WO2007135430A2

WO2007135430A2 - A condensate trap

Info

Publication number: WO2007135430A2
Application number: PCT/GB2007/001911
Authority: WO
Inventors: James Robert Lowrie; Michael Hopkingson; David Anthony Clark; Paul Mee
Original assignee: Microgen Energy Limited
Priority date: 2006-05-23
Filing date: 2007-05-23
Publication date: 2007-11-29
Also published as: GB0610217D0; GB2452453A; GB0823028D0; WO2007135430A3; GB2452453B

Abstract

A condensate trap comprising a housing (4) with a condensate inlet (1) at the top. A first tube (5) depends from the top of the housing (4), the inlet leading to a space between the first tube (5) and housing (4). A second tube (6) within the first tube (5) extends upwardly from the bottom of the housing (4). A third tube (7) within the second tube (6) depends from the top of the housing (4). A vent tube (8) opening at the bottom of the housing (4) extends upwardly between the second (6) and third (7) tubes. An outlet tube (9) extends upwardly within the third tube (7) and terminates below the top of the vent tube (8). The housing (4) is sealed other than at the inlet (1), and openings for the vent tube (8) and outlet tube (9).

Description

A CONDENSATE TRAP

The present invention relates to a condensate trap.

Such condensate traps are well-known in domestic condensing boilers. These are required to allow liquid condensing from the cooling gases within a heat exchanger to drain from a system. As this fluid is largely acidic, and therefore corrosive, it is important that it does not accumulate within the system components. In addition to causing corrosion of components, a build-up of condensate inside the combustion chamber could impair combustion and potentially lead to an increase in harmful emissions such as carbon monoxide (CO) and lead to unexpected failure modes.

The design of condensate traps is well-known technology with designs such as the Baxi trap (from the HE Plus range of domestic condensing boilers) in use within the boiler industry.

Conventionally, a "U" bend together with an auto-siphon effect is used within the condensate trap to allow the drainage of liquid without allowing combustion products from the heat exchanger to continuously leak through. Any blockage of the siphon tube, or outlet tube, by particles passing from the heat exchanger in the condensate would cause the liquid levels to rise within the trap. Eventually, this liquid would accumulate within the heat exchanger, impairing combustion of any burner located within the body of the heat exchanger, and potentially damaging the gas tight seals, thereby spilling out through the seals, onto surrounding components. As the condensate liquid is corrosive, this overflow is undesirable in any domestic boiler and a variety of blockage detectors have been designed to avoid any resulting hazards.

The applicant is involved in a project to develop a domestic combined heat and power (DCHP) system which uses a Stirling engine to generate electricity, with the heat from exhaust gases being recovered for use in domestic heating. A supplementary burner provides additional heat to satisfy the local requirement. Any spillage of condensate fluid onto the head of the Stirling engine (operating at an optimum metal temperature of up to 600⁰C) could be damaging and must be avoided. A safe design of condensate trap is therefore essential.

If the flue becomes blocked, in addition to a reduction in the quality of combustion within the associated burner (s), the fan which draws air into the heat exchanger casing and expels exhaust gases can cause the air space within the heat exchanger to become pressurised. This pressure acts on the liquid within the condensate trap and can cause it to be driven out of the siphon thereby sending gases which are potentially harmful due to the impaired combustion, into the surrounding area.

Previous designs of condensate trap used with heat exchangers have a rectangular design in which an inlet chamber is positioned next to an outlet/siphon chamber. The two chambers are separated by a partition, the top edge of which provides a weir in one which the condensate flows.

Such a design is relatively complex to manufacture. In addition, previous designs use a separate protective fluid column ("U" -bend) and siphon system within the trap. This allows the two systems to be optimised, but can increase the size of the overall trap.

According to the present invention, there is provided a condensate trap comprising a housing with a condensate inlet at the top, the trap comprising:

a first tube depending from the top of the housing and terminating above the bottom of the housing, the inlet leading only to a space between the first tube and housing; a second tube within the first tube, extending upwardly from the bottom of the housing and terminating below the top of the housing; a third tube within the second tube depending from the top of the housing and terminating above the bottom of the housing; a vent tube opening at the bottom of the housing and extending upwardly between the second and third tubes,- and an outlet tube open at the bottom of the housing and extending upwardly within the third tube and terminating below the top of the vent tube; wherein the housing is sealed other than at the inlet, and openings for the vent tube and outlet tube.

With such an arrangement, the various tubes are in a largely "co-axial" arrangement, thereby facilitating the assembly of the design.

