WO2008015431A2

WO2008015431A2 - Condensate traps

Info

Publication number: WO2008015431A2
Application number: PCT/GB2007/002929
Authority: WO
Inventors: Richard Quentin Carmichael
Original assignee: Spirax-Sarco Limited
Priority date: 2006-08-02
Filing date: 2007-08-01
Publication date: 2008-02-07
Also published as: WO2008015431A3; GB0615362D0; GB2440548B; GB2440548A

Abstract

A condensate trap comprises an inlet (6) and an outlet (8), and a valve (14, 40) which opens to allow discharge of condensate but closes to prevent the discharge of vapour (such as steam). The flow path between the inlet (6) and the outlet (8) includes a swirl duct (30). Vapour leaking past the valve (40) generates a vortex within the swirl duct (30) which restricts vapour flow through an exit passage (36). Consequently, leakage of vapour is restricted, even if the valve (40) fails in an open condition.

Description

CONDENSATE TRAPS

This invention relates to condensate traps, and particularly, although not exclusively, to condensate traps intended for use in steam systems, for discharging condensed water. In such contexts, condensate traps are referred to as "steam traps".

In industrial processes, steam is utilised on a large scale to provide, for example, heat for industrial processes. As energy is extracted from the steam, the pressure and/or temperature of the steam is reduced and some of the steam condenses as water. It is desirable to remove this condensed water from the steam system. Steam traps achieve this by means of a valve which automatically opens when condensate is present, so as to discharge the condensate, and closes when steam is presented, in order to avoid steam loss.

Any steam discharged to the atmosphere represents wasted energy and also represents an undesirable increase in atmospheric carbon. Considerable effort is made to monitor steam traps and to rectify any that have failed, but nevertheless a leaking steam trap is not always easy to detect. Consequently, it is desirable that, should a steam trap become faulty so that steam is discharged, the quantity of discharged steam is minimised.

GB 2397032 discloses a steam trap comprising a vortex chamber. Incoming flow generates a vortex in the vortex chamber and is subsequently discharged through an escape aperture. The pressure regime in the vortex results in a reduction in mass flow rate when steam passes through the steam trap by comparison with the mass flow rate of water. However, the escape aperture is always open, so there is a loss of steam when no condensed water is present.

According to the present invention there is provided a condensate trap comprising an inlet, an outlet and a flow path extending between the inlet and the outlet, the flow path including a valve which is operable to open in the presence of condensate and to close in the presence of vapour, the flow path having a region which is configured to create a vortex in a flow vapour through the flow path.

If such a steam trap fails to close properly, for example, as a result of dirt accumulating on sealing surfaces of the valve, then the vapour will generate a vortex in the vortex- creating region. The vortex acts as an obstruction in the flow path, so restricting the flow of vapour to the outlet. The vortex generating region may comprise a swirl duct in the flow path, having an inlet directed to promote swirl in a flow passing through the swirl duct. The swirl duct may be convergent over at least part of its length, in the direction between the inlet and the outlet of the condensate trap. The swirl duct may converge from an initial diameter to a diameter which is not greater than half the initial diameter. The duct, or the convergent part of the duct, may be of frustoconical form, the inlet of the swirl duct may extend tangentially, and may be one of two or more inlets.

Preferably, the swirl duct is disposed between the valve and the outlet of the condensate trap. The condensate trap may comprise an outlet passage which extends from the valve and communicates with a manifold having exit openings communicating with the or each inlet of the swirl duct. The manifold may be annular, and may surround an inlet passage of the valve.

The swirl duct may have a single inlet, or two or more inlets spaced apart circumferentially about the duct.

In a preferred embodiment, the condensate trap may comprise a single body component provided with the inlet, the outlet and the vortex-creating region of the flow path.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-

Figure 1 is a sectional view of a steam trap;

Figure 2 is a sectional view taken on the line H-Il in Figure 1 ; and

Figure 3 is an enlarged view of the region III in Figure 2.

As shown in Figure 1 , the steam trap comprises a body 2 provided with a cap 4. The body 2 has an inlet 6 and an outlet 8. The inlet communicates with a strainer chamber 10 which, in use, accommodates a strainer and is closed at its lower end by a cap (not shown). The strainer chamber 10 communicates through an inlet passage 12 with a trap chamber 14, defined between a face 16 of the body and the cap 4. The face 16 has an annular groove 18 from which extends an outlet passage 20. The outlet passage 20 opens into an annular manifold 22 having exits 24 which communicate with inlets 26, 28 of a swirl duct 30. The manifold 22 extends around the inlet passage 12. The swirl duct 30 has a cylindrical region 32 and a frustoconical region 34 which is convergent in the direction towards the outlet 8. The narrower end of the frustoconical portion 34 communicates with the outlet 8 through an exit aperture 36. The diameter of the cylindrical portion 32 is at least double, and possibly more than three times, the diameter of the exit aperture 36. In a specific embodiment, the diameter of the cylindrical portion 32 is 15.5 mm while that of the exit aperture 36 is 2 mm.

At the end of the cylindrical portion 32 away from the frustoconical portion 34 there is a cylindrical boss 38 having a diameter slightly larger than that of the exit aperture 36 (6 mm in the specific embodiment referred to above), so that the region of the cylindrical portion 32 into which the inlets 26 open is of annular form.

