Membrane
filtration for sugar manufacturing It’s as though shelves in department stores have undergone a major makeover.
Regular brands have been replaced by ‘herbal’, ‘natural’
and ‘organic’ food. Even advertisements use the biggest font type
to announce ‘pesticide-free’, and ‘100% natural’ food.
Of all the items in the shopping list, sugar too has made consumers read labels
carefully. ‘Mind you’, the savvy shopper will tell you, ‘it
has to be sulphur-free’. And now a sweet innovation Though many laboratory experiments and bench-scale trials with this technology
have been conducted since the 1970s, TERI’s demonstration is one of the
few done worldwide where polymeric membrane modules have been successfully employed
for applications above 60 °C. The only other similar attempt in the sugar
industry has been reported by Koch Membrane Systems, USA. Why membrane filtration? Differences in sugar cane variety, soil and growing conditions, weather patterns,
and seasonal and periodic fluctuations in the manufacturing process itself have
acted as speed breakers. Also, the conventional liming-sulphitation process
does not remove colloidal and dissolved impurities, and thus lends a turbid,
dark brown-yellow colour to the clarified juice. This high-colour sugar (>100
ICUMSA [International Commission for Uniform Methods of Sugar Analysis]) compares
unfavourably with refined sugar (<50 ICUMSA) in the international market.
Further, there are concerns regarding the high sulphite
content (up to 70 PPM [parts per million]) in plantation white sugar. Moreover,
conventional refining of sugar is both capital- and energy-intensive.
Cleaner, healthier, sweeter
A membrane module
Though India is the largest manufacturer of plantation white sugar in the world
(annual production is estimated to be about 26 million tonnes raw value), its
high-sulphur content and high colour does not attract many takers in the export
market. With the help of the STM (Sugar Technology Mission) and TIFAC (Technology
Information Forecasting and Assessment Council), TERI’s path-breaking
demonstration in a sugar mill has established that membrane filtration guarantees
consistently better, clarified juice that leads to superior sugar quality.
A side view of the membrane filtration system
The Indian sugar industry is continually exploring ways to enhance recovery,
improve the quality of the final product, and also reduce energy consumption
in the manufacture of plantation white sugar.
Membrane filtration for
sugar cane juice clarification: a clean, environment-friendly technology
Greater sugar recovery since less sugar loss in molasses
Sparkling clear
sugar cane juice results in superior sugar colour
Shorter juice boiling
times and faster crystal growth rates increase productivity
Easy to integrate,
install and scale up with limited space requirement
Easy to operate
system with minimal maintenance requirement
Not just clear, crystal clear
Any change is difficult, especially one that uproots decades of well-established
processes. The Indian sugar industry too has resisted any modification in its
70–80-year old manufacturing scheme.
Newer ideas like membrane filtration were met with a high
degree of scepticism since it was seen as a ‘laboratory product’
incapable of operation in a sugar mill environment.
 |
| A front view of the membrane filtration system |
To convince the sugar industry about the applicability of membrane filtration for juice clarification, TERI demonstrated the technique through an industrial-scale pilot plant of 10 TPH (tonnes per hour) feed capacity employing indigenous polymeric membranes at the Simbhaoli Sugar Mills Limited, Simbhaoli, Uttar Pradesh. The trials confirmed that the filtrate was consistently superior to the clarified juice obtained by the conventional liming-sulphitation process.
Thanks to the semipermeable membranes that distinguish between molecules on the basis of size, and, to a lesser extent, the shape and chemical composition, as compared to conventionally-clarified juice, the membrane-filtered juice was sparkling clear, had purity higher (by 0.9 units), reduced juice colour (by about 50%), and a drop in the inorganic content (by 5%) .
 |
From left: Retenate, feed, and filtrate |
Beneficiaries
The membrane filtration technology has succeeded in generating interest among
sugar mill owners. Through this demonstration, dissemination of findings, and
one-to- one interactions with decision-makers, TERI has elicited interest in
the progress of this technology among several sugar factories. In addition,
the trials have provided valuable inputs for the improvement of the existing
manufacturing process. The Simbhaoli Sugar Mills Limited, the venue of the pilot
study, has adopted a full-scale juice pre-filtration system that was tested
during pilot trials for the removal of suspended solids from clarified juice.
Applications/benefits
TERI is in the process of investigating membrane improvements to ensure the
operational reliability of the system and also establish the economic implications
of the process. This will lay the foundation for a scale-up and the subsequent
commercial plant design.
The process has been jointly patented by TIFAC and TERI, and the work has won, twice in a row, the prestigious Noel Deer Gold Medal awarded by the Sugar Technologists Association of India.