directions for the organization of waste less metallurgical processes

7/26/2019 Directions for the Organization of Waste Less Metallurgical Processes .

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TRANSLATION FROM RUSSIAN LANGUAGE

42 YDK 669.1.504. 064. 43 Code 53.31

D. E Esezobor, V. I. Rostovsky, O. A Tunik, O. A Baidin

Directions for the Organization of Waste less Metallurgical Processes.

Technical Report Deposited with Ukraine Technical Information, 16.02.93 No

179-Yk93, January, 1993. 15 pages.

ABSTRACT

The paper presents the analysis of various sources of iron bearing wastes generated

in iron making and methods employed by Ukraine Government, Institutions of high

learning and Research Institutes of wastes-free technology to recover and recycle

iron-bearing wastes of metallurgical processes.

The wastes (residues) are produced during iron making, steelmaking, and rolling

operation and further treatment of steel products. These residues comprise slags,

dusts, sludges and mill scales and constitute almost 7% of steel production. Other

residues include spent pickle liquor and other iron-bearing materials. 25% and 50%

of the total quantity of iron-bearing wastes generated in the steel industry are derived

from sintering and iron making operations respectively.

The methods employed in Ukraine to recover waste materials in the steel industry

include mechanical, chemical and thermo-chemical methods. The choice of any of

these methods depends on the composition and properties of wastes and the specific

condition of operations. The popular methods of reclaiming steel mill wastes are

agglomeration and metallization.


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Introduction

Iron and steel industry includes all activities associated with iron-and steelmaking,

from coke production, sintering, pelletization, pig iron and sponge-iron production to

the production of finished steel products, including cold-rolled and cold- finished

products, coated products, wire and tubes. During these processes, significantamounts of usable or unusable materials referred to as by - products or wastes are

produced. In USSR, over 20 tons of solid wastes are produced per ton of rolled

products [1-2]. These include:

- Overburden and rock from the extraction of ore, fluxes and refractory materials-

14.7 tons

- Iron and steel scrap0.4 tons

- Ore (iron, manganese and chrome) enrichment tailings -3.0. tons

- (blast furnace, steelmaking and ferroalloy) slag3.0 tons

- Iron and steel scrap0.4 tons

- Products bearing iron (screenings, dusts, sludges, mill scale and hearth cinder

0.2 tons (dry mass).

- Others (refractory and non-ferrous-metal scrap, wood waste, textile waste,

waste containing rubber, etc)0.8tons

- Water87% of it recycledis used in the industry at the rate of 360 m3/ton

while 9.5 m3/ton of this value is dirty water.

The economic status of Ukraine, one of the 15 republics in USSR is based largely on

industrial and agricultural development and constantly improving transport system.

The state is located on a relatively small territory of Donetsk-Krivoroghsky basin with

a high population density, Hence her mineral, power, water, forest and land resourcesare intensively utilized.

In Ukraine, up to 35 million tons of iron is lost annually in the steel industry. Half of

this amount is from iron-ore mining sector, in the form of waste products. These are

non-magnetic and oxidized ores which are difficult to enrich by the existing

operational methods. 9 million tons of iron bearing waste materials is generated in the

steel plants annually. These by- products and wastes (residues) are produced during

iron making, steelmaking and rolling operation and further treatment of steel

products. They are slags, dusts, sludges and mill scales which constitute almost 7%

of steel production.

In the steel industry, various methods of recovery and assembly of dusts obtained

from gas and air dedusting system are employed. In most cases, the dusts from dry

dedusters are discharged and transported by hydro power. During this process, the

dust is transformed to sludge and with other sludges from water flushing of the

surroundings are conveyed to sludge storage tank or pit or sludge dewatering plant

(fig 1.), as in the case of baghouses (BH) and cyclones of sinter plant No 1 and No 2

of Zapadno-Sibirskovo Metallurgical Complex in Russia Federation. The particulates

and dusts from the entire length of the sintering strand to the wind boxes of the BH of

sinter plant No 3 are connected to two inclined scraping conveyors. The first conveyor


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receives materials from the side of charging burden while the second conveyor from

the discharging of sinters.

The shortcomings of these processes include the secondary emission of dusts to the

environment during its assembly and discharge to the conveyor and also the difficultyencountered during the treatment of these dusty materials.

This paper presents the analysis of various methods employed by Ukraine

Government, institutions of higher learning and research institutes to recover and

recycle the iron and steel industrys wastes.

