GB2211198A

GB2211198A - A method of recovering lubricating oil

Info

Publication number: GB2211198A
Application number: GB8724607A
Authority: GB
Inventors: Tajwar Shadikhan; John Andrew Shillinglaw
Original assignee: ZIMMARK
Current assignee: ZIMMARK
Priority date: 1987-10-21
Filing date: 1987-10-21
Publication date: 1989-06-28
Also published as: CN1032671A; GB8724607D0

Abstract

A method of cleaning dirty lubricating oil in which the oil is heated and subjected to flash evaporation. Initially in the flash evaporation water evaporates off and then the pressure is reduced to flash off the fuel. After the flash evaporation, the oil is treated with a coagulant to flocculate the micron and sub-micron sized insoluble and cleaned oil is separated for reuse.

Description

RECOVERY OF LUBRICATING OIL This invention relates to the recovery of lubricating oils and in particular a process whereby a dirty and contaminated lubricating oil from, for example, the crank case of an internal combustion engine can be cleaned up for re-use.

After lubricating oil has been in use in an internal combustion engine for some time, it becomes contaminated with micron and sub-micron sized particles of carbon, metals and other insolubles and also contains varying amounts of water and fuel. In time therefore its desired lubricating properties become affected by these contaminants and the oil must be replaced to avoid damage to the engine. It has been found however that the properties of the lubricating oil itself are largely unchanged provided that the contaminants can be removed.

According to one well-known process, the solid contaminants are removed by adding a coagulant which will flocculate micron and sub-micron sized insoluble particles and a suitable coagulant is an aqueous based compound containing hydroxylic and single or complex oxygen-function amino compounds.

This coagulant causes the solid particles to separate leaving a clear lubricating oil which can then be reused. This process is described in United Kingdom Patent Application No. 7905434 of British Rail. An advantage of this process is that un-used oil additives are un-affected by the process.

There is however still a problem with the liquid contaminants, mainly unburnt fuel, and in the past these have been tolerated and the cleaned oil brought to a re-useable condition by blending it with fresh oil so as to give the physical properties required by the user.

It is therefore an object of the present invention to remove these liquid contaminants.

According to the invention a body of dirty lubricating oil to be cleaned is heated to a temperature below that of which the oil and any additives it contains significantly decompose and is subject to flash evaporation at a reduced pressure to remove substantially all of the condensed water, in a subsequent step the pressure of the flash evaporation is reduced so as to remove condensed fuel contaminant whilst still keeping the temperature of the body of oil below one at which substantial decomposition occurs, thereafter the thus-treated oil is treated with a coagulant to flocculate the micron and sub-micron sized insolubles, and the cleaned oil is separated from the solid contaminants and coagulant for reuse.

By operating in this way and first removing the water, it is possible to use simple apparatus. Thus the water can be removed at a higher pressure than the final pressure required to evaporate the fuel, and so it is possible to remove the water and thereafter condense the resulting water vapour with readily available cooling water without having to use chilled cold water. In the first stage therefore the pressure is kept sufficiently high to ensure that the water vapour can be completely condensed whilst using ordinarily available cooling water. However once substantially all of the water has been removed from the oil to be cleaned, then the pressure can be reduced further to cause the fuel to evaporate and since this has a much higher boiling point than water one can again use ordinary cooling water to condense the fuel vapour and prevent fuel vapour from entering the vacuum pump.

Generally speaking, in the first stage to remove the water, the dirty oil is subjected to a reduced pressure in the range of 400 mm to 550 mm mercury, whilst the oil is itself warmed to a temperature in the range of 40 to 85 c. Under these conditions water will vaporise at a temperature in the range of 40 to 80 C. The water vapour can however be condensed out so that it does not pass to the vacuum pump in a condenser such as a shell and tube condenser by contact with cool readily available cooling water at say a temperature of up to 400 C, or more preferably no more than 260C.

In the second stage the pressure is further reduced so that the fuel will evaporate.

The ultimate reduced pressure will to some extent depend on the fuel contaminant in the oil. In the case of petrol this can be evaporated off at temperatures in the range of 35 to 80C corresponding to pressures of 400 to 600 mm of mercury. Diesel fuel however has a much higher boiling temperature and normally boils in the temperature range of 250 to 350 C. So it is necessary to reduce the pressure to a very low figure to ensure that it will boil at a temperature in the range of 110 to 125 ac, ie., at a temperature below that at which substantial decomposition of the oil and/or its additives occurs.The reduced pressure therefore should be in the range of 5mm of mercury or less and preferably should approach lmm of mercury at which pressure the diesel fuel will boil at a temperature about 105 to 115 0c. The dirty oil being treated therefore needs to be heated to a temperature in the range of 115 to 125 C to ensure the evaporation of the diesel fuel whilst ensuring that the temperature is not too high to cause decomposition of the oil and the additives.

We have also found according to a further feature of the invention that it is desirable to maintain the temperature of the dirty oil during the flash step and whilst it is falling through the flash chamber so as to ensure the best vapour separation. This can be achieved by providing heated baffles and/or plates within a spray chamber for the dirty oil so as to restore heat to the sprayed oil as heat is removed by the evaporation of the water or fuel.

