SYSTEM OF CANE SUGAR FACTORY CONTROL

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SYSTEM O F

CANE SUGAR F A C T O R Y C O N T R O L

G a r d e n s Point.

A 2 2 8 1 0 9 9 4 B

S y s t e m o f c a n e s u g a r f a c t o r y c o n t r o l

THIRD EDITION

E d i t e d b y J . L . C L A Y T O N

P U B L I S H E D F O R T H E I N T E R N A T I O N A L S O C I E T Y O F S U G A R C A N E T E C H N O L O G I S T S

b y Q.S.S.C.T.

1971

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A22810994B

Wholly set up and printed in Australia by WATSON, FERGUSON AND COMPANY

Brisbane, Q.

1971

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PREFACE TO THE T H I R D EDITION

T h e f i r s t e d i t i o n o f t h e b o o k " S y s t e m o f C a n e Sugar F a c t o r y C o n t r o l "

a l t h o u g h p u b l i s h e d b y a C o m m i t t e e o f t h e I.S.S.C.T. w a s , i n f a c t , w r i t t e n b y D r . F . W . Z e r b a n , a n d i t i n c o r p o r a t e d n o t o n l y his s t y l e b u t also c e r t a i n o f his p e r s o n a l o p i n i o n s .

W h e n I r e v i s e d t h e b o o k i n 1955 I t o o k pains t o a l t e r i t n o m o r e t h a n necessary t h o u g h I d i d n o t s u b s c r i b e t o s o m e o f t h e claims and p o l i c i e s t h e r e i n .

A f t e r t h e 12th C o n g r e s s I set o u t t o p e r f o r m a f u r t h e r r e v i s i o n b u t I was s o dissatisfied w i t h t h e r e s u l t s t h a t I a b a n d o n e d t h a t l i n e o f a c t i o n . I d e c i d e d t h a t t h e o n l y s a t i s f a c t o r y c o u r s e was t o r e w r i t e t h e b o o k e n t i r e l y .

T o t h e 13th C o n g r e s s I t o o k t h e m a j o r p o r t i o n o f t h e n e w t e x t i n p r o o f f o r m a n d d i s t r i b u t e d i t t o a panel o f t e c h n o l o g i s t s r e p r e s e n t i n g a w i d e r a n g e o f sugar c o u n t r i e s . I i n v i t e d c o m m e n t s f r o m t h e m a l l , and I h e r e e x p r e s s m y t h a n k s t o t h o s e w h o w e r e g o o d e n o u g h t o assist m e w i t h t h e i r a d v i c e . I have d o n e m y best t o use i t c o n s t r u c t i v e l y .

J . L . C L A Y T O N . 1971

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PREFACE TO THE SECOND EDITION

When the Committee on Uniformity in Reporting Factory Data met during the Eighth Congress in British West Indies in 1953, one of its resolutions was that the booklet "System of Cane Sugar Factory Control of the I.S.S.C.T." be

"brought up to date and r e p r i n t e d " .

On the same occasion the resignation of Dr. F. W. Zerban as Chairman of the Committee was accepted with regret, and the w r i t e r was appointed to that office, with Mr. J. L. Clayton as Secretary. The major portion of Dr. Zerban's excellent composition in the original booklet remains unchanged in the new edition, the preparation of which is due to Mr. Clayton.

The question of bringing the booklet " u p to date" has occasioned con- siderable thought. Certain revisions had been approved by the Committee as a body but others arose for consideration and it was a question whether they should be included without formal approval. The policy adopted was to select those items which needed revision but were not of a highly contentious nature and to submit proposals to the regional sub-committees. The response was gratifying, the proposals being either approved or commented upon in con- structive manner. Our thanks are due to the members of the sub-committee who assisted.

In the current edition t w o appendices have been included. The first presents data on the units employed in various countries and deals extensively with English-Metric conversions. The second deals with the Tables used in sugar technology. Though there were several requests for the publication of standard Tables it was decided not to print these, for reasons explained in Appendix II.

Thanks are due to the Queensland Society of Sugar Cane Technologists, which body has undertaken the financial responsibility for the printing of this booklet.

It is hoped that the current edition w i l l prove a worthy successor to the first and that its publication will serve to further the good work of the Committee.

NORMAN J. KING, Chairman.

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PREFACE TO THE FIRST EDITION

HISTORY A N D AIMS OF T H E COMMITTEE

The Special Committee on Uniformity in Reporting Factory Data was created at the Second Conference of the Society, held at Havana in 1927, upon motion made by M. A. del Valle, who pointed out that the confusion of terms used in sugar factory reports, and the multiplicity of control methods employed made it impossible fairly to judge the results obtained and to make mutual comparisons.

He urged a study of this question and the establishment of uniform methods by common consent.

The Committee members appointed at the beginning were M. A. del Valle (Puerto Rico), P. C. Tarleton (Cuba), and F. W. Zerban (U.S.A.), chairman. At the Third Conference (Soerabaja, Java, 1929) E. C. von Pritzelwitz van der Horst (Java) was appointed, vice P. C. Tarleton ; he resigned prior to the Fifth Conference (Brisbane, Queensland, 1935), and no new appointment was made to replace him.

The chairman was empowered to co-opt further members. In order to make the Committee truly international in scope, the co-operation of prominent sugar technologists in all the important sugar cane countries was solicited, those connected with official institutions or technical organizations being chosen wherever possible. The response was most gratifying, and the following men have served on the Committee at various times, many of them throughout the entire period during which it has been functioning:

Argentine: W. E. Cross;

Australia: Norman Bennett, W. R. Harman, A. Jarratt, G. S. Moore;

British and French West Indies: Walter Scott, J. G. Davies;

Cuba: A . J . Keller, W. B. Saladin, H. D. Lanier, A. P. Fowler, Jose Santos;

Hawaii: W. R. McAllep, W. L. McCleery, S. S. Peck;

India: Noel Deerr, J. H. Haldane, K. C. Banerji;

Japan: Migaku Ishida, S. Kusakado;

Java: P. Honig, C. Sijlmans, Ph. van Harreveld;

Louisiana: C. E. Coates, A. G. Keller;

Mauritius: Louis Baissac;

Mexico: T. H. Murphy;

Natal: H. H. Dodds, G. C. Dymond;

Peru: Gerardo Klinge;

Philippines: Herbert Walker, E. T. Westly;

Puerto Rico: M. A. del Valle, Jaime Annexy, E. M. Copp;

Santo Domingo: Rafael Cuevas Sanchez.

In some of these countries sub-committees were formed to advise the members of the Committee.

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To all these men the chairman again expresses his sincere gratitude because without their willing, sympathetic, and efficient help it would have been impossible to accomplish the large and difficult task allotted to the Committee.

Since the members of the Committee are scattered all over the world it was necessary to undertake the work largely by means of questionnaires and correspondence. The replies to the various questionnaires were analysed, arranged, and summarized by the chairman, who then prepared comprehensive reports for each of the meetings of the Society. These reports were discussed at the Conferences by the Committee members present or their proxies, and all amendments agreed upon were entered in the reports. The revised reports were submitted to the Society as a whole, were adopted by it, and published in the Proceedings. The general terms and definitions, and the system of milling control were thus disposed of at the Third Conference in 1929. The control of the boiling house, and the methods of weighing, measuring, sampling, and analysis were reported at the Fourth Conference in 1932, but since the Committee was poorly represented at that meeting it was decided to resubmit the report to all the members of the Committee by correspondence. The final report was presented at the Fifth Conference in 1935, and was adopted. But the Committee was retained in office in order to keep the methods up to date and to revise them from time to time, in keeping with progress in sugar technology.

