[0001] This invention relates to a continuous and automatic process for the treatment and
the recovery of fillers and/or crudes having a high content of water, salts and sediments
such as for instance slop-oil, with low energy consumption.
[0002] This invention relates also to an apparatus for the realization of said process.
[0003] The fillers commonly referred to as "slop-oil" are usually characterized by high
contents of water (up to 50% by volume) and salts and sediments (1-5% by weight on
the average) and low contents of gasolines and light fractions (3-5% by volume on
the average).
[0004] Slop-oils, given the high percent of water they contain, cannot be sent directly
in charge to the atmospheric distillation plant, unless on prior dehydration of the
same and separation of at least the greatest part of salts and sediments.
[0005] The methodologies adopted at present in the refineries to reduce the contents of
water contained in slop-oils (at least up to 0.5% by volume) are substantially the
following ones:
- The water contained in slop-oils is separated by evaporation through a mild heating
of the filler (oven outlet temperature about 140°C), to obtain the separation of water
from filler through evaporation. Such conditioning treatment of slop-oils involves
however too high a fuel consumption for ovens, high maintenance costs of the apparatuses
and, due to the presence of salts and sediments, a reduction in the effectiveness
of heat exchange of the plant and a worsening in quality of products. Besides, some
salts may crystallize causing the formation of acids which corrode the apparatuses.
- Suitable de-emulsifiers are added to the filler stored in the tank, so as to obtain
the separation of water directly during the storing. However, such treatment involves
long times of permanence of the filler in the tank, high costs of the chemicals utilized,
and due to the layering which creates in the tank, the formation of a strong emulsifying
layer which can be broken only by thermodynamic methods.
- Before being conveyed to the distillation plant, slop-oil is caused to pass through
a desalter. The filler is pre-heated at a given temperature and water is added. Sometimes,
to easier the breaking of the emulsion, also a de-emulsifying agent is added, which
is intimately mixed to the filler together with the process water. Once the mix has
entered the desalter, it is submitted to a strong electrostatic field, which causes
the water drops present to aggregate and precipitate on the bottom of the vessel.
[0006] In this case, besides the consumption of chemicals and electric energy necessary
for the process, a rather poor working of the desalter is observed, which needs beeing
regulated continuously; this is due to the desalter being effective only if it works
with a filler whose characteristic parameters remain constant in the long run, which
does not happen with slop-oil also because of the layering which creates in the storing
tank.
[0007] An object of this invention is to provide a process for the treatment of slop-oils,
such as to allow to separate in practice by one only operation all the water and the
most part of salts and sediments of the oily fraction, obtaining an oily fraction
which can be fed directly without further treatments to the atmospheric distillation
plant.
[0008] Another object of this invention is to provide a process for the treatment of slop-oils
such as to allow to separate water even when the latter is present in very great amounts,
up to 50%, substantially without any marked increase in costs compared to smaller
amounts. Still another object of this invention is to provide a continuous and fully
automatic process for the treatment of slop-oils utilizing also discontinuous working
apparatuses and allowing to obtain an aqueous phase already substantially separated
from the sediment containing phase.
[0009] These and still other objects and related advantages which will be made clear by
the following description are achieved by a process for the treatment of crudes with
high contents of water, salts and sediments, such as slop-oil and the like, which
process, according to this invention, comprises the following stages:
- heating of the crude or the slop-oil at a temperature not above 100°C;
- centrifugation of the so heated crude, obtaining a first fraction constituted by purified
crude suitable to be directly submitted to distillation, of a second fraction constituted
by water and a third fraction constituted by sludges.
[0010] In fact, it has been observed that said purified crude has normally a water content
of less than 0.5% by volume and a sediment content of less than 50% by weight relatively
to the sediment content in the crude fed, so that, as said, it can be submitted to
distillation directly in the topping plant, without drawbacks and with very high yields.
[0011] Always according to this invention, said second fraction constituted by water is
submitted to a purification process comprising the following stages:
- heating at a temperature not above 100°C, and possible addition of de-emulsifiers
of a known type;
- concentration by centrifugation, obtaining a fraction of purified oil suitable to
be directly submitted to distillation and a fraction constituted by purified water
suitable to be treated according to disposal processes of a kwown type, on prior possible
cooling and possible gravity separation by decantation or the like of the oil droplets
still present as such.
[0012] In fact, it has been observed that said purified water coming out from said concentration
by centrifugation has an oil content below 500 ppm and a sediment content below 3%
by volume.
[0013] The third fraction coming out from said crude centrifugation stage, constituted by
sludges, has normally an oil content below 20% and a water content below 50%. Advantageously,
according to the process subject matter of this invention, crudes, slop-oils and the
like are treated that have the following characteristics:
Specific weight |
0.85 - 1.0 kg/l at 15°C |
Water content |
0 - 50% by volume |
Viscosity |
5 to 60 cst at 50°C |
Sediments |
0 - 5% by weight |
[0014] Said centrifugation stages, in particular the centrifugation stage of the crude and
the concentration by centrifugation of the water to be purified are preferably realized
by means of vertical axis centrifuges. Further characteristics and advantages of this
invention shall appear more clearly from the following description, made with reference
to the practical embodiment and the drawing given by way of mere non limitative example
of the invention, wherein Fig. 1 shows in form of a block diagram the example of process
realized according to this invention.
EXAMPLE
[0015] Fig. 1 shows an embodiment of the process constituted by a unit which can treat a
stream of 32 m³/h of slop-oil.