Quantification of Steel Residues

Volume of wastes generated and their utilization were determined from the value of

production yield of the industry, the quantity of the plant, state of pollution control

system and its efficiency. Table 1 presents the main by -products generated in the

steel industry.

Table 1. The main by-products generated in the steel industryS/N Production process Wastes (residues) Yield, kg per

ton of product

1 Sintering

Gas cleaning Sludge 30-60

Dust 20-50

Water flushing and pollution control system Sludge 20-30

2 Blast

Furnace

(BF)

Flue dust 15-90

BF sludge 15-80

Screenings Sinter 80-150Pellets 30-60

Water flushing and pollution control system

Sludge

20-40

Casting machines 6-10

3 Steel

Making

OHF

Sludges

5-25

BOF 15-30

Electric Furnaces 5-20

OHF

Slag

70-120

BOF 90-120

Electric furnaces 60-100

Graphite dust of mixer workshop 0.2-0.4

Lime (0-8 mm) Screenings 20-40

Limestone (0-20 mm) 10-20

Lime Breeze from gas cleaners and pollution control system 10-20

4

Rolling

Mills

Mill scale Primary sedimentation 20-40

Secondary sedimentation 10-30

Grinding and cutting wastes 20-55

Sludge from roll grinding shop 10-40

Sludge from Gas cleaners 5-15

Metallic dust 10-30

Residues from metal degreasing and cleaning 5-10


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Sintering

The main sources of residues (wastes) in the sinter plant are the dust and sludge

generated during the discharge of particulate dusts from the BHs of the gas collector

and pollution control systems. Dust and sludge are also generated from the gas

dedusting systems and water flushing of the surroundings. Sulphur dioxide is emittedfrom the sinter machine off-gas.

The dust generated from the sinter plant can be classified as:

- dust resulting from mechanical treatment, handling charging or discharging of the

materials and the sintered products as well as the recycled materials and

- dust in the off- gas from the sintering machine.

The dusts components (coke and ore) are held back in dedusters (cyclones,

electrostatic precipitators and partly in graveled bed filters. The total amount of sinter

dust is on average 1 - 2.5% of the sinter produced. The sinter plant generates 25% of

the total quantity of ironbearing wastes in the steel industry [3].

Figure 1-2 are schematic diagrams of the various processes (reviewed) of recovery,

assembly and recycling of wastes in the sinter plant. The coarse particulates dusts

from the BHs are generally discharged and transferred to the sintering machine in

form of sludge in Dneprovsky metallurgical plant (Dzerjinskovo), Enakevsky,

Makeevka (fig 1). In some plants, where the level of utilization is high, the dusts are

recycled in form of solid materials (Azovstal,

Dnepropetrovsk). The dusts from the BHs and electrostatic precipitators (EP) of the

sinter plant are conveyed to the sinter return conveyor in their dried form by means of

vacuum pneumatic conveyor and reused as part of sinter charges(Figure 2)

The disadvantages of the first scheme (fig.1) include the huge capital and operational

costs, excess water consumption, huge maintenance cost of the dewatering plants and

sedimentation pit as well as low coefficient of utilization of iron bearing sludges.

However, the level of utilization of the above mentioned dusts and sludges in Ukraine

is 61% [Ministry of Steel, Soviet Socialist Republic of Ukraine].

Blast FurnaceIn the iron making division more than 10 types of wastes are generated. The

significant ones among them include flue dust, casthouse dust, sludge, sinters andpellets fines and BF slags.

Large fraction of the dusts generated in the blast furnace is released with the flue dust.

Other sources of dusts usually regarded as unorganized emission are from cone-bell

space, molten metal and slag, casthouse, dust bin and slag-granulation workshop.

