Plastic compact heat exchangers for single-effect desalination systems

Use of plastic materials and compact heat exchangers remains to be found on a limited scale in the desalination industry. This work focuses on perform ance evaluation of plastic and compact heat exchangers in the single-effect mechanical vapor compression desalination system. The analysis considers a number of tubing materials that includes PTFE plastic, high steel alloys, Cu/Ni 90/10 and Cu/Ni 70/30, and titanium. The analysis includes determinat ion of the specific power consumption and the evaporator and preheaters spe cific heat transfer area for various materials. Analysis is made as a funct ion of variations in the condensate and the brine boiling temperatures. The specific cost is evaluated for various construction materials. Results sho w that the specific power consumption is independent of the construction ma terial and depends only on the compression range. Also, the lowest specific heat transfer area is calculated for Cu/Ni 90/10. However, the lowest cost is obtained for the PTFE system because of the much lower cost of the mate rial. Corrosion considerations and the associated reduction in the cost of corrosion inhibitors give an added edge for the use of PTFE plastic. Other factors that favor the use of plastic evaporators and preheaters include ea se of construction and machining, lower installation and erection cost, abi lity to operate at higher top brine temperatures without fear of the effect s of scale formation, use of acid cleaning, and virtual elimination of in-l eakage problems. These merits of the plastic and compact heat exchangers an d the analysis results should encourage the industry to take active steps i n adopting these systems.