TECHNICAL FIELD OF THE INVENTION

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

BACKGROUND OF THE INVENTION

Purification of contaminated oils, such as for example mineral oil, industrial oils, processing oils or hydraulic oils, is important for the possibility to reuse the oils and therefore an important factor for the environmental future and the limited nature resources of oils. The contaminated oil can be 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. There is still a need to improve the purification process for contaminated oils.

SUMMARY

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

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

Hereby by filtering the oil phase after sedimentation any possible remaining separation aid and impurities in the oil can be removed and an improved purification of the oil is achieved.

In one aspect of the invention a method for purification of oil is provided. Said method comprises the steps of:providing separation aid and oil to be purified to at least one sedimentation tank;waiting for allowing a sludge phase to sediment to a bottom part of the sedimentation tank, said sludge phase comprising the separation aid together with impurities from the oil;removing an oil phase not comprising said sludge phase from the at least one sedimentation tank; andfiltering said oil phase through a depth filter for removing any possible remaining separation aid and impurities.

In another aspect of the invention a system for purification of oil is provided. Said system comprises:at least one feed tank comprising oil to be purified;a separation aid dosing device;at least one sedimentation tank comprising at least one inlet connected to the at least one feed tank for receiving oil to be purified and to the separation aid dosing device for receiving separation aid, said sedimentation tank further comprising at least one oil phase outlet for removing an oil phase from the sedimentation tank after sedimentation of a sludge phase to a bottom part of the sedimentation tank, said sludge phase comprising the separation aid together with impurities from the oil; anda filter module connected to the oil phase outlet of the at least one sedimentation tank, wherein said filter module comprises a depth filter.

In still another aspect of the invention a computer program product is provided. Said computer program comprising instructions which, when executed in a processor in a control system in a system for purification of oil, cause the control system to perform the method according to the invention.

Hereby also very small impurity particles in the oil can be effectively filtered out form the oil phase. A combination of the depth filter and any remaining separation aid which will get caught in the depth filter will improve the efficiency for removal of small impurity particles. A depth filter is a filter which can retain impurities within a bulk structure of the filter medium in contrast to conventional thin layer surface filters which only filter at the surface. The depth filter will absorb any remaining separation aid and contaminations and the absorbed separation aid will also be able to catch small contamination particles from the oil and hereby improve filter efficiency.

In one embodiment of the invention said filtering is performed by adding a cellulose fiber powder to a part of said oil phase and circulating said part of said oil phase over a carrier layer for building up a depth filter, also called a filter cake, and wherein the remaining part of the oil phase then is filtered through the depth filter. Said filter module is also configured for such type of filtering. Hereby a very effective, flexible, easy and cost efficient depth filtering is achieved. The depth filter is easy to change between batches of oil to purify and this type of depth filter is very effective for the removal of small particles. Furthermore an automation of the process can easily be achieved, both for the building up of the filter cake and for the changing of the filter. Furthermore the size, i.e. the depth of the depth filter can very easily be changed from case to case by just adopting the amount of added cellulose fiber powder.

In one embodiment of the invention the method further comprises the step of mixing and warming the oil and separation aid when provided into the sedimentation tank.

In one embodiment of the invention the at least one sedimentation tank further comprises a mixing device, at least one temperature sensor and at least one heating device configured for heating the content of the sedimentation tank in dependence of the temperature(s) measured by the at least one temperature sensor.

Hereby separation effectivity can be improved.

In one embodiment of the invention the method further comprises measuring a temperature of the content in the sedimentation tank in at least one position in the sedimentation tank and controlling the warming of the content in the sedimentation tank in dependence of said measured at least one temperature.

In one embodiment of the invention the method further comprises the step of warming the oil phase removed from the sedimentation tank in a heating tank before the step of filtering. Hereby the filtering can be more effective.

In one embodiment of the invention the method further comprises detecting the presence of an oil phase or a sludge phase in at least one position in the sedimentation tank by at least one content detection sensor provided in the tank and controlling the removing of the oil phase in dependence of said detection, said controlling being performed by a control system connected to sensors, pumps and valves in the system. Hereby it can be assured that only oil phase is removed through the oil phase outlet.

In one embodiment of the invention the step of detecting comprises detecting if it is an oil phase or a sludge phase at substantially the level in the sedimentation tank where an oil phase outlet is provided.

In one embodiment of the invention the method further comprises removing at least a part of the sludge phase from the sedimentation tank before another batch of contaminated oil to be purified is provided to the sedimentation tank.