The blast furnace gas is usually purified through multiple stages which may be more

than 3 - 4 consecutively attached equipment (dust catchers). The gas polluted with

dusts undergoes first stage of dedusting in radial and tangential dry dust catchers

(cyclones) where particles of flue dust with sizes above 100m are separated from the

BF gas. 60-75% of the total dust in the off-gas is collected in the above dedusters. The


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Radial

Clarifier

Thickener

Wastes

Mix

Sinter Returns

Iron ore 0-10mm Concentrates

Limestone 0-3mm

Coke breeze

Figure 1. A typical scheme of recovery and recycling of wastes using wet gas dedusters

Over- flowed

water

Dried iron bearing wastes

Filtrate

Drum Blender DB

S iral MixerLime fines

Disc Vacuum Filter

Classifier

Sus ended Solids

Water

Water

Drum

Mixer

Drum Kneader

CyclonesScrubber

To

Atmosphere

ToAtm

osphere

ToAtmosphere

Drag Vacuum Filter

Sinter Returns

Water

Sinter Returns

Drum Cooler

0-10mm

10-15mmSinter

Returns

Collector

Cyclones

Scrubber

+10mm

To DB

Collector

Precipitator

Iron bearing wastes Mix

Dust

Sludge


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resulting BF gas has a dust content ranging from 3 to 10 g /m3gas. Depending on the

separation efficiency, between 20 and 30kg of dust is removed for every ton of pig

iron produced.

Further purification of the gas is performed in scrubbers to obtain semi-fine particles

with sizes 20 m and density 0.6-1.6 g/m3. 10-50 kg of BF dust per ton molten iron inthe form of sludge is extracted by grid-type scrubbers. The efficiency of the

equipment (scrubber) does not exceed 60-70 %. The efficiency of gas purification can

be enhanced by including venturi-tube [4], while blast furnace operating on high

pressure may require the erection of both venturi and wet electro - precipitators. The

choice of equipment for BF gas cleaning depends mainly on the capital layout and

operational / maintenance cost. The technical economic indices of BF gas purification

are shown in Table 2

From the literature reviewed and field findings, a typical scheme of wastes generationand their recycling process is deduced and illustrated in Figure 3

Figure 2. A typical scheme of recovery and recycling of wastes using dry gas dedusters

Atmosphere

BH

SINTER

PLANT

B F

DSC

Sinter

EPLimestone Lime kilns

Iron ore

Coal coke ovens

Iron concentrate

Wastes

Chimney

Sinter Fines (bed)DB

Kneader

Sinter Fines (bed)

EP


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Figure 3. A typical scheme of wastes generation and their recycling process in iron making

A-Additives DDC- Dry Dust Catcher BOF- Basic Oxygen Furnace

S- Sinter EP- Electro Precipitator BF- Blast Furnace

P- Pellet CHCast House ST- Sedimentation Tank

C- Coke FD- Flue Dust DB- Drum Blender

- Moisture PR- Pellet Return SRSinter Return

D- Dust DF- Disc Filter SP- Sinter Plant

FT

D FDPRSR

CPSA

BF

DDC

Molten iron

DDC

cycling Grid-typeScrubber

H20

H20

DezincificationSludge Basin

Water washed

Surrounding

Granulation

SP

to SP (DB)

Pig iron

casting

EP

0-3 0-3

Blast air

SlagCH

0-1010-25mm BOF

BOF

ST

Plough spiral mixer

Sinter Plant=10-15%

Sinter

Plant

Atmosphere

Atmosphere

BLAST FURNACE

DF

Recycle

Mixer


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Table 2 The Technical Economic Indices of BF gas Purification [5]S/n Indices Dry Cleaning Wet Cleaning

Coarse particles Semi fine Fine particulates

Radial

De-Dusters

Cyclones Scrubbers

with venturi

Disintegrators Electro

filters1 Dust content in the gas, g/m

3

- Input 9-56 3-23 1.5-16.0 0.02-2.3 0.02-2.3

- yield (output) 3-23 1.5-16 0.02-2.3 0.006-0.05 0.005-0.05

2 Efficiency 50-75 40-60 80-99 95-98.8 95-98.8

3 Consumption Rate Per 100 m3gas

Electrical energy, kwh - - - 2.5-6.1 0.085

- water, m - - 4.7 0.5-1.3 0.3-0.4

4 Relative Quantity of dust to BF gas % 60-95 5-40

5 Relative capital cost to the total coat of BF gas

purification

4-10 90-95

Worldwide, various equipment of gas purification had been developed. This includeselectro filter and metallic fiber filter. These equipment have high efficiency of

purification up to 10 mg/m3at 200-300oC. At such temperature, gases can be recycled

or spent to produce electrical energy [6]

The emission of dust at the cone bell space can be effectively reduced by installing

autonomous de-dusting systems. In some plants the quantity of generated dust from

the furnace top laboratory is greatly reduced by recycling the gas after filtration to the

furnace top.

