Process and rotary kiln for the decarburization of fine-grained, carbonaceous iron

Description

[0001] Method and rotary kiln for decarburizing fine-grained, carbonaceous iron. In the decarburization of pig iron without which e.g., for tempering cast iron objects and also used in the old annealing process, the Cast iron in chambers together with an oxygen-releasing material, for example with hematite iron ore, by means of external heat supply glowed.

[0002] However, this method is unsuitable if it is a matter of rapid decarburization of finely layered carbonaceous iron or such iron alloys are involved, partly because the annealing time is too long due to the poor thermal conductivity of the material, and partly because the process It is discontinuous and therefore expensive and uneconomical. To make the decarburization process economically viable, it is necessary to... to introduce the required quantity of worms in an approximately even distribution within the material and to continue the process continuously. and to make it as automatic as possible so that operating costs are kept low. For this to work, the material must be kept in motion during heating. To achieve rapid decarburization, it is advantageous, as practical experiments have shown, to keep the temperature as high as possible, e.g. For example, in our case: approximately rooo°C or higher. At this temperature, however, it is difficult to prevent the mixture of finely layered Iron sintered together with oxygen-releasing material, e.g., iron ore. or adheres to the oven walls, making the continuous movement of the goods difficult or even impossible.

[0003] According to the invention, the carbonization is not carried out by adding oxygen-releasing substances to the material, but by supplying gaseous, free or bound oxygen. This eliminates the need to mix the (iron pieces) with other, more easily sintering additives. and the temperature can be kept higher without risk of operational disruptions. Another advantage of the new method is in that the product remains free of acid-containing additives and any impurities that may be introduced with them, so that a completely pure, A metallic product is obtained.

[0004] According to the invention, oxygen-containing gas, e.g. air, is supplied above the constantly moving material, so that decarburization occurs. This also causes the CO gas escaping from the material to be burned, along with any excess. A gas ratio of CO:CO is used in the... The reaction zone was maintained so that no significant oxidation of the iron took place.

[0005] Free oxygen should not come into direct contact with the iron, but should first be converted into carbonic acid. Decarburization proceeds mainly according to the reaction scheme C - h CO, -> 2 CO. Carbonic acid also has a strong oxidizing effect on iron. if the decarburization gas does not simultaneously have a sufficient CO content.

[0006] In order to prevent a gas consisting of CO and CO₂ from having a decarburizing, but not an oxidizing, effect on unalloyed iron, the CO₂ should be The CO2 content at 100°C should not fall below approximately 25%; if the gas is diluted with other gases, the CO2 content must be kept even lower. earth.

[0007] Since decarburization is an endothermic process, heat must be supplied. However, experiments have shown that it is possible to carry out decarburization without heat. to make the entire system exothermic by supplying free oxygen, for example by blowing in air. However, the oxygen must be in such a way It is supplied in such a way that it mixes with the escaping CO-rich reaction gas and is converted into CO2 by combustion of the same. before it can reach the iron. The reaction proceeds according to the equation: C -I- O2 =CO2. The heat generated according to this The equation is large enough to carry out the procedure if heat losses are low due to good thermal insulation and other measures. be held.

[0008] However, if the oxidation of the carbon is carried out using iron ore, which must be reduced at the same time, the process proceeds endothermic, which means a relatively large heat input from the outside is required. 'This is one of the reasons why high-temperature carbonization on This method can only be carried out with great difficulty or not at all. Normally, one should strive to remove the reaction gas before to burn completely upon exiting the carbonization furnace. However, if the heat generation is insufficient to heat the material to the reaction temperature... and if the amount of gas is sufficient for the decarburization of the iron pieces, it is possible to increase its size by supplying combustible gas, e.g. blast furnace gas, from the outside. Any potential lack of heat can also be remedied by electrical heat generation, with the heat being supplied primarily to the zone. should be fed to the final reaction because it is difficult to maintain the required temperature there without causing excessive heat. An oxidizing oven atmosphere is created.

[0009] An additional heat input is particularly necessary when ordinary, soft scrap metal with, for example, 0.25 °C is largely to be decarburized because the carbon content of such a feed is insufficient for the required heat generation, even under particularly favorable conditions. Under certain circumstances, this is insufficient. To accelerate the reaction, it may be advantageous to use hydrogen either in free form or as water vapor. to supply the good.

[0010] To carry out the method according to the invention, various types of furnaces can be used, e.g. a multi-level furnace, such as those used for the The roasting of pyrite is known. The finely granulated pig iron, etc., is continuously transported downwards and, by means of an ascending [context missing], [context missing]. The process involves heating hot decarburization gases, the composition of which is controlled according to the invention. In the simplest way, the process is described in a long, The process was carried out using a horizontal rotary tube. It was found that decarburization was possible at temperatures above 100°C, even at 1200°C. C, without the pieces tending to stick together. The continuous movement of the goods through the oven is smooth, and as a result The rotation of the oven ensures very effective mixing of the contents. This results in complete heating of the oven contents without dangerous risks. Superheating is achieved even if the heating is only carried out by combustion of the reaction gas above the feed point.

