Is it usual to have a generation Capacity on Natural Gas (95% Methane) is little bit greater than Capacity on Liquid Fuel (Diesel) of a typical Gas Turbine (Especially GE 9E)? If so, can somebody explain why?
Capacity of Gas Turbine on different types fuel
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Yes.
You should probably download GE publication GER-3620. It will have answers to your questions--the one you ask now, and the ones you haven't asked yet.
Please don't assume that the power produced by a gas turbine will be the same regardless of the fuel being combusted. All fuels don't have the same BTU content and don't combust exactly the same. Particularly if the turbine has low emissions combustors.
You should probably download GE publication GER-3620. It will have answers to your questions--the one you ask now, and the ones you haven't asked yet.
Please don't assume that the power produced by a gas turbine will be the same regardless of the fuel being combusted. All fuels don't have the same BTU content and don't combust exactly the same. Particularly if the turbine has low emissions combustors.
Thanks for your reply WTF? Yes, I know the heating value facts of different fuels. I have one more specific question. Is it practical to get the same heat rate considering same ambient conditions, same fuel type (say, gas), same load setpoint, but different HHV of gas. I've found the gas consumption is not responding reversely respectively with HHV deviation. Is it practical, or theoretical only.
You asked initially about differences between gas fuel and liquid fuel ratings. Now, the topic has changed.
You ARE NOT clearly stating under what conditions the observations are being taken. Same load? Base Load? Part Load? Are the IGV LVDTs calibrated properly? Again--does the machine have DLN combustors (which affect a LOT of other control schemes (IGV control, specifically). There are a LOT of variables. Does the machine have fuel heating (for performance enhancement)? There are just a LOT of variables to be considered and under such conditions. We don't know what kinds of variations you are experiencing in HHV numbers. (I presume the machine is burning LNG and that's how the fuel constituencies are varying--but we don't know that. There's also Wobbe numbers to be considered.)
If you're having concerns that the unit isn't performing as it should, you should involve the OEM or a reputable firm in troubleshooting and be prepared to collect a LOT of data--because actionable data is the only way you are going to get answers to your queries about performance versus fuel.
My thermodynamic class is LONG behind me, and it was really just an introduction to terms and concepts--most of which I never used in my career. And, I'm not a combustion engineer, a performance engineer or a thermodynamics engineer. I know enough to be a good control system engineer (someone who can get a unit to start and stop reliably with no alarms (yes; that IS possible!!!) and troubleshoot operational and perceived problems). When it comes to squeezing a few BTU/kWH out of one fuel or another, that's for factory engineers. I can gather data and learn from the analysis, but I don't perform those types of analysis.
Again, if you don't have a copy of GER-3620, I strongly recommend you obtain one as it has a lot of good information about various machines and performance issues and fuels.
You ARE NOT clearly stating under what conditions the observations are being taken. Same load? Base Load? Part Load? Are the IGV LVDTs calibrated properly? Again--does the machine have DLN combustors (which affect a LOT of other control schemes (IGV control, specifically). There are a LOT of variables. Does the machine have fuel heating (for performance enhancement)? There are just a LOT of variables to be considered and under such conditions. We don't know what kinds of variations you are experiencing in HHV numbers. (I presume the machine is burning LNG and that's how the fuel constituencies are varying--but we don't know that. There's also Wobbe numbers to be considered.)
If you're having concerns that the unit isn't performing as it should, you should involve the OEM or a reputable firm in troubleshooting and be prepared to collect a LOT of data--because actionable data is the only way you are going to get answers to your queries about performance versus fuel.
My thermodynamic class is LONG behind me, and it was really just an introduction to terms and concepts--most of which I never used in my career. And, I'm not a combustion engineer, a performance engineer or a thermodynamics engineer. I know enough to be a good control system engineer (someone who can get a unit to start and stop reliably with no alarms (yes; that IS possible!!!) and troubleshoot operational and perceived problems). When it comes to squeezing a few BTU/kWH out of one fuel or another, that's for factory engineers. I can gather data and learn from the analysis, but I don't perform those types of analysis.
