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phillipwon
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Join Date: Nov 2011
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Why Minimum Cooling Flow to LP Steam Turbine?

12/26/2012 9:00 AM

Suppose that there are two pressurized steam turbine, High and Low pressure and we extract steam from the pipe between high and low pressure turbine. Some brochure says that there needs minimum cooling flow to Low pressure turbine for the component cooling like blade.

Then, Could someone please let me know why component cooling is neccessary? In other words, why the components are heated up if it rotates by itself without steam flow?
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lyn
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#1

Re: why minimum cooling flow to LP steam turbine?

12/26/2012 9:29 AM

This might help:

Session 11: Turbines
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Joshi
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#2

Re: why minimum cooling flow to LP steam turbine?

12/26/2012 9:30 AM

Catch-up on your reading:

Why minimum cooling flow to LP steam turbine?

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ronseto
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#3

Re: Why Minimum Cooling Flow to LP Steam Turbine?

12/26/2012 10:48 AM

It might have to do with expansion and contraction of the components and condensation. Turbines are designed to operate within temperature ranges and if outside the range, they won't operate at their best efficiency. "Off the top of my head".

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RAMConsult
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#4

Re: Why Minimum Cooling Flow to LP Steam Turbine?

12/26/2012 2:50 PM

The type of steam turbine and its design operating conditions dictate the whether or not steam flow is required for cooling or not. You are describing an extraction turbine where process steam is "extracted" between stages, and in some case, at the last stage as well, in which case there is no condenser.

If a steam turbine is operated at less than full vacuum and/or minimum design steam flow at its last stage outlet when it is designed to be at full vacuum, then the spinning blades do work on the atmosphere between the static blades. This work is called "windage losses" and can raise the temperature of the air and the friction surfaces (the blades) to unacceptable levels, just like dragging the brakes in your car.

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Bob Sullivan
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Location: Located in South eastern North Carolina, I am a retired Supt of Public Works. also I am wheelchair confined due to an INdustrial accident of the Bends (Caissone Disease) from a construction Diver/underwater mechanic.
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#5

Re: Why Minimum Cooling Flow to LP Steam Turbine?

12/29/2012 12:32 PM

Th low side turbine discharges the condensate at a vacuum that is what creates the flow (extraction) through the low side turbine. Otherwise the flow would stop at 0 psi, as it is used. There would be no rotation at 0 psi without the water cooled condenser to create this vacuum and consequent cooling of the condensate.
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RAMConsult
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#6
In reply to #5

Re: Why Minimum Cooling Flow to LP Steam Turbine?

12/29/2012 10:15 PM

Sorry, that's not how an extraction turbine works. Steam is deliberately "extracted" at various temperatures and pressures depending upon the exact design of the steam/power plant. There are even turbines that are designed with no condenser at all, the low quality steam on the last stage of the low pressure turbine is used for general heating or heat tracing use. One thing that you can't have is water droplets in the steam as goes through these turbines (unless so designed) since it causes blade erosion and/or high windage losses.

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