Accordingly, a report was presented at the Sixth Conference in 1938, but only few changes in the methods were made at that time.

In the present book the reports of the Committee have been rearranged and systematized so that they may be more readily consulted. In some instances the original text has been somewhat condensed, in others amplified, always keeping in mind the intent of the Committee's work. The purpose of this treatise is not to serve as a complete manual of control methods, but rather to explain the principles which guided the Committee in arriving at its decisions, and to emphasize essential points. Those well known methods the details of which may be readily found in any of the generally used handbooks of factory control are not described at length, but simply referred to by name. But the methods recommended by the Committee which are not so widely known, are given in full in Chapter VII. In other words, the book is not meant to replace existing manuals, but to supplement them and to be used as a guide for those countries or associations that desire to bring their control methods in line with those recommended by the Committee, and thus to accomplish the purpose for which the latter was created. It is hoped that the publication of this international system of factory control may be found helpful toward that end.

The Committee accepted for its guidance the following principles enunciated by S. S. Peck: " Y o u r committee should strive for three main objectives, namely, accuracy, clarity, and simplicity; and of these three I consider the last as important as the first t w o . In striving for greater accuracy, formulas have become so complex that they are practically useless. If the committee stress simplicity of statement which will not conflict with accuracy and clarity, they may be able to do some persuading to an agreement on t e r m s . " It was also postulated that wherever direct determinations can be accurately and simply made, they should be preferred to indirect determinations or calculations, and further, that practical considerations should be favoured against theoretical speculations.

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CHAPTER I

Introduction and Some Premises

The manufacture of cane sugar from sugar cane is a distinc- tive industrial process in that it involves no element of synthesis.

Sucrose comes into the factory in the cane, and, subject to some physical losses and some destruction, emerges in the product, crystal sugar. The process is essentially a combination of separation and concentration.

The materials other than sucrose in the cane are collectively known as impurities, and may be classified as dissolved and in- soluble respectively. The first step is the separation of sucrose and the impurities in solution from the insoluble impurities, together called fibre. This is the function of the milling plant, and the process is commonly called extraction. The second step is the treatment of the extracted juice for the removal of some insoluble and some dissolved impurities, and this is known as clarification. A consider- able proportion of the water present is then removed in the process called evaporation. The further stages constitute the separation of impurities by crystallization of the sucrose. The processing of juice to crystal sugar takes place in the boiling house, and the separation of sucrose is called recovery. The overall separation of sucrose from cane is also known as recovery.

The proprietor of a sugar factory is naturally interested in knowing how much of the sucrose in the cane he purchases is present in the sugar he sells, and he also wishes to know how good or how bad is the achievement. This demands a series of measure- ments, analyses and calculations which constitute the system known as chemical control.

The main purposes of chemical control are threefold—

1. To ensure that the various unit operations in the process of manufacture are conducted at the highest efficiency. This is the most important function of chemical control—to provide

"live" data for the immediate guidance of the plant operators.

As this book does not pretend to be a manual of instruction for operators, it touches lightly on this function of chemical control.

2. To provide a quantitative account of materials and their com- ponents entering the process, in transit, in stock, and leaving the process. From the basic data convenient measures of per- formance—such as sucrose extraction or overall recovery—

may be derived, but most of such records are dispassionately factual.

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3. To assess the merits of performances achieved. Sugar technolo- gists realized long ago that it is not reasonable to judge sugar factory results against the standard represented by perfection.

Other things being equal, an extraction of 96 is better than an extraction of 94; but in practice other things are commonly not equal, and the 94 may represent a more meritorious per- formance than the 96.

The system commonly adopted is to compare the actual result with an abitrary standard result—a standard result which tempers prefection by recognition of the prevailing circumstances. Since the formulation of a standard involves speculation, none of the arbitrary standards is above reproach, and different lines of speculative reasoning can lead to different standards for the same operation.

This book discusses many of these standards and attempts to select the best for common usage.

Not all the "figures of merit" involve a comparison against a standard. Some are purely factual, and express merit only by virtue of an accompanying assumption; for instance, lost absolute juice per cent fibre is a statement of fact but it is regarded as a figure of merit by those—and there arc many—who accept as a general truth that lost absolute juice is an index of milling efficiency.

Sucrose and Pol.

Although the material of primary importance in the sugar factory is sucrose and the accounting for sucrose should constitute the main material balance, this is not generally so. The determination of sucrose as such is laborious and more prone to error than the measure of apparent sucrose by direct polarization, known as pol.

There is no doubt whatever that pol is used more generally than sucrose as the basis of chemical control, and, until there is some significant change, pol must be the common basis. It is all very well to point to the superior merits of sucrose, but, if the sugar industry of a country will not adopt sucrose in its own interests, it is hardly likely to do so for others.

In plain fact, the normal relationships between pol and sucrose are gratifyingly stable and most of the time chemical control on a pol basis is entirely satisfactory. If suspicious results arc recorded at any time, the pol-sucrose relationshipscan be checked for abnormality.

For every pol and every derivative from pol there is a sucrose equivalent. This should be kept in mind, because, to save wearisome repetition, this book deals primarily in pol. Those who prefer the alternative, sucrose, as a basis of control, are welcome to adhere to it, but should qualify reports accordingly.

There is one important exception. The concentration of optically active impurities in final molasses is so high that the pol and appar- ent purity of final molasses are practically meaningless. Those figures should be used, as required, for purpose of calculation, but only purities based on sucrose have any absolute significance.

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CHAPTER II

Principles of Milling Control

T h e chemical c o n t r o l over the o p e r a t i o n of milling involves accounting for four materials—cane, bagasse, mixed juice a n d w a t e r — a n d their c o m p o n e n t s . Before p r o c e d u r e s m a y be discussed some features of t h e materials are d u e for consideration.

Cane.

C a n e m a y be t a k e n to comprise fibre, being t h e aggregate of all c o m p o n e n t s in the solid phase, juice, being t h e aggregate of all c o m p o n e n t s in t h e liquid phase, a n d , possibly, hygroscopic water, being water physically a d s o r b e d by some of the fibre.

At this stage it is pertinent to m e n t i o n t h a t terms like " s o l i d "

or " i n s o l u b l e " or " u n d i s s o l v e d " h a v e to be accepted with some reservations. In m a n y ways N a t u r e does n o t deal in clear distinctions, a n d the technologist w h o studies the structure of cane in m i n u t e detail will find c o m p o n e n t s to which classification as solid or liquid c a n n o t be applied with certainty. F o r o r d i n a r y p u r p o s e s fibre is a solid or insoluble c o m p o n e n t , b u t in finer degree fibre h a s to be distinguished as a " n o n - l i q u i d " c o m p o n e n t , a n d even this distinction is not absolute.

T h e c o m p o n e n t called juice is really a heterogeny of j u i c e s — the rich juice of the pith cells, the p o o r e r juices of the rind a n d the internodes, a n d the watery c o n t e n t of t h e fibro-vascular bundles.

