1Introduction
Lubricant
oils are a common element in our daily lives, as they are needed to
allow many engines and mechanisms to function. However, through their
use, they loose their properties, become contaminated and at some
point they cease to be fit for the use they were originally intended.
These used oils are then replaced by fresh lubricating oils and we
are left with some waste oils. Some 50% of what is purchased will
become waste oils (the rest is lost during use, or through leakages,
etc.).
Waste oils are
hazardous waste as they display some hazardous properties. Waste oils
that are found in rivers, lakes and streams threaten aquatic life.
Indeed, a litre of waste oil can contaminate a million litres of
water. Furthermore, severe soil contamination can result from waste
oils being left on the ground.
Thus, it is crucial
to collect as much as possible this very valuable resource, in order
to avoid the contamination of the environment and to be able to
profit from the very high recovery potential of this waste stream.
Industries, consumers, garages and do-it-yourselfers have to
participate, by not dumping these precious liquids but by handing
them to authorised collectors that will ensure their adequate
recovery & ethical placement of that profit.
2Uses of Waste oil
Used oil, or 'sump
oil' as it is sometimes called, should not be thrown away. Although
it gets dirty, used oil can be cleaned of contaminants so it can be
recycled again and again. There are many uses for recycled used oil.
These include:
- Industrial burner oil, where the used oil is dewatered, filtered and demineralised for use in industrial burners;
- Mould oil to help release products from their moulds (e.g. pressed metal products, concrete);
- Hydraulic oil;
- Bitumen based products;
- An additive in manufactured products; or
- Re-refined base oil for use as a lubricant, hydraulic or transformer oil.
Once you have taken
your used oil to your local collection facility, used oil collectors
take the used oil and undertake some pre-treatment and recycling of
the used oil or sell it to a specialised used oil recycler.
3Method of recycling waste oil
3.1Pre-treatment or Dewatering
Pre-treatment of
used oil involves removing any water within the oil, known as
dewatering. One way of doing this is by placing it in large settling
tanks, which separates the oil and water.
Further recycling
steps include:
- Filtering & demineralisation of the oil, to remove any solids, inorganic material and certain additives present in the oil, producing a cleaner burner fuel or feed oil for further refining;
- Propane de-asphalting to remove the heavier bituminous fractions, producing re-refined base oil; and
- Distillation to produce re-refined base oil suitable for use as a lubricant, hydraulic or transformer oil. This process is very similar to the process undergone by virgin oil.
Water is found in
used oil as free water or bound water, for example in emulsions. The
term dewatering is usually taken to mean the removal of free water.
Where water has been emulsified with oil, the emulsion has to be
"broken" with a demulsifier before the water can be
separated from the oil.
Dewatering is a
simple process relying on the separation of aqueous and oil phases
over time under the influence of gravity. The used oil is allowed to
stand in a tank (raw waste oil) and free water drops to the bottom
where it can be drained, treated (waste water treatment) and
discharged appropriately to sewer or stormwater depending on quality
and local regulations.
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Heating and stirring
the used oil in a tank (A) and driving off the water through
evaporation can speed up the dewatering process.
The "dried"
or dehydrated oil is then suitable for further processing or for use
as a burner fuel.
3.2Filtering & Demineralisation
The purpose of
filtering and demineralisation is to remove inorganic materials and
certain additives from used oil to produce a cleaner burner fuel or
feed for re-refining.
Used oil feedstock
is transferred to a reaction tank (A) and mixed with a small quantity
of sulphuric acid and heated to about 60oC. A chemical surface-active
reagent, called a surfactant, is added to the reactor (A) and after
stirring the mixture is allowed to stand. This allows the mixture to
separate into two "phases" - i.e. oil and water-based or
aqueous. The reagent causes the contaminants to accumulate in the
aqueous phase, which settles to the bottom of the tank (A) and is
drained off as slurry. This phase contains acid, used oil
contaminants, including metals and some of the oil additives. The
water is dried off; leaving a solid waste that must be disposed of.
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The demineralised
oil is filtered (B) to remove suspended fine particles (to solid
waste) and run off to storage (C) as a clean burner fuel. It can be
further diluted or "cut" with a lighter petroleum product
(called cutter stock) to produce a range of intermediate to light
fuel oils depending on the fuel viscosity requirements of the burner.
3.3Propane De-asphalting
The Propane
De-asphalting (PDA) process is an important pre-treatment step in the
re-refining process producing de-asphalted lube-oil, which becomes a
feedstock for the next step in a re-refining facility. The other
output (which is also an input) is propane, which is recovered from
both streams and re-used within the process.
The PDA process
relies on the greater solubility of the paraffinic and naphthenic (ie
essentially the base oil) components versus the contaminated waste
material in a stream of propane.
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The separation of
the lubricating oil fraction from used oil is a continuous process
and is conducted at ambient temperature when processing used oil.
The used oil is
pumped into the middle of the extraction column (A). Liquid propane
is charged to the bottom of the column (A). The oil being heavier
than propane, flows down the column (A); the propane rises in a
counter-flow thus mixing the input streams within the column (A). The
rising propane dissolves the more soluble lube oil components, which
are carried out the top of the column (A) with the propane, and the
propane insoluble material is removed from the bottom of the column
(A).
