GB2126494A - Fluid flow distribution system for fluidised bed reactor - Google Patents

Abstract

A flow distribution system for the plenum chamber (12) of a gas-liquid- solids fluidised bed reactor includes a downwardly directed conduit (10) and a flow distributor device such as a baffled nozzle (16) attached to the inner end of the conduit, the nozzle containing at least two parallel baffle plates for mixing and radial flow dispersion of gas-liquid materials in the lower portion of the plenum (12); the initially downward flow is then deflected generally upwardly by the curved lower head of the reactor plenum chamber and passes uniformly upwardly through a flow distribution grid (18) into the fluidised bed (20). A sparger (40) can be provided in the plenum above the flow distributor device for feeding additional gas-liquid mixture into the reactor. In an alternative embodiment, the flow distribution system includes a conical- shaped flow deflector device (46) having its base rigidly attached to the plenum lower wall and having its apex aligned with the conduit. <IMAGE>

Description

SPECIFICATION Downwardly-directed fluid flow distribution system for ebullated bed reactor This invention relates to a fluid flow distributor device and system for introducing feed and recycle fluid streams uniformly into a plenum and an ebullated catalyst bed of a reactor. It relates particularly to such a flow distribution system for handling petroleum and coal-oil slurry and gas streams in which the flow is initially directed downwardly for substantially uniform flow distribution into an ebullated catalyst bed.

Experience in operating pilottplant and commercial reactors used in H-Oil (Trade Mark) and H-Coal (Trade Mark) processes has shown that improper design of the inlet flow distribution in the reactor plenum can cause operational difficulties, such as coke formation in the plenum, flow maldistribution in the catalyst bed, localized catalyst bed slumping, and formation of coke in the bed. These problems have reduced catalyst utilization, and resulted in frequent reactor shutdowns and shortened periods of operation.

The prior art has apparently not provided an adequate solution to this flow distribution problem in fluidized bed catalytic reactors. For example, U.S. Patent No. 3,197,288 to Johanson shows a catalytic reactor configuration using simple conduits for introducing the inlet feed and recycle liquid into the reactor plenum chamber, and U.S. Patent No.

3,202,603 to Keith et al shows use of dual spargers in the lower end of a reactor. Also, U.S. Patent No. 3,540,995 to Wolk et al generally discloses operation of a coal hydrogenation process using an ebullated catalyst bed reactor in which feed and recycle liquid streams are introduced into the reactor lower end plenum below a flow distribution grid means. However, introducing such gas and liquid streams into a reactor plenum at high velocity requires more specific arrangements for the streams to achieve adequate mixing and uniform flow distribution. For this reason, improved designs of flow distributor devices to provide desirably uniform flow patterns in the reactor plenum have now been developed.

The present invention provides a fluid flow distributor device and flow distribution system for feeding hydrocarbon liquid or slurry and a gas uniformly into a plenum chamber and an ebullated catalyst bed of a reactor. The invention comprises a flow distributor device for providing uniform flow distribution of a gas/ liquid mixture into an ebullated bed of a reactor, the flow distributor device being located in a plenum of the reactor, said plenum being formed by a distribution grid and the lower end and lower walls of the reactor below the grid, the flow distributor device comprising a conduit extending into said plenum from outside the reactor with the conduit inner end being directed downwardly in the plenum, and a baffled nozzle positioned at the inner end of the conduit within the plenum and downwardly directed toward the lower walls of the reactor for recycling a hydrocarbon fluid at least partially derived from a reaction within the ebullated bed, said baffled nozzle having at least two substantially parallel baffles spaced apart from each other and rigidly attached to the inner end of said conduit, the innermost baffle consisting of a solid plate, and at least one other baffle having a central opening and located upstream of the solid plate baffle, whereby said baffled nozzle mixes a gas and a liquid material fed through said conduit into said plenum, and is arranged in combination with said distribution grid to effect a substantially uniform flow distribution of the gas/liquid mixture upwardly into said ebullated bed.