In earlier years there seems to have been s o m e d o u b t a b o u t the existence of the t h i r d c o m p o n e n t " h y g r o s c o p i c w a t e r " . It can n o w be stated categorically t h a t hygroscopic water exists a n d t h a t when cane fibre h a s been steeped in dilute juice or water, t h e hygroscopic water which it a d s o r b s is s o m e w h a t variable in quantity, b u t is of the order of 25 per cent of the weight of fibre.

Hygroscopic water was referred to as a " p o s s i b l e " c o m p o n e n t of cane because, a l t h o u g h its existence in bagasse is beyond question, its existence in cane is n o t proven, a n d there is substantial evidence t h a t if it is at all p a r t of cane it is present in a very small p r o p o r t i o n .

Undiluted Juice.—Probably in o r d e r to avoid t h e complexity of allowing for t h e variations within the t r u e juice of c a n e , the technologists of t h e J a v a sugar industry a d o p t e d a concept t h a t the juice left in cane after d r y crushing h a d the same Brix as the juice expressed by dry crushing, i.e., p r i m a r y juice. T h e whole juice of t h e cane, c o m p u t e d on this basis, was t e r m e d undiluted juice.

In general the Brix of the residual juice is lower t h a n t h a t of the p r i m a r y juice, so if the residual juice is credited with a higher Brix

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than it possesses, its q u a n t i t y is less t h a n the true juice. This leaves a deficiency in the materials balance, a n d the t e r m " u n d e t e r m i n e d water" was applied to the closure. C a n e was p r e s u m e d to consist of fibre, undiluted juice a n d u n d e t e r m i n e d water. It can be r e a s o n e d t h a t this u n d e t e r m i n e d water m u s t consist of water which is p a r t of the true juice but not p a r t of the undiluted juice, together with a n y hygroscopic water.

A weakness of this concept for practical purposes is t h a t the Brix, a n d therefore the quantity, of undiluted juice depends on the Brix of p r i m a r y juice which is subject to external influences, spec- ifically, the crushing conditions.

Absolute Juice.—To provide a m o r e stably based quantity t h a n undiluted juice the concept of absolute juice was a d o p t e d . T h e a s s u m p t i o n is the ultimate in simplicity—that cane consists entirely of fibre a n d absolute juice. If there is any hygroscopic water, it is regarded as p a r t of the absolute juice.

Absolute juice was n o t presumed to exist as such, a n d it certainly does not in bagasses, b u t its existence in cane may be closer to reality t h a n is generally imagined.

It is well k n o w n t h a t the milling factor—that is, the factor converting the Brix of first expressed juice to the Brix of absolute juice, is of the order of 0.975. This factor m a y be regarded as the p r o d u c t of two subsidiary factors, one to convert the Brix of first expressed juice to the Brix of true juice, and one to convert the quantity of true juice to the quantity of absolute juice (that is, to allow for hygroscopic water). If the first of these two factors were unity, t h a t is, if the factor 0.975 were solely to correct for hygroscopic water, the correction w o u l d represent 17.5 per cent hygroscopic water at 12.5 fibre in c a n e ; b u t it is invariably found that the Brix of the true juice is below t h a t of the first expressed juice, a n d therefore the hygroscopic water allowed for is less t h a n stated above. Actually the factor to convert Brix of first expressed juice to Brix of true juice is of the same order as the overall factor, 0.975, a n d therefore the second factor is a p p r o x i m a t e l y unity.

It is n o t p r o p o s e d to p u r s u e this subject exhaustively but evidence from practical milling results, from press tests, a n d from alternative m e t h o d s of d e t e r m i n a t i o n of fibre in cane all leads to the one conclusion t h a t , for practical p u r p o s e s , there is no hygroscopic water in cane as cane. T h e r e is a suggestion t h a t t h e a d s o r p t i o n of hygroscopic water begins w h e n cells are disrupted a n d proceeds at a quite m o d e r a t e rate. This can explain why cane pieces crushed in a press yield juice of declining Brix ; b u t w h e n the pressing is interrupt- ed and resumed later, the Brix of the juice j u m p s to a new level a n d declines again. W h a t e v e r be the explanation, experimental results suggest t h a t hygroscopic water should n o t be allowed for in original cane, b u t m u s t be allowed for in bagasses a n d disintegrator slurries.

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Bagasse.

Bagasse here m e a n s final bagasse, the end p r o d u c t of the milling train. It comprises fibre, juice a n d hygroscopic water. T h e fibre is almost t h e whole of t h a t originally present in the cane from which t h e bagasse w a s derived. Losses are negligible, but a p r o p o r t i o n a p p r o x i m a t i n g 0.5 p e r cent on cane passes out of the milling t r a m with the mixed juice. In strict a c c o u n t i n g this q u a n t i t y has to be allowed for, b u t for general purposes it is assumed t h a t the fibre in c a n e all becomes fibre in bagasse.

T h e juice is a m i x t u r e ranging from virtually water to original juice still enclosed in a few inaccessible cells. T h e fibre contains hygroscopic water in q u a n t i t y usually assumed to be 25 p e r cent of the weight of fibre.

Since a final bagasse contains some 50 per cent of fibre which in turn holds some 25 per cent of hygroscopic water, the quantity of this last item is substantial—12.5 per cent of the bagasse. This m a k e s an appreciable difference between the true residual juice, 37.5 per cent, and the absolute residual juice, 50 per cent. If the bagasse contains 4 per cent Brix, then the concentration of the a b s o l u t e residual juice is 8 Brix, but the concentration of the true residual juice is a b o u t 10.7 Brix.

There is rarely occasion to consider the average composition of the residual juice. Residual juice is c o m m o n l y regarded as a mixture of some s t a n d a r d juice a n d w a t e r ; the m o s t p o p u l a r stand- a r d juice was undiluted juice, first expressed juice h a s been used by m a n y , but the r e c o m m e n d e d choice is absolute juice. If the Brix of the absolute juice of the cane was 20, then the bagasse referred to previously m a y be said to comprise 50 per cent fibre, 20 per cent absolute juice a n d 30 p e r cent water, the water being m a d e up of 12.5 per cent hygroscopic water a n d 17.5 per cent imbibition water.

T h e p r o p o r t i o n of absolute juice was derived on a Brix basis, a n d this is the s t a n d a r d practice; but it can be derived on a pol basis, a n d such a p r o c e d u r e is inherent in the R e d u c e d Extraction formula of Noel Deerr.

T h e s t a n d a r d m e t h o d of analysis of bagasse at present involves the d e t e r m i n a t i o n of dry substance a n d pol. T h e Brix is generally derived from the pol using the p u r i t y of last expressed juice or last mill juice. F o r generations it has been acknowledged t h a t neither of these purities is even close to the p u r i t y which is really involved—the purity of the residual juice in bagasse.

In earlier years the direct determination of Brix in bagasse was k n o w n to be possible b u t was considered to be t o o exacting for r o u t i n e use. N o w a d a y s the high speed wet disintegrator provides a ready m e a n s of releasing the Brix into an extract, a n d a precision refractometer serves to determine the Brix of the extract. Direct analysis for Brix is still n o t r e c o m m e n d e d in relation to every sample,

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b u t it is practicable to analyse a sufficient n u m b e r of extracts for p o l a n d Brix to maintain an a d e q u a t e measure of the prevailing purity of residual juice in bagasse.

Mixed Juice.

Mixed juice is the m a i n liquid p r o d u c t of the milling train.

