CONDENSATE TRAP

This invention relates to condensate traps.

Condensate traps are commonly employed to remove condensed water from steam utilised in plant and equipment, in which context they are normally referred to as steam traps. Many different designs of steam traps have been developed to suit a variety of circumstances. The majority of traps involve a self-actuating mechanism which detects the presence of condensate in the trap, and when necessary opens to allow the condensate to drain. These traps have moving parts and consequently are prone to mechanical failure. An alternative form of trap is a fixed orifice trap. These are generally reliable as they have no moving parts, and in the simplest form comprise an aperture through which condensate is discharged. Flash steam produced as the pressure drops during flow through the aperture acts to reduce the amount of steam that escapes through the aperture.

GB 2397032 discloses a condensate trap comprising a vortex chamber, an inlet and a single outlet, the inlet being disposed to admit fluid into the chamber in a manner to promote a rotational flow of the fluid in the chamber about a longitudinal axis of the chamber, and the outlet comprising an escape aperture at an axial end of the chamber.

In a condensate trap of this kind, the rotational flow creates a region of reduced pressure around the longitudinal axis of the chamber. Hot condensate reaching the reduced pressure region flashes to steam which serves to choke the escape aperture to restrict the leakage of live steam from the chamber.

A condensate trap of this kind can have an escape aperture which is sufficiently large to permit a high rate of discharge of condensate, particularly when cold, yet the choking action which occurs as a result of the vortex, particularly if flash steam is generated, minimises the leakage of live steam from the trap.

Nevertheless, any steam passing through the escape aperture represents lost energy, and it is desirable for this to be minimised.

According to the present invention there is provided a condensate trap comprising a vortex chamber, an inlet nozzle disposed to admit fluid into the vortex chamber in a

manner to promote a rotational flow of the fluid in the chamber about a longitudinal axis of the chamber, a condensate outlet comprising an escape aperture at an axial end of the chamber, and a flash steam outlet having an entrance situated within the vortex chamber.

The flash steam outlet of a condensate trap in accordance with the present invention provides an alternative route for the discharge of steam from the vortex chamber, so that the energy of this steam can be utilised.

The vortex chamber may have a cylindrical portion and/or a frusto-conical portion. In a preferred embodiment, the vortex chamber has a cylindrical portion which adjoins the wider diameter of a frusto-conical portion, in which case the inlet nozzle may open into the cylindrical portion. In such a configuration, the escape aperture may be disposed at the narrower end of the frusto-conical portion, preferably on the longitudinal axis of the vortex chamber.

In use, the condensate trap is preferably positioned with the longitudinal axis disposed vertically, with the escape aperture at the lower end of the vortex chamber, and the flash steam outlet extending from the top of the vortex chamber. The flash steam outlet preferably comprises a duct extending axially from the entrance of the flash steam outlet.

In accordance with a further aspect of the present invention, there is provided a steam system comprising a first steam utilisation device having a steam inlet and a steam outlet, the steam outlet being connected to the inlet nozzle of a condensate trap as defined above, the flash steam outlet of the condensate trap being connected to a steam inlet of a second steam utilisation device.

The second steam utilisation device may have a steam outlet connected by a further steam trap, which may be of any kind, to a discharge duct which is also connected to the condensate outlet of the condensate trap.

According to a further aspect of the present invention, there is provided a method of recovering energy from a flowing mixture of steam and condensate, in which method the flow is directed through a nozzle into a vortex chamber in a direction so as to create a vortex within the vortex chamber, conveying flash steam from the vortex chamber

through a flash steam outlet and conveying condensate from the vortex chamber through a condensate outlet.

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 N-Il in Figure 1; and

Figure 3 shows part of a steam system including the steam trap of Figures 1 and 2.

With reference to Figure 1 , the steam trap 1 comprises an upper flange 2, a lower flange 6, and a main body 4 secured between the upper and lower flanges 2, 6.

The body 4 defines a vortex chamber 8, having an upper portion 10 and a lower portion 12. The upper portion 10 of the vortex chamber is cylindrical and closed off at its upper edge by the upper flange 2. The lower portion is a conical frustum, continuing from the cylindrical wall of the upper portion 10 and tapering to a smaller diameter at its flat base 14. An escape aperture 16 is provided in the base 14, leading to a bore 18 extending downwardly from the aperture 16. In the embodiment shown, the aperture 16 is at the centre of the base 14 on the central axis 30 of the trap 1 , but in alternative embodiments it could be offset from the axis 30. The escape aperture 16 is approximately 5mm diameter in this example. The bore 18 communicates at its lower opening with the surrounding environment or to a condensate return pipe (not shown in Figure 1), via a circular opening 5 in the lower flange 6.