From investigations, loss of iron with flue dust and sludge from BF is averagely 80 kg

per ton of molten iron produced. The output of these wastes depends on the quality of

raw materials. In the BF No4 of the metallurgical complex at Krivorostal, where highquality raw materials are used and the sinter and pellets are screened prior being

charged into the furnace, the quantity of dust and sludge generated does not exceed 20

kg per ton pig iron. In Enakievsky metallurgical plant where screening is not done, the

value exceeds 160 kg per ton molten iron.

Steel ProductionThe use of oxygen to intensify steel making processes had raised the yield of metal

oxides dusts.

Open Hearth Furnace (OHF)

The open hearth furnace as a traditional steel smelter features great flexibility asregards the use of scrap, pig iron and fuels. Prevalent methods are the pig-iron /scrap

process (50-80% pig iron / scrap process (50-80% pig iron).

In Soviet Union, the development of modern OHF had been based on the tandem

process to increase the melting rate by preheating scrap.

Data from NPO Energostal indicates that the yield of OHF sludge is 5-15 kg per ton

steel and 10-25 kg per ton from tandem process. The quantity of emitted dust from the

surrounding air to the atmosphere is 1.8 kg /ton for OHF and for tandem process4.6

kg per ton steel.


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The quantity of OHF sludges generated in 1985 and 1990 in some metallurgical plants

in Ukraine is displayed in table 3

Table 3. The Yield of OHF Sludges in Some Metallurgical Plants in Ukraine

S/N PLANT 1985 1990

1 Dneprovsky (Dzerjinskovo) 23,000 50,000

2 Ilicha 30,000 45,000

3 Zaporodstal 18,000 20,000

4 Kommunarsky 71,000 85,000

5 Krivorodsky 65,000 90,000

6 Makeevsky 43,000 60,000

Basic Oxygen Furnace (BOF)

The major by-products of BOF are metallic by-product, slags, dusts and sludgesrefractory materials, fuels, lime dust and other materials.

BOF steel making dust and sludge are generated as a result of the cleaning of the off-

gas emitted from the process. The primary cleaning of the gases is normally achieved

by washing the gases with water and in a few cases, by means of dry electrostatic

precipitators.

The wet gas cleaning system is usually a 2-stage process. In the first stage, the gases

are cooled and the coarse dust is removed. During the second stage, the fine dust

fraction is washed out of the gas

The following types of dust collectors are mostly employed in the steel production

a) Inertial. De-dusting system of this type are of 2 folds namely i) Dust collector

with settling chambers whose operation is based on gravitational settling of dust

particles from the furnace off-gas and ii) cyclone de-dusters in which the dust

separation effect is achieved due to centrifugal acceleration

b) Impact- action typewhere the dust-laden gas flow encounters a solid body

(or a liquid, such as water droplets), and

c) Electrostatic precipitation (EP)

In many cases, exhaust gases, which contain nearly 90% CO are combusted with

entrained air, then cooled, cleaned and released into the atmosphere through a stack.

In some cases the gases are cooled with water sprays or waste-heat boiler upon

leaving the furnace and vented through a flare stack. Thus producing a certain

quantity of steam which can be used as process steam or for heating.


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Figure 4 shows schematically the gas cleaning system of a converter without

combustion of CO which makes it possible to utilize the latter as fuel at the works

(Enakievsky plant).The cleaning system comprises a waste heat boiler, gas cleaners, a

moisture separator with a whirler, a blower and burner. On passing through the boiler,

exhaust gases are cooled to 850oC and are then cooled further in a water sprayed gas

duct and enter the gas cleaning system comprises two stages of venturi tubes:

Converter

Sludge

Burner

U thrust

Blower

Dust collector

Gas

De-duster

Spray gas duct

Radial boiler

cooler

Sludge

Sludge

Figure 4 Schematic Diagram of the gas cleaning system of a converter without combustion of CO


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i) 2 parallel rectangular venturi tubes and ii) highpressure venturi tubes with a

moisture separator and a whirler.