The valve chamber 14 accommodates a valve disc 40. The steam trap shown in the drawings is a thermodynamic steam trap, the operation of which is well known. In summary, if steam is present in the inlet passage 12, the temperature in the chamber 14 is high, and any condensate above the valve disc 40 will flash to steam, creating an increased pressure in the chamber 14 to maintain the valve disc 40 against the surface 16, so closing the inlet passage 12 and the annular groove 18. Flow through the steam trap is therefore blocked. If condensate reaches the steam trap, the steam in the chamber 16 will cool, and eventually condense. This reduces the pressure above the valve disc 40, allowing system pressure to drive any condensate in the trap past the valve disc 40 through the outlet passage 20 and the swirl duct 30 to the outlet 8. Eventually, when all condensate has been discharged, steam flows through the inlet passage 12 to heat the chamber 14, so that the cycle begins again.

If the trap fails in the open position, for example if dirt accumulates between the surface 16 and the valve disc 40, steam will continue to leak past the valve disc 40 to the outlet 8 even after all condensate has been discharged. Should this occur, the steam flows from the chamber 14 through the annular groove 18, the outlet passage 20 and the manifold 22 to the swirl duct 30. The steam enters the swirl duct 30 through the inlets 26 and 28, which are oriented to cause the steam to enter the cylindrical region 32 in a tangential direction, to create a swirling flow in a clockwise direction as seen in Figure 3. The swirling flow is accelerated as it flows through the convergent frustoconical portion 34. This has the effect of reducing the pressure in the central region of the swirl duct 30, adjacent the exit aperture 36. This reduces the pressure drop across the exit aperture 36 so reducing the mass discharge rate. The reduced pressure in the swirl duct 30 also increases the specific volume of the vapour/water mixture, further reducing the discharge of the vapour (steam) and energy loss.

Furthermore, any condensate that may be entrained in the flow of steam through the trap will, when exposed to the reduced pressure at the centre of the vortex in the frustoconical portion 34, flash off as steam. This further raises the specific volume of the mixture, so that the exit aperture 36 becomes choked, further restricting the escape of steam.

When the trap is operating normally, and is open to discharge condensate, the non- compressible liquid water flow through the swirl duct 30 takes place relatively unhindered and so can be discharged rapidly through the exit aperture 36.

The effect is that the exit passage 36 can be made relatively large, to allow rapid discharge of water. The swirl duct 30 has the effect of throttling the flow of steam, to provide a discharge rate similar to that which would be achieved with an orifice plate of substantially smaller diameter than that of the exit aperture 36. The steam trap can therefore discharge condensed water rapidly, while significantly reducing the flow of steam to the outlet 8 should the trap fail in an open condition.

Although the invention has been described with reference to a thermodynamic steam trap, it will be appreciated that the basic principle underlying the invention is applicable to any kind of steam trap, including float traps, bucket traps and thermostatic traps.

In the embodiment shown in the Figures, the swirl duct 30 is situated downstream of the valve chamber 14. In other embodiments, the swirl duct may be situated upstream of the valve chamber.

Claims

1. A condensate trap comprising an inlet, an outlet and a flow path extending between the inlet and the outlet, the flow path including a valve which is operable to open in the presence of condensate and to close in the presence of vapour, the flow path having a region which is configured to create a vortex in a flow of vapour through the flow path.

2. A condensate trap as claimed in claim 1 , in which the vortex-creating region of the flow path comprises a swirl duct having an inlet directed to promote swirl within the swirl duct.

3. A condensate trap as claimed in claim 2, in which the swirl duct has a longitudinal axis about which, in use, the vortex is generated, the swirl duct having an exit aperture which is aligned with the longitudinal axis.

4. A condensate trap as claimed in claim 2 or 3, in which the swirl duct comprises a portion which is convergent in the direction from the inlet to the outlet of the condensate trap.

5. A condensate trap as claimed in claim 4, in which the convergent portion of the swirl duct is frustoconical.

6. A condensate trap as claimed in claim 5, when appendant to claim 3, in which the exit aperture is situated at the smaller diameter of the frustoconical portion, the exit aperture having a diameter which is not greater than half the larger diameter of the frustoconical portion.

7. A condensate trap as claimed in any one of claims 2 to 6, in which the inlet of the swirl duct extends tangentially of the swirl duct.

8. A condensate trap as claimed in any one of claims 2 to 7, in which the swirl duct is disposed in the flow path between the valve and the outlet.

9. A condensate trap as claimed in any one of claims 2 to 8, in which an outlet passage extends from the valve and communicates with a manifold having an exit communicating with the inlet of the swirl duct.

10. A condensate trap as claimed in claim 9, in which the manifold is annular, and surrounds an inlet passage of the valve.

11. A condensate trap as claimed in any one of claims 2 to 10, in which the inlet of the duct comprises one of at least two inlets which are spaced apart from each other circumferentially about the swirl duct.

12. A condensate trap as claimed in any one of the preceding claims, which comprises a single body component provided with the inlet and the outlet of the condensate trap and with the vortex-creating region of the flow path.