Barrier system for mechanical seal

Abstract

A barrier system for a dual mechanical seal, the system comprising means for controlling barrier fluid pressure relative to product pressure. The pressure control means comprises means for monitoring the volume of barrier fluid in the system and for supplying additional fluid to the system to maintain the volume within a desired range. The system further comprises means for maintaining the barrier fluid pressure at a pre-determined pressure above product pressure.

Claims

1. A barrier system comprising: a dual mechanical seal comprising a pair of seals with a barrier seal chamber between the pair of seals, wherein the barrier seal chamber has a barrier seal pressure (P.sub.barrier); and, a controller comprising a product pressure reference (P.sub.ref) input, a valve output controlling flow of a barrier fluid into the barrier seal chamber, and pre-determined pressure (P.sub.bias) setting above the product pressure reference (P.sub.ref); wherein the controller is configured to track the P.sub.barrier and control the barrier fluid flow to maintain the P.sub.bias in the barrier seal chamber over the product pressure; wherein the controller further comprises a volume monitor adapted to monitor a volume (V.sub.barrier) of barrier fluid in the system; and, wherein the volume monitor comprises one or more flow meters selected from the group consisting of: a flow meter between a bladder accumulator and the barrier seal chamber; a flow meter receiving fluid flowing from the barrier seal chamber; a pair of flow meters with one of the pair upstream to the barrier seal chamber and one of the pair downstream from the barrier seal chamber; and three flow meters.

2. The barrier system of claim 1, wherein the pair of seals are spaced along a shaft.

3. The barrier system of claim 1, wherein a product having the product pressure is in contact with one of the pair of seals on a side opposite the barrier seal chamber.

4. The barrier system of claim 3, wherein the product having the product pressure is in direct contact with at least one of the seals.

5. The barrier system of claim 1, wherein the controller is adapted to provide the pressure in the barrier seal chamber of P.sub.bias over the product pressure when the product pressure reference (P.sub.ref) input is zero.

6. The barrier system of claim 5, wherein the controller is adapted to control flow of the pressurized gas through a valve to a barrier fluid accumulator which provides barrier fluid to the barrier seal chamber.

7. The barrier system of claim 6, wherein the flow of the pressurized gas through the valve controls the P.sub.barrier of the barrier seal chamber.

8. The barrier system of claim 7, further comprising a bladder accumulator adapted to receive the pressurized gas and provide the barrier seal chamber with a barrier fluid at P.sub.barrier.

9. The barrier system of claim 1, wherein the volume monitor is adapted to monitor a volume of barrier fluid consumed by leakage through the seals.

10. The barrier system of claim 1, wherein the system is configured to monitor the barrier seal chamber pressure and increase the barrier seal pressure when the P.sub.barrier is less than the P.sub.ref plus the P.sub.bias.

11. The barrier system of claim 1, wherein the controller is adapted to maintain the P.sub.barrier at a P.sub.bias above the P.sub.ref, and adapted to monitor the (V.sub.barrier) in the system and supply additional fluid to the system to maintain the (V.sub.barrier) within a desired range.

12. The barrier system of claim 11, wherein the controller is adapted to receive pressure readings from the product and from the barrier fluid; and wherein the controller releases pressure from the barrier system when the P.sub.barrier is above P.sub.ref plus P.sub.bias.

13. The barrier system of claim 1, wherein the system is adapted to maintain P.sub.barrier at P.sub.ref plus P.sub.bias.

14. The barrier system of claim 1, wherein the barrier fluid is a liquid.

15. The barrier system of claim 1, wherein the volume monitor comprises a flow meter measuring a loss of fluid through the barrier seal chamber.

16. The barrier system of claim 1, wherein the product pressure reference (P.sub.ref) input comprises a tracked product pressure.

