Query about Frame 9E Gas Turbine with Mark IV Control

On frame 9E Gas Turbines(Mark IV), if additve dosing panel trips while m/c is running on furnace oil then it converts to HSD on auto & also takes shutdown command. Now if m/c is not restarted with in two minutes then boiler(HRSG) trips (while GT is running in combined cycle mode).

Now as far as Siemens V94.2 Gas turbines are concerned, if dosing panel trips while GT is running on LSFO then it only converts to HSD on auto i.e. no shutdown command.

Now in case of GE frame 9E GTs, after tripping of dosing panel, m/c takes shutdown command after time delay of 10 seconds whereas fuel changeover valve takes about 20-25 seconds to change its position from furnace oil to HSD.

So, if we increase time delay for shutdown to 30 seconds then fuel changeover valve would change its position during that time & hence there would be no shut down. Result would be that m/c will be running on furnace oil with out additive dosing for approx. 20 seconds.

Kindly advise me whether this modification should be made or not. Has anyone performed this kind of modification on his GT (Frame9E with MarkIV control)?

There was a reason for the sequencing which was in the panel at the time it was installed, but, being a Mark IV, it's likely that no one will recall exactly what the reason was.

You have a choice: Contact the original packager or GE for guidance on how long your turbine can safely run (be sure to specify the load(s) at which the problem is being experienced; you didn't in your question here) with the heavy fuel oil ("furnace oil") being burned in your unit (be prepared to provide a fuel analysis), or, make the change and live with the consequences, if any.

Your description of the sequencing doesn't really make too much sense. If by "shutdown" mean a controlled, automatic fired shutdown where the unit is unloaded and then shut down normally, not a unit trip (emergency shutdown), if the unit goes into an automatic shutdown when this happens, have you tried having an operator initiate a Start command, or give the unit a Raise- or Lower Spd/Load command to try to abort the shutdown? Maybe initiate a Master Reset and then try initiating another Start or Raise/Lower Spd/Load command?

Or is that what you're saying, because it's not clear. Because, if your description is to be believed, the problem is just that the fuel transfer is taking too long and a shutdown is being initiated before the transfer valve has reached the distillate position, in which case just changing the timer would be all that would be required. But, if a shutdown is initiated on a treatment skid failure and that signal latches in and also latches the shutdown, then there must be some other sequencing changes made to be effective.

If your unit has a typical motor-operated fuel transfer valve, then as soon as the transfer valve starts moving the heavy fuel oil flow is being reduced as the distillate fuel flow is being increased, so, the heavy fuel oil won't be flowing at maximum for the entire time it takes the valve to transit from the heavy fuel oil position to the distillate fuel oil position. But, if the unit is running at Base Load, the high temperatures are why the treatment additive is necessary to prevent the plating of heavy metals on nozzles and buckets.

Ok CSA, I realize that I was not clear enough in my description earlier. I now try to clarify things further.

Our GTs always run at base load. By GT shutdown, I mean normal shutdown in which m/c unloading starts & it has to be restarted by operator.

When additive dosing panel trips or additive dosing stops for some reason. A relay picks up because of no flow rate of additive & initiates a signal to heavy fuel permissive check relay because of which fuel changeover command to HSD is initiated. Now same signal of no additive flow rate also goes to turbine normal shutdown relay. In addition to this signal, turbine normal shutdown relay also takes into account a signal about position of fuel changeover valve (pneumatic operated). If position of this valve is not towards HSD within 10 seconds of initiation of additive no flow rate signal then turbine will take shut down command. As I have mentioned in my previous post that fuel changeover valve takes about 20 to 25 seconds to change its position from furnace oil to HSD. So, if we increase delay in turbine shutdown command signal from 10 to 30 seconds then with in this time of 30 seconds changeover valve would change its position towards HSD & hence there will be no shutdown signal (as conditions for shutdown would not meet because of changeover valve position would be towards HSD). Result would be that turbine may run on furnace oil for 20 seconds without dozing. Is that too much??

Moreover, there is no problem with fuel changeover valve or fuel transfer taking too long. I am just asking for a possibility. Because as I mentioned earlier in my previous post that if after initiation of turbine shutdown command, it is not restarted with in two minutes then connected HRSG trips & we have faced a lot of trips because of this.

I hope things are quite clear now. But if you still need more clarification then give me your e-mail address, I would send you a file which explains this with the help of Speedtronic drawing.

We will certainly ask OEM before any such modification but I just want to know your or someone else's opinion on that. Please reply.

It would seem that you have done your homework on the fuel transfer timing issue, and that a simple timing value change will resolve one problem.

There's still the issue with the treatment skid tripping or stopping dosing, which is the real cause of the problem.

It also sounds like the operators aren't really paying too much attention to unit operation if they can't issue a start withing two minutes of a shutdown to prevent the HRSG from tripping.

But changing the timer will help with the overall problems.

Well, it is not necessary that we will perform this modification. We are still thinking on that.
What I am trying to ask you (and other members of this site) is that what is the need of shutdown on dosing skid trouble? As I have also compared this with Siemens V94.2 Gas turbines in my previous posts where no shutdown takes place on dozing skid trouble & GT only converts to HSD. Shouldn't this be enough on GE GTs also? That's actually my thinking & I want to know how you having much more experience & knowledge) & other people on this site think about it. No doubt that GE people, who designed these turbines, knew a lot more than I do.

Moreover, as far as my modification is concerned, if GT runs at base load for 25 or 30 seconds without dosing, is that too much?

Dear CSA,

So far you have been very nice as you have answered all my queries & I have gained a lot of knowledge from you regarding power plants. But you never replied to my last post regarding this modification.

It will be so nice of you if you kindly answer my last few questions (regarding this post) on the basis of your rich knowledge & vast experience regarding power plants & specially GE turbines.

My questions are:
1. In your opinion, should this modification be made or not?
2. In your opinion, What is the need of GT shutdown on no additive flow rate? (as I have compared this situation with Siemens V94.2 GTs)
3. If GT runs for 25 seconds on base load with out additive dosing, is that too much for GT?
4. Do you think that GE will agree to this modification or not?

It will be nice if someone other than CSA also gives his opinion about this post.

Thanx in advance.

1. My opinion should not matter.

2. Every turbine manufacturer/packager has different criteria for controlling and protecting their turbines. I don't know what criteria Siemens uses or what the internal combustion gas temperatures of V94.2 GTs are nor do I know what kind of residual fuel is being burned at your site; residual fuels do vary, even from the same source (refinery) as their crude stock may vary or they may change their refining process or change the type of petroleum products being produced at the refinery.

3. Probably not; but doesn't it depend on the make-up of the residual oil and how often the dosing skid "fails"? We have no idea how often this occurs (dosing skid problem) but it sounds like it's fairly often. So one 25-second failure in a week isn't much, but if it happens daily or even more frequently, those 25-second periods add up.

4. GE doesn't usually review such requests.

There aren't that many plants that operate on residual fuel oil. It's not as common as you may think. Most GE-design heavy duty gas turbines have a lower output when operated on residual fuel, to try to reduce the higher temperatures that result in the deposition of heavy metals on hot gas path parts, and most owners/Customers don't like this "penalty" for running on residual fuel.

Every question is not black and white.