PROCESS AND REACTOR ASSEMBLY FOR THE ENHANCEMENT OF HYDRODYNAMICS IN A GAS-SOLIDS FLUIDIZED BED REACTOR

Abstract

A process for polymerizing olefin monomer(s) in a gas-solids olefin polymerization reactor comprising a top zone; a middle zone, which comprises a top end in direct contact with said top zone and which is located below said top zone, the middle zone having a generally cylindrical shape; and a bottom zone, which is in direct contact with a bottom end of the middle zone and which is located below the middle zone; comprising the following steps: introducing a fluidization gas stream into the bottom zone; polymerizing olefin monomer(s) in the presence of a polymerization catalyst in a dense phase formed by particles of a polymer of the olefin monomer(s) suspended in an upwards flowing stream of the fluidization gas in the middle zone; introducing a jet gas stream through one or more jet gas feeding ports in a jet gas feeding area of the middle zone at the dense phase in the middle zone of the gas-solids olefin polymerization reactor; wherein the kinetic energy (E.sub.JG) input in the reactor by the jet stream is between 1.5 and 50 times higher than the kinetic energy (E.sub.FG) input in the reactor by the fluidization gas stream (FG).

Claims

1. A process for polymerizing olefin monomer(s) in a gas-solids olefin polymerization reactor comprising: a top zone (1); a middle zone (2), which comprises a top end in direct contact with said top zone and which is located below said top zone (1), the middle zone (2) having a generally cylindrical shape; and a bottom zone (3), which is in direct contact with a bottom end of the middle zone (2) and which is located below the middle zone (2); comprising the following steps: a) introducing a fluidization gas stream (6, FG) into the bottom zone (3); b) polymerizing olefin monomer(s) in the presence of a polymerization catalyst in a dense phase (4) formed by particles of a polymer of the olefin monomer(s) suspended in an upwards flowing stream of the fluidization gas in the middle zone (2); c) introducing a jet gas stream (8, JG) through one or more jet gas feeding ports (5) in a jet gas feeding area of the middle zone (2) at the dense phase (4) in the middle zone (2) of the gas-solids olefin polymerization reactor; wherein the kinetic energy (E.sub.JG) input in the gas-solids olefin polymerization reactor by the jet stream (JG) is between 1.0 and 50 times higher than the kinetic energy (E.sub.FG) input in the gas-solids olefin polymerization reactor by the fluidization gas stream (FG) as expressed by relation (I) $\begin{array}{cc}1.0\le \frac{E_{\mathrm{JG}}}{E_{\mathrm{FG}}}\le 50& \left(I\right)\end{array}$ wherein the kinetic energy of the fluidization gas (E.sub.FG) is calculated according to equation (II): $\begin{array}{cc}{E}_{\mathrm{FG}}=P_{\mathrm{FG}}.Math.V_{\mathrm{FG}}.Math.\ln \left(\frac{P_{\mathrm{FG}}}{P_{\mathrm{FG}}-h.Math.\rho .Math.g}\right)& \left(\mathrm{II}\right)\end{array}$ with E.sub.FG being the energy dissipated by the expansion of the fluidisation gas into the fluidized bed, [W] P.sub.FG being the pressure of the fluidisation gas at the bottom of the gas-solids olefin polymerization reactor, [Pa] V.sub.FG being the volumetric flow rate of the fluidisation gas, [m.sup.3/s] h being the bed height of the collapsed bed, [m] ρ being the bulk density of the collapsed bed, [kg/m.sup.3] g being the gravity constant, [m/s.sup.2] and wherein the kinetic energy of the jet gas (E.sub.JG) is calculated according to equation (III): $\begin{array}{cc}{E}_{\mathrm{JG}}=P_{\mathrm{JG}}.Math.V_{\mathrm{JG}}.Math.\ln \left(\frac{V_{{\mathrm{FG}}_2}}{V_{\mathrm{JG}}}\right)& \left(\mathrm{III}\right)\end{array}$ with E.sub.JG being the energy dissipated by the expansion of the jet gas into the fluidized bed, [W] P.sub.JG being the pressure of the jet gas at entry in the gas-solids olefin polymerization reactor, [Pa] V.sub.FG2 being the volumetric flow rate of the fluidisation gas, [m.sup.3/s] V.sub.JG being the volumetric flow rate of the jet gas, [m.sup.3/s].

