METHOD FOR MAINTENANCE OF THE REACTOR

Field of the disclosure The disclosure relates generally to a reactor of a hydrocarbon processing plant e.g. a petroleum refinery. More particularly, the disclosure relates to a tubular riser for a reactor. Furthermore, the disclosure relates to a grid plate assembly for a reactor. Furthermore, the disclosure relates to a method for maintenance of a reactor.

Background A catalytic hydroconversion process can be used to convert heavy hydrocarbon feedstock or coal to lighter products. For example, US4400263 describes an exemplifying ebullating bed reactor that is employed in the Fl-Coal process, US4526676 describes an exemplifying ebullating bed reactor that is employed in the H-Oil process for hydrotreating of residuum, and US4886644 describes an exemplifying ebullating bed reactor that is employed in the LC-fining process for hydrotreating of residuum. An exemplifying ebullating bed reactor for upgrading heavy oil feedstock employing colloidal or molecular catalyst is described in US7449103.

An ebullating bed reactor of the kind mentioned above comprises typically a reactor vessel that contains a grid plate dividing the reactor into two zones, a zone above the grid plate and a zone below the grid plate. The reactor comprises a plurality of tubular risers extending through the grid plate to transmit hydrogen gas and hydrocarbon feedstock from the zone below the grid plate to the zone above the grid plate. Typically, the tubular risers are welded to the grid plate. Each tubular riser has a portion above the grid plate and another portion below the grid plate. Each tubular riser has an open bottom end for ingress of the hydrogen gas and hydrocarbon feedstock, whereas the top of each tubular riser is provided with a bubble cap for distributing the flow of the hydrogen gas and hydrocarbon feedstock to the portion above the grid plate in a desired way. Each tubular riser comprises a mechanical check valve for allowing the hydrogen gas and hydrocarbon feedstock to flow from the above-mentioned zone below the grid plate to the zone above the grid plate and for preventing the hydrogen gas and hydrocarbon feedstock from flowing in an opposite direction from the zone above the grid plate to the zone below the grid plate.

The above-mentioned mechanical check valve comprises a ball or another suitable piece located above a seat. The diameter of an orifice in the seat is less than the diameter of the ball. The ball is unobstructed to move within the tubular riser vertically from the seat. When there is a flow from the zone below the grid plate to the zone above the grid plate, the flow rises the ball and the mechanical check valve is open. Pressure in an opposite direction pushes the ball against the rim of the orifice of the seat and thereby the mechanical check valve is closed.

A challenge related to a tubular riser of the kind described above is that the ball of the mechanical check valve is moving and repeatedly hits against inner walls of the tubular riser, against the rim of the orifice of the seat, and against other structures inside the tubular riser. The ball may for example whirl along the inner walls of the tubular riser and/or oscillate back and forth in the axial and/or radial directions of the tubular riser. This wears the surfaces which are in mechanical contacts with the ball. Furthermore, the ball wears too. The wear of the surfaces of the tubular riser shortens the lifetime of the tubular riser and thus there is a need to replace the tubular riser with a new one after a certain operation time has elapsed. An ebullating bed reactor may comprise hundreds of tubular risers, e.g. from 500 to 900 tubular risers. Therefore, it is very laborious and time consuming to replace the tubular risers with new ones. For example, a downtime needed for maintenance can be long because of a long time needed for replacing worn tubular risers with new ones.

Summary

The following presents a simplified summary in order to provide a basic understanding of some embodiments of the invention. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention. In accordance with the invention, there is provided a new tubular riser for a reactor of a hydrocarbon processing plant, e.g. a petroleum refinery. The reactor can be for example a reactor for the LC-fining process, the H-Oil process, the H-Coal process, the T-Star process, or some other hydroconversion process for converting heavy hydrocarbon feedstock or coal to lighter products.

A tubular riser according to the invention comprises:

- a lower section for being attached to a grid plate of the reactor and for conducting feed upwardly, and

- an upper section having one or more outlet openings for conducting the feed out from the tubular riser, the upper section comprising a mechanical check valve for allowing the feed to flow from the lower section to the upper section and for preventing the feed from flowing in the opposite direction from the upper section to the lower section.

The above-mentioned upper section and the lower section comprise a joint, e.g. a threaded joint, for attaching the upper section to the lower section so that the upper section is detachable from the lower section without a need for deformation of material of the lower section.

