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Claims  |
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What is claimed is:
1. A gear pump for pumping highly viscous media comprising: housing means
defining an inlet passage at one end, an outlet passage at an opposite end
and a chamber therebetween; a pair of pump gears generally horizontally
positioned within said chamber having intermeshing teeth and being
rotatably mounted in said housing, said chamber and said pump gears
defining therebetween a media free space; said chamber and each of said
gears defining gear sealing zones adjacent said outlet passage, each
sealing zone having a minimum length equal to the circumferential distance
between two adjacent gear teeth across the full axial length of the gears
at the outside diameter of said gears; said media free space expanding
from the end of said seal zones remote from said outlet passage such that
an increasing hydraulic radius is produced at least to the plane of the
tops of said gears, said increasing hydraulic radius being produced by an
increasing horizontal dimension of the chamber from the end of said seal
zones remote from said outlet passage to the plane of the tops of said
gears, whereby a pressure gradient is created to fill the gear cavities
with said viscous media; said outlet passage adjacent said sealing zones
having a cross-sectional area of from 0.2 to 2.0 times the product of the
gear width and the gear tooth height; and said chamber increasing in
cross-sectional area above the tops of said gears to the top of said
chamber, thereby enhancing the pumping capacity and volumetric efficiency
of said gear pump.
2. The pump in accordance with claim 1 wherein said outlet is generally
rectangular in shape having a width equal to the gear face width and a
length equal to the gear tooth height with the major dimension being
parallel to the gear axis.
3. The pump of claim 1, wherein the ratio of media free space clearance to
the circumferential distance from said seal zone is in the range of about
0.2 to 0.9.
4. The pump of claim 1, wherein said media free space is defined by the
interior surface of said housing such that the free space increases in
cross section from said seal zone in a smooth continuous curve, to a
location upstream of said gears.
5. The pump of claim 1, wherein said housing comprises a pair of modular
housing portions defining said media free space at their interior surfaces
and symmetrical about the mesh line of said gears; a pair of end structure
modules abutting the axial ends of said housing portions and rotatably
mounting said gears, said end structures extending beyond said housing
portions; and a modular outlet structure nested with the outlet of said
housing portions between said end structures, and means interconnecting
said modules.
6. The pump of claim 1, further including means in said housing means for
introducing an additive to said viscous media.
7. The pump of claim 6, wherein said introducing means includes an extruder
having its outlet positioned adjacent said free space and its inlet
exterior of said housing.
8. The pump of claim 7, wherein said housing means defines a feedback
chamber extending from said pump outlet to a point upstream of said
extruder outlet, whereby polymer may be initially mixed with the additive
in said extruder.
9. The pump of claim 8, wherein introducing means is positioned to
introduce the additive at a location upstream of said chamber.
10. The pump of claim 1, further including a pair of feed rollers rotatably
mounted upstream of said pair of gears, the axis of each roller being
substantially parallel to the axis of the associated gear, and said
rollers being spaced apart to define a media nip substantially coplanar
with the mesh line of said gears; said housing means including wiper means
adjacent each roller; and means for rotating said rollers to draw said
media into and feed said gears.
11. The pump of claim 10, wherein said means for rotating said rollers
includes a gear train operatively coupling each roller to its associated
gear, whereby the rollers are driven conjointly with said gears.
12. The pump of claim 10, wherein said means for rotating said rollers
includes a drive means operatively coupled to said rollers, whereby said
rollers are driven independently of said gears.
13. The pump of claim 10, wherein said rollers are modular in construction,
whereby the axial length thereof may be varied.
14. The pump of claim 1, wherein said housing is modular and includes two
interconnected portions.
15. The pump of claim 14, wherein said housing modular portions are
symmetrical about the mesh line of the gears.
16. The pump of claim 14, wherein said housing modular portions are
symmetrical about the plane extending transversely to said gear axes.
17. The pump of claim 16, further including modular housing insert means
interposed between and complementary to said modular portions.
18. The pump of claim 14, wherein said housing includes removable central
insert means, said insert means defining said media free space at their
inner surface.
19. The pump of claim 18, wherein said insert means extends the full axial
dimension of said gear face width.
