Crude oil
clarification
Objectives
1. Efficient separation
of pure oil from crude oil.
2. Optimum recovery of
pure oil at minimum oil loss.
3. Efficient separation
& disposal of free water.
4. Efficient separation
of solid impurities & dissolved moisture.
The composition of
crude oil
- A mixture of oil
& water.
* Non-dispersed oil in water – free oil.
* Highly dispersed oil in water – mass under
high pressure and oil is forced through the capillary ducts in the press cake –
homogenized in watery medium.
- Oil in water emulsion
– oil is highly dispersed in water with
the present of emulsifiers.
- Water in oil emulsion
– oil recovery is easy with temperature
between 80 – 100 degree Celsius.
Figure 1: The flow of oil and sludge in oil
clarification
Process that need to
be monitor
1. Oil content in Clarifier underflow, to monitor the efficiency of
clarification process.
-should
not exceed 8.0% ( wet basis).
2. Oil content in Centrifuge waste, to monitor final oil loss.
-should
not exceed 0.75% & 1.5% (wet basis) respectively.
3. FFA, PV, moisture and dirt in production oil, to monitor production oil
quality.
-dirt:
should not exceed 0.02%.
-moisture:
should be less than 0.20%.
Vibrating screen
The vibrating screen is
a machine that functions as a filter that separates the oil and sludge from
impurities, dirt and fibres that has not been separated by the sand trap.
Vibrating screen are used before crude oil tank and before sludge tank. Before
crude oil tank, the vibrating screen is used with the mesh size of 30 per inch.
The vibrating screen before the sludge tank is using 40 per inch mesh size. The
separated fibre, dirt and impurities will be returned to the digester to press
out the oil. The oil and sludge will flow to crude oil tank.
Figure 2: vibrating screen
Crude oil tank
Crude oil tank is a
tank that functions to store raw oil before being transferred to the vertical
clarifier. There are pumps that will pump up the oil from crude oil tank to
vertical clarifier and the pump is triggered by a weight lever mechanism as when the oil in the crude oil tank reached a certain
height, the pump will start running. Steam will be injected to keep the oil and
sludge at 90 degree celcius to prevent the oil from solidify.
Vertical clarifier
The function of vertical clarifier is to
separate pure oil and sludge and to minimize oil loss in sludge underflow.
Vertical clarifier consists of a large vertical tank with a conical bottom. In
the center of the tank is a large inlet pipe for the diluted crude oil (DCO).
The oil builds up to a rather high depth of pure oil and leaves the tank
continuously through an adjustable oil skimmer, usually a funnel of sufficient
size. The sludge collects near the bottom of the tank and is flowing upward
through a pipe. The discharge of underflow pipe is installed somewhat lower
than the level of the adjusted oil skimmer. When no more DCO is fed to the
tank, the discharge of oil and sludge will stop once oil layer equal sludge
outlet layer. The oil layer will then be pressed upward and can be drained out
preferably up to a foot of oil being left to prevent sludge water from being
drained off. There is a pair of arm near the bottom part of the clarifier. The
arm functions to stir the suldge that help to separate the oil particle that
still stick to the sludge. The arm is stirring at slow rate. The Clarifier is
also fitted with a steam heating coil in order to raise the temperature of the
sludge and oil in the tank during the initial operation. Sand and other heavy
impurities should be drained off periodically through the conical bottom of the
Clarifier. The temperature of the clarification tank content is maintained at
about 90 degree celcius to enhance oil separation.
Diluted Crude oil/FFB = Diluted crude oil / oil
* Oil/FFB
= 263% * 21% =
55.26%
Average mill throughput: 85MT/hr
85MT/hr x 55.26% DCO= 46.971MT DCO/hr
Clarifier retention time: 2 hours
Clarifier capacity: 2 hr x 46.971 MT DCO/hr =
93.942MT DCO
Clarifier capacity is ~ 94MT
Figure 4: Vertical clarifier
Pure oil tank
Pure oil tank is a tank that used to store and
heat up pure palm oil before being sent to the vacuum dryer. Pure oil tank is
basically a reception and storage tank for the oil. Closed heating coil are
normally installed in the tank to raise the temperature of the oil.
