Good morning/evening



We are experiencing difficulties with our MS7001EA 85MW single shaft Turbine which driving the Propane refrigeration compressors,during summer months as we reach the turbine temperature control limit and the helper motor limits (14MW)so any extra power shall be beneficial as an extra cooling capacity.



So I’m asking about any information about fogging systems (cheapest option)( water flow rate required/ water specs/ cost/ all water evaporates or only makeup required ) any such data .



Note

1-during summer day time temp=31. Rh= 70%(max) (I know humidity is an important factor but even with that humid according to psychrometric chart 5-7 degrees Celsius can be obtained.

2-only 2M/Hr Demineralized Unit capacity is available but two mechanical vapor compression Desalination unit with 9M/hr each are available with conductivity=2ms/cm. & chloride <1 mg/L.



Thanks for your time

 

Hi,

Good questions. Let me start by saying that just about ANY type of inlet cooling has its own problems/issues. AND, if the unit has DLN-I combustors and IBH (Inlet Bleed Heat) that can be problematic when selecting and using inlet cooling systems.

Fogging can take several forms ("low pressure," "high pressure")--but in my personal opinion water cleanliness is the single most important determinant of reliability and performance. It's best to use demineralized water--in my personal opinion--which means treating the water costs money and involves some strong chemicals and/or expensive equipment, and often there is waste discharge which must be dealt with (depending on which part of the world the plant is located in). Also, these days, just finding "raw water" and paying for it is not inexpensive.

High-performance fogging usually involves very small orifices, which can become easily clogged. Piping cleanliness is extremely important, as is filtration. High-performance fogging usually involves expensive pumps, which are expensive to maintain. And sometimes are "staged" depending on required flow-rates. These pumps consume power. And, the infrastructure for the electric pumps and controls as well as the fogging "skids" themselves are not inexpensive.

Basic evaporative cooling is always touted as being "self-regulating"--meaning that the evaporation will occur naturally and doesn't require much human attention. That is FAR from the truth, as changing ambient conditions throughout even a normal day can affect evaporation rates. Contanimants in the air flow across the cooler media (dust; vehicle exhaust fumes; type of dust (dirt; fine sand; concrete; particulates from a nearby process plant; etc.) can all affect evaporation rate, water flows across (down) the media, carryover, cause dry spots/streaks, and leave contaminats sticking to the media (salts; dust; dirt; etc.). Evaporative coolers require a lot of attention to ensure they are working at their optimal level. And, again, in my personal opinion they also require demineralized water. And, some kind of "pre-filtration" to try to reduce any airborne contaminants to the extent possible.

Chillers--where electricity, say, from low usage periods (overnight, for example) is used to make an ice slush which is stored in large tanks (often underground) and them pumped through pipes in the inlet duct to cool the incoming air is probably the single most efficient method of cooling the air. The cycle is closed-loop, but will have some make-up water requirements. And, I would imagine that demineralized water is best for reliability. But, as you can see from the description it requires a VERY LARGE investment in equipment and storage facilities and manifolds and control systems. When properly configured they work very well, and can really improve turbine output. But, again, it's not inexpensive.

You are recommended to talk to different manufacturers and their representatives to obtain information about the equipment and the state of the "art" of inlet cooling. It may well be that your plant can put one of these systems to good use improving turbine output power and can more than cover the cost of the equipment and installation and "consumables" required for the equipment.

I think GE has some publications about performance improvements and their ROI (return on investment); I just don't know the publication numbers. Again, most manufacturers of these types of inlet air cooling will be able to give you some very good information about requirements. Just don't fall into the trap of believing that any of these systems are "self-regulating" and require little human oversight or maintenance--it's just not true. They all require knowledgeable, trained people to maintain and troubleshoot (and they will all require troubleshooting--some more than others) to maintain day-to-day reliability and operation. And, at the risk of sounding redundant: Water cleanliness is EXTREMELY important. If you don't use a system for even a month or so, even with demineralized water, bacteria can grow. Most of the plants I visit that have foggers don't use them; mostly because of pump maintenance requirements and plugged spray orifices. The plants with evap coolers struggle with keeping dry spots to a minimum, or with reducing carryover (which can cause serious rust of inlet duct work enclosures and supports). The number of chillers is growing, but the investment is huge even though the returns can usually be very high.

Best of luck in your research!

 

firstly thanks for your reply and time

regarding the water availability we are desalinating sea water by mechanical vapor compression units 9M/hr and the Quality of desalinated water is almost very close to demineralized water ( with anti bacterial treatment done), and we have another small demineralization unit with 2M/hr capacity . According to a GE publication almost 1% spray water of inlet air flow turbine cause 5 degrees Celsius drop, as 2% spray will cause fraction of water carryover to compressor suction (which can be beneficial in term of power augmentation but on the other hand can cause problems on the long run with the blades) so 1% (almost 1M/hr. is enough.

regarding (self regulating) point i read before about fogging system which furnished with Relative humidity and temperature sensors so it can calculate the maximum achievable wet bulb temperature and adjust the fogging flow to it .

can you tell me more about how fogging can affect the DLN system as we already had one .

thanks again for your valued contribution

 

Humidity sensors have been used with very mixed results over the last three or four decades. And just adding instrumentation to a system that is highly susceptible to mechanical issues (plugged orifices) isn’t going to solve the main problems with the system.

