MXPA99003953A - Nozzle for atomizing a fluid in a fluidised bed - Google Patents

Abstract

A continuous gas fluidised bed process for the polymerisation of olefins, especially ethylene, propylene, or mixtures thereof with other alpha-olefins by cooling the recycle gas stream to condense some liquid (e.g., a comonomer), separating at least part of the liquid and spraying it under pressure through a nozzle (1) directly into the fluidised bed by pressurising the liquid and feeding it to a spray nozzle (1) having a mechanical device (6) for atomising the liquid, under conditions such that the spray is formed within a spray-forming zone (5) of the nozzle outlet. The spray-forming zone (5) is preferably shielded from the fluidised bed particles by a wall or walls which can be, for example, a tube or a plate. Also described is a nozzle having two or more series of outlets, each series being fed and controlled independently to enable improved turn-up/turn-down of the liquid supply to the bed.

Description

NOZZLE FOR ATOMIZING A FLUID IN A FLUIDIZED BED Field of the invention The present invention relates to a nozzle suitable for use in the injection of liquid in a fluidized bed in a continuous process for the polymerization of olefins by gas phase, and in particular , to a nozzle that allows an improved control of the injection of liquid in said fluidized bed. BACKGROUND OF THE INVENTION Processes for the homopolymerization and copolymerization of olefins in the gas phase are well known in the art. Such processes can be conducted, for example, by introducing the gaseous monomer into a stirred and / or fluidized bed comprising polyolefin and a catalyst for polymerization. In the polymerization of fluidized bed olefins, the polymerization is conducted in a fluidized bed reactor wherein a bed of polymer particles is maintained in a fluidized state by means of a rising gas stream comprising the gaseous reaction monomer. The initiation of such polymerization generally employs a bed of preformed polymer particles similar to the polymer to be made. During the course of the. polymerization, fresh polymer is generated by the catalytic polymerization of the monomer, and the polymer product is separated to maintain the bed at a more or less constant volume. An industrially favored process employs a fluidization grid to distribute the fluidizing gas to the bed and to act as a support for the bed when the gas supply is cut off. The polymer produced is generally separated from the reactor through a discharge conduit installed in the lower portion of the reactor, near the fluidization grid. The fluidized bed comprises a bed of growing polymer particles. This bed is maintained in a fluidized condition by the continuous upward flow coming from the base of the fluidizing gas reactor. The polymerization of olefins is an exothermic reaction and is therefore necessary to provide means for cooling the bed in order to remove the heat of the polymerization. In the absence of such cooling the bed would increase its temperature and the polymer particles would eventually begin to fuse. In the polymerization of fluidized bed olefins, a commonly used method to remove the heat of polymerization is to supply a gas to the polymerization reactor, passing the fluidizing gas, which is at a temperature lower than the desired polymerization temperature, to through the fluidized bed to remove the heat of the polymerization, removing the gas from the reactor and cooling it when passing through an external heat exchanger, and recycling it to the bed. The temperature of the recyclable gas can be adjusted in the heat exchanger in order to keep the fluidized bed at the desired polymerization temperature. In this polymerizing alphadefine method, the recyclable gas generally comprises the monomeric olefin, optionally together with, for example, a gaseous chain or diluent gas transfer agent such as hydrogen. In this manner, the recyclable gas serves to supply the monomer to the bed, to fluidize the bed, and to maintain the bed at the desired temperature. The monomers consumed by the polymerization reaction are usually replaced by adding processing gas to the recyclable gas stream. It is well known that the production rate (that is, the production in time and space in terms of the weight of the polymer produced per unit volume of the reactor space per unit time) in commercial gas fluidized bed reactors of the type above mentioned, it is restricted by the maximum speed at which the heat of the reactor can be removed. The rate of heat removal may be increased, for example, by increasing the velocity of the recyclable gas and / or changing the heat capacity of the recyclable gas. Nevertheless, there is a limit to the speed of recyclable gas, which can be used in commercial practice. Beyond this limit, the bed may become unstable or even move out of the reactor in the gas stream, leading to blockage of the recycle pipe and damage to the recyclable gas compressor or blower. There is a limit to the degree to which the recyclable gas can be cooled in practice. This is basically determined by economic considerations, and in practice is usually determined by the temperature of the industrial cooling water available at the site. Cooling can be used if desired, but this adds costs to production. Thus, in commercial practice, the use of cooled recyclable gas as the only means to remove the heat of polymerization from the polymerization of fluidized bed olefins, has the disadvantage of limiting the maximum production speeds obtainable. The prior art suggests several methods to increase the heat removal capacity of the recycle stream, for example, by introducing a volatile liquid. GB Patent 1415442 relates to the phase polymerization of vinyl chloride gas in a fluidized or stirred bed reactor, the polymerization being carried out in the presence of at least one gaseous diluent having a boiling point below that of vinyl chloride. Example 1 of this reference describes controlling the temperature by intermittently adding vinyl chloride to the fluidized polyvinyl chloride material. The liquid vinyl chloride evaporated immediately in the bed, results in the removal of heat from the polymerization. US Patent 3625932 describes a process for the polymerization of vinyl chloride wherein the beds of vinyl chloride particles within a multi-stage fluidized bed reactor are kept fluidized by the introduction of gaseous vinyl chloride monomer into the bottom of the reactor. The cooling of each of the beds to remove the heat of the polymerization generated therein is provided by the spraying of liquid vinyl chloride monomer in the rising gas stream beyond the trays on which the beds are fluidized. . Patent FR 2215802 relates to a spray nozzle of the non-return valve type, suitable for spraying liquids in fluidized beds, for example, in the gas-fluidized bed polymerization of ethylenically unsaturated monomers. The liquid used to cool the bed may be the monomer to be polymerized, or if the ethylene is to be polymerized, it may be a hydrocarbon saturated with