Introduction to sugar technology; rev. ed.

INTRODUCTION

TO

SUGAR TECHNOLOGY

by

E. MOURIS

Revised edition

1984

DEPARTMENT OF CHEMICAL ENGINEERING AND CHEMISTRY DElFT UNIVERSITY OF TECHNOlOGY

INTRODUCTION TO SUGAR TECHNOLOGY by E. Mouris revised edition 1984

DEPARTMENT OF CHEMICAL ENGINEERING

AND CHEMISTRY

I

INTRODUCTION TO SUGAR TECHNOLOGY

1. INTRODUCTION

2. HISTORY OF SUGAR

3. THE SUGAR PLANTS

4. SOURCES FOR MANUFACTORING SUGAR

5. SUGAR PRODUCTION FROM SUGAR CANE

6. SUGAR PRODUCTION FROM SUGAR BEET

7. REFINING OF RAW CANE SUGAR

1.1 What is sugar? 1 1.2 Properties of sugar 2 1.3 The sugar cycZe 5

2.1 Sugar in the oZd 6 and new worZd

3.1 Sugar Cane 3.2 Sugar beet 4.1 GeneráZ methods 4.2 Sugar cane as a source 9 14 18 18 4.3 Sugar beet as a 21 source 5.1 GeneraZ 5.2 The processing of sugar cane 23 23 5.3 By-products of cane 27

6.1 The beet sugar factory 28 6.2 The manufactoring 28 -proces 6.3 By products of beet 50 6.4 Off-campaign 50 7.1 Sugar refineries 52

8. SUGAR t.fARKETS AND CONSUMPTION

9. NEW AND OTHER USES FOR SUGAR 8.1 Sugar distribution 8.2 Consumption 9.1 Sugar as energy souraes 9.2 Sugar as alternative souraes for the

ahemiaal industries 11 55 56 57 57

The great sugar house was a wilderness of tubs

and tanks and vats and filters, pumps, pipes,

and machinery. The process of making sugár is

exceedingly interesting. First, you heave your

cane into the centrifugals and grind out the juice;

then run i t through the evaporating-pan to extract

the fiber; then through the bone-filter to remove

the alcohol; then through the clarifying-tanks to

discharge the molasses; then through the

granulating-pipe to condense it; then through the vacuum-pan to

extract the vacuum. It is now ready for market. I

have jotted these particulars down from memory. The

thing looks simple and easy. Do not deceive yourself.

To make sugar is really one of the most difficult .

things in the world. And to make i t right is nextto

impossible. If you will examine your own supply every

now and then for a term of years, and tabulate the

result, you will find that not two men in twenty can

make sugar without getting sand into i t .

Mark Twain

111

1

1. INTRODUCTION

1 . 1. What is sugal'?

Crystallised sunlight.

Apart from water and the air around us, there is nothing quite as important to human life as sugar, for i t forms the basic food for both plant and animal.

Plants manufacture sugar by the process of photosynthesis which is not dissimilar to the principle by which electric batteries in space vehicles are recharged by harnessing solar energy. This process, though much studied, is not yet completely understood, but i t is known that plant leaves, by virtue of a green pigment called chlorophyll, use sunlight te create sugar. Recent studies have shown that the reaction takes place in minute plant cells called chloroplasts, which are only visible under an electron micrescope, the chlorophyll acting as a catalyst.

During photosynthesis carbon dioxide (C0₂) from the air

and water (H

20) from the plant are combined to form

sucrose (CI2H22011) with the release of oxygen (02) into the air. The reaction is simply represented by the

chemical equation:

+ catalyst

chlorophyll

---. . - - C12H22011

Sucrose, the chemical name for what is usually called sugar, is required by the plant in order to live and

2

grow. l t can be looked on as crystallised sunlight which the plant supplies to man.

1.2. Praperties af sugar

Sucrose, C12H22011 is a disacharide composed

of~-D­

glucose and,&~D-fructose (Fig. 1-1). lts use was at

first restricted to the wealthy, owing to its early high price, but ancient Chinese doctors and those of other early people described i t as a medicinal.

Today our syrups, elixirs, and pills are still compounded with sugar. Sucrose is said to be the first pure carbo-hydrate to separate from the photosynthetic process. As such, i t is the progenitor of all plant and animal sub-stances and the origin of coal and petroleum, our

principal sourees of heat and power.

For the purpose of establishing standards of identity for foods, the u.S. Food and Drug Administration has defined the term "sugar" as "refined sugar (sucrose)". Refined sugar, whether of cane or beet origin, is the organic substance produced in pure form in the greatest

volume, and is one of the purest of all substances pro~

duced in considerable volume. lts analysis is, approxi-mately: sucrose, 99.90%: invert sugar, 0.01%: asb (in-organic material), 0.03%: moisture, 0.03%: (in-organic mate-rial, 0.03%. There is a slight variation in the

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4

refined, but this is relatively insignificant.

It is the material of greatest food value economically,

in the sence that an acre devoted to the cultivation of sugar, whether beet or cane, is capable of producing more calories than any other food erop. It is the cheapest souree of calories known. However, sugar is all energy

(Joules ) and contains no proteins, virtually no mine-rals, and no vitamins, which must come from supplementa-ry diet materiaIs.

5

1.3. The sugar cycZe.

When man consumes sugar his body needs oxygen to convert his basic fuel, blood sugar, into energy and in the

course of this reaction the body liberates carbon dioxide, which is exhaled, whereas the plant inhales carbon dioxide

in order to live and grow and exhales oxygen. The process of sugar consumption is thus the reverse of sugar forma-tion and is represented by the equaforma-tion:

C12H22011 + 12°2 ~

(Enzyme)

11 H

20 + 12 CO2

+ (energy).

An enzyme is a natural organism which enables such changes as digestion to take place.

Sugar thus moves in a natural cycle, beginning with its formation in plants and completing its course with its consumption and use for growth, the renewing of celIs, and providing energy for all our activities.

Sugar is made by most plants but not usually in sufficient quantities to be harvested commercially. It is obtained from the maple tree in Canada, from sorghum, from certain palm trees and from the carob tree, but the two principal sources are:

a) sugar cane b) sugar beets

The biology, history, cultivation and extraction will be described in the following chapters.