The characteristics of the system are as follow:

Maximum flow rate of converter gas170,000 m3/hr

Gas temperature

At converter outlet 1700oC

After cooler 850oC

After 2ndstage Venturi tubes 50oC

Flow rate of water 1900 m3/h

Final dust content in gases 100 mg/m3

Maximum Rating power of boiler 182 t/h

Electric Furnace

Electric furnace are devices mainly used to produce high quality steel. Electric arc

furnace (EAF) is mostly preferred than any other electric furnaces. The rate of

generation for EAF dust in Ukraine ranges from 5-15 kg per ton steel melted. These

figures depend on the composition of the furnace burden, intensity of air injection into

the furnace laboratory. It also depends on the methods of oxygen application and

furnace capacity. The dust is collected by evacuation into a BH

Rolling and Finishing

Rolling may be done hot or cold. The principal residues produced from rolling and

related surface preparations are mill scale, rolling sludges pickle liquor and grinding

swarf. These residues constitute 0.7% of overall steel production and other residue

which includes dusts collected during maintenance and clean-up operations.

Figure 5 gives a schematic diagram of the metallic yield and different types of metal

losses, proceeding from in - got casting, the production of semi-finished products and

rolled steels as well as cold working on metallurgical products.

The value of material losses in rolling mills, i.e. slags, mill scale and scale sludge, is

approximately 4.5% of the total steel produced [7]. The quantity of these residues can

be influenced and reduced by heating furnace operation and deformation parameter


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such as optimum combustion in the heat treating furnaces, operation and rolling

sequence, reduction in the level of utilization of casting agents and types of fuel

MAMetal yield of respective production stage in percentage of ingot steel

Figure 5. Metal yield and losses at individual production stages in Rolling

Methods of Treatment and Utilization

In Ukraine, out of the 9 million tons of iron bearing waste products (sludge, dust

sinter fines, mill scales, slag etc) generated in the steel industry annually only 82% of

Ingot steel

mAO= 100%

Manufacture of semi-

finished productsScale

Crop losses

Fetting lossesMA, = 87.78%

Hot forming

Hotrolled rolling steel

MA2= 79.40% Rejects

Trimming Scrap

Scale scrap

Crop losses

Residuals

Cold Forming

Further

treatment

MA3= 73.57%

Rejects

Felting and

Pickling losses

Annealing,

planning peeling

and grinding losses

Residuals

Trimming scrap


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these products are recycled. Sludge (up to 3.2 million tons) is difficult to reclaim and

a little more than 50% of it is utilized. Table 4 provides data about the quantity of

generated sludge and its coefficient of utilization in the major metallurgical plants in

Ukraine. Data were obtained from field studies and literatures.

Steel could be regarded as the most recycled materials on earth. While this recycling

record has been impressive, more must be accomplished to identify and implement

cost effective methods for retaining all possible iron units within the production use-

recycle life cycle.

Several techniques are currently employed to treat iron-bearing residues in the

industry. Nevertheless the determinant factors of these methods are the sizes and the

end usage of the products. Figure 5 provides overview of steel by-product/wastes

treatment

Table 4. Overview of the quantities of sludges generated and usage in the major

metallurgical plants in Ukraine (1990)

S/N Plant /Complex Sinter Plant Blast Furnace Open Health

Furnace

Basic Oxygen

furnace

Electric

furnace

Quantity

Generated

Coefficient

of

utilization

Quantity

generated

Coefficient

of

utilization

Quantity

generated

Coefficient

of

utilization

Quantity

generated

Coefficient

of

utilization

Quantity

generated

Coefficient

of

generated

1 Dzepjinskovo 60,000 50 175,000 0 50,000 78 NA NA

2 Ilicha 920,000 79 115,000 100 45,000 0 61,00 50

3 Azovstal 20,00 100 150,000 50 18,000 44 65,000 100

4 Zaporldstal 40,000 100 190,000 110 85,000 100 NA NA

5 Enakeivsky 41,000 100 220,000 100 NA NA 53,000 0

6 Kommuarsky 150,000 100 140,000 50 71,000 0 NA NA

7 Makeevsky 210,000 100 219,000 17 60,000 50 NA NA

8 Dnepropetrovsky 109,000 40 54,000 100 NA NA 40 50 10,000 50

The choice of methods of wastes treatment for possible use in the sinter plant can be

grouped into three schemes: thickening of sludge with 300-500g of solid per litre ofwater, mechanical dewatering sludge to 5-40% moisture and further thermal

dehydration to 3-8% or blending the sludge cake with lime, cement or dry wastes

products. Analysis of these systems showed the use of the thickened sludge as the

simplest and most cost effective among them. The process does not require additional

expenses to treat sludge. The thickened sludge obtained from the thickener is

conveyed to the drum blender where the entire burden is blended together. However,

this process is feasible if reliable and durable pumping systems and feeders of sludges

are in place.

