U.S. patent application number 12/024251 was filed with the patent office on 2008-08-07 for method for reducing quench oil fouling in cracking processes.
This patent application is currently assigned to BAKER HUGHES INCORPORATED. Invention is credited to Enrico Madeddu, Marco Respini.
Application Number | 20080185316 12/024251 |
Document ID | / |
Family ID | 39675255 |
Filed Date | 2008-08-07 |
United States Patent
Application |
20080185316 |
Kind Code |
A1 |
Respini; Marco ; et
al. |
August 7, 2008 |
Method for Reducing Quench Oil Fouling in Cracking Processes
Abstract
Quench oil aging and its propensity to cause fouling may be
evaluated by determining the amount of a precipitant necessary to
cause the flocculation of polymer species present in the quench
oil. The propensity of quench oil to cause fouling may be used as a
basis to mitigate fouling in cracking processes.
Inventors: |
Respini; Marco;
(Casalmorano, IT) ; Madeddu; Enrico; (Cagliari,
IT) |
Correspondence
Address: |
MADAN, MOSSMAN & SRIRAM, P.C.
2603 AUGUSTA DRIVE, SUITE 700
HOUSTON
TX
77057-5662
US
|
Assignee: |
BAKER HUGHES INCORPORATED
Houston
TX
|
Family ID: |
39675255 |
Appl. No.: |
12/024251 |
Filed: |
February 1, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60888466 |
Feb 6, 2007 |
|
|
|
Current U.S.
Class: |
208/48Q |
Current CPC
Class: |
C10G 2400/02 20130101;
C10G 2400/20 20130101; C10G 2400/04 20130101; C10G 9/00
20130101 |
Class at
Publication: |
208/48.Q |
International
Class: |
C10G 11/00 20060101
C10G011/00 |
Claims
1. A method for reducing fouling from quench oil comprising:
treating a hydrocarbon feed using a cracking process having a
quenching step wherein: quench oil used in the quenching step has a
known tendency to cause fouling; and the known tendency of the
quench oil to cause fouling has been determined by measuring a
tendency of the quench oil to precipitate polymeric species.
2. The method of claim 1 further comprising adjusting process
conditions in the cracking process based upon the tendency of
quenching oil in the quenching step to cause fouling.
3. The method of claim 1 wherein the quench oil is selected from
the group consisting: of crude oil; the precursors of naphthalene,
phenanthrene, pyrene, quinoline, and hydroquinone; alkyl
derivatives of naphthalene, phenanthrene, pyrene, quinoline, and
hydroquinone; and mixtures thereof.
4. The method of claim 1 wherein the quench oil is selected from
the group consisting of: steam cracked quench oils; steam cracked
tars; cat cracked tars; cat cracked cycle oils; cat cracked
bottoms; coker gas oils; coal tar oils; aromatic extent oils; cuts
of steam cracked quench oils, steam cracked tars, cat cracked tars,
cat cracked cycle oils, cat cracked bottoms, coker gas oils, coal
tar oils, and aromatic extract oils; and mixtures thereof.
5. The method of claim 1 wherein the hydrocarbon feed is selected
from the group consisting of: crude oil, intermediate refinery
products resulting from the refining of crude oil, and mixtures
thereof.
6. The method of claim 1 wherein the hydrocarbon feed is used to
produce ethylene, gasoline, diesel fuel, other fuel oils, or
coke.
7. The method of claim 6 wherein the hydrocarbon feed is used to
produce ethylene.
8. The method of claim 1 wherein the tendency of the quench oil to
precipitate polymeric species is determined by measuring light
scattering.
9. A method for reducing fouling from quench oil comprising:
treating a hydrocarbon feed using a cracking process having a
quenching step, and introducing an additive to reduce fouling to
the cracking process based upon a tendency of the quench oil in the
quenching step to cause fouling which is determined by measuring a
tendency of the quench oil to precipitate polymeric species.