While these plants provide sugar, their harvesting is not as simple as th at for example of wheat, barley or fruit. The sugar has to be extracted using technology which has been developed over centuries.

2. HISTORY OF SUGAR

2.1. Sugar in the oZd and new worZd

Sugar has been defined by chemists as a substance which is soluble in water, has a sweet taste and is capable of fermentation. The culture of sugar started at a very early period, sugar was known in India and the Orient long before the Christian era. The Greeks and Romans knew of the existence of sugar cane and probably of crystallized sugar, but the first positive evidence of sugar in solid form dates from Persia about A.D. 500.

So, in Sanscrit, sugar is called sarKara and the word candy is also derived from the Sanscrit kanda.

The practice of sweetened food also dates from an early period in world history and antedates the knowledge of sugar. In Northern Europe sugar came into use as an article of food during the time of the Crusaders, but does not appear to have been generally known prior to the middle of the thirteenth century. In 1148 the sugar cane, which had been brought from Asia, was exten'sively cultivated in Cyprus. About 1505 i t was introduced from Cyprus to the West Ind~es.

The discovery of America and the introduction of sugar cane in the new areas resulted in the rapid deve10pment

of sugar manufacture. About 1600 the production of raw sugar in the West Indies and tropical America was said to be the largest industry in the world of that day.

Sugar refining is said to have been invented by a Venetian, around 1550, who probably got the idea from China, where the art of refining sugar and making sugar

loaves had been practised for centuries. The first

Englishman who described the method of crystall~zing

7

and purifying sugar was called Bartholomew, but the

methods used were crude until the introduction of vacuum boiling and decolourization by bone char around 1802. So, many sugar refineries sprang up in the seaports of Great Britain and Western Europe.

In 1605 the suggestion to use beets for making sugar was made by Oliver de Serres. He wrote a book on "Art of agriculture and management of land" in which he stated:

"The beet root when boiled yields a juice similar to syrup of sugar, beautiful to look at because of its vermillion colour". A German chemist, named Andrea Marggraf, made sugar from beet roots in 1747, and some fifty years later one of his pupils, Franz Karl Achard, established a factory for commercial manufacture of beet sugar.

It was not, however, until the English blockade against cane sugar imports and the impetus given by the Emperor Napoleon the First in 1811 tothe growth of the sugar

beet and to the discovery of the best methods to obtain the juice and to extract the sugar from it, that the

manufacture of beet sugar became a practical proposition. Starting from 1830 the rise of beet sugar manufacturing was so rapid that within 50 years as much beet sugar as cane sugar was produced in the world. The overall world sugar production was for 1982 estimated at 98,5 million tonnesjyear, divided into:

world cane sugar production: 61.9 million tonnesjyear, world beet sugar production: 36,6 million tonnesjyear. Consequently the proportion nowadays is: 37.2 percent beet- and 62.8 percent cane sugar.

("International sugar economie yearbook and directory", Lichts, F.O., enclosure, p. 31, Verlag Dr. Albert

Bartens, Berlin (1983)).

9

3. THE SUGAR PLANTS.

3.1. Sugar cane.

Sugar Formation in the Cane.

Sugar cane is like a huge grass which grows perenially in tropical areas. It reaches a height of 4 to 5 metres. The top of the cane is crowned by an erect tuft of short green leaves where the process of photosynthesis takes place and the sugar is formed in the chloroplasts from carbon dioxide in the air and water in the plant.

The stem is divided into sections of 15 to 25 centimetres by 'nodes' or knots from which grow buds, concealed by long, drooping leaves. The outside of the stalk of mature cane is hard and golden yellow in colour, with spots of red and green, and inside i t are softer fibres os vascu-lar bundIes.

In fig. 3-1 is shown the botanical structure of the stem. The vascular bundIes are tubatar channels(Fig. 3-2) within the stem which allow for the passage of plant food,

dissolved in water, from the roots to the leaves, and also the movement of the products of photosynthesis from the leaves to the stalk for storage.

The bud, situated at the node, shows clearly. If acutting is taken, including the bud, and planted in moist soil at

a temperature of 19 to 220C three major growth processes

begin Fig. 3-3.

First, the root primordia develop short 'sett' roots, enabling the plant to anchor itself in the ground and to absorb water. Secondly a shoot is iniated in the bud, and thirdly, a permanent root system emerges from the base of the budo This development uses the stored sugar for food

and en~rgy until such time as the shoot can form leaves

and the process of photosynthesis can begin in the gro-wing plant. When the plant is established, the 'sett' roots become defunct and decay.

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-Cane cuttings or portions of the staik. As planting material the cuttings are usually selccted from the growing-point reg ion of the cane staik. Af ter ]. P. MARTJl"J 1 I .- ,'- _{3· 1 Sligar cane} --- - - - -111 1)111' :

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Two kinds of growth rings. Left, the growth ring is bent upward at the bud side of the stalk j

right, it is more or less horizontal and thus passes behind the budo After ]ESWIET.

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11 VasculM bundies Cor cracks Bud furrc'N Growth ring Root band

Leaf scar (node)

Wax ring

Roet primordia Bud

Corky patch

Growth crack

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A cross section of a portion of an H 109 ca ne leaf. After

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14

Cane does not need to be planted each year, for af ter i t is cut the roots remain, and from these

sprout fresh shoots which flourish and qrow, providinq the text year's crop. This process is called 'ratooning'.

Cane usually contains 10-15% o~ sugar and a canefield

will yield anything from 45 to 90 tons of sugar cane/ha

wi th is equivalent 4-.5 to 12 tons of sugar per hectare

3.2. Sugar beet.

Sugar Formation in the Beet.

