Dear

I have a question regarding frame 9E gas turbine just for general knowledge purpose.The question is:

1) How many impulse and how many reaction stages do we have in frame 9E gas turbine and what is the reason for that number of stages?

2) some compressor stages have special coating on specific number of stages i-e stage 5 to 10 in frame 9E. What is the reason for that special coating? I mean why there is no coating on other stages.

Thanks
Izhar
[email protected]

 

Dear,

1) A GE-design Frame 9E heavy duty gas turbine typically has three turbine stages, and as many as seventeen axial compressor stages. Generally, the turbine buckets/blades in most turbines of any type these days are "blends" of impulse and reaction types. The buckets/blades may be impulse near the base (the "root") and reaction near the outer end. This allows the maximum forces to be developed as the gases are expanded through the turbine section--especially those turbines with limited numbers of stages.

2) I believe you are confusing turbine stages with axial compressor stages. As air is compressed it is heated, and depending on some ambient conditions (humidity; contaminants; etc.) the wear on certain axial compressor stages can be higher than on others. So, some axial compressor stages may have particular coatings that others do not require. Coatings may also be applied for other reasons (to reduce air flow pulsations and to add rigidity to blades).

Unfortunately, most manufacturers don't do a very good job of documenting in the manuals provided with the turbines (and axial compressors!) the details of why sections are coated with this or that coating--or why not--and of the details of the design/construction of the components. A lot of this is considered proprietary and provides the manufacturer with added benefits that others can't provide, hoping that owners will keep purchasing parts from the OEM rather than from third-party providers.

Many times these third-party providers will have more information they will share about the OEM's designs/practices in order to promote their products over the OEM's. One has to take information where one can get it, applying the appropriate amount of critical analysis and thinking before just accepting everything.

 

Thanks CSA for the detailed response. It helped me a lot.

 

Izhar,

Though CSA has provided enough information, you may consider reading GER-3569G--"Advanced Gas Turbine Materials and Coatings" (page no.21 contains information regarding compressor blade coatings).

SB

 

Hello There,

Compressor Section
Stage 0-1 C450 compressor bladeing (carpenter custom 450) i.e. 15Cr,6Ni.

GECC-1: This material provides corrosion resistance and significantly increase the strength of blades, with application of GECC-1 on stage 2-6 (a thermal coating), fouling a lesser tendency to occur and build up is more easily washed off coated blades.

Turbine Section: New tech. stage -1 bucket made from GTD-111*. In-738 used on stage 2 buckets with cutter teeth.

Actually GE used In-738 as first stage blade material 1984, when it was replaced by GTD-111. It was specifically designed for land based turbine rather than aircraft gas turbine.

Explaining the superiority of GTD-111: This alloy can be directionally solidified in form of large hollow blades. Also owing to single crystal (SC) castings, all grain boundaries are eliminated from the microstructure, and there is no need of using C, B, Zr, and Hf which were used earlier for grain boundary strengthening. This helped in raising firing temperature.

GECC-1 coating: The raising of air temp. through compressor vaporizes any moisture by stage 7 or 8. For this reason first 2 stages are GTD-450, which is the most corrosion resistant compressor material. hence up to stage 7 blades are coated with GECC-1 to prevent any damage or degradation due to moisture content. In your system I hope this coating is for stage 2-6.

I hope this will be of some help to you.

Regards,
fluidflow