10. The method of claim 9 wherein the tendency of the quench oil to
precipitate polymeric species is determined by measuring light
scattering.
11. The method of claim 10 wherein differences in solubility
parameters of candidate quench oils for use in a cracking process
and for polymeric species present therein is measured and this
measurement used as a basis for evaluating the propensity of the
quench oil to undergo a polymer phase separation which may cause
the deposition of foulants during a cracking process.
12. The method of claim 11 wherein the quench oil candidate is
placed in a container with a probe capable of measuring light
scattering properties of the quench oil.
13. The method of claim 12 further comprising introducing aliquots
of a precipitant to the quench oil and measuring the light
scattering properties of the quench oil.
14. The method of claim 13 wherein a quench oil candidate requiring
more precipitant to increase light scattering is considered less
likely to foul than a quench oil candidate requiring less
precipitant.
15. The method of claim 13 wherein the precipitant is selected from
the group consisting of pentane, hexane, heptane, octane,
isobutane, cyclohexane, and mixtures thereof.
16. The method of claim 12 wherein the probe is a fiber optic
probe.
17. The method of claim 16 wherein the fiber optic probe is
selected from the group consisting of transmission probes,
reflectance probes, and attenuated total reflectance probes.
18. The method of claim 17 further comprising using an automatic
titrator to measure the light scattering properties of the quench
oil.
19. The method of claim 9 further comprising using solvent to
dilute the quench oil prior to measuring the tendency of the quench
oil to precipitate polymeric species.
20. The method of claim 19 wherein the solvent is selected from the
group consisting of: benzene, toluene, xylene, ethyl benzene, and
mixtures thereof.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This Application claims priority from the U.S. Provisional
Patent Application having the Ser. No. 60/888,466 which was filed
on Feb. 6, 2007; the contents of which are fully incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method for reducing
fouling in cracking processes. The present invention particularly
relates to a method for reducing fouling from quench oil in
cracking processes due to aging of the quench oil.
[0004] 2. Background of the Art
[0005] Petrochemical plants, which include both Chemical Production
Installations as well as Oil Refineries are known to employ two
basic types of furnaces. The first of these is a steam cracker
furnace. Steam crackers are used in applications including the
production of ethylene. The second of these is a "steam reformer"
furnace, which can be used to make hydrogen. Both types of furnaces
include a number of tubes, generally arranged vertically, that form
a continuous flow path, or coil, through the furnace. The flow path
or coil includes an inlet and an outlet. In both types of furnaces,
a mixture of a hydrocarbon feedstock and steam are fed into the
inlet and passed through the tubes. The tubes are exposed to
extreme heat generated by burners within the furnace. As the
feedstock/steam mixture is passed through the tubes at high
temperatures the mixture is gradually broken down such that the
resulting product exiting the outlet is ethylene in the case of a
steam cracker furnace and hydrogen in the case of a steam reformer
furnace as well as other products including gasoline and coke.
[0006] During the cracking processes, the feed materials are heated
to very high temperatures, in some embodiments, up to 900.degree.
C. This output is cooled by mixing it with a colder fluid and fed
in a fractionating column where the separation of ethylene and
light gasoline from a heavier oil takes place. The quality of the
distillation, i.e. the amount of ethylene, light olefins and
gasoline extracted from the top of the column, may be influenced by
the temperature of the feed in the fractionating column. A higher
temperature results in a higher yield of light products, which is
often desirable. Attempting to handle such hot materials is usually
not desirable and thus the need for a cooling step.
[0007] In some processes, the cooling step is implemented by
admixing the very hot products from the cracking units with a
comparatively cool fluid. The cool fluid, often an oil and most
often a heavy oil, is typically referred to in the art as a "quench
oil." The heavy quench oil may be extracted from the process and is
marketable as fuel oil.
[0008] In many processes, a minor amount of the quench oil is
extracted to be used as a fuel, while the remaining part is
recycled, sometimes back into the cracking process as a feed to the
cracking unit or as reuse as a quench oil or both. During the
course of its use, the heavy oil which is used as a quench oil may
be continually exposed to temperatures ranging from 100 to
220.degree. C. for extended periods of time.
