Process and apparatus for aerodynamic separation of components of a gaseous stream

Claim 2

A process for separating liquid and/or solid particles from a gaseous stream containing said particles suspended in a gaseous medium, said process comprising: introducing the gaseous stream into a separation zone having an external wall, an internal wall and, between said walls, an array of deflecting blades and a separate array of straightening blades, said arrays each having generally rounded cross-sections, extending generally in the same direction as said axis and being spaced apart from one another in a direction transverse to said axis to define between them an intervening zone, passing the stream into said intervening zone through said deflecting blades for accelerating the stream and for inducing within the accelerating flowing stream a swirl which causes the gaseous medium to follow helico-spiral streamlines in said intervening zone, within the intervening zone, subjecting the swirling gaseous stream to acceleration, expansion and increased subsonic velocity while maintaining the resultant velocity in a major portion of the cross section of the gaseous stream substantially uniform upon those streamlines encompassed by said portion, causing said particles in the swirling gaseous stream, with the aid of said substantially uniform resultant velocity and of their inertia, to separate from the encompassed streamlines under the influence of substantially similar centrifugal forces which drive the particles outward along paths which diverge from said streamlines and cause the particles to concentrate in an outer layer of the gaseous stream, withdrawing at least part of said outer layer of the gaseous stream, with concentrated particles, from the separation zone, and causing remaining gaseous medium not so withdrawn from the gaseous stream to decelerate, while suppressing its swirling motion, by passing it through the array of straightening blades of the separation zone.

Claim 3

A process according to claim 1 wherein said arrays of deflecting and straightening blades are fixed in place in said separation zone.

Claim 4

A process according to claim 1 wherein said array of deflecting blades at least partly surrounds said array of straightening blades.

Claim 5

A process according to claim 1 wherein the particles are separated from the encompassed streamlines in the intervening zone under the influence of centrifugal forces that are substantially identical at any point within said portion of the cross section of the gaseous stream, and that drive the particles towards the outer layer of the flowing gaseous stream.

Claim 6

A process according to claim 1 wherein at least part of said outer layer is withdrawn from the gaseous stream by a stripping wall spaced inwardly from and of substantially similar shape to said external wall.

Claim 7

A process according to claim 1 wherein at least part of said outer layer is withdrawn from the gaseous stream by a stripping wall located adjacent the downstream end of the intervening zone.

Claim 8

A process according to claim 1 wherein at least part of said outer layer is withdrawn from the gaseous stream by a stripping wall located adjacent the downstream end of the array of straightening blades.

Claim 9

A process for at least partially extracting a condensable component existing at least partially in the form of condensable vapor in a gaseous stream which is composed of multiple components including said condensable component and a gaseous medium, said extraction being performed by passing the gaseous stream substantially adiabatically and substantially iso-exergetically through an aerodynamic separator, said process comprising: introducing the gaseous stream into a separation zone having an external wall, an internal wall and, between said walls, an array of deflecting blades and a separate array of straightening blades, said arrays each having generally rounded cross-sections, extending generally in the same direction as said axis and being spaced apart from one another in a direction transverse to said axis to define between them an intervening zone, passing the stream into said intervening zone through said deflecting blades for accelerating the stream substantially adiabatically and substantially isoexergetically and for inducing within the accelerating flowing stream a swirl which causes the gaseous medium to follow helico-spiral streamlines in said intervening zone, within the intervening zone, subjecting the swirling gaseous stream, substantially adiabatically and substantially iso-exergetically, to acceleration, expansion and increased subsonic velocity sufficient for causing substantial condensation of at least part of the condensable component in said intervening zone, while maintaining the resultant velocity in a major portion of the cross section of the gaseous stream substantially uniform upon those streamlines encompassed by said portion, thereby forming new particles of condensate and/or forming enlarged particles by deposition of condensate on preexisting particles in the gaseous stream, causing said particles in the swirling gaseous stream, with the aid of said substantially uniform resultant velocity and of their inertia, to separate from the encompassed streamlines under the influence of substantially similar centrifugal forces which drive the particles outward along paths which diverge from said streamlines and cause the particles to concentrate in an outer layer of the gaseous stream, substantially adiabatically and substantially isoexergetically withdrawing at least part of said outer layer of the gaseous stream, with concentrated particles, from the separation zone, and causing remaining gaseous medium and condensed and/or condensable components not so withdrawn from the gaseous stream to decelerate substantially adiabatically and substantially iso-exergetically, while suppressing their swirling motion, by passing them through the array of straightening blades of the separation zone.

