FIELD OF INVENTION
This invention generally relates to a separating mechanism used to isolate the
reheater in a thermal power plant. More particularly, the invention relates to a
separating device for reheaters in power plant.
BACKGROUND OF INVENTION
In a boiler-turbine power plant, working on Rankine thermodynamic cycle, the
technique of reheat and generation is employed to increase the overall efficiency
of the power plant. In such an arrangement the high pressure steam from the
boiler expands in the high pressure turbine and before entering into the
intermediate pressure turbine, the same is admitted into a heat exchanger called
Reheater.
The reheater is located inside the boiler and it needs to be isolated during the
hydrotest. At least two separating devices are welded one each to the pipeline in
the inlet of the reheater (Cold line) and outlet of the reheater (hot line), which
form a part of the piping system. These devices are kept open during normal
operation and offers no resistance to flow. When the reheater is to be isolated
for carrying out the hydrotest, the device is closed by means of a closing
member called, a separator assembly.

OBJECTS OF INVENTION
It is therefore an object of the invention to propose a separating device for
reheaters in power plant, which eliminates an additional step of cutting the
pipeline and welding a dummy flange into the line and vice versa after testing
the reheater.
Another object of invention is to propose a separating device for reheaters in
power plant, which forms a part of the pipeline so as to reduce the pressure drop
of the medium in the system.
Yet another object of invention is to propose a separating device for reheaters in
power plant, which substantially reduces the maintenance cost.
A further object of invention is to propose a separating device for reheaters in
power plant, which is optionally provided with an assembly to improve the
temperature unbalance between the lines left and right sides of the reheater.
SUMMARY OF THE INVENTION
Accordingly, there is provided a separating device for reheater in power plants,
comprising:

a cast steel casing having an inlet port and an outlet port with a third port at top,
the casing having two parallel faces inside its central chamber, which each has a
plurality of stepped bores in which a plurality of rings are fitted and welded from
the rear side;
a tight-fitting pressure seal bonnet which has an annular cavity in the outer
diameter in which a pressure sealing ring and a supporting ring are fixed;
a split ring which has four splits, and which engages the casing and the top of
the pressure seal bonnet;
a separator assembly which has a groove in one of its faces;
an elastic seal inside the groove in the separator assembly;
a locating plate with at least two alien screws;
a jacking screw to apply the initial pressure; and optionally,
an orifice plate assembly.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows an embodiment of the invented device in opened condition
(overall sketch).

Figure 2 shows the device of figure 1 in closed condition (overall sketch).
Figure 3 shows a bonnet and sealing arrangement of the device according to the
invention.
Figure 4 shows a separator assembly of the device according to the invention
Figure 5 shows the Orifice plate assembly of the device according to the
invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION:
OPERATION:
During normal operation, the arrangement of the separating device will be as
shown in figure-1. In this configuration, a third port (4) is provided in a cast-steel
casing (1), apart from an inlet port (2) and an outlet port (3). A tight-fitting
pressure seal bonnet (5) is provided in the third port (4), which has an annular
cavity in the outer diameter in which a pressure sealing ring (6) and a supporting
ring (7) are fitted. A split ring (8) which has four splits, engages in the recess of
the casing (1) and the top of the pressure seal bonnet (7). The pressure seal
bonnet (5), the pressure sealing ring (6) and the supporting ring (7) are retained
by the split ring (8). The sealing between the casing (1) and the pressure seal

bonnet (5) is produced by the pressure sealing ring (6) which is made up of
grafoil with inconel reinforcement.
The detail of the seal can best be seen with reference to figure -3. During normal
operation, the pressure sealing ring (6) gets compressed by the flow medium
outwardly against the casing (1) and the supporting ring (7) ensuring an
effective seal. A cover plate (9) rests on the top of the Casing (1) which has
multiple holes. Through these holes, corresponding number of studs (17) extend
downwards into the threaded holes in the pressure seal bonnet (5) which help to
hold the pressure seal bonnet (5) securely in place and to adjust the sealing
tightness as required, by tightening nuts (18). During this normal working, the
separating device forms a part of the piping system and practically offers no
resistance to the flow medium, and the pressure drop is negligible. The casing
(1) has two parallel faces having stepped bores in which a plurality of rings (16)
are rigidly fixed.
ISOLATION:
The arrangement during isolation is shown in figure-2. During hydrotest, it is
usually required to block the line. At the time of hydrotest, the cover plate (9)
and the pressure seal bonnet (5) along with the split ring (8), supporting ring (7)
and pressure sealing ring (6) are removed and the Separator assembly (10) (as
shown in the figure-4) is lowered into the center chamber of the separating
device from the top and located in the machined cradle in the lower part of the
casing (1).

