Method for continuous transfer of polymer slurries

A polymer slurry composed of solid polymer particles and a diluent such as an inert hydrocarbon and or an inert halogenated hydrocrbon, kept at a sufficient super-atmospheric pressure to maintain the diluent in the liquid state, is continuously introduced into a heating tube divided into a first and a second heating zone, the diameter of the second heating zone being larger than that of the first heating zone. The flow rate of the slurry passing through the first heating zone is controlled by regulating the amount of heat supplied to the first heating zone. Substantially all of the vaporized diluent is then introduced into a separation zone and separated from the solid polymer particles.

BACKGROUND OF THE INVENTION 
This invention relates to improvements in a method for the transfer of 
polymer slurries and, more particularly, to a method for the continuous 
transfer of a fluid slurry composed of solid polymer particles and a 
diluent wherein the polymer slurry kept under pressure is continuously 
passed at a controlled flow rate through two heating zones to vaporized 
the diluent therefrom and then is introduced into a separation zone to 
separate the solid polymer particles from the vaporized diluent. 
Prior to this invention, it had been proposed (U.S. Pat. Nos. 3,285,899 and 
3,428,619) that a polymer slurry should be transferred through a flash 
tube adapted to separate the solid polymer particles from the diluent. 
More specifically, U.S. Pat. No. 3,285,899 discloses a method for the 
transfer of a polymer slurry composed of solid polyolefin and a diluent, 
wherein the pressurized polymer slurry is introduced into a sealed heating 
zone of lower pressure and gradually increasing cross-sectional areas to 
vaporize the diluent from the polymer slurry. The resulting dispersion of 
substantially dried polyolefin particles in the diluent vapor is so 
treated as to isolate the solid polyolefin. It is evident from the 
description of the example of U.S. Pat. No. 3,285,899 that the flow rate 
of the polyolefin slurry introduced into the heating zone is regulated by 
means of an intermittently-actuated valve installed immediately upstream 
of the heating zone. However, the polyolefin slurry is intermittently 
introduced into the heating zone because the aforesaid valve is controlled 
by the on-off action of a timer. As a result of such intermittent 
introduction, the pressure and flow rate of the stream leaving the heating 
zone downstream of the valve tend to pulsate considerably. 
U.S. Pat. No. 3,428,619 discloses improvements in a similar method of 
transfer of a polymer slurry. Also in this method, the polymer slurry is 
introduced into a heating zone by way of an intermittently actuated valve, 
the supply of polymer slurry being regulated by varying the period of its 
opening and closing cycles. Accordingly, the pressure and flow rate of the 
stream leaving the heating zone downstream of the valve still tend to 
pulsate heavily with time. 
When the transfer of polymer slurries is carried out on an industrial 
scale, the above-described heavy pulsations of the stream leaving the 
heating zone bring about the following disadvantages. 
Firstly, since the diluent vapor separated from the solid polymer particles 
is cooled and then compressed for liquefaction, a surge tank of very large 
size is required in order to minimize the effect of the pulsations and to 
even the load on the compressor. 
Secondly, the intermittently actuated valve for regulating the flow rate of 
the polymer slurry can easily be damaged because it opens and closes with 
high frequency and the difference between its upstream and downstream 
pressures is great. Moreover, while the valve is closed, the deposited 
solid polymer particles, swollen with the diluent, melt on the inner wall 
of the heating zone, which thus tends to clog. This tendency increases 
especially when copolymers of low softening point are handled. 
Thirdly, since the polymer slurry is intermittently supplied to the heating 
zone, the zone is loaded with slurry only for a fraction of the time and, 
therefore, a large-size apparatus is required. 
SUMMARY OF THE INVENTION 
It is therefore an object of this invention to provide a method for the 
continuous transfer of polymer slurries. 