Claim 10

A process for at least partially extracting a condensable component existing at least partially in the form of condensable vapor in a gaseous stream which is composed of multiple components including said condensable component and a gaseous medium, said extraction being performed by passing the gaseous stream substantially adiabatically and substantially iso-exergetically through an aerodynamic separator, said process comprising: introducing the gaseous stream into a separation zone having an external wall, an internal wall and, between said walls, an array of deflecting blades and a separate array of straightening blades, said arrays each having generally rounded cross-sections, extending generally in the same direction as said axis and being spaced apart from one another in a direction transverse to said axis to define between them an intervening zone, passing the stream into said intervening zone through said deflecting blades for accelerating the stream substantially adiabatically and substantially isoexergetically and for inducing within the accelerating flowing stream a swirl which causes the gaseous medium to follow helico-spiral streamlines in said intervening zone, within the intervening zone, subjecting the swirling gaseous stream, substantially adiabatically and substantially iso-exergetically, to acceleration, expansion and increased subsonic velocity sufficient for causing substantial condensation of at least part of the condensable component in said intervening zone, while maintaining the resultant velocity in a major portion of the cross section of the gaseous stream substantially uniform upon those streamlines encompassed by said portion, thereby forming new particles of condensate and/or forming enlarged particles by deposition of condensate on preexisting particles in the gaseous stream, causing said particles in the swirling gaseous stream, with the aid of said substantially uniform resultant velocity and of their inertia, to separate from the encompassed streamlines under the influence of substantially similar centrifugal forces which drive the particles outward along paths which diverge from said streamlines and cause the particles to concentrate in an outer layer of the gaseous stream, substantially adiabatically and substantially isoexergetically withdrawing at least part of said outer layer of the gaseous stream, with concentrated particles, from the separation zone, and causing remaining gaseous medium and condensed and/or condensable components not so withdrawn from the gaseous stream to decelerate substantially adiabatically and substantially iso-exergetically, while suppressing their swirling motion, by passing them through the array of straightening blades of the separation zone.

Claim 11

A process according to claim 8 wherein said gaseous stream is accelerated by said deflecting blades up to a velocity of at least about 80% of the maximum mach number attained by the stream in the intervening zone.

Claim 12

A process according to claim 8 wherein the swirling gaseous stream is accelerated within the intervening zone up to a subsonic velocity of at least about mach 0.6.

Claim 13

A process according to claim 8 wherein the swirling gaseous stream is accelerated within the intervening zone up to a subsonic velocity of at least about mach 0.9.

Claim 14

A process according to claim 8 wherein the swirling gaseous stream is accelerated within the intervening zone while maintaining the resultant velocity in a portion representing at least about 75 percent of the cross section of the gaseous stream substantially uniform upon those streamlines encompassed by said portion.

Claim 15

A process according to claim 8 wherein the swirling gaseous stream is accelerated within the intervening zone while maintaining the resultant velocity in a portion representing at least about 90 percent of the cross section of the gaseous stream substantially uniform upon those streamlines encompassed by said portion.

Claim 16

A process according to claim 8 wherein the swirling gaseous stream is accelerated within the intervening zone while maintaining the resultant velocity in a portion representing substantially all of the cross section of the gaseous stream substantially uniform upon those streamlines encompassed by said portion.

Claim 17

A process according to claim 8 wherein the gaseous medium is decelerated by the array of straightening blades to a velocity of about mach 0.65 or less.

Claim 18

A process according to claim 8 wherein the gaseous medium is decelerated by the array of straightening blades to a velocity of about mach 0.4 or less.

Claim 19

A process according to claim 8 wherein said arrays of deflecting and straightening blades are normally stationary during performance of said process.

Claim 20

A process according to claim 8 wherein said aerodynamic separator has means with a longitudinal axis defining a flow path for movement of said gaseous stream at subsonic velocity substantially throughout said path, said path extending generally in the direction of said axis from a position upstream in said separator through a plurality of zones to a position downstream in said separator, said gaseous stream is caused to flow substantially axially in an axially extending inlet plenum zone which is upstream of and in communication with the separation zone and in which the cross-section of said path decreases in the downstream direction for accelerating the stream substantially adiabatically and substantially iso-exergetically, the accelerated stream is introduced into the separation zone while flowing substantially axially, the array of deflecting blades of the separation zone at least partly surrounds the array of straightening blades and, after passage through the separation zone, gaseous medium decelerated by the straightening blades is introduced into an axially disposed outlet plenum zone defining a flow path cross-section which increases in the downstream direction for further decelerating the gaseous medium substantially adiabatically and substantially iso-exergetically.