As the upper section and the lower section of the above-described tubular riser are separate pieces of material that are attached to each other with the above- mentioned joint, there is no need to change the whole tubular riser but only the upper section which comprises the mechanical check valve. The upper section can be changed during e.g. a maintenance stoppage of the reactor without need to detach the lower section from the grid plate of the reactor. Thus, the downtime needed for maintenance is reduced compared to a case where the whole tubular risers need to be changed. Furthermore, as the upper sections are straightforward to change, the above-described tubular riser facilitates testing different upper sections for finding out an advantageous design of the upper section.

In accordance with the invention, there is provided also a new grid plate assembly for a reactor of a hydrocarbon processing plant. A grid plate assembly according to the invention comprises: - a grid plate for dividing the reactor into a zone above the grid plate and a zone below the grid plate, and

- a plurality of tubular risers according to the invention and extending through apertures of the grid plate so that an upper section of each of the tubular risers is above the grid plate and the lower section of each of the tubular risers is attached, e.g. welded, to the grid plate.

In accordance with the invention, there is provided also a new reactor for a hydrocarbon processing plant. The reactor comprises:

- a reactor vessel, - a grid plate assembly according to the invention and arranged to divide the interior room of the reactor vessel into a zone above the grid plate and a zone below the grid plate, and

- bubble caps mechanically connected to the upper sections of the tubular risers of the grid plate assembly. In accordance with the invention, there is provided also a new method for maintenance of a reactor a hydrocarbon processing plant. The method comprises:

- detaching upper sections of one or more tubular risers of the reactor from lower sections of the one or more tubular risers without detaching the lower sections of the tubular risers from a grid plate of the reactor, and - attaching unused upper sections to the lower sections of the one or more tubular risers, wherein each of the upper sections comprises a mechanical check valve for allowing a flow from a zone of the reactor below the grid plate to a zone of the reactor above the grid plate and for preventing a flow in the opposite direction from the zone of the reactor above the grid plate to the zone of the reactor below the grid plate, and the upper sections and the lower sections comprise joints for attaching the upper sections to the lower sections so that the upper sections are detachable from the lower sections without a need for deformation of material of the lower sections. Exemplifying and non-limiting embodiments of the invention are described in accompanied dependent claims.

Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying embodiments when read in connection with the accompanying drawings.

The verbs“to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in the accompanied dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of“a” or“an”, i.e. a singular form, throughout this document does as such not exclude a plurality.

Brief description of the figures Exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater details below in the sense of examples and with reference to the accompanying drawings, in which: figure 1 illustrates a reactor that comprises tubular risers according to an exemplifying and non-limiting embodiment, figures 2a, 2b, 2c, 2d, and 2e illustrate a tubular riser according to an exemplifying and non-limiting embodiment, figures 3a and 3b illustrate details of a tubular riser according to another exemplifying and non-limiting embodiment, figures 4a, 4b, and 4c illustrate modifying a tubular riser according to the prior art to be a lower section of a tubular riser of the kind illustrated in figures 2a-2e, figure 5 illustrates a detail of a tubular riser according to an exemplifying and non limiting embodiment, and figure 6 shows a flowchart of a method according to an exemplifying and non-limiting embodiment for maintenance of a reactor a hydrocarbon processing plant.

Description of exemplifying embodiments

The specific examples provided in the description below should not be construed as limiting the scope and/or the applicability of the accompanied claims. Lists and groups of examples provided in the description are not exhaustive unless otherwise explicitly stated.

Figure 1 shows a schematic section view of a reactor that comprises tubular risers according to an exemplifying and non-limiting embodiment. The section plane is parallel with the xz-plane of a coordinate system 199. One of the tubular risers is denoted with a reference 121 . The reactor comprises a reactor vessel 124 that contains a grid plate 122 dividing the reactor into two zones: a zone 125 above the grid plate 122 and a zone 126 below the grid plate 122. Feed 133 is supplied to the zone 126 below the grid plate. The reactor may comprise a feed distributor through which the incoming feed is distributed to the zone 126 in a desired way. The feed distributor is not shown in figure 1 . The feed 133 may comprise for example hydrogen gas and hydrocarbon feedstock.

