Ion exchange resins for the power generation industry
Water-steam circuits are at the heart of all thermal power plants that generate electricity from fossil or nuclear fuels. Here, the water and steam serve as an energy carrier and cooling medium.
Around the world, Lewatit® ion exchange resins help to ensure the efficient, safe and reliable operation of these power plants over many years. For example, they are essential for demineralizing the cooling and make-up water and for condensate polishing in the water-steam circuits. They are the only means of preventing scale formation, thus promoting optimal heat transfer on an ongoing basis. In addition, they can effectively reduce or even prevent corrosion in this way. These effects, together with the high regenerability of the resins, ensure long-term, economical power plant operation.
In nuclear power plants, ion exchangers are also important components in the chemical and volume control system (CVCS) that controls and monitors water volumes and dissolved constituents in the cooling circuits. With the aid of selective ion exchangers, both radioactive and non-radioactive ions can be removed from the process water and the waste water flow. The water in the holding basins for spent fuel elements is also passed through ion exchangers for treatment.
For all of these and other applications, LANXESS offers a comprehensive range of ion exchangers that are tailored to specific requirements. Our LewaPlus® design software can model various combinations of ion exchange resins and exchange stages on a made-to-measure basis and analyze their properties. This provides the user with maximum confidence that they will obtain the optimum treatment solution for the relevant feed water and the required process water quality for the given situation.
Thanks to its high specific heat capacity, water is an excellent heat exchanger. Steam is an effective energy carrier. These properties are utilized in water-steam circuits in numerous industrial processes. Depending on the quality of the feed water used in such cycles, this may require desalination or softening beforehand.
Steam boiler manufacturers provide detailed specifications for feed water based on VGB guidelines (e.g. max. electrical conductivity; silicic acid, sodium and organic compound content) in order to ensure optimal operation. For example, forced-circulation boilers that work under high pressures of up to 290 bar and at hot steam temperatures of 600 °C require very pure, desalinated water. This is the only way to prevent turbines, for example, from becoming corroded, contaminated, or damaged or to avoid deposits forming there.
The usual sources for feed water are well or surface water, reused waste water, and seawater. This variety makes clear that the treatment steps also need to be configured individually. Our LewaPlus® design software is suitable for this.
In most cases, the make-up water is conditioned with ammonia in the water-steam circuit in order to create an alkaline environment, which aids corrosion protection. Nonetheless, impurities are created during operation in a water-steam circuit, which for the most part find their way into the condensate in the form of ions.
Moreover, even very small cooling water leaks can allow the ingress of inorganic salts and organic compounds that then increase the risk of corrosion or lead to foaming under the extreme pressure and temperature conditions in the boiler. Therefore, treatment with ion exchangers is sensible or necessary in many cases in order to ensure reuse of the condensate as make-up water.
The ion exchange resins from the Lewatit® KR series stand out thanks to their particularly high degree of regeneration and boast particularly good mechanical, chemical and osmotic stability.
Their monodispersity with a very low fines content creates the conditions for very low pressure losses compared with heterodisperse standard ion exchangers. When used in radioactive water circuits, they perform a variety of tasks and produce a water quality that can meet all the requirements of the nuclear power industry. Thanks to their outstanding hydraulic properties, these resins allow particularly high flow rates.
In nuclear power plants, ion exchangers are important components in the chemical and volume control system (CVCS). CVCS controls aspects including the boric acid content in the water of the primary circuit. Since 10B is a highly effective neutron absorber, its concentration has a direct effect on reactor performance.
High-purity ion exchanger mixed beds containing cation exchangers partially preloaded with 7Li serve as purification filters. Together with initially Li-free depletion filters that are connected in parallel and absorb the 7Li that was also produced from boron in the reactor process as a result of neutron capture (coordinated B-Li mode of operation), they ensure a largely constant concentration of lithium hydroxide that acts as an alkalization agent.
