Turbine control valve 1

[Adam001]

The graph of the control valve of the turbine has opening vs flow rate , so what if we increase flow rate from boiler at a fixed opening of valve will the pressure upstream valve increase ? Any other things will occur ?

 

[byrdj]

sight terminology distinction... the steam turbine control valve should not be "fixed", its opening can be "limited" to provide the scerneo you are asking about (but the controls should always be able to close the CV).

operating with the CVs limited at a set position and changing boiler firing to increase steam flow could be reffereed to as "sliding pressure" operation. as the steam flow increases, the upstream pressure will increase along with the steam flow through the turbine (and its power output increase)

 

[Adam001]

Is the sliding pressure operation is when the CV is limited to any set point or when the valve is only fully opened ?

 

[byrdj]

I worked on the turbine side, so I might not be correct in boiler control terminoligy,

having the CVs set at a less than 100% opening and sliding boiler pressure to control load was a practice I witnessed.

I discussed with several plants about choosing an exact "best valve position", ie close sequential CVs for a 4 valve unit, so #1 & #2 are open to point where #3 is just closed, and use that position to slide pressure for nightly reduced load operation

 

[MikeHalloran]

1. Yes.
2. Chernobyl.


Mike Halloran
Pembroke Pines, FL, USA

 

[byrdj]

2. Chernobyl.

why?

 

[MikeHalloran]

Sound like an impromptu experiment is being considered. Those generally don't end well.


Mike Halloran
Pembroke Pines, FL, USA

 

[rotw]

I can hardly understand how you are going to do this procedure, as there should be a dozen of instrument across the steam supply line with interlocks

Anyway, if you do something that is not designed for originally could have serious consequences (and according to Murphy law it WILL). In this respect, I also agree to the reference to Chernobyl.

 

[stgrme]

One concern in changing turbine operation from "constant" ("fixed") pressure to "sliding" pressure would be prevention of water carryover from the boiler on loss of firing. Most large steam turbines are equipped with an inlet pressure controller (IPC), or throttle pressure regulator (TPR). On loss of firing and a sudden drop of turbine inlet pressure, the IPC or TPR will close the governing valves to maintain the inlet pressure and prevent water carryover.

Some IPCs or TPRs are set up to operate at a single fixed pressure below normal (rated) inlet pressure (fixed pressure type). If the turbine is operated in a sliding pressure mode and if it operates at a pressure lower than rated pressure for extended periods, this type or water carryover protection may not function to protect the turbine.

Other IPCs or TPRs may operate based on the rate at which the inlet pressure falls (rate-sensitive type). This type is more appropriate for sliding pressure operation.

Best of luck!