Water quality improvement studies in LTTD plant

• Published in: Desalination and water treatment 2016-11, Vol.57 (52), p.24705-24715
• Main Authors: Balaji, D., Jayaraj, K., Phani Kumar, S.V.S., Ramana Murthy, M.V.
• Format: Article
• Language: English
• Subjects: Chambers; Cooling water; Deep sea; Demister; Desalination; Entrainment factor; Evaporation; Flash chamber; Floods; Heat exchangers; High tides; Low temperature; LTTD; Pool evaporation; Salinity; Seawater; Spout pipe; TDS; Tides; Water quality
• ISSN: 1944-3986; 1944-3994; 1944-3986
• DOI: 10.1080/19443994.2016.1145601

Low-temperature thermal desalination plant (LTTD) is a process which involves evaporation of warm surface seawater at 28–29°C inside a vacuum flash chamber, which is maintained at a subatmospheric pressure of around 24–27 mbar [abs] and the resultant vapor is condensed in the shell and tube heat exchanger using cooling water drawn from deep sea, which is available at 12–13°C. Two configurations have been used to conduct experiments, namely bare spout and elevated demister configuration. During the operation of LTTD plant located at Agatti Island, an increase in the salinity of product water from 110 ppm during low tide to 570 ppm during high tide is observed in the bare spout configuration. Increased tide level leads to increased flood level inside flash chamber. Increased flood level results in reduction in the separation distance between the brine liquid level and the de-mister. As a result, the salinity level of product water is increased beyond an acceptable limit. In order to bring down the salinity level, a modification is performed on the geometry of the spout pipe and elevation of demister inside flash chamber which is named as elevated demister configuration. The mechanism, which improves water quality by implementing elevated demister configuration and drawbacks of bare spout configuration are discussed in this paper. Necessary experiments are conducted for studying the effect of both the configurations on the product quality. Results based on the experimental studies show a significant improvement in the water quality ranging from 4 to 45 ppm between low and high tides when implementing the elevated demister configuration.