The Separator assembly (10) has a groove in one of its faces. The sealing
between the Separator assembly (10) and the ring (16) is achieved by inserting
an elastic seal (15) inside the groove in the separator assembly and turning a
jacking screw (12) in the clockwise direction to apply the initial pressure.
Subsequent pressure on the elastic seal (15) is applied by the testing fluid itself
and the elastic seal (15) gets compressed against the stainless steel deposited
face of the ring (16) and provides a perfect sealing. A dome screw (14) is used
as a pivot and two alien screws (13) are used for holding the separator assembly
(10) in place. Replacing the top pressure seal closure isolates the reheater and is
ready for hydrostatic test.
Once the hydrotest is over, the top pressure seal closure along with the pressure
sealing ring (6) are lifted and the Separator assembly (10) is removed out. A new
pressure sealing ring (6) is placed in portion and the pressure seal closure is
reinstalled in position.
ATTACHMENT
An attachment namely, an Orifice plate assembly as shown in figure 5 can be
mounted in place of the separator assembly (10), if the temperature unbalance
between the lines, left and right of the reheater needs to be improved. This
arrangement consists of an orifice plate (21), a locating plate (22), two studs
(23) and two tighteners (24). The orifice plate (21) is provided with a passage of
smaller area than the passage area of the device resulting in a pressure drop and

corresponding change raise of the temperature. This temperature change helps
to improve the temperature unbalance between the lines left and right sides of
the reheater.
According to the invention, the reheater can be isolated by directly installing the
separator assembly (10) across the flow passage inside the casing (1) without
cutting the pipeline and welding the dummy flange. Also the reheater can be put
into normal operation by simply removing the separator assembly (10) from the
casing (1) without cutting the dummy flange and rewelding the pipelines. Top
entry design of the separator assembly (10), eliminates the necessity of cutting
the device out of line.
The rectangular pressure sealing ring (6) is of grafoil material and made stiff
enough with Inconel reinforcement. The grafoil flows easily into the surface
crevices in the sealing area and offers better sealing than the soft iron gasket.
The possibilities of sealing surfaces subjecting to cracks etc, are completely
eliminated.
The invention provides a separator assembly (10) which is of straight cylindrical
shape instead of conventional wedge shape, which eliminates the difficulties
while removing it out of the valve, because of the thermal strains induced by the
flowing medium. In the present invention, once the jacking screw (12) is
loosened, the separator assembly (10) becomes free and can be easily removed
out o the valve with the help of eye bolts.

The separator assembly (10) is a very simple closure element in which the
sealing is achieved by tightening the jacking screw (12) to apply the initial
pressure and all the subsequent pressure is applied by the testing fluid itself.
The elastic seal (15) inside the groove of the separator assembly gets
compressed against the surface of the Ring (16) during isolation and offers
effective sealing. As the resilience of the elastic seal (15) is the predominant
factor for the effective sealing, the surface roughness of the sealing surface of
the Rings (16) need not be of high lapping finish.
The orifice plate assembly (21, 22, 23, 24) as shown in figure 5 can be mounted
in place of the separator assembly, if the temperature unbalance between the
lines, left and right of the reheater needs to be improved. This arrangement
consists of an orifice plate (21), a locating plate (22), two studs (23) and two
tighteners (24). The orifice plate (21) is provided with a passage of smaller area
than the passage area of the device resulting in a pressure drop and
corresponding temperature change of the medium. This temperature change
helps to improve the temperature unbalance between the lines left and right
sides of the reheater.
The Rings (16) are introduced with seat welded on it instead of direct welding on
Casing (1) making the process easy to implement

The Cover plate (9) is made from a hollow ring covered with a metal sheet (19)
at the centre. The metal sheet (19) is held along with the cover plate (9) by
means of two screws (20), making it more compact and optimum in weight.
According to the invention, an optimum performance with low pressure drop is
achieved once the separator assembly (10) is removed. Thus, the device literally
effectively becomes a part of the piping system. The straight flow design without
any deflections allows a smooth, in-line flow with unobstructed passage and
pressue drop is kept to an absolute minimum.
The device entails minimum maintenance with no replacement parts required,
other than the pressure sealing ring (6).