It i n c o r p o r a t e s all the extracted juice of the cane together with t h e major p a r t of t h e imbibition water. It also contains a solid c o m - p o n e n t m a d e up of soil, particles of fibre, a n d other m i n o r items.

C a n e of a high s t a n d a r d of cleanliness yields a b o u t 0.3 p e r cent insoluble m a t t e r in mixed juice, a n d when the cane is dirty this figure m a y rise well over one per cent.

This insoluble m a t t e r is technically fibre, n o t juice, a n d it should be t a k e n into account accordingly. W h e n the mixed juice is weighed, a sample should be analysed for insoluble m a t t e r , a n d the gross weight of mixed juice should be a p p o r t i o n e d between fibre in mixed juice a n d clean mixed juice. N o t only is this correct as regards a c c o u n t i n g for materials, b u t also it relates t h e analysis of the mixed juice to the material actually analysed.

T h e p o l of mixed juice will n o r m a l l y be determined by the dry lead m e t h o d . T h e pol t h u s m e a s u r e d is the pol of the liquid p h a s e , the clean mixed juice. T h e Brix should be determined on filtered mixed juice, because, if t h e juice is n o t filtered, the inflationary effect of t h e suspended m a t t e r is interpreted as extra dissolved solids which do n o t really exist.

Water.

T h e water referred to in this context is the net q u a n t i t y of water which is a d d e d in t h e milling process. M o s t of it is, of course, applied as imbibition, a n d a little m a y c o m e in t h r o u g h hoses or steam lines. On t h e other h a n d , a substantial q u a n t i t y is lost by e v a p o r a t i o n , particularly when hot milling is practised.

The Mass Balance.

A c c o r d i n g to the previous edition of this b o o k " t h e f u n d a m e n t a l e q u a t i o n for the weights of the p r o d u c t s entering a n d leaving the mill states t h a t cane plus water equals mixed juice plus b a g a s s e " . This is a d a n g e r o u s over-simplification, for it fails to specify t h a t t h e t e r m " w a t e r " h a s t o m e a n t h e net balance o f a d d e d water.

M o r e precisely, the f u n d a m e n t a l equation is:

C a n e + w a t e r a d d e d = juice + bagasse + w a t e r lost.

In earlier days it was n o t practical to weigh bagasse, a n d t h e q u a n t i t y thereof was calculated by subtracting the weight of mixed juice from the c o m b i n e d weights of cane a n d a d d e d water. T h e result is n o t truly t h e weight of bagasse b u t t h e c o m b i n e d weights of bagasse a n d water lost. T h e loss of water is m a i n l y by e v a p o r a t i o n from the milling t r a i n . Extensive tests on a milling train w o r k i n g u n d e r h o t conditions have disclosed a loss of water by e v a p o r a t i o n

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representing 3 per cent of the weight of i n c o m i n g material. U n d e r these conditions, t h e weight of bagasse calculated by difference will be inflated by 18 per cent. T h e example m a y be extreme, b u t in a n y case the error d u e to e v a p o r a t i o n is serious e n o u g h to discourage t h e use of the simple m a s s balance to determine the weight of bagasse.

F u r t h e r m o r e this m e t h o d is c u m b e r s o m e , a n d t h e b a n on the use of u n m e t e r e d water at the mills h a s a high nuisance value.

N o w a d a y s the weighing of bagasse can be carried o u t as a routine o p e r a t i o n a n d the statement t h a t " t h e best way to determine the weight of bagasse is to weigh i t " is no longer facetious.

T h e weights of mixed juice a n d bagasse, individually a n d directly determined, represent a powerful c o m b i n a t i o n . T h e weight of a d d e d water can be dispensed with, a n d even the weight of cane is unnecessary if one key component—fibre or Brix or pol per cent c a n e — c a n be determined.

W h e n it is impossible or inconvenient to determine the weight of bagasse t h e best p r o c e d u r e is to weigh the cane a n d determine its fibre content. T h e weight of fibre in cane, less the weight of fibre in mixed juice, is the weight of fibre in bagasse. This leads to the weight of bagasse a n d its c o m p o n e n t s . This system was originally accepted by t h e I n t e r n a t i o n a l Society with some misgivings as to sampling cane for fibre. It is sufficient to state here t h a t reliable sampling can be achieved a n d the scheme w o r k s well in practice.

A very i m p o r t a n t c o n t r i b u t i o n to factory c o n t r o l — a n in- n o v a t i o n since the previous edition of this b o o k — h a s been the development of the direct analysis of cane using the wet disintegrator.

This operation has n o w been established as practical a n d reliable subject to the n o r m a l d e m a n d s on diligence a n d m a i n t e n a n c e . Its success depends u p o n the provision of reliable samples of cane b u t this requirement c a n generally be met.

If t h e weight of c a n e is k n o w n , a n d the analysis of t h a t cane is d e t e r m i n e d , m o s t of the purposes of the m o r e complicated systems are achieved. F i b r e in c a n e , corrected approximately for fibre in mixed juice, gives fibre in bagasse, hence the weight of bagasse a n d its c o m - p o n e n t s . Pol in cane less pol in bagasse gives pol in mixed juice, hence the weight of mixed juice a n d its c o m p o n e n t s . If the weight of cane is u n k n o w n , then the weight of mixed juice should be determined a n d the a b o v e p r o c e d u r e applied with the necessary modifications.

T h e previous editions of this b o o k listed five other bases of control. E a c h of t h e m i n c o r p o r a t e s an a r b i t r a r y factor or a question- able a s s u m p t i o n , a n d n o n e was formally a p p r o v e d for use. There is no p o i n t in re-stating t h e m here.

It r e m a i n s only to a d d t h a t , in some factories, cane, water, bagasse a n d mixed juice are n o t t h e only materials entering or leaving t h e milling train. A n y other material involved, such as decant fluid from m u d t r e a t m e n t , m u s t be a c c o u n t e d for as to q u a n t i t y a n d c o m p o s i t i o n a n d taken into the materials balances.

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CHAPTER Ell

Determinations and Calculations for Milling Control

In C h a p t e r II the general basis of milling control was discussed, a n d several schemes were outlined broadly. It is now desirable to classify these schemes, express t h e m in m o r e detail, and go on to derive all the items of a full control p r o g r a m m e .

F o r this p u r p o s e a system of symbols has been devised, as follows. T h e materials a n d c o m p o n e n t s are represented by letters—

C a n e C, c Brix B, b Bagasse ( A m p a s ) A, a Pol P, p

N e t A d d e d Water I, i Fibre F,f Mixed Juice (actual) M , m Water W,w Mixed Juice (clean) J, j Purity Q

Excepting purity, the capital letters are used to refer to q u a n t i - ties, a n d the reference material is identified by a lower case subscript letter. Hence Ac is the a m o u n t of bagasse o b t a i n e d from the original weight of cane, and Fa is the weight of fibre in t h a t bagasse. Lower- case letters are used to express one item as a p r o p o r t i o n of a n o t h e r , a n d , for simplicity, a unit basis has been a d o p t e d . H e n c e pc is p o l per unit cane a n d fa is fibre per unit bagasse. T w o subscripts are occasionally necessary as in pfa, pol per unit fibre in bagasse.