[0009] Recycling quench oil may result in a number of serious
unfavorable side effects. For example, viscosity increases of the
recycled quench oil may be observed. In fact, the recirculating
quench oil may remain in the circuit at relatively high
temperatures for long periods of time, and this causes its aging.
Symptomatic of this aging is the presence of unsaturated compounds,
polymer and rubber formation, and a resulting viscosity increase.
All of these side effects obviously may cause a negative impact
upon the functioning of a production plant. Such negative impacts
include an increase in the power required by the recirculation
pumps, a reduction of the thermal exchange coefficients involved in
steam production, and an increase of the maintenance costs involved
in the cleaning of the plant components exposed to the quench
oil.
SUMMARY OF THE INVENTION
[0010] In one aspect the invention is a method for reducing fouling
from quench oil comprising treating a hydrocarbon feed using a
cracking process having a quenching step, wherein: quench oil used
in the quenching step has a known tendency to cause fouling; and
the known tendency of the quench oil to cause fouling has been
determined by measuring a tendency of the quench oil to precipitate
polymeric species.
[0011] In another aspect the invention is method for reducing
fouling from quench oil comprising treating a hydrocarbon feed
using a cracking process having a quenching step, wherein process
conditions in the cracking process have been adjusted based upon
the tendency of quenching oil in the quenching step to cause
fouling which is determined by measuring the tendency of the quench
oil to precipitate polymeric species.
[0012] In one aspect the invention is a method for reducing fouling
from quench oil in a cracking process comprising treating a
hydrocarbon feed using a cracking process having a quenching step,
introducing an additive to reduce fouling to the cracking process
based upon a tendency of the quench oil in the quenching step to
cause fouling which is determined by measuring a tendency of the
quench oil to precipitate polymeric species.
[0013] In another aspect, the invention is a method for predicting
the tendency for a quench oil to cause fouling in a cracking
process by measuring the tendency of the quench oil to precipitate
polymeric species.
[0014] In still another aspect, the invention is a method for
measuring the tendency of the quench oil to precipitate polymeric
species.
[0015] In another aspect, the invention is an apparatus for
measuring the tendency of the quench oil to precipitate polymeric
species.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] For a detailed understanding of the present invention,
reference should be made to the following detailed description of
the preferred embodiments, taken in conjunction with the
accompanying drawing(s) wherein:
[0017] FIG. 1 is graph showing the typical output of a
transmittance probe in a quench oil sample during the addition of a
precipitant to the quench oil sample.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] In one aspect the invention is method for reducing fouling
from quench oil in a cracking process comprising treating a
hydrocarbon feed using a cracking process having a quenching step.
Cracking processes are well known in the art of refining oil and
other chemical processes. Such processes include, but are not
limited to those disclosed in U.S. Pat. Nos. 6,096,188; 5,443,715;
and 5,215,649; which are fully incorporated herein by reference. In
the practice of one embodiment of the invention, a quench oil is
contacted with an intermediate or even a final product of a
cracking process.
[0019] The quench oils useful with some embodiments of the present
invention may be selected from the group consisting of crude oil;
the precursors of naphthalene, phenanthrene, pyrene, quinoline, and
hydroquinone; alkyl derivatives of naphthalene, phenanthrene,
pyrene, quinoline, and hydroquinone. The quench oils may also be
selected from the group consisting of aromatic molecules containing
phenol groups and aromatic molecules containing non-phenolic oxygen
substitutes. Also useful as the quench oil in some embodiments of
the present invention are those compounds selected from the group
consisting of steam cracked quench oils, steam cracked tars, cat
cracked tars, cat cracked cycle oils, cat cracked bottoms, coker
gas oils, coal tar oils, and aromatic extent oils and cuts of steam
cracked quench oils, steam cracked tars, cat cracked tars, cat
cracked cycle oils, cat cracked bottoms, coker gas oils, coal tar
oils, and aromatic extract oils.
