We have a 7EA DLN1 gas turbine with a Mark V control system. We recently did a combustion inspection and installed brand new hardware. Since then, our NOx has been low and our CO has been high. We don't see anything abnormal with exhaust spreads or temperatures. We would like to try tuning our turbine and trade some CO for NOx. We have a SCR.

I read a previous post concerning DLN tuning and have a couple additional questions. Our FXKSP5 and FXKSP6 are 81 and 77. If we lower both of them in 1% increments, should we see NOx increase and CO decrease? Is that all that needs to be done to adjust the split?

Thanks,

Jeff

 

Hi Jeff,

Lowering the split value would normally in my experience increase the NOx and decrease the CO.

Adjusting FXKSP5 and FXKSP6 is the only thing I have ever done to adjust the split. On our machines (9E’s) the split FXSP2 is likely to be at one end of this band. I would start by just moving one at a time, hopefully FXSP2 is sitting at the higher end and you can reduce the value of FXKSP5 and achieve the desired result. Before we were in contract with GE, we would tune the split ourselves but always remain within our original split parameters of 81-84, 77-81 in your case. Since we have entered into a contact with GE, we don’t generally tune the split ourselves. GE take the split outside of this original band from 77-85% to find the optimum position. We have tuned the split ourselves while under contract but anything outside of the 81-84% has required approval from GE before implementing. As you have 7EA’s I would take I wouldn’t necessarily use the figures I have quoted as our original split settings were higher than yours.

I guess you have already read this from your post but I would recommend reading the other recent post: http://www.control.com/thread/1026250018#1026250132 regarding DLN tuning, as CSA seems to be very knowledgeable on this and just about all things GT/MKV related.

Hope this helps.

Simon

 

One needs to be very careful when changing splits; very careful. And, this condition is also possibly injurious to the machine; GE has noted that extremely low NOx levels on a DLN-I machine can mean high combustor dynamics which can lead to premature combustion hardware wear and even failure.

DLN-I combustion systems, even though they are considered to be a "mature" technology (they were the first-generation of DLN combustion systems), are still pretty mysterious. And, worse, there are only a couple of ways to adjust emissions: fuel splits and dilution hole sizes. There is a limit to what can be done with fuel split adjustment; if that doesn't work, the liners have to be removed and the dilution holes re-sized and then re-installed and another round of tuning performed. (At least that's my recollection; it's been a few years since I've "had the pleasure" of working on a DLN-I unit.)

Adjusting fuel splits to increase NOx and decrease CO can result in unwanted primary zone reignitions and flame instability. Decreasing the fuel split leans the primary combustion zone even further which is the reason that primary zone reignitions and flame instability can occur. (Even though GE says there's no flame in the primary combustion zone during Premix Steady State operation, they still list flame stability as one of the parameters affected by changing fuel splits.)

Really, it's best to get someone familiar with DLN-I tuning to site to help with the situation. It will most likely be money well spent!

Have you tried the 7EA Users Group for help or resources?

I don't know how to say this. This is really one of my worst fears about forums like this. Making fuel split adjustments seems like an easy thing to do but mistakes can be and have been made. They may not be apparent immediately. I don't and can't condone DLN tuning by proxy. It's just too risky. We don't know enough about what else was done or not done during the CI (like calibration of gas valve LVDT feedback). We don't know what kind of gas valve arrangement is at the site. We don't know if the splits are changed with load. We don't know anything about the combustion hardware that was installed in the turbine.

I would strongly urge Simon and others to leave DLN tuning to on-site tuners or to remote tuners for those sites with the capability. I think this is one of the reasons that Companies don't want their employees or contractors contributing to sites like this; there can be liability issues should a catastrophic failure occurs. An insurance company with a legal department can have a lot of reasons to go looking for a scapegoat. The road to ruin was paved with good intentions.