2. The process according to claim 1, wherein the fluidization gas is removed from the top zone (1) of the reactor and at least a part of the fluidization gas is introduced into the jet gas stream (8) and into the fluidization stream (6).

3. The process according to claim 1, wherein the jet gas stream (JG) fed through at least one of the one or more jet gas feeding ports (5) is provided by a flash pipe (FP) from a preceding reactor, preferably a reactor for polymerizing polypropylene, more preferably a loop reactor for polymerizing polypropylene.

4. The process according to claim 1, wherein the jet gas stream (JG) is cooled to yield a partially condensed jet gas stream and wherein the fluidization gas stream (FG) is not condensed.

5. The process according to claim 1, wherein the fluidization gas stream (FG) in the first line (6) and the jet gas stream (JG) in the third line (8) are heated up, wherein the temperature difference between the jet gas stream (JG) and the fluidization gas stream (FG) is at least 20° C., preferably at least 30° C. and most preferably of at least 38° C., wherein the temperature of the fluidization gas stream (FG) is higher than the temperature of the jet gas stream (JG).

6. A reactor assembly for polymerizing olefin monomer(s) comprising a gas-solids olefin polymerization reactor comprising: a top zone (1); a middle zone (2), which comprises a top end in direct contact with said top zone (2) and which is located below said top zone (1), the middle zone (2) having a generally cylindrical shape; and a bottom zone (3), which is in direct contact with a bottom end of the middle zone (2) and which is located below said middle zone (2); one or more feeding ports (5) located in a feeding area of the middle zone (2); a first line (6) for feeding a fluidization gas stream (FG) into the bottom zone (3) of the gas-solids olefin polymerization reactor, a second line (7) for withdrawing a stream comprising fluidization gas from the top zone (1) of the gas-solids olefin polymerization reactor, a third line (8) for introducing a jet gas stream (JG) into the middle zone (2) of the gas-solids olefin polymerization reactor via the one or more feeding ports (5), and means (9) located in the first line (6) for providing kinetic energy to the fluidization gas stream (FG) prior to entry of the gas-solids olefin polymerization reactor and means (10) located in the third line (8) for providing kinetic energy to the jet gas stream (FG) prior to entry of the gas-solids olefin polymerization reactor, wherein the means for providing kinetic energy to the fluidization gas stream (9) and the means for providing kinetic energy to the jet gas stream (10) are configured so that the kinetic energy (E.sub.JG) input in the gas-solids olefin polymerization reactor by the jet stream (JG) is between 1.0 and 50 times higher than the kinetic energy (E.sub.FG) input in the gas-solids olefin polymerization reactor by the fluidization gas stream (FG) as expressed by relation (I) $\begin{array}{cc}1.0\le \frac{E_{\mathrm{JG}}}{E_{\mathrm{FG}}}\le 50& \left(I\right)\end{array}$ wherein the kinetic energy of the fluidization gas (E.sub.FG) is calculated according to equation (II): $\begin{array}{cc}{E}_{\mathrm{FG}}=P_{\mathrm{FG}}.Math.V_{\mathrm{FG}}.Math.\ln \left(\frac{P_{\mathrm{FG}}}{P_{\mathrm{FG}}-h.Math.\rho .Math.g}\right)& \left(\mathrm{II}\right)\end{array}$ with E.sub.FG being the energy dissipated by the expansion of the fluidisation gas into the fluidized bed, [W] P.sub.FG being the pressure of the fluidisation gas at the bottom of the gas-solids olefin polymerization reactor, [Pa] V.sub.FG being the volumetric flow rate of the fluidisation gas, [m.sup.3/s] h being the bed height of the collapsed bed, [m] ρ being the bulk density of the collapsed bed, [kg/m.sup.3] g being the gravity constant, [m/s.sup.2] and wherein the kinetic energy of the jet gas (E.sub.JG) is calculated according to equation (III): $\begin{array}{cc}{E}_{\mathrm{JG}}=P_{\mathrm{JG}}.Math.V_{\mathrm{JG}}.Math.\ln \left(\frac{V_{{\mathrm{FG}}_2}}{V_{\mathrm{JG}}}\right)& \left(\mathrm{III}\right)\end{array}$ with E.sub.JG being the energy dissipated by the expansion of the jet gas into the fluidized bed, [W] P.sub.JG being the pressure of the jet gas at entry in the gas-solids olefin polymerization reactor, [Pa] V.sub.FG2 being the volumetric flow rate of the fluidisation gas, [m.sup.3/s] V.sub.JG being the volumetric flow rate of the jet gas, [m.sup.3/S]

7. The reactor assembly according to claim 6, wherein the means for providing kinetic energy to the jet gas stream (10) is a flash pipe (FP) from a preceding reactor, preferably a reactor for polymerizing polypropylene, more preferably a loop reactor for polymerizing polypropylene.