The tubular risers of the reactor are arranged to extend through the grid plate 122 as illustrated in figure 1 . Typically, the tubular risers are welded to the grid plate 122. The tubular risers and the grid plate 122 constitute a grid plate assembly 123 that transmits the feed from the zone 126 below the grid plate to the zone 125 above the grid plate. Each tubular riser has an open bottom end for ingress of the feed, whereas the top of each tubular riser is provided with a bubble cap for distributing the flow of the feed to the zone 125 in a desired way. In figure 1 , the bubble cap connected to the tubular riser 121 is denoted with a reference 127. Each tubular riser comprises a mechanical check valve for allowing a flow from the above- mentioned zone 126 below the grid plate 122 to the zone 125 above the grid plate and for preventing a flow in the opposite direction from the zone 125 above the grid plate to the zone 126 below the grid plate. The feed flows through the tubular risers into a catalyst bed maintained in the zone 125 above the grid plate 122. The catalyst may comprise for example a hydrogenating component on a porous refractory, inorganic oxide support. The grid plate assembly 123 prevents the catalyst and other materials from falling into the zone 126 below the grid plate 122. An ebullating pump 137 circulates oil from a recycle pan 138 through a downcomer 128 and the tubular risers. The rate is sufficient to lift and expand the catalyst bed from its initial settled level to its steady state expanded level. The product stream 135 of hydrotreated oil and hydrogen-rich reactor tail gases is withdrawn from the reactor through a product line 134. The reactor comprises a feed line 129 for feeding fresh catalyst into the zone 125 above the grid plate 122 and a discharge line 131 for removing spent catalyst 132 from the bottom area of the zone 125. The spent catalyst typically contains deposits of metal, such as nickel and vanadium, which have been removed from the influent feed during hydrotreating.

Figure 2a shows a section view of the tubular riser 121 . The section plane is parallel with the xz-plane of a coordinate system 299. The flow through the tubular riser 121 is illustrated with arrow headed curved lines. The mechanical check valve of the tubular riser 121 comprises a ball 203 and a seat 204. The diameter of an orifice in the seat 204 is less than the diameter of the ball 203. The 203 ball is unobstructed to move within the tubular riser vertically from the seat. When there is an upwards directed flow in the tubular riser 121 , the flow rises the ball 203 and the mechanical check valve is open as shown in figure 2a. Pressure in the opposite direction pushes the ball 203 against the rim of the orifice of the seat 204 and thereby the mechanical check valve is closed. The bubble cap 127 is seated upon the tubular riser in an umbrella-like manner for distributing the flow in a desired way. The bubble cap 127 is attached with a bolt 215 to the top of the tubular riser 121 . The fastening arrangement of the bubble cap 127 comprises advantageously mechanical locking for preventing unintentional rotation of the bolt 215. The mechanical locking may comprise for example a washer having a bendable portion being against a side surface of the head of the bolt 215 and a collet for encaging with a slot in the bubble cap 127 and a slot in the top of the tubular riser 121 . The mechanical locking is not shown in figure 2a.

Figures 2b and 2c illustrate the tubular riser 121 in more details. Figures 2b and 2c show section views where the section plane is parallel with the xz-plane of the coordinate system 299. Figure 2e shows a magnification of a part of figure 2c. Figure 2d shows a cross-section taken along a line A-A shown in figure 2b. The section plane related to figure 2d is parallel with the xy-plane of the coordinate system 299. The tubular riser comprises a lower section 201 attached to the grid plate of the reactor and for conducting the feed upwardly, and an upper section 202 having outlet openings for conducting the feed out from the tubular riser. One of the outlet openings is denoted with a reference 214. The upper section 202 comprises the mechanical check valve constituted by the ball 203 and the seat 204. The upper section 202 and the lower section 201 comprise a joint 205 for attaching the upper section 202 to the lower section 201 so that the upper section 202 is detachable from the lower section 201 without a need for material deformation in the lower section 201 . In this exemplifying case, the joint 205 is a threaded joint. The lower section 201 comprises an end part 212 that constitutes one side of the threaded joint 205 and a body part 213 that is welded to the end part 212. It is also possible that the lower section 201 is made of a single piece of material.