It follows, for example, t h a t — A x pa = Pa a n d Fc ÷ fc = C

Preliminary Data.— When cane is analysed the items deter- m i n e d directly are water, wc, Brix, bc, a n d p o l pc. F i b r e is d e t e r m i n e d by difference, fc = 1 — wc — bc

Bagasse is analysed directly for water, , a n d pol, pa. Brix is determined from pol a n d t h e p u r i t y of the residual juice, here expressed as Qa, (again on a unit basis). Hence ba — pa ÷ Qa. F i b r e is then determined by difference, fa = 1 — wa — ba.

Mixed juice is analysed for fibre, / , „ , a n d it follows t h a t J=

M — Fm or jm = 1 —fm. The clean mixed juice is analysed for Brix, bj, a n d p o l , pj. It is assumed that, in all cases, ba, pa, fa, wa,

fm, pj, a n d bj are k n o w n . Basic Control Schemes.

Class I—When the weight of cane is known.

Scheme A—Cane weighed a n d analysed.

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Scheme D—Cane, Mixed Juice and A d d e d Water weighed.

T h i s is the familiar " m a s s b a l a n c e " m e t h o d . T h e derivation of results usually starts with the a s s u m p t i o n t h a t the actual weight of water a d d e d equals the n e t weight J. T h i s is a dubious assumption but, in the absence of knowledge regarding incidental gains or losses of water, it h a s to be m a d e .

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This listing of schemes may not be exhaustive but it should cover all the cases likely to be encountered in practice and amenable to absolute calculation. Conspicuous by its absence is the case where nothing is known of the cane—neither its weight nor any of its components quantitatively. In such a case the weight and composi- tion of the cane cannot be determined by any absolute method; some empirical factor or arbitrary assumption must be invoked.

The procedures above outlined lead to full knowledge of the weight and composition of each of the materials involved, and it is possible to draw up mass balances for Brix, pol, fibre, etc., as desired. Certain transitions from one material to another have been based on pol where Brix might have been used instead. The reason is that the main goal is considered to be a pol balance; the consequence is that the Brix may not, and probably will not, balance exactly but the error should be tolerable. If, for a particular purpose, it is desired that the Brix balance be exact, then let Brix be used instead of pol for the transitions.

Having pursued the subject so far, the reader should not need to be instructed in the derivation of such obvious quantities as mixed juice per cent cane or pol in bagasse per cent fibre; however a few terms are worthy of some explanation.

Absolute juice, as explained in Chapter II is that part of the cane which is not fibre. If b

c

is the Brix per unit cane, then the Brix per unit absolute juice is b

c÷ (1 —fc); likewise the pol is pc

÷ (1 —fc). These are used to find quantities of absolute juice in other materials, usually on a Brix basis, but optionally on a pol basis. The quantity of absolute juice relative to fibre in bagasse is an important criterion of milling performance.

For reporting purposes the net added water is called Imbibition, which explains the symbol I. Part of the imbibition water added appears in the mixed juice, and this part is known as Dilution;

the rest emerges as Imbibition Water in Bagasse. For the purposes of determining the division of the imbibition it is assumed that the original juices extracted into the mixed juice were the same as those left in the bagasse; both are treated as absolute juice, and calculation has traditionally been on a Brix basis. However, the milling per- formance figures which will be recommended for reporting are on a pol basis, and such a basis might well be adopted here.

Since the absolute juice in the mixed juice is regarded as being identical with the absolute juice of the cane, it follows that the extraction of absolute juice equals the pol extraction. The quantity of clean mixed juice is known from the mass balance; the quantity of absolute juice therein is the quantity of absolute juice in cane multiplied by the pol extraction (unit basis). The remainder of the mixed juice is the dilution, which can then be expressed relative to cane or absolute juice in cane.

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T h a t quantity of absolute juice not accounted for in the mixed juice is in the bagasse, a n d the difference between this absolute juice a n d the absolute residual juice in the bagasse is c o u n t e d as imbibition water in bagasse—a figure of doubtful accuracy. T h e a s s u m p t i o n t h a t the original juice left in the bagasse h a s the same pol as absolute juice in the cane m a y be expected to be appreciably in error.

Figures Used for Judging Milling Results.

Extraction (sucrose, pol, Brix, juice) is purely a quantitative statement of fact. If all canes were of one composition then extraction w o u l d also be a figure of m e r i t — b u t cane is not uniform, a n d to t h e extent that it d e p a r t s from uniformity so extraction becomes deficient as an index of the performance achieved.

Recognizing this, technologists have sought criteria which would take account of variations in the c o m p o s i t i o n of the cane a n d allow for t h e m in assessing milling results. T h e three significant variables in cane (the only three t h a t can be considered) are fibre, Brix and pol. T h e various criteria which have been proposed for indicating milling efficiency differ fundamentally in the a s s u m p t i o n s m a d e regarding t h e effects of these variables.

It is a feature of all the criteria t h a t , either in the first instance or entirely, they regard milling efficiency as i n d e p e n d e n t of fibre in c a n e ; in other words, at a c o n s t a n t order of merit, the loss of pol or Brix or juice in milling is expected to vary directly with fibre in cane. Efficiency is j u d g e d either by expressing the loss relative to fibre, or by " r e d u c i n g " the loss to w h a t it w o u l d h a v e been at a s t a n d a r d fibre in c a n e .

O n e m a y argue t h a t when the fibre in cane rises, a mill grinding at a c o n s t a n t cane rate is o p e r a t i n g at a higher fibre rate a n d m a y be expected to incur higher losses of p o l p e r u n i t of fibre. T h e a r g u m e n t is s o u n d e n o u g h , b u t it encroaches i n t o the field of performance per unit of e q u i p m e n t , which is beyond the present considerations. Even so, it is well to keep in m i n d t h a t milling performance criteria envisage a c o n s t a n t fibre rate r a t h e r t h a n a c o n s t a n t cane rate.

W h e r e a s in respect of fibre in c a n e t h e various criteria are virtually at one, this is not so as regards pol in cane. Here there are t w o f u n d a m e n t a l p r o p o s i t i o n s — o n e , t h a t the r a t i o o f p o l t o f i b r e in bagasse is i n d e p e n d e n t of p o l in c a n e : the other, t h a t the ratio is directly p r o p o r t i o n a l to p o l in cane, or p o l in juice.

It is convenient at this p o i n t to discuss various criteria of milling p e r f o r m a n c e .

1. Extraction: T h e w o r d alone normally signifies p o l e x t r a c t i o n ; it is possible to calculate also the extraction of sucrose or Brix or absolute juice, in which case t h e t e r m should be suitably qualified.

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T h e formula for calculation of pol extraction (here expressed on a unit basis) i s :

but, when a m a s s balance is t a k e n out, p o l extraction is normally calculated as Pj ÷ Pc.

T h e last expression in the f o r m u l a is the c o m p l e m e n t of extraction, t h a t is, t h e p r o p o r t i o n of pol lost in bagasse. It m a y be rendered into the f o r m —

ratio of pol to fibre in bagasse ratio of pol to fibre in cane

Mill engineers in general m a i n t a i n t h a t the response of this term, a n d therefore the response of extraction, to t h e ratio of pol to fibre in cane is a false index of milling performance. Extraction is a statement of fact a n d an inevitable p r o d u c t of q u a n t i t y a c c o u n t i n g , but it is universally acknowledged to be a p o o r figure of merit.

2. Milling Loss: Milling loss is the ratio of pol to fibre in bagasse, usually expressed as a percentage. It is a simple expression of the contention t h a t , regardless of the pol a n d fibre in cane, milling performance is best when the pol lost per unit of fibre is least. It has the a d v a n t a g e of simplicity a n d the disadvantage t h a t as per- f o r m a n c e improves it decreases.