The bore 18 has a length which is greater than the diameter of the escape aperture 16, for example greater than twice the diameter of the escape aperture. In the embodiment shown, the length of the bore 18 is 12mm.

A nozzle 20 is formed in the main body 4, and opens into the wall of the chamber 8 at the lower region of the upper portion 10. As shown in Figure 2, the outermost edge 22 of the nozzle 20 continues tangentially from the cylindrical wall of the chamber 8. The innermost edge 24 of the nozzle 20 is offset from the central axis 30 of the chamber 8

towards the outer edge 22. At the end of the nozzle away from the chamber 8, the nozzle 20 is connected to an internally screw threaded bore for receiving a connector to connect the nozzle 20 to a source of steam and condensate.

A flash steam outlet in the form of a pipe 32 projects into the chamber 8 through the upper flange 2. The pipe 32 is aligned with the central axis 30, and its entrance end 34 is situated just below the junction between the cylindrical portion 10 and the frusto- conical portion 12 of the vortex chamber 8. The end 36 of the pipe 32 outside the chamber 8 is provided with connection means (not shown) for connecting the pipe 32 to further pipework of the steam system in which the trap 1 is installed.

In use, a mixture of steam and condensate is introduced tangentially into the chamber 8 through the nozzle 20. With the nozzle 20 oriented as shown in Figure 2, the steam and condensate mixture flows around the wall of the chamber 8 in an anti-clockwise direction, creating a vortex. The central axis of the vortex lies on or close to the central axis 30 of the chamber 8.

The nozzle 20 acts as a flow restriction in the steam flow, and consequently there is a substantial pressure drop along the nozzle 20. The pressure drop resulting from the nozzle 20 may be sufficient to reduce the pressure to below saturation in the nozzle exit, thereby creating flash steam and greatly increasing the velocity and cyclonic or vortex action in the chamber 8. For example, the pressure at the nozzle exit may be not more than 75%, and possibly about 50%, of the pressure in the line upstream of the nozzle 20. Furthermore, the vortex in the chamber 8 creates a further pressure reduction at its centre. Since the escape aperture 16 is located on the central axis 30, the vortex thus provides a low pressure region directly upstream of the aperture 16. This reduces the discharge rate through the escape aperture 16 and the bore 18, and accordingly a larger bore 18 can be used, reducing the likelihood of it becoming blocked. Additionally, the self-regulatory mechanism of the vortex enables the discharge rate of liquid condensate to be substantially higher than that of live steam, owing to the following characteristics of the trap:

During plant start up, cold condensate builds up within the steam system, and the condensate load on the trap is at its highest. Under these conditions, liquid condensate is discharged through the nozzle 20 into the chamber 8, and passes through the escape aperture 16 and the bore 18. Because the water is cold, little or no

flash steam is created, and the cold water will flow freely through the bore 18 at a relatively high mass flow rate of, for example, 200 kg/h.

As the temperature at the steam trap increases, the water will eventually reach the saturation temperature for the pressure prevailing at the centre of the vortex. At this point, vapour or flash steam will begin to form. If the escape aperture 16 is choked with condensate, this flash steam will pass through the pipe 32. In some circumstances, the aperture 16 may not be fully choked, and so some of the flash steam may be expelled through the escape aperture 16. This has the effect of reducing the mass discharge through the escape aperture 16, as the density of the flash steam is much lower than that of water.

The low pressure created at the centre of the vortex also reduces the pressure drop along the bore 18, and this will also reduce the discharge rate.

The flow in the trap is in practice very complex. In accordance with the present invention the vortex chamber creates an area of low pressure upstream of the escape aperture. As is well known in the art, in a vortex pressure energy is converted to kinetic energy. From the conservation of energy (Bernoulli) equation, as the velocity increases the pressure falls. Therefore, low pressure results in low density at any given point, in this case the centre of the vortex. By creating this condition, as steam reaches the escape orifice, the mass discharge rate is reduced in accordance with the flow equation for a single phase fluid:

Q = C _d x (πd ² / 4) x V(p x δp _c ) where

Q = flow rate

C _d = discharge coefficient d = orifice diameter p = fluid density δp _c = critical pressure drop

Since the density of water at 2O ⁰ C is 998 kg/m ³ and the density of steam at 5 barg is 3.2 kg/m ³ , the ratio of the mass discharge rates of steam and water is:

Thus, when flash steam is generated just upstream of the escape aperture 16, the mass discharge rate of the steam is smaller than that of water by a factor of more than 17.