Again, if you don't have a copy of GER-3620, I strongly recommend you obtain one as it has a lot of good information about various machines and performance issues and fuels.
I want to add that often times when I get these kinds of queries I learn that someone got a screenshot while the machine was being started-up and loaded and then tried to compare it to another similar load point--also noted when the machine did not have time to stabilize internal temperatures. This is very important when trying to determine performance: The machine MUST be allowed to stabilize internal temperatures when taking these kinds of readings. Full stop. Period. Simply stopping for a few minutes at 60 MW while on the way to 90 MW is not going to produce good information. The definition of stabilized internal temperatures is no change of more than 5 deg F of any wheelspace temperature in 15 minutes. And, during starting and loading that usually requires about 4 hours or so to achieve at any given load (unless the machine was started while it was still very warm or hot).
ALSO, it's not clear from your post what instrumentation you are using to make your own calculations. Does the machine or the site have its own gas chromatagraph? Are you using the gas flow measurement equipment provided by the turbine OEM? (Because if so, it's a pretty crude flow measurement system and not really suitable for detailed performance analyses.)
If the machine in question has DLN combustors and/or it exhausts into an HRSG (Heat Recovery Steam Generator; "boiler") then it's very likely that the IGVs are modulated (varied) during Part Load operation. NOTE the OEM almost never makes any kind of performance guarantee at any load other than Base Load. One of the definitions of Base Load is that the IGVs much be at their maximum operating angle while the machine is operating on Base Load exhaust temperature control (either CPD-biased or CPR-biased). It's a well-known fact that modulating IGVs at Part Load decreases gas turbine efficiency (slightly) while increasing overall combined cycle plant efficiency. So, if you're taking measurements/analysis points at anything other than Base Load after the machine has stabilized internal temperatures for approximately 40 hours or so then the data is not very useful and the OEM won't generally make any kind of performance adjustments or honor any typical guarantees.
Finally, IGV and compressor cleanliness and condition are very important when making any kind of performance analysis. If internal clearances are greater than allowable or the IGVs aren't operating properly (usually because of some LVDT calibration issue or actuator gear wear/slop) then a good performance isn't normally possible. There are also correction diagrams for ambient temperature and humidity (from nameplate conditions) which should also be taken into consideration when making any kind of performance analysis. (These are usually found in the Operations & Maintenance manuals provides with the machine.)
Yes, under typical conditions one would expect a increase in HHV would result in an increase in performance (a decrease in BTU/kw), but there are a lot of conditions. And, again, the only real condition that counts is when the unit is operating at steady state conditions (stable internal temperatures as described above) at Base Load with the (well-calibrated IGV LVDTs) IGVs at their maximum operating angle, the ambient conditions are at or near rated (or corrected with the OEM diagrams), the compressor and IGVs in a new and clean condition and exhaust duct back-pressure within normal range. The fuel should also be within specification (as listed in the machine Control Specification provided with turbine control system). The inlet filters should also be relatively clean. So, you see--there are a lot of conditions for analyzing performance; it's not just a simple matter of taking a couple of screenshots and making some calculations.
ALSO, it's not clear from your post what instrumentation you are using to make your own calculations. Does the machine or the site have its own gas chromatagraph? Are you using the gas flow measurement equipment provided by the turbine OEM? (Because if so, it's a pretty crude flow measurement system and not really suitable for detailed performance analyses.)