[0020] The hydrocarbons feeds that can be treated using the process
of the present invention include, but are not lime tied to crude
oil and intermediate refinery products resulting from the refining
of crude oil.
[0021] In the process of treating a hydrocarbon feed using a
cracking process, many products may be made including ethylene,
gasoline, diesel fuel, other fuel oils, and coke. Processes
producing heavy oils and coke are often subject to fouling. For the
purposes of this application, fouling is a condition wherein
materials having a very high viscosity and mixtures of viscous
materials and solids such as coke deposits from the quench oil and
accumulate within process equipment causing reduced operational
efficiency or even shutting down the processing equipment. For
example, when fouling occurs, it may cause transfer pipes to clog
which in turn may require the cracking unit to reduce process
throughput or even shut down the unit. Such slow-downs and
shut-downs often result in increased operating costs for the units
affected and also any integrated units upstream or downstream of
the affected unit.
[0022] In one aspect, the invention is a process for reducing
fouling from quench oils by selecting quench oils that have a
reduced tendency to produce fouling. In the practice of the
invention, the tendency to produce fouling of a quench oil is
determined by measuring the tendency of the quench oil to
precipitate polymeric species. Stated another way, the difference
in solubility parameters of candidate quench oils for use in a
cracking process and for polymeric species present therein can be
measured and this measurement used as a basis for evaluating the
propensity of the quench oil to undergo a polymer phase separation
which may cause the deposition of foulants during a cracking
process.
[0023] The tendency of candidate quench oils to precipitate
polymeric species may be determined by any means known to those of
ordinary skill in the art of making such determinations to be
useful. For example, in one embodiment of the invention, a sample
of a quench oil candidate is placed in a container with a probe
capable of measuring light scattering properties of the quench oil.
In this embodiment, aliquots of a precipitant are added to the
quench oil and the light scattering properties of the quench oil
measured. A precipitant having a high light transmission level
relative to the quench oil is used and the "dilution" effect of the
precipitant will initially cause a reduction of light scattering in
the sample until sufficient precipitant is added to the sample to
cause precipitation of the polymer species thereby increasing light
scatter. By comparing the amount of precipitant required to cause
an increase in light scattering, sometimes also referred to as
flocculation, quench oil candidates may be compared. In one
embodiment of the invention, quench oil candidates requiring more
precipitant to increase light scattering are considered less likely
to foul than those candidates requiring less precipitant.
[0024] Precipitants useful with the invention include any which
have a higher light transmission than the quench oil samples to be
tested and which will cause a precipitation of polymer species from
the quench oil. In one embodiment, these precipitants are selected
from aliphatic solvents. Typical aliphatic solvents useful with the
present invention may include pentane, hexane, heptane, octane,
isobutane, cyclohexane, and the like. Any precipitant may be used
as long as it meets the specified criteria.
[0025] In the practice of the invention, it may be desirable to
dilute the quench oil with a solvent. For example, in the case of
colored quench oil candidates, it may be desirable to dilute the
quench oil candidates to a point that they are within a specified
transmission scale for a particular type of probe. The solvents
used should be selected so that they do not materially interfere
with the precipitation of polymeric species. For example, in one
embodiment of the invention, the solvents used with the present
invention are aromatic solvents. Such solvents include, but are not
limited to benzene, toluene, xylene, ethyl benzene, and mixtures
thereof.
[0026] Once the amount of precipitant necessary to cause onset of
flocculation is known, it may be desirable to repeat the experiment
with differing amounts of solvent and determine the flocculation
point by means of a linear regression calculation. Any method of
comparing the results from the measurements may be used to evaluate
the relative propensity of various quench oil candidates to
precipitate polymer species.
