Gland sealing steam

[Drexl]

Hi,
Could someone describe in reasonable detail why a high pressure steam turbine needs gland sealing steam supply?

Drex

 

[byrdj]

By having seperate HP turbine and LP turbine steam sealing systems/headers, your system is unlike any I have ever seen. Thus the reason for confussion.

does the LP turbine system get its start up feed from main steam, same as HP turbine system?

If the LP turbine system becomes self substained at load and the feed valve closes, then at least one end of the LP turbine must have steam pressure agaisnt the gland seal. I have been thinking both ends of the LP turbine gland seal will only see condensor vacuum.

Is this so, that one end of your LP turbine has steam pressure that varies with load agaisnt the seal? would the LP turbine be a single flow within a seperate casing/hood?

Is there a valve that dumps the LP turbine sealing steam to the condensor if the gland leakage was to exceed flow need for being self substained?

If the LP turbine system can become self substained with load, I would think the HP turbine would do the same.

does the HP turbine steam seal header pressure stay about 0.5bar from startup to full load?

Is there a valve that dumps the HP turbine sealing steam if it were to try to become self substained and its feed valve remained open?

Are we confussion HP and LP turbine sealing systems with the fact that a single steam seal system has two headers, the sealing header with is low pressure, pure steam and the gland exhaust header with is just a few inches of water LESS than atmosphiric and is a mix of sealing steam and air that ingresses at the turbine ends going to the gland exhauster condensor?

we difinately need to be see actual P&IDs since we are own completely different pages.

 

[ScottyUK]

Yes, Hex 63 is definitely a separate gland steam condenser. One of the last big outages I was involved with on that set had a tormented return-to-service and we couldn't establish vacuum. The G/S condenser was choked with about 200lb of sandy debris, which was finally discovered after every instrument on the whole machine was blamed ahead of it.

The 'signals from the DEH' are just a single 4-20mA loop, and the two I/P positioners are calibrated so that at mid-span (12mA) both valves are closed. Movement below 12mA opens one, above 12mA opens the other. A single actuator and common linkage would have been a far better solution.

The DEH was a good system, more capable than most of that era.

I can follow your GE terminology and translate it with a little effort. Yes, all nice and clear. We need a P&ID because drexl appears to have something slightly unusual - wonder if it is an Eastern European design?

Found this on Youtube, not sure if it will help drexl:

http://www.youtube.com/watch?v=xKtpL5DB7LY

 

[byrdj]

Thanks for ensuring my narritive makes sense...
I too have search, looking for a system like Drexl appears to be discribing. I found that youtube. that system appears to be similair to what each of us have presented, except the vidio's narrative is either misleading or just incomplete. I noticed at 0:54 to 0:58 there is a connection to the supply piping teeing off to a control valve that then is piped to the condensor, thus the header unloader valve for when the HP leak off becomes excessive for LP sealing. then at 1:01 to 1:04, you can notice that sealing steam is going towards the HP seal

that HP leak off that goes accross the top does not appear to used by the seal, but just a means to utilize some of HP leak off for making MWs and reduce the HP leakoff going to feed the seal steam header.

Durring searching, I did notice a "patent" drawing that look like it had seperate pressure regulating valves for the LP and HP seal, but the link to a readable drawing was dead.

"Tuning" the pnumatic controllers on the GE system was pure Voodo. 20 years ago, we came up with settings that were suppose to be suppleid in GEKs. without that info from the factory or able to find my old notes, it becomes the most difficult challange to a new unit since you need the operating extreme conditions to gather response and asking for a full load trip for testing is not appreacaite by any utility. where with the old MHC regulator, all the controlling engineer (lead/lag/gains & overlap) was bult into it, just get the linkage in good order and it worked

I am very curoius about Drexls system and hope we can see a P&ID. it is still nice to learn

 

[ScottyUK]

byrdj,

You got me looking more closely and Hex 063 goes to the MAIN condenser. It has been a few years since I was on this unit and my memory is terrible. The gland steam condenser itself is shown on the P&ID I posted. Sorry for the error.

You studied that animation in some detail, I missed those inconsistencies that you spotted.

I love the little things that the OEMs leave for the field guys to figure out. WH were no better, we had plenty of little notebooks and crib sheets filled with critical information which the OEM didn't share with us; I don't think we were unique in that respect by any means.

 

[byrdj]

Drexls, any chance to see your P&ID?

 

[abeltio]

One reason to pull vacuum with sealing system on in the whole train (HP, RH and LP) is to minimize windage losses, potential overheating of the buckets and rubs.
The sealing system serves two purposes: avoiding ingress of air and exit of steam

saludos.
a.

 

[byrdj]

QUOTE
------------------
Are we confussion HP and LP turbine sealing systems with the fact that a single steam seal system has two headers, the sealing header with is low pressure, pure steam and the gland exhaust header with is just a few inches of water LESS than atmosphiric and is a mix of sealing steam and air that ingresses at the turbine ends going to the gland exhauster condensor?
------------------

I marked up an illustration that shows a HP and LP turbine end packing with the sealing and gland exhaust headers.
It is shown with a HP stage pressure that is being leaked off into the steam seal header.

this can be combined with the illustration of the seal steam header controls that shows the SSH being supplied by main steam during startup, then transitioning to HP stage leakoff as the turbine is loaded. thus the SSH feed valve will close as turbine is loaded.

the gland exhauster header is allows maintained at a slightly below atmosperic pressure so that it prevents steam from escaping the turbine and since this steam is mixed with room air, it is taken to the gland exhauster condensor.

 

[Drexl]

Hi,
I gathered some more informaation and the issue seems to be solved now. Unfortunately I can not give a P&ID but this is not required to understand what the function of the higher pressure steam is.

The reason why the HP steam is supplied to the HP-turbine has nothing with air to do. Instead it is supplied so that the steam from the turbine will not leak through the labyrinth - instead this HP-steam will leak into the turbine. The reason is that the steam leaving the HP-turbine is wet, and the steam would cause erosion in the labyrinths. The HP-steam is instead dry with some superheating and no erosion occurs.

Thanks for all the good answers!

 

[byrdj]

Thanks...That makes perfect sense ...

ScottyUK, I appreaciate the information related to WH. Are you familair with the IGTC site?

 

[ScottyUK]

byrdj,

No hadn't seen that one but have just had a little look. You might see a familiar name appear there if they let me in. ;-)

No problem with the information from Big W, I have a reasonable amount of info on that particular set and some fairly detailed knowledge of the DEH control system and the generator & AVR.