DE2336496C2 - Process for the production of pre-reduced iron oxide pellets with a low sulfur content - Google Patents

Description

The invention relates to a method for producing prereduced iron oxide pellets with a low sulfur content made of iron oxide pellets with integrated carbon, which are made by pelletizing a mixture Iron oxide ore and a fluid, sulfur- and carbon-containing binder and subsequent coking getting produced.

In US-PS 36 42 465 a method of described above, according to which a liquid, carbonaceous additive material (oil) at a temperature above 148 ° C on preheated fine divided ore is sprayed so that the oil cracks on contact with the ore. Only one occurs here little or no agglomeration; but it will be a

Jf) uniformly dispersed ore-carbon mixture obtain. After any intermediate grinding that may be necessary, the mixture is converted into a Pelletiser kept at a lower temperature. There is also residual oil at a high temperature sprayed on, with little or no cracking occurring, and the formation of the pellets in the Size range carried out from 6.35 to 50.8 mm. The pellets are placed in a koker that is on top of a Temperature of 482 to 760 ° C is maintained, in which the volatile portion of the pellets kinked and drifted off will. Since the amount of volatile matter in the pellets is small, it causes gas evolution no significant change in size during coking, and pellets of clearer and clearer obtained

4> fine-pored structure (see LSPS 34 20 656). the coked pellets contain enough carbon to achieve the desired degree of reduction of iron oxides in the Effect pellets. The hot, coked pellets are then used to form highly pre-reduced pellets

> o brought into a calcination device whose Temperature is about 980 to 1260 C. After the reduction, the reduced pellets are sieved and chilled. The cracked gas is taken from the carbonizer and the coker and combined into one

ü Distillation plant led where by-products are obtained will.

Partially reduced pellets of the type described are as Blast furnace charges are very useful and come as part of the ore charge or as a whole

bo use. The blast furnace is a very effective one Reduction device and does not require or benefit from very highly reduced feed (see: Agarwal and Pratt: "The Thermodynamic Aspects of Using Partially Reduced Burdens", Transactions, AIME Ironmaking Conference, 1965).

Compared to the blast furnace, the electric furnace is not a very effective reduction device, but it is an excellent one Melting pan. Therefore, the electric

oven from the use of highly pre-reduced loads. (The one used here Expression)> highly pre-reduced «means the removal of at least 85% bound oxygen.) There is many areas where electric beam generation is economically attractive; therefore were younger Much effort has been devoted to methods of producing highly metallized pellets for use to be developed as a feed for such systems. Although different methods of technical maturity κι many problems still exist. Some processes use rotary kilns or Traveling grids in which the pellets can be easily damaged, or other devices in which the pellets rest during the reduction. In the latter, the damage to the pellets is less one Problem, but the installation and maintenance of the devices are expensive, the production figures low and at least in one case the manufactured ones Pellets pyrophoric.

Most of the known processes use coal or coke as a reducing agent. The above known methods mentioned use a liquid, carbonaceous material such as residual oils and / or a coal tar pitch. For the use of residual oils and similar materials as Reducing agents speak of some advantages. The main advantage is that the cracked gases recovered and sold as high quality by-products. Under certain conditions ·: so tongues, the value of these by-products is at least equal to the cost of the liquid, carbon-containing one Additional material, and the precipitated and a's reducing agent used carbon so provides is practically no cost factor. Another advantage of using hydrocarbon oils is that that no other binders are required. The coke structure in the pellets is fine-grained, even dispersed and porous and enables rapid and uniform reduction.

It is possible to produce highly prereduced pellets by the processes mentioned, but the im Commercially available liquid, carbonaceous additives contain varying amounts of sulfur, which can be found in the pre-reduced pellets. This fact makes pellets of this type for that Use in blast furnaces is undesirable and in many cases unsuitable for melting in electric furnaces.

The invention is therefore based on the object of creating a method of the type mentioned at the beginning. > o with which it is possible. Achieve a very extensive pre-reduction / u without significant effort and to press the sulfur content in the pellets so far that it does not have a disadvantageous effect when the pellets are used

According to the invention, this object is achieved by that the pellets are heated to a treatment stamp atur from 982 to 1371 C in such a way that the Heating from 81 3 C to the treatment temperature in makes less than 1 hour if Jer in dpn pellets bo integrated carbon is only sufficient with a reduction of 85% or less at the treatment temperature, tfnd performs a reduction in 1 to 6 hours, if the carbon integrated in the pellets is sufficient VGn more than 85% at treatment temperature cause the pellets to be kept at the treatment temperature until the prereduced ones Iron oxide pellets have a maximum sulfur content of 0.25%.