In order to ensure removal of both the water and the fuel during the evaporation steps, it will normally be necessary to recirculate the stream of the dirty oil continuously through a spray chamber in which the water vapour or fuel vapour is flashed off. This means that the oil which is passed through the flash chamber has to be removed by means of a pump and returned to the bulk of the oil for recirculation. This requires a pump capable of moving the oil under the very low pressures existing in the flash chamber during the last stages of the fuel removal when the pressures can be as low as lmm mercury. This can be achieved according to one preferred embodiment to the present invention by using a mechanical pump in series with a venturi pump.The mechanical pump can provide a flow of oil which is circulated through the venturi pump to provide a very low pressure suction boost effect capable of removing oil from the spray chamber and the mechanical pump having one outlet for returning a portion of the oil to the main bulk of the oil for re-circulation through the spray chamber and another outlet for supplying oil to the venturi pump as the operating liquid.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagram showing the process of removing fuel from dirty oil according to the invention; Figure 2 is a diagram illustrating the overall process for cleaning dirty oil and incorporating the process illustrated in Figure 1; and Figure 3 is an enlarged detail of components in the flash chamber for evaporating of water and fuel from the dirty oil.

Referring first to Figure 2, dirty oil is collected in a holding tank 10 and normally will be tested to determine the types and proportions of contaminants. When a batch of waste oil has been collected it is transferred by means of a pump 12 into a clarifying tank 14. In the clarifying tank it is maintained at a constant temperature and coagulant material is added through the inlet 16.

This is mixed in with the waste oil and the waste oil is then left to settle into an upper clean component and a lower sludge component. In the clarifying tank 14 separation can be achieved by gravity given sufficient time or alternatively various forms of centrifuge and/or filtering are possible. The sludge can be removed through the outlet 18 and often has uses in printing ink manufacture because it contains a high proportion of fine carbon particles whilst the clean and clarified oil is removed through an outlet 20 to a clean oil holding tank 22.

This process is well-known and in use and is generally described in United Kingdom Patent Application No. 7905434 to which reference is made for a full description.

The coagulant can be an aqueous based coagulant containing hydroxylic and single or complex oxygen-function amino compounds and again is described in the above-noted United Kingdom Patent Application.

This process does not however remove any significant amount of the fuel contaminants in the waste oil. Therefore the oil sent to the clarifying tank 14 is treated according to the present invention to a vacuum dehydration step 24 to remove the water and fuel before the coagulant is added.

The vacuum dehydration process 24 is shown in more detail in Figure 1.

Referring to Figure 1 oil is removed through an output line 26 from the clarifying tank 14 by a pump 28 and circulated through a flash chamber 30 before being returned by a pumping apparatus 32 to the clarifying tank 14 via a return line 34. Before entering the flash chamber 30 the oil passes through booster heater 38 containing a heating element 40 which raises the temperature of the oil to a suitable temperature for flashing off water and/or fuel.

In the flash chamber 30 the heated oil is brought into a fine droplet form by means of a spray nozzle 42 to give an extended surface area so as to promote evaporation of water andjor fuel. Vapours which are flashed off leave the spray chamber 30 through outlet 44 whilst the oil collects in the bottom of the flash chamber 30 and is removed through a line 46 by the pumping apparatus 32.

Referring to a Figure 3, means are provided in the flash chamber 30 to keep the oil at an elevated temperature so as to avoid recondensation of the vapour and fuel. Initially the droplets from the spray nozzle 42 collect on the surfaces of a number of concentric cylindrical baffles 50 which are held apart by spacers 51 and whose surfaces are kept hot by individual spirial heating pipe 52 through which are circulated portions of the hot process oil from the booster heater 38. The oil which collects on the surfaces of the cylindrical baffles 50 runs down these surfaces as a film and then collects in the lower part of the chamber 30.

Vapours which flash off in the flash chamber 30 pass to a shell and tube condenser 60 which is provided with cooling water to condense the vapours. The condensate passes down to a liquid condensate tank 62 where it is collected.

A reduced pressure is provided in the flash chamber 30 by means of a vacuum pump 64 and to protect this vacuum pump 64 from any particules which might be carried along with the vapours a filter 66 is provided. The degree of reduced pressure can be controlled by an air bleed 67 to the condensate tank. When this is fully closed the pump 64 will produce a very low pressure in the tank 30, tube condenser 60 and tank 62.

Because of the low pressure existing in the flash chamber 30 during the process, the pump arrangement 32 must be capable of removing the oil from the chamber 30 and returning it to the clarifying tank 14. This pumping arrangement comprises a mechanical pump 68 having an outlet 70.

The outlet 70 is branched and one branch is formed by the return line 34 which returns the oil to the clarifying tank 40. The other branch 72 completes a loop and powers a jet pump or venturi pump 74. This pump 74 is powered by the oil circulating through the loop 72 and has an inlet joined to the line 46.

This venturi pump therefore provides a boost to the pumping power of the pump 68 and enables the pumping arrangement 32 to remove the oil from the flash chamber 30 despite the very low pressures which may exist therein.

