WO1994023187A2

WO1994023187A2 - Diverter valves

Info

Publication number: WO1994023187A2
Application number: PCT/GB1994/000673
Authority: WO
Inventors: Anton Frederick Squirrell; William F. Koch
Original assignee: Wes Technology Inc.
Priority date: 1993-03-31
Filing date: 1994-03-30
Publication date: 1994-10-13
Also published as: GB9306772D0; EP0692079A1; WO1994023187A3; JPH08508331A

Abstract

A diverter valve provided at a three-way junction through which passes a high temperature gas, the valve having a closure member (5) pivotable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, and a turning vane assembly (20) having at least one turning vane (22) provided at the said junction for assisting the flow of gas through the one outlet branch when the valve closure member closes the other outlet branch, characterized in that the turning vane assembly (20) is separate from the valve closure member (5) but is coupled with an operating means (10) for the valve closure member for pivoting the turning vane assembly upon operating the valve closure member. Preferred (and independent) features of the invention are as follows: 1) the floor (32) of the diverter valve is inclined upwards, at an angle of about 10 degrees; 2) the centre-line (50) of the valve stack (42) and silencer (43) is offset from the centre-line (51) of the diverter valve; 3) the valve closure member has a multi-flap structure (61, 62) wherein a lower, smaller, flap closure member (62) is inclined at an angle of about 45 degrees in the closed position thereof.

Description

DIVERTER VALVES

This invention relates to diverter valves, particularly diverter valves provided at a three-way junction through which passes a gas at a sufficiently high temperature for it to be practical or desirable to extract heat from the gas exhaust. More specifically the invention relates to diverter valves used in exhaust systems of gas turbine combined cycle generating plant or co-generation plant or other plant where by-pass arrangements exist, to minimize the back pressure loss and hence improve the cycle efficiency.

Gas turbines are frequently used to drive rotating machinery such as compressors, pumps and electric generators. Thermodynamically the gas turbine is a relatively inefficient prime mover, because, although the inlet temperature of the working fluid is high, the reject temperature is also relatively high and much high grade heat is lost. However, it is now common practice to couple a simple cycle gas turbine with a heat recovery steam generator (HRSG) or other heat exchanger to extract more heat from the working fluid to provide superheated steam for a steam turbine in combined cycle plant, or saturated steam for some process, or both, in cogeneration systems. In the exhaust ducting systems following the gas turbine discharge, gas flow velocities are maintained at relatively high levels to reduce the size of ducting and silencers and to promote high rates of heat transfer in the heat recovery equipment. With these high velocities, pressure drops in the exhaust system can be considerable, and these pressure drops increase the back pressure which reduces the power output of the turbine. This back pressure may have substantial economic implications as an increase in turbine back pressure of 100 mm H«0 can reduce the power output by 1%.

Diverter valves or isolating dampers are invariably fitted in the exhaust system where heat recovery equipment is installed, to perform the following functions:

(1) to provide isolation capability for the heat recovery steam generator to enable maintenance to be carried out while the turbine operates on simple cycle, i. e. discharging through the by-pass without any heat recovery from the working fluid;

(2) to minimize the heat loss to the by-pass when the heat recovery system is in operation;

(3) to provide flow control for start up, shut down and part load operation. These diverter valves or dampers are often situated at or adjacent to points in the system where T-junctions occur, typically at HRSG inlet and by-pass locations. These T-junctions cause high pressure drops, of the order of 115% of velocity pressure when the flow of gas is directed around a sharp bend. Depending on the plant layout, the flow through the bend may occur either when the plant operates on by-pass or on heat recovery mode.

Turning vanes, or splitters, which are frequently fitted to sharp bends in ducting systems to reduce the pressure drop to about 35% of velocity pressure, cannot be fixed in the ducting at a T-junction because they would obstruct the flow when it is directed in the straight through mode.

Although most plants with waste heat recovery systems will be normally expected to operate with the by-pass closed, it can be that a plant may operate for extended periods through the by-pass, perhaps because the plant operates initially on simple cycle while construction of the heat recovery equipment proceeds, or because of reduced load demand or for maintenance of the heat recovery equipment. It is therefore apparent that, even when the bend in the flow direction is to the by-pass, considerable economic savings may be made by providing equipment which causes the inherent pressure loss of the bend to be reduced. It is now considered the state of the art to install diverter valves in gas turbine combined cycle or cogeneration plants. Their function is as follows:

a) To isolate the heat recovery steam generator (HRSG) for gas turbine start up;

b) To control the flow of exhaust gas to the HRSG for change over to combined cycle mode operation;

c) To allow HRSG inspection and maintenance whilst in simple cycle mode operation;

d) To facilitate phased construction/operation of the plant, i. e. it is normal for the gas turbine to run in simple cycle mode whilst the HRSG and steam turbine are being constructed.

