DE102007017508B4 - Process for the purification and / or treatment of oil emulsions, in particular of cooling lubricants - Google Patents

Abstract

Process for cleaning and / or processing oil emulsions (10), in which the oil emulsion is passed through an ultrafilter (11) in a filtering step (II), in which emulsified components (12) of the emulsion to be cleaned are separated as valuable substances and are concentrated, which filtration step (II) is preceded by a pre-cleaning step (I) in which the oil emulsion (10) to be cleaned is at least partially separated from solids, characterized in that in the pre-cleaning step (I) in a three-phase Centrifuge (9) as the heavy phase, the solids suspended in the oil emulsion (10), as the light phase, the foreign oil components that are only weakly bound via emulsifiers, and as the middle phase, an emulsion concentrate is separated as a valuable substance, which is sent to the filter (11) is passed on, the emulsified constituents (12) of the emulsion concentrate retained in the ultrafilter (11) being re-mixed with deionized fresh water (15) back into the K ühlschmier emulsion cycle can be returned, and the water content is fed as a saline, aqueous phase from the ultrafilter (11) and fed into an evaporator (13), which ...

Description

The invention relates to a process for the purification and / or treatment of oil emulsions, in particular of cooling lubricants, according to the preamble of patent claim 1.

In the metalworking industry, large quantities of cooling lubricants are used to cool the tools. Such coolants contain, for example, oils emulsified in water, whereby a tool wear is reduced and a good workpiece surface quality is ensured, as well as resulting metal chips are removed. So-called water-mixed cooling lubricants are used in circulation systems with up to 100 cubic meters of liquid for the longest possible service life before they have to be disposed of. The maximum possible service life of the cooling lubricants significantly influences the amount of waste produced in a metalworking operation and the costs for their disposal.

However, the maximum achievable service life is limited by the so-called salification of the cooling lubricant. Salination occurs when water is evaporated from the coolant due to the process heat generated during metal cutting. In the evaporation of water, the salts remain in the cooling lubricant, so that it comes in the course of time to an accumulation of dissolved salts. In addition, alloying components dissolved from the working metals, such as heavy metals, aluminum and magnesium.

Salting may lead to corrosion, emulsion breakage or residue formation due to salt precipitation in the cooling lubricant. As a result, the performance characteristics of the coolant are impaired. The thus required early disposal results in high costs and large amounts of waste.

A generic method for the purification and / or treatment of oil emulsions is from TORNAU, Dieter et. al .: cooling lubricants and equipment. Renningen-Malmsheim: expert-Verl., 1999 (contact &study; Bd. 579) pp. 134-147 and 178-193. ISBN: 3-8169-1160-9 known. As a result, ultrafiltration systems with an upstream centrifuge are used for cleaning and conditioning of cooling lubricants. From the DE 100 11 513 A1 is the combination of centrifuge and ultrafiltration for the treatment of cutting suspensions known.

From the US 5137654 A the separation of an oil-water emulsion by means of the ultrafiltration membrane is known. From the DE 25 28 990 A are generally known ways for the splitting of emulsions. From the DE 18 10 630 C and from the DE 23 21 749 A are known processes for the separation of emulsions from the machining deformation of metal parts, that is, solid-containing emulsions. From the DE 295 18840 U1 It is known that three-phase centrifuges are advantageous for the treatment of coolants containing solids.

From the US 5137654 A is a method for cleaning and treatment of a cooling lubricant is known, which is passed to a ultrafilter after a machining process. The ultrafilter separates the emulsified oil components from the water, which is passed as a filtrate through a membrane of the ultrafilter.

The separated water has a high proportion of dissolved salts and low molecular weight ingredients and may optionally be subjected to a further treatment stage for the separation of interfering ions. The oil components retained in the ultrafilter are re-mixed with fresh water as a valuable material to again ensure an optimum state of cooling lubricant emulsion. Subsequently, the recyclable material is returned to a storage tank.