Propane is vaporised
from both streams [ie., the de-asphalted lube-oil stream (B) and the
waste stream (C)] in "stripper" units (B) and (C), then
condensed and returned to the propane storage tank.
The de-asphalted
lube-oil component is feed for the next processing stage. The
residuum (waste) component is mixed with bottoms from the vacuum
distillation tower to produce an asphaltic material.
3.4Distillation
Distillation (or
Fractionation) is the physical separation of components of
lubricating oil by boiling range. Depending on the type of
distillation, the boiling ranges can produce gases and gasolines at
the lower boiling points with heavy lubricating oils being distilled
at higher boiling points. Distillation is the core process for a
facility capable of producing re-refined base-oils to virgin base-oil
quality.
There are 2 types of
distillation, atmospheric and vacuum.
3.5Atmospheric Distillation
Atmospheric
distillation is generally (but not always) considered a pre-treatment
step for vacuum distillation and does not require de-watered
feedstock. Atmospheric distillation is carried out at normal
atmospheric pressure and with temperatures up to 300°C.
Prior to the
atmospheric distillation process, the feedstock can have undergone
PDA treatment, but this is not an absolute pre-requisite.
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Atmospheric
distillation is a relatively simple process separating lower boiling
point liquids at ambient pressure. Used oil is heated (A) and charged
to a distillation tower (B). Lower boiling point hydrocarbons present
in the used oil (eg gases, petrol and solvents) and water are
collected at the top of the tower (B). Some of these hydrocarbons can
be condensed and collected for use as a fuel in the refining process.
This process is only
suitable for temperatures up to 300oC, as temperatures above this can
lead to "thermal cracking" of the larger molecule (higher
boiling point) hydrocarbons, ie. the actual lube oil molecules we are
aiming to recover.
After atmospheric
distillation the oil usually undergoes vacuum distillation. Note that
used oil can be sent directly from a "drying" process to a
vacuum distillation unit without necessarily undergoing atmospheric
distillation. However, it is generally accepted that water and lower
boiling point hydrocarbon components be removed prior to vacuum
distillation.
3.6Vacuum Distillation
Vacuum distillation
is considered the key process in used oil re-refining. If atmospheric
distillation is utilised, the oil from the atmospheric distillation
column is the feedstock for the vacuum distillation column. In vacuum
distillation the feedstock can be separated into products of similar
boiling range to better control the physical properties of the lube
base stock "distillate cuts" that will be produced from the
vacuum tower products.
The major properties
that are controlled by vacuum distillation are viscosity, flash point
and carbon residue. The viscosity of the lube-oil base-stock is
determined by the viscosity of the distillate in terms of its
relative viscosity separation, eg. light, medium and heavy oil.
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The used oil
feedstock (usually from the atmospheric distillation unit) is heated
in a furnace (A) and flows as a mixture of liquid and vapour to the
heated vacuum distillation column (B) where the vapour portion begins
to rise and the liquid falls. Steam can be added to assist
vaporisation.
A vacuum is
maintained in the column (2-10 mm Hg) by a vacuum system connected to
the top of the tower (B). By reducing the pressure, materials
normally boiling at up to about 540oC at atmospheric pressure, can be
vaporised without thermal cracking.
As the hot vapours
rise through the column (B), they cool and some condense to a liquid
and flow back down the column. Similarly, some of the downward
flowing liquids are re-vaporised by contacting the rising hot
vapours. Special devices in the column allow this upward flow of
vapours and downwards flow of liquids to occur continuously.
At various points in
the column (B), special trays, called draw trays, are installed which
permit the removal of the liquid from the column. If three cuts or
"fractions" of oil are required to produce light, medium
and heavy base stocks, then three draw trays are positioned
appropriately. This can be reduced to two draw trays if, for example,
only 2 cuts or fractions are required.
Some of the material
does not boil even under this vacuum. This remains in the vacuum
tower and is run out as the vacuum tower bottoms (VTBs). This
material contains the heaviest molecules, including some lube oil
additives and carryover contaminants not removed in the PDA process.
(Note: not all re-refining plants have PDA units).
4Conclusion
The central idea of
this whole activity is to utilized the used engine oil, we have
discussed the recycling methodology in quite detail , so first of
all we are starting this activity on our group level, we get the our
car/bike used engine oil and sold it out to professional recycler of
used oil and the handsome amount which are quite enough to help a
poor family, so the theme of the project is to create awareness in
our society that we should use this kind of wastage and help out
those poor peoples who are needy one, here I would like to quote
hadith:
“Bukhari
Volume 2, Book 24, Number 512:
Narrated Abu Burda bin Abu Musa:that his father said, "Whenever
a beggar came to Allah's Apostle or he was asked for something, he
used to say (to his companions), "Help and recommend him and you
will receive the reward for it; and Allah will bring about what He
will through His Prophet's tongue."
So
whenever the Prophet Muhammad (PBUH) would encounter with a poor
person, he would tell his companions to help and give for that
person, and they would be rewarded for it. The prophet would not
simply ignore them and let them be, as would have been the custom of
the time, rather he gave advise and teaching to his companions to
help these people.”
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