Manuel Collares-Pereira, INETI — Instit. Nac. Tecnologia e Engenharia Industrial — DER Joao Farinha Mendes, INETI — Instituto Nac. Tecnologia e Engenharia Industrial — DER Pedro Horta, INETI — Instituto Nacional de Tecnologia e Engenharia Industrial — DER

Water desalination is an important idea to alleviate potable water scarcity all around the World and there are already many commercial solutions. An important challenge still persists if one wants to use solar energy as the energy input to the system, thereby taking advantage of the fact that often this problem arises in areas of the world with abundant sunshine and little other energy resources.

The ongoing AQUASOL project [3] is one more attempt at putting solar energy to use in this context, with the objective of improving the economical and environmental performance of a MED desalination plant [1]. Within this project, reported elsewhere, an advanced solar dryer is being studied, allowing for brine concentration and/or ultimate salt recovery from the MED brine effluent. The idea is to add economical value to the investment in a MED plant, by providing one more product — salt — using the fact that the effluent of the MED plant has a higher salt concentration already and that the whole system might be integrated in a classical Saltworks, as one more step in the process.

1. Introduction

In recent decades, an increasing exploitation of water resources has lead to several forms of water shortage in many European regions (and elsewhere in the World), a problem assuming more alarming levels especially in semi-arid climate areas, where water, for human or agricultural consumption is either not supplied or supplied with scarcity and/or lack of quality. Often, in such areas, abundance of sea water and solar irradiation could use desalination as means for a medium-term sustainable process for potable water production. Yet, taking into account the proximity of sensible environments such as marine/tidal ecosystems, eventual negative impacts related with desalination effluent discharges must also be considered.

In light of the arguments above, the undergoing AQUASOL project [3] aims first at the development of a lower cost MED desalination technology with improved energy and environmental performance, promoting the use of solar energy both in the desalination and in the effluent treatment processes. The reduction of energy consumptions in the MED process, together with the exploitation of NaCl as a sub-product resulting from the effluent treatment process through brine concentration in a solar passive dryer, constitute likely means to accomplish a lower water cost objective. This will hopefully increase the competitiveness of MED technology when compared with the more common RO process. The present paper addresses the effluent treatment issue, taking into account the specificities of NaCl production. After development of a new concept of a passive solar dryer, based in the study of a numerical model describing dryer operation under given yearly climate conditions, a prototype is under test, allowing a deeper knowledge of the design and identification of further evaporation enhancement strategies.

The paper is organized as follows: in 2. a description of the dryer prototype is made; in 3. an overview of preliminary evaporation results, as well as comparison with simulation results, after the original numerical model, is presented; in 4. results analysis and numerical model correction is addressed; in 5. a brief idea is given of further prototype developments; in 6 a simulation of yearly results for the corrected numerical model is presented, and in 7 conclusions are presented.