DE3418468A1 - METHOD FOR HARD-BURNING IRON ORE PELLETS ON A WALKING GRATE - Google Patents

Description

METALLGESELLSCHAFT May 16, 1984

Public limited company SCHR / LWÜ / 1483P

6000 Frankfurt / Main 1

Prov. No. 9098 LC

Method of hard burning iron ore pellets on a

Traveling grate

The invention relates to a method for hard burning iron ore pellets on a traveling grate under oxidizing conditions by means of hot gases passed through, with the pellets contain solid, carbonaceous material bound, which supplies part of the amount of heat required for hard firing.

The firing of iron ore pellets at temperatures of about 1200-1350 ⁰ C is performed on straight or circular traveling grates, which are provided with gas hoods, and also referred to as a pellet burning machines. These pellet burning machines have - seen in the direction of travel - different treatment zones, namely drying zone, burning zone and cooling zone. These zones can be subdivided into, for example, pre-drying and post-drying zones, heating zones, pre-burning zones, main burning zones, post-burning zones and first and second cooling zones.

In oxidizing hard burning, the iron content of the finished pellets is largely in the highest oxidation state, ie as Fe-O-. When hard-burning magnetitic _{pellets or pellets containing magnetite (Fe 3} O ₄ ), the amount of heat to be brought in by means of the hot gases is lower than with hematological

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table pellets, as the oxidation of Fe ₃ O ₄ to Fe-O _{3 is} exothermic. The specific throughput of a pellet burning machine depends to a large extent on the level of the magnetite content of the ore to be processed and increases with increasing magnetite content. Therefore, many attempts have been made to increase the throughput of hematite processing. For this purpose, solid, carbonaceous material was incorporated into the pellets in fine-grained form. This results in a considerable increase in the specific throughput, but the compressive strength of the pellets _{drops sharply at contents above about 1.3% C fixed} and the specific throughput also drops again at higher contents. Up to this C _f . Content, an increase in throughput is achieved with good pellet quality, the amounts of exhaust gas and the temperatures are reduced ( _B Aufziehungs-Technik ", No. 12, 1973, pages _{783-788). A C fix} content of about 1.3% C _fix produces about as much heat during its combustion as would be generated by the oxidation of Fe ₃ O ₄ to Fe-O, and would be _{sufficient for the reduction of Fe-O 3} to Fe ₃ O ₄ ; an integration of solid, carbonaceous Material in magnetite pellets led to a great decrease in the strength of the pellets.

The invention is based on the object with good throughput the pellet burning machine and good pellet quality to reduce energy consumption even further.

The object is achieved according to the invention in that the Cf. -Content of the solid, carbonaceous in the pellets Material is above the stoichiorometric amount required to reduce hematite to magnetite, and / or is above the amount necessary for the decomposition of heat-consuming Aggregates is required, and that the hot gases in the combustion zone of the traveling grate with a negative pressure from 5 to 20 mbar can be passed through the pellet bed. The pellets can be made from pure hematite ores or from a

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Mixture of hematitic and magnetitic ores exist. The solid, carbonaceous material can consist of highly reactive coals or weakly reactive coals. The coals can contain low or high levels of volatile components. The C ^ brought in by the coals. -Content can be up to about 50% above the stoichiometric amount. The stoichiometric amount is always based on the ematite content of the dry ore or the dry ore mixture.

If additives such as basic carbonates are mixed with these ores, then these additives consume heat when they decompose. In this case, the C _f ^ _x content can be increased accordingly, over and above the amount that is required by combustion to cover this heat consumption. The amount added can again be up to about 50% higher.

In the case of pure magnetitic ores, the addition of Cfj can only be occur when such heat-consuming additives are added, and the amount is calculated accordingly.

The carbonaceous material is introduced into the mixture in the grain size required for pelletizing.

The negative pressure with which the hot gases in the combustion zone are passed through the pellet bed is considerably reduced to 5 to 20 mbar compared to the values of around 30 to 40 mbar (millibars) otherwise usual for pellet burning. By the term "firing" the thermal treatment of the pellets is meant at temperatures above about 1250 ⁰ C. The specific amount of gas (amount of gas in Nm / kg of the charge in the combustion zone) is also reduced accordingly. The term "burning zone" includes both the heating zone, in which the dried pellets are heated to the desired burning temperature, and the actual burning zone, in which the pellets are kept at the desired burning temperature.

Surprisingly, through the combination of reduced negative pressure in the combustion zone and increased C _f - _X content in the pellets, the mechanical strength of the pellets can be retained, the reducibility of the pellets increased, the performance of the pellet burner maintained and the consumption of electrical energy and hot gases are lowered.

In the case of coals with a low proportion of volatile combustible components, the C _f . -Content of the pellets should be slightly higher than that of coals with a higher proportion of volatile combustible components.

The most favorable C _f for each operating case. -Content and vacuum can be determined empirically.

