Steam turbine VWO startup

[byrdj]

back in 1995, an Utility published an article where they started their 500MW turbine by opening turbine valves, then began boiler firing. the intent was to ramp boiler and turbine temperture together and let the turbine slow roll as boiling began.
Does anyone have any experiance with this method of turbine startup?

http://www.power-eng.com/content/pe...edure-speeds-cold-start-protects-turbine.html

 

[stgrme]

I have no direct experience with this start-up method. However, I do remember an article or presentation by someone at Exelon (PECO) about using this method at the Eddystone Plant. Perhaps, you can find some results using Google.

Best of luck!

 

[byrdj]

thanks for the Exelon referance, I found a paper presented at the 2008 ASME Power Conferance.
I can't recall my ASME library sign on, so I haven't seen the matereial yet

 

[davefitz]

There is a lot more to it than the original post describes. First, you cannot admit steam to a steam turbine unless you are certain the steam temperature is within allowable limts, so opening the turbine valves prior to starting the boiler cannot be permitted.

Second, there needs to be speed control of the turbine prior to synchronization, so opening the turbine valves without speed control override can only be done once, and then you would need a rbine, and a new pair of underwear as well.

I think the topic is better described as "variable pressure operation" or sliding pressure operation of the turbine ( and boiler). The optimum method is a function of whether the tubine uses arc admission ( siemens and westinghouse) or partial arc admission ( GE and Hitachi) of the inlet throttle valves. Also, the type of turbine bypass avaialable affects the startup mode ,and also there is distinction between admitting steam to the IP turibne follwoed by transfer of laod control, or simply admitting steam to the HP stage first. And finally, the type of boiler you have also affects the startup procedure, some differences being a constant pressure style drum boiler, a variable pressure style drum boiler, a constant furnace waterwall pressure once thru steam generator, a varible furnace water pressure steam generator, and there are other differences.

In any case, once you have synchronized the steam turbine, the pressure at the superheater outlet will vary linearly with steam flow if the steam turibne valves are left in a fixed position.

 

[davefitz]

WEll, I should have read the article first. There are some other concerns related to the boiler. Most large boilers have non-drainable platen or pendant superheaters in the furnace, and it usually takes at least 45 minutes to dry out the condensate in those legs ; it is not permitted to fire over 10% MCR heat input until those non-drainable legs boil out.

Operating a boiler when the HP steam is at vacuum conditions implies it will be tough to drain the steam traps, main steam line drains, and any drain routed to a flash tank. Normally one needs at least 50 psig in the HP superheater prior to being assured that these drain devices work. I am familiar with the issues related to using reheater drains when the reheater is under vacuum and it is not drained to the condenser- those same problems will visit the HP superheater.

The article claims that rotor and blade ductility are met at a 250 F temperature- I had thought that high temperature blading needed to be over 350 F to meet ductility requirements prior to speed operation.

But it looks like an interesting experiment they are undertaking- I hope it works out.

 

[byrdj]

thanks for your reply Dave.
I'm hoping I'll make contact with the authur of the ASME paper.
I am more curious about the method than in dire need of operationaly data. one of the other things that I wanted to ask is how can they apply steam seals without boiler steam. Also, at what pressure would the turbine be at rated with CVWO. I'm thinking under 50 psi, so do you now bring the govenor down to throttle the CVs and allow drum pressure to build before sychronizing.

I was thinking HP/IP ductal transition was 300/350F, but LP was 200/250F

Joe