In fact, it might just make the system even less reliable.

If fogging was more reliable it would be widely used. GE promoted fogging systems (called SPRITS if I recall correctly) for a couple of years. Most of them have been decommissioned or abandoned in place.

The spreadsheet economics of fogging are very appealing. The day-to-day reality of reliable operation is something entirely different. Some plants have better experiences than others, but that’s ONLY because they invested time and considerable effort in understanding the system, the equipment, and working with suppliers to improve reliability. They also train their operators and maintenance personnel to anticipate issues and respond in a timely manner—as well as investing in spare parts and upgraded equipment. It’s not a “set it up and forget it” system. Usually, the supplied equipment is inadequate for the application and service duty requirements (because better equipment would increase the initial cost of the system).

Just sayin’ ….

Ask some of the suppliers of fogging systems for references from other users. Join some GE-design heavy duty gas turbine User’s Groups and read the forums about inlet air cooling systems, foggers in particular, and ask questions there.

Caveat emptor.

Best of luck.

 

Mo.Badawy,

As for how fogging can affect the DLN system, you will have to look at several blocks. The combustion reference temperature calculation probably uses relative humidity (there is usually a relative humidity sensor in the inlet duct above the axial compressor bellmouth). It may also be used in calculating air flow. It may also be used in calculating exhaust flow (though I think GE changed that several years ago--but we don't know how long the units have been operating at your site).

My experience with inlet air cooling and DLN-I combustion systems is pretty limited. But, on sites where the ambient is drier (less ambient humidity) when the inlet air cooling system is switched on and the inlet air temperature drops fairly quickly if the unit is not at Base Load there can be problems with primary zone reignitions. Sometimes, tuning of the DLN system can mitigate some of the problems (especially at sites which have large fluctuations of ambient temperature). Most of my experience with fogging is on F-class machines that use a different DLN combustion system. DLN-I combustion systems are a little more intolerant of sudden changes in air flow (which will occur when inlet cooling is enabled and its effects really start to be felt), and especially if not operating at or very near Base Load.

Frame 7EA GE-design heavy duty gas turbines used as mechanical compressor drives at LNG plants don't generally operate at a fixed speed (if I recall correctly) and that also affects air flow (because the axial compressor speed is not so steady). Changing air density with inlet air cooling can also have effects on axial compressor loading. Because of the staged nature of combustion in DLN-I combustors they are relatively intolerant of things that affect air flow. And, I have seen sites with inlet air cooling and IBH (Inlet Bleed Heating) operated at Part Load with BOTH systems active.... And, it's NOT a GE problem (well, in my personal opinion GE could shut off inlet air cooling when IBH becomes active, but usually inlet air cooling was added by the owner/operator after commissioning); it's an operations problem....

Again, you would do well (VERY well) if you talked with other owners/operators that used inlet air cooling--and fogging if you are leaning heavily towards fogging--about their experience(s) with the equipment and the reliability and the actual performance improvements. Ask also about axial compressor cleanliness/cleaning when using inlet air cooling, because axial compressor cleanliness greatly impacts performance of a combustion (gas) turbine. I don't think you're going to find many mechanical drive Frame 7EA GE-design heavy duty gas turbines with inlet air cooling (but I might be surprised with the proliferation of LNG compression plants!) AND DLN-I. But, it's worth trying.

Again, best of luck. Finding and contacting other people with similar equipment as you are considering is NOT fun or easy. But, it's really the best indicator of your future experience and success. Best to get information now, than to find that others have had the same or similar experiences as you are after making a very large investment. It's AMAZING how things come up in conversations with other operators/technicians AFTER making a very large investment which would have been nice to know BEFORE making a very large investment.... (You would be VERY surprised to learn how often this happens....)

Control.com is not like a gas turbine user's group. If you're not a member of a GE-design heavy duty gas turbine user's group and you're working at a site/plant with GE-design heavy duty gas turbines--you should be (a member of a user's group). Control.com's heavy duty gas turbine questions/answers are more about controls-related problems and solutions. I don't want to discourage anyone from reading or posting to Control.com, but it's a forum for many other controls-related issues, not just gas turbine controls-related issues.

 

where are you based ??

 

I am trying to find someone you can talk to. I came from an LNG site in Karratha, West Australia in 2013 which had a new LNG train with 2 x Frame 7. A discussion with them might help you.

 

Oh !! Never mind.

 

Thanks so much for your time and informative replies.. I really appreciate it

 

sorry for the delay .. Working scheduled changed and a sleeping problem sorry.

I am in Egypt Sir.

 

Please wait until after the holiday weekend and I'll try and get a Controls Engineer from Australia. In summer we had 40-45 Deg.C and 80%Rh and similiar problems with you needing more output. I don't know if they tried any inlet cooling but we can ask.
Have a good New Year

 

Thanks so much … Happy New Year

 

I had some discussions with an engineer From Dampier, Karratha LNG where they have 7 LNG trains + the new Pluto 1 train plant. They discussed various Inlet cooling systems but didn't implement. With any wet system they saw problems with their DLN Fuel systems and had fresh water problems as well, anything else they saw as too expensive to install. They are very independent but still keep a close contact with GE who supplied the turbines and I'm guessing were not very positive.
Sorry about that but it was worth a try

Good Luck

 

Thanks so much for your help and time . I really appreciate it