A preferred embodiment is that the hot gases in the suction drying zone with a negative pressure of 5 to 20 mbar can be passed through the pellet bed. Drying generally takes place in two stages. In the first stage takes place a pressure drying, where hot gases are forced up through the pellet bed from the bottom up. In the second stage takes place drying in a suction fan, with hot gases being sucked through the bed from top to bottom. By reducing the Underpressure and the specific amount of gas in the suction drying process, the advantages are further increased.

A preferred embodiment is that the hot gases in the combustion zone of the traveling grate with a negative pressure of 10 to 15 mbar can be passed through the pellet bed. At this negative pressure and the corresponding specific amount of gas particularly favorable results are achieved.

A preferred embodiment consists in that 1.7 to 2.0 Gev; .-% C _fix , based on dry ore, are pelletized into hematitic pellets. The addition to C _f . is on the

Hematite content of the ore or the ore mixture related. If heat-consuming aggregates are added to the ore, their amount can be added to the hematite content. This addition to C _f . gives very good results.

A preferred embodiment consists in that 1.8 to 1.9% by weight of _fixed C, based on dry ore, are pelletized into hematitic pellets. Any heat-consuming additives that may have been added can also be added here. This addition gives particularly good results.

The invention is explained in more detail by means of examples.

The hematite concentrate had the following analysis (in% by weight, based on on dry ore):

Fe total 66.6

Fe ¹¹ 0.9

SiO ₂ 2.6

Al ₂ O ₃ 0.93

CaO <: 0.05

MgO <: 0.05

TiO ₂ 0.06

P ^: 0.03

The magnetite concentrate had the following analysis (in% by weight, based on dry ore):

Fe total 65.6

Fe ¹¹ 18.7

SiO ₂ 1.6

Al ₂ O ₃ 0.93

MgO 0.58

P 0.04

S 0.20

The charcoal had the following analysis (in% by weight, based on dry coal):

C _fix 54.0

Ash 18.8

Fugitive 27.2

The anthracite had the following analysis (in% by weight, based on dry coal):

C _fix 88.7

Ashes 3.1

Fleeting 8.2

The coke had the following analysis (in% by weight, based on dry coal):

^c fix ⁸ ^ ¹

Ash 13.9

Fleeting 5.3

Firing of the pellets was carried out on a 26.5 cm diameter pan.

Experiments with hematite pellets are shown in Table I. The pellets were produced with the addition of 2% by weight Ca (OH) ₂ and 2% by weight CaCO ₃ . Integrated solid fuel is shown in the table. The humidity of the green pellets was between 8.8 and 9.75%. The first stage of drying took place as pressure drying, ie the gases were forced through the feed from the bottom up. Suction drying, heating and firing were carried out with the gases being sucked through from top to bottom. The "suction zone" comprises these three steps.

Experiments with magnetite pellets are shown in Table II.

The pellets were produced with the addition of 10% by weight of dolomite and 0.5% by weight of bentonite. The humidity of the green pellets was between 9.0 and 9.3%.

Table I.

Attempt no.

1. Fuel additive quantities
C _fix content

2. Firing scheme

Pressure drying time

temperature
pressure

Suction drying
Time

temperature
negative pressure

Warm up

Time

temperature

negative pressure

Burn
Time

temperature
negative pressure

Cool

Wt% wt%

Charcoal coke

2.2 2.2 3.4 4.0 2.0 2.3

1.18 1.18 1.84 2.16 1.8 2.1

Time
pressure

min

° C

mbar

mn

° C

mbar

mm

mbar

mm

⁰ C

mbar

min mbar

Total test time min power tato / tif

3 3 3 3 3 6th 3 3 275 260 270 250 270 250- 270 265 35 40 40 30th 30th 1250 30th 30th 3 6th 7th 3 2 7-10 3 3 350 280 300 250 250 10 250 250 30th 30th 30th 20th 5 1320 20th 20th 5 6th 6th 6th 10 6th 6th 350- 280- 300- 300- 10.1 250- 250- 1250 1250 1250 1250 30th 1200 1200 35 11th 10 10 31.1 10 10 13th 11th 16 12th 23.4 12th 11th 1300 1250 1250 1320 1300 1300 40 30th 10-40 10 10 10 10.3 10 9.3 10.2 10.2 10.9 45 40 40 30th 30th 30th 34.1 36 41.3 34.2 34.2 33.9 23.8 22.4 19.6 22.0 23.8 24.0

Table I - continued

3. Specific exhaust gas quantities NnT / kg 0 .56 0 .5 0 .57 0 .52 0 .54 0 .5 0 .5 Pressure drying NnT / kg 2 .37 2 .2 2 .73 1 .46 0 .94 1 .39 1 .4 Suction zone Nm ³ / kg 2 .18 1 .7 1 .65 1 .63 1 .59 1 .47 1 .66 Cooling zone