8. The reactor assembly according to claim 7, wherein the gas-solids olefin polymerization reactor further comprises: one or more flash pipe feeding ports (18) located in a feeding area of the middle zone (2); and a sixth line (19) for introducing a flash pipe gas stream (FP) into the bottom zone (2) of the gas-solids olefin polymerization reactor via the one or more flash pipe feeding ports (18).

9. The reactor assembly according to claim 6 further comprising a heat exchanging device (16) in the first line (6) and/or a heat exchanging device (17) in the third line (8).

10. The reactor assembly according to claim 9, wherein the heat exchanging device (17) is a cooler for cooling the jet gas stream (JG) to a partially condensed jet gas stream and wherein the fluidization gas stream (FG) is not condensed.

11. The reactor assembly according to claim 9, wherein the heat exchanging device (16) in the first line (6) and the heat exchanging device (17) in the third line (8) are heaters and wherein the heat exchanging devices (16, 17) are configured to heat the fluidization gas stream (FG) in the first line (6) to a higher temperature than the jet gas stream (JG) in the third line (8).

12. The process of claim 1, wherein the carry-over of particles of the polyolefin of the olefin monomer(s) into the second stream withdrawn from the top zone of the gas-solids olefin polymerization reactor is reduced.

13. The process of claim 1, wherein the bulk density of the dense phase is increased during polymerization.

14. The reactor assembly of claim 6, wherein the carry-over of particles of the polyolefin of the olefin monomer(s) into the second stream withdrawn from the top zone of the gas-solids olefin polymerization reactor is reduced.

15. The reactor assembly of claim 6, wherein the bulk density of the dense phase is increased during polymerization.

Description

SHORT DESCRIPTION OF THE FIGURES

[0121] FIG. 1 shows a fluidized bed reactor as known from the prior art.

[0122] FIG. 2 shows a fluidized bed reactor according to the present invention having jet gas injection and means for providing energy to the fluidization gas and jet gas.

[0123] FIG. 3 shows a fluidized bed reactor according to the present invention having heat exchangers in the first line (6) and or the third line (8) FIG. 4 shows a fluidized bed reactor assembly according to the present invention having jet injection capabilities connected to a flash pipe from a preceding polymerization reactor.

[0124] FIG. 5 shows a schematic view of the reactor assembly as used in the examples RE1, CE1, and IE1-3.

[0125] FIG. 6 shows a diagram exemplifying the results of example IE4.

[0126] FIG. 7 shows a diagram exemplifying the results of examples RE3, CE4, and IE6.

DETAILED DESCRIPTION OF THE FIGURES

[0127] FIG. 1 shows a fluidized bed reactor as typically used. Typical hydrodynamic patterns are depicted. Gas bubbles generated by the distribution plate move preferably in the center of the reactor upwards. These bubbles in the center create a cylindrical hydrodynamic patter, in which the inner parts of the cylinder move upwards, while the outer parts move downwards. In the lower part of the reactor, where the centralizing of the bubbles has not happened yet, the above-described pattern induces another hydrodynamic pattern, which acts counter wise. As a result, there is a calm zone, in which the solid-gas mixture is not moving very rapidly. In this zone, wall sheeting can occur. Furthermore, as a result of solid entrainment into the disengaging zone, sheeting can also occur further upstream of the reactor middle zone.

[0128] FIG. 2 shows an embodiment of the process according to the present invention in a fluidized bed reactor.

