Injection device, in particular for injecting a hydrocarbon feedstock into a refining unit

Abstract

Embodiments of an injection device shaped in order to atomize a liquid into droplets by means of a gas are disclosed herein. The injection device may comprise a body having a gas inlet orifice intended to be connected to a gas supply duct. The injection device may further comprise an outlet orifice for discharging the atomized liquid. The injection device may also comprise a straight internal duct connecting the inlet orifice to the outlet orifice along an axial direction of said body. At least two liquid inlet ducts may be intended to be connected to at least one liquid supply duct pass through said body radially or substantially radially and open into said internal duct. These liquid inlet ducts may each have an axis and are arranged so that their axes intersect at one and the same point on an axial line extending inside the internal duct.

Claims

1. An injection device shaped in order to atomize a liquid into droplets by means of a gas, comprising a body having: a gas inlet orifice intended to be connected to a gas supply duct, an outlet orifice for discharging the atomized liquid, a straight internal duct connecting the inlet orifice to the outlet orifice along an axial direction of said body, characterized in that said injection device comprises at least two conical liquid inlet ducts intended to be connected to at least one liquid supply duct, said liquid inlet ducts passing through said body radially or substantially radially and opening into said internal duct, said liquid inlet ducts each having an axis and being arranged so that their axes intersect at one and the same point on an axial line extending inside the internal duct, and wherein the injection device comprises a chamber external to the body and coaxial therewith, arranged so that said liquid inlet ducts are in fluid communication with said external chamber, wherein at least one of said liquid inlet ducts is positioned perpendicular to an axial line of the external chamber, said external chamber being in fluid communication with at least one liquid supply duct and at least two or more inlet ducts which are in fluid communication with the internal duct, and wherein the external chamber is configured such that the liquid flows through the external chamber counter currently to the flow of gas.

2. An injection device according to claim 1, characterized in that said axial line forms an axis of symmetry of said body.

3. An injection device according to claim 1, characterized in that the axis of each liquid inlet duct extends perpendicular to the axial direction of said body, wherein each liquid inlet duct is in a same radial plane.

4. An injection device according to claim 1, characterized in that it comprises an even number of liquid inlet ducts , the inlet ducts being paired up, the axes of two ducts of a same pair extending in a same plane containing the axial line.

5. An injection device according to claim 1, characterized in that it comprises an odd number of liquid inlet ducts.

6. An injection device according to claim 1, characterized in that all the inlet ducts have a cross section of the same area.

7. An injection device according to claim 1, characterized in that the liquid inlet ducts project into the internal duct.

8. An injection device according to claim 1, characterized in that said at least one liquid supply duct extends perpendicular relative to the axial line extending inside the internal duct.

9. A catalytic cracking reactor for treating a hydrocarbon feedstock, comprising at least one injection device according to claim 1 positioned so that its outlet orifice opens into said reactor.

10. A process for the catalytic cracking of a hydrocarbon feedstock in at least one reactor, in which said hydrocarbon feedstock is injected, into said at least one reactor, said hydrocarbon feedstock being injected through the liquid inlet ducts of at least one injection device according to claim 1, a gas simultaneously supplying each injection device through the gas inlet orifice.

11. A catalytic cracking process according to claim 10, in each injection device , in which the proportion of gas with respect to the hydrocarbon feedstock is from 1.5% to 5% by weight.

12. A catalytic cracking process according to claim 11, in which the flow rates of hydrocarbon feedstock and of gas supplying each injection device are controlled so as to obtain a hydrocarbon feedstock flow rate at the outlet of each injection device that ranges from 15 to 80 t/h.

