TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method and a system for purification of oil.

RELATED ART

Purification of contaminated mineral and synthetic based industrial oils, such as for example lubricating oil, honing oil, rolling oil, gear box oil, quenching oil, processing oils, hydraulic oils or pretreated slop oils is important for the possibility to use/reuse the oils and therefore an important factor for the environmental future and the limited nature resources of oils. These oils play an important role in for example lubrication, shock absorption, heat dissipation, rust prevention and extension of mechanical service life of vehicles, ships and mechanical processing equipment. During use of for example a lubricating oil an amount of pollutant particles in the oil will increase and this will increase friction and shorten equipment lifetime. The oil can be purified by different methods. Gravity settling and filtration are commonly used purification methods. However, small particles are difficult to remove. Coagulant flocculation is sometimes also used together with gravity settling for purification of oil. In some examples the contaminated oil is purified, or recovered, by means of a liquid two- phase separation process, wherein a liquid separation aid is added to the oil and mixed therewith. Impurities will be captured by the separation aid and will accumulate in a bottom phase.

In WO2018/199837 a method and system for purification of oil is disclosed where a separation aid is used and where a filtration step also is provided for purification of the oil.

Small particles are often hard to remove and gravity settling after flocculation is sometimes very slow due to a high viscosity of the oil. Filtration requires large quantities of filter elements. Efficiency in the purification may be low. For some methods, such as distillation and dehydration, energy consumption may be large.

There is a need to improve the purification process for contaminated oil. SUMMARY

It is an object of the present invention to provide an improved method and system for the purification of oil.

A further object of the invention is to provide a method and system for purification of oil where small contaminating particles are efficiently removed.

This is achieved in a method and a system according to the independent claims.

According to one aspect of the invention a method for purification of oil is provided, wherein the method comprises at least two purification steps, wherein the at least two purification steps comprises: a particle charging step, comprising treating the oil to be purified in a particle charging unit, whereby some particles are being positively charged and some particles are being negatively charged in the particle charging unit (6); and a chemical step, comprising adding a separation aid to the oil to be purified and dispersing the separation aid into the oil to be purified, wherein the separation aid is liquid at the temperature at which the process is carried out and will by chemical interactions adsorb/absorb contaminating solids and/or dissolved impurities in the oil to be purified and wherein the separation aid composition is substantially insoluble in the oil to be purified because of its polar properties, forming a two-phase mixture upon mixing with the oil to be purified.

According to another aspect of the invention a system for purification of oil is provided, said system comprising: a particle charging unit in which oil to be purified in the system can be received and treated, whereby some particles are being positively charged and some particles are being negatively charged in the particle charging unit (6); and a chemical treatment part comprising: o a separation aid dosing device comprising separation aid, wherein the separation aid is liquid at the temperature at which the process is carried out and will by chemical interactions absorb contaminating solids and/or dissolved impurities in the oil to be purified and wherein the separation aid composition is substantially insoluble in the oil to be purified because of its polar properties, forming a two-phase mixture upon mixing with the oil to be purified and wherein the separation aid has a density different from that of the oil to be purified; and o a dispersion unit which is fluidly connected to the separation aid dosing device for receiving separation aid and which is connected in the system for receiving oil to be purified and which is configured for dispersing the separation aid into the oil to be purified.

Hereby an effective method and system for purification of oil is provided. By combining the use of a liquid separation aid for a liquid two-phase separation process with treatment of the oil in a particle charging unit an effective process is achieved which process is efficient for removal of also very small particles. The process according to the invention is time efficient. A settling process is for example very time consuming. In the particle charging unit some particles will be charged positively and some will be charged negatively and thereafter they will attract each other and combine into larger particles or agglomerates. Hereby small particles will agglomerate into larger particle agglomerates and possibly into droplets of separation aid whereby settling and/or filtration and/or centrifugation afterwards will be faster and/or more effective. Settling after the use of a separation aid according to the invention may be time consuming, especially for high viscosity oils. By the combination with a particle charging technology according to the invention the particles will agglomerate into larger particle agglomerates and a possible settling step afterwards will be faster and more effective. In some examples of the invention a filtration and/or centrifugation is provided instead of, or as a complement to a settling step. However, also both filtration and centrifugation will be more effective when the use of a separation aid is combined with the particle charging step because larger particle agglomerates are easier to separate than small particles both by a filter and in a centrifuge. This invention will speed up the purification process significantly. Hereby a higher flow rate can be provided through the system which is suitable for overall process efficiency. Furthermore, a less amount of separation aid may be needed when the process is combined with the particle charging step.

