Method for purification of cooling agents and/or lubricants used in rolling mills

For purification of liquids used for cooling and/or lubrication interspersed with metallic and/or other materials contaminations, especially for separation of rolling scale and of substances containing oil or grease from the industrial process water in open or exposed cooling circulation cycles in the smelting industry, especially in rolling mills, it is proposed to separate the coarse rolling scale by gravity sedimentation from the contaminated process water, to subsequently remove the mid-size and fine rolling scale particles from the process water prepurified in this manner by magnetic separation, to divide by flotation the thus finished clarified or purified process water into fractions containing oil concentrate, water and the finest rolling scale particles carrying little oil, the purified process water is to be used as a cooling agent, the entire rolling scale separated out of the process water is smelted in the form of sinter and the concentrate containing oil is either rejected or subjected to a waste oil purification.

BACKGROUND OF THE INVENTION 
The invention deals with a method for purifying cooling liquids used for 
cooling and/or for lubricating, that are interspersed or loaded with 
metallic and/or other material impurities, especially for separation of 
rolling scale and oily or greasy substances from industrial process or 
efflux water in open cooling circulation cycles or systems in the iron or 
steel industry, especially in rolling mills. This invention deals also 
with a pertinent purification installation or plant for performing the 
method. 
From year to year higher requirements concerning the chip removal output or 
the shaping output and very high requirements concerning the quality of 
the surface are specified for the products which are processed by the 
different processing methods in the machining as well as the non-cutting 
shaping or deformation technology. The heat generation arising during the 
chip removal output or during the non-cutting shaping output must be held 
within limits, for which reason cooling is required in most cases in order 
to keep the temperatures constant during the processing operation. With 
the required surface smoothness or quality, care must be taken that 
particles which have already been removed are rapidly and completely 
conveyed away from the machining or processing points. Especially in the 
case of chipless deformation technology, for instance in rolling mills 
care must be taken that the surfaces do not contain any solid foreign 
materials in the regions where the shaping tools or the rolls of a rolling 
stand come in contact with the workpiece, since otherwise these are rolled 
into the material of the workpiece and the charge involved must possibly 
be completely scrapped. The cooling and lubricating agents are therefore 
continuously contaminated with a fine dust or grit from the shaping 
process. In case of lubricants, aging products are additionally formed. 
Since these cooling and lubricating agents consequently are continuously 
enriched by fines or grit and other contaminations, they must be purified. 
The process behavior and the useful life of these media are considerably 
improved not only by a thorough and continuous purification of the cooling 
agents or lubricants, but the overall results of the machining and the 
chipless forming technology are optimized. 
A listing of different individual machines or of individual separation 
arrangements such as sedimentation tanks, hydrocyclones, centrifuges, 
separators, band filters, pressure filters, sedimentation filters is 
enumerated in the Technical Information, 68th year, Vol. 7/8, 1975 dealing 
with cooling lubricant care and its purification as well as with 
separation of waste emulsions. However, no pointers are provided as to how 
these individual machines must functionally interrelate with each other in 
order to attain optimum purification results, for instance in rolling 
mills for the open cooling water circulation cycles used there. The 
diagrams shown in this publication, dealing with a sedimentation filter 
installation for grinding oil purification or the therein explained 
diagram of a thermal emulsion separation installation or an ultrafilter 
installation for separation of emulsions, are not suitable for use in a 
rolling mill environment. 
