GB1594732A

GB1594732A - Flexible expansion joint or seal

Info

Publication number: GB1594732A
Application number: GB2360477A
Authority: GB
Original assignee: Northern Engineering Industries PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 1978-04-21
Filing date: 1978-04-21
Publication date: 1981-08-05

Description

(54) FLEXIBLE EXPANSION JOINT OR SEAL (71) We, NORTHERN ENGINEERING IN DUSTRIES LIMITED, a British Company of NEl House Regent Centre Newcastle on Tyne NE3 3SB do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to assemblies including flexible expasion joints or seals.

In plant in which hot gases circulate, it is a requirement that flexible expansion joints or seals are provided between components of the plan to permit relative movemovement of the components owing to thermal expansion and contraction of the components.

A prior proposal for such a joint or seal comprised a layer or layers of mineral or ceramic fibres superimposed onto an external plastics or rubber membrane. The mineral or ceramic fibres are used to provide mechanical strength and temperature resistance in the joint or seal, and the membrane makes the joint or seal impermeable to the gases. If the operating temperature of the gases is greater than that which the membrane can sustain for long periods, the fibre layer has to be of a thickness and thermal conductivity such that the membrane is properly insulated from the full gas temperature.

Where the gases contain acid vapours, for example the exhaust gases from oilfired or coal-fired boilers, furnaces and incinerators, the insulating effect of the fibre layer on the membrane may lead to the gas-side surface of the membrane being below the dew point for the acid vapours.

This would cause condensation of the acid vapours on the membrane surface which could lead to corrosion of the fibres and the adjacent components of the plant.

It has been proposed to overcome this problem by providing further insulation on the external side of the membrane in order to maintain the membrane at a temperature above the dew point of the vapours.

However, the long term reliability of such joints or seals is in doubt because of possible changes in the thermal conductivity of the fibres with time and the unpredictability of heat transfer to the surroundings because of variable draughts and radiation from adjacent plant. In addition, the increased thickness of the joint or seal increases its susceptibility to mechanical damage from flexing.

Some acid vapour condensation will also occur whenever the plant is started up or shut down.

According to the present invention, an assembly comprises two adjacent components by or through which hot gases are to be passed and a flexible non-metallic expansion joint or seal extending between the two components, respective members being secured to the components, the joint or seal comprising a first inner layer of mineral or ceramic fibres and a second outer layer formed by a flexible rubber or synthetic plastic gas-impermeable membrane, both layers being secured to the members and forming a primary seal wall and the seal further comprising an outer secondary seal wall secured to the two members and being of flexible substantially gas-impermeable material, the two members and the two seal walls defining a chamber having a gas inlet and a gas outlet whereby gas can be passed through the chamber at a temperature greater than the dew point of acid varpous present in hot gases passing by or through the components and less then the maximum operating temperature of the membrane.

The invention includes plant having an assembly as set forth in the preceding paragraph and in which a gas supply means by which gas at said temperature can be supplied to the joint or seal is provided.

An assembly including a flexible expansion joint will now be described by way of example to lillustrate the invention with reference to the accompanying drawings, in which: Figure 1 is a vertical section through a part of an assembly in accordance with the invention; and Figure 2 is a schematic line diagram showing a gas supply means for the joint shown in Figure 1, the joint being represented in plan view.

The drawings show a vertical duct 10 at, for example, the exhaust side of an oilfired or coal-fired boiler in a power-generating plant; the duct has an expansion joint 12.

The duct 10 is substantially rectangular in transverse cross-section and has an upper section 14 and a lower section 16.

The sections 14 and 15 have respectively outwardly-extending flanges 18.

The expansion joint 12 consists of a chamber 20 formed by angle plates 22 bolted to each of the flanges 18, an inner primary seal wall 24 and an outer secondary seal wall 26.

The primary seal wall 24 consists of a first inner layer of mineral or ceramic fibre cloth 28 and a second outer layer 30 formed by a flexible rubber or synthetic plastic gas-impermeable membrane. The fibre cloth 28 may be made from, for example, mineral fibres known as "Refrasil" (Trade Mark). The membranes 30 may be of, for example, polytetrafluoroethylene (PITh).

The seal wall 24 is secured at its edges by clamp plates 32 bolted to the horizontal limb of the angle plates 22.

The outer secondary seal wall 26 is of a flexible substantially gas-impermeable non-metallic material and may be, for example, the same as the membrane 30, i.e.

P.T.F.E., or glass impregnated with "Viton"( Trade Name).

The seal wall 26 is secured at its edges by clamp plates 34 bolted to the vertical limb of the angle plates 22.

An external lagged shroud (not shown) may be provided for the protection of personnel.

A gas supply means 40 (see Figure 2) comprises a fan 42, a supply ring main 44 and an exhaust ring main 46. A stand-by fan 42a can be provided in case of failure of the fan 42.

The fan 42, or 42a, is connected by con- duit 48 through a non-return valve 50 or 50a, respectively, to a cooler 52 which is connected by conduit 54 in series with a heater -56. A conduit 58 connects the heater outlet to the supply ring 44.

Take-off conduits 60 connect the supply ring main to inlets 62 at the corners of the joint 12. Outlets 64 from the joint 12 are connected by conduits 66 to the exhaust ring main 46. The outlets each have a vent valve 68. Conduit 70 connects the exhaust ring main 46 to the inlet of the fan 42, or 42a.

A temperature sensor 72 is provided in conduit 70 and a control line 74 connects the sensor 72 to the controllers of the cooler 52 and heater 56 to actuate one or the other to cool or heat gas passing through them.