Other dewatering methods include mechanical thickening and dewatering, thermal

drying, chemical dewatering (mixing) and others. These methods are needed and


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preferences are given to those that are capable of economically reducing sludge

moisture to levels approximately 10%.

Dusts and sludges from iron making and steelmaking as well as scale and sludges

from rolling operations are mainly composed of oxides primarily iron oxide. Theseresidues are usually recycled through the blast furnace via sinter plant (if available).

The main limits to recycling the iron making and steelmaking residues are (their zinc

content, the presence of oil, water and other contaminants and the large content of fine

particles. Specifically, sludges suffer from the disadvantage of two much moisture,

and some rolling scale and sludges are hampered by the amount of oil they contain.

Moisture: Most agglomeration processes require the moisture content of mixed

incoming materials to be in the 5 to 10% range. The moisture content of a mixture can

be controlled by the adjustment of the proportions and sequencing of incoming wet

and dry materials so as to obtain the desired moisture level. However, the quantity of

wet by-products generated at a steel plant normally far outweighs the quantity of dry

by-products generated.

Mechanical dewatering of sludge characterizes the separation (classification) of

sludge into 2-3 parts, each of which is organized in separate machinery. The coarse

particulates are usually dewatered in classificators, semi-coarse in the belt-type

vacuum filter and fine particulates at the disc or drum vacuum filters.

Spiral classificators are exclusively used for treating coarse grain pulp with solid

content of 100-500 g/l while the grit /pulp from the spiral classifier is made of 35-

40% moisture. Further dehumidifications are performed in vacuum filters to obtain

13-18% moisture [8-9]. Filter presses are used to reduce moisture content of sludgesto 20-30% [10-13].

There are about 25 different types of dryers. Among them are rotary drum dryer,

bottom-weigh dry, tube-dryers, etc. In CIS convective (fluidized) drying is often used

[14].

In some situation, the required moisture content of the sludges may not be achieved in

the filters due to their grain sizes. Hence the sludges are further dewatered in the

thermal dryer.

The disadvantages of these equipment include the need to dedust the exhaust gasesembedded with large quantity of dust approximately 20% weight of dried sludge and

dusting of the dried sludge during its transfer and transportation to place of usage. The

drying process deprives the materials of some valuable technological properties

needed for agglomeration. These include water receptivity, moisture capacity,

dispersity and lumpiness. Moreover, thermal drying of materials process is expensive.

One of the best methods of treating sludge for sinter plants is the process of blending

the sludge with dried wastes produced. The pre - drying of sludge with dried wastes

materials (such as flue dust, sinter and pellet fines, lime, etc) to produce


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homogeneous, thickened and portable wastes mix enhances the use of these materials

in large quantities.

One of the methods of eliminating the use of dryer is the mixing of the moistened

material with non-slaked lime. The reduction of the moisture is achieved not only due

to the mixture of dried materials but also due to the chemical reaction of the lime andheat effect of the waste mix.

Various works on chemical dewatering of sludge with lime [15-18] and other several

additives (cement, organic absorbent, etc) [18-20] were carried out.

Two technologies have been implemented for the utilization of the iron units

contained in the steel mills sludge and dusts: cold and hot bonding (briquetting) of the

fines particles to make them suitable for use as a raw material in iron making and

reduction in a Rotary Hearth furnace and as additive to other burden materials. These

processes are feasible for materials with low content of harmful impurities.

The use of the sludge and dust in the iron making process does not allow the full use

of the wastes generated. Hence attention is given to the production of pre-reduced

pellet where these wastes serve as the primary raw materials.

All the processes and methods of production of metalized pellets can be generally

grouped into 2: processes in which reduction of iron is obtained as a result of gas-

reductant (mainly in shaft furnace) and processes where the solid fuel and gas are the

reducing agent (for example, processes occurring in the rotary kiln. These processes

are mainly used to separate harmful impurities (such as zinc, lead and others) from the

iron bearing materials.

The principle behind these processes is the same. The raw material (sludges) after

dewatering are palletized and subjected to thermal treatment in the presence of a

reducing agent

Recycled dust and sludges can contain up to 5% zinc which adversely affects blast

furnace operation and refractory life (internal scaffolding and slips of the furnace

stack and damages to the refractories. The maximum permissible zinc concentration

in materials to be charged to the blast furnace varies from steel plant to steel plant and

from country to country. The control level of zinc (maximum) in France is 0.15kg per

ton molten iron, 0.5kg per ton molten iron in UK. In USA it is0.5-1.0kg per tonmolten iron, while in Japan the value is considered to be 4kg per ton molten iron [12].

