SINTERMAKING UNDER PRESSURE

SINTERMAKING UNDER PRESSURE

(OUTLINE OF THE PROCESS

AND PROPOSAL ON HOW TO USE IT)

::1::

Introduction............................................................................

1. Validity of the revolving sinter machine design for implementing

3

sintering-under-pressure technology

2. Laboratory-scale study of the sintering-under-pressure process ...

3

Production of iron-bearing flux (extra-high basicity sinter) in a revolving

machine..................................................................................

3. Production of iron Bearing flux (extra-high basicity sinster) in a revolving4

machine..

4. Recycling and dezincing of dust and sludge from iron and steel making

13

shops .

4.1. Sintering under pressure as used for recycling and dezincing dust and15

sludge from iron and steel making shops ........

4.2. Good use of iron making and steel making sludge.

17

5. Production of sinter for iron making .

19

5.1. Sintermaking process. . . . . . . . . . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . . . . ..19

5.2. Specification of the revolving sinter machine and its make-up.............22

5.3. Sinter machine operating flow-chart............................................24

5.4. Arrangement and layout ... ... ... ... ... ... ... ... ... ... ... ... ......

26

5.5. Automatic control and monitoring .....

27

5.6. Environment friendliness of the process Recycling of wastes.............. 28

5.7. Bill of main equipment 29.

Annex:

Drawings: NoNo TMI01.00.000 sheets. 1,2,3

TMI01.00.000-TX sheets. 1,2

Introduction

This technical proposal for the implementation of the sintering-under pressure technology has been compiled by TOTEM Co Ltd.

The process for making sinter under pressure with the help of a revolving sintering machine has been developed by TOTEM Co. Ltd. and the Central Research Institute for Iron and Steel Industry. This proposal dwells upon three areas of implementation of the offered design and technology:

1. Recycling of zinc-bearing dust and sludge, obtained from iron making, to make at that

an iron-bearing modulated product (sinter) featuring low zinc content and by-product, which would contain zinc, lead, germanium and other valuable elements in quantities, economically sufficient for arranging their recovery afterwards.

2. Production of specific grades of sinter, such as iron-bearing flux to be used in steelmaking, purging sinter for blast furnaces, sinter of higher strength.

3. Production of sinter for small volume blast furnaces at small-size (mini) steel works.

1. Validity of the revolving sinter machine design for implementing sintering-under- pressure technology.

In many countries of the world a growing production of iron and steel made it necessary to look for better ways of recycling tens of millions of such wastes like dust and sludge, that were generated in sintermaking, iron and steel making processes.

The content of iron in these wastes would amount to 33-70%, which makes it possible to recover from them, if recycled, additionally about 450kg of metal. Besides, as has been noticed, in sludge there is an elevated as compared with the primary iron ore material, content of carbon, calcium, magnesium and manganese oxides, that are the components needed in the production of iron and steel.

As a rule, the iron-bearing raw material is to be balled before smelting, in conveyer-type sintering machines or roasting machines. If the scope of production of sinter is not big or there is a necessity to recycle metallurgical wastes, such as dust and sludge generated in iron and steel making, for the production of iron flux etc., the efficiency of a conveyer-type machine is likely to be drastically lower both in terms of techno- economics and in respect of pollution. This can be accounted for by difficulties in balling highly dispersed and moist-containing material, as well as high content in it of impurities deleterious especially for iron making, such as zinc, lead, and alkali metals oxides. In such a case the traditional vacuum sintering technology with the help of a conveyer-type sintering machine would be inefficient for elimination these impurities.

As has been proved by research, this problem can be solved through the sintering-under pressure technology, suggested here, which makes it possible to recycle highly dispersed material, containing detrimental impurities, and make at that a high quality iron-bearing modulated product (sinter) and by-products that contain zinc, lead, germanium, etc., useful for steel industry. Over and above, the recycling of the wastes that have not been utilized so far, will substantially improve the environment-friendly situation at steel works.

The possibility to sinter a high (up to 500 mm and above) bed, using the sintering-under pressure technology makes it possible to enhance specific productivity of the machine and through that to decrease the production cost.

It is the revolving type of a sintering machine which is the most preferable; as it meets the multifaceted production needs such as balling, sublimation of detrimental elements, dust arrest. It features also good techno-economic and environment-friendly properties.

Laboratory-scale study of the sintering-under-pressure process

Initially, the laboratory tests were carried out in a 115mm diameter sinter pot, which was equipped with a specially designed air-heater. The schematic diagram of the plant is shown in Figure 2.1. This design provided an opportunity to understand the impact of cold compressed air and air heated up to 500-950C upon the sintering process in progress.

The first series of sintering tests was carried out to see how the temperature of compressed air fed for sintering would tell upon the techno-economics of the process and quality of sinter.

To make the juxtaposition of the test results possible, the preparation method of sinter mix and its components were kept the same, and the bed height also remained the same- 300mm.In all test the sintermix was ignited under vacuum, during 1 minute. The base sintering was carried out in line with usual technology, when suction under the grid was 10.8 kPa. The test sintering under both cold compressed air and preheated air was

carried out with the under-bed pressure of 98 kPa.