Claim 21

A process according to claim 18 wherein said gaseous stream is caused to flow substantially axially at a velocity which is about mach 0.25 or less in the inlet plenum zone.

Claim 22

A process according to claim 18 wherein said gaseous stream is accelerated in said inlet plenum zone to a velocity of about mach 0.4 to about mach 0.6.

Claim 23

A process according to claim 18 wherein said gaseous stream is accelerated in said inlet plenum zone to a velocity of at least about 60% of the maximum mach number attained by the stream in the intervening zone.

Claim 24

A process according to claim 18 wherein gaseous medium decelerated by the straightening blades is further decelerated in the outlet plenum zone to a velocity which is about mach 0.25 or less.

Claim 25

A process according to claim 18 wherein said gaseous stream is caused to flow in a generally axial direction throughout the inlet plenum zone and until it enters the array of deflecting blades.

Claim 26

Aerodynamic separator apparatus for separating liquid and/or solid particles from a gaseous stream containing such particles suspended in a gaseous medium, said apparatus comprising: a separation zone having an external wall, an internal wall and, between said walls, an array of deflecting blades and a separate array of straightening blades, said arrays each having generally rounded cross-sections, extending generally in the same direction as said axis and being spaced apart from one another in a direction transverse to said axis to define between them an intervening zone, said deflecting blades being positioned for receiving the stream, for passing it into said intervening zone, for accelerating the stream and for inducing within the accelerating flowing stream a swirl which causes the gaseous medium to follow helico-spiral streamlines in said intervening zone, said intervening zone being shaped for subjecting the swirling gaseous stream to acceleration, expansion and increased subsonic velocity while maintaining the resultant velocity in a major portion of the cross section of the gaseous stream substantially uniform upon those streamlines encompassed by said portion, and for causing said particles, with the aid of said substantially uniform resultant velocity and of their inertia, to separate from the encompassed streamlines under the influence of substantially similar centrifugal forces which drive the particles outward along paths which diverge from said streamlines and cause the particles to concentrate in an outer layer of the gaseous stream, means for withdrawing at least part of said outer layer of the gaseous stream, with concentrated particles, from the separation zone, and said array of straightening blades being positioned for causing remaining gaseous medium not so withdrawn from the gaseous stream to decelerate while suppressing its swirling motion.

Claim 27

Aerodynamic separator apparatus for separating liquid and/or solid particles from a gaseous stream containing such particles suspended in a gaseous medium, said apparatus comprising: a separation zone having an external wall, an internal wall and, between said walls, an array of deflecting blades and a separate array of straightening blades, said arrays each having generally rounded cross-sections, extending generally in the same direction as said axis and being spaced apart from one another in a direction transverse to said axis to define between them an intervening zone, said deflecting blades being positioned for receiving the stream, for passing it into said intervening zone, for accelerating the stream and for inducing within the accelerating flowing stream a swirl which causes the gaseous medium to follow helico-spiral streamlines in said intervening zone, said intervening zone being shaped for subjecting the swirling gaseous stream to acceleration, expansion and increased subsonic velocity while maintaining the resultant velocity in a major portion of the cross section of the gaseous stream substantially uniform upon those streamlines encompassed by said portion, and for causing said particles, with the aid of said substantially uniform resultant velocity and of their inertia, to separate from the encompassed streamlines under the influence of substantially similar centrifugal forces which drive the particles outward along paths which diverge from said streamlines and cause the particles to concentrate in an outer layer of the gaseous stream, means for withdrawing at least part of said outer layer of the gaseous stream, with concentrated particles, from the separation zone, and said array of straightening blades being positioned for causing remaining gaseous medium not so withdrawn from the gaseous stream to decelerate while suppressing its swirling motion.

Claim 28

Apparatus according to claim 24 wherein said arrays of deflecting and straightening blades are fixed in place in said separation zone.

Claim 29

Apparatus according to claim 24 wherein said array of deflecting blades at least partly surrounds said array of straightening blades.

