We have a dual fuel Frame 6B (standard combustor) with Mark VIe operating on gas in combined cycle.
The unit has low spreads at low power outputs but spread increases at higher power outputs and high spreads even occur when operating in simple cycle on IGV temperature control mode even on part load (with HRSG out of service whilst running IGV mode to simulate how unit will operate during part load operation with HRSG on with diverter damper open).
We removed the fuel nozzles and found some sticky residue on the nozzles, all nozzles were then removed and cleaned and were re-installed. The unit ran with a failed atomising air compressor for a few weeks before it was replaced. After cleaning and re-installing the FNs the issue still persists. Unit runs the latest and greatest combustion hardware (advanced extendor) and has done 22000 hours (still 10,000 hours from the next MI). Spreads appear to rotate with the swirl so it appears to be a combustion issue. Any advice if we can continue to run another 10000 hours on this machine, ignoring the spread alarms. The machine doesn't seem to be tripping on high spread presently.
Another issue was that unit was test run and the three conditions we have in our MkVIe logic (as per an old MKV revision of the control spec ) for trip triggered by combustion monitor were fulfilled. i.e.,
SP1>SPL
SP2>0.8 x SPL
Adjacency of the SP1 and SP2
But the unit did NOT trip. The above criteria met quite a few times after we took the raised load from 20MW in 2MW increments with IGV temperature control mode ON.
After we looked at the MKVIe control logic block for combustion monitor , it seems to be using the TTXM but the logic is not clear and help pages are pretty scarce in helpful information. Is MKVIe using TTXM-TTXD(min) to calculate SP1 (etc.) instead of TTXD(max) - TTXD(min)?
The unit has low spreads at low power outputs but spread increases at higher power outputs and high spreads even occur when operating in simple cycle on IGV temperature control mode even on part load (with HRSG out of service whilst running IGV mode to simulate how unit will operate during part load operation with HRSG on with diverter damper open).
We removed the fuel nozzles and found some sticky residue on the nozzles, all nozzles were then removed and cleaned and were re-installed. The unit ran with a failed atomising air compressor for a few weeks before it was replaced. After cleaning and re-installing the FNs the issue still persists. Unit runs the latest and greatest combustion hardware (advanced extendor) and has done 22000 hours (still 10,000 hours from the next MI). Spreads appear to rotate with the swirl so it appears to be a combustion issue. Any advice if we can continue to run another 10000 hours on this machine, ignoring the spread alarms. The machine doesn't seem to be tripping on high spread presently.
Another issue was that unit was test run and the three conditions we have in our MkVIe logic (as per an old MKV revision of the control spec ) for trip triggered by combustion monitor were fulfilled. i.e.,
SP1>SPL
SP2>0.8 x SPL
Adjacency of the SP1 and SP2
But the unit did NOT trip. The above criteria met quite a few times after we took the raised load from 20MW in 2MW increments with IGV temperature control mode ON.
After we looked at the MKVIe control logic block for combustion monitor , it seems to be using the TTXM but the logic is not clear and help pages are pretty scarce in helpful information. Is MKVIe using TTXM-TTXD(min) to calculate SP1 (etc.) instead of TTXD(max) - TTXD(min)?