Essentially, according to the invention, a lower sulfur content is thus controlled Heat treatment achieved. If a pre-reduction below 85% is desired, the pellets are quickly, i.e. H. in less than 1 hour, to the treatment temperature in the range mentioned, preferably to 1037 to 1148 ° C heated. Pellets that are highly pre-reduced should, on the other hand, contain more carbon, and slow heating for them, i. H. from 1 to 6 Hours, on the treatment temperature is beneficial.

With the above-mentioned content of 0.25% residual sulfur in the pellets, they have no adverse effect in the Blast furnace can be used. However, if it is to be used in an electric furnace, an advantageous one Further development of the method according to the invention provided that in the production of the pellets sulfur-binding additives are added in an amount of 0.1 to 5% by weight, based on the ore. This allows the residual sulfur to be reduced to a level of 0.03% or less.

High pre-reduction and see ·. Can heat it up combined by limiting the carbon content in the pellets and by reducing it from the outside added carbon can be completed.

It is stated above that the pre-reduction. on 85% here as the transition point from faster too slow heating is considered. However, the advantages of the respective heating speeds are under 85% or over 90% the most obvious. while the desulphurisation at final reduction values between these values does not depend in the same way on the heating rate. The ones to be treated Pellets can be made in a number of ways. The carbonizer can be a rotary kiln that is equipped with various devices for the injection of hot residual oilers in order to produce pellet "none" which then grow to the desired size. Circulated coke particles, ore particles etc. can be used as seeds Also coke made in a delayed coker and then finely powdered residue can be used. In the embodiment according to the invention, in which highly prereduced, low-sulfur pellets from a high-sulfur residual oil The product from the carbonizer is made from the outside of the ore pellets in the High reduction stage added.

For pelletizing, the oil is preferably fed at a temperature at which it flows easily but is still below the cracking temperature. For many back mandrel oils, this temperature is between 148 and WTC. Carbonising the finely zer '^ ILTE ore is heated in a kart onisator to a much higher temperature from 482 to 700 ⁰ C. The average temperature obtained is usually in the range from 398 to 394 C. If necessary, an agent capable of binding the sulfur can first be sprayed in a suitable amount onto the ore. The sulphurous oil is then moved to the He? sprayed on and cracks immediately if in contact with it. Since the carbon deposits on the ore particles, the particles increase in size, even if little or no agglomeration occurs. It is therefore recommended that the carbonized mixture be subjected to a grinding process in order to obtain the correct size for pelletization. For use in the pelletiser, the particle size is

preferably 50 to 80% below 0.044 mm. It is good. the oil injection into the pelletiser towards the crowd limit which allows the best pelletization with the best properties in the green pellet, and although usually to 7 to 50 wt .-%, based on the -. Weight of solids.

The pelletization is carried out with the ore-carbon mixture and the residual oil at 176 to 427, preferably 204 to 399 ^° C., although deviations from this are also possible with certain oils. The desired size of the pellet is usually in the range of 6.35 to 50.8 mm and depends on its use. All types of pelletizers. which are able to work at high temperatures can be used in this process stage. The total amount of carbon of any form that is incorporated into the pellets depends on the degree of reduction and end use. as will be explained.

The green pellets are fed directly into the coking furnace while they are still hot. The furnace must be heated differently than directly in order to enable the recovery of the cracking gases from the carbon binder. In the furnace, the temperature of the pellets is increased to approximately 482 to 760.2 %, preferably 537 to 705 ^° C., and hard, strong pellets with a porous, fine-grain coke structure are produced in the process. For blast furnace pellets, the total amount of residual oil for the carbonization and pelletization stage is adjusted so that the carbon content of the pellets slightly exceeds the stoichiometrically necessary amount for the total extent of the total reduction. For electric furnaces, the carbon content in the pellets is limited so that it is only sufficient for a 25 to 50% reduction, as explained below. It is common and economical to use the exhaust gas from the reduction furnace, possibly together with additional fuel, as heating means for the coking furnace. The hot, coked pellets are conveyed from the coking furnace directly into the reduction furnace or calciner, which can be fired directly.

