CEE April-June 2012

- GIVING THE ENERGY INDUSTRY A NEW LEASE OF LIFE The challenging nature ofconverting surface water to feed-wltter has supported the introduction ofmodern treatment technology. Thus, conventional boiler feed– water pretreatment methods are currently being replace£!, by modem membrane-based ultrafiltration (UF) technology. Hyflux Membrane Manufacturing ($) Pte Ltd. 80% of the world's electricity is generated by thermal power plants. More specifically, this electricity is generated by boiler-driven steam turbines operating within these plants. In order to fully maximize a turbine's performance, the feed water entering its boiler should be of high quality, with all impurities filtered prior to the production of steam. Water has been proven to absorb more heat for a given temperature rise than any common inorganic substance. Expanding 1,600 times as it evaporates to form stream at atmospheric pressure, it also has the capability of carrying large quantities of heat. These unique properties of water make it the ideal raw material for heating and power generating processes. At thermal power plants, feed-water (drawn mainly from surface water bodies) is usually stored in a feed-water tank before being pumped into a boiler. However, due to extreme operating conditions (e.g. high temperature and pressure), the feed water has to first undergo extensive treatment and conditioning. If incomplete or inconsistent removal of impurities from the feed-water should occur, microorganisms, colloidal silica and other suspended particle matter form deposits that can cause boiler scaling, impacting the plant negatively. In the beginning Conventional boiler feed-water pretreatment methods implemented to remove impurities include: coagulation, ion exchange, clarifiers, sedimentation tanks and sand/gravel bed filtration . However, due to the unpredictable and varying effluent quality that is produced by such methods, a key issue is the inability of downstream filtration systems to cope with the sudden changes in feed-water conditions; resulting in increased total suspended solids levels present in the permeate. This is also reflected in the permeate Silt Density Index (SOl) or turbidity values, all of which are tell-tale signs of potential boiler scaling. Other key drivers for an alternative pretreatment method are similar to those already affecting the water/waste water treatment business as whole, including: Environmental issues State and federal regulatory bodies are placing increased pressure on the industry to minimize plant discharges. Global awareness to protect ground and surface water bodies has also caused international legislative action to be put in place. Integrated water management The need to preserve water resources and at the same time create new sources supply through desalination, recycling, and other technologies. Outsourced water treatment The industry's desire to focus on its core activities, and to achieve consistent water quality and service. The need for change The challenging nature of converting surface water to feed-water has supported the introduction of modern treatment technology. Technology that delivers performance and economic advantages. Thus, conventional boiler feed-water pretreatment methods are currently being replaced, in many cases, by modern membrane-based ultrafiltration (UF) technology. Advanced surface water treatment systems for power plants usually include steps of UF pretreatment, reverse osmosis (RO) and/ore exchange. In most cases, raw surface water poses a number of serious challenges. Particulates and fouling potential are generally high, and feed-water quality varies considerably throughout the year. In these conditions conventional pretreatment systems, like the ones mentioned above, of struggle to effectively protect the foulant, sensitive RO system. Thus, the 'absolute barrier' UF method is pressed into service as a better alternative for RO pretreatment; in recent years, UF has proven to deliver superi or filtrate water quality, independent of increasingly lower quality feed-water. UF systems significantly enhance the RO flux and produces better quality water at lower cost, sometimes with fewer membrane elements. Because membrane fouling such a serious problem for RO, the cost of UF systems can be justified. Advantages of using UF membranes The advantages of using UF membranes for ROP pretreatment instead of ordinary sand filters include: (i) lower life-cycle costs; (ii) reliability; (iii) excellent and consistent permeate quality regardless of fluctuations in feed water quality; and (iv) smaller footprint. 30