WO2014046702A1

WO2014046702A1 - Improved reactor seal apparatus

Info

Publication number: WO2014046702A1
Application number: PCT/US2013/000206
Authority: WO
Inventors: Gene Franklin HOLLAND; James Brooks SMITH
Original assignee: Penn A Kem LLC
Priority date: 2012-09-21
Filing date: 2013-09-09
Publication date: 2014-03-27

Abstract

An improved mechanical seal for a reaction vessel wherein the stationary sealing ring is comprised of an upper ring and a lower ring, the lower ring functioning as a carrier of the upper ring and being composed of a resilient material, preferably polytetrafluoroethylene or an advanced elastomer.

Description

IMPROVED REACTOR SEAL APPARATUS

BACKGROUND OF THE INVENTION

In a chemical reaction vessel, efficient sealing around the agitator shaft is crucial. One type of such a seal is the rotary face seal. Sealing is achieved by arranging at least two rigid durable sealing rings having flat, radially extending sealing surfaces axially adjacent to each other and concentrically about the shaft so that the faces are in sealing contact. One seal ring is held stationary in the seal housing while the other ring rotates with the shaft, i.e., the stationary ring and the rotating element, respectively. The stationary ring may also act as a bushing for the shaft.

The sealing rings may be composed of two or more pieces to facilitate their replacement, as described in U.S. Patent 6,485,024, which is incorporated herein by reference in its entirety. The sealing rings may be made of one of a number of materials such as various ceramics, tungsten alloys, silicon carbide, or other alloys. The material is chosen for compatibility with the expected chemicals to be used or made in the reaction vessel. Ceramic is a preferred material in some circumstances due to its non-reactive properties and surface hardness.

The sealing rings are subjected to physical stresses as the agitator is started and stopped and to hydraulic forces created by the mixing action of the agitator. Failure of the rings is a too common occurrence, most commonly occurring in the stationary sealing ring. Failure can lead to damage to the shaft and to the vessel itself. Damage to the vessel is more common when the vessel is lined with glass, as is necessary for some chemical reactions.

Repairs are costly and may be time consuming, particularly for glass-lined vessels and shafts, resulting in lost production time.

It would therefore be desirable to have sealing rings that are both durable and capable of absorbing the stresses without breakage or damage to the vessel or the shaft.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved seal for the shaft of an agitator inserted into a vessel wherein the seal is less likely to fail due to fracture of one or both of the sealing rings and the shaft or vessel is less likely to be damaged due to stresses at the seal.

It is a further object of the present invention to provide an improved seal for the shaft of an agitator inserted into a vessel wherein the stationary sealing ring is supported by an element that absorbs stresses on the sealing rings, shaft, and vessel.

It is a still further object of the present invention to provide an improved seal for the shaft of an agitator inserted into a vessel wherein the stationary sealing ring is replaced with a ring having a more narrow profile along the shaft and a carrier element composed of a resilient substance. Yet another object of the present invention is to provide an improved mechanical face seal wherein the stationary seal ring is supported and optionally surrounded by a carrier element of resilient material. In one embodiment, the stationary seal ring assembly includes an upper ring composed of a strong rigid material and a carrier element composed of a resilient material. In another embodiment, the lower ring extends along the outer face of the upper ring, thereby covering all or part of its outer face and providing additional resilience to the entire stationary seal ring. Further details of present invention will become apparent from the drawings, the description, and the claims.

DESCRIPTION OF THE DRAWINGS

Figure 1 is a cross-section of a portion of the housing and an improved stationary seal ring of a mechanical seal of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an improved mechanical face seal commonly used for the shaft of an agitator for a reaction vessel, particularly the stationary ring of the seal. The stationary ring 1 is composed of two members. The upper ring 2, comprising the seal face 7 of the stationary ring, is supported by, and optionally surrounded by a carrier element 3 composed of a resilient material.

The upper ring 2 may be made from any of a number of hard materials that allow for the rotating ring to move easily but closely against the upper face of the upper ring 2. In the past, the stationary ring of a mechanical seal was made entirely of a very hard material, preferably a ceramic, tungsten carbide, or silicon carbide, which are particularly for a chemical reaction vessel.

The upper ring 2 may be manufactured as two pieces, for example, two halves. This is described in U.S. Patent 6,485,024. The purpose of the two halves is to make replacement of the stationary ring easier and to make the ring less likely to break during replacement. However, this two-piece construction is not preferred for the present invention.