The invention also comprises a flow distribution system for providing a uniform flow distribution of a fluid material into an ebullated catalyst bed of a reactor, the distribution system comprising a plenum provided in the lower part of the reactor and formed by the lower end and side walls and also by a distribution grid located below the ebullated bed in the reactor; a conduit extending into the plenum for carrying a flowable fluid material initially downwardly into the plenum; and a flow distributor device located in the lower end of the plenum and associated in flow relationship with the conduit, whereby the distributor device mixes a gas and a liquid material fed through said conduit into said plenum and is so arranged in combination with the distribution grid to effect a substantially uniform flow distribution of the gas/liquid mixture upwardly into the ebullated bed of the reactor.

In another embodiment of the invention, the flow distribution system comprises a plenum provided in the lower part of the reactor and formed by the reactor lower end and side walls and also by a distribution grid located below the ebullated bed in the reactor; a conduit extending into said plenum for carrying a flowable fluid material initially downwardly into the plenum; and comprises a conical-shaped flow deflector device located in the lower end of the plenum, said deflector having its base rigidly attached to the plenum lower end and having its apex oriented towards the inner end of a conduit, the centre line of the conical-shaped deflector being substantially aligned with the centre line of the inner end of the conduit, whereby said conical deflector mixes a gas and a liquid material fed through said conduit into said plenum and is arranged in combination with the distribution grid to effect a substantially uniform flow distribution of the gas/liquid mixture uniformly upwardly into said ebullated bed of the reactor.

This invention is particularly useful for handling hydrocarbon feedstreams such as petroleum and coal slurries for uniform distribution together with hydrogen gas into an ebullated catalyst bed reactor, particularly when the superficial velocity in the feed conduit exceeds about 8 ft/sec (2.4 m/s). Accordingly, the term gas/liquid mixture is understood to include also gas/liquid slurry mixture containing fine particulate solids.

In the present invention, the feed stream such as a mixture of coal-derived liquid slurry and hydrogen at 650-950'F (343-510"C) temperature and 500-3000 psig (34-207 bar gauge) pressure conditions is passed through a conduit and a distributor device such as a disc-donut type baffled nozzle into a plenum located at the lower end of a reactor.

The inner end of the conduit is downwardlydirected and the plenum distributor device is positioned at the inner end of the conduit within the plenum and is also downwardly directed toward the lower wall of the reactor.

The distributor device usually contains a series of substantially parallel spaced-apart baffle plates located at an angle of 45-90" to the centre line of the conduit inner end, which device provides lateral or radially outward flow deflection within the plenum. The inlet flow distributor device for the reactor plenum of gas-liquid-solids fluidized bed reactors provides a fouling-free distributor device for dispersion of the kinetic energy in the flowing fluids fed into the plenum chamber. The distributor device prevents "jetting" of the recyle liquid and gas stream in the plenum, and disperses the liquid flow uniformly in the plenum.

Depending on the reactor operating conditions and the space available in the plenum, the flow distributor device can have various configurations. The liquid flow distributor device can consist of at least two preferably circular baffle plates located at the outlet of the recycle liquid conduit. For a central vertical nozzle location within the plenum, these baffle plates are usually equally spaced from each other. The distributor device bottom plate is solid, and deflects the inlet flow laterally to prevent direct impingement of liquid on the bottom of the plenum. The other baffle or dispersion plates in the device have central openings sized to intercept and deflect portions of the liquid flow laterally or radially outwardly into the plenum.The flow paths of these lateral streams are directed to sweep the plenum bottom to eliminate stagnation zones and provide good mixing of gas/liquid (or gas/liquid slurry) and substantially uniform flow upwardly through openings in the flow distribution grid into the ebullated bed.

