REPURIFYING USED OIL.
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Waste which Should be Avoided, How Solid Particles and Diluents from the Fuel can be Removed. Overcoming the Difficulty of Emulsification. Details of a Promising Process.
moil: reclamation of oil which has I. become contaminated by particles of carbon, dust and abraded metal from the cylinders, pistons and bearings and by fuel diluents is of great importance to all who wish to study methods for improving transport economy. Many makers of motor vehicles strongly advise their engine sumps should be emptied stud refilled with fresh oil after comparatively short mileages, but this is a somewhat expensive process, although in SOMA eases use can be found for a proportion of the oil in lubricating gearboxes and axles, but even here, and particiderly with worm-driven axles, it is really always advisable to employ fresh ubri ea nt.
Many attempts have been made to devise a satisfactory means for the purlfiention of such oil. The original theory that oil permanently loses its lubricating properties through some unexplained breaking down of its constituent molecules no longer bolds good, as it has been proved on many occasions that with careful cleansing a used oil may regain practically all its original charaeteristics, but so far, whilst success has been gained in the employment of certain systems of recovery, yet its success • is by no menus certain in every instance, as it depends to a great extent upon the particular characteristics of the oil upon which the process is being employed.
In one process the operation of removing the solid matter has been combined with that of extracting the heavier constituents of the petrol which have been absorbed. This process has in some instances given notable successes, stud in other eases proved quite useless.
Without going into minute details, the process consists of putting some washing powder into the oil in a tank and Hewing steam through the oil for some three hours, after which the contents the tank are allowed to settle and the oil drawn from the top. The steam is partially condensed, thus dissolving the washing powder, which possesses the property of surrounding the solid particles in the oil and carrying them to the bottom, sosforming a layer of sludge between the oil and the solution. The remainder of the steam and the vaporized diluents are carried away.
The troubles with this process are that it does not completely remove thee.bsorhed petrol end that, in some cases, the oils employed become emulsified, this emulsion being difficult or impossible to break olawn, in which case the resultant mixture is a mess with practically no powers of lubrication.
American outfits for carrying out this process have been sold by two wellknown concerns, but there is not very much demand, owing to the limitations mentioned, although we understand they have proved of value in connection with the treatment of oil taken from the crankcases of Diesel engines.
In a process worked out by C. D. Associate Engineer of the Alabama Polytechnic Institute, Auburn, Alabama, and .,described by him some
tims ago in " Bus Transportation," the operations e re in two phases. First, the solid matter is removed ; next, the absorbed fuel evaporated, so restoring the oil to its proper viscosity. In the first pert oi! the process the oil is washed with hot water containing washing powder in solution, this being such as might be employed for washing clothes or dishes, and it can be used with oils that have a strong tendency to emulsify, this being avoided through the application of the principle that emulsification
does not occur readily, if at all, between water or a water solution and oil, so long as the two liquids do not mingle is the presence of matter in a gaseous state ; in other words, so long as there is no free liquid surface in the region in which the two liquids come together. Following this rule, it is obvious that the methods of agitation by Mowing air or stettm through the solution and the
oil, and by ordinary churning, cannot be employed.
Various ways of obtaining the desired effect have, however, been devised. The simplest and, apparently, the one preferred is to introduce a solution above the surface of the oil in the centre of a vertical cylindrical tank, allowing it to flow down through the oil to the bottom, where it is drawn off and again passed through the oil. It will be found better to have the liquid hot, at least, when commencing, as this allows a bet ter action on the solid matter. The washing treatment is continued for about one hour and the oil then allowed to settle, usually during the night.
To remove the oil without taking out any of the sludge it is overflowed from the top of the treating tank by running in water or washing solution at the bottom.
It has been found that the demarcation between the sludge and oil is fairly sharp, similar to that between cream and milk. The sludge has • a curd-like consistency, the particles apparently knitting themselves together as they settle.. If the oil has been kept hot (this can be done by an electric heater), as is better, it can he run through a cloth of fine mesh, such as that f rein which handkerchiefs are made, so that any particles of solid matter that may inadvertently have been permitted to pass over with the last of the oil can be extracted.
Without the washing treatment it is found that centrifugal separation does not entirely remove the finer particles of solid matter.
To get rid of the absorbed fuel the oil obtained from the washing process is run into a tank heated 'to a temperature of 350 degrees P. to 380 degrees P., and steam is blown through it from the time it is a few degrees above the boiling Point of water until it reaches the desired atmosphere. If the oil temperature be raised to 360 degrees, continued steaming will carry off more of the lighter constituents, but the same result is obtained more rapidly by raising the temperature to the higher figure. It must be noted that the heavy constituents of fuel are closely akin to the lighter constituents of lubricating oil.
Both the steam and high temperature are essential to the removal of the heavy ends of the fuel, as these do not vaporize at lower temperatures, such as that of boiling water or saturated steam. They will not even boil away normally at the temperatures used ; it is only by opening up the mass of liquid by the steam that they can readily and completely be removed.
New oil has in it some light and volatile constituents, and with this process iris claimed that it is quite possible not only to restore the oil to its original consistency, but, actually, to make it thicker by continuing the heating and steaming process. The higher the temperature the thicker the oil, within limits depending upon its nature. Air would carry off the vapour, but it is unsuitable on account of the oxidation of the oil which results from contact with air while it is hot. If the steaming be carried out in an open vessel there is apt to be some oxidation of the oil through contact with the air, this forming a dark-brown solid matter—apparently a carbonized material which has not reached the final stage of carbonization. This can be removed by a second washing treatment similar to the first, followed by the usual settling. It is preferable, however, to steam the oil in a completely closed tank, so that it does not come into contact with the air while It is hot.
In connection with the use of steam it is essential to prevent the entry of water, as this causes spluttering due to its sudden conversion into steam. It might even be dangerous. To catch water entering with the steam, the latter it led down to a trap immersed in the oil, the outlet from which passes up above the surface of the oil and down by a return bend to an outlet nozzle at the bottom of the tank. Any water caught in the trap is volatilized and passes off as steam ; at the same time the steam itself is superheated.
It is essential not to let the boiler cool off and condense the steam within It without opening the steam pipe to the oil tank to the atmosphere ; otherwise, condensation of steam within the boiler and water trap will draw the oil into the trap and the boiler. The vapour from the oil can be allowed to escape into the air or can be condensed and then serves as a cleaning fluid.
Fleet engineers responsible for the mechanical efficiency of large numbers of vehicles will study, with considerable interest, the system of oil repnrification outlined in this article and will, we trust, let our readers have the benefit of their experience should they install an apparatus for the purpose.