A METHOD OF CLEANING WATERY VENTILATING AIR CONTAINING LIQUIDS WHICH HAVE BEEN GASIFIED DURING COOLING OR LUBRICATION OF CONVERTING MACHINES, PARTICULARLY ROLLING MILLS, AND AN APPARATUS FOR CARRYING OUT THE METHOD

Abstract: A method of cleaning watery ventilating air containing liquids which have been gasified during cooling or lubrication of converting machines, particularly rolling mills, comprises cooling of the ventilating air in one or several stages (I-IV) to temperature below the condensing point of the gasified substances in the ventilating air, so that these substances condensate. In connection with the condensation the larger portion of the condensated cooling or lubricating liquids is separated from the water and reused. The condensated water mixed up with the rests of the condensated cooling and lubricating liquids is returned to the cleaned and dried ventilating air and is caused to be absorbed by the ventilating air. By dividing the cooling operation into two steps, the cooling and lubricating liquids can be caused to condensate in the first stage without condensation of any water and water can be caused to condensate substantially only in the second stage. A portion of the cooling and lubricating liquids condensated in the second stage are separated in a separation tank (24). An apparatus for carrying out the method comprises a plurality of heat exchangers (11-16). The first heat exchangers (11-14) are used for cooling the ventilating air, and the following exchangers (15-16) are used for heating the cleaned and dried ventilating air, so that this air can absorb the condensated water mixed up with the rests of the cooling and lubricating liquids in a moistening device (16a).

Description: A method of cleaning watery ventilating air containing liquids which have been gasified during cooling or lubrica¬ tion of converting machines, particularly rolling mills, and an apparatus for carrying out the method. Technical field The present invention is related to a method of clea¬ ning watery ventilation air containing liquids which have been gasified during cooling or lubrication of converting 5 machines. The method comprises cooling of the ventilating air in one or several steps to a temperature below the con¬ densing point of the gasified substances in the ventilating air, so that said substances condensate, and collecting the condensated liquids. The invention is also related to an 10 apparatus for carrying out the method and is preferably intended for use in oil-cooled rolling mills or other oil- or liquid-cooled converting machines. Background Art In rolling mills, the rollers coming into contact with 15 the ingots or metal billets to be rolled have to be force¬ fully cooled. This cooling is normally carried out by spraying an oil-based liquid over the rollers. During the cooling large quantities of oil will be gasified and- absor¬ bed by the ambient air. For environmental reasons, this air 20 has to be cleaned before it is released to the atmosphere or reused. The air quantities can be very large, e.g. of the order of 50000 m 3 /h. The polluted air contains in addition to oil periodi¬ cally also large quantities of water due to changes in 25 atmospheric humidity. When cleaning the air by conventional cooling in order to condensate the gasified oil also large quantities of water will condensate, e.g. of the order of 40 m " " per 24 hours at 100000 rn 3 /h, as the air has to be cooled to a comparatively low temperature to obtain a suf- 30. ficient cleaning of the air. V/hile a large portion of the condensated oil -comparatively easily can be separated from the water and reused, a certain quantity of condensated oil will remain in the condensated water. It is very time con¬ suming and expensive to completely separate the oil from the water. The quantity of oil remaining in the water after an economically justified separation of oil and water is so large that the water should not be released to a municipal sewerage without further cleaning. The cleaning of ventila¬ ting air containing oil and water thus includes a problem that is difficult to solve in an economically satisfactory way due to the obtained quantities of water containing oil. Disclosure of Invention The main object of the invention is to provide a meth¬ od and an apparatus for cleaning watery ventilating air that is mixed up with gasified cooling or lubricating liquids, the main portion of the used cooling.or lubri¬ cating liquids being recovered for reuse and the obtained water ' being disposed of in a way that does not involve any disadvantages from an environmental point of view and that is satisfactory also from an economical point of view. This object is obtained by a method and an apparatus