Note: Descriptions are shown in the official language in which they were submitted.
CA 02242742 1998-07-10
WO 97/27273 PCT/CA97/00053
_ 1
TITLE: PROCESS AND APPARATUS FOR THE TREATMENT OF
WASTE OILS
TECHNICAL FIELD
This invention relates to a process and apparatus
for reclaiming waste oils from various sources.
BACKGROUND ART
Used oil represents a major environmental problem.
For example, in 1992, the U.S. Environmental Protection
Agency estimated that of the 4.9 million cubic meters
(1.3 billion gallons) of used oil produced annually in
the United States, only about 2o was being re-refined,
despite the existence of a large number of physical and
chemical processes developed for reclaiming or re-
refining industrial and automotive lubricants. The
remainder of the waste oil, presumably, was being dumped
or discarded into the environment in various ways.
An early major treatment process involved re-
refining waste oil with sulfuric acid and clay. Sulfuric
acid acts as an extraction medium for the removal of
unsaturates, dirt, additives and colored materials from
the waste oil. The clay is used as an adsorbent to
remove impurities. Disadvantageously, in this process,
large quantities of spent acid sludge and clay are
produced and must be disposed of as a process waste.
In order to avoid the waste disposal problems from
acid-clay processes, different types of distillation
processes have been developed, for example, as
disclosed in U.S. Patent No. 3,625,881 and U.S. Patent
No. 4,071,438. These processes produce a recycled
lubricant as a major product and a carbon-black slurry as
a process waste.
Recently, the development of a process for
reclaiming useful fuel has resulted in the production of
diesel fuel from waste oil, as disclosed, for example, in
U.S. Patent Nos. 5,271,808 and 5,286,349. U.S. Patent
,. _.
- 2 -
No. 5,2'71,808 discloses a process for reclaiming waste
oil wherein a vessel Heater is used. In this process,
because a large volume of feedstock is held in a heater'
vessel under high temperature for a long residence time,
undesired polymerization, oxidation and dehydrogenation
take place, resulting in the production of an unstable
diesel fuel and a large volume of ash cake residue_
Additionally, the run length of the process is quite
short.
DE-A-3,224,114 discloses a proepss and apparatus for
cracking used motor. vehicle engine oil by heati~~g with
microwaves. The used oil cracks on heating to the
distillation point. The volatile products are removed in
a condenser.
JP-56 082886 disc7.oses a process to suppress local
coking and to improve the yield a.f light oil, by mixing
a
catalyst with a heavy oil to form a uniform slurry. The
slurry is cracked in the liquid phase catalytically.
EP-0 308669 discloses processing materials
containing halogenated hydrocarbons by pyrolysie in a
fluidised bed of basic substance.
US-5,I43,S97 describes a used lubricant oil
recycling process in which a used lubricating oil. is
infected to a delayed coker downstream of the coker
furnace whereby the used oil is thermally cracked into
hydrocarbon fuel products.
S 7~~QF THE INVENTION
An object of the present invention is to overcome
some or all of the disadvantages of prior ~nraste oil
reclaiming techniques by providing an effective, low cost
process and apparatus for reclaiming waste oil.
. Another object of the present invention, at least in
its preferred forms, is to provide a process for
reclaiming waste oil that results in the production of an
.. _. ._._ _. ._.. , ___..__ _:.___ _...-__. -. ;-
r
- 2 ,~"~.~ -
acceptably stabla and valuable ~2 diesel fuel. or
gasolina.
Still ancthe= cbjec~ or !.re in vent. ion is to provide
a prrcess for rec=ai:.iing ;caste of i thar_ results r the
.. for-r:ation of less res=dL:e char. any ;~riar ,process wrila
snabling longer run times betweer_ shutdowns.