20. A gear pump for pumping highly viscous media provided to the pump in
rope-like strand form comprising: housing means defining an inlet passage
at one end, an outlet passage at an opposite end and a chamber
therebetween; a pair of pump gears located within said chamber having
intermeshing teeth and being rotatably mounted in said housing, said
chamber and said pump gears defining a media free space; said chamber and
each of said gears defining gear sealing zones adjacent said outlet
passage, each sealing zone having a minimum length equal to the
circumferential distance between two adjacent gear teeth across the full
axial length of the gears at the outside diameter of said gears; said
media free space expanding from the end of said seal zones remote from
said outlet passage such that an increasing hydraulic radius is produced
at least to the plane of the tops of said gears, said increasing hydraulic
radius being produced by a dimension of the chamber measured in a plane
parallel to the plane passing through the axes of said gears, said
dimension increasing from the end of said seal zones remote from said
outlet passage to the plane of the tops of said gears, whereby a pressure
gradient is created to fill the gear cavities with said viscous media;
said outlet passage adjacent said sealing zones having a cross-sectional
area of from 0.2 to 2.0 times the product of the gear width and the gear
tooth height; said chamber increasing in cross-sectional area above the
tops of said gears to the top of said chamber, thereby enhancing the
pumping capacity and volumetric efficiency of said gear pump; and a pair
of feed rollers rotatably mounted in said chamber upstream of said gears,
the axis of each roller being substantially parallel to the axis of the
associated gear and said rollers being spaced apart to define a media nip
substantially coplanar with the mesh line of said gears, and means for
rotating said gears and rollers, whereby said rope strand is drawn into
and feeds the gear cavities and thereafter pumped by said gears.
21. The pump in accordance with claim 20, wherein said outlet is generally
rectangular in shape having a width equal to the gear face width and a
length equal to the gear tooth height with the major dimension being
parallel to the gear axis.
22. The pump of claim 20, wherein the ratio of media free space clearance
to the circumferential distance from said seal zone is in the range of
about 0.2 to 0.9.
23. The pump of claim 20, wherein said means for rotating said rollers
includes a gear train operatively coupling each roller to its associated
gear, whereby the rollers are driven conjointly with said gears.
24. The pump of claim 20, wherein wiper means are provided adjacent each of
said rollers. |
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Claims |
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Description |
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The present invention relates to apparatus for handling polymers and more
particularly to apparatus for handling compositions of polymers and
volatile constituents, such as polyethylene and ethylene, and means for
increasing the efficiency of compounding systems for these compositions.
As employed herein, the term "polymer(s)" is understood to mean organic
homopolymers, copolymers, and polymeric mixtures either alone or
containing additives of the type normally encountered in the plastics
field, e.g., stabilizers, fillers, processing aids, colorants and other
additives (such as anti-block, anti-oxidation, anti-static and the like).
BACKGROUND
In the typical production of low density polyethylene, a reactor discharges
a stream which is a mixture of polymer and unreacted materials to a
product receiver. The product receiver operates at a pressure
substantially below the reactor pressure and flow of the reactor discharge
is controlled by the product valve. In the product receiver, the major
portion of the unreacted materials are removed due to flashing which
results from the drop in pressure experienced by the mixture. The flashed
material, commonly referred to as the return gas, is subsequently returned
to the reactor. The remaining polymerized material settles in the product
receiver and still contains some unreacted materials which are removed in
the remainder of the polymer recovery system.
The polymer discharged from the product receiver is fed to an extruder
through a polymer flow control system. The extruder performs two functions
in this system: (1) final devolatilization to remove the remaining
unreacted material; (2) pumping of the polymer through a screen pack, if
one is being used, and a pelletizer die plate.
The material enters the side of the extruder and the unreacted materials
flash and form a foam having a very low density. Therefore an extruder
having a very large volumetric conveying capacity in the feed section is
necessary to handle the material as the final devolatilization is
occurring. Normally, an extruder having a two-diameter screw or an
oversize single-diameter screw is necessary to obtain the necessary
conveying capacity to handle the material entering the extruder. In some
installations a portion of the flashed material is removed from the
extruder through a top mounted vent stack.
As the production rate of single low density polyethylene (LDPE) reactors
are increased, larger and larger extruders, which become prohibitively
expensive, are needed. In an effort to eliminate the use of two-diameter
extruders or oversized extruders, some existing units have been modified
to include a secondary ethylene separation (flashing) operation upstream
of the extruder inlet subsequent to the primary product receiver ethylene
separation (flashing) operation.