Generally, the control level charge into the BF is about 0.1% of the charge [21].

Apart from the fresh raw ore materials zinc enters into the BF mostly from the

recycled products of steel productiondusts and sludges of iron and steel making.

In a situation where neither BF flue dust nor sludge are recycled, 75-83% of zinc is

released through exhausted gas, while during partial close loop system (recycling of

flue dust) 90% of zinc is released through BF sludge [22,23]. However when the


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quantity of wastes recycled with BF does not exceed 10% of the charge, the effect of

zinc lead or alkali metals content will be negligible [12]

The behaviour of alkali metals in the BF is similar to the behaviour of zinc, but it

differs in the sense that at favourable condition of BF operation, large part of thesemetals are transferred to the slag and little quantity passed through the flue gases.

However, accumulation of alkali metals occurred when the quantity in the furnace

exceeds the quantity the slag can absorbed. This condition worsens the gas

permeability of the burden, formation of crusts and reduction of coke quality.

Analysis of reports from various countries showed that the maximum allowable

concentration of alkalis in Western Europe is 4.5kg per ton molten iron while in

Eastern Europe it is 6.0kgper ton molten iron [24]

Hydrometallurgy (classification of wastes and leaching) and pyrometallurgy

(reduction with volatization and chloridizing of iron oxides) are currently used to

remove harmful impurities.

Wet classification processes and selective chemical leaching tend to be ineffective

due to the fineness of the material and the form in which the zinc is present zinc

ferrite (oxide) in particles.

For over a long period in Japan, zinc is separated from clean ore and wastes through

the process called Waelz [25] which involves the heating of green pellets obtained

from zinc bearing sludges and reductant in rotary kiln at temperature 1050oC.

Institute Metallurgy Uralskovo Scientific Central AN Russia, Kuznetsk Metallurgicalplant and Belsky Zinc Plant collectively designed technology of treating blast furnace

sludges consisting of 7-10% Zn, 20-28%Fe, upto 0.3Pb, and 0.2-0.3S with the

separation of Fe and zinc in a rotary kiln [26]. This Waelz process can use cement as

binder for producing green pellets and about 10-15% graphite, semi -coke and

pulverized coal as fuel.

The disadvantages of Waelz process include high consumption rate of scarce fuel

(coke), the need to maintain constant or regulate furnace temperature and composition

of the charge to prevent the formation of crusts and treating of dusts and sludge with

not less than 4% Zn.

Increased recycling of galvanized steel is increasing the zinc content in steelmaking

dusts and sludges. If the zinc could be kept out of the BOF scrap charge, either by

segregation or by dezincing, the resulting BOF fume would have the concentration of

zinc unchanged. A broader solution to this problem may be in processes that remove

the zinc, with or without reducing the iron oxide, thereby creating two separate

recyclable streams.

That is, the partition of the high zincbearing fine dusts and sludge from the low zinc

containing coarse fraction dust and sludge. The latter can be recycled directly to a

sinter plant or agglomerated.


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17

In a Canadian Steel Plant in Hamilton, BF dusts and sludges preheated in a rotary

furnace are sieved and fraction-6.35mm is blended with 2% bentonite. The green

pellets obtained are roasted in a shaft heating furnace. The products are later treated in

with coke gas in an annular rotary kiln.

The ultimate conditions for treating burden mix in a rotary kiln are:

The consumption rate of air for fuel combustion in cyclone kiln should be 0.5-09

Temperature of products of fuel combustion 1200-1450oC

The pressure at the rotary kiln-140-160MPa

Temperature of off-dusty gas 50-500oC

At this condition pre-reduced pellets with homogenous phase compound, dissolution

of zinc constituents, its reduction, volatilization and separation as vapour [27] can

effectively occur.

ConclusionLarge volume of wastes in form of dusts and sludges is generated annually in various

steel plants in Ukraine. The recycling of these products into the production of iron and

steel will have a great effect on water, forest and land resources. Various methods of

recovery, assembly and recycling of these iron bearing wastes are employed in

Ukraine. Preference is given to the recycling of iron and steel mills dusts and sludges

through sintering-blast furnace.