It is a fu=tier object of this -nvertio:: to p=:vi~~:e
a pyrolysis unit ar_d a cy' irdrical reacror for use '= ~ a
r~rccess of tre ~nventior_ .
y0 r~ccerding to one aspect of the present invea~on,
tere is pravided a process for tr°ating was44 ail
ccntain_ng heavy ::ydrocarbron,s ant. c~oncar~inar_ts . Thp
process ccr.;prises ra~.sirg the temperat:~re of a geed
-nixtwre of fires; waste oil a ~~ a recyG~aad non-~rclatiic
15 __sidue tc a range of 400°C tc 490°C (:n_sured at ire
cu=ova of the i-~eati~=g unit) fc; a t;me suf zcient to
cause p<<rolysis of the haav-; hydrocarbons ccnta-r_ed -_..
tilt fEed ,i,i:Lt',.l.~c'Y, ~1.:~ l:.suffiC~E.'~l~ t0 DG~riCult
Si:~a~.al~_Llal
~.~F~D~D ~HEE~
CA 02242742 2004-05-21
- 3 -
undesired polymerization, oxidation and dehydrogenation reactions
to take place in the feed mixture. In a preferred embodiment the
time is from 1 to 15 seconds and the heating is conducted under
pressure of about 276 kPa to 1034 kPa (40 to 150 p.s.i.g.). The
resulting pyrolized waste oil mixture is then cooled to a
temperature in the range of 300°C to 455°C, preferably
300°C to 425°C and most preferably 300°C to 375°C,
and
maintained at this temperature while allowing volatile
components in the pyrolyzed waste oil mixture to
evaporate, leaving a non-volatile residue containing the
contaminants. The evaporated volatile components are
condensed to form a reclaimed oil product, and the non-
volatile residue is mixed with fresh waste oil to form
more of the feed mixture. The steps of raising the
temperature, cooling, evaporation and mixing are then
repeated on a continuous basis, while volatile components
evaporated from the pyrolyzed waste oil mixture continue
to be conSensed.
The process temperature to which the waste oil is
heated for pyrolyzation depends on the designed
conversion. That is to say, higher temperatures will be
20' used for higher percentage gasoline yields, and lower
temperatures for higher percentage diesel oil yields.
In a preferred form of the process, when the yield
of the reclaimed oil product falls below a predetermined
level, the temperature of the feed mixture is raised
above the range of 400°C to 490°C to promote "deep
cracking" of the heavy hydrocarbons, and a resulting
pyrolyzed waste oil mixture is then subjected to further
cooling, evaporation and mixing steps.
In yet another preferred form of the process, when
contaminants in the pyrolyzed waste oil mixture increase
to a predetermined level, the non-volatile residue
containing the contaminants is heated to a temperature in
the range of 470°C to 590°C for a short time, and is then
brought to a temperature in the range of 440°C to 570°C
and is maintained at that temperature under a pressure of
CA 02242742 1998-07-10
WO 97127273 PCTICA97/00053
- 4 -
21 kPa to 172 kPa (3 to 25 p.s.i.g.) to cause the residue
to undergo a further pyrolysis and a coking reaction,
creating further volatile components and a solid coke,
whereupon the further volatile components are removed and
condensed, and the solid coke is collected and discarded.
In still another preferred form of the process, the
feed material is mixed with steam before being raised in
temperature.
According to another aspect of the invention, there
is provided an apparatus for treating waste oil
containing heavy hydrocarbons and contaminants. The
apparatus comprises a heating unit for raising a
temperature of a feed mixture of fresh waste oil and a
recycled non-volatile residue to a range of 400°C to
490°C for a time sufficient to cause pyro:Lysis of the
heavy hydrocarbons contained in the feed mixture,
depending on the designed conversion of the cylindrical
reactor, but insufficient to permit substantial undesired
polymerization, oxidation and dehydrogenation reactions
to take place in the feed mixture; a container for
receiving the resulting pyrolyzed waste oil mixture and
for holding and maintaining the pyrolyzed waste oil
mixture at a temperature in the range of 300°C to 455°C,
preferably 300°C to 425°C, most preferably 300°C to
375°C, while allowing volatile components in the
pyrolyzed waste oil mixture to evaporate, leaving a non-
volatile residue containing the contaminants; a condenser
for condensing the evaporated volatile components to form
a reclaimed oil product; and pumping equipment and.piping
for mixing the non-volatile residue from said container
with fresh waste oil to form more of said feed mixture,
for continuously recirculating said feed mixture through
said heating unit to said container, and for conveying
said volatile components from said container to said
condenser.
