MXPA97006740A - Assembly of food nozzle - Google Patents

Abstract

The present invention relates to a feed nozzle assembly for introducing gas, for example steam, and liquid, for example a heavy petroleum hydrocarbon, into a container, for example a catalytic disintegration reactor, characterized by the nozzle assembly of feeding because it comprises: (a) a nozzle body having a substantially cylindrical inner tube defining a gas conduit and an outer tube accommodated around the inner tube, wherein the inner surface of the outer tube defines an annular liquid conduit, and wherein each of the tubes has an inlet end and an opposite outlet end, b) a tip of the first nozzle fixedly coupled to the outlet end of the inner tube, having a substantially cylindrical inlet end coupled to the outlet end of the inner tube, and an opposite outlet end in the form of a dome, whose exit end in the form of a dome is provided with at least a passageway: c) a tip of the second nozzle fixedly coupled to the outer end of the outer tube, and accommodated around the tip of the first nozzle, which tip of the second nozzle has a substantially cylindrical inlet end coupled to the end of the second nozzle; outlet of the outer tube, and an opposite dome-shaped outlet end provided with at least one elongated slot having substantially parallel walls, whose dome-shaped outlet end of the tip of the second nozzle extends beyond the outlet end in the form of dome from the tip of the first boquil

Description

ASSEMBLY OF POWER SUPPLY NOZZLE DESCRIPTION OF THE INVENTION The invention relates to a feed nozzle for introducing a gas and a liquid into a container, particularly for introducing steam and hydrocarbon feed into a catalytic disintegration reactor. Many units of chemical plants and petroleum refineries use nozzles to distribute liquid and / or gas supply to the unit. In some units, the ability of the nozzle to distribute the power to the unit is very important for the productivity of the unit. For example, a catalytic disintegration unit is a reactor to disintegrate long-chain hydrocarbon molecules found in crude oil, into smaller and more valuable commercial products, such as gasoline hydrocarbons and diesel oils. Typically, vacuum distillates are introduced through the feed nozzles into a vertical upflow pipe reactor where the feed is contacted with solid particulate catalysts, REF: 25564 regenerated. The catalyst selectively aids the desirable disintegration reactions. For maximum reactor performance, it is essential that the nozzle distribute the feed in a fine spray that has uniform coverage and a narrow drop size distribution. Such spraying increases the surface area of the feed droplets and facilitates contact with the catalyst particles. The existing nozzles have difficulty, however, to achieve this desired performance. Some nozzles use very small openings or complex tip designs which easily get clogged by various impurities in the feed. The time lost and the replacement cost in the repair of such block is very disadvantageous. Existing nozzles can produce fine droplets and / or a desirable spray pattern. Accordingly, it could be advantageous to have a nozzle capable of achieving a narrow distribution of fine droplets, a thin layer of spray, and not having a tendency to block. To this end the assembly of feed nozzle for the introduction of gas, for example steam, and liquid, for example a heavy petroleum hydrocarbon, into a container, for example a catalytic disintegration reactor, according to the present invention, it comprises: (a) a nozzle body having an internal substantially cylindrical tube defining a gas conduit, and an outer tube accommodated around the inner tube, wherein the outer surface of the inner tube and the inner surface of the outer tube define a annular liquid conduit, and in "where each of the tubes has an inlet end and an opposite outlet end; (b) a first nozzle tip fixedly coupled to the outlet end of the inner tube, which has an inlet end substantially cylindrical, coupled to the outlet end of the inner tube, and an opposite exit end in the form of a dome, whose exit end in the form of a dome is provided with at least s a way of passage; (c) a second nozzle tip fixedly coupled to the outlet end of the outer tube, and accommodated around the first nozzle tip, the second nozzle tip of which has a substantially cylindrical inlet end coupled to the outlet end of the outer tube, and an outlet end in the form of an opposing dome, provided with at least one slot having substantially parallel walls, the dome-shaped exit end of the second nozzle tip extending beyond the dome-shaped exit end of the dome; the first nozzle tip. The invention will be described by way of example with detailed description with reference to the accompanying drawings, wherein: Figure 1 shows a longitudinal section of the feed nozzle assembly of the invention; Figure 2 shows a longitudinal section of the upper end of the feed nozzle assembly of the invention, drawn to a scale that is larger than the scale of Figure 1; Figure 3 shows a section along the line III-III of Figure 1; Figures 4A, 4B, and 4C show the dome-shaped outlet end of the first nozzle ("steam") in a front view, a section along the line IVB-IVB and a section along the IVC-IVC line; Figures 5A, 5B and 5C show the dome-shaped outlet end of the second nozzle ("feed") in a front view, a section along the line VB-VB and a section along the line VC-VC; Figure 6 shows a front view of a dome-shaped outlet end alternative shown in Figure 5A; Figure 7 shows a sectional view of a dome-shaped outlet end alternative of the first nozzle, as shown in Figure 4B, drawn to a different scale; Figure 8 shows a sectional view of a dome-shaped exit end alternative of the second nozzle, as shown in Figure 5B, drawn to a different scale; Figure 9 shows a partially sectional, longitudinal view of a side entry reactor configuration, drawn not to scale; Figures 10A and 10B show a known nozzle of the publication of the European patent application NO. 423, 876.