liquid. The spray nozzle is described in relation to the fluidized bed polymerization of vinyl chloride. Patent GB 1398965 discloses the fluidized bed polymerization of ethylenically unsaturated monomers, especially vinyl chloride, wherein the technical control of the polymerization is effected by the injection of liquid monomer into the bed using one or more spray nozzles located at a height between 0 and 75% of the fluidized material in the reactor. US Patent 4390669 relates to the homo- or copolymerization of olefins multi-stage gas phase process which may be carried out in stirred bed reactors, fluidized bed reactors, stirred fluidized bed reactors or tubular reactors. In this process, the polymer obtained from a first polymerization zone is suspended in an intermediate zone in an easily volatile liquid hydrocarbon, and the suspension thus obtained is fed to a second polymerization zone where the liquid hydrocarbon is evaporated. In Examples 1 to 5, the gas coming from a second polymerization zone is conducted through a cooler (heat exchanger) where part of the liquid hydrocarbon is condensed (with comonomer if it is used). The volatile liquid condensate is partially sent in the liquid state to the polymerization vessel where it is evaporated for use in the removal of heat from the polymerization by its latent evaporation heat. Patent EP 89691 refers to a process to increase the production in time and space of the continuous processes of the fluidized bed by gas for the polymerization of fluid monomers, the process comprising the cooling of all or part of the unreacted fluids in order to form a mixture of double gas phase and mixed liquid below the condensation point and the introduction of said double phase mixture into the reactor. The specification of EP 89691 states that the basic limitation on the degree to which the recyclable ace stream can be cooled below the dew point is under the condition that the gas to liquid ratio is maintained at a sufficient level so that the liquid phase of the double phase fluid mixture is kept in a suspended or included condition until the liquid evaporates, and further establishes that the amount of liquid in the gas phase should not exceed about 20 weight percent, and preferably it should not exceed about 10 weight percent, always taking into account that the speed of the double phase recycle stream is high enough to maintain the liquid phase in the suspension in the gas and to support the fluidized bed inside the reactor . EP 89691 further discloses that it is possible to form a double phase fluid stream within the reactor at the point of injection by separately injecting gas and liquid under conditions that will produce a double phase current, but there is no advantage observed in the operation in this manner due to the added and unnecessarily annoying cost of separating the gas and liquid phases after cooling. EP 173261 relates to a particular means for introducing a recycle stream in the fluidized bed reactors and, in particular, to a means for introducing a recycle stream comprising a double gas phase mixture and liquid included, as described in EP 89691 (above). WO 94/25495 describes a fluidized bed polymerization process comprising the passage of a gaseous stream comprising monomer through a fluidized bed reactor in the presence of a catalyst under reactive conditions in order to produce a polymeric product and a stream comprising unreacted monomer gases, compressing and cooling said stream, mixing said stream with feed components and returning a gas and liquid phase to said reactor, a method for determining stable operating conditions comprising: (a) observing changes in density of the fluidized volume in the reactor associated with changes in the composition of the fluidizing medium; and (b) increasing the cooling capacity of the recycle stream by changing the composition without exceeding the level at which a reduction in the density of the fluidized volume or a parameter indicative of the same becomes irreversible. US Pat. No. 5,436,304 relates to a process for polymerizing alpha-olefin (s) in a gas phase reactor having a fluidized bed and a fluidizing medium wherein the fluidizing medium serves to control the cooling capacity of the reactor and where the volume density function (Z) is maintained at a value equal to or greater than the calculated limit of the volume density function. The published application WO 94/28032, which is incorporated herein by reference, refers to a gas phase fluidized bed continuous process in which the productivity of the process is improved by cooling to recyclable gas stream up to a temperature sufficient to form a liquid and a gas, separating the liquid from the gas and feeding the separated liquid directly into the fluidized bed. The liquid can be suitably injected into the fluidized bed by means of one or more nozzles installed therein. It has now been found that by using a particular designed nozzle, the liquid can be more effectively introduced into the fluidized bed, which results in improved control over the cooling of the fluidized bed belonging to the improved liquid distribution. within the nozzle spray zone (s). Additional benefits include a reduction in nozzle purge gas requirements and significant reductions in operating costs. SUMMARY OF THE INVENTION Thus, according to the present invention, a continuous gas-fluidized bed process is provided for the polymerization of olefin monomer selected from (a) ethylene, (b) propylene, (c) mixtures of ethylene and propylene and (d) one or more other alpha-olefins mixed with (a), (b) or (c), in a fluidized bed reactor by continuously recycling a gas stream comprising at least some ethylene and / or propylene through a fluidized bed in said reactor in the presence of a polymerization catalyst under reactive conditions, cooling at least part of said gaseous stream separated from said reactor to a temperature at which the liquid condenses, separating at least part of the condensed liquid from the gaseous stream and introducing at least part of the separated liquid directly into the fluidized bed by: (a) pressurizing the liquid; (b) feeding the pressurized liquid into a liquid inlet of a nozzle; and (c) discharging the liquid in the fluidized bed through an outlet of the nozzle in which the liquid was atomized by the use of a mechanical device positioned within the outlet and an atomized spray is formed within a forming zone of the liquid. dew from the exit. DETAILED DESCRIPTION OF THE PREFERRED MODALITY It was found that in the absence of a spray-forming zone the liquid can not penetrate beyond the fluidized bed and the subsequent construction of liquid around the nozzle results in defluidization of the bed in the region of the fluid. nozzle. It is believed that atomization of the liquid and formation of a spray is inhibited by the presence of the solids of the fluidized bed at or near the outlet of the nozzle. The dew-forming zone is protected from the fluidized bed, thereby allowing the atomization process to proceed and the dew to develop.

