During the process of steam generation in power plants, the steam cools and condensate forms. The condensate is collected and then used as boiler feedwater. Prior to re-use, the condensate must be purified or "polished", to remove impurities which have the potential to cause damage to the boilers, steam generators, reactors and turbines. Both dissolved (ex. silica oxides) and suspended matter (ex. iron oxide particulate), as well as other contaminants which can cause corrosion and maintenance issues are effectively removed by condensate polishing treatment.
Condensate polishers are typically ion exchange, resin-based systems. Siemens' condensate polishing systems feature a mixed bed design, which uses both cation and anion bead resins. Also referred to as deep bed systems, our polishers use strong acid and strong base bead resins to produce a very high quality demineralized water. Typical resin bed depth totals approximately 3 feet, (1 meter) which is sufficient to keep pressure drop across the bed low while achieving a pure condensate quality and acceptable polisher run length.
In-bed filtration of suspended solids and particulate also takes place as the condensate passes through the resin bed. A higher flowrate allows solids to penetrate the bed surface and the remaining bed is used to capture fines.
Deep bed condensate polishers are typical in applications where high levels of total dissolved solids (TDS) are present and in cases where the power plant may have minor condenser leaks. Nuclear power plants, in particular, tend to favor deep bed condensate polishers due to the strict water purity needs of their system.
Typically, Siemens' condensate polishing systems involve several service vessels operating in parallel. When the exchange capacity of the resins are exhausted, the "spent" resin is transferred to an external system for separation, backwashing and regeneration. Regeneration can be done either off-site at a Siemens regeneration facility, or on-site using the customer's own regeneration station. Following a rinse step, the resins are recombined and returned to the vessels. Many nuclear power plants in North America, however, no longer regenerate resins, instead choosing to transfer them for use in rad-waste treatment applications.
Condensate polishers save power utilities money through a reduction in facility unit start up times, thereby saving fuel, direct labor and minimizing blowdown.
Condensate Polishing Technologies for Your Industrial Process Water Applications:
Ion Exchange Systems