As the test showed, an increase in cold air pressure up to 98 kPa had resulted in a higher, more than threefold increase of specific productivity of the machine, as compared with the base sintering. The specific productivity value came to 4.46 tlm2 hour, with coke breeze content in sintermix being 3.3%. The sinter strength, made under pressure, was also threefold higher than that of the sinter, made under vacuum.

An increased temperature of air fed for sintering under elevated pressure brought about some growth in specific productivity and enabled to decrease the coke breeze rate in sintering, thus improving sinter strength.

At the air temperature being 600C and 2% coke breeze rate, the specific productivity came to 4.7 tlm2 hour, and after strength tests the -5 fraction yield was lowered by 30%, as compared with the strength of sinter made under cold compressed air. The results of the first series of tests are given in Figures 2.2 and 2.3.

The second series of tests was used for looking into the effect of air pressure upon the

Process indices and quality of sinter.

To investigate how the pressure alone would affect the sintering process indices the sintering process was arranged with cold air at 19.6 kPa to 196 kPa and air preheated up to 600C, under 49 to 196 kPa pressure. An increase of air pressure within this range resulted in an increase in the sintering vertical velocity from 30-40 up to 80-85 mm/min. At air pressure being 196 kPa, the specific productivity, as compared with the vacuum sintering, increased five times. The specific rate of both cold and hot air for sintering under pressure happened to be within the range of 420-530 m3/t of sinter, which is considerably less than in the case of vacuum sintering process.

Thanks to a substantial pressure drop in the sintered layer, a higher sintering vertical velocity under pressure makes it possible to heighten the bed manifold. The impact of the sintered layer thickness upon the sintering process had been looked into with the help of a specifically designed sintering pot, 1 meter in height and 0.125 mm in diameter (figure 4). As can be seen form the Figure, there are annular manifolds 2 along the pot height, that are connected with the pot inside through 5 mm bores. The span between the manifolds is 130 mm. To make the escape of flue gas easier, the summary area of bores in the manifolds exceeds the cross section area of the flue gas main. The annular manifolds are connected with each other by a common flue gas uptake 4. If desired, they can be cut off the gas uptake with the help of valves 3. The pot is sealed airtight by caps 1 and 7 from the top and bottom.

For tests the same composition of sintermix was used: 67% of blend of concentrate with ore, 20% of return fines, 3.5% of coke breeze and 9.5% of limestone, which produced sinter of 1.3 basicity. The iron ore bearing part of sintermix consisted of concentrate from SS Beneficiation Plant (70%) and Atasuy Mines ore (30%).

After ignition, the pot was closed airtight by cap 1 and sintering was carried out with constantly maintained air pressure of 98 kPa above the layer.

The sintering test results are given in Table 2.1.

Table 2.1

The sintering test results (coke breeze rate in sintermix under

pressure - 3.5%, under suction - 4.0%)

Test No.Pressure

Above layer

KPaLayer bed

Height mm/minAir Rate

M 3/tYield

%Drum index- 5mm fraction

19824041.074.325

224040.075.124

348029.080.423

448028.081.524

572024.082.221

696021.781.318

796019.8-19

8*)96039.7--

9*)96043.0--

1019696038.8--

11Suction24020.0-28

1224021.5-30

*) - sinter was made with annular manifolds 2 kept open (Figure 2.4).

As can be seen from the table, an increase in the layer height from 240 to 960 mm was accompanied with a drop in the sintering vertical velocity (twofold). The correlation between sintering vertical velocity and layer height is plotted in Figure 2.5. This correlation is described by equation:

Y = ,

1

a+bx

where:-

y - sintering vertical velocity, mm/min;

x - layer height, mm

An increase in pressure above the layer from 98 kPa to 196 kPa, with its 980 mm height enabled to raise the sintering vertical velocity almost twofold. Based on the data, generated by measuring pressure along the layer height, curves were plotted to show variations of pressure in the course of sintermaking process (Figure 2.6).

The figures on curves denominate the level (horizon) of the sintered layer, in which the temperature was measured.

A drop in pressure at the initial stage of the sintering process can be explained by gas

dynamic resistance of the combustion zone and the inception of formation of the excessive moisture pick-up zone, which features the lowest gas permeability. As the formation of the excessive moisture pick-up zone was over, pressure in the lower layers would drop to zero, because there had been a drop in gas head in the upper layers.

The movement of the combustion Zone (sintering zone) in the course of the process was traced by measuring temperatures layer by layer. The curve, which characterizes the moving speed of the maximum temperature zone (full line) is shown in Figure 2.7. The same Figure shows how isobar lines are distributed along the layer height (dotted line). The field above the full line means finished sinter, below - raw sintermix. As can be seen from Figure 2.7, pressure in the finished sinter layer would be retained at 98 kPa till the end of the process, while in the sintermix layer it would be gradually coming down to zero.

Based on the experimental data, a curve had been plotted to show the variations in the sintering vertical velocity along the layer height (Figure 2.8). The minimum of sintering vertical velocity (14 mm/min) was registered practically in the middle of the layer at 450 - 550 mm distance from its top. Such a correlation can be explained, most probably, by the impact from the excessive moisture pick-up zone.