Reference is made to Figures 1, 2 and 3, which show one embodiment of the invention. The feed nozzle assembly 100 for the introduction of gas, for example steam, and liquid, for example a heavy petroleum hydrocarbon, into a container (not shown), for example a catalytic disintegration reactor comprising a body 101 of nozzle having a substantially cylindrical inner tube 105 defining a gas conduit 106 and an outer tube 115 accommodated around the inlet tube 105, wherein the outer surface of the inner tube 105 and the inner surface of the outer tube 115 define an annular conduit 116 of liquid. The inner tube 105 has an inlet end 120 and an opposite outlet end 130, and the outer tube 115 has an inlet end 125 and an opposite outlet end 135. The central longitudinal axis of the inner tube 105 is indicated by the number reference 136. The feed nozzle assembly 100 further comprises a tip 140 of the first nozzle, fixedly coupled to the outlet end 130 of the inner tube 105. The tip 140 of the nozzle has an inlet end 141 substantially cylindrical coupled to the end of exit 130 of the inner tube 105, and an exit end 142 in the form of a dome, opposite. The exit end 142 in the form of a dome is provided with at least one passageway 145. The feeding nozzle assembly 100 further comprises a tip 150 of the second nozzle fixedly coupled to the outlet end 135 of the outer tube 115 and accommodated about from tip 140 of the first nozzle. The tip 150 of the second nozzle has a substantially cylindrical inlet end 151 coupled to the outlet end 135 of the outer tube 115, and an outlet end 152 in the form of an opposing dome, provided with at least one elongated slot 155 having substantially substantial walls. cylindrical 156 (see Figure 2). The dome-shaped exit end 152 of the tip 150 of the second nozzle extends beyond the dome-shaped exit end 142 of the tip 140 of the first nozzle. The inner tube 105 and the outer tube 115 are fixedly joined by spacer pins 310. Reference is now made to Figures 4A, 4B and 4C, which show in particular embodiments, the dome-shaped exit end 142 of the tip 140. of the first nozzle ("steam"). The tip 140 of the first nozzle is provided with two rows of passageways 145. The exit end 142 in the form of a dome has a hemispherical shape or a hemielytic shape. The angle formed substantially from the center (not shown) of the dome-shaped exit end 142 through the length of a row of passageways 145, is suitably in the range of 45 ° to 120 °, and suitably 75 ° to 105 °. It will be understood that when the exit end 142 is hemispherical, the center is the spherical center, and when the exit end is hemielytic the center is the elliptical center. Reference is now made to Figures 5A, 5B and 5C, which show in particular embodiments the exit end 152 in the form of a tip dome 150 of the second nozzle ("hydrocarbon feed"). The tip 150 of the second nozzle is provided with two elongated parallel slots 155. The dome-shaped exit end 152 has a hemispherical or hemielytic shape. The angle formed substantially from the center (not shown) of the dome-shaped exit end 152 of the tip 150 of the second nozzle, through the length of the elongated groove (s) 155, is substantially contiguous with the angle formed from the center of the dome-shaped exit end 142 of the tip 140 of the first nozzle, through the length of the row or rows 145. It will be understood that when the exit end 152 is hemispherical, the center is the center spherical, and when the exit end is semi-elliptical the center is the elliptical center. The feed nozzle assembly is suitably used in a process to catalytically disintegrate a heavy petroleum hydrocarbon. In such a process, a heavy petroleum hydrocarbon is preheated, mixed with steam, and fed into a vertical catalytic disintegration reactor pipe. The heavy petroleum hydrocarbon is then contacted with a disintegration catalyst to produce light hydrocarbons and the spent catalyst is coated with a thin layer of coke. The light hydrocarbons are removed from the reactor. A portion of the spent catalyst coated with the thin layer of coke is passed to a regenerative reactor. At least a portion of the coke is then burned from the spent catalyst. This results in a regenerated catalyst. During the normal operation of the feed nozzle assembly 100 according to the present invention, the steam is passed through the substantially cylindrical inner tube 105 and the heavy hydrocarbon is fed to the inlet end 125 of the outer tube 115, and passes to through the annular conduit 116 for liquid. The steam leaving the passages 145 passes into the hydrocarbon, and results in the formation of a fine mixture of two phases of jet steam bubbles through the hydrocarbon mixture. The function of the tip 150 of the second nozzle is the passage of the mixture of steam and heavy petroleum hydrocarbon out of the feed nozzle assembly 100. The tip 150 of the second nozzle is adapted to atomize substantially uniformly the mixture of vapor and heavy petroleum hydrocarbon within a catalytic disintegration reactor (not shown). This results in a mixture of steam and heavy petroleum hydrocarbon which is passed into a catalytic disintegration reactor. The passageways 145 outside the outlet end 142 of the gas conduit 106 do not become clogged. The obstruction due to carbonization of the heavy oil feed is avoided since the flow of the heavy oil feed near the outlet end 142 of the gas conduit 106 has a cooling heat transfer function. In this way, the temperature in the passageways 142 is sufficiently low so that the contact of vapor and heavy oil results in the formation of coke or carbonization and blocking of the passageways 142. An aspect of the present invention is a nozzle assembly for feeding a heavy petroleum hydrocarbon into a vertical pipe catalytic disintegrator reactor. The body 101 of the nozzle is typically oriented horizontally, vertically, or diagonally within the vertical pipe reactor (not shown). Other orientations are possible. When oriented vertically, the body 101 of the nozzle will typically extend upwardly from the