FR2792852A1 - Spring nozzle for injecting condensed liquid into polymerisation reactor comprises inlet pipe and sleeve with orifices sliding inside and at pipe end returned by spring - Google Patents

Abstract

The liquid injector nozzle comprises an inlet pipe (1) with a sleeve (2) sliding inside and at the end of the pipe. The position of the sleeve along the pipe is induced by the supply liquid pressure (3) and the return force of a calibrated spring (4). The sleeve has a number of orifices (10,11). The spring is fixed at the downstream end of the pipe to a stop by a hollow circular piece onto an internal circular edge (5) in the pipe. The other end is fixed by another circular piece held by a nut (6) screwed onto a rod (7) integral with the sleeve. When the nozzle is out of use the circular stop (8) rests on the edge of the supply pipe end. The pipe edge and the sleeve stop have support surfaces (12,13) giving good sealing.

Description

The present invention relates to an apparatus consisting of a nozzle

  liquid injection method and a method using said nozzle for the introduction of condensed liquid into a (co) polymerization reactor of ethylene and / or propylene in the gas phase in a fluidized bed. It is known to polymerize one or more monomers in the gas phase under a pressure higher than atmospheric pressure in a fluidized bed reactor o particles of polymer being formed are kept in the fluidized state by means of a reaction gas mixture containing the or the monomers to be polymerized and circulating in an ascending current. The polymer thus produced in powder form is generally withdrawn from the reactor in order to maintain the bed at a more or less constant volume. A preferred process on an industrial scale uses a fluidization grid which distributes the reaction gas mixture through the bed and which serves as support for the bed in the event of a flow cut in the ascending gas. The reaction gas mixture exiting from the top of the fluidized bed reactor is recycled to the base of the latter under the fluidization grid via an external

circulation equipped with a compressor.

  The polymerization of the monomers is an exothermic reaction. It is therefore necessary to provide a means suitable for cooling the bed in order to extract the heat of polymerization therefrom. The preferred method for the polymerization of ethylene and / or propylene in a fluidized bed consists in cooling the reaction gas mixture below the polymerization temperature, which makes it possible during the passage of this fluidization gas through the bed of compensate for the excess heat generated by the polymerization. Thus, during its return, the reaction gas mixture is generally cooled using at least one heat exchanger disposed on the external circulation pipe so as to eliminate the heat produced by the polymerization reaction and to maintain the temperature polymerization

desired level.

  Particular efforts have been made in recent years to optimize the gas phase polymerization process so as to increase the production of polymer in existing workshops. We therefore reasoned in terms of polymer production rate, namely in terms of yield by weight of polymer produced per unit volume of the reactor and per unit time (kg / h / m3). In commercial fluidized bed reactors of the type mentioned above, it is known that the production rate depends directly on the rate of removal of heat generated in the reactor. This removal rate can be increased, for example by increasing the speed of the fluidizing gas, and / or by reducing the temperature of the fluidizing gas, and / or by

  increasing the thermal capacity of the fluidizing gas.

  For example, BP Chemicals Limited proposed in its patent application WO94 / 28032 a process for the polymerization of olefin (s) in the gas phase in which the recycle gas stream is cooled to a temperature sufficient to form a liquid and a gas. By separating the liquid from the gas and introducing the liquid directly into the fluidized bed, it is possible to increase the total quantity of liquid introduced into the fluidized bed reactor, which makes it possible to cool the bed better by evaporation and therefore reach higher levels. productivity. Many

  methods for introducing the liquid into the fluidized bed have already been described.

  It has now been found an apparatus consisting of a liquid injection nozzle which has a large number of advantages compared to

  nozzles described in the prior art.

  The invention relates to a nozzle for injecting a liquid, characterized in that said nozzle comprises a liquid supply pipe and, a sleeve sliding inside and at the end of said pipe, the sleeve being fixed. to said line by a calibrated spring, the position of the sleeve along the supply line being induced by the pressure of the supply liquid and the return force of the calibrated spring, said sleeve being hollow and comprising at least one orifice for evacuation of the feed liquid to the outside when the pressure of said

liquid is sufficient.