[0129] Reference signs [0130] 1 top zone (disengaging zone) [0131] 2 middle zone [0132] 3 bottom zone [0133] 4 fluidized bed (dense zone) [0134] 5 jet gas feeding port(s) [0135] 6 first line (fluidization gas (FG) input) [0136] 7 second line (fluidization gas output) [0137] 8 third line (jet gas (JG) input) [0138] 9 means for providing kinetic energy to the fluidization gas [0139] 10 cooler means for providing kinetic energy to the jet gas [0140] 11 feeding port for polymerization catalyst [0141] 12 polymer withdrawal [0142] 13 fluidization grid [0143] 14 fourth line connecting the third line (8) and the second line (7) [0144] 15 fifth line connecting the third line (8) and the first line (6)

Description of FIG. 2

[0145] FIG. 2 shows an embodiment of the gas-solids olefin polymerization reactor system according to the present invention. The fluidized bed reactor comprises a top zone (1), a middle zone (2) and a bottom zone (3). The first stream of fluidization gas (6) enters the fluidized bed reactor through the bottom zone (3) and flows upwards, thereby passing a fluidization grid (13) and entering the middle zone (2). Due to the substantially cylindrical shape of the middle zone (2) the gas velocity is constant so that the fluidized bed (4) is established after the fluidization grid (13) in the middle zone (2). Due to the conical shape of the top zone (1) the gas entering the top zone (1) expands so that the gas disengages from the polyolefin product of the polymerization reaction so that the fluidized bed (4) is confined in the middle zone (2) and the lower part of the top zone (2). The polymerization catalyst together with optional polyolefin powder polymerized in previous polymerization stage(s) is introduced into the fluidized bed reactor through at least on feeding port (11) directly into the fluidized bed (4). The polyolefin product of the polymerization process is withdrawn from the fluidized bed reactor through outlet (12).

[0146] The fluidized gas is withdrawn from the top zone (1) as second stream of fluidization gas (7). The first line (6) transporting the fluidization gas comprises means (9) for providing kinetic energy to the fluidization gas. Furthermore, the third line (8) transporting the jet gas comprises another means (10) for providing kinetic energy to the jet gas. These means are configured in that the ratio of the kinetic energy of the jet gas (EJG) introduced into the reactor to the kinetic energy of the fluidization gas introduced into the reactor is 1.0 to 50, preferably 1.7 to 25, and most preferably 2.0 to 15. The means can be any means for providing the gas streams with kinetic energy. Such means comprise blowers, compressors, such as screw compressors, and fans. Preferably, the means are blowers or compressors. More preferably, the means are blowers. In one preferred embodiment, the means for providing kinetic energy to the fluidization gas is a blower and the means for providing kinetic energy to the jet gas is a screw compressor.

[0147] In a particularly preferred embodiment of the invention, the solids-gas reactor according to the present invention (FIG. 2b) further comprises a fourth line (14) connecting the second line (7) and the third line (8) as well as a fifth line (15) connecting the third line (8) and the first line (6). Hence, in this embodiment at least part of the fluidization gas leaving the reactor from the top zone is recycled and reintroduced into the reactor either as fluidization gas or jet gas. The advantage of such an arrangement is that lower amounts of fluidization gas is needed and the overall process is less energy consuming as at least part of the heat as removed with the fluidization gas from the reactor is reintroduced at the bottom or via the jet gas feeds reducing the amount of energy needed to bring the gas streams to the temperature as needed for the reaction on the reactor.

[0148] FIG. 3 shows another embodiment of the process according to the present invention in a fluidized bed reactor.

REFERENCE SIGNS

[0149] The reference sign 1-15 are identical to FIG. 2. [0150] 16 heat exchanger located in the first line (6) for feeding the fluidization gas into the reactor. [0151] 17 heat exchanger located in the third line (8) for feeding the jet gas into the reactor

Description of FIG. 3

[0152] FIG. 3 demonstrates a first preferred embodiment of the present invention. In addition to the setup as shown in FIG. 2 and described above, the reactor assembly comprises heat exchangers (1, 17) in the first line (6) for introducing fluidization gas and in the third line (8) for introducing jet gas into the reactor. These heat exchangers might be used for cooling and/or for heating the respective gas streams.

[0153] In a first more preferred embodiment of the first preferred embodiment of the present invention, both heat exchangers are used for heating up the streams to a certain temperature suiting the needs for the polymerization reaction in the reactor. More preferably, the reactor assembly comprises heat exchangers (16) and (17) at the first line (6) and the third line (8), respectively. These heat exchangers are configured to heat the fluidization gas and the jet gas up to temperatures having a temperature difference of at least 20° C., preferably at least 30° C. and most preferably of at least 38° C., whereas the fluidization gas has higher temperature than the jet gas.

[0154] In a second more preferred embodiment of the first preferred embodiment according to the present invention, the reactor assembly comprises only heat exchanger (16) in the first line (6), whereas the jet gas stream (8) is not heated at all and the fluidization gas is heated up to 40° C., preferably 50° C. and most preferably 60°.