In some embodiments of the invention the at least two purification steps further comprise a following separation step, comprising separating the oil to be purified in a separation device, wherein the following separation step is performed after the particle charging step and the chemical step. The separation device is positioned in the system such that oil to be purified first is treated in both the particle charging unit and the dispersion unit and then forwarded to the separation device which comprises a filter and/or a centrifuge and/or a settling tank. The following separation step will be very efficient thanks to the combined effect from the particle charging technique and the separation aid by which the oil already has been treated.

In some embodiments of the invention the chemical step is performed before the particle charging step, wherein the dispersion unit is provided between at least one feed tank comprising contaminated oil to be purified which is provided in the system and the particle charging unit such that oil to be purified which is transferred from the at least one feed tank to the particle charging unit will pass the dispersion unit first.

In some embodiments of the invention the chemical step is performed after the particle charging step, wherein the dispersion unit is provided in fluid connection with an outlet from the particle charging unit such that oil to be purified which has already been treated in the particle charging unit is transferred for further chemical treatment in the dispersion unit.

In some embodiments of the invention the method further comprises analysing a degree of contamination of the oil having been purified by the method and possibly redirecting the oil to a previous purification step in dependence on the analysed degree of contamination. The system comprises hereby in some embodiments an analysing equipment positioned in the system such that it can analyse a degree of contamination of oil having been purified in the system, and a redirection arrangement configured such that it can redirect the oil having been purified in the system for further purification in the system in dependence of the analysed degree of contamination.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure la is a flow chart of a method according to one example of the invention. Figure lb is a flow chart of a method according to one example of the invention. Figure 2a shows schematically a system according to one example of the invention. Figure 2b shows schematically a system according to one example of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Contaminated mineral and synthetic based industrial oils, such as for example lubricating oil, honing oil, rolling oil, gear box oil, quenching oil, processing oils, hydraulic oils or pretreated slop oils can be purified by a method and a system according to the invention. During use of for example a lubricating oil an amount of pollutant particles in the oil will increase and this will increase friction and shorten equipment lifetime. The oils can according to the invention be purified separately in a batch or continuously during use in a purification system which is connected to the equipment using the oil, i.e. integrated purification. Hereby the system according to the invention can be connected directly to an equipment using for example a lubricating oil or another industrial oil for continuous, integrated purification or the system can be positioned separately and purify contaminated oil in batches.

The invention is first described in general with reference to all the drawings. Figures la and lb show flow charts of two examples of the method according to the invention and Figures 2a and 2b show schematically two examples of a system according to the invention.

A method and a system 10a, 10b for purification of oil is provided. An initial method step SI of providing oil to be purified into the purification system 10a, 10b is first provided. According to the invention the method further comprises at least two purification steps which are denoted SB and S3'. The at least two purification steps comprise a particle charging step S3 and a chemical step S3':

S3: The particle charging step comprises treating the oil to be purified in a particle charging unit. In a particle charging unit according to the invention particles and possibly also droplets, are being charged. Some particles are being positively charged and some particles are being negatively charged. The oppositely charged particles will then attract each other and combine into larger particles, also called agglomerates which also may comprise separation aid droplets. One example of such a particle charging unit is a balanced charge agglomeration, BCA, unit, where the main media flow is split into two streams, one stream becomes net positively charged and the other stream becomes net negatively charged while flowing over electrodes. Thereafter the positive stream and negative stream are recombined and positively and negatively charged particles will attract each other, and larger agglomerates will be formed.

S3': The chemical step comprises at least two sub-steps:

S3'a: Adding a separation aid to the oil to be purified and

S3'b: Dispersing the separation aid into the oil to be purified. The dispersing step S3'b could possibly be combined with the adding step S3'a if the adding step S3'a for example is provided via a nozzle through which the separation aid is sprayed into the oil to be purified or if separation aid for example is pushed/forced through a membrane into the oil to be purified. Possibly the separation aid can be provided into the oil to be purified (for example via a nozzle or membrane) with a controlled droplet size in order to optimize the effect of the separation aid and improve efficiency. Dispersing can also be mixing the separation aid with the oil to be purified in a mixing device, for example a mixer comprising a stirring mechanism or a rotor-stator mixer or a static mixer or an inline static pipe mixer. The mixing could also be provided via a pump.