An adverse influence of this zone is corroborated by the data, generated by tests 8 and 9 (Table 2.1). As these tests were conducted, all the annular manifolds 2 and common flue gas uptake 4 (Figure 2.4) were kept open, which made it possible to eliminate a considerable quantity of moisture from the drying zone, thus wording off moisture pick-up in sintermix. As the sintering zone moved down, the manifold opposite to this zone was closed and flue gas escaped through the next manifold. As can be seen from Table 2.1, such a method of carrying gas off made it possible to increase the sintering vertical velocity up to 39-43 mm/min, with 960 , mm layer, which correlates with the velocity when 240 mm layer is sintered, using traditional method of carrying flue gas off.

While analyzing the test results, an idea cropped up, as to how intensify the sintering process by way of developing a new method of sintering, based on arranging two opposite sintering zones, using compressed air under elevated pressure.

As can be seen in Figure 2.9, there is a flow-chart of the suggested sintering under pressure process. As it is shown, the process starts when both the top and the bottom layers of sintermix are ignited. After ignition, compressed air is fed from above and underneath. As it happens, flue gas is carried off into manifolds 2 through bores, located evenly along the pot (1) height. As the sintering zones are moving towards each other, the manifolds are closed one after another in step and by the end of the process only one manifold would remain open, the manifold in the middle of the pot. Thus, there will be two sintering zones, moving towards each other. Thanks to that, the summary sintering velocity would be increased twofold and the sintering time at that would be decreased also twofold. The number of manifolds should be chosen depending on the layer height.

To verify this technology, a specially designed sintering pot was used (100 mm in diameter). Sintermix for experimental and reference tests consisted of 63% of concentrate from Olenegorsk Beneficiation Plant, 13% of limestone, 4% of coke breeze and 20% of return fines.

In all cases the layer was 400 mm in height, air pressure 147/296kPa.

The analysis of tests results testified to the fact that in comparison with the reference single - layer tests, in case of two-layer sinterrnaking the productivity was 1.7-1.9 times higher thanks to the suggested technology.

Implementation of this technology will enable to enhance substantially productivity of sintering machines or, neglecting increase in productivity, work under a lower air pressure. In addition, there will be no need to set up the bed.

Simultaneously with the research work and development of the innovative sintering process, various approaches as to how implement this technology in the existing conveyer type sintering machines were studied.

Since it was, however, difficult to seal the working part of the machine airtight, as to heighten air pressure above the layer while the machine is moving non-stop, it became impossible to implement this innovative process in conveyer-type machines.

3. Production of iron-bearing flux (extra-high basicity sinter)

in a revolving machine.

As a result of the above-mentioned endeavors, it was decided to use for sintering under pressure the machine with pots, of carousel type, as pilot units, erected at Toulachermet Steel Plant. The schematic drawing of the machine is given in Figure 3.1.The unit consists of a revolving platform with four pots on it, 500mm in diameter and 800 mm in height each.

The unit was used for streamlining various modes of operation in the production of complex iron-bearing flux from zinc-containing sludge, meant for converters and production of iron ore sinter, meant for iron making.

The sinter mix for the production of iron-bearing flux consisted of the following

components, content in %:

sludge blend from Novo-Lipetsk Steel Works

19.0-21.0

Limestone

37.0-39.0

Dolomite

9.0-11.0

Return fines

24.0-26.0

Coke breeze

7.0-8.0

Table 3.1 shows main characteristics of the sintering process, when an experimental batch of iron-bearing flux was made for using it in a 10-tons converter, to see the efficiency of this material in steel making.

Table 3.1

Process indices as iron-bearing flux was sintered under pressure

IndicesUnitValue

Layer HeightMm750

Pressure under the layerKpa167-186

Air RateM 3/t of sinter540-580

Filtration mean velocityM/s1.25-1.46

Sintering TimeMin3.4-4.2

Sintering vertical velocityMm/min180-210

Specific productivityT/m 2 hour7.5-9.4

Yield%69.8-72.0

It should be noted that the above-mentioned indices had been generated by selecting optimum fuel and return fines rate in sinter mix and its moisture.

The chemical composition of iron bearing flux(%) is given in Table 3.2CA

Table 3.2

Fe totalFemetSIO2CaOMgOAl2O3SFeOCaO/SiO2

22.62.14.548.98.01.80.226.810.9

26.05.46.353.110.42.30.469.78.4

As petrographic tests showed, the macrostructure of this flux was compact, with large pores. The microstructure was fine grained, consisting mainly of calcium ferrites.

Exactly as was expected from the previously carried theoretical work and laboratory tests, the use of iron-bearing flux for making steel from low-manganese hot metal in a top-blown converter accounted for a considerable economic benefit. At iron-bearing flux rate being 45 - 50kg/t steel the lime rate fell down by 25-30 kg/t of steel. At the same time it became possible to remove an expensive and scares available fluorite from sinter mix.

The results thus achieved can by explained by a low melting point of flux, as it is shown in table 3 (1300C), which would accelerate the formation of slag, reduce loss of metal (spattering drops). Yield would increase by 0.6-1.0%

The encouraging results of research work helped to realize the proposal for the production of the experimental batch of iron-bearing flux from zinc-containing blast furnace sludge, obtained from Kouznetsk Steel Works. As a matter of fact, this sludge had not been used as a component of sintermix since early forties.

Iron-bearing flux was made in a conventional 75 m2 Sinter making machine.Iron-bearing flux was used in open-hearth heats to save lime.