[0155] Above-mentioned features could also be applied to a reactor assembly independently from the means for providing energy to the fluidization gas and jet has stream (9, 10) without losing the technical advantage. As indicated in FIG. 3b, the features of the additional heat exchangers can be combined with the features of the fluidization gas recirculation (e.g. lines 14/15).

[0156] These embodiments have the technical advantage that in the reactors of these embodiments show reduced solid entrainment in the upper part of the reactor at maintained cooling capabilities of the reactor. Further, improved mass and heat transfer results from setups according to the first more preferred embodiment.

[0157] In a third more preferred embodiment of the first preferred embodiment of the present invention, the heat exchanger (17) located in the third line (8) is a cooler. In such an embodiment, the cooler (17) is configured to provide an at least partially condensed jet gas stream into to be introduced into the reactor.

[0158] Also in the third more preferred embodiment of the first preferred embodiment of the present invention, above-mentioned features could also be applied to a reactor assembly independently from the means for providing energy to the fluidization gas and jet has stream (9, 10) without losing the technical advantage. As indicated in FIG. 3b, the feature of the additional cooler can be combined with the features of the fluidization gas recirculation (e.g. lines 14/15).

[0159] Such a setup has the technical advantage of improving heat removal by increased heat transfer without having the risk of blocking of the distribution grid and wetting of the lower part of the fluidized bed avoiding formation of agglomerations such as lumps.

[0160] FIG. 4 shows another embodiment of the process according to the present invention in a fluidized bed reactor.

REFERENCE SIGNS

[0161] The reference sign 1-15 are identical to FIG. 2. [0162] 18 flash pipe jet gas feeding port(s) [0163] 19 sixth line connecting a flash pipe (FB) to reactor via feeding port(s) 18. [0164] FP flash pipe from a preceding polymerization reactor

[0165] As can be seen in FIGS. 4a-c, in this second preferred embodiment of the present invention, either the whole jet gas injection system is completely replaced by a solids-gas stream derived from a flash pipe (FP, 5, 8; FIG. 4a) or at least one jet stream is derived from a flash pipe (FP, 18, 19, FIG. 4b-c) in addition to the jet stream as already described in the embodiments of FIGS. 2 and 3 (JG, 5, 8; FIG. 4b-c). Further combinations can be implemented, e.g. a reactor assembly having flash pipe jet gas input and fluidization gas recirculation without the jet gas injection as described in the embodiments of FIGS. 2 and 3 (i.e. line 8 via port(s) 5). As indicated by the dotted lines of the heat exchanger (16, 17), the features of the present embodiment can be used in combination with the features and improvements of the embodiment according to FIG. 3, but also without. The same holds in parallel to the embodiments according to FIG. 3 for the feature of the means for providing kinetic energy to the fluidization gas and the jet gas, respectively.

[0166] The stream derived from a flash pipe of a preceding polymerization reaction, preferably a polymerization reactor for the polymerization of polypropylene, most preferably a loop polymerization reactor for the polymerization of polypropylene, has a very high energy (momentum). Hence, the resulting jet gas stream has also much higher energy than the jet gas stream as provided by the fluidization gas. The technical effect of such an embodiment is that the hydrodynamic pattern as found in typical fluidized bed reactors (i.e. without jet gas injection) can be more efficiently destroyed yielding an increase in bulk density at reduced solids carry-over.

[0167] FIG. 5 shows the reactor assembly as used in the examples in the present invention. The numbers given in the figure relate to respective heights and widths of the components of the assembly given in centimeters. The fluidization gas (FG) is accelerated by an 11 kW blower and an 18 kW blower and enters the bottom zone of the reactor before passing the distribution grid (Distributor 1). The jet gas (JG) is compressed by a 30 kW screw compressor and passes a mass flow meter (MFM) before entering the reactor to determine the kinetic energy provided to the jet gas stream. Finally, the fluidization gas removed from the top zone is directed to a double suction filter to analyze the solids carry over effect.

