Continuous centrifugals - ColourQ 1700 CC
In continuous centrifugals the instrument helps improve the separation by indicating the colour of the crystals rolling up the screen. At the same time it monitors the amount of "fingers" of mother liquor. The "fingers" transport mother liquor up the screen and counteract the good separation. With the information from the instrument it is possible to adjust the steam and water applied through the many valves on the machine to the optimum settings for separation of the current massecuite. As soon as the massecuite changes, the instrument will display the change, so the operator can adjust the settings.
The "colour ring" you see inside the continuous centrifugal is an optical illusion. Please see the photo below, showing the basket in a stroboscopic light. Due to the high speed of the basket your eyes see just a colour gradient from the bottom to the top of the basket, while the variation really is a combination of two:
1. The crystals getting brighter and brighter as they move up the basket.
2. The "fingers" getting thinner and thinner.
This photo shows the area of measurement on the screen, and the fingers of liquor taking non-sugar with the crystals.
Analysing the above photo you realise the fingers give a major contribution to the liquor/non-sugars conveyed up the screen and leaving the basket with the crystals. Therefore, in order to get a good separation in the centrifugal it is essential to avoid - or at least to reduce to a minimum - the fingers. Based on this, a good adjustment of the centrifugals consists of two elements:
A. Reducing the fingers to a minimum by ensuring an even distribution of the massecuite around the basket.
B. Adjusting the spray water to find a good compromise between removal of the film of mother liquor on the
crystals and minimising melting of good sugar from the crystals.
Splitting the adjustment job in two separate parts makes the adjustment much easier and allows a much better separation to be obtained.
It is here the ColourQ 1700 CC comes in as a tool. It measures not only the colour of the combined crystals/fingers moving up the screen, but gives also a measurement of the relative amount of fingers. With these two indicators you may first reduce the fingers and then adjust the cleaning of the crystals.
The instrument has shown results that challenge the commonly accepted rules of thumb. New settings have improved the separation. For after-product/low-grade raw the crystal purity has been improved and/or the molasses purity reduced.
The ColourQ 1700 CC is mounted on the top plate, looking through a hole vertically or at an angle down to the crystals. Here it is possible to measure how well the crystals are cleaned and if "fingers" of mother liquor follow the crystals up the screen.
The task of controlling the process in the centrifugals is a never-ending challenge, because the massecuite changes constantly. By measuring in real-time you have a chance to follow the changes and do timely readjustment of the centrifugal.
The ColourQ 1700 CC instrument installed on a continuous centrifugal
Graph showing natural variations without making adjustments
Graph showing variations, when doing manual adjustments
Graph showing variations in colour (orange) and amount of fingers (blue)