US3389973A

US3389973A - Internal sealing means for autoclave motor housing

Info

Publication number: US3389973A
Application number: US648290A
Authority: US
Inventors: Fitzpatrick Kerien
Original assignee: Rexall Drug and Chemical Co
Current assignee: Dart Industries Inc
Priority date: 1967-06-23
Filing date: 1967-06-23
Publication date: 1968-06-25
Anticipated expiration: 1985-06-25
Also published as: DE1767668B1; GB1224032A; NL6808827A; FR1571014A; NL151909B

Description

June 25, 1968 K. FITZPATRICK 3,389,973

INTERNAL SEALING MEANS FOR AUTOCLAVE MOTOR HOUSING Filed June 23, 1967 FIQQRE Q KERIEN FITZPATRICK FIGURE l INVENTOR.

BYW

ATTORNEY United States Patent 3,389,973 INTERNAL SEALING MEANS FOR AUTOCLAVE MOTOR HOUSING Kerien Fitzpatrick, Odessa, Tern, assignor to lgexall Drug and Chemical Company, Los Angeles, Callf., a corporation of Delaware Filed June 23, 1967, Ser. No. 643,290 4 Claims. (Cl. 23-290) ABSTRACT OF THE DISCLQSURE Sealing means between reaction and agitator motor sections comprises disc having peripheral grooves containing resilient and expander rings with clearance provided for fluid passage 'to spaces between grooves and expander rings whereby fluid pressure from reaction section urges resilient rings against autoclaves wall preventing passage of fluid to motor section.

BACKGROUND OF INVENTION (1) Field of invention This invention relates to a combination of an autoclave and means for sealing 01? an internal motor section from fluid from the reactor section of the autoclave. The term autoclave used herein refers to a pressure vessel comprising a shell and a head generally operating at high pressures, i.e., 100 to 15,000 atmospheres.

(2) Description of prior art The prior art autoclaves found in the processing industry are cylindrical or spherical and are positioned either vertically or horizontally, and have :at least one flat, dished or semihemispherical head. The autoclave most commonly found in industry in high pressure service is a vertical, substantially cylindrical type of vessel having a removable top head and an agitator, or other means forstirring the contents of the autoclave, extending through or from the top head and along the longitudinal axis of the autoclave.

Such vessels have found wide acceptance as reactors for either batch or continuous reactions. For example, it is well known to polymerize ethylene in an autoclave at pressures ranging from 15,000 psi. or below to 45,000 psi. and higher and at temperatures of about 200 to 600 F. in the presence of a free radical initiator. Such polymerization reactions require vigorous agitation to provide intimate contact between the feed and the contents of the autoclave. The autoclave is provided with an agitator or other means for mixing its contents and a motor or other means for driving the agitator. The agitator motor within its housing is usually mounted on the exterior surface of the autoclave (see US. Patent Nos. 2,897,183, and 2,964,515). The entire motor housing has been enclosed within the interior of the autoclave. Heretofore, this has not been too successful because no sealing devices have been available in the industry which completely seal oif the internal motor and housing from fluids in the reaction section. The sealing devices of the prior art allow reactants from the reaction section of an autoclave to pass into the space between the exterior of the motor housing and the interior of the autoclave. The reactants polymerize and accumulate in this space making removal of the motor housing difficult. The polymerized reactants even Work their way into the motor windings impairing the performance of the motor.

SUMMARY An object of the present invention is to prevent fluid from the reaction section of a stirred autoclave from back flowing into the drive means section of the agitator.

Another object of the present invention is to provide 3,389,973 Patented June 25, 1968 an apparatus combination including a sealing means for completely sealing off the internal agitator motor from fluids in the reaction section.