Examples

[0168] A gas-solids olefin polymerization reactor according to FIG. 5 (values in cm) was used for examples RE1, CE1, and IE1-3. This reactor is equipped with a fluidization grid (Distributor 1), a catalyst feeding port and a disengaging zone to assess the effect of the ratio of the power inputs on the solids carry over. The reactor had a diameter of 0.8 m and height of 4.4 m. The following experimental procedure steps were followed for all the gas experiments: [0169] i) Starting to inject fluidization gas (FG, air) into the bottom of the fluidized bed reactor to form the bottom of the fluidized bed (FB) [0170] ii) Feeding polyolefin powder with a powder feed of 10 kg/min through the catalyst feeding port to form the fluidized bed (FB) [0171] iii) Increasing the fluidized bulk density (BD) of the bed in the middle zone of the fluidized bed reactor to about 310 kg/m.sup.3 [0172] iv) Starting to inject air (jet gas (JG)) through one feeding port situated in the middle zone of the fluidized bed reactor (only CE1 and IE1-3) [0173] v) Stopping polymer powder feed [0174] vi) Keeping fluidization gas (FG) and (JG) feed constant

Reference Example 1 (RE1)

[0175] The gas-solids olefin polymerization reactor was filled with LLDPE powder up to 130 cm height yielding a bulk density of 445 kg/m.sup.3 and was fluidized with air with a density equal to 1.2 kg/m.sup.3 under a volumetric flow of 543 m.sup.3/h (corresponding to a superficial gas velocity of 0.30 m/s). The pressure drop over the bed was 56.31 mbar and the power dissipated to the fluidized reactor via the fluidization gas calculated according to equation 1 was 0.876 kW.

Comparative Example 1 (CE1)

[0176] Reference Example 1 was repeated with the only difference that jet gas was used with a split of 25% v/v. Thus, 407 m.sup.3/h air was used as fluidization gas and the rest (136 m.sup.3/h) was used as jet gas. The pressure drop across the jet gas line was equal to 0.3 bar and a nozzle with an internal diameter equal to 3.3 cm was employed to inject the jet gas. The power input by the jet gas line to the fluidized reactor calculated according to equation 2 was 0.989 kW, the energy split (i.e., power input by the jet gas divided by the power input by the fluidization gas), was 1.13. No reduction in solids carry over and no increase in fluidized bed density was observed during operation.

Inventive Example 1 (IE1)

[0177] Comparative Example 2 was repeated with the same jet gas split. Thus, 407 m.sup.3/h air was used as fluidization gas and the rest (136 m.sup.3/h) was used as jet gas. The pressure drop across the jet gas line was 0.5 bar and a nozzle with an internal diameter of 2.6 cm was employed to inject the jet gas. The power input by the jet gas line to the fluidized reactor calculated according to equation (III) was 1.53 kW, the energy split (i.e., power input by the jet gas divided by the power input by the fluidization gas), was 1.75. A reduction in solids carry over and an increase in fluidized bed density was observed during operation starting from the injection of the jet gas. At the steady state the increase was 3%.

Inventive Example 2 (IE2)

[0178] Comparative Example 1 was repeated with the same jet gas split. Thus, 407 m.sup.3/h air was used as fluidization gas and the rest (136 m.sup.3/h) was used as jet gas. The pressure drop across the jet gas line was 1.0 bar and a nozzle with an internal diameter of 1.8 cm was employed to inject the jet gas. The power input by the jet gas line to the fluidized reactor calculated according to equation (III) was 2.6 kW, the energy split (i.e., power input by the jet gas divided by the power input by the fluidization gas), was 3.0. A significant reduction in solids carry over and an increase in fluidized bed density was observed during operation starting from the injection of the jet gas. At the steady state the increase was 7%.

Inventive Example 3 (IE3)

[0179] Comparative Example 1 was repeated with the same jet gas split. Thus, 407 m.sup.3/h air was used as fluidization gas and the rest (136 m.sup.3/h) was used as jet gas. The pressure drop across the jet gas line was 2.0 bar and a nozzle with an internal diameter of 1.3 cm was employed to inject the jet gas. The power input by the jet gas line to the fluidized reactor calculated according to equation (III) was 4.14 kW, the energy split (i.e., power input by jet gas divided by the power input by the fluidization gas), was 4.75. A significant reduction in solids carry over and a significant increase in fluidized bed density was observed during operation starting from the injection of the jet gas. At the steady state the increase was 12%.

TABLE-US-00001 TABLE 1 Results dependent on the EJG/ EFG ratio. RE1 CE1 IE1 IE2 IE3 E.sub.FG [kW] 0.876 0.876 0.876 0.876 0.876 E.sub.JG [kW] − 0.989 1.53 2.6 4.14 E.sub.JG/E.sub.FG − 1.13 1.75 3.0 4.75 Reduction solids 0 0 + ++ ++ carry over Increase bulk 0 0 + + ++ density 0 no reduction/increase + reduction/increase ++ significant reduction/increase

Inventive Example 4 (IE4)

[0180] This example is used to illustrate the technical effect of the first preferred embodiment according to FIG. 3.

