Mill Material Balance
CHAPTER I
INTRODUCTION
Mill material balance is a tool for the milling control normally used to evaluate the performance of sugar factory operations, mainly the extraction done by the mills for juice, the Brix and the Pol (sugar) as well. There were several methods of calculation for mill material balance, such as the “Brix Method” and the “Dry Method”. The weighing works for cane, mixed juice and imbibition water are required for the purpose of mill material balance calculation. We also need the analyses of cane, the Pol and Brix degrees of the juice extracted by each mill and the analyses of bagasse exhausted by the last mill. Empirical test reference and some unlovable assumptions were used by those methods; such as for instance the “Brix Method” uses 2 (two) major assumptions, i.e.: §
The Brix degree of cane juice has the same value with the Brix degree of the first extracted juice. This will make a significant error in the calculation, in which a residual material will be obtained, which’s normally called the “Brix free cane water”. Thus the calculation is not exactly balance.
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The Brix degree of first mill juice is carried along for the calculations of juice extracted by each mill after the second mill. The juice extracted by mill after the second mill is not relevantly related with the first mill juice.
While the “Dry Method” needs additional analyses for bagasse exhausted by each mill, which considered time consuming when it should be done as routine work every day. Another method uses assumption for the value of re-absorption factor (defined from the empirical tests), assumption or projection for the total sugar (Pol) extraction and assumptions for the other figures as well. The calculation system created here has only 2 (two) assumptions, i.e.: 1. The density of juice in the incoming material equals to the density of juice extracted by the respective mill (no significant error). 2. The density of bagasse when being milled is equal to the density of fiber (in terms of atmospheric humidity), which is of course acceptable. The same analysis applies for Pol and Brix degrees as normally done in every sugar factory, they are the analyses for cane and juice extracted by each mill, the mixed juice and for the last mill bagasse.
Introduction Introduction
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Mill Material Balance
The result of calculation presents a complete mill material balance. All the figures normally used as assumptions for evaluation such as, re-absorption ability factor, fiber index, fiber loading, sugar extraction, imbibition rate, mill settings, etc. will be determined and obtained by this complete mill material balance calculation system. And further, enable us to directly evaluate and define the followings: §
The extraction of juice, Pol and Brix due in each mill.
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Is the mill settings coincidentally agreeable to the cane quality / the local condition?
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Is the fore worker (knives, shredder, etc.) working properly, or needs additional / adjustment?
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Is there any juice extracted by the feed opening?
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How much is the suitable quantity of imbibition water and what is the best application?
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Obtaining the correct ratio of the feed and delivery work openings.
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Is there any mill in danger for crack during the operation?
1.1
The extractions of juice, Pol and Brix due in each mill.
Besides the extractions by weight for juice, Pol and Brix individually in each mill, the calculation also defined the weights and volumes for the juice content together with the Pol and Brix percentages in the incoming as well as the out-coming portions of the respective mill. So that the performance of each mill can be evaluated, at least knowing which mill of the tandem has not extracting juice normally, and their constraints. Hence, enable us to define applicable remedies to promote the extraction (especially during the campaign). By knowing the extraction individually, consequently we will also know the overall extraction for juice; Pol and Brix made by the whole train. 1.2
Is the mill settings coincidentally agreeable to the cane quality / the local condition?
If the calculation of mill material balance made daily or weekly as routine work (with the program), especially within the period after four to six weeks from the beginning of the crushing season, it will be detected easily whether the mill settings agreeable to the average cane quality recently crushed. The mill material balance program includes the calculation of fiber index as well as the fibers loading occurred in each mill. The fiber index indicates the capability of the respective mill to press the fiber for every escribed volume unit of the work opening. The bigger the value means good capability. While the fiber loading indicates the capability of the respective mill, i.e. the loading of fiber when pressed for every square unit of the roller escribed surface. For a better
Introduction Introduction
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Mill Material Balance
extraction each roller has a limited value of fiber loading, and it depends on the size of its diameter. Usually, assumption for the value of fiber index is taken for the calculation of mill settings. Frequently different actual value found when calculation made during the evaluation. In this regard, the mill setting is not agreeable to the recent cane crushed. Nevertheless with the use of the program, the value for each mill will be defined during the run of the evaluation program, and the value is the maximum fiber index affordable to the mills. Hence, the mill settings should be made with the defined values instead of the assumptions previously made. 1.3
Is the fore worker working properly, or needs additional / adjustment? adjustment?
We have the philosophy that, the first mill has to extract juice as much as possible. The capability of extraction of the first mill depends on how the ultimate equipment (the fore worker) does the preparation work. This could be detected by the value of fiber index and the compression ratio due in the first mill (compression ratio = the ratio of volume of the incoming material to the volume of bagasse when pressed under the delivery opening in the same time unit). For the first mill, if both the values are lower than the projection or the assumption, the other conclusion is that the fore worker does not work properly. The Index of Preparation of the cut cane is lower than 86%. It may needs adjustment, or replacement for the knives rotor. Or, if it would not help, then additional knives or shredder has to be installed. Both the values of fiber index and the compression ratio due for the first mill can be detected directly by the program and for the other mills as well. 1.4
Is there any juice extracted by the feed opening?
At least we’ll know the extraction of a mill is good, when sufficient amount of juice is extracted by the feed opening. But if the extracted juice by the feed opening is too much, the extraction process could be hindered by the s lip occurred in the respective mill. While observing the mills operation, sometimes we’ll found some of the mills were not or merely not extracting any juice from its feed openings. This is because incorrect ratio between the feed and delivery work openings was applied during the setting of the respective mill. The ratio definitely was too high. The evaluation program of material balance includes the calculation to detect such, while the projection program determine the best setting of the subject ratio.
Introduction Introduction
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Mill Material Balance
1.5
How much is the quantity of imbibition water and what is the best application?
The projection program for the material balance includes the facility for the simulation of imbibition water quantity and how the application should be made. This is to resolve the frequent trouble faced by most of mill engineers, how to eliminate choking of the last mill operation and obtaining sufficiently dry bagasse. 1.6
Obtaining the correct ratio of the feed and delivery work openings.
Usually, the ratio between the feed and delivery work openings was determined by the value experienced from the previous seasons practiced. They could have the opinion to set the mills with decreasing values from the first to the ensuing mills. On the other hand, increasing values were also used by most mill engineers, but it is to be noted that, too narrow ratio especially for the first mill, caused the crushing capacity will not be achieved easily. Since the program includes the calculation for the subject ratio proportional to the compression ratio occurred in each mill, then it is easy for the mill engineer to set the mills with the subject ratio defined by the program. 1.7
Is there any mill in danger for crack during the operation?
The program of mill material balance also includes the calculation, whether any mill in the tandem has potential for crack during its operation. Especially when the mill settings are made on mill with headstocks provided without hydraulic for the top roller, or when the mills with hydraulic but are set with fixed gap only for its lifting. The calculation is simple. The different between the height made by the bagasse when pressed at the delivery opening with the actual work opening when set, equals to the potential deflection made by the roller. The theory and the formulas defined for all the above-mentioned items will be thoroughly enlighten in this book.
Introduction Introduction
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