In operation dirty lubricating oil is collected in the holding tank 10. When a sufficient volume has been collected it is transferred by the pump 12 to the clarifying tank 14. The oil in the clarifying tank 14 is then circulated through the vacuum dehydration apparatus 24.

The vacuum pump 64 is in operation and the air bleed 67 set to provide a reduced pressure of about 600mm of mercury. The dirty oil is then circulated through the pipe 26 into the apparatus by the pump 28. It is heated in the booster heater 38 and flashed in the flash tank 30. The collected oil droplets are removed from the base of the tank by the pumping apparatus 32 and returned through the pipe 34 to the clarifying tank 14.

In the booster heater 38 the oil is brought to a temperature of about 806c and kept at about that temperature in the flash tank 30 by the heating pipe 52 and coil 56. At a reduced pressure of about 600mm of mercury the water in the oil will flash off and the water vapour will pass through the outlet 44 to the condenser 60 in which the water vapour will be condensed and collected in the tank 62. The water will be completely condensed by the cooling water supplied to the condenser which can be a room temperature, eg. up to maximum of about 350C and does not need to be chilled water. Therefore no water vapour will pass through to the vacuum pump to damage it.

Once the oil has been circulated for some time, substantially all of the water will have become removed and so the vacuum pressure can be progressively reduced by closing the air bleed 67 so as to cause the fuel in the dirty oil to boil off in the flash tank 30. In the case of diesel fuel this requires a minimum pressure of about 5mm of mercury preferably a pressure of about lmm of mercury and more if the temperature of the oil is to be kept below to about 1150C so as to avoid decomposition of the oil and/or its additives. The vacuum pump is therefore progressively allowed to reduce the pressure in the flash tank 32 to about lmm of mercury. Then the diesel fuel in the dirty oil will flash off in the tank 30 and will condense in the condenser 60, the condensed fuel collecting in the condensate tank 62.

The oil is circulated in this way until substantially all of the water and fuel have been removed. Then pumping is stopped and coagulant is added through the inlet 16. This is mixed with the dirty oil and the solid contaminants allowed to settle. The clean oil is thereafter removed through the outlet 20 to the clean oil tank 22 whilst the sludge is removed through the outlet 18. The clean oil can be used on its own or if required blended with fresh oil and/or additives to restore its lubricating properties to within the ranges required for any particular use.

Claims

C L A I M S:

1. A method of cleaning dirty lubricating oil comprising heating it to a temperature below that of which the oil and any additives it contains significantly decompose, subjecting it to flash evaporation at a reduced pressure to remove substantially all of the condensed water, subsequently reducing the pressure of the flash evaporation so as to remove condensed fuel contaminant whilst still keeping the temperature of the body of oil below one at which substantial decomposition occurs, and thereafter the oil is treated with a coagulant to flocculate the micron and sub-micron sized insolubles, and cleaned oil is separated from the solid contaminants and coagulant for reuse.

2. A method as claimed in Claim 1 in which in the flash evaporation to remove the condensed water the dirty oil is subjected to a reduced pressure in the range of 400mm to 550mm mercury, whilst the oil is itself is at a temperature in the range of 40 to 850C.

3. A method as claimed in Claim 2 in which the water vapour flashed off is condensed using cooling water at a temperature of no more than 260C

4. A method as claimed in any preceding claim in which the oil is contaminated with petrol fuel and in which the fuel is evaporated at a temperature 0 in the range of 35 to 80 C corresponding to a pressure of 400 to 600mm of mercury.

5. A method as claimed in any of claims 1 to 3 in which the oil is contaminated with diesel fuel and in which the fuel is evaporated at a temperature 0 in the range of 110 to 125 C and a reduced pressure in the range of 5mm of mercury or less.

6. A method as claimed in Claim 5 in which the pressure is about lmm of mercury and the temperature is about 105 to 1150C.

7. A method as claimed in any preceding claim in which the dirty oil is heated to a temperature in the range of 115 to 125 0C to ensure the evaporation of the fuel whilst ensuring that the temperature is not too high to cause decomposition of the oil and the additives.

8. A method as claimed in any preceding claim in which the temperature of the dirty oil during the flash evaporation and whilst it is falling through a flash chamber is maintained by providing heated baffles and/or plates within the flash chamber for the dirty oil so as to restore heat to the sprayed oil as heat is removed by the evaporation of the water or fuel.

9. A method as claimed in any preceding claim in which a stream of the heated dirty oil is continuously recirculated through a spray or flash chamber in which the water vapour or fuel vapour is flashed off.

10. A method as claimed in Claim 9 in which the oil is recycled from the flash chamber using a mechanical pump in series with a venturi pump, the mechanical pump providing a flow of oil which is circulated through the venturi pump to provide a very low pressure suction boost effect capable of removing oil from the spray chamber, the mechanical pump having one outlet for returning a portion of the oil to the main bulk of the oil for re-circulation through the spray chamber and another outlet for supplying oil to the venturi pump as the operating liquid.

11. Lubricating oil cleaned by a method as claimed in any preceding claim.