The cooling lubricant to be cleaned here is loaded with solids, such as metal particles from the cutting process, which build up a filter cake on the filter membrane of the ultrafilter and thus clog the ultrafilter early, whereby regeneration phases of the ultrafilter are required in short time intervals.

From the DE 43 40 218 C1 For example, a filter device for filtering solids laden liquids is known. The filter device has a cross-flow filter, in which a parallel to the surface of the filter membrane extending flow component is generated in the turbid to be filtered, which prevents premature deposition of solids on the filter membrane.

From the DE 24 08 637 A a method for the treatment of cooling liquids is known in which after a cutting process, the coolant is first passed into a settling tank and then by means of a pump to an ultrafilter, is separated in the saline water from an emulsion concentrate. Possibly. For example, the refrigerant from the settling tank may be previously freed of suspended particulates which do not settle by gravity with ordinary filters or sieves. From the US 3 814 307 A For example, a centrifuge is known in which small concentrations of solids or oil suspended in water can be separated.

The object of the invention is to provide a process for the purification of oil emulsions, in particular of cooling lubricants, in which the cleaning or treatment process can be operated permanently with good filtration quality.

The object is solved by the features of claim 1. Advantageous developments of the invention are disclosed in the subclaims.

According to the invention, the filtration step, in which the emulsified constituents of the emulsion to be purified are separated off as recyclable material, is preceded by an additional prepurification step in which the emulsion to be purified is centrifuged in a centrifuge. As a result, the oil emulsion to be cleaned can be precleaned in comparison to other mechanical filter methods with little expenditure of time and high filter quality, whereby even small particle sizes of up to 2 μm can be separated from the oil emulsion.

The suspended solids in the oil emulsion to be purified are separated in the centrifuge as a heavy phase. It is preferred for high filter quality if the centrifugal force of the centrifuge is within a range of at least 3 to 4 g. This ensures that even the solids with small particle sizes of about 2 microns are reliably filtered out. Such fines or fine chips would settle without the pre-cleaning step according to the invention on the filter surface of the downstream filter and clog it prematurely.

In addition to the centrifugal force, the flow rate through the centrifuge per unit of time forms another important process parameter with which the residence time of the oil emulsion to be cleaned in the centrifuge can be determined. The centrifugal force of the centrifuge is preferably adjusted so that the emulsifiers in the oil emulsion to be cleaned are not destroyed. The emulsifiers cause the oil content to be kept finely distributed in the carrier substance, for example water, without coagulating. Experiments have shown that the emulsifiers are stable up to a centrifugal force of 6 to 7 · g and are destroyed by larger centrifugal forces.

The cleaning result of the pre-cleaning stage is further increased by the use of a three-phase centrifuge. In contrast to other mechanical filters, a light oil phase can be separated in a simple manner in addition to the heavy solid phase. The light phase may contain, for example, hydraulic oil as a foreign oil, which is only weakly bound to the emulsifiers and readily dissolves and coagulates during centrifugation from the emulsifiers. The foreign oil would pass without upstream centrifugation step to the filter, such as the ultrafilter, and add the filter pores as sludge.

When using the three-phase centrifuge so at the same time solids and foreign oil components, such as hydraulic oil, can be separated from the recyclable material. A middle phase produced during centrifugation is passed as an emulsion concentrate to the filter, in which the emulsified constituents can be filtered out of the concentrate.

Usually, an oil emulsion is used as a cooling lubricant or a cooling lubricant emulsion, in which the oil content is kept dispersed by means of emulsifiers in water. In the water content of the cooling lubricant emulsion accumulates after its use in the metalworking process dissolved salts and / or dissolved alloying components, eg. As heavy metal, aluminum or magnesium, which affect the performance characteristics of the cooling emulsion. By separating the salt-containing aqueous phase, therefore, the cooling lubricant emulsion can be desalted.

