U.S. patent number 3,742,822 [Application Number 05/168,613] was granted by the patent office on 1973-07-03 for close clearance viscous fluid seal system.
This patent grant is currently assigned to Union Carbide Corporation. Invention is credited to Wayne Mason Talbert.
United States Patent |
3,742,822 |
Talbert |
July 3, 1973 |
CLOSE CLEARANCE VISCOUS FLUID SEAL SYSTEM
Abstract
A close clearance viscous fluid seal system has been developed
for use in high pressure reciprocating pumps. This system does away
with the conventional high pressure packings used in such pumps and
relies on a viscous fluid to form the seal between the plunger and
the pump body. A floating piston seal is employed to separate the
pumped fluid from the viscous fluid and impose the pumped fluid
pressure to the viscous fluid sealant.
Inventors: |
Talbert; Wayne Mason (Houston,
TX) |
Assignee: |
Union Carbide Corporation (New
York, NY)
|
Family
ID: |
29407087 |
Appl.
No.: |
05/168,613 |
Filed: |
August 3, 1971 |
Current U.S.
Class: |
92/86; 92/168;
417/437 |
Current CPC
Class: |
F04B
53/164 (20130101); F16J 15/40 (20130101) |
Current International
Class: |
F16J
15/40 (20060101); F04B 53/00 (20060101); F04B
53/16 (20060101); F01b 031/00 () |
Field of
Search: |
;417/437
;92/168,86.5,86 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Freeh; William L.
Claims
What is claimed is:
1. A pumped fluid actuating system comprising, in combination, a
reciprocating positive displacement pump having pressure viscous
fluid circulating means, pumped fluid chamber, low pressure pumped
fluid source means and a high pressure pumped fluid receiver means;
a plunger arranged interior of said reciprocating positive
displacement pump and adapted to move reciprocally therein in a
continual series of compression strokes and return strokes to
effect discharge of pumped fluid at a high pressure from said
pumped fluid chamber during each of the compression strokes and
intake of pumped fluid into said pumped fluid chamber during each
of the return strokes; an annular close clearance viscous fluid
sealant seal zone annularly surrounding at least a portion of said
plunger at an area discrete from the pumped fluid chamber; floating
piston seal means separating said pumped fluid chamber from said
annular close clearance viscous fluid sealant zone contacting said
pumped fluid chamber on one side thereof and responsive to changes
in pressure in said pumped fluid chamber and contacting said
annular close clearance viscous fluid sealant seal zone situated
between the plunger and the pump body on the other side thereof to
impose the pumped fluid pressure on the viscous fluid sealant; said
pressure viscous fluid circulating means connected to said annular
close clearance viscous fluid sealant seal zone to effect
substantially constant delivery of viscous fluid sealant thereto;
control means operatively connected to said pressure viscous fluid
circulating means to effect delivery of viscous fluid sealant into
and out of the annular close clearance seal zone.
2. A pumped fluid actuating system as claimed in claim 1, wherein
the floating piston seal means is in contact with and between the
main body and plunger of said reciprocating positive displacement
pump, and wherein the viscous fluid sealant passage means and check
valve means are located in the plunger.
3. A pumped fluid actuating system as claimed in claim 1, wherein
the floating piston seal means and viscous fluid sealant check
valve are located in the main body of said reciprocating positive
displacement pump.
4. A pumped fluid actuating system as claimed in claim 1, wherein
the floating piston seal means is in contact with and between the
main body and plunger of said reciprocating positive displacement
pump and the viscous fluid check valve means is located externally
thereto.
5. A pumped fluid actuating system as claimed in claim 1, wherein
the floating piston seal means and the viscous fluid check valve
means are located externally of said reciprocating positive
displacement pump.
Description
The present invention relates to an improvement in apparatus for
producing high pressures in pumped fluids and more particularly to
a close clearance viscous fluid seal system used in such
apparatus.
Many of today's commercial processes require the use of extremely
high pressures for the introduction of materials into reaction
equipment that is being operated at extremely high pressures. Such
pressures require specially designed equipment that will withstand
the pressure and also require the use of pumps that have the
capacity of functioning for prolonged periods of time at the high
pressures. It is known that in many instances the pressure will
exceed 40,000 psig.
