Note: Descriptions are shown in the official language in which they were submitted.
WO 9S/13338 ~ 1 5 3 3 9 5 PCr/uss3llo75o
ppor~R FOR R~ uV~KY OF TAN~
BOTTO~ llAQTE8
R~r~ PO~ND OF IN~ENTION
l . Fi-ld of Inv-nt~ on. The present invention
relates to processing tank bottom wastes, pit wastes, and
other petroleum-based sludges to produce products that meet
refinery st~Ards and improve environmental attributes.
2. BaC~16~. In recent times tank bottom
wastes, sometimes referred to as sludge and often shortened
to just tank bottoms, have become an increasing problem
since their regulation has often classified them as
environmentally hazardous wastes with the corresponding
difficult and eype~cive handling problems. However by
appropriate processing this designation can disappear and
the resulting constituents become potential product
material or can be disposed of in an ordinary manner.
Additionally their composition, being a mixture of crude
oil, solids, and water, is unacceptable for refineries
which would require the removal of significant portions of
solids and water.
The amount of this potential tank bottom waste
builds to large quantities not only because of the large
oil field, pipe line, and refinery capacities in this
~OUI1~LY~ but also because of the storage of these tank
bottoms until some disposal method can be employed.
Particularly in remote oil fields far from refineries,
storage has continued for many years.
Earlier attempts at processing such tank bottoms
often employed several common approaches. Filtration using
stAn~Ard commercial filter presses has been accomplished
for some tank bottoms that were easily pumpable and oil
recovery was significant as well as producing a solid,
easily disposable residual. For further enhanced recovery
of useful products, solvent extraction was employed
particularly if the unit is operated in conjunction with a
refinery where such a solvent stream, such as propane, is
readily available. The resultant extracted stream then was
WO95/13338 ~ 3~3gS PCT~Ss3/10750
returned to the refinery for further processing of the
extracted oil. The solvent extraction was utilized on the
filter cake from pre-meçh~n;cal treatment or employed
directly into the tank before pumping. Additionally
sometimes bioremediation is utilized to treat such tank
bottoms both directly and indirectly.
Prior art United States patents covering the above
mentioned tank bottoms processing include:
No. Inventor Year
5,022,992 Looker l99l
4,927,530 Ueda 1990
4,897,205 Landry l990
Referring to the above list, Looker discloses a
sludge removal apparatus with sloping tank sides and
recirculation with an appropriate skimmer designed to
remove floating sludge paint particles from water. Ueda
discloses a processing unit employing anaerobic bacteria to
treat excess sludge from sewage water treatment or other
sludge-type material that is acted upon by such bacteria.
Landry discloses a process for treating waste material
employing steam and recirculated liquid to lower the
viscosity of the waste material, such as liquid hydrocarbon
and solids, in order to allow removal and subsequent
separation by settling; this is particularly used for
cleaning tanks.
8UMMARY OF INVENTION
The objectives of the present invention include
overcoming the above-mentioned deficiencies in the prior
art by providing a process that treats tank bottoms to
recover refinery st~n~rd products and to make any disposal
environmentally acceptable. In addition the process is
potentially portable and useful for field operations giving
an enhanced economic advantage by reducing transportation
WO95/13338 2 1 ~ 3 3 ~ 5 PCT~S93/10750
requirements. Further because of its low operating costs,
it can process small amounts of tank bottoms in remote
regions.
The subject invention uniquely combines an initial
flash recovery unit with a stripping reactor along with
conventional unit operations to perform this economic
recovery and treatment of tank bottoms.
BRIEF D~r~TPTION OF THE DRAWING
Figure l shows the flow sheet for a typical
operation of the process.
DET~TTT~n n~Pr~TPTION OF Ihv~lON
One key to successful processing of tank bottoms,
particularly if portable operation is required, is to make
effective use of regenerative components to lower the heat
requirements so that a stripping and pyrolysis reactor
system becomes feasible.
The best mode for processing of these tank bottoms
is to employ the main steps of flashing of water and light
hydrocarbons, utilizing hot gas stripping to further
extract hydrocarbons, and employing final pyrolysis,
including some thermal cracking, since the residue is
largely solid material.
Hot gas is a generic term that could include a wide
variety of sources. It represents vaporous material in a
gaseous state at an elevated temperature, but in all
instAnc~C the temperature is higher than the dew point. It
is producible by combustion gas or other burning or
alternatively supplied through a separate heat exchanger
that heats any desired gaseous composition.