having the eatures set forth in the claims. Due to the fact that the condensated water mixed up with the rests of the condensated cooling and lubricating liquids are returned to and absorbed by the cleaned.venti¬ lating air, no complete separation of the cooling or lubri¬ cating liquids from the water is required. Neither is any extended cleaning of the water necessary. Therefore, the necessary separation can be performed in a comparatively simple way at a low cost. The water that Is returned to the ventilating air can have a degree of pollution that makes a direct release of the water into the nature or into a muni¬ cipal sewerage system impossible, but that does not entail any serious degree of pollution of the released or recircu- lated ventilating air. Due to the principle of returning the condensated water to the ventilating air, a liquid balance is obtained in the system and the cooling of the ventilating air can proceed much further than would have been possible otherwise. This results in a lower degree of pollution of the released or recirculated ventilating air than has been possible to obtain previously. Brief Description of Drawing The invention will now be described more in detail with reference to the accompanying drawing which schemati¬ cally shows an oil recovering and air cleaning apparatus according to the invention. Best Mode for Carrying Out the Invention The cleaning apparatus for ventilating air shown on the drawing comprises four cooling stages I-IV and two hea¬ ting stages V-VI. Each one of the four cooling stages com¬ prises a cooling device 11-14 that consists of heat ex- changing units. Also the first heating stage V comprises a device 15 including heat exchanging units. The second hea¬ ting stage VI comprises ' a device 16 including heat exchang¬ ing units and a moistener 16a. The separate stages are arranged serially and are passed in turn by the ventilating air -to be cleaned. Thus, the ventilating air is entering through the drum 17 to the left in the Figure and passing out through the drum 18 to the right in the Figure. The first two cooling stages I and II are connected with the first heating stage V, so that the heat removed from the entering ventilating air in the first cooling stages is used for heating the ventilating air in the first heating stage. The third and fourth cooling stages III and IV are conntected to a separate cooling machine 19 of any type. The second heating stage VI is heated by waste heat from the cooling machine IS. The first two cooling stages I and II are further con¬ nected to a receptacle 20 having two separate compartments 21,22 for collecting the condensate formed in the two sta¬ ges. The receptacle 20 is provided with a drain 23 for the collected condensates. The third and fourth cooling stages III and IV are further connected to a receptacle 24 having two communicating compartments 25,26 for collecting the condensates formed in these stages. A smaller separate col¬ lecting receptacle 27 is positioned adjacent the receptacle 24.- One compartment 26 of the receptacle 24 is connected to a circulation receptacle 29 through a drain 2δ. The circu- lation receptacle 29 is provided with a level controlling float 30 and is in turn connected to the moistener 16a through a feeding conduit 31 and a return conduit 32. The described apparatus operates in the following way for cleaning the ventilating air from e.g. an oil-cooled rolling mill. The moist air containing oil enters through the drum 17 and then has a temperature around +35 degrees centigra¬ de. In the first cooling stage I the air is cooled to about +20 degrees centigrade, and in the second cooling stage II the air is cooled to about +13 degrees centigrade. These temperatures are below the condensing point of the gasified oil in the ventilating air but above the condensing point of water. Thus, in the first two cooling stages substan¬ tially only oil is condensated, and this oil is collected first in the compartment 21 to the right in the receptacle 20. When this copartment has been filled up, the oil is collected in the left compartment 22. The wall between the. two compartments then operates as a spillway, so that the water possibly condensated in the first two stages remains at the bottom of the first compartment and can be drained off through a bottom valve. The collected oil is drained through the conduit 23 for reuse in the rolling mill. In the- third cooling stage III the air is cooled to about +1 degree centigrade, and in the fourth stage IV the air is cooled to about -10 degrees centigrade. These temperatures are below the condensing point of water. Therefore, in the¬ se two stages substantially water but also some rest quan¬ tities of oil are condensated. The