If the machine in question has DLN combustors and/or it exhausts into an HRSG (Heat Recovery Steam Generator; "boiler") then it's very likely that the IGVs are modulated (varied) during Part Load operation. NOTE the OEM almost never makes any kind of performance guarantee at any load other than Base Load. One of the definitions of Base Load is that the IGVs much be at their maximum operating angle while the machine is operating on Base Load exhaust temperature control (either CPD-biased or CPR-biased). It's a well-known fact that modulating IGVs at Part Load decreases gas turbine efficiency (slightly) while increasing overall combined cycle plant efficiency. So, if you're taking measurements/analysis points at anything other than Base Load after the machine has stabilized internal temperatures for approximately 40 hours or so then the data is not very useful and the OEM won't generally make any kind of performance adjustments or honor any typical guarantees.
Finally, IGV and compressor cleanliness and condition are very important when making any kind of performance analysis. If internal clearances are greater than allowable or the IGVs aren't operating properly (usually because of some LVDT calibration issue or actuator gear wear/slop) then a good performance isn't normally possible. There are also correction diagrams for ambient temperature and humidity (from nameplate conditions) which should also be taken into consideration when making any kind of performance analysis. (These are usually found in the Operations & Maintenance manuals provides with the machine.)
Yes, under typical conditions one would expect a increase in HHV would result in an increase in performance (a decrease in BTU/kw), but there are a lot of conditions. And, again, the only real condition that counts is when the unit is operating at steady state conditions (stable internal temperatures as described above) at Base Load with the (well-calibrated IGV LVDTs) IGVs at their maximum operating angle, the ambient conditions are at or near rated (or corrected with the OEM diagrams), the compressor and IGVs in a new and clean condition and exhaust duct back-pressure within normal range. The fuel should also be within specification (as listed in the machine Control Specification provided with turbine control system). The inlet filters should also be relatively clean. So, you see--there are a lot of conditions for analyzing performance; it's not just a simple matter of taking a couple of screenshots and making some calculations.
I got the answer to my 1st question.
Secondly, let me mention some operating conditions and other parameters for your understanding.
1. Our machine 9E.03 mostly runs in FGMO (Free Governor Mode of Operation), in that case, we're not getting stabilized internal temperature. I understand. a steady base load condition is needed for performance measurement.
2. IGV LVDTs are properly calibrated.
3. Non-DLN combustor
4. GT Gas inlet temperature before SRV is 65±3 Deg C, with No extra fuel heating.
5. HHV & Wobbe Index variation: (1045~1075 BTU/SCF & 1370~1391 BTU/SCF), yes mostly LNG so far we experienced.
6. Coriolis mass flow meter by OEM
7. Exhaust through HRSG; At base load, exhaust temperature control mode is activated.
8. Just a month back, Compressor water wash was performed. So clean I guess.
So far these are the operating conditions you asked for.
Anyways, I need to consider steady base load condition again. Thanks for your cooperation dear.
If you have any more comments please put them here. Thanks again for your consideration.
Secondly, let me mention some operating conditions and other parameters for your understanding.
1. Our machine 9E.03 mostly runs in FGMO (Free Governor Mode of Operation), in that case, we're not getting stabilized internal temperature. I understand. a steady base load condition is needed for performance measurement.
2. IGV LVDTs are properly calibrated.
3. Non-DLN combustor
4. GT Gas inlet temperature before SRV is 65±3 Deg C, with No extra fuel heating.
5. HHV & Wobbe Index variation: (1045~1075 BTU/SCF & 1370~1391 BTU/SCF), yes mostly LNG so far we experienced.
6. Coriolis mass flow meter by OEM
7. Exhaust through HRSG; At base load, exhaust temperature control mode is activated.
8. Just a month back, Compressor water wash was performed. So clean I guess.
So far these are the operating conditions you asked for.
Anyways, I need to consider steady base load condition again. Thanks for your cooperation dear.
If you have any more comments please put them here. Thanks again for your consideration.
FGMO is basically pure Droop Speed Control. It's nothing special, and it's the best method of operating a GE-design heavy duty gas turbine at Part Load. Full stop. Period. It allows the turbine control to properly respond to grid frequency disturbances when operating at Part Load without any interference. It helps to stabilize the grid during frequency excursions instead of making them worse--which is what happens when Pre-Selected Load Control is used at Part Load.