CA 02242742 1998-07-10
WO 97/27273 PCTICA97100053
- 5 -
The heating of the feed material. is preferably
carried out in a tubular heating unit. capable
of operating at a high liquid velocity (e.g. a
velocity in the range of about 0.6 m to 4.5 m/s
(2 to 15 feet/second), and more preferably 1.2 m to
3.0 m/s (4 to 10 feet/second)), and the pyrolyzed mixture
is preferably cooled and the volatile components
evaporated in a preferably cylindrical reactor acting as
the container mentioned above. The temperature of the
l0 cylindrical reactor is controlled by adjusting the volume
of preheated feedstock introduced into the cylindrical
reactor. Due to a short residence time in the tubular
heating unit (i.e. 1 to 30 seconds, preferably 1 to 15
seconds and most preferably 3 to 10 seconds), and
relatively low temperatures in the cylindrical reactor,
undesired side reactions are minimized.
Under the high temperatures present in the tubular
heating unit, all of the metal constituents and other
contaminants of the waste oil are decomposed to metals,
hydrocarbons and heavy residues. The light fuel vapors
with any accompanying steam emanating from the
cylindrical reactor are preferably introduced into a heat
exchanger to preheat the fresh waste oil feedstock
(e. g. to a temperature in the range of 110°C to 150°C).
The remainder heavier oil in the cylindrir_al reactor with
fresh waste oil feedstock is pumped into the tubular
heating unit again for a second heating and pyrolysis
reaction, and this procedure is repeated continuously.
When high boiling point oil in the cylindrical reactor
accumulates to such an extent that process production
decreases, the temperature in the tubular heater is
increased for deep cracking. After that, the temperature
is returned to normal.
As an option, steam injection into the tubular
heater for steam cracking can be used. This improves oil
CA 02242742 1998-07-10
WO 97/27273 PCT/CA97/00053
- 6 -
stability and decreases coke formation. The steam may be
produced by the tubular heating unit.
The preheated feedstock is normally introduced into
the upper part of the cylindrical reactor and is sprayed
downwardly at the center. The heated pyrolyzed mixture
from the heated tubes in the tubular heating unit is
introduced near the bottom of the cylindrical reactor.
The feedstock lines for the heating tubes are introduced
from the bottom of the cylindrical reactor, then pass a
pump into the tubular heater. The feedstock from the
cylindrical reactor can enter the tubular heater from
either the top or the bottom. If desired, the preheated
feedstock can be pumped directly to the tubular heater
without passing through, or only partially passing
through, the cylindrical reactor depending on the
temperature of the fluid within the cylindrical reactor.
The products generated from reclaiming waste oil
using the process and apparatus of the present invention
include #2 diesel fuel, gasoline and coke. The process
and apparatus can be operated without causing significant
waste disposal problems.
The process feedstock can be any type of waste oil,
such as motor oil, industrial lubricants, vegetable oil,
fish oil, industrial oil sludge and spilled waste crude
oil.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic view of an example of
apparatus that may be used to operate the process of the
present invention;
Fig. 2 is a schematic representation of a preferred
tubular heater used in the apparatus of Figure 1;
Fig. 3 is a schematic representation of a preferred
cylindrical reactor used in the apparatus of Figure 1;
Fig. 4 is a schematic representation of an example
of an apparatus having two cylindrical reactors;
CA 02242742 1998-07-10
WO 97127273 PCTICA97100053
Fig. 5 is a schematic representation of an example
of an alternative arrangement for the apparatus of the
invention; and
Fig. 6 is a schematic representation of an
alternative cylindrical reactor.
BEST MODES FOR CARRYING OUT THE INVENTION
An example of the overall process of the invention,
and typical apparatus used therefor, is illustrated with
reference to Fig. 1. In the illustrated process, fresh
waste oil, the process feedstock, is fed by suitable
pumping equipment (not shown) from feedstock tank 10 via
pipe I2 to the top of a heat exchange column 14
(more than one such column may be provided, if required?,
where it flows downwardly and is pre-heated (generally to
a temperature in the range of 110°C to 150°C) by heat
exchange with product vapor (derived in a manner to be
described later). The preheated feedstock is then pumped
from the bottom of the heat exchange column 14 via line
16 into a cylindrical reactor 18 which forms a container
for receiving and holding a pyrolyzed waste oil mixture
from a tubular heating unit 20. The pyrolyzed mixture is
held within the reactor 18 at a predetermined temperature
within the range of 300°C to 455°C, preferably 300°C to
425°C, most preferably 300°C to 375°C, while volatile
components are evaporated therefrom, as will be described
more fully later. The preheated waste oil from line 16
is sprayed downwardly into the pyrolyzed waste oil
mixture held at the bottom of the cylindrical reactor 18
to create a mixture of the fresh preheated waste oil and
the pyrolyzed waste oil mixture for further treatment.
