Process and apparatus for the treatment of waste oils

The present invention is directed to a process and apparatus for the reclaiming and re-refining of waste oils. The process comprises raising a temperature of a feed mixture of fresh waste oil and a recycled non-volatile residue to a range of 400.degree. C. to 490.degree. C. for a time sufficient to cause pyrolysis of said heavy hydrocarbons contained in the feed mixture, but insufficient to permit substantial undesired polymerization, oxidation and dehydrogenation reactions to take place in said feed mixture; cooling the resulting pyrolyzed waste oil mixture to a temperature in the range of 300.degree. C. to 425.degree. C., and maintaining said temperature while allowing volatile components in the pyrolyzed waste oil mixture to evaporate, leaving a non-volatile residue containing said contaminants; condensing the evaporated volatile components to form a reclaimed oil product; and mixing the non-volatile residue with fresh waste oil to form more of said feed mixture and repeating said temperature raising, cooling, evaporation and mixing steps on a continuous basis, while continuing to condense volatile components evaporated from said pyrolyzed waste oil mixture. The apparatus comprises a heating unit, a container, a condenser and pumping equipment and piping. The process and apparatus of the present invention generate #2 diesel fuel, gasoline and coke from waste oil.

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 2% 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. Pat. No. 3,625,881 and U.S. Pat. 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. Pat. Nos. 5,271,808 and 5,286,349. U.S. Pat. No. 
5,271,808 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 process and apparatus for cracking used motor 
vehicle engine oil by heating with microwaves. The used oil cracks on 
heating to the distillation point. The volatile products are removed in a 
condenser. 
JP-56 082886 discloses a process to suppress local coking and to improve 
the yield of 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 pyrolysis in a fluidised bed of basic substance. 
U.S. Pat. No. 5,143,597 describes a used lubricant oil recycling process in 
which a used lubricating oil is injected to a delayed coker downstream of 
the coker furnace whereby the used oil is thermally cracked into 
hydrocarbon fuel products. 
SUMMARY OF THE INVENTION 
An object of the present invention is to overcome some or all of the 
disadvantages of prior waste 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 acceptably stable and valuable #2 diesel fuel or 
gasoline. 
Still another object of the invention is to provide a process for 
reclaiming waste oil that results in the formation of less residue than 
any prior process while enabling longer run times between shutdowns. 
It is a further object of this invention to provide a pyrolysis unit and a 
cylindrical reactor for use in the process of the invention. 
According to one aspect of the present invention, there is provided a 
process of treating waste oil containing heavy hydrocarbons and 
contaminants. The process comprises raising the temperature of a feed 
mixture of fresh waste oil and a recycled non-volatile residue to a range 
of 400.degree. C. to 490.degree. C. (measured at the output of the heating 
unit) for a time sufficient to cause pyrolysis of the heavy hydrocarbons 
contained in the feed mixture, but insufficient to permit substantial 
undesired polymerization, oxidation and dehydrogenation reactions to take 
place in the feed mixture. The resulting pyrolyzed waste oil mixture is 
then cooled to a temperature in the range of 300.degree. C. to 455.degree. 
C., preferably 300.degree. C. to 425.degree. C. and most preferably 
300.degree. C. to 375.degree. 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 condensed. 
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 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.degree. C. to 490.degree. 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.degree. C. to 590.degree. C. for a short 
time, and is then brought to a temperature in the range of 440.degree. C. 
to 570.degree. C. and is maintained at that temperature under a pressure 
of 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.degree. C. to 490.degree. C. for a 
time sufficient to cause pyrolysis 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.degree. C. to 455.degree. C., preferably 
300.degree. C. to 425.degree. C., most preferably 300.degree. C. to 
375.degree. 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. 
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 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.degree. C. to 150.degree. C.). 
The remainder heavier oil in the cylindrical 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 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.

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 12 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.degree. C. to 150.degree. 
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.degree. C. to 455.degree. C., preferably 300.degree. C. to 425.degree. 
C., most preferably 300.degree. C., to 375.degree. 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.degree. C. to 455.degree. C. Light oil 
and water from the fresh preheated waste oil and from the pyrolyzed waste 
oil mixture are evaporated and distilled off, 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.degree. C. to 490.degree. 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 may 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.degree. 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 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.degree. C. to 490.degree. 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 pyrolyzed 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 oil 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.degree. C.-360.degree. C.), is generally 
collected in tank 38, light fuel (usually condensing at 75.degree. 
C.-150.degree. C.) and water are collected in tank 40 and heating fuel 
(condensing at temperatures greater than 360.degree. 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 to 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 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 75% 
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.degree. C. to 520.degree. 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.degree. C. to 590.degree. C. measured at the outlet of the tubes. The 
heated stream is fed back into the 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.degree. C. to 570.degree. 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 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 the 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 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.degree. 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 62 and 64. 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.degree. C. to 590.degree. 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.degree. C. 
to 570.degree. C. When the heavy residue 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 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 reactor 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 equipment and to recycle and use contained heat for 
preheating and various process steps. For example, an alternative 
operation is shown in FIG. 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.degree. 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 of distillation column 32 is mixed with 3% to 10% steam and is 
pumped by pump 72 through line 73 to tubular heater 20 where the 
temperature is raised to 450.degree. C. to 530.degree. 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.degree. C. to 455.degree. C. Vapour fuel from the cylindrical reactor 
18a or 18b is passed via line 75 to the bottom of the distillation column 
32 to preheat the feedstock from flash drum 70. The vapour fuel in the 
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 70 has the effect 
of cooling the pyrolyzed waste oil mixture to the desired temperature 
range of 375.degree. C. to 455.degree. C. The residue in the bottom of the 
cylindrical 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 
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.