In this division of the factory control there is not quite as much disagreement about fundamentals as in the milling division, and it is considered unnecessary to devote separate chapters to the principles of the boiling house control and their practical applica- tion. All those points about which there is a difference of opinion are discussed in detail under their respective headings, and the reasons for the decisions of the Committee arc fully explained.
Q U A N T I T I E S O F P R O D U C T S .
The operations of the boiling house begin with the mixed juice, except in those cases where milling and clarification form a com- pound system. The mixed juice is to be weighed, as has already been explained. Where this is not possible because of clarification practice the clarified juice is to be weighed.
The Committee has decided that the filter cake, the final molasses, and the sugars are to be weighed also. If there is more than one kind of filter cake, as for instance from juice and syrup filtration, these are to be weighed separately; the same applies to different types of sugar made. If no scales are available, filter cake and molasses have to be measured, but this is not recom- mended because accuracy demands the weighing of these products.
If settlings are returned to the mill they should also be weighed, likewise filter washings returned to the mill, but the latter may be measured and the volume converted to the weight basis. The weights of such settlings and filter washings are needed only to apply corrections to the control data, and they do not appear in the completed reports.
The syrup is weighed in some places, and this practice helps to trace entrainment and inversion losses in a given factory. But there is no need to report syrup weights for international comparisons.
The weights of mixed (clarified) juice, filter cake, sugars, and molasses are to be given as per cent. by weight of cane. The actual weight is to be reported only for the cane ground, in metric tons.
The quantities of the various massecuites are to be measured in the pan and reported, in hectoliters per 10 metric tons (100 quintals) of standard sugar.
The lime used is to be reported in terms of available calcium oxide per thousand parts of cane, that is kilograms per metric ton.
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ANALYTICAL F I G U R E S .
Brix and Pol.—These are to be determined upon mixed juice, clarified juice, syrup, massecuites, intermediate and final molasses, also on filter washings and on settlings returned to the mill, b u t in the last two instances the data are used only to apply corrections.
Brix is to be determined on low grade sugars only, b u t not on high grade, because in the latter case the experimental error may exceed the total moisture content.
A specific gravity determination must be made on muds returned to the mill in order to find the quantity of clear juice contained in them, b u t again this figure docs not appear in the completed report.
Dry Substance and Pol.—Although control on a dry substance basis would be very desirable, results of dry substance determina- tions on liquid products are time consuming, and in the presence of levulose on the one hand and of insoluble matter on the other they are so uncertain t h a t they offer no real advantages over Brix determinations, in spite of all the recognized shortcomings of the latter. If Brix determinations based on specific gravity are to be replaced by something more useful, the refractometer promises much better chances of success than drying methods.
Dry substance and pol are to be determined on filter cake.
Gravity solids in filter cake, if desired for a Brix balance, must be determined separately or calculated.
Dry substance and pol are to be determined and reported on all high grade sugars. In calculations, the dry substance is to be used for Brix or gravity solids.
Sucrose.—As has been previously stated, the entire control should be based on sucrose rather than pol figures. The principal reason for this is that the relative proportions of other optically active components, mainly dextrose and levulose, vary from place to place, and may also change considerably during the manufactur- ing process. This has a profound effect on the ratio of pol to sucrose. Although the sucrose figure is usually higher t h a n the pol, it may be, and often is, lower. The s-j-m formula, and similar formulas, give correct results only if sucrose data are employed.
There is still another important reason why pol figures are unreliable.
Polarization results would be comparable only if they were made always and everywhere at the same temperature. Temperature corrections are out of the question because the temperature coefficient of each optically active constituent would have to be considered, and this would necessitate a complete analysis, including a sucrose determination. Furthermore, the direct polarization is greatly affected by the quantity of lead subacetate used for clarifica- tion. Sucrose determinations, on the other hand, are corrected for temperature, and are largely independent of the q u a n t i t y of clarifying agent employed.
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The Committee has decided that sucrose is to be determined and reported for mixed juice and for final molasses, and also for sugars, except those returned to process or of such high grade that pol and sucrose are the same within the limit of error. In those factories which start the boiling house control with the clarified juice, sucrose must be determined in the latter. For purposes of a sucrose balance, pol in filter cake can safely be used as being equal to sucrose, within the limits of experimental error, but sucrose must be determined in filter washings and muds returned to the mill, to apply necessary corrections. Sucrose need not be deter- mined in the syrup since it has been decided to base recoveries on sucrose in mixed juice, nor in massecuites and intermediate molasses, where pol is sufficient for running control.