In the exemplifying tubular riser illustrated in figures 2a-2e, the joint 205 comprises a mechanical locking for preventing the upper section 202 from rotating with respect to the lower section 201 so that the upper section is detached from lower section. In figure 2e, the mechanical locking is denoted with a reference 206. As illustrated in figures 2c and 2e, the upper end of the lower section 201 is inside the lower end 208 of the upper section 202 when the lower and upper sections are attached to each other. Edge portions 209 of the lower end of the upper section 202 are bent against locking surfaces of the lower section 201 . The bending of the edge portions is depicted with arrows in figure 2e. The locking surfaces of the lower section 201 are shaped to deviate from a circular cross-sectional shape to prevent the upper section 202 from rotating with respect to the lower section 201 when the edge portions of the lower end of the upper section are bent against the locking surfaces of the lower section. The locking surfaces of the lower section are illustrated in figure 2d where two of the locking surfaces are denoted with a reference 210. In this exemplifying case, the locking surfaces are bevels which deviate from a circular cross-sectional shape. It is also possible that the locking surfaces define axially directed grooves into which the edge portions of the lower end of the upper section are bent. In the exemplifying tubular riser illustrated in figures 2a-2e, the edge portion of the lower end of the upper section 202 comprises axial slits defining axially directed collets between the axial slits. The axial slits make it easier to bend the edge portions against the locking surfaces of the lower section. In figure 2b, one of the axially directed collets is denoted with a reference 21 1 .

Figures 3a and 3b illustrate details of a tubular riser according to another exemplifying and non-limiting embodiment. The tubular riser comprises a lower section 301 and an upper section 302. The upper section 302 and the lower section 301 comprise a joint 305 for attaching the upper section 302 to the lower section

301 so that the upper section 302 is detachable from the lower section 301 without a need for material deformation in the lower section 301 . In this exemplifying case, the joint 305 comprises radially extending projections 316 on the lower section 301 and L-shaped grooves 317 on the upper section 302. The upper section 302 can be attached to the lower section 301 by axially moving the upper section 302 in the direction defined by an arrow 350 shown in figure 3a, and subsequently rotating the upper section 302 with respect to the lower section 301 according to an arrow 351 shown in figure 3a.

The joint 305 comprises a mechanical locking 306 for preventing the upper section

302 from rotating with respect to the lower section 301 so that the upper section is detached from lower section. In this exemplifying case, the mechanical locking is implemented with a lock washer 318 that is between axially facing surfaces of the lower and upper sections and has bendable portions for locking to locking surfaces of the lower and upper sections. The locking surfaces of the lower section 301 are denoted with a reference 319 in figure 3a, and one of the locking surfaces of the upper section 302 is denoted with a reference 320 in figure 3b. The locking surfaces of the lower and upper sections 301 and 302 are shaped to deviate from a circular cross-sectional shape to prevent the upper section 302 from rotating with respect to the lower section 301 when the bendable portions of the lock washer 318 are bent against the locking surfaces as illustrated in figure 3b.

Figures 4a, 4b, and 4c illustrate how a tubular riser 421 according to the prior art can be modified to be a lower section 401 of a tubular riser such as illustrated in figures 2a-2e. First, the tubular riser 421 is cut along a line 440 shown in figure 4a. Thereafter, an end-part 412 is attached, e.g. welded, to the body part of the cut tubular riser to form one half of a threaded joint of a tubular riser of the kind illustrated in figures 2a-2e. An upper section such as the upper section 202 illustrated in figures 2b-2e can be attached to the lower section 401 shown in figure 4c.