In arrangements with louvre or flap dampers and also with current diverter valve configurations, by pass operation involves turning the flow through 90 degrees using a sharp bend, resulting typically in a pressure loss of 1.15 times the velocity pressure. This causes a reduction in the power output and efficiency and results in turbulence which can lead to vibration problems in the plenum or in adjacent ducting. PCT patent application no. PCT/GB91/01585 (WO 92/05380) describes one possible way of overcoming such problems, wherein a diverter valve is provided at a three-way junction through which passes a high temperature gas, the valve having a closure member pivotable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, wherein the closure member carries one or more turning vanes for assisting the flow of gas through the one outlet branch when the closure member closes the other outlet branch.

In the invention of PCT/GB91/01585 turning vanes are mounted on the diverter valve blade in such a way that for simple cycle operation the turning vanes effectively reduce bend losses. For most common applications, in the valve position for combined cycle operation the turning vanes retract into the space above the diverter valve blade.

In many applications of the invention of PCT/GB91/01585, however, the diverter valve blade becomes so large that the addition of turning vanes directly mounted on the blade structure imposes a very high burden of additional torque, and in the case of toggle drive diverter valves becomes difficult because of the presence of the toggle drive shaft and linkage. In general, toggle drive systems have the advantage that, for very large diverters, the required actuator torques are reduced when compared with diverter valves driven directly from a pivot shaft. Also, they provide additional support at the blade centre which reduces the effect imposed by dynamic pressure fluctuations in the gas flow. The toggle shaft rotates typically through an angle of 90 to 170 degrees depending upon the linkage geometry. For example, a diverter valve having a toggle driven system may be designed for 90 degree blade rotation, or in an alternative construction the linkage arrangement may provide for typically 70 degree blade rotation and about 90 degree toggle shaft rotation.

A known alternative to blade mounted turning vanes as described in the invention of PCT/GB91/01585 is to use a separately pivoted turning vane system with separate operating mechanism, i. e. independent of the operating system for the diverter valve. The disadvantage of such an alternative arrangement is that it is fully reliant on an effective interlocking system to prevent operation out of sequence causing the diverter valve blade and the turning vanes from interfering with each other. Interlocking systems of this nature are notoriously fallible, and many failures have been known to occur on similar types of application (e. g. interlocked louvre dampers) with disastrous consequences. The present invention aims to overcome the above described disadvantages of diverter valves provided with turning vanes in known systems, whether the turning vanes are directly mounted on the diverter valve blade or whether the turning vanes are operated independently of the diverter valve.

The invention instead provides turning vanes for diverter valves, in which the vanes are separately pivoted but directly driven from the diverter valve blade operating system. This system is particularly applicable to very large diverter valves.

The present invention, in a first aspect, provides a diverter valve provided at a three-way junction through which passes a high temperature gas, the valve having a closure member pi otable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, and a turning vane assembly having at least one turning vane provided at the said junction for assisting the flow of gas through the one outlet branch when the valve closure member closes the other outlet branch, wherein the turning vane assembly is separate from the valve closure member but is coupled with an operating means for the valve closure member for pivoting the turning vane assembly upon operating the valve closure member. Thus, according to the invention, there is provided a separately pivoted vane assembly which is coupled directly with the diverter valve operating system.

As is well known, the bend losses (pressure losses) in a diverter valve are strongly influenced by the geometry of the inside corner of the bend. Severe separation losses and even reverse flow can be experienced. The use of vanes to direct the flow into the region downstream of the corner of the inside of the bend can reduce the loss due to separation and recirculation. It is the vanes closer to the inside of the bend which have the most effect.

In the diverter valve of the invention, the turning vanes assembly is preferably directly driven by one or more operating arms fixed to a toggle drive shaft and by a link or links from the outer end of the arm(s) to the vane assembly.

In a preferred construction according to the invention, a toggle drive shaft carries an operating arm or arms for the diverter valve closure member and an operating arm or arms for the turning vane assembly, wherein the said operating arms are connected by respective links to the valve closure member and to the turning vane assembly, whereby rotation of the toggle drive shaft will simultaneously pivot the valve closure member and the turning vane assembly.