Positive displacement type pumps in which a reciprocating plunger
is used to compress the pumped fluid and raise it to the desired
pressure are commonly used in high pressure processes. One of the
major problems encountered in this equipment is the deterioration
and failure of the packing materials and plungers used in the
pumps. The reciprocating action of the plunger rapidly deteriorates
the packing materials surrounding the plunger, necessitating the
shutting down of the equipment. This requires the replacement of
the packing material with consequent loss in operating time. To
date most of the reciprocating pumps in use rely on solid packing
materials to maintain a seal. Though these packing materials are
not completely satisfactory they are practically the sole known
means used in the industry, and much effort in time and money has
been expended in attempts to improve the known materials and to
find better lower cost substitutes. The reciprocating motion of the
plungers has a wearing effect on them and in many applications
solid tungsten carbide plungers must be used to obtain reasonable
packing and plunger life. These plungers are very expensive and
present a hazard due to the brittle type fracture failure that is
characteristic of this material. Several instances have been
reported in which solid tungsten carbide plungers have failed and
shattered fragments thereof together with a flammable fluid or gas
were released into an operating area.
According to the instant invention the use of conventional packing
materials in high pressure positive displacement pumps can be
obviated. This is accomplished by the use of pumping apparatus
having a close clearance viscous fluid seal in the annular space
between the reciprocating plunger and the barrel of the pump in
which the plunger is located. Throughout this annular close
clearance seal zone there is maintained a flowing viscous fluid
which has approximately the same pressure imposed on its high
pressure side as the pressure of the pumped fluid. The viscous
sealant fluid acts as a seal and it is introduced into the annular
close clearance seal zone by sealant fluid circulating means that
are readily constructed from available equipment with known
technology. The upstream pressure of the viscous fluid in the
annular close clearance seal zone is maintained by means of said
sealant fluid circulating means and by means of a floating piston
seal which separates the pumped fluid chamber from the viscous
sealant fluid and imposes the pressure of the pumped fluid on the
sealant fluid.
In the present invention, as the plunger compresses the pumped
fluid, the pumped fluid in turn applies an equivalent pressure to
the floating piston seal located in a floating piston seal chamber.
This floating piston seal moves in the opposite direction of the
movement of the plunger during the compression stroke and exerts
pressure on the viscous sealant fluid located on the sealant fluid
side of the floating piston chamber forcing viscous sealant fluid
into the annular close clearance zone between the plunger and the
main body of the pump. During the return stroke of the plunger,
when low pressure pumped fluid is drawn into the pumped fluid
chamber, the floating piston seal reverses direction and the
viscous sealant fluid circulating means replaces any viscous fluid
which passed out of the system during the cycle. In one version,
where the viscous sealant fluid is introduced via a bore in the
plunger (see FIG. 3), the viscous sealant fluid is replenished
during a short period of the suction stroke, and sealant fluid
passes through the annular close clearance zone during the pumping
cycle. In the operation of this invention, viscous fluid sealant
physically separated from the pumped fluid chamber is always
present between the plunger and the main body of the pump. It is
possible to maintain this viscous sealant fluid in the annular
close clearance zone even at relatively high pressures because of
the close clearance between the plunger and the main body of the
pump and the viscosity of the lubricant itself.
The seal is so designed and a viscous sealant selected so that
classic laminar flow conditions will always exist in the annular
close clearance zone. With laminar flow conditions, the flow rate
of sealant through the annular clearance zone is directly
proportional to pressure differential, varies as the square of the
clearance in the annulus, is inversely proportional to the sealant
viscosity and the length of the annulus. The speed and direction of
the plunger also affects the flow rate in accordance with basic
text book laminar flow theory. An acceptable flow rate of sealant
through the annulus for a given pump and a given set of operating
conditions can be obtained by selecting proper values for the above
variables.
Pressure and temperature both significantly change the viscosities
of most fluids. As an example the viscosity of a typical paraffinic
oil with a given viscosity at atmospheric pressure and 100.degree.
F. will have a viscosity 500 times greater at 40,000 psig and
100.degree. F., 4 times greater at 40,000 psig and 210.degree. F.,
and 0.08 times at 40,000 psig and 425.degree. F. Silicone fluids
have significantly different properties. As an example, the
viscosity of a typical silicone oil with a given viscosity at
atmospheric pressure and 100.degree. F. will have a viscosity 1,900
times greater at 40,000 psig and 100.degree. F., 10 times greater
at 40,000 psig and 210.degree. F., and 0.64 times at 40,000 psig
and 425.degree. F.
