cover story Quotable quotes TSE can be used for other purposes, not only for district cooling. It can be used for flushing or irrigation. TSE with 300 or 220ppm of chlorine cannot be used directly but only after polishing, which means there is more energy consumed, so seawater with cooling towers is a feasible option. –Prabhakar Naik, John Buck International
DC Pro Engineering, points out. “In Fujairah, we did district cooling with 2,000 TR that used seawater cooled with titanium and fibreglass tubes,” he says. Amar Farjo of JCI backs Berbari’s observation. “We need seawater cooling towers, because they can save 57,600 gallons of potable water per kilo of cooling every day,” Farjo says.
A gamut of issues While there is a growing favour for seawater cooling in some circles, there are several aspects to consider. The various components – be they cooling towers, chillers, heat exchangers or intake systems – come with their attendant issues and challenges. Cooling towers, for instance, come with a gamut of sub-issues. Typical questions revolve around the impact of seawater on the sizing of the cooling towers, the materials needed in building the towers and the environment around them. Seawater impacts thermal performance in three ways, says Kent Martins of SPX Cooling Technologies. If seawater has 70,000 ppm of TDS, it lowers vapour pressure by five per cent, which is a negative impact, Martins says. The same seawater characteristic reduces specific heat (0.92 compared to 1 for freshwater). “The cooling tower,” he says, “must be sized three to seven per cent larger to compensate for 32
the reduced heat transfer characteristics of seawater at 70,000 ppm TDS in circulation.” When it comes to material selection for cooling towers, corrosion of compounds can occur. Fibreglass, Martins says, is a good material for seawater exposure. Likewise, concrete towers also hold good, he says, but they would require a specialty mix and rebar design. Generally speaking, he recommends premium hardware materials and coatings. Another sub-issue is the drift from the cooling towers. Circulating water is distributed as droplets or films to maximise surface area. Exit water for cooling towers contains water vapour, drift droplets and condensate droplets. It, therefore, becomes essential to reduce drift, and for this, careful installation is of paramount importance. “It is crucial to reduce drift at the source with the best available drift eliminator,” Martins says. “That way, salt deposition will not be a major concern. Also, drift eliminator data should be specific to the distribution system used. Further, it would help to site the tower downstream from the prevailing wind direction and away from high-rise structures.” Heat exchangers and chillers also come with a string of challenges, considering the corrosive nature of seawater. Newer plants use titanium to
CLIMATE CONTROL MIDDLE EAST
February 2010
TSE is not going to be readily available. What is the load profile of TSE, people may leave AC on when they go off for the summer, so demand for cooling, but no water. For me, only option to supplement TSSE with seawater and RO. –Robert Miller, FVB Energy
TSE is best solution economically, but the problem is that you need quite a lot of TSE, and in Dubai, STPs are under a lot of strain. TSE is definitely a good solution but use it with seawater and even potable. –Paul Beaudry, SNC Lavalin Gulf Contractors
Seawater is a green option. It is a sustainable option. –Aslan Al Barazi, IMEC
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