The turning vane assembly will typically carry three turning vanes, but the actual number of turning vanes is dependent on the unit size and limitations imposed by the space allowed by the location of the toggle drive shaft.

The diverter valve closure member (diverter valve blade) is suitably arranged to be inclined, preferably at an angle of about 20 degrees to the vertical, in the closed to HRSG position, giving an operating blade rotation of about 70 degrees. This is a preferred arrangement which assists in reducing the pressure loss, vibration and noise in the simple cycle operating position and improves flow distribution in the bypass. It is alternatively possible to have the toggle shaft operated vane assembly in conjunction with a conventional diverter valve blade configuration, that is one in which the blade is perpendicular to the approach flow in the closed to HRSG position.

It is also possible, according to a second aspect of the invention, to provide a diverter valve the floor of which is inclined upwards, at an angle typically but not necessarily of about 10 degrees, at a location upstream of the valve closure member. That is, the invention in a second aspect provides a diverter valve provided at a three-way junction through which passes a high temperature gas, the valve having a closure member pivotable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, wherein the diverter valve has a floor inclined upwards, at an angle typically but not necessarily of about 10 degrees, at a location upstream of the valve closure member.

The provision of such an inclined floor in the diverter valve is particularly applicable in the case that the valve closure member (blade) is inclined (at an angle of preferably about 20 degrees to the vertical) in the closed to HRSG position, giving an operating blade rotation of about 70 degrees, as described above. In this case the inclined blade and raised (inclined) floor reduce the possibility of areas of flow recirculation adjacent to the intersection of the blade and floor and effectively replace the effect of an outer vane or vanes. The height of the raised floor is such that no significant pressure loss or flow disturbance is created downstream in the open to HRSG position.

The provision of an inclined floor is also applicable in the case that the valve closure member is perpendicular to the approach flow in the closed to HRSG position. It is to be noted that the provision in a diverter valve of an upwardly inclined floor as described above is applicable both to a diverter valve according to the first aspect of the present invention, or to a known diverter valve, whether of the type according to PCT/GB91/01585 wherein the valve closure member carries the turning vanes, or of the type wherein the turning vane system thereof has a separate operating mechanism independent of the valve closure member operating mechanism, or is applicable even to a diverter valve having no such turning vane system.

It is also preferred that the inside corner of the diverter valve be mitred, which also contributes to a reduction of the amount of downstream flow separation.

It is further possible, according to a third aspect of the invention, to provide a diverter valve wherein the centre-line of the valve stack and silencer is offset from the centre-line of the diverter valve.

That is, the invention in a third aspect provides a diverter valve provided at a three-way junction through which passes a high temperature gas, the valve having a closure member pivotable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, wherein the centre-line of the valve stack and silencer is offset from the centre-line of the diverter valve.

The centre-line of the diverter valve is taken with respect to the centre-line of the bypass outlet aperture. The centre-line of the silencer is offset towards the HRSG side of the valve to improve the flow path to the bypass. This improvement of the flow distribution into the bypass is important for efficient operation of the silencer.

Where a toggle drive system is provided for operating the diverter valve closure member, it is convenient to locate the toggle drive shaft on the centre-line of the valve stack and silencer. However, it should be noted that this arrangement according to the third aspect of the invention could equally be applied to pivot shaft drive diverter valves.

The feature according to the third aspect of the invention of offsetting the centre-line of the valve stack and silencer from the centre-line of the diverter valve, as described above, is applicable both to a diverter valve according to the first and/or second aspects of the invention, or to a known diverter valve, whether of the type according to PCT/GB91/01585 wherein the valve closure member carries the turning vanes, or of the type wherein the turning vane system thereof has a separate operating mechanism independent of the valve closure member operating mechanism, or is applicable even to a diverter valve having no such turning vane system.

It is yet further possible, according to a fourth aspect of the present invention, to provide a diverter valve having a multi-flap structure wherein a lower, smaller, flap closure member thereof is inclined, at an angle typically but not necessarily of about 45 degrees, in the closed position thereof.

That is, the invention in a fourth aspect provides a diverter valve provided at a three-way junction through which passes a high temperature gas, the valve having a closure member pivotable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, wherein the valve closure member has a multi-flap structure wherein a lower, smaller, flap closure member thereof is inclined, at an angle typically but not necessarily of about 45 degrees, in the closed position thereof.