Sugar beet (fig. 3-4) is a biennial plant which stores sucrose in the root during the first year of growni if allowed

to grow for a second year the plant would use some of this

sucrose in producing tall seed-bearing foliage. For sugar manufacture, therefore, the root is harvested in the first season. The sucrose is produced by photosynthesis in the green portions of the leaves of the beet. Atmospheric carbon dioxide is absorbed by the stomata (pores in the epidermia of the leaf). The carbon dioxide diffuses to

the chloroplasts where, in the presence of adequate light

temperature, and water content, the radiant energy of the light is absorbed to convert the carbon dioxide and water, through a complex cycle of intermediate products, into sucrose and other carbohydrates.

The sucrose is translocated through the conductive tissues

of the vascular system to the root, where i t may either

be retrained in storage cells or conducted back to other

parts of the plant and utilised for growth. The picture of a typical sugar beet, below, shows the small rootlets remaining with the beet as harvested but the very fine

tap root and root hairs reach about 2 metres belo~ ground

level in suitable soils.

Below the normal leaves and sterns, part of the growing

beet protrudes above ground level and the presence of

residual leaf scars serves to differentiate the crown of the beet from the root proper.

Sugar Beet (8ela vulgaris) Petiole Crown Leaf scars Root \ \

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Fig. 3-4 Sugar beet

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17

Although the crown portion of the beet does contain some sugar, the juice from this portion is of low quality con-taining a relatively high proportion of the reducing sugars, glucose and fructose, which would seriously interfere with the production of high quality crystal-line sugar. At harvest, the beet are 'topped'to remove the leaf and crown portion which may be fed to cattie or ploughed in as green fertiliser. The tops from each hec-tare of beet have a cattie feed value equivalent to about that of 0.5 hectare of kale.

The root portion of the beet, as sent for processing, has an average weight of some 350 g to 800 g depending on growing conditions and soil type and contains some

50 g to 130 g of sugar, as weil as pulp. Each hectare of beet provides some 5 tons of white sugar.

4. SOURSES FOR MANUFACTURING SUGARS.

4.1. GeneraZ Methods

In general there are two methods to manufacture sugar.

In previous chapters the two principle sourees, sugar

cane-and sugar beet, are already discussed.

In Fig. 4-1, an overall scheme show the in-and outputs

for manufacturing sugar from these two sourees.

4.2. Sugar cane as a course.

Cane is a Tropical Plant

18

Sugar cane needs strong sunlight an abundant water. In

some tropical areas natural rainfall is insufficient and

irrigation either by canals or overhead sprays is

neces-sary.Where natural rainfall is sufficient i t is at times

too heavy and in such areas drainage systems are required.

Tropical hurricans and cyclones can drastically reduce

the yield, drought can be most damaging and cane is also

subject to insect pests.

Af ter eropping the root is left in the ground and sprouts

again for the following year. This practice, known as

'ratoonir~', can be continued for 6 or 7 years or longer

and is one of the economie advantages of cane over annual

crops.

Planting is carried out with short sections of growing

cane Fig. 4-2. Plant cane is usually cut af ter 11-18

months. The yield of sugar per hectare varies from

4.5 to 12 tons depending on soil and climate.

Much of the world's cane is still hand cut, but rising

costs are causing the introduction of mechanical

harves-ting. Just before eropping, the lower leaves are usually

removed by controlled burning. The cane is cut as close

to the soil as possible. The top leaves, which are

remo-ved in the field, may be used as cattie fodder. Once

cut, the cane is loaded into trucks or trailers and taken

CANE

BAGASSE

EXHAUST GASES _FACTORY

WATER

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RAW SUGAR. L _ _ _ WHITE/SUGAR FUEL WATER MOLASSES

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I REFINERY WHITE SUGAR MARKET CONSUMER

Fig, 4-1 DIFFERENT SUGAR PROCESSES.

19

BEET

CATTLE FEED

FACTORY EXHAUST GASES

WATER

RAW SUGAR

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" Can~ s~cd rlac~d 'cnd !O end' in m>rrnal planting at Victmias \Iilling Co"

Philirrincs, !'laflling go("l '1uality sc'cd in this rnanncr \\'ith ade'lu:lt~ suil m"isture or \I'ith \\'ater for irrigati"n rcsults in ade4uar~ stands and in sunstanti:d sa\'ings "f

secd,

Fig. 4-2 Planting sugar cane

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21

4.3. Sugar beet as a souree

Sugar beet as a Temperate Zone Plant

Sugar beet is grown throughout Europe, the United States, Canada and the U.S.S.R. For sugar production i t is plan-ted in the spring and cropped the same autumn. The seed is planted in rows at about 60.000 plants per hectare. Until the early 1960s each seed contained a number of germs and produced several plants which has, af ter

sprouting, to be 'singled' down by hand to one, but since 1965 plant breeders have produced a monogerm seed which gives single plants. Other operations such as drilling, weeding and fertilising are carried out mechanically. Beet is subject to attack from a number of insect pests, of which the worst is the aphid, a carrier of a disease called virus yellows, which seriously affects the yield and must be controlled by spraying.

The sugar content is also improved by application of fertilizer. It is never planted two years running in the same field but is rotated with cereals and other crops. Before the days of beet, cereals were rotated with mangolds and turnips but this was expensive in labour and the roots could only be used as cattIe feed. In the early days farmers had to be persuaded to change to beets. Whereas cane stores sugar in the staIk, beet stores in the root. Harvesting normally begins in mid-September and

continues t i l l the end of the year. Af ter this the beet is liable to swift deterioration if a frost is followed by a thaw, though in European countries the campaign can continue t i l l end of December. Harvesting is performed entirely with machines which left the beet, top i t and feed i t into trailers. The green tops are used as animal feed.

Af ter harvesting, the beet is either sent directly to the factory or stored in clampsunder straw at the roadside until the factory can receive it.

22

From small beginnings 60 years ago, sugar beet has become a major factor in European and U.S.A. farming. It is a welcorne cash crop and because of the nature of its

roots, with their long thread-like rootles, i t irnproves the quality of the soil. Yields od cereal per hectare have enorrnously increased by the introduction of beet as a rotation erop.

23

5. SUGAR PRODUCTION FROM SUGAR CANE.

5.1. GeneraZ

Sugar cane deteriorates quickly af ter i t has been cut and should be processed as soon as possible.

A simple methode (still in use in under-developed countries) to manufacture sugar from cane is shown in Fig. 5-1.

