Turbine Bypass Valves/Systems
Turbine bypass valves play a very major role in Power Plant applications. Within a short period of twenty four hours, a power plant may be required to operate at minimum load, increase to maximum capacity for major part of the day, immediately lower back to minimum load and then back to maximum capacity. Bypass System permit unit start up and shutdown in a lifesaving manner for critical heavy components in boiler and turbines. Jet Flow Bypass valves are supplied with hydraulic, electric or pneumatic actuators as per the process requirements alongwith complete control systems as an option.
Functions:
- To perform quick and economic start up, including cold start, warm start and hot start in a lifesaving manner for critical heavy components in boiler and turbine.
- To operate with the boiler shutdown.
- To perform warm and hot startup in a short time after a trip i.e. brings the unit back to load
- To run the unit down to house load.
- To perform real “two-shift’ operation”.
- To avoid condensate losses to the atmosphere and reduce the start up noise to the ambient outside the plant.
Applications:
There are two different applications:
1) Bypass Systems which are occasionally in operation. Among these there are startup and shutdown conditions and emergency conditions, for example after turbine trip.
2) Bypass System
which are often or permanently in operation, for example for process steam or heating application.
Actuators:
Bypass valves can be supplied with Pneumatic Piston & Cylinder, Electric or Hydraulic Actuators alongwith power pack and complete control system as per the requirements of the system.
Materials:
For most sizes, casting or forgings in Carbon and Alloy Steel can be supplied. For extremely large sizes, units are fabricated. Bypass Valves are normally supplied with butt weld ends. However, if required can be supplied with flanged ends.
Multi-Stage Multi-Path Pressure Reduction via Velocity Control trim technology:
- Jet Flow Jet Stack trim has stack of discs and each disc is tailor made for a particular flow path that has a variety of features:
- OurJet Stack trim technology uses a series of multi-stage multi-path disc stack for successful operation of our valves in severe service conditions.
The passes through an extremely tortuous path at right angle turns thereby reducing the fluid velocity and therefore reduces the noise and eliminates erosion and vibration problems. The Jet Stack disc stack is tailor-made as per the requirement of our customers.
The thickness of the wall of Jet Stack trim is such that it ensures maximum tortuous flow path. It ensures the fluid has a uniform velocity and as it passes through the disk it is streamlined. - Its design ensures the flow to be distributed evenly throughout the disc. The open flow channel ensures even distribution.
- Irrespective of flow direction, multi channels are provided. Multi channels evenly distribute fluid around the plug for full stroke thereby ensuring complete control, reliability and stability.
Advantage of Jet Flow Turbine Bypass Valves with Jet Stack Velocity Control trim and laval jet nozzle -
- Series of pressure reducing stages are incorporated in the valve that can go as high as 60 for severe service let down applications. This ensures complete velocity control for the full load with noise levels reduced below 85 dBA.
- Complete tight shut off valve maintaining class V seat leakage.
- High rangeability of 50:1 as a standard is provided, however, higher turn down of 100: [can also be provided upon request.
- Minimum wall thicknesses of the body as per the design conditions to minimize thermal stress and shock.
- Complete trim assembly is easy to assemble and
- disassemble since no welded designs are incorporated.
- Extremely low maintenance cost with rapid trim
- change over from top.
- The trim has a very long life on account of extremely
- low velocities and with proper use of selected
- materials.
- Laval jet atomizing desuperheater incorporated in the valve ensures no impingement of the water on the downstream piping and thereby no need to install expensive thermal sleeves or liners.
- Substantial savings from the point of installation since the downstream straight length required is extremely short and therefore transition sockets and pipes can be installed very close to the valve.
- Extremely installation friendly. The valve can be installed in either vertical or horizontal direction.