While multi-flap diverter valves are known in which the lower, smaller, flap closure member is vertical in the closed to HRSG position, the arrangement according to the fourth aspect of the invention wherein this flap is inclined in the closed position of the valve is novel, and improves the flow to the valve bypass by eliminating an area of flow recirculation at the bottom of a vertical diverter valve closure member.

The feature according to the fourth aspect of the invention of arranging for the lower, smaller, flap closure member of a multi-flap diverter valve to be inclined in the closed position, as described above, is applicable both to a diverter valve according to the first, second and/or third aspects of the present invention, or to a known diverter valve, whether of the type according to PCT/GB91/01585 wherein the valve closure member carries the turning vanes, or of the type wherein the turning vane system thereof has a separate operating mechanism independent of the valve closure member operating mechanism, or is applicable even to a diverter valve having no such turning vane system.

The diverter valve according to the invention is particularly intended for use in a T-junction through which flows high temperature exhaust gas from a gas turbine, one junction outlet leading to a by-pass stack and the other junction outlet leading to a heat recovery steam generator or other heat exchanger. However, it will be appreciated that the present invention is not limited to such applications, and that diverter valves according to the invention may be provided at any three-way junction through which there passes a gas at a sufficiently high temperature for it to be practical or desirable to extract heat from the gas for exhaust.

The diverter valve according to the invention is able to perform HRSG inlet and isolation functions in one piece of equipment, and the turning vanes provided reduce the pressure loss when the gas flow is diverted through a bend, typically but not necessarily 90'. When the gas flow is straight the turning vanes are moved into the isolated space behind the closure member.

The diverter valve may suitably comprise a frame fixed across the two outlet ducts of a three-way junction, the frame having two sets of sealing surfaces one in each outlet path, and a closure member comprising a pivotable flap carrying two sets of seals for respectively co-operating with the sealing surfaces of the frame. The flap is suitably operated by turning a toggle drive shaft to which the flap is linked. This arrangement ensures that the flap cannot be closed to both flow directions at the same time, so that the system is inherent!v safe. The invention will be further described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a diverter valve according to the invention fitted in a T-junction, the closure member of the valve being shown in the position wherein gas is deflected through one outlet of the junction;

Figure 2 is a schematic view of a diverter valve having an inclined floor upstream of the valve closure member;

Figure 3 is a schematic view of a diverter valve the centre-line of which is offset from the centre-line of the valve stack and silencer;

Figure 4 is a schematic view of a diverter valve the closure member of which has a multi-flap structure, the lower flap of which is inclined in the closed position of the valve; and

Figure 5 is a schematic view of a known diverter valve the closure member of which has a multi-flap structure, both flaps of which are vertical in the closed position of the valve.

By way of background, reference is made to figures 1 to 3 of PCT/GB91/01585, which show typical gas turbine cycle layouts. In the present application, figure 1 shows a diverter valve 1 wherein the high temperature exhaust gas flow from a gas turbine is shown by arrows 2, the gas flow to a heat recovery steam generator (HRSG) is shown by arrows 3, and the alternative gas flow to a by-pass is shown by arrows 4.

The diverter valve 1 has a valve closure member or blade 5 which comprises a flap arm 6 which is pivotably mounted at 7 to be movable between the position shown in figure 1 (closed to HRSG position) and a position (not shown) in which the valve closure blade 5 closes the by-pass outlet. The flap arm 6 carries on its opposite faces a pair of sealing plates 8 each provided with peripheral seals (not shown), preferably of the type described in British patent no. GB-A-1308801 or GB-A-2060824 or in PCT application no. PCT/GB89/01382 (WO 90/06460) or PCT/GB89/00975 (WO 90/02279). The diverter valve further comprises a suitable frame arranged around the peripheries of the two outlet ducts of the junction in which the diverter valve is mounted. The frame is provided with two sets of sealing surfaces i. e. one set of sealing surfaces being associated with each outlet duct, the sealing surfaces of the frame being adapted to cooperate with the peripheral seals provided on the plates 8. A toggle drive system 10 comprises a toggle drive shaft 11 and pairs of operating arms 12 and 13, the one pair of operating arms 12 being connected to the valve closure blade 5 through a pair of links 14 extending from the ends of the arms 12 to the blade 5. The other pair of operating arms 13 of the toggle drive system is connected to a turning vane assembly 20 through a pair of links 15 extending from the ends of the arms 13 to the turning vane assembly. Only one set of arms 12 and 13 and one set of links 14 and 15 are shown in figure 1, the other elements of each pair being disposed behind the corresponding arms 12, 13 and links 14, 15 shown in the drawing.