condensated water mixed up with oil is lead to the compartment 25 to the left in the receptacle 24, as shown in the Figure. This compartment communicates at the .bottom with the second compartment 26 in the receptacle, and the condensated water will therfore -^URE OMP flow into the second compartment 26. However, the receptac¬ le has such a large volume that the water in the two com¬ partments 25,26 only flows slowly, so that the oil mixed up with the water to a large extent has time to separate from the water and rise to the water surface of the first com¬ partment 25. The collected oil can be drained off to the collecting receptacle 27. The . water flowing into the second compartment 26 still contains a certain quantity of oil, e.g. of the order of 50 g/m 3 , and is therefore not suitab- le for releasing into a sewage disposal system. This water is drained off to the circulation receptacle 29. From the circulation receptacle the condensated water containing oil is fed to the moistener 16a, where the oil and the water are absorbed by the passing ventilating air which has been heated in the stages V and VI to +12 degrees centigrade and +32 degrees centigrade, respectively, and passes out through the drum 18. The level controlling float 30 of the circulation re¬ ceptacle 29 detects the level of the water in the receptac- . le 29 and controls the heat supply to the heating device 16 in such a way that the heat supply increases, when the level in the circulation receptacle is rising, so that the absorbing capacity of the air increases, and the heat supp¬ ly decreases, when the level in the circulation receptacle is falling. This will make sure, in an easy way, that the condensated water containing oil always will be absorbed by the ventilating air leaving the cleaning device with a mi¬ nimum of heat supply. Furthermore, the tubing system contains a number of pumps which have been indicated by circles surrounding an arrowhead without reference numerals. Due to the fact that the condensated water is returned to the ventilating air, the temperature of the ventilating air in the cleaning apparatus can be reduced comparatively far, e.g. to -10 degrees centigrade, as in the above examp¬ le. At this temperature, the ventilating air only comprises about 60 mg gasified oil per m 3 which is a very low value. -BUR- E OMP If the temperature would be lowered to e.g. O degree cen¬ tigrade, the ventilating air would contain about 130 rng oil per m 3 . At a temperature of +10 degrees centigrade the air would contain about 250 mg oil per m 3 . The saturation cur- ve for gasified oil in air thus falls rapidly with decrea¬ sing temperature. Because a portion of the oil in the con¬ densated water can be collected in the collecting receptac¬ le 27, the leaving ventilation air will contain only an acceptable quantity of oil also after the return to the air of the condensated v/ater containing oil. Thus, the princip¬ le of the invention provides for a good cleaning of the ventilating air at a reasonable cost. While only one embodiment of the apparatus according to the invention and only one application example have been described, it is obvious that many modifications are pos¬ sible within the scope of the invention. The last cooling stage, in which the temperature is reduced to -10 degrees centigrade and therefore ice is formed, can be doubled, so that one stage is in operation, while ice is being removed from the parallel stage. The cooling temperatures in the separate stages can further be modified depending upon need and available cooling power. The separation of oil or any other cooling or lubricating liquid from the water can be performed in many different ways, so that e.g. only one cooling stage will be needed. It is, however, very conve¬ nient to use at least two cooling stages having different temperatures, so that the used cooling or lubricating li¬ quid can be deposited in one stage and the water substan¬ tially in a second stage, as described above, because this will considerably facilitate the recovery of the cooling or lubricating liquid. The supply of cooling and heating po¬ wer, respectively, to the separate stages can also be pro¬ vided in many ways. In this connection, heat pumps may be used to take up the waste heat appearing in the system. The number of cooling and heating stages can also be varied within wide limits upon need. In the winter e.g. normally only one heating stage is required, and this stage can be supplied with heat from any of the preceding stages. In the summer, however, normally a second heating stage is requi¬ red, which must be supplied with heat from the outside, to make it possible for the leaving ventilating air to absorb the condensated water.

