AU2002308827B2 - Recycling Method of Waste Material by Using of Coal Based Iron Making Process - Google Patents

Description

RECYCLING METHOD OF WASTE MATERIAL BY USING OF COAL BASED IRON

MAKING PROCESS

TECHNICAL FIELD

The present invention relates to a recycling method of dust

and sludge produced in iron and steel works, and more particularly,

to a recycling method by which waste material such as dust and

sludge outputted in an iron and steel working process can be

recycled as fuel and raw material in a coal based iron making

process .

BACKGROUND ART

In general, by-products outputted in most iron and steel

works can be mainly discriminated into slag, dust and sludge.

Although dust and sludge can be recycled as raw material in some

iron and steel working, smelting or cement manufacturing

processes since they are abundant with Fe and C components, a

large portion of the by-products tend to be buried through

solidification without recycling. Therefore, treatment and

recycling of the by-products are gradually becoming important environmental problems in the ironworks . The iron and steel works output dust and sludge in each

process. Dust and sludge are mainly comprises compounds of carbon component useful as both of heat source and reducing agent,

Fe component useful as raw material of iron and Ca, Mg and so

on useful as supplementary raw material. Although dust and

sludge have particles sizes of 1mm or less, occasionally the

particle sizes thereof reach up to 8mm. Moisture content is

remarkably different according to processes of outputting sludge

and dust, or between dust and sludge.

Recycling of the dust and sludge is greatly dependent upon

several conditions such as component difference, moisture

content, particle size and so on. Therefore, dust is recycled

by a large quantity since it has low moisture content and can

be simply treated, whereas outputted sludge is recycled by about

half only.

The COREX process, i.e. one of coal based iron making process, generally uses two reactors such as a melter gasifier

20 and a reduction furnace 10. In the iron making process, iron

ore used as raw material is charged together with supplementary

raw material into the top of the reduction furnace 10, where iron

ore and supplementary raw material undergo reduction and

sintering due to reducing gas blown through the bottom of the

reduction furnace 10. Reduced iron ore and sintered supplementary raw material are fed into the melter gasifier 20,

where they are hot melted to yield pig iron. Coal is charged into the hot melter gasifier 20 to produce reducing gas, which

is fed into the reduction furnace 10, in which char of the

remaining coal is used as heat source as it reacts with oxygen

at the bottom of the melter gasifier 20. In the meantime,

reference numerals 12, 210 and 222 each indicate an ore-charging

duct, a dust-recycling duct and an exhaust gas duct.

In the coal based iron making process using the above two

reactors, a large quantity of reducing gas is fed into the upper reduction furnace 10 from the lower melter gasifier 20 so that

fine dust of coal, reduced ore and supplementary raw material

can be fed on reducing gas into the reduction furnace 10. Since

this is a major reason for deteriorating the internal status of

the reduction furnace, a cyclone 21 is installed between the

melter gasifier 20 and the reduction furnace 10 in order to remove

fine dust from gas.

Fine dust trapped by the cyclone 21 is blown again through

a two-stage charging vessel into the melter gasifier 20, in which

melting condensation is carried out with a dust burner 213 in

order to prevent blown fine dust from dispersing again. In such melting condensation, oxygen is fed together with the fine dust

into the dust burner to burn fine dust at the leading end of the dust burner by using carbon contained in coal as fuel and blown

oxygen and oxygen contained in some of reduced ore as oxidizing agent .

This makes reduced ore melt and condense thereby

restricting re-dispersion. The dust burner blows again fine

dust outputted from the melter, and fine dust is

melting-condensed at the leading end thereof and thus restricted in its re-dispersion.

SUMMARY OF THE PRESENT INVENTION

It is therefore an object of the invention to provide a

recycling method in a coal based iron making process, which allows

recycling of waste material such as dust and sludge outputted from iron and steel works.

In order to obtain the above object, the invention provides

a recycling method of waste material in use for a coal based iron

making process by using a reduction-melting apparatus which includes a reduction furnace for reducing ore and supplementary

raw material, a melter gasifier for reduction-melting reduced iron fed from the reduction furnace into hot metal, a cyclone

for trapping fine dust in exhaust gas from the melter gasifier

to circulate trapped fine dust to the melter gasifier and to feed exhaust gas cleared of fine dust to the reduction furnace as

reduction gas, and a dust burner with one end connected to the

cyclone and the other end connected to the melter gasifier and

for executing melting condensation to and then blowing fine dust

into the melting gasifier, in which the method comprises the

following steps of: collecting and drying waste material so that

the total composition of T.Fe, C, CaO and MgO reaches at least

50wt%; sorting dried waste material to have a particle size of

5mm or less; and blowing sorted waste material into the melter

gasifier with the dust burner.

BRIEF DESCRIPTION OF THE DRAWINGS

The above object and other advantages of the present

invention will become more apparent by describing in detail the

preferred embodiment of the present invention with reference to the attached drawings in which:

Fig. 1 schematically illustrates a general coal based iron

making process; and

Fig. 2 is a schematic view illustrating a recycling

apparatus of waste material in an iron making process according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter the present invention will be described in

detail.