The turning vane assembly 20 itself is pivotably mounted about a turning vane pivot shaft 21 and the assembly carries a series of curved turning vanes 22. When the diverter valve is in the position shown in figure 1 (closed to HRSG position), for effecting flow to a by-pass stack, the turning vanes 22 function to assist the gas flow. When on the other hand the toggle drive system 10 is rotated to the position shown by chain-dotted lines (closed to bypass position) for permitting flow to a heat recovery steam generator, the turning vanes 22 are withdrawn from the gas flow path. In figure 1 the diverter blade 5 is not indicated for the closed to bypass position (horizontal) for reasons of clarity. Reference numeral 23 indicates the extent to which the turning vane assembly 20 moves to the right in figure 1 before pivoting upwards to the position shown in chain-dotted lines when the assembly 20 is rotated to the closed to bypass position.

The turning vane assembly 20 shown in figure 1 has three vanes 22, but the actual number is dependent on the unit size and is limited by the space allowed by the location of the toggle drive shaft 11.

The use of the turning vanes 22 to direct the gas flow into the region downstream of the corner of the inside of the bend can reduce the loss due to separation and recirculation. It is the vanes closer to the inside of the bend which have the most effect.

In accordance with the present invention, as shown in figure 1, the turning vane assembly 20 is separate from the valve closure member 5 but is coupled with the toggle drive system 10 for the valve closure member 5 for pivoting the turning vane assembly 20 upon operating the valve closure member. Thus the turning vanes 22 are separately pivoted but directly driven by the valve blade operating system comprised by the toggle drive shaft 11, and this construction is particularly suitable for very large diverter valves. Figure 1 shows the diverter valve blade 5 inclined at an angle of approximately 20 degrees in the closed to HRSG position, giving an operating blade rotation of 70 degrees. This is a preferred arrangement which assists in reducing the pressure loss, vibration and noise in the simple cycle operating position. It is also possible to utilise a conventional diverter valve blade configuration, that is one in which the blade is perpendicular to the gas approach flow in the closed to HRSG position.

As described more particularly in PCT/GB91/01585, the turning vanes 22 most suitably consist of a series of curved plates, which may be of single or double skin construction, arranged radially out from the inside corner of the bend of the three-way junction to the outside in their operating position. These vanes are as close to the full duct width as possible.

These vanes 22 may suitably be of two types, as described in PCT/GB91/01585. That is, they may be of thin sheet spanning the mitre of the bend, or in cases where the inlet flow is poorly distributed vanes of a generally aerofoil type section can be used.

Thus there is provided a diverter valve fitted in a three-way junction and having turning vanes to reduce the pressure drop when the gas flow is being directed through an angle, typically but not necessarily 90'. Such a diverter valve provides inherent safety by ensuring that both outlet flow paths cannot be closed simultaneously.

Figure 2 shows a diverter valve 30 with the valve closure member or blade 31 thereof inclined at an angle of approximately 20 degrees in the closed to HRSG position, and with the diverter valve floor 32 inclined upwardly, at an angle typically but not necessarily of about 10 degrees, at a location just upstream of the valve closure member 31. As shown, the diverter valve floor is horizontal immediately upstream of the valve closure member, and then falls away downstream of the closure member 31 so that the latter preferably makes an angle of approximately 90 degrees with the downwardly inclined valve floor.

Also as shown in figure 2, the inside corner 33 of the bend is mitred.

The inclined blade 31 and raised floor 32 reduce the possibility of areas of flow recirculation ad-acent to the intersection of the blade and floor and effectively replaces the effect of an outer turning vane. The mitred inside corner 33 also contributes to a reduction of the amount of downstream flow separation. The height of the raised floor is such that no significant pressure loss or flow disturbance is created downstream in the open to HRSG position.

No turning vane assembly or toggle drive system is shown in figure 2. As previously noted, the features illustrated in figure 2 may be used in combination with the aspects of the invention illustrated in figure 1, or may comprise a separate aspect of the present invention.

