GB2108003A

GB2108003A - Packed bed reactor for solids- containing feeds

Info

Publication number: GB2108003A
Application number: GB08229709A
Authority: GB
Inventors: David C Kramer
Original assignee: Chevron Research and Technology Co; Chevron Research Co
Current assignee: Chevron USA Inc
Priority date: 1981-10-29
Filing date: 1982-10-18
Publication date: 1983-05-11
Also published as: CA1182984A; GB2108003B; DE3233345A1; JPS5876137A; NL8203376A; JPH0547255B2; BE894861A

Abstract

Plugging which occurs particularly when packed bed reactors comprising predominantly particles having diameters below 1/8 inch (0.32 cm) are used to process fluid feeds containing suspended solids can be reduced by employing at least two guard beds upstream of the packed processing bed, the first guard bed extending at least 3 inches (7.62 cm) in the direction of flow and comprising predominantly particles at least 3/8 inches (0.95 cm) in diameter and the second guard bed, which is in fluid communication with the first guard bed and downstream thereof, extending at least 10 inches (25.4 cm) in the direction of flow and comprising predominantly particles having a diameter within the range from 3/16 to 5/16 inches (0.48 to 0.79 cm) and smaller than the average diameter of particles in the first bed. <IMAGE>

Description

SPECIFICATION Packed bed reactor for solids-containing feeds This invention relates to the processing of fluid feeds containing suspended solids and more particularly to processing in packed bed reactors. Packed bed reactors are employed in a number of industries for converting fluid feedstocks. The packing can be reactive material, catalytic material, or inert material and can also act as deposition sites for reactants or products.

Plugging problems can occur when packed bed reactors are used to process fluids which contain suspended solids. Plugging is manifested by an unacceptable pressure drop across the reactor causing premature shutdown, for example, the shutdown of catalytic reactors while usable catalytic activity remains.

Plugging is particularly troublesome in downflow packed bed reactors. In the hydrocarbon processing industry plugging is often encountered in downflow reactors that employ catalysts about 1/8 inch in diameter or below, e.g., 1/32 to 3/32 inches in diameter.

One technique used in the hydrocarbon processing industry is to employ one or more guard beds above active catalyst particles in order to protect the catalyst from incoming particulates in the feed.

Such guard beds have had only limited success, however. Even when multiple guard beds are used, catalytic reactors often experience unacceptable plugging, causing premature shutdown.

One guard bed configuration is described in U.S. Patent 3,562,800 wherein layers of 1/2 inch and 1/4 inch aluminum balls are used above a 1/32 inch catalyst bed. The depths of the beds are unspecified, however. Table 1 depicts several guard bed sequences which have been used for downflom packed catalyst beds in the hydrocarbon processing industry.

TABLE 1 Particle Depth Diameters Configuration (inches) (inches) Type A 6-12 1/2-3/4 spheres B 6 1-1/2 saddles 6 1/2-3/4 spheres C 12 1/4 rings 24 3/1 6 tablets 24 1/5 trilobes D 12 1/3 spheres 12 1/6 spheres E 4 1/2 saddles 3 3/4 spheres 3 1/2 spheres 3 1/4 spheres 4 1/2 saddles According to this invention, there is provided a packed bed reactor for treating a fluid feed containing suspended solids, which comprises:: (a) a first guard bed of particles in fluid communication with a feed inlet to said reactor, said first guard bed extending at least 3 inches (7.62 cm) in the direction of flow and comprising predominantly particles at least 3/8 inches (0.95 cm) in diameter; (b) a second guard bed of particles in fluid communication with said first guard bed and downstream of said first guard bed, said second guard bed extending at least 10 inches (25.4 cm) in the direction of flow and comprising predominantly particles having a diameter within the range from 3/1 6 to 5/1 6 inches (0.48 to 0.79 cm) and smaller than the average diameter of particles in said first guard bed; and (c) a packed bed of particles in fluid communication with said second guard bed and downstream of said second guard bed, said packed bed comprising predominantly particles having a diameter below 1/8 inch (0.32 cm).

In one embodiment an additional bed can be placed downstream of the second guard bed and in fluid communication therewith. This additional guard bed will comprise particles having diameters within the range of 1/1 6 and 3/1 6 inches and smaller than the average diameter of particles in the second guard bed. The third guard bed will be followed by a packed bed in fluid communication with the third guard bed and downstream of the third guard bed and comprising predominantly particles having diameters below 1/8 inch, and smaller than the average diameter of the particles in the third guard bed.

