Ion exchange resins for the paper and pulp industry
Water is an essential material for manufacturing paper and pulp and is used in large quantities. This begins with the pulping of wood as the raw material and extends to its use in the giant paper machines on which cellulose fibers are separated from an aqueous suspension and then gradually drained. Finally, the finished paper is wound onto rolls at a rapid speed of up to approximately 2,000 meters per minute. Already, this high production speed necessitates the most stringent of requirements for reproducible process conditions that are adhered to precisely.
To ensure that this complex process works reliably and produces paper of a consistently high quality, the water used must also meet strict requirements. The better the water quality, the more reliably and efficiently good paper can be produced. In particular, the type and concentration of the dissolved constituents, whether they be inorganic salts or organic molecules, must be kept constant within narrow limits.
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.
Ion exchangers are also indispensable wherever steam is used – for heating tanks during pulping, for example, or for drying paper webs. As in thermal power plants, they ensure that water-steam circuits operate reliably and with little maintenance. This requires careful treatment of the make-up water and also high-performance condensate polishing.
Finally, process water recirculation is vitally important for the sustainability and cost effectiveness of the manufacturing process, especially because of the large quantities of water used in the paper industry. Even if this is already largely realized today, there is still potential for improvement. This applies to the use of the hood condensate from the moist exhaust air of the dryer section, for example, which is separated from the exhaust air in the course of heat recovery.
For these and other applications, LANXESS offers a comprehensive range of special ion exchange resins that are tailored to specific requirements. Find the best product for your needs now.
Having as few dissolved substances such as iron, ammonium, calcium and magnesium salts as possible in the process water provides the most favorable conditions for paper manufacturing. Only then can various paper chemicals such as optical brighteners, colorants, fillers, and retention agents take optimum effect. That is why the fresh water used for paper manufacturing in Germany is generally of potable quality.
Lewatit® ion exchanger types can be combined to beneficial effect to soften or even completely desalinate (demineralize) the fresh water. This allows the water required to be obtained reliably and economically. When used paper is used as a raw material along with or instead of native pulp in particular, calcium salts from fillers that it contains can enter the process water in larger quantities and also increase water hardness.
Our Lewatit® ion exchangers are used in paper plants around the world to ensure, for example, that added optical brighteners give the paper the highest degree of whiteness by reliably removing ionic, organic compounds such as humic acids from the process water. Such humic acids even absorb UV light and would otherwise compete with the brighteners.
Through droplets that are carried along when the paper is being dried, salts – together with a variety of organic compounds from the white water – find their way into the hood condensate. Using LewaPlus® software, a multi-stage solution for treatment can be calculated based on the results from the analysis of this condensate from the heat exchangers.
Since the hood condensate is less polluted than standard feed water that is used, it can be assumed that ion exchangers can be successfully used for purification. The resultant water can be fed into the process water cycle. Following an increase in the pH value, sufficient reduction in water hardness, and a reduction in organic impurities, it can also be mixed with the make-up water.
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 are operated 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 leaks can allow the ingress of 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.
