C
I like to know details about difference between Inlet Fogging and Evaporator in Case of GT world.
Cris,
Both are methods for decreasing the temperature of the air entering the axial compressor inlet, which increases the density of the air, which increases the mass flow of air through the axial compressor and turbine and therefore increases the power that can be produced by the gas turbine. Both types of systems are designed to be operated when the gas turbine is at Base Load, with the Inlet Guide Vanes fully open and air flow can be at it's highest for maximum effect.
An evaporative cooler is a series of corrugated media, usually upstream of the inlet air filters. Water (demineralized is best, but "tap" water has been used with mixed results) is pumped to headers above the tops of the media and allowed to run down the media. Warm, relatively dry (low humidity) air being drawn across the media causes the water to evaporate, which creates a temperature decrease due to the hear of vaporization. This cools the air, which increases the air density, which increases the mass flow, and so on.
Fogging is similar, but instead of relying on "passive" vaporization high-pressure pumps are used to spray tiny streams of water through banks of nozzles into the inlet air stream. Because the water is already highly atomized, it vaporizes quickly, reducing the air temperature, increasing the air density, increasing the mass flow, and so on.
Both methods have their advantages and disadvantages. NEITHER of them are "set-it-and-forget-it", meaning both of them require adjustment and maintenance. The flow of water down evaporative cooler media must be sufficient to rinse any dirt and salts off the media, prevent dry spots, and yet the flow-rate must not be so high that large drops of water (called carry-over) are pulled off the media by the air flow across it. And, as ambient temperature changes throughout the day, the amount of evaporation will necessarily change, as well, which means there may need to be some manual inspection and possible adjustment during the day, or during the weeks or months of operation.
Another unseen problem with evaporative cooler media is that is essentially made of paper, impregnated with chemicals (including formaldehyde in some cases), and can ignite when dry. I have personally seen fires caused during erection and maintenance when fire "blankets" were not used to protect the media from welding sparks and hot slag. I have also seen evaporative coolers burn when a fuel leak beneath the inlet filter house was ignited and the flames were drawn into the media, and that was quite a spectacular fire.
Fogging, on the other hand requires high-pressure pumps, which require more electricity than the low-pressure pumps used with evaporative coolers. The nozzles also get plugged very easily since the orifices in the nozzles are very, very small. Even though demineralized water (also expensive) is used along with stainless steel pipe, there always seem to be dirt and foreign materials which enter the system at some point and cause problems with pumps and nozzles, particularly nozzles. When the spray is not properly atomized it usually dribbles, and the water droplets are entrained in the inlet air flow and enter the axial compressor. While a small amount of this (carryover) is not problematic, large amounts can be.
Foggers also usually have a lot more in the way of instrumentation and controls, meaning more devices which require calibration and adjustment, including, in some cases, humidity sensors.
Both are "inexpensive" ways of increasing mass flow on warm days (usually above 22 deg C, minimum) in ambients where the humidity is low when ambient temperature is high. (Neither works well in tropical environs.) Both are seemingly simple, but for the most optimal operation both require attention and adjustment--and that just seems to be more than most power plant operators can adequately perform. So, most systems are either so ineffective that the cost of operating them (demineralized water; electricity) outweighs the benefit, or there is so much carryover that inlet duct work eventually rusts and creates FOD (Foreign Object Damage) which is quite costly to repair and in terms of lost generation.
You asked for details; I hope this was detailed enough. You can search the Internet for companies which offer these systems for more information; one company is Mee Technology, I believe.
There is yet another form of inlet air cooling called "chilling" and that is quite involved, requiring refrigeration systems to produce ice/slush; storage tanks; pumps; evaporative heat exchangers. It does produce very dramatic temperature drops, but at a cost. And the increased operational costs and maintenance are also quite considerable, not to mention the cost of purchase and installation.
Hope this helps!
Both are methods for decreasing the temperature of the air entering the axial compressor inlet, which increases the density of the air, which increases the mass flow of air through the axial compressor and turbine and therefore increases the power that can be produced by the gas turbine. Both types of systems are designed to be operated when the gas turbine is at Base Load, with the Inlet Guide Vanes fully open and air flow can be at it's highest for maximum effect.
An evaporative cooler is a series of corrugated media, usually upstream of the inlet air filters. Water (demineralized is best, but "tap" water has been used with mixed results) is pumped to headers above the tops of the media and allowed to run down the media. Warm, relatively dry (low humidity) air being drawn across the media causes the water to evaporate, which creates a temperature decrease due to the hear of vaporization. This cools the air, which increases the air density, which increases the mass flow, and so on.
Fogging is similar, but instead of relying on "passive" vaporization high-pressure pumps are used to spray tiny streams of water through banks of nozzles into the inlet air stream. Because the water is already highly atomized, it vaporizes quickly, reducing the air temperature, increasing the air density, increasing the mass flow, and so on.