The proportion of total material flowing radially outwardly from the space between each baffle plate can be varied by selecting the dimensions of the distributor device, but usually a greater percentage of the flow is emitted from the lowest space. In a typical deflector device design, about 40-45% of the inlet liquid flow is deflected by the first plate, 25-35% is deflected by the middle plate, and the remaining flow is deflected radially outwardly by the bottom innermost plate. For a nozzle configuration entering the plenum from one side and not located on the plenum centre iine, the baffle plates are oriented at an angle varying from about 0 to about 10 with the adjacent baffle to provide a uniform dispersion of the gas/liquid flow within the plenum.

For small diameter reactors having inside diameters less than about 5 feet (1.5m), it is usually more convenient to mix the feed liquid and gas streams with the reactor recycle liquid external to the reactor prior to uniformly distributing the combined mixture in the reactor plenum, utilizing the distributor device of Fig.

1 as described below. For reactors having diameters larger than about 6 ft. (1.8m), it is usually desirable to introduce the feed liquid and gas mixture into the reactor plenum through separate distributor devices. For example, a circular perforated sparger ring is usually located in the plenum upper portion and can be used to distribute the gas-liquid feed mixture uniformly across the reactor plenum. Uniform flow of small bubbles and liquid feed is produced by providing a pressure drop across the sparger and directing the mixed gas-liquid streams from the sparger downwardly to substantially dissipate the stream kinetic energy in the liquid. This kinetic energy is utilized to increase the intensity of liquid backmixing in the plenum.Pressure drops across the sparger ring openings usually range from 1-15 psi (0.069-1.034 bar) for typical heavy petroleum crude upgrading and coal liquefaction processes.

In an alternative embodiment of the invention, the flow distributor device consists of a conical-shaped deflector having its base rigidly attached to,the plenum lower wall and having its apex oriented toward and substantially aligned with the centre line of the inner end of the conduit.

This inlet flow distributor device is used upstream and in combination with the reactor distribution grid to provide an improved flow distribution system for an ebullated bed catalyst reactor. The pressure drop across the baffled nozzle distributor device at rated flow is usually 5-25% of the total pressure drop across both the distributor device and the distributor grid. Although the distribution grid can consist of a perforated plate, it preferably contains multiple vertical tubes each provided with a cap over the tube upper end. This distribution system provides improved gasliquid contacting the gas mixing in the reactor plenum, eliminates undesired direct impinge ment of the fluid streams on the distribution grid, and minimizes coke formation in the plenum and in the catalyst bed.

Reference is now made to the accompanying drawings, in which: Figure 1 is a vertical cross-sectional view of the lower portion of an ebullated bed reactor according to an embodiment of the invention; Figure 2 is a vertical cross-sectional detail view of a baffled nozzle flow distributor device which may be used in the invention; Figure 3 shows a vertical cross-sectional view of an alternative embodiment of the invention in which feed and recycle streams are introduced through separate flow devices; and Figure 4 shows another embodiment of the invention similar to Fig. 3.

The invention will be further described with reference to Fig. 1, which shows an inlet conduit 10 inserted into a plenum chamber 1 2 of a reactor 1 4. The conduit has a baffled nozzle or disc-donut type flow distributor device 1 6 oriented generally downwardly in the plenum for feeding a liquid and gas mixture into the plenum, then passing the mixture uniformly upwardly through openings 1 9 in a flow distribution grid 1 8 into an ebullated catalyst bed 20.Reactor liquid is withdrawn from above the catalyst bed downwardly through a central conduit 24 to a recycle pump (not shown), from which the liquid is recycled together with fresh liquid and gas feed through the inlet conduit 10 to the flow distributor 1 6. The plenum 1 2 preferably has a height equal to 5-10 times the inner diameter of the conduit 10, and the distribution grid 1 8 preferably has a diameter equal to 4-1 2 times the inner diameter of the conduit 10.

As shown in greater detail in Fig. 2, the flow distributor device 1 6 comprises at least one annular-shaped plate 30 having a central opening 31 located upstream of a bottom circular solid-plate 32, and all retained together by three circumferentially equallyspaced structural rods 33, which are preferably located at the baffle plate outer edges.