Heat is generated in the annulus as viscous fluid is sheared by
differential pressure and the motion of the plunger. A typical
temperature rise for a silicone sealant passing from 38,000 psi to
atmospheric pressure through an annulus is 350.degree. F., provided
no heat is removed during the throttling. A controlled rate of
sealant leakage through the annulus can be obtained by controlling
sealant viscosity. This is achieved by knowledgable selection of
sealant fluid, initial viscosity of the fluid, and the amount of
heat removed as it passes through the annulus. The approximate
leakage rate for a 27/8 inches diameter plunger during the
compression stroke, moving at 1 foot per second, is 1.8 cubic
inches per second when the plunger is positioned concentrically in
the annulus, the annulus radial clearance is 0.008 inch, the length
of the annulus is nine inches, the differencial pressure across the
annulus is 38,000 psig, the average viscosity of the sealant in the
annulus is 5,000 centipoises. Clearance at operating conditions is
greater than initial clearance due to the expansion of the cylinder
and contraction of the plunger caused by the very high operating
pressures. This effect must be calculated so that a seal can be
assembled to an initial clearance that will give the desired
clearance at operating pressure.
The present invention finds particular application in the known
high pressure process for the polymerization of ethylene both in
the compression pumps used to compress the ethylene to the desired
pressure and in the injection pumps used to introduce catalysts and
other reactants into the reaction process.
Accordingly, the present invention comprehends a system for pumping
fluids at high pressures wherein reciprocating plungers of positive
displacement pumps, intensifiers or injection pumps are sealed
against leakage along their axial length and annularly by means of
an annular close clearance seal and a floating piston seal which
forces the viscous sealant fluid to flow through the close
clearance annulus. This eliminates the need for conventional
packing materials and their periodic replacement.
With the foregoing in mind and other features which shall
hereinafter more fully appear, the present invention will be
described in greater particularity with reference to the appended
drawings.
FIG. 1 is a schematic diagram of the mechanical portion of a high
pressure process system containing the close clearance viscous
fluid seal according to the present invention.
FIG. 2 is a schematic diagram of another modification of the
mechanical portion of a high pressure process system containing the
close clearance viscous fluid seal showing only the main body,
plunger and seal sections of the pump.
FIG. 3 is a schematic diagram of a modification of the mechanical
portion of a high pressure intensifier or injection pump system
containing the close clearance viscous fluid seal, showing only the
main body, plunger and seal sections of the pump.
FIG. 4 is a schematic diagram of a modification in which the free
floating piston seal is located extraneous of the high pressure
process system containing the close clearance viscous fluid
seal.
Referring to FIG. 1 of the drawings there is shown a positive
displacement pump, designated generally as 101, comprising a main
body 102 and a pumped fluid chamber 103. A plunger 104 is arranged
in the pumped fluid chamber 103. Not shown are the mounting means
for the positive displacement pump 101, the motive means for
activating the plunger 104, viscous fluid reservoir means and
cylinder cooling facilities. The plunger 104 moves reciprocally in
the pumped fluid chamber 103 during operation of the pump. An
annular pressure zone 105 connects the pumped fluid chamber 103 to
annular seal chamber 106a and 105b which contains therein an
annular floating piston seal 107 having thereon an outside and
inside scraper-seal 108 and 109 (both made of conventional packing
material) thus dividing the seal chamber into two sections, 106a
connecting through annular pressure zone 105 to pumped fluid
chamber 103 and 106b connecting through a close clearance annular
seal zone 110 to viscous fluid chamber 111, which is sealed by an
annular seal 112 made of conventional packing material. Viscous
fluid chamber 111 connects via pressure fluid conduit 113 to
viscous fluid reservoir 114. Constant pressure viscous fluid pump
115 operates with a discharge pressure slightly higher than the
minimum pressure that occurs during the suction stroke in fluid
chamber 103, it pumps the viscous fluid through pressure fluid
conduit 116 into the viscous fluid side of seal chamber 106b
through passage 117 bored through the main body 102 of the positive
displacement pump 101. Located on pressure fluid conduit 116 are
suitable viscous fluid check valves 118 and pressure regulator 119.
At a point distant from passage 117 a vent passage 120 attached at
its exterior end to a suitable pressure valve 121 activatable in
the event of an emergency can be included; this, however, is not a
necessary part of the apparatus.
In an embodiment shown in FIG. 1, the compression stroke of the
pump 101 involves a movement of the plunger 104 from left to right.