An installation for purification of liquids or liquors in rolling mills 
containing contaminants, residues and/or aging products is known from the 
DE-OS 36 16 426. The contaminated liquids used for cooling and/or 
lubrication in rolling mills are, to begin with, collected in a collection 
tank and are plumped from there towards several diaphragm filters which 
are located in a reverse flushing cycle and are cyclically activated. The 
filter outputs of the diaphragm filters lead to a presetting tank, from 
which the purified liquid can be drawn off by means of an initial pump and 
be directed to its intended use, for instance to a rolling mill to be 
cooled. A separate precipitation vessel is provided for purifying the 
highly contaminated liquid passing through the diaphragm filters during 
the flushing process. The contaminants deposit or accumulate on the highly 
sloping base of this precipitation vessel and are directed to the lowest 
point of the base so that they can be conveyed away from there by a 
drawing off device. Overflow troughs or ducts are provided in the upper 
region of the precipitation vessel, into which the liquid precleaned by 
the precipitation can overflow. The liquid collected in the overflow 
troughs is at least partially pumped back by a pump in a regulated manner 
to the diaphragm filters and serves there, as a reverse flushing means for 
cleaning or purifying the diaphragms arranged in the filters. The water 
management in rolling mills can be largely automated by means of such a 
purification installation and the cooling agent circulation cycle, 
characteristically open in rolling mills, can be operated with clearly 
lower losses. 
SUMMARY OF THE INVENTION 
Proceeding from such a purification method and purification installation 
for cooling agents or lubricants in rolling mills, it is an object of the 
present invention to refine the separation of rolling scale as well as oil 
and grease from the used industrial process water with the help of 
space-saving installations which are as efficient as possible, so that not 
only can the purified water be returned to the rolling mill as a highly 
impure industrial process water, but the oil/grease can be reused after a 
purification of waste oils, and the separated rolling scale can be smelted 
without any difficulties. 
Pursuant to this object, and others which will become apparent hereafter, 
one aspect of the present invention resides in a method for purifying 
industrial process water in open cooling circulation cycles, having the 
following features: the coarse rolling scale is separated from the 
contaminated process water by means of gravity sedimentation; and the 
rolling scale particles of average or finer size are removed from the 
process water prepurified in the above manner preferably by magnetic 
separation. The thus finely clarified process water or effluent is 
subjected to flotation and separated into fractions containing oil 
concentrates, water and very fine rolling scale particles containing 
little oil. The individual fractions, such as the clarified process water 
are reused as cooling agents and the entire rolling scale separated from 
the process water is smelted as iron sinter. The oil-rich concentrates are 
either discarded or subjected to a waste oil purification. 
The inventive method is performed in a purification installation according 
to the invention by a precipitation tank for the supply of used and 
contaminated process water as well as a device for removal of sedimented 
coarse rolling scale, and a device for the transfer of the preclarified 
process water into a presetting tank with an additional solid material 
separator installed therein, this is preferably a magnetic separator for 
average and fine rolling scale particles, as well as a device for transfer 
of the finish-clarified process water into a flotation apparatus with 
forced or positive aeration or cooling, whose fraction outlets are 
provided with conveyance means for return of the fractionalized products 
such as process water into the cooling cycle of the rolling mill and for 
transfer of the separated rolling scale into a smelting or metallurgical 
plant as well as for transfer of the filtrate containing oil into a waste 
oil purification apparatus. 
It is achieved by the present invention to separate the industrial process 
water interspersed primarily by rolling scale and oil-containing up to 
grease-containing substances into extraordinarily pure fractions. This is 
accomplished at a reduced cost in a compact purification plant. These 
fractions include pure water which is returned as industrial process water 
into the open or exposed cooling cycle of the rolling plant and into 
rolling scale which is largely free of substances containing oil to such 
an extent that it can be directly fed to the sinter belt and into the 
smelting or metailurgical plant, without jeopardizing the electric filters 
which are normally located downstream of such an installation. The 
concentrate-containing oils, meaning the waste oil emulsion largely devoid 
of solid materials and merely binding certain H.sub.2 O shares, can be 
directly fed to a waste oil purification apparatus and thereafter be 
directed to various specific utilization modes. 
The essential advantage of the invention lies consequently in that the 
formation of the rolling scale sludges containing oil and hitherto 
separated out of the water circulation cycles in rolling mills are 
completely eliminated. It is well known that these rolling scale sludges, 
containing from 20 to 30% of oil shares which accumulate in conventional 
cleaning procedures and which hitherto were dumped, present a considerable 
load on the environment. 