An analysis of tank bottoms yields an example
composition of 90% oil, 5~ water, and 5% solids. However
it is not uncommon to process tank bottoms that are as
little as 20% oil or as high as 50% solids; the water
conc~ntration is normally not limiting although 75% is a
suggested practical limit. The important aspect is that
such tank bottoms be pumpable. The normally encountered
emulsion of oil, water and solids will not separate by
WO95/13338 pcT~ss3llo7sn
3~ 4
settling and can only be handled by very expensive
centrifugal treatment, a method not employed herein.
Two largely economic criteria are ideally met in
processing such tank bottoms. First is to recover 85-90
percent of the initial oil and the flashing and stripping
operations are designed to perform this. Secondly is to
recover 90-95 percent of the initial organic carbon present
in the oil so only 5-10% is lost as coke, and the pyrolysis
and cracking operations expect to reach this st~n~Ard.
Because coke formation is common with pyrolysis, some tank
bottoms may have a composition where this second criteria
cannot be met.
In some instances where this recovery of organic
carbon is C~cQn~Ary~ sufficient oil recovery can often
occur by only using the stripping reactor and omitting
entirely the pyrolysis reactor. However, the solid
discharged from only the stripping reactor is not as
environmentally advantageous as that coming from the
pyrolysis reactor.
Because of the flash tank prece~;ng the stripping
reactor, the latter only has to handle approximately 50-75
percent of the original tank bottoms in a typical case.
This reduction in reactor input is an important economical
aspect of the subject invention.
A typical flow sheet for the process is shown in
Figure 1. The tank bottoms 11 are present in some type of
holder lO which can be a field pit, sludge pond, or an
actual tank either stationary or truck mounted. Such tank
bottoms may or may not need pretreatment before pumping.
The pump 12, perhaps with a skimmer, removes the tank
bottoms ll and pumps them through a regenerative heat
exchanger 13 where they are heated by a vapor stream 50
coming from the stripping section 22 of the screw reactor
or screw apparatus 51, or other stAn~rd screw conveyor.
The heat exchanger 13 should contain sufficient heat
transfer surface to produce a thermal efficiency in the
range of 70-90 percent and partial condensation of the
WO95/13338 21 ~ ~ 3 ~ ~ PCT~S93/10750
heavy oil fraction in said heat exchanger represents a
feasible operating condition. The hot tank bottoms 1~
which are in the range of approximately 250-450 F and are
under pressure of about 20-500 psia from regenerative
heating and conventional pumping, are fed into a flash tank
15 where flashed light oil and water leave as flashed
overhead and are separated by a light oil con~pncer 16 and
a separator 17 for such oil, water, and gas. The light oil
is pumped 18 to appropriate storage; however, some is
recycled for fuel if neC~ssAry. The gas 19 from the
separator contA i n ing a high proportion of Cl-c5 components
is collected and normally recycled to provide fuel for the
hot gas generator which in the subject case is combustion
gas; however, if eycecc gas occurs, it is burned with a
flare 80. The heavier bottoms from the flash tank 15
representing a liquid 20 in a temperature range of about
200-425 F, are pumped 21 into the screw reactor 51
stripping section 22 where hot gas 71, with a temperature
above about 250 F, contacts them and strips off additional
vapor containing oil making up part of the vapor stream 50
entering the regenerative heat exchanger 13 which then
leaves through a heavy oil con~n-c~r 52, and such heavy oil
is pumped 53 to storage. The overhead steam 5~ from the
heavy oil condenser 52 is collected and either burned with
a flare 80 or recycled for fuel or sweep gas. The screw
reactor 51 further transmits the solid material or
remainder through a vapor lock 6~ section into a heat
exchanger 23 where supplementary heat, such as by
electrical resistance heating or high temperature steam, is
applied 59, to bring the solid material to approximately
1000 F, or likely somewhat higher, to allow pyrolysis, and
in some instances oxidation, to occur. A sweep gas 60,
which may be recycled from other parts of the process,
picks up the pyrolysis products and leaves as a vapor
stream 61 and is combined with the previous vapor stream 50
entering the regenerative heat exchanger 13. The solid
residue 62 is stored 63 for further disposal. The vapor
wos~ll3338 2~533~ PCT~S93/10750
lock 64 keeps the stripping vapors from leaking into the
pyrolysis section where the high temperature will produce
unwanted coke. A hot gas generator 70 uses fuel to produce
the needed hot gas 71, in this case combustion gas,
entering the stripper section 22 of the screw reactor 51.
