US2754197A - Method and a rotary kiln for the manufacture of sponge iron - Google Patents

Description

July 10, 1956 F. o. WIENERT 2,754,197 METHOD AND A ROTARY KILN FOR THE MANUFACTURE OF SPONGE IRON Filed Sept. 26, 1952 4 Q T r -;-WEF Q m 1 T ai I l 5 5 I U Ma Q E k \Q-\ IN VEN TOR Q? BY m i y ATTORNEY Q United States Patent NIETHOD AND A ROTARY KILN FOR THE MANUFACTURE OF SPONGE IRON Fritz Otto Wienert, Brooklyn, N. Y. Application September 26, 1952, Serial No. 311,593

6 Claims. (CI. 75-36) This invention relates to the reduction of iron oxides by solid fuel.

It is well known to produce sponge iron from mixtures of iron ore and solid carbon containing reduction materials, such as coal, coke, anthracite. As the reduction process consumes heat, the mixed raw material has been heated by means of a flame produced by the combustion of gas, liquid fuel, or also of pulverised fuel. In order to obtain a satisfactory reaction speed, it is necessary to heat the charge in the kiln to a temperature above 900 C., so that a substantially higher flame temperature is required.

With such methods the following difficulties have been observed. As a result of the high temperature of the flame, accretions were formed at the lining of the kiln, particularly where the flame impinges upon the lining. Moreover, conglomerations and lumps were formed in the bed, which block the discharge openings, and which could be utilised economically, if at all, only with great difiiculties, as they contain not yet reduced oxides and slag. In order to remove the accretions on the furnace wall, it was necessary to interrupt the operation, and the laborious removal of the accretions entails the danger of damaging the lining.

It has been proposed already to avoid a local overheating by carefully maintaining a favourable shape and size of the flame. The results were however unsatisfactory, and the output of such rotary kilns was small.

Also the use of coal with a high proportion of volatile matter has been tried in order to save expenses connected with the preparation of coke or char. However, accretions of tar at the charging end of the rotary kiln caused disturbances, and the volatile matter could only be utilised partly within the rotary kiln, although combustion air has been drawn into the kiln through tubes from the atmosphere. If a greater quantity of air has been drawn in as a result of the required depression within the rotary kiln, then again accretions occurred and local overheating resulted. Moreover, due to the depression in the kiln also false air has been drawn in through the discharge end of the rotary kiln which resulted in a re-oxidation and accretion formation. An effective control of the sucked in air proved to be impossible, so that eventually the use of coal with volatile components has been discontinued.

With another known method coke has been used for the reduction process and air has been drawn in through a number of tubes which were equipped with slide valves and distributed over the length of the kiln. In view of the fact that with a change of the adjustment of each single valve the depression in the kiln was influenced and with it also the quantity of air delivered through each of the other valves, an efiective control of the air and with it of the temperature was very diflicult to obtain. A good tightening at the discharge end of the kiln, which is required owing to the high depression within the kiln, can be maintained for a length of time only with greatest difiiculties. If the seal begins to leak, then the above mentioned disturbances, such as re-oxidation and accretions, occur again also with this method.

The method according to the invention overcomes the above mentioned difiiculties. It is characterised in that the air, required for the combustion of the volatile matter from the reducing material and of the solid carbon, as well as for the oxidation of the carbon monoxide which develops in the bed of the kiln, is introduced into the kiln under pressure. A number of tubes for the supply of air are arranged in spaced relationship along the kiln and lead into its interior, advantageously up to its axis, and each tube has its own control device, e. g. a slide valve or a throttle flap valve, and it is connected with a source of compressed air. The tubes are so distributed and the quantity of delivered air is so determined that a combustion of the gases occur and a high temperature in the greater part of the kiln is produced which however remains below the sintering temperature.

It has proved to be advantageous to blow in the air in the direction of the rotary axis of the kiln.

Another method is known in which reducing gas is introduced into a rotary kiln and air is blown into it to such an extent only that the atmosphere remains reducing iron oxides. However, the capacity of a rotary kiln is low if such reactions between bed and atmosphere have to take place.

With the new method and rotary kiln, reducing gases from outside sources are not used and sufiicient air is introduced, as mentioned above, to burn all or at least most of the combustible gases in the atmosphere over the bed. The reduction to iron within the bed is fast because the high temperature causes carbon dioxide and solid carbon to quickly generate monoxide which partly reduces iron oxide in the bed and partly burns over the bed.

The invention will now be explained in more detail with reference to the accompanying drawings, which represent by way of example some embodiments of the invention.

Figure 1 is a longitudinal section of a kiln with one form of air supply. Compressed air is delivered by means of a stationary blower 1 which is connected by means of a sllding connection 2 with a rotary tube 3 of the rotary kiln 4. The latter tube 3 is centrally disposed and fixed preferably to the loading end of the kiln 4. From this tube 3 branch oif, behind the charging chute 5, preferably two or more tubes 6 and 7, which lead outwards and extend along the outer face of the kiln. Branch pipes 8 with control devices 9 (see Figure 3) lead back into the axis of the kiln.