The reduced pellets are kept in a protected, non-oxidizing atmosphere at a temperature Chilled below 121 "C

The production of the pellets can also be carried out in the same way as the one mentioned at the beginning It is a great advantage to have an intimate ore-carbon mixture To produce blending of a carbonaceous material of low volatility with the ore. Fine Ground, preferably deashed, coal or coke can be used for this purpose. FIux means or sulfur acceptors or substances that promote the removal of sulfur can be the ore-carbon mixture be admitted.

The amount of carbon present in contact with the pellets in the reduction furnace, determines the degree of pre-reduction that will be achieved. According to the invention, this can be divided into five categories or schemes, which are shown in Table I are put together.

The first scheme concerns the production of blast furnace pellets with low pre-reduction, preferably 35 to 50%. The carbon for the reduction is only from the liquid binder material, without additional carbon placed The ratio of binder: solids is chosen so that a good pelletization with high strength of the pellets is made possible. Depending on the binder, or more precisely, on the Coriradson carbon number Sufficient carbon integrated in the pellet is deposited for the reduction. In general, residual oils will give enough carbon for a reduction of 25 to 60%.

According to the second scheme, a certain amount of solid carbon is added to the ore before pelletizing added and thereby the ratio of carbon: ore increased, while at the same time the ratio Binder: ore is held at a level that corresponds to good pelletization. That happens primarily with a pre-reduction in the range of 50 to 80%. and the reheating must be done quickly.

The third scheme differs from the second in that it has enough solid carbon to achieve it a high pre-reduction (+ 85%) is added. In this case, the treatment temperature iur slowly erhii / i graze, ύύίϊιϋ uic desired Desulfurization occurs.

The fourth scheme can be used as a combination of the first or second scheme (i.e., relatively low Reduction with rapid heating) with a second heat treatment with inclusion from the outside Pellets of added carbon can be considered.

The fifth scheme involves the use of a very high carbon internal binder, such as coal tar Or right, with faster heating for up to 85% and slower heating if a higher reduction is desired will.

An embodiment of the invention is explained in more detail with reference to the drawings.

F i g. Figure 1 is a simplified flow diagram illustrating a preferred embodiment according to the invention shows according to which highly reduced pellets are produced which are suitable for electric ovens and where High-sulfur petroleum residue oils are used:

FIG. 2 is a diagram showing the heating and reduction profiles for known pellets according to the invention shows, and

F i g. 3 is a simplified flow diagram illustrating an alternate embodiment in accordance with the invention for the production of highly prereduced pellets shows which are suitable for electric stoves and which are high in sulfur Petroleum residue oils can be used.

F i g. 1 and 2 explain in a greatly simplified form the fourth scheme for generating highly reduced Pellets (about 100%) with a maximum sulfur content of 0.03%. i.e. pellets used for electrical Steel making are well suited.

When the pellets are formed, there is only so much residual oil used that the carbon remaining after coking to reduce the pellets to 25 to 50% is used up. In the embodiment according to FIG. 3 is used before a first stage of heat treatment sieved in order to obtain pellets and particles of too small size and to return them to the pelletiser.

The first stage of the heat treatment is carried out with rapid heating to the treatment temperature in a directly heated furnace, such as a rotary kiln, practically the entire Carbon in pellet used up; the partially reduced pellets obtained are very porous and only contain about 0.003 to 0.03% sulfur You will be put directly in the furnace for the treatment temperature second stage of heat treatment for high reduction

promoted, together with a sloichiometrically considerable excess of carbon and lime or another sulfur binding agent. The particle size of these additives (laughing at the end of the heat treatment is sufficiently smaller than that of the pellets and then allows separation by sieving. Lie the pellets, for example, in a size of 15.88 to 19.05 mm, then the heat-treated, Pass a sieve with 0.35 mm mesh size in front of the reduced particles.

The furnace for the second stage of the heat treatment is also directly heated; preferably the Stress factor kept low, to around 8 to 15, preferably below 12%. to the heat transfer from the furnace wall into the bed and by direct radiation from the flame as much as possible. Because of the Porosity of the pellets, the reduction proceeds much faster than that of the solid pellets (i.e. CO can enter the pellet more easily and COj exit the pellet much more easily).

The excess of carbon for the high reduction stage can optionally from carbonized Residual oil may consist of agglomerated to the correct size, or it may be an external carbon source can be used, such as coal or coke of any origin, cut to the right size are ground.

In the high-reduction stage, there is no further contamination of the pellets by sulfur, since none More sulfur is added and the sulfur in the reduced material is bound with lime or dolomite is.