The present invention also provides a method of processing a fluid feed containing suspended solids which comprises passing the feed through the above-described packed bed reactor.

According to this invention it has been found that a packed bed of particles less than 1/8 inch in diameter can be protected from plugging by disposing guard beds upstream of the packed bed of particles and which have a graded particle size, which decreases in the direction of flow. The maximum particle size in the guard beds is typically 3/8 to 1 2 inch, however, larger particles can be used if desired. The minimum particle size is slightly above the above particle size of the principal contact particles or catalyst. In one preferred embodiment of the invention, the first guard bed comprises predominantly particles within the range from 3/8 to 1 inch (0.95 to 2.54 cm) in diameter, and said packed bed comprises predominantly particles from 1/32 to 3/32 inches (0.079 to 0.24 cm) in diameter.In another preferred embodiment, the first guard bed comprises predominantly particles within the range from 2 to 1 2 inches (1.27 to 3.81 cm) in diameter, and said packed bed comprises predominantly particles from 1/32 to 3/32 inches (0.79 to 0.24 cm) in diameter.

Particles will be described herein in terms of diameters. While spherical particles are very much preferred for use in the guard bed, the guard bed particles can be in other configurations. For non spherical particles, the diameter is defined as the smallest diameter, i.e., the smallest surface-tq-surface dimension through the center or axis of the particle, regardless of the shape of the particle.

This invention is primarily applicable in downflow packed bed systems. The packed bed can be any gravity-packed bed configuration, for example, a fixed bed, a moving bed, or a bed which permits incremental addition of fresh particles.

The feeds can be liquid-solids, gas-solids, or gas-liquid-solids, and will generally contain no more than about 0.1 weight percent particles. The most preferred application for this invention is the processing of fluids containing less than 10 ppmw of solids, which is typical of petroleum refinery streams. The optimum guard bed design will depend upon the particle size distribution in the feedstream. Typical particle distributions of interest have an average particle diameter between about 5 and 1 ,000 micrometers. Particles smaller than about 5 micrometers generally do not cause plugging problems in small concentrations. Particles above 1,000 micrometers in diameter generally are easily filtered by conventional means, prior to treatment in packed bed reactors.Particle distributions suitable for this invention are found in a variety of feed in the hydrocarbon processing industry. For example, naphthas, vacuum and atmospheric residua, vacuum gas oils, diesel and medium distillate streams, and a variety of other feedstocks, including certain solids-lean synthetic oils derived from coal, oil shale and tar sands, etc. The suspended particles in petroleum-derived streams are primarily iron sulfide particles from scaling of upstream equipment and piping, however, other particles may be present as well.

This invention employs in part the theory of impaction in packed beds which is described in Jackson et al. "Entrained Particle Collection in Packed Beds" AICHE Journal, November 1966, pages 1075-1078.

According to this invention, however, it is found that impaction alone was not adequate to describe the behavior of particles in packed beds. While impaction theory might predict substantially all particles of a certain size should be trapped within the first few inches of a particle bed, it has been discovered that in practical applications particles which have impacted become re-entrained and travel further into the bed to impact other particles. Consequently, the guard beds for trapping the particles need to be significantly deeper than would be expected from impaction theory.

It has been found that with typical feed particle size distributions, at least about 10 inches of 3/1 6 to 5/1 6 inch particles are needed in the guard bed. If the depth of the 3/16 to 5/16 inch diameter particle bed is insufficient, particles will pass through and tend to agglomerate at the interface between that bed and the adjacent bed.

In the ideal situation, a guard bed would have a continuously decreasing particle size including a region 10 inches or deeper of particles in the 3/1 6 to 5/1 6 inch diameter range. In practice, however, such continuously decreasing size is difficult to achieve. Satisfactory results can be obtained with a plurality of discrete guard beds with each bed containing particles of predominantly the same size.

Consequently, the term "bed" as used herein will include a region of particles of varying particle size within the particle size limits defined for the bed.

It is conceivable that thin intermediate beds or screens may be disposed between one or more of the guard beds. While the reactor should preferably comprise particles whose diameter decreases essentially monotonicly in the direction of flow, the thin intermediate beds may contain particles larger than those in one or more of the upstream beds. The thin intermediate beds should not, however, comprise particles smaller than downstream beds, as this will promote uneven solids capture, leading to premature pressure drop build-up.