It is another object of this invention to provide a method for the 
non-pulsating transfer of a polymer slurry in which the flow rate of the 
slurry introduced continuously into a heating zone is controlled 
indirectly without using any intermittently-actuated installed in the 
stream of the slurry flow. 
It is still another object of this invention to provide a method for the 
continuous transfer of a polymer slurry easily and with small-size 
apparatus, and without clogging in the heating zone. 
These and other objects, features and advantages of this invention will 
become apparent from the following brief description of the improvement 
contributed to the art. 
In the method of transfer of a polymer slurry composed of solid polymer 
particles and at least one diluent selected from the group consisting of 
inert hydrocarbons and inert halogenated hydrocarbons, the polymer slurry, 
kept at a sufficient super-atmospheric pressure to maintain the diluent in 
the liquid state, is passed sequentially through a first elongated heating 
zone of a relatively small diameter and a second elongated heating zone of 
a diameter larger than that of said first heating zone. Both first and 
second heating zones are heated with vapors of a heating medium or with 
steam so as to vaporize said diluent into a carrier vapor to convey the 
resulting polymer particles. The mixture of diluent vapor and dried solid 
polymer particles is passed into a separation zone to separate said solid 
polymer particles from said diluent. The improvement provided by this 
invention comprises introducing the polymer slurry continuously into the 
first heating zone, and controlling the flow rate of the polymer slurry 
passing through said first heating zone by regulating the amount of heat 
supplied to the first heating zone by the heating medium or steam.

DETAILED DESCRIPTION OF THE INVENTION 
Among the solid polymer particles which can be treated by the method of the 
invention are: a particulate homopolymer or copolymer of mono-1-olefin(s) 
having from 2 to 8 carbon atoms, such as polyethylene, polypropylene, 
polybutene and the like; a particulate polyvinyl chloride; and a 
particulate copolymer of mono-1-olefin(s) and vinyl chloride. 
Diluents which can be used to suspend the solid polymer particles may be 
any inert hydrocarbon or inert halogenated hydrocarbon that remain liquid 
when kept under pressure and become gaseous at approximately atmospheric 
pressure and at about 20.degree. C. Examples of such diluents include 
propane, propylene, butane, butene, vinyl chloride, and methyl chloride. 
The polymer slurry, kept in a slurry vessel at a pressure sufficient to 
maintain the diluent in the liquid state, is then passed into a heating 
zone, and then introduced into a separation zone which is kept at 
essentially atmospheric pressure. The heating zone comprises a first 
elongated heating zone of relatively small diameter and a second elongated 
heating zone of a diameter larger than that of the first heating zone, 
both first and second heating zones being heated (preferably) with steam. 
A discharge valve is installed between the slurry vessel and the first 
heating zone. This valve is kept fully open throughout the slurry transfer 
operation. Accordingly the polymer slurry is continuously passed from the 
slurry vessel into the first heating zone. 
Generally, industrial production based on continuous processes involves 
variations in output (due to load fluctuations). It is desirable, 
therefore, that each process step is continuously carried out at any load 
factor of between 50% and 100%. 
The goal of this invention is focused on the way in which the flow rate of 
the polymer slurry is passed from the slurry vessel into the first heating 
zone. In case of fluid flow, flow control valves of the type which can be 
continuously throttled to cause a pressure drop necessary for flow rate 
regulation have been used widely. In case of a slurry, however, since 
protruded parts in the flow path tend to cause clogging due to the thick 
deposition of solid particles, no throttling can be applied to ensure a 
substantial pressure drop. This invention employs a novel control method 
which, instead of using a flow control valve, is based on the following 
fundamental findings: 
(1) The ratio of vapor to liquid at different points in the flow path of a 
polymer slurry can be controlled by modifying the heating conditions along 
the flow path; (2) If the mass velocity is fixed, the pressure loss across 
a length of section varies widely according to the ratio of vapor to 
liquid; (3) Accordingly, the flow rate of the polymer slurry passing 
through a section across which a given pressure difference exists can be 
controlled by modifying the heating conditions and hence the vaporization 
rate of the diluent along the flow path; and (4) Heat transfer from 
condensation of vapor such as steam, exhibiting a high heat transfer 
coefficient, should be used in order to transfer heat to a fluid flowing 
at high velocity. 