The heat treatment in the presence of integrated or externally added carbon for Production of pre-reduced pellets of 90% and more can also be done in a single heat treatment stage be performed.

The insert Y / leaving the high-reduction furnace is subjected to a split. Will the size The carbon pellets are carefully monitored as described above, then it is appropriate to adjust to carry out a sieving of the desired proportions. The insert is first placed on a sieve to remove the withhold finished pellets and take them off. In the embodiment according to FIG. 3 becomes the sieve passage again subjected to size separation. The second sieve residue consists primarily of partially consumed coke, which is returned to the use end of the high-reduction furnace in the circuit will. The undersized material consists of coke particles, calcium compounds, gangue and ferrous fine particles. Depending on local and economic conditions, these materials can cooled and discarded or a magnetic sieve

Table I.

or subjected to some other treatment to obtain the iron and carbon. After Embodiment of FIG. 1, the sieve passage is subjected to magnetic separation and the Carbon recycled.

As such, pre-reduction and the use of externally added carbon are not new. To however, in the prior art, the rate of reduction is relatively slow and it is obvious

difficult to achieve high pre-reduction values. It dwell times of many hours are required, as well as high working temperatures, sometimes above of 1094 ° C. but the melting and inclusion problems cause. A high stress factor (20 to

40%), large ovens and a long dwell time are required because of the low porosity and the

large excess of carbon present to achieve a reasonable yield.

The pellets produced by the method described at the beginning contain after coking integrated carbon and a uniform porous structure and have a noticeably higher reducibility as demonstrated in the examples. The following advantages are evident from FIG. 2 you can see which Bring heating and reduction courses for inventive and known pellets:

(1) Comparable reduction values can be achieved in a fraction of the residence time, the known Need pellets.

(2) Essentially complete reduction can be achieved in the usual residence time (2 to 2 hours) achieve, while with known pellets only 54% reduction is obtained in two hours and only there is little likelihood in a practical period of time to much more than a 60% reduction get.

(3) In addition, the generated gas has a markedly lower CO / CO2 · ratio. With comparable If the pre-reduction values were used, the ratio would be even more favorable. That means a more effective one Utilization of the reducing agent and also a considerable reduction in the heat load the system and the system size.

As a result of these advantages, it is possible to heat treat the pellets in a rotary kiln more practical and economical to carry out. Furthermore, the high reactivity of the pellets Use of lower temperatures in the final phase of the heat treatment (from about 40 to 60% reduction the intended reduction value in the end product). an area particularly prone to the problems. -which are associated with stickiness and the observation of the furnace.

Scheme

carbon

Rcdukiionsweri%

Broad Preferred Heating

Area Area Speed

S15auff C

I. Integrated: only from Erdöl-Rück
stands binder 25th 60 35 50 fast II Integrated: from crude oil residue
Binder + solid C 25th 85 5 & SO fast HI Integrated- from petroleum residue-
Binder + solid C S5 i00 90 ! 00 slow

230225/124

continuation

Scheme K

IV

VA

VH

HrcMci area

KiilukiinnwwH He \ iii '/ ni! Ler I rhii / iinuv

Area (ieMlnulukl

SI * ml I <

Integrated: only petroleum residue collector. C Integrated: only from strongly carbonaceous binders, such as coal tar pitch Integrated ■ only from strongly carbonaceous binders, such as coal tar pitch 40 100 5 (1 100

50 X 5

W) S 5

fast
fast

X5 Hill ¹ X) K) (I.

After the heat treatment, the finished pellets are in a protective atmosphere to avoid them from reoxidation, as usual, cooled. However, it is advantageous to move the pellets while they are cooling down, as this promotes the closing of the pores in the pellets and the "cen weathering" resistance elevated. You can also move the pellets with finely divided ore or lime, as both the Fill pores (and both are preheated) and so in the same way the resistance to Increase weathering.

As can be seen from Table I, Schemes I, II, IV, and VA call for proper desulfurization to be done quickly Heat. Effective desulfurization is achieved by heating the pellets quickly over a period of time less than one hour and preferably less than 45 minutes, from a temperature of 815 to a higher one temperature from 982 to 137 Γ C, preferably 1037 to 1149 ° C, and maintaining this upper temperature over a period of 15 minutes to six hours, preferably 30 minutes to two hours. Desulfurization can be defined as follows:

where Sb = sulfur content of the finished pellets if the all the sulfur of the integrated carbon remains, and S> = actual sulfur content of the finished pellets is. According to the method described above, a desulphurisation according to the Invention from 50 to 85%.

