DE2120598C3 - Process and device for the reduction of powdery metal oxides stored in layers on sieve floors - Google Patents

Description

The invention relates to a method and a device for reducing powdery, in Layers of metal oxides, in particular tungsten trioxide, stored on the sieve bottom in a continuous process Process by means of hydrogen supplied in countercurrent.

In addition to the extraction of tungsten powder in discontinuous ovens, push-through ovens have long been known in which the initially in oxidic Form present metal powder in so-called boats, mostly broken out in thin layers, the furnace happen. The reduction is done by hydrogen, which in turn is directed over the property, and / was in such an excess that the water produced in the reduction is carried away in sufficient quantities. The degree to which that happens is of

• i decisive influence on the completeness of the reduction. Please refer to the publication in the magazine "Metall" 23rd year. Issue 4, page 314 "Gas reactions and structural features of throughput ovens" by Mobius and Krall pointed out. This means that the

H) Relation that the filling height of the boat is rather limited, in that the hydrogen flowing away over the filling is that in the depth of the layer resulting reduction water can only insufficiently lead away. In order to counteract this,

known that aim at the hydrogen to forward me from below to the production goods, in which you fill this onto fine-meshed sieves and / wipe the underside of the sieve and the bottom of the boat leaves a gap. But it turns out that there too

2 (i only achieved partial success because of the hydrogen between the sieve and the boat bottom flows more slowly than above the bed. For a quantitative reduction In any case, only small dump heights of no more than 5 to 10 mm are permitted. Given

j-> production volume leads to large boats and thus correspondingly large furnace units. Attempts have been made to limit these furnace sizes. Shuttles with several storage levels on top of each other to arrange. This measure alone has only

ι »limited effect for the reason set out above. Indeed, with a horizontal flow of hydrogen it is hardly possible for all bulk containers to have a uniform gas flow to subjugate.

It has now been found that the disadvantages of

η known methods can thereby be avoided. that the

Guiding the shuttle in the vertical direction downwards

takes place and this by a reducing gas stream in flow in the opposite direction upwards.

In this case, you can have any number

from the sieve bottom one on top of the other, since always the whole gas flow is uniformly passed through all layers. In this way, each oxide particle becomes uniform regardless of its location from the reducing gas flows around, with the characteristics of the so-called

■ r. static bed in the sense of the treatise "The Theory of the Fluidized Bed" by C. T hο r r e, Austrian engineering newspaper 7th year, page 159 for Application. Experiments have shown that with such an arrangement Rcsaucrstoffgchallc of

w 4 ppm and less cr can be achieved, while with the Method 20 to 30 ppm mentioned at the outset can be achieved at best.

The arrangement of overlapping sieve bottoms with the same layer height in each case, the flow

ίΐ resistance of the hydrogen through the layers in wearable limits and the same from layer to layer. In the case of tungsten oxide, the individual Layer heights between 5 and 10 cm were chosen, the ratios of the static bed being observed can. If the individual layer heights are increased, sliding surfaces can form, whereby the Powder mass gets into whirling motion, which often results in an undesirable change in grain size. One used to perform the procedure Device is illustrated by Fig. I while F i g. 2 shows enlarged the sieves combined in sleeves into groups.

A vertical pipe 10 is outside of a

Heater, /, B. an electric furnace 11, heated, This furnace is equipped with several separately adjustable TemperaiursHifen 12. Below the heated zone is a water-cooled stirring section IJ attached, at the lower end of a elastically inwardly tapering sealing and clamping zone 14 is attached. Under this is the Aussehleuskammer 15, consisting of a cross slide 16 and a chamber door 17 as well as a Senkmeehanisnuis 18, by not shown in Mechanisms can be moved vertically up and down. Above the cross slide 16 is the supply of the Reducing gas 19 is arranged, another gas supply 20 takes place above the Kiemmorgan 14. Right at the top, Above the heating device 11, the pipe 10 is denoted by π equipped with a further elastic clamping point 21, over which a I'aßring 22 is attached.

The F i g. 2 shows tubular sleeves which are pushed coaxially one above the other by centering steps 24. In each of the sleeves several removable> »sieve plate 25 are arranged one above the other. It is particularly advantageous that the end faces of the sleeves 23 finely machined at right angles to the sleeve axis: have surfaces. These sieve bottoms 25 are charged with the material to be reduced in uniform layers 26 ji.