A clear saving of installation cost is achieved in the invention by the 
circumstance that in the last stage of the industrial process water 
purification a much less costly flotation apparatus is now used instead of 
the conventional very fine purification by means of expensive gravel bed 
filters. 
The convincing economy of the inventive method and purification plant can 
also be seen in that the accumulating rolling scale containing 1 to 3% of 
steel throughput is limited to residual oil contents of approximately 0.1% 
and can be quantitatively returned into the smelting process. 
In a method of a different type described in European Patent 0 080 589 it 
has indeed been proposed to detach the fatty substances from the solid 
materials in oil contaminated rolling scale sludges by breaking-up the 
solid materials to grain sizes under 1 mm, wherein these are subjected to 
a solid body mechanical stress, then are washed in flotation, wherein the 
committed solid materials are separated out of the underflow flotation and 
are dried in a dehydrating manner, and wherein the overflow liquor 
obtained at the overflow of the flotation process, which has been 
subsequently freed from the fatty substances, is returned to the 
purification process. We are dealing here with the purification or 
dressing of already generated rolling scale sludges, which are deposited 
in dumps. The method of the invention prevents the formation of such oily 
rolling scale sludges from the start. 
In a further embodiment of the invention, the clear water obtained from the 
flotation process is filtered and subsequently sprayed in a cooling tower 
and collected and returned to the point of use in the rolling mill. 
Installation technology-wise, the fraction outlet of this flotation 
apparatus for clear process water is in this case possibly connected with 
the filter, whose filter output is connected to a cooling tower and with a 
pump collection or header tank arranged thereunder, whose pump is in 
connection with a cooling water user in the rolling mill through 
connection lines. The repeated filtering of the clear water from the 
flotation apparatus is indicated if any sort of operational malfunction 
with solid material penetrations should occur in the flotation cells. By 
spraying the clear water in a cooling tower, large quantities of water can 
be very steeply cooled, as is required in rolling mills, where for 
instance circulating water quantities of 5000 m.sup.3 /h must be very 
quickly cooled from about 50.degree. C. to 30.degree. C. 
It is provided in a particularly advantageous embodiment of the invention 
that the rolled scale particles containing little oil separated in the 
flotation process are ground up and suspended in water. The suspension is 
then separated into fractions in a secondary flotation, containing oil 
concentrate, water and very fine rolling scale particles. This is 
accomplished by the fraction outlet of the flotation apparatus for 
separated rolled scale particles being connected to a comminution machine, 
especially to a mill, whose product outlet is connected to a suspension 
tank, whose suspension line is conducted to a second flotation cell with 
positive aeration or cooling. Mechanical processing of the scale particles 
occurs, among other things, in the mill whereby the adhering oil particles 
are entirely detached or can be more easily separated in a suspension tank 
located downstream. Detergents such as tenside, surfactant, or the like 
can be expediently added at that point. The thus prepared suspension can 
be separated in a particularly simple manner by means of subsequent 
flotation into the three named fractions. 
In a further development of the claimed method and purification plant, the 
concentrate-containing oil emanating from the initial flotation of the 
process water and the concentrate-containing oil emanating from the finer 
flotation of the suspension are separated into several material phases 
especially into the fractions with oil, water and small shares of rolling 
scales. From a plant technology point of view this is achieved by 
connecting the fraction outlet of the concentrate containing oil of the 
first flotation apparatus and/or the second flotation apparatus with a 
centrifuge, especially with a three-phase separator with outlet apertures 
for purified water, waste oil as well as solid materials. In this way 
flowable waste oil in separated from the water purification process, which 
can be filled into oil barrels and can easily be temporarily stored, 
before it is transported into a waste oil dressing or purification plant, 
or can again be used in the rolling mill. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
At the outset, the following technical background will be provided. The 
largest quantities of scale accumulate especially in rolling mills with 
continuous casting installation, where simultaneously large quantities of 
exposed or open cooling water are used. The rolling scale is formed by 
oxygen in the air combining with iron. The scale is composed of the 
different forms of iron oxide FeO, Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4. 