After Schemes II and VB (+ 85% reduction) achieved an effective desulfurization by following a schedule with slow heating for a period between 1 hour and 6 hours, preferably I ^1/2 hours to 3 hours, from 815 up to an upper Temperature from 982 to 1371, preferably 1037 to 1149 ° C and maintaining this upper temperature for 30 minutes to six hours, preferably 45 minutes to two hours. In this way, a desulphurisation of up to 91% can be achieved.

The use of certain additives in connection with the heating programs described above left one recognize a remarkable increase in the ease and the achievable degree of desulfurization. the the following combinations were found to be effective:

CaCl ₂

CaCO ₃ + NaQ
CaO + NaQ
CaCO j + CaCl ₂
MgCl ₂
CaSO ₄ + FeCl ₃

In general, the additives from metal chlorides, preferably alkali or alkaline earth chlorides, or iron chloride together with calcium sulfate, alkaline earth oxides or carbonates. The additives are put into the pellets by inserting them into the pelletiser with the ore and in dpn carbonizer or by suspending in finely divided form in the binder before spraying in the pelletizer or carbonizer. Water soluble additives (i.e., metal chlorides) can be added to the ore in a conventional manner prior to drying and Heating the ore to be sprayed. The only limitation to be aware of is that the additives are uniformly dispersed into the pellet and the particle size of the dispersed Additions are at least less than 0.149 mm and preferably 100% less than 0.074 mm. The addition to Additives can be very small: good results are obtained with dosages in the range of 0.01 to 5%, but the range from 0.5 to 3% is preferred for uniform results. These quantities relate to

J5 is the weight of the ore used.

The use of the above additives in connection with the heat treatments specified above allows desulphurisation of up to 99% with schemes I, II. IV and VA and with schemes III and VB up to uu 04%.

Examples

The hot ore is fed into the carbonizer at 648 ° C, where oil of 7.4 ° API is sprayed on. Before the

Spraying the oil is heated to 315 ° C so that it cracks on contact with the ore. The cracked gases are captured. The outgoing solids are sifted and sifted; part of it goes to the pelletizing stage. The rest is in heat exchange reheated to hot process streams and recirculated to the carbonizer. The returned pellets with undersize and the fine particles formed during the process are reduced to about 80% Milled 0.044 mm particle size. The solid products from the carbonizer will be about the same Shredded size range

The mixture from this stage with a temperature of 371 to 455 ° C is together with the preheated Ore conveyed into the pelletizing drum where

In addition, preheated oil is sprayed on and the pellets are formed. The pellets contain 7.6% solid carbon and 13.2% residue. The hot pellets, mainly in the size range from 19.05 to IZ / now, are brought into the coking furnace. Circulating hot sand can be used as a bed for the pellets during coking. The coking product is sieved off and the sand is returned.
According to the invention, the heat treatment

Different pellets carried out without desulfurization additives: the results are shown in Table II. Run A illustrates the advantage of slow heating with high prereduction, and shows that a high treatment temperature is not necessary. Run B 12

proves that if the prereduction is lower, slow heating is preferable. Run C represents for ti5% Reduction states that quick heating is better, but that is a "gray area".

Table II

Konirolle des SchweR-lgelia read the pellets effect of / eil and lemper.tliir

/ hey

A. 1 6.0 (slow) lO'M A. ? SO (slow) 1149 Λ 3 0.2 (fast) 1204 / “!,.. “IK I HC

I, ml / eil of Xl5 (Uehand-

.iiil / ■ (lungs- / '(

Hours temperature hours

7 C

2.0! 0.0 0.5 0Λ 0 ^ 5 8.0 0.5 0.5 0.5 0.5 0.5 0.5 0.5 10.0 0.5 0.5 0.5

S- <rch.ill Her Sdehall Wirkl S- Heoh Oxicl- Coked. ' in handling I'el- (iehullin Im- Red- PeIIeIs lel>. if Cie-hand. Pel- ».h * c- level

! iiiinl-S verlets felling in bcliand.