Figure 3 shows a diverter valve 40 with the valve closure member or blade 41 thereof inclined at an angle of approximately 20 degrees in the closed to HRSG position. The valve 40 essentially comprises a stack 42, and a silencer 43 above the valve bypass outlet 44. The valve closure member 41 is pivotably mounted to be movable between the position shown in figure 3 (closed to HRSG position) and a position (shown in phantom lines) in which it closes the valve bypass outlet 44.

A bypass outlet section 45 will normally be square or rectangular in cross-section and effectively comprises a duct extension or toggle drive housing in the case that a toggle drive system is provided for operating the valve closure member 41. A toggle drive shaft 46 is shown schemically in figure 3. A transition section 47 of the valve stack is of square or rectangular section at the bottom 48 thereof, and is circular in section at the top 49 thereof which also comprises the bottom of the silencer 43.

The centre-line of the valve stack 42 and silencer 43 is indicated by reference numeral 50 in figure 3, and the centre-line of the diverter valve 40 itself is indicated by reference numeral 51. The centre-line 51 of the valve is taken as the centre-line of the bypass outlet aperture 44. As will be apparent, the centre-line 50 of the valve stack and silencer is offset from the centre-line 51 of the valve, in the direction towards the HRSG side of the valve, and this arrangement has been found to improve the flow path to the valve bypass. Such an improvement in the flow distribution into the bypass is important for efficient operation of the silencer 43.

Where a toggle drive system is provided for operating the valve closure member 41, for example as described with reference to figure 1, it is convenient to locate the toggle drive shaft 46 on the centre-line 50 of the valve stack and silencer. However, it should be noted that the offsetting of the centre-lines 50 and 51 as described could equally be applied to a pivot shaft drive diverter valve, when the section 45 would be regarded as an inclined duct extension. No turning vane assembly is shown in figure 3. As previously noted, the features illustrated in figure 3 may be used in combination with the aspects of the invention illustrated in figure 1 and/or in figure 2, or may comprise a separate aspect of the present invention. Indeed, the diverter valve shown in figure 3 has an inclined floor 52, as described in more detail with reference to figure 2.

The diverter valve according to the invention may optionally incorporate a closure having a multi-flap structure, and figure 5 shows a known type of multi-flap diverter valve 70 wherein both flap closure members 71 and 72 are vertical in the closed to HRSG position.

Figure 4 shows a diverter valve 60 according to another aspect of the present invention, wherein the valve closure has a multi-flap structure. More particularly, as shown in figure 4, the valve closure comprises an upper, larger, flap closure member 61 and a lower, smaller, flap closure member 62, the flap closure members 61 and 62 being pivotably mounted at 63 and 64 respectively.

The closure member 61 is pivotably mounted to be movable between the position shown in figure 4 (closed to HRSG position) and a position (shown in phantom lines) in which it closes the valve bypass outlet, while the closure member 62 is pivotably mounted to be movable between the position shown (closed to HRSG position) and a position (not shown) in which it rests in a well 65 provided in the diverter valve floor. A bar 66 is provided with suitable seals or seal seats for sealing against the closure members 61 and 62 in the closed to HRSG position.

The lower, smaller, flap closure member 62 is inclined, at an angle typically but not necessarily of about 45 degrees, in the closed to HRSG position thereof. This arrangement, wherein the closure member 62 is inclined in the closed position of the valve, improves the flow to the valve bypass by eliminating an area of flow recirculation (indicated by reference numeral 73 in figure 5) which would otherwise form at the bottom of a vertical multi-flap diverter valve closure member of the known type as illustrated in figure 5.

No turning vane assembly or toggle drive system is shown in figure 4. As previously noted, the features illustrated in figure 4 may be used in combination with the aspects of the invention illustrated in figure 1, in figure 2 and/or in figure 3, or may comprise a separate aspect of the present invention. In particular, the closure member 61 may itself carry or be coupled with a turning vane structure, either as described in PCT/GB91/01585 or as described with reference to figure 1 of the present application.

Claims

CLAI MS:

1. A diverter valve provided at a three-way junction through which passes a high temperature gas, the valve having a closure member (5) pivotable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, and a turning vane assembly (20) having at least one turning vane (22) provided at the said junction for assisting the flow of gas through the one outlet branch when the valve closure member closes the other outlet branch, characterized in that the turning vane assembly (20) is separate from the valve closure member (5) but is coupled with an operating means (10) for the valve closure member for pivoting the turning vane assembly upon operating the valve closure member.