bottom or the inlet end of the reactor. When not vertical, the body 101 of the nozzle will typically project through the walls of the reactor in an orientation between vertical and horizontal. Different orientations will typically require different output designs since the ideal spray pattern depends on the orientation of the nozzle. The nozzle assembly 100 of the invention is suitable for any of these orientations, since the configuration of the elongated slots 155 of the second output end 150 can be modified to achieve the desired spray pattern. Typically with a vertically oriented nozzle body 101, the elongated slots 155 will be crescent shaped or otherwise non-linear in order to configure the spray to adapt to the conduit. In a side entry nozzle body 101, the elongated slots 155 or the substantially straight lines when viewed from the front as in Figure 5A. The tip 140 of the first nozzle as shown in Figures 4A-4C is provided with two rows of passageways 145, in other embodiments there may be only one passageway, or a row of passageways depending on the application. The tip 150 of the second nozzle as shown in Figures 5A-5B is provided with two elongated parallel grooves 155, in other embodiments only one groove may exist depending on the application. The dome-shaped exit end 142 typically has at least one passageway 145 corresponding to each elongated slot 155 at the exit end 152 of the tip 150 of the second nozzle. For example, if the tip 150 of the second nozzle having two elongated slots 155, then the tip 140 of the first nozzle will have at least two corresponding through passageways 145. A row of passageways 145 can be replaced by a groove. Typically, the passageways 145 at the tip 140 of the first nozzle will consist of at least one row of small holes which are aligned with one another corresponding to the elongated slot 155 at the tip 150 of the second nozzle. However, the tip 140 of the first nozzle may have more than one row of holes corresponding to each side groove 155 in the tip 150 of the second nozzle. The angle formed from the center of the dome-shaped outlet end 152 of the tip 150 of the second nozzle, through the length of the elongated slots 155, is preferably substantially contiguous with the angle formed from the center of the outlet end. 142 in the shape of a dome of the tip 140 of the first nozzle, across the width of the row of passageways 145. Suitably, the outer tube 115 has a diameter in the range of 0.05 to 0.25 m (2-9 inches) ), or from 0.1 to 0.25 m (4-9 inches), or from 0.12 to 0.2 m (5-7 inches). The dome-shaped exit end 152 of the tip 150 of the second nozzle, which extends beyond the dome-shaped outlet end of the tip 140 of the first nozzle, is adapted to atomize substantially uniformly mix the vapor and heavy petroleum hydrocarbon within a catalytic disintegration reactor. Suitably, the distance between the dome-shaped exit end 152 of the tip 150 of the second nozzle and the domed exit end 142 of the tip 140 of the first nozzle, is typically from about 0.006 to 0.030 m ( 0.25-1.25 inches). The tip 140 of the first nozzle is fixedly coupled to the outlet end 130 of the inner tube 105, the coupling is by any conventional means such as a threaded connection or a welded connection. Such a connection is also applicable to the tip 150 of the second nozzle, coupled to the outer tube 115. Optionally, an erosion-resistant material is used as a coating 158 (see Figure 5C) in the erosion-sensitive areas of the elongated slots. 155 and the outlet end 152 of the tip 150 of the second nozzle. Typically, such areas are the portions of the elongated slots 155 and the outlet end 152 in contact with the catalyst particles. Such particles are abrasive and in this way an erosion resistant coating prolongs the life of the outlet end. An example of such erosion resistant material is STELLITE, trade name for a series of alloys with cobalt, chromium, tungsten and molybdenum in various proportions. Reference is now made to Figure 6, which shows a front view of an alternative dome-shaped output end 150 shown in Figure 5C. In this embodiment, each elongate slot 155 is integrally connected at a point 157 along its walls, to provide structural strength. In the feed nozzle assembly as described with reference to Figures 1-6, the plane (not shown) defined by a row of passages 145, is substantially parallel to the central longitudinal axis 136 (see Figure 1) of the pipe internal 105. Also the plane (not shown) defined by an elongated slot 155 is substantially parallel to the central longitudinal axis 136 of the inner tube 105. However, there are applications, for example for vertical pipe or column reactors with currently available nozzle designs. , where the injection angle adjustment of the supply requires expensive modifications of the device. It could therefore be desirable to be able to only replace the feed nozzle, in order to adjust the feeding angle of the feed, without the need for other equipment modifications. Reference is now made to Figure 7, which shows a sectional view of an alternative dome-shaped output end 140 of the first nozzle, as shown in Figure 4B, drawn to a different scale. In the embodiment shown, the angle between the plane 146 defined by a row of passageways 145 and the central longitudinal axis 146 of the inner tube (not shown) is in the range of 3 ° to 60 °. Where the nozzle assembly is a lateral entry into the reactor, this angle will be from about 0 ° or about 3 ° to about 45 °. Where the feed nozzle assembly is a bottom or bottom entry, the angle will be greater, for example, from about 0 ° to about 60 °, or preferably from about 15 ° to about 45 °, or from about 20 ° to about 40 °. °, or from about 25 ° to about 35 °. For bottom entry configurations, the angle is typically toward the center of the vertical pipe reactor from the longitudinal axis of the steam pipe. This angle for the passageways of the tip of the first nozzle at the exit end will be substantially equal to the angle for the elongated slots at the exit end of the tip of the second nozzle.