The present invention comprises in combination: an autoclave having a reaction section, an agitator extending along the longitudinal axis of the autoclave, means for driving the agitator positioned within a drive means section above the reaction section and sealing means for preventing back-flow of fluid into the drive means section. This sealing means comprises a disc positioned between the reaction section and the drive means section and a resilient ring and an expander ring seated between the sidewalls of a groove encircling the periphery of the disc. The diameter of the disc is substantially equal to the inside diameter of'the autoclave and is preferably normal to the longitudinal axis of the autoclave. The peripheral encircling groove of the disc is generally rectangular in cross section. The outer periphery of the resilient ring abuts the inner wall of the autoclave and the outer periphery of the expander ring abuts the inner periphery of the resilient ring. An annular space is formed between the inner periphery of the expander ring and the inner surface of the groove. Sufiicient clearance is provided between the sidewalls of the groove and the respective edges of the resilient and expander rings to permit the passage of fluid from the reaction section to the annular space. Means are provided for pressuring the autoclave whereby fluid pressure transmitted from the reaction section via the clearance and the annular space urges the resilient ring against the inner Wall of the autoclave to effect a sealing. contact between the outer periphery of the resilient ring and the inner wall.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more readily understood and the future objects and advantages thereto will be more readily apparent when read in conjunction with the accompanying drawings in which:

FIG. 1 is a vie-w, partially in cross section, showing the autoclave, agitator, internal motor and sealing means;

FIG. 2 is an enlarged detailed view taken along line A-A of the sealing means;

FIG. 3 is a view of the transverse section taken along line BB of the sealing means set within the shell of the autoclave.

PREFERRED EMBODIMENT OF THIS INVENTION In the preferred embodiment of this invention there is provided a substantially cylindrical, vertically elongated autoclave having a removable top head, a motor section below the top head and a reactor section immediately below the motor section; an agitator extending along the longitudinal axis of the autoclave; an agitator motor Within a housing positioned in the motor section; a sealing ring comprising a disc having a plurality of peripheral encircling grooves and a plurality of resilient rings and expander rings each positioned as indicated under the Summary section; and means for pressuring the autoclave whereby fluid pressure is transmitted from the reaction section via the clearance provided between the sidewalls of at least the lowermost groove closest to the reaction section and the lower edges of at least the lowermost resilient and expander rings and via at least the lowermost annular space. The pressure urges at least the lowermost resilient ring vertically upward against the upper sidewall of at least the lowermost groove and urges at least the lowermost resilient ring radially outward against the inner wall of the autoclave normal to its surf-ace to effect sealing contact between the outer periphery of at least the lowermost resilient ring and the inner wall. The exact path the fluid that exerts the pressure takes is not fully understood. Whether the fluid actually fills the annular space and forces the expander ring against the resilient ring which is forced, in turn, against the inner wall or whether the fluid works between the expander ring and resilient ring and forces the latter directly against the inner wall is not critical so long as the net eifect is the same.

Resilient and expander rings in the grooves above the lowermost grooves are providedas a precaution to assure that none of the fluid from the reaction section passes through this plurality of rings and into space between the motor housing and the inner surface of the motor section. It is understood that any fluid that passes above the lowermost resilient ring follows a path within each of the grooves similar to that taken by the fluid in the lowermost groove.

Referring now to FIG. 1, autoclave 1 comprises metal shell 2 having an inside diameter (ID) of several inches and removable top head 3 which is held into position by at least one clamp 4 or other suitable means. Autoclave 1 can be provided With a bottom head and clamp (not shown) similar to that shown in FIG. 1 or with a bottom heat that is integral to the shell. Autoclave 1 can also be provided with an external jacket or other means (not shown) for heating or cooling its contents. If the autoclave is used for carrying out continuous reactions, suitable inlets and outlets (not shown) are provided for feed, initiator and efiiulent. Agitator shaft 6 extends through substantially the entire length of reaction section of autoclave 1. Agitator blade members 7 which are bent into spiral or helical configuration or other suitable means for mixing the centents in the reaction section are disposed along the length of shaft 6. Internal electric motor 8 within motor housing 8A or other suitable drive means for the agitator is operably connected to shaft 6 and is disposed in motor section 9 above reaction section 5. Internal sealing ring 10 is mounted below motor section 9 and above reaction section 5 to prevent fluid from backfiowing from reaction section 5 into motor section 9 and accumulating in the annular space between motor housing 8A and the inner walls of motor section 9.