The number of guard beds and the size of the bed particles will depend upon the characteristics of the feed. The following examples describe the cases of liquid-solid, gas-solid, and gas-liquid-solid feeds. The examples will illustrate the use of inert guard bed particles above catalyst beds, however, it should be understood that the guard bed particles may themselves contain active catalyst materials such as transition metals, etc. The guard bed particles may, in fact, be of the same composition as the main catalyst or contact particles.

The guard bed designs depicted herein are suitable for processing a wide variety of fluids under a wide variety of conditions. The designs depicted in the following examples are suitable for processing hydrocarbonaceous feedstocks at typical refinery processing conditions, for example, pressures of 0--3 500 psig and temperatures of 50-1 5000 F.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, in the following Examples, to the accompanying drawings in which: Figure 1 is a schematic representation of a packed bed reactor having two guard layers; and Figure 2 is a schematic representation of a packed bed reactor having three guard layers.

EXAMPLE 1 Liquid-Solid Feed Referring to FIG. 1 the feed enters the reactor 1 through an inlet and encounters a first guard bed 3 containing particles about 3/8 inch, preferably 3/8 to 1 inch, and most preferably about 2 inch in diameter. The first guard bed is at least about 3 inches deep and can extend up to about 1 8 inches or more in depth, e.g., 24, 36 inches, etc. The preferred depth of the first guard bed is 6 inches. The function of the first bed is to trap large particles and to stabilize the lower beds and protect them from inlet surges, etc. The second guard bed 2 contains predominantly particles in the range of 3/1 6 to 5/1 6 inches in diameter, preferably about 1/4 inch in diameter.The second guard bed is at least about 10 inches deep and can be 48 or more inches deep, preferably 12 to 48 inches, advantageously about 2 ft deep. The main catalyst bed contains cylindrical extrudate catalyst 1/32 to 3/32 inches in diameter, preferably about 1/16 inch in diameter and with a length to diameter ratio of from 2 to 10. The main catalyst bed can be any depth. Preferably the first and second beds contain spherical particles. This design is especially well suited for capturing particles with an average diameter of about 5 to 1 ,000 micrometers, preferably 25 to 250 micrometers average diameter. If most of the feed solids by weight are present as particles smaller than 50 microns in diameter, the second guard bed can be replaced by about 12 inches of 3/16 to 5/16 inch diameter spheres on top of about 12 inches of 1/16 to 3/16 inch diameter spheres.The additional 1/16 to 3/16 inch spheres should also be used where the main catalyst bed contains catalyst smaller than about 1/1 6 inch in diameter. If most of the feed solids by weight are present as particles larger than 300 microns in diameter, the first guard bed should be increased in depth.

EXAMPLE 2 Gas-Solid Feeds Again referring to FIG. 1 the first particulate bed 3 in this case should contain spheres above 3/8 inch, preferably 1/2 to 12 inches in diameter, and most preferably about 3/4 inches in diameter. The first guard bed is at least about 3 inches deep and can extend up to 1 8 or more inches, e.g., 24, 36 inches, etc. The first guard bed is preferably about 9 inches deep. The second guard bed contains predominantly particles diameter 3/1 6 to 5/1 6 inches, preferably about 1/4 inches, and should extend from about 10 inches to 48 or more inches in depth, preferably 1 2 to 48 inches, advantageously about 24 inches.The main catalyst bed is again a cylindrical extrudate catalyst 1/32 to 3/32 inches in diameter, preferably 1/16 inch in diameter and having a length to diameter ratio of 2 to 10. Again, this design is suited for capturing particles of 5 to 1 ,000 micrometers in diameter, preferably with an average particle diameter of 25 to 250 micrometers. If most particles to be captured by weight are smaller than 50 micrometers, the second guard bed can be replaced by 1 8 inches of 3/1 6 to 5/1 6 inch spheres followed by about 6 inches of 1/1 6 to 3/1 6 inch spheres. Also the first guard bed can be replaced by about 6 inches of about 1/2 inch diameter spheres. In gas phase reactors a number of flakes of sulfides from upstream equipment can be much larger than the remainder of the feed particles.When this condition is encountered or when most of the feed solids by weight are present as particles larger than 300 micrometers in diameter, the first particulate bed should contain about 12 inches of spheres of about 1 inch in diameter.

If severe plugging problems are expected, an additional bed, about 12 inches deep, of spheres 1/16 to 3/1 6 inches in diameter can be employed between the second guard bed and the main catalyst bed. The additional bed of 1/1 6 to 3/1 6 inch spheres should also be used when the main catalyst bed contains catalyst smaller than about 1/1-6 inch in diameter.