Capacity 1-5 tons cane a day. The largest factories can

grind as rnuch as 20.000 tons a day. A erop lasts from

5 to 8 rnonths and is of ten called a 'campaign' .

5.2 The process&ng of sugar cane

At the factory (Fig. 5-2), cane is cleaned of trasts and other unwanted matter and passes first through

shredding knives to brak up the hard rind and expose the inner core. It is then crushed between squeezing rollers (see Fig. 5-3) under high pressure and sprayed with hot water. The juice from this station is heated and lime is added. This, af ter filtration in vacuum filters, leaves a clarified juice which is concentrated by evaporation. The thickened juice is boiled in steam-heated pans under vacuum until a mix or 'massecuite' of crystals and mother syrup is produced. The mixture is then spun in centrifugal machines to separate the sugar crystals (raw cane sugar)

from the residual syrup (cane molasses).

Some cane sugar is consumed locally but a larger proportion is shipped as raw cane sugar (not as cane) to rnetropolitan areas where the main markets exist.

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Flow diagram of !t Tnw-sugar fadory (J> pre,:illre; Vac VaCIIIIIl1; T (empcratmc).

Fig. 5-2 Processing of sugar cane

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FLEDING Ol' MILLS AND CONVEYING Ol' BAGASSE

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Fig. 5-3 Cross section sugar cane mill

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27

5.3. By produets of Cane

Molasses is converted into rum and baker's yeast and into cattIe food. 'Bagasse', the residual fibre of cane, is mainly used as fuel in the factories. Some is converted into paper and building board. Mud from the filters is used as fertilizer in the canefields.

6. SUGAR PRODUCTION FROM SUGAR BEET

6.1. The Beet Sugar Factory

There are resemblances between a cane factory and a beet

factory. Both extract the sugar from a plant but whereas

sugar cane is a tough, intractable material, sugar beet

28

is relatively soft and its cells could be destroyed by

crushing. It has to be treated differently from cane.

There are also differences in the raw juices obtained from the two plants although the end product is precisely the same. Compare page 24 a and page 30.

6.2. The manufacturing process.

It should be emphasized that a beet sugar factory does

not really manufacture sugar; the sucrose is synthesized

by process of nature in beet roots and the so-called

manufacturing process is essentially one of separating

the sugar, eventually in a pure form, from the various

materials with which i t is associated in the beet roots.

The process may be described by the block schemes Fig.6-1, 6-2 and the flow sheet illustrated in Fig. 6-3.

From this flow sheet one can see that a long and complex

processing is required for the production of sugar from

beets. The actual "season" or "campaign" is short, from

mid September until the end of December, a period of

about 80 days. Beet sugar factories work continuously during this period, the processing going on day and

night.

Although not shown in the flow sheet, there is a boiler

house, power house and its attendant auxiliaries.

Much stearn is used as weIl as plenty of water and

large supplies of coal, oil or natural gas, coke and

8EETS WATER L - - _ _ _ _ _ FUEl

f'-'-

'

-

'

-'-,

--+---'--

'

-

'

1

- I . L . . . . _ . FUEl I

-'-l

I

..

FUEl

1. beet reception and storage

2. water treatment

3. juice extraction and

purification 4. evaporation 5. cristallisation 6. sugar house SUGAR 7. pulp drying 8. lirne kiln

9. steamboiler and power

station.

PROCESS CONNECTION - - - - DISCONNECTION POSSIBlE

POWER

_._. - '- VAPOUR OR CON DENSWATER

Fig.

6-1

-

.

A bloek seheme of a sugar faetory. IV

Brandstof.

Bieten

Na ter

/(a!ksleen

cokes

-Slib

-Wa'Ssen

en Snijden Wa

ter-beho.nol.

I

kalKollen

r

J

Dror;1erlj

Na/Ie

pulp

1

,

D if'fuS

ie

Sap-r--

_,oroce~ I - -

_Zuivering'

r---5njdseL Ruw-

I

Dun-sap

I

Sap

~

Water

I

j

Na./er

I

I

I

I

Ca.Or~O=

ka.lleme!k

I

r - - - ~

- - - -

C02 g'as ~

Hele

g'a55en

Bron

cis

10

_{1. -}

.

Sit>OrnkeleL

./'

k0

.

+

een/rede

~

_stoom

-

-Fig, 6-2 FLOWSHEET BEET SUGAR FACTORY,

Do.rnp

•

Yerdamping'

~ r

-

.n,-k-Sap

...,

1

kri~tQ.L

-proces

eentriT'

+-.Dro9'en

Co,.,densor

--Deunp DrCX)?

pulp

SchUimaarde.

Su/ker

!'1efa.5se

-SLib

CaO BEET SUGAR Beets I ScaJes I Recelving station . I To factory bins, or long· term storage _,

Stone and trash

removers WJ~her Sli~ers I Pulp flrcss water or sacchJrate caKe Water _ _ D i f l u s e r - - - ,

J

I F irst I I C.Jrbonatlon I I Juree : I Second CO, - -carbonation I Filters Filters Evaporators

Ddf~slon

_JUlce

I

Screens I First _ C O . carbonation . I Clarifier I ·To lime or saccharate milk Intermediate and raw Standard liquor and second carbonat Ion press cakes or recaJcine(1

Thick jUi~e sugars filter aid

Melter

Fil:ers Cake, to .first

-"7"-.J==~-carbonatlon

~ ~ ____ ._S_lu,dge ~H~i~gh~~~----~~L~o~w~

High green ~ wash White pans I Mixers I Centrtfuges· Drier I Granulators Condit'ioning Scre~ning Storaq'c bins ~ To specialty manufJcturing, packJgrng, or bulk sa Je wash ·Intermediate pans I Mixers I Centrifuges To melter

I

W"~'"

! Presses I fvlolasses. +-conc Steffen L---r--~: fdtrate Low green Driers I

I

Mo lasses a I idried pulp Storage. use, sale Raw pans I Mixers Crystai I i zers Centrifuges To melter Storage 1 To· pressed pulp, Stetten process or sale

Fig ~ 6-3 _{Flow sheet beet sugar factory}

The power absorbed varies between 140 and 180 kW per 100 tonnes of beet worked per 24 hours.