stayed

(lew% wt.% Ciew%% pellets

A 5
BI
B 2
B-3
B 4
B 5
B 6
B-7
B 8
Cl
C-2
C3
C4

, 2 is fast)
, 6 (slow)
, 2 (fast)
, 2 (fast)
, 2 (fast)
, 2 (fast)
.2 (quickly)
.2 (quickly)
.2 (quickly)
.0 (slow)
.2 (quickly)
.2 (quickly)
.2 (quickly)

1371 1093 1204 1093 1093 1093 982 1315 1371 1204 1093 1204 1371

0.98 0.99
0.98 0.99
0.98 0.99

Q OS! Q _- QQ

0.98 0.99

0.54

0.54

0.54

0.54

0.54

0.54

0.54

0.54

0.18

0.18

0.18

0.18 .66
.66
.66

My

.66
0.79
0.79
0.79
0.79
0.79
0.79
0.79
0.79
0.27
0.27
0.27
0.27

0.11 0.12 93 0.10 0.11 94 1.43 1.92 0 ! .09 1.27 79 0.88.1.62 25th 0.85 0 0.38, 0.39 51 0.43 45 0.59 25th 0.63 20th 0.55 30th 0.43 45 0.32 60 0.20 26th 0.07 / 0.09 70 0.OR 70 0.035 87

99 +

99 +

99 +

99 +

99 +

77/79

77/79

77.79

77/79

77/79

77/79

77 79

77 79

Desulfurization achieved due to the weight loss of the pellets during the time-temperature relationship

The reduction without simultaneous desulphurization is a is made through the use of chemical additives, such as

Increase in the specified sulfur content to calcium, sodium, magnesium and iron compounds

expect and are decreases in the sulfur content 40 gene, further improved. The ones with various additives

proportionally greater than the specified values. Results obtained are shown in Table III.

The advantageous through the one described above

jixlle III

Control of the sulfur result of the pellets effect of the

L. j ui trhit ^ -Cioehvv HehandlurtL's- \ in / ieh / eit at S-content in ver Uereehn S- (iehalt Real S-dehall Observed Oxid-Red - Lot. / llSill / Elapsed Zm temperature <dealer temperature coked pellets in handy pellets. in handy pellets 1 ntschwe- Level hand (iew 'Ό : ■. · / space from heating ι hours if the entire S IeI u ng l'elk-is on 1 u on SI? C hours remained (icwichi (ieu ", ι (iew "/, ι (ieu '",, "'(I "" t> I 0.2 (fast) 1260 0.5 0.15 0.175 0.15 0.17 9 38 40 D- 2 0.2 (fast) 1260 0.5 0.15 0.175 0.150.17 9 38 40 3.0% CaCOv D 3 0.2 (fast) 1260 0.5 0.15 0.175 not noticeable strong 38 40 5.0% CaCU D-4 0.2 (fast) 1260 0.5 0.15 0.175 bar strong 38 40 1.0% CaCl '. D-5 0.2 (fast) 1260 0.5 0.15 0.P5 0.0025 0.0026 98 38 40 0.5 ",, CaCU D 6 0.2 (fast) 1260 0.5 0.15 0.175 0.002 99 38 40 IMIl "" CaCU D 7 0.2 (fast) 1260 0.5 0.15 0.175 0.0055 97 38 40 s '-' l " CuCO ₁
NuC I D-8 0.2 (fast) 1260 0.5 0.15 0.175 0.002 99 38 Ai) 3.5% CaCO ₁
Nad D 9 0.2 (fast) 1260 0.5 0.15 0.175 0.005 0.008 96 IS 411 3! O% CaCO, 0.025 ", , CaCI, E · t 6.0 (slowly Ji 1232 10.0 0.12 0.192 0.05 4th 95 F t 6.0 (slow) 1232 10.0 0.11 0.182 0,0250,027 86 97 0.22 ",, Cad, Ci 1 6.0 (slow) 1232 10.0 0.14 0.234 0.0! 2 95 44 CuCU HI 2.5 (slow) 1260 1.0 0.78 1.31 0.26 80 98 + 3.0%
1.0% CaCO ₁
Nad H 2 2.5 (slow 1260 1.0 0.78 1.31 0.33 75 98 + 3.0%
1.0% CaO
NaC! H 3 4.0 (slow) 1260 16.0 0.78 1.31 0.53 60 98 + 3.0%
1.0% CaO
CaCl, H-4 4.0 (tangible) 1260 16.0 0.78 1.31 0.11 92 98 + 3.0%
1.0% CaO "
NaCl J-1 1.0 1148 16.0 0.7 0.78 1.24 0.25 80 98 + 3.0% 1 ι Cl * ·. I.
MgCl J-2 2.5 (slow) 1260 16.0 0.70.78 1.24 0.16 87 98 + 1.0%
1.0% CaSO ₄
FeCl, i 3 2.0 (slow) 1260 2.0 0.7 0.78 1.24 0.24 SI 98 - · - 4.0% MgCU J 4 3.0 (slow) 1315 16.0 0.7 0.78 1.24 0.060.08 94 98 + 3.0% MgCU J S 0.5 (fast) 1093 2.0 0.47 0.48 0.65 0.Γ0.2 77 64 6 (p 3.0% MgCl ".