The spraying of the fresh waste oil also has the effect
of cooling the pyrolyzed waste oil mixture to the desired
temperature range of 300°C to 455°C. Light oil and water
from the fresh preheated waste oil and from the pyrolyzed
waste oil mixture are evaporated and distilled off,
CA 02242742 1998-07-10
WO 97/27273 PCTICA97/00053
_ g _
leaving a non-volatile residue, and the resulting vapor
is removed from the cylindrical container 18 via pipe 22
leading to the heat exchange column 14.
The mixture of fresh waste oil and the non-volatile
residue of the pyrolyzed waste oil mixture formed in the
cylindrical reactor 18 in the manner stated, is pumped by
pump 24 as a feed mixture via pipe 25 to a series of
heating tubes 26 (only one of which is shown in Fig. 1,
but see Fig. 2) within the tubular heating unit 20. The
unit 20 acts as an apparatus for rapidly raising the
temperature of the feed mixture to a desired range of
400°C to 490°C for a short period of time (usually 1 to
30 seconds, preferably 1 to 15 seconds and most
preferably 3 to 10 seconds). Heat is created within the
unit 20 by means of burners 28, turning the interior of
the unit into a fire chamber. The burners rnay burn a
conventional fuel or a fuel or a gas from the reclamation
process itself.
The feed mixture passing through the tubes 26 is
heated rapidly by virtue of the large surface area of the
tubes and the relatively small volume of feed mixture
within the tubes. The tubes 26 are preferably straight,
with a length of preferably from 1.8 m to 6.0 m (6 to 20
feet), although the number and length of heating tubes
depends on the per day volume of feedstock to be
processed and the velocity of the feed mixture through
the tubes (preferably 0.6 m to 4.5 m/s (2 to 15
feet/second), and ideally 1.2 m to 3.0 m/s (4 to 10
feet/second)). The heating tubes 26 could be coils. As
the temperature difference between the contents of the
tubular heating unit 20 and the contents of the
cylindrical reactor 18 is only about 100°C, the heat
consumption in the tubular heating unit is normally quite
low, thus minimizing the size of the tubular heating unit
20. The diameter of the heating tubes 26 is most
CA 02242742 1998-07-10
WO 97127273 PCT/CA97100053
4 _
preferably in the range of 1.25 cm-12.5 cm (0.5-5 inches)
for efficient heating of the feed mixture within the
heating tubes.
As already noted, the feed mixture is heated to the
desired temperature of 400°C to 490°C in the tubes 26 for
a period of time sufficient to cause pyrolysis of heavy
hydrocarbons in the feed mixture, but insufficient to
permit substantial undesired polymerization, oxidation
and dehydrogenation reactions to take place. This time
period depends to a certain extent on the type of feed
mixture, but is generally in the range of 1 to 30
seconds, preferably 1 to 15 seconds and most preferably
3 to 10 seconds.
The resulting hot streams of pyro~ly~ed waste oil
mixture from tubes 26 are passed to the bottom of the
cylindrical reactor 18 via a pipe 30. The temperature of
the fluid in the cylindrical reactor 18 decreases from
bottom to top due to an endothermic pyrolysis reaction
that continues to take place in the reactor 18 and due to
cooling caused by the spray of fresh waste oil feedstock
from pipe 16. The volatile oil and water components from
the reactor 18, on being removed from the reactor through
pipe 22, are first passed upwardly through heat exchange
column 14 to pre-heat the fresh waste ois. feedstock, as
already described, and are then fed to a distillation
column 32 via pipe 34 to form reclaimed oil fractions,
the desired product, and water that may be re-used, as
will be described later.