32

Water use averages from 800 to 1000 tonnes per 100 tonnes of beet and 4 to 4.5 tonnes oil or 6 to 8 tonnes of coal on the same basis.

["Notebook - sugar course 1958", Mouris, E., p.10 to 24, School voor Suikerindustrie, Amsterdam (1958).]

6.2.1. Sugar beet supplies.

Growers deliver their truck loads of beets to beetrecei-ving stations located either at the factory or at conve-nient rail side locations in the harvesting areas. At the latter, the beets are transferred to railcars or transport trucks for shipment to the factory side. On arrival at works, beets are weighed and tipped into silos or flumes.

6.2.2. Beet preparation for diffusion.

6.2.2.1. Beet pumps pick up the beets and drop the roots into a washer. This washer consists of an open, perforated trough with revolving arms. Earth, small rocks, stones etc. are removed. Af ter washing, beets are lifted by bucket

elevators to the top of the building, where they are deposi-ted in supply hoppers over the beet-slicing mechnisms.

6.2.2.2. Beet sugar manufacture requires cutting of the beets into slices offering a large surf ace when being in contact with the water during extraction, conventionally known as the diffusion process. Slices of beets are called "cossettes", measuring 0.075 to 0.10 m in length at about 3 mm thickness.

33

Fig. 6-4 Overall vieuw beet sugar factory

6.2.3. Diffusion.

The sliced beet from the beet slicers are, af ter they have been weighed, immediately run into a continuous diffuser. The sliced beets are propelled up into a diffusion tower (system BMA

=

Braunsch-weigische Maschinenbau Anstalt, or Buckau

=

Buckau R. Wolf) or in a long trough with perforated plates (system DdS

=

De danske Sukkerfabrikker). Hot water enters at the top or upper end, flowing down countercurrently to the direction of the sliced beet movement and leaving the separator or lower end

of t.he diffuser as diffusion juice or raw juice. The

sugar depleted sliced beet leaving the upper end of the diffuser is known as pulp. During this process water and juice are heated by heat exchangers for better extraction. Fig. 6-6 and Fig. 6-7

6.2.4. Diffusion juice or raw juice.

The raw juice is light grey in colour, slightly acid, containing about 12 to 15 % dry substance and about 88 to 90 % sugar per 100 parts solid in the

juice.

6.2.5. Juice purification.

6.2.5.1. Milk of lime to neutralize juice and precipitate some impuri ties. Jui-ce is stirred for some time

before being passed on to the next process.Fig. 6-8.

6.2.5.2. High tanks containing raw juicé through which CO 2 is pumped.

The CO

2 combines with the lime, CaO, to form Cac0

Abscheidung von lult und Gasen schützt den Turm vor Korrosio:1 Schaumzerstörung ~---

--ohne Schaumöl ~

Abgeschiedene

interz:"ular~

-

--~

,

Gase verdrängen luft-

~

,

sauerstoff aus den Schnitzeln "

-~ ''''-,

""

Schnitzeleinlührung oh ne Schaumerzeugung

~

". .. _~ ". <;lrnmlinienlörmige Rührarme kein r ransport, daher Anpas-sung an alle leistungsbereiche ohne Drehzahländerung nur durch Niveaueinste"ung

l

'

'.

", Beste Frischwasserverteilung: rotier!!!de .Q.~senberieselung

11.

--

'! F' h fh L .. sc wasserzu u r --.. - '----"--. '._

-Zulührung von entgastem PreBwasser (BW-PreBwasser-entgasung)

~---

---Beste PreBwasserverteilung durch rotierende Rührarme

.~

G1eichmäBige Gegenstrom-führung von Schnitzel und Saft. Höchste Schnitzelfü"ung

BW-AUSLAUGER erzwingt schne"sten Saltdurchlauf lultabschluB durch

hohen Flüssigkeitsstand im Schnitzelschacht

---"~-Abspülung der anhal-tenden Erdbakterien

Rohsaftabgabe

Fig. 6-6

Für 200 bis 5000 tato Einze"eistung

Entsandung in der Aulbereitungsanlage - - --.--.. _- ._----_. ---./' (/' I l!.u!~~~ftent~~ndung Diffusion process

" leitflügel von absoluter

'-" Betriebssicherheit,

'",Keine Schnitzelstauungen

~ _ _ __ S_i_e_b.:..p_a_ra_I_lele Schnitzelaulgabe

I

Verstoplungssichere Regelung

L

der Pumpenleistung bei konstanter Drehzahl - --_._. _ ..

_-

-_. ---_ .. _.

-Einwandfreie Siebreinigung durch selbsttätig sich einste"ende Siebabstreiler Gasarme Schnilzelmaschine -_ lange lebensdauer '--- -W 'è~\

36 Ul )..1 Q) ~ o +J ~ o .~ Ul :::l 4-1 4-1 .~ Cl

'~/'t

sleen

Coke

S .

•

~-~

J;e6ranc/e

ia/k

--

Water

-

la!kme!k

r _____

~~c~'O~2.

_

:-

-

~

...:...

Fig. 6-8 JUICE PURIFICATION.

I

/"Car60na.

--Ia.fle

-Ala-fillra~e

I

Ontharde"

37

JJunsab

38

bubble through until the lime content of the juice is reduced to about 0.1 %.uCarbonatation~

thickens the juice and a good deal of scum is

formed by the precipitation of organic irnpurities.

Some authors use the word "carbonation" but on the European Continent and in the United States of

America the word "carbonatation" is generally used. Por example Oliver Lyle also used the word

"carbonatation" in his book ["Technology for sugar refinery workers", Lyle, 0., p. 26, 58, 304,

Chapman & Hall, London (1957)

J.

Also the "Glossaria interpretum" ["Glossary of sugar technology", Müller, C.A., p. 20 to 21, Elsevier Publishing Company, Amsterdam (1970)

J

gives the same meaning to this subject.