In the method of the invention, the aforesaid fundamental findings are 
employed as described here below. The polymer slurry introduced into the 
first heating zone is heated with steam to vaporize the diluent. The ratio 
of vaporized diluent to the remaining liquid in the first heating zone is 
controlled by regulating the amount of heat supplied to the polymer 
slurry. The amount of heat supplied to the polymer slurry is regulated 
either (1) by varying the temperature of the heating medium or steam in 
the first heating zone, (2) by varying the flow rate of the heating medium 
or steam in the first heating zone, or (3) by dividing the first heating 
zone into at least two separate heating subzones of identical diameter and 
supplying a desired number of separate heating subzones with the heating 
medium or steam to vary the heat transfer surface area. The ratio of vapor 
to liquid in the first heating zone changes in proportion to the amount of 
heat supplied to the polymer slurry. At a fixed mass velocity, vapor shows 
a much greater pressure loss than liquid, so that the pressure drop 
between the inlet and outlet of the first heating zone varies widely 
according to the amount of heat supplied to the polymer slurry. As a 
result, the flow rate of polymer slurry passing through the first heating 
zone also varies. The flow rate of polymer slurry can be increased or 
decreased by decreasing or increasing the amount of heat supplied to the 
first heating zone, respectively. 
The stream leaving the first heating zone is then introduced into a second 
heating zone. In the second heating zone, the remaining liquid diluent is 
vaporized and the diluent is maintained in the vapor phase. Accordingly, 
the second heating zone is always heated with steam. 
While the polymer slurry is passing through the first and second heating 
zones, substantially all of the liquid diluent in the polymer slurry is 
vaporized. The resulting high-velocity stream of diluent vapor maintains 
the solid polymer particles in a uniformly suspended state and carries 
them into the separation zone, where the dried solid polymer substantially 
free of diluent is separated from the diluent vapor. 
The heating zones used in the method of the invention preferably comprise 
steam jacketed pipes. The ratio of the diameter of the first heating zone 
to that of the second heating zone is suitably in the range of from 1:1.2 
to 1:3. If both heating zones have an identical diameter, the flow rate of 
polymer slurry may fail to be controlled satisfactorily. Preferably, the 
diameter of the first heating zone is not less than about 0.6 cm. In 
consideration of the amount of polymer slurry to be treated and other 
conditions, those skilled in the art will be able to properly determine 
its optimum diameter without any difficulty. 
In order to maintain the separated solid polymer particles in a well-dried 
condition, the length of each heating zone is desirably determined so as 
to be approximately proportional to its diameter. For either of the first 
and second heating zones, the ratio of diameter to length is preferably in 
the range of from 1:400 to 1:6,000. If the ratio is too high, the flow 
rate of polymer slurry may fail to be controlled satisfactorily, while if 
it is too low, the separated solid polymer particles may not be properly 
dried. 
Preferably, the flow velocity of polymer slurry at the inlet of the first 
heating zone is in the range of from 3 to 20 m/sec, and the flow velocity 
of polymer/diluent mixture at the outlet of the second heating zone is in 
the range of from 14 to 150 m/sec. 
Preferably, the pressure in the slurry vessel is in the range of from 10 to 
30kg/cm.sup.3 G, the pressure at the inlet of the first heating zone is in 
the range of from 10 to 30kg/cm.sup.2 G, the pressure at the outlet of the 
first heating zone is in the range of from 5 to 27kg/cm.sup.2 G, and the 
pressure at the outlet of the second heating zone is in the range of from 
0.1 to 7 kg/cm.sup.2 G. The pressure in the separation zone is also in the 
range of from 0.1 to 7kg/cm.sup.2 G. 