The dew-forming zone of the outlet can be located within the nozzle, or it can be an area associated with a member that projects, or is secured in spatial relation, to the nozzle. The spray-forming zone comprises a protected path along which the liquid travels as the spray proceeds and the spray develops. The spray-forming zone is preferably defined by a wall that can be an integral part of the nozzle, or can protrude from the nozzle, or can be secured in spatial relationship to the nozzle. The wall may comprise, for example, a tube or a plate. In the case that the wall is tubular, the cross section may be, for example, circular, rectangular, square, triangular, hexagonal or elliptical. The tubular wall may have a uniform internal or non-internal cross-section through its entire length. For example, the cross section may be generally circular cylindrical, cylindrical elliptical, frustro-conical, frustro-pyramidal, an ellipsoidal section, single-leaf hyperbola, bell-shaped or horn-shaped. Preferably, the tubular wall has an increasing cross section in the direction of the flow of the liquid spray. In the case where the wall comprises a plate, the plate can be flat or curved, for example, a flat plate, an inclined plate, a disc-shaped plate, a profiled channel plate, a helical plate or a spiral shaped plate. The spray-forming zone of the outlet must be at least 10 mm in length, preferably at least 25 mm in length, in order to develop the spray and adequately protect the bed. The nozzle may be placed within the fluidized bed or may protrude through the walls of the reactor so that the outlet of the nozzle is in communication with the fluidized bed (preferably with the associated pipe located external to the reactor). The nozzle may have a single outlet or a plurality of exits. When the nozzle is placed inside the fluidized bed, the preferred number of outlets is from 1 to 4, more preferably from 2 to 4. When the nozzle protrudes through the walls of the reactor, the preferred number of outlets is from 1 to 20. It is believed that such nozzles have a different spray profile (a wider spray angle) than the nozzles placed inside the fluidized bed and that this may require more outputs of smaller cross-sectional area.

The outlet (s) may include circular holes, slots, ellipses or other suitable configurations. Preferably, when the outlet (s) is (are) slot (s), they are elliptical in shape. When the outlet (s) is (are) groove (s), the grooves may typically have an amplitude in the range of 2.5 to 12 mm and a length in the range of 8 to 50 mm. The cross-sectional area of the grooves can be in the range of 26 to 580 mm2. When the outlet (s) is (are) circular hole (s), the diameter of the holes can be in the range of 5 to 25 mm. The cross-sectional area of the circular holes can be in the range of 19.6 to 491 mm2. It is important that the outlet (s) of the nozzle be of sufficient size to allow the passage of any fine particles that may be present in the separate liquid stream. When the nozzle has a plurality of outlets, these can be installed at different levels within the nozzle, for example, the outlets can be installed in a number of rows around the circumference of the nozzle. The preferred number of outputs of each row is from 1 to 8, more preferably from 1 to 4.