[0181] The fluidized bed (FB) of the reactor was filled up to 86 cm with HDPE powder and fluidized with cold fluidization gas first. The superficial gas velocity just above the distribution grid was 0.37 m/s.

[0182] At t=2.5 min (cf. FIG. 6), the heating of the fluidization gas stream was switched and the fluidization gas stream was heated up to 65° C. The fluidized bed was heated at a constant fluidization gas flow of 91 m.sup.3/h until thermal equilibrium was reached after 70 min.

[0183] At t=72 min, the jet gas injection was switched on for cooling at flow of 46 m.sup.3/h jet gas and at a pressure drop of 3 bar. The temperature of the jet gas was 25° C. (room temperature).

[0184] It can be seen from the temperature profile as depicted in FIG. 6 that the cooling of the powder by the jet gas stream is very effective. The contact between gas and powder leads to an improved heat exchange and the good mixing of the bed leads to a smooth decreasing of bed temperature. Consequently, the jet gas stream does not only contribute in decreasing the solids carry over, sufficient heat removal but also in close to ideal gas-solids mixing.

[0185] The latter effect is evident by the fact that the temperature in the dense phase of the fluidized bed (i.e. T1, cf. FIG. 6) is very close to the temperature of the fluidization gas in the top zone (T3) as well as the temperature of the jet gas (T2). Such a temperature profile is a good indication of efficient mixing conditions (T1, T2 and T3 collapse to the same line from t=72 min onwards).

Reference Example 2 (RE2)

[0186] In the following examples RE2, CE2-3 and IE5 the technical effect of the second preferred embodiment according to FIG. 3 is demonstrated.

[0187] An ethylene-1-butene polymerization process in a gas-solids olefin polymerization reactor equipped with a distribution plate was used. 5% mole of 1-butene was added to the gas-solids olefin polymerization reactor. The reactor was operated at an absolute pressure of 20 bar and a temperature of 85° C. Propane was used as fluidization gas. The bed was formed from polyethylene (LLDPE) particles having an average diameter (d.sub.50) of 400 μm. The LLDPE had a density of 923 kg/m.sup.3 and a MFR.sub.5 of 0.23 g/10 min.

[0188] The dimensions of the reactor assembly were:

[0189] Height of the bottom zone: 900 mm

[0190] Height of the middle zone: 2700 mm

[0191] Height of the upper zone: 415 mm

[0192] Diameter of the middle zone: 540 mm

[0193] The reactor as described above was operated so that flow rate of the fluidization gas was 570 m.sup.3/h. The bed was filled with LLDPE with a filling degree of about 60% of the volume of the middle zone. The superficial gas velocity at the gas inlet, where the diameter of the reactor was 100 mm, was 16 m/s and in the middle zone 0.7 m/s. The heat removal rate was estimated around 1.7 K/h. No jet gas stream was employed.

Comparative Example 2 (CE2)

[0194] The procedure of Reference Example 2 was repeated with the exception that 15 wt % of the gas feed was condensed (i.e. 15 wt % condensed fluidization gas). The heat removal rate was 1.9 K/h.

Comparative Example 3 (CE3)

[0195] The procedure of Reference Example 2 was repeated with the only difference that jet gas injection was employed with a central cooler for both the jet gas line and the fluidization gas line. Hence, 25 vol % of the gas-liquid mixture volume was injected as jet gas and the remaining 75 vol % was fed to the reactor via the bottom zone as fluidization gas. Overall 15 wt % condensed fluidization gas was injected in the reactor. This fluidization gas was condensed by the central cooler. Consequently, 75 wt % of the condensed fluidization gas was fed in the bottom zone and the remaining 25 wt % was fed via the jet gas line. The heat removal rate was 2.2 K/h.

Inventive Example 5 (IE5)

[0196] The procedure of Comparative Example 3 was repeated with the only difference that the jet gas was employed following the process design illustrated in FIG. 3. Hence, the cooler was placed separately in the jet gas line only. Thus, 25 vol % was injected as jet gas stream and the remaining 75 vol % of was fed to the reactor via the bottom part. Overall, 15 wt % condensed fluidization gas was injected in the reactor. In contrast to Comparative Example 1, it was fed exclusively via the jet gas feeding port. The heat removal rate was 2.6 K/h.

