Water Quality for Turbine Inlet Cooling using Evaporative Cooling 1

[gtsim]

Hi Forum,

I understand (from the literature on the web) that we can use raw water for evaporative cooling in gas turbines. If so, what is the quality of the raw water that we can use before treatment is necessary? If treatment is necessary, what is the treatment that is required?

Any information will be very much appreciated - thanks.

Best wishes,
gtsim

 

[rmw]

Is this referring to evaporative media cooling, or straight evaporative cooling. If the latter, then suspended solids have to go somewhere, and that is usually downstream.

rmw

 

[gtsim]

Hi rmw

This is evaporative media cooling rather than evaporative cooling, which I believe is also know as fogging. I understand that with fogging system we must use demineralised water. Also some OEMs do not allow fogging due to potential fouling and damage to the compressor.

Regards,
gtsim

 

[toothless]

An evap cooler manufacturer can answer this question. When running the system you will have to operate it similar to a cooling tower using a bleed to avoid concentrating the contaminants.

 

[rmw]

Google for Munters and see if their site contains any useful information.

rmw

 

[gtsim]

Thanks Forum. Shall follow your suggestions.

Regards,
gtsim

 

[abeltio]

water into the compressor must always be demin water, period.

any other will either foul the compressor or damage the hot gas path.
as an additional "benefit" the exhaust thermocouples will fail in a very short time...

this is like pouring tap water into the battery of your car.



saludos.
a.

 

[gtsim]

Thanks saludos for your response.

I agree you need demin water for fogging due to the reasons you have stated. But with evaporative cooling using wetted media, I undetsand, you can use raw water. Munsters web site, as suggested by rwm, gives the required water quality. Also some manufacturers do not allow fogging due to potential damage to the compressor (please see Turbin Inlet Cooling Association website).

Regards,
gtsim

 

[toothless]

I respectfully say that "abeltio" is incorrect. If you use demin water in an evaporative cooler, then your entire inlet duct had better be constructed of stainless steel or plastic. The demin water will eat it up.

Demin water is used for foggers, cooling water make-up type water for evaps. The spec for our evap cooler (circulating water) is given below. This would be after the water has "cycled up" about 6 times.


H 7-9
conductivity (in micromhos) 2000 to 2500
calcium carbonate 100 to 250
total alkalinity 100 to 250
SiO2 <100 ppm

 

[gtsim]

Good point toothless, indeed demin water absorbs mineral etc. This raises another question for me. If we used chillers to cool the inlet, at high humidity we get water vapour condensing. I am correct is assuming this water vapour is effectively demin water and therefore the ducting associated with this water should also be made from stainless steel or plastic?

Regards,
gtsim

 

[toothless]

We haven't gone as far as chilling our inlet yet, but you will definitely condense the moisture out of the air. You can do the calculations to determine if the amount of moisture you condense is a significant fraction of the total water volume being circulated (that volume will be very large). Off the top of my head I think the condensed water volume will not be enough to significantly affect the water chemistry.

Munters, Donaldson, or Braden could answer this.

 

[gtsim]

Thanks for your response. Well, condensation can be quite significant. We developing gas turbine simulators and currently we are including turbine inlet cooling, hence these questions I am asking. The analysis for a Frame 6 operating at 35C and 60% relative humidity (approx 28C wet bulb temperature) shows a water demand for evaporation of about 28 tonnes/day for wetted media, about 30 for fogging and a staggering 110 tonnes/day (condensation) for chillers. The condensation from chiller can be over three to four times that required for evaporative cooling systems. The cooling load is 9MW.

In tropical countries the humidity can get even higher and therefore the condensation even greater. I suppose this level of condensation would require special ducting to handle this water as it should be treated as demin water? Your response will be very much appreciated - thanks.

Regards,
gtsim

 

[gsfitzsr]

I have some experience with chilled inlet gas turbine packages in Latin America. These units were 40MW with dual pass chilling coils on the filter house inlet. The amount of condensate created at full power was incredible. We captured that water and routed it back to cooling towers which saved on water use. Our inlet systems were not stainless and stood up for years. Filter elements were special materials to withstand high moisture levels.

As far as using raw water in your evap system: I doubt the OEM would allow it. Anything you put into the engine (air,fuel,oil) must be as clean as possible. Would you drink it? If not, then don't put it in the inlet. OEM's are known for creating specifications that are strict. They have to warrant these multi-million dollar machines, all over the world, various fuel qualities, good maintenance poor maintenance, you name it. If your machine is in a industrial area it may suffer due to the poor air quality. You can only filter so much.

Good Luck

Greg FitzGerrell
GSF Services Inc.

http://www.infrared-gsf.com

 

[gtsim]

Thanks Greg,

Appreciate your response, but I don’t think I will drink that water (as demin water tastes horrible and absorbs minerals from the body – I am told).

I am too sure about the effect of water purity - as I understand it some OEMs do allow fogging as means of turbine inlet cooling. I ‘believe’ this could be due to the demin water entering the compressor and attacking the blades? This is augmented by the comment by “toothless” above, where demin water can attack metals. It is interesting to note that your inlet had lasted. I suppose there are deflector screens to prevent this water from entering the engine as we would have with wetted media using raw water?