The plurality of outlets is preferably evenly spaced around the circumference of the nozzle. When the plurality of outlets are installed in rows around the circumference of the nozzle, it is preferred that the outlets of each adjacent row be decentered from each other. The mechanical device any mechanical device that imparts a flow pattern to the liquid adapted to promote atomization of the liquid can suitably be. Preferred mechanical devices are those that provide a broad spray profile and a reasonably uniform droplet size. Known mechanical devices for atomizing liquids such as water (for fire suppression) and paint (for coating purposes) can be employed if desired. The energy for atomization can be provided, for example, by the pressure drop of the liquid arising from a hole, or by the use of external means such as electrical or mechanical power. Suitable mechanical devices for atomizing the liquid include, for example, turbulence devices or gate plates for imparting turbulent flow patterns in the liquid in order to promote the disruption and atomization of the liquid as it arises from orifice shock devices. , ventilation devices and ultrasonic devices. A simple form of mechanical device that is capable of generating a spray comprises a uniform cylindrical tube having an inlet for pressurized liquid and a flat outlet from which a liquid injection arises. As the injection moves away from the outlet, it gradually breaks into drops that form a liquid spray. A simple system of this type can be employed in the present invention taking into account that the dimensions of the tube and the pressure of the liquid are adjusted in order to provide a satisfactory spray structure. However, with this type of system the liquid injection tends to travel substantial distances before separating into dew drops, and the spray thus formed may not necessarily have the desired structure. Accordingly, in the present invention it is preferred to increase the spray production by the use of complementary means, for example, gates located in the liquid stream leading to the outlet, or shock devices that separate the injection of liquid in a spray . Preferably, the spray is introduced, from the spray-forming zone of the outlet, directly into the fluidized bed above the upper limit of the temperature gradient between the inlet fluidising gas (the gas stream fed to the reactor) and the rest of the fluid. bed. Commercial processes for the polymerization of gas-fluidized-bed olefins are generally operated under continuous, substantially isothermal state conditions. However, although almost the entire fluidized bed is maintained at the desired substantially isothermal polymerization temperature, there is usually a temperature gradient in the lower region of the bed. This temperature gradient arises due to the fact that the recyclable gas used to fluidize the bed is normally cooled to a temperature well below the temperature prevailing in the bed volume. Under these circumstances, the region of the bed immediately above the point of introduction of the gas stream cooled to the bed is cooler than the bed volume. The lower temperature limit of this region where the temperature gradient exists is the temperature of the cold inlet gas stream, and the upper limit is the substantially isothermal bed temperature (i.e., the bed volume temperature). In commercial reactors of the type that employ a fluidization grid, and have a fluidized bed height typically of about 10 to 20 m, this temperature gradient typically exists in a layer of approximately 15 to 30 cm (6 to 12 inches) per on top of the grid. A single nozzle may be used or a plurality of nozzles may be installed within the fluidized bed or projecting to the walls of the reactor. A preferred installation is to provide a plurality of nozzles spaced substantially evenly within the fluidized bed over a given circular contact diameter or evenly spaced around the circumference of the reactor in the region of liquid introduction. The number of nozzles to be used is the number that is required to provide sufficient penetration and dispersion of the spray in each nozzle in order to achieve a good dispersion of the liquid through the bed. A preferred number of nozzles is from 1 to 8, more preferably from 1 to 4, more preferably four nozzles located inside the bed or from 4 to 8 for the nozzles located externally. If desired, each of the nozzles can be supplied with separate pressurized liquid by means of a common conduit suitably installed inside the reactor. This can be provided, for example, by means of a conduit passing through the center of the reactor. Each nozzle may have a series of outputs installed in groups circumferentially around the nozzle with each group of outputs connected separately to a supply of pressurized liquid. Typically, the output groups can be installed in a number of rows around the circumference of the nozzle. The preferred number of departure groups is two. In a preferred embodiment the nozzle has two groups of outputs installed in two rows, decentering each group from each other. In this way, the liquid discharged from the lower group will not interfere with the discharge from the upper group. Preferably, each group of outlets is connected separately with the supply of pressurized liquid to the nozzle by means of appropriate pipe installed inside the nozzle. The supply of pressurized liquid to each group of outlets can be controlled by the use of properly installed valves. In this way, the liquid supply to each group of outputs can 'Control in order to control the amount of liquid that is discharged from the nozzle. For example, it is possible to direct liquid only to the group of outputs installed in the upper part of the nozzle. This ability to control the amount of liquid discharged from the nozzle is particularly important during the start of the fluidized bed process. Also the ability to reduce or increase the amount of liquid entering the fluidized bed allows greater control and flexibility during the operation of the fluidized bed. The nozzles used in the process of the present invention are preferably installed in such a way that they protrude substantially vertically in the fluidized bed, but can be installed in such a way that they protrude from the walls of the reactor in a substantially horizontal direction. The speed at which liquid can be introduced into the bed basically depends on the degree of cooling desired in the bed, and this in turn depends on the desired production rate of the bed. The production rates obtainable from the commercial fluidized bed polymerization processes for the polymerization of olefins depend, among other things, on the activity of the catalyst used and on the kinetics of such catalysts. Thus, for example, when a catalyst having a very high activity is employed, and high production rates are desired, the rate of addition of the liquid will be high. Typical rates of introduction of the liquid can be, for example, in the range of 0.1 to 4.9, preferably from 0.3 to 4.9 cubic meters of liquid per cubic meter of bed material per hour. For conventional Ziegler catalysts of the "superactive" type (ie, those based on transition metal, magnesium halide and organometallic cocatalyst), the rate of liquid addition can be, for example, in the range of 0.5 to 1.5 meters cubic of liquid per cubic meter of bedding material per hour. It is known that catalysts based on certain transition metal complexes, for example, metallocenes activated with for example alkyl alumoxanes, have extremely high activities. The increased rates of heat evolution that accompany the use of such polymerization catalysts may make the use of the process of the present invention particularly desirable. The addition of liquid to a gas fluidized bed according to the present invention can provide a reduction in the occurrence of heat stains generated in the reactor by the introduction of highly active fresh catalyst. If desired, the catalyst can be introduced by itself as a suspension or solution in the liquid that is sprayed into the bed. By injecting fluid into the fluidized bed in this way, any catalyst that is introduced into the liquid can benefit from the localized cooling effect of the liquid surrounding the nozzle, which can prevent heat stains and consequent agglomeration. In the process of the present invention it is important to achieve a good dispersion and penetration of the liquid in the fluidized bed. The factors that are important in the achievement of a good penetration and dispersion are the moment and the direction of the spray of the atomized liquid that enters the bed (the profile of the spray), the number of nozzles per unit of cross-sectional area of the bed , and the spatial installation of the nozzles. Preferably, the walls of the spray-forming zone are bent so that the spray adopts a suitable spray profile. For example, if the walls of the spray-forming zone diverge at an angle of 60 ° in the horizontal plane of the fluidized bed, the spray will cover an angle of approximately 60 ° in the horizontal plane of the bed. The atomized liquid spray is preferably injected into the bed in a substantially horizontal direction. In the event that the outlets supply the atomized liquid spray in a different direction to the horizontal, preferably the direction of the atomized liquid spray will be at an angle not greater than 45 °, more preferably not greater than 20 ° with respect to the horizontal plane. In the spray zone of the nozzle, the liquid charges in. the bed can be from 16 to 656 m 3 of liquid / h / m 3 from the spray zone of the nozzle and the rate of addition of the liquid to the fluidized bed can be in the range of 50 to 300 te / h. Preferably, the nozzle has a liquid flow rate, described above for typical exit cross-sectional areas and for liquid addition rates of between 50 and 300 te / h, in the range of 1.5 to 200 m3 of liquid / s / m2 of cross-sectional area • outlet, more preferably 9.5 to 70 m3 of liquid / s / m2 of cross-sectional area of outlet, where the liquid flow rate of the nozzle is defined as the flow rate volumetric liquid (m3 / s) per unit area of cross section (m2) of the outlets from which emerges the atomized liquid spray. The pressure drop on the nozzle should be sufficient to prevent the entry of particles from the fluidized bed. The pressure drop is suitably in the range of 0.5 to 100 bar, more preferably in the range of 0.5 to 70 bar and more preferably in the range of 0.5 to 30 bar. The pressure drop on the nozzle also provides a means to control the proportion of liquid flow through the nozzle. The proportion of the basic flow of liquid that passes through the mechanical device placed inside the outlet (s) of the nozzle is related to the pressure drop on the mechanical device. The following "Equation 1" provides a reasonably accurate means to determine the effect of a change in the pressure applied to the liquid on the liquid flow rate: m2 / m1 =] [? P2 /? P Equation 1 where? PX is the pressure drop of the mechanical device at a liquid flow rate of mx and P P2 is the pressure drop of the mechanical device at a liquid flow rate greater than m2, such that m2 >; m1. The data given in Table 1 refer to the pressure drop and the liquid flow rate for a typical mechanical device that begins to atomize the liquid at a liquid flow rate of 0.4 m3 / h and a pressure drop of 0.5 bar.