4. Energy figures

Suction zone kJ / kg 3386 2565 3314 1842 1470 1747 1721 WE a kJ / kg 849 491 980 302 194 281 287 WE off kWh / to 7.74 4.2 6.3 1.35 0.6 0.9 1.28 Blower energy .) ⁰ C 690 484 786 311 171 278 254 Grate bar temperature (max

5. Burned pellets

Compressive strength

Average N / P 4454 2153 2933 3001 1110 4494 3820

ISO abrasion test

+6.3 mm% 92.8 84.5 88.4 94.7 95.0 94.8 96.0

-0.5 mm% 7.0 14.7 11.3 5.1 4.4 5.0 3.9

Reduction behavior

88.5 32.3 95.4 80.5 9.5 22.1 3.2 4.3

NTZ test (500 ⁰ C) 95.3 • ♦ -6.3 mm% 4.5 -0.5 mm% Pressure softening test

(Burghard test) 1050 ° C DR / dt ₄₀ % / min 1.2 back pressure mm / WS 7.0

Degree of reduction% 80

1 .2 1 .2 1 .12 1 .05 13th 35 8th .0 15th 80 80 80 80

Table II

attempt I: r. Weight - ^1;: 8th 9 10 11th 1. Fuel additive Wt% _ A η t h r a ζ i t amounts - 0.5 1.0 1.5 C _fix content - 0.45 0.9 1.35 2. curling iron min Pressure drying ° C Time mbar A.5 2.5 3.0 3.0 temperature 260-280 260-280 260-280 260-280 pressure nin 40 40 30th 30th Suction drying ⁰ C Time mbar 3.5 2 2 2 temperature 250-350 250-350 250-350 250-350 negative pressure min 20th 10 20th 20th Warm up ⁰ C Time mbar 12th 9 8th 8th temperature 350-1250 350-1250 350-1250 350-1250 negative pressure 20-30 10 20-10 20-10

Burn

Time min 10 15.5 15.0 12th temperature ⁰ C 1250-1300 1250-1300 1250-1300 1250-1300 negative pressure mbar 50 20th 20th 15th Cool Time min 12th 10 12th 9.5 pressure mbar 40 40 40 40 Total test time min 42 39.5 39.0 34.5 power tato / nf 18.8 19.6 19.2 21.2

Table II - continued

3. Specific exhaust gas quantities Nm ³ / kg 0 .7 0 .5 0 .4 0 .5 Pressure drying Nm / kg 2 .3 1 .6 1 .7 1 .6 Suction zone Nm / kg 2 .1 1 .9 2 .1 2 .0 Cooling zone

. Energy figures

WE a kJ / kg 3276 2483 2561 2300 WE off kJ / kg 992 510 523 423 Blower energy. kWh / to 7.0 3.5 2.5 1.6 Roststabterni. (:: ) ⁰ C 780 552 552 478

5. Burned pellets

Compressive strength average

ISO abrasion test

N / P

2562

2337

2223

1379

+6.3 mm% 96.1 95.1 96.1 96.2 -0.5 mm% 3.3 4.0 3.3 3.6 Reduction behavior NTZ test (500 ⁰ C) +6.3 mm 53.1 69.5 54.7 61.8 -0.5 mm 17.5 10.0 12.1 11.7 Pressure softening test (Burghard test) 1050 ⁰ C DR / dt,% / min 1.32 1.5 1.34 1.49 Back pressure mm / WS 1.8 0.7 0.6 0.5 Degree of reduction% 80 80 80 80

The advantages of the invention are that the heat consumption and energy consumption of the pellet burning machine is reduced, the burned pellets have good mechanical strength and reducibility and the investment costs for the system are reduced with the same throughput.

Claims (5)

Claims 1. A method for the hard burning of iron ore pellets on a traveling grate under oxidizing conditions by means of passed hot gases, the pellets containing solid, carbonaceous material bound which supplies part of the amount of heat required for hard burning, characterized in that the C _f . -Content of the solid, carbonaceous material bound in the pellets is above the stoichiometric amount that is required to reduce hematite to magnetite, and / or above the amount that is required to decompose heat-consuming additives, and that the hot gases in the combustion zone of the traveling grate can be passed through the pellet bed with a negative pressure of 5 to 20 mbar. 2. The method according to claim 1, characterized in that the hot gases in the suction drying zone are passed through the pellet bed with a negative pressure of 5 to 20 mbar. 3. The method according to claim 1 or 2, characterized in that the hot gases in the combustion zone of the traveling grate are passed through the pellet bed with a negative pressure of 10 to 15 mbar. 4. The method according to any one of claims 1 to 3, characterized in that 1.7 to 2.0 wt .-% C _fix , based on dry ore, are pelletized in hematite pellets. 5. The method according to claim 4, characterized in that in hematitic pellets 1.8 to 1.9 wt .-% C ". , based on dry ore, are pelletized.