Continuous Separation Techniques in Sweetener Production
Reduced deashing and decolorizing costs in producing HFCS and sugar
By Brad Ahlgren, Calgon Carbon Corporation
Summary
Continuous techniques for ion exchange are now widely used in the production of sweeteners from corn, beet, cane and other feedstocks. The latest versions of the process are also suitable for chromatographic separation.
This article gives an overview of the benefits to be obtained, by comparison with fixed bed technology, and the range of potential applications.
Introduction
About 50% of new separator capacity worldwide is now attributed to continuous techniques for extracting sweeteners from sugar syrups. As a result, processors are achieving significant process economies compared to conventional intermittent fixed bed or activated carbon separation, with comparable or better color and ash removal. Processors who have adopted continuous separation typically report the following results:
(i) 70% less resin loading;
(ii) 30% savings in regenerant costs;
(iii) 70% lower water consumption;
(iv) 50% or better waste reduction.
The ISEP® and CSEP® Systems
The systems they are using are the patented continuous separation systems manufactured by Calgon Carbon Corporation. ISEP (Ionic SEParation) is a continuous ion exchange separator, while CSEP is either a continuous chromatographic or ion exchange separator. Since their introduction to the sweetener industries in 1990, approximately 65 commercial plants, ranging from 1-1500 gallons per minute (GPM), account for 10% of the world's installed base. The 30 newer ones are CSEP installations. The majority are in deashing service, while 5% are in decolorization applications.Economic benefits, though considerable, are not the only considerations. Many processors with deashing requirements have bought ISEP/CSEP simply to improve quality, expecting thereby to increase export sales.
On average, based on a 60 ton/hr cane sugar plant, a fixed bed resin plant achieves about 220 cycles at 30 hours per cycle prior to a resin change. An equivalent ISEP process can extend the same resin to over 500 cycles prior to change out. Regeneration chemical cost savings for the same operation are in the order of $300,000/year. An added benefit is the 50% reduced regeneration chemical and water volumes, which represent significant effluent disposal savings, an important factor in areas with strict environmental regulations.
With the CSEP continuous separation system, savings on resin consumption are as high as 70-75%, with even less waste than the ISEP. Clarity and purity have also improved. Processors ordering a continuous separation system for retrofits or new expansion generally get the improved CSEP deionization or chromatographic equipment.
External Drivers for Process Change
Let's take a closer look at the external drivers for higher-grade sweeteners, and why processors are favoring continuous separation. World demand for superior quality sweeteners is growing. U.S. producers of soft drinks, particularly Pepsi and Coca-Cola, are the largest single sweetener buyers for beverages in the market. They set their own subjective standards for clarity and purity. Other manufacturers have their own high standards, but the demand from the U.S., the most sizable sweetener market, drives the trend toward higher grade sweeteners.Another part of the equation relates to consumer preference and world trade. As income per capita grows worldwide, consumers gain increased financial independence. They demand more and better quality sweeteners (color, odor, taste and purity) for self-consumption.
Common market treaties, such as NAFTA, open the doors to the U.S. market. Producers vying for a share of the sweetener business strive to produce higher grade, partially processed raw sweeteners competitively for refining in the U.S.
These and other economic factors drive world markets toward competitive technologies to extract sweeteners and produce better products at lower prices.
Typical Applications
A few field highlights underscore the overall successes of sweetener processors who have moved to continuous separation:Argentina: A dextrose producer utilizes 70% less resin with two ISEPs as compared with stationary fixed bed separation. The ISEPs deash 45m3 of corn syrup per hour.
Vietnam: A cane processor decolorizes 60m3/hr of melt liquor with an ISEP with approximately half the resin previously used.
China: A fructose/dextrose producer utilizes chromatographic separation for a 42% fructose feed in a small-scale CSEP operation. Even in smaller plants, capital savings over competitive technology are 25-30%.
Mexico: A glucose producer saves approximately 66% in resin costs vs. his former process in a 30m3/hr corn deashing operation. With the ISEP, he is also in compliance with NAFTA environmental requirements.
For economic reasons, totally new sugar processing plants are scarce. The majority of new sweetener processing units installed worldwide are either upgrades or expansions of older plants.
Feedstocks
Processors utilizing CSEP and ISEP are processing any number of feedstocks: corn, cane, beet, wheat, chicory, sorbitol, etc. The majority of sugar-winning processes are based on corn (maize) or cane syrups. These feedstocks account for about 70% of the world sugar supply. The U.S. is the largest producer of corn sugars. Corn processing requires deashing, or removing salts, flavors, and other impurities. Cane liquors require decolorization/clarifying to specified ICUMSA or other color standards.Feedstock type, to some extent, dictates plant design. Processors also have to specify what impurities need removing, color specifications, budget, preferred construction material, environmental considerations, etc. Standard equipment is seldom a perfect fit in any installation. Processors usually need customized separation systems designed to suit their needs, and, if required, pilot tested to confirm operating parameters prior to full-scale operation.
