Variable Nozzle Technology Being Used In Steam Turbines?

[crshears]

Hello all,

My field of labour has been predominantly in the electrical area for a number of years, but I do try to keep informed about related fields as well, hence the question. There's also a slight chance I could be speccing out a back-pressure steam turbine in the future, and if this technology was available, I'd definitely be looking at it closely for the application under consideration.

Turbochargers are now made that employ VNT, and Pelton wheel hydraulic turbines have been made with needle-controlled nozzles for many years, both of these being done in an effort to reduce/eliminate the pressure drop across the throttle valves and thereby reduce the associated losses.

Maybe I've missed it, but I have yet to see VNT applied to steam turbines; I recognize this might be both tough to implement and perhaps not worth the trouble on main turbogenerators, but it would seem to me to be quite doable on the smaller scale industrial steam turbines...or am I way off base?



CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[FredRosse]

I have not seen this application.

Steam turbines generally accomplish variable nozzle flow area with multiple valves and partial arc admission. Having said that, partial arc admission, which is slightly more efficient for partial loads on the machine, is often superceded by single valve machines in today's plant practice. Most new utility installations are single valve machines, no variable nozzle area.

The reason for abandoning partial arc machines is the extra costs, maintenence and machinery wear, high temp steam is hard on machinery, especially with moving parts. At the pressure ratios common in steam turbine practice, the steam jet velocities do not change much at partial loads.

 

[crshears]

Thanks, FredRosse.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]