Control.com - Nerds in Control

Dear All,

We manage 2 block of gas turbine 3x100 MW dan steam turbine 180 MW. We have a policy to reduce the consumption of oil fuel in our power plant. One of these policies is to change fuel in power plant from HSD to MFO (Marine Fuel Oil) or residual fuel. So our power plant will be the pilot project to conduct that.

Beside of the hardware installation of MFO (including pre-oil treatment and its waste), we understand that some rung of our Mark V control system should be changed too. Result of our study comparation in the other power plant told that MFO using in GT after loaded 30 MW. So during start up we should use HSD. (It happened during shutdown process too, before zero RPM must be transfer to HSD). But unfortunately, they do not use same Turbine Control (Mark V).

Our questions are:
1. Is the re-design for Mark V (adding rung) only for rung start up and shutdown process that there is transfer fuel from HSD to MFO and its opposite?
2. How the percentage of process transfer from HSD to MFO (and MFO to HSD) is direct, or must there be a hold at some procentage first, and how does the transfer effect our running GT?
3. If we are using MFO as the fuel at GT, is the setting of Turbine protection at Mark V changing or still the same as distillate fuel (HSD)?

We wait for your kindly response.

Thanks,

Aiko

Very briefly, any unit which uses heavy fuel oil (marine fuel oil, bunker, crude, etc.) usually requires the fuel to be heated to flow and to improve atomization. Most GE-design heavy duty gas turbines which operate on heavy fuel oil are required to be started and stopped on distillate, mostly because the heavy fuel oil can't be heated sufficently to flow well enough or to atomize properly during the low fuel flows during starting and stopping.

Further, if a turbine is stopped (either intentionally or tripped) while running on heavy fuel oil the fuel can harden in the lines in just a few hours depending on the ambient conditions and then they have to be manually removed and cleaned. Just because a turbine can be tripped while running on heavy fuel oil, there are usually special piping components to assist with flushing the lines in the event a trip occurs while running on heavy fuel oil. There are considerable modifications for operation on heavy fuel, including fuel nozzles and hot gas path components.

The point at which the transfer from distillate to heavy fuel oil is made is dependent on many factors including pumps and auxiliary equipment; I've seen it occur at FSNL (Full Speed-No Load) and at any load above that.

And, yes, usually turbine inlet temperature (sometimes called "firing temperature") must be reduced if there is the possibility of heavy metal deposition (even with treatment) on turbine nozzles and buckets. But, it depends on the expected fuel characteristics.

GE and many companies can provide quotes for an entire system, including fuel treatment equipment, fuel heating equipment, and all control system modifications to ensure optimal turbine life and performance. I highly recommend that you consult with a competent firm to assist with the conversion.

Thank you very much for your kind response, I would help our conversion project.

So sorry, seem we have further questions from your explanation. Why did you say that "firing temperature" must be reduced? And how?? Because as far as I know, we can't control turbine inlet temperature or "firing temperature". I'm a little bit confused about this. Our GTG is in outdoor area, so I think it's difficult to conduct that.

Thank you for your attention...

Regards,

Aiko

"Firing temperature" and "turbine inlet temperature" in this case are the same: the temperature of the hot gases entering the first stage of the turbine.

This temperature is controlled by controlling the fuel flow-rate. When the unit is operating at rated output, the axial compressor Inlet Guide Vanes are open to their maximum setting, and increasing fuel flow-rate raises the temperature of the hot gases entering the first stage of the turbine; decreasing the fuel flow-rate decreases the temperature of the hot gases entering the first stage of the turbine.

The control system can be programmed to do this automatically when heavy fuel oil is selected. When the unit runs on distillate, it will have the "normal" control parameters; when it runs on heavy fuel oil, it will have a slightly different set, based on the analysis of the expected fuel to be burned in the unit.