We have GE frame 9e gas turbine.We have protection of transfer of fuel from gas to HSD in case of gas temperature low.

What are the problems associated with the low gas temperature up to 6 Deg C

Any erosion etc in Gas CV and SV
Any Loss in output.

Please comment...

 

We don't have enough information about the unit and conditions at your site. Do you have conventional combustors or DLN combustors? Usually, DLN combustion systems have a requirement for a minimum of 50 deg F of superheat on the gas fuel in order to prevent primary zone reignitions while operating in Premix Steady State combustion mode.

Even turbines with conventional combustors can experience severe to catastrophic failures or nuisance exhaust over temperature trips if condensed gas liquids make their way into the combustors. An old rule of thumb was that a quart of condensed gas fuel liquids making their way into the combustors of a Frame 5 was equivalent to about 10 MW or more of increased output, if I recall correctly (or about a 50% or more output increase in a very short period of time!). Just imagine what that could do a combustor or a turbine section.

When your turbine was installed, the expected gas fuel supply conditions might have caused some concern and so the protection was added to transfer to distillate to prevent damage to the machine.

Conditions might have changed since, so you can gather current fuel characteristics and forward them to GE or the packager of the unit(s) at your site and ask them for a review.

But, those are some of the more typical concerns with gas fuel. You may also be burning some mix of gas fuel and other gaseous fuels that might have a tendency to condense as they pass through the valves (SRV, GCV, etc.) and nozzles and cause potential problems.

You might find some information in the Control Specification provided with the Speedtronic turbine control system. (And you might not; it is kind of hit or miss on these kinds of things.)

But, we just don't have enough information to answer this question here. It is recommended you study and understand the fuels being burned at your site versus what was expected when the units were first installed (or the units were converted to run on the fuels!) and get some analysis from GE or one of the packagers of their turbines.