Description

(1) The invention is now described with reference to the non-limiting appended drawings, in which:

(2) FIG. 1 represents an axial cross-sectional view of an injection device according to one embodiment of the invention;

(3) FIG. 2 represents an axial cross-sectional view of an injection device according to another embodiment of the invention;

(4) FIGS. 3a and 3b are photographs of the sprays obtained respectively with a conventional impact injection device and with an injection device according to the embodiment from FIG. 1;

(5) FIG. 4 is a graph representing the distribution of the mean droplet size as a function of the spray angle at a relative distance from the outlet orifice, for a conventional impact injection device (reference) and for an injection device according to the embodiment from FIG. 1 (invention) as a function of the distance to the discharge axis (X axis from FIG. 1).

(6) The expression “substantially parallel or perpendicular” is understood to mean a direction that deviates by at most ±20°, or even by at most 10° or by at most 5° from a parallel or perpendicular direction.

(7) FIG. 1 represents an injection device 10 shaped in order to atomize a liquid into droplets by means of a gas. This injection device 10 comprises a body 12 having: a gas inlet orifice 14 connected to a gas supply duct 16, an outlet orifice 18 for discharging the atomized liquid, a straight internal duct 20 connecting the inlet orifice 14 to the outlet orifice 18 along an axial direction X of the body 12.

(8) The internal duct 20 forms a mixing zone for the gas and atomized liquid. It usually has a cylindrical shape, as does the body 12, like in the present example.

(9) Usually, the injection device 10 may be produced as one or more parts, made of steel, in particular stainless steel, or other material.

(10) According to the invention, this injection device 10 comprises at least two liquid inlet ducts intended to be connected to at least one liquid supply duct. These liquid inlet ducts pass through the body 12 radially or substantially radially, and open into the internal duct 20. They each have an axis and are arranged so that these axes intersect at one and the same point on an axial line extending inside the internal duct.

(11) In the example represented in FIG. 1, the injection device 10 comprises two liquid inlet ducts 22 and 24 each connected to a liquid supply duct 26, 28 respectively. The two ducts 22, 24 each have an axis X.sub.1, X.sub.2, which here are coincident. The axial line is coincident with the axial direction X, which here forms an axis of symmetry of the body 12 and of the internal duct 20. The axes X.sub.1, X.sub.2 thus intersect the axial line X at a point I.

(12) The internal dimensions of the injection device represented in FIG. 1 are similar to the dimensions customarily used for impact injection devices for impact with a target, the surface of which extends in a plane containing the axial line X. By way of example, the internal diameter of the openings 22a, 24a, and of the inlet orifice 14, usually of circular shape as in the example represented, are of the order of one inch, i.e. around 2.5 cm. The internal diameter of the internal duct 20 may be of the order of three to six inches, in other words of the order of 7 to 16 cm, or even optionally reaching eight inches, i.e. around 20 cm. As seen in FIG. 1, the gas supply duct 16 has a convergent shape, here a conical shape, along the gas flow direction, making it possible to accelerate the gases at the inlet thereof into the internal duct 20 of the body 12. Similarly, the inlet ducts 22, 24 open into the internal duct 20 via openings 22a, 24a, respectively, which have a cross section of reduced area relative to the area of the cross sections of these ducts, also for inducing an acceleration of the hydrocarbon feedstock when it enters into the internal duct 20. Here, the inlet ducts 22, 24 have a conical shape, their openings 22a, 24a being circular.

(13) It should also be noted that the inlet ducts 22, 24 are positioned in the immediate vicinity of the inlet orifice 14 of the body 12. This corresponds to the customary position of the inlet duct in an impact injection device 20, for impact with a solid target, and enables good entrainment of the droplets formed by the gas.

(14) The end of the injection device 10 through which the atomized liquid spray exits is generally rounded, for example spherical. The outlet orifice 18 of this end may have a shape similar to the shapes of conventional impact injection devices and may be chosen as a function of the desired spray shape. It may be a cylindrical or truncated cone orifice, a slit, etc.