In the apparatus as shown in Fig. 1, three fractions
are obtained from distillation column 32 and are
transferred to tanks 36, 38 and 40. Remaining gas and
light ends are discharged through pipe 42 and condensed
in liquid collection tank 44. The most desired product,
#2 diesel fuel (usually condensing at. 110°C-360°C), is
generally collected in tank 38, light fuel (usually
CA 02242742 1998-07-10
WO 97/27273 PCT/CA97/00053
- lU -
candensing at 75°C-150°C) and water are collected in tank
40 and heating fuel (condensing at temperatures greater
than 360°C) is collected in tank 36.
As an alternative to the procedure indicated above,
it is possible, for example when the pyrolyzed waste oil
mixture in cylindrical reactor 18 requires no further
cooling, to divert the preheated fresh waste oil
feedstock issuing from heat exchange column 14 completely
or partially from the cylindrical reactor- 18 t.o the inlet
of the tubular heating unit 20 via pipe 46. The fresh
waste oil feedstock then mixes directly with the non-
volatile residue of the pyrolyzed waste oil mixture from
reactor 18 within pump 24 before the resulting feed
mixture enters the tubes 26.
As a further alternative, the feed mixture being
delivered to the heating unit 20 from thE: cylindrical
reactor 18 is admixed with steam from a steam heater 48,
in amounts ranging from 3 to 50 mole percent, preferably
10 to 50 mole percent, steam, prior to entry of the feed
mixture into the heating tubes 26. The steam heater 48
is a tube coil or a steam boiler which may be set in the
upper portion of the tubular heater 20. The mixed stream
is heated in heating tubes 26 and enters cylindrical
reactor 18, as before. The added steam, in conjunction
with light fuel vapor, passes through the heat exchanger
14 via pipe 22, is then separated in distillation column
32 into storage tank 40. The hot water in tank 40 may
then be pumped to steam heater 48 for re-use.
During the process of the invention, it is usual to
provide a pressure of 276 kPa to 1034 kPa. (40 to 150
p.s.i.g.) within the heating tubes 26. The pressure can
be controlled by suitable adjustment of a. valve (not
shown) in the tubular heater outlet line 30.
The amount of fresh waste oil added from tank 10 may
be balanced with the amount of product produced by the
CA 02242742 1998-07-10
WO 97/27273 PCT/CA97/00053
- 11 -
system so that the process may be operated on a
continuous basis indefinitely. However, after a period
of operation, it is generally found that the yield of the
desired reclaimed oil product declines as the content of
contaminants increases within the recirculating pyrolyzed
mixture. For example, the yield may decline to 750 of
the desired yield. When this occurs, it has been found
that the temperature of the fluid within the tubular
heating unit 20 may be raised to the range of 460°C to
520°C, to effect "deep pyrolysis" of the heavy
hydrocarbons within the fluid, i.e. a greater degree of
hydrocarbon cracking than is normally achieved. While
this also risks undesired polymerization reactions and
the like, it substantially increases the amount of
volatile components available for distillation from the
reactor 18, and thus improves the yield. The flow of
fluid through the tubes 26 during this step is kept
generally the same as during the regular part of the
process and so the residence time within the tubes at the
stated high temperature is about 1 to 15 seconds. The
time required for the deep pyrolysis step, and the
improvement in yield thereby obtained, are very much
dependent on the nature of the feedstock, e.g. the
content of sludge and other contaminants.
According to an important feature of the invention,
after the process has run continuously for a long time
{i.e. 1 to 6 months, depending on the nature of the waste
oil), the heavy residue and sludge in the cylindrical
reactor, which contains metals from waste oil additives
and dirt, accumulates to an unacceptable level and a
coking process must be carried out. To effect the coking
process, the residue is heated in tubes 26 or a separate
set of coking tubes (not shown) to a temperature in the
range of 470°C to 590°C measured at the outlet of the
tubes. The heated stream is fed back into the
CA 02242742 1998-07-10
WO 97/27273 PCTICA97/00053
- 12 -
cylindrical reactor where it undergoes a pyrolysis
reaction with the help of its entrained heat, under
pressure of 21 kPa to 172 kPa (3 to 25 p.s.i.g.) and at a
temperature of 440°C to 570°C, the pressure being
controlled by means of a control valve 50. The oil
vapors produced thereby are distilled off in the normal
way to form the desired product, and the coke containing
metals and the like is deposited in the cylindrical
reactor. After the coke has been formed, the system is
shut down for decoking. The ultimate residue of the
process of the invention is therefore a coke in
relatively small amounts that can be disposed of using
conventional means to avoid environmental pollution, or
can be used as an industrial fuel.