Figure 5 illustrates a detail of a tubular riser according to an exemplifying and non limiting embodiment. The tubular riser comprises a lower section 501 for being attached to a grid plate of a reactor and for conducting feed upwardly i.e. in the positive z-direction of a coordinate system 599. The tubular riser comprises an upper section 502 having outlet openings for conducting the feed out from the tubular riser. In figure 5, one of the outlet openings is denoted with a reference 514. The upper section 502 comprises a mechanical check valve for allowing the feed to flow from the lower section to the upper section and for preventing the feed from flowing in the opposite direction from the upper section to the lower section. The mechanical check valve is not shown in figure 5 but it can be e.g. such as the mechanical check valve shown in figures 2b and 2c. The upper section 502 and the lower section 501 comprise a joint 505 for attaching the upper section to the lower section so that the upper section is detachable from the lower section without a need for deformation of material of the lower section. The joint 505 comprises a mechanical locking 506 for preventing the upper section 502 from rotating with respect to the lower section 501 so that the upper section is detached from lower section. In this exemplifying case, the mechanical locking is implemented with droplets 552 and 553 of weld on the seam between the upper and lower sections on the outer surface of the tubular riser. In this exemplifying case, there are two droplets of weld on opposite sides of the tubular riser. It is however also possible that there is only one droplet of weld or there are three or more droplets of weld that can be e.g. equally spaced along the circular seam line between the upper and lower sections. In this exemplifying case, the joint 505 is a threaded joint as illustrated with dashed lines in figure 5. It is however also possible that the joint 505 is a joint of some other kind, e.g. such as the joint 305 presented in figures 3a and 3b.

The exemplifying reactor illustrated in figure 1 is a LC-fining“LCF” reactor. It is to be noted that tubular risers of the kind described above as well as tubular risers according to other embodiments of the invention can be used also in other reactors such as for example H-Oil, H-Coal, and T-Star reactors.

Figure 6 shows a flowchart of a method according to an exemplifying and non limiting embodiment for maintenance of a reactor a hydrocarbon processing plant. The method comprises:

- action 601 : detaching upper sections of one or more tubular risers of the reactor from lower sections of the one or more tubular risers without detaching the lower sections of the tubular risers from a grid plate of the reactor, each upper section comprising a mechanical check valve for allowing a flow from a zone of the reactor below the grid plate to a zone of the reactor above the grid plate and for preventing a flow in the opposite direction, and the tubular risers comprising joints between the upper and lower sections so that the upper sections are detachable from the lower sections without a need for deformation of material of the lower sections, and

- action 602: attaching new, i.e. unused, upper sections to the lower sections of the one or more tubular risers.

In a method according to an exemplifying and non-limiting embodiment, the joints are threaded joints. The detaching the upper sections comprises rotating the upper sections with respect to the lower sections in a first direction and the attaching the unused upper sections comprises rotating the unused upper sections with respect to the lower sections in a second direction opposite to the first direction.

In a method according to an exemplifying and non-limiting embodiment, the joints comprise radially extending projections and L-shaped grooves. The detaching the upper sections comprises first rotating the upper sections with respect to the lower sections and then axially pulling the upper sections away from the lower sections and the attaching the unused upper sections comprises first axially moving the unused upper sections with respect to the lower sections and then rotating the unused upper sections with respect to the lower sections.

In a method according to an exemplifying and non-limiting embodiment, the detaching the upper sections comprises opening mechanical lockings which prevent the upper sections from rotating with respect to the lower sections and the attaching the unused upper sections comprises making mechanical lockings which prevent the unused upper sections from rotating with respect to the lower sections. The mechanical lockings ensure that the upper sections do not get detached from the lower sections during operation of the reactor.

In a method according to an exemplifying and non-limiting embodiment, the making the mechanical lockings comprises bending edge portions of lower ends of the unused upper sections surrounding the lower sections against locking surfaces of the lower sections, where the locking surfaces of the lower sections are shaped to deviate from a circular cross-sectional shape to prevent the unused upper sections from rotating with respect to the lower sections when the edge portions of the lower ends of the unused upper sections are bent against the locking surfaces of the lower sections.

In a method according to an exemplifying and non-limiting embodiment, the making the mechanical lockings comprises bending portions of lock washers between axially facing surfaces of the lower and unused upper sections against locking surfaces of the lower and unused upper sections, where the locking surfaces of the lower and unused upper sections are shaped to deviate from a circular cross- sectional shape to prevent the unused upper sections from rotating with respect to the lower sections when the portions of the lock washers are bent against the locking surfaces of the lower and unused upper sections.

In a method according to an exemplifying and non-limiting embodiment, the making the mechanical lockings comprises making, for each of the one or more tubular risers, at least one droplet of weld on a seam between the lower and unused upper sections on an outer surface of the tubular riser under consideration.

The specific examples provided in the description given above should not be construed as limiting. Therefore, the invention is not limited merely to the exemplifying and non-limiting embodiments described above. Lists and groups of examples provided in the description are not exhaustive unless otherwise explicitly stated.