Claim 30

Apparatus according to claim 24 wherein said means for withdrawing at least part of said outer layer of the gaseous stream is a stripping wall spaced inwardly from and of substantially similar shape to said external wall.

Claim 31

Apparatus according to claim 24 wherein said means for withdrawing at least part of said outer layer of the gaseous stream is a stripping wall located adjacent the downstream end of the intervening zone.

Claim 32

Apparatus according to claim 24 wherein said means for withdrawing at least part of said outer layer of the gaseous stream is a stripping wall is located adjacent the downstream end of the array of straightening blades.

Claim 33

Aerodynamic separator apparatus for at least partially extracting a condensable component substantially adiabatically and substantially iso-exergetically from a gaseous stream which is composed of multiple components including said condensable component and a gaseous medium, said apparatus comprising: means with a longitudinal axis defining a flow path for movement of said gaseous stream at subsonic velocity substantially throughout said path, said path extending generally in the direction of said axis from a position upstream in said separator through a plurality of zones to a position downstream in said separator, a separation zone having an external wall, an internal wall and, between said walls, an array of deflecting blades and a separate array of straightening blades, said arrays each having generally rounded cross-sections, extending generally in the same direction as said axis and being spaced apart from one another in a direction transverse to said axis to define between them an intervening zone, said deflecting blades being positioned for receiving the stream, for passing it into said intervening zone, for accelerating the stream substantially adiabatically and substantially iso-exergetically and for inducing within the accelerating flowing stream a swirl which causes the gaseous medium to follow helico-spiral streamlines in said intervening zone, said intervening zone being shaped for subjecting the swirling gaseous stream, substantially adiabatically and substantially iso-exergetically, to acceleration, expansion and increased subsonic velocity sufficient for causing substantial condensation of at least part of the condensable component in said intervening zone, while maintaining the resultant velocity in a major portion of the cross section of the gaseous stream substantially uniform upon those streamlines encompassed by said portion, thereby forming new particles of condensate and/or forming enlarged particles by deposition of condensate on preexisting particles in the gaseous stream, and causing said particles, with the aid of said substantially uniform resultant velocity and of their inertia, to separate from the encompassed streamlines under the influence of substantially similar centrifugal forces which drive the particles outward along paths which diverge from said streamlines and cause the particles to concentrate in an outer layer of the gaseous stream, means for substantially adiabatically and substantially iso-exergetically withdrawing at least part of said outer layer of the gaseous stream, with concentrated particles, from a downstream portion of the separation zone, and said array of straightening blades being positioned for causing remaining gaseous medium and condensed and/or condensable components not so withdrawn from the gaseous stream to decelerate substantially adiabatically and substantially iso-exergetically while suppressing their swirling motion.

Claim 34

Aerodynamic separator apparatus for at least partially extracting a condensable component substantially adiabatically and substantially iso-exergetically from a gaseous stream which is composed of multiple components including said condensable component and a gaseous medium, said apparatus comprising: means with a longitudinal axis defining a flow path for movement of said gaseous stream at subsonic velocity substantially throughout said path, said path extending generally in the direction of said axis from a position upstream in said separator through a plurality of zones to a position downstream in said separator, a separation zone having an external wall, an internal wall and, between said walls, an array of deflecting blades and a separate array of straightening blades, said arrays each having generally rounded cross-sections, extending generally in the same direction as said axis and being spaced apart from one another in a direction transverse to said axis to define between them an intervening zone, said deflecting blades being positioned for receiving the stream, for passing it into said intervening zone, for accelerating the stream substantially adiabatically and substantially iso-exergetically and for inducing within the accelerating flowing stream a swirl which causes the gaseous medium to follow helico-spiral streamlines in said intervening zone, said intervening zone being shaped for subjecting the swirling gaseous stream, substantially adiabatically and substantially iso-exergetically, to acceleration, expansion and increased subsonic velocity sufficient for causing substantial condensation of at least part of the condensable component in said intervening zone, while maintaining the resultant velocity in a major portion of the cross section of the gaseous stream substantially uniform upon those streamlines encompassed by said portion, thereby forming new particles of condensate and/or forming enlarged particles by deposition of condensate on preexisting particles in the gaseous stream, and causing said particles, with the aid of said substantially uniform resultant velocity and of their inertia, to separate from the encompassed streamlines under the influence of substantially similar centrifugal forces which drive the particles outward along paths which diverge from said streamlines and cause the particles to concentrate in an outer layer of the gaseous stream, means for substantially adiabatically and substantially iso-exergetically withdrawing at least part of said outer layer of the gaseous stream, with concentrated particles, from a downstream portion of the separation zone, and said array of straightening blades being positioned for causing remaining gaseous medium and condensed and/or condensable components not so withdrawn from the gaseous stream to decelerate substantially adiabatically and substantially iso-exergetically while suppressing their swirling motion.