Typically, exhaust gases flowing in the duct 10 in the direction of, for example, arrow A (see Figure 1) is at a temperature of approximately 400"C. The maximum operating temperature of the P.T.F.E. membrane 30 is approximately 250"C.

In an oil-fired or coal-fired boiler the dew point of acid vapours in the exhaust gases has been found to be in the region of 1500C-1700C.

To prevent condensation of the acid vapours and yet maintain the membrane 30 below its maximum operating temperature, the gas supply means 40 is operated to supply gas to the joint 12 at approxlmately 200"C.

Typically the gas supplied by the means 40 is air.

The controls of the cooler 52 and the heater 54 are arranged to respond to an increase or decrease, respectively, of the air temperature detected by the sensor 72.

The vent valves 68 in the conduits 66 maintain the static pressure of the circuit substantially constant by allowing air to vent out of the circuit if the pressure increases or to take air into the circuit if the pressure decreases.

During a start-up of the boiler, the joint is first brought up to temperature before the boiler is fired to prevent acid vapour condensation on the joint owing to the joint being cold.

Similarly, during shut down of the boiler, the joint is maintained at its operating temperature until shut down is complete to prevent acid vapour condensation on the joint owing to the joint cooling down as the temperature of the exhaust gases falls.

Where air is used as the circulating gas, it is not necessary that the seal 26 is completely gas-impermeable.

If, however, some other gas, for example nitrogen, is used then the seaI should be completely gas-impermeable and means other than the vent valves 68 would have to be provided to maintain the static pressure of the circuit substantially constant.

This other means could, for example, be in the form of a reservoir of the gas and lose the heat in the air to atmosphere and to flow into or out of the reservoir for an increase or a decrease in the circuit pressure, respectively.

In a modification (not shown), where air is used as the circulating gas, the fan could take the - air direct from atmosphere, feed it through a heater and exhaust to atmosphere with an exhaust temperature sensor controlling the heater. However, this would a control mechanism -which causes the gas would consequently have a higher power consumption.

In a further modification (not shown) the position of the conduits 60 and 66 could be reversed or otherwise arranged and a different number could be used provided the gas flow distribution in the joint is substantially even.

WHAT WE CLAIM IS: 1. An assembly comprising two adjacent components by or through which hot gases are to be passed and a flexible nonmetallic expansion joint or seal extending between the two components, respective members being secured to the components, the joint or seal comprising a first inner layer of mineral or ceramic fibres and a second outer layer formed by a flexible rubber or synthetic plastic gas-impermeable membrane, both layers being secured to the members and forming a primary seal wall and the seal further comprising an outer secondary seal wall secured to the two members and being of flexible substantially gas-impermeable material, the two members and the two seal walls defining a chamber having a gas inlet and a gas outlet whereby gas can be passed through the chamber at a temperature greater than the dew point of acid vapours present in hot gases passing by or through the components and less than the maximum operating temperature of the membrane.

2. An assembly according to claim I, in which the two members have spacedapart first faces opposed to one another and the inner layer of the primary seal wall lies partly against the first faces of the two members, the primary seal wall extending between the two members in a curved form which is concave towards the secondary seal wall.

3. An assembly according to claim l or claim 2, in which the two members have spaced-apart second faces and the secondary seal wall lies against the second faces of the members and extends between th members in a curved form which is concave towards the primary seal wall.

4. An assembly according to any preceding claim, in which the inlet and outlet comprise openings through the primary seal wall and through the members at their first faces.

5. An assembly according to any preceding claim in which the components define a duct which is rectagular in transverse cross-section and in which the joint or seal extends along all four sides of the duct.

6. Plant having an assembly according to any preceding claim and also comprising a fan or other means for supplying gas into the chamber of the joint or seal, means for changing the temperature of gas leaving the fan or other means and a one-way valve being connected between the fan or other means and the inlet to the chamber.

7. Plant according to claim 6, in which the pressure in the chamber is kept substantially constant by vent valves connected to the chamber interior.

8. An assembly according to claim 1, substantially as described herein with rd- erence to Figure 1 of the accompanying drawings 9. An assembly according to claim 1, substantially as described herein with reference to Figures 1 and 2 of the accompanying drawings.

10. Plant having an assembly according to claim 1, substantially as described herein with reference to Figures 1 and 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. would consequently have a higher power consumption. In a further modification (not shown) the position of the conduits 60 and 66 could be reversed or otherwise arranged and a different number could be used provided the gas flow distribution in the joint is substantially even. WHAT WE CLAIM IS:

1. An assembly comprising two adjacent components by or through which hot gases are to be passed and a flexible nonmetallic expansion joint or seal extending between the two components, respective members being secured to the components, the joint or seal comprising a first inner layer of mineral or ceramic fibres and a second outer layer formed by a flexible rubber or synthetic plastic gas-impermeable membrane, both layers being secured to the members and forming a primary seal wall and the seal further comprising an outer secondary seal wall secured to the two members and being of flexible substantially gas-impermeable material, the two members and the two seal walls defining a chamber having a gas inlet and a gas outlet whereby gas can be passed through the chamber at a temperature greater than the dew point of acid vapours present in hot gases passing by or through the components and less than the maximum operating temperature of the membrane.

8. An assembly according to claim 1, substantially as described herein with rd- erence to Figure 1 of the accompanying drawings

9. An assembly according to claim 1, substantially as described herein with reference to Figures 1 and 2 of the accompanying drawings.