Reference is now further made to Figure 8, which shows a sectional view of a dome-shaped exit end alternative of the second nozzle 150, as shown in Figure 5B, where the angle between the plane 156 defined by an elongated slot 155 and the central longitudinal axis 136 of the inner tube (not shown) is in the range of 3o to 60 °. Where the nozzle assembly is a side entrance into the reactor, this angle will be about 0o, or about 3o to about 45o. Where the feed nozzle assembly is an entry in the bottom, the angle will be greater, for example, from about 0 ° to about 60 °, or preferably from about 15 ° to about 45 °, or from about 20 ° to about 40 °. °, or from about 25 ° to about 35 °. For the inlet configurations in the bottom, the angle is typically towards the center of the vertical pipe reactor from the longitudinal axis of the steam duct. This angle for the elongated slots of the tip of the second nozzle, at the exit end, will be substantially equal to the angle for the passageways at the exit end of the tip of the first nozzle.

Typically, where the nozzle assembly is a lateral entry into the reactor, the angle between the central longitudinal axis of the inner tube and the central longitudinal axis of the reactor will be about 0o, or about 3o to about 45o. With reference to Figure 9, which shows a partially sectional, longitudinal view of a side entry reactor configuration. The feed nozzle assembly 100 according to the present invention is accommodated in the side wall 380 of a reactor 390, whose side wall is internally lined with a thermal insulating material 395. The feed nozzle assembly 100 comprises a housing 400. in which they are accommodated in the outer tube 115 and the inner tube 105. In the embodiment as shown, the angle between the central longitudinal axis 136 of the inner tube 105 and the central longitudinal axis 410 of the reactor 390 is 45 °, and the angle between the planes 146 and 156 defined by a row of passageways 145 and defined by an elongated slot 155, respectively and the central longitudinal axis 136 of the inner tube 105, is 30 °.

