In general, the evaporation station of a beet sugar factory is treated with an alkaline cleaning solution at first after the campaign. Thanks to the application of antiscalents intermediate cleanings during the campaign are carried out in exceptional cases only.
In the cane sugar industry, however, intermediate cleanings cannot be avoided until now because of the special properties of the juice. During the alkaline treatment calcium compounds - such as calcium oxalate and calcium sulfate - insoluble in acid are converted into calcium carbonate which is soluble in acid. The highly alkaline solution containing caustic soda well dissolves degraded organic substances.
KELLER & BOHACEK early started to recommend and improve the cleaning procedure with caustic soda and sodium carbonate by using additives. The result of the cleaning with sodium carbonate and caustic soda alone is not that efficient. Often this process takes time as layers which are difficult to penetrate prevent the further conversion of the scale. Only the addition of dispersants and surface-active activators complete the process so that in most cases the alkaline cleaning is sufficient.
Principle of action of the KEBO alkaline cleaning: The success depends on the conversion of the components of the scale which are difficult to dissolve and the destruction resp. detachment from the tube walls at sufficient reaction velocity. The conversion of e.g. calcium oxalate into calcium carbonate is connected with a modification of the volume in the crystal structure.
The tensions occurring at this process may lead to detachments of the individual layers from each other but also from the wall. This process is favoured by the sequestering and dispersing components of KEBOSOL which also detach, decompose and finally disperse the layers of the scales.
The surface-active properties of the activator in the KEBOSOL support the penetration of the cleaning solution into the capillary interspaces between the layers as well as between scale and tube wall. The interaction of all components succeeds in many cases in getting a clean evaporation station only with the alkaline cleaning.
Boiling tubes with smooth surface as in case of VA-tubes are advantageous as they are easier to clean. Also the application of the antiscalent KEBO DS in the preceding campaign has a favourable influence on the cleaning, as the mainly thin scale nevertheless being formed, however, is softer in its structure.
It is of high importance that prior to using the KEBO alkaline cleaning procedure no other alkaline procedure has been carried out as calcium carbonate which has been formed without using the dispersant adheres at the tube surfaces. The additive concentrations used for Robert evaporators may vary for falling film evaporators or plate evaporators depending on the construction. We advise you if requested.
If there are still residual scales after the first alkaline cleaning, a second one is useless. A scale sample should be taken to be analyzed in our laboratory. Then KELLER & BOHACEK can elaborate a recommendation for a further cleaning. In most cases an acidification is necessary. It has become unusual to reach the aim by mechanical cleaning.