Patent Application
20240131488
The object of the invention is a separation and stripping enclosure, in particular for effluent coming from a fluidised-bed catalytic cracking unit, comprising a debris filtration grille.
Separation and stripping enclosures are generally used in fluidised-bed catalytic cracking or FCC methods. In these enclosures, the effluent leaving the catalytic cracking reactor is separated from the particles that it contains, namely coked catalytic particles, which undergo a stripping operation before being sent to the regenerator of the FCC unit in order to be regenerated therein by combustion of the coke.
These separation and stripping enclosures, also referred to as a “disengager/stripper”, thus normally comprise at least one particle separation system and a particle stripping section located downstream of the at least one separation system with respect to the circulation of the particles inside the enclosure, generally from top to bottom. It may however happen that pieces of coke and/or of a protective cladding covering the internal face of the side wall of the separation and stripping enclosure detach and fall, then being located in the stripping section. Such pieces present in this stripping section may degrade the stripping process, particularly when the stripping section contains structured internal elements, also referred to as “linings” or “packings”, and which may be blocked by these pieces.
However, in an FCC unit, it is essential to separate as effectively as possible the hydrocarbons trapped in the coked catalyst grains. Insufficient stripping of the coked grains gives rise to an increased entrainment of cracked hydrocarbons trapped in the porous system of the catalyser to the regenerator, leading to an increase in the temperature of the regenerator. Such an increase may lead to a reduction in the output of the cracking unit, to an increase in the production of dry gases, to the need to reduce the quantity of heavy load (atmospheric residue, etc.) that can be processed in the unit, to a loss of production of expected converted products such as C3 to C4 olefins, gasoline and gasoil bases. Furthermore, overheating of the regenerator could cause metallurgical damage in extreme cases and accelerated deactivation of the catalyst. Moreover, partial blocking of the stripper restricts the cross section of passage of the catalyst and therefore the circulation flow thereof (and therefore its stripping efficacy, etc.).
When the stripper is equipped with internal elements with a more open cross section of passage than structured packings (baffles for example), the fall of large pieces of coke/debris coming from the reactor may pass through the internal elements of the stripper and enter the standpipe located at the bottom of the stripper and bringing the stripped catalyst to the regenerator. In severe cases, the quantity of debris may be such that it causes total or partial blocking of the standpipe and of the valve regulating the speed of circulation of the catalyst that it generally contains, which may lead to a stoppage of the circulation of catalyst and therefore of the FCC unit. US2005040075A1 describes a stripping device having a grille for recovery of coke debris and of refractory material located at the outlet of the stripping zone, downstream of the internal elements present in this zone. This approach does not prevent the blocking of the internal elements of the stripper located upstream of this recovery system and therefore does not avoid the problem described above.
There is therefore a need for protecting the stripping section of a separation and stripping enclosure of an FCC unit.
For this purpose, an enclosure for separating and stripping an effluent containing particles is proposed, including a side wall delimiting an internal volume having a longitudinal axis and, inside the internal volume, a particle separation section and a particle stripping section located downstream of the separation section with respect to the circulation of the particles inside the enclosure.
According to the invention, the enclosure comprises, upstream of the stripping section or of a zone of the stripping section provided with stripping elements extending across the internal cross section of the enclosure, at least one grille extending transversely to the longitudinal axis. It may include a single grille or two or more grilles. According to the invention, the projection of a single grille or of all the grilles onto a transverse plane perpendicular to the longitudinal axis covers 80 to 100% of the internal cross section of the enclosure. Thus from 80 to 100% of the cross section of the inside (measured perpendicularly to the longitudinal axis) is covered by the single grille or by the superimposition of all the grilles.
The grille or grilles will make it possible to retain some of the pieces of coke and/or of cladding coming from the upper part of the enclosure and prevent them from entering the stripping section, thus reducing the risks of disturbance of the stripping operation.
