he most important formula is:
Q = K x S x DT
Q : thermal energy exchanged in the evaporator (proportional to evaporated water)
K : Exchange coefficient
S : Exchange surface
DT : Difference of temperature between steam and vinasses.
The exchange surface never change and will still the same.
During 1 hour we can consider the exchange coefficient is still the same.
So if you open the steam regulation valves, the flow of steam increases, and the Q will increase in the exchanger. If Q increases, DT will increase (because S and K are still the same). So the pressure and the temperature will increase in the exchanger (outside the tubes).
So when you increase the capacity, the pressure difference between calandria and separator will increase, so the DT will increase.
If you consider all the installation, by increasing the steam valve, you will increase the global DT of the installation (difference between the equivalent temperature on the 1st calandria PT.72.11.01 and the temperature on the last separator PT.72.32.01).
You will be limited by:
- Low pressure in the condenser: by decreasing the pressure in condenser you will decrease the temperature, and it will be more and more difficult to cool all the vapor in condenser with cooling water.
- High pressure in the effect 1 and 1’: The effect 1 cannot be over 0.5 bars g, and the effect 1’ cannot be over 2 bar g. Over this pressure the safety disk will open. Another limit is 0.5 bars g in CO.72.42 (PT.72.22.01). Except this limit, our advice is to not have a vinasses temperature over 108°C (TT.72.11.01)
All along operating, the exchange coefficient will decrease because the vinasses will clog in the tube, some calcium deposit will appear etc…
So the exchanger coefficient K will decrease. Q will not change (opening of the steam valve is still the same, so flow of steam don’t change), so to keep the same capacity, the DT will increase.