This system differs from the side fed extruder top mounted vent stack type
in that the material is fed into the top of the vent stack and essentially
all of the remaining unreacted materials are released before the polymer
stream enters the extruder. This provides a material to the extruder which
has a much greater density and eliminates the need for two-diameter
extruders or large single-diameter extruders. The devolatilization and
pumping functions of the original, two-diameter extruder system have now
been separated, i.e. the final devolatilization is performed in the vent
stack and only the polymer pumping is performed by the extruder. However,
extruders pump polymer by developing viscous drag, and are very
inefficient pumps.
SUMMARY OF THE INVENTION
The present invention has utility in a plastics recovery system in which
polymer produced in a reactor is partially devolatilized in a product
receiver, transferred to the top of a vent stack for further
devolatilization and flood feed to a low net positive suction head gear
pump.
The use of the specially designed gear pump of the present invention having
a free filling space surrounding substantially the entire periphery of the
gears allows an interaction of the material being pumped caused by the
rotating gears and the pump body above the sealing zones to generate
pressure above the pump inlet pressure, similar to the pressure generation
that occurs in a hydrodynamic bearing, to facilitate filling of the gear
tooth cavities. Additionally, the shear areas and energy dissipation in
shear is an order of magnitude lower than comparable positive displacement
pumps.
Specifically, the gear pump includes a pair of intermeshing, rotatable
gears surrounded by a filling chamber increasing in volume toward the pump
inlet. Horizontal gear axis orientation is preferred, but not essential.
The gears seal with the housing at a minimum seal area sized to seal
substantially the distance between adjacent teeth across the fill axial
length near the outlet of the pump, said outlet having a cross-sectional
area from 0.2 to 2.0 times the product of the gear tooth height and the
gear face width.
The outlet is preferably rectangular in shape with the major dimension
parallel to the axes of the gears. The outlet may, however, be circular,
oval or of any other cross-sectional shape desired from the operating
standpoint.
In some polymer processing systems where the polymer is discharged in the
form of a rope, a pair of rollers is provided directly above the gears.
The rollers pull the polymer rope into a charging area between the rollers
and gears to fill the gear cavities and also densify the foamed polymer.
Suitable instrumentation is disclosed for monitoring pump parameters to
provide on line viscosity and production rate control.
Thus, the features to be described in greater detail below include a
comprehensive low density polymer recovery system which includes a novel
gear pump for reduced capital, operational and maintenance cost.
Another feature is a novel gear pump structure for handling a broad range
of production rates.
A further feature is a gear pump having roller charging capabilities for
pumping polymer material produced in the form of strand or rope.
Yet another feature is the provision of on line additive injection at the
pump of a recovery system and modular construction of the pump body, feed
gears and rollers.
These and still other features will be readily apparent from the drawings
and disclosure to follow.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a low energy recovery system in accordance
with the present invention;
FIG. 2 is an enlarged cross-sectional view of a gear pump for use in the
low energy recovery system of FIG. 1;
FIG. 3 is a cross-sectional view with certain portions broken away for
clarity taken generally along line 3--3 in FIG. 2;
FIG. 4 is a top plane view taken generally along line 4--4 of the pump in
FIG. 2;
FIG. 5 is a cross-sectional view of a gear pump with feed rollers for
handling feed in rope form;
FIG. 6 is a sectional view taken along line 6--6 in FIG. 5;
FIG. 7 is a top plane view of the pump of FIG. 5;
FIGS. 8A and 8B are schematic views illustrating compounding systems
equipped with the pump of FIGS. 2 and 5, respectively;
FIG. 9 is a schematic view illustrating the use of a gear pump of the
present invention in combination with an extrusion die or mold in a
fabrication process;
FIG. 10 is a cross-sectional view of a modular gear pump with feed rollers
wherein the entire inlet/gear cylinder section is replaceable;
FIG. 11 is a sectional view taken along line 11--11 in FIG. 10;
FIG. 12 is a cross-sectional view of a modular gear pump wherein the body
is formed by two halves for increasing the gear width by modular
additions;
FIG. 13 is a sectional view taken along line 13--13 in FIG. 12;
FIG. 14 is a top plane view of a modular gear pump with feed rollers
wherein the gears and rollers are modular for increasing the capacity of
the pump;
FIG. 15 is a cross-sectional view taken generally along line 15--15 in FIG.
