Packed Bed Condenser for Fresh Water Production

Abstract

To tackle the expected increase in fresh water shortage in the world, alternative water production methods are required. One such a possible method is Ocean Thermal Water Production (OTWP). This thesis continues on the innovative concept of the use of OTEC waste water as a cooling fluid for atmospheric water production introduced in previous work.

In this thesis, an experimental study on a structured packed bed condenser column is presented. This work was carried out on an experimental OTWP set-up installed in the Process & Energy lab at the Delft University of Technology. Additionally, a numerical Python model was used to investigate the heat transfer and condensation characteristics of the packed bed column. The condenser function of the Python model was used to compare the prediction performances of different mass transfer coefficient and hydraulic correlations. The Python model simulations were compared both to the predictions of Aspen plus, an established chemical process software, and to the experimental results. The correlation by Olujic et al. (1999) was chosen as the most suitable for the transfer rate and hydraulic behavior predictions for the Python condenser model. A mean average error in the mass transfer predictions of 2.5 % and in the hydraulic predictions of 16.9% was reached in relation to the experiments. outperforms the Aspen plus model, that has respective mean average errors for the mass and pressure drop predictions of 9.5% and 13.0 % for the correlation proposed by Rocha et al. (1993). The Python model was extended with functions that calculate the pressure drop over the remaining necessary equipment for an OTWP plant.

The aim of the developed model was to predict the processes in the OTWP condenser column and design a pilot-plant. The model was used to perform a sensitivity analysis on a large-scale column. A preliminary economic analysis identified that reducing the diameter of the condenser column reduces the cost of water production but increases the energy requirement. For an OTWP pilot-plant with a production of 25 m3/day, the chosen column diameter of 6.6 m leads to a system energy requirement of 3.5 kWh/m3 and a levelized cost of water production of 8.08 $/m3. Those production costs can be reduced by an optimization study of the full OTWP pilot-plant.