Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
11773F~S
01 GAS-POCKET DISTRIBUTOR FOR AN UPFLOW REACTOR
BACKGROUND OF THE INVENTION
1. Field of the Invention
05 This invention pertains to a reactor feed dis-
tributor that is useful in upflow reactors for mixed phase
feed streams. The distributor is particularly useful in
catalytic coal liquefaction reactors which must be capable
of accommodating feeds comprising gases, liquids and
solids.
2. Prior Art
For many processes an upflow reactor is superior
to the more common downflow reactors. This is partic-
ularly true in those situations in which a liquid feed
also contains solids since the solids tend to pack and
form obstructions in the downflow mode. The problems are
further amplified if the feed stream is comprised of gases
as well as solids and liquids.
Upflow reactors are commonly employed in coal
liquefaction systems such as the liquefaction process
disclosed in U.S. Patent No. 4,083,769, issued to
Hildebrand et al on April 8, 1978. As taught in the ref-
erence, hydrogen, ground coal and solvent are preheated
and passed to a dissolver wherein the coal is substan-
tially dissolved at a temperature in the range 750-900F
(379-482C) and at a pressure in the range 3100-5000 psi
(217 kg/cm2-350 kg/cm2). The dissolver is an empty upflow
reactor vessel which provides sufficient residence time
for the dissolution of the ground coal particles to occur.
Solvent, dissolved coal, coal residue and hydrogen from
the dissolver are passed to an upflow catalytic hydro-
genation reactor operating at a temperature 25-150F
(13.9-83.3C) lower than the dissolver.
Since the hydrogen is mixed with the coal slurry
prior to the preheating step to avoid coking in the
q~
117738S
,~
.,
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01 heater, little or no control is exerted over the degree of
liquid and gas mixing which occurs in the dissolver or
catalytic reactor. With multiphase flow, gas channeling
and/or slugging in these units may occur. The presence of
either condition is undesirabl~ since both result in
inadequate contacting of the reactants and the slugging
may also create damaging equipment vibrations. Further-
more, inadequate hydrogen mixing can lead to coking of the
reactants and equipment fouling at the described process
conditions.
Thus, it is apparent that a need exists for a
distributor which will accept feed streams comprising
liquids, gases and solids and evenly distribute the phases
without plugging or suffering undue erosion.
Although numerous mixed phase distributors are
known in the art, such as those disclosed in U.~. Patents
Nos. 3,524,731; 4,111,663; 3,146,189; 3,195,987 and
4,187,169, a need remains for an efficient and economical
solution to the problem.
SUMMARY OF THE INVENTION
There is provided by the present invention a
distributor for a gas-liquid or gas-liquid-solid feed
upflow reactor vessel having a feed inlet port in the
i lower portion thereof and an effluent outlet port in the
i 25 upper portion thereof. The distributor is comprised of a
substantially horizontally disposed plate mounted in the
vessel between the inlet and outlet ports. The plate has
a plurality of holes extending therethrough and at least
one downwardly extending tube in open communication with
the reactor vessel volume below said plate and in open
communication with the reactor vesse1 volume above said
plate~ The cross sectional area of the plate perforations
- and the cross sectional area and length of the tube are
designed such that under equilibrium feed conditions a gas
pocket forms below the plate having a height less than or
1177385
01 equal to the length of the tube. Substantially all, i.e.,
at least 75% and preferably greater than 95~, of the feed
gas will pass through the plurality of holes in the plate
and substantially all, i.e., at least 75% and preferably
05 greater than 95%, of the feed liquid or feed liquid and
solids will pass through the tube.
The distributor of the present invention will
preferably be used in a reactor which contains a fixed or
moving bed of particulate catalyst for evenly distributing
the gas and liquid or gas, liquid and solids throughout
the catalyst bed. However, it may advantageously be used
in non-catalytic vessels such as dissolvers to insure good
contacting of the hydrogen gas with the liquids and solids
to prevent coking within the vessel.
Preferably, means are also provided for prevent-
ing the direct vertical passage of feed gas bubbles into
the lower end of the tube. If the distributor is used in
a catalytic reaction vessel, the distributor should be
located far enough below the lowest level of catalyst such
that any gas fingering that occurs will be totally within
the liquid volume situated immediately below the catalyst.
Although a single distributor can suffice in some reac-
tors, in commercial practice multiple distributors will
generally be vertically spaced throughout a reactor.
Furthermore, the distributor of the present
invention is particularly suitable for gas quenching or
gas withdrawal applications.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. l depicts an upflow fixed bed catalytic
reactor having a single distributor.
FIG. 2 depicts an upflow fixed bed catalytic
reactor having multiple distributors and adapted for the
injection of gas between distributors.
