We are having H25 (Hitachi) Gas turbine. One unit is having high CO (250 mg/m3) in Exhaust Of Turbine. we suspecting it due to HRSG burner but even no supplementary firing CO is very High.
transmitter were calibrated even inter changed with other Turbine, found OK.
Spread is also good.
How does the NOx now (with the high CO) compare to the NOx before the high CO?
What fuel is being burned when the CO is higher than expected?
Is the unit capable of operating on more than one fuel, and if so, how often is it operates on each fuel?
Does the unit use water- or steam injection for NOx emissions reduction when the CO is higher than expected? (It's presumed the units have DLN (Dry Low NOx) combustors, or have some kind of emissions reduction technology in the turbine combustion system; specifically, what technology is used for emissions reduction?)
Has the fuel supply recently changed?
What load is the turbine with the high CO operating at?
What combustion mode is the turbine with the high CO operating in?
How long has it been since the last maintenance outage?
When you say the turbine was checked and found to be okay, precisely--what checks were done, and what were the results of the checks? We're the combustors boresecoped? Were the fuel nozzles removed and examined? What was found?
What turbine control system is used on the units?
>How does the NOx now (with the high CO) compare to the NOx
>before the high CO?
>What fuel is being burned when the CO is higher than expected?
>Is the unit capable of operating on more than one fuel, and
>if so, how often is it operates on each fuel?
Yes HSD, very rare
>Does the unit use water- or steam injection for NOx
>what technology is used for emissions reduction?)
>Has the fuel supply recently changed?
>What load is the turbine with the high CO operating at?
>What combustion mode is the turbine with the high CO operating in?
>How long has it been since the last maintenance outage?
>When you say the turbine was checked and found to be okay,
>precisely--what checks were done, and what were the results
>of the checks? We're the combustors boresecoped? Were the
>fuel nozzles removed and examined? What was found?
>What turbine control system is used on the units?
So, this problem has developed since the last maintenance outage? If so, that would seem to point something that was done during the maintenance, don't you agree?
How does the steam injection flow-rate after the outage compare to the flow-rate before the outage for the same fuel flow-rate? So, if the steam flow-rate was 8.5 #/sec at a fuel flow-rate of 6.5 #/sec before the outage, what is the steam flow-rate now at a fuel flow-rate of 6.5 #/sec?
Was either the steam injection flow-rate sensing system or the fuel flow-rated sensing system worked on during the maintenance outage? Or, possibly both systems?
How does the power output and fuel flow-rate at Base Load after the maintenance outage to the power output and fuel flow-rate at Base Load before the maintenance outage?
Steam injection flow-rate can affect CO production as well as NOx production.
I'm not familiar with the term 'RLNG'--I understand the LNG part of the term, but what's the R stand for?
If new fuel nozzles or combustion liners (or refurbished parts) were installed during the maintenance outage is it possible the newly-installed components are not exact replacement parts for the ones which were removed? Could they have different orifices or flow characteristics than the previously-installed parts they replaced?
Do you see the intent of the questions? It would seem that something changed during the maintenance outage which has resulted in higher-than-normal CO. Usually CO is burned by the diffusion flame, and reducing the diffusion flame temperature will reduce the NOx (because high diffusion flame temperature results in high NOx--that's why steam or water injected into the combustors reduces NOx , by reducing diffusion flame temperature).
Also changes in combustion liner or fuel nozzle flow characteristics can also impact CO and/or NOx production.
You didn't provide any detail about how the turbine was checked or what was found; just "OK." It's quite common for the Mechanical Department, or the Sourcing Department, to claim all work was done properly and the parts purchased and installed are similar to the original equipment. They (the Mechanical Department or the service provider) don't want to take the unit apart again. And the Sourcing Department believes what the salesperson told them about the parts, if they were purchased from a non-OEM (Original Equipment Manufacturer) supplier. And, in some cases the OEM has also provided the wrong parts.
So, it's best to look at the work which was done during the maintenance outage and/or the parts which were replaced during the maintenance outage, to understand what is the cause of the high CO.
Have you asked Hitachi what might cause unusually high CO?
Was any work done on the turbine control system which might affect the fuel flow-rate calculation or the steam injection flow-rate calculation?
Are you certain there is no leakage of fuel into the HRSG through the auxiliary firing system?
Is there any kind of emissions reduction done in the HRSG or exhaust stack that might adversely affect the CO reading or sampling? New sampling hoses or a change in port position?
Please write back to let us know how you fare in resolving the issue. We don't need answers to all the questions--they are just to help with understanding the possible causes for the problem. (It's presumed, because that's how it's typically done, that the required steam injection flow-rate is calculated based on the fuel flow-rate. But that's not always the case; we don't know how it's done at your site.)
Hope this helps!