17. The barrier system of claim 1, wherein the pre-determined pressure (P.sub.bias) setting above the product pressure has a value greater than zero.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings are as follows:

(2) 1. FIG. 1 illustrates diagrammatically the system for providing barrier fluid to a dual mechanical seal;

(3) 2. FIGS. 2 to 6 show various stages in the installation operation of a barrier system in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) The present invention will now be described, by way of example only, with reference to the accompanying drawings.

(5) Referring to FIG. 1 of the accompanying drawings, a system for supplying barrier fluid to a dual mechanical seal comprises a bladder accumulator 1 to which is connected a pressure tracking device 3, there being located between device 3 and accumulator 1 an adjustable valve 5. Pressure tracking device 3 is in turn connected to a source of pressurized nitrogen and to a location at which the pressure of barrier fluid in the system (the reference pressure) can suitably be determined. This position could be a vessel chamber of the seal.

(6) Connected to the pressure tracking device 3 is a silencer 9. Also connected to bladder accumulator 1 is a flow meter 11 which measures liquid flow to and from the bladder accumulator. Barrier fluid flow through flow meter 11 can take place to the seal vessel chamber 16 via flow meters 13 and 15. Barrier fluid can be supplied to the system via feed 17 and system vents are provided at 19 and 21 and the system drains at 23 and 25. They can also be provided with one or both of pressure indicator 27 and electronic indicator 29 to control the system.

(7) Referring to FIGS. 2 to 5 of the accompanying drawings, there is illustrated various stages in the operation of a system such as that shown in FIG. 1. The system is shown in simplified form with the bladder accumulator 1, pressure tracking device 3, valve 5 and flow meters 11, 13 and 15. As shown in FIG. 2, the system pressure (P.sub.Barrier) is equal to the product pressure (P.sub.Ref) and the bias pressure (P.sub.Bias).

(8) Referring to FIG. 2, there is illustrated the position when the system is initially commissioned. The supply gas is attached and the system pressure (PBarrier) “sets” itself. When set with all other inputs at zero pressure, the dual seal 18 loop is pressurised (PBarrier) and it equals biased pressure (PBias), the product 20 pressure (PRef) being at zero. In this case, (PRef) is assumed to be 2 barg (30 psig).

(9) Once the pressure is set, the bladder accumulator gas pressure is locked so that the volume of gas remains constant. Barrier fluid can then be pumped in to the fluid circuit so that the volume of barrier fluid (V.sub.Barrier) is as desired. Typically, the volume of barrier fluid does not exceed 80% of the available volume of the accumulator.

(10) Once the barrier fluid volume is set, the bladder accumulator gas pressure is allowed to equalise back to the set bias pressure (pressure having being increased due to the reduced gas volume).

(11) The system “tracks” input pressure (P.sub.Ref) maintaining a positive pressure differential such that the barrier pressure (P.sub.Barrier) equals the reference pressure (P.sub.Ref) plus the bias pressure (P.sub.Bias).

(12) The system will continue to operate in this manner as the volume of barrier fluid is consumed by the mechanical seal being serviced by the system.

(13) FIG. 4 shows the position when there is a “normal” amount of fluid in the system, the product pressure (P.sub.Ref) is 10 barg and the (P.sub.Barrier) pressure is 12 barg.

(14) In FIG. 5 the amount of barrier fluid has reduced (V.sub.Barrier2) due to the loss of barrier fluid from the seal. During this process (P.sub.Barrier) is maintained at 12 barg.

(15) FIG. 6 shows the position after the additional fluid has been supplied to the bladder accumulator. During this process the SmartTrack pressure tracking device continues to regulate the pressure in the system by allowing excess gas to vent to atmosphere as the volume of liquid increases.

(16) In order for the system to be effectively controlled, the volume in the system (V.sub.Barrier) needs to be known and monitored. This is achieved by the use of three flow meters that log flow of liquid into the system and consumption of fluid by the mechanical seal. In other embodiments of the present invention this monitoring of the volume of liquid can achieved by other means.