Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~7~ 8
The present invention relates to a method for removing the mois-
ture and the grease deposit from a rolling mill sludge, with a view to util-
i~ing the treated sludge as a sinter raw material. A rolling mill sludge
containing a grease deposit and having a high moisture water content is
deposited in a waste water pit of a steel rolling mill.
A scale or a cutting scrap in a small quantity is conventionally
mixed with iron ore fines to serve as a sinter raw material. Along with
the recent drastic increase in pig iron production, there is a rapidly in-
creasing demand for sinter as an iron-making raw material, thus requiring
installation of large-scale sintering machines. The resultant increase in
the consumption of iron sources other than iron ore leads to the utilization
of scales and cutting scraps having a high content of grease deposit in
larger quantities. From the point of view of pollution control, on the
; other hand, it is now a general practice to use an electrostatic precipita-
tor for collecting the dust contained in the exhaust gas from a sintering
machine.
More specifically, in conventional practice, a raw sinter mix is
fed from a raw material feeder into a pallet driven by sprocket wheels, -
ignated by an ignition furnace, and then sintered while evacuating the ex-
haust gas through a wind box and a duct. The dust contained in the ex-
haust gas in a large quantity is collected by an electrostatic precipitator.
The exhaust gas thus cleaned is discharged through a blower.
In this practice, however, if a sinter raw material containing a
grease deposit such as, for example, a scale or a cutting scrap is mixed
in a large quantity into the raw sinter mix, the combustion of the raw sin-
ter mix from its upper portion on the pallel by the ignition furnace would
raise the temperature of the middle and the lower portions thereof and
cause evaporation of the deposited grease. The grease vapor would then be
directed, together with the exhaust gas, into the electrostatic precipita-
tor through
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the wind box and the duct. The dust collected in the electrostatic precipi-
tator Lherefore would have a grease content of from 0.1% to 10%. This
grease~ if deposited in a large quantity on the electrodes of the electro-
static precipitator, would be burnt by the spark between the electrodes or
by the high temperature exhaust gas, and cause troubles such as, for ex-
ample, a fire in the electrostatic precipitator.
~ ecause a rolling mill sludge deposited in a waste water pit of
a steel rolling mill has a moisture (water)-content of from 20% to 30%, and
a grease content of from 2% to 3% even after dehydration through a filter
~0 press, the following measures are generally taken for the treatment there-
;~ of.
(1) To use the rolling mill sludge for reclamation or to dump the same for
ocean disposal;
(2) To utilize the rolling mill sludge as an iron source after removing
the grease deposit thereof by chemical washing (i.e., washing with a
chemical);
(3) To utilize the rolling mill sludge as an iron source after removing
the grease deposit thereof by combustion.
However, in view of the Fe content of from 60% to 70% of the rol-
ling mill sludge, method (1) above is not preferably from the standpoint of
the effective use of iron resources. Furthermore, the increasing require-
ment ~or pollution control more and more restricts the places for reclama-
tion or dumping of the same9 and the disposal of rolling mill scale by this
method may be virtually impossible in the near future.
Because of the small particle diameters and the high moisture
(uater) content of from 20% to 30% even a~ter the dehydration through a
filter press, the rolling mill sludge has ~ high viscosity. Treatment of
the rolling mill sludge by methods (2) or (33 above therefore, is not easy.
In
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method (2) above, furthermore, the very difficult separation of the grease
limits the use of this method.
Method (3) above requires high equipment costs ofr a fluidized bed
furnace, a rotary kiln, a multi-s~ate combustion furnace and other facilities9
and high OperatiOD costs. In any of these furnaces, the treatment of the rol-
ling mill scale at a high temperature of from 700C. to 800~C. causes agglomera-
tion of the rolling mill sludge, thus forming another disadvantage of this
method. There are many other problems in this method, such as, for example,
the necessity to install an electrostatic precipitator for collecting the dust
contained in the combustion waste gas.
For these reasons, no satisfactory results are being obtained by any
methods (1) to (3) described above.
An object of a broad aspect of the present invention is therefore to
provide a method for effectively utilizing as a sinter raw material a rolling
mill sludge containing a grease deposit and having moisture content. This
sludge is deposited in a waste water pit of a stell rolling mill.
An ob;ect of another aspect of the present invention is to provide
a method for substantially completely removing the moisture and the grease
deposit of the rolling ~11 sludge very easily`and with low equipment and
operation costs, with the use of the heat of the sinter produced by a sinter-
ing machine.