The revolving sinter making machine offered here can be successfully used for making iron-bearing flux. With sintering area being 11.1m2 and specific productivity of 7t/m2 hour such a plant can fully supersede a conveyer type 75 m2 sintering machine, to make 650 thousand tons of such product annually.

4. Recycling and dezincing of dust and sludge from iron and steel making shops

4.1. Sintering under pressure as used for recycling and dezincing dust and sludge from iron and steel making shops.

The of wastes from iron and steel making that contain hazardous impurities, can be considered at two angles:

1. Whether it is economically viable to recycle wastes with the purpose of saving raw material;

Protection of environment from wind-dispersed hazardous fine waste when it is transported or stored in dumps, washed out by rain, etc. Besides, an immediate in- house recycling of waste, i.e. on the spot, where it has been generated, will make it possible to reclaim vast areas of land, that have been occupied by dumps, settling ponds and alike.

Over the last 10-15 years, a lot of attention used to be paid at the steel plants of the erstwhile USSR, to the development of dust and sludge recycling methods. While doing it, the technology when dust and sludge are returned to sintermix at sinter plants was acknowledged as being the best.

To this end a member of rotary furnaces have-been erected at several works for drying sludge in them- At some works they made use of the equipment meant for injecting wet sludge into-mixing drum at sinter plant.

As of late, there has been a trend to increase the share of solid charge in converters, using coated metallic scrap, which accounts for an increase or zinc content in converter sludge. The recycling of this sludge in the production of sinter through a conventional technology would result in an excessive delivery of zinc (0.3 kg/t of hot metal) into blast furnaces, which should not be allowed. Because of that the use of this sludge in sinter making has been stopped.

In turn, it has lead to the situation where on the territories of the erstwhile USSR more than 3.0 million tons of zinc-containing sludge is sent to dumps annually.

The necessity to assess the methods used in various countries for recycling zinc containing wastes called for resuming research on how to use the sintering of iron ore bearing material under air-pressure above the layer, the method which was developed about 20 years ago in the Central Research Institute for Iron and Steel industry.

At usual vacuum sintering of mix which contains zinc-containing waste, an increase in fuel rate up to 25% will ensure a considerable removal of zinc from the layer. However, at the same time, a quantity of liquid phase in the sintered layer will be increased, which would lead to a sharp deterioration of the layer permeability and as a result, to a slower pace of the process. Besides, the fine suspension of zinc and lead oxides in flue gas would stick to the exhauster blades thus impairing their life.

Laboratory tests had been carried out to see how sludge could be dezinced through sintering under pressure. The tests were made on the equipment which was used for streamlining the sintering under-pressure technology.

Sintermix was-made of sludge blend from iron and steel making shops-of Novolipetsk Steel Works, with 52.2% iron and 2.54% zinc. Carbon content was 9.4%/

As had been established by preliminary theoretical work on optimum conditions of dezincing, zinc, lead alkali and other elements could be eliminated from the layer to a greater extent if specific additions ate put into sinter mix. The additions are envit6iiiiient friendly and do not deteriorate the quality of sinter. The extent of dezincing, achieved in tests was 80-85%. The addition rate-at that was 10-1;%, and coke-breeze - 6.0%.

Optimum air pressure above the layer was found out in the course of research work. It was also found out that 1.5 size was optimum for the addition and fuel. The size granules of sludge, which had been dehydrated in a rotary furnace, was 5-25 mm. Before blending, sludge was crushed in a jaw crusher into less than :3mm size. In other respects, the preparation or sintermix for desincing under pressure did not differ from the conventional vacuum sintering technology. It should be noted that the above mentioned degree of dezincing is a mean value for the cake.

In the layer of the cake zinc would be removed by 95%, which is explained by the zinc elimination mechanism under sintering, which consists of the following:

zinc in the sintered zinc is reduced into metallic phase, than it starts simmering and its vapour goes to the lower, colder layers, where zinc would be oxidized again and settled in the form of zincite. A good deal of zinc would get settled on the grid.

The laboratory equipment and caroussel machine, available at Toulachermet Plant, did not have gadgets to catch sublimates, as zinc-containing mix was sintered under pressure. In this connection a test stand of bigger size was erected in the central research institute for iron and Steel Industry. Its sinter pots were 800 x 800 x 800mm in size.

The process was carried out in the suction-blast mode of operation. The stand was

equipped with a standard metallic portable filter, which is used in non-ferrous metallurgy for catching metallic and other elements sublimates.

Below there is the chemical composition of sublimates, taken from the filter of the

dezincing stand:

pb-24

Mgo1,33

V206,2

Ge-0,0032

Zn-9,7

Si-0,6

Na2o0,5

Sn- 0,00068

Fe-10,1

SiO2-1,33

Cl-0,5

As-0,010

Al2O3-0,34

C-6,1

Mn-0,17

Loss of ig.-33,3

CaO-1,06

S-4,7

Ti02-0,11

The test stand was operated with interruptions, and the first stage of gas cleaning was not isolated from the sublimate catching filter. From the beginning of the sintering process the gas which was passing through the filter, was excessively wet, and by the end of the process, fine particles of sintered mix and even of unburned coke breeze fell on the filter. In view of the above, a real content of lead and zinc, caught by the filter, was 45.0 and 18.0%, respectively.