A particularly effective cleaning of the oil emulsion results from the combination of the centrifuge according to the invention with an ultrafilter. The ultrafilter is used to desalt the emulsion concentrate recovered from the centrifuge. The ultrafilter retains the emulsified oil components and separates the aqueous phase with the dissolved salts. The filter membrane of the ultrafilter can have a pore size in a range of 10,000 to 30,000 daltons, while a suitable filtration pressure can already be in the range of only 0.5 to 1.5 bar. The filtration step preferably takes place in a cross-flow filter technique in which a flow component running parallel to the surface of the filter membrane is produced in the emulsion concentrate to be filtered. This prevents premature clogging of the filter surface. Especially in connection with the upstream centrifuge, the service life of the ultrafilter can be considerably increased without the need for regeneration phases to clean the filter.

Preferably, the pre-purification step according to the invention is carried out in two stages with a centrifugal upstream mechanical filtration in which already larger solids from the oil emulsion to be cleaned can be removed. The prefiltration can be carried out by a mechanical filter or by sedimentation in a settling tank.

After the filtration step, the retained emulsified oil components are re-supplied as valuable material to the cooling lubricant emulsion circuit. For this purpose, the recyclable material is mixed with fresh water and optionally further additives in order to ensure again an optimal state of cooling lubricant emulsion.

An exemplary embodiment of the invention is described below with reference to the appended FIGURE, which shows in a schematic flow diagram a method for processing a cooling lubricant emulsion.

The flow chart relates to a metalworking process with two consecutive processing steps 1 . 2 for chip processing of metal components.

After machining, the components become a scrubber 3 guided in which they are cleaned by means of a cleaning liquid.

The metalworking process is a cooling lubrication emulsion cycle 4 with a coolant center 5 assigned. The coolant central system 5 guides the cooling lubricant emulsion 10 from a storage tank 6 the machining tools in the metalworking process, to protect them from wear, to ensure a good workpiece surface quality and to dissipate the generated metal chips.

As a cooling lubricant emulsion, a water-mixed cooling lubricant is known to be used, in which the oil components are kept finely dispersed by means of emulsifiers in water. Thus, the cooling lubricant emulsion is a mixture of a lubricating component (oil content) and a cooling effective components, namely water, which occupies about 85% of the main portion of the emulsion.

The storage tank 6 the coolant center 5 is one of the cooling lubricant emulsion cycle 4 independent reprocessing cycle 7 assigned. The treatment cycle 7 leads independently of the coolant circuit 4 the cooling lubricant emulsion from the storage tank 6 from. After cleaning and conditioning, the cooling lubricant emulsion is returned to the storage tank 6 recycled.

The treatment cycle 7 has a centrifuge 9 in which, in a pre-cleaning step I, the cooling lubricant emulsion to be cleaned is mechanically pre-cleaned. The pre-cleaning step can take place in two stages with an upstream filter device, not shown, which is located in the storage tank 6 can be arranged.

The centrifuge 9 In the present case, a three-phase centrifuge with which the discharged, to be cleaned coolant emulsion can be divided into three phases. The light or oily phase consists of weakly bound via emulsifiers foreign oil components, ie, for example, a hydraulic leakage oil. In contrast, the heavy phase or solid phase consists of chips or components of machined alloys, such as silicon and corundum of a grinding wheel. The middle phase, in contrast, as an recovered valuable substance is an emulsion concentrate, which is further treated as valuable material.

That from the centrifuge 9 The emulsion concentrate obtained as the middle phase then becomes an ultrafilter 11 forwarded. In the ultrafilter 11 In a filtering step II, the emulsified components 12 of the emulsion concentrate from a filter membrane of the ultrafilter 11 retained, which allows the water content through. In ultrafiltration, a filter membrane with a pore depth of 10,000 to 30,000 daltons is used, with which fine chips up to a particle size of 2 μm can be filtered out.