[0027] In one embodiment of the invention, an automatic titrator is
used in conjunction with a light probe to determine the
flocculation point of a quench oil. An automatic titrator
advantageously can dispense exact aliquots of precipitants and,
when networked with suitable equipment, also record light
scattering of sample therein. In an alternative embodiment, the
automatic titrator, probe, and other equipment are networked to a
controller. In many such embodiments, the controller is a personal
computer.
[0028] The flocculation point of a quench oil is determined in some
embodiments of the method of the invention by noting the point at
which during a series of addition of precipitant to a quench oil
sample, that light scattering starts to increase. The ability of a
sample of quench oil to scatter light may be measured by any means
known to useful to those of ordinary skill in the art of making
such measurements. Preferably, the measurement is made using a
probe and most preferably using a fiber optic probe. Exemplary
fiber optic probes include transmission probes, reflectance probes,
and attenuated total reflectance probes. Each of these probes has
strengths and weaknesses that would make them more or less
desirable for any given set of conditions. Those of ordinary skill
in the art of making such measurements will know which probe to
select for an application. For example, where the sample have a
high level of opacity, it may be more desirable to use an
attenuated total reflectance probe rather than a transmission
probe. In one preferred embodiment, a fiber optics diffuse
reflectance probe is used wherein a single fiber acts as a light
source and 6 other fibers arranged around the source collect
backscattered light.
[0029] The type of light employed by each probe may also be
selected according to the conditions of the desired testing
conditions. For example, the light employed may be UV, VIS or NIR.
Such probes often employ silicon or germanium detectors. Any device
useful for measuring light intensity may be used with the present
invention.
[0030] The type of probe used will determine whether flocculation
is observed by a decrease or an increase in light intensity at a
detector. As a sample increases in ability to scatter light, less
light passes directly through the sample. Transmittance probes
function by measuring the amount of light passing through a sample.
Using a transmittance probe, a measurement according to the
invention would see an increase in the power of the light reaching
the detector until the flocculation point at which time the power
may rapidly decrease. For a reflectance probe, the observations
would be the inverse with power decreasing until the flocculation
point.
[0031] In additional to making single determinations, the method of
the invention may be used continuously. In this embodiment of the
invention, the flocculation point of recycled quench oil is
measured as a function of time. As the amount of precipitant need
to cause flocculation decreases, the likelihood of fouling
increases. At some point in time, either based upon prior
experience or use of a predictive model, the determined tendency of
the recycled quench oil to foul is used as a basis to divert the
quench oil from recycle to an alternative disposition such as use
as a fuel oil or the like. In an alternative embodiment of the
invention, rather than diverting quench oil as it reaches a certain
tendency to foul, the process parameters may be changed to slow or
prevent quench oil "aging." For the purposes of the present
application, "quench oil aging" means the phenomena where quench
oil has a greater tendency to foul with time held at high
temperatures such as is observed with quench oil that has been
recycled. In still another embodiment of the invention, the
measured tendency of the quench oil to foul can be used as a basis
for a decision to introduce additives into the cracking process to
reduce fouling.
[0032] Additives useful for quench oil viscosity fouling reduction
and control include, but are not limited to, well known chemistries
to those skilled in the art, such as dispersants, radical
scavengers and fouling control additives made of overbased metal
carboxylates and sulphonates. In some embodiments of the invention,
additives these could include blends of the commercial
dispersant/antifoulant product BPR34260 supplied by Baker Petrolite
Corporation, antioxidants based on sterically hindered phenols and
phenols, and their blends with amines such phenylene diamine and
magnesium oxide overbase.
[0033] In the practice of the invention, the density, type and
opacity of the quench oils to be evaluated will determine how the
quench oils will be tested. Those of ordinary skill in the art of
running a cracking unit are knowledgeable regarding the methodology
necessary to test their processes. Still, generally, samples tested
according to the invention may have sample sizes running from about
3 grams to about 50 grams. When diluted, the quench oils may be
diluted in ratios (quench oil: Aromatic solvents) ranging from
about 10:1 to about 1:20, and in some embodiments from about 2:1 to
about 1:3. Typically, samples of quench oil are heated to from
about 45 to about 60.degree. C. prior to testing.
