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Our's is a new CCPP with 3 new GE MS9001E generators.
<b>Here is the overall CCPP configuration</b><pre>
Natural Gas |--Centrifugal compr 1--| |---GT1--Bypass--HRSG--|
| ----3bar----|--Centrifugal compr 2--|---|---GT2--Bypass--HRSG--|--ST
| |---GT3--Bypass--HRSG--|</pre>
[I was unable to format the ASCII text properly, the forum software kept pulling the GT3 line to the left. In fact it is sharing the same connection as GT1 &2]
The GTs have dual fuel capability (Gas + HSD). Combustors are DLN-1.
<b>The Problem:</b>
If all three GTs are running on baseload, and one of the compressors trips (effectively reducing gas supply to 50% ), and the GT's continue to run on baseload, within seconds the gas pressure will fall and the GTs will trip.
<b>The Wish:</b>
We would like to have "reject to part load" and quick changeover to backup fuel options available at our disposal on any number of GTs so we can have more operational flexibility in designing a scheme to manage this sudden "gas load shedding".
<b>My Questions:</b>
<b>1-</b> In the Island mode, the Remote DCS setpoint would approximate the "predicted island load". This 4-20ma signal would always be arriving at the GT. When the line breaker opens, GT controls will know how to schedule gas to the combustors to minimize frequency excursions. Is this understanding correct?
<b>2-</b> Is it correct to say that "reject to part load" in a "gas load shedding" scenario is equivalent to typical GT "islanding operation" from a controls point of view? ( that is to say, in islanding: reduce load suddenly* to avoid over speed/over frequency; in gas loadshedding, reduce load suddenly* to avoid too low gas pressure). In both cases, controls just sheds load quickly).
<b>3-</b> Is it possible on 9E generators to instantaneously* reject load from baseload to, lets say, half load? (120MW ---> 60MW)? Have you seen this implemented anywhere?
<b>4-</b> Are there any known limits on the amount of instantaneous* load that can be rejected on a 9E?
<b>5-</b> When fuel changeover from gas to liquid fuel is initiated, it takes about 30secs for the Transfer to complete (FSX1=3.3%/s).Lets say at T=0s, Gas ---> HSD transfer is initiated, and at the same time gas pressure starts depleting to a point at T=N seconds that had the GT been running on gas alone, it would trip. What would be an acceptable value of <b>N</b> for the transfer to occur without a flame out/combustion trouble, albeit with a drop in load? Would N change depending on the load on the GT at the time the transfer is initiated? If yes, what would N be for Baseload? At half load? This will come from your experience and I understand these would be estimates at best.
<b>6-</b> If the answer to question 2 is YES, then realistically speaking, is it asking too much of the control system (or even the combustion system) if we try to reject to part load AND do the changeover concurrently?
*by instantaneous I mean in the same time frame as that of a Full load reject or breaker opening event.
<b>Here is the overall CCPP configuration</b><pre>
Natural Gas |--Centrifugal compr 1--| |---GT1--Bypass--HRSG--|
| ----3bar----|--Centrifugal compr 2--|---|---GT2--Bypass--HRSG--|--ST
| |---GT3--Bypass--HRSG--|</pre>
[I was unable to format the ASCII text properly, the forum software kept pulling the GT3 line to the left. In fact it is sharing the same connection as GT1 &2]
The GTs have dual fuel capability (Gas + HSD). Combustors are DLN-1.
<b>The Problem:</b>
If all three GTs are running on baseload, and one of the compressors trips (effectively reducing gas supply to 50% ), and the GT's continue to run on baseload, within seconds the gas pressure will fall and the GTs will trip.
<b>The Wish:</b>
We would like to have "reject to part load" and quick changeover to backup fuel options available at our disposal on any number of GTs so we can have more operational flexibility in designing a scheme to manage this sudden "gas load shedding".
<b>My Questions:</b>
<b>1-</b> In the Island mode, the Remote DCS setpoint would approximate the "predicted island load". This 4-20ma signal would always be arriving at the GT. When the line breaker opens, GT controls will know how to schedule gas to the combustors to minimize frequency excursions. Is this understanding correct?
<b>2-</b> Is it correct to say that "reject to part load" in a "gas load shedding" scenario is equivalent to typical GT "islanding operation" from a controls point of view? ( that is to say, in islanding: reduce load suddenly* to avoid over speed/over frequency; in gas loadshedding, reduce load suddenly* to avoid too low gas pressure). In both cases, controls just sheds load quickly).
<b>3-</b> Is it possible on 9E generators to instantaneously* reject load from baseload to, lets say, half load? (120MW ---> 60MW)? Have you seen this implemented anywhere?
<b>4-</b> Are there any known limits on the amount of instantaneous* load that can be rejected on a 9E?
<b>5-</b> When fuel changeover from gas to liquid fuel is initiated, it takes about 30secs for the Transfer to complete (FSX1=3.3%/s).Lets say at T=0s, Gas ---> HSD transfer is initiated, and at the same time gas pressure starts depleting to a point at T=N seconds that had the GT been running on gas alone, it would trip. What would be an acceptable value of <b>N</b> for the transfer to occur without a flame out/combustion trouble, albeit with a drop in load? Would N change depending on the load on the GT at the time the transfer is initiated? If yes, what would N be for Baseload? At half load? This will come from your experience and I understand these would be estimates at best.
<b>6-</b> If the answer to question 2 is YES, then realistically speaking, is it asking too much of the control system (or even the combustion system) if we try to reject to part load AND do the changeover concurrently?
*by instantaneous I mean in the same time frame as that of a Full load reject or breaker opening event.
