Note: Descriptions are shown in the official language in which they were submitted.
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VAPORIZING HEAVY~HYDROCARBON FEEDSTOCKS WITHOUT COKING
BACKGROUND OF THE INVENTION
The present invention relates to the heating and
vaporizing of heavy hydrocarbon feedstock materials without
coking. More particularly, it relates to a method for
providing a vaporized heavy hydrocarbon feedstock which avoids
the formation of coke in the feed heaters and is useful in a
process for upgrading and/or converting the heavy hydrocarbon
to lighter products, such as in a thermal hydrodealkylation
process.
One barrier to successful hydrodealkylation of heavy
hydrocarbon aromatic materials such as steam cracker tar to
produce mono-ring product materials is vaporization of the
liquid phase feed material without producing excessive coke
formation during the preheating step. It has generally been
found that such heavy hydrocarbon liquids when preheated to
above about 550~F are susceptible to coking. To overcome
~0 this pxoblem of undesired coke formation during preheating
and to permit feeding of heavier vaporized feedstock materials
to thermal or catalytic reaction processes, it has been found
possible to make use of superheated hydrogen and/or hydrocarbon
vapors mixed with the heavy hydrocarbon feed to rapidly heat
and vaporize the heavy hydrocarbon liquids to provide a vapor
phase material without coking of the heavy hydrocarbon feed
material. Although it is known in industry to use preheated
hydrogen mixed with feed liquids upstream of a reaction step,
such heated hydrogen has apparently not been previously used
to vaporize hydrocarbon heavy feedstock materials which
contain constituents which are prone to coking in a
conventional tubular fired heater preheating step.
SUMMARY OF INVENTION
This invention provides a method for providing a
vaporized heavy hydrocarbon feedstock which avoids the
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formation of coke in the feed heaters and is useful in a
process for upgrading and/or converting the heavy hydrocarbon
to lighter products, such as in a thermal hydrodealkylation
process. The method comprises heating a heavy hydrocarbon
feedstock to a temperature below its coking temperature,
heating hydrogen-rich gas to a temperature sufficiently above
the temperature of the heated heavy hydrocarbon feedstock so
that upon mixing the heated hydrocarbon feedstock and
hydrogen together the heavy hydrocarbon feed material is
completely vaporized without forming any coke. In a second
embodiment of the invention, a heavy hydrocarbon feedstock
is first fractionated into a lighter fraction normally
boiling below about 550F and a heavier fraction having a
normal boiling range of about 550F to about 850F. The
heavier hydrocarbon fraction is heated to a temperature below
its coking point, and the lighter fraction and hydrogen-
rich gas are heated separately to a temperature below the
coking point of the lighter fraction and sufficiently above
' the temperature of the heated heavy hydrocarbon fraction to
210 provide heat content sufficient that upon being mixed with
the heavy hydrocarbon fraction the latter is vaporized without
forming any coke. Using this invention, the temperature of
the mixing chamber wall can be maintained at a significantly
lower temperature than would be required for the wall
temperature of a tubular type fired preheater for vaporizing
the feedstock.
This invention for vaporizing heavy hydrocarbon
feedstocks i5 useful at a pressure range of 50-5000 psig. The
vaporized hydrocarbon material stream can then be further
heated and fed to a reaction step such as hydrodealkylation to
produce hydrodealkylated products.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a flow diagram illustrating a method for
vaporizing a heavy hydrocarbon feedstock according to the
present invention; and
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FIG. 2 is a flow diagram of a second embodiment of
the method illustrated in FIG. 1.