EXAMPLE 3 Gas-Liquid-Solid Feed Referring to FIG. 2, the feed to the reactor 1 encounters the first guard bed 6 which contains particles of diameter about 3/8 inches, preferably 3/8 to 1 inch, and most preferably about 1/2 inch. The depth of the first guard bed is at least about 3 inches, and can be up to 1 8, 24, 36 or more inches, preferably about 6 inches. The second guard bed 5 contains spheres predominantly 3/1 6 to 5/1 6 inches in diameter and is 10-48 or more inches in depth, preferably about 1 8 inches in depth. The third guard bed 4 contains particles of 1/16 to 3/16 inches in diameter, preferably about 1/8 inch in diameter.The third guard bed is at least about 3 inches to 1 8 or more inches in depth, preferably about 6 inches in depth. The main catalyst bed is preferably cylindrical extrudate catalyst 1/32 to 3/32 inches in diameter, preferably about 1/16 inch in diameter and having a length to diameter ratio of about 2 to 10. Again, this example is well suited for capturing particles with an average size in the range of 5 to 1,000 micrometers, preferably 25 to 250 micromers in diameter. If most of the particles to be captured by weight are smaller than about 50 micrometers in diameter, the third guard bed 4 should be increased in depth to about 12 inches and the second guard bed 5 can be reduced in diameter to about 12 inches.If most of the particles to be captured by weight are larger than about 300 micrometers, the first guard bed should be about 1 2 inches in depth. Where the main catalyst bed contains particles smaller than about 1/16 inches in diameter, the third guard bed should be at least about 12 inches deep.

The configurations described in Examples 1 through 3 are primarily suited for reactors which in the absence of the guard beds form undesirable plugs when less than 20% of their normal catalyst life would be utilized. If the reactors would operate substantially more than about 20% of their normal catalyst run life without the guard beds, then the guard bed design could be modified to reduce the depth of particles in the second packed bed, i.e., the 3/16 to 5/1 6 inch particles.

EXAMPLE 4 The following experimental results illustrate the drastically improved performance of a downflow cold model pilot plant reactor 4 inches in diameter containing 1/16 diameter extrudate catalyst. The feed was hexane containing 1/2 to 1% solids which had been collected from a fouled reactor and which comprised essentially iron sulfide particles. These particles are representative of the particles encountered in commercial practice. Hexane was chosen to approximate the density and viscosity of liquid naphtha at normal process temperature and pressure. The concentration of the feed particles was deliberately much higher than ordinarily encountered in practice in order to reduce the time of the experiment. The results are depicted in Table 2. The reactor loading is in the downward direction.

TABLE 2 Collected Pressure Length Reactor Solids Drop of Run Loading (Ibs/sq. ft) (psi) (min) 12 inches of 1/1 6 inch diameter 3.4* 10 6 cylindrical extrudate 12 inches of 1/2 inch spheres + 12 inches 2.1* 10 4 of 1/16 inch diameter cylindrical extrudate 12 inches of 1/4 inch spheres + 12 inches 7.6 0.3 16 of 1/16 inch diameter cylindrical extrudate 24 inches of 1/4 inch spheres + 12 inches 13.9 0.4 21 of 1/1 6 inch diameter cylindrical extrudate 6 inches of 1/2 inch spheres + 12 inches 22.8 1.5 43 of 1/4 inch spheres + 6 inches of 1/8 inch spheres + 12 inches of 1/1 6 inch diameter cylindrical extrudate * Most solids collected in first 2-3 inches of 1/1 6 inch catalyst bed.

It is seen that when no guard bed is used a very low solids loading was obtained, and the 10 psi pressure drop occurred after only 6 minutes of operation. With a guard bed containing only 12 inches of 1/2 inch spheres, the solid loading was also low and the 10 psi pressure drop occurred after only 4 minutes. With guard bed containing 12 or 24 inches of 1/4 inch spheres, the solids collection was significantly increased with only a very low pressure drop after much longer run times. The triple guard bed was allowed to operate to a higher solids loadings and pressure drop.

Those skilled in the art will recognize that the guard bed design depicted herein can be modified to account for differences in feed solids, etc. without departing from the scope of this invention. Such modifications are contemplated as equivalent of the embodiments particularly described herein.

