Peter Brewer describes how IONEX, PuriTech’s patented and innovative continuous ion-exchange process, can be applied to various applications in sugar processing as well as a number of other separation requirements in various industries, including water treatment where the technology is effectively used to minimise waste and reduce environmental impact. This IChemE Award-winning process allows effective purification of cane sugar, sugar beet and corn syrup by using a combination of demineralising, decolourising and softening technology configurations.
Since 1996, PuriTech has continuously refined its IONEX technology to meet increasing global demand from a range of industries for an enhanced and cost-effective ion-exchange process. PuriTech set out to dramatically improve existing ion-exchange technologies including fixed-bed and continuous counter current systems.
Fixed bed resin vessels are used in around 90% of ion-exchange projects. Their design is based on batch operation but compared with continuous countercurrent systems their performance, in terms of treated water quality and cost-effectiveness, is relatively low. Environmental impact is higher as fixed bed units typically waste 2–4% of the treated fluid-flow.
Continuous counter current ion-exchange, which makes use of a turntable, offers an improved approach with some advantages over fixed-bed alternatives. This technology is well established but installation has been relatively expensive, requiring a turntable, or carousel, to rotate the resin vessels around a central valve. This requires complex control sequences to be programmed, controlled and monitored, adding to cost and complexity.
Figure 1
IONEX multi-port valve following factory acceptance testing
The problems identified above have been resolved by PuriTech. Based on an innovative design developed over a number of years, IONEX uses a single, multi-port distribution valve (see Figure 1) as the key component of the process system. The technology is different from other continuous, counter current ion-exchange systems because instead of using a turntable to move large resin vessels, the process disc within the IONEX valve rotates around a central axis. This means that the vessels and pipework remain stationary whilst the valve distributes the different flow streams to the ion-exchange vessels in the different operational zones (see Figure 2).
Figure 2
Stainless steel IONEX multi-port valve installed on a PuriTech continuous ion-exchange system
Ion-exchange separation generally comprises two-phase mass-transfer. This includes an adsorption cycle and a desorption cycle, separated by washing or rinsing of the solid phase between these mass transfer steps. During a full rotation of the IONEX valve, each resin vessel is subjected to an entire sorption cycle, with part of the ion-exchange resin being continuously removed and regenerated, and then returned to the treatment system. The cycle consists of each vessel passing through the Adsorption Zone and the Regeneration Zone, with rinsing cycles taking place in between (see Figure 3). This approach eliminates long periods of down time for regeneration whilst maintaining consistent product and waste characteristics.
Figure 3
Typical ion exchange vessel configuration
With IONEX, rigid pipes can be used between the valve and ion-exchange vessels, which greatly simplifies sealing and eliminates the risk of leaks. Also, a simplified control unit can be used because the system does not use a turntable, and the vast array of automated valves seen on traditional fixed bed systems can be eliminated.
It is also possible to build compact systems based on the technology. The ion-exchange vessels can be positioned in any desired pattern, providing maximum flexibility. IONEX can be retrofitted to replace an existing ion-exchange system, regardless of where the ion-exchange vessels are placed. Also, easy access to the valve, the system's only moving part, and the ion-exchange vessels, simplifies maintenance procedures.
IONEX is well suited for use in the sugar industry as the process can be effectively integrated into the production of sucrose and glucose syrups. Major process applications are demineralisation and decolourising. Decolourising is typically used for removing colour in sugar cane and corn syrups. Demineralisation of sugar syrups is required to typically remove anions, cations and some organic components. Demineralisation is usually used in the purification of sugar cane and corn syrup. The specific removal of calcium is required in the purification of sugar beet. Here, an IONEX system is configured as a softener.
As an example, we will now look at how an IONEX system could be configured for decolourising. The exact setup required would depend on a number of site specific factors that would be evaluated by PuriTech’s engineers. Detailed site evaluations would often include the use of pilot test equipment to determine system design parameters and optimise the operational set-up.
Decolourising is an essential process in the production of sugar. The high costs of traditional decolourisation systems and increased competitiveness in the sugar industry have allowed the advantages of IONEX technology to be exploited in this application.
In the Adsorption Zone, hot syrup is typically fed to the IONEX system and processed through IONEX vessels in parallel. Since the syrup flow rates and viscosities are significantly higher than all the other process streams, the majority of the IONEX system is allocated to the Adsorption Zone. Typically, in excess of 20 vessels would be required.
The feed syrup is distributed by the IONEX valve through the ports to specific resin vessels. A dual resin system can be utilised for decolourising depending on the colour removal level required. As the syrup flows through the bed, the colour impurities are adsorbed on both resins.
Treated syrup from the Adsorption Zone passes back through the IONEX valve and out to product. Sometimes a double pass system is required, the syrup exiting being contacted again with fresh resin. This two-pass arrangement can be done easily in one IONEX unit, and improves colour removal efficiency due to counter current operation – the cleanest resin polishes the cleanest syrup.
After the resin has been saturated with colour, following adsorption and prior to regeneration, an Adsorption Rinse is undertaken, referred to as ‘sweetening-off’ in the industry. The syrup is displaced from the resin using clean hot water while the colour remains adsorbed on the resin. The hot wash water is fed to the IONEX under flow control. The wash zone typically contains 2-3 vessels configured in series. Rinse water can be recycled to the feed or upstream processing or combined with the product syrup.
In the Regeneration Zone, which typically utilises three IONEX vessels, the resin is regenerated and colour removed using a hot salt solution. The solution is typically sodium chloride with a small amount of alkali added. The Regeneration Zone is typically configured as down flow, the opposite of the Adsorption Zone.
After the resin has been regenerated, the resin moves on to the Regeneration Rinse Zone. In this operation, caustic brine is displaced from the vessels using clean water. The hot wash water is fed to the IONEX system under flow control. The rinse zone typically comprises three vessels in series. The rinse effluent is typically reused as dilution water for the concentrated salt regeneration solution, thus maximizing the usage of the recovered salt. After rinsing out the caustic brine, syrup is used to displace clean water from the resin bed in a single vessel ‘sweeten-on’ operation. This additional step reduces syrup product dilution.
Useful Links
PuriTech website: www.PuriTech.co.uk
About the Author
Peter Brewer is General Manager at PuriTech, contact via their website.