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Forced Cool Down
What is forced cooldown

How to make IVG bleed valve turbine speed and gas control valve open when accelerated cooling in gas fluid?

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I presume you are asking about forced cooling of the axial compressor and turbine rotor? Forced cooling involves using the starting means to spin the rotor at a faster speed than when on cooldown in order to force more air through the compressor, turbine and exhaust to cool the unit faster than when on normal cooldown. Some sites also take some action to open the IGVs to maximum operating angle--but some starting means are not capable of maintaining shaft speed when such a large volume of air is being moved through the unit with the IGVs at maximum operating angle when only the starting means is providing the torque to spin the shaft.

Why would you want to open the gas control valve during forced cooling of the axial compressor and turbine?

Forced cooling is more or less an "emergency" operation, not to be used at all times for rotor cooling. The starting means, which would be used during forced cooling, must be capable of running for long periods of time--and some starting means are not (capable of running for long periods of time).

Forced cooling causes thermal stress on rotor components, and even axial compressor casings and axial compressor blades, as well as on turbine sections and buckets. And, the OEM is making LOTS of noise these days about rotor end-of-life statistics and how various operations--including cooldown (and by extension, forced cooling) can affect end-of-life calculations (because of thermal stresses). [That's right--I've read recently that two hours of cooldown operation is the same as one hour of fired operation when it comes to calculating rotor end-of-life duration! Even though the OEM control systems don't calculate hours on cooldown like it does fired hours....]

If you would tell us more about the unit at your site, the type of starting means and the type of control system we could provide some guidelines and information about when and how to implement forced cooling of the axial compressor and turbine rotor. And, please be sure to explain why it's felt it's necessary to open the gas control valve for forced cooling.