3. Whole Reduced Extraction: In a p a p e r presented before the I n t e r n a t i o n a l Society in 1962, B. L. M i t t a l i n t r o d u c e d the t e r m W h o l e R e d u c e d Extraction which he defined a s :

W . R . E . (unit basis) = 1 —p-"c

Jc

This expression p r o b a b l y h a d an eye to the availability of the d a t a , pol in bagasse per cent cane and fibre per cent cane. Its significance is m o r e readily appreciated when it is converted to the f o r m :

W . R . E . -— 1 — Pa

This shows t h a t W . R . E . is the c o m p l e m e n t of Milling Loss.

T h r o u g h the reversal of t h e sign of the variable, the result rises, with i m p r o v i n g p e r f o r m a n c e , t o w a r d s a limit of 1 (100 p e r cent).

Like milling loss, it ignores the composition of the cane.

4. Extraction Ratio: Extraction ratio is n o r m a l l y defined as t h e percentage ratio of (100 — extraction) to fibre per cent cane.

Mathematically, on a unit basis:

E.R. _ JL=li

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This is m o r e readily u n d e r s t o o d when rendered into the f o r m :

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m a n y years indicates that they m u s t have some element of realism.

It is suggested that the t r u t h , if there be any, lies between the t w o . T h e absolute juice theory depends u p o n the a s s u m p t i o n that, if t h e average juice of C a n e A has twice the Brix or pol of the juice of C a n e B, then the same ratio applies to the juices of the last few cells in bagasse. Tests suggest t h a t there is a t r e n d t o w a r d s uniformity (at a level well above zero, by the way). If the end result were uniformity, then W . R . E . would be the best choice.

In a factory r e p o r t p o l extraction will be either recorded or readily available by reference to the loss of p o l in bagasse. R . E . (Mittal) is easily calculated from the loss of pol in bagasse or from W . R . E . It is r e c o m m e n d e d t h a t the milling p e r f o r m a n c e figures for r e p o r t i n g b e W h o l e R e d u c e d Extraction a n d R e d u c e d Extraction (Deerr).

Imbibition

Milling performance is so responsive to the p r o p o r t i o n of water used in the process t h a t a milling result c a n n o t be properly assessed w i t h o u t an a c c o m p a n y i n g expression of imbibition.

W h e n the actual weight of imbibition water can be measured or deduced, the intensity of imbibition is best expressed as p a r t s of imbibition water per 100 p a r t s of fibre in cane, c o m m o n l y called imbibition per cent fibre.

It is sometimes convenient, b u t s o m e w h a t less satisfactory to relate the a d d e d water to cane, rather t h a n fibre in cane, hence the terms a d d e d water resp. imbibition per cent cane.

L a c k of d a t a m a y m a k e it necessary to relate the a d d e d water to the weight of a juice, such as absolute juice, undiluted juice or first expressed juice. T h e calculation requires only the Brixes of the original juice a n d the diluted juice (mixed juice) but t h e result has significant limitation. Technically the " o r i g i n a l " juice is the extracted juice as it w o u l d be if undiluted, but this juice is n o t available, nor is its Brix; however, any one of the three juices specified above will serve. T h e second p o i n t is t h a t the mixed juice does n o t contain all the i m b i b i t i o n water, some of which passes o u t of the milling train in the bagasse. In an earlier example a final bagasse was found to contain 17.5 per cent imbibition water. This bagasse c o n t a i n e d 50 per cent fibre so t h a t the imbibition per cent fibre was 35. This is a substantial q u a n t i t y to ignore in a total of the order of 200, b u t at least t h e discrepancy is fairly c o n s t a n t . A t h i r d p o i n t is t h a t the mixed juice m u s t be the u n a d u l t e r a t e d p r o d u c t of the milling train, for if it contains filtrates or any o t h e r additives its Brix no longer reflects the dilution d u e t o imbibition.

Despite its limitations, dilution p e r cent " u n d i l u t e d " juice is a useful criterion, certainly w o r t h reporting if imbibition per cent fibre or c a n e is n o t available.

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Milling Plant Performance.

It is reiterated here that the performance figures discussed

represent attempts to compensate for variations in the cane not the equipment. The only feature related to plant is the inherent as- sumption of a constant fibre rate. As most of the mills of a train are affected more by fibre rate than cane rate, the basis is reasonable, and accords well with plant capacity formulae which are usually based on fibre rates.

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CHAPTER IV

Control of the Boiling House

Mixed Juice.

Though mixed juice is the raw material of the boiling house, it is better regarded as an end product of the milling process, since most of the interest in mixed juice is related to milling. In the boiling house, the mixed juice is about to be supplemented by filtrates, limed, perhaps treated with phosphoric acid or sulphur dioxide or special additives, then boiled and settled. In these pro- cesses and operations the components of the mixed juice are so thor- oughly re-shuffled that the original composition hardly matters.

The weight of mixed juice is known from the milling records, and the juice should be analysed for suspended matter, and pol and Brix of filtered mixed juice. The densimetric Brix of mixed juice as weighed is a false figure that gives rise to an erroneous purity and a purity rise on clarification that is mostly spurious. Previous editions recommended the determination of reducing sugars and ash in mixed juice but these would not seem to provide information of any use.

Clarification.

In the clarification process pH at various points is kept under control or observation but the only figure of record is the pH of clarified juice. The phosphate and starch contents of mixed juice may be of local significance from time to time, and clarified juice may be analysed for sulphur, calcium, phosphorus, starch, turbidity and suspended matter, but the results are not for publication.

It has been customary to report the amount of lime used for clarification, nominally as available calcium oxide per 1,000 parts of cane. This quantity is responsive to so many features of material, process and conditions that it has only local significance.

The clarification process yields primary mud which nowadays is usually supplemented by bagacillo and additives and passed to the rotary vacuum filters. Other types of filter may be used, and the alternative process of extracting sugar by decantation survives to a limited extent, but in any case there is a filter cake or mud leaving the factory, and filtrates or decant fluids returning to process.

The waste product, which is referred to as filter cake, contains a quantum of sucrose lost from the process, and therefore the weight and sugar content of the filter cake are essential components of the chemical control. Dry substance and bagacillo content may be of interest in relation to filter performance, and the purity of the liquid component serves to check on deterioration, but only the

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quantities of cake a n d pol in cake are of external interest. T h e r e is a technical p o i n t t h a t some of t h e loss of p o l in filter cake, being associated with its bagacillo content, has already been accounted for as p o l in bagasse. It is possible to m a k e allowance for this, b u t n o t t o o precisely, a n d , as the error is of the o r d e r of 10 per cent of t h e p o l in cake, it is usually ignored.

Clarified Juice.

F r o m a chemical p o i n t of view, clarified juice is the raw material of the boiling process, a n d , where mixed juice is n o t weighed, sometimes the analysis of clarified juice is used as the analysis of mixed juice for milling control. Its Brix is i m p o r t a n t in j u d g i n g t h e performance of the e v a p o r a t o r s , and, as m e n t i o n e d earlier, it m a y be analysed a n d tested extensively, but only its pH a n d purity are c o m m o n l y reported. Its weight is usually determined from t h e weight of mixed juice, with allowance for the p o l lost in filter cake.