[0016] The slop-oil coming from the tank yard enters storage 1 (25 m³), whose level is automatically
kept constantly at about 50%, is conveyed through two centrifugal pumps to a battery
2 constituted by four centrifuges (separators), on prior heating of the product through
a battery of plate-type exchangers 3, two of which exchange heat with the anhydrous
product coming out of the centrifuge, and the other two exchange heat with a 2 bar
saturated steam.
[0017] The inlet temperature of slop-oil (T
max=100°C) is suitably regulated and kept constant through a system of regulation of
the steam flow to the exchangers, while the control of the stream of slop-oil (about
8 m³/h per separator) takes place through a regulation system located on the feed
line of each machine.
[0018] From the three outlets of each so fed centrifuge, one has:
- a first fraction 4 constituted by purified slop-oil
- a second fraction 5 constituted by water
- a third fraction 6 constituted by slurries.
[0019] The purified slop-oil 4, already conform to specification as concerns water content,
is conveyed to storage 7 (15 m³), and from here, through a centrifugal pump, having
exchanged heat with the slop-oil which feeds the machines, is conveyed to the storing
tank and then to the topping plant. Such stream of slop-oil is continuously modulated
so as to keep stable at 50% the level of storage 7.
[0020] The second fraction 5, constituted by the water coming from the four machines, is
conveyed to a fifth centrifuge 8 (concentrator) as it might contain some percent points
of hydrocarbons whose value depends on the consistency of the emulsifying phase present.
Such stream, before arriving at 8, enters the smallest part of tank 9 (16 m³). The
latter is in fact divided into two parts by a vertical partition (9A with a capacity
of 4 m³ and 9B with a capacity of 12 m³); such parts are in communication with one
another in the upper part.
[0021] The water to be purified, with a constant stream, is conveyed, through a centrifugal
pump, to the concentrator, on prior heating with a steam plate-type exchanger 10 (temperature
of the outgoing water nearing 100°C) and on line addition of a demulsifying agent.
[0022] The purified water coming out from centrifuge 8, re-enters tank 9 and more precisely
at 9B, so that the possible oil traces still present, floating on water, overflow
at 9A.
[0023] The level of the latter is constantly kept at about 50% by a regulation system which
modulates the stream of purified water taken from the bottom of 9B and which is conveyed,
always through a centrifugal pump, to water treatment, on prior refrigeration with
water in water plate-type exhanger 11.
[0024] Sludges 6 are instead collected, together with those 13 coming out from the concentrator
8, in tank 12 (5 m³). From here, through a volumetric pump controlled by an on/off
level located on 12 and whose capacity is regulated according to the consistency of
sludges, the latter are conveyed to a decanter 14 which provides to separate the fluid
phase 15 from the solid one 16.
[0025] A volumetric pump, controlled by a load cell system, provides to conveying the solid
phase of sludges into suitable caissons for the disposal.
[0026] As concerns the purified slop-oil 17 coming out from the concentrator 8, it reaches
tank 18 and is conveyed hencefrom by means of a volumetric pump, on prior refrigeration
with water in a plate-type exchanger 19, to storing and then to topping.
[0027] Besides the advantage of feeding directly, with the addition of purified slop-oil,
the atmospheric distillation plant, the process described is fully automatic, does
not require the utilization of ovens, reduces markedly the consumption of possible
de-emulsifiers necessary, obtains at the plant outlet three streams having the following
characteristics:
PURIFIED SLOP-OIL
[0028]
- water below 0.3% by volume
- sediments below 50% by weight compared to those contained in the slop-oil entering
the plant.
PURIFIED WATER
[0029]
- oil below 300 ppm
- sediments below 1% by volume, taking into account that the oil stream coming out from
the concentrator is on the average below 3.5% of the feeding stream of slop-oil to
the plant.
SLUDGES SOLID PHASE
[0030]
- oil below 15%
- water below 40%
Besides, for the realization of the above described process for the treatment of
slop-oils, discontinuously running machines are utilized (centrifuges) which, suitably
located in the circuit together with prefixed capacities and suitable regulation systems,
allow to carry out the transit and the treatment of slop-oils through such machines
in a continuous and fully automatic way.
1. Process for the treatments of crudes having a high content of water, salts and sediments
such as slop-oils and the like, characterized in that it comprises the following stages:
- heating of crude or slop-oil at a temperature not exceeding 100°C;
- centrifugation of the crude so heated, obtaining a first fraction constituted by
purified crude suitable to be directly submitted to distillation, a second fraction
constituted by water and a third fraction constituted by sludges.
2. Process according to claim 1, characterized in that said second fraction constituted
by water is submitted to a purification process comprising the following stages:
- heating at a temperature not exceeding 100°C and possible addition of de-emulsifyiers;
- concentration by means of centrifugation, obtaining a fraction of purified oil suitable
to be directly submitted to distillation and a fraction constituted by purified water
suitable to be treated according to disposal processes of known type.
3. Process according to claim 1, characterized in that said centrifugation of crude and
said concentration through centrifugation of water to be purified are carried out
by utilizing vertical axis centrifuges.
4. Process according to claim 1, characterized in that discontinuously running machines
are utilized, such as centrifuges, suitably located in the circuit together with fixed
capacities and suitable regulation systems, so that the passing and treatment of slop-oils
takes place in a continuous and fully automatic way.