Table 1 In order to increase the flow rate of the liquid passing through the mechanical device, the pressure drop on the mechanical device must be increased according to Equation 1. It is desirable to have the ability to increase / decrease (i.e., increase or decrease). reduce) the amount of liquid flowing through the mechanical device. In order to have a reasonable increase / decrease capacity, the pressure drop on the mechanical device of Table 1 needs to be in the range of 0.5 to 100 bar (over which range the increase capacity is from 1 to 14.24). However, high pressure drops are undesirable due to the costs involved in pressurizing the liquid at high pressures, for example, increased pump costs and the need for high pressure liquid lines and safety devices. For economic reasons, it is desirable to minimize the number of nozzles, the number of mechanical devices in each nozzle, as well as the pressure drop on the mechanical devices while maintaining adequate liquid spray profiles and the increase / decrease capacity of each nozzle . It has now been found that the lower limit of operation of a typical mechanical device (pressure drop of 0.5 bar) can be extended if a small amount of gas is introduced into the liquid before the liquid passes through the mechanical device (hence henceforth called operant in an effervescent mode). Under normal process conditions, the mechanical device of such effervescent nozzles can be designed to operate at a moderate pressure drop of, for example, 30 bar, extending the operating range (ie, decreasing) to below 0.5 bar where the nozzle operates in effervescent mode. This allows a good control of the liquid capacity introduced in the fluidized bed during the start of the process when it may be necessary to introduce small amounts of liquid into the bed, ie, well below the capacity of the nozzle to atomize the liquid under non-effervescent conditions. Examples of gases that can be introduced into the liquid when it is desired to operate in effervescent mode are the monomer gases undergoing polymerization, for example, ethylene or propylene, or inert gases, for example, nitrogen or argon. Preferably, the amount of gas used in such effervescent nozzles is in the range of 0.5 to 10 weight percent, based on the total weight of the gas and the liquid passing through the nozzle. Suitably, the gas pressure is from 1 to 5 bar above the liquid pressure.

Preferably, the gas is introduced into the pressurized liquid through small holes in the liquid supply pipe in the nozzle so that they form small bubbles in the pressurized liquid. It is believed that the gas bubbles pass through the outlet (s) of the nozzle, the pressure drop on the outlet (s) of the nozzle causes the bubbles to expand, thereby increasing the fragmentation and atomization of the liquid. The nozzles used in the process of the present invention can be provided with an emergency gas purge to prevent blockage of the nozzle by the entry of particles from the fluidized bed if there is an interruption of the supply of pressurized liquid to the nozzle. The purge gases are selected from any gas that does not adversely affect the process. Preferred purge gases are monomer gases that undergo polymerization, for example, ethylene or propylene, or inert gases, for example, nitrogen or argon. The gaseous recyclable stream separated from the reactor comprises unreacted gaseous monomers and, optionally, inert hydrocarbons, inert gases such as nitrogen, activators or reaction moderators such as hydrogen, as well as included catalyst and / or polymer particles. The recycled gaseous stream fed into the reactor additionally comprises sufficient construction monomers to replace those monomers polymerized in the reactor. The process according to the present invention is suitable for the production of polyolefins in the gas phase by the polymerization of one or more olefins, at least one of which is ethylene or propylene. Preferred allyl olefins for use in the process of the present invention are those having from 3 to 8 carbon atoms. However, small amounts of alpha olefins having more than 8 carbon atoms, for example 9 to 18 carbon atoms, can be used if desired. In this way, it is possible to produce ethylene or propylene homopolymers or copolymers of ethylene or, propylene with one or more C3-C8 alpha-defines. The preferred alpha-olefins are butylene, pentylene, hexylene, 4-methylpentylene, octylene and butadiene. Examples of major olefins that can be copolymerized with basic ethylene or propylene monomer, or as a partial replacement for the C3-C8 alpha-olefin comonomer, are the decylene and ethylidene norbornenes. When the process is used for the copolymerization of ethylene or propylene with larger alpha-olefins, ethylene or propylene is presented as the main component of the copolymer, and is preferably present in an amount of at least 70%, more preferably at least 80% by weight of the total monomers / comonomers. The process according to the present invention can be used to prepare a wide variety of polymer products, for example, linear low density polyethylene (LLDPE) based on copolymers of ethylene with butene, 4-methylpentylene or hexene and high density polyethylene. (HDPE), which may be for example, homopolyethylene or ethylene copolymers with a small portion -of greater alpha-olefin comonomer, for example, butene, pentylene, hexylene, 4-methylpentylene. The liquid that condenses out of the recyclable gaseous stream can be a condensable monomer, for example, butene, hexene or octene used as a comonomer for the production of LLDPE or it can be a condensable inert liquid, for example, butane, pentane or hexane . In this specification, the term "condensable" means that the dew point of the gaseous composition comprising the condensable material is above the lower temperature of the recycling cycle.

It is important that the atomized liquid should be vaporized within the bed under the polymerization conditions that are employed so that the desired cooling effect is obtained and to avoid a substantial accumulation of liquid within the bed. The process is particularly suitable for the polymerization of olefins at a pressure between 0.5 and 6 MPa and at a temperature between 30 ° C and 130 ° C. For example, for the production of LLDPE the temperature is suitably in the range of 75-90 ° C and for HDPE the temperature is typically 80-105 ° C depending on the activity of the catalyst used. The polymerization reaction can be carried out in the presence of a Ziegler-Natta type catalyst system, which consists of a solid catalyst comprising essentially a transition metal compound and a cocatalyst comprising an organic compound of a metal (ie, an organometallic compound, for example an alkylaluminum compound). High activity catalyst systems are already known for several years and are capable of producing large amounts of polymer in a relatively short time, and therefore it is possible to avoid a step of removing catalyst residues from the polymer. These high activity catalyst systems generally comprise a solid catalyst consisting essentially of transition metal, magnesium and halogen atoms. It is possible to use a high activity catalyst consisting essentially of a chromium oxide activated by a heat treatment and associated with a granular support based on a refractory oxide. The process is also suitable for use with metallocene catalysts and Ziegler catalysts supported on silica. The catalyst can be suitably used in the form of a prepolymer powder, prepared manually during a prepolymerization step with the aid of a catalyst as described above. The prepolymerization can be carried out by any suitable process, for example, polymerization in a liquid hydrocarbon diluent or in the gas phase using a batch process, a semi-continuous process or a continuous process. Preferably, substantially all of the recycle gas stream is cooled and the condensed liquid is separated and substantially all of the separated liquid is directly introduced into the fluidized bed through the nozzle (s) as a spray of atomized liquid.