During the compression stroke plunger 104 will displace pumped
fluid from pumped fluid chamber 103 through the discharge valve 122
into the high pressure pumped fluid receiver 123 through high
pressure pumped fluid conduit 124. During this compression stroke
inlet suction valve 125 is closed preventing the pumped fluid from
escaping via low pressure pumped fluid conduit 126 into low
pressure pumped fluid source 127. At the same time the pressure
produced on the pumped fluid by the compression stroke exerts a
pressure on floating piston seal 107 causing it to move from right
to left; this movement imposes a pressure on the viscous fluid in
seal chamber 106b forcing some of it into close clearance annular
seal zone 110. The amount of this leakage is low because of the
laminar flow conditions established by the fluid viscosity and the
close clearance in the annulus. The amount of viscous fluid or
pumped fluid flowing past scraper-seals 108 and 109 is minimal
since there is essentially no differential pressure across the
scraper seals to force flow. The return stroke involves a movement
of the plunger 104 from right to left. During this return stroke
discharge valve 122 is closed, inlet suction valve 125 opens
permitting pumped fluid to fill pumped fluid chamber 103 from low
pressure pumped fluid source 127 via low pressure pumped fluid
conduit 126. At the same time floating piston seal 107 is forced
from left to right until it mechanically rests against the end of
floating piston seal chamber by viscous fluid that is pumped into
oil seal chamber 106b by the constant pressure viscous fluid pump
115 via pressure fluid conduit 116 and passage 117 to replace the
viscous fluid that may have leaked out through annular seal zone
110 during the compression stroke. In this manner pumped fluid is
transferred from a low pressure source to a high pressure zone
using pumping means that do not have the conventional packing
materials in annular close clearance seal zone 110. The annular
close clearance surface and the plunger are not subject to
excessive wear since they are separated by a continuous strata of
viscous fluid having lubricating properties.
Referring to FIG. 2 of the drawings, there is shown the barrel
portion of a reciprocating compressor pump designated generally as
201, comprising a main body 202, a pumped fluid chamber 203 and a
plunger 204 arranged in the pumped fluid chamber 203. Not shown are
the mounting means for the reciprocating compressor pump 201, the
motive means for activating the plunger 204, cylinder cooling
facilities, the pumped fluid portion of the equipment designated by
numerals 122 to 127 inclusive of FIG. 1 and the viscous fluid
circulating means designated by numerals 113, 114, 115, 116, 118
and 119 of FIG. 1. The plunger 204 moves reciprocally in the pumped
fluid chamber 203 during operation of the pump. The main body 202
is preferably of several pieces that are assembled together. A
pressure pumped fluid passage 205 connects via an annular pressure
zone 205a to the pumped fluid chamber 203 and to annular seal
chamber 206a and 206b which contains therein an annular floating
piston seal 207 having thereon a scraper-seal 208 and 209 (made of
conventional packing material) thus dividing the seal chamber into
two sections with 206a connecting through annular pressure zone
205a through pressure pumped fluid passage 205 to pumped fluid
chamber 203, and 206b connecting to the viscous fluid circulating
means of the close clearance seal 214. The external viscous fluid
circulating means are not shown except for the viscous fluid inlet
point 210 and the viscous fluid exit point 211 both of which
connect to circulating means similar to those described in FIG. 1.
The viscous fluid is pumped in through viscous fluid inlet point
210, passes check valve 212, continues through viscous fluid
conduit 213 bored through a section of main body 202 and into the
viscous fluid side of seal chamber 206b which connects to a close
clearance annular seal zone 214 to annular viscous fluid receiving
chamber 215 which connects to viscous fluid exit point 211 via
viscous fluid passage 216 bored through a section of main body 202.
Conventional low pressure packing 217 is used to confine the
viscous fluid. A plunger scraping seal ring 218 prevents excessive
amounts of viscous fluid from entering pumped fluid chamber 203 and
in operation the end of plunger 204 does not pass to the left of
plunger scraping seal ring 218.