The condensate trap provides a protective fluid column defined by the annular space between the housing and the second tube. This column is bounded at the top end by the top of the second tube and at the bottom end by the bottom of the first tube. This determines the pressure which the trap can withstand without losing its fluid. The present invention allows this to be designed independently of the inner fluid volume which determines the siphon charge.

Preferably, the difference between the level of the bottom edge of the first tube and the top edge of the second tube is at least 15cm and more preferably at least 20cm.

The condensate flowing into the trap through the inlet fills up an outer annulus between the housing and the first tube and an inner annulus between the first and second tubes. However, only the outer annulus is exposed to the heat exchanger gases. Thus, the pressure within the heat exchanger, resulting from a blocked flue, only acts on part of the condensate thereby making it more difficult for this to be driven out of the drain. In practice, this allows a more compact design of trap.

Preferably, an overflow switch is provided in the upper part of the housing. This will provide an indication that trap overflow is occurring and allow a system controller to take the necessary action to shut down operation and provide an indication to a user. The overflow switch may be a pressure switch, electrodes, or an optical switch, but the current preference is to use a float switch.

In order to simplify the construction of the device, the first and third tubes are preferably integrally formed. These components may also be integral with an upper part of the housing which comprises the inlet. Preferably, the second tube, vent tube and outlet tube are integrally formed. Preferably, these are also integral with a lower part of the housing.

The tubes may have a tapered or otherwise uneven cross- section along their length. However, they are preferably cylindrical. The tubes may have any cross-section, but most conveniently, they have a substantially circular cross- section.

An example of a condensate trap in accordance with the present invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 is a schematic view of a heat exchanger having a condensate trap; and

Fig. 2 is a cross-section through the trap.

Fig. 1 shows a heat exchanger 20 having a coil 21 through which a recipient fluid is circulated. Burner gases 22 enter the heat exchanger on the left-hand side and give up their heat to the fluid in the coil 21. The cooled gases are despatched along flue 23. As the gas cools, residual liquid in the gas condenses and flows into condensate trap 24. In practice, the lower edge of the heat exchanger will be inclined to ensure that the condensate flows into the trap 24. A trap flue vent 25 is provided which vents gas from the trap bypassing the heat exchanger 20 and leading directly to the flue 23. The detailed design of the trap is shown in Fig. 2.

The trap has an inlet 1 at the top to receive condensate fluid from a heat exchanger 20. The inlet 1 is provided within inlet block 2 which forms the upper part of the housing. The inlet block 2 is connected to casing 3 which forms the remainder of the housing 4.

The housing 4 contains a number of upwardly and downwardly depending tubes as set out below.

The outermost tube is a first tube 1 which depends downwardly from the inlet block 2 and terminates above the bottom of the housing 4. The second tube 6 is within and substantially concentric with the first tube 5 and extends upwardly from the base of the housing 4 terminating adjacent to, but slightly below, the inlet block 2. The third tube 7 is off-set with respect to and is within the second tube 6 and extends downwardly from the inlet block 2 terminating slightly above the bottom of the first tube 5.

A vent tube 8 is open at the bottom of the housing 4 and extends upwardly between the second tube 6 and third tube 7 terminating below the top of the second tube 6. An outlet tube 9 is open at the bottom of the housing 4 and extends upwardly within the third tube 7 terminating below the top of the vent tube 8.

Preferably, the first 5 and third 7 tubes are integrally moulded. These are shown as being attached to the inlet block 2 by a fastener 10 but could equally be integrally moulded with the inlet block 2. Similarly, the casing 3, second tube 6, vent tube 8 and outlet tube 9 are integrally moulded. This part is fitted from below into the position shown in the Figure, and the top of the casing 3 is silicone sealed to the block 2. An alignment marking (not shown) on the two parts is used to ensure that the tubes of the two parts are correctly orientated with respect to one another.

There are three defined spaces: (i) a first annular space 11 between the first tube 5 and the casing 3, (ii) a second annular space 12 between the second tube 6 and the first tube 5, and (iii) a cylindrical space 13 (excluding the internal space of vent tube 8 and outlet tube 9) within the second tube 6. These spaces form the 3 limbs of a trap which are functionally equivalent to the three limbs of a conventional "S-bend" trap.

During operation, the condensate flows downwardly over the outside of the first tube 5 filling the first and second annular spaces 11, 12.

Continued flow causes the condensate to overflow the second tube 6 filling the cylindrical space 13 between the second tube 6 and the outlet tube 9.

The extended length of the fluid columns within the trap ensures that the gases at the inlet to the trap, pressurised by fans feeding gas burners, will not be sufficient to drive the fluid through and out of the trap.