The gaseous recycle stream is suitably cooled by means of a heat exchanger or intercalator at a temperature such that the liquid condenses in the recycle gas stream. The appropriate heat exchangers are well known. The recycle gas stream leaving the top of the reactor may contain an amount of catalyst and / or polymer particles (fine particles) and these may be removed, if desired, from the recycle gas stream by means of a cyclone. A small proportion of these particles can remain contained in the recycle gas stream and after cooling and separating the liquid from the gas, the fine particles can be reintroduced, if desired, into the fluidized bed together with the liquid stream separated through the liquid. (s) nozzle (s). In order to avoid obstruction of the nozzle (s), it is important to ensure that the mechanical device placed inside the outlet (s) has sufficient cleanliness to allow the passage of any fine particles that may be present. in the separate liquid stream. In addition, the outlet (s) of the nozzle (s) must be of sufficient size to allow passage to the fluidized bed together with the liquid spray.

The recycle gas stream may also comprise inert hydrocarbons used for catalyst injection, reaction activators or moderators in the reactor. The processing monomers, for example, ethylene to replace monomers consumed by the polymerization reaction, can be added to the recycle gas stream at any suitable place. The condensable working monomers, for example, butene, hexene, 4-methylpentylene and octene, to replace the condensable comonomers consumed by the polymerization reaction can be introduced as liquids and added to the gaseous stream of recyclable gas at any suitable place. The liquid can be separated from the gaseous recycle stream in a separator. Suitable separators are for example cyclone separators, large vessels that reduce the velocity of the gas stream that effects the separation of the condensed liquid (knock-out drums), showing gas-liquid separators and liquid separators, for example, Venturi separators. Such separators are well known in the art. The use of a separator of the gas-liquid separator type is particularly advantageous in the process of the present invention. The use of a cyclone separator in the recycle gas stream is preferred before the separator. This removes most of the fine particles from the gas stream leaving the reactor, thereby facilitating the use of a particle separator type separator and also reducing the possibility of separator failure, resulting in more efficient operation. An additional advantage of using a particle separator-type separator is that the pressure drop within the separator may be lower than in other types of separators, thereby improving the efficiency of the total process. A particulate separator type separator particularly suitable for use in the process of the present invention is a commercially available vertical gas separator known as "Peerless" (e.g., DPV type P8X). This type of separator uses the coalescence of liquid droplets on a gate installation to separate the liquid from the gas. A large liquid container is provided in the lower part of the separator for collecting the liquid. The liquid container allows the liquid to be stored, thereby providing control over the discharge of the liquid from the separator. This type of separator is very efficient and gives a 100% separation of the condensed liquid coming from the gas stream. If desired, a filter screen or other suitable means may be installed in the separator liquid container to collect any remaining fine particles present in the separated liquid. Alternatively, any fine particle can be kept in suspension and thus avoid faults in the separator when agitated, for example, the liquid in the separator (mechanical agitation), bubble a gaseous stream through the liquid or continuously circulate the liquid by means of an external cycle, that is, the liquid is continuously separated and returned to the separator. Preferably, a portion of the liquid in the separator is circulated continuously by means of a pump. Suitably enough liquid is circulated to allow the pump to operate continuously. A portion of the circulating liquid can be introduced directly into the fluidized bed through a valve that opens to allow liquid to enter a supply line to the nozzle (s). Preferably, the valve is operated through a liquid level controller that monitors and maintains the liquid level in the separator between the established limits.