The sublimate buildup on the grid and flue gas side pipe in the immediate vicinity of the sinter pot bottom edge contained 46.9% zinc and 38.2% lead.

Hence it follows, that the industrial scale machine design should have a special arrangement of a valve to cut the primary gas cleaning system off the filters for the time when wet gas is leaving the sintered layer or a possibility to put the pot into the position when it would be connected with the filter only, as the flue gas temperature reaches 250-350c.

4.2. Good use of iron making and steel making sludge

To estimate the economics of sludge recy"c1ing,the main attention was paid to the

production of zinc-free sinter, because it is this production that would make the productivity of the machine the lowest and the cost of additions into sintermix and solid fuel would considerably excess that spent for the production of ordinary sinter.

To analyze the likely production cost of sinter, they used actual production data from Novo-Lipetsk Steel Works, whence sludge blend was taken for testing various dezincing technologies. On balance, the good use of dezincing technology can be achieved thanks to the following:

reduced production cost, by selling by-product outside which is a zinc- containing dust, to non-ferrous industry;

reduced cost of handling and selling dehydrated sludge to other industries, say, cement making companies;

saving of iron ore material;

enhanced availability of zinc in the domestic market.

As is known, the world-wide practice of using pyrometallurgy methods for the dezincing of sludge, is not economically efficient, despite the high degree of dezincing and use of dezinced product. These methods are resorted to mainly to meet the requirements of environment protection.

Below is Table 4.2.1 there are indices of some foreign methods of dezincing and the method in offer (sintering under pressure), from the viewpoint of energy consumption.

Table 4.2.1

IndicesSintering under

PressureRotary furnace Japanese technologyPlasma

Sweden

1. Dezincing PlantSintering machineRotary furnace

Shaft furnace

2. OutputSinter+ zinc containing DustReduced pellets + Iron + metallic zinc

Containing dustIron + metallic Zinc

3. Dezincing degree

80-8595-9890-100 %

4. Rate per 1t of iron bearing

- coal (coke breeze), kg

60(0.06)*)340(0.34)350(0.35)

- sludge carbon, kg100(0.1)100(0.1)-

- coke, kg--50(0.05)

-power, kWh--2200(0.73)

- total heat

consumption eq.f.t/t

0.160.441.13

*) -In brackets- equivalent fuel rate.

As can be seen from the table, the power consumption of dezincing if carried out through sintering under pressure, will be lower than that for other technologies.

It should be noted that there are some more benefits of the described process. First of all, it is an easy and simple method of preparing sintermix and running the process. The temperature level of the process is conditioned by the rate of fuel in sintermix only and vacillations within the range of. l 00-200C would not ten- upon the operating time and dependability of the equipment.

At the same time it is known that such variations in temperature in the processes that are carried out in rotary furnaces, may result in building up accretions and/or a drop of efficiency of the process.

The sintering-under-pressure process is controlled by the temperature of flue gas only. And at that it is not the absolute value of temperature that is the main parameter, but the moment when it reaches its maximum and then starts falling down, which testifies to the fact that the sintering process is over.

There is an interesting publication, which points out that Berzelius-Umwell-Service (BUS) Company in Germany is planning to enhance capital investment into the development of technology for recycling zinc - containing dust from electric arc furnaces, to recover zinc and lead and improve environment condition.

The company believes that it would be economically viable to recycle through Waels process the dust which contains at least 15% of zinc. The recycling of such dust is considered to be a good source for getting metallic zinc. For instance, the recycling of 55 thousand tons of dust will bring in about 14 thousand tons of zinc thus recovered, 2 thousand tons of lead, 2.5-3 tons of cadmium and some quantity of copper, indium and germanium.

As a result of the expansion policy, the Company has embarked upon recycling dust received not only from Germany, but also from Autstria, Scandinavian countries and Belgium. And yet, due to a high content of iron and low content of zinc (2-3%),1 million ton of converter dust and sludge a year have not been recycled.

The solve the issue for recycling dust, sludge and roll scale, BUS Company has entered into cooperation with other companies, including Scundust from Sweden.

Hence, it follows that so far there has been no technology developed for dezincing sludge and dust with low zinc content.

5. Production of sinter for iron making

For the practical implementation of the iron-bearing production-under-pressure technology TOTEM Co. Ltd. has designs of revolving sinter machines with 6 sinter pots (8m2 sintering area, productivity of 220 -280 thousand tons a year) and 9 sinter pots (11.1 m2 sintering area, productivity of 350- 400thousandtonsa year).

In case of "mini" steel plants, there is no need to set up blast furnace of big volumes. Therefore, while making calculations of the required productivity of the revolving sintering machine, a 750 m3 blast furnace was chosen, which was supposed to produce 620 thousand tons of hot metal annually.

To determine the productivity of the machine it was estimated that the iron ore part of sintermix should be 1600 kg per 1 ton of hot metal, including sinter (1120 kg). So, it will be 2120 t/day of skip sinter (~700 thousand tons a year).

To ensure non-stop supply of sinter it is suggested to erect two revolving sinter machines with 11.1m2sintering area and productivity up to 48tlhour (350-400 thousand tons a year) each.