Usually an additional annular-shaped plate 34, having a progressively smaller central opening 35, can be located intermediate plates 30 and 32 to provide a preferred baffled nozzle configuration for further radial distribution of the flow from the conduit 10.

The greater percentage of flow should preferably be emitted from the lowest space, because of the greater distance of travel in the plenum 1 2 before reaching the distribution grid 1 8.

For a flow distributor device 1 6 having three plates, the plate dimensions are preferably selected such that about 40-45 volume percent of the fluid flow is deflected radially outwardly by the bottom baffle 32, about 25-35 volume percent is deflected outwardly by the second baffle 34, and the remaining flow is radially deflected by top plate 30. If desired, at least one flow straightening vane 36 can be centrally oriented longitudinally inside the conduit 10, so that the flow pattern reaching the distributor device 1 6 is substantially undirectional. Such a flow straightening vane is particularly useful when the angle of deflection for the flowing fluid in the conduit 10 exceed about 30 .

Fig. 3 shows an alternative configuration of the fluid flow distribution system of this invention, wherein the flow distributor device 1 6 for recycle liquid in conduit 10 is centrally located and downwardly oriented in the bottom part of the plenum chamber 1 2 below the distribution grid 18, and is located above the bottom of the reactor pleum by a distance equal to 1.0-2.0 times the inside diameter of the inlet conduit. The flow distribution grid 1 8 preferably contains multiple vertical tubes 26 having an inner diameter of 0.75-1.5 inches (1.91-3.81 cm) and which extend below the grid by a distance equal to 4-10 times the tube inner diameter. The tubes 26 extend above the grid by a distance equal to about 1.5-4 times the tube inner diameter.Above the upper end of each tube 26, a cylindricalshaped cap 28 is provided, which is spaced away from the tube and is rigidly supported from the tube by suitable structural members (not shown). The cap 28 is oriented so as to prevent entry of catalyst solid particles 22 from the ebullated bed into the tubes 26 whenever there is no upward fluid flow through the tube, such as may occur during operational upsets or occurs at process shutdown.

A circular sparger ring 40 for liquid and gas feed having uniformly spaced openings 41 on its lower side is provided above the flow distributor device 1 6 (as shown in Fig. 2) to uniformly distribute gas and liquid flow in the upper portion 1 2a of the plenum chamber.

The sparger 40 encircles the downcomer conduit 24 for recycle liquid, passing to the recycle pump and is particularly useful for large diameter reactors, such as those exceeding about 8 feet (2.4m) inside diameter. The openings 41 are sized to provide a uniform pressure drop and are located to direct the flow downwardly so as to substantially dissipate its kinetic energy and increase the backmixing action of gas and liquid in the plenum 12.

In another embodiment of the invention as shown by Fig. 4, the flow distributor device consists of a conical-shaped deflector 46 which is centrally-located within the bottom portion of the plenum 12, and has its base rigidly attached to the plenum bottom wall 49. The apex 48 of the deflector 46 is centrally aligned with the downwardly oriented end 11 of the inlet conduit 10, so that the flow from the conduit 10, aligned by flow vane 36, is deflected substantially uniformly radially outwardly against the lower walls 49 of the plenum 1 2. The conical surface of deflector 46 can be made straight, or curved outwardly at the lower end to facilitate a gradual outward deflection of the flow of the gas/liquid mixture in the plenum.Thus, the flow distributor device 46 operates similarly as for the distributor device 1 6 of Fig. 2, whereby the total flow passes radially outwardly and against the walls of the plenum. A circular sparger 40 is provided in the plenum chamber 1 2 centrally located above the flow distribution device 46, similarly as for the Fig.

3 configuration. The other components in Fig.

4 are as described for the previous embodiments.

The effectiveness of using the inlet flow distributor device configuration is illustrated by the following Examples, which should not be regarded as limiting the scope of the invention.

