GB2078537A

GB2078537A - Distributor for a gas-liquid or gas-liquid-solid feed upflow reactor

Info

Publication number: GB2078537A
Application number: GB8118041A
Authority: GB
Original assignee: Chevron Research and Technology Co; Chevron Research Co
Current assignee: Chevron USA Inc
Priority date: 1980-06-19
Filing date: 1981-06-12
Publication date: 1982-01-13
Also published as: NL8102816A; GB2078537B; FR2484864B1; AU537031B2; DE3123695A1; FR2484864A1; AU7048581A; DE3123695C2; CA1177385A

Abstract

A distributor for use in a multiphase upflow reactor vessel comprises a horizontally disposed plate mounted in the vessel above the feed inlet port, and having a plurality of perforations therethrough and at least one downwardly extending tube passing through the plate. The perforations and tube are sized such that under equilibrium feed conditions a gas pocket forms below the plate having a height less than or substantially equal to the tube length. Substantially all of the feed gas passes through the plate perforations and substantially all of the feed liquid, or liquid and solids, passes through the tube. The vessel may contain catalyst beds and/or a plurality of the distributors in series, as illustrated. <IMAGE>

Description

SPECIFICATION Distributor for a gas-liquid or gas-liquid-solid feed trpflow reactor This invention pertains to a reactor feed distributor 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.

For many processes an upflow reactor is superior to the more common downflow reactors. This is particularly 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 reference, hydrogen, ground coal and solvent are preheated and passed to a dissolver wherein the coal is substantially dissolved at a temperature in the range 750-900"F (379"482"C) and at a pressure in the range 3100-5000 psi (217 kglcm2-350 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 hydrogenation reactor operating at a temperature 25 -1505F (13.9"-83.3"C) lower than the dissolver.

Since the hydrogen is mixed with the coal slurry prior to the preheating step to avoid coking in the 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 undesirable since both result in inadequate contacting of the reactants and the slugging may also create damaging equipmentvibrations. Furthermore, 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 renown in the art, such as those disclosed in U.S.

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.

According to one aspect of the invention, there is provided a distributor for use in a gas-liquid or gasliquid-solid feed upflowvessel having feed inlet means in the lower portion of said vessel and effluent outlet means in the upper portion of said vessel, which distributor comprises:: a substantially horizontally disposable plate capable of being fixedly mounted in said vessel between said inlet means and said outlet means, the plate having a plurality of perforations therethrough and at least one downwardly extending tube which is attached to the plate and is open at both ends so as to be capable of open communication with the vessel volume below said plate and of open communication with the vessel volume above said plate, the cross-sectional area of the perforations and of the tube being such that under equilibrium feed conditions a gas pocket forms below said plate having a height less than or substantially equal to the length of the tube and such that substantially all of the gas feed to said distributor passes through said plurality of perforations and substantially all of the liquid feed to said distributor passes through said 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 greaterthan 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, liquids and solids throughout the catalyst bed. However, it may advantageously be used in non-catalytic vessels such as dissolversto ensure good contacting of the hydrogen gas with the liquids and solids to prevent coking within the vessel.

Thus in accordance with another aspect of the invention, there is provided a gas-liquid or gasliquid-solid feed vertically disposed upflow vessel having feed inlet means in the lower portion of the vessel and effluent outlet means in the upper portion of the vessel and having mounted in said vessel between said inlet means and said outlet means at least one distributor comprising a substantially horizontally disposed plate having a plurality of perforations therethrough and at least one downwardly extending open-ended tube attached to the plate which is in open communication with the vessel volume below said plate and in open communication with the vessel volume above saidplate, the crosssectional area of the perforations and of the tube being such that under equilibrium feed conditions a gas pocket forms below said plate having a height less than or substantially equal to the length of the tube and such that substantially all of the gas feed to said distributor passes through said plurality of perforations and substantially all of the liquid feed to said distributor passes through said tube.

Preferably, means are also provided for preventing 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 reactors, 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.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: FIG. 1 depicts an upflow fixed bed catalytic reactor having a single distributor; and FIG. 2 depicts an upflow fixed bed catalytic reactor having multiple distributors and adapted for the injection of gas between distributors.

Referring to FIG. 1 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 particulate catalyst 40 is maintained in the vessel between a lower support grid 50, attached to the inner wall of vessel 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 innerwall 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 conventional 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 conventionally 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 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 require a cap to prevent substantial gas from entering the tube.