The hot gas generator 70 is potentially fueled from the
various collected gases 73 of the process as well as by
additional fuel 7~ of light oil or even heavy oil if
appropriate. Burner air 72 is added as needed. Left over
gas containing some burnable components is burned in a
flare 80 if appropriate using an air blower 81. The heavy
oil condenser 52 and the light oil condenser 16 may be air
cooled if appropriate or some of the separated water 90, is
potentially usable in conjunction with a cooling tower.
As noted previously in selected circumstances the
pyrolysis reactor is not employed; thus, the solid material
or remainder left from the stripping reactor is the final
~jsrhArged solid. Also in this instance the stripping
reactor is likely operated with a higher temperature hot
gas.
Several equivalents can be employed. For instance,
the hot gas generator 70 is replaceable by a steam
generator using recycled overhead flash water as feed or a
separate steam source, if available, is employed. The
stripping gas now is high temperature steam; however, the
condensed heavy oil will must be separated from water
condensing from said steam.
Another equivalent substitutes a fluidized bed
reactor for the screw reactor where pyrolysis, or in some
instances both pyrolysis and combustion, can proceed,
separately if the overhead streams from a series of
fluidized beds are employed and are collected
independently. Another advantage for using a fluidized bed
is that it eliminates the hot gas generator as a separate
unit; it and the fluidized bed are combined. The economics
generally favors a screw reactor for a small process with
a portable system; however, if the process is setup
WO95/13338 2 1 ~ 3 3 9 ~ PCT~S93/10750
permanently in a refinery, then the fluidized bed form is
likely more efficient.
Another equivalent substitutes a moving screen, or
alternatively a moving porous belt or other moving floor
reactor, for the screw reactor either in the stripping or
pyrolyzing sections or both.
The reactor is shown horizontal in Figure 1;
however, it is potentially usable at inclined angles,
perhaps up to 15 degrees for either the stripping section
or the pyrolyzing section or both. Thus a further
equivalent substitutes an inclined fluidized bed reactor
for the screw reactor either in the stripping or pyrolyzing
sections or both.
The sweep gas employed by the pyrolysis is often
separately supplied but potentially is obtainable from some
~xres~ hot gas. Although said sweep gas is often inert, in
this instance such hot gas can contain oxygen in small
amounts if compatible with the hydrocarbon characteristics
of the tank bottoms.
The largely pure water condensed from the overhead
of the flash tank is returnable to the field pit or sludge
pond if desired and represents a potential recycled
component.
The general design criteria represents a potential
recovery of about 85-90 percent of the amount of original
oil in the tank bottoms. The recovery split between heavy
and light oil is difficult to generalize since it depends
so much upon the original composition of the tank bottoms.
The pyrolysis unit is designed to enh~re the gas
generation usable for fuel as well as reduce the oil
content of the residue solid.
The designation of light and heavy oil is somewhat
arbitrary; however, with this process definitely one
collected oil liquid is heavier, that is, more viscous with
a higher st~n~rd boiling point curve, than the other. Of
course, in both instances these liquid oil streams are now
of refinery standard since water and solids have been
WO95/13338 ~S 3 3 ~ S PCTNS93/10750
largely removed.
Common regenerative heat exchangers are employed
and it is desirable to obtain 70-90 percent thermal
efficiency. The regenerative label means that at least one
stream is recycled from some other part of the process. An
open-type heat exchange is employed in the stripping
section of the reactor since the two streams physically mix
and in addition mass transfer occurs between the streams.
In all cases the discharged residue may have the
additional option of being burned 80 as to render any
metals into an environmentally acceptable oxidized state.