14;
FIG. 16 is a cross-sectional view taken generally along line 16--16 in FIG.
15;
FIG. 16A is a cross-sectional view similar to FIG. 16, illustrating an
external drive for the feed rollers;
FIG. 17 is a side elevation view with certain portions broken away in
cross-section illustrating a completely modular gear pump embodiment; and
FIG. 18 is a front elevation view of the pump of FIG. 17 with certain
portions broken away in cross-section.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
While this invention is susceptible of embodiment in many different forms,
there is shown in the drawings and will hereinafter be described in detail
a preferred embodiment of the invention, and modifications thereto, with
the understanding that the present disclosure is to be considered as an
exemplification of the principles of the invention and is not intended to
limit the invention to the embodiments illustrated.
THE RECOVERY SYSTEM
FIG. 1 illustrates an integrated system for the production of low density
polyethylene in accordance with the present invention. A composition of
liquid polyethylene and entrained ethylene is produced in a reactor (not
shown), as is well known in the art. The composition is discharged from
the reactor through line 10 into a product receiver 12. The mixture flow
to product receiver 12 is controlled by a product valve 14 and a pressure
relief valve 16 in line 10. The bulk of the entrained ethylene gas is
removed from the mixture by flashing in product receiver 12 and the thus
removed ethylene gas is condensed and recycled to the reactor through line
12A for further use. The partially devolatilized polyethylene collects at
the lower portion of product receiver 12 and is transferred through line
20 to the inlet of vent stack 22.
Transfer of the liquid polyethylene to the vent stack is accomplished by a
pressure gradient which exists between product receiver 12 and vent stack
22. The product receiver operates at pressures in the order of 1000 p.s.i.
or higher and the vent stack is operated at pressures at or slightly above
or below atmospheric pressure. The flow rate of polyethylene to vent stack
22 is controlled by a feed control valve 24 in line 20, and a sufficient
level of liquid polyethylene is maintained in the product receiver to
prevent blow through of ethylene directly to the vent stack.
As the polyethylene enters vent stack 22, substantially all of the
remaining entrained ethylene flashes from the mixture due to the
pressure-equilibrium relationship at the pressure of the vent stack. The
low pressure in the vent stack and removal of the ethylene is accomplished
through a return line 26 which includes a pumping means 28, such as a
venturi nozzle or vacuum line. The return fluid in line 26 is collected
for further processing in the reactor.
Polyethylene melt P settles in the vent stack and is allowed to achieve a
liquid level L. The lower portion of vent stack 22 is in fluid
communication with a gear pump 30, described in greater detail below,
through a tapered outlet portion 22A. The level of the liquid polymer in
the vent stack is preferably maintained such that polyethylene-ethylene
interface is above the pump inlet and the diameter of the vent stack is
such that the pressure drop caused by the flowing polymer pool is equal
to, preferably less than the pressure head formed by the liquid level of
the polymer. Thus, gear pump 30 is flood-fed by the liquid polymer P in
the vent stack.
Gear pump 30 is driven by a variable speed drive 32 and torque coupling 34
to withdraw polymer from the lower portion of the vent stack and pump it
under pressure through conduit 36 into a pelletizer 38 for final
processing and delivery of the polymer to product hopper 40.
Control of the system is provided by a central process control 42 which, in
addition to monitoring the function and operation of the reactor, as is
known in the industry, monitors and controls the above-mentioned
equipment. More specifically, a liquid level controller 44, which may be
either of the displacement or rate types, as discussed more fully below,
senses the level (or rate of change of level) of polymer in the vent
stack. This variable is utilized by the process control 42 to set the
variable speed drive 32 to insure flood feed operation and full capacity
capability of the pump. Also, the level control may be utilized to provide
an indication of production rates, as discussed below.
Additionally, the process control unit monitors power input to the pump,
and inlet and outlet pressures and temperatures at the pump through lines
46. The exact instrument for monitoring these variables are well known in
the instrumentation art and include torque meters, pressure transducers,
either mechanical or electrical, e.g., piezoelectric transducers and
thermocouples or thermistors, respectively. From these measured variables
on-line viscosity monitoring is achieved. Viscosity is inversely related
to the product melt index which is a primary control variable for reactor
control in the production of polymers. Thus, these measured variables are
fed back in the process control unit 42 to provide control of polymer
production in the reactor.