In operation a mixed phase feed stream, preferably 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 introduced into the bottom of vessel 10 through inlet port 20.

In accordance with the invention, the distributor 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 belowthe 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 pius the static pressbre 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 (pi - pg)h, wherein P1 is the density of the liquid and solids stream in the tube and pg is the gas density.

Preferably the distributor is designed with a minimum value for h of approximately 5-10 centimeters. More preferably, h should be set atapprox- imately 10-20 centimeters and a design tube length selected of approximately 20 centimeters. These values will allow for substantial 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, preferably with the catalyst in the tube at substantially the same level as the rest of the catalyst bed. Also, the gas pocket can contain aportion of the catalyst, if desired.

Claims

1. A distributor for use in a gas-liquid or gasliquid-solid feed upflow vessel having feed inlet means in the lower portion of said vessel and effluent outlet means in the upper portion of said vessel, which distributor comprises: a substantially horizontally disposable plate capable of being fixedly mounted in said vessel between said inlet means and said outlet means, the plate having a plurality of perforations therethrough and at least one downwardly extending tube which is attached to the plate and is open at both ends so as to be capable of open communication with the vessel volume below said plate and of open communication with the vessel volume above said plate, the cross-sectional area of the perforations and of the tube being such that under equilibrium feed conditions a gas pocket forms below said plate having a height less than or substantially equal to the length of the tube and such that substantially all of the gas feed to said distributor passes through said plurality of perforations and substantially all of the liquid feed to said distributor passes through said tube.

2. A distributor as claimed in Claim 1 and further comprising means for preventing the direct vertical passage of feed gas bubbles into the lower open end of said one downwardly extending tube.

3. A distributor as claimed in Claim 1 or 2, wherein said perforations are distributed evenly over the total area of the plate with from 20 to 250 perforations per square metre.

4. A distributor as claimed in Claim 1, 2 or 3, wherein said one downwardly extending openended tube is axially positioned with respect to the plate.

5. A distributor for use in a gas-liquid or gasliquid-solid feed upflow reaction vessel, substantially as hereinbefore described with reference to, and as shown in, Figure 1 or 2 of the accompanying drawings.

6. A gas-liquid or gas-liquid-solid feed vertically disposed upflow vessel having feed inlet means in the lower portion of the vessel and effluent outlet means in the upper portion of the vessel and having mounted in said vessel between said inlet means and said outlet means at least one distributor comprising a substantially horizontally disposed plate having a plurality of perforations therethrough and at least one downwardly extending open-ended tube attached to the plate which is in open communication with the vessel volume below said plate and in open communication with the vessel volume above said plate, the cross-sectional area of the perforations and of the tube being such that under equilibrium feed conditions a gas pocket forms below said plate having a height less than or substantially equal to the length of the tube and such that substantially all of the gas feed to said distributor passes through said plurality of perforations and substantially all of the liquid feed to said distributor passes through said tube.

7. An upflow vessel as claimed in Claim 6, wherein said vessel further comprises a particulate bed of solids disposed below the effluent outlet means and above said one distributor plate.

8. An upflowvessel as claimed in Claim 6 or7 and further comprising means for preventing the direct vertical passage of feed gas bubbles into the lower open end of said one downwardly extending tube.

9. An upflow vessel as claimed in Claim 6,7 or 8, comprising a plurality of said distributors spaced vertically apart within said vessel.

10. An upflow vessel as claimed in Claim 6,7, 8 or 9, and further comprising means for introducing gas into the, or at least one of the, said gas pocket(s).

11. An upflow vessel as claimed in Claim 6,7, 8, 9 or 10, and further comprising means for withdrawing gas from the, or at least one of the, said gas pocket(s).

12. An upflow vessel as claimed in any one of Claims 6 to 11, wherein the or each distributor has a plate having said perforations distributed evenly over the total area of the plate with from 20 to 250 perforations per square metre, and the plate extends over the full cross-sectional area of the vessel.

13. An upflow vessel as claimed in any one of Claims 6 to 12, wherein said one downwardly extending open-ended tube of the or each distributor is axially positioned with respect to the plate and the vessel.

14. An upflow vessel as claimed in any one of Claims 6 to 13, wherein the or each distributor is fixedly attached to the inner wall of the vessel.

15. An upflowvessel substantially as hereinbefore described with reference to, and as shown in, Figure 1 or2 of the accompanying drawings.