Vacuum dryer
Vacuum dryer functions to remove moisture from
the crude palm oil. High moisture content of the purified oil will preclude a
further set up of FFA content during storage and shipment. The oil must be
further dried to a final moisture content of below 0.20% which is the final
step in the oil recovery process. The oil will then being sent to oil storage
tank and the process for the oil is finished. Every hour, the reading flow
meter at of the oil will be recorded to know the amount of oil is being sent to
storage tank. The water from vaccuum dryer will be flowing back to the hot
water tank to be used as dilution water in press.
Figure 6: vacuum dryer working principle
Oil storage tank
The dried oil is transferred to storage tank for
storage prior to dispatch from the mill.
Since the rate of oxidation of the oil
increases with the temperature of storage the oil is normally maintained around
50°C, using steam-heating coils, to prevent solidification and fractionation.
Iron contamination from the storage tank may occur if the tank is not lined
with a suitable protective coating.
Sludge tank
Sludge tank is reception and storage for the
sludge with some oil before send to desander. The sludge from the vertical
clarifier will be send to vibrating screen to remove the dirt and fibre and
then goes to sludge tank. Live steam will be injected in the sludge tank to
prevent the sludge from clogging. The The sludge will then being sent to
desander afterwards. There is an opening below the sludge tank. The opening is
used to clean out the sand deposition on the bottom of the sludge tank.
Desander
Desander’s function is to remove the sand
contained in the sludge prior to centrifugal separation. The desander consists
of a pump and a stainless steel cyclone which has a waste receiver connected
below it. The sludge contain a significant amount of fine sand. If it is not removed,
it will cause the nozzle in centrifuge stork to rapid abrasive wear. Sludge is
pumped to the desanding cyclone and is admitted tangentially. Centrifugal force
set up in the cyclone will cause the heavy sand particles to move towards the
wall of the cyclone and then flow into the waste receiver. The lighter phase
move through the primary vortex in the middle of the cyclone out to the next
stage. 2 bar differential pressure between inlet and outlet must be achieved.
There is a timer in the system to set the time to empty the waste receiver
every 15 minute.
The desander station in this mill is double stage desanding system. The
sludge will flow through the 1st stage desander, some of the sand
are removed. The sludge will then pump to the tank and flow to 2nd
stage desander to remove the excess sand. The sludge flow back to the tank and
then will be pump to feeding tank before go to stork centrifuge. The sand will
be sent to a vibrating screen to filter out the sludge that being washed out
with the sand. The sludge will be recycle back to the sludge tank.
Figure : desander working principle
Figure: Double stage desander
Stork centrifuge
Stork centrifuge function to separate the oil
from the sludge to recover the oil losses in the sludge without affecting the
throughput of the mill. There are a total number of 16 stork centrifuge in the
mill. The capacity of the stork centrifuge is 3.5 mt/hr. The stork centrifuge
consists of a casing divided between top and bottom half, with an inspection
cover on the top section to permit access to the nozzles. The bowl housing
consists of two disc-shaped sections of cast iron which together with the
wearing strips, form the protective casing to the cast iron material external
casing. The rotor which is constructed entirely from s/steel is in the shape of
a star and at the end of each fin or tip is fitted a nozzle holder which holds
a nozzle with sizes of 1.7mm. The non-oily sludge water is jetted through the
nozzle. In operation, the sludge oil tank is fed by gravity flow from the
sludge feed tank.
The machine is normally rotated at 1400 rpm. Due
to centrifugal force, the heavier particles of dirt and water are forced to the
extreme end of the rotor and passed out through the nozzles and discharged off.
The pure oil being lighter in comparison builds up in the center of the bowl
and discharged through the oil recovery stainless steel pipe. The oil is then
flow to crude oil tank.
Figure : Stork centrifuge internal view
