Hi All,
We are operating 2 frame 6b gas turbines manufactured in 1987 and I have few questions around compartment ventilation system. Any information would be highly appreciated.

01. There is a ventilation fan mounted in-between accessary compartment to Turbine compartment (88BT). Does the design look into pressurize the Turbine compartment? the only settings I could found was the fan start and stop settings from compartment temperature switches.

02. Fan installed is Solvent- Vent HMP 50 model. does anyone have the drawings/performance curve for this fan?
03. Any performance/reliability improvement projects done of this fan. May be installing another fan or any external fan installation.
04. Compartment temperatures close to roof levels are around 150C. is this normal?

thanks,

Ken

 

@KEN,

You might could ask GE in Belfort France if they have any records from that period.

Generally the vent vans drew air into the Accessory Compartment (through gravity-operated dampers on the door(s)) and pushed the air into the turbine compartment. It was difficult to open the Accessory Compartment doors because there was a slight negative pressure (vacuum) in the Accessory Compartment, and the Turbine Compartment doors would "jump" out at someone if they weren't expecting it (because of the slight positive pressure) in the Turbine Compartment.

High temperatures in the turbine compartment, especially at the roof, were not uncommon. Sometimes in the neighborhood of 275 deg F to 300 deg F (135 deg C to 150 deg C)--especially if the ambient temperatures were above 95-104 deg F (35-40 deg C). If the machine is dual fuel (gas/liquid) or liquid fueled the Atomizing Air temperature will add to the compartment temperatures, as well. And, of course the axial compressor casing, combustors and turbine casing will radiate a lot of heat into the Turbine Compartment. I don't recall what the temperature switches were set for. Most of the machines I worked on started 88BT when flame was detected in the machine, and then a temperature switch stopped them after a shutdown or trip. (It should be noted that it's NOT recommended to open the Turbine Compartment doors to help accelerate the cooling of the Turbine Compartment. That will just cool the axial compressor casing faster than the compressor rotor and could cause rubs and blade damage. Also, if the door are open and 88BT is running it won't move air in the compartment very well--it will just blow out the door (the path of least resistance).

Check to make sure any dampers (gravity-operated, usually) in the Turbine Compartment are opening as they should. Some may even be latched open continually and close when fire extinguishing agent is discharge into the compartment when a fire id detected--and OFTEN the latches vibrate open, or they weren't latched very well to begin with, or they weren't latched open to begin with, or the chains or the hooks rusted and dampers closed (due to gravity). That will mean the air being blown into the Turbine Compartment will not be exiting the compartment as it should be, which means cooling will be reduced. A lot of time dampers are neglected for long periods of time; a good greasing of the pivot points and inspection of the mechanisms--and any CO2 latch mechanisms--will reveal problems due to age and neglect which can be pretty easily resolved to help lower Turbine Compartment temperatures. (By the way, if air is unable to escape the Turbine Compartment normally, that means the proper air flow into and through the Accessory Compartment will also be inhibited, which means Accessory Compartment temperatures will be higher than normal, and the compartment doors will be easier to open (not as much vacuum keeping the closed if the fan isn't moving the normal amount of air).

Finally, it's not uncommon for 88BT to be rotating in the wrong direction. In fact, it happens fairly regularly. There should be an arrow in the outside of the blower housing indicating fan direction of rotation--but it often gets painted over or the rivets holding it in place rust and the arrow falls off. So, make sure the fan is rotating in the correct direction.

Again, the typical air flow--as indicated on the Cooling and Sealing Air P&ID drawing!--will be drawn into and through the Accessory Compartment and blown into and out of the Turbine Compartment. Typical. But, sometimes the Belfort Boys had a better idea--so check the Cooling and Sealing Air P&ID to be sure what they intended....!



The tube-axial fans were pretty powerful, as I recall. I don't recall what kind of current the motors drew, but that could help one sort of reverse engineer the amount of air that was possibly moved.

Perhaps someone here has some original blower manufacturer nameplate data they could share.?.?.?

 

Hi WTF,

Thank you for the above information.
I managed to get the model and the fan curve. It is designed for 3.6m3/s at -90mm h2o total head. Model is HMP 50-6-21VA from Solyvent Ventec.

