We have 3 GE Frame 9E machines control is of GE Mark-VIe. On each machine we have HRSGs. We want to control exhaust temperatures due to some limitations in metallurgy of our HRSGs. Normally machines are running on base load on Temperature control FSR.
TTRX is the reference value for IGV to operate for controlling of temperature values.
Algorithm that is used for the calculation of TTRXP (Primary Exhaust temperature control reference)
The primary exhaust temp. control reference is calculated as below:
TTRXP = TTKn_I - TTKn_S * (CPD - TTKn_C) + TTRXDSP + CT_BIAS + WQJG.
& for TTRXS (Secondary Exhaust temperature control reference is calculated as below:
TTRXS = TTKn_I - TTKn_M * (FSR - TTKn_K) + TTRXDSP + CT_BIAS + TNH_BIAS + WQJG.
Is this possible? Can we use (-ve real time values) for TTRXDSP so that it can limit exhaust temperature or if there is any other option available to limit exhaust temperature for the protection of HRSGs?
This is a question best answered by working with GE to ensure you are maintaining the required protections for the turbine, compressor and combustion system. Especially if the turbines use DLN combustors.
Really, though, whatever you do to try control or limit exhaust temperatures by using the turbine control system is going to limit turbine-generator power output--and reduce efficiency (heat rate) of the turbine. Is that an acceptable long-term fix for an HRSG metallurgy problem? Is steam production more important than electricity production and fuel costs?
The GE operation in Belfort, France, has responsibility for the GE-design Frame 9 heavy duty gas turbines (Es, Fs, HAs). They have proven to be a fertile incubator for non-standard designs--but beware: They can quickly and needlessly over-complicate anything they touch. You might end up with what you want--but it may be a mess to maintain and troubleshoot.
So, it would be best to invest the time and energy (and it's going to take a LOT of both--plus patience) to find the right group in Belfort to help you with understanding the limitations of what is or isn't possible and then to help with developing a simple and elegant solution (something they haven't always been able to provide).
In the end, you might wish you had corrected the HRSG issues instead of trying to create a work-around with the turbine controls.