The Gear Pump
FIGS. 2-4 illustrate gear pump 30 specifically designed to provide a
minimum net positive suction head and improved polymer pumping capability.
Pump 30 is modular in construction and includes an inlet structure 50,
gear housing 52, and steam jacket 54. Inlet structure 50 includes two
plate-like elements 50A and 50B of generally L-shaped configuration and
having interlocking end portions 50C And 50D as best illustrated in FIG.
4. Inlet structure 50 is coupled to a peripheral flange 22B on the outlet
of vent stack 22A and to gear housing 52 by a plurality of fasteners 56,
FIG. 2.
Gear housing 52 is generally rectangular in outer dimension and includes an
upper flange portion 52A, which abuts against the lower surface of inlet
structure 50, and sidewalls which define a gear chamber 58 at their inner
surface and taper downwardly at two opposite outer surfaces 60 to define
the inner surface of the steam chest. The steam jackets 54 are removably
mounted to the gear housing 52 by means, not shown, and complement the
tapered sides 60 to form a steam chest about the gear pump. The steam
jackets include a steam inlet 54A and condensate outlet 54B for admitting
steam from a source (not shown) to maintain the pump at a temperature
above the melting temperature of the polymer. Alternatively, passageways
such as drilling, described below, may be utilized in a solid pump body
configuration.
Referring particularly to FIGS. 2 and 3, inlet structure 50 defines an
inlet 66 whose width (parallel to the gear axis) is approximately equal to
the gear width, FIG. 3, and whose minimum length (normal to the gear axis)
taper downwardly to complement the gear chamber 58.
A pair of rotating, intermeshing gears 70 are positioned in gear housing
52. Any one of a wide variety of gear pairs may be employed, intermeshing
herringbone gears being preferred.
As shown in FIG. 3, a pair of intermeshing herringbone gears 70 are
rotatably mounted in gear housing 52 by means of journal bearings 71 and
end plates 72. One of the gears (the drive gear) includes a drive shaft
70A which extends outwardly from the gear pump to be coupled to the torque
coupling 34 and thereby provide power input to the pump. The other gear is
driven by the intermeshing relationship of the herringbone gears.
Journal bearings 71 are lubricated by the polymer melt, and as discussed
below provide a means for monitoring the viscosity of the polymer melt.
The length and diameter of the bearings and clearances are such that high
pressure leakage is minimized by a throttling effect.
The chamber 58 in which the intermeshing gears 70 are located is designed
to achieve an inlet of minimum restriction of polymer flow to improve
volumetric efficiency. Substantially all of the faces of the gears are
exposed to the media free space (the volume between the gear faces and
walls of chamber 58). This configuration permits the development of a
pressure gradient within the media free space to facilitate the filling of
the gear tooth cavities with polymer.
To achieve the necessary large media free space and still provide the
necessary seal between the outlet 103 and the low pressure inlet of the
pump, the pump discharge opening 103 and seal zone 74 must be minimized.
The portion of outlet 103 in direct communication with the gear chamber
defines a generally rectangular shaped opening having a width 103A, FIG.
3, equal to the gear face width and a length 103B, FIG. 2, equal to about
the gear tooth height.
The outlet is defined, in part, by high wear resistant seal zone inserts
75, which are removably secured to a seat 58A in the gear housing as by
bolts, not shown. Each seal zone extends from the tip 75A of the inserts
75 for a circumferential distance at least equal to the distance between
adjacent teeth across the full axial length of the gears to provide an
effective seal between the gear teeth and gear housing. The start of the
seal zone is generally indicated by numeral 75B, and the seal extends to
tip 75A. It should be noted that a seal length larger than that just
specified does not significantly increase seal effectiveness.
The inner surface of chamber 58 increases in dimension from the start of
the seal 75B in a continuous smooth curve to join the inlet structure
chamber 66 just above the top of gears 70. In one pump embodiment the gear
chamber or media free space boundary extended from a location 75B
53.degree. below the horizontal passing through the center of gear axis in
a circular arc to a location 15.degree. below the horizontal to provide a
radial distance between the tooth tip and chamber surface of 1/2 inch at
that point, and extended linearly from the 15.degree. point to the top of
the pump. In general, the ratio of free media space expansion to the
circumferential distance (as measured from the end of seal zone 75B) is
optimized in accordance with lubrication theory to achieve an increasing
hydraulic radius in the media free space to fill the gear tooth cavities
with polymer. The media free space increases from the seal zone 75B to
produce a maximum pressure gradient at a point preferably below the
horizontal elevation of the gear axes. The optimal media free space
configuration is a function of the particular polymer being pumped. A
ratio of the clearance (gear tooth tie to chamber wall) to the
circumferential distance from the seal zone in the range of about 0.2 to
0.9 is a typical value for polymers having viscosities in the range of 0.2
to 1.4 lb. sec/in.sup.2, respectively.
