How do they do it in a coal-fired power plant?
How do they do it in a coal-fired power plant?
(OP)
How do they relieve pressure in the event that a turbine trips? Is there a fast-acting vent valve or do they rely on 'safety relief valves' to allow time for the boiler to react?





RE: How do they do it in a coal-fired power plant?
RE: How do they do it in a coal-fired power plant?
I'm at a larger cogeneration plant now and they just let their reliefs lift when the load drops a substantial amount in a small time interval.
I liked the setup at the smaller plant better because the operation of the safety reliefs was reserved for true emergencies and one didn't have to worry about one not re-seating.
Comments?
RE: How do they do it in a coal-fired power plant?
With turbines that have a inlet that is constant with output it is true that it is difficult to stop the superheater outlet and even sometimes the drum safety valves from lifting. One way is to install an electrically assisted safety valve at the superheater outlet. This valve would be sized for say 15 to 20% of rated output and would be extra to any safety valves required by the code. Thi intention would be for this valve to lift before the code valves and preventing them from lifting. Hence the code valves are retained for boiler protection. Sometimes the electrically assisted valve is fitted with an inlet isolating valve or valves so they can be maintained while the boiler is in service.
For turbines that operate in sliding pressure mode where the turbine inlet pressure varies with turbine output. Higher output = higher pressure, it is normal practice to have a steam turbine bypass that is not a safety valve but opens when the turbine inlet pressure exceeds the control set pressure by some value. This bypass would normally discharge through the reheater to the condenser.
athomas236
RE: How do they do it in a coal-fired power plant?
RE: How do they do it in a coal-fired power plant?
Note that these systems are also useful for bringing the turbine online. The boiler and condenser can be brought online and optimized with the bypass valve open and the main turbine control valves closed. Once the boiler and condenser are operating well, the main turbine bypass valves are opened to ramp the turbine up to speed while the bypass valve is closed.
The key on these systems is actuating time and reliability. Many of them use a hydraulic actuator on the bypass valve for speedy operation (< 1 sec for full stroke). Also, some type of spring package is almost always present in the actuator or valve to force the valve to an open or close position in the event of a failure.
RE: How do they do it in a coal-fired power plant?
the boiler safety valve will never be poned when the turbine is triped