(15) The injection device 10 represented in FIG. 1 operates in the following manner: the hydrocarbon feedstock is injected via the ducts 22 and 24 into the internal duct 20 of the body 12 along the directions of the arrows F1, F2 respectively. An atomizing gas is itself introduced into the internal duct 20 through the duct 16, then the inlet orifice 14, along the direction of the arrow F3. The two hydrocarbon feedstock jets from ducts 22 and 24 come into contact with one another at the centre of the internal duct substantially on the axial line X thus inducing the formation of droplets. These droplets are entrained by the gas flowing in the direction F3 up to the outlet orifice 18 of the injection device 10. In the zone of the internal duct 20 located downstream of the point of impact I of the jets, the droplets of the hydrocarbon feedstock end up mixing with the gas homogeneously before the exit thereof through the outlet orifice 18.

(16) In the example represented in FIG. 1, the inlet ducts 22, 24 are thus connected to two separate hydrocarbon feedstock supply ducts. When the surroundings of the injection device are restricted, this arrangement may prove to take up too much space. It may then be advantageous to produce an injection device as represented in FIG. 2.

(17) The embodiment represented in FIG. 2 differs from that represented in FIG. 1 essentially by the hydrocarbon feedstock supply of the inlet ducts. The same elements are denoted by the same references with the addition of a prime symbol“′”.

(18) In FIG. 2, an injection device 10′ also comprises a body 12′ comprising an inlet opening 14′, an outlet opening 18′, and two inlet ducts 22′; 24′, respectively. In a manner similar to the preceding embodiment, a gas supply duct 16′ is connected to the inlet opening 14′. On the other hand, the liquid inlet ducts 22′ and 24′ are no longer each connected to a supply duct but are in fluid communication with an external chamber 30′, which coaxially surrounds the body 12′ of the injection device 10′. Here, the external chamber 30′ has a cross section of annular shape, the body 12′ having a cylindrical shape. The inlet ducts 22′, 24′ are arranged symmetrically opposite, their axes X′.sub.1, X′.sub.2 being coincident and intersecting the axial line X′ at a point I′.

(19) The external chamber 30′ is itself in fluid communication with a single supply duct 25′. This external chamber 30′ may be shaped so that the liquid is distributed equitably between the two inlet orifices 22′ and 24′. For example, and according to a first embodiment, an equitable distribution between the two inlet orifices 22′ and 24′ may be obtained when they are positioned equidistant from the liquid supply duct 25′. A method according to a second embodiment consists in laterally moving the duct 25′ so that it opens into the external chamber 30′ at one of the ends 60′ or 70′, said external chamber 30′ taking the shape of a plenum chamber 50′ arranged so that the stream resulting from the liquid supply duct 25′ is forced to pass along a wall 40′ before passing through the inlet ducts 22′, 24′ positioned at the other of the ends 70′ or 60′.

(20) This liquid supply duct 25′ has a shape similar to the inlet ducts 22, 24 from the preceding example, namely a conical shape, the cross section of which decreases in the fluid flow direction. For their part, the inlet ducts 22′, 24′ open at an opening 22′a, 24′a respectively into the internal duct 20′. These openings 22′a, 24′a here have a cross section smaller than the cross section of the ducts 22′, 24′ respectively. However, these cross sections could be of the same dimensions as the ducts 22′, 24′. Here, the ducts 22′ and 24′ are of cylindrical shape, the openings 22′a, 24′a being circular.

(21) In the various embodiments represented with reference to FIGS. 1 and 2, the cross sections of the openings 22a, 24a or 22′a, 24′a are of the same area, and here are identical.

(22) The operation of the injection device represented in FIG. 2 is similar to that of the injection device from FIG. 1, the arrows represented showing the flow directions of the various fluids.

(23) The invention is not limited to the embodiments described, nor to the particular forms described in these embodiments. More than two inlet ducts may in particular be envisaged, for example three that are regularly distributed, or more, for example 4 or more depending on the dimensions of the injection device and the desired dimensions of the cross sections of the inlet ducts.

EXAMPLE

(24) An injection device similar to that described with reference to FIG. 1 was tested for the atomization of water, the gas being air. The device tested was produced with dimensions such that the diameter of the internal duct is 10 times smaller than the diameter of a device customarily used for an application in a catalytic cracking reactor.