Claim 35

Apparatus according to claim 30 comprising means with a longitudinal axis defining a flow path for movement of said gaseous stream at subsonic velocity substantially throughout said path, said path extending generally in the direction of said axis from a position upstream in the separator through a plurality of zones to a position downstream in said separator, an axially extending inlet plenum zone which is upstream of and in communication with the separation zone and in which the cross-section of said path decreases in the downstream direction for accelerating the stream substantially adiabatically and substantially isoexergetically and for introducing this accelerated stream, while flowing substantially axially, into the separation zone, said array of deflecting blades of the separation zone at least partly surrounding the array of straightening blades, and an axially disposed outlet plenum zone, in communication with the separation zone, positioned for receiving gaseous medium decelerated by the straightening blades, and defining a flow path cross-section which increases in the downstream direction for further decelerating the gaseous medium substantially adiabatically and substantially iso-exergetically.

Claim 36

Apparatus according to claim 30 wherein said arrays of deflecting and straightening blades are mounted in such a manner that they are normally stationary during operation of said apparatus.

Claim 37

Process for at least partially extracting components existing at least partially in the form of a condensable vapor in a gaseous stream including multiple components, in which this extraction is performed adiabatically and quasi iso-exergetically in an axisymmetrical aerodynamic subsonic separator comprising an axial inlet plenum with a decreasing cross-section, an axisymmetrical separation chamber bounded by an external wall and an internal wall, and by an inlet section comprising a fixed cascade of deflecting blades and an outlet section comprising a fixed cascade of straightening blades, said separator further comprising an axial outlet plenum with an increasing cross-section, the process comprising introducing axially through the inlet plenum of the separator the gaseous stream having a low velocity, then accelerating adiabatically and quasi iso-exergetically said gaseous stream in a generally axial direction up to the inlet section of the separation chamber, then accelerating adiabatically and quasi iso-exergetically said stream through the cascade of deflecting blades, thereby inducing within the accelerating flowing stream a swirl which causes the streamlines of the gaseous medium to follow helico-spiral paths, then accelerating adiabatically and quasi isoexergetically the gaseous stream within the separation chamber up to a maximum subsonic velocity, said expanded stream containing at least particles having formed and/or increased in size as a result of vapor condensation caused by expansion of the gaseous stream and having followed as a result of their inertia paths diverging from the streamlines of the gaseous stream and having thus been caused to move towards the outer layer of the gaseous stream and to concentrate in said outer layer, then withdrawing adiabatically and quasi iso-exergetically from the main stream the outer layer of the gaseous stream containing the thus concentrated particles, by stripping off this layer from the main gaseous stream at a location situated towards the end of the separation chamber, then decelerating within the cascade of straightening blades of the separation chamber adiabatically and quasi iso-exergetically the gaseous stream and suppressing its swirl, thereby causing the velocity of the gaseous stream to regain a low value and a generally axial direction, then decelerating adiabatically and quasi iso-exergetically the main gaseous stream having left the separation chamber and entering the outlet plenum of the separator, characterized in that the high subsonic velocity resulting from the total expansion accelerating the gaseous stream is identical or quasi-identical for all streamlines within the gaseous stream, and in that the particles separating from any streamline of the gaseous stream are subject to identical or quasi-identical centrifugal forces driving them towards the outer layer of the flowing gaseous stream.

