GB2514447A

GB2514447A - Mechanical seal support system

Info

Publication number: GB2514447A
Application number: GB1404306.1A
Authority: GB
Inventors: Thomas Broadbent
Original assignee: A E S ENGINEERING Ltd; AES Engineering Ltd
Current assignee: A E S ENGINEERING Ltd; AES Engineering Ltd
Priority date: 2013-03-12
Filing date: 2014-03-11
Publication date: 2014-11-26
Anticipated expiration: 2034-03-11
Also published as: US20140265143A1; DE102014103358A1; GB201404306D0; GB2514447B; GB201304435D0

Abstract

A mechanical seal support system is provided. The seal support system comprises a pre-pressurised bladder-type accumulator 2 containing barrier fluid and a gas under pressure. A cooling circuit 1 including a mechanical seal means for feeding barrier fluid from the accumulator 2 to the cooling circuit 1 is further provided. A pressure regulating device 10 is located between the accumulator 2 and the cooling circuit 1, and is responsive to the pressure in the cooling circuit 1 for indicating a pressure below a pre-determined level.

Description

Mechanical Seal Support System

Field of Invention

The invention relates to mechanical seal support systems and, in particular, to a method for maintaining constant barrier fluid pressure in a mechanical seal loop.

Background to Invention

An API Plan 53B seal support system is a pressurized barrier fluid circulation system in an outboard seal of dual seal configuration. Circulation is maintained by using pumping ring in running condition. The pressure is maintained in the seal circuit by a bladder accumulator.

In an API Plan 53B seal support system barrier fluid is stored and the pressure is maintained through the use of a pre-pressurised bladder-type accumulator. The barrier fluid is not circulated through the bladder accumulator but around a cooling loop, which will include a separate heat exchanger. The accumulator is effectively on a dead leg and its sole purpose is to store fluid and pressure. It does not play any part in cooling the barrier fluid. Flow is maintained by an internal pumping ring within the seal. The pressure will vary depending on the level of the liquid in the reservoir, and a pressure switch is used to alarm for a low liquid level based upon pressure in the system. Volume of fluid in a bladder accumulator cannot be directly measured.

API Plan 53B systems with their trapped gas volume are very susceptible to changes in ambient temperature. Where there are large diurnal and seasonal changes in ambient temperature, barrier fluid pressure will correspondingly be affected. If ambient temperature conditions are not taken into consideration when designing the alarm strategy, in extremely hot ambient conditions, it may be possible that the accumulator becomes completely depleted of liquid without triggering the pressure alarm. On extremely cold nights pressure alarm may be activated when there is still sufficient liquid remaining in the accumulator. The operator will then refill the barrier fluid, causing excessive fluid volumes in the accumulator, which may over pressurise the system if the temperature rises the following day. Solar radiation can amplify this problem. Software can provide the user with a proposed alarm strategy however adopting this may force users to specify unnecessarily high barrier fluid pressure. This will cause unnecessary wear and stresses on the seal faces and may limit operators in the use of back to back dual seals, which have compromised reliability on contaminated services. Another proposed strategy, which is included in the Draft International Standard for the 4th revision of API 682 ISO 21049, will propose that the simple pressure switch is replaced by a pressure and a temperature transmitter. Taking both readings and using simple logic of a distributed control system (DCS) the actual liquid level is thus calculated.

Statements of the Invention

According to the present invention the issues relating to variable pressures in the system produced by varying ambient temperatures and depleting levels of barrier fluid are overcome with the use of a pressure regulation device between the system and the mechanical seal loop. Located on the seal feed line it creates a constant pressure area in the mechanical seal loop and a variable pressure area in the system. The system may comprise in one embodiment: * An API Plan 53B system * A pressure regulating device * A mechanical seal with cooling loop * Control mechanisms in the constant pressure area to highlight when the pressure has decreased and so the barrier fluid level has diminished.

Preferably the pressure regulation device is of modular design so that it can be fitted to a standard pressurized barrier fluid circulation system, for example an API Plan 53B system.

Preferably the pressure regulation device is set prior to installation onto the system.

Preferably the pressure regulation device is self-relieving so that any unsafe increases in pressure do not become dangerous.

Preferably the pressure regulation device can be isolated via ball valves located on its inlet and outlet.

Preferably the control mechanisms consist of a pressure and temperature transmitter located in the constant pressure area to highlight when the barrier fluid level has depleted to an undesirable level.

Brief Description of Drawings

Figure 1 shows a schematic diagram of the present invention with relation to a pressurized barrier fluid circulation system configuration and mechanical seal.

Detailed Description

A pressurized barrier fluid circulation system in the form of an API plan 53B system (1) comprises a bladder accumulator (2) which has its bladder pre-charged with nitrogen to a specified percentage above the maximum product pressure. Included in the system are various ball valves and piping paths for venting (3), draining (4) and filling (5) the system. The number and type of ball valves depends on customer and application stipulation. Once the bladder is pre-charged the system is filled with bairier fluid with the fill (5) and vent (3) ball valves in open configurations. The check valve (6) ensures that back flow does not occur. The system is filled to a pre-determined pressure specific to the application. Various pressure indicators and transmitters (7) are located in the system lines so that the pressures can be viewed and the system is correctly set.

A flange fixture (8) is located on the line to the seal loop (9) allowing further piping to be connected. In the invention a pressure regulation device (10) is fitted at this location between ball valves (11) which allow isolation of the system (1), pressure regulator (10) and the seal loop (9) to be achieved if required. An example of a suitable pressure regulation device is a Go Regulator PR-i Series Adjustable Pressure Reducing Regulator. The location of the pressure regulation device 00) means that as pressure fluctuates in the system (1) due to changes in temperature conditions a constant pressure is maintained in the seal loop (9) after it. Depending on the application it may be preferable for other various instrumentation or fixtures and fittings to be incorporated into the system before or after the pressure regulation device (10).

Should the pressure in the seal loop (9) increase to a greater level than in the system arrangement (1) the pressure regulation device (10) will preferably allow relief of the pressure either in the counter direction to normal operation or to the atmosphere.

Claims

Claims 1. A mechanical seal support system comprising a pre-pressurised bladder-type accumulator containing barrier fluid and a gas under pressure, a cooling circuit including a mechanical seal means for feeding barrier fluid from the accumulator to the cooling circuit, a pressure regulating device located between said accumulated said cooling circuit and means, responsive to the pressure in the cooling circuit, for indicating a pressure below a pre-determined level.
2. A system according to Claim 1 wherein the pressure regulating device is set prior to installation onto the system.
3. A system according to Claim 1 or Claim 2 wherein the pressure regulating device is of a modular design and may be retrofitted into to existing systems.
4. A system according to any of the preceding claims, wherein the pressure regulating device has self-relieving capabilities.
5. A system according to any of the preceding claims, wherein the pressure regulating device is provided with ball valves at its inlet and/or its outlet.
6. A system according to any of the preceding claims, wherein the system includes a pressure and temperature transmitter located adjacent the pressure regulation device.
7. A mechanical seal support system substantially as herein described with reference to and/or as described in any appropriate combination of the text and/or drawing.