The vapor-to-liquid ratio of diluent at the inlet of the first heating zone 
may vary from 0%, but is preferably in the range of from 0 to 20%. The 
vapor-to-liquid ratio of diluent at the outlet of the first heating zone 
may increase to as much as about 80%. The operating conditions of both 
heating zones should be controlled so that the vapor-to-liquid ratio of 
diluent at the outlet of the second heating zone will be substantially 
100%. 
It is desirable that the temperatures of the first and second heating zones 
do not exceed the softening point of the solid polymer particles in the 
polymer slurry by more than 50.degree. C. The lower limit of these 
temperatures may be determined, according to the type of diluent, so that 
the separated solid polymer particles will be maintained in a well-dried 
condition. 
The method of the invention can suitably be applied to flash drying 
processes in which a polymer slurry derived from a process for preparing 
homopolymers and copolymers as defined above is expanded by reducing the 
initial super-atmospheric pressure to essentially atmospheric pressure and 
the diluent is thereby separated from the solid polymer to obtain 
substantially dried solid polymer particles. During the preparation of the 
polymer, a catalyst suspending agent such as pentane, hexane, heptane, 
benzene, toluene or xylene is generally used. In addition, a catalyst 
decomposing agent such as propylene oxide, acetylacetone, or isopropanol 
is often used in the catalyst decomposition step following the 
polymerization step. Accordingly, the diluent used in the method of the 
invention may contain not more than 20% by weight of the aforesaid 
catalyst suspending agent and/or catalyst decomposing agent. 
PREFERRED EMBODIMENTS OF THE INVENTION 
In order that those skilled in the art may better understand the invention, 
two preferred embodiments thereof are described below with reference to 
the accompanying drawings. 
Referring first to FIG. 1, the polymer slurry which is provided in a slurry 
vessel 1 kept under pressure is passed by way of a discharge valve 2 
(which is kept fully open throughout the slurry transfer operation) 
sequentially through a first heating zone 3 (comprising a jacketed heating 
pipe of relatively small diameter) and a second heating zone 4 (comprising 
a jacketed heating pipe of relatively large diameter), and then is 
introduced into a separation zone (cyclone) 5. Thereafter, the separated 
solid polymer particles are withdrawn through a rotary valve 6 into a 
removal line 8. On the other hand, the diluent vaporized in first and 
second heating zones 3 and 4 is removed directed through an effluent line 
9 to a separate recovery process. 
As illustrated in FIG. 1, the first heating zone 3 is equipped (preferably) 
with a steam supply line 10 which serves to introduce steam into its 
heating jacket and has a steam flow regulating valve 7, and with a steam 
trap 11 for separating the steam condensate produced in its jacket and a 
steam condensate discharge line 12 connected thereto. Similarly, the 
second heating zone 4 is equipped with a steam supply line 13 which serves 
to introduce steam into its heating jacket and has a steam inlet valve 14, 
and with a steam trap 15 for separating the steam condensate produced in 
its jacket and a steam condensate discharge line 16. The steam inlet valve 
14 installed in steam supply line 13 is kept open throughout the slurry 
transfer operation and is not manipulated even if it is desired to vary 
the flow rate of the polymer slurry. 
In contrast, the steam flow regulating valve 7 is manipulated in response 
to the desired flow rate of polymer slurry. That is, the flow rate of 
steam supplied to the first heating zone 3 is regulated until the flow 
rate of polymer slurry is adjusted to the predetermined level. 
FIG. 2 shows the relationship between the amount of steam supplied to the 
jacket of the first heating zone 3 and the flow rate of polymer slurry 
passing through the first heating zone 3, on the basis of data obtained 
from a series of runs which will hereafter be described in Example 1. The 
data reveal that the flow rate of polymer slurry observed when steam flow 
rate regulating valve 7 is fully open is reduced to about 50% of that 
achieved when no steam is supplied to the jacket of the first heating zone 
3. 
