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I’ve been reading the ASME Performance Test Code (PTC) 30.1 – 2007 for Air-Cooled Steam Condensers to learn how best to assess performance of an ACC. Most of the Code relates to acceptance testing, but “[r]ecognizing … the importance of minimal turbine exhaust pressure on plant generation, the Committee also featured two Appendices of the Code that address both methods of Performance Monitoring and Routine Performance Testing.”
I’m most interested in Non-Mandatory Appendix I – Performance Monitoring.
Here’s where I got confused. In section I-3, there is a list of parameters that should be monitored.
Section I-4 states, “[t]he performance monitoring variables are listed in Table I-4.” They’re largely the same as those listed in Section I-3, but leaves out ACC Initial Temperature Difference, estimated recirculation and heat load.
Section I-5 states “the variables shown in the listing of section I-3 are recommended to be plotted with respect to time. This would include, e.g., condenser pressure, initial tempeature differences (ITD), inlet air temperature, the apparent recirculation, wind speed, fan power, the condenser capability, gamma factor, condensate temperature, air inleakage, dissolved oxygen, and generation.” Most of the parameters listed after e.g. are not included in the list in Section I-3.
As you can see, none of these lists agree with each other and I’m struggling to understand what’s important and what isn’t.
Which of these (many) parameters should be compared to design values to assess the thermal performance of the ACC? I can obtain or calculate all of them, I suppose, but I would really like to know which ones are most important and what a deviation from design really means in terms of efficiency loss.
I’d appreciate any insight on this from the group.
Dan Cicero
Senior Industry Development Manager
Nalco Water, Power Group -
The study carried out by John Maulbetsch for the DOE at Caithness touched this subject while searching for parameters.
If memory serves, there was not clear cut parameter or set of parameters that could be used to measure ACC performance as the ACC performance is dependant on a number of variables varying from anything from for for example, surface pollution of the bundles, temperatures, wind, air leakage between cells and from cells to the environment, excessive cooling cooling the condensate too much deceasing the HRSG efficiency etc…
As John put significant effort into this I would advise reaching out to him for advice.
My impression is that there is too much happening in the ACC to have a magic gauge showing efficiency per se, but a balanced verdict must be made based on several parameters -
Thank you very much for the reply, Desmond. I’ve downloaded the paper. It’s 165 pages long, so it’s going to take me some time to work through it in detail, so I appreciate your summary.
On casual inspection, I found, “Figure 1 which shows the variation in turbine exhaust pressure vs. ambient temperature for a range of wind speeds.” The author makes the point that at “ambient temperatures above 100°F, the difference between no wind or low wind and high winds (above 20 mph) can be 1.5 to 2.inches Hga with a correspondingly significant effect on turbine output.”
That’s just one example of variables over which the operator has no control (ambient temperature and wind speed) that greatly impact the efficiency of the ACC.
And I think your impression is correct, based on my reading to date, that there is no magic gauge showing efficiency per se. I think that’s true of water-cooled condensers too. A lot of people watch backpressure, cleanliness factor and TTD, but none of those values, alone, give a complete picture of what’s happening in the condenser. A little detective work is always necessary to diagnose a performance issue (or, in some cases, to determine if a performance issue actually exists).
Dan
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One point that may be missed here is that on windy days, lets say > 5 mph, the wind and wind direction will reduce fan airflow into the ACC especially on the windward fans. If you are operating on a hot day, the loss of airflow will certainly increase your back pressure and even possibly trip the turbine. The windscreens described in the referenced report were installed only for protection of the fan blades. There have been wind screen configurations optimized using CFD Analysis, that have been proven to reduce wind related deficiencies. If you would like to discuss this further you can contact me at gmirsky@galebreaker.com
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Thank you for the additional reference. I’ve read through it and found it very helpful.
I’m struggling to reconcile the Calculation of LMTD in the Appendix A with Section 5. In Section 5 the LMTD calculation requires:
A = heat exchange surface area, m2
LMTD = log mean temperature difference, K
Q = heat duty, W
U = overall heat transfer coefficient, W/m2/K
hfg = design value of the latent heat of vaporization, J/kg
m = design value of the steam mass flow rate, kg/s
x = design value of the steam qualityIn Appendix A, th same calculation requires:
A = heat exchange area, m2
hfg = latent heat of vaporization at design backpressure, J/kg
m = design steam mass flow rate, kg/s
Q = ACC heat load, W
U = overall heat transfer coefficient, W/m2-K
x = design steam qualityAnd then, in the example calculation…
A = heat exchange surface area (total air side), m2 = 1,150,643
hfg = latent heat of vaporization, kJ/kg = 2,390.3
m = design steam mass flow, kg/s = 234.6
Q = heat load, kW = 560,856.3
U = heat transfer coefficient, W/m2-°C = 34.49
x = exhaust steam quality, .932
LMTD = log mean temperature difference, °C = 14.13I suspect this is a unit conversion problem, but I can’t seem to get the given equations and given values to calculate the answer of 14.13. I’ve highlighted the different units used in these calculations.
Has anyone else seen this difference between the same calculations in different parts of this document? Any ideas about how I might resolve this?
Dan
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