EXAMPLES In a coal hydrogenation plant using the H Coal (Trade-Mark) Process for coal liquefaction and having an ebullated bed catalyst reactor with 5 ft. (1.5m) inside diameter (200 tons/ day (203 t/day) Catlettsburg H-Coal Pilot Plant Reactor), the feed coal slurry and gas is mixed with the recycle ebullation liquid flow external to the reactor. The total combined stream is then distributed through a sideentering nozzle equipped with three inclined baffle plates, as generally described in the Fig. 1 embodiment of this invention. Following installation of the distributor nozzle in the plenum, coking in the reactor ebullated catalyst bed due to flow maldistribution therein is substantially eliminated.

In a commercial H-Coal (18,000 tons/day or 1 8288 t/day) Plant reactor design, an 11 ft. (3.4m) inside diameter plenum contains a side-entering nozzle equipped with three inclined baffle plates for dispersion of the recycle liquid slurry flow and a circular sparger ring for distributing the feed liquid slurry and gas. In a commercial H-Oil (Trade Mark) (35,000 bbl/day) Plant reactor design, having 10 ft. (3.0m) inside diameter, the inlet flow distribution system in the reactor plenum consists of a vertical nozzle equipped with three horizontal plates for dispersion of the recycle ebullating liquid flow, and a sparger ring for distribution of the feedstream liquid and gas.

Claims (23)

1. A flow distributor device for providing a uniform flow distribution of a gas/liquid mixture into an ebullated bed of a reactor, said flow distributor device being located in a plenum of said reactor, said plenum being formed by a distribution grid and the lower end and lower walls of said reactor below said grid, said flow distributor device comprising; (a) a conduit extending into said plenum from outside the reactor with the conduit inner end being directed downwardly in the plenum; and (b) a baffled nozzle positioned at the inner end of said conduit within said plenum and downwardly directed towards the lower walls of the reactor for recycling a hydrocarbon fluid at least partially derived from a reaction within said ebullated bed; said baffled nozzle having at least two substantially parallel baffles spaced apart from each other and rigidly attached to the inner end of said conduit, the innermost baffle consisting of a solid plate, and at least one other baffle having a central opening and located upstream of the solid plate baffle, whereby said baffled nozzle mixes a gas and a liquid material fed through said conduit into said plenum, and is arranged in combination with said distribution grid to effect a substantially uniform flow distribution of the gas/liquid mixture upwardly into said ebullated bed.

2. A flow distributor device as claimed in claim 1, wherein said conduit has at least one flow-straightening vane located upstream of said nozzle.

3. A flow distributor device as claimed in claim 1, wherein said spaced-apart baffles are oriented at an angle of 45-90" with the centre line of the inner end of said conduit.

4. A flow distributor device as claimed in any of claims 1 to 3, wherein the baffled nozzle device is centrally located on the longitudinal centre line of said plenum with the centre line of said conduit entering the plenum being at an angle of 45-90 with the vertical centre line of said plenum and reactor.

5. A flow distributor device as claimed in any of claims 1 to 4, wherein said device consists of three circular baffle plates, the upper first plate having a central opening, the intermediate second plate having a central opening smaller than that in said upper first plate, and the lower third plate being solid.

6. A flow distributor device as claimed in claim 5, wherein said upper first plate central opening has a diameter of 0.6-0.75 times the conduit inner diameter, and said intermediate plate central opening has a diameter of 0.4-0.5 times the conduit inner diameter.

7. A flow distributor device as claimed in any of claims 1 to 6, wherein said baffle plates are spaced apart by a distance equal to 0.3-0.5 times the conduit inner diameter.

8. A flow distributor device as claimed in any of claims 1 to 7, wherein the fluid pressure drop across the distributor device is 5-25% of the total fluid pressure drop across the device and said distribution grid.

9. A flow distribution system for providing a uniform flow distribution of a fluid material into an ebullated catalyst bed of a reactor, said distribution system comprising: (a) a plenum provided in the lower part of the reactor and formed by the lower end and side walls and also by a distribution grid located below the ebullated bed in the reactor; (b) a conduit extending into said plenum for carrying a flowable fluid material initially downwardly into the plenum; and (c) a flow distributor device located in the lower end of said plenum and associated in flow relationship with said conduit, whereby said distributor device mixes a gas and a liquid material fed through said conduit into said plenum and is so arranged in combination with said distribution grid to effect a substantially uniform flow distribution of the gas/liquid mixture upwardly into said ebullated bed.