The one with several sieves 25 on which the material to be reduced is applied in uniform layers 26 is loaded, sleeves 2} are placed on the lowering mechanism 18 and meet the tube 10 in in full height. The lowering mechanism 18 is initially with the slide 16 open in its highest position, i.e. just below the sealing and clamping zone 14 Removal of the lowest sleeve, the contact pressure in the sealing and clamping zone 14 is reduced and the r. Scnkmcchanisimis 18 moved down. Glide in the process all over it sleeves 23 until the lower edge of the penultimate sleeve is above the Slide 16 is located. Now the contact pressure in the Klcmmzone 14 is increased so that the column of the sleeves for Standing comes while the lowermost sleeve is completely lowered into the chamber 15 and the slide 16 is closed will. The sleeve can now be removed through the door 17. Through this process is at the top of the Rohres space was created for a new filled case. r> The device is therefore for continuous operation set up. The sleeves thus pass through the heating zones 12, the cooling zone 13 and the Lock 15.

The hydrogen required for the reduction is fed in above the slide 16 through the pipe 19 and, through the action of the sealing and clamping zone 14, is passed through the sleeves, the material on the sieves 25 being flowed through. Measurements have shown that at a layer height of 6 cm / dm 'screen area 2 m' / h hydrogen can be passed through the material, with a flow resistance of 25 mm water column per screen. If, for example, a total of 40 sieve trays are arranged one above the other, the sum of all flow resistances is 1000 mm WS or 0.1 atm. If the total of all layer heights were to be filled into the sleeves without an intermediate sieve bottom, a multiple of this pressure would be necessary to pass the amount of gas mentioned and a shooting vortex would form, which would, among other things, result in unusable dusting of the fine oxide powder. This overpressure at the gaps of the lowermost sleeves cannot be completely sealed off by the fine machining of the end faces of the sleeves; some of the hydrogen escapes into the gap between the inner wall of the tube 10 and the outer wall of the sleeves. In order to counteract this, the elastic sealing zone 21 is attached to the upper opening of the pipe 10, by means of which the escape of the gas from the gap into the open is prevented. In addition, a small additional hydrogen stream is fed to said annular space at 20, the pressure of which is kept constant by a regulating device. While hydrogen flows out of the deeper sleeve gaps into the interspace, through suitable pressure adjustment as a result of the internal pressure falling from sieve to sieve, gas in the higher gaps from the annular space can flow back into the inside of the sleeve. This shunt is essential for the reduction. The hydrogen flow inside the sleeve is preheated by the sleeves entering the cooling zone and more humid in the hot rejection zone by taking over the oxide from the sieve / sieve, so that with a stoichiometric gas supply all hydrogen would be converted into water. This water is mixed again with fresh hydrogen by the return flow described above into the interior of the sleeve, so that the reduction is maintained through all layers one above the other. The formation of the _{W grain resulting from WO 1} is influenced by temperature and humidity. Due to the described gas return flow into the inside of the horn on the one hand and by setting the temperatures in the heating zones 12, the method is able to produce any desired Komart.

The elastic sealing zone 21 does not necessarily have to be completely gas-tight. A caliber ring 22 is attached above it, through which leakage losses of hydrogen can escape and can be burned off. Likewise, the hydrogen carried along by the reduction water in the exhaust gas from the top layer is also burned off freely. A gas circulation device, as is often used in the horizontal ovens that have been customary up to now, is unnecessary with this method. _{The O 2} content of the material, which decreases from step to step downwards, is countered by ever purer, ie drier, hydrogen, so that the almost complete reduction mentioned at the beginning is achieved with only a small excess of hydrogen.

1 sheet of drawings

Claims (7)

Claims; 1. Process for the reduction of powdery, Metal oxides stored in layers on sieve trays, in particular tungsten trioxide, in a continuous process by means of countercurrent feed Hydrogen, characterized that the guidance of the vessels takes place in the vertical direction downwards and this from one reducing gas flow are flowed through in the opposite direction in a known manner upwards. 2. The method according to claim!, Characterized in that the moist from layer to layer dry fresh gas is added to the gas flow through the column. 3. The method according to claim 1, characterized in that the material is passed through several Tcmperalurstufen whose temperatures according to the partial pressures of water present in the fleas concerned in order to achieve a certain grain shape is set. 4. Apparatus for performing the method according to claim I, characterized in that in one vertical tube furnace with several temperatures, a cooling zone connected below, removal lock and mechanical lowering device the material in cylindrical cans on an evenly attached sieve bottom at the same layer height is arranged, the individual sleeves guided by centering stages in the vertical axis and the The end faces of the sleeves are aligned exactly at right angles to the axis and placed one above the other in a gastight manner. 5. Apparatus according to claim 4, characterized in that above the Sch.euse an elastic Pressure and sealing zone is attached, by means of which the vertical movement of the sleeves stopped periodically and the reducing gas is passed into the sleeves under the sieves without loss. 6. Apparatus according to claim 4, characterized in that at de? Entry opening for the pods a seal, is attached, through which a certain gas pressure in the space between the shaft pipe and the outside of the sleeves is adjusted. 7. Apparatus according to claim 4, characterized in that this gap pressure at such a height is kept that the reducing gas driving overpressure from the lower area in the Annular gap and in the upper area is fed back into the interior of the sleeves, with fresh gas being added.