Reducing Sugars.—Although reducing sugar determinations present a valuable tool for detecting losses and are therefore encouraged by the Committee, the reporting of such figures for the purpose of international comparisons is not recommended, except in the case of mixed juice and final molasses.
Ash.—What has been said with regard to reducing sugars applies also to ash figures. The Committee recommends that ash be reported upon mixed juice and final molasses. The reporting of both reducing sugars and ash is of importance in view of the work of Thieme, showing that the exhaustibility of molasses is correlated with the ratio of reducing sugars to ash, and even more patently with the ratio of ash to non-sucrose (non-pol).
The reporting of complete analyses (sucrose, reducing sugars, ash and moisture) of the commercial sugars produced, either raw or higher grade, is made optional.
Acidity and Alkalinity; pH.—Although the determination of titrated acidity and alkalinity is still practised to some extent in juice clarification, it is now generally accepted that p.H values are of greater importance in factory operation than titration figures.
The Committee recommends the reporting of pH for hot limed juice, clarified juice, and syrup.
Lime Salts in Clarified Juice.—These need not be reported for international comparisons.
Suspended Solids.—The Committee has decided that these need not be determined (see discussion under "Corrections when juice is Weighed", page 43, and "Corrections when Juice is Measured", page 4 3 ; also "Suspended Solids in Mixed Juice", page 61, and
"Suspended Solids in Final Molasses", page 62).
Turbidity, or Clarity.—These need not be reported, for either clarified juice or sugars.
Sulphur Dioxide.—This need not be reported, for either juices, syrups, or sugars.
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CALCULATED F I G U R E S .
Purities.—Since the Committee has decided t h a t the control be based on sucrose rather than pol, it logically follows t h a t gravity purities are to be reported wherever sucrose values are required.
However, as it may take some time, for practical reasons, until sucrose figures are determined universally, it will be necessary for all factories which use the sucrose basis to make reports also on a pol basis, giving both gravity and apparent purities, sucrose and pol balances, etc.
Ratios of Reducing Sugars or Ash to Other Constituents.—The Committee recommends t h a t no such ratios be reported except in the case of final molasses, where the R.S.-Ash Ratio, and the Ash-Non-Sucrose (and Ash-Non-pol) Ratio should be shown for reasons given above.
Purity of the Filter Cake.—This is to be reported; the pol is divided by the dry substance.
Weight of Dry Substance in Filter Cake, per Square Metre of Filtering Surface, in 24 Hours.—This figure is one of the best for comparison of filter press results, but concerns efficiency of mechanical operation rather than chemical control. There are other objections to it, and the Committee has decided to omit this figure.
Difference between Non-pol in Mixed and Clarified Juice, per cent, of Non-pol in Mixed Juice.—This figure has been abandoned in J a v a , where it was formerly in use. It is not to be reported.
Purity Change from Mixed Juice to Syrup.—This figure may be readily ascertained from data to be reported, and there is no need to report it separately.
Deterioration Factor, and Dilution Indicator.—Since sucrose and dry substance are to be reported for sugars not returned to process, these data can be readily calculated if desired, and they need not be reported as such.
Sugar and Molasses in Process.—The possible error in estimat- ing the quantities of stock is relatively large, and for this reason a certain latitude is permissible in determining sugar and molasses in process. The logical procedure is to express these in terms of the products as they are actually turned out by the factory in question. The s-j-m formula or an equivalent one may be used, but the calculation should be made on the basis of gravity purities wherever possible. For the purity of the initial material t h a t actually determined is always taken, and for the purity of the sugar and molasses that observed to date.
Balances.—For reasons repeatedly stated, sucrose balances are preferable to pol balances. However, until sucrose figures become
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available everywhere, those factories which determine sucrose should report both sucrose and pol balances. The Committee recommends that only one basis be used, viz., sucrose (pol) in cane, and that balances on sucrose in mixed juice, or on cane be omitted.
Only the weights of the different products are to be reported on the basis of cane ground (see p. 28).