Also, one of the documents I read referred BT fan as pressurization fan and that confused me a lot. With the current design, it does pressurize the turbine compartment, but is it a requirement? (may be good for flex seal) The newer 6B designs I worked with has two BT fans mounted on the top of Turbine compartment where turbine and auxiliary compartments are maintained in a negative pressure.

Any further information would be much appreciated.
regards,

Ken

 

@Yoganak,

Compartment cooling and ventilation has evolved over the years--especially with the advent of DLN (Dry Low NOx) technology, with so many additional gas manifolds, piping, valves and nozzles causing potential for more leakage. Also CFD (Computational Flow Dynamics, I think it's called) studies have also evolved.

Originally the main purpose of 88BT was to have cooling air flow through both the Accessory and Turbine Compartments--using a single fan. This required drawing outside, ambient temperature air into one compartment (ostensibly the cooler compartment, relatively speaking) and blowing that same air into the turbine compartment--again, primarily for cooling purposes but also to try to force any combustible gases/fumes which might accumulate in the Turbine Compartment out of the compartment. Many older Frame 5s only burned distillate/liquid fuels and it was thought the vapors from any leaks could be easily blown out of the compartment by 88BT flow, which would also cool the Turbine Compartment.

Enter natural gas fuel (and other combustible gases used for turbine operation) and, well, a LOT of people were simply terrified of the possibility of explosion--including local and national regulatory agencies (a lot of natural gas burned outside of North America IS NOT odorized, and it's basically smell-less--hence some of the apprehension around gas fuel, particularly natural gas).

Particularly with the advent of DLN combustion systems, the size of the Turbine Compartment (for new machines) increased (due to the volume of piping!) and the old 88BT arrangement just wasn't going to work, even for cooling. AND, with 88BT there was no redundancy (because there just wasn't room for a second fan in the typical location). When many gas turbines were used primarily for peak load shaving and only ran the equivalent of a few days a year, a single ventilation fan wasn't a real problem (until it had to be changed or repaired!!!). But, now that gas turbines run for weeks, months even years redundancy is very important.

So, there are lots of reasons newer machines have different Turbine Compartment ventilation schemes, and philosophies. Technology; changes in combustion systems; changes in technical standards and regulations; redundancy requirements; and so on. In my experience many Accessory & Turbine Compartments use negative pressure to (primarily) remove combustible gases (from fuel leaks) and for cooling (drawing ambient-temperature air into and through the compartment, which means the air temperature is slightly lower than drawing it through the Accessory Compartment before passing it through the Turbine Compartment). Also, many locales and insurance companies now require hazardous gas monitors for the compartments--and it's apparently easier to sample the discharge of a fan drawing air into and through a compartment before it's discharged to the atmosphere. (I personally have a problem with this line of thinking because the hazardous gas sensors get caked with dirt and fumes and require near constant attention, which usually requires shutting the machine down.... BUT, apparently the CFD studies prove otherwise, so, who am I to argue? BUT, I can tell you sites get VERY upset when they are told they have to shut the machine down (repeatedly) to clean those hazardous gas monitors which are sensitive and touchy and prone to give false readings (high as well as low--part of the technology which hasn't kept up with requirements of the process (the weak link, as it were)!

Anyway, that's my take on things. Oh, one more thing--DLN combustions systems radiate a LOT of heat into the Turbine Compartment, so cooling is very important. Those little tube-axial fans used for 88BT move a lot of air, BUT, not enough for sufficient cooling in the Turbine Compartment. (I also believe that many Customers complained--a lot--about the Turbine Compartment doors opening so quickly when the compartment is pressurized for cooling and ventilation. It can surprise people the first time (some even the seventh time...) when the door "jumps" open and nearly knocks them down. (I've been screamed at for this very "offense.") And, because of the temperature of the air in the compartment blowing out when the door is opened people can (and have) automatically assumed (and we all know how to spell ass-u-me...!) there is some kind of severe leak in the Turbine Compartment. That's a couple of the "political" reasons for some of the changes to compartment ventilation. (I, for one, am glad the compartment doors are difficult to open when a compartment has a negative pressure for cooling and ventilation. Keeps the riff-raff out. If you know what I mean. ;-) )

 

Nice one WTF.
Thank you very much!