Hello,
I have found one interesting question on the other forum:
http://control.com/thread/1026249316
I think that it is more appropriate to discuss this here.
I post reply on that forum, and it will be there tomorrow.
Id appreciate your comments.

I think it is have something in common with control exploatation concepts of steam units control.
I know there are two control concepts:
1. boiler leading, when power stepoint is transferred to boiler controller which adjust coal (fuel) firing. This will provide constant pressure in fron of turbine but units output power could swing a bit.
2. turbine leading, when powr setpoint is directly connected with control valve position. Every changes in desired power affect control valves immediately, and boiler controller maintains pressure. This provides constant output power but steam pressure swings a bit.

Am I right here?

Best regards,

Mikas

Without reading the link you posted in your reply, I will give my .02- Sliding pressure and constant pressure mode deal with turbine throttle pressure in that when sliding pressure is enabled, the unit will adjust throttle pressure to match a preset curve in the logic for a given load. Constant pressure would be just that- constant... would rely on operator input for setpoint. Neither of these would change load (steady state to steady state) as the LDC MW setpoint had not been changed. The control scheme you were referring to would be in our case the LDC mode. Turbine follow would be using turbine valves (ie throttle pressure) to acheive megawatts, then the boiler/fuel master would dump in fuel to raise pressure back to setpoint (assuming it was a ramp up). Conversly, if you were in Boiler follow mode, the boiler/fuel master would dump in fuel to ramp up- throttle pressure would then increase- turbine valves would open to lower pressure- steam flow through turbine would increase and hence MW generation would increase. There would be an obvious lag in generation in Boiler follow mode initially as it takes a few minutes in this mode for coal increase to translate directly into throttle pressure increase. Hope this helps-

Chris

The Constant Volume Type Turbine works on the Atkinson Cycle.It has become now outdated and has been superseded by the Constant Pressure Type Gas. Sliding pressure turbines reduce thermal stress at various load points. Pressure increases as load changes whereas, constant pressure remains fixed at all load points. New combined cycle plants are mainly sliding pressure units.

These all seem about right. We run our Turbine on constant pressure control. With 3 1350psi boiler in front of it. inlet pressure to the turbine stays constant. As the coal fired boiler push or lag, the turbine inlet control valves open or close to keep pressure at setpoint, this will increase or decrease the turbine load. MW will increase or decrease depending on inlet valve position. This makes for better boiler controls, but not constant turbine loading. When we take our unit out of pressure control the load on the turbine is constant, the inlet control valves do not move. but the 1350psi header will swing or sag with boiler loading.

Which is the difference between throttle pressure and live steam pressure?

What means LDC?

LDC - Load Dispatch Center

i am not clear about the pressure control modes of steam turbine operation

Limit pressure - Initial Pressure !!!!!

Fixed pressure - Sliding pressure !!!!!!

i am working with combined cycle power plant

we have two modes of operation
Limit pressure (remains till bypass closes)
Initial pressure (active when Bypass closes)
can any one explain why we need these modes of operation !!!!!
Boiler or Turbine which decides the modes of operation !!!!!

some time i read about Boiler follow mode and Turbine follow Mode


with lots of terminologies