The Figure 2 is a part similar view of a kiln having another arrangement for the production of compressed air which has proved to be very satisfactory for the present purpose. At the outside of the kiln 4 one or preferably a number of blowers 10 are mounted. The electric driving motors 11 receive the driving current over sliprings. The blowers force the air into the distributing tubes 6 as also shown in Figure 1.

The Figure 3 is a cross sectional view of a kiln.

It has been found that a pressure in the kiln above atmospheric pressure, particularly at the discharge end of the rotary kiln, prevents any re-oxidation of the finished sponge iron and facilitates its discharge into the succeeding cooler. Such an overpressure can be obtained by a corresponding adjustment of the draught in the chimney 12.

The use of compressed air has the additional advantage that a smaller number of tubes with a smaller diameter is required, and that the discharge of the air in an axial direction with high speed renders a good distribution without the danger of local overheating or sintering. Moreover, the air, moving at high speed, cools effectively 3 the discharge tubes so that they are subjected to a lesser degree to wear in the case they are not made of alloys resistive against corrosion.

In view of the fact that the greatest part of the required heat is produced by the compressed air, it is possible to use for the kiln a small burner 13 with the result that, any local overheating caused by the, burner is prevented. It has been found that the burner 13 can be operated with incomplete combustion of its fuel, i. e. With a small heat production, and that in this way, similarly as by means of an overpressure in the kiln, re-oxidation of the iron during its discharge is avoided. It was an unexpected result that this beneficial effect could also be obtained .by feeding the burner with an excess of air or. even with air only, provided that a larger quantity of solid reducing material is present in the discharge.

The discharged material is then cooled in a manner known per se, and the sponge iron is separated from the surplus of reducing material by means of a magnet separator.

If the solid reducing material, as for instance coal,

peat, sawdust, contains a great proportion of volatile matter, it has been found advantageous to feed'it separated from the ore through one or more scoops 14 or similar devices at a suitable distance from the charging end of the rotary kiln. In this manner all volatile matter, as far as it is combustible, can be utilised for the heating of the charge.

Such a rotary kiln which, as above described, is supplied with compressed air at difierent places along its length, can be used advantageously for other purposes, e. g. for the roasting of sulfides and for the carbonisation of coal, as well as for the reduction of iron chromite ores. rutile, and the like.

What I claim is:

l. A process for producing sponge iron in a rotary kiln which comprises introducing into the kiln oxydic iron bearing material and carbonaceous matter, and forming a mixture thereof, the carbon content of said matter being in excess of the stoichiometric quantity required to reduce the iron completely, introducing oxygen containing gas under pressure in amount sufficient to convert carbon monoxide generated in the reduction operation to carbon dioxide and to combust other volatile products from the carbonaceous matter, the oxygen being introduced into said kiln at a plurality of points generally along the long axis of the kiln and flowing generally.

countercurrently to the normal flow of the generated gases.

2. Process according to claim 1 wherein the quantity of air introduced at each point is controlled so that an oxidizing atmosphere is maintained in the kiln.

3. Process according to claim 1 wherein the pressure of the gaseous atmosphere in the kiln is above atmospheric pressure.

4. Process according to claim 1 wherein the carbonaceous matter is introduced into the kiln separately from a the oxydic iron bearing material.

5. Apparatus suitable for producing sponge iron from iron oxides comprising in combination a rotary kiln, a stationary blower positioned apart from said kilnand operably connected to a rotatable air conducting tube axially disposed in and near the feed end of said kiln, said air conducting tube being provided with at least one branch leading out to and along the outer surface of the rotary kiln, said branch having a plurality of vents extending into said kiln with discharge openings axially positioned in said kiln and directed away from the feed end of the kiln.

V 6. Apparatus suitable for producing sponge iron from iron oxides comprising in combination a rotary kiln and a number of air blowers mounted on the outside of said kiln, said blowers having at least one vent extending into said kiln with a discharge opening axially positioned in said kiln and directed away from the feed end of the kiln.

References Cited in the file'of this patent UNITED STATES PATENTS 1,760,078 Newkirk et al May 27, 1930 FOREIGN PATENTS 636,677 Great Britain May 3, 1950

Claims (1)

1. A PROCESS FOR PRODUCING SPONGE IRON IN A ROTARY KILN WHICH COMPRISES INTRODUCING INTO THE KILN OXYDIC IRON BEARING MATERIAL AND CARBONACEOUS MATTER, AND FORMING A MIXTURE THEREOF, THE CARBON CONTENT OF SAID MATTER BEING IN EXCESS OF THE STOICHIOMETRIC QUANTITY REQUIRED TO REDUCE THE IRON COMPLETELY, INTRODUCING OXYGEN CONTAINING GAS UNDER PRESSURE IN AMOUNT SUFFICIENT TO CONVERT CARBON MONOXIDE GENERATED IN THE REDUCTION OPERATION TO CARBON DIOXIDE AND TO COMBUST OTHER VOLATILE PRODUCTS FROM THE CARBONACEOUS MATTER, THE OXYGEN BEING INTRODUCED INTO SAID KILN AT A PLURALITY OF POINTS GENERALLY ALONG THE LONG AXIS OF THE KILN AND FLOWING GENERALLY COUNTERCURRENTLY TO THE NORMAL FLOW OF THE GENERATED GASES.

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