WE CLAIM
1. A separating device for reheaters in power plant, comprising:
- a cast steel casing (01) welded to the pipeline;
- a tight-fitting pressure seal bonnet (5) which has an annular cavity
in the outer diameter in which a pressure sealing ring (6) and a
supporting ring (7) are fixed;
- a split ring (8) which has four splits each engaging in the recess of
the Casing (1) and the top of the pressure seal bonnet (5);
- a separator assembly (10) configured with a straight cylindrical
shape, and having a groove in one of its faces;
- an elastic seal (15) inside the groove in the separator assembly
(10);
- a locating plate (11) with at least two alien screws (13);
- a dome screw (14); and
- a jacking screw (12) to apply the initial pressure.

2. The device as claimed in claim 1, wherein the casing (1) comprises an
inlet port (2) and an outlet port (3) including a third port (4) at the top.
3. The device as claimed in claim 1, wherein the sealing between the casing
(1) and the pressure seal bonnet (5) is produced by the pressure sealing
ring (6).
4. The device as claimed in claim 1 or 3, wherein the pressure sealing ring
(6) comprises grafoil with inconel reinforcement, and wherein during the
operation, the flow-medium compresses the pressure sealing rings (6)
outwardly against the casing (1), and the supporting ring (7) achieves an
effective sealing.
5. The device as claimed in claim 1, comprising a cover plate (9) having
multiple holes, wherein a corresponding number of studs (17) being
disposed through a plurality of threaded holes configured on the pressure
seal bonnet (5) to hold the bonnet (5) in place for sealing, and wherein
the sealing tightness is achieved by tightening nuts (18) provided with the
studs (17).
6. The device as claimed in claim 1, wherein the elastic seal (15) is inserted
inside the groove in the separator assembly (10), wherein the jacking
screw (12) is turned to apply the initial pressure, and wherein the testing
fluid applies further pressure on the elastic seal (15) to allow the

elastic seal (15) to get compressed on the ring (16) which achieves a
perfect sealing.
7. The device as claimed in any of the preceding claims, wherein the dome
screw (14) is used as a pivot, and wherein the at least two alien screws
(13) hold the separator assembly in place.
8. The device as claimed in claim 1, wherein an orifice plate assembly (21 to
24) is provided to replace the separator assembly (10) in case of the
reheater needing improvement in the temperature unbalance between the
pipe lines.
9. The device as claimed in claim 8, wherein the orifice plate assembly
comprises an orifice plate (21), a locating plate (22), two studs (23), and
two tightening nuts (24), the orifice plate being provided with a passage
of smaller area than the passage area of the device to enable a pressure
drop including a corresponding temperature change of the flow medium.
10.The device as claimed in any of the preceding claims wherein a metal
sheet (19) is disposed at the centre of the cover plate (9) and held by
means of two screws (20).

11. A separating device for reheaters in power plant as substantially described
and illustrated herein with reference to the accompanying drawings.

The invention relates to a separating device for reheater in power plant, comprising, a cast steel casing (01) welded to the pipeline; a tight-fitting pressure seal bonnet (5) which has an annular cavity in the outer diameter in
which a pressure sealing ring (6) and a supporting ring (7) are fixed; a split ring
(8) which has four splits each engaging in the recess of the Casing (1) and the top of the pressure seal bonnet (5); a separator assembly (10) which has a trapezoidal groove in one of its faces; an elastic seal (15) inside the groove in the separtor assembly (10); a locating plate (11) with at least two allen screws
(13); a dome screw (14); and a jacking screw (12) to apply the initial pressure.