The carrier element 3 of the present invention may be composed of any resilient material that is resistant to the heat and chemicals that might be used or produced in the reaction vessel. As used herein, "resilient" is defined as the property of a strained body to absorb physical stress and recover its size and shape after deformation caused by

compression. One preferred material is polytetrafluoroethylene (PTFE). An example is the material sold under the trademark "TEFLON." Other preferred materials are advanced elastomers or thermoplastic elastomers. An example is the plastic sold under the trademark "VESCONTTE." The particular type of PTFE or advanced elastomer to be used can be selected by one of ordinary skill in the art based on the heat resistance and chemical compatibility needs of the reaction or reactions to be carried out in the vessel.

The carrier element 3 of the present invention may be molded in the desired shape or may be prepared by machining a larger block of the desired resilient material. It will preferably be made with one or more drive lugs that fit into holes on the upper ring 2 so as to hold the two pieces together and prevent their sliding against one another. The drive lugs may be part of the molded shape of the carrier element 3 or may be created by drilling small holes into the face of the carrier element 3 and inserting short pieces cut from a thin rod of the same or similar material. The number of drive lugs is not critical, but more than one is preferred.

The exact shape of the parts of the stationary ring 1 of the present invention may vary according to the overall shape of the mechanical seal assembly. The relative sizes of the upper ring 2 and the carrier element 3 may also vary; however, it is preferred that the upper ring 2 be of sufficient thickness and diameter to resist breakage due to the stress of the movements of the shaft and the rotating ring of the seal. The carrier element 3 should be of sufficient thickness, particularly in the portion next to the shaft, to absorb as much of the movement of the shaft as possible so as to protect the upper ring 2, the vessel, and the shaft itself. It is the resilience of the carrier element 3 that provides some of the advantages of the present invention, and these may be amplified by using a carrier element 3 of relatively thick diameter, which still fits within the mechanical seal assembly. The exact dimensions of the parts of the stationary ring of the present invention will depend on the size and shape of the opening in the vessel and the shaft with its attached rotating ring, and may be determined by one of ordinary skill in the art.

The upper ring 2 and the carrier element 3 may also be held in place by O-rings 4, 5, and 6. One O-ring 4 may be set in a circumferential groove in outside or lower face of the upper ring 2 and contacting the face of the carrier element 3. Additionally, an O-ring 5 may be inserted into a circumferential groove cut or molded into the outer face of the carrier element 3 to hold the stationary ring to the neck of the vessel. Another O-ring 6 may be set into a circumferential groove in the housing 7 of the seal assembly to hold the upper ring 2 in the housing 7. Alternatively, grooves running parallel to the shaft may be molded or cut into the outer face of the carrier element 3 and matched to ridges formed on the inner face of the housing 7.

All patents and publications referenced herein are incorporated by reference. The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than a specifically described above.

Claims

CLAIMS:

1 . A mechanical seal for a reaction vessel comprising a rotating ring and a stationary ring, wherein the stationary ring is comprised of an upper ring comprising one of the seal faces and a carrier element composed of a resilient material.

2. The mechanical seal of Claim 1 wherein the carrier element surrounds all but the seal face and inner face of the upper ring.

3. The mechanical seal of Claim 1 wherein the carrier element is composed of polytetrafluoroethylene.

4. The mechanical seal of Claim 1 wherein the carrier element is composed of an advanced elastomer.

5. A carrier element for the stationary ring of a mechanical seal shaped to support the upper ring comprising the seal face of the stationary ring, said carrier element being composed of a material selected from polytetrafluoroethylene and advanced elastomers and.

6. The carrier element of Claim 5 wherein the outer wall of the carrier element surrounds the outer face of said upper ring.

7. The carrier element of Claim 5 wherein the carrier element is composed of polytetrafluoroethylene.

8. A stationary ring of a mechanical seal comprising two elements, (1 ) an upper ring comprising the sealing face of the stationary ring and (2) a carrier element shaped to support the upper ring and composed of a material selected from polytetrafluoroethylene and advanced elastomers.

9. The stationary ring of Claim 8 wherein the outer wall of said carrier element surrounds the outer face of said upper ring.

10. The stationary ring of Claim 8 wherein said carrier element is composed of polytetrafluoroethylene.