[0011] In the drawing, Fig. 1 shows a rotary kiln designed for the decarburization of fine-grained iron or such iron alloys, which is heated by the combustion of the reaction gas and, if necessary, an additional fuel supplied from the outside, e.g., blast furnace gas. Fig. z is a cross-section through the furnace along line AA and Fig. 3 along line BB in Fig. i. The material is fed through the opening. i is introduced and moves through the oven, which is rotated at such a speed that a rapid mixing of the material takes place. Before the pieces of iron flow continuously out through the opening at the opposite end of the furnace, they must pass through a sluice-like section. of a known type, which only allows the iron, but not the furnace gases, to pass through. By cooling the lock from the outside with water or Air can dissolve iron They are cooled before leaving the system, thus preventing any unwanted oxidation. The required Combustion air is supplied through pipe 3; the combusted reaction gases pass through the furnace in the opposite direction and escape. then through opening i. In a similar way to air, an additional fuel, e.g. oil, blast furnace gas or coal powder, can also be introduced.

[0012] It has proven difficult to achieve effective heat transfer from the combustion gases to the material without the furnace to form too long a structure. To facilitate and improve heat transfer, a number of transversely positioned partitions q can be advantageously used. These transverse walls are provided with holes 5 for the flow of gases and so that the gas is forced to change its direction of movement in the oven. This ensures effective heat transfer. Gases to the '«bands, which transfer the heat to the material that is constantly in contact with other @t-?andteilen:.

[0013] The mixing of the iron pieces during the rotation of the furnace is indeed necessary for a uniform, but not excessively high, heating of the Feeding is favorable, but can have the disadvantage that mixing also occurs in the axial direction, so that already decarburized Iron particles migrate back towards the inlet end of the furnace, while other particles, not sufficiently decarburized, pass through the furnace. This can reduce the oven's performance. To avoid this, it may be advisable to use a majority of openings. The transverse partitions 6 are also to be installed in the reaction zone to control the movement of the cut zn, thus preventing mixing. can be bent forward in an axial direction.

[0014] The combustion air is introduced into the oven above the material through nozzles: 7. It is distributed along the length of the oven in such numbers that The oxygen supply at no point can become so great that oxidation of the material occurs.

[0015] The intended additional fuel can be introduced through the tube 3. For economic reasons, the piece size of the iron is of great importance. The decarburization rate increases particularly rapidly with a reduction in particle size. Ice has proven effective in experiments. This shows that a satisfactory particle size can be achieved by granulating molten iron through rapid cooling, e.g. in water. It can be done. It is desirable that the material has an average particle size of such a size that it requires a sieve with 5 mm holes. This can happen.

[0016] Although decarburization according to the invention is mainly to be carried out using gaseous oxygen, it can also be carried out using Oxygen in solid form, e.g., using iron oxides, can be decarburized simultaneously. It can also be advantageous to add some iron ore to the iron. to add, but only in such quantities that a relatively rapid reduction of the oxide is possible. The reduction acts on the The main part of the process, involving the supply of oxygen in gaseous form, is not disruptive.

[0017] The process is not limited to the decarburization of pig iron, but can also be advantageously used for the decarburization of other materials, low-carbon, finely divided iron, e.g. steel granules, turning chips, sponge iron, etc., can be used.

[0018] It is of particular importance that the decarburization according to the invention not only takes place very quickly, but also goes much further It can be decarburized more effectively than with any of the known decarburization methods. It has been found that heating small Rapid decarburization of pig iron pieces at 1200°C down to below 0.0i % C is possible if the ratio of CO2 and CO is adjusted accordingly. that only the carbon, but not the iron, is oxidized. This occurs if the gas is diluted with hydrogen or nitrogen, for example, or if the decarburization process... At reduced gas pressure, the carbon content can be reduced even further. An increase in temperature to approximately 1200°C This promotes decarburization, but the use of even higher temperatures does not appear to offer any further advantages.

Claims

[0019] PATENT INT.I. Process for the decarburization of finely granular carbonaceous iron or such iron alloys in continuous process by supplying first-charring gases, characterized in that above the constantly moving So much oxygen-containing gas, e.g., air, is supplied to the material that decarburization occurs and the excess is used to remove the material from the... The CO gas escaping from the working material is burned, whereby a CO:CO2 gas ratio is maintained in the reaction zone such that a significant oxidation of the iron is avoided.

2. Method according to claim i, characterized in that the decarburization is carried out in an approximately The process is carried out in a rotary tube furnace inclined against the horizontal, through which the material passes lengthwise with constant mixing.

3. Method according to claim i and 2, characterized in that, in order to influence the composition and temperature of the reaction gas in In the decarburization zone, an additional fuel, e.g., blast furnace gas, hydrogen, coal powder, or fuel oil, is introduced into the furnace. q.. Method according to Claims i to 3, characterized in that the decarburized material is cooled in the absence of air before leaving the furnace.

5. Method according to claims 1 to 4, characterized in that the reaction gas is introduced by means of a suitable airlock arrangement at the The emptying end of the oven is prevented from escaping and moves in the opposite direction to the movement of the material. Preheating of the material by the The feed opening is withdrawn.

6. Method according to claims 1 to 5, characterized in that the carbon content of the material is so high It is chosen that the required heat is generated entirely or predominantly by the combustion of the carbon contained in the 'good'.

7. D-rotary tube furnace for carrying out the method according to claims 1 to 6, characterized in that approximately centrally through the charging opening (i) A pipe (3), preferably equipped with several nozzles (7), is routed above the goods for the supply of oxygen-containing gas, e.g., air. Rotary kiln according to claim 7, characterized in that a pipe (8) for the supply of Additional fuel, e.g. blast furnace gas, water, oil, coal powder, has been introduced.