The projection of the grille or grilles may extend across the whole of the internal cross section of the enclosure. This may however be difficult to achieve when the space available is small, in particular because of the presence of internal equipment of the particle-separation device type, reactor, etc.
Advantageously, the projection of a single grille or of all the grilles onto a transverse plane perpendicular to the longitudinal axis will be able to cover from 80 to 100% of the surface of an internal free volume of the enclosure projected along the longitudinal axis in the plane of the single grille or in the plane of the proximal grille of the stripping section or of the zone of the stripping section provided with stripping elements (the lowest grille). This internal free volume of the enclosure is defined as a part of the internal volume of the enclosure devoid of any equipment other than a grille according to the invention and located upstream of the single grille or of the proximal grille. In other words, the grille or grilles do not then necessarily extend under the equipment present inside the enclosure along the longitudinal axis. The geometry of the grille or grilles will thus be able to depend on the geometry of the equipment present inside the enclosure, in particular in the separation section thereof.
Generally, it will be possible to provide one or more grilles, typically one or two grilles. When two grilles or more are provided, they can preferably be disposed at different positions along the longitudinal axis. When two grilles or more are provided, the projections thereof onto a transverse plane perpendicular to the longitudinal axis may overlap partly or not.
Advantageously, said at least one grille, and in particular each grille, can extend continuously over at least 300° around the longitudinal axis and the projection thereof onto a transverse plane perpendicular to the longitudinal axis may cover at least part of the internal cross section of the enclosure and extend radially over at least a part of the distance separating the longitudinal axis from the side wall of the enclosure. This can facilitate the positioning of the grille inside the enclosure, in particular when the internal volume of the enclosure is encumbered by equipment.
Advantageously, the projection of said at least one grille may cover a part of the internal cross section of the enclosure extending radially over only a part of the distance separating the longitudinal axis of the side wall of the enclosure.
This part can in particular be selected from:
It will in particular be possible to provide a grille of each type, these grilles been located at different positions along the longitudinal axis so that the projection of these two grilles covers all or a major part (80% or more) of the internal cross section of the enclosure.
The stripping section of an FCC unit in general has a part provided with stripping elements the function of which is to promote contact between the stripping fluid and the solid particles to be stripped. The stripping elements may be baffles or linings, called “packing” in English, located upstream (with respect to the direction of circulation of the particles) of the main injection system for the stripping fluid, which circulates in counterflow to the particles. The stripping elements extend across the internal cross section of the enclosure and can be distributed in several stages along the longitudinal axis of the enclosure. Examples of packings are described in the documents EP719850, U.S. Pat. Nos. 7,022,221, 7,077,997 and WO2007/094771, WO00/35575, CN1763150, EP1577368, EP1577368A1. A stripping section may comprise one or more other stripping fluid injection systems located between stages of stripping elements and/or at the entry to the stripping section, and therefore upstream of the stripping elements. The solid particles entering the stripping section thus first pass through a stripping element located furthest upstream of the stripping section with respect to the circulation of the particles.
When the zone of the stripping section provided with stripping elements has an entry face defining openings in a plane perpendicular to the longitudinal axis, said at least one grille can advantageously be formed from a plurality of intersecting walls defining meshes and the dimensions of a mesh, measured in a plane perpendicular to the longitudinal axis, can advantageously be less than the dimensions of an opening in the zone of the stripping section, measured in a plane perpendicular to the longitudinal axis. Thus, the grille allows only debris to pass the dimensions of which are less liable to block the openings of the stripping element furthest upstream.
Whatever the embodiment, said at least one grille can be formed by a plurality of intersecting walls defining meshes and these walls can extend parallel or substantially parallel to the axis of the enclosure. In this way the impact of the grille on the circulation of the stripping fluid and of the cracked hydrocarbons inside the enclosure is reduced. When the grille is located in a particle circulation zone, this arrangement also reduces the impact of the grille on the circulation of the particles and limits the erosion of the grille by them.