Sealing ring 10, as shown in FIGS. 1, 2 and 3, comprises disc 11 which has an outside diameter about Ai-inch less the ID. of shell 2 and has three peripheral encircling grooves 12, Grooves 12 have a rectangular cross section about %-inch wide and about /4-inch high. Seated within the outer portion of each groove 12 adjacent the inner wall of shell 2 is resilient ring 13 which has an CD. of about pi -inch greater than the ID. of shell 2 and has a square cross section of about /4-inch. Resilient rings 13 are formed of heat-resistant rubber, plastic or similar material which has high elasticity and is compressible on sealing engagement with the inner walls of shell 2. Preferably, resilient rings 13 are made of tetrafluoroethylene (TFE) fluorocarbon resins, sold under the trademark Teflon by E. I du Pont de Nemours and Company. An expander ring 14 about As-inch thick and made of metal, preferably stainless steel, is seated within the middle portion of each groove 12 abutting respectively each resilient ring 13. Each expander ring 14, of the type commonly found in the compressor art, respectively urges each resilient ring 13 radially outward against the inner walls of shell 2 with sufficient force to effect initial sealing contact therewith during the period the pressure in the autoclave is increased to operating pressures. Clearance 15 of about -inch is provided between the lower sidewall of each groove 12 and the lower edges of each resilient ring 13 and expander ring 14 to allow fluid pressure in reaction section 5 to be transmitted to annular space 16. Space 16 is the inner portion of groove 12, i.e., the space remaining after resilient ring 13 and expander ring 14 are seated between the walls of groove 12. A A compressor or other means (not shown for pressuring autoclave 1 urges the lowermost resilient ring 13 upward against the sidewall of the lowermost groove 12 and radially outward against the inner wall of shell 2. This effectively .seals motor section 9 against fluid in reaction section 5 and prevents undesirable reaction to take place therein. The sets of resilient and expander rings above the lowermost set are merely provided as a safety factor against possible leakage into motor section 9.

Disc 11 of sealing ring 10 has a recess to receive the lower portion of motor housing 8A. Four countersinks 20 are provided in the outer periphery of the recess through which four cap screws 21 are passed to fasten sealing ring 10 to motor housing 8A. A bore extends through the center of the recess through which agitator shaft 6 passes. Motor housing 8A is fixedly attached to the inner surface of top head 3 so that top head 3, motor housing 8A, sealing ring 10 and the agitator assembly are removable as a unit.

EXAMPLE This example is given to further illustrate the operation of the apparatus of this invention and to indicate the type of process to which such an apparatus is applicable. Ethylene and an organic free radical initiator were continuously added through inlets into a reaction section of an autoclave of the type shown in FIG. 1. The conditions that were maintained in the reaction section to convert the ethylene to polyethylene include a pressure in the range of about 18,000 to 30,000 psi. and a temperature in the range of about 300 to 600 F. In the motor section, the pressure was about the same as that in reaction section and the temperature was less than about 200 F. When the autoclave was brought off-stream, the removable unit, comprising the top head, the agitator motor housing, the sealing ring, and the agitator assembly, of the type discussed in the above section was removed without difiiculty with no evidence of polymer accumulation in the annular space between the motor housing and the inner walls of the motor section.

A great deal of difiiculty was experienced in removing a removable unit containing a sealing ring of the type commonly found in the prior art in place of the sealing ring of this invention. Accumulations of polyethylene were found on the external walls of the motor housing and on the walls of the motor section and some polyethylene was even found within the motor housing in the motor windings. It is theorized that the prior art sealing ring had deformed under the high temperatures and very high pressures used in the autoclave and allowed small amounts of ethylene and initiator to circulate in the motor section. This caused the temperature in the motor section to rise above the polymerization temperature and to cause polymerization.

The essential feature of the present invention is to introduce a relatively simply internal sealing ring into an autoclave to provide an eiiective seal between agitator motor section and the reaction section.

While only one particular embodiment of this invention is illustrated herein, it will be understood that the apparatus of this invention is obviously subject to the variations and modifications without departing from its broader aspects. All such variations and modifications that fall within the scope of the appended claims are intended to be embraced thereby.

What is claimed is:

1. In combination:

(1) an autoclave having a reaction section,

(2) an agitator extending along the longitudinal axis of said autoclave, (3) means for driving said agitator positioned within a drive means section above said reaction section,

(4) sealing means for preventing back-flow of fluid into said drive means section, said sealing means comprising:

(a) a disc positioned between said reaction section and said drive means section, said disc having its diameter substantially equal to the inside diameter of said autoclave and having a peripheral encircling groove generally rectangular in cross section,

(b) a resilient ring seated between the sidewalls of the groove, said resilient ring having its outer periphery abutting the inner wall of said autoclave, and

(c) an expander ring seated between the sidewalls of the groove, said expander ring having its outer periphery abutting the inner periphery of said resilient ring and forming an annular space between its inner periphery and the inner surface of the groove, sufficient clearance being provided between the sidewalls of the groove and the respective edges of said resilient ring and said expander ring to permit fluid from said reaction section to fill the annular space, and

(5) means for pressuring said autoclave whereby fluid pressure transmitted from said reaction section via the clearance and the annular space urges said resilient ring against the inner wall of said autoclave to effect sealing contact between the outer periphery of said resilient ring and said inner wall.