Both methods have their advantages and disadvantages. NEITHER of them are "set-it-and-forget-it", meaning both of them require adjustment and maintenance. The flow of water down evaporative cooler media must be sufficient to rinse any dirt and salts off the media, prevent dry spots, and yet the flow-rate must not be so high that large drops of water (called carry-over) are pulled off the media by the air flow across it. And, as ambient temperature changes throughout the day, the amount of evaporation will necessarily change, as well, which means there may need to be some manual inspection and possible adjustment during the day, or during the weeks or months of operation.
Another unseen problem with evaporative cooler media is that is essentially made of paper, impregnated with chemicals (including formaldehyde in some cases), and can ignite when dry. I have personally seen fires caused during erection and maintenance when fire "blankets" were not used to protect the media from welding sparks and hot slag. I have also seen evaporative coolers burn when a fuel leak beneath the inlet filter house was ignited and the flames were drawn into the media, and that was quite a spectacular fire.
Fogging, on the other hand requires high-pressure pumps, which require more electricity than the low-pressure pumps used with evaporative coolers. The nozzles also get plugged very easily since the orifices in the nozzles are very, very small. Even though demineralized water (also expensive) is used along with stainless steel pipe, there always seem to be dirt and foreign materials which enter the system at some point and cause problems with pumps and nozzles, particularly nozzles. When the spray is not properly atomized it usually dribbles, and the water droplets are entrained in the inlet air flow and enter the axial compressor. While a small amount of this (carryover) is not problematic, large amounts can be.
Foggers also usually have a lot more in the way of instrumentation and controls, meaning more devices which require calibration and adjustment, including, in some cases, humidity sensors.
Both are "inexpensive" ways of increasing mass flow on warm days (usually above 22 deg C, minimum) in ambients where the humidity is low when ambient temperature is high. (Neither works well in tropical environs.) Both are seemingly simple, but for the most optimal operation both require attention and adjustment--and that just seems to be more than most power plant operators can adequately perform. So, most systems are either so ineffective that the cost of operating them (demineralized water; electricity) outweighs the benefit, or there is so much carryover that inlet duct work eventually rusts and creates FOD (Foreign Object Damage) which is quite costly to repair and in terms of lost generation.
You asked for details; I hope this was detailed enough. You can search the Internet for companies which offer these systems for more information; one company is Mee Technology, I believe.
There is yet another form of inlet air cooling called "chilling" and that is quite involved, requiring refrigeration systems to produce ice/slush; storage tanks; pumps; evaporative heat exchangers. It does produce very dramatic temperature drops, but at a cost. And the increased operational costs and maintenance are also quite considerable, not to mention the cost of purchase and installation.
Hope this helps!
C
Cris
I appreciate your detailed explanation.
Thank you very much.
Thank you very much.
S
Shaji
It was really a wonderful explanation.
I have read that adding moisture into air will make air lighter than cooling, similarly as humid air will be lighter than dry air.So a bit confused how power increases.
Does any of these cooling system effect the combustion system, turbine blades etc. in long run?
I wonder with the inlet pressure drop, axillary power required, how will one make an economic justification for usage of such cooling system. Can you please provide some guidance?
Does one need to evaluate the total hours in the year which it will be in use with favorable climatic conditions, capital cost of these systems, operation & maintenance cost etc being deducted and Net extra power produced.
Thanks
Regards,
Shaji
I have read that adding moisture into air will make air lighter than cooling, similarly as humid air will be lighter than dry air.So a bit confused how power increases.
Does any of these cooling system effect the combustion system, turbine blades etc. in long run?
I wonder with the inlet pressure drop, axillary power required, how will one make an economic justification for usage of such cooling system. Can you please provide some guidance?
Does one need to evaluate the total hours in the year which it will be in use with favorable climatic conditions, capital cost of these systems, operation & maintenance cost etc being deducted and Net extra power produced.
Thanks
Regards,
Shaji
R
Ram
The amount of air molecules will increase with higher density; if you quantify the air flow it will be clear for you (kg/sec of air mass entering the compressor)
> Does any of these cooling system effect the combustion system, turbine blades etc. in long run?
Sure it could if you do not perform a proper maintenance in either system you could have a "carry over" flow which is essentially water injection in the compressor; if the drop size of water is big enough then you can damage the blades or less worse you can build corrosion in your compressor and eventually plug the cooling air holes of the vanes and blades. Also the rotor life might be affected due to the high corrosion.
The power augmentation provided by the inlet cooling in most of the markets will give you a ROI of 2 to 3 years; I have both evaporative cooler and fogging system and my preference is the fogging system using dematerialize water. MW increase by fogging ~ 8 MW compared to MW increase by evaporative cooler 5 MW.
During a summer run where the MW price jumps to the roof the power augmentation will pay off fairly quickly
Both systems are only in service at based load and during summer runs (high ambient temperature) therefore based on your geographical location you might be able to calculate how many operating hours per year your system will work and calculate the cost per hr of operation. (Ex. How many hrs the ambient temperate was above 22 deg C in your current location)
Cheers
> Does any of these cooling system effect the combustion system, turbine blades etc. in long run?
