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Water Quality for Turbine Inlet Cooling using Evaporative Cooling

Water Quality for Turbine Inlet Cooling using Evaporative Cooling

Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)

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

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

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

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)

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

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

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.  

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

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

rmw

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)
Thanks Forum. Shall follow your suggestions.

Regards,
gtsim

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

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.

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)
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

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

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

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)
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

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

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.

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)
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

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

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.
www.infrared-gsf.com

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)

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

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

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.

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)
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

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

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

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)

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

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

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.

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)
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

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

gtsim
If the effectiveness is .95 then the only benifit from fogging would be its very low airside pressure loss.  Typically fogging is less than 0.1 inwc, with wetted media at .95 you'll be at least 0.4 inwc.  On a retro-fit fogging is normally lower cost than evaporative media.  If elevated inlet you must account for the weight on the structural members. Location of the media and fogging arrays is also a consideration, if media or fogging is placed upstream of the filters, then the moisture effect on the filters will need to be evaluated.  If media is installed upstream of the filter, then dirt entering the media will become clogged and the media fill will require replacement.  Both systems will require maintenance of pumps.  

Back to the wet compression, you are correct if not installed properly you can induce all kinds of problems.  Uneven instroduction of water will result in casing distortion.  One Turbine manufacturer will give you new blades if wet compression is shown to have caused blade issues.  Combustor stability and dynamic pressure are also concerns.  Compressor surge and other issues must be evaluated before applying wet compression.

I worked on a project in the early 90's that chilled the air to a Frame 7 down to 39F.  We had no issues with the CT, but the liner panels in the HRSG came off.  After doing a RCA on the unit it was found the panels were not design for the mass flow at this lower temperature.  Just goes to show you must look at the BOP when looking into plant augmentation or modifications. There is not a one size fits all approach when it comes to power augmentation systems, each one has its own niche.

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)

Thanks CWCT, and this discussion is turning out to be a very interesting one. No doubt you’re very knowledgeable on this subject.

Indeed high inlet losses with wetted media would be an issue but I don’t see it as a show stopper. I understand, and why I asked this question in this forum, that wetted media can use raw water where as fogging requires demin water. Therefore there could be reduced OPEX with wetted media to compensate for the higher pressure loss. This might be too small, I don’t know? We develop gas turbine simulators including turbine inlet cooling (wetted media, fogging and chilling). Now that you have raised this I shall see what the impact is. But as you quite rightly point out each site has to be looked on its own merit (“one size doesn’t fit all”).

Thanks for your very useful comments on wet compression, but considering that chillers can reduce compressor inlet temperatures to below 10 degC why bother with wet compression? Chillers doesn’t have any of the risks of wet compression and the self contained nature of the gas turbine is preserved, however in humid climate it would produce a significant amount of (condensate) water which has to be disposed of as stated by ‘gsfitzsr’. Of course if the chillers are of the vapour compression type then the parasitic losses will be significant – but would be very small with vapour absorption system provided a suitable waste heat source is available.

On your (1990) project, I am a little surprised that you when down to such low temperatures (39F=3.89degC). The resultant high humidity at the compressor inlet and such low temperatures would risk the formation of ice and can damage the engine?

Best wishes,
gtsim

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

gtsim,
Why bother with wet compression?  Good question.  Since wet compression works basically by evaporating water in the compressor as long as the inlet temperature is above 45F your gain in power is constant.  For Frame machines a good rule of thumb is that for every 1 GPM of water put into the compressor you will get 160 kW of additional power,  In simple cycle frame applications for each 1% of mass introduced the heat rate is reduce by about 1.25%, and the NOx is reduced on conventional combustor machine about 25%.  As an example take an 80 mW (ISO) class machine operating in simple cycle with a 95F dry-bulb 73F wet-bulb design point with no cooling its output would be approximately 70mW.  Put fogging on the machine, say 21 GPM, you will have about 5mW more power with a 2.5% reduction in heat rate, add wet compression say a 1% system you would add another 42 GPM of water and gain an additional 6.7 mW of with a reduction in heat rate of another 1.25%, so you total power gain would be 11.75mW for a total 0f 81.75 mW with a reduction in heat rate of 3.75% at the design point.  Take that same machine and chill it to 50F using electrical chillers.  As a net gain one would expect no more than 15% improvement in output with little to no impact on heat rate. So your output would be 80.5 mW. The chiller system would require about 200 GPM of make-up water for the cooling tower, plus maintenance of the rotating equipment.  One could install chilling and wet compression together and get 80.5 mW + 6.7 mW to get a total of 87.2 mW gain. Also consider the plant will not always operate at design point, thus the net gain in output will vary with fogging, evaporative media, and chilling, so one would need to look at the net gain over the expected plant operating time. Now in most cases the fogger and CWCT will cost about ¼ to 1/3 of the chiller system, so one might consider it on mature robust machines, by weighing all the risks versus the rewards.  Just a side note the LM6000 has wet compression as a standard offering as E-Sprint.

The nice thing about absorption chillers are the very lower parasitic losses, they do tend to have higher maintenance cost, and do not like to operate at part load conditions, so a combination of absorption and compression maybe an attractive method.

The 1990 project was actually designed it to cool the inlet air to 42F.  The owner had been warned of the potential for icing and decided to experiment with temperatures,  In theory icing occurs due to the acceleration of the air as it is going into the compressor.  In the different papers presented on this topic, the temperature depression is between 8 and 10F. In this case icing did not occur, but you are correct there was the possibility.

Hope this helps you, but may have only raised more questions which is good also!