In an embodiment as shown in FIG. 2, the compression stroke of the
reciprocating compressor pump 201 involves a movement of the
plunger 204 from left to right. During the compression stroke
plunger 204 will displace pumped fluid from the pumped fluid
chamber 203 into the high pressure fluid receiver (not shown). At
the same time the pressure produced on the pumped fluid by the
compression stroke exerts a pressure on the floating piston seal
207; this pressure is imposed on the viscous fluid in seal chamber
206b forcing some of the viscous fluid to flow in close clearance
annular seal zone 214. The amount of this leakage is low for the
reasons discussed in relation to FIG. 1. The return stroke involves
a movement of the plunger 204 from right to left. During this
return stroke pumped fluid fills pumped fluid chamber 203 from a
low pressure pumped fluid source (not shown). At the same time
floating piston seal 207 moves from left to right until it is in
its full position to the right. Viscous fluid is pumped into seal
chamber 206b via viscous fluid conduit 213 by viscous fluid
circulating means (not shown) to replace viscous fluid that passes
through annular seal zone 214 into annular viscous fluid receiving
chamber 215 and out through viscous fluid receiving chamber 215 and
out through viscous fluid passage 216 during the compression
stroke. In this manner pumped fluid is transferred from a low
pressure source to a high pressure zone using pumping means that do
not have the conventional packing materials in annular close
clearance seal zone 214 without excessive wear or significant
sealant contamination of the pumped fluid, as discussed in relation
to FIG. 1.
Referring to FIG. 3 of the drawings, there is shown the barrel
portion of a reciprocating pump, designated generally as 301,
comprising a main body 302, a pumped fluid chamber 303 and a
plunger 304 arranged in the pumped fluid chamber 303. Not shown are
the mounting means for the reciprocating pump 301, the motive means
for activating the plunger 304, the cylinder cooling facilities,
the pumped fluid portion of the equipment designated by numerals
122 to 127 inclusive of FIG. 1 and the viscous fluid circulating
means designated by numerals 113, 114, 115, 116, 118 and 119 of
FIG. 1. The plunger 304 moves reciprocally in the pumped fluid
chamber 303 during operation of the pump. An annular pressure zone
305 connects pumped fluid chamber 303 to annular seal chamber 306a
and 306b which contains therein an annular floating piston seal 307
having thereon an outside scraper-seal 308 and an inside
scraper-seal 309 (both made of conventional packing material) thus
dividing the seal chamber into two sections, 306a connecting via
annular pressure zone 305 to pumped fluid chamber 303, and 306b
connecting to the viscous fluid close clearance seal system. The
external viscous fluid circulating means are not shown except for
the viscous fluid inlet point 310 and the viscous fluid exit point
311 both of which connect to viscous fluid circulating means
similar to those described in FIG. 1. These points can be located
on throttling bushing 312 which can have a static annular packing
seal 313 to prevent viscous fluid leakage from seal chamber 306b
along main body 302 and low pressure packing seal 314 to prevent
viscous fluid leakage from plunger 304. Fitted into the face end of
plunger 304 is check valve 315 at the end of viscous fluid passage
316 bored through the lengthwise direction of plunger 304. Viscous
fluid passage 316 is connected at the check valve 315 end to
annular seal chamber 306b via viscous fluid conduit 317 and at the
other end to annular viscous fluid chamber 318 via viscous fluid
conduit 319. Viscous fluid conduits 317 and 319 are borings through
plunger 304 that intersect viscous fluid passage 316.
In an embidiment as shown in FIG. 3, the compression stroke of
reciprocating injection pump 301 involves a movement of plunger 304
from left to right. During the compression stroke plunger 304 will
displace pumped fluid from pump fluid chamber 303 into the high
pressure pumped fluid receiver (not shown). At the same time the
pressure produced on the pumped fluid by the compression stroke
exerts a pressure on annular floating piston seal 307 causing it to
impose a pressure on the viscous fluid in seal chamber 306b forcing
viscous fluid to flow in annular close clearance seal zone 320.
During the compression stroke check valve 315 is closed preventing
viscous fluid from leaving seal chamber 306b via viscous fluid
conduit 317 and into viscous fluid passage 316; the only path for
the viscous fluid to follow is into annular close clearance seal
zone 320. The small amount of viscous fluid that flows through
annular close clearance seal zone 320 enters annular viscous fluid
chamber 318 and by the external viscous fluid circulating means is
recycled; the amount is small for the reasons discussed in relation
to FIG. 1. The return stroke of plunger 304 involves a movement
from right to left. During the latter portion of this return stroke
pumped fluid fills pumped fluid chamber 303 from a low pressure
pumped fluid source (not shown). During the initial portion of the
return stroke annular floating piston seal 307 moves from right to
left until viscous fluid conduit 319 contacts the viscous fluid
chamber 318. When this occurs check valve 315 opens because the
pressure in the viscous fluid circulating means system is greater
than the pressure of the suction pressure of the pumped fluid and
viscous fluid is pumped in to fill seal chamber 306b by external
viscous fluid circulating means (not shown) via viscous fluid inlet
point 310 passing through viscous fluid conduit 319, viscous fluid
passage 316 and viscous fluid conduit 317 into seal chamber 306b.