Whatever the embodiment, said at least one grille can be formed by a plurality of intersecting walls defining meshes and adjacent meshes can have wall portions with different heights measured parallel to the longitudinal axis. This can make it possible to limit the return of pieces of coke/debris outside the grille. Such a return may result from a bounce when they fall or vibrations of the plant, in particular when the grille extends in a horizontal plane.
At least one grille from said at least one grille may have a cone or truncated cone shape splaying from upstream to downstream with respect to the circulation of the particles. The grille is thus inclined with respect to the longitudinal axis, promoting the discharge of the debris towards the side wall of the enclosure and retention thereof. This type of grille will therefore preferably be secured to the side wall of the enclosure, in particular only thereto, the debris then accumulating between the edge of the grille and the side wall of the enclosure and leaving clear the centre of the enclosure for circulation of fluids. Thus, preferably, this type of grille will be able to extend radially from the side wall towards the longitudinal axis over a part of the distance separating the side wall from the longitudinal axis, in particular over 360° around the longitudinal axis.
The angle at the top of a grille in the form of a cone or truncated cone can be from 20° to 70°, preferably from 30° to 50°.
At least one grille from said at least one grille may be a planar grille that extends in a plane perpendicular to the longitudinal axis. This type of grille may be secured solely to the side wall or solely to at least one separation device located in the separation section.
Generally, whatever the embodiment, said at least one grille may be secured solely to the side wall of the enclosure. Alternatively, when the separation section comprises a plurality of separation devices distributed around the longitudinal axis, said at least one grille may be secured solely to at least two separation devices, or even to at least four securing devices, optionally to each of the separation devices. Furthermore, advantageously, said at least one grille may not extend beyond the separation devices radially, which can reduce the risks of vibration of the grille. In other words, the grille then extends solely between the separation devices, at a distance from the side wall.
When the separation devices are each provided with a conduit for discharging the particles to the stripping section, generally extending parallel or substantially parallel to the longitudinal axis, such as cyclones, said at least one grille may be secured solely to at least two discharge conduits, or even to at least four discharge conduits, optionally to each discharge conduit.
Depending on the position of the grille inside the enclosure and the elements present in the separation section, it may be necessary to provide orifices through the grille.
Thus, when the separation section comprises at least one separation device, said at least one grille may include at least one orifice through which said at least one separation device passes. This orifice may in particular surround the separation device at a distance from the latter corresponding to an expansion clearance. In this way the grille coming into contact with the separation device at the orifice will be avoided. In particular, when the separation device is a separation device provided with a discharge conduit to the stripping section, this conduit generally extending parallel or substantially parallel to the longitudinal axis, the orifice may have the discharge conduit passing through it. When the enclosure comprises a separation device extending along the longitudinal axis, the orifice may then be central for surrounding this separation device.
Furthermore, when the separation section comprises at least one separation device provided with a conduit for discharging the particles to the stripping section, generally extending parallel or substantially parallel to the longitudinal axis, said at least one grille may be located downstream of the discharge conduit of said at least one separation device. It may then include an orifice located under the discharge conduit of said at least one separation device in a direction parallel to the longitudinal axis. This facilitates the passage of the particles leaving these discharge conduits through the grille but especially limits the erosion and the degradation of the grille through the flow of solid particles that would pass through it in the absence of this orifice. In this case, the grille can advantageously be located just below the ends of the discharge conduit or conduits, so that the orifices are located as close as possible to the ends of these discharge conduits, but however at a distance greater than the movement of a valve secured to the end of the discharge conduit.
However, preferably, for better operation of the stripping section, said at least one grille may be located upstream of an end of the particle discharge conduit of at least one separation device of the separation section, or even upstream of the ends of the discharge conduits of all the separation devices of the separation section.
It should be noted that it will nevertheless be possible to provide a plurality of grilles, one or more of which are located upstream of an end of the particle discharge conduit of at least one separation device of the separation section, and one or more grilles located downstream of this end.