In tests, it has been shown that, for a steam line pressure of 11 bar (ie the pressure upstream of the nozzle 20), the combined effect of the restriction provided by the nozzle 20 and the vortex causes the pressure to fall to 7 bar at the centre of the vortex. At 7 bar, the saturation temperature is 165°, and so if the temperature of the condensate entering the trap falls below 165 ⁰ C, no flash steam is generated and the condensate is discharged rapidly through the escape aperture 16. Above this temperature the volume of flash steam generated will steadily increase, progressively reducing the rate of discharge of the escape aperture 16. It has been found that the mass rate of discharge falls to 50% of its initial (coid water) value as the condensate temperature increases from ambient temperature to near saturation temperature.

Therefore a fixed orifice trap including the vortex chamber 8 in accordance with the present invention utilises the Bernoulli effect to provide a naturally self regulating discharge characteristic. Cold water is discharged at a high rate but the discharge diminishes rapidly as the saturation temperature of the fluid is approached and flash steam is generated. Once the discharge rate exceeds the condensate load, some steam is inevitably lost, but the high flow resistance of the vortex minimises this so that at the extreme where no condensate is present, the loss is just 5% of the cold water discharge capacity of the escape aperture. In a more typical application where the hot condensate load is 60% of the capacity of the discharge escape aperture, the loss will be around 2% of the cold water capacity.

In the absence of the pipe 32, all of the steam entering the vortex chamber 8 through the nozzle 20 and all flash steam generated within the chamber 8, is discharged through the escape aperture 16. Since the steam contains heat, its loss from the system represents a waste of energy. By adding the pipe 32 to the steam trap, some of this energy can be recovered as flash steam, which can be used for additional heating purposes in the plant in which the steam system operates.

In a test, a steam trap in accordance with Figures 1 and 2 was operated with an inlet flow to the nozzle 20 comprising 98 kg/h of condensate and 2kg/h of steam at 10 barg.

The discharge from the bore 18 contained 82.37 kg/h of condensate and 10.4 kg/h of flash steam at atmospheric pressure. In addition 7.24 kg/h of usable steam was discharged through the pipe 32 at a pressure of 5 barg. Based on a fuel cost of £0.015/kWh the value of the recovered flash steam from the pipe 32 can be estimated at £1276 per annum.

By comparison, a similar steam trap, but without the pipe 32, discharges, from the bore 18, 81.9 kg/h of condensate and 18.1 kg/h of flash steam. In economic terms, the cost of energy lost in flash steam discharged through the escape aperture 16 in a trap without the pipe 32 can be estimated at £1432 per annum, while the corresponding loss in a trap as shown in Figure 1 can be estimated as £887 per annum. Thus, the recovery of flash steam by means of the pipe 32 can represent a saving of £241 per annum for each steam trap.

Figure 3 shows an example of the use of a steam trap as shown in Figures 1 and 2 in a steam installation. In Figure 2 a heat exchanger 40 is supplied with steam at high pressure on a line 42. After passing through the heat exchanger, the steam is supplied along a line 44 to the nozzle 20 of the steam trap 1. Lines 46 represent additional supplies of steam from other equipment of the system. Since the steam will have lost energy passing through the heat exchanger 40, the flow through the lines 44 and 46 will contain condensate mixed with the steam flow.

As described above, the condensate and steam mixture entering the chamber 8 creates a vortex, and this results in some of the condensate in the line 44 flashing into steam. The remaining condensate, and some of the steam, is discharged through a condensate discharge line 48, which receives flow from the bore 18 of the steam trap 1. Flash steam flowing from the chamber 8 of the steam trap 1 through the pipe 32 passes to a transfer line 50 which supplies the flash steam to a first heating matrix 52 in an air heating duct 54. Further heating matrices 56, supplied from a separate source of steam 57, are also provided to heat air flowing through the air duct 54. The outlets of the matrices 52, 56 are connected, via steam traps 58, to a condensate manifold 60, which also receives the condensate from the steam trap 1 through the line 48. Condensate from the manifold 60 flows to a condensate return pump 62, which returns the condensate to the boiler of the system.

It will be appreciated that the flash steam flowing through the first heater matrix 52 is steam which, but for the flash steam outlet provided by the pipe 32, would have been discharged through the line 46 directly to the condensate return pump 62, with the consequent loss of the energy contained in the flash steam. It will therefore be appreciated that the use of a steam trap in accordance with the present invention in a plant which may have several hundred steam traps can lead to substantial energy and therefore cost savings.