In general terms, it can be seen from Table III that CaCl. and CaO-NaCl, Mg Cl .. and CaSO ₄ -FeCh the more effective and CaCO ₁ , MgCOj and MgO the less effective additives.

A Rückstandsol with S, 3 ° / o sulfur was used to generate El? Ktroofen pellets with 00:03% sulfur used.

The procedure was as follows:

Coked pellets were made as in the D-series runs (Table HI). A Taconite concentrate was mixed or mixed into a slurry in aqueous solutions of MgCb, in which the neutral salt was 2% by weight of the Taconite. The ore was dried and then pelletized at 371 to 394 ° C with residue containing 33% sulfur. These green pellets were then coked ^{at 50 ° C.} This amount of residue deposited enough integrated carbon to pre-reduce the pellets by 40 to 45% in the first stage heat treatment.

Made from the same one containing 33% sulfur

Coke pellets were produced without the addition of additives by adding residue to a residue Carbonizer was sprayed. After coking, the sulfur content of these coke pellets was 4.6 to 4.8%.

The coke pellets were ground to a particle size between 1.59 mm and 0.074 mm and mixed with 5% by weight of ground CaCOj. The previously prepared coked Taconite pellets were stirred into this mixture; then rapid heating (from 815 to 1094 ^° C.) was carried out in less than 30 minutes.

After a residence time of two hours at this temperature, the calcination tube was cooled. the Pellets produced in this way were reduced to 99% +: the sulfur contents ranged from 0.01 to 0.03%. the Results are summarized in Table IV.

The coke from this treatment was successfully used together with an addition of 2 to 3% CaCCb or Dolomite, based on the ore weight, recirculated per pass.

1 .ibellc IV

Desulfurization with a combination, integrated carbon charging with carbon from the outside

L .ml Sulfur in Sthttctel in / cit / um Ir- / ( / hurry Sulfur- Before- /iis.ii/e CaCO. \ crkokun Knk-loading hii / cn from T C Ind-Ciehall rcduk- IVMets scIiKkiine N | s .ml T ( Sense- lion CaCC), (ICW ".. Cicw "n Siumlen the (. lew '· " ° n (iew 'Ό M-I 0.3 0.35 4.0 5.6 ο .: 1093 -> 0.01 0.03 <W + ■ Pellet 2% McCI. CaCO. Loading 5 "o M-: 0.2 () .: 5 4.6 5.2 0.5 I (W? 1 IU) I 0.02 Pellet 2% MgCl. Loading 5% M-3 03/11 0.4 4.6 4 » (1.5 1 (165 0.02 0.03 Pellet 2% MgC "!. Loading 5%

To compare the reducibility of the pellets produced by the method mentioned at the beginning (i.e. produced by agglomeration with residue and subsequent coking) with commercially available, after known methods produced pellets (agglomeration with bentonite and subsequent calcination) 150 g samples were subjected to heat treatments with equal time and temperature conditions.

In each experiment, the pellets were placed in a vertical tube with an internal diameter of 25.4 mm packed with a substantial excess of granulated coke. The tube was in a vertical electric furnace was used, with the 355.6 mm running batch being entirely in the heated zone. That The upper end of the tube was closed and fitted with a device for collecting and measuring the gases tied together. In each experiment the temperature rose rapidly to 704 ° C., then over an hour gradually increased to 1093 "C and held at this temperature until the evolution of gas had practically ended. The gas samples were examined for CO and CO2 at periodic intervals. The results of this Experiments are compiled in Table V and Fig. 2.