DETAILED DESCRIPTION OF INVENTION
In the present invention for vaporizing heavy
hydrocarbon feedstocks, so as to avoid formation of coke,
hydrogen-rich gas is heated to a temperature sufficient that
upon mixing with the heavy hydrocarbon feedstocks will
effectively heat same through their dry point and vaporize
the heavy feedstock without coking. The heated hydrogen-rich
gas is mixed with the heavy feedstock in a suitable mixing
step such as a venturi mixer. The temperature of the heated
hydrogen-rich gas is much higher than the temperature of the
heavy hydrocarbon feed material, and is sufficiently high,
such as 900-1250F, that it supplies all the heat needed to
vaporize the heavy hydrocarbon liquid feedstock, which
normally boils above about 550F and preferably has a boiling
- range of 550-650F. Because of the rapid heat transfer which
occurs between the mixed streams in the mixing step, this
heating method avoids transferring heat from a hot wall to
the hydrocarbon feedstock and minimizes the time required to
vaporize the heavy feed material and avoids coking of the
material.
In a second embodiment of the invention, the
hydrogen-rich gas can be premixed with a light hydrocarbon
fraction having a normal boiling range of about 400-650F and
heated together to a temperature below the coking point of
the light hydrocarbon fraction and sufficient that upon
mixing with the heavy hydrocarbon feedstock fraction will
rapidly heat same through its dry point and completely vaporize
the heavy hydrocarbon feedstock without coking of the heavy
hydrocarbon feedstock material.
This invention can be used for vaporizing any
heavy hydrocarbon feed material for which a vapor phase
reaction is required, such as for vaporizing heavy gas oils
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and steam cracker tar derived from petroleum, and coal-derived
liquids, prior to feeding the vaporized hydrocarbon material
to a reaction step such as thermal hydrocracking or hydro-
dealkylation to produce hydrodealkylation products. Useful
pressure ranges for the invention are 50-5000 psig, and
preferably 200-1000 psig.
As shown in the Fig. 1 drawing, a heavy hydrocarbon
feedstock material such as heavy gas oil, is provided at 10,
pressurized at 11 to at least about 200 psig and heated in
furnace 12 to a temperature such as about 560F, which will
not produce coke deposits inside the tubes 13 of the furnace.
The heated feedstock stream at 14 is passed to a mixing step
at 20. Also, hydrogen-rich gas is provided at 16 and heated
in furnace 18 to a temperature well above the temperature of
the mixing step 20 and also passed to the mixing step.
Mixing step 20 may comprise any suitable known mixing
device which provides complete mixing at relatively high
velocities, such as a length of pipe, nozzle or venturi, with
, the heavy oil stream 14 preferably being introduced into the
throat section of a venturi type mixer device. The heat
content provided in hydrogen-rich stream 19 is sufficient to
completely vaporize the heavy hydrocarbon feed stream 14, and
thus avoids heating the hydrocarbon feedstock through its dry
point by contact with a hot metal wall maintained at higher
temperature than the feedstock and thereby prevents any
coking of the heavy feed material during such heating.
The resulting vaporized material at 21 is further
heated in heater 22 to about 1250F and passed to a reaction
step 24, such as for a hydrodealkylation process, to produce
a product 26.
In an alternative embodiment of the invention, as
shown in Fig. 2, a heavy feedstock material such as steam
cracker tar is provided at 30 and fed into fractionation
tower 32, which is usually maintained at operating conditions
of about 200-300F temperature and 1-5 psia pressure. From
tower 32, a vapor stream can be withdrawn at 33, a light liquid
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stream normally boiling up to about 550F is withdrawn at 34,
a heavy liquid stream having a normal boiling range of 550-
850F is withdrawn at 36, and a heavier bottoms material
boiling above about 850F is withdrawn at 38.
Light liquid stream 34 is pressurized at 35 to at
least about 200 psig, hydrogen-rich gas is added at 40 and
heated at 41, and the resulting mixture is heated in heater 42
to a temperature above about 950F and passed as stream 43 to
~ mixing device having a reduced pressure and increased velocity
at the throat section. The heavy boiling liquid stream 36
is pressurized at 37 to at least about 200 psig, heated at 46
to a temperature sufficiently low to avoid coking in the tubes
of heater 46, such as about 550F, and also passed to mixing
step 44. The heat provided in stream 43 is sufficient to
vaporize liquid stream 47, so that the resulting mixed stream
which emerges at 45 from mixer 44 is completely vaporized.