~17'73~5
01 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG.l there is shown a vertically
oriented reactor vessel 10 having a lower feed inlet port
20 and an effluent outlet port 30. A fixed bed of porous
S particulate catalyst 40 is maintained in the vessel
between a lower support grid 50, attached to the inner
wall of ve~sel 10, and, if desired, a catalyst retaining
screen 60, also secured to the vessel inner wall.
The distributor of the present invention,
generally characterized by reference numeral 70, is
attached to the inner wall of vessel 10, between inlet
port 20 and catalyst support grid 50. The distributor may
be affixed to the vessel wall in any convenient or conven-
tional manner such as by welding or bolting.
Distributor 70 is comprised of a plate 80
extending over the full cross sectional area of vessel 10.
The plate has a plurality of perforations or holes 90
extending therethrough. Preferably the perforations are
evenly distributed over the total cross sectional area of
the plate with about 20-250 or more preferably about
40-250 perforations per square meter. An open-ended tube
100 is conventionally affixed to plate 80 and extends
downwardly from a central aperture in said plate.
Although only a single tube is shown in the drawing, it is
within the scope of this invention to provide more than
one tube if same is required by the feed conditions or
reactor size. Preferably about ten or twenty tubes will
be used per square meter of plate surface.
A cap 110 is provided at the lower end of tube
100 to prevent gases in the feed from passing directly up
through the tube. Although cap 110 is shown as being con-
ventionally secured to the end of tube 100 by extension
120, it may be replaced by an equivalent baffle secured to
the vessel wall. It is also possible to offset the inlet
port from the end of tube 100 in such a manner as to
11773~5
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01 obviate the problem. In the event a cap is used as shown
in the drawing it will preferably be about 20% larger than
the tube diameter. When multiple distributors are
employed in a vessel, the upper distributors may not
05 require a cap to prevent substantial gas from entering the
- tube.
In operation a mixed phase feed stream, prefer-
ably comprised of liquid, gas and solid components, such
as might be introduced to a dissolver or catalytic reactor
of a coal liquefaction unit, is pumped or otherwise intro-
duced into the bottom of vessel 10 through inlet port 20.
In accordance with the invention, the distri-
butor is designed for the feed conditions such that a gas
pocket, or vapor space 130, having a height, h, which is
substantially equal to or less than the length of tube 100
extending below the plate, is formed under steady state
conditions and substantially all, i.e., at least 75%, of
the gas and vapor components of the feed pass through
holes 90 and substantially all of the liquid and solid
components of the feed pass through tube 100.
It is observed that the required flow path of
the gases and liquids will be realized if the pressure
drop of the vapor flow through the plurality of holes, 90,
is balanced by the pressure drop of the flow of liquids
and solids through tube 100 plus the static pressure
differential between the liquids and solids of height h
and the gas pocket, i.e., the static head of the liquids
and solids through the tube.
The pressure drop due to gas flow through a
perforated plate may be predicted by the orifice equation.
If the liquid and solids pressure drop in the tube is
negligible, the gas pressure drop may simply be balanced
against the static pressure differential, equal to
(pl-pg)h, wherein Pl is the density of the liquid and
solids stream in the tube and pg is the gas density.
~1773~35
01 Preferably the distributor is designed with a
minimum value for h of approximately 5-10 centimeters.
More preferably, h should be set at approximately 10-20
centimeters and a design tube length selected of approx-
05 imately 20 centimeters. These values will allow forsubstantial variation in vapor rates and therefore gas
pocket heights. At the design flow rates these values
will also ensure that the lower end of the tube is
substantially even with or below the liquid surface to
prevent significant gas entry from the tube upon liquid
surface disturbances.
The upper surface of the horizontal perforated
plate should be preferably disposed approximately 3-10
centimeters below lower grid 50, depending upon gas bubble
growth.
Although the preferred embodiment has been
particularly described with reference to feeds for coal
liquefaction units, it is apparent that the distributor of
the present invention may be used in any system having
gas-liquid or gas-solid-liquid feeds. Furthermore, if the
unit is to be used as gas quenching apparatus, the gas
need only be injected below plate 80 for even thorough
distribution.
FIG. 2 depicts the apparatus of this invention
having multiple distributors 70 and multiple catalyst beds
40. The catalyst beds 40 are drawn smaller than scale in
order to depict the distributor detail. Quench gas, such
as recycle gas containing hydrogen for a catalytic coal
liquefaction process, is added through ports 150, into
vapor spaces 130. Ports 150 can also be used to withdraw
gas from vapor spaces 130. If desired, tube 100 can
extend into the upper portion of catalyst beds 40, pref-
erably with the catalyst in the tube at substantially the
same level as the rest of the catalyst bed. Also, the gas
pocket can contain a portion of the atalyst, if desirGd.