EXANPLE 1
A pilot plant scale operation was employed to test
the overall process for a heat load design that could be
potentially field employed. An operating screw obtained
from Moore Bearing Co., Cheyenne, Wyoming, was converted
into the small screw reactor. It had a two inch diameter
screw easily turning in a cylindrical case slightly larger;
tolerances from one sixteenth to one quarter inch are
common. Ideally the stripper section, about six foot long,
would utilized trough container for the screw with a lower
plenum chamber to distribute the hot gas flow, since direct
contact between the hot gas and the solid material was
desired; however, for this experimental setup a temporary
hot gas plenum was employed. An upper plenum directed the
flowing vapor stream leaving the stripper section into a
conventional gas transfer system. The vapor lock section
consisted of a plain section of screw and cylindrical
container, maybe two foot in length, since the solid
material augering through acted as a sealing medium. Thus
any reasonable length representing several screw
revolutions acted as an appropriate seal since no large
pressure difference existed across it. The pyrolysis
section was about four foot in length with a jacketed outer
chamber containing a heating medium, such as steam, or
alternately wrapped with electrical heating tape, to heat
the augered material to pyrolysis temperatures. Provision
WO95/13338 21 5 3 3 ~ ~ PCT~S93/10750
to have a countercurrent sweep gas was incorporated. A
variable speed drive was used and adjusted so that the
residence time of the feed was approximately 30 to 45
minutes, preferably the latter. In the subject runs ten
pounds per hour became the feed rate. The hot gas at about
900 F fed the stripper section, while the pyrolysis section
was electrically heated to approximately lO00 ~ with a
separate sweep gas employed. In all instances the target
of 85 percent recovery of the oil in the tank bottoms was
obt~ine~. However, heat load conditions were such that it
became imperative to add a flash tank, Figure l, before the
screw reactor to not only regeneratively recover heat but
largely pre-recover the water and certain light oil and
thus lower the load on said screw reactor.
E~AMPLE 2
The screw reactor is not a usual off-the-shelf
compQnent; however, it is potentially obtAin~ by
specifying the characteristics, such as size, length, pitch
of screw, material of screw and housing, non-st~n~rd
housing characteristics, motor size and speed, type of
drive such as belt or chain, gear reduction box ratios,
type of bearings, provisions for adding and removal of
solids, temperature range of operation, and any other
unique characteristics. With these specifications
fabrication is performed of the desired screw reactor, such
as by Acrodyne Corporation, Denver, Colorado, or Moore
Bearing Co., Cheyenne, Wyoming.
Further United States Letters Patent Number
4,347,ll9 described in considerable detail similar screw
reactors employed for oil shale and tar sands usage, and
information from this specification is hereby incorporated
by reference.
EXAMPLE 3
The control for the system was several fold. The
residence time was set by the screw speed to 30-45 minutes;
however, the preferred time was closer to the latter. For
this residence time sufficient contact area was supplied
Woss/l3338 2~3g PCT~S93/10750
for the stripping section to target the desired recovery of
approximately 95 percent of the liquid oil. The
temperature of the hot gas feeA;ng the stripper section was
adjusted to approximately the temperature n~e~e~ to make 95
percent vapor from the original tank bottoms feed oil as
determined by numerical simulation, or alternatively by
experiment. A common atmospheric boiling point curve run
on this tank bottoms feed oil sample can obtain this
information. For instance, in typical simulation tests on
a representative tank bottoms sample the 95 percent boiling
temperature was estimated at 893 F; thus, 900 F was used
as a set point for the hot gas.
The pyrolysis section was heated 8Uf f iciently to
bring the solid material being augered through to a
temperature of at least approximately 1000 F. This was a
practical temperature limitation since the pyrolysis and
thermal cracking that occurred produced a significantly
higher f raction of coke as the temperature increased much
beyond this value.
Depen~;ng upon the original tank bottoms
composition the gas yield at the heavy oil condenser and
the light oil con~enser and water separator is usually
sufficient to produce needed hot gas to obtain the proper
hot gas temperature. In the test runs this was the
situation, for in fact, extra gas was present that was
flared. If insufficient gas were present, then auxiliary
fuel, either light or heavy oil, is needed in the hot gas
generator.
Wo95113338 2 1 ~ 3 3 9 5 PcT~sg3/l075n
EXAMPL~ ~
A typical test run of the process produced the
results as shown in Table l and met well the design
criteria stated above.
The foregoing description of the specific
embodiments will so fully reveal the general nature of the
invention that others can, by applying current knowledge,
readily modify and/or adapt for various applications such
specific embodiments without departing from the generic
concept, and therefore such adaptations or modifications
are intended to be comprehended within the meaning and
range of equivalents of the disclosed embodiments. It is
to be understood that the phraseology or terminology herein
is for the purpose of description and not of limitation.