Claims: Claims 1. A method of cleaning watery ventilating air containing liquids which havς been gasified during cooling or lubrica¬ tion of converting machines, particularly rolling mills, comprising cooling of the ventilating air in one or several stages (I-IV) to a temperature below the condensing point of the gasified substances in the ventilating air and of the water, so that said gasified substances contained in the ventilating air condensate, arid collecting and draining the condensated cooling or lubricating liquids and the con- densated water, characterized in that the condensated water mixed up with rests of the condensated cooling or lubrica¬ ting liquids is returned to the cleaned and dried ventila¬ ting air and is caused to be absorbed by the ventilating air.. 2. A method according to claim 1, comprising cooling in a first stage (I-II) to a temperature below the condensing point of the gasified cooling or lubricating liquids but over the condensing point of water, so that substantially only the cooling or lubricating liquids condensate in this stage, and cooling in a second stage (III-IV) to a tempera¬ ture below the condensing point of water, so that water an further quantities of the cooling or lubricating liquids condensate, characterized in that a substantial portion of the rests of the cooling or lubricating liquids mixed up with the water is separated from the water, whereupon the water including the remaining quantities of the cooling or lubricating liquids is returned to the cleaned and dried ventilating air. 3. A method according to claim 1 or 2, characterized in that the ventilating air is cooled to at least about -10 degrees centigrade In the last cooling stage (IV). 4. A method according to any of claims 1-2, characterized in that the cleaned ventilating air is heated to take up the condensated water and the cooling or lubricating " UR O liquids mixed up with the water. 5. An apparatus for carrying out the method according to claim 1 for cleaning watery ventilating air containing liquids which have been gasified during cooling or lubrica- tion of converting machines, particularly, rolling mills, comprising two or several successive cooling devices (11-14), a first cooling device (11,12) cooling the ven¬ tilating air to a temperature below the condensing point of the gasified cooling or lubricating liquids but above the condensing point of the water, and a second cooling device (13,14) cooling the ventilating air to a temperature-below the condensing point of the water) and means (20,24) for collecting the cooling or lubricating liquids condensated in the first cooling device and the water including the rests o the condensated cooling or lubricating liquids mixed up with the water condensated in the second cooling device, respectively, characterized by means (25,26,27) for separation of a substantial portion of the cooling or lubricating liquids remaining in the water from the water and by means (16,16a) for returning the condensated water mixed up with the cooling or lubricating liquids to the - cleaned and dried ventilating air. 6. .An apparatus according to claim 5, particularly when the gasified cooling or.lubricating liquids consist of oil, characterized in that the means for separation of a portion ' of the oil remaining in the water from the water comprises a receptacle (24) having a large volume, in which the water containing oil is collected and maintained during such a long time period that at least a substantial portion of the oil has time to separate from the water and rise to the surface of the water, and in that a moistener (16a) is pro¬ vided to receive the water including the remaining quantity of oil and to transfer the water including the oil to the cleaned and dried ventilating air. 7. An apparatus according to claim 5 or 6, characterized in that a heating device (15) is provided for heat supply to the cleaned ventilating air, in order to make the air To capable to take up the condensated quantity of water. 8. An apparatus according to claim 7, characterized in that mean are provided for heat transfer from the first cooling device (11,12) to the heating device (15) for the cleaned ventilating air, . 9.. -An apparatus according to claim- 8, in which a cooling machine (19) is connected to the second cooling device (13,14), characterized- in that, a further heating device (16) is provided for' heat supply to the cleaned ventilating air and in that this " further heating device is supplied with waste heat from the cooling machine (19). 10. An apparatus according to claiπi 7, characterized in that the water containing oil is fed to a circulation receptacle (29) and. in that control means (30) are provided to detect the level in the receptacle to control the heat supply to the ventilating air depending on the water level in the circulation, receptacle.

Inventors: ABRAHAMSSON LARS OLOF, KAOGSTROEM PER-OLOF, ABRAHAMSSON, LARS, OLOF, KAOGSTROEM, PER-OLOF
Applicants: GRAENGES ALUMINIUM AB, GRAENGES ALUMINIUM AKTIEBOLAG
Application year: 1983
Main classification: B01D5
IPC codes: B01D5, B21B27, F24F3