SDCS Regenerator Inlet Air Condition Effect
Figure 6.10 presents the effect of inlet air relative humidity on regenerator performance. The relative humidity range studied was 50-80 % at a constant temperature of 30 °C. Figure 6.10a shows that as the inlet air relative humidity
Fig. 6.10 SDCS regenerator performance with inlet air relative humidity increases, the moisture addition rate decreases from 0.2968 g s-1 at 50 % RH to 0.06915 g s-1 at 80 % RH. Figure 6.10a also shows that as the inlet air RH increases the latent (regenerator) effectiveness decreases from 35.43 % at 50 % RH to 13.9 % at 80 % RH. Figure 6.10b shows that as the inlet air RH increases, the regenerator thermal input decreases, from 1296 W at 50 % RH to 912.9 W at 80 % RH. The temperature difference of the heating water flowing through the regenerator plate heat exchanger (PX2) ranged from 6.5 to 9.3 °C, an important consideration for tri-generation system integration.
It is evident that performance of the regenerator is greater at lower inlet air RH. Furthermore, if we compare results at air temperature of 30 °C and RH of 60 % (Fig. 6.10a) with results at an air temperature of 26 °C and RH of 60 % (Fig. 6.11a) at 256 m3 h-1 it is apparent that the regenerator performance is greater with a lower inlet air temperature. This is because a lower inlet air temperature and relative humidity will exhibit a lower air side vapour pressure. Thus, at a constant solution inlet condition to the regenerator, a greater vapour pressure differential will exist, and therefore increased potential for mass transfer from the desiccant solution to the air stream. Therefore in a tri-generation system application, it is beneficial to system performance to operate the regenerator on the lowest air temperature and relative humidity possible. This will mean for a given thermal output from the SOFC CHP system, the moisture addition rate in the regenerator will be higher, and thus the allowable moisture removal rate in the dehumidifier can be higher. This will lead to a greater cooling output for the given thermal input, and thus elevated tri-generation system efficiency. Although dehumidifier cooling output increases in hot and humid conditions, when operating the regenerator on fresh outside air regeneration capacity reduces with increasing inlet air relative humidity and temperature and thus liquid desiccant system performance will be poorer in hot and high humid climates.