Claim 38

Process for at least partially extracting components existing at least partially in the form of a condensable vapor in a gaseous stream including multiple components, in which this extraction is performed adiabatically and quasi iso-exergetically in an axisymmetrical aerodynamic subsonic separator comprising an axial inlet plenum with a decreasing cross-section, an axisymmetrical separation chamber bounded by an external wall and an internal wall, and by an inlet section comprising a fixed cascade of deflecting blades and an outlet section comprising a fixed cascade of straightening blades, said separator further comprising an axial outlet plenum with an increasing cross-section, the process comprising introducing axially through the inlet plenum of the separator the gaseous stream having a low velocity, then accelerating adiabatically and quasi iso-exergetically said gaseous stream in a generally axial direction up to the inlet section of the separation chamber, then accelerating adiabatically and quasi iso-exergetically said stream through the cascade of deflecting blades, thereby inducing within the accelerating flowing stream a swirl which causes the streamlines of the gaseous medium to follow helico-spiral paths, then accelerating adiabatically and quasi isoexergetically the gaseous stream within the separation chamber up to a maximum subsonic velocity, said expanded stream containing at least particles having formed and/or increased in size as a result of vapor condensation caused by expansion of the gaseous stream and having followed as a result of their inertia paths diverging from the streamlines of the gaseous stream and having thus been caused to move towards the outer layer of the gaseous stream and to concentrate in said outer layer, then withdrawing adiabatically and quasi iso-exergetically from the main stream the outer layer of the gaseous stream containing the thus concentrated particles, by stripping off this layer from the main gaseous stream at a location situated towards the end of the separation chamber, then decelerating within the cascade of straightening blades of the separation chamber adiabatically and quasi iso-exergetically the gaseous stream and suppressing its swirl, thereby causing the velocity of the gaseous stream to regain a low value and a generally axial direction, then decelerating adiabatically and quasi iso-exergetically the main gaseous stream having left the separation chamber and entering the outlet plenum of the separator, characterized in that the high subsonic velocity resulting from the total expansion accelerating the gaseous stream is identical or quasi-identical for all streamlines within the gaseous stream, and in that the particles separating from any streamline of the gaseous stream are subject to identical or quasi-identical centrifugal forces driving them towards the outer layer of the flowing gaseous stream.

Claim 39

Apparatus for at least partially extracting components existing at least partially in the form of a condensable vapor in a gaseous stream including multiple components, in which this extraction is performed adiabatically and quasi iso-exergetically in an axisymmetrical aerodynamic subsonic separator comprising an axial inlet plenum with a decreasing cross-section, an axisymmetrical separation chamber bounded by an external wall and an internal wall and an inlet section comprising a fixed cascade of deflecting blades and an outlet section comprising a fixed cascade of straightening blades and an axial outlet plenum with an increasing cross-section, these elements being formed by means including an axisymmetric outer wall having the shape of a convergent/divergent nozzle, a central inner core coaxial with the outer wall and comprising a suitably rounded upstream extending nose portion the downstream base of which is joined to the upstream base of an elongated conical portion which is located downstream from the nose portion, means binding the fixed cascade of deflecting blades and the fixed cascade of straightening blades with the inner core and with the outer wall, an inner stripping off wall coaxial with the outer wall and of which the upstream portion is located close to the downstream end of the cascade of straightening blades and having a shape similar to the shape of the surrounding outer wall, characterized in that the inlet and the outlet cross-sections of each the cascade of deflecting blades and the cascade of straightening blades are cylindrical surfaces coaxial with the outer wall and inner core.

Claim 40

Apparatus for at least partially extracting components existing at least partially in the form of a condensable vapor in a gaseous stream including multiple components, in which this extraction is performed adiabatically and quasi iso-exergetically in an axisymmetrical aerodynamic subsonic separator comprising an axial inlet plenum with a decreasing cross-section, an axisymmetrical separation chamber bounded by an external wall and an internal wall and an inlet section comprising a fixed cascade of deflecting blades and an outlet section comprising a fixed cascade of straightening blades and an axial outlet plenum with an increasing cross-section, these elements being formed by means including an axisymmetric outer wall having the shape of a convergent/divergent nozzle, a central inner core coaxial with the outer wall and comprising a suitably rounded upstream extending nose portion the downstream base of which is joined to the upstream base of an elongated conical portion which is located downstream from the nose portion, means binding the fixed cascade of deflecting blades and the fixed cascade of straightening blades with the inner core and with the outer wall, an inner stripping off wall coaxial with the outer wall and of which the upstream portion is located close to the downstream end of the cascade of straightening blades and having a shape similar to the shape of the surrounding outer wall, characterized in that the inlet and the outlet cross-sections of each the cascade of deflecting blades and the cascade of straightening blades are cylindrical surfaces coaxial with the outer wall and inner core.