Lubricating oil is an important resource and a petroleum base product. The high price of oil and objective of saving valuable foreign exchange has resulted in efforts for regeneration of used lube oil.

Mismanagement of waste lube oil is a serious environmental problem. Almost all types of waste oil have the potential to be recycled safely, saving a precious non-renewable source and at the same time minimizing environmental pollution. Unfortunately, most of used oil is handled improperly. Some is emptied into sewers for going directly into water waste, adversely affecting water treatment plants. Some is dumped directly on to the ground to kill weeds or is poured on to dirty roads or is dumped in deserts, where it can contaminate surface and ground water.

Disposal of used lubricating oil into the ecosystem creates environmental hazards. Tough laws are being enacted throughout the world for the disposal of waste petroleum products and every genuine effort should be made for its re-use. In most cases, used oil can be re-used after reconditioning with or without the addition of any additives resulting in huge saving and conservation of precious oil. Thus regeneration, reclamation or recycling of spent lubricating oils has become an important process industry, adopting various techniques for oil purification.

Regeneration of used lubricating oils is based on the fact that, "Petroleum lubricating oil are almost indestructible". We can say, "Lubricating oil never wears out". Lubricating oils are impaired temporarily only because of accumulation during use or handling of contaminants coming from extraneous impurities and products of oil deterioration, which can be separated from the used oil by re-refining or re-conditioning. The treated oil, then, becomes almost equivalent to fresh/virgin oil.

The major extraneous impurities in the waste oil are:
1. Metallic impurities
2. Non-metallic impurities
3. Water, moisture and untreated acid
4. Carboneous particles
5. Fuels, impaired additives and their by products.
6. Chemical contaminates, and
7. Polycyclic aromatic hydrocarbons (PAHs).

In India, re-recycling waste oil industry is mainly an un-organised one. Although some public service units (PSU) also doing re-recycling but most of the market demand is furnished by the small scale industrial units (SSIs). Most of the SSI units, till now, were adopting "Acid Clay Process", which now has been dis-approved by the pollution control boards, resulting in their closure until they adopt new certified process.

Acid Clay Process
In the conventional acid clay process the used lubricating oil is settled or filtered after collection and is dehydrated. The oil is then treated with concentrated sulphuric acid to remove polymers, asphalts, degraded additives and other products of degradation. The sludge formed is allowed to settle and removed.

The oil is neutralised with activated clay, at elevated temperatures. The clay also bleaches the oil and adsorbs certain impurities not removed by acid treatment. The clay-oil slurry is filtered to remove clay and other solids. If the raw material contains more than one grade of lube oil product further processing may be required.

Environmentally Sound Technologies (EST)
The Govt of India's legislation and amendments for waste oil re-cycling rules 1989 and as amended, Central Pollution Control Board (CPCB) has been designated as the authority for grant of registration to such re-cyclers, re-processors for re-processing of hazardous wastes who comply with the norms of the CPCB.

Re-refiners and re-cyclers, now have to use only environmentally sound technologies (EST) while re-cycling and refining waste oil. In case of oil re-refiners using acid clay process or modified acid clay process have been advised to switch over to EST only or close down.

The following processes have been approved as Environmentally Sound Processes:
1. Vacuum distillation with clay treatment, Figure.1
2. Thin Film evaporation process, Figure 2
3. Vacuum distillation with hydro treating.

Process Characteristics

Advantages
1. Simple process
2. Low initial investment
3. Low energy input

Disadvantages
1. Unacceptable process to Pollution Control Boards.
2. Generates large quantity of pollutants.
3. Unable to treat modern Multi-Grade oils
4. Difficult to remove Asphaltic impurities

Spent oils, which have not deteriorated to great extent, are often clay contracted or treated with adsorbents without any acid treatment. They are generally given a preliminary settling, filtering, centrifuging or vacuum dehydrating treatment. Insulating oils and transformer oils are often treated in this way.

