Gas Turbine Power Augmentation using Fogging System

[ahung]

Does anyone know or have any experience using Fogging system for power augmentation in gas turbine (501D5) operating in symple cycle? I have some questions:

How many additional MW can you obtain using this Fogging system. One of site condition is the average humidity around 70%

How much demin water do you need to increase the power output?

What are the consequences over the internal parts of the Combustion Turbine for example axial compressor diaphragms and blades using fogging system?

What happens with the heat rate when you get more power using fogging system?

I apprecciate any comments or advices.


Alberto J. Hung C.
Caracas Venezuela




Regards

Alberto J. Hung C
Caracas Venezuela

 

[rmw]

Inlet fogging is a very common thing for combustion turbines in all cycle configurations. The benefits are well accepted in the industry. I can't specifically speak for 501D5 turbines, but for all classes of turbines there are two types, one which applies just enough fog so as to evaporate all the water prior to any moisture coming in contact with rotating turbine parts and others that actually allow the first several stages of compression to run wetted. The latter is questionable in my mind and only your turbine vendor can say whether or not your machine(s) are suitable for that. Me for my part, I never was comfortable with compressor blades running wet.

The heat rate is improved for two reasons; first, the fogging reduces the inlet air temperature by evaporation and the turbine operates closer to ISO conditions. Second, the vapor added by the fogging adds mass flow through the turbine and the turbine is basically a mass flow device, not caring whether the working fluid is water or air.

70% humidity level is a good candidate for fogging.

I can't tell you the added power offhand (others may be able to), and it varies by the minute with the ambient condition variations (humidity and temperature and atmospheric pressure) but as a generality I can say that the payoff must be good based on the number of fogging (and inlet chilling-a different method but the same result) systems I see on combustion turbines in lots of places. I saw one just last week in Canada on the north side of one of the Great Lakes and was surprised to see that in what I considered to be a cold climate.

Try contacting the 501D5-D5A Users group to see how many of their members are already using fogging.

rmw

 

[jlforsyth]

Fogging is always limited to cooling to the prevailing wet bulb temperature as a theoretical low limit. You mention 70% RH, but this can mean many things depending on the prevailing dry bulb temperature. For example, at 35C dry bulb temperature, 70% RH and sea level, the wet bulb temperature is 30C. Inlet fogging at this condition cannot cool lower than 30C and most likely will only get to around 31C under best conditions. Typical effectiveness for a fog system will run around 80 to 85%, that is, it will cool around 80 to 85% of the way down to wet bulb. If all you want to do is cool around 4C, then I guess you could call it a "good candidate". The increase in mass flow through the GT due to added water is almost trivial - it is the increase in air mass flow due to increased density through adiabatic cooling that is significant. Inlet fogging is also not without its risks. No fog nozzle produces a homogeneous droplet size, rather the droplets are produced over a range of sizes. The larger droplets are unlikely to evaporate in time and will impinge on IGV's and row 0 compressor blades, causing erosion. A significant amount of the water will also impinge on duct surfaces, silencers etc. requiring an extremely effective drain system and a lined duct since the demin water is quite aggressive. If the drain system is ineffective and/or fails, a slug of water could be ingested into the compressor causing catastrophic failure. Bear in mind that the inlet velocity going into a GT compressor is up around Mach 0.8 to 0.9 (highest for aeroderivatives) so pooled water near the inlet bellmouth is extremely dangerous. For complete evaporation from typical high pressure fog nozzles, a residence time of around 3s is required. Typical GT inlet ducts that are designed for dry operation will only provide 1-2s at best - all of that unevaporated water will be ingested into the compressor.
The appeal of inlet fogging is low initial cost, not high performance. If you are serious about maximizing power output from your GT's, consider the use of turbine inlet chilling (TIC). A TIC system can deliver much lower inlet temperatures - probably around 10C for a W501D5 - that are independent of the prevailing wet bulb temperature with no risk to your turbine.Granted that the investment is significantly higher, but so is the benefit, so if you evaluate based on $/KW (augmented) and NPV, the TIC system will come out ahead.

 

[toothless]

Mee Industries is a leading in the fogging technology and equipment. They can answer your questions on this subject.

http://www.meefog.com

(I am not affiliated with Mee)

 

[ahung]

Thanks for all of yours valuables comments and advices. I really appreciate all of them.



Regards

Alberto J. Hung C
Caracas Venezuela

 

[NCTHAI]

JLFORSYTH has covered majortiy of points. The use of fogging is not recommendedif you can avoid it. It also leads to corrosion of front end compressor. Another important issue is if do not have good atomisation of water being injected, you have chances of damage to
IGV or front compressor blades. If you want to have approximate estimation of how much power can be gained, run On line water wash and check what happens to output.