  A nonlimiting example of the device of the invention is shown

  schematically in the appended figure.

  According to the present invention, the nozzle comprises a pipe

  supply and a sliding sleeve inside and at the end of said pipe.

  The supply line can allow the supply liquid to be directed towards its end. The dimensions of the sleeve can be any but must be chosen to allow it to slide in the supply line. The part

  upper part of the sleeve preferably has an ogival shape.

  According to the present invention, the sleeve is fixed to the supply line by a calibrated spring. The calibrated spring can be fitted by any

  suitable means, in order to produce its effect by working in compression or expansion.

  The ends of the calibrated spring can be fixed to the sleeve and to the supply line either directly or using one or more intermediate mechanical parts. The method of attachment can be any, such as integral or by a

contact in stop.

  For example, the calibrated spring can be fixed by its end downstream of the supply pipe to this same pipe by a contact in abutment on an internal circular flange in said pipe. The other end can be fixed by a contact in abutment with a targeted nut on a rod integral with the sleeve. In this example, the nut can be screwed onto the rod integral with the sleeve by partially compressing the spring, so as to maintain a circular abutment of the sleeve in abutment with the flange of the end of the pipe. In this case, the calibrated spring works in compression and its calibration corresponds to the initial compression force of the calibrated spring induced by the tightening of the nut on the rod. You can define the calibration pressure of the calibrated spring

  as the minimum pressure allowing movement of the sleeve.

  According to the present invention, the position of the sleeve along the supply line is induced by the pressure of the supply liquid and the restoring force of the calibrated spring. The displacement of said sleeve can take place on a substantially longitudinal axis along the supply pipe. Under the effect of the pressure of the feed liquid, said sleeve tends to be pushed back towards the outside of the pipe. When the pressure is sufficient, said sleeve can be effectively pushed back and partially displaced outside the supply line. By sufficient pressure is meant the pressure necessary for the resulting force to be greater than the restoring force corresponding to the setting of the spring. According to the present invention, the sleeve is hollow and comprises at least one orifice for discharging the supply liquid. In the case where there is more than one orifice, these can be grouped on the same level around the sleeve or on several levels. The number of levels can vary from 1 to 4, preferably from 1 to 2. Generally the orifices are arranged around the circumference of the sleeve in an equidistant manner. The number of orifices per level can be between 1 and 16, preferably between 4 and 16. This or these orifice (s) can have a shape making it possible to optimize the penetration of the liquid as well as the shape of the (or ) liquid jet (s). By calculating the pressure drop of the liquid through the orifice, it is possible to calculate an injection speed of the feed liquid, and to determine ultimately, from the shape of the orifice (s) ) a watering volume per unit of flow

  volume. The orifice (s) may be a hole or a slot, preferably a hole.

  The shape of the orifice (s) can be circular, ellipsoidal or any other suitable shape. Preferably 1 '(or) orifice (s) is a hole having a circular shape. The length of an ellipsoidal opening can be between 8 and 50 mm, the width between 2.5 and 12 mm and the surface between 26 and 580 mm2. The diameter of a circular orifice can be between 2 and 25 mm and the surface between 3 and 491 mm2. It is important that the opening (s) is large enough to allow the passage of fine solid particles which can

to be in the liquid.

  The orifice (s) may also include mechanical elements making it possible to atomize the liquid at the outlet of said (or said) orifice (s), as is

  described in British patent WO98 / 8548 of BP Chemicals Limited.

  According to the present invention, the injection of the feed liquid by the

  or the discharge orifices take place when the pressure of said liquid is sufficient.

  The pressure of the supply liquid may be sufficient to inject said liquid outwards when it generates a force greater than the return force of the spring corresponding to the calibration of the latter. Above this limit, i.e. above the setting pressure, the sleeve can be moved to allow injection of the

feed liquid.

