integration of solid oxide fuel cells and ... - Ea Energianalyse

E. OPTIMIZATION GRAPHS
E.1.3.2
∆ T,Tower
∆ T,Tower is the difference between point 37 and 39. And since T 39 is given
by the cooling tower and ambient conditions, ∆ T,Tower will effectively
control T 37 . In a physical system this is done by regulating the water flow
in the circuit point 35 to 39. In lack of exact numbers, it has been assumed
that the outlet temperature of the air remains at the same relative position
between the water in- and outlet of the tower (green curve relative to the
two blue lines in figure E.7B). This seemed more realistic than keeping
∆T min constant at the 3 ◦ C, which would have made the air outlet become
colder than the water outlet for ∆ T,Tower < 3.
Figure E.7: A: Efficiencies, COP, and water consumption. B: Air and water temperatures.
T air,in = T 45 ,T air,out = T 47 ,T water,in = T 37 and T water,out = T 39 .
As can be seen in figure E.7, the COP of the absorption unit increases
when ∆ T,Tower is reduced because T 39 is decreased. But the fan power
rises considerably mainly because of the increased air flow, which comes
from the increased amount of water evaporated. Hence the electrical
efficiency decreases.
282