ACC max capacity

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    • #2002
      Franco Liza

      Dear Fellow
      Has any of users calculate the real capacity of combined cycle ACC in order to know how much flow would allow. Could you share the experience with us about it? Is it possible that slightly increased steam flow could affect ACC performance? Is there any procedure to determine the real capacity of ACC.
      Thanks in advance for your feedback

      Franco Liza

    • #2117

      You can refer to HEI Standard for Air Cooled Condenser for some general info, but you should have performance curve(s) from the OEM which would indicate your design limits. Yes, an increase in steam flow (above the design steam flow) to the ACC would impact the ACC performance because the overall heat input has increased and if you cannot increase your cooling air speed any further than you would have a decrease in performance, likely shown as increased turbine backpressure. Usually, the ACC would be designed for a baseload or max load case steam flow conditions coincident with a site summer design ambient air temperature case. That would size the overall surface area and air speed (i.e. fan & motor sizing). Then your main variable for a performance curve is ambient air temperatures and/or reduced cycle steam flow cases. If your ACC was undersized then you could investigate increasing your fan blade pitch to increase air flow, but the motor load would need to be checked to know how much margin you have. You also need to be wary of freezing concerns in winter operation, depending on your site location.

      Recently we contracted EVAPCO to perform an assessment of our ACC including cleanliness of fins, thermal imaging, air flow measurements, and operational data analysis to determine ACC performance and available capacities. They did a pretty good job.

    • #2123
      Ockert Augustyn

      I’d like to add that an ACC can handle whatever you give it (obviously within reasonable limits), the question is what saturation temperature you will operate at. If you increase steamflow, you’ll produce more MW but you’ll pay for it in efficiency if your ACC was not designed for it. Usually in our case, the turbine last stage blades have some limit and you shouldn’t operate at higher values than that. Sometimes, we find that even at design steamflow, our backpressures are so high (because of wind etc.) that we have to “deload” i.e. reduce steam flow.

      Cleaning tubes (the presence of fouling), changing fan pitch etc. all just try to help you to get the saturation temperature down for a given heat load and that could change over time for various reasons.

      In our case, which is not combined cycle, only coal, you can increase steamflow until you reach a upper backpressure limit – then you’ve reached “capacity” but obviously you’re less efficient (burning more coal) at that specific operating point.

      The best way to know is to run it up slowly and see what happens 🙂

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