  According to a variant of the present invention, the sleeve is provided on its circumference with a circular stop which rests on a flange of the end of the supply line when the pressure of the supply liquid is not sufficient to move said sleeve. This thus makes it possible to stop or to keep stopped the injection of said liquid. The pressure of the feed liquid may not be sufficient to move the sleeve if it generates a force less than the return force of the spring corresponding to the calibration of the latter. Below this limit, that is to say below the setting pressure, and thanks to the return force of the spring, the circular stop integral with the sleeve can be kept in contact with the flange of the end of the pipe. feed. According to another variant of the present invention, the flange of the end of the supply line as well as the circular abutment of the sleeve are each provided with a bearing surface whose contact surface is minimized to allow good sealing . The bearing surfaces are preferably flat. The bearing surface of the edge of the end of the supply line can be

  reduced thanks to a chamfer inside said rim.

  According to yet another variant of the present invention, it is possible to limit the movement of the sleeve by a locking device. This device can be a ring secured to the rod, which is itself secured to the sleeve, said ring resting on an abutment of the supply line when the sleeve reaches its

maximum travel.

  As long as the nozzle is in operation, the pressure of the feed liquid must be maintained above a limit Pi, also called the set pressure of the

  spring, from which the opening (s) begins to open to the outside.

  Between Pl and a limit P2 higher than Pi, beyond which 1 '(or) orifice (s) is completely open, the larger opening of 1' (or) orifice (s), generated by the increase of the pressure and therefore the flow rate of the supply liquid, makes it possible to limit the speed of said liquid at the outlet of the said orifice (s) and therefore to limit the

  length of the jets of said liquid outside the nozzle.

  In general, by means of the pressure of the supply liquid, it is always possible to link the flow of said liquid through the nozzle with the position of the sleeve in the supply line. The opening of one or more levels of additional orifices makes it possible to increase the flow rate of the supply liquid and to limit the speed of said liquid through the orifice (s) and therefore to limit the

  length of the jet (s) of said liquid outside the nozzle.

  For the design of a nozzle operating in a given flow range and the length of the feed liquid jets must be limited, parameters such as: the position of the orifice (s) must therefore be taken into account ) along

  of the sleeve, the dimensions of the said orifice (s) as well as the spring tare.

  According to the process claimed in the present invention, the nozzle described above is used for the injection of a condensed liquid into a continuous gas phase polymerization reactor with a fluidized bed. The (co) polymerization can be carried out from an olefinic monomer chosen from (a) ethylene, (b) propylene, (c) their mixture, and one or more other alpha-olefins in combination with (a) , (goat). The gaseous phase supporting the fluidized bed and flowing through it, being heated in contact with the polymerization catalyst under reactive conditions and polymer grains in formation, is continuously recycled and cooled to a temperature at which the liquid condenses. Said condensed liquid is preferably separated from the gas phase and introduced directly into the bed reactor

  fluidized by means of one or more nozzles previously described.

  The (co) polymerization is generally carried out by continuous or semi-continuous addition of a catalyst of the Ziegler-Natta type comprising at least one transition metal, associated with a cocatalyst comprising an organometallic compound, for example an organoaluminum compound. The catalyst essentially comprises an atom of a transition metal chosen from the metals of groups IV to VI of the Periodic Table of Elements, such as titanium, vanadium, chromium, zirconium or hafnium, optionally an atom of magnesium and a halogen atom. It is also possible to use a Ziegler-Natta metallocene type catalyst. The catalyst can be supported on a porous refractory oxide such as silica or alumina, or be combined with a solid magnesium compound, such as chloride, oxide, hydroxychloride or a magnesium alcoholate. It is also possible to use a catalyst complexed with iron and / or cobalt, such as for example those described in patent application WO98 / 27124 or WO98 / 2638. It is also possible to use a catalyst essentially consisting of a chromium oxide activated by

  heat treatment and associated with a granular support based on a refractory oxide.