The iron content amounts to 70 to 75%. In continuous casting and rolling 
mills sawdust, oxyacetylene cutting and scale oxidation must be added to 
the scale losses. In continuous casting plants the scale is obtained over 
a distance from the ingot mold up to the loading arrangements. In large 
blooming mill trains in hot rolling mills the scale is obtained in the 
form of large flat cakes and so-called fish. On roller tables and cooling 
beds it is obtained in the form of small plates and pellets down to grain 
sizes of a few thousandths of a millimeter. The scale obtained in rolling 
mills always amounts to 1 to 3% of the rolled material which has been put 
through or processed. The cooling water supplied to the rolling process is 
simultaneously used in an advantageous manner as a conveyor means for the 
accumulating rolling scale and other solid materials and for washing away 
the lubricants utilized, approximately 2 liters of oil or grease per ton 
of rolled steel. For collecting the used industrial process water, scale 
ducts or channels are usually arranged in the foundation, which have an 
appropriate gradient or slope in order to achieve a good scouring or 
washing away effect. 
The highly contaminated process water W.sub.1 flowing in the scale channels 
is, to begin with, supplied according to the invention to a sedimentation 
tank 1 arranged externally of the rolling mill proper. A coarse 
purification occurs in the sedimentation tank 1 by large scale flat cakes 
and scale fish as well as large particles of the flame cutting and scale 
oxidation accumulating on the bottom of the sedimentation tank. In this 
sedimentation tank 1 the coarse rolling scale Z.sub.1 with an average 
diameter larger than 0.5 mm is separated to the extent of 80% from the 
process water by the action of gravity. The separated coarse rolling scale 
is decidedly low in oil content. It is from time to time lifted out of the 
sedimentation tank 1 by a crane installation 18 shown diagrammatically, 
and is supplied by a conveyor belt 19 to a smelting or metallurgical plant 
21. 
In the course of a second purification step the process water, which has 
been coarse clarified in the sedimentation tank 1, flows subsequently 
through a magnetic separator 3 installed in a downstream pump collection 
or header tank. In a smooth-as-possible zone of the pump header tank 2, 
the average and fine rolling scale particles Z.sub.2 between 0 and 0.5 mm 
diameter are separated by means of the magnetic separator 3 from the 
process water with a separation efficiency of 50 to 80% and are scraped or 
wiped off the magnetic separator above the water level. The mid-size and 
fine rolling scale particles can still be classified as containing little 
oil and can therefore together with the coarse rolling scale from the 
sedimentation tank 1 be supplied by means of the conveyor belt 19 to the 
smelting plant 21 after being drained in a drainage tank 20. Due to the 
low oil content in the coarse rolling scale as well as the mid-size and 
fine rolling scale particles obtained through magnetic separation, there 
is no danger during the smelting process that electric filters used for 
dust removal in such installations will be affected. The low share of 
oil-containing substances in the rolling scale Z.sub.1 and Z.sub.2 in the 
first few purification stages results from the circumstance that the oily 
phase does not adhere to rolling scale particles which have a relatively 
large surface. Thus, during the transfer of the precleaned industrial 
process water from the first sedimentation stage into the second 
purification stage with magnetic separation, no appreciable turbulence; 
can be allowed to arise, so that the oily phase cannot adhere to the 
rolling scale particles. 
