Thanks for your input @ HUUBHUBREGTSE;
1) Do you mean that we can use this as a Terminal temperature Difference?
We have individual street temperature (condensate) at each fan, and individual incondensable temperature for each of the 3 legs. I am analysing these readings to see if this is possible. We normally see a drop in incondensable temperature, while condensate temperature in each leg remains consistent. which make me think that the cooling effect is not in steam side but on incondensable side.
2) The difference of temperature b/w Turbine exhaust and temperature at Extraction Pump isn’t far off generally, but I have seen instances where the CEP temp is plunged, although we haven’t trended incondensable temperature vs turbine exhaust temp. We don’t see a reduction in actual back pressure while set-point for back pressure remains at its previous value.
What I understand from our DCS is that the Logic isn’t controlling the fans start/stop to temperature difference, but back pressure on the steam turbine, (not knowing whether this is the correct approach for us to follow but this is how the logic has been set-up) there is a cascade mode to control set-point for back pressure and fans are added in or out of service or when all fans are i/s then they are moved to high speed mode gradually.
What we have also find is that the system is not actively changing the back pressure set-point even if the load requirement on ST (& condensate amount in condenser) is increased from 30% to 80%.
To compensate for high cell temp deviation we have started to switch off those fans on the street where delta is high and start them again manually to control this anomaly. however this in not so popular among our teams.