In one embodiment of the invention at least a part of the sludge phase settled in the bottom part of the sedimentation tank in a previous purification cycle performed in the sedimentation tank is reused in a next purification cycle where oil to be purified is provided into the sedimentation tank, whereby the sludge phase is mixed into the newly provided oil by a mixing device provided in the sedimentation tank possibly together with an amount of new separation aid corresponding to an amount of removed separation aid in the sludge phase removed from the previous purification cycle. It is economically beneficial to reuse the separation aid and hereby also a larger amount of separation aid can be used for each cleaning cycle. This will improve purification efficiency.

In one embodiment of the invention the method further comprises controlling removal of a sludge phase from the sedimentation tank through at least one sludge phase outlet while monitoring an output from a content detection sensor provided at substantially the same level as an oil phase outlet of the sedimentation tank and stop the removal of a sludge phase when the output from the content detection sensor indicates that an oil phase instead of a previous sludge phase is provided at the level of the oil phase outlet. Hereby the position of an interphase between an oil phase and a sludge phase can be controlled and it can be assured that only oil phase is removed from the sedimentation tank through the oil phase outlet.

In one embodiment of the invention the method further comprises providing oil to be purified to one sedimentation tank while removing and filtering an oil phase from another sedimentation tank which has been provided with oil to be purified in a previous cycle of the purification process, while possibly also allowing a sludge phase to sediment to a bottom part of a third sedimentation tank which has already been provided with oil to be purified in a previous cycle of the purification process.

In one embodiment of the invention the method further comprises controlling feed of oil to be purified into at least two sedimentation tanks provided in the system and removal of purified oil phase from the at least two sedimentation tanks cyclic such that a continuous flow of oil in and out form the system is provided, said controlling being provided by a control system provided in the system connected to sensors, valves and pumps in the system.

Hereby oil to be purified can be continuously provided into the system and purified oil phase can continuously be removed out from the system. Hereby the system can be used as an online system for continuous purification of oil.

In one embodiment of the invention said system further comprises:a control system connected to sensors, pumps and valves in the system and configured for controlling flows in the system in dependence of predefined settings, sensor signals and possibly also user inputs.

In one embodiment of the invention the at least one sedimentation tank further comprises at least one content detection sensor for detecting the presence of an oil phase or a sludge phase in at least one position in the sedimentation tank and wherein said control system is configured for controlling the removing of the oil phase form the sedimentation tank in dependence of said detection.

In one embodiment of the invention said sedimentation tank comprises a content detection sensor provided at substantially the same level in the sedimentation tank as an oil phase outlet of the sedimentation tank and said content detection sensor is configured for detecting if it is an oil phase or a sludge phase at this level in the sedimentation tank. Hereby it can be assured that only oil phase is removed through the oil phase outlet.

In one embodiment of the invention the system further comprises at least one sludge tank connected to at least one sludge removal outlet in a bottom part of the at least one sedimentation tank and configured for receiving a sludge phase from the sedimentation tank.

In one embodiment of the invention the sedimentation tank comprises at least two sludge removal outlets provided at different levels in the bottom part of the sedimentation tank, both connected to the at least one sludge tank. Hereby the user can chose which part of the sludge phase he wants to remove and which part he wants to keep in the tank for reuse. For example the lowermost bottom part of the sludge phase could be kept for reuse.

Hereby a heavier fraction of the sludge phase can be kept in the tank for reuse and a lighter fraction of the sludge phase could be removed.

In one embodiment of the invention the system further comprises a heating tank provided between the oil phase outlet of the at least one sedimentation tank and the filter module.

In one embodiment of the invention a control system provided in the system is configured for controlling removal of a sludge phase from the sedimentation tank through the at least one sludge phase outlet while monitoring an output from a content detection sensor provided at substantially the same level as an oil phase outlet of the sedimentation tank and stop the removal of a sludge phase when the output from the sensor indicates that an oil phase instead of a previous sludge phase is provided at the level of the oil phase outlet.

In one embodiment of the invention the system further comprises at least two sedimentation tanks connected in parallel in the system.

In one embodiment of the invention the system comprises a control system connected to sensors, pumps and valves of the system and configured for controlling feeding of oil to be purified into the at least two sedimentation tanks and removal of oil phase from the at least two sedimentation tanks such that one sedimentation tank is receiving oil to be purified while the oil phase is removed from another sedimentation tank and possibly while the sedimentation process is going on in a third sedimentation tank.