Referring to Fig. 2, this shows in more detail a
preferred form of the tubular heating unit 20. As can be
seen, the heating tubes 26 are straight and contain no
coils. When steam is used, coiled tubes could
alternatively be provided in order to increase the
residence time of the heavier feedstock. The tubes may
be set vertically, obliquely or horizontally. The hot
feedstock and steam (when steam is used) enter the
heating tubes 26 via valves 52, then leave via valves 54
for the cylindrical reactor 18. Plugs 56 at the bottom
of each reaction tube are used for.decoking and cleaning.
The temperature of the pyrolyzed mixture leaving the
tubular heating unit 20 may be measured by temperature
measuring devices 57, e.g. remotely monitored
thermocouples.
Each reaction tube can be isolated by the indicated
valves, so that failure of one tube does not affect the
operation of the entire system and it can be replaced
while the system continues to operate. As indicated
above, a different set of coking tubes (not shown} may be
provided, if desired, for the coking reaction in order to
CA 02242742 1998-07-10
WO 97/27273 PCT/CA97/00053
- 13 -
avoid undue deposition within the heating tubes 26. Such
tubes would be much the same as tubes 26, but would have
diameters in the range of 5 cm to 12.5 cm (2 to 5
inches), and would be arranged within th.e heating unit 20
parallel to tubes 26, but would only be fed with fluid
when required for coking by the operation of appropriate
valves (not shown). However, the reaction tubes 26 may
themselves be used for the coking reaction since coke
deposition is kept to a minimum by using high liquid
velocities (e.g. from 0.6 m to 4.5 m/s (2 to 15
feet/second)), straight heating tubes and, optionally,
steam injection, as already indicated.
Fig. 3 shows in more detail a preferred embodiment
of the cylindrical reactor 18. Fig. 6 shows an
alternative cylindrical reactor. In each the pipe 16
introduces preheated feedstock into the cylindrical
reactor 18 and the pipe 25 is a line for delivering
mixture to the tubular heating unit 20. In fact, the
pipe 25 may be a series of tubes with inlets at different
levels within the cylindrical reactor. The heated fluid
from the heating tubes 26 is recirculated to the
cylindrical reactor 18 by pipe 30, which can be one tube
or a number of tubes depending on the size of the tubular
heating unit 20. Oil and steam vapors are transferred to
the heat exchange column 14 by tube 22, which is located
at the top of the cylindrical reactor 18. A flange 58 is
provided for coke cleaning, and a line 60 is for
sampling. The reactor is made cylindrical for economy
and for better containment of the usual reaction
pressures, however, other shapes could be provided, if
required. The top and bottom of the cylindrical reactor
may be flat or cone-shaped, as desired.
During normal use, the coke formation in the
cylindrical reactor 18 is limited by the high turbulence
of the fluid within the reactor caused by the entrance of
CA 02242742 1998-07-10
WO 97127273 PCT/CA97I00053
- 14 -
the high velocity oil and steam from the tubular heating
unit 20, as well as the low reaction temperature of the
cylindrical reactor where it is below 455°C. Therefore
long run lengths can be achieved in this process.
Decoking is normally required after the coking process
has been carried out, and this may be achieved by steam
decoking, water decoking, mechanical decoking or other
methods.
For continuous operation without: having to shut down
the system for decoking, another cylindrical reactor can
be provided to continue the reaction while the first
reactor is being decoked and cleaned. The two
cylindrical reactors will have the essentially same
structure. Fig. 4 shows in more detail a preferred
embodiment of an apparatus having two cylindrical
reactors 18a and 18b. When one cylindrical reactor 18a
is undergoing the decoking process, the feedstock from
the heat exchanger 14 and heated effluent from the
tubular heating unit 20 can be switched to the other
cylindrical reactor 18b by valves 52 and &4. The
apparatus of Fig. 4 is otherwise the same as that of
Fig. 1.