With particular reference to FIGS. 2 and 3, the outlet 103 changes from the
slot-like opening adjacent the gears to a circular discharge outlet 103C
at its lower end, which is in fluid communication with conduit 36.
The herringbone gears 70 may have helix angles ranging up to 30.degree.;
however, smaller helix angles, 15.degree. or less, are preferred to avoid
leakage at gear intermesh. Most preferably, herringbone gears with a helix
angle of 7.degree.-10.degree. are used to avoid trapping polymer in the
tooth cavities. The use of herringbone pattern gears is preferred to
constant helical or spur gears due to reduced stress loading on the gears
and housing realized with the herringbone gears.
The use of a gear pump and more particularly a gear pump with herringbone
gears provides economic savings in capital cost, operating cost and
improved performance in comparison to screw extruders used for the polymer
recovery system. More specifically, for a recovery system capable of
handling 30-50,000 lbs/hr, system investment cost may be up to 50% less
for a gear pump equipped system. In gear pump recovery systems for the
indicated capacities, horsepower requirements ranged from 7 to 17
horsepower as opposed to 35 to 60 horsepower for a comparable extruder
system. A comparable reduction in shaft horsepower equates to an annual
cost savings for a 50,000 lb/hr system in the order of $150,000/year
assuming 3.6 cents/kw. hr. electric costs.
Finally, the viscous shear dissipation work is greatly reduced by the use
of the gear pump as compared to a screw extruder. The reduction in this
work is about one order of magnitude. This reduction, of course, results
in a reduction in the temperature rise of the polymer as it passes through
the gear pump. Steady state temperature rises of 1.degree. to 4.degree. C.
have been experienced with the gear pump of this invention, as compared to
10.degree. to 35.degree. C. for a comparable screw extruder. The reduced
temperature rise provides better product property control and less thermal
degradation of the polymer product.
The gear tooth helix angle and media free space of the gear pump provide
improved handling and volumetric efficiency. Table I indicates a
comparison of operating parameters for several configurations which
illustrate the effects of gear tooth angle and media free space on gear
pump performance. The body types include the one described above and
designated as "FULL" and one designated "MIN" which had a media free space
inlet dimension located 25.degree. above the horizontal gear axis and
extended therefrom in a circular arc to a location 20.degree. below the
horizontal gear axis (the start of the seal zone). Each unit was equipped
with herringbone gears with the indicated helix angles and identical
outlet shapes.
From Table I, it will be noted that the FULL media space configuration,
i.e., the least restricted inlet configuration, provided volumetric
capacities which were essentially constant for the range of product
tested. The gear pump of the present invention is essentially insensitive
to viscosity and pressure conditions with respect to its pumping capacity,
and its volumetric efficiencies are essentially 100% over a range of gear
pitch line velocities up to 150 ft/min.
The designations MIN and FULL as well as the characteristics of the pump
structure given in connection with Table I are illustrative embodiments
and should not be interpreted as setting forth the limits of applicants'
invention. The values listed in the first six columns from left to right
represent short tests for peak performance of the gear pump, while the
last two columns represent long term steady-state operating conditions for
a reactor system having the indicated production rates.
An additional advantage of the gear pump is increased recovery system
operation. Unlike a screw extruder system which is highly sensitive to
polymer viscosity, the gear pump being a positive displacement pump will
continue to pump even if large changes in viscosity are experienced. An
extruder on the other hand, would have to be shut down and cleaned, when
high or low viscosity are introduced into it. Thus, reactor down time is
decreased and reliability is greatly increased with the gear pump.
TABLE I
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Body Type Min.
Min.
Min.
Full
Min.
Full
Full
Full
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Gear Angle (Degrees)
30 15 15 15 15 15 15 15
Melt Index 5.7 5.7
2.1
2.1 0.1
0.1
0.1
2.1
Rate (lbs./hr.)
10,000
9,000
8,500
9,000
7,60 | | |