Balances of Brix, standard sugar, non-sucrose (non-pol), etc., are often useful for individual factories, but need not appear in reports for international comparison.
Recoveries and Yields.
General Definition.—This subject is in a bad state of confusion, because not only the terms used, but also the methods of calculation vary markedly in different countries. The term "recovery" should be restricted to the quantity of sucrose, pol, or standard sugar in the sugar produced, expressed on the basis of sucrose (pol) in the initial boiling house material, while the quantity based directly on cane should be termed "yield". Both recovery and yield must be further specified as shown below.
Boiling House Recovery (Sucrose, or Pol).—This term, also called "retention" in Cuba, used to be generally accepted to mean sucrose (pol) in sugar produced per cent, sucrose (pol) in mixed juice. The Committee recommends that this definition be main- tained, and that the boiling house recovery, as thus defined, be reported, but that it be further qualified by adding "sucrose" or
"pol", as the case may be.
It is true that losses in the boiling house occur during other operations besides boiling to syrup and to grain, but nevertheless they do occur in the boiling house as defined by the Committee, and the term "Boiling House Recovery" accords with that conception.
Those countries which have adopted another definition for the term "Boiling House Recovery" should change the term expressing the new definition, in order to avoid confusion. Noel Deerr prefers the term "Boiling House Extraction" to "Boiling House Recovery", but "recovery" is more generally used and is understood to refer to boiling house operation, while the "extraction" refers to the milling operation, having been defined by the Committee as sucrose (pol) in mixed juice, per cent. sucrose (pol) in cane.
Basic Boiling House Recovery.—In order to ascertain what relation the quantity of sugar actually obtained bears to that which under the best possible conditions could have been produced, various systems of calculating "available" sugar have been proposed. The sucrose in the filter cake may or may not be considered available;
the purity of the molasses may be that actually observed, or it may be fixed arbitrarily; apparent or gravity purities may be used,
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etc. To avoid further confusion, the Committee recommends the term "Basic Boiling House Recovery", as defined below, instead of the former "available".
In Cuba the available pol per cent. pol in mixed juice is calculated by the Winter Formula is the apparent purity of the mixed juice. This formula is equivalent to the s-j-m formula, with a sugar purity of 100 and an apparent purity of 28.57 for final molasses. In Hawaii three methods are used to find available sucrose per cent. sucrose in the original material; (1) the s-j-m formula direct, with observed gravity purities for syrup and final molasses; (2) for comparative purposes the same as (1), but with a fixed gravity purity of 30 for final molasses;
(3) if only pol data are available for syrup and sugar, these are corrected to obtain probable gravity purities, and the s-j-m formula is applied, with the gravity purity of molasses actually observed, or else assumed. In Natal the s-j-m formula is employed, with observed gravity purities for sugar and for mixed juice or syrup, and with a fixed molasses purity of 45. Still other systems have been or are being used in other countries, but the above examples will suffice for purposes of illustration. The Committee defines the Basic Boiling House Recovery as the percentage of the sucrose in the mixed juice which would be obtained, according to the s-j-m formula, adopting values of 100 and 28.57 for s and m respectively, and for j, the gravity purity of the mixed juice. This figure need not be reported as such.
Actual versus Basic-Boiling House Recovery.—This comparison is generally made on a percentage basis, but the resulting figure is not recommended by the Committee for international comparisons, because these are to be made on the basis of Equivalent Standard Granulated (see below).
Standard Sugar.—It has long been recognized that if any com- parisons are to be made between factories which produce sugars of one type and others producing a different type, recoveries based on sucrose (pol) in the sugar do not furnish a satisfactory criterion.
In such a case it becomes necessary to convert the quantity of sugar produced into a mutually comparable equivalent. In some countries this has been done in the past by dividing the recovery by the polarization of the standard sugar chosen, such as 96, and multiplying by 100, the result being considered the equivalent quantity of 96° sugar. This method is obviously incorrect as it disregards the purity of the sugar.
In other systems proposed a standard sugar of given polariza- tion and purity, and a molasses of given purity have been assumed.