Best wishes,
gtsim

 

[CWCT]

I’ve got a few things to add to the discussion, Raw water or Demin-water is used in evaporator coolers. If demin-water is used a stainless steel sump is typically used. Then the only issue is if carry over occurs the duct work must have a good epoxy coating. As for Fogging Demin-water must be used, a the water is evaporated in the air stream. If other water is used or the air is not clean plating of particles will occur in the compressor. If wet compression is used the water is evaporated in the compressor, this has been applied to GE LM6000’s, GE LM2500’s, GE 6B’s, Alstom GT-24’s and GT-26’s, Siemens W501D5’s, V84’s, V94’s without issues. The reason some manufacturers are against fogging (which is only on certain machines in their product lines)is poor application and marginal blade design, as they also didn’t want operators to use evaporative cooling or water wash systems with out inspections When water is collected on surfaces in the ductwork and not removed from the air-stream the water will become entrained in the air as large droplets and cause blade damages. The size of the droplet that causes damage is up for debate. Online/Offline water wash system must have droplets of 100 to 140 microns or they do not clean the compressor. If raw water is used in evaporative media if total dissolved solids are high you will have clogging of the evaporative media will occur overtime. With evaporative media the important thing is to keep the water in the evaporative media section of the ductwork. I hope that helps you some.

 

[gtsim]

CWCT,

Indeed your comments are very useful and very much appreciated.

The immediate question that arises is why does the compressor damage you refer to not occur in the other engines you have mentioned with fogging or wet compression? Wouldn’t such entrainment of water occur in these engines and cause compressor damage. Wouldn’t demi water attack the compressor blade material during continuous use or is the blade material and other engine components exposed to demi water resistant to such attack?

With respect to wet compression on the engines mentioned, how long have these engines operated with wet compression. Is it a sufficiently long period of time to conclude that there are no issues with wet compression on these engines?

It also seems from what you say those OEMs who object to evaporative cooling also object to compressor washing? Is this correct? Could you possibly elaborate, e.g. what are they looking for during the mentioned inspections?

Thanks and best regards,
gtsim

 

[CWCT]

Gtsim,

The typical blade materials in the compressors are not made of high carbon materials, thus they are not going to be affected by the demin-water. If the droplets are kept small enough and water removed from the duct as it collects on surfaces fogging or wet compression can be applied without causing damage to compressors.

The lead GT-24 puts on about 6000 hours per year with wet compression and has been in operation since 2001. The others typically operate between 1500 and 2500 hours per year with wet compression on them, ranging from recent install to 12 years back or so.

On the OEM’s, they have several points of view depending on whom you talk with inside the individual companies. For instance the Germans only allow fogging, wet compression, chilling, or evaporative media, if they are supplying it. Their general statement is “It must be approved by engineering”. The only way for that to occur is if they supply it. This is only an issue if you have a L.T.S.A. or the lender requires OEM approval. This is also the same for the folks out of Switzerland. Now the OEM in Florida has a different approach for the machines they control, it seems the Customer is always right provided they follow prudent engineering guide lines. And for the other Major, they see benefits to all types of cooling if applied correctly. The issue they had was with a specific model machine in which the blade design was marginal, and yes the objected to prolonged online compressor washing their bulletin put out stated no more than 100 hours total operation of cooling and online water washing without inspection and dental modes made of the compressor blades, if issues occurred they would do a stress relieve at the first row blade hub area, then you could continue on with your operation. One thing to keep in mind is most OEMs would prefer you to buy a new unit instead of augmenting the one you currently have.

If you are considering chilling the air, if you keep the air velocity low enough you can catch the water in drain pans and prevent water carrying down stream.

I hope that helps some

 

[gtsim]

Thanks CWCT for your detailed response,

Indeed OMEs want us to buy new engine and if we won't then they would want us to buy TIC from them. However, as operators we should alway keep our options opened and select what makes best commerical sense.

Thanks once again and best regards,
gtsim

 

[CWCT]

If you check out the difference power conferences (PowerGen, IGTI, American Electric Power) you will see a lot of presentations on fogging and wet compression, not so much on chilling as it is not as controversial. On the subject of wet compression, up to 3% of ISO flow rate has been introduced into CT’s. With this much flow erosion of the blades did occur as far back as the fifth row of blades, but the erosion was not enough to prevent the continued use of the wet compression. In fact the owner looked at the cost of replacement blades over a period of time versus the benefit gains and found the wet compression won out. Did you know the first application of wet compression was done to get jets off aircraft carriers? Later on when the 747 was launched wet compression was used to get the plane airborne on the shorter run ways at the time, the same pump used for this application is now in use for wet compression and online/off line water wash systems.

 

[gtsim]

Yes, I agree there is controversy about fogging and wet compression.

As an operator I will be a little concerned about the compressor blade erosion due to wet compression as this could lead to other damage (e.g. compressor surge due to increase tip clearance, imbalance resulting in increased vibration) and hence engine failure. I would have thought it prudent not to anything to the engine that gives rise to blade erosion.

Returning to fogging, if wetted media effectiveness is about 0.95, then the benefits of fogging would be marginal????

Yes you are correct - water-methanol injection was used on aircraft engines to augment the take-off thrust. I didn’t know that the same pump for used for wet compression and wash systems of industrial gas turbine.

Regards,
gtsim