The particle charging step, S3, and the chemical step, S3', can be performed in any order according to the invention. In Figures la and 2a an example of a method and a system in which the chemical step, S3', is performed before the particle charging step, S3, is performed is illustrated. In Figures lb and 2b an example of a method and a system in which the chemical step, S3', is performed after the particle charging step, S3, is performed is illustrated.

By combining such a chemical purification using a liquid separation aid with a treatment in a particle charging unit a very effective purification of the oil is achieved. The purification is effective because also very small particles will be effectively removed by the combination of two different types of agglomeration techniques, where one is chemical using the liquid separation aid and the other is physical using the particle charging. The purification is also effective in terms of time used for the purification because the particle charging treatment will combine particles into larger particle agglomerates which will speed up a possible next step of purification. If the separation aid was added before the particle charging step the separation aid droplets with adsorbed/absorbed contamination particles may also be combined into larger agglomerates of separation aid droplets and contamination particles in the particle charging unit. If for example settling is a next step of the purification this will be speeded up thanks to the larger particle agglomerates and/or larger droplets will be settling faster than smaller particles and smaller droplets and if a centrifuge is used as a next step of purification this step will also be more effective because larger particle agglomerates and larger droplets are easier to remove in the centrifuge. If a filtration step is used as the next purification step larger agglomerates of particles and separation aid droplets with adsorbed/absorbed contaminating particles are more effectively removed by the filter.

According to the invention the system 10a, 10b for purification of oil comprises both a chemical treatment part 15 and a particle charging unit 6 in which oil to be purified in the system can be received and treated. The chemical treatment part 15 comprises a separation aid dosing device 1 and a dispersion unit 5 which is fluidly connected to the separation aid dosing device 1. The separation aid dosing device 1 comprises separation aid and the dispersion unit 5 receives separation aid from the separation aid dosing device 1. The dispersion unit 5 is further connected in the system 10a, 10b for receiving oil to be purified. The dispersion unit 5 is configured for dispersing the separation aid into the oil to be purified.

The separation aid is liquid at the temperature at which the process is carried out and will by chemical interactions adsorb/absorb contaminating solids and/or dissolved impurities in the oil to be purified. The separation aid composition is substantially insoluble in the oil to be purified because of its polar properties, forming a two-phase mixture upon mixing with the oil to be purified. The separation aid can in some embodiments have a density different from that of the oil to be purified.

The use of a separation aid, also called a chemical booster, for capturing contaminations/impurities in contaminated oil has been described before, see for example WO 2018/199839. A liquid separation aid is added to the oil and mixed therewith and impurities in the oil will be captured by the separation aid. The separation aid is substantially insoluble in the oil, forming a two phase mixture upon mixing and the separation aid attracts impurities in the oil during mixing of oil and separation aid. The separation aid will by chemical interactions adsorb/absorb contaminating solids, and/or dissolved impurities in the contaminated target oil. The separation aid should be liquid at the temperature at which the process is carried out. The separation aid composition should be substantially insoluble in the contaminated target oil, forming a two-phase mixture upon mixing with the contaminated oil. The liquid separation aid can also have a density different from that of the contaminated oil to be purified.

The separation aid is not soluble in the contaminated target oil because of its polar properties and thus colloids consisting of small droplets of the liquid separation aid composition are formed by the stirring, which through chemical interactions (hydrophilic, hydrophobic, and charge interactions) may absorb unwanted solid or the dissolved impurities in the contaminated target oil. In instances where the separation aid has a higher density than the oil the separation aid will at a gravity separation form a lower phase together with the solid and/or dissolved impurities. In instances where the separation aid has a lower density than the contaminated target oil, it will form an upper phase on gravity separation.

The liquid separation aid for use in the invention can be made up based on the following components: a) a polar polymer; b) a hydrotrope/solubilizer; and, c) a co-tenside.

Suitable separation aids with the properties described above, that can be used in the inventive process, may e.g. constitute a composition comprising a mixture of polar polymers such as polyethylene glycols, polypropylene glycols or similar polyalkylene glycols, organic surface active components with nonionic, anionic, cationic and amphoteric properties with the ability to enhance the solubility of solid or dissolved impurities in to the separation aid.