10. A flow distribution system as claimed in claim 9, wherein said conduit has at least one flow-straightening vane located upstream of said flow distribution device.

11. A flow distribution system as claimed in claim 9 or 10, wherein said distribution grid comprises multiple vertical tubes each covered by a cap over the tube upper end.

1 2. A flow distribution system as claimed in any of claims 9 to 11, wherein an annulusshaped sparger is provided in said plenum below said distribution grid and above said flow distribution device.

1 3. A flow distribution system for providing a uniform flow distribution of a fluid material into an ebullated bed of a reactor, said distribution system comprising: (a) a plenum provided in the lower part of the reactor and formed by the reactor lower end and side walls and also by a distribution grid located below the ebullated bed in the reactor; (b) a conduit extending into said plenum for carrying a flowable fluid material initially downwardly into the plenum; and (c) a baffled nozzle rigidly attached to the inner end of said conduit, said baffled nozzle having at least two substantially parallel baffles spaced apart from each other, the innermost baffle consisting of a solid plate, and at least one other baffle having a central opening and located upstream of the solid plate baffle, whereby said baffled nozzle mixes a gas and a liquid material fed through said conduit into said plenum and is arranged in combination with said distribution grid, to effect a substantially uniform flow distribution of the gas/liquid mixture uniformly upwardly into said ebullated bed.

14. A flow distribution system as claimed in claim 13, wherein the spaced-apart baffles are oriented at an angle of 45-90" with the axis of the inner end of said conduit.

1 5. A flow distribution system as claimed in claim 1 3 or 14, wherein said baffled nozzle is centrally located in said plenum with the axis of said conduit entering into said plenum being at an angle of 45-90" with the vertical centre line of said plenum and reactor.

1 6. A flow distribution system as claimed in any of claims 1 3 to 15, wherein said nozzle consists of three circular baffle plates, the lower first plate having a central opening, the intermediate second plate having a central opening smaller than that in said upper first plate, and the lowest third plate being solid.

1 7. A flow distribution system as claimed in any of claims 1 3 to 16, wherein said lower first plate central opening has a diameter of 0.6-0.75 times the conduit inner diameter, and said intermediate plate central opening has a diameter of 0.4-0.5 times the conduit inner diameter.

1 8. A flow distribution system as claimed in any of claims 1 3 to 17, wherein said baffle plates are spaced apart by a distance equal to 0.3-0.5 times the conduit inner diameter.

1 9. A flow distribution system as claimed in any of claims 1 3 to 18, wherein an annulus-shaped sparger is provided in said plenum below said distribution grid and above siad baffled nozzle.

20. A flow distribution system for providing a uniform flow distribution of a fluid material into an ebullated bed of a reactor, said distribution system comprising: (a) a plenum provided in the lower part of the reactor and formed by the reactor lower end and said walls and also by a distribution grid located below the ebullated bed in the reactor; (b) a conduit extending into said plenum for carrying a flowable fluid material initially downwardly into the plenum; and (c) a conical-shaped flow deflector device located in the lower end of said plenum, said deflector having its base rigidly attached to the plenum lower end and having its apex oriented toward said inner end of said conduit and having the centre line of said deflector substantially aligned with the centre line of the inner end of said conduit, whereby said conical deflector mixes a gas and a liquid material fed through said conduit into said plenum and is arranged in combination with said distribution grid to effect a substantially uniform distribution of the gas/liquid mixture uniformly upwardly into said ebullated bed.

21. A flow distribution system as claimed in claim 20, wherein said conduit contains at least one flow-straightening vane located upstream of said flow deflector.

22. A flow distributor device substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

23. An ebullated bed reactor including a flow distributor device as claimed in any of claims 1 to 22.