The water content is as a saline, aqueous phase from the ultrafilter 11 led and into an evaporator 13 fed. The ultrafilter 11 retained emulsified ingredients 12 of the emulsion concentrate are then re-mixed with desalted fresh water 15 returned to the cooling lubricant emulsion circuit. The desalinated fresh water is thereby through the evaporator 13 , For example, a low-energy evaporator, recovered from the salt-containing aqueous phase of the emulsion. The residue thus becomes a strongly saline aqueous medium from the evaporator 13 dissipated.

In the treatment circuit according to the invention 7 It should be noted that if centrifugal forces are too high, the centrifuge 9 the emulsifiers in the emulsion could be destroyed and the oil could coagulate. The centrifuge 9 is therefore designed according to the invention with an effective centrifugal force of not more than 6 to 7 · g. On the other hand, to achieve long regeneration cycles in the ultrafiltration, it is necessary to separate especially fine chips from the pre-purified emulsion concentrate. The centrifugal force of the centrifuge 9 is therefore at least 3 to 4 g to centrifuge such fine particles up to 2 microns reliably from the cooling lubricant emulsion to be cleaned.

Claims (10)

Process for the purification and / or treatment of oil emulsions ( 10 ), in which, in a filtration step (II), the oil emulsion is passed through an ultrafilter ( 11 ), in which emulsified constituents ( 12 ) of the emulsion to be purified are separated off as material and concentrated, to which filtration step (II) a precleaning step (I) is connected upstream, in the oil emulsion to be cleaned ( 10 ) is at least partially separated from solids, characterized in that in the pre-purification step (I) in a three-phase centrifuge ( 9 ) as a heavy phase in the oil emulsion ( 10 ) suspended solids, as a light phase, the weakly bound emulsifiers via foreign oil components and as the middle phase, an emulsion concentrate is separated as a valuable material, the filter ( 11 ), where in the ultrafilter ( 11 ) retained emulsified constituents ( 12 ) of the emulsion concentrate with renewed mixing with desalinated fresh water ( 15 ) are recycled back into the cooling lubricant emulsion circuit, and wherein the water content as saline, aqueous phase from the ultrafilter ( 11 ) and into an evaporator ( 13 ), the fresh water desalted from the salt-containing aqueous phase of the emulsion ( 15 ) for the mixing of the emulsion concentrate with desalinated fresh water wins. Method according to claim 1, characterized in that the centrifuge ( 9 ) is designed for the separation of solids of a particle size up to 2 microns or larger. Method according to one of the preceding claims, characterized in that the centrifugal force of the centrifuge ( 9 ) is greater than 3 to 4 g. Method according to one of the preceding claims, characterized in that the centrifugal force of the centrifuge is designed so that the emulsifiers of the oil emulsion remain nondestructive. Method according to claim 4, characterized in that the centrifugal force of the centrifuge ( 9 ) is less than 6 to 7 g. Method according to one of the preceding claims, characterized in that the filter ( 11 ) is associated with an agitator, with which a parallel to the filter surface directed transverse flow of the oil emulsion to be cleaned is generated. Method according to one of the preceding claims, characterized in that in the oil emulsion ( 10 ) the oil content is kept finely dispersed by means of emulsifiers in water. Method according to one of the preceding claims, characterized in that the pre-purification step (I) in two stages with the centrifuge ( 9 ) and sedimentation in an upstream settling tank ( 6 ). Method according to one of the preceding claims, characterized in that that of the filter ( 11 ) in the filtration step (II) retained emulsified oil components ( 12 ) with water ( 15 ) and to a storage tank ( 6 ) are returned. Method according to one of the preceding claims, characterized in that the centrifuge ( 9 ) and the filter ( 11 ) a conditioning cycle ( 7 ), which is independent of the coolant circuit ( 4 ) for coolant supply of the metalworking process discharges cooling lubricant emulsion and cleans.

Images