This forces the free floating piston seal 307 to its extreme right
position. In this manner pumped fluid is transferred from a low
pressure source to a high pressure zone using pumping means that do
not have the conventional packing materials in annular close
clearance seal zone 320 without excessive wear, or significant
sealant contamination of the pumped fluid as discussed in relation
to FIG. 1. An advantage of the arrangement shown in FIG. 3 is that
viscous fluid passages are not required to be drilled in the main
body 302 section of the high pressure reciprocating pump, but
rather the viscous fluid sealant enters via the plunger 304. This
arrangement eliminates stress raisers in the main body 302 of the
high pressure pump which would lessen its fatigue resistance and
reduce its service life. Stress raisers in the plunger 304 do not
shorten its life since it is always in compression and stress
raisers are of little significance to the life of a component that
is always in compression.
Referring to FIG. 4 of the drawings, there is shown a reciprocating
compression pump, designated generally as 401, comprising a main
body 402 and a pumped fluid chamber 403. A plunger 404 is arranged
in the pumped fluid chamber 403. Not shown are the mounting means
for the reciprocal compression pump 401, the motive means for
activating plunger 404, the cylinder cooling facilities and the
viscous fluid circulating means. Plunger 404 moves reciprocally in
pumped fluid chamber 403 during operation of the pump. A pressure
fluid conduit 405 connects pumped fluid chamber 403 to floating
piston seal chamber 406 which contains therein a floating piston
seal or diaphragm 407 having thereon a scraper-seal 408 (made of
conventional packing material) that divides the floating piston
means into two sections, seal chamber 406a connecting to pumped
fluid chamber 403 through pressure fluid conduit 405 and bore 409
and seal chamber 406b connecting to viscous fluid circulating means
hereinafter described. Bore 409 can enter pumped fluid chamber 403
at any point through main body 402 and is not limited to the
position shown. Viscous fluid is pumped into seal chamber 406b by
constant pressure pump 410 from viscous fluid reservoir 411. The
viscous fluid sealant travels through pressure conduit 412, check
valve 413 and pressure conduit 414; essentially constant pressure
is maintained by means of pressure regulator 415. The same pump 410
is used to pump viscous fluid into annular close clearance seal
zone 416 via pressure conduit 412, check valve 413, pressure
conduit 417 and bore 418. Annular oil seal and scraper rings 419
prevent mixing of the viscous fluid and the pumped fluid. At a
point distant from bore 418, one can, if desired and as shown, have
a vent bore 420 attached at its exterior end to a suitable pressure
valve 421 activatable in the event of an emergency. This feature is
optional and not a necessity. Viscous fluid chamber 422 connects
annular close clearance seal zone 416 to viscous fluid reservoir
411 via pressure conduit 423. Conventional packing material is used
in annular seal 424.
In an embodiment shown in FIG. 4, the compression stroke of pump
401 involves a movement of plunger 404 from left to right. During
the compression stroke plunger 404 will displace pumped fluid from
pumped fluid chamber 403 through discharge valve 425 into high
pressure pumped fluid receiver 426 through high pressure pumped
fluid conduit 427. During this compression stroke inlet suction
valve 428 is closed preventing pumped fluid from escaping via low
pressure pumped conduit 429 into low pressure pumped fluid source
430. At the same time the pressure on the pumped fluid by the
compression stroke exerts a pressure on floating piston seal 407,
this imposes a pressure on the viscous fluid in seal chamber 406b,
closing check valve 413 and pressuring viscous fluid via pressure
conduit 417 and bore 418 into annular chamber 431 and through
annular close clearance seal zone 416. The amount of viscous fluid
passing through annular close clearance seal zone 416 is low for
the reasons discussed in relation to FIG. 1. The return stroke
involves a movement of plunger 404 from right to left. During this
return stroke discharge valve 425 is closed, inlet suction valve
428 opens permitting pumped fluid to fill pumped fluid chamber 403
from low pressure pumped fluid source 430 via low pressure pumped
fluid conduit 429. At the same time floating piston seal 407 moves
from left to right until it is restrained by the end of floating
piston seal chamber 406 due to the viscous fluid sealant pumped
into viscous fluid seal chamber 406b by constant pressure pump 410
via pressure conduits 412 and 414 and through check valve 413 to
replace the viscous fluid that has passed through annular close
clearance zone 416 during the compression stroke of the pumping
operation. In this manner pumped fluid is transferred from a low
pressure source to a high pressure zone using pumping means that do
not have the conventional packing materials in annular close
clearance seal zone 416 without excessive wear or significant
sealant contamination of the pumped fluid as discussed in relation
to FIG. 1.
