Air-cooled condenser, A-frame induced draft
Condenses turbine exhaust steam in A-frame bundles, with fans above the apex drawing the air through them.
The same A-frame bundles condensing turbine exhaust, with the fans above the apex instead of below it. The order in which the air meets the fan and the bundle changes, and the rest follows: the bundle receives ambient air instead of air already heated by the fan; the fan handles the hot, less dense discharge and must be larger for the same mass flow rate; the draft chain is Eq. 8.1.17 in place of Eq. 8.1.26; and the flow through the bundle is uniform, so there is no maldistribution penalty. Kröger publishes no worked example for an induced-draft A-frame, so this system has no textbook verification case of its own; its parts are verified as Examples 8.1.2 and 8.1.4.
Pack: Mechanical draft. In the plans: Pro (as its one pack), Expert, Enterprise and Academic. Plans
The analyses it offers
- RatingThe plant at one condition, solved once.
- DesignFix a target and solve for one dimension.
- Parametric sweepThe rating repeated along one or more axes.
- Performance curvesBack pressure against inlet air, one curve per steam flow (ASME PTC 30.1).
- Acceptance testA test's runs corrected to guarantee conditions, with its uncertainty (ASME PTC 30.1).
- Annual runThe rating once per weather point over a year.
- Transient simulationThe plant after an event.
The transient scenarios
- Fan start from rest
- Fan stop
- Step on one boundary channel
- Step in the ambient temperature
- The ambient temperature following a profile
What it predicts, and what that was compared with
The app's capability statement for this system, as every report prints it.
| Analysis | Predicts | Compared with | Agreement |
|---|---|---|---|
| Steady rating, and the sweep, design and annual runs built on it | Air mass flow rate, heat transfer rate, fan power and steam back pressure of an A-frame condenser unit or bank | Kröger's worked Example 8.1.4 | Air mass flow rate, heat transfer rate and fan power within 0.011%; every loss coefficient to five significant figures |
| Discretised transient | Steam back pressure, heat transfer rate and air mass flow rate through a fan ramp or a load change | Its own steady rating, the state it settles to; no measured start-up or run-down | Settles to the steady rating within 0.1% on the air mass flow rate and the heat transfer rate |
Its limits
Wind on a fan-driven bank is Kröger's Section 9.3 procedure on Duvenhage's CFD tables, held constant beyond 3 m/s at 5.7 m, without any representation of the site. Not modelled for this system: hot-air recirculation between streets, fouling that develops in service and degradation (a stated fouling resistance is carried as given), freezing and freeze protection, hybrid or adiabatic inlet assistance, and the plume. Every correlation is a fit over a declared range; the report lists any excursion at the solved state, and a result outside a declared range is an extrapolation and not a prediction.
The validation cases of this system
- Another modelInduced-draft A-frame condenser: a regression pin with no published answer
- Another modelBekker et al. 2022A 20-fan induced-draft ACC bank, against the section 8.3 and 8.4 correlations
- Another modelBekker et al. 2022The induced-draft bank under wind, along and across its axis
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