As set forth above, it is a main feature of the present

invention that sludge and dust outputted from iron and steel works

are blown after adjusting composition and particle size thereof,

thereby recycling them in an iron making reduction-melting

process .

First, in the present invention, sludge and dust outputted in an iron and steel working process are collected for recycling

thereof. At this time, sludge and dust are required to contain

useful components in the iron working process such as Fe, C and

supplementary raw material (CaO, MgO) whose total composition

is at least 50wt%. It is because charging of waste material

cannot be effectuated as additional charging of fuel and raw

material unless the total composition of the useful components

reaches 50wt%.

If collected sludge and dust contain those components such

as alkaline metal compounds, Zn, S, and P by a large portion

dropping the total composition of the useful components under

50wt%, such sludge and dust are not suitably used in the iron

making process since those components would deposit within the melter or act as heavy load in a hot metal pretreatment .

That is, if sludge and dust are mainly composed of those

elements including Si, Al, S, P, Cl, Zn, Na and K rather than

the above useful components, those elements may create severe

problems in the operation of the iron making process.

Specifically, Si and Al components removed as slag in the iron

making process directly affect properties of slag such as melting

point, viscosity, desulfurizing ability and so on. So there are

a number of difficulties in recycling sludge or dust containing

the Si and Al components by a large quantity. Further, in selection of fuel, raw material and supplementary raw material,

those components are strictly restricted since they otherwise

would yield low-grade pig iron and form deposits within the

furnace while creating environmental problems .

In this regard, the invention preferably restricts the

composition of waste material so that collected sludge and dust may contain Si and Al compounds each at 20wt% or less, Zn, Na

and K components each at 5wt% or less and S, P and Cl components

each at lwt% or less. The following Table 1 shows examples of

dust and sludge applicable to the invention. Any waste material meeting the above composition standard

is collected and then dried. Where the moisture content is too

high, it is difficult to transport waste material on a belt or

via air, and waste material is unsuitable for the iron making

process.

The moisture content of dried waste material is controlled

with a drier, preferably, at 10% or less.

Above dried waste material is sorted to have a certain

particle size or less. Dried waste material is classified according to its particle size applicable to a dust burner, that

is, for example, about 70mm or less since a blowing portion of

the dust burner has an inside diameter of about 70mm.

Sludge and dust are necessarily melted and condensed in

flames of a dust burner for being recycled in the iron making

process, however, the present inventors found out through

researches that dust particles having a particle size of 5mm or

more hardly melt or condense in the dust burner based upon iron

ore regardless of their melting degrees which are varied

depending on their components. Further, the inventors found out

that in case where the iron ore particles have the large specific

gravity and a particle size of 5mm or more, it is required to

blow the air with a velocity of about at least 20m/s in order

to pneumatically carry them up to a charging bin which is installed at least 50m high from the ground, thereby not ensuring

an efficient blowing.

Therefore, the invention restricts the particle size of

waste material at 5mm or less, and preferably, at 3mm or less

considering efficient blowing and melting.

And waste material having thus classified particle size is blown into the melter gasifier with the dust burner, and

therefore, the waste material outputted in the iron and works

can be efficiently recycled as fuel and raw material of the iron

making process.

Hereinafter the following detailed description will

discuss a detailed blowing method of the waste material prepared

as above.

Fig. 2 is a schematic view illustrating a coal based iron

making apparatus according to an embodiment of the invention, in which the apparatus generally comprises a reduction furnace

10 adapted for reducing ore and supplementary raw material, a

melter gasifier 20 adapted for manufacturing pig iron through

reduction-melting of reduced iron fed from the reduction furnace

10 and a cyclone 21 for trapping exhaust gas from the melter gasifier 20 to circulate fine dust in exhaust gas through a dust

recycling duct 210 to the melter gasifier 20 and feed exhaust gas cleared of fine dust through a gas duct 22 to the reduction

furnace 10 as reduction gas.

Further, the reduction furnace 10 is connected through an ore-charging duct 12 to the melter gasifier 20 in an

ore-communicating relation, and includes a dust burner 213

having one end connected to the cyclone 21 and the other end

connected to the melter gasifier 10 and for executing melting

condensation to and then blowing the fine dust into the melter gasifier 20.

First, waste material such as sludge and dust produced from

processes in iron and steel works is collected in a storage 41.

The collected waste material is dried in a drier such as a rotary

kiln 42 for adjusting the moisture content suitable for recycling.

Dried waste material is adjusted in a sorting machine 43 to have

a particle size suitable for recycling. Coarse waste material

sorted in the sorting machine 43 is sent again to a grinding

machine 44, where coarse waste material is ground into a desired particle size.

In this manner, waste material having certain degrees of

moisture content and particle size is stored in a storage 31, and stored waste material is fed through a rotary feeder 34 and

a feeding line 35 to a temporary storage 36 which temporarily

stores waste material. Waste material in the temporary storage 36 is fed through a rotor feeder 37 under the storage 36 to a

storage 212 and then to the dust burner 213, by which waste material is blown into the melter gasifier 20.

