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GE Fr9E Turbine Inner Barrel Temperature
GE Fr 9E Turbine inner barrel temperatures (TTIB) have increased from 155 Deg C to 195 Deg C while GT ramped up from 60MW to base load (125MW).

During ramping up of GT (GE Fr9E) from 60MW to base load (125MW), turbine inner barrel temperatures start rising from 120 Deg C to 195 DegC, and Load compartment temperatures rise from 95 Deg C to 145 Deg C. As Load compartment reaches 145 Deg C, Load compartment fan#2 cut in and temperature of inner barrel reduces from 195 Deg C to 155 Deg C.

We adjusted the TK88 (Exhaust Frame Cooling Fan) discharge pressure to 30 inch H2O from 37 Inch H2O, and inner barrel temperatures reduced to 155 Deg C during ramp up from 60MW to 125MW.

Following are my question on above scenario:

1. What is reason for high temperatures of Inner barrel during load ramp up?

2. What is the affect of Load compartment fans on Inner barrel?

3. What is the impact of TK88 discharge pressure on inner barrel?

Hello,

Let me understand by inner barrel do you mean the load tunnel area where bearing no 3 is housed?

In this area maximum temperature is controlled by radial air flow holes which provide part of shell cooling fan air to this area. The number and location of open holes is usually tuned during commissioning.

regards

novice001,

>In this area maximum temperature is controlled by radial air
>flow holes which provide part of shell cooling fan air to
>this area. The number and location of open holes is usually
>tuned during commissioning.

Hmmm..... Is this something GE Belfort are doing with newer GE-design Frame 9E heavy duty gas turbines?

AAkhan,

When did this problem start? After a maintenance outage? If so, and novice001 is correct, it's possible the number and location of open holes needs to be tuned after the outage.

But, that begs the bigger question: What is the change you are seeing now versus a week ago, or a month ago, or at the same time last year? Don't the temperatures in the load tunnel area increase the load all the time? As exhaust temperatures increase, that increases the heat on the insulation and metal around the load tunnel (surrounding the #3 bearing area), and that's going to make the load tunnel temperature increase. As the temperature of the hot combustion gases entering the turbine section increase, the temperature of the cooling air supplied to the turbine frame by the 88TK fans/motors LEAVING the turbine frame (and entering the load tunnel area) will also be increasing.

I also don't understand how reducing the exhaust frame blower discharge pressure can cause the load tunnel temperature to decrease, but then we can't examine the P&IDs for the Cooling & Sealing Air system for the unit in question.

There isn't much air flow in the load tunnel area (and the signal name TTIB is a VERY POOR choice of signal names, because the area around the #2 bearing area is also called an "inner barrel"--but we all know GE is nothing if not consistently inconsistent). And, the Load Compartment vent fans don't really cause air circulation to occur in the #3 bearing area, which I've always believed is one reason the exhaust frame cooling air is discharged into the #3 bearing area--to provide some air flow.

But, REALLY--the bigger question is: What has been the change in temperatures over time during loading? What was the TTIB temp at 60 MW one week ago, one month ago and one year ago? Was was the TTIB temp at 120 MW one week ago, one month ago and one year ago? AND, when did this problem of "high" temperatures begin?

What does the GE Operations & Service Manual's Cooling & Sealing Air section say about load tunnel (#3 bearing area) temperatures and temperature control?

>When did this problem start? After a maintenance outage? If
>so, and novice001 is correct, it's possible the number and
>location of open holes needs to be tuned after the outage.

We cannot link it with outage since the adjustment of Exhaust frame cooling blowers discharge pressure resulted in reduced temperatures. Also, we have traced the history and we have found the similar behavior in the past but since it has not breached the alarm condition hence was not under radar. However, after implementation of GE APM, it was identified to have changed with load ramp up only.

>But, that begs the bigger question: What is the change you
>are seeing now versus a week ago, or a month ago, or at the
>same time last year? Don't the temperatures in the load
>tunnel area increase the load all the time? As exhaust
>temperatures increase, that increases the heat on the
>insulation and metal around the load tunnel (surrounding the
>#3 bearing area), and that's going to make the load tunnel
>temperature increase. As the temperature of the hot
>combustion gases entering the turbine section increase, the
>temperature of the cooling air supplied to the turbine frame
>by the 88TK fans/motors LEAVING the turbine frame (and
>entering the load tunnel area) will also be increasing.

Yes you are right. Temperature should increase with load but after rampup is complete and GT is on Base load, the temperature of inner barrel reduced from 190 DEg C to its normal 155 Deg C and as I stated, the adjustment of exhaust frame blower discharge pressure resulted in no abnormal increase.

>I also don't understand how reducing the exhaust frame
>blower discharge pressure can cause the load tunnel
>temperature to decrease, but then we can't examine the P&IDs
>for the Cooling & Sealing Air system for the unit in
>question.

Does it relate to thermal expansion of cracks in Struts at bearing#3? Do we suppose there are cracks on Structs Side.

>There isn't much air flow in the load tunnel area (and the
>signal name TTIB is a VERY POOR choice of signal names,
>because the area around the #2 bearing area is also called
>an "inner barrel"--but we all know GE is nothing if not
>consistently inconsistent). And, the Load Compartment vent
>fans don't really cause air circulation to occur in the #3
>bearing area, which I've always believed is one reason the
>exhaust frame cooling air is discharged into the #3 bearing
>area--to provide some air flow.

Yes as per Manual, the exhaust frame cooling blower air after cooling the structs partially injects in Load tunnel (turbine inner barrel) and it was not mentioned whether it really cools down the turbine inner barrel. And we have to keep both load compartment exhaust fans ON in order to maintain the temperature during base load condition.

>But, REALLY--the bigger question is: What has been the
>change in temperatures over time during loading? What was
>the TTIB temp at 60 MW one week ago, one month ago and one
>year ago? Was was the TTIB temp at 120 MW one week ago, one
>month ago and one year ago? AND, when did this problem of
>"high" temperatures begin?

Same trend as noted now. It was triggered by GE APM module.

>What does the GE Operations & Service Manual's Cooling &
>Sealing Air section say about load tunnel (#3 bearing area)
>temperatures and temperature control?

It says, Exhaust Frame Cooling blowers cools down the bearing#3 struts and part of it goes at Turbine Wheel Space 3 Aft and part of it released in Turbine inner barrel and then to atmosphere.

Regards
Ahmad

Hello,

>Let me understand by inner barrel do you mean the load
>tunnel area where bearing no 3 is housed?
>
>In this area maximum temperature is controlled by radial air
>flow holes which provide part of shell cooling fan air to
>this area. The number and location of open holes is usually
>tuned during commissioning.

Ok TK88 exhaust frame cooling blowers control the temperature of inner barrel. But what is the impact of discharge pressure of these blowers on inner barrel? Do we suppose there are cracks developed in struts that could have increased due to thermal transient during load ramp-up?