The invention thus describes the use of one or more grilles in a separation and stripping enclosure for an effluent containing particles, the grille or grilles being as previously described and positioned as previously described. The grille or grilles are able to (make it possible to) retain pieces of coke and/or cladding coming from the upper part of the enclosure and prevent them from entering the stripping section, thus reducing the risks of disturbance of the stripping operation.
The invention is now described with reference to the accompanying non-limitative drawings, wherein:
In the present description, the terms upper, lower, above, below refer to a vertical or substantially vertical direction, in the direction of gravity, corresponding to the longitudinal direction of the enclosure in its usual position of use.
Substantially horizontal, longitudinal or vertical means a direction/a plane forming an angle of no more than ±20°, or even no more than 10° or no more than 5° with a horizontal, longitudinal or vertical direction/plane.
Substantially parallel, perpendicular or at right angles means a direction/angle differing by no more than ±20°, or even no more than 10° or no more than 5° from a parallel or perpendicular direction or from a right angle.
In the usual manner, an internal cross section of the enclosure designates a cross section of the enclosure perpendicular to the longitudinal axis X.
In the conventional manner, the enclosure 10 comprises an inlet 100 for the effluent to be treated, a top outlet 101 for the separated gaseous effluent and a bottom outlet 102 for the solid particles. In the embodiments in
The enclosure 10 comprises, inside its internal volume, a separation section 13 and a stripping section 14 for the particles located downstream of the separation section with respect to the circulation of the particles inside the enclosure. This circulation of particles typically takes place from top to bottom. In the separation section 13, the solid particles are separated from the gaseous fluids contained in the effluent entering the enclosure 10. For this purpose, the separation section comprises at least one separation device, generally several. These separation devices, which may or may not be directly connected to the outlet of the catalytic cracking reactor, are essentially separators of the ballistic or centrifugation type, which impart a rotation movement to the suspension, so that the particles separate from the gas by centrifugal effect. Typically, a separation section includes two stages of separation devices of the cyclone type or a primary separation device (of the QTS or RSS type described below) and one or two stages of separation devices of the cyclone type. The invention is however not limited to a particular type of separation device.
In the example shown in
The separation device 15 is here of the QTS type (quarter turn separator) and has an inlet 150, a body 151, an outlet 152 extending parallel or substantially parallel to the longitudinal axis X above the body 151 for discharging the gaseous fluids with low residual particle content, and a lower discharge conduit 153 for discharging particles and a little gaseous fluid to the stripping section 14. This outlet 152 is connected to the inlet 161 of the separation devices 16 detailed hereinafter.
In the example shown in
Cyclones 16 are well known devices and comprise an enclosure, generally essentially cylindroconical, designed to impose a rapid rotation on the gas and on the particles that it contains introduced into the body, for example by causing the gas loaded with solid particles to enter tangentially to the circumference of the enclosure, in the vicinity of the wall. Under the effects of centrifugal force, the solid particles taken in the vortex move towards the wall, lose their speed there by friction and fall into the lower part of the apparatus, before leaving through the apex of the cone. The gas follows the wall as far as the vicinity of the apex and, once the particles have been removed, rises to the upper part to leave through a discharge conduit, which partly projects inside the enclosure.
A cyclone thus normally comprises:
In the stripping section 14, the particles emerging from the separation section 13 undergo stripping during which the hydrocarbons trapped in these particles are extracted by means of a gaseous stripping fluid, generally steam. For this purpose, a stripping section 14 normally comprises a main injection system 140 for stripping fluid disposed in the lower part of the stripping section. Other stripping-fluid injection systems can be provided upstream of the main injection system 140. Here, a secondary injection system 141 is positioned at the inlet of the stripping section 14, to implement a pre-stripping of the particles before they enter the stripping section. In addition, the stripping section 14 is usually equipped with stripping elements that can extend in one or more stages upstream of the main injection system 140. In the example shown, stripping elements of the structured packing type occupy the zone 142 of the stripping section 14. The particles circulating from top to bottom enter the zone 142 through openings 143 defined by an inlet face 144 thereof, this inlet face extending transversely to the longitudinal axis X. These openings 143 are shown schematically in
The stripping section 14 generally corresponds to the part of the enclosure 10 of reduced cross section.