This vapor stream 45 is then passed through heater 48 for
further heating such as to 1200-1250F temperature before
passing to reaction step 50, which may preferably be a hydro-
dealkylation step. If the feedstock at 30 is a polynuclear
aromatic or polyalkylated phenol material, the light liquid
stream at 34 can contain mainly alkylated naphthalene material,
which is heated with hydrogen-rich gas at heater 42 to a
temperature sufficient so that upon being mixed with the
heated heavy stream 47, which can be mainly alkylated
phenanthrenes, the latter is completely vaporized. The
resulting vaporized material is then fed to a hydrodealkylation
reaction process step at 50 to produce product at 52.
This invention will be further described by reference
to the following examples, which should not be construed as
limiting in scope.
EXAMPLE 1
To show the method and utility of the present
invention, a heavy hydrocarbon feed material such as gas oil
normally boiling above about 600F temperature is pressurized
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to about 650 psia pressure and heated to a temperature at
least 600F but below which vaporization or any coking of the
feed occurs. The heated feed material is then vaporized by
being mixed with a hydroyen-rich stream heated to a temperature
sufficiently above the mixing temperature to have a heat
content sufficient that upon being mixed with the heavy liquid
feed will completely vaporize the feed without coking. The
molar flow ratio of hydrogen-rich gas to feed liquid is about
13, and the hydrogen stream contains 90% hydrogen and 10%
methane. Results of the heating and mixing steps for various
hydrocarbon feedstock fractions are shown in Table 1.
TABLE 1
VAPORIZING HYPROCARBON FEEDSTOCK
BY MIXING WITH HEATED HYDROGEN
Liquid Feedstock Liquid Feed H2 Gas Mixing
Avg.BP, F Temp, F Temp, F Temp, F
600 600 1000 690
' 650 600 1125 735
700 650 1250 803
It is seen that the heavy hydrocarbon feed materials
having average boiling points between 600 and 700F can be
heated and completely vaporized without coking by being mixed
with a hydrogen-rich gas stream heated to a higher temperature
but not exceeding about 1250F to provide a hydrocarbon vapor
material.
EXAMPLE 2
A heavy hydrocarbon feed material such as steam
cracker tar is fractionated into at least a light fraction
having a normal boiling lange OL 300-550F and a heavy fraction
having a boiling range of 550-850F. The heavy hydrocarbon
fraction is heated to a temperature below its coking point and
passed to a mixing step. The light fraction stream is mixed
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with heated hydrogen-rich gas and the resulting mixed stream
is heated to a temperature higher than that of the heavy
fraction and such as to provide a heat content sufficient
that upon mixing the two preheated hydrocarbon streams together
the heavy hydrocarbon stream is completely vaporized without
any coking. Results of the heating and mixing steps for various
hydrocarbon feedstocks at 650 psi using 13 moles hydrogen, 1
mole light hydrocarbon fraction and 1 mole heavy hydrocarbon
fraction feed are shown in Table 2.
TABLE 2
VAPORIZING HEAVY HYDROCARBON FRACTION BY MIXING
WITH HEATED HYDROGEN AND LIGHT HYDROCARBON FRACTION
Heavy Light Liquid
Liquid FeedstockLiquid Feed and H2 Gas Mixing*
Avg.BP, F Temp, F Temp, F Temp, F
600 600 1000 830
650 600 1000 825
~ 700 600 1000 820
*Temperatures are + 3pF.
.
It is seen that the heavy hydrocarbon feedstocks
having initial normal boiling points between about 600-700F
can be heated and completely vaporized without coking by being
mixed with a light hydrocarbon liquid fraction and hydrogen-rich
gas mixture heated to a temperature sufficiently above the mixing
temperature, but not exceeding about 1000F to heat and vaporize
the heavy feedstock and provide a hydrocarbon vapor material.
Although this invention has been described broadly
and with reference to certain embodiments thereof, it will be
understood that modifications and variations to the method can
be made within the spirit and scope of the invention, which is
defined by the following claims.
