Batch centrifugals - ColourQ 1700 BC
START spraying at the right time - STOP spinning at risk of vibration
The ColourQ 1700 BC detects the (often several) colour shifts of the wall of crystals during acceleration.
The first shift occurs as soon as enough mother liquor has been purged to bare the crystals in the inner layer of the wall. Depending on the massecuite this may happen already during filling. Usually it happens a little after start of acceleration. In extreme cases it happens late in the acceleration. The two easily detected extremes are unwanted, because they may give large and dangerous vibrations.
For a standard massecuite the colour shift happens in the early acceleration. The earlier the colour shift, the greater the risk that the wall of crystals will be left standing without any liquor left between the crystals. In this case the centrifugal force will pump air through the wall and dry out the remaining film of liquor on the crystals, making it difficult for the spray water to remove the film. Further, the resulting increased film of mother liquor will seal the crystal surfaces and trap more internal water within the crystals during drying, impeding conditioning before storage.
For massecuites with a large CV there is a risk the crystals (with the higher density) will sediment in front of the screen, impeding the purging of the liquor. At that moment the liquor can be seen as a layer of liquid on the inside of the crystal wall. Now it is important to hold the spray water. The thicker the layer of liquid, the greater the risk of waves in the liquid. Once the visible liquid has disappeared, the spray water may be started. If the visible liquid has not disappeared at higher rotational speed, there is a risk of a breakthrough of the liquid. This will give imbalance in the basket, so the signal from the instrument should be used to stop the rotation before a critical speed is reached.
For a slowly purging massecuite, there is a risk that the spray water may catch up with the liquor. Then the water mixes with the liquor and loses some of its ability to wash off the liquor. When the rate of spraying is larger than the rate of purging, a layer of liquid will again be visible inside the wall of crystals. The instrument will detect this and give a signal to stop spraying until it is safe to resume.
The ColourQ 1700 BC instrument mounted on top of a centrifugal
The measurement spot inside the centrifugal basket
Graph showing the colour (orange curve) going high from the moment the massecuite reaches the point of measurement and staying high until the acceleration has started. In this example the spraying starts relatively late.
Graph showing a start similar to the previous example. Here the CV of the crystals is relatively large. When the (higher density) crystals are forced towards the screen by the increasing centrifugal force, they make a dense sediment in front of the screen, forcing the liquor inwards in the basket. The liquor is seen as a layer of dark liquid on the inside of the crystal wall. Only after further acceleration the centrifugal force is strong enough to push the liquor through the dense wall of crystals.
In this example the mother liquor purges slowly. When the spraying starts with water being added at a higher rate than the liquor is purged, the total amount of liquid in the sugar wall increases.
This continues to a point, where the liquid gets visible inside the wall of crystals. For two reasons this should be avoided:
The free liquid is a safety concern, because it may get waves and cause imbalance in the basket.
The water catches up with the liquor and mixes with it. The water is less efficient for cleaning, when mixed with the liquor, so more water is needed to clean the liquor film off the crystals.