2. In combination:

(1) an autoclave having a substantially cylindrical, vertically elongated shell, a removable top head, a reaction section and a motor section above said reaction section,

(2) an agitator extending along the longitudinal axis of said autoclave,

(3) an agitator motor within a housing positioned within said motor section,

(4) a sealing ring for preventing back-flow of fluid into the space between the motor housing and the inner surface of said motor section, said sealing ring comprising:

(a) a disc positioned between said reaction section and said motor section, said disc having its diameter substantially equal to the inside diameter of said autoclave and having at least one peripheral encircling groove generally rectangular in cross section,

(b) at least one resilient ring seated between the sidewalls of the groove, said resilient ring having its outer periphery abutting the inner wall of said autoclave, and

(c) at least one expander ring seated between the sidewalls of the groove, said expander ring having its outer periphery abutting the inner periphery of said resilient ring and forming an annular space between its inner periphery and the inner surface of the groove, sufllcient clearance being provided between the sidewalls of the groove and the respective edges of said resilient ring and said expander ring to permit fluid from said reaction section to fill the annular space, and

(5) means for pressuring said autoclave whereby fluid pressure transmitted from said reaction section via the clearance and the annular space urges said resilient ring against the inner wall of said autoclave to eifect sealing contact between the outer periphery of said resilient ring and said inner wall.

3. In combination:

(1) an autoclave having a substantially cylindrical, vertically elongated shell, a removable top unit, a reaction section and a motor section above said reaction section wherein said removable top unit comprises:

(a) a top head fixedly attached to said shell,

(b) an agitator extending along the longitudinal axis of said autoclave,

(c) an agitator motor within a housing positioned within said motor section and operably connected to said agitator, the motor housing being fixedly attached to the inner surface of said top head,

(d) a sealing ring for preventing back-flow of fluid into the space between the motor housing and the inner surface of said motor section, said sealing means com-prising:

(I) a disc positioned between said reaction section and said motor section, said disc having:

(A) its diameter substantially equal to the inside diameter of said autoclave,

(B) a recess to receive the lower portion of said motor housing,

(C) a bore extending through the center of the recess to receive said agitator,

(D) at least one peripheral encircling groove generally rectangular in crosssection,

(E) a plurality of holes through the outer periphery of the recess, and

(F) fastening means passing through the holes to fixedly attach said disc to the motor housing,

(II) at least one resilient ring seated between the sidewalls of the groove, said resilient ring having its outer periphery abutting the inner wall of said autoclave, and

(III) at least one expander ring seated between the sidewalls of the groove, said expander ring having its outer periphery abutting the inner periphery of said resilient ring and forming an annular space between its inner periphery and the inner surface of the groove, suflicient clearance being provided between the sidewalls of the groove and the respective edges of said resilient ring and said expander ring to permit fluid from said reaction section to fill the annular space, and

(2) means for pressuring said autoclave whereby fluid pressure transmitted from said reaction section via the clearance and the annular space urges said resilient ring against the inner wall of said autoclave to effect sealing contact between the outer periphery of said resilient ring and said inner wall.

4. The apparatus of claim 3 wherein said disc comprises a plurality of peripheral encircling grooves, Wherein said resilient and expander rings are seated between each of said grooves, and wherein the fluid pressure urges at least the lowermost resilient ring upward against the upper sidewall of at least the lowermost groove and urges at least the lowermost resilient ring radially outward against the inner wall of said autoclave, normal to its surface thereof.

References Cited UNITED STATES PATENTS 2,897,183 7/1959 Christl 26094.9 2,964,515 12/1960 Rader 26094.9 2,991,161 7/1961 Gasche 23--29O 2,996,363 8/1961 Ruyak 259-l08 X 3,287,092 11/1966 Scudder 23290 ROBERT W. JENKINS, Primary Examiner.