FIG. 3 illustrates a second embodiment of the invention in which, instead 
of using steam flow regulating valve 7 to directly regulate the flow rate 
of steam supplied to the jacket of the first heating zone 3, the first 
heating zone is divided into a plurality of separate heating subzones 
having a relatively small diameter and the amount of diluent vaporized in 
the first heating zone is controlled by varying the heat transfer surface 
area. More specifically, the apparatus of FIG. 3 is similar to that of 
FIG. 1 except that the first heating zone 3 is replaced by five separate 
heating subzones 30-1 to 30-5 of identical size. In these separate heating 
subzones 30-1 to 30-5, steam is supplied form a main steam supply line 20 
through steam flow regulating solenoid valves 21-1 to 21-5 to their 
respective jackets and steam condensate is discharged from steam traps 
22-1 to 22-5. In the second heating zone 30-6, steam is supplied through a 
steam inlet valve 21-6 to its jacket, the steam inlet valve 21-6 being 
kept at a predetermined degree of opening throughout the slurry transfer 
operation, and steam condensate is discharged from a steam trap 22-6. If a 
maximum flow rate of polymer slurry passing through the subdivided first 
heating zone is desired, all of the solenoid valves 21-1 to 21-5 are to be 
closed. As the desired flow rate of polymer slurry decreases, solenoid 
valves 21-1 to 21-5 are sequentially opened. When all of them are opened, 
the flow rate of steam supplied to the first heating zone is maximized 
and, therefore, the flow rate of polymer slurry passing through the first 
heating zone is minimized. Thus, the flow rate of polymer slurry is 
controlled stepwise by varying the heat transfer surface area of the first 
heating zone. The greater the number of the separate heating subzones is, 
the more delicately the flow rate of polymer slurry can be controlled. 
As described above, the method of the invention makes it possible to 
control the flow rate of a polymer slurry over a wide range. Therefore, 
when the amount of polymer slurry to be treated has changed for good 
operational reasons, the amount of heat supplied to the polymer slurry may 
be correspondingly controlled during the slurry transfer operation. Thus, 
the method of the invention enables one to continuously transfer a polymer 
slurry from the slurry vessel through a first and a second heating zone to 
a separation zone and continuously collect substantially dried solid 
polymer particles and diluent vapor from the separation zone. 
Moreover, as a result of the continuous (i.e. not intermittent) transfer of 
polymer slurry, the method of the invention requires only a small-size 
apparatus on account of the high operating efficiency of the heating zones 
and thereby achieves greater economy than conventional methods involving 
intermittent transfer of the polymer slurry. Furthermore, as contrasted 
with conventional methods using an intermittently actuated valve, diluent 
vapor is continuously fed to a recovery process, whereby the recovery 
process can be operated without disturbance in the flow and the surge tank 
for absorbing pulsating flows can be reduced in size. 
To further illustrate this invention and not by way of limitation, the 
following examples are given. 
EXAMPLE 1 
This example is described with reference to FIG. 1. 
(a) Preparation of the slurry 
A catalyst suspension composed of 0.15 kg/hr of titanium trichloride, 0.3 
kg/hr of diethylaluminum chloride, and 19 kg/hr of heptane was added to 
869 kg/hr of propylene (containing 6% by weight of propane), which was 
thereby polymerized to produce 522 kg/hr of polypropylene. To the 
resulting polymer slurry, 6 kg/hr of isopropanol and 6 kg/hr of propylene 
oxide were added so as to decompose the catalysts. The polymerization and 
catalyst decomposition steps were carried out at a temperature of 
60.degree. C. and a pressure of 24 kg/cm.sup.2 G. 