The angle between the plane 146 defined by a row of passageways 145 and the central longitudinal axis 136 of the inner tube 105 is substantially contiguous with the angle between the plane 156 defined by an elongated slot 155 and the central longitudinal axis 136 of the tube. internal 105, so that during normal operation the direction of the fluid leaving the passages 145 is directed towards the elongated groove (s) 155. The feed nozzle assembly of the present invention is suitable for the vertical pipe reactors of input power configuration in the bottom and side entrance. In the process of renovating a vertical pipe reactor of lateral inlet configuration, optionally, only the nozzle and the associated steam and the supply ducts are replaced. In the bottom entry configurations, the nozzle of the invention is particularly beneficial in economic savings. There is a very high cost associated with the renovation of a vertical pipe or column reactor entering the bottom in a vertical side inlet pipe reactor. Renovation may be non-economic if the improved performance of a side-entry reactor is displaced too much by the high renovation costs. By using the nozzle of the invention, this economic problem is overcome. A vertical pipeline inlet reactor at the bottom may remain so and still have a benefit from a vertical inlet pipeline reactor. In this embodiment of the invention, the feed and steam conduits will be raised, optionally, parallel to the wall and along the outer circumference of the interior of the vertical pipe reactor. The nozzle with angled outlets is then coupled to the respective vapcr and feed ducts. This, in effect, simulates a vertical pipe reactor with side entry, without the high cost of effectively having the lateral entrance. Reference is now made to Figures 10A and 10B, which describe a known nozzle 3 of European Patent Application Publication No. 423,876. This nozzle 3 is used in the Experiment discussed in the section of the embodiment illustrated below, comparing the operation thereof against a modality of the feed nozzle assembly of the invention. As shown in Figures 10A and 10B, the known nozzle 3 has open end conduits 7 for the hydrocarbon feed and an outer space 10 for the steam, which surrounds the conduits 7 and which is closed at its downstream end . The outer conduits 7 have multiple side entrances 8 for the passage of vapor from the outer space 10. The invention is further described in the following illustrative embodiments. The illustrative embodiments are for illustrative purposes only, and are not intended to limit the scope of the invention in any way. In the following illustrative embodiment, an experiment was conducted to compare the numerous operating factors that resulted from the operation of one embodiment of the feed nozzle assembly of the invention, as shown in Figures 1-5, with that of the known nozzle as described in European Patent Application Publication No. 423 876, as described in Figures 10A and 10B. To simplify the experiment, air and water were used instead of steam and a heavy petroleum hydrocarbon. The air was fed into the steam conduit and water was fed into the heavy oil hydrocarbon ring conduit. The feed rates, feed pressures and temperatures were substantially the same for each nozzle. Table 1 gives the results of the experiment Table 1. Results of a comparison between the known feed nozzle assembly and the feed nozzle assembly as described with reference to Figures 1-5.

Table 1 (continued). Results of a comparison between the known feed nozzle assembly and the feed nozzle assembly as described with reference to Figures 1-5.

As shown in the above results, the feed nozzle assembly of the invention performs superiorly in 8 of the 9 categories. The same experiment was performed with the feed nozzle as described with reference to Figures 7 and 8. Table 2 gives the results.

Table 2. Results of a comparison between the known feed nozzle assembly and the feed nozzle assembly as described with reference to Figures 7 and 8.

Table 2. (continued) results of a comparison between the known feed nozzle assembly and the feed nozzle assembly as described with reference to Figures 7 and 8.