The separated liquid is suitably introduced into the fluidized bed through installed nozzle (s) above the upper limit of the temperature gradient between the inlet fluidizing gas and the rest of the bed. The nozzle (s) may be in a plurality of points within this region of the fluidized bed and these may be at different heights within this region. The nozzle (s) is installed in such a way that the local concentration of liquid does not adversely affect the fluidization of the bed or the quality of the product, and to allow the liquid to disperse rapidly from each point and evaporate in the bed to remove the polymerization heat from the exothermic reaction. In this way, the amount of liquid introduced for cooling purposes can be more accurately approximated to the maximum load that can be tolerated without disturbing the fluidization characteristics of the bed and thus offers the opportunity to achieve improved levels of reactor productivity. If desired, fluid can be introduced into the fluidized bed through the nozzles located at different heights within the bed. Such a technique can facilitate improved control over the incorporation of comonomer. The controlled introduction of liquid into the fluidized bed through the nozzles provides useful additional control over the temperature profile of the bed, and in the case that the liquid contains comonomer, provides useful control over the incorporation of comonomer into the copolymer . In order to gain the maximum benefit from the cooling of the separated liquid, it is essential that the nozzle (s) be located above the region where this temperature gradient exists, that is, in the part of the bed that has substantially reached the temperature of the recycle gas stream leaving the reactor. The nozzle (s) may for example be approximately 20-200 cm, preferably 50-70 cm above the fluidization grid. In practice, the temperature profile within the fluidized bed can be determined first during the polymerization by the use, for example, of thermocouple located on or on the walls of the reactor. The nozzle (s) is then installed to ensure that the liquid enters the region of the bed in which the returned gas stream has substantially reached the temperature of the recyclable gas stream that is being separated from the reactor. It is important to ensure that the temperature inside the fluidized bed is maintained at a level that is below the agglutination temperature of the polyolefin that constitutes the bed. The gas coming from the separator is recycled in the bed, usually towards the bottom of the reactor. If a fluidization grid is employed, such recirculation is usually towards the region below the grid, and the grid facilitates even distribution of the gas in order to fluidize the bed. The use of a fluidization grid is preferred. The process of the present invention is operated with a gas velocity in the fluidized bed that must be greater than or equal to that required to achieve a bubbling bed. The minimum gas velocity is generally 6-12 cm / sec but the process of the present invention is preferably carried out by the use of a gas velocity in the range of 30 to 100, more preferably 50 to 70 cm / sec. If desired, liquid or liquid-soluble additives, for example, activators, cocatalysts and the like, can be introduced into the bed via nozzle (s) together with the separated liquid. In the case where the process of the present invention is employed to make ethylene homo- or copolymers, the manufacture of ethylene, for example, to replace the ethylene consumed during the polymerization, can advantageously be introduced into the gas stream separated before. of its reintroduction into the bed (for example, below the fluidization grid if such is used). The separated liquid stream can be subjected to additional cooling (for example, by the use of cooling techniques) before being introduced into the fluidized bed through the nozzle (s). An advantage of this particular aspect of the present invention is that, upon cooling the liquid prior to its introduction into the fluidized bed through the nozzle (s), any tendency for the catalyst or prepolymer to be able to be reduced will be reduced. to be contained in the liquid stream causes polymerization before introduction into the bed. Before starting the introduction of liquid by using the process according to the present invention, gas phase fluidized bed polymerization is initiated by charging the bed with particulate polymer particles, and then initiating gas flow through the bed. According to a further embodiment of the present invention, there is provided a process for liquid injection into a fluidized bed comprising: (a) pressurizing the liquid; (b) feeding the pressurized liquid into a liquid inlet of a nozzle; and (c) discharging the liquid in the fluidized bed through an outlet of the nozzle in which the liquid is atomized by the use of a mechanical device placed inside the outlet and an atomized spray is formed within a forming zone of the liquid. dew from the exit. According to still another embodiment of the present invention, there is provided a suitable nozzle for use in the injection of liquid in a fluidized bed, said nozzle comprising: (a) an inlet of pressurized liquid; (b) a liquid outlet in which a mechanical device is provided within the liquid outlet for atomizing the liquid and the liquid outlet is provided with a dew-forming zone. The outlet of the liquid, the mechanical device and the dew-forming zone may have the characteristics described above. The nozzles according to the present invention will be further illustrated with reference to figures 1 to 3, and 5 to 9. Figure 1 depicts a nozzle 1 that is typically provided with four outlets 2 installed equally equally around the circumference of the main region 3 of the nozzle. Pressurized liquid is provided to the nozzle by an inlet (not shown) which is in communication with a centrally located conduit 4 with respect to the main region 3 of the nozzle, where it passes through the outlets 2 and the zones dew-forming 5 towards the fluidized bed. Each outlet is provided with a mechanical device 6 for atomizing the liquid. Figure 2 represents a nozzle 1 provided with two groups of outputs 2 and 7 in which the lower group is placed offset from the upper group. Pressurized liquid is provided to the nozzle through line 8 and controlled by pump 9. Each group of outlets is provided with a separate supply of the pressurized liquid through lines 10 and 11. The supply of liquid to each group of Outlets are controlled by valves 12 and 13. Each outlet is provided with a mechanical device 6 and a spray-forming zone 5. Figure 3 represents an effervescent nozzle. The nozzle 1 is provided with outlets 2. The pressurized liquid is provided to the nozzle by an inlet (not shown) which is in communication with a centrally located conduit 4. Gas is supplied to the nozzle through a conduit 14 and is passed into the pressurized liquid through openings 15.

Each outlet is provided with a mechanical device 6 and a spray-forming zone 5. A polymerization process according to the present invention will be further illustrated with reference to Figure 4. Figure 4 illustrates a phase-bed fluidized reactor of gas consisting essentially of a reactor body 16 which is generally a vertical cylinder having a fluidization grid 17 located in its base. The reactor body comprises a fluidized bed 18 and a velocity reduction zone 19 which is generally of increased cross-section compared to the fluidized bed. The gaseous reaction mixture leaving the upper part of the fluidized bed reactor constitutes the recyclable gaseous stream and is passed through the pipe 20 to a cyclone 21 for the separation of most of the fine particles. The fine particles removed can be suitably returned to the fluidized bed. The recyclable gas stream leaving the cyclone passes into a first heat exchanger 22 and a compressor 23. A second heat exchanger 24 is provided to remove the heat of compression after the recyclable gas stream has passed through the compressor 23.

The heat exchanger or exchangers can be installed either upstream or downstream of the compressor 23. After cooling and compression to a temperature such that a condensate is formed, the resulting gas-liquid mixture is passed to the separator 25 where it is removed the liquid The gas leaving the separator is recycled through the pipe 26 to the bottom of the reactor 16. The gas is passed through the fluidization grid 17 towards the bed, whereby it is ensured that the bed is maintained in a fluidized condition. The separated liquid from the separator 25 is passed through the pipe 27 to the reactor 16 where the liquid is introduced into the reactor 16 through a nozzle according to the present invention. If necessary, a pump 28 can be located suitably in the pipe 27. The catalysts or prepolymers are fed to the reactor through line 29 into the separate liquid stream. The product polymer particles can be suitably removed from the reactor through line 30.