From the foregoing description it will be recognized by those
familiar with the art that the apparatus according to this
invention comprehends a high pressure fluid activating system or
pumping system comprising a reciprocating pump having a plunger
arranged interior of the pump and adapted to move reciprocally
therein in a continual series of compression and return strokes to
compress and transfer pumped fluid from pumped fluid chamber to the
high pressure pumped fluid receiver or reactor, a close clearance
viscous fluid seal zone situated annularly to the plunger and the
pump body and separated from the pumped fluid chamber by a floating
piston seal, and viscous fluid circulating means. During each
compression cycle, pumped fluid at high pressure is expelled from
the pumped fluid chamber into the high pressure pump fluid
receiver. Simultaneously, the pressure of the pumped fluid exerts a
pressure on a floating piston seal that separates the pumped fluid
chamber from the viscous fluid sealant side of the seal chamber in
which the floating piston seal is situated and from the close
clearance viscous fluid seal zone. The pressure exerted on the free
floating piston is transmitted to the viscous fluid sealant forcing
viscous fluid from the viscous fluid seal chamber into the annular
close clearance seal zone and forcing the floating piston seal in a
direction opposite to the direction of the plunger. The pressure of
the viscous fluid sealant is essentially equivalent to the pressure
of the pumped fluid. During the return stroke low pressure pumped
fluid is drawn into the pumped fluid chamber and simultaneously the
floating piston seal or diaphragm again moves in a direction
opposite to the direction of movement of the plunger during a
period that is all or just a portion of this stroke. During the
compression and return strokes, the viscous fluid circulating means
are in continuous operation to maintain an adequate supply of
viscous fluid in the high pressure fluid activating system,
particularly in the viscous fluid seal chamber and the annular
close clearance seal zone. During the return stroke, accompanied by
the movement of the floating piston seal, the viscous fluid
circulating means pumps viscous fluid sealant into the viscous
fluid sealant seal chamber to replace that viscous fluid that was
forced through the annular close clearance seal zone during the
compression stroke and return stroke. By this manner of operation
high pressure can be achieved in a system that does not employ the
conventional solid packing materials normally used as sealants
around the plunger of a reciprocating pump. The pressure of the
system can vary from slightly above atmospheric pressure to a
pressure of about 40,000 psig or higher.
The clearance between the plunger and the pump body will vary
depending upon the size, alignment capability, the specific viscous
fluid sealant selected, and the operating pressure, temperature and
speed of the pump. This clearance is sufficient to permit free
movement of the plunger in the pump but it is not of such a size as
to permit the viscous fluid sealant to flow through in uncontrolled
amounts. In view of the teachings disclosed herein, one skilled in
the art of constructing high pressure pumps and determining viscous
flow rates can readily determine the clearance required for a
particular size pump. Among the main reasons that the dimensions of
the annular close clearance viscous fluid seal zone cannot be set
forth with particularity is that the dimensions will vary not only
for the reasons previously stated but also with the size of the
pump, and the pumping capacity of the reciprocating compressor
pump. Thus, this invention can be used in pumps that vary in size
from small laboratory units in which capacity is measured in grams
per hour to large commercial units in which capacity is measured in
tons. The pressure at which the unit is operated will also vary
from slightly above atmospheric to 40,000 psig, or higher.
The apparatus and system described in this specification can be
used, for example, in the high pressure polymerization of ethylene.
In such processes ethylene is compressed to reaction pressures of
from 10,000 psig to 40,000 psig by huge reciprocal compressor pumps
and pumped into the polymerization reactors. Often these processes
employ additionally, high pressure reciprocating injection pumps
used to introduce catalysts and other modifiers to the reaction.
The concept disclosed here can be used in both types of these high
pressure pumps. The pumps of the instant invention are, of course,
used in conjunction with the necessary support equipment in which
the reaction is carried out.
* * * * *