2. A diverter valve as claimed in claim 1, characterized in that the turning vane assembly (20) is directly driven by one or more operating arms (13) fixed to a toggle drive shaft (11) and by a link or links (15) from the outer end of the arm(s) (13) to the vane assembly (20).

3. A diverter valve as claimed in claim 1 or 2, characterized in that a toggle drive shaft (11) carries an operating arm or arms (12) for the diverter valve closure member (5) and an operating arm or arms (13) for the turning vane assembly (20), and in that the said operating arms (12, 13) are connected by respective links (14, 15) to the valve closure member (5) and to the turning vane assembly (20), whereby rotation of the toggle drive shaft (11) will simultaneously pivot the valve closure member and the turning vane assembly.

4. A diverter valve as claimed in any of claims 1 to 3, characterized in that the turning vane assembly (20) carries three turning vanes (22).

5. A diverter valve as claimed in any of claims 1 to 4, characterized in that the floor (32) of the diverter valve is inclined upwards, at a location upstream of a valve closure member (31).

6. A diverter valve as claimed in claim 5, characterized in that the said diverter valve floor (32) is inclined upwards at an angle of about 10 degrees.

7. A diverter valve as claimed in any of claims 1 to 6, characterized in that the closure member (5; 31) is arranged to be inclined in the said second position thereof wherein it closes the said other outlet branch of the junction.

8. A diverter valve as claimed in claim 7, characterized in that the closure member (5; 31) is arranged to be inclined at an angle of about 20 degrees to the vertical in the said second position thereof, giving an operating closure member rotation of about 70 degrees.

9. A diverter valve as claimed in any of claims 1 to 8, characterized in that the centre-line (50) of the valve stack (42) and silencer (43) is offset from the centre-line (51) of the diverter valve.

10. A diverter valve as claimed in claim 9, characterized in that a toggle drive shaft (46) for operating a valve closure member (41) is located on the said centre-line (50) of the valve stack and silencer.

11. A diverter valve as claimed in any of claims 1 to 10, characterized in that the valve closure member has a multi-flap structure (61, 62) wherein a lower, smaller, flap closure member (62) thereof is inclined in the closed position thereof.

12. A diverter valve as claimed in claim 11, characterized in that the said lower, smaller, flap closure member (62) is inclined at an angle of about 45 degrees in the closed position thereof.

13. A diverter valve (30) provided at a three-way junction through which passes a high temperature gas, the valve having a closure member (31) pivotable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, characterized in that the diverter valve has a floor (32) inclined upwards at a location upstream of the valve closure member.

14. A diverter valve as claimed in claim 13, characterized in that the said diverter valve floor (32) is inclined upwards at an angle of about 10 degrees.

15. A diverter valve as claimed in claim 13 or 14, characterized in that the said closure member (31) is arranged to be inclined in the said second position thereof wherein it closes the said other outlet branch of the junction.

16. A diverter valve as claimed in claim 15, characterized in that the closure member (31) is arranged to be inclined at an angle of about 20 degrees to the vertical in the said second position thereof, giving an operating closure member rotation of about 70 degrees.

17. A diverter valve (40) provided at a three-way junction through which passes a high temperature gas, the valve having a valve closure member (41) pivotable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, characterized in that the centre-line (50) of the valve stack (42) and silencer (43) is offset from the centre-line (51) of the diverter valve.

18. A diverter valve as claimed in claim 17, characterized in that a toggle drive shaft (46) for operating the valve closure member (41) is located on the said centre-line (50) of the valve stack and silencer.

19. A diverter valve (60) provided at a three-way junction through which passes a high temperature gas, the valve having a closure member pivotable between a first position wherein it closes one outlet branch of the junction and a second position wherein it closes the other outlet branch of the junction, characterized in that the valve closure member has a multi-flap structure (61, 62) wherein a lower, smaller, flap closure member (62) thereof is inclined in the closed position thereof.

20. A diverter valve as claimed in claim 19, characterized in that the said lower, smaller, flap closure member (62) is inclined at an angle of about 45 degrees in the closed position thereof.

21. A diverter valve as claimed in any of claims 1 to

20, characterized in that the inside corner (33) of the diverter valve is mitred.

22. A diverter valve as claimed in any of claims 1 to

21, characterized by a frame fixed across the said two outlets of the three-way junction, the frame having two sets of sealing surfaces one in each outlet path, and the said closure member comprising a pivotable flap carrying two sets of seals for respectively cooperating with the said sealing surfaces of the frame.