The installation shown in Figure 4 is particularly suitable for use when retrofitting the existing gas phase polymerization reactors using the fluidized bed processes. Figures 5, 6, 7, 8 and 9 illustrate nozzles, or parts thereof according to the present invention having a variety of characteristics. Figure 5 shows a vertical cross-section of a nozzle 40 in the plane of the axis of a duct 41 of circular cross-section for the pressurized liquid. Generally, a dew-forming zone 42 is contained within a cylindrical housing 43. The end 44 of the duct est. { It is manufactured to provide a ventilation type outlet which, when viewed over the end, has an elliptical appearance. The combination of the liquid pressure and the geometry of the end 44 provides the mechanical device to generate a spray. The housing 43 protects the spray-forming zone, allowing the spray to develop before a direct, substantially horizontal outlet 45 emerges to the fluidized bed (not shown). Figure 6 shows a vertical cross-section of a nozzle 46 in the plane of the axis of a conduit 47 of the circular cross-section for pressurized liquid and a dew-forming zone 48 which is protected from the fluidized bed (not shown) by a plate placed horizontally 49. The end 50 of the conduit is manufactured to provide a vent type outlet which, when viewed above the end, has an elliptical appearance. The combination of the liquid pressure and the geometry of the end 50 provide the mechanical device to generate a spray. The plate 49 protects the spray-forming zone 48 allowing the spray to develop before the substantially horizontal direct outlet 51 emerges into the fluidized bed. Figure 7 shows a vertical cross section 52 in the axis plane of a conduit 53 of circular cross-section for pressurized liquid and a dew-forming zone 54 which is protected from the fluidized bed (not shown) by an integral housing 55 having a conical internal cross section. The nozzle is provided with a gate system 56 to generate turbulent flow in the liquid. The liquid spray generation begins at a restriction 57 between the conduit 53 and the dew-forming zone 54. The combination of the liquid pressure, the restriction 57 and the gate system 5 provide the mechanical device for generating a spray. The housing 55 protects the spray-forming zone 54 allowing the spray to develop before the direct, substantially horizontal outlet 58 emerges to the fluidized bed. Figure 8 shows a vertical cross-section of a nozzle 59 in the axis plane of a conduit 60 of circular cross-section for pressurized liquid and a dew-forming zone 61 which is protected from the fluidized bed (not shown) by a plate placed on horizontal way 62 and an arched member 64 integral with the nozzle. An injection of vertical liquid (not shown) arises from the end 63 of the duct 60 and presses on the curved surface 64, thereby generating a spray of the liquid. The spray is protected by the Spray-forming zone 61 that allows the spray to develop before it emerges substantially horizontally in the fluidized bed. Figure 9 shows a vertical cross-section of a nozzle 65 in the axis plane of a conduit 66 of circular cross-section for pressurized liquid and a deforming zone 67 which is protected from the fluidized bed (not shown) by a plate placed on horizontal manner 68 and an integral helical extension 70 of the nozzle. A vertical liquid injection (not shown) arises from the end 69 of the duct 66 and presses partially on the helical extension 70 and partially on the plate thereby generating a spray of the liquid. The spray is protected by the spray-forming zone 67 which allows the spray to develop before it emerges substantially horizontally around the helical extension 70 towards the fluidized bed.

Claims (17)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as novelty and therefore the content of the following claims is claimed as property. 1. A gas fluidized bed continuous process for the polymerization of olefin monomer selected from (a) ethylene, (b) propylene, (c) mixtures of ethylene and propylene and (d) one or more different alpha-olefins mixed with (a), (b) or (c), in a fluidized bed reactor by the continuous recycling of a gas stream comprising at least some ethylene and / or propylene through a fluidized bed in said reactor in the presence of a polymerization catalyst under reactive conditions, cooling at least part of said gaseous stream separated from said reactor being cooled to a temperature at which the liquid condenses, separating at least part of the condensed liquid from the gas stream and introducing at least part of the liquid separated directly in the fluidized bed by: (a) pressurizing the liquid; (b) feeding the pressurized liquid into a liquid inlet of a nozzle; and (c) discharging the liquid in the fluidized bed through an outlet of the nozzle in which the liquid is atomized "by the use of a mechanical device placed inside the outlet and an atomized spray is formed within a spray-forming zone of the outlet 2. A process according to claim 1, characterized in that the spray-forming zone of the outlet is locates inside the nozzle 3. A process according to claim 1, characterized in that the spray-forming zone is defined by a wall that is integral part of the nozzle, or which protrudes from the nozzle, or which is secured in relation to the nozzle. with a nozzle 4. A process according to claim 3, characterized in that the wall comprises a tube or a plate 5. A process according to any of the preceding claims, characterized in that the nozzle is placed inside the fluidized bed and has 2 to 4. A process according to any of the preceding claims, characterized in that the outlet is a groove having an elliptical shape 7. A process according to any of the re Claim 1, characterized in that the fluidized bed reactor is provided with a plurality of nozzles. A process according to any of the preceding claims, characterized in that the nozzle has a series of outlets installed in groups circumferentially around the nozzle. 9. A process according to claim 8, characterized in that the groups of outlets are installed in a number of rows around the circumference of the nozzle. A process according to claim 8 or 9, characterized in that each group of outputs is connected separately to a supply of pressurized liquid. 11. A process according to any of the preceding claims, characterized in that the atomized liquid spray is injected into the bed in a substantially horizontal direction. 12. A process according to any of the preceding claims, characterized in that the nozzle has a liquid flow rate in the range of 9.5 to 70 m liquid / s / m3 output cross-sectional area where the liquid flow proportion of The nozzle is defined as the liquid volumetric flow rate (m3 / s) per cross section area per unit (m2). A process according to any of the preceding claims, characterized in that a small amount of gas is introduced into the liquid before the liquid passes through the mechanical device. 14. A process according to claim 13, characterized in that the amount of gas is in the range of 0.5 to 10 weight percent, based on the total weight of gas and liquid that passes through the nozzle. 15. A process according to any of the preceding claims, characterized in that the catalyst is activated transition metal based on the metallocene catalyst. 16. A process for injecting liquid into a fluidized bed comprising: (a) pressurizing the liquid; (b) feeding the pressurized liquid into a liquid inlet of a nozzle; and (c) discharging the liquid in the fluidized bed through an outlet of the nozzle in which the liquid is atomized by the use of a mechanical device positioned within the outlet and an atomized spray is formed within a forming zone of the liquid. dew from the exit. 17. A suitable nozzle to be used for the injection of liquid in a fluidized bed, said nozzle comprising: (a) an inlet of pressurized liquid; and (b) a liquid outlet in which a mechanical device is provided within the liquid outlet to atomize the liquid and the liquid outlet is provided with a dew-forming zone.