Table V

Comparable reducers in the still, with coke and l'cllets packed Hell

Mn back, iil (usual hcrpesiellle IVIIeIs

Pellets 1

Linsate / amount of pellets 150 ρ from 55 bii Her 150 230 225/124 Gas generation: Her «Co 25.6 * 1 Her 18.60 liters CO, 10.15 I. Her 4.40 liters H, O (protected) 2.20 I. 1.40 liters C iesall 38.0 »I. 24.40 Liier 60 ratio (.0, C (J ₃ 2.52 4.23 Reduction% related to generated gas 97.0 51.0 based on the Analy * 65 se of the pellets 99.5 54.0 *) These pellets were released 1 carbon oil chcml of a priority ! 60%.

These experiments demonstrate a remarkable improvement in the use of the pellets produced according to the invention and according to the above-mentioned method of Erfindungsgestallung compared iu the usual pellets. Faster reduction is achieved. For example, a reduction of 54% is achieved after 0.8 versus 2 hours with conventional pellets at a maximum temperature of 1057 versus 1093 ° C. A practically complete reduction (98%) was obtained within a period of two hours, which can be justified for the practical and economical design of the rotary kiln. The visual extrapolation of the reduction curve for conventional pellets gives a maximum reduction of perhaps 60 to 65% even after a residence time of Vh to 4 hours. ι>

The CO / COj ratio in the evolved gas as a whole is much lower despite the higher degree of Pre-reduction. With the exclusion of externally supplied carbon during the low prereduction (i.e. to practically all of the integrated carbon is consumed), as was shown in the preferred embodiment, even lower results CG7CO2 ratios. That means corresponding savings in carbon and energy.

The finished pellets are uniform, dense and free from cracks and defects. The usual pellets containing those with varying diameters (corresponding generally variations in Reduktionsg ^r ad) and showed considerable cracks and broken pieces.

! Km

BLiH

Claims (12)

Patent claims: 1. Process for the production of pre-reduced iron oxide pellets with a low sulfur content Iron oxide pellets with integrated carbon, which are produced by pelletizing a mixture of iron oxide ore and a fluid, sulfur- and carbon-containing binder and subsequent coking are produced, characterized in that the pellets are heated to a treatment temperature from 982 to 137TC heated in such a way that the heating from 815 ° C to the treatment temperature is carried out in less than 1 hour, if the carbon integrated in the pellets only leads to a reduction of 85% or less in the Treatment temperature is sufficient and carried out in 1 to 6 hours if the in the pellets integrated carbon is sufficient to reduce the treatment temperature by more than 85% cause, and that one keeps the pellets so long at the treatment temperature until the prereduced Iron oxide pellets have a maximum sulfur content of 0.25%. 2. The method according to claim 1, characterized in that in the production of the pellets Sulfur-binding additives were added in an amount of 0.1 to 5% by weight, based on the ore graze. 3. The method according to claim 2, characterized in that the sulfur-binding additives Calcium chloride, sodium chloride, calcium oxide, calcium sulfate. Calcium carbonate. Magnesium chloride, magnesium oxide, Iron chloride or a mixture thereof can be used. 4. The method according to a t..r claims 1 to 3, characterized in that the pellets during the heat treatment in the presence of carbon, that from the outside in an excess over the stoichiometric amount required for the final reaction is added, and a smaller proportion of a sulfur-binding additive can be reduced. 5. The method according to claim 4, characterized in that as externally added carbon Coal, coke or genes thereof can be used. 6. The method according to claim 4, characterized in that that lime or dolomite is used as a sulfur-binding additive. 7. The method according to claim 1, characterized in that in the heat treatment of pellets, which allow a reduction of 85% or less, the pellets 0.25 to 6, preferably 0.5 to 2 hours, be kept at the treatment temperature. 8 The method according to claim 7, characterized thereby. that the heating to the treatment temperature carried out in less than 0.75 hours will. 9. The method according to claim 7 or 8 thereby characterized in that the treatment temperature is 1037 to 1149 C. 10. The method according to claim 1, characterized in * distinguishes that in the heat treatment of pellets, which allow a reduction of over 85%, the Pellets are kept at the treatment temperature for 0.5 to 6, preferably 0.75 to 2 hours. 11. The method according to claim 10, characterized in that the treatment temperature 1037 to 1149 ° C. 12. The method according to claim 1, characterized in that that the pellets first undergo a first heat treatment stage with a pre-reduction from 25 to 50% in the presence of a sufficient one contained in the pellets themselves Amount of carbon and a sulfur-binding additive are subjected, and that subsequently a second heat treatment stage at the treatment temperature with a reduction of up to 85% or less.