[0034] In an alternative embodiment of the invention, Hildebrand
solubility parameters are determined for a sample of quench oil.
The Hildebrand solubility parameters are determined by making
several runs with the quench oil dissolved in varying amounts of
aromatic solvent. The quantity of precipitant needed to reach the
flocculation point is divided by the sample size of the quench oil
and linearly correlated with the dilution ratio. From this
relationship, the Hildebrand solubility parameters are then
determined.
[0035] In some embodiments of the invention, it may be desirable to
adjust process conditions in the cracking process based upon the
tendency of quenching oil in the quenching step to cause fouling.
While those of ordinary skill in the art are well aware of how to
adjust a specific cracking process based upon a understanding of
whether or not the quench oil used in the cracking process is
likely to cause fouling, generally process parameters that could be
adjusted include process temperatures, pressures, and residence
times. For example, in at least some cracking processes, if an
operator of the cracking process was aware that the quench oil used
in the cracking process was likely to cause fouling, the operator
may elect to decrease residence times, lower cracking temperatures,
or increase pressures within the cracking process. In other
embodiments, an operator may select to make the same or different
adjustments based upon the specific characteristics of the subject
cracking process. In one specific example, an operator may elect to
change quench oil column (also known as Pyrolysis Column) bottom
temperature, bottom column level, and rate of reflux of pyrolysis
gasoline to the quench oil column.
[0036] While not wishing to be bound by any theory, it is believed
that the polymer species that is precipitated from quench oils that
result in the deposition of foulants within a cracking process are
heavy aromatic polymers.
EXAMPLES
[0037] The following examples are provided to illustrate the
present invention. The examples are not intended to limit the scope
of the present invention and they should not be so interpreted.
Amounts are in weight parts or weight percentages unless otherwise
indicated.
Example 1
[0038] A sample of quench oil is placed into an automatic titrator.
The reservoir of the automatic titrator is filled with normal
heptane. A transmission probe is placed into contact with the
quench oil sample and both the transmission probe and the automatic
titrator are attached to a controller that records both light
scattering and ml of n-heptane introduced into the sample. A curve
showing a plot of this experiment is displayed in FIG. 1.
Example 2
[0039] Five quench oil candidate materials are tested on an
apparatus substantially identical to that of Example 1. Each
material is tested 5 times and the data compared. For each sample,
the repeatability of flocculation point is less than 3 percent of
the precipitant used.
Example 3 (Hypothetical)
[0040] The samples tested in Example 2 are evaluated for use with a
steam cracker unit. The samples have a comparative value for
flocculation point of: [0041] Sample I: 1.2 [0042] Sample II: 2.9
[0043] Sample III: 1.7 [0044] Sample IV: 1.7 [0045] Sample V: 1.0
Sample II is selected as the quench oil for the unit.
Example 4 (Hypothetical)
[0046] The recycle quench oil is tested substantially identically
to Example 1 except that samples are removed from a cracking unit
every 12 hours. The rate in decrease of the flocculation point is
measured and compared against known conditions resulting in
increased fouling. When the flocculation point decreases to the
point that increased fouling appears likely to occur, the recycle
quench oil is diverted for alternative disposition.
Example 5 (Hypothetical)
[0047] Example 4 is repeated substantially identically except that
instead of diverting the quench oil from recycle, additives are
introduced into the cracking unit to reduce fouling.
Example 6 (Hypothetical)
[0048] Example 4 is repeated substantially identically except that
instead of diverting the quench oil from recycle, the conditions in
the cracking unit are adjusted to extend the useful life of the
quench oil.
Discussion of the Examples
[0049] Example 1 and FIG. 1 clearly show that from the beginning of
the experiment until about 23.5 ml of precipitant had been
introduced into the sample, light transmission increased, caused by
the dilution effect of the precipitant. At about 23.5 ml,
scattering stop decreasing and began increasing. This is the point
at which flocculation occurred.
* * * * *