In the meantime, the invention preferably mixes any

material such as ore or coal, which is used as fuel or raw material in the iron making process, into above prepared waste material

before feeding waste material to the dust burner 213 in order

to enhance the melting condensation efficiency of waste material

having the above composition and particle size distribution.

For the purpose of complete combustion of blown fine dust, at the leading end of the dust burner, the art examines the

oxidation states of carbon component (raw material) and ore

(regarding oxygen in metal oxide which is not completely

metalized as reducing agent) while adjusting the quantity of

oxygen which is blown in together with fine dust. Therefore,

the degree of compounding between coal and ore can be changed

into any value according to the carbon content and the oxidation

degree of iron oxide in waste material to be treated. The

compounding ratio is flexibly adjusted according to operating

situations, that is, oxidizing agent component can be overly

mixed to stop temperature elevation when the melter gasifier is

so heated to excessively elevate its temperature due to complete

combustion. The following example will provide a more detailed

description of the invention without restricting the extent of the invention.

EXAMPLE

The following experiment was performed in order to know

whether sludge/dust can be recycled in the iron making process.

The composition of sludge/dust used in this experiment is

reported in the following Table 2. In Table 2, Inventive

examples 1 to 3 each contain T.Fe, C, CaO and MgO components whose

total composition is 50wt% or more, while Comparative examples

1 and 2 each contain the same components whose total composition

is under 50wt%. In the meantime, sludge/dust particles used in

this experiment are so sorted to have a particle size of 3mm or

less.

TABLE 2

Sludge/dust waste materials having the above composition

and sorted with their particle sizes were respectively blown into

the melter gasifier of the reduction-melting apparatus

configured as shown in Fig. 2 at a blowing speed of 5ton/hr for

3 days in order to make molten iron while evaluating any problems

in operation and facilities related to blowing of the waste

materials .

First, in order to determine the quantity of blown

sludge/dust which leaves on reduction gas out of the melter

gasifier 20 without melting condensation, it is measured the

quantity of dust circulating in the dust recycling duct 210 and

the air permeability of the reduction furnace 10 before and after

blowing. As a result, it can be seen that both of sludge and

dust waste materials have no effect on the air permeability of

the reduction furnace and the quantity of circulating dust has

no variation before and after blowing by the following reason.

That is, since both of the sludge and dust waste materials have

a particle size of 3mm or less within the inventive range, they

could be effectively melted and condensed when blown into the melter gasifier.

Then, the effects for the composition of the blown

sludge/dust are examined. As a result, in case where the waste

materials of Inventive examples 1 to 3 within the inventive range are blown into the melter gasifier, there was almost no variation

in the operation while increasing the yield of molten iron.

On the contrary, in blowing the waste materials of the

Comparative examples 1 and 2 having composition beyond the

inventive range, it is required to additionally charge certain

quantities of lime and dolomite to adjust the basicity of slag

thereby increasing the output of slag. That is, when blown into

the melter gasifier, sludge and dust which contain a small amount

of useful components (e.g. T.Fe, C, CaO, MgO) and a large amount

of Si and Al increase the output of slag by itself because they

perform the same role as those components outputted as slag.

Also, it is needed to further charge supplementary raw material

to adjust the basicity of slag thereby dropping productivity.

As described above, in order to recycle sludge and dust

outputted in the iron and steel working process in the coal based

iron making process, it can be understood that sludge and dust

necessarily contain T.Fe, C, CaO and MgO whose total composition

is at least 50wt% as well as have particle sizes of 5mm or less

by taking account of the increasing hot metal output and reduction

in use of heat source and supplementary raw material.

According to the present invention as set forth above,

there is a useful effect that dust and sludge produced in the iron and steel works and generally subject to burial are recycled

as fuel and raw material in the iron making process.

Claims

CLAIMSWhat is claimed is:

1. In a coal based iron making process by using a

reduction-melting apparatus which includes a reduction furnace

for reducing ore and supplementary raw material, a melter

gasifier for reduction-melting reduced iron fed from the

reduction furnace into hot metal, a cyclone for trapping fine

dust in exhaust gas from the melter gasifier to circulate trapped

fine dust to the melter gasifier and to feed exhaust gas cleared

of fine dust to the reduction furnace as reduction gas, and a dust burner with one end connected to the cyclone and the other

end connected to the melter gasifier and for executing melting

condensation to and then blowing fine dust into the melting

gasifier, a recycling method of waste materials comprising the following steps of:

collecting and drying waste material so that the total

composition of T.Fe, C, CaO and MgO reaches at least 50wt%;

sorting dried waste material to have a particle size of

5mm or less; and

blowing sorted waste material into the melter gasifier with

the dust burner.

2. The recycling method according to claim 1, wherein

waste material is dried to have a moisture content at 10% or less .

3. The recycling method according to claim 1, wherein

dried waste material is sorted to have a particle size of 3mm

or less.

4. The recycling method according to claim 1, wherein the

blowing step of sorted waste material comprises: mixing a proper

amount of ore or coal into sorted waste material.