Claims

1. A packed bed reactor for treating a fluid feed containing suspended solids, which comprises: (a) a first guard bed of particles in fluid communication with a feed inlet to said reactor, said first guard bed extending at least 3 inches (7.62 cm) in the direction of flow and comprising predominantly particles at least 3/8 inches (0.95 cm) in diameter; (b) a second guard bed of particles in fluid communication with said first guard bed and downstream of said first guard bed, said second guard bed extending at least 10 inches (25.4 cm) in the direction of flow and comprising predominantly particles having a diameter within the range from 3/1 6 to 5/1 6 inches (0.48 to 0.79 cm) and smaller than the average diameter of particles in said first guard bed; and (c) a packed bed of particles in fluid communication with said second guard bed and downstream of said second guard bed, said packed bed comprising predominantly particles having a diameter below 1/8 inch (0.32 cm).

2. A packed bed reactor as claimed in Claim 1, wherein said first guard bed extends from 3 to 1 8 inches (7.62 to 45.72 cm) in the direction of flow and said second guard bed extends from 12 to 48 inches (30.48 to 121.92 cm) in the direction of flow.

3. A packed bed reactor as claimed in Claim 1 or 2, wherein said first guard bed comprises predominantly particles within the range from 3/8 to 1 inch (0.95 to 2.54 cm) in diameter, and said packed bed comprises predominantly particles from 1/32 to 3/32 inches (0.079 to 0.24 cm) in diameter.

4. A packed bed reactor as claimed in Claim 3, wherein said first guard bed comprises predominantly particles about 1/2 inch (1.27 cm) in diameter and said second guard bed comprises predominantly particles about 1/4 inch (0.63 cm) in diameter.

5. A packed bed reactor as claimed in Claim 1 or 2, wherein said first guard bed comprises predominantly particles within the range from 3 to 11 inches (1.27 to 3.81 cm) in diameter, and said packed bed comprises predominantly particles from 1/32 to 3/32 inches (0.079 to 0.24 cm) in diameter.

6. A packed bed reactor as claimed in Claim 5, wherein said first guard bed comprises predominantly particles about 3/4 inch (1.90 cm) in diameter and said second guard bed comprises predominantly particles about 1/4 inch (0.63 cm) in diameter.

7. A packed bed reactor as claimed in any preceding claim, wherein said first and second guard beds comprise substantially spherical particles.

8. A packed bed reactor as claimed in any preceding claim, wherein the reactor is adapted for downflow operation.

9. A packed bed reactor as claimed in any preceding claim and further comprising a third guard bed of particles in fluid communication with said second guard bed and downstream of said second guard bed, the third guard bed comprising predominantly particles having a diameter within the range from 1/16 to 3/16 inches (0.16 to 0.48 cm) and smaller than the average diameter of particles in said second guard bed.

10. A packed bed reactor as claimed in Claim 9, wherein said third guard bed comprises substantially spherical particles.

11. A packed bed reactor as claimed in Claim 9 or 10, wherein said third guard bed extends from 3 to 18 inches (7.62 to 45.72 cm) in the direction of flow.

12. A packed bed reactor as claimed in Claim 9, 10 or 11 , wherein said first guard bed comprises predominantly particles about 1/2 inch (1.27 cm) in diameter, said second guard bed comprises predominantly particles about 1/4 inch (0.63 cm) in diameter, and said third guard bed comprises predominantly particles about 1/8 inch (0.32 cm) in diameter.

13. A packed bed reactor as claimed in any preceding claim, wherein the packed bed of particles is composed of catalyst particles.

14. A packed bed reactor as claimed in Claim 1 3, wherein the catalyst particles are cylindrically shaped.

1 5. A packed bed reactor in accordance with Claim 1, substantially as described in any one of the foregoing Examples.

1 6. A method of processing a fluid feed containing suspended solids, wherein said feed is passed through a packed bed reactor as claimed in any one of Claims 1 to 14.

17. A method according to Claim 16, wherein said fluid feed comprises gas and solids and is passed downwardly through said reactor.

1 8. A method according to Claim 16, wherein said fluid feed comprises liquids, gas and solids and is passed downwardly through said reactor.

19. A method according to Claim 1 6, 17 or 18, wherein said fluid feed contains less than 0.1% by weight solids.

20. A method according to Claim 19, wherein said feed contains less than 10 ppm by weight solids.

21. A method according to Claim 16, 17, 18, 19 or 20, wherein the solids in said feed have an average diameter in the range from 25 to 250 micrometers.

22. A method of processing a fluid feed containing suspended solids substantially as described in any one of the foregoing Examples.