Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/545366
PROJECTS | 26 | Desalination & Water Reuse | August-September 2015 By moving away from the existing desalination and purification technology employed at the refinery, the system designed by Sychem, incorporating CEDI, made substantial savings. The capital cost of a CEDI system is 1-1.25 times the cost of RO, for each m 3 /h of output. For smaller systems this is on level terms with MBDI including regeneration skids. As the treatment plant size increases, CEDI becomes more expensive to install but where a neutralization system is required, MBDI always has the higher capital cost. Of greater importance, however, is the marked difference in operating costs. As acid and caustic costs continue to rise each year, the costs of operating a chemically regenerated MBDI plant rise with them. The chief operating cost element for CEDI is electricity, which a system typically consumes at less than one third of the rate of a reverse osmosis booster pump. A direct cost comparison between the cost of the existing MSF/XI units operated by the refinery and the cost of the UF/RO/ CEDI units operated by Sychem arrived at the following: MSF/XI permeate – € 4/m³ (US$ 4.4 including power, cost of steam, spare parts, manpower, regeneration chemicals and other consumables); and UF/RO/CEDI permeate – € 1/m 3 (US$ 1.1 including power and fixed cost for operation and maintenance contract). With total water production at 2,366,000 m 3 /year, the calculated annual saving is US$ 7.83 million giving a payback time of one year. ChallEngES and ThE fuTuRE Some challenges lie in dealing with the wide variation in feed water quality available to refineries and power stations. Developments in membrane microfiltration to meet these challenges, for example, have included real advances in water clarification, carbon dioxide degassing and pre-treatment. However, it is at the demineralization stage that the treatment process has undergone a revolution. The rise of CEDI in polishing demineralization parallels a global trend towards high- efficiency technologies that recycle and reuse materials. It meets the need to reduce chemical usage and to comply with increasingly stringent waste discharge limits. And it reduces health and safety concerns by minimising bulk chemicals handling. Crucially, CEDI can contribute to significant savings in the cost of ownership of skilfully designed water treatment schemes. l Straits ahead: significant savings in the cost of water treatment schemes.