This output can be obtained from a conventional conveyer type sinter machine of 75 m2 sintering area. However, the suggested technology of sintering under pressure, with two revolving sintering machines, has a number of advantages:

the weight of the process-related equipment for sintering under pressure is considerably lower than that for vacuum sintermaking;

- Revolving sinter machine complete with electricals,

hydraulic drive, charging, and ignition devices,

lubrication system

-2 Numbers-350t

- 75 m2 sinter machine complete with electricals,

ignition hood, distributor and lubrication system

-1 Number,-550 t

possibility to make the shop lay-out rather compact. All the equipment for preparation and sintering of mix can be accommodated in one building, which would reduce the scope of civics, mount-work and capital cost;

it desired to erect two sinter machines, the sinter plant can be constructed by stages.

In case of capital repair, one machine will be in reserve.

5.1. Sinter making process

A flow-chart for making sinter in the revolving machine is shown in Figure 5.1 It includes the following:

- Storage of sinter mix components;

- Crushing of flux and fuel;

- Weighing and portioning of components;

- Blending and balling of sinternix;

- Bed formation and charging in sinter pots;

- Sinter mix ignition;

- Baking of sinter mix in blast;

- Cooling of the cake (optional);

- Crushing

- Screening (separating into yield, bed and return fines)

The offered process can produce sinter of any desired grade, depending on needs and

actual situation.

5.1.1. Storage and preparation of sintermix.

All components of sintermix are to be stored and piled separately. The quantity of

material thus accumulated, should be sufficient for 5-10 days of operation.

The prime material size distribution:

coke, flux

-25 mm maximum

iron bearing material

-8 mm maximum

Crushing and milling of flux and fuel:

flux additions are to be crushed into size

- less than 2 mm;

solid fuel

- less than 3 mm

Before crushing, coke is to be classified by an unbalanced-throw screen. Coarse lumps of

coke (the oversize of 12-15 mm) is to be crushed in a roll crusher, and then the material and undersize are to be milled in a mill into desired size.

Portioning of the sintermix components

Sintermix components are portioned from the hoppers through weighers, component after

component. Returns thus generated ~re to be added to sintermix before the mixer.

There is a provision of automatic portioning, with the help of belt-conveyer weighers with vybro-funnels (AO TOCHMASH design).

Sintermix blend

One mixing drum will be needed for the blending and balling of sintermix.

Mixing drum:

- Diameter

- 2.8 m

- Length

- 6.0m

Mixing drum operating parameters:

- Output

- 150 t/hour

-RPM

- 6-9

- Filling ratio

- 10%

The bed and layer are shaped up by a specific charging device:

- Bed height

- 100mm

- Size distribution in bed

- 16-25mm

- Sintermix height (without bed) - 500 mm

5.1.2. Ignition and finished sinter

Sintermix is ignited with the help of an ignition hood, which would light up the top layer under air-pressure and at 1350C temperature.

Baking takes place under blast at air pressure of - 30-150kPa.

Air pressure for sintering

- 30-150kPa

Air rate (positions 4-9)

- 20000-25000 m3/hour

Suction in wind-box

- 0.1-0.5 kPa

Flue gas volume

- 19000-2000 m3/hour.

As cake is to be discharged periodically and its size is up to 1300 mm, it seems that the best way of doing it would be to unload it first on a breaking slab. After that sinter goes to the apron conveyer first and then to a belt conveyer to be delivered to the crusher and then screen.

The estimated temperature of finished sinter is likely to be 200-300C maximum.

If there is a need to make cold sinter, one can use a line cooler, which may be installed immediately after the machine, on the discharge route.

The primary screening provides three fractions: +25 mm, 16-25 mm, -16 mm + 25 mm fraction is a finished sinter. Fraction 16-25 mm goes to the bottom layer (bed), and its surplus is added to the finished sinter.

Fraction -16 mm is screened on the secondary screen into two fractions: 5-26 mm one goes to the finished sinter, and -55 mm one together with dust from filters goes to the return fines hopper.

The finished sinter is sent to the user on a belt conveyer with weighing scales, to the finished sinter bins.

The sinter bulk density is 1.6-2.2 t/m3.5.1.3. Gas flows arrangement

The sinter machine design and its performance are based on the following gas flow

circuits:

1). Ignition circuit consists of gas feed system, compressed air feed, ignition hood, wind box, gas uptakes and fan.

The ignition temperature is 1300-1350C.

At the moment of ignition, suction in wind-box is 4-6 kPa. The sucked gas temperature is

20-30C.

2) Sintering circuit consists of a blower, air pipes, pot caps, wind-boxes, exhauster, gas cleaning cyclones.

Dust content in flue gas is 3-4 g/m35.2. Specification of the revolving sinter machine and its make-up

The general view of the revolving machine for sintering under pressure in shown in Drawing N. TM101.00.000, sheet 1,2,3.

Specification of the machine:

Productivity, t/hour

- 48

Sintering area, m 2

- 11.1

Operating duty

-nonstop

Cake discharge-to-discharge time,

- up to 2 minutes

Number of mobile sinter pots:

- on the mix preparation platform

3

- on sintering platform

6

- total number of sinter pots that are

in operation at a time

9

Sinter pot diameter, mm

1300

Components weight in sinter pot, kg

~1600

Platform turning mechanism

-hydraulic

Layer surface smoothing device

- electro-mechanic

Ignition hood travel, mm

- 70

Pusher travel, mm

- 2955

Pusher moving speed, m/sec

- 0.112

Pushing force, kgs

- 600

Lock throw, mm

- 100

The sintering machine consists of the following subassemblies:

. Charging device;

. Sintermix preparation platform

. Sintering platform

. Mobile sinter pot (9 numbers)

. Ignition device

. Sinter pots pusher

. Cap take-off device

. Discharge device

. Gas uptakes

. Platform turning drive

. Platform position catches]

. Gantry (support struts, maintenance platforms, etc.)