Syrup.

Syrup is a comparatively u n i m p o r t a n t intermediate p r o d u c t . Its Brix is i m p o r t a n t in reference to the performance of t h e evapor- ators a n d the provision of suitable m a t e r i a l for the p a n s ; its purity is of interest as t h e starting level for t h e sugar boiling process, a n d these two items, Brix a n d purity are normally reported. It is n o t normally weighed, a n d its weight is rarely of concern.

Pan Products.

Various grades of massecuites a n d molasses are involved in the sugar boiling system, a n d their purities a n d Brixes are u n d e r c o n s t a n t observation or c o n t r o l in the interests of the process. A full report will normally include the average purity of each grade of massecuite a n d molasses. T h e purity of m a g m a should also be reported.

Sugars.

Several grades of shipment sugar m a y be t u r n e d out, a n d each should be accounted for separately as to weight a n d analysis. T h e s t a n d a r d d a t a for a sugar are p o l (corrected to 20°C) a n d water.

O p t i o n a l extras are reducing sugars, ash a n d o t h e r o r g a n i c m a t t e r . Sugars m a y also be tested for grain size, starch content, filterability, colour, etc., b u t such d a t a are n o t usually published.

Sugars returned to process in the factory are of internal interest only.

Final Molasses.

As final molasses contains o n e of the major losses of sucrose in process, its wreight a n d analysis are i m p o r t a n t . T h e weight s h o u l d be determined directly, a n d if this is n o t possible, a densimetric basis

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m u s t be a d o p t e d . Pol should be determined for the pol balance, a n d a p p a r e n t purity for the general record. As the a p p a r e n t p u r i t y of final molasses m a y be very deceptive, true purity should also be determined a n d r e p o r t e d , together with reducing sugars, ash a n d sucrose, so t h a t exhaustion formulae may be applied.

Recoveries and Performances.

Introduction. - T h a t p r o p o r t i o n or percentage of the pol in cane which passes into the mixed juice is referred to as the extraction.

T h a t p r o p o r t i o n of the pol in mixed juice which passes into the sugar m a n u f a c t u r e d is referred to as boiling house recovery. T h e p r o d u c t of the two represents the p r o p o r t i o n of pol in cane " r e c o v e r e d " as pol in sugar, a n d is k n o w n as overall recovery. Like extraction, these t w o recoveries are purely quantitative statements a n d do not necessarily constitute measures of efficiency. Let the purity of the mixed juice decline, t h e boiling h o u s e recovery will normally do the same when the s t a n d a r d of performance in terms of merit remains u n c h a n g e d .

In the case of extraction, there was only one variable to consider—the cane. T h e c o u n t e r p a r t in respect of recovery is the mixed j u i c e ; but there is a n o t h e r variable to consider also—the quality of the sugar p r o d u c e d . P o u r some of the final molasses over the sugar before the latter is weighed a n d analysed a n d the recovery will rise, b u t t h e performance of the factory has certainly not improved.

Hence, in a t t e m p t i n g to assess the merits of a recovery figure, one h a s to t a k e a c c o u n t of b o t h the mixed juice a n d the sugar.

A c t u a l recoveries, s t a n d a r d recoveries a n d v a r i o u s performance figures to be discussed are almost invariably expressed as percentages, b u t it simplifies m a t h e m a t i c a l expressions a n d derivations greatly if the terms are referred to the basis of unity r a t h e r t h a n 100. T h e former basis has been a d o p t e d .

All t h e terms can be, a n d ideally should be, based on t r u e analyses—sucrose a n d d r y s u b s t a n c e — b u t pol and Brix are accepted as the w o r k i n g s t a n d a r d s a n d the t e r m s , unqualified, are t a k e n to be based on these a p p a r e n t measures.

Actual Recoveries:

Boiling House Recovery.—As previously stated, Boiling H o u s e Recovery is pol in sugar as a p r o p o r t i o n of pol in mixed juice.

Overall Recovery.—As previously stated, Overall Recovery is pol in sugar as a p r o p o r t i o n of pol in cane.

Standard Recoveries.

The S-J-M Formula.—When a r a w material containing sucrose a n d impurities is processed into a final p r o d u c t , rich in sucrose a n d a waste p r o d u c t c o n t a i n i n g m o s t of the impurities, all c o m - p o n e n t s being a c c o u n t e d for, t h e r e is a m a t h e m a t i c a l relationship

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between t h e materials a n d their c o m p o n e n t s . T h e m o s t familiar expression of this is the s-j-m formula of Noel Deerr, which pictures a notional juice being processed into sugar a n d molasses only. If t h e purities o f the materials respectively b e j , s a n d m , t h e n the recovery, r, i.e., t h a t p r o p o r t i o n of the sucrose in the juice which is contained in the sugar is determined by the f o r m u l a :

j (s — m)

This is mathematically true when s, j a n d m are literally t r u e a n d there is no loss of any material. When a p p a r e n t values are used for s, j a n d m, the formula is no longer correct in general. T h e large disparity between the t r u e a n d a p p a r e n t purities of final molasses might suggest t h a t the use of a p p a r e n t purity would yield a b s u r d results, but there is a significant m e a s u r e of c o m p e n s a t i o n . T h e difference between the two purities for mixed juice is appreciably less t h a n for molasses, b u t t h e formula is m u c h m o r e sensitive to j t h a n to m. A difference of 3 units of purity in juice is equivalent to a b o u t 7 units of purity in molasses, a n d these figures are not t o o r e m o t e from t h e real differences between true a n d a p p a r e n t purities in the t w o cases.

Given values of s, j, m a n d r from the records, a n d a d o p t i n g t h e s-j-m formula, it is possible to c o m p a r e the actual recovery with the ideal figure. T h e former result will be the lower because of the k n o w n a n d u n k n o w n losses of sucrose other t h a n in molasses. T h e r a t i o of the t w o recoveries w o u l d be a figure of merit, t a k i n g account of the p u r i t y of mixed juice, showing up losses other t h a n in molasses, b u t accepting the purities of sugar a n d molasses at their actual values.

The Winter Formula.—Before 1900, Winter a n d C a r p in- dependently concluded t h a t t h e yield of commercial sugar to be expected from a mixed juice could be predicted by deducting from the p o l in the mixed juice 40 p a r t s for every 100 p a r t s of impurities.

This is expressible in t h e f o r m : r = 1.4- 0.4

J

where r w a s , originally, the recovery of c o m m e r c i a l sugar per unit of pol in mixed juice of purity j (unit basis).

W h e n the s-j-m formula was devised it was soon recognized t h a t t h e s-j-m formula w o u l d yield the same values of r when s was fixed at 1 (100 per cent) a n d m at 0.2857 (28.57 per cent). T h e formula of Winter a n d C a r p , generally called the Winter formula n o w a d a y s , is generally regarded as a special case of the s-j-m formula, b u t this is m a t h e m a t i c a l r a t h e r t h a n historical.

Regardless of its origin, the Winter formula is c o m m o n l y used to p r o v i d e a s t a n d a r d recovery for the boiling h o u s e , designated Basic Boiling H o u s e Recovery. It recognizes t h e purity of t h e

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mixed juice, it allows no losses of pol except in molasses, it provides for a molasses of 28.57 purity, and it takes no account of the purity of the sugar made.