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)
Thanks CWCT, more good stuff!

Your dry and wet bulb temperature gives a relative humidity off about 35%, which I would consider to be too low. For example, in the tropics the humidity rarely falls below 60% but the ambient temperature would be about 30 to 35 DegC or 86 to 95F. This would give a wet bulb temperature of about 28 DegC or 83F. Thus your gains with evaporative cooling will be significantly smaller?? Electrical chillers would not perform much better because of the level of condensation will be great and most of the cooling load will be use to produce the condensate rather than cooling the inlet air. Hence, parasitic losses will be significant. This is where I believe absorption chillers win and would be hard to beat on performance. I do agree that the CAPEX of chillers is an issue and would like to see them reduce significantly.

In general, I still feel the potential compressor damage using wet compression is too great a risk. Although you say OEMs will replace any damaged blades, would they replace the engine if it surge due to such compressor blade erosion. I doubt very much that they would compensate for the unscheduled downtime and resultant lost revenue/profit, which could easily wipe out gains we would have made using TIC. I would also be concerned that the OEMs would try to lock us into buying TIC systems from them rather than from third parties as they would be unlikely to offer such blade replacements in this event.

Yes, I was aware the LM6000 sprint uses wet compression on the HP compressor but the later engine, LMS100, uses an intercooler.

I agree that combining TIC technologies would be the answer, but would propose the following: Use an absorption chiller to cool the inlet air and an intercooler such as we find on the LMS100 (or RR WR21) to reduce the compression work. The heat rejected from the intercooler can be used to drive the absorption chiller.

Of course, your comments and suggestion are always welcomed.

Best wishes,
gtsim

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

gtsim,

You are correct on the higher humidity reducing both the fogging and chilling system attractiveness in high humidity areas of the world.  I went back and took a look at all of the numbers on operating hours closing in on 300,000 hours of operation without detrimental blade or unit availability issues, but nevertheless your concerns are valid.  The wet compression systems do require more attention to be paid to the operating conditions than chillers.  In our analysis of worse case scenarios of failures, the wet compression and chiller systems both have some very detrimental issues, all of which can be guarded against.  Say for instance you have tube failure on your cooling coils, from a stray bullet, how much water will be sprayed into the engine before it is notice?  Yes, I have seen that issue and others similar to that. For the wet compression say half the nozzles plug on one end of the arrays, how do you prevent damage due to the uneven loading on the blades?  

You are absolutely correct on the OEM only supplying the blade and not covering other cost, and they would want to sell you the TIC to be eligible for the blades, etc…  The last few contracts I’ve seen from OEM’s specifically call out that no consequential damages are allowed on complete new units.  If you have a LTSA with an OEM on your units you may want to examine it closely.  I’ve seen these have clauses that cause owners great pain, such as modifying fired hours, etc… which make it harder for an owner to justify any type of TIC.

There is not doubt your approach of a chiller and intercooler would have great benefits.  Keep in mind the issues with part loading an absorption unit.  Also the amount of cooling water required for an absorption unit is higher than for a mechanical chiller, so you higher wet-bulb will have an effect on cooling tower size.  I’ve not looked into an intercooler but would question if the OEM would bless the use of it.  I would image if you need the power or can sell the power the addition of a chiller and an after cooler would have a reasonable payback as compared to a new unit.

One thing we have done in the past to help customers select what type of power augmentation they what to use was to make a table with benefits, cost, risk, payback, and incremental cost, etc...  This can be a lot of work, but certainly the customer will end up with a selection they are comfortable with.  The “bean counters” do not typically agree with us “engineering types”, so we have seen the “bean counters” select something that may not be what us “engineering types” would want to install.

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

(OP)

CWCT,

Thanks once again for the useful information provided and it is very much appreciated.

Why do you say that there are issues with off design (part load) operation using absorption chillers? Gas turbines operate over a wide range of ambient temperatures and powers without any major issues. Do you mean there are concerns with the transient performance using absorption chillers?

I agree that bean counters do not see the technical issues clearly as we techies do. I should know as my other half is a bean count. However, I do consult her on financial issues and I think it is partly our fault as we do not pay enough attention to what they do. It is quite elementary what they do and we can easily make the case provided we do the bean counting for them and present it in a format that they are familiar (i.e. do not include too much technical information but emphasis the business case).

It is interesting that you do such work as apart of the services you offer. It is quite laborious as one would need to consider ambient temperature data over a year or more on a day by day basis to determine the most suitable TIC technology. We have developed gas turbine simulators that facilitate such analysis.

Thanks once again.
Best wishes,
gtsim

RE: Water Quality for Turbine Inlet Cooling using Evaporative Cooling

Gtsim

The main issue with part load conditions is the ability of the absorption machine to keep the concentrations correct in Lithium-Bromide chillers.  Most of the manufacturers will not tell you there is an issue with part loading, but they will hint at it.  Much in the same way as I have suggested having both a absorption and electrical/steam chiller for the cycling.  The other issue with the absorption unit is starts and stops, the maintenance cost will go through the roof due to corrosion issues with tubes. One service tech put it this way to me “This is a balanced chemical process, upset the balance point and issues are abound.  Keep the balance and all will be well.”   The other issue is there are a few and far between service techs that understand absorption units, making it harder to get good service if an issue occurs.  I suspect this is one of the issues we do not see a lot of absorption units in the inlet cooling market unless they are fully loaded.  Looking back to say 1983 or so from known installations of chillers only a handful of absorptions are seen.

We have found doing such work helps with making sure the owner is getting a system that works for them, it also lends impartiality to the equation.

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