  The catalyst can be used in the form of a prepolymer powder prepared in advance during a prepolymerization step from the catalysts described above. The prepolymerization can be carried out by any process, for example, a prepolymerization in a liquid or phase hydrocarbon

  gaseous according to a discontinuous, semi-continuous or continuous process.

  Catalyst or prepolymer can be introduced into the reactor

  continuously or discontinuously.

  The nozzle (s) can be placed anywhere in the fluidized bed reactor and can be supplied separately, in series or in parallel by conventional devices. The nozzle (s) can be oriented in any direction. The reactor comprises from 2 to 8, preferably from 4 to 6 nozzles. These nozzles can, for example, be oriented in a vertical position, in which case they pass through the fluidization grid and / or in a horizontal position, in which case they pass through the vertical wall of the reactor, so that the orifices are well within the bed. fluidized, preferably in the lower part of the fluidized bed. For example, for a commercial reactor which has a fluidized bed with a height ranging from 10 to 20 m above the grid, the orifices of the nozzles will be located above said grid and in

  below a height ranging from 3 to 7 m above said grid.

  The method and the device of the invention described above present

multiple advantages.

  One of the advantages is to be able to adapt the opening of the orifices as a function of the flow rate of the supply liquid desired, which makes it possible to limit the length of the jet (s) of said liquid outside the nozzle. In the case where the sleeve has several levels of orifices, it is possible to open the lower orifice levels of the sleeve in order to increase the capacity of the nozzle while at the same time limiting the length of the jets of said liquid to the outside of the nozzle. This allows the nozzle to operate efficiently and optimally in a very wide range

  while controlling the length of the feed liquid jets.

  This is particularly advantageous for the process of the present invention where it is very important to ensure that the jets of condensed liquid

  do not reach the walls of the polymerization reactor.

  Another advantage lies in the fact that while operating in a very wide range of flow rates, the return of the powder from the fluidized bed reactor is also avoided.

in the nozzle.

  Yet another advantage lies in the fact that the fluctuations of the pressure of the supply liquid cause an oscillatory movement and of small amplitude of the sleeve in the supply line. These fluctuations inherent in the pumping system used thus make it possible to limit the risks of blockage of the

  sleeve in the supply line.

  The method of the invention is particularly advantageous when it is desired to temporarily deactivate one or more nozzles. This operation cannot be envisaged with other nozzles which must always be kept in service

  to prevent the powder from returning.

  The appropriate choice of the shape of the orifices allows the dispersion of the feed liquid in the fluidized bed to be varied as desired. The claimed process applied to fluidized bed polymerization offers considerable technical and economic interest in that it allows effective control of the polymerization reaction both from the thermal point of view and from the

polymerization conditions.

  Thanks to this process, industrial reactors can be used.

big size.

  By way of example, the fluidized bed polymerization of ethylene was carried out using four nozzles as described above and shown

  schematically in the appended figure.

  The general conditions for the polymerization are those described below: Quality of the polymer: HDPE 1 HDPE 2 Temperature of the fluidized bed reactor: 910C 104 C Pressure of the fluidized bed reactor: 23.5 bara 23.5 bara Composition of the gas phase of said reactor:% mass by weight of ethylene: 31% 29.7%% by mass of hydrogen: 20% 13.4%% by mass of butene-1: 0.3% 0%% by mass of pentane: 5.7% 8.8%% by mass of nitrogen: 43% 48.1% Temperature of the gas phase at the inlet of the reactor: 36 C 46 C Fluidization speed: 65 cm / s 64 cm / s Mass production of polyethylene: 28.5 T / h 25 T / h Mass flow rate of liquid condensed by nozzle: 17.6 T / h 11.5 T / h At the end of the test, after dismantling the nozzle, we note that it does not

  contains no trace of the fluidizing solid, nor of crusting.

  The appended figure constitutes a nonlimiting example of the device for

  the invention claimed in the present invention.

  This device is a nozzle for injecting a liquid which comprises a supply line (1), a sleeve (2) sliding inside and at the end of said line (1). The position of said sleeve along the supply line (1) is induced by the pressure of the supply liquid (3) and the return force of a

calibrated spring (4).