It's most likely the unit is operating at Part Load with IGV Temperature Control active--also called Combined Cycle Mode. This mode uses the IGVs at Part Load to maximize exhaust temperature to maximize steam production when at Part Load. This mode is know to reduce GT efficiency (again, slightly) but the overall effect is to increase overall plant thermal efficiency at Part Load. And all of my explanations are based on HRSG without auxiliary burners (also called "duct burners"). Not the same as CPD- or CPR-biased exhaust temperature control. (Yes; there's IGV exhaust temperature control and CPD- or CPR-biased exhaust temperature control. Are we having fun yet?)
Again, I'm not a thermodynamics expert, nor a GT performance expert, nor a combustion engineer. I can't be of any further help. Except to reiterate data points need to be taken at stable internal operating temperatures (as described above) AND the OEM almost NEVER makes any kind of performance guarantee (BTU/kW) at any other operating condition than Base Load when the IGVs are at maximum operating angle. So trying to get performance data at Part Load, particularly with IGV exhaust temperature control active, is not really worth the effort. My recommendation is to always compare apples to apples--meaning take your data points when the unit is operating on different gas fuels at Base Load. If you see significant discrepancies from what you think should be happening as fuel constituents vary, then I would consider involving the OEM or the packager of the GT for more assistance. And, you would have the kind of data the OEM will be asking for to begin with. Instead of having to run more tests with different fuels to get the data they would likely be requesting.
And, read that GER. The problem with that document is that it tries to cover EVERY machine GE makes in one document, and that's very difficult to sift through and understand. Remember, you're looking for E-class conventional combustor data only, so you can ignore most everything else (the fanciest and newest H-class machines, and F-class machines and even DLN-I E-class machines. That doesn't leave a whole lot of information you have to consider--it's just finding only the relevant information more difficult in a document that tries (and doesn't do a very good job of) being a one-size-fits-all document.
Best of luck!
It's most likely the unit is operating at Part Load with IGV Temperature Control active--also called Combined Cycle Mode. This mode uses the IGVs at Part Load to maximize exhaust temperature to maximize steam production when at Part Load. This mode is know to reduce GT efficiency (again, slightly) but the overall effect is to increase overall plant thermal efficiency at Part Load. And all of my explanations are based on HRSG without auxiliary burners (also called "duct burners"). Not the same as CPD- or CPR-biased exhaust temperature control. (Yes; there's IGV exhaust temperature control and CPD- or CPR-biased exhaust temperature control. Are we having fun yet?)
Again, I'm not a thermodynamics expert, nor a GT performance expert, nor a combustion engineer. I can't be of any further help. Except to reiterate data points need to be taken at stable internal operating temperatures (as described above) AND the OEM almost NEVER makes any kind of performance guarantee (BTU/kW) at any other operating condition than Base Load when the IGVs are at maximum operating angle. So trying to get performance data at Part Load, particularly with IGV exhaust temperature control active, is not really worth the effort. My recommendation is to always compare apples to apples--meaning take your data points when the unit is operating on different gas fuels at Base Load. If you see significant discrepancies from what you think should be happening as fuel constituents vary, then I would consider involving the OEM or the packager of the GT for more assistance. And, you would have the kind of data the OEM will be asking for to begin with. Instead of having to run more tests with different fuels to get the data they would likely be requesting.
And, read that GER. The problem with that document is that it tries to cover EVERY machine GE makes in one document, and that's very difficult to sift through and understand. Remember, you're looking for E-class conventional combustor data only, so you can ignore most everything else (the fanciest and newest H-class machines, and F-class machines and even DLN-I E-class machines. That doesn't leave a whole lot of information you have to consider--it's just finding only the relevant information more difficult in a document that tries (and doesn't do a very good job of) being a one-size-fits-all document.
Best of luck!