(b) Process of the invention 
The resulting polypropylene slurry (containing 58% by weight of solid 
polypropylene particles) was continuously passed from slurry vessel 1 
through a fully opened discharge valve 2 first into a heating zone 3 
comprising jacketed pipe of about 0.9 cm inner diameter and 30 m in length 
and the N into a second heating zone 4 comprising a jacketed pipe of about 
1.9 cm inner diameter and 40 m in length, the jacket of each heating zone 
being independently supplied with steam having a pressure of 2 kg/cm.sup.2 
G and a temperature of 135.degree. C., and finally into a separation zone 
5, which included a cyclone, and had its outlet kept at a pressure of 0.4 
kg/cm.sup.2 G. Dried polypropylene powder was separated from the 
accompanying propylene vapor carrier and then removed through a rotary 
valve 6, while the propylene vapor was continuously exhausted through an 
effluent line 9 to a separate recovery process. 
Throughout the above-described operation, the steam inlet valve 14 present 
in the steam supply line leading to the jacket of second heating zone 4 
was kept fully open. On the other hand, the flow rate of steam supplied to 
the jacket of first heating zone 3 was regulated by varying the degree of 
opening of a steam flow regulating valve 7. The flow rates of 
polypropylene slurry observed in a series of runs are shown in FIG. 2. 
In this example, the flow rate of polypropylene slurry could be controlled 
over a range of from 500 to 1,000 kg/hr. The residual volatile content of 
polypropylene powder collected from withdrawal line 8 was 0.15% by weight. 
Control 1 
A polypropylene slurry similar to that of Example 1 was passed through a 
3/4-inch V-port valve (nominal) into a heating zone kept at a pressure of 
0.4 kg/cm.sup.2 G at the downstream end. The heating zone comprised a 
double tube 1.9 cm (3/4 inch) in inner diameter and 40 m in length. This 
tube was heated by supplying its jacket with steam having a pressure of 2 
kg/cm.sup.2 G and a temperature of 135.degree. C. The relationship between 
the degree of opening of the V-port valve and the flow rate of 
polypropylene slurry is shown in Table I. 
Table 1 
______________________________________ 
Degree of Opening of 
Flow Rate of Polypropylene 
V-port Valve (%) 
Slurry (kg/minute) 
______________________________________ 
100 19.5 
50 19.5 
20 18.0 
______________________________________ 
From the data shown in Table I it is noted that the flow rate of 
polypropylene slurry remained almost unchanged when the degree of opening 
of the V-port valve was varied. 
Table II shows the results of a series of runs in which several orifices of 
difference diameter were inserted in place of the V-port valve. As it is 
evident from the date shown in Table II, the flow rate exhibited only a 
very slight decrease even when an orifice of 7 mm diameter was inserted. A 
run using an orifice of 5 mm diameter had to be discontinued because the 
orifice was blocked with polymer particle immediately after starting the 
run. 
Table II 
______________________________________ 
Diameter of Orifice 
Flow Rate of Polypropylene 
(mm) Slurry (kg/minute) 
______________________________________ 
none 19.5 
10 19.3 
7 17.3 
______________________________________ 
EXAMPLE 2 
This example is described with reference to FIG. 3. A polypropylene slurry 
containing 45% by weight of polypropylene particles in propylene was 
provided in a slurry vessel 1 kept at a temperature of 40.degree. C. and a 
pressure of 14 kg/cm.sup.2 G. The polypropylene slurry was continuously 
passed from the slurry vessel 1 through a fully open outlet valve 2 into a 
first heating zone divided into five separate subzones 30-1 to 30-5. 
Thereafter, it was passed through a second heating zone 30-6 and then 
introduced into a separation zone 5 comprising a cyclone kept at a 
pressure of 0.3 kg/cm.sup.2 G. 