  The calibrated spring (4) can be fixed by its end downstream of the supply pipe to this same pipe (1) by a stop contact, by means of a hollow circular part (18), on a flange circular (5) internal in said pipe. The other end can be fixed by a contact in abutment with another circular part (19) held by a nut (6) aimed on a rod (7) integral with the sleeve. In this example, the nut (6) can be screwed onto the rod (7) integral with the sleeve by partially compressing the spring (4), so as to maintain a stop

  circular (8) of the sleeve in abutment with the flange (9) of the end of the pipe (1).

  In this case, the spring (4) works in compression and its calibration corresponds to the force

  initial compression of the spring (4) induced by the tightening of the nut (6) on the rod.

  The sleeve (2) is provided with a circular stop (8) on its circumference

  and orifices (10) and (11) which are, in this case on two levels.

  When the nozzle is out of service, the circular stop (8) rests on the flange (9) of the end of the supply line. Said flange (9), as well as the circular stop (8) of the sleeve are provided with a bearing surface (12) and (13) the

  contact surface is minimized to allow a good seal.

  When the pressure, represented by the arrow (16), of the supply liquid (3) is sufficient to move the sleeve (2), said injected liquid towards

  the exterior through the orifices (10) and (11).

  The movement of the sleeve (2) is limited by a locking device.

  This device can be a ring (14) integral with the rod (7), which is itself integral with the sleeve (2), said ring (14) resting on a stop (15) of the supply line (1 ) when the sleeve (2) reaches its maximum clearance,

  represented by the double arrow (17).

Claims (11)

  1. Nozzle for injecting a liquid characterized in that said nozzle comprises a liquid supply line and, a sleeve sliding inside and at the end of said line, the sleeve being fixed to said line by a calibrated spring, the position of the sleeve along the supply line being induced by the pressure of the supply liquid and the return force of the calibrated spring, said sleeve being hollow and comprising at least one orifice for evacuation of   supply liquid to the outside when the pressure of said liquid is sufficient.   2. Nozzle according to the preceding claim, characterized in that the   sleeve has from 1 to 4, preferably from 1 to 2 levels of orifices.   3. Device according to the preceding claim, characterized in that the   number of orifices per level is between 4 and 16.   4. Device according to the preceding claim, characterized in that the orifices are holes of cylindrical shape whose diameter is between 2 and 25 mm.   5. Device according to any one of the preceding claims,   characterized in that the orifices include mechanical elements making it possible to atomize the liquid at the outlet of said orifices, as described in the patent   W09818548 from BP Chemicals Limited.   6. Device according to any one of the preceding claims,   characterized in that the sleeve is provided on its circumference with a circular stop which rests on a flange of the end of the supply line when the   pressure of the feed liquid is not sufficient to move said sleeve.   7. Device according to the preceding claim, characterized in that the flange of the end of the supply line as well as the circular stop of the sleeve are each provided with a bearing surface whose contact surface is   minimized to allow a good seal.   8. Device according to any one of the preceding claims,   characterized in that the movement of the sleeve is limited by a locking device. 9. Process for the introduction of condensed liquid into a continuous process for the gaseous phase polymerization of an olefinic monomer chosen from (a) ethylene, (b) propylene, (c) their mixture, and one or more others alpha-olefins in combination with (a), (b) or (c), in a fluidized bed reactor, by continuously recycling the gas phase supporting the fluidized bed and circulating through it, said gas phase having been heated to contact of the polymerization catalyst under reactive conditions and of the polymer grains in formation, by cooling said recycled gas phase to a temperature at which liquid condenses, by separating said condensed liquid from the gas phase and by introducing it directly into the fluidized bed, the process being characterized in that the injection of the condensed liquid   is done by means of one or more devices according to the preceding claims.   10. Method according to the preceding claim, characterized in that the   polymerization reactor comprises from 2 to 8 nozzles.   11. Method according to any one of claims 9 and 1 O, characterized   in that the nozzles are oriented in a vertical position.