PRELIMINARY ASSESSMENT OF THE POTENTIAL OF INDIRECT EVAPORATIVE COOLING FOR ENHANCED INDUSTRIAL WASTE HEAT RECOVERY

Effective energy use having become an evident priority, latent heat recovery from flue gases emerges as a key innovation in sustainable combustion processes. Instead of releasing flue gases with a significant amount of residual energy into the stack, condensing the water vapour within these gases provides a dual benefit: reducing stack temperature and increasing system efficiency. The Indirect Evaporative Cooling (IEC) is a technique that allows this operation by using water evaporation on the inlet air side, to enable the direct and efficient recovery of the latent heat released during water vapour condensation from flue gases. Moreover, injecting water enables direct modulation of the heat exchanger curves, allowing for the adjustment of the heat capacity of the flue gases. Although the concept appears as promising, no real prove of its potential has been presented yet. In this paper, we present a first study of indirect evaporative cooling to evaluate its potential for waste heat recovery from 100°C flue gases. A generic IEC model, based on the M-saturator, was constructed in Aspen Plus using typical performance data (i.e. wet bulb effectiveness). First results indicate a potential reduction of the stack temperature down to 38°C. Furthermore, a sensitivity analysis shows that as expected, the outlet temperature of the IEC and inlet air relative humidity significantly impact the potential for additional waste heat recovery. Finally, the modulation potential of the heat exchanger curves is illustrated for several heat exchanger outlet temperatures.