As an alternative, when one cylindrical reactor 18a
has been used for a time for the process of the
invention, the heavy residue and sludge in the
cylindrical reactor 18a can be pumped to the tubular
heating unit 20 and heated to a heater outlet temperature
of 470°C to 590°C. The heated effluent from the tubular
heating unit 20 is switched to the other cylindrical
reactor 18b to undergo a coking reaction under 21 kPa to
172 kPa (3 to 25 p.s.i.g.) pressure and at a temperature
of 440°C to 570°C. When the heavy residua_ and sludge in
cylindrical reactor 18a is pumped out to the tubular
heating unit 20, fresh waste oil is pumped into the
cylindrical reactor 18a to be subjected to normal
CA 02242742 1998-07-10
WO 97/27273 PCTlCA97100053
_ 15 _
cooling, evaporation, mixing and temperature raising
steps. The cylindrical reactor 18b is then subjected to
the decoking process. After completing the decoking
process, the heated effluent from the tubular heating
unit 20 is switched to the cylindrical raactor 18b and
the fresh feedstock supply for the cylindrical reactor
18a is stopped. The cylindrical reactor 18b is subjected
to normal cooling, evaporation, mixing and temperature
raising steps. The cylindrical reactor :18a is ready for
the next coking and decoking processes.
As a further alternative, the process may be
performed to make most efficient~use of the equix~ment and
to recycle and use contained heat for preheating and
various process steps. For example, an alternative
operation is shown in Figure 5.
Waste oil feedstock from tank 10 is pumped via pump
65 to heat exchanger 14 to preheat the feedstock to a
temperature of about 115°C with steam. The preheated
feedstock is passed via line 66 to a flash drum 67 where
water is evaporated from the feedstock and passed via
line 68 to a heat exchanger 69 for cooling. The
evaporated water is removed. The heated feedstock from
flash drum 67 is pumped via pump 70 through line 71 to
distillation column 32 for further preheating with the
hot vapour stream from cylindrical reactors 18a and 18b.
The heavy oil fraction from the bottom cf: distillation
column 32 is mixed with 3o to 10% steam and is pumped by
pump 72 through line 73 to tubular heater 20 where the
temperature is raised to 450°C to 530°C. The heated
effluent from tubular reactor 20 is passed via line 74 to
the bottom of one of the cylindrical reactors 18a or 18b
for further reaction at 375°C to 455°C. Vapour fuel from
the cylindrical reactor 18a or 18b is pa~;sed via line 75
to the bottom of the distillation column 32 to preheat
the feedstock from flash drum 70. The vapour fuel in the
CA 02242742 2004-05-21
- 16 -
distillation column 32 travels upward through the column
and is separated into #2 fuel which is removed through
stripper 76 which leads to heat exchanger 77, light fuel
is passed via line 78 through heat exchanger 79 for
cooling and recovery, and some #4 fuel is passed via line
80 through heat exchanger 81 for cooling and recovery.
A portion of the feedstock from the flash drum 70
can be sprayed downwardly via line 82 into the pyrolyzed
waste oil mixture held at the bottom of the cylindrical
reactor 18a or 18b to create a mixture of fresh preheated
waste oil and the pyrolyzed waste oil mixture for further
treatment. The spraying of the waste oil feedstock from
the flash drum 67 has the effect of cooling the pyrolyzed
waste oil mixture to the desired temperature range of
375°C to 455°C. The residue in the bottom of the
cylindric'~1 reactor 18a or 18b is mixed via a recycle
line 83 with feedstock in the bottom of the distillation
column 32 into tubular heater 20. When one of
cylindrical reactors 18a or 18b is filled with coke the
20~ heated effluent from tubular reactor 20 is switched to
the other reactor to undergo the pyrolysis and coking
reaction. The first reactor can then be subjected to a
decoking process.
The decoking procedure can be carried out by methods
such as steam decoking, water decoking and mechanical
decoking.
While the invention has been described in detail
above, it will be apparent that various modifications and
alterations will be possible without departing from the
spirit and scope of the invention.