Equivalent Standard Granulated Sugar.—It has been mentioned

that the quality of the sugar is a factor in recovery. Not all of the sucrose in a commercial sugar is truly "recovered" because, in the ultimate removal of the remaining impurities, some sucrose will inevitably be lost. Hence the sucrose content of any commercial sugar has to be discounted for potential loss if recovery is to be truly assessed.

Many standards of comparison of sugars, e.g., raw value, net titre, titrage, and many standard sugars, e.g., 96 degree, Standard Muscovado—have been or are used in practice, but most of them have a local and usually a commercial significance.

Noel Deerr suggested that the sugar itself was as good a subject for the assessment of a process recovery as any other factory product.

He proposed the use of the Winter formula, and to the material expected to be recovered he gave the name Equivalent Standard Granulated, usually abbreviated to E.S.G. The Winter recovery, being a recovery of pol, is applied to the pol of the sugar to yield the E.S.G. factor. Hence:

pol of sugar x Winter recovery = E.S.G. factor tons sugar x E.S.G. factor = tons E.S.G.

The actual recoveries referred to earlier are of pol in actual sugar; the Basic Boiling House Recovery is of pol in pure sugar. For comparison purposes either the actual recoveries might be adjusted to pure sugar, or the basic recovery to actual sugar.

Conventionally the first choice is adopted; comparisons are made in terms of pure sugar, that is, E.S.G.

Criteria of Performance.

Boiling House Efficiency.—The ratio of Actual B.H.R. to

Basic B.H.R. is frequently worked out (as a percentage) and reported as Boiling House Efficiency. As a criterion it compensates for the purity of the mixed juice and it responds to losses, but it takes no account of the quality of the sugar produced, and it postulates a standard purity of 28.57 for final molasses.

Boiling House Performance.—The neglect of sugar quality in

B.H.E. can be rectified by expressing the actual recovery as E.S.G.

instead of pol. The result can then be matched against Basic B.H.R.

which, being a recovery of pure pol, may legitimately be entitled Basic B.H.R.E.S.G. Thus B.H.P. is the ratio (usually as a percentage) of Actual B.H.R.E.S.G. to Basic B.H.R.E.S.G.

By previous specifications, the term B.H.P. was to be associated only with sucrose and gravity purities. No name was specified for

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of boiling h o u s e performance would a p p e a r to be the ratio of R . B . H . R . E . S . G . to Basic B . H . R . (s 100, j 85, m expected purity). F o r the p o l basis of reporting, the expected purity would need to be adjusted from true p u r i t y to a p p a r e n t purity according to the prevailing local difference.

Overall Performance.- With the performance of the milling station expressed in one figure, a n d the performance of the boiling h o u s e expressed in a n o t h e r , it was natural to think of c o m b i n i n g the t w o into one overall performance figure for the factory. This was d o n e originally by c o m b i n i n g the two Noel D e e r r criteria, R . E . a n d R . B . H . R . E . S . G . as R e d u c e d Overall Recovery E.S.G.

In view of the preference for G u n d u R a o ' s recovery formula Reduced Overall Recovery E.S.G. m a y n o w be defined as the percentage p r o d u c t of R . E . (Deerr) a n d R . B . H . R . E . S . G . ( G u n d u R a o ) . It is not as significant a term as might be expected at first t h o u g h t , because the milling d e p a r t m e n t and the boiling house arc so distinct t h a t the expression of their performances together in a single result gives little satisfaction.

In the consideration of overall p e r f o r m a n c e there is a s t r o n g tendency to go back to a cane basis. T h e Overall Recovery E.S.G.

multiplied by pol per unit cane gives the Yield of E.S.G. a n d the Reduced Overall Recovery E.S.G. treated similarly gives Reduced Yield of E.S.G. These arc not performance criteria at all, but, as actual or corrected yields of pure sucrose they are c o m m o n l y m a t c h e d against expected yields a n d so efficiency is j u d g e d . Tech- nically the venture is bold because the meagre d a t a available in respect of the cane are i n a d e q u a t e for the prediction, within reasonable limits, of a s t a n d a r d yield; economically the c o m p a r i s o n is well a n d truly justified when the price of the cane purchased is based u p o n the projected yield of sucrose. V a r i o u s formulae have been devised a n d are in regular use for the derivation of a standard yield of sucrose from cane according to the composition of the cane, b u t these are mainly commercial formulae a n d are not recognized for technical evaluation of performances.

Recapitulation.—In the consideration of terms to be a d o p t e d to express the p e r f o r m a n c e of a sugar factory, for the p u r p o s e s of I n t e r n a t i o n a l c o m p a r i s o n s , it is necessary to s u b o r d i n a t e precision in detail to the wide range of conditions to be catered for. Various criteria discussed in previous editions have been ignored here, not so m u c h on the g r o u n d s of lack of merit as on the c o n t e n t i o n t h a t they belong in a different field—the continuing study of the performance of o n e factory. This applies particularly to the m a n y formulae based on detailed a c c o u n t i n g for impurities.

Given as d a t a t h e p u r i t y of mixed juice, t h e p u r i t y of sugar a n d the actual boiling h o u s e recovery, it does n o t seem possible to derive any better criterion of t h e work of the boiling h o u s e t h a n R . B . H . R . E . S . G . ( G u n d u R a o ) . T h e m o s t obvious avenue for im-

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provement lies in using the composition of the molasses to n o m i n a t e a target purity for that material, and using t h a t purity to provide a value for m in the formula, instead of the traditional a n d in- discriminate figure of 28.57.

T h e r e is p r o b a b l y no need to d e p a r t from the Winter formula for the p u r p o s e of determining E.S.G. The effect of a change of molasses purity is very slight, the relationships between impurities in the sugar are not necessarily the same as in the final molasses, a n d one can find some virtue in a c o m m o n formula for all sugars.

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CHAPTER V

Methods of Weighing and Measuring

Chemical control necessarily involves the determination of weights of material, either directly or inferentially. The variations in layout and procedure within factories and the range of equipment available make it necessary to restrict the discussion of weighing and measuring to general principles of operation and types rather than specific brands or equipment.

Weights and Measures.

Whilst the universal adoption of an international decimal system of weights and measures is the ultimate goal, the fact remains that the local systems are strongly entrenched and most of them are not likely to be supplanted in the foreseeable future.

Fortunately the great majority of data in a record of chemical control are relative within themselves and thus independent of units. International trade and communications have fostered the adoption of one or other of the major systems of units in preference to minor local systems in many countries, and the cane sugar world may be said to be divided between the British and the metric systems, with minor local variations. The adoption of either one of these would appear to be the most that one can ask for at this juncture. The tendency to express parts of a major unit in decimals is developing and is to be encouraged, for this is a positive step towards ultimate uniformity.

Weight of Cane.

Cane is almost invariably weighed on a platform weighbridge designed to accommodate the vehicle by which a load of cane is carried.

As a weighing machine used for trade purposes, the cane weigher often comes under the jurisdiction of the Authority con- trolling weights and measures within the Country, and, if so, cali- bration and certification are performed by that Authority. If not, the procedures for testing, which arc too lengthy to be set out here, are readily available from any recognized testing Authority. The operation of testing and calibrating is usually performed annually.

Certain routine checks are called for. The practice of testing the zero regularly should be observed; this is readily achieved by making it the first task of each weighbridge operator coming on duty. He should also check the tare counterweights for identity and position. There should be a mobile test weight on the premises, weighing about the same as the average commercial load. Correct

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