6.2.5.3. In order to facilitate filtration, carbonated

i

juice is heated to 950 C and filtered in filter presses or in vacuum drum filters, which remove the sludge containing caC0

3 and non-sugars precipitated during the first carbonatation

process. The juice has a light yellow colour and still contains a slight surplus of lime in solu-tion. I t is, therefore, subjected to a second carbonatation process with carbon dioxide and the precipitated CaC0

3 is again filtered off in filter presses.

39

6.2.5.4. 8ulfitation.

The resulting juice undergoes a treatment with gaseous 802 (sulfitation) for additional decolour-ization and is again filtered in filters. The resulting light-yellow juice (thin juice) contains approximately 15 % dry substance. This dry matter consists bf 95 percent of pure sugar and 5 percent of non-sugar.

6; 2.6. Evaporation station.

Triple or quadruple effect evaporators are used to

remove the excess of water in the thin juice. Fig. 6~9.

They work as follows: The first evaporator is heated by exhaust steam from the turbo generator, which, on giving its heat to the thin juice, condenses. The steam produced from the juice passes over to heat the second, the process being repeated for the third and fourth if used. BecausBof the heat given up to the next, the condensation of this juice steam pro-duces a lower pressure over the juice, thus reducing the boiling temperature of the juice.

The juice leaving the last evaporator is called "Thick juice" and has 65 % dry substance. The dry substance consists of 94 percent sugar and 6 ~ercent

:\1,1>, -; Scht'lIla t'iner \'ierslufi~l't1 \'enlalllpferallla!.!t·:

"I \'orwiirJllt'r riir ,'inZlldick,'ndt' Lii"UIH(, bi KOlldl't1sat-I'\lInpt', c) Pumpt' zum Ab7.ieht'1l

dl'r ,'ill:(edit-kten Lü,ulll(

Di" ~, 'iltlfe II\'} arl>l'itet lInler \'aklllllll, \ Entnollllllen: l'lIlllanll. Etlz. d. tedm, Chl'lll .•

\liilld\l'n t1l1d Ikrlill, Bd, 1. Ul.5l, S, ,,):3S)

condensor l

-,

40 I 1 I

_L----r-~

_{1 I}

I

_{1 I}

I

steaffi thin juice

i

.-

-+-I I I I

.-JL

I

-~

condensate

Fig. 6-9 Four effect evaporator

I

'

-t

I

I

I I I I ~

L

___

._-.-J

+

I Ithick juice 1... _ _

+

41

Fig. 6-10 Juice heaters.

42

6.2.7. Crystallization.

The thick juice from the evaporating station and melted liquor from the intermediate sugar- and low-grade (affination) sugar melters are mixed; filter

aid is added - usually diatomaceous earth - and a

briqht filtration follows. The filtered liquor, or standard liquor, provides the feeding material for the vacuum pan boiling of the first or A-product. Vacuum pans usually are vessels with conical bottoms

containing steam coils. The pans are connected to

acondenser, 50 that boiling is carried out under

vacuum. The content of a vacuum pan is called

masse-cuite and consists of a mass of crystals (50 %) and

of mother liquor. The massecuite is discharged into a mixer tank for temporary storaqe to supply the

centrifuqes. ·'Fier. 6-12

6.2:8. Centrifuges.

Separation of suqar crystals from massecuite is

done in centrifuqe~ which are rotatïnq rapidlv

(about 1000 rpm) ~n vertical drums with perforated

side walIs. In the centrifuqes the suqar is spun free of syrup and is then briefly washed with hot water. This suqar, af ter dryinq and screeninq, is the final product: white qranulated suqar.

~--~

JJa.mjJ naar

CondenSDr

D/~SQ.é

---~

~9~mollen

ju/ier

of siroop

Fig, 6-12 SIMPLE

BOILI~G

SCHEME,

kook.pan

110.1

Q. X eu r

( koel.

trog' )

suiker

Centrifuge

sIroop

43

44

6.2.9. Intermediate or B-suqar.

The syrup spun off the white or A-suqar centrifuqes is known as "high- or A-syrup" and provides the vacuurn-pan feed for the second or intermediate boiling. The intermediate boiling process and con-tents of the vacuum pans is also known as B-masse-cuite. The centrifuqinq of the intermediate- or B-massecuite provides B-suqar, one of the two suqars which, af ter meltinq, is used to make .

standard liquor.Fig. 6-13

6.2.10. Low qrade- or C-suqar.

The syrup from the intermediate centrifuqes pro-vides the feed supply for the third or C-crystal-lization process. The massecuite from the C_vacuum pans is held from 16 to 50 hours in crystallizers, where the temperature is qradually lowered,

allow-inq time for the slow rates of crystallization in this low purity material to crvstallize out all the suqar possible. The C-suqar from the centri-fuqes becomes the other part of the standard liquor, while all of the syrup spun from the C-massecuite is called molasses. The molasses con-sists of 20 % water, while the dry substance has 60 parts of suqar and 40 parts non-suqar.

H.A.Syrup 3t/75 vapour to condensor 1 3 , 7 t . . -1n1i te sugar 13,1 ti 1 00 vapour to condensor 3,5t vapour to H.B.syrup 3,3t/75

.condensor 1 ,55t' -Molasses 3,8t/84 ... ~ _ _ _ _ ~ I----~ Thick juice 27 t/60,5 Remelted sugar 15,6t/65 Massecuite 31,9t/90 A-syrup 17,7t/75 Hassecuite 17,5t/91 lvater I, 3t - - - B-su ar 7 6t 9 r-___ ~~~B--~s~v~ru~n~~5t/75 6,4t/75 lIassecuite 6,151 3 C-sugar 3,36t/98 syrup 2,3t/75 Aff.sugar 2,6t/98

Fig. 6-13 A three sugar boiling scherne.

mixer

5,4 t

water

46

6.2.11. Final granulated product.

The granulated white sugar is bagged or stored in silos for later package or bulk sale. It is also possible to manufacture liquid sugar and powdered sugar from the granulated product. Generally there has been more use of large scale storage of granu-lated sugar recently.

