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WATER SOFTENING TECHNIQUE


Washing Dishes

COUNTER CURRENT REGENERATION BACKGROUND ION EXCHANGE

This is a proven technology that has been commercialized for many decades. Applications for ion exchange include both simple processes, such as softening, as well as the more complex systems such as deionization for water recycling. Recently, the technology has expanded to include more selective processes which target certain contaminants such as nitrate and arsenic removal. With an expanding interest in ion exchange applications, it is appropriate to review one of its fundamental principles: the regeneration process.

Regeneration is the backbone of any ion exchange application, since without the ability to reverse the ion exchange process (or regenerate), this technology would prove inefficient and uneconomical for most applications. Upon further examination of the regeneration process, we find that for most applications, a counter-flow regeneration method (regenerant flow in the opposite – or counter - direction of the service flow) can provide substantial returns to the end-user in terms of product quality and operating cost reductions.

The growing concerns regarding total life cost management and environmental impact will encourage the industry to re-learn the art of counter current regeneration. The process of counter current regeneration has been around since the 1970s; however, this treatment method has been typically restricted to high-end applications, as it requires more exacting controls over the regeneration process. Industrial and commercial softening systems have been dominated by simpler, co-current products, a design intended to minimize the users’ initial capital cost.

Long viewed as a complicated process, in reality, the sequence used in counter current regeneration is no more complex than its co-current counterpart. The perception of complexity is likely rooted in the fact that it is different. Understanding the practice of counter current regeneration starts with an understanding of the process by which an ion exchange media is exhausted. Following the service flow through the media bed, one will find the greatest concentration of exchanged ions at the entry point of the media bed.

As the flow path is followed through the depth of the media bed, a natural concentration gradient is formed. Understanding this phenomenon is the key to unlocking the benefits of the counter current process. By reversing the flow through the exhausted bed, the concentration gradient works in favor of counter current regeneration. In principle, this allows regenerant chemicals to be introduced first to the media that is least exhausted and then, gradually, to the completely exhausted media at the service entry to the tank.

Benefits of this regeneration orientation include enhanced efficiencies as well as improved product quality. These benefits are further explained as the comparison between the two regeneration processes is discussed.


TECHNIQUE COMPARISON

Co-current, the common In examining co-current regeneration, we find the sequence typically consists of four stages: backwash, brine, slow rinse and fast rinse. During the backwash stage, any debris trapped within the bed is backwashed out and the bed is reclassified and settled. Reclassification optimizes the regenerant flow through the bed and improves the effectiveness. Let's illustrate this principle:

COUNTER CURRENT REGENERATION BACKGROUND ION EXCHANGE

BACKWASH & TECHNIQUE COMPARISON

A FINAL NOTE


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