In accordance with broad aspects of the present invention, a method
is provided for removing water and grease deposits from a rolling mill sludge
to convert the sludge into a sinter raw material, the sludge having a water
content of at least 20 percent by weight, which comprises the sequence of steps
of: (1) positively reducing ehe water content of the sludge within the range
of from 1 to 10 percebt by weight, thereby reducing the viscosity thereof so as
to ensure a smooth supply of the sludge; and (2) feeding Lhe water-reduced
sludge onto hot sinter at at least one sintering operation stage consistlng of
(i) a sinter discharge section, (ii) an entry section of a sinter cooler,
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(iii) a belt-conveyor for fines return provided adJacent to a hot screen
therein, and (iv) a return hopper of a sintering apparatus for the opera-
tion, heat of the sinter produced in the operation substantially completely
removing the water and the grease deposit of the sludge.
By a variant thereof, the water content of the rolling mill
sludge is reduced within the range of from 1 to lO percent by weight by
heating the sludge with waste heat of a sinter cooler at a temperature of
from 120C to 200C.
By another variant, the water content of the rolling mill sludge
is reduced within the range of from 1 to 10 percent by weight by mixing the
sludge with a mill scale having a water content of up to 6 percent by
weight.
By yet another variant, the rolling mill sludge is a deposit in
a waste water pit of still rolling mill.
By another variant, the rolling mill sludge is so heated at a
temperature of from 140C. to 150C.
By yet another variant, the rolling mill sludge has a water con-
tent of from 20 to 30 percent and a grease content of from 2 to 3 percent.
In the accompanying drawings,
Figure 1 is a partial side elevation~ schematically illustrat-
ing a conventional sintering practice of a raw sinter mix by a sinteringmachine;
Figure 2 is a partial side elevation schematically illustrating
an embodiment of one aspect of the present invention; and
Figure 3 is another partial side elevation schematically illus-
trating another embodiment of another aspect of the present invention.
Referring firstly to the prior art as shown in Figure 1, a raw
sinter mix is fed from a raw material feeder 4 into a pallet 1 driven by
sprocket wheels 2, ignited by an ignition furnace 3, and then, sintered
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while sucking the exhaust gas through a wind box 5 and a duct 6. The dust
contained in the exhaust gas in a large quantity is collected by an elec- :trostatic precipitator 7, and the exhaust gas thus cleaned is discharged
through a blower 8.
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EXAMPLE 1
Before describing Example 1, a description of Figure 2 will be given,
in which Figure 2 is a partial side elevation schematically illustrating an em-
bodiment of the present invention. As shown in Figure 2, a raw sinter mix 10
having a known conventional composition, fed from a raw material feeder 4 onto
a pallet 1 of a sintering machine A is ignited by an ignition furnace 3 and
sintered as it travels to the left in the figure. A sludge feeder 9 provided
at a sinter discharge section B of the sintering machine A feeds a dried rolling
mill sludge 11, the moisture content of which has been reduced as will be de-
scribed below, and which contains a grease deposit, in substantially equalbatches, and feeds the batches onto the sinter on pallet 1. The dried mill
sludge 11 fed onto the sinter is heated by the heat of the sinter 13 while it
travels to a hot
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screen 1~ through a sinter breaker 12, and the grease deposit is substanti-
ally completely removed through combustion or evaporation. The rolling
mill sludge 11, the grease deposit of which has thus been removed, is
sieved through the hot screen 14, and is sent, together with the under-
screen fines, to a return hopper 19 through a belt-conveyor 21 for fines
return for temporary storage. The portion of the sinter remaining on the
screen 14 is sent to a sinter cooler 15, where it is cooled.
On the other hand, part of the cooling gas (air) heated by heat
exchange with the sinter 18 (for example, a fluidized bed dryer), where
the hot gas dries a rolling mill sludge charged therein. The sludge
which contains a grease deposit which has a high moisture content is one
which is deposited in a waste water pit of a steel rolling mill. For
e~ample, in the case where a rolling mill sludge, containing 28.0%
moisture (water) and 2.0% grease, charged into dryer 18, was dried at a
drying temperature of 140C. to 150C.for 15 minutes to 20 minutes, a
dried rolling mill sludge containing 1.13% moisture and 2.5% grease was
obtained. A drying temperature of the rolling mill sludge exceeding 200C.
in dryer 18 causes evaporation of the grease deposit, and this requires the
installation of equipment for c~llecting the grease vapor thus produced
in dryer 18. Such grease collecting equipment is not shown in Figure 2.
If the drying temperature is under 120C., drying of the rolling mill
sludge would take an excessive amount of time. Test results reveal that the
drying temperature should be from 120C. to 200C., preferably ~rom 140C.
...
to 150C. In the present invention in its various aspects, therefore, the
rolling mill sludge is dried with the use of the fraction having a temper-
ature of 120C. to 200C., preferably of 140C. to 150Co ~ out of the
cooling gas heated by the heat exchanger.
