Abstract
Metal-alloys tubes are used in the falling-film evaporator of the multi-effect distillation
(MED) that is the dominant and efficient thermal seawater desalination process. However, the harsh
seawater environment (high salinity and high temperature) causes scale precipitation and corrosion
of MED evaporators’ metal tubes, presenting a serious technical challenge to the process. Therefore,
the metal/metal alloys used as the material of the MED evaporators’ tubes are expensive and require
high energy and costly tube fabrication process. On the other hand, polymers are low-cost, easy to
fabricate into tubes, and highly corrosion-resistant, but have low thermal conductivity. Nevertheless,
thermally conductive fillers can enhance the thermal conductivity of polymers. In this article,
we carried out a feasibility-study-based techno-economic and socioeconomic analysis, as well as
a life-cycle assessment (LCA), of a conventional MED desalination plant that uses titanium tubes
and a plant that used thermally enhanced polymer composites (i.e., polyethylene (PE)-expanded
graphite (EG) composite) as the tubes’ material. Two different polymer composites containing 30%
and 40% filler (expanded graphite/graphene) are considered. Our results indicate that the MED
plant based on polymer composite tubes has favored economic and carbon emission metrics with
the potential to reduce the cost of the MED evaporator (shell and tubes) by 40% below the cost of
the titanium evaporator. Moreover, the equivalent carbon emissions associated with the composite
polymer tubes’ evaporator is 35% lower than titanium tubes. On the other hand, the ozone depletion,
acidification, and fossil fuel depletion for the polymer composite tubes are comparable with that
of the titanium tubes. The recycling of thermally enhanced polymers is not considered in this LCA
analysis; however, after the end of life, reusing the polymer material into other products would lower
the overall environmental impacts. Moreover, the polymer composite tubes can be produced locally,
which will not only reduce the environmental impacts due to transportation but also create jobs for
local manufacturing.
Keywords
life cycle assessment (LCA)
Multi-Effect Desalination (MED)
Sustainability
Techno-economics
Socio-economics
Thermally enhanced polymer
Titanium
Tubes