Time That The Unit Must Remain In Turning Gear, Before Start

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Thread Starter

elomoon

In a single S109FB turbine shaft configuration, the time that the unit must remain in turning gear, at a minimum should be four hours, before the start if the shaft is stopped.

What is the technical foundation that must be four hours instead of three hours?

Is there any way to reduce this time, rotating the shaft every week is 180, for example, or increasing the speed of rotation before start when this unit with steam seals and void before starting?
 
To be competitive by reducing the startup time for start-ups in real time, the toner unit is the critical path. Reducing this time is gained in competitiveness.
 
I know you don't have a GE machine but below is GEs comments from their Maintenance Manual. It all really depends on how the machine was shut down and for how long. As you can see, GEs recommendations caused some industry controversies by quoting 4 or 6 hours Turning Gear for a cold machine before restart. If the machine was cooled down properly before an extended out of service, I don't think that you need to be too concerned, yes maybe a shaft rotation occasionally would make you feel more confident before an unplanned re-start.


Heavy-Duty Gas Turbine Operating and Maintenance Considerations
GE Energy | GER-3620K (11/04)
F) Turning Gear/Ratchet Running Guidelines
Scenario Turning Gear (or Ratchet) Duration
Following Shutdown:
Case A.1 - Normal. Restart not anticipated for >48 hours
Case A.2 - Normal. Restart not anticipated for <48 hours Continuously until restart. Rotor unbowed.
Case B - Immediate rotor stop necessary. (Stop >20 minutes)
Suspected rotating hardware damage or unit malfunction
None. Classified as bowed.
Before Startup:
Case C - Hot rotor, <20 minutes after rotor stop 0–1 hour(3)
Case D - Warm rotor, >20 minutes & <6 hours after rotor stop 4 hours
Case E.1 - Cold rotor, unbowed, off TG <48 hours 4 hours
Case E.2 - Cold rotor, unbowed, off TG >48 hours 6 hours
Case F - Cold rotor, bowed 8 hours(4)
During Extended Outage:
Case G - When idle
(1) Time depends on frame size and ambient environment.
(2) Cooldown cycle may be accelerated using starting device for forced cooldown. Turning gear, however, is recommended method.
(3) 1 hour on turning gear is recommended following a trip, before restarting. For normal shutdowns, use discretion.
(4) Follow bowed rotor startup procedure. See Operation and Maintenance Manual.
(5) Avoids high cycling of lube oil pump during long outages.
Until wheelspace temperatures <150F.(1) Rotor classified as
unbowed. Minimum 24 hours.(2)
1 hour/day
Case H - Alternative No TG; 1 hour/day at full speed (no load).(5)

If you want the complete page from the document, drop me am email to [email protected]
 
>To be competitive by reducing the startup time for
>start-ups in real time, the toner unit is the critical path.
>Reducing this time is gained in competitiveness.

I completely agree--the toner unit is the key. Always use the OEM's toner unit, unless a third-party toner unit offers a significant competitive advantage.

Using a non-OEM toner unit that does not offer a significant competitive advantage can be depressing.
 
Glenmorangie,

Actually, I think a S109FB is a single-shaft STAG Frame 9FB. So your answer may be very appropriate.

>I know you don't have a GE machine but below is GEs
>comments from their Maintenance Manual. It all really
>depends on how the machine was shut down and for how long.

I also believe Rev. L of the GE publication is on the streets.
 
Thanks for answering.

The recommendations, I guess they must be based on technical criteria, keeping a safety margin, GE recommended time to avoid trips by vibrations, because, the shaft when standing time curve/bowl. So if prolonging the purge time when the unit starts (currently 12 minutes at 705 rpm or adjusting the temperature of steam seals) could reduce the time from 4 hours to 3 1/2 hours ( for example).

Thanks
 
elomoon,

The criteria varies depending on the length of time since the unit was shutdown/tripped. If the shaft is warm; if it's been on turning gear since the last shutdown/trip; if it's been at rest.

You need to clearly state conditions the turbine/shaft is in when you're asking about reducing the time on turning gear.

There is no one cut and dried, cast in concrete, written in stone answer. GE gives lots of variability depending on various conditions--why? Because if they list one condition people will always ask, well, what about if this or that or the other thing. You have to learn to read the GE publication, choose the condition that best matches your situation and go from there.

If the unit is under warranty or some kind of LTSA with the OEM or a third-party, the OEM/packager or the provider of the LTSA services should be consulted, because they will monitoring the operation of the unit to be sure it is being operated as per their conditions for warranted operation and maintenance.

However, if you own the machine and there is no warranty or LTSA then you can decide how you want to operate your machine--as long as you are willing to accept the consequences of your decisions. If you want to take a little more risk, and go for 3-1/2 hours instead of four, you're certainly well within your rights as owner/operator of the machine to do so. If the unit trips on high vibrations or wipes steam seals, well, you'll know you can't do 3-1/2 hours for that machine condition. If you don't experience any issues (that you're aware of!) and the next time you want to go for 3-1/4 hours, you're certainly well within your rights as the owner/operator of the machine to do that.

You should be aware that single-shaft STAG units have extra consideration (I presume the S in S109FB stands for STAG (Steam Turbine And Gas turbine-generator coupled together into a single-shaft machine) have extra considerations because of the steam turbine warming and sealing necessary, in addition to the vacuum. You need to be referring to the proper section of GER-3620R for the proper information and guidance.

You can always ask the OEM/packager--but it sounds like you aren't very happy with their answer(s). GE is rather conservative, but when it comes to F-class machines they are correct to be so. They aren't the most robust machines in the world as they are being operated in modes and service other than they were originally intended for (which was Base Load operation)--and you seem to be trying to reduce start-up time as much as possible so as to receive as much money as possible for capacity and reserve payments--which means you want to start the unit often and as fast as possible. Well, you're likely going to have to develop your own criteria based on the acceptable risk level you wish to take. Careful monitoring of machine operating conditions as well as parts condition during maintenance will help you to assess the effects of your decisions and provide the basis for further risk--or not, as the case may be.

Just be aware that if you buy turbine parts (gas and/or steam) and they wear out faster because of the operating conditions they have been subjected to you probably won't get any relief from the parts supplier/manufacturer.

Operating turbines in today's environments is all about risk--acceptable levels of risk. You would do well to study your machine, formulate a plan based on your knowledge and any experience you can gain from other operators (Users Groups are best for this exchange of information) and decide on a plan based on your allowable level of risk, execute the plan, and analyze the data and parts conditions in one-, two or three years, and then decide how you want to proceed with your testing and analysis.

Just be aware that you are responsible for the consequences of your decisions--just like if you drive your car harshly and ignore the manufacturer's recommendations, it's probably not going to last very long, unless you do frequent maintenance and repairs.

Best of luck--and, don't forget: Use the proper toner.

;)
 
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