SOLID LUMP FUEL TO OCCUPY THE LOWER PORTION OF THE SHAFT FURNACE BELOW SAID TUYERES INTRODUCING AIR FOR COMBUSTION AT SAID TUYERES, INTRODUCING A SERIES OF METAL-SOLID LUMP FUEL CHARGES AT SAID UPPER END PORTION OF THE SHAFT FURNACE, IGNITING SAID SOLID LUMP FUEL AT AN UPPER PORTION OF THE SHAFT FURNACE AND SAID AIR AND SAID SOLID LUMP FUEL PRODUCING A COMBUSTION ZONE AT AND BELOW SAID TUYERES WHICH PRODUCES HOT GASES SUBTANTIALLY ALL OF WHICH PASS DOWNWARD THROUGH THE SHAFT FURNACE, SAID COMBUSTION ZONES BEING RICH IN OXYGEN TO PRODUCE AN OXIDIZING ZONE AND SAID DOWNWARD FLOW OF GASES PRODUCING A REDUCING ZONE CONTAINING SUBSTANTIALLY NO FREE OXYGEN AT A POINT IN THE SHAFT FURNACE BELOW SAID COMBUSTION ZONE, SAID METAL CHARGE MELTING IN SAID OXIDIZING ZONE AND THEREAFTER FALLING THROUGH SAID REDUCING ZONE AND THEN PASSING THROUGH SAID CONDUIT INTO SAID METAL RECEIVER.

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