The actual values of these figures have varied from country to country. Thus, the "Standard Muscovado" of Java was based on a sugar containing 96.5 per cent. pol, 0.7 per cent. moisture (97.18 purity), and on the molasses purity being obtained at the factory
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in question. As the production of white sugar increased in Java, the Standard Muscovado became unsatisfactory for purposes of comparison, and it has been replaced by "Crystal", which is calculated by multiplying the weight of the non-sugar in the sugar produced by the factor rj (100— r), and subtracting the product from the weight of pol in the sugar; r is the apparent purity of the molasses being turned out by the factory. As another example of a standard raw sugar that proposed by Peck may be cited; this contains 96 per cent, sucrose and 1 per cent, moisture (96.97 purity), and the conversion is to be made by the s-j-m formula, with an assumed gravity purity of for molasses.
Equivalent Standard Granulated (E.S.G.).—This type of standard sugar has been introduced by Deerr, and is defined as the quantity of dry, pure sucrose (100 per cent, sucrose, 100 purity), which could theoretically be obtained from a sugar or other raw material, using the s-j-m formula and assuming a gravity purity of 28.57 for final molasses. This molasses purity is identical with the apparent purity assumed in the Winter formula.
The E.S.G. differs from the J a v a "crystal" in that gravity purities are used in the calculation, and that the purity of the molasses is fixed. Although objections have been raised against the latter feature it must be admitted that Deerr's proposal furnishes a more logical basis for comparing quantities of different types of sugar than any of the other systems. The actual molasses purities vary considerably from factory to factory, and more so from country to country, but all can strive to exhaust their molasses further, and the low standard purity chosen is an incentive in that direction. The Committee has therefore recommended Deerr's
"Equivalent Standard Granulated", as above defined, for adoption.
Boiling House Recovery, E.S.G.—This is calculated in the same way as the Boiling House Recovery (p. 32), except that the quantity of Equivalent Standard Granulated corresponding to the sugar produced is substituted for the sucrose in sugar produced. The Committee has decided that this figure be reported.
Basic Boiling House Recovery, E.S.G.—This is the same as the Basic Boiling House Recovery, as defined on p. 32, since it is expressed as 100 per cent, sucrose. It need not be reported as such.
Boiling House Performance.—This figure, also introduced by Deerr, is calculated by dividing the Boiling House Recovery, E.S.G., by the Basic Boiling House Recovery (Sucrose), and multiplying by 100. It is similar to the Winter Rendement (crystal) reported in Java, but in the latter case observed apparent purities are used in the calculation.
In Java the relation between crystal produced and available crystal is also expressed as a percentage loss figure ("Loss in avail- able crystal per cent, pol in mixed juice") rather than as a ratio.
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It thus forms an item in the crystal balance. The Committee has voted not to adopt this Java figure because only a sucrose balance is to be reported.
Since a better comparison figure than the "Boiling House Performance", namely, the "Reduced Boiling House Recovery, E.G.S.", has been developed by Deerr, the Committee has decided to make the reporting of the Boiling House Performance optional.
Reduced Boiling House Recovery, E.S.G.—This figure is analogous to the Reduced Extraction (p. 22), and defined as the Boiling House Recovery, E.S.G., that would have been obtained under existing conditions if the factory had worked a mixed juice of a standard gravity purity of 85. It is found in the following manner:
First the "virtual" gravity purity of the molasses, mv, is calculated by the s-j-m formula from the observed gravity purity of the mixed juice, j, and the actual boiling house recovery, E.S.G., Y by the formula
or according to McAllep more simply
The value of mv is then substituted in the formula
This formula may be alternatively expressed, without reference to virtual purity of molasses-
where r85 denotes the Reduced Boiling House Recovery, E.S.G.
It is a measure of the performance, and may be used directly for international comparisons. It should be emphasized that all purities are gravity purities, and that the recovery is expressed as Equivalent Standard Granulated, as previously defined. The Committee has decided that this figure be reported.
There is an old saying in the medical sphere that if there are many remedies for a complaint, none of them is entirely satisfactory. Similar conditions seem to apply to methods of expression of the standard of efficiency of the boiling house. In his contribution to the I.S.S.C.T. in 1950 (Proc.
7th Congress) S. N. Gundu Rao discussed six recognized efficiency indicators and went on to propose a seventh -which he had derived and which he recom- mended for adoption by the Committee. Gundu Rao's Reduced Boiling House Recovery is based on reasoning mainly parallel to t h a t adopted by
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