FIELD OF THE INVENTION
The present invention relates to a quick closing device for steam in cold reheat line
of power plant.
BACKGROUND OF THE INVENTION
Now that it is becoming common practice to fit steam bypass valves around the
turbine HP cylinder, even when the boiler is of the drum type, it is necessary to fit a
check valve(s) in the cold reheat pipework. In this situation, if the check valve does
not close, high temperature steam will be fed back into the turbine. The moving
blades will generate additional heat rising to point where the blades are destroyed.
Because sticking of the disc can have such severe consequences on Bled Steam
applications, customers are unwilling to depend on gravity closure, no matter how
reliable it may theoretically be, on those lines where the steam contains a significant
amount of energy. However, on some of the very low pressure lines there are no
valves at all and others have gravity closing check valves. This is a practical
consideration with most designs of Swing Check valves where the hinge pin is
located above the seat. The available power in the actuator has to be such that it
can be used with the plant on full load to demonstrate that the disc is not stuck in
the open position.
Another consideration of this equipment is how quick it will close the valve when
the forward flow ceases. As the disc moves towards the closed condition, the feed
water heater will continue to condense the available steam. The available steam will
be that passing through the partially closed valve, in the pipe and the heater shell.
Hence the actuator has to be selected in such a way as to close the valve in less
than 1 sec.

Hence the main functional requirement of a Non return valve in the cold reheat line
are as follows:
• Prevent reheat steam from returning to turbine on trip.
• Simplifies Hydrotesting of the Reheater.
• Protect the high pressure turbine exhaust from bypass steam and water when
the turbine bypass system operates.
• Isolate high pressure turbine exhaust when auxiliary steam is supplied to the
IP turbine in a combined cycle unit, to synchronize the steam turbine
generator or start the gas turbine on a single shaft machine.
SUMMARY OF THE INVENTION
According to the invention, the device is a cold reheat Non return valve (CRH NRV)
having a pressure seal bonnet arrangement and a servomotor on one side and a
limit switch assembly on the other side. The Servomotor is either hydraulic or
pneumatically operated. The flap of the device is positively coupled with a shaft of
the non-return valve operable and closable by a quarter turn actuator.
According to the invention, a swing check valve with power assist is installed in the
steam line between a turbine outlet and a reheater. This protects the high-pressure
turbine against steam flowing back from the cold reheat (CRH) line. In normal
operation, the flap is held in an open position by the steam flow. The valve is closed
on shutdown and during faulted operating conditions. Closing is initiated by a close
command which releases a closing spring. The valve is both opened and closed by a
pneumatic actuator. The closing time of the valve is less than 1 seconds.
The valve body is configured in such a way to ensure a minimum pressure drop at
normal operating conditions. The valve is provided with a pneumatically operated
actuator mounted either on LHS or RHS of the valve.

According to the invention, the actuator is a quarter turn Scotch yoke type with a
spring return mechanism. The actuator develops sufficient torque to lift the heavy
flap from its initial seating position. The actuator is selected in such a way that the
maximum torque at the maximum air pressure does not exceed the maximum
allowable stem torque value.
Along with the valve and the actuator, one eaeh solenoid valve, air filter regulator
and limit sensors (contact/proximity) are provided. The quick closing of the valve is
ensured by the solenoid valve. The Solenoid valve is selected in such a way that the
closing of the valve occurs in less than 1 second. An air filter cum regulator ensures
a regulated supply pressure and a sintered bronze filter of the regulator ensures
supply of clean air to the actuator. The opening, closing and intermediate position of
the valve is indicated by a plurality of proximity limit sensors. These sensors allows
sensing of the position of the valve, at any point of time by at least one sensor.
OBJECTS OF THE INVENTION
It is therefore an object of the invention is to propose a quick closing device for
steam in cold reheat line of power plant.
Another object of the invention is to propose a quick closing device for steam in cold
reheat line of power plant, which prevents back flow of steam in high pressure
turbine of power plants.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 Shows a cross sectional view of the device of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Figure - 1 illustrates a cold reheat non return valve of the invention. The device
comprising a body (01) or shell encompassing the fluid, said body (01) having an
inlet aligned from an inlet piping turbine and an outlet uniaxial with the inlet pipe; a
bonnet (02) connected to the body (01) either by a gasket bolting or pressure seal
bolting; a Seatring (05) which is firmly held onto the body (01) by means of welding;
a Stem (10) made from a single rod, a Disc (03) made from forging is provided, and
having a convex profile to ensure tight seating with the seat ring. With the convex
design, having an increasing area for the fluid pressure allows reducing of the
thickness of the disc (03) and vis-a-vis the weight of the flap. A Gland consisting of
a set of packing, a bridge type Gland Flange which is used for applying pressure to
the Packing through a Gland follower; at least two Studs including corresponding
Nuts for arresting the leakage through the gland in which the Studs pass through
the hole of the Gland Flange and are held by two nuts on either side and which
interalia facilitates adjusting of the leakage by tightening the gland nuts. The
maximum opening of the flap is restricted to 85 deg thereby ensuring that the flap is
continuously available in the flow path and any return flow enables closing of the
flap. The maximum opening angle is controlled by a stopper provided in the body.

WE CLAIM :
1. A quick closing device in a cold reheat line connecting a high pressure turbine
to a Reheater, the device comprising:
- a body (001) which encompasses a steam supply circuit in the turbine;
- the body (001) having an inlet aligned to an inlet piping from the
turbine, and an outlet uniaxial to the inlet pipe;
- a bonnet (02) connected to the body (01) either by one of gasket
bolting and pressure seal bolting;
- a Seat ring made of hard material in cast form, firmly held onto the
body (01); and
- a disc (03) made from forging and, having a convex profile to allow
tight seating of the disc with the seat ring.

2. The device as claimed in claim 1, comprising an adjustable leak-prevention
means consisting of a set of packing, a gland flange for applying pressure to
the packing via a gland follower, and at least two studs with corresponding
nuts.
3. The device as claimed in claim 1, wherein a maximum opening of 85deg of
the flap allows availability of the flow path.

ABSTRACT

The invention relates to a quick closing device in a cold reheat line connecting a high
pressure turbine to a Reheater, the device comprising: a body (001) which
encompasses a steam supply circuit in the turbine; the body (001) having an inlet
aligned to an inlet piping from the turbine, and an outlet uniaxial to the inlet pipe; a
bonnet (02) connected to the body (01) either by one of gasket bolting and pressure
seal bolting; a Seat ring made of hard material in cast form, firmly held onto the
body (01); and a disc (03) made from forging and, having a convex profile to allow
tight seating of the disc with the seat ring.