Demineralization, or the removal of virtually all ionic mineral contaminants from water, is crucial for producing water of sufficient purity for a variety of industrial applications. Demineralized process water is used to ensure the quality and consistency of various products, as well as to ensure consistent and predictable function of sensitive equipment. While it’s clear that demineralized water is useful for a range of applications, you might be wondering “What is the best way to demineralize industrial process water?”
Although demineralization can be accomplished by other technologies, this article will focus on ion exchange resin technology. We’ll describe common demineralization system designs and offer some considerations for determining which technologies are best for your plant and processes.
Choosing the best demineralization technologies
By definition, demineralization is the near-total removal of inorganic salts from water. In most industrial process water treatment applications, this is accomplished through ion exchange (IX). Given that IX demineralization systems can be designed to meet various needs, there is no one best way to demineralize process water. Instead, choosing the best demineralization strategies comes down to matching IX system design to your unique process conditions, purity specifications, and plant environment.
The underlying principles of the demineralization process are the same from one system to the next, but there are two main aspects where a system can be customized to fit a specific application. The first of these is system configuration. IX demineralization systems are typically offered in either of two configurations, including:
- Twin-bed ion exchangers. Twin-bed demineralization systems consist of two columns or beds, one containing a cation exchange resin, and the other containing an anion exchange resin. Process water is cycled through the beds sequentially, first through the cation resin, where mineral contaminants are replaced by hydrogen ions, and next through an anion resin, where mineral contaminants are replaced by hydroxyl ions, which combine with the hydrogen ions to form pure water.
- Mixed-bed ion exchangers. Mixed-bed demineralization systems are a single unit or column that houses a mixture of cation and anion exchange resins. As process water is cycled through the resins, IX reactions take place repeatedly within the unit, resulting in comparatively greater removal of ionic contaminants comparative to twin-bed systems.
The second aspect is the selection of specific resin products to be used within the IX unit. There are hundreds of IX resins on the market today, many of which offer functional benefits for specific applications. Below, we’ve outlined some key factors to consider in order to help you to navigate these key aspects of IX system design, and ultimately zero in on the best demineralization solution for your needs.
Process water quantity and consumption
Plants whose processes demand large quantities of demineralized water are often better served by twin-bed IX demineralization systems. The reason for this is twofold. First, dual bed systems consist of multiple columns versus the single column mixed-bed configuration. Secondly, twin-bed IX systems offer a comparatively simpler resin regeneration process, allowing for potentially less downtime, and less consumption of regenerant chemicals and/or rinse water each time the IX resins are exhausted.
You can get a rough estimate of the total volume of process water that your demineralization system can treat before a regeneration cycle is needed by simply dividing the exchange capacity of IX unit by the total dissolved solids (TDS) present in a representative sample of your process water. Understanding your capacity needs will help you to predict the frequency of resin regeneration cycles and resin life, and to decide whether it’s worth it to invest in a larger unit.
Process water purity specifications
Finding the best demineralization strategy also depends on the level of purity needed to support a given process or to protect downstream equipment from corrosion or other damage. Mixed-bed demineralization units produce water of a comparatively higher purity than do twin-bed units, and are therefore employed for processes requiring the most stringent purity standards, such as microelectronics and pharmaceutical manufacturing, or feed water for high-pressure boilers. Mixed-bed demineralization typically employs a mixture of strong acid cation (SAC) resins and strong base anion (SBA) resins, generally with a higher ratio of SAC relative to SBA resin. Typically, mixed-bed units are deployed for polishing to achieve extremely pure water.
For processes with slightly more forgiving purity standards, dual-bed demineralization systems may be a better choice, as they can be less costly to maintain. Twin-bed demineralization systems employ sequential IX columns, most commonly with a SAC resin followed by an SBA resin. This general-purpose IX system configuration produces demineralized water of a sufficient grade to support most industrial processes, such as rinse water for food and beverage manufacturing and low pressure boilers. Alternatively, twin-bed systems that use a SAC resin followed by a weak base anion (WBA) resin are sufficient for applications requiring a relatively lower grade of demineralized water. These systems are sometimes used for rinse or cleaning water in industrial settings, or where there is relatively little silica present in a feed stream.
There are a variety of other factors to consider in identifying an optimal demineralization strategy. These include:
- Temperature. In order to ensure the longest possible operating life for your resins, it is advisable to select resin products that accommodate the temperature of your process stream. When in doubt, be sure to consult manufacturer recommended operating temperatures when selecting an IX resin.
- Hardness/TDS. Streams with high hardness can put a strain on demineralization systems, forcing more frequent regeneration cycles, and shorter overall resin life. This can be mitigated by employing a two-step IX system with a WAC unit ahead of a SAC unit, or by employing some form of pretreatment, such as RO.
- Variable stream content. Mixed-bed units are more susceptible to resin fouling and inferior system function in the presence of unanticipated contaminants. Thus, if the contents of your process stream fluctuates over time, a twin-bed demineralizer may be a better choice. Alternatively, various pre-treatment strategies may be employed ahead of a demineralizer to protect it from variability in stream content.
- Maintenance and downtime. IX resins will become exhausted through normal use cycles, and will require periodic regeneration and replacement. For lower-capacity systems, it is possible to contract with a servicer for offsite resin regeneration and replacement, as is the case for most modular demineralization systems. If your plant would prefer to shoulder its own resin maintenance, however, you’ll need to determine how much downtime is acceptable to permit periodic resin maintenance. For production lines with low tolerance for downtime, it may be best to choose a design the permits removal of resin for external regeneration. This allows for the flexibility to rotate in a backup quantity of resin while one batch is being regenerated.
These are just some of the process conditions that will determine which types of demineralization are best suited to a given process. Choosing the best demineralization system for your plant is often a highly individualized undertaking which can be simplified by a qualified water treatment specialist. An expert can perform analyses to help you understand your demineralization goals and challenges, and can help you to identify the best water treatment technologies for your unique process water needs.
How SAMCO can help
SAMCO has over 40 years’ experience in identifying appropriate IX resin technologies to help lower costs and waste volumes while increasing product quality. For more information or to get in touch, contact us here to set up a consultation with an engineer or request a quote. We can walk you through the steps for developing the proper solution and realistic cost for your IX treatment system needs.
To learn more about SAMCO’s innovative IX resin solutions, visit our page on ion exchange resin technologies here.