Utilization of Solar Energy for Thermal Desalination

¶ … Solar Energy for Thermal Desalination

Desalination of seawater is a process that is becoming increasingly important due to the falling water tables worldwide in addition to the projections of water shortage that is likely to occur in the near future. Various processes exist that can be utilized in desalination of seawater however; the Multi-Effect Desalination process is touted to be one that is more effective and economical than the others.

The question that the research proposed in this study addresses is why it is that multi-effect is becoming the most efficient and economic desalination process?

The study has as its purpose the examination of desalination processes and the determination of why the multi-effect is the desalination process that is most efficient and economic.

Methodology

The methodology chosen for the proposed research study is one of a qualitative nature and one that will involve an extensive review of literature in this area of study.

Literature Review

The work of Blanco, et al. (2008) states that seawater desalination "is one of the most promising fields for the application of solar thermal energy due to the coincidence, in many places of the world, or water scarcity, seawater availability and good levels of solar radiation." In fact, all international institutions that are relevant acknowledge the fact that over the next twenty years "power and water supply will be two major issues mankind will have to face and solve during the present 21st century." (Blanco, et al., 2008) Water scarcity is already a global problem of a serious nature and this problem will only become larger and more daunting in the future. Blanco et al. (2008) states "Problems associated to water scarcity, gradual destruction and contamination of fresh water resources is becoming more pressing in many areas of the planet, causing concern even at countries that, so far, do not have these problems." Additionally reported by Blanco, et al. (2008), is that water, which is critical to all life in a world with 6,600 million individuals, is a problem issue for approximately 600 million individuals who are presently "suffering chronic water scarcity" with approximately 1 billion individuals presently lacking in access to drinking water that is safe as well as unsafe water and poor sanitation characterizing the environment of 80% of individuals in the developing world. (Blanco, et al., paraphrased) Should the present trend continue, it is estimated "…two out of three people on Earth will live in water stressed areas by 2025 with the worst impact at arid developing countries where water availability per person will only be about 15% of the per capital availability in 1950." (Blanco, et al., 2008) Primary solar energy applications to water processes that are presently being developed include the following two approaches of solar water desalination: (1) combined solar power and desalination plants; and (2) medium to small solar thermal desalination systems (kW range); (2) Solar detoxification -- this uses the near-violent and visible aspect of the solar spectrum to promote a strong oxidation reaction by the generation of oxidizing species, either bound hydroxyl radical or free holes, which attack oxidizable contaminants, producing a progressive breaking of molecules yielding to CO2, H2O and dilute mineral acids; (3) Solar Disinfection -- use of previous detoxification techniques based on supported photocatalyst to generate powerful oxidant species to control and destroy pathogen water organism. (Blanco, 2008) The method of water desalination that appears to be the most effective and economical is the desalination process known as the 'Multi-Effect' desalination process. The Multi-Effect desalination process is a thermal distillation process in which the feed water "is sprayed or otherwise distributed onto the surface of the evaporator surface of different changes in a thin film to promote evaporation after it has been preheated in the upper section of each chamber." (Review of CSP and Desalination Technology, nd) The evaporator tubes are then steam heated using steam extraction from a powercycle or boiler with the steam produced. It is reported that the surfaces of the other effects receive heat by the steam from the preceding effect and that each effect is required to have pressure that is lower than the previous one. The process is repeated up to 16 effects with the steam produced in the last effect being condensed separately in a heat exchanger referred to as the final condenser stated to be cooled using the incoming seawater. The incoming seawater is stated to be used as "preheated feed water for the desalinati8on process." (Review of CSP and Desalination Technology, nd) The Multi-Effect Desalination method has better thermal performance than other processes of desalination and can be used both for high or low temperature desalination operations. There are various configurations of the MED process making it more versatile for use in desalination processes. (Review of CSP and Desalination Technology, nd)