The charging device consists of a bed hopper, sintermix hopper, two chutes, bed drum and sintermix drum.

The sintermix preparation platform is a steel structure, which rests on 8 support wheels.

The platform has a central thrust bearer, which takes side loads and serves as a pivot.

The sintering platform is designed in the same manner; it is a steel structure, which rests on 12 support wheels and is located in the center of the thrust bearer.

The mobile sinter pot in assembly is a 4-wheel trolley with a pot on it.

The pusher is a steel structure on wheels.

It is moved by an electro-mechanical drive. The pusher has an electric magnet driven grip for securing rigid contact with the pot trolley, when pot is being delivered from the preparation platform to the sintering platform and back.

The ignition device consists of a hearth, related structure, lifting hydro-cylinder, air and fuel feed pipes.

The discharge device consists of a hydraulic rack-and-gear drive, at the end of its shaft there is a lever to handle sinter pots.

The cap take-off device consists of a supporting gantry, which is mounted on the

sintering platform, 6 caps, that are suspended on the gantry by means of spring jacks, hydraulic cylinder to lift the caps, 6 air feed pipes. The device to feed air into the pot inside consists of a support, which is mounted on the sintering platform. It bears a manifold with six air mains connected with air feed pipes and caps.

The sintermix preparation gas uptake consists of pipelines to take dust-containing gas away from hoppers in the ignition device zone and finished cake discharge zone. To control the flow there is a provision of throttles.

The sintering platform gas uptake arrangement consists of a steel structure, which creates an annular housing which binds the blast zone.

The annular housing is made airtight with the help of mobile rubber seals.

The gantry is a steel structure, which includes decks, maintenance platforms, charging device support struts, ignition device struts, hydraulic system actuators struts, guides for the pusher.

The sintermix preparation and sintering platforms turning drives have two-speed electric motors, capable of decreasing inertia forces of the drives and thus to slow down the platform turning speed as they are coming to a stop.

The platform position catches are a steel structure with a locking lever, which is driven by a hydraulic cylinder.

5.3. Sinter machine operating flow-chart

Figures in the schematic diagram of the sinter-under-pressure machine' (Figure 5.2) denote the process positions that are sequentially taken by sinter pots. The dotted line shows the positions of wind-boxes. Arrows show the platforms revolving direction, when they are moved from one platform to another. There is a provision of 9 mobile sinter pots.

At position 1, sinter pots are charged sequentially with bed and preliminary prepared sintermix. First comes the portion of bed (screened-off 15-20 mm size sinter), then if necessary, a smoothing device is put on, to level the surface of the charge. Next comes the portion of basic product (sintermix), which is to be smoothed also.

At position 2, the mix top layer is ignited.

Position 3 is an auxiliary one, it is used for moving sinter pots from the mix preparation platform to the sintering platform and back. It is done with the help of a pusher.

At position 4, sinter pots are received on the sintering platform from the mix preparation platform. There mix is sintered, as each pot is traveling from position 4 to position 5, When the sintering process is over, a sinter pot is delivered from position 4, over position 3 to position 10, where cake is discharged. Then by a conveyer, cake is sent to the crusher.

The following operations on the mix preparation platfon11 can be fit i11totwo minutes period.

1. At position "discharge", a sinter pot with finished cake is unloaded. After that the pot waits for being turned into the charging position.

2. At position "charge", pot is charged with bed and sintermix.

3. At position of ignition, the following operations take place: hood is lowered and

pressed down then ignition takes place, holding and hood is lifted up.

4. Pusher moves the sinter pot from the mix preparation platform to the sintering

platform.

Pots are shoved off when the pusher emphasizes on the pot platform but end. While approaching, the pusher relieves the pot from the catch by means of a special pressing cleat. After rolling the sinterpot over to the sintering platform, the pusher comes back to its initial position on the sintering platform.

5. At the beginning of charge, the sintering platform is in a situation where position 4 is free for receiving sinter pot from the mix preparation platform. The cap is lifted and hanged above this position. As it happens, the throttle of air feed into the pot inside is closed.

Having moved the pot by the pusher from the mix preparation platform to the sintering platform the cap is lowered to close the pot. As it happens the cap lifting hydraulic cylinder remains in the lower position together with the catching clamp, waiting for the next cap closed pot.

As the cap goes down, the throttle is opened and the air purging of the pot begins. The purging starts and keeps going as the sintering platform is turning, after that the pot which has been sintered, is put into the conveying position. The other pots remain in the sintering cycle positions.

6. Further, the pusher moves the sinter pot from the sintering platform to the mix preparation platform. It is done with the help of a special catch on the pusher.

The mix preparation and sintering platforms are turned by cycles, independently from each other, but only after the operations at each position are over.

5.4. Arrangement and layout

~

The arrangement of material storage, how and where to do it, how to prepare sinter mix are to be decided by the Customer.

