Makeup sprays for summertime performance

[MVachon]

I have an ACC in Maine. It is a small horizontal unit, not an A frame. It was designed to operate at a 40 degree ambient temperature. Unfortunately in the summertime, the ambient temperature can get into the 80s and occasionally 90s. At around 60 degrees ambient, all my fans are maxed out, 100% output. From there I start losing vacuum. It can drop to 21″HG and lower. The electrical production drops with it. I’ve tried increasing fans speeds and changing blade pitches only to have the amps max out on the motors. Bigger motors would mean bigger in house loads. We only make 3MWs to start. I also tried misting water ahead of the fans to cool the air only to worry about scale build up on the outside of the tubes and fins that I wouldn’t be able to clean. I was wondering if anyone has any experience with spraying make up water into the steam trunk ahead of the condenser to try to keep the vacuum from dropping off in hot weather.

Marc

[Harry Keller]

Water injected upstream of the ACC can drain back into the steam turbine causing turbine damage if proper drainage provisions are not included. Also the injection water should be demineralized and deaerated to prevent adding unacceptable dissolved solids and non-condensable gases to the condensate. I have seen plants where water has been injected in steam turbine exhaust hood sprays to protect steam turbines from overheating during periods of high backpressure.

[gmirsky@galebreaker.com]

Hi pressure misting systems has been used especially on some horizontal units with very good success. Demin water is a good idea and wind screens to assure the mist stays in the cells it is intended for are normally incorporated. These systems can be readily retrofitted.

[rp@ax-system.com]

Hi, my first advice would be to check that your fins are very clean, and if not to buy a good cleaning system and use it frequently. The first reason of vacuum dropping is the fouling of the fins which reduce the heat exchange.
If you’re still loosing vacuum in your ACC, misting is a good idea but:
– If your relative humidity is high (more than 80%, the results is not going to be signifiant). More your air is dry, more it is efficient.
– it’s better to use soft water that demin water which required 316L materials.

Please contact me to get more information about our ACC Cleaning Robots and our Fogging Modular Solutions. (www.ax-system.com )

[Andy Macqueen]

Our ‘fogging’ system is very effective at times of hi ambient temps, using demin water. Note that , because of the high pressure needed, the atomisation pump motor kWh are not insignificant, as well as the water treatment. But it certainly does the job.

[Desmond de Haan]

The above comments about cleaning fins, adding water mist to the air and considering wind screens are all very valid points.

Is your ACC a flat horizontal or a hexacoil system?

You state that your fans are maxed out.
I assume that you mean these are at maximum pitch and/or the amperage draw from the motors is maxed out.
Both of these do not neccesary mean that the aerodynamic performance is maximized.

I would suggest to have the fan performance valuated by having the aerodynmaic performance measured, with clean bundles is best. There may very well be the potential to increase th air flow in the ACC with minimal technical impact and low investment.

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