It is desirable to reduce the viscosity of the rolling mill sludge '-
by drying the rolling mill sludge to a moisture (water) content not exceeding
10%~thereby ensuring a smooth supply of the rolling mill sludge by the sludge
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feeder 9; however lt is not necessary to reduce the moisture content to un-
der 1%. The rolling mill sludge 11 thus dried but still containing a
grease deposit is fed from the dryer 18 to the sludge feeder 9 (as shown in
broken lines) and then is fed by the sludge feeder 9 onto the sinter as
described above to remove the grease deposit thereof.
The exhaust gas containing dust, grease combustion gas and
grease vapor generated in the process between the sinter discharge section
B and the hot screen 14, is collected through a hood 16, sent to a wet dust
collector (not shown) where it is cleaned, and then discharged. The dehy-
drated and degreased rolling mill sludge and return fines set from the re-
turn hopper 19 and the sinter raw materials sent from a raw material hopper
(not shown) are mixed into a known conventional compos~tion by a mixer 20,
and fed to the raw material feeder 4 in the form of pellets produced by a
pelleti~er (not shown) in amounts as required for carrying out the process.
The aforementioned ~ odiment covers the case with the sludge
feeder 9 installed at the sinter discharge section B. It is also possible,
by lnstalling the sludge feeder 9 at an entry section C of the sinter cool-
er 15 as shown in Figure 3, continuous:Ly to feed the dried rolling mill
sludge 11 containing a grease deposit :Ln substantially equal batches to the
; 20 entry section C of the sinter cooler 15, and thus,to utilize the heat of
~ the sinter in the sinter cooler 15. In this case, the grease deposit of
., .
; the dried rolling mill sludge 11 is removed by evaporation whlle the sin~
~ ter is cooled in cooler 15. The exhaust gas containing the greas~e vapor --
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produced in cooler 15 is collected by a hood 24 and is sent to a wet dust
collector (not shown) where it is cleaned and then discharged. In thls em-
bodiment, part of the cooling gas (air) heated by heat exchange with the
sinter in cooler 15, if directly brought into the sludge dryer 18, conta-
minates the rolling mill sludge in dryer 18 with the grease vapor. It is
therefore desirable to dry the rolling
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'7~362~
mill sludge in dryer 18 with the use of another hot gas (air) after heat
exchange with the hot gas from cooler 15 by installing a heat exchanger
25. The rolling mill sludge, the srease deposit of which has thus been
removed, is separated from the cooled sin~er by a sieving equipment 22
provided at the exit section D of cooler 15, and sent to the return hopper
19 through a belt-conveyor 23 for fines return. Explanation o the other
reference numerals in Figure 3, being the same as in Figure 2, is omitted
here.
It is also possible to use the dried rolling mill sludge contain-
ing a grease deposit, by dividing it into substantially e~ual batches,
and feeding the batches onto the belt-conveyor 21 for return fines provided
adjacent to the hot screen 14 or into the return hopper 19, shown in
Figure 2, and thus to remove the grease deposit of dried rolling mill
sludge through evaporation with the use of the heat of the fines return. .:
In this case, the grease vapor produced on belt-conYeyor 21 or in return
` hopper 19 is collected by employing the above-mentioned means.
EXAMPLE 2
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A scale mi~er (not shown) was prov.ided in place of the sludge .
dryer 18 in Example 1. A rolling mill sludge containing from 20% to 30% ~:
moisture (water) and having a grease deposit, and a mill scale containing
not more than 6% moisture and collected without the use of roll cooling :;
water were charged into the scale mixer at a ratio of 1:3 and mixed up .
for from 2 minutes to 3 minutes. A mixture containing from 7% to 10%
moisture was thus obtained. As in the embodiments in E~ample 1 described . ~ .
above with reference to Figures 2 and 3, this mixture was fed to any of ..
. the sinter discharge section B, the entry section C of the sinter cooler . ;
15, a belt-conveyor 21 or fines return provided adjacent to the hot
,
, screen 14 and a return hopper 19, and a grease deposit of the mixture :. ::
was removed through combustion or evaporation with the use of the heat ~ .
of the sinter of the fines return. In this embodiment, a mill ~ :
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~78628
scale containing not more than 6% moisture was mixed, because the use
of a mill scale containing more than 6% moisture requires a large
quantity of mill scale to reduce the moisture (water) content of the
mixture to under 10%. Detailed description is-omi*ted here because
the process in Example 2 is identical with that in Example 1 except
only for the replacement of the sludge dryer 18 in Example 1 by a scale
mixer.
According to aspects of the present invention, as described in
detail above, it is possible substantially to remove the moisture
(water and the grease deposit from a relatively fine and very viscous
rolling mill sludge containing a grease deposit and having a high
moisture content through very simple treahnent and with very low equip-
ment and operation costs. Hence it is possible to utilize the rolling
mill sludge in a large quantity as a sinter raw material as well as
being possible substantially to prevent fire accident in an electro-
static precipitator caused by the grease deposit of a rolling mill
sludge, thus providing industrially useful eEfects.
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