The process water contaminated with oil and grease and still interspersed 
with specific shares of fine rolling scale particles as well as with very 
fine rolling scale particles (grain size of approximately 0.001 mm) is 
subsequently conveyed out of the collection or header tank 2 by pumps 4 
through a line 5 to a flotation apparatus 6 located above the level of the 
smelter. The finish clarified process water in the flotation apparatus 6 
is separated into fractions of oil concentrates, water, and scale 
particles with very little oil. In order to achieve this, the process 
water and materials it contains flow with positive guidance through the 
flotation apparatus 6, wherein air is added in as fine a dispersion as 
possible. The finest particles as well as oil contained in the process 
water adhere to or are deposited on the finely dispersed air bubbles, in 
order to float to the top together with these. A bubbly foam is obtained 
which is continuously drawn off and removed from the upper region of the 
flotation cell through an adjustable annular space. Various reagents can 
be added for assisting the flotation process, if necessary. 
The thus obtained oil concentrate flows through a line 6.3 into a separator 
7. In this three-phase separator 7 the product supplied is separated into 
fractions of waste oil, water and extremely slight shares of the most fine 
rolling scale. The process water clarified in the flotation apparatus 6 is 
directed through the line 6.1 having a gradient through a gravity filter 8 
utilized as a final filter, which is to fulfill its filtering tasks only 
if the degree of separation cannot be precisely achieved in the flotation 
apparatus 6, and solid materials pass into the process water which as such 
has been purified or clarified. After the gravity filter 8, the clarified 
process water is directed to a cooling tower installation 9 where the 
water is sprayed, cooled and collected in the pump collection or header 
tank 10 located below the cooling tower. During this cooling process the 
water sprayed throughout the cooling tower is cooled down to the required 
operational temperature. The clarified industrial process water W.sub.2 is 
again conveyed back from the pump collection tank 10 by the pump 11 and 
the line 17 to the users in the rolling mill. 
The fine to finest rolling scale with the particle size of between 0.001 mm 
to 0.5 mm separated to the extent of 90 to 95% in the flotation apparatus 
from the process water is collected in the underflow 6.2 of the flotation 
apparatus 6 and from there is supplied to a mill 12. The rolling scale 
containing oil is ground up in the mill and is herein exposed to shear 
forces among others. The product obtained thereby arrives into a 
suspension tank 13 enriched with water, where the oil phase can again 
separate from the rolling scale particles. The suspension is introduced by 
means of a positive action pump 14 and a pipeline 15 into a second 
flotation apparatus 16 for final flotation. In the flotation apparatus 16 
the suspension is separated into three fractions by means of a process 
described in connection with the flotation apparatus 6. The oil 
concentrate accumulating therein is supplied to the separator 7 through a 
pipeline 16.3 and is divided in the separator, as has been described 
previously, into waste oil, water and smallest shares of the most fine 
rolling scale. The water clarified in the flotation apparatus 16 is sent 
by gravity through a pipeline 16.1 to the pump collection tank 2. This 
quantity of water, which can correspond to the quantity of water lost, is 
thus returned into the water purification circulation cycle. The finest 
oil-poor rolling scale Z.sub.3 in the; underflow 16.2 of the flotation 
apparatus 16 is drawn off from there and arrives together with the 
remaining rolling scale Z.sub.1 from the sedimentation tank 1 and the 
rolling scale Z.sub.2 from the pump collection tank 2 onto the sinter belt 
19 and from there, after it has been drained in the drainage tank 20, into 
the smelting or metallurgical installation 21. 
Not only can rolling scale generated in considerable quantities be directed 
to an economic use by means of the described method and the associated 
installation for purification of the greatly contaminated industrial 
process water accumulating in rolling mills, but also the lubricating oil 
and lubricating grease used in significant quantities in the rolling 
process can be recovered in the shape of waste oil and can be directed to 
other usages. It has to be particularly emphasized, that the dumping and 
waste disposal problems with rolling scale sludges containing oil, as they 
accumulate in conventional process water purification methods, does not 
even arise in the performance of the method in the invention. 
While the invention has been illustrated and described as embodied in a 
method and apparatus for purifying cooling agents and lubricants used in 
rolling mills, it is not intended to be limited to the details shown, 
since various modifications and structural changes may be made without 
departing in any way from the spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention. 
What is claimed as new and desired to be protected by letters patent is set 
forth in the appended claims.