In a separation and stripping enclosure 10, in particular of the type shown on
In order to avoid the accumulation of this debris in the stripping section 14, the invention makes provision for positioning, upstream of the stripping section 14 or of a zone 142 of the stripping section provided with stripping elements extending across the internal cross section of the enclosure, at least one grille 20, 21, 22, 23 extending transversely to the longitudinal axis.
The grille or grilles thus have the function of retaining the debris falling inside the enclosure 10 in order to prevent it entering the stripping section 14. They are therefore disposed rather in the separation section 13, preferably upstream of the end of a discharge conduit of one or more (or even all) of the separation devices present in the separation section. However, the grille or grilles could be placed in the stripping section, upstream of the zone 142 containing stripping elements, for example between the secondary injection system 141 and this zone 142, or even distributed over the height of the enclosure upstream of the zone 142 or of the stripping section.
Furthermore, the form and the dimensions of the grille or grilles will be selected so that the projection of a single grille (grilles 22 or 23 in
Generally, according to the invention, the grille or grilles are thus “bare” grilles that do not support functional elements or functional particles on their surface. In other words, no bed of particles or no assembly of functional elements rests on these grilles, only any pieces of coke or other debris initially attached to the side wall of the enclosure or of internal equipment of the enclosure are liable to be supported by the grille or grilles. It is therefore not necessary to provide a reinforced structure for this type of grille other than to ensure the integrity thereof when debris falls and to support the total weight of the grille and debris until the end of the cycle of the FCC unit (defined as the period between two planned maintenance stoppages). Typically, it will thus be possible to produce a grille around ten centimetres in height.
In the embodiment shown on
Another grille 21 is placed higher along the longitudinal axis X, above the inlet 100 of the enclosure. This grille 21 is in the form of a truncated cone splaying from upstream to downstream with respect to the circulation of the particles, in particular, in the example, the projection thereof onto a transverse plane perpendicular to the longitudinal axis X covers an annular peripheral part of the enclosure 10 extending radially from the side wall 11 of the enclosure towards the longitudinal axis X, here over a distance enabling the parts 152, 160 of the separation devices 15 and 16 respectively to pass, present at this point in the enclosure 10. This grille 21 is here secured solely to the side wall 11.
In the embodiment shown on
In the embodiment shown in
The grilles are now described in more detail with reference to
The top grille 21 shown in
The grille shown on
For a simpler installation, the grille is formed by a plurality of portions 35, here forming sectors 35, assembled on each other through their radial sides. This assembly can be implemented by keys, bolts, by interlocking, or any other suitable means or by a combination of these means. On
The bottom grille 20 shown on
Thus it will be understood that the form and the dimensions of the grille or grilles will be adapted according to the equipment other than grilles present inside the enclosure and in particular above the lowest grille, namely the proximal grille of the stripping section 14 or of its zone 142. In particular, the form and the dimensions of the grille or grilles will be selected so that, seen from above along the longitudinal axis, the whole of the internal cross section of the enclosure (or at least 80%) is covered by the grille or grilles. When the enclosure comprises internal equipment other than the grille or grilles, typically one or more separation devices, or even a reactor, then the form and the dimensions of the grille or grilles will be selected so that, seen from above along the longitudinal axis, the whole of the internal cross section of the enclosure (or at least 80%) is covered by the grille or grilles and the item or items of internal equipment.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2014103 | Dec 2020 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2021/052413 | 12/21/2021 | WO |