Reference Example 3 (RE3)

[0197] In the following examples RE3, CE4, and IE6 the technical effect of the embodiment according to FIG. 4 is demonstrated. The following experimental procedure was followed for all experiments: [0198] i) Injection of fluidization gas (FG) in the bottom zone of the reactor. [0199] ii) Starting the powder feed via the feed screw (7.65 kg/min) into the reactor. [0200] iii) Increasing the reactor fluidized bed density until it reaches 300 kg/m.sup.3. [0201] iv) Optionally injecting jet gas (JG, CE4, IE6). [0202] v) Stopping the powder feed. [0203] vi) Keeping the fluidization gas (FG) and jet gas (JG) streams constant.

[0204] In this example no jet gas injection was employed. The superficial gas velocity at the end of the dense phase of the fluidized bed reactor (i.e., end of the cylindrical section of the reactor) was constant and equal to 0.60 m/s (also the superficial gas velocity just above the distribution plate was equal to 0.6 m/s since not jet gas was introduced). The conditions and the main results related to the reference fluidization experiment are illustrated in Table 2.

TABLE-US-00002 TABLE 2 Experimental fluidization conditions using a jet gas stream. Conditions Values FG Flow, m.sup.3/h 152.5 (100% split) JG Pressure drop,  P.sub.JG, bar 0 JG Flow, m.sup.3/h 0.00 (0% split)  JG Velocity, m/h 0.00 Overall Gas Feed, m.sup.3/h 152.5 SGV, m/s 0.60 SGV.sub.Distr, m/s 0.60 Fluidized Bed Density, ρ.sub.bed, kg/m.sup.3 115

Comparative Example 4 (CE4)

[0205] Reference Example 3 was repeated by employing superficial gas velocity just above the distribution plate equal to 0.51 m/s (i.e. 129.2 m.sup.3/h). Moreover, 23.3 m.sup.3/h was used as jet gas with a pressure drop of 1 bar so that the overall superficial gas velocity was 0.60 m/s, cf. Table 3. It can be seen that the jet gas stream significantly reduces the solids carry over, while the bulk density of the fluidized bed increases from 115 kg/m.sup.3 to 200 kg/m.sup.3).

TABLE-US-00003 TABLE 3 Experimental fluidization conditions using a jet gas stream. Conditions Values FG Flow, m.sup.3/h 129.0 (84.7% split) JG Pressure drop, ΔP.sub.JG, bar 1 JG Flow, m.sup.3/h  23.3 (15.3% split) JG Velocity, m/h 0.09 Overall Gas Feed, m.sup.3/h 152.50 SGV, m/s 0.60 SGV.sub.Distr, m/s 0.51 Fluidized Bed Density, ρ.sub.bed, kg/m.sup.3 155

Inventive Example 6 (IE6)

[0206] Reference Example 3 was repeated by employing superficial gas velocity just above the distribution plate of 0.33 m/s (i.e. 84.5 m.sup.3/h). Moreover, 68.0 m.sup.3/h was used as jet gas stream with a pressure drop of 5 bar so that the overall superficial gas velocity was 0.60 m/s.

[0207] The huge pressure drop across the jet gas injection pipe was selected to simulate the energy input coming from the gas-solid stream which in practice can be injected e.g. from a loop reactor via a flash pipe.

[0208] It can be seen from Table 4 that introducing such an energy input into the reactor makes it possible to substantially increase the fluidized bed density which in turn to reduces the solids carry over.

[0209] Hence, Inventive Example 7 suggests that injecting a gas-solid mixture with an increased pressure drop as jet gas results in increase of the bulk density and in decrease of the solids entrainment (cf. also FIG. 7).

TABLE-US-00004 TABLE 4 Experimental fluidization conditions using a gas-solids stream (simulated via 5 bar pressure drop across JG injection pipe). Conditions Values FG Flow, m.sup.3/h 84.5 (55.4% split) JG Pressure drop, ΔP.sub.JG, bar* 5 JG Flow, m.sup.3/h 68.0 (44.6% split) JG Velocity (equivalent), m/h 0.27 Overall Gas Feed, m.sup.3/h 152.5 SGV, m/s 0.60 SGV.sub.Distr, m/s 0.33 Fluidized Bed Density, ρ.sub.bed, kg/m.sup.3 200