EVALUATION OF THE HUNTERLAB COLOUR MEASURING INSTRUMENT
Preliminary work done by the Sugar Milling Research Institute (SMRI) showed that the HunterLab colour measuring system could possibly be used to estimate the colour of raw sugar. With this system it was possible to measure the colour within a short time (less than one minute). The instrument (ColorQuest LAV 4S0/0") has been used for several seasons at the Transvaal Sugar Limited Malelane (ML) factory for measuring the colour of brown sugar. Work was also done on refined and C-sugars. This paper summarises the evaluation of this instrument by both the SMRI and ML. Introduction Due to market requirements, ML produces two types of raw sugar, namely light (1000 ICUMSA 420 colour) and dark ( 1 500 ICUMSA 420 colour) and the same equipment (pans, crystallisers, etc.) in the raw sugar factory is used to make the two types of sugar. In order to assist the packaging department personnel to decide which type of brown sugar has to be bagged, a rapid indication of raw sugar colour is required. The thirty minutes required to determine colour by Figure I. the ICUMSA method is too long and it was therefore decided to evaluate instruments that could measure the colour of The spectrally based system is considered to measure 'what sugar "on-line". the eye sccs' and utilises the measurement of three parameThere are a number of instruments available which are suitable for this task (Nielson, 1996 ; Anon, 1996). The SMRI evaluated two HunterLab instruments during 1995 and 1996, namely the Miniscan which is a portable instrument (Dunsmore, 1995) and the ColorQuest LAV 45"/0°, which is a laboratory model, with a view to their suitability for use in the South African sugar industry. The laboratory model was subsequently evaluated by the Malelane factory and used i n the factory during the past three seasons. Description and basis of operation of the ColorQ~iest system The ColorQuest spectrophotometer (Figure 1) is a colour measurement system with a choice of optical sensors depending on the application. Each sensor has its own illumination and viewing geometrics. The system evaluated was the ColorQuest LAV 45"/0°. ters, the tristimulus values. These parameters are represented by three axes, which are illustrated in Figure 2. The vertical axis depicts the lightness "L" of the sample expressed on a scale of 0 to l00 where black = 0 and white = 100, the horizontal axis runs left to right and depicts "a" the redness or greenness, where the redness is positive and the greenness is negative, and the third axis runs from front to back and represents "b", the yellowness (positive), or blueness (negative). In addition, the instrument's software allows these three parameters to be combined and expressed in one of three indices. These are "Z", the brightness index, "WI", the whiteness index and "YI", the yellowness index. The system consists of a sensor and a detector. The sensor uses circumferential illumination, which is provided by a fibre optic ring, to accommodate a variety of samples. Light from the fibres illuminates the sugar sample (400 grams) to be analysed at an angle of 45". The diffused light reflected from the sample is collected at 0" and then directed to a difProc S Afr Sug Teclznol Ass (1999) 73 Evaluation of the HunterLab colour measuring instrument M Moodley, A Dunsmore & L De Jager
Evaluation of the Saccharoflex 2000 reflectance measuring instrument for refined sugar colour estimation at Huletts refinery.
Due to the successful use of the Saccharoflex 2000 reflectance measurement instrument on the estimation of refined sugar colour elsewhere in the world, it was decided by Tongaat-Hulett Sugar to evaluate the instrument at the refinery in Durban. Tests were carried out on first, second, third and fourth refined sugars, the results of which showed a good correlation between the ICUMSA colour measurement and the reflectance reading obtained from the Saccharoflex 2000. The instrument offers a number of advantages, the main one being that a refined sugar colour value can be obtained in less than a minute. The refinery has therefore purchased one for process control.
INCREASED CAPACITY OF CONTINUOUS CENTRIFUGALS LOW GRADE MASSECUITES
Modifications to BMA K850 centrifugals permitted increased throughputs of "C" massecuite in the order of 100%. The resultant molasses purities were little affected, but brixes were two degrees lower than before modification. Tests showed that the prototype BMA KllOO can handle four tons of "C" massecuite per hour with molasses purities comparable with those of standard centrifugals, but with brixes lower than normal. Techniques of process water application were examined. Introduction The paper has been divided into two parts. The first covers what will be termed "commercial" tests, which deal with the uprating of the BMA K850 and performance of the BMA K1100; the second covers experimental tests involving the addition of process water within the stream of massecuite. In recent years a number of authors have shown that continuous centrifugals can handle higher "C" massecuite throughputs than was previously considered possible. A throughput of 1,2 tons per hour (30 ft3 per hour) of massecuite was established as a normal working load for a standard BMA K850 on fore-curing duty at Darnall in 1969.3 In 1973, also at Darnal1,l de Robillard compared the performance of a standard K850 with a unit which had been modified in various respects (see table 2 explaining modifications). A capacity increase of 60 %, representing a throughput of 1,9 tons per hour, was achieved. In that author's opinion, the feed modifications were the major contributions to this increase. Atherton and Kirby2 also mentioned in a review of their centrifugal research work, between 1963 and 1973, that restrictions in the massecuite feed piping had been to a considerable extent responsible for throughput limitations on continuous centrifugals. The Huletts group has a large number of BMA K8501s employed on C-massecuite and the possibility of uprating these machines is therefore of considerable interest. It was felt, however, that further attention should be given to two particular aspects of operation at high throughputs, before a final decision on uprating could be taken. ( I ) The possible difference between centrifugal performance under experimental conditions and routine operation. (2) The effect of higher throughput on molasses purity. It was therefore decided that five of the ten fore-curers at Darnall should be modified and investigations be carried out to clear up the above points. One of the disadvantages of experimental test runs is that the results indicate what the centrifugals can achieve under special supervision, and reflect data gathered over relatively short periods of time. The tests reported here covered periods of at least one week, with data recorded every four hours. The weekly averages should be less liable to distortion by random error than single-test data. As the centrifugals were entrusted to the mill operating staff, the results, it is hoped, will relate more closely to performance levels attainable during actual routine operation. Laboratory methods of measuring brix and pol are not sufficiently accurate to detect fractional differences of purity between two determinations from single samples. The emphasis consequently has been on the average of a large number of apparent purity determinations rather than true purity results from single (or duplicate) analyses of composites. In fact, analyses of true purity duplicates have indicated that the between duplicates variance is not significantly less than that of apparent purity determinations. The centrifugals Specifications of the centrifugals are shown in Table 1, and features of particular interest of the standard BMA K850, modified K850 and BMA KllOO can be found in Tables 2 and 3. TABLE 1 Specifications of the Centrifugals * Gravity factor multiplied by screen area in square metres. Centrifugal