Each of the separate heating subzones 30-1 to 30-5 comprised a jacketed 
tube of about 2.5 cm inner diameter and 16 m in length, and the second 
heating zone 30-6 comprised a jacketed tube of about 3.75 cm inner 
diameter and 60 m in length. Steam having a pressure of 1.4 kg/cm.sup.2 G 
was supplied from a main steam supply line 20 and distributed to the 
separate subzones 30-1 to 30-5 and to the second heating zone with the aid 
of hand-operated valves 21-1 to 21-5 and an on-off valve 21-6. 
The on-off valve 21-6 was kept fully open throughout each run. In contrast, 
the hand-operated valves 21-1 to 21-5 associated with the respective 
separate heating subzones were either fully opened or fully closed. Table 
III shows the relationship between the number of separate heating subzones 
supplied with steam and the flow rate of polypropylene slurry. 
The dried polypropylene powder was withdrawn through a rotary valve 6 and 
the diluent vapor was continuously removed overhead through an effluent 
line 9 and sent to a recovery process. 
Table III 
__________________________________________________________________________ 
Flow Rate of 
Temperature of 
Volatile Content 
Number of Separate 
Polypropylene 
Collected of Collected 
Heating Subzones 
Slurry Polypropylene 
Polypropylene 
Supplied with Steam 
(tons/hours) 
(C.degree. ) 
(% by weight) 
__________________________________________________________________________ 
5 4.9 120 0.05 
3 7.5 110 0.10 
0 10.3 95 0.18 
__________________________________________________________________________ 
In all runs, the volatile content of polypropylene powder collected from 
withdrawal line 8 was not higher than 0.2% by weight, suggesting that the 
powder was in a well-dried state. 
Control 2 
A polypropylene slurry similar to that of Example 1 was introduced into a 
heating zone kept at a pressure of 0.3 kg/cm.sup.2 G at the downstream 
end. The heating zone comprised 10 series-connected jacketed tube about 
1.9 cm in inner diameter and 4 m in length. Steam having a pressure of 2 
kg/cm.sup.2 G and a temperature of 135.degree. C. was supplied through 
hand-operated valves to the jackets of the tubes. The hand-operated valves 
were so manipulated as to supply only a desired number of tubes with 
steam. Table IV shows the relationship between the number of tubes 
supplied with steam and the flow rate of polypropylene slurry. 
Table IV 
______________________________________ 
Number of Flow Rate of Temperature of 
Tubes Supplied 
Polypropylene Collected 
with Steam Slurry (kg/minute) 
Polypropylene (.degree. C) 
______________________________________ 
10 19.5 125 
8 19.9 118 
6 21.5 95 
4 26.0 60 
______________________________________ 
As the number of tubes supplied with steam decreased, the flow rate of 
polypropylene slurry increased but the temperature of the collected 
polypropylene decreased. When only four pipes were supplied with steam, 
the volatile content of collected polypropylene was as high as 3.0% by 
weight. 
EXAMPLE 3 
A polyethylene slurry containing 40% by weight of polyethylene particles in 
isobutane was provided in a slurry vessel kept at a temperature of 
80.degree. C. and a pressure of 16kg/cm.sup.2 G. Using the apparatus of 
Example 1, the polyethylene slurry was continuously fed in the same manner 
as described in Example 1. It was observed that when steam was not 
supplied to the heating jacket of first heating zone 3 with valve 7 fully 
closed, the flow rate of the polyethylene slurry was 1,200 kg/hr, while 
when 4.0kg/hr of steam was supplied with valve 7 fully open, the flow rate 
of the polyethylene slurry was 500 kg/hr and when the valve 7 was half 
open, the flow rate of the polyethylene slurry exhibited an intermediate 
value. 
On the other hand, steam inlet valve 14 was kept fully open throughout each 
run, so that steam was always supplied to the heating jacket of second 
heating zone 4. 
In all runs, the temperature of the polyethylene collected from line 8 was 
in the range of from 80.degree. to 120.degree. C. and the volatile content 
was in the range of from 0.1 to 0.4% by weight. No blockage of the heating 
zones was observed.