The key barrier to the recycling of these products directly back to the blast furnace is

its chemistry. Dusts and sludge can contain up to 5% zinc, which adversely effectsblast furnace operation and refractory life. It is advisable to determine the value of

these harmful impurities and devise the appropriate technology for its removal.

References1. V.G Barishinkov, A.M. Gorelov, G.I Papkov, et al.

Secondary Materials Resources in Steel Industry. Tom 2 sludges, slag, wastes

(formation and utilization) Handbook: Moscow; Economika, 1986-p3-240

2. P.E. Ostaneko, N.F MiasnickoV. Waste free technology: treatment of ferrous

metals ore. Moscow, Nedra, 1988- p271

3. O. P Baidin, V. I. Rostovsky, D.E Esezobor. Organization of Wasteless Technology

in Blast Furnace Operations. Journal of Environmental Control and Rational

Utilization of Natural Resources. Donestsk, 1992 Vol. 1517, No2. p 32-36

4. Tashiro K., Onozawa M., Nagai T. et al A high efficiency gas cleaning system for

high top furnace blast furnaces //Nippon Steel Technical Report Oversea (Japan).-

1972-No 1 p32-36


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5. The problem of raising blast furnace workshops gas-clearning system efficiency

G.N. Popov, Y. V Shukin, V.A. Kzachishen et al Izestia Vuzov: Chernia metallurgia-

1987-No-11- p.30-33

6. Danilin V.V., Tkachenko V.V-Blast furnace gas cleaning in dry electrofilters //Industrial and Sanitational dedusting of gases: Materials from scientific and technical

information Institute headquarters Himneftemash Moscow, 1979-No3 p7-9

7. Phillipp, J.A and Maas, H. Abfallwirtshaft in einem Hiittenwerk (Waste

Management in a Metallurgical Plant) Stahl and Eisen, 104 (1984) No 8 p403-407

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treatment and recycling of valuable products and secondary water in SEV and SFRU

countries // Bulletin NTI: Chernia Metallurgia, 1980-No 4- p2-12

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Kiev zHaHue, (serial VII New on Science, Engineering Industry), No 12. 1985- p48

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recovery and dewatering.Moscow: Nedra, 1968203p

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1975.- No 4 p 162- 123.

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International197649No3 p. 173, 175-177, 179-181, 183-185.

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countries // Bulletin NTI. Chernia Metallurgia 1980-No13- p12-21

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1976 p. 223.

15. Patent Application 61-44137 Japan, MKI S 22 V 7 /00. Recycling of iron bearing

materials from Direct Reduction of Iron process / Tekemura Tetsus, Mutsuida Banko,

Kume Seiti et all No- 59167191; Applied 08.08.84; Publ. 03.03.86.

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sludges treatment / Sakupail Masaro- No 57-11339; Applied 26.01.82 publ. 03.08.83.

17. Patent Application 53 135803 Japan, MKI S 22 V 1/00. Treatment of Blast

Furnace and steelmaking sludges / Hanada Mitsuo, Fukuro Koiti- No 52 49998;

Applied 02. 05 .77 publ. 27. 1178.

18. Patent 4119455 USA, MKI C 22 V. 7/02. Method of recovering iron-bearing

product flue dust / E. Boud Cass, W. David Coate, R. Joseph QiugleyNo 837386;

Applied 28.09.77 Pub. 10.10.78.


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19. Patent 52-52924 Japan, MKI S 04 V 13/22. Method of recycling dust from blast

furnace / Kokura Fumikadzu, Savada Tadasi-No 50-128537; Applied 24.10.75 Publ.

28.04.77

20. A.S 804703 USSR, MKI S 22 V 1 /00 Method of treating sludge for sinter plant-/

G.L Gursky, A.Z. Kridevsky, A.A Gotovtsev et al. No 2749989, Applied 10.04.79

Publ. 18.02.81.

21. Waste Oxide Recycling Steel Plants: Proceedings Symposium, Hamilton, 1974-

Hamilton, p. 1-10

22. Lihodievsky V.A, Gubanov V.I, Ispolatorv V.B and other Peculiarities of

designing waste-free technology of iron ore treatment in an integrated steel plant.

Stal-1984 No5-p-5-8.

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Wiadowosci Hutnicre- 1981 No 11-12. p 276-280(Poland) Translation No 85p

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directions for the organization of waste less metallurgical processes

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