One example of a separation aid which can be used in this invention comprise: a) at least one polar polymer not soluble in oil and with a higher density than the oil, such as polyethylene glycol with an average molecular weight of 190-210 g/mole, e.g. Carbowax PEG 200 (Dow Chemical Company); b) at least one surface active hydrotrope/solubilizer, such as anionic sulfonic acids, phosphate ester-based substances or non-ionic surfactants from the poly-glycoside family, such as Simulsol SL 4, Simulsol SL 7 G and Simulsol AS 48 (Seppic, Air Liquide group); c) at least one amphoteric Co-surfactant, such as an propionate type e.g. Ampholak YJH-40 (Akzo Nobel) which is a sodium caprylimino dipropionate.

In some examples of the invention but not necessarily the at least two purification steps of the method further comprise a following separation step, S5. The following separation step comprises separating the oil to be purified in a following separation device 7. The separation device 7 can for example comprise one or more settling tanks, filtering devices and/or centrifuging devices. This following separation step S5 is performed after both the particle charging step S3 and the chemical step S3'. The separation device 7 is positioned in the system 10a, 10b such that oil to be purified first is treated in both the particle charging unit 6 and the dispersion unit 5 and then forwarded to the separation device 7.

In some examples of the invention but not necessarily the method further comprises the step of analysing, S6, the oil which has been purified in the system, also called the purified oil, and determining in dependence of said analysing if further purification is needed. If further purification is needed the method may comprise a step of redirecting, S7, the purified oil back to a previous step in the purification method. This may be redirection to any of the previous steps. Hereby the system 10a, 10b may comprise some kind of analysing equipment 12, such as a sensor 12, and a redirection arrangement 13 such that purified oil can be redirected back to a previous part of the system, such as for example the dispersion unit 5 or the particle charging unit 6. The analysing equipment 12 can be connected in fluid communication with an outlet 7b from the separation device 7. The redirection arrangement 13 is only schematically shown in Figure 2b by dotted redirection arrows. However, such a redirection arrangement 13 comprises fluid connections 13a which are in fluid connection with the outlet 7b of the separation device 7 and with for example the inlet 6a of the particle charging unit and/or an inlet 5a of the dispersion unit 5. The redirection arrangement 13 comprises furthermore one or more valves 13b and a control system 13c which is connected to the one or more valves 13b and to the analysing equipment 12 such that redirection of the purified oil can be performed in dependence of analysed results of the purified oil. For example, a degree of contamination of the purified oil can be measured by the analysing equipment 12.

The system 10a, 10b comprises furthermore suitably a feed tank 2 comprising the oil to be purified. The system comprises also one or more pumps for pumping oil to be purified from the feed tank 2 and further into the system 10a, 10b for purification and for pumping separation aid from the separation aid dosing device 1 further into the system. In the examples shown in Figures 2a and 2b a separation aid pump 3 is provided for pumping separation aid from the separation aid dosing device 1 into the dispersion device 5 and an oil pump 4 is provided for pumping contaminated oil from the feed tank 2 into either first the dispersion device 5 (Figure 2a) and then the particle charging unit 6 or first the particle charging unit 6 and then the dispersion device 5 (Figure 2b).