Selection of Vacuum Pumping System
In order to ensure satisfactory operation of any vacuum process it is essential that suitable vacuum pump be used. There is generally no single pump that meets all the requirements of the process. Combination of pumps is increasingly being used to optimise the process performance. Process condensable and non-condensable loads, air leakage loads, out-gassing loads and the working process pressures are the important parameters that influence the pump selection. Various empirical load estimation charts, and leak tests must be referred for the proper selection of the vacuum system. Some of the widely used pumps for vacuum process are described below along with their limitations.

Water Ring Pump, Liquid Ring Pump
These pumps use water or low vapour pressure fluid as the pumping medium. For this reason, the ultimate vacuum achieved gets limited to the vapour pressure of the pump fluid at the working temperature. Owing to the above, water ring pump would stall at around 60 Torr abs. (700 mmHg) and their working range would be between 60 to 150 Torr (700-610 mmHg). They have further disadvantage of being energy inefficient, because most of the power is lost in friction losses of moving the pump fluid inside the pump. This restricts the water ring pump to relatively modest volumetric pumping capacities. Another disadvantage of ring pumps is that the working fluid often has to be treated before it can be discharged or reused as it contains the carry over of condensed product.

Steam Ejectors (Single & Multi-stage)
Steam ejectors have relatively high volumetric speeds. However, they require the maintenance of a complete high pressure steam generation facility confirming to IBAR regulations and inspection. They are generally not available as stand alone installations but are found where high pressure process steam is readily available.

Multistage steam ejectors demand inter-stage condensing putting considerable load on the cooling towers. Apart from the direct steam generation cost, large energy and maintenance cost of secondary equipment such as circulation pumps, cooling tower, softening plant, DM plant and boiler maintenance add to recurring expenses.

Rotary Vane and Piston Pumps
These type of pumps have high power-to-capacity ratios and are therefore, not available in large volumetric capacities. They are effective for pumping non-condensable loads but have limitations of not being able to pump large and regular quantities of water vapour (condensable loads) released in low pressure vacuum processes.

Mechanical Vacuum Booster
Mechanical Vacuum Boosters are being extensively used in chemical process industry to boost the performance of vacuum pumps where conventional vacuum pumps have poor volumetric efficiency. These boosters are capable of moving large quantity of gases at low pressures with far smaller power consumption than for any other equipment now available.

The internals of the boosters are totally free of any sealant fluid and therefore the pumping dry. Also because of vapour compression action by the booster the pressure at the inlet of backing pump is relatively high resulting in higher volumetric efficiency and low back streaming of sealing fluid.

Table 1 gives the general range of Vacuum/Pressures different vacuum pumps are designed for. The Ultimate/Blank-off may be slightly higher than the table values but is of little importance since at the ultimate pressure, the pump's pumping speed is Zero.

The last column, Table 1 gives the approximate pressure regime a single stage Booster-Pump combination can easily achieve. Further lower pressures (better vacuum) can be achieved by multi-staging of boosters. With suitable combinations pressures in the range of 0.001 Torr can easily be achieved. However, it is strongly advised that the system should be designed for the required pressure since lower pressures than the desired by the process would only add to initial and working costs without much benefit.

Table 2 gives the general pressure range essentially necessary for the successful operations generally involved during the oil refining process. These are guidelines only and may differ design to design.

From the table, it is evident that Mechanical Vacuum Boosters are very versatile and can be used with practically any vacuum pump to achieve higher efficiencies, which otherwise would not be possible economically.

Used motor oil can be re-refined to make to new lube oils. Re-refining is an efficient and sophisticated process, which removes contaminants and impurities producing premium grade base oil. One gallon of used motor oil would yield about 0.7 gallons of re-refine oil. Lube oils can be re-used indefinitely in an endless cycle from refinery to engine to refinery again. The one main thing which is common in all three environmentally sound technologies (EST) is that the vacuum requirement in each process, as per the specification furnished by Govt. of India, is about 758 mmHg (2 Torr) or better 2 mmHg at the final distillation with temperature of about 320-340?C. Whatever the process may be, the process vacuum demands a combination of vacuum pumps.

(This article has been compiled by the technical team of: Everest Transmission, New Delhi. Telefax: 91-11-28114944, 28114955, 28117469, 28116307. Email: info@everestblowers.com)