6.2.12. Power and steam.

6.2.12.1. Steam consumption.

Sugar factories nowadays generally are equipped with water-tube boilers of various types. These

aresimple in comparison with boilers in large modern steam power stations. They normally will have superheaters and economisers and will be fitted with furnaces for burning oil, natural gas or coal.

Large quantities of steam are used for juice heating, for concentration of the juice and 'for boiling of the massecuite. For the main purposes only low-pressure steam is used, which can be ob-tained as exhaust steam from back pressure tur-bines supplemented by reduced live steam, or as

vapour from the evaporators. Fig. 6-14, and Fig. 6-15. While in old-fashioned plants of ten 60 tO 80

ton-nes of steam per 100 tonton-nes of beets are required, modern plants nowadays require only 35 to 40 ton- .

Simultaneously, there is an increase of power, requirements in connection with mechanisation, automatization andwater .purification systems.

6.2.12.2. Power consumption.

47

It is considered that the power required for pro-cessing 100 tonnes of beet per 24 hours in a modern sugar factory is: 180 kW in plants proces-sing between 1,500 tonnes and 3,000 tonnes of beet per 24 hours and 150 kW in plants processing more than 3,000 tonnes of beet per 24 hours.

hj I

t"'"" ""

~'EA""UUILlH~ <..D: f-'o l.Q

.

INT(RN LO!.!>fS I I 0\ I ...

';=-~ SRuBSEAWA TER TAANSPQRTATIQN

H 4fL05SES ';ILN 0>

C

;~

V(RSIO

'

l~

1 ___ ... _r.TllAt~l ~ 0" r-' ~ATlOSS(S

a

MIUUlIM[ MllK OF lIME _{CO 2} G.~

[)(HAUS T wET PUlP

Ul GAS 'VAPOUR

l

H AT lOSSES ..., lAANSPQRTATION ""U

:u

% ~ PAESS WA TEA 0 '" '" ~ ~ () 0 0 ₍₎ Hl z z z 0 .. 0 '" rrl '" " z

g:

:: ~ _'" O[NSEA (f) '" 0 ~ _(f) (!) ~

..

_'" '" := ()ENSAT( ~

ffi

..

Hl'" losse!> Pl 'HleK )UIC[ rt C) Cl' .... 0 t.J Hl ""U ~A"OUH r-' ~ C ~ ~ ~ ~ ~ ~ ~

~

m I r 0 r • n ~ ~ 0 • ~ ~ • - ~ - m ~

C,pNOENSEA Ilif AT IN nOCK lUIer

!

~ ~

;

~ ~ p : ~ _~ o ~ ~ 0 : ~ 2 D ~ S:~NOf.NSAT( ~ ~ ~; a ~ ~ ~ ~ rrl ~AT LOS!.ES (J1 ~ ~ ~ ~ ~

:u

Hf AT IN SUGAA Ul a : ~ ~! ~ (f)

s

'" _{z .,.} z _{c '"'} 0

~

; (J ~ ~ ~ " "

.. ..

o '" .. _-i "

..

" _-~

Hl z ₀ TRAHSPORT.'ION I WARM WATER

'" Pl

..

~

0 _Z "

..

f-'o (!) _~ Ul _ex>

r

19

ST AIR FuEl

I

E. houst 9 cues

~ ~

I

~

! POWER

I

-~ STATION

I

:

I

) I

~

BPn RJn

~-~J:

OJn RJm -TJn OJm FCJ_n SCJn TS_N RJ_cr , -13

I

I

1 1 OJ_u OJ_ru

LL ;

I

~

STEM"BOILER. GENERATION EVAPORATOR

I

~"'''-''-o,:

__

1

I

1

r-1

7

1

I

I

I

I

I

L

AIA rUEl Fig. 6-15

r - -~lURRY _{WATER PURIFICATION}

WET OlrFU~ION PULP VAPOUR 1---,.---,,.--.--OR I EO PUL P ~--'--_ PELLETS PULP ORYING

The division of the heat seheme.

T-18

I

1

RJn RJ_ru Fe)

1

Fe

j::-

sCJ

Hl

lJ.,

LJ

JUICE HEAliNG COKE LIME STONE BURNEO UME STONE LlME KILN

- - - - ,

liP Ir BPl!l

I

5+9

,·-

--

-1-

.

(ë1l

_I

., P

I

I

__

___ J

~

:

I

1

L

~C02G .. S WATER BOILI r~G PANS POWER STATION

I

I

I

I

-I

I

I

l

r

19

1 P 1 BEET TRANSPORT 2 WATER TRANSPORT 1 SLICING ,OIFFuSION 1

I

I

I

I

• JUICE TRAN!)PQHT 4 EVAPQAAtlON

~ BOIllP4G PANS .VACUUM 6 SUGAR HOUSE

7 PULP DRY ING • TRANSPORT 8 II ME KlU'\! 11 STEAM BOilERS • GENERATORS

1 ___ _

__ J

I

*"

\.0

50

6.3. By-products of beet.

By-Products of Beet

The chief by-product is beet pulp, which is dried Fig.

6-16and mixed'with beet molasses into pulp nuts, which

have a wide scale as animal feed.

Molasses, another important by-product, is used in many industrial processes. The leaves and crowns of the beet, which are cutt of during harvesting, provide valuable animal feed for many farmers.

6.4. Off-campaign

In order to enable more beet to be processes without additional equipment, some of the tickened juice is stored in huge tanks and the sugar from i t crystallised af ter the campaign. White sugar is stored in 10.000 ton silos for marketing between one campaign and the next. During the off-campaign, people who work in the factory undertake repairs of the equipment, which must be able to work continuously day and night without a halt for

8rano/slof

LtJcl~t

-

_Q7en

--Fig, 6-16 PULP SCHEME,

Ir

Pz.rSen

'20.

