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SUGAR PRODUCTION

Client: British Sugar – York and Newark UK

Operating parameters: heating raw sugar juice solutions using condensate and pan vapours

BACKGROUND INFORMATION

Increasing pressure on costs within the sugar production industries has led to the need for increased efficiency in the various thermal process that take place within the sugar factories. The waste products from the processes are therefore reused whenever possible to extract and reuse as much energy as the processes will allow.

Many of the fluids and vapours are contaminated and can present a severe fouling problem when heated. At the British Sugar factory at York they reuse condensate to heat the raw sugar juice immediately after crushing and steeping and this results in severe fouling on the Raw Juice fluid circuit as protein and dirt deposit out on the surface.

At the Newark factory they needed to boost production at one stage of the process which uses Pan Vapours from a previous stage to heat the sugar solution while maintaining the same basic size envelope and connecting to the existing pipework connections.

THE DESIGN PROBLEM

Because of the fouling nature of the product HRS were asked to supply corrugated tube heat exchangers for the Raw Juice heating at York and subsequently for a Pan Vapour condenser at Newark. Experience has proved that the enhancement in heat transfer rates can be significant when corrugated tubes are used but British Sugar were more interested in these cases in reducing maintenance costs by minimising the size of the heat exchangers and if possible reducing the down-time for cleaning. The units had to be designed for retrofitting into existing installations and connection centres and positions had to be respected.

THE SOLUTION

Because the Sugar Juice is likely to be contaminated with solid particles and fibres at the stage of the process where the HRS Spiratube units are used it was decided to used 25 mm tubes ‘Hard’ corrugated in vertically mounted fixed tubeplate heat exchangers.

It has been found during several campaigns that the corrugated tubes give the enhancement in heat transfer originally forecast. The rate of fouling, because it is essentially a chemical process which does not depend on either tube wall temperature or fluid turbulence, is the same as on the original plain tube heaters but has proved to be significantly easier to remove from the tube surface. The cleaning process used by British Sugar uses a high-pressure water jet to break the fouling layer away from the tube surface and flush it through the heat exchanger. Because of the significantly high turbulence generated by the corrugated tube the fouling film that forms on the tube is discontinuous, the inner ‘peak’ of the corrugation remaining clean even when the remaining tube surfaces are fouling rapidly. This enable the water jets to break the fouling layer away from the tube wall far more easily than with the smooth tube units.

TESTS

Because of the variability of the Sugar solutions during the processing stages British Sugar provided facilities within the York factory for HRS Spiratube to carry out heat transfer tests on several different forms of corrugation using several different sugar products.

The test results as presented to British Sugar illustrate that significant heat transfer enhancement can be achieved during the several stages of the sugar production process when using corrugated tubes in their various forms.