The example as disclosed in Figures la and 2a will now be described in further details. In this example the separation aid is added to the oil to be purified before the oil together with the separation aid is provided into the particle charging unit 6. The separation aid dosing device 1 is hereby fluidly connected by a fluid line 101 via a pump 3 to the dispersion unit 5 and the feed tank 2 with oil to be purified is fluidly connected by a fluid line 102 via a pump 4 to the dispersion unit 5. Alternatively, the separation aid dosing device 1 can be fluidly connected to the fluid line 102 connecting the feed tank 2 with the dispersion unit 5 whereby separation aid is added into the oil to be purified in the fluid line 102. The dispersion unit 5 is configured to disperse the separation aid into the oil to be purified as described above. The dispersion unit 5 can for example comprise a mixing device. The dispersion unit 5 may also be configured such that the separation aid can be added via for example a pump, static mixer, membrane or via a nozzle. Hereby the separation aid can be added into the oil to be purified in small droplets which will result in larger specific surface area and which will improve the adsorptive efficiency for adsorption of impurities. The separation aid will attract impurities in the oil to be purified and hereby form agglomerates (also called floes) of separation aid droplets together with impurity particles. The oil to be purified together with the separation aid will then be transferred into the particle charging unit 6. In the particle charging unit some particles are being positively charged and some particles are being negatively charged. The oppositely charged particles will then attract each other and combine into larger particles, also called agglomerates which also may comprise separation aid droplets. One example of such a particle charging unit is a balanced charge agglomeration, BCA, unit, where the main media flow is split into two streams, one stream becomes net positively charged and the other stream becomes net negatively charged while flowing over electrodes. Thereafter the positive stream and negative stream are recombined and positively and negatively charged particles and agglomerates of particles and/or separation aid droplets will attract each other, and larger agglomerates will be formed in the particle charging unit. These larger agglomerates of particles and droplets of separation aid will improve purification efficiency. Both a purification quality and a speed of purification may be improved. Thanks to the use of both a separation aid according to the invention and a particle charging technique even very small contamination particles in the oil to be purified can be separated out from the oil efficiently. Furthermore, a next step of purification, which is provided in the separation device 7 in Figure 2a, can be both speeded up and more effective thanks to the larger agglomerates of particles and separation aid droplets. If the separation device 7 is a settling tank or centrifuge the separation of a sludge phase will be faster thanks to the larger size of the agglomerates having a higher density difference to the oil. Such a settling/separation step can otherwise be very time consuming especially for high viscosity oils. If the separation device 7 is a filter this step will also be more effective thanks to the larger agglomerates being more effectively separated in the filter. Thanks to the invention where both separation aid and particle charging is combined there will be very small amounts of small impurity particles in the oil to be purified when reaching the separation device 7 which is suitable. The smallest particles are often difficult to separate in both a centrifuge and a filter. The separation device 7 can be fluidly connected to an outlet 6b of the particle charging unit 6 via a pump 9. However, the pump 9 may be omitted. Further units may be provided in the system, such as pumps, valves, tanks and filters. For example a prefilter may be used before the particle charging unit 6 as is shown in Figure 2b.

The example as disclosed in Figures lb and 2b will now be described in further details. In this example the separation aid is added to the oil to be purified after the oil to be purified has been treated in the particle charging unit 6. A feed tank 2 with oil to be purified is connected via a pump 4 to an inlet 6a of the particle charging unit 6. In the example as shown in Figure 2b, but not necessary, a prefiltration device 11 is provided between the feed tank 2 and the particle charging unit 6 such that oil to be purified which is transferred from the feed tank 2 to the particle charging unit 6 will pass the prefiltration device 11 on its way to the particle charging unit 6. The prefiltration device 11 comprises some kind of a filter which will filter out larger impurities from the oil to be purified, and function to prevent blockage/damage to particle charging unit. A prefiltration device 11 can also be provided before the particle charging unit in the example as shown in Figure 2a even if it is not shown in Figure 2a. In the particle charging unit the main media flow is split into two streams, one stream becomes net positively charged and the other stream becomes net negatively charged while flowing over electrodes. Thereafter the positive stream and negative stream are recombined and positively and negatively charged particles and agglomerates of particles will attract each other and larger agglomerates of particles will be formed in the particle charging unit. Hereby, when transferred out from the particle charging unit 6 the oil to be purified comprises agglomerates of impurity particles and a less amount of small impurity particles than before the particle charging unit 6. A dispersion unit 5 is connected to an outlet 6b of particle charging unit 6 whereby the oil to be purified is transferred into the dispersion unit 5 after it has been treated in the particle charging unit 6. A separation aid dosing device 1 is connected via a pump 3 to the dispersion unit 5 whereby a separation aid provided in the separation aid dosing device 1 can be provided into the dispersion unit 5 and into the oil to be purified as described above. The dispersion unit can comprise for example a mixing device and/or a nozzle and/or another mixing function as described above in relation to the example shown in Figure 2a, by which the separation aid can be dispersed into the oil effectively. The separation aid according to the invention, as described in more detail above, will effectively attract the impurity particles and the agglomerates of particles in the oil to be purified. The combined effect of the treatment in the particle charging unit 6 and the use of the liquid separation aid will effectively collect impurities in the oil to be purified. Agglomerates of impurity particles and separation aid droplets will be formed which can be easily and effectively separated out in a following separation step of the method as described above. I.e. in a separation device 7 which is connected to an outlet 5b from the dispersion unit 5, possibly via a pump 9. The pump 9 may however not be needed. The separation device 7 can as described above be for example a settling tank, a filter or a centrifuge or more than one of these.