./)rood

-frommel çc~ooicle

pull:>

0É.slaq'

~

q'w-~e

pul;.,

~ ~ ~ Pe~JvateÎ

naa.r

en

dif/L1S'/e

t

DÎ

.lJa.rnh I

!3raK{es

é.ersen

•

51

52

7. REFINING OF RAW CANE SUGAR.

7.1. Sugar Refineries

While sugar factories are located as centrally as possible in growing areas, refineries are invariably sited at deep water ports such as London, Liverpool and New-York and in the past Amsterdam. This is to facilitate the reception of imported raw sugar ih large quantities from ocean-going bulk carrying vessels. They also take in raw beet sugar delivered either by bulk trucks or coasters. The material entering the refinery consists of sugar crystals with impurities and a coating of molasses. The outer layers are softened with warm syrup and the mixture, cal led 'magma', is passed into centrifugal

machines, which are high speed rotating perforated drums, and which separate the syrup from the crystals. In the separation some sugar is taken off with the impurities and this must be recovered. In a process known as

'recovery' this syrup undergoes successive boiling under vacuum and centrifugal separation. The recovered sugar

is melted and goes on through the refining process,

joining the washed raw crystals.

The final syrup, from which i t is no longer economie to recover sugar, is called refinery molasses. AltholJltJh partially clean there are still impurities within the crystals which are now dissolved in water. The solution is treated with lime and carbon dioxide bubbled ih. The

53

resulting chalk precipitate traps impurities present in

the 'liquor'. The chalky filter aid and impurities are

removed in a filter press and the emerging liquor is now

a clear amber colour. Next, the non-sweetening colouring

matter and virtually all soluble impurities are removed

by passing the liquor over bone charcoal or some other

decolourising agent. The liquor is now clear and

colour-less.

The process of crystallisation and preparation for

packing in a refinery is similar to that used in white

sugar factories, i.e. boiling under a vacuum in large

enclosed pans at low temperatures to avoid colour

formation and the destruction of sugar by heat.

The recrystallisation of sugar has until recently been

entirely a matter of human skill, the pansman judging

the correct degree of supersaturation in the pan, inducing

the formation of crystals by introducing a small quantity

of 'seed' crystals and then continuing to grow the grain

so formed to the requisite size before stopping the

evaporation, breaking the vacuum and running off the

'massecuite' of crystals and syrup. Automatic

recrystal-lisation has now been developed to a degree where i t may

replace manis skill.

The crystals are, as before, separated from the mother

syrup in centrifugal machines and dried in granulators.

While different sizes of crystals are normally produced

by variations in boiling technique, there is always some

54

crystals by screening before packing as granulated,

finest granulated or caster. Icing sugar is made by

pulverising crystals in a mill and cube sugar by

55

8. SUGAR MARKETS AND CONSUMPTION

8.1. Sugar distribution

Most beet sugar is eaten where i t is made, as is much cane sugar (e.g. in India), but there is a traditional trade in cane raws, on which many developing countries depend for external earnings. Markets for this generally lie far from the country of origin, and the sugar is shipped in bulk in large single-deck ships of 12 to

25,000 tons capacity, of ten owned by the sugar refiners. These come alongside in deep-water ports and are either discharged direct into the refinery or, where such

facilities do not exist, taken to i t by barge or truck. One of the reasons for this is economy. Another is that refining as near the market as possible enables control of quantity to be properly exercised for the consumer, and packets, which are easily burst, to be handled better. Af ter processing the sugar is distributed, either in

special bulk lorries to manufacturers or in packets to the grocer. Home-grown white sugar from beet is similarly distributed.

The sugar is sold to sugar dealers, retail organisations, and food manufacturers, a discount being given on

quantity. Dealers purchase large tonnages which they sell to thousands of outlets throughout the country. Physical delivery, whether of products or of bulk, is undertaken by the refiners and the Sugar Corporations, storing in

56

depots throughout the country and having large fleets of specialised lorries. Certain manufacturers also

purchase liquid sugar in bulk. Some, such as the pharma-ceutical and soft drink industries, require specialised delivery.

8.2. Consumption

More than half the sugar eaten in the world is consumed

in the form of manufactured foods - biscuits, sweets,

57

9. NEW AND OTHER US ES FOR SUGAR

9.1. Sugar as energy sourees

Although i t is natural to think of sugar as a food, and this is its prime use, since 1960 i t has been studied as a natural source of many of mankind's modern needs. Such products as detergents, plastics and chemicals and so forth have until recently been based almost entirely on crude oil, but the rise in price of oil may make i t less economically attractive as a source, and in some cases, for example, that of detergents, the product is under criticism from an environmental point of view.

Petro-chemical detergents are non-biodegradable, meaning that they do not break down af ter use and, when dis-charged into a river or into the sea, affect the natural life in the water. A detergent manufactured from sugar or molasses is completely biodegradable and under no such disadvantage. The cost of the raw material is now

approaching that of oil.

9.2. Sugar as alternative sourees for the chemical

industries

The plastics industry depends largelyon phenol. Oil

prices have made this scarce and costly. Sucrose contains, like phenol, carbon, hydrogen and oxygen, though in

Ethylene oxide, much used in the chemical industry can be made from sucrose, and although the economics of the process are not yet established i t remains a future possibility.

In the past decade the chemistry of the sucrose molecule has been the subject of considerable study and many

possible uses can be foreseen.

58

Microbiology has been applied to sucrose and its by--products and wastes, and a number of new fields are being opened up. In particular the vegetable waste,

bagasse, as weIl as molasses, can be converted by certain micro-organisms into a protein-containing cattIe food, which may help to increase edible protein consumption in developing countries which are short of cattIe because they lack the fodder.

Recent (1976) trials in feeding liquid sugar to pigs

prior to slaughter have shown considerable improvement in the quality of the meat.

Sugar and molasses are also widely used in fermentations

to prod~ce not only alcohol, but also such chemicals as

citric acid, lactic acid and sodium glutamate. Itaconic acid, a component of same plastics, is produced by

fermentation, while drugs such as penicillin and cephalosporin are the metabolic by-products of

micro--organism growing on sugar solutions. Yet others ''Convert

sugar into polysaccharides or sugar polymers. Examples of these gums are dextran, a blood plasma substitute, and alginate which is normally obtained from seaweed and is

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used in many products.

Several hundred thousand tons of sugar are used every year in fermentations, quite apart from that used in wine production and brewing. Sugar in all its forms is there-fore a very versatile and important raw rnaterial.