As shown in the above results, the feed nozzle assembly of the invention had superior performance in 8 of the 9 categories, in addition, ejection of displaced shaft with the feed nozzle assembly of the invention is possible. The small droplet size is important since the surface is increased. A uniform spray is desirable since this results in uniform utilization of the catalyst. The spray coverage in the reactor is significant since the higher the coverage the greater the contact with the catalyst. A rapid expansion of the spray is required to get contact with more catalyst. A simple spray contact zone with the catalyst is important in order to control the contact time of the catalyst with the feed. The "operation window" refers to the range or range of the proportion of the vapor to the hydrocarbon feed on which the nozzle can operate effectively. A large interval is desirable as fluctuations in steam availability occur routinely during normal operations of the refinery. The operation without any steam flow is useful in the case of a total steam loss. It is very useful to reduce the waiting time and the repair time to be able to have quick access to the steam holes, since these can sometimes get clogged. In addition, rapid mixing of the feed of the catalysts to vaporize the feed is desirable. The fine mixture of two phases passes through the outlet of the feed nozzle to the catalytic disintegration reactor. A benefit of the nozzle assembly of this invention is that, for example, where two elongated outlet slots are used, two sheet-shaped spray fans are produced which, possibly due to the vacuum effect between them, converge on a sheet while they are still in close proximity to the tip or at the exit. In this way, fine atomization is obtained while also achieving a desirable uniform spray pattern, for example, a flat sheet when the nozzle outlet is straight lines. It is noted that theorizing as the scientific principle that produces the simple spray sheet does not mean that it is limiting of the invention, since other explanations may be applicable.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Having described the invention as above, property is claimed as contained in the following:

Claims (11)

1. A feed nozzle assembly for introducing gas, for example steam, and liquid, for example a heavy petroleum hydrocarbon, into a container, for example a catalytic disintegration reactor, characterized the feed nozzle assembly because it comprises: (a) ) a nozzle body having a substantially cylindrical inner tube defining a gas conduit, and an outer tube accommodated around the inner tube, wherein the outer surface of the inner tube and the inner surface of the outer tube define an annular liquid conduit , and wherein each of the tubes has an inlet end and an opposite outlet end; (b) a tip of the first nozzle fixedly coupled to the outlet end of the inner tube, having a substantially cylindrical inlet end coupled to the outlet end of the inner tube, and an opposite outlet end in the form of a dome, the end of which dome-shaped outlet is provided with at least one passageway; (c) a tip of the second nozzle fixedly coupled to the outer end of the outer tube, and accommodated around the tip of the first nozzle, whose tip of the second nozzle has a substantially cylindrical inlet end coupled to the outlet end 'of the tube outer, and a dome-shaped opposite outlet end provided with at least one elongated slot having substantially parallel walls, whose dome-shaped exit end of the tip of the second nozzle extends beyond the exit end in the form of the tip of the first nozzle.

2. The feed nozzle according to claim 1, characterized in that the tip of the first nozzle is provided with a plurality of passageways accommodated in at least one row, wherein the angle formed substantially from the center of the exit end in the form of dome, across the length of a row, is 45 ° to 120 °, and where the angle formed substantially from the center of the dome-shaped exit end of the tip of the second nozzle through the length of the elongated groove (s) is substantially contiguous with the angle formed from the center of the dome-shaped exit end of the tip of the first nozzle through the length of the row (s).

3. The feed nozzle according to claim 2, characterized in that the angle formed from the center of the dome-shaped outlet end through the length of the row (s) is 75 ° to 105 °.

4. The feed nozzle according to claim 2 or 3, characterized in that the passageways in the first nozzle are arranged in two or more rows, and wherein the outlet end of the tip of the second nozzle is provided with two or more slots.

5. The feed nozzle according to any of claims 2 to 4, characterized in that the plane defined by a row of passageways is substantially parallel to the central longitudinal axis of the inner tube.

6. The feed nozzle according to any of claims 2 to 4, characterized in that the plane defined by an elongated slot is substantially parallel to the central longitudinal axis of the inner tube.

7. The feed nozzle according to any of claims 2 to 4, characterized in that the angle between the plane defined by a row of passageways and the central longitudinal axis of the inner tube is in the range of 3 ° to 60 °, and suitably in the range of 15 ° to 45 °, and wherein the angle between the plane defined by an elongated slot and the central longitudinal axis of the inner tube, is in the range of 3 ° to 60 °, and suitably in the range from 15 ° to 45 °.

8. The feeding nozzle according to claim 7, characterized in that the angle between the plane defined by a row of passageways and the central longitudinal axis of the inner tube, is substantially contiguous with the angle between the plane defined by an elongated slot and the central longitudinal axis of the inner tube.

9. The feed nozzle assembly according to any of the claims 1 to 8, characterized in that the passageways at the tip of the first nozzle consist essentially of holes.

10. The feed nozzle assembly according to any of the claims 2 to 9, characterized in that each row comprises a plurality of passageways, the number of passageways being suitably in the range of 7 to 15.

11. The power assembly according to any of claims 1 to 10, characterized in that the tip of the second nozzle is provided with a covering or coating consisting of a material resistant to erosion in the areas sensitive to erosion of the the elongated slots, and the exit end of the tip of the second nozzle.