The Argentinean Dextrose Plant
A recent expansion from an intermittent fixed bed to a continuous separator at a corn wet mill in Argentina was custom-built to the owner's specifications. It consists of two ISEP systems. Total flow rate is approximately 200 GPM and total system dimensions are 25 x 10 ft. The processor saved 10% cost and 40% area with the ISEP plant. Fixed bed plants have larger footprints, because usually they need considerable auxiliary equipment to treat the chemical wastes from the resin-stripping wash. The ISEP systems do not; they recycle most of the wash.
The Argentine ISEP system processes corn by deashing to purify dextrose. Hourly feed processing rate is 45m3/hr (200GPM). The estimated into fixed bed resin volume is 50m3 or 1765 ft3. With the ISEP system, the processor utilizes 17m3 of resin or 600 ft3, an almost 70% improvement. Continuous bed deionizers generally operate with the same monospheric resin as in fixed beds.
Yearly savings based on such an improvement represent about $115,000 in resin costs alone. Looking beyond first cost, most processors justify the switchover with the 40% operating cost differential over fixed bed. Savings of this magnitude can return the capital investment on a comparable size plant in 18 months.
Growth Market in Asia
A large growth opportunity is purification of dextrose and sorbitol in Asia. A new $750,000 processing plant in China has expanded its fixed bed unit with a continuous bed ion exchanger. The new plant boosts sorbitol-dextrose production by 50%. The continuous separation unit produces the same volume of sorbitol-dextrose with 5m3 of resin compared to 10m3 previously. The processor expects the 50% resin productivity gains will more than justify the investment, as the yearly savings represent $120,000.For a typical CSEP plant of throughput 150-200 GPM, the capital investment is between U.S. $650,000 and $750,000. The higher recoveries and the resultant added revenues could justify replacing even a new fixed bed unit in areas where environmental regulations are strict. Processors can start up operations in about seven months from the time of the initial order.
Ion Exchange vs. Chromatographic Separation
Although both perform continuous separation, the ISEP and CSEP units operate by different chemical principles.Deionization removes electrically charged impurities by attracting negative and positive ions to oppositely-charged cathodes and anodes.
Chromatography separates particles by the velocity/speed with which they migrate through a medium. Velocity is determined by different sizes, shapes, etc. In chromatographic separation, sweeteners are adsorbed by a resin and are subsequently recovered in a resin-stripping wash.
Continuous units for sweetener processing may be either CSEP or ISEP stand-alone, or an ISEP-CSEP combined system. In either case, processors utilize the same resins as with previous methods.
ISEP Continuous Separation
In a typical ISEP, a carousel arrangement of 30 moving columns of small ion exchange beds slowly rotates between 20 stationary ports. The carousel, rotating under the distribution ports, moves the columns through the normal ion exchange sequence: adsorption, backwash, regeneration and rinse. By contrast, fixed bed ion exchangers perform these steps one at a time in an intermittent batch process. To maintain production continuity, they require backup units for regeneration and wash cycles.In fixed bed deionization, eluent concentration increases rapidly to a maximum, then falls off considerably. The whole ion exchange sequence unfolds over a 12-hour cycle. The chemical regeneration step can take 1-2 hours. In continuous ion exchange, the concentration of eluent is relatively constant since fresh chemical and exhausted resin are continually brought into contact with each other. In such a near steady-state situation, efficiency remains high.
Table I. CSEP/ISEP Continuous Separators Installed Globally
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corn syrup, dextrose, fructose, sucrose |
deashing, decolorizing |
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corn syrup, fructose, dextrose |
deashing, decolorizing |
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dextrose, fructose, sorbitol |
deashing, chromatographic purification |
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dextrose, fructose |
deashing, decolorizing |
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dextrose, sorbitol |
deashing |
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dextrose |
deashing, decolorizing |
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cane liquor |
decolorizing |
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dextrose |
deashing, decolorizing |
Total: 65
CSEP Continuous Separation
The newer CSEP unit works for either continuous ion exchange or continuous chromatographic separation, depending on customer preference. ISEPs, unlike CSEPs, are designed only for deionization applications.
CSEPs allow strict flow segregation with no backflow potential, because the valve indexes from port to port. This feature makes them ideal for chromatographic separation. ISEPs, on the other hand, transition from port to port smoothly, allowing some mixing of different flow streams.
A CSEP carousel arrangement of up to 20 moving columns indexes counter-currently between 20 stationary upper and lower ports. The process typically has three steps: separation, elution and recovery. As the feedstock flows through the columns, it binds to absorbent resins. As the column advances, the sweetener is recovered in an eluent wash. Next, the resin is reloaded, and the cycle repeats.
In deionization, CSEPs offer capital cost advantages over ISEPs. Typically, a system with 20 slightly larger ports is more cost-effective than a system with 30 smaller ones. A 20-port CSEP can offer the same efficiency as a 30-port ISEP due to the elimination of back mixing.
Other Applications
Many sugar producers throughout the world have adopted continuous separation for sweetener production. It is already a mature technology in many areas, and is breaking new ground in others.
A recent application has been the separation of lactoferrin from cheese whey, for the health care market. Food and pharmaceutical processors, fertilizer producers and other chemical processing industries are now realizing the efficiencies and profits inherent in the ISEP/CSEP continuous systems. Any procedure requiring ion exchange decolorization or chromatographic separation is a candidate for this breakthrough technology.
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