Greetings to all.
I will try to provide as much details here, so we can learn from each other.
The unit I speak about is 7 FA turbine, dual fuel with DLN2. The unit has 14 Cans and 27 thermocouples to monitor the exhaust temperature. The igniters are on Cans 2 and 3. The flame detectors are on 11, 12, 13, and 14. The liquid fuel system is equipped with 3 way purge valves and re-circulation system.
Usually we keep the re circulation ON during summer when the unit runs on gas. We run the unit on liquid for testing in the winter. the nitrogen purge system is not ready yet. so when a problem happens in the re circulation system and get isolated, the liquid remaining in the 3-way purge valve cokes since it can't be purged with nitrogen (nitrogen purge system is not ready yet).
Recently, we run a turbine that had the re circulation system off during gas operation for long period of time. so high exhaust spread is normal and expected. The main purpose of this thread is that how can we determine the problematic Can from looking into the exhaust temperatures?
Before running the turbine, we made sure that the liquid lines are free from air. The unit started from turning gear [Liquid Mode]. The spreads are shown in the following link. After taking 10.25 Seconds for purging, the firing started. I know that there is a way to check which valve has the problem by using the selector valves, but two problem arise here.
1- The flow divider has 14 ports for 14 Cans. In some units, the selector valve is not working for some ports. I mean for example I can read the pressure for 12 ports while the remaining 2 ports has their selector valve damaged.
2- I don't think It is accurate to measure the pressures at each selector while the unit is accelerating, because the back pressure is increasing. and when the unit reaches 95% of rated speed, it would trip if there is high exhaust temperature. So, there is no enough time to get an accurate measurement.
3- One of CSA replies says that if the pressure at one of the 3-way valves is less or more than 10% of the average pressures, this valve would be suspected. But consider a case where 5 or 6 of the valves have problems and the other 9 or 8 valves are intact. wouldn't that affect this method.
Finally, Checking the selector valve during acceleration didn't come to my mind because I was told by a control engineer from GE that you can determine which 3-way valve mostly have the problem by using the exhaust temperatures from the 27 thermocouples. During our last start-up in liquid we brought the turbine up to approximately 3200 RPM then stopped the turbine to avoid trip. The exhaust temperatures are shown in the link, and according to the GE Control Engineer, he advised to inspect the 3-way valves at Cans 1 and 14. He also added that It is better to inspect Can 13 also since it established the flame late. Frankly, I don't know how he has reached this analysis.
Just to clear one more thing. The arrangement of the annular Cans are as such. The top one is Can 14. The lower one is Can 7. And counting is in anti-clockwise direction. Please don't direct me to previous threads, As I have already read many.
https://drive.google.com/file/d/0B9R-rponHkn5Vkp1R2FKOEVrT3c/view?usp=sharing
https://drive.google.com/file/d/0B9R-rponHkn5Yk8xT3laeG9UREU/view?usp=sharing
Best Regards
I will try to provide as much details here, so we can learn from each other.
The unit I speak about is 7 FA turbine, dual fuel with DLN2. The unit has 14 Cans and 27 thermocouples to monitor the exhaust temperature. The igniters are on Cans 2 and 3. The flame detectors are on 11, 12, 13, and 14. The liquid fuel system is equipped with 3 way purge valves and re-circulation system.
Usually we keep the re circulation ON during summer when the unit runs on gas. We run the unit on liquid for testing in the winter. the nitrogen purge system is not ready yet. so when a problem happens in the re circulation system and get isolated, the liquid remaining in the 3-way purge valve cokes since it can't be purged with nitrogen (nitrogen purge system is not ready yet).
Recently, we run a turbine that had the re circulation system off during gas operation for long period of time. so high exhaust spread is normal and expected. The main purpose of this thread is that how can we determine the problematic Can from looking into the exhaust temperatures?
Before running the turbine, we made sure that the liquid lines are free from air. The unit started from turning gear [Liquid Mode]. The spreads are shown in the following link. After taking 10.25 Seconds for purging, the firing started. I know that there is a way to check which valve has the problem by using the selector valves, but two problem arise here.
1- The flow divider has 14 ports for 14 Cans. In some units, the selector valve is not working for some ports. I mean for example I can read the pressure for 12 ports while the remaining 2 ports has their selector valve damaged.
2- I don't think It is accurate to measure the pressures at each selector while the unit is accelerating, because the back pressure is increasing. and when the unit reaches 95% of rated speed, it would trip if there is high exhaust temperature. So, there is no enough time to get an accurate measurement.
3- One of CSA replies says that if the pressure at one of the 3-way valves is less or more than 10% of the average pressures, this valve would be suspected. But consider a case where 5 or 6 of the valves have problems and the other 9 or 8 valves are intact. wouldn't that affect this method.
Finally, Checking the selector valve during acceleration didn't come to my mind because I was told by a control engineer from GE that you can determine which 3-way valve mostly have the problem by using the exhaust temperatures from the 27 thermocouples. During our last start-up in liquid we brought the turbine up to approximately 3200 RPM then stopped the turbine to avoid trip. The exhaust temperatures are shown in the link, and according to the GE Control Engineer, he advised to inspect the 3-way valves at Cans 1 and 14. He also added that It is better to inspect Can 13 also since it established the flame late. Frankly, I don't know how he has reached this analysis.
Just to clear one more thing. The arrangement of the annular Cans are as such. The top one is Can 14. The lower one is Can 7. And counting is in anti-clockwise direction. Please don't direct me to previous threads, As I have already read many.
https://drive.google.com/file/d/0B9R-rponHkn5Vkp1R2FKOEVrT3c/view?usp=sharing
https://drive.google.com/file/d/0B9R-rponHkn5Yk8xT3laeG9UREU/view?usp=sharing
Best Regards