Sure it could if you do not perform a proper maintenance in either system you could have a "carry over" flow which is essentially water injection in the compressor; if the drop size of water is big enough then you can damage the blades or less worse you can build corrosion in your compressor and eventually plug the cooling air holes of the vanes and blades. Also the rotor life might be affected due to the high corrosion.
The power augmentation provided by the inlet cooling in most of the markets will give you a ROI of 2 to 3 years; I have both evaporative cooler and fogging system and my preference is the fogging system using dematerialize water. MW increase by fogging ~ 8 MW compared to MW increase by evaporative cooler 5 MW.
During a summer run where the MW price jumps to the roof the power augmentation will pay off fairly quickly
Both systems are only in service at based load and during summer runs (high ambient temperature) therefore based on your geographical location you might be able to calculate how many operating hours per year your system will work and calculate the cost per hr of operation. (Ex. How many hrs the ambient temperate was above 22 deg C in your current location)
Cheers
> I have read that adding moisture into air will make air lighter than cooling,
> similarly as humid air will be lighter than dry air.
Um, in my mind adding water or water vapour to air increases the weight of the air--at least on a per unit basis. Can you provide references to your reading? I've done some Internet searches and can't confirm this yet, but I am confident that cooling the air by any means (evaporative cooling, or passing the incoming air over coils filled with icy water) increases the density of the air being drawn into the axial compressor. Denser air means more mass flow through the axial compressor which should be spinning at a constant speed when driving an AC synchronous generator. More mass flow means more power.
And, yes, one needs to factor into the decision all the things you suggested to determine if it's economically feasible.
And, yes, there is some effect on compressor blades when using evaporative cooling. But, the effects are not substantial, unless the unit is located on a seaside coastal area where the air can contain salt, or in some area there air-borne contaminants from some plant or process can precipitate out in the axial compressor.
When using evaporative cooling it is very important to prevent "carry-over", which is large droplets of water being pulled off the evaporative cooler media and drawn through the compressor. It is a very fine line when operating evaporative coolers to ensure the media stays wet, has enough flow to wash any salts (if tap water is used instead of demineralized water) and dirt off the media, and prevent carry-over. If you have a newer machine, or have replaced the first stages of the axial compressor blading (rotating and stationary) with newer blades made of newer materials they are probably not as prone to any corrosion as older compressor blading might have been. Some vendors do offer coated/treated blading for various atmospheres.
And, remember, the air (including any water/water vapour) is heated as it travels through the axial compressor; axial compressor discharge temperatures can be as high as approximately 370-390 deg C. So, the steam will not adversely affect the turbine hot gas path components.
> similarly as humid air will be lighter than dry air.
Um, in my mind adding water or water vapour to air increases the weight of the air--at least on a per unit basis. Can you provide references to your reading? I've done some Internet searches and can't confirm this yet, but I am confident that cooling the air by any means (evaporative cooling, or passing the incoming air over coils filled with icy water) increases the density of the air being drawn into the axial compressor. Denser air means more mass flow through the axial compressor which should be spinning at a constant speed when driving an AC synchronous generator. More mass flow means more power.
And, yes, one needs to factor into the decision all the things you suggested to determine if it's economically feasible.
And, yes, there is some effect on compressor blades when using evaporative cooling. But, the effects are not substantial, unless the unit is located on a seaside coastal area where the air can contain salt, or in some area there air-borne contaminants from some plant or process can precipitate out in the axial compressor.
When using evaporative cooling it is very important to prevent "carry-over", which is large droplets of water being pulled off the evaporative cooler media and drawn through the compressor. It is a very fine line when operating evaporative coolers to ensure the media stays wet, has enough flow to wash any salts (if tap water is used instead of demineralized water) and dirt off the media, and prevent carry-over. If you have a newer machine, or have replaced the first stages of the axial compressor blading (rotating and stationary) with newer blades made of newer materials they are probably not as prone to any corrosion as older compressor blading might have been. Some vendors do offer coated/treated blading for various atmospheres.
And, remember, the air (including any water/water vapour) is heated as it travels through the axial compressor; axial compressor discharge temperatures can be as high as approximately 370-390 deg C. So, the steam will not adversely affect the turbine hot gas path components.
S
Shaji
Thanks Ram and CSA.
From my understanding by adding H2O (Mw 18) will displace Air (Mw=29) and hence by adding moisture, overall air will become lighter.At this point of time unable to find the reference in internet.
Is there any source where we can find the economics of adding such cooling techniques capital cost, $/kW cost, O&M cost etc.
Thanks
Regards,
Shaji
From my understanding by adding H2O (Mw 18) will displace Air (Mw=29) and hence by adding moisture, overall air will become lighter.At this point of time unable to find the reference in internet.
Is there any source where we can find the economics of adding such cooling techniques capital cost, $/kW cost, O&M cost etc.
Thanks
Regards,
Shaji