Drawing TM10l.00.000-TX sheet 1 shows the process flow-chart.

Drawing TMI 01.00.000-TX sheet 2 shows an approximate layout of the equipment and Space for the sintering-under-pressure machine.

Sinter mix components (iron-bearing raw material, fuel, flux and other additions) are delivered either by road or by rail to the store.

There must be stock sufficient for 5-10 days of operation, depending upon the type and source of transportation.

It should be an indoor raw-material storage, unheated, with a grab crane. Material is kept in stockpiles.

Stock can be unloaded from trucks directly into the receiving hoppers and from there delivered by a conveyer to the shop bins.

All equipment for mix preparation, sintering and further treatment of cake should be installed in one and the same building.

Solid fuel and flux from the receiving hoppers are sent to crushers. After that, from the shop bins, through weighers, the desired quantity of fuel and flux is sent to the sintermix hopper.

The prepared stock is delivered by a pneumatic system to the sintermix hoppers, therefrom together with return fines and additions it goes to a mixing drum. Then sintermix is sent to the revolving sinter machines and charged into sinter pots to be sintered under pressure.

The sintering process proceeds as per the flow-chart, described earlier.

If there is a need, it will be possible to install a second balling drum after the mixing drum.

Dust from cyclones and gas uptakes goes to the belt conveyers and then to the return fines conveyer.

It zinc-containing sludge is used for sinter, dust from special precipitators will be sent to the user for further processing.

There are the following rooms and bays in the main building: operators station, maintenance and repair bay, electro-technical rooms with respective equipment, pluming fixtures

5.5. Automatic control and monitoring

There is a provision of automatic control system to control the process (ACS), which consists of two, upper and lower levels.

The lower level of ACS is capable of controlling automatically the following systems:

milling of the mix components;

portioning;

mixing and balling;

charging of sinter pots;

sintering;

cooling of cake and its crushing.

This systems are equipped with sensors, primary control means , microprocessor controllers.

The basic parameters under control are as follows:

raw material consumption;

quality of sinter; .

height of the mix in a sinter pot;

temperature in the ignition hood; .

process parameters of suction and pressure in the hood and gas uptakes;

flue gas temperature; .

dust content in emission after the sintermaking processed.

The upper level of ACS is responsible for collecting and primary processing of parameters under control, as well as monitoring of equipment condition, consumption of raw material and power, formation and supply of information to the operating personnel.

There is an informative subsystem of control at this level.

These subsystems are realized through PCS. To control the sinter machine and conveyance facilities there is an operators desk, equipped with computers and allied equipment, means of communication and annunciation.

5.6. Environment friendliness of the process. Recycling of wastes.

The basic most harmful aspects of the sintering process are: heat and dust emission during classification and loading of sinter and dust, at junctions.

There is a provision in the sinter machine design for keeping all the dust generating points in proper places, with facilities to arrest and clean dusty air in cyclones.

There is a provision of aeration to fight heat emission.

As to volume of such emissions like oxides of sulfur, nitrogen, carbon is rather small, there is no provision for cleaning process gas.

Dust from process gas, spillage, aspirator dust are brought back to the process together with return fines.

If zinc-containing dust and sludge are used in sintering, it is necessary to install additionally special precipitators before cyclones as to catch sublimates that are generated in the course of the process. The temperature of flue gas at that should be higher than dew point.

5.7. Bill of main equipment

Pos no.ITEMSQUANTITYTOTAL WEIGHT (APPROX)REMARKS

1Belt conveyer, B-650 mm, N= 14kWh 1 18.0

118.0

2 Discharger, B=650 mm, N=3kW 1 3.013.0

3Revolving sinter machine2300.0

4Mixing drum, 2.8x8.0129.0

5One-roll crusher122.5

6One-deck unbalanced-throw screen12.5

7Double-deck unbalanced-throw screen13.5

8Lift, H=14. m, N=15 kW25.0CRUSHING BAY

9Crusher, N=211 kW25.5

10Separator2

11Cyclone, 15-700-4UP22.5

12Cyclone, 15-500-4UP22.5

13Classificator4

14Bag filter63.0

15Screw conveyer, N=2.2 kW1.0

16Lock feeder, N=1.1 kW0.3

17Lock feeder, N=1.1 kW20.20

18. Fan, N=30 kW20.7

19Fan, N=l1 kW20.5

20Pneumatic screw pump, 75 kW2.50

21Electric hoist, cap. 1t50.40

22. Electric hoist, cap., 0.5t10.08

23Blower, N=400 kW220.0

24Exhauster, N=75 kW24.0

25Fan, N=90 kW26.6

26Cyclone.82.0

27 Weigher62.5

28 Electric traveling crane, cap. 5t, L=27.5118.0

29Electric hoist cap=3.2t25.0

30 Conveyer, B=500mm, N=7kW333.0

31Conveyer, B=500mm, N=4.57kW635.0

32Conveyer, B=500mm, N=7kW216.7

33Conveyer, B=500mm, N=ll kW24.5

34Belt conveyer, B=800mm, N=7 kW22.0

35Belt conveyer, B=800mm, N=7.5 kW112.0

36Apron conveyer, B=1000mm215.0

37Sintermix hopper1

38Bed hopper1