This will be the case, even where the main flue becomes blocked and the pressure within the heat exchanger rises to the maximum sustainable by the fans. In this situation the fluid will be forced into the trap, with the fluid level between the housing 4 and first tube 5 reducing as the inlet pressure rises. The maximum possible fan pressure and relative tube lengths ensures that a protective fluid column will always be present between first tube 5 and second tube 6, preventing the trap emptying of fluid.

Enclosed within the second tube 6, the outlet tube 9 together with the third tube 7 comprises a siphon system.

The siphon system has as its outer limb 14 the annular space between the second tube 6 and the third tube 7, and as its inner limb 15 the annular space between the third tube 7 and the outlet tube 9.

The Figure shows the siphon full to maximum capacity. Thus, when additional fluid enters the trap, causing fluid to flow over the weir formed by the top of second tube 6 , the siphon action is initiated: the fluid level in both limbs 14, 15 of the siphon rises, and fluid starts to overflow the top of the outlet tube 9, causing reduced pressure inside the third tube 7 as the liquid in the outlet tube seals the third tube from atmosphere while the siphon is discharging.

This reduced pressure, together with the incompressibility of the fluid, ensures that the flow continues, under suction, until the level of fluid in the outer limb 14 of the siphon reaches the bottom of the third tube 7. At this point, air from the vent tube 8 can access the space inside the third tube 7, equalising the pressure on either side of the siphon, with the result that the siphon action ceases. The remaining fluid with the two limbs 14, 15 of the siphon will reach a common level, between the bottom of third tube 7 and the top of outlet tube 9.

This auto-siphon effect ensures that fluid leaves the trap in regular volumes (e.g., 80-150ml depending on the relative tube heights) which will be less susceptible to freezing at the outlet than if the discharge was a constant low flow.

An additional feature of the design is the inclusion of an overflow sensor 16 sealed into the inlet block 2. This is shielded from the inlet 1 by the portion of the inlet block 2 containing the fastener 10 to prevent a false overflow signal due to splashing. Although not apparent from the cross-section of Fig. 2, sensor 13 is in the same annular chamber 17 as the inlet 1. If an integral structure for the upper part of the housing is used, it is still beneficial to have some form of splash prevention at this position, although not essential.

The sensor 16 may be a pressure sensor, electrodes, or an optical sensor as shown here, but is preferably a mechanical float switch.

Should the drain tube 18 to which the vent tube 8 and outlet tube 9 lead become blocked during operation, fluid would accumulate within the trap filling the annular chamber 17 and eventually (without detection) backing up into the heat exchanger 20. This can be detected by the overflow sensor 16. Should fluid levels rise into the inlet block 2, the sensor 16 will indicate to a controller that there is an outlet blockage, and corrective action can be initiated.

Whilst in the example described above, the tubes and casing are circular in section, alternative sections such as square, hexagonal, triangular, oval or other section which is convenient for manufacture may be used. Further, the tubes are not limited to the cylindrical configuration shown, but may equally be of any conical or pyramidal configuration convenient for the manufacturing process.

Claims

1. A condensate trap comprising a housing with a condensate inlet at the top, the trap comprising:

a first tube depending from the top of the housing and terminating above the bottom of the housing, the inlet leading only to a space between the first tube and housing; a second tube within the first tube, extending upwardly from the bottom of the housing and terminating below the top of the housing; a third tube within the second tube depending from the top of the housing and terminating above the bottom of the housing; a vent tube opening at the bottom of the housing and extending upwardly between the second and third tubes; and an outlet tube open at the bottom of the housing and extending upwardly within the third tube and terminating below the top of the vent tube; wherein the housing is sealed other than at the inlet, and openings for the vent tube and outlet tube.

2. A trap according to claim 1, wherein the difference between the level of the bottom edge of the first tube and the top edge of the second tube is at least 15cm.

3. A trap according to claim 2, wherein the difference between the level of the bottom edge of the first tube and the top edge of the second tube is at least 20cm.

4. A trap according to any of the preceding claims, wherein an overflow switch is provided in the upper part of the housing.

5. A trap according to any of the preceding claims, wherein the first and third tubes are integrally formed.

6. A trap according to claim 5, wherein an upper part of the housing is integral with the first and third tubes.

7. A trap according to any of the preceding claims, wherein the second tube, vent tube and outlet tube are integrally formed.

8. A trap according to claim 7, wherein a lower part of the housing is integrally formed with the second tube, vent tube and outlet tube.

9. A trap according to any one of the preceding claims, wherein the tubes are substantially cylindrical.

10. A trap according to any one of the preceding claims, wherein the tubes have a substantially circular cross- section.