(25) The injection device tested has the following dimensions: diameter of the opening that opens into the internal duct for the injection of the liquid: 1.56 mm, diameter of the opening that opens into the internal duct for the injection of the gas: 1.58 mm, diameter of the internal duct: 8 mm, length of the internal duct: 132.5 mm outlet orifice: slit of thickness 2.52 mm and of angular amplitude of opening of 105° (slit made on a spherical end having an external radius of 5.6 mm).

(26) A conventional impact injection device having the same dimensions was also tested. This conventional impact injection device has a single liquid inlet duct and a solid target, the impact surface of which containing the axial line X is located opposite the liquid inlet duct. Such a conventional impact injection device is similar to that represented in patent U.S. Pat. No. 4,434,049, with however an outlet orifice of different shape.

(27) The test conditions are the following: Water flow rate: 226.2 kg/h, Air flow rate: 6.1 kg/h, Velocity of the gas at the inlet orifice: 300 m/s, Velocity of the water at the opening 22a, 24a: 15 m/s, Gas/liquid ratio: 2.7% by weight.

(28) Spray shape obtained

(29) FIGS. 3a, 3b represent images of the atomized liquid sprays leaving each of the injection devices. These images are recorded on a black background by direct illumination using a stroboscope. It is observed that the sprays obtained have similar shapes, the spray obtained with the device according to the invention however appears denser.

(30) Measurement of the Pressure Drop

(31) The injection devices tested diffused into the ambient air. Consequently, the relative pressure of liquid at the inlet is equal to the pressure drop. The measurement was carried out by means of a manometer measuring the inlet pressure. The relative pressure of liquid at the inlet is measured at 10 barg for the conventional impact injection device. This value is slightly higher than the value estimated by calculation (8.2 barg). The relative pressure of liquid at the inlet was measured at 2.6 barg for the injection device according to the invention, i.e. a reduction by a factor of 3 to 4.

(32) Measurement of the size of the droplets and the distribution thereof

(33) The mean size of the droplets and also their distribution at the outlet of the injection devices was measured by means of a particle size analyser using the laser diffractometry technique enabling the measurement of: the diameter of a set of spherical or non-spherical particles, the spatial concentration of particles.

(34) The apparatus used is a particle size analyser sold by the company Malvern using a helium-neon gas laser having a power of 4 mW generating a beam of red light having a diameter of 10 mm and a wavelength of 632 nm. The light scattered forward by the particles is collected via a Fourier lens through a receiving part, colinear to the laser, comprising a detector formed of silicon photodiodes positioned in concentric rings. This receiving part records the diffraction pattern resulting from the laser beam crossing the jet of particles. The measurement range of the particle size analyser used covers sizes from 0.1 μm to 1000 μm.

(35) FIG. 4 is a relative comparison of the performances of an impact injector according to the prior art and of an injector according to the invention. The y-axis represents the mean diameter values of the droplets (relative value, arbitrary unit) measured at a distance of 300 mm from the outlet orifice parallel to the discharge axis (corresponding to the axial line X from FIG. 1), the x-axis represents a relative value of spray width (or spray angle) (relative value, arbitrary unit) corresponding to the ratio of the measurement distance with respect to the discharge axis in a direction perpendicular to this discharge axis over the total width of the spray. In other words, the value 0.0 of the x-axis corresponds to a measurement carried out on the discharge axis whereas the value 1.0 corresponds to a measurement made level with a maximum spray width.

(36) It is observed that the sprays obtained with the injection device according to the invention and the conventional impact injection device are similar and homogeneous. The mean size of the droplets is less than 150 μm.

(37) In conclusion, the injection device according to the invention makes it possible to obtain a spray of droplets similar to the impact injection devices but with a considerably reduced pressure drop, enabling the treatment of heavy feedstocks without having to use powerful pumps or an excessively large amount of steam.