Since 8 involves a calculation, values for it have been computed, and are given in Table 6-l

128 BEET�SUGAR TECHNOLOGY

Since 8 Since 8 involves a calculation, values for it have been computed, and are given in Table 6-l

Once K has been determined, the expected. losses can be calculated with

variation of factors such

as

temperature, diffusion time, draft, or thickness

of slice. These losses

_can

then be balanced against other effects produced

by a contemplated change in operating conditions, and thus a more rational

conclusion rea�ed

as

to the desirability of making the change. To facilitate

the determination of losses, Table' 6-2 has been constructed. To use the

table, multiply the percent sugar in the cossettes entering by the tabulated

value corresponding to the KP and draft, to obtain the calculated loss.

THE DIFFUSION PROOESS

161 In Sweden, considerable use has been made of Siline's equation in attempts to find the economically optimum operating conditions. The study, as yet incomplete, is summarized by Wintzell and

.A.kermark.1

Table

6-2

Pulp Sugar Calcu.lated aB Fraction of Sugar in Original C088eUea

Dmf, KP

0 1 , , • S , 1 8 • 10

--- -- -- -- -- -- -- -- -- -- -- -- lOO

1 .0000

_.2809

. 155' . 1012 .0718 . 0535 . 041 . 0324 .0259 . 0209 . 0171 102 1 . 0000 . 2816 . 1496 .0951 .0657 .0477 . 0357 .0273 .0212 . 0156 .0131 104 1 . 0000 .2770 . 1442 .0395 .0603 .0425 . 0309 . 0230 .0173 . 0131 .0101 106 1 . 0000 . 2731 . 1391 .0342 .0553 .0380 .0269 . 0193 .0141 . 0104

_.0077

108 1 . 0000 . 2694 . 1 343 .079<

_.0503

.0340 .0233 . 0163 ,0115 .0032

_.0059

110 1 . 0000 .2655 . 1297 .0749 .0468 .0304 .0203 .0138 .0094 .0065 .0045 112 1 . 0000 .2620 .1253 .0707 .0431 .0273 .0177 .0116 .0077 .0052 .0035 114 1 .0000 .2586 . 1212 .0669 .0397 .0245 .0154 .0099 .0064 .0041 .0027 116 1 .0000 .2553 . 1 173 .0633 .0367 .0220 .0135

.0084 .0053

.0033 .0021 118 1 .0000 .2521 .1136

_.0600

.0339 .0198 . 0118

_.0071

.0043 .0027 .0016 120 1.0000 .2489 .1101 .0568 .0314 . 0179 . 0104 .0061 .0036 .0022 .0013 122 1 . 0000

_.2460

. 1068 .0539 .0291 .0162 .0092 .0052 .0030 .0017 .0010 124 1 . 0000 .2432 . 1036 .0513 .0270 .0147 .0081 .0045

_.0025

. 0014 .0008 126 1 .0000 .2404 .1006 .0438 .0251 . 0133 .0072 .0039 .0021 .001' .0006 128 1 . 0000 .2377 . 0978 .0465 .0234 .0121 .0064

_.0034

:�:�

^.0009

^.0005

130 1 .0000 .2351 . 0951 .0443 .0218 .0110 .0057 .0029

_.0003

.0004 132 1 . 0000 .2326 .0926 .0422 .0204 .0101 .0050 .0026 .0013

_.0007 .0003

134 1 .0000 .230 . 0900

_.0408

.0191 .0092

_.0045

. 0022 . 0011

_.0006

.0003 136 1 . 0000 .2279 .0877 .0386 .0179

.0084 .0040

.0019 .0009 .0005

_.0002

138 1 .0000 . 2257

_.0856 .0369

.0167 .0078 .0036 . 0017

_{.0003 .0004}

.0002 140 1.0000 .2235 .0833 .0353 .0157 .0071 .0033 . 0015 .0007 .0003 .0001 142 1 . 0000 . 2214 . 0813 .0339 .0148 .0056 .0030 .0013

_.0006

.0003 .0001 144

•

1 .0000 .219

4

. 0794 .0325 .0139 .0061 .0027 . 0012

.0005 . 0002

.0001 146 1 .0000 . 2173 . 0775 .0312 .0131 .0056

_.0024

.0010

.0005 . 0002 . 0001

148 1.0000

.0l54

. 0757 .0300 .0124 .0052 .0022

_.0009 .0004 .0002 .0001

150 1 .0000 .2136 .0740

_.0288

.0117

_.0048 .⁰⁰²⁰ .0008

.0003 .0001 .0001 152 1.0000 .2118 .0723 .0277 .0111 .0045 .0018 .0007

_.0003

.0001 .0001 154 1 . 0000 . 2101 . 0708 .0267 . 0105 .0042 .0017 .0007

.0003

.0001

.0000

156 1 . 0000

_.2084

.0693 .0258 .0099 .0039 .0015

_.0006 .0002

.0001

.0000

158 1 . 0000 .2067 . 0679 .0248 .0094

_.0036

.0014

_.0005

.0002 .0001

_.0000

160 1 . 0000 .2051 . 0665 .0240

_.0090 .0034

.0013

_{.0005 .}0002

.0001

.0000

In a continuous diffuser

J the

process is uniform throughout, and ,the only losses are in the pulp. In the Roben, or bateh type battery, sugar is lost in: the pulp water

BB

well. When a tail cell i. dis ... sociated from the battery of N .active cells, there is a sudden change in the new tail cell.

Before

the

separation, a dilute juice was entering the top of this cell, while

after flhe separation fresh water enters. In England, attempts have been

152

BEET·SUGAR TECHNOLOGY

made' to extend the theory to make corrections for

this

change in the tail cell, a

summary

of which follows.!! (See also Siline's original paper.6)

Initially, eN is calculated for the battery, from Equation (12), as if it were a continuous diffuser. Knowing this, the concentration of sugar in the cassettes,

c,

at any point within the battery can be calculated using Equation (12) , by considering the point to be the point of entry of a partial continuous diffuser; that is, by assuming c

⁼

Co. For this partial diffuser,

fJ

may be,

and

t is different than in the whole diffuser. Let

81

and t' apply to the last ceil, and

(i'

and tH apply for the last two cells. For the last cell, t' will be tiN, and for the last two cells, t" will be 2t1N. Therefore, for the last cell, KP will be (O//ON) times KP for the whole diffuser, and for the last two cells, 20H ION times KP. With these values,

and

the calculated

CN,

c'

and CH, the concentrations of the sugar in the cossettes at the top and bottom of the next to the last cell can be calculated, at the moment it becomes the last cell, from Equation (12) .

Let n' be the ratio of the juice in a cell to the juice within the cassettes in the cell. The ratio of the juice flowing through the last cell (for juicing up and drawing off) to the juice within the cassettes in the cell, will then be n' + n, of which n' was already in the cell, and n was fresh water. The average sugar of the pulp,

Cw,

exposed to the action of the water is cal-

culated to be .

=

!_(c' + c'n' + clfn )

c'"

2

n' + n (14)

The average difference of concentration, AC, between pulp and juice for the , last cell,

is

calculated as

do ^�

� (CN + C' ^{_ C'} � CN) '

(15)

The complete loss,

X,

from both pulp

and

pulp water

'is

then calculated from the equation

c' ---;;;;c- . - CN n

2.303 l

og

Y

^{� ,}

11.'

+ n + �

^2l1c

^c N

which, rearranged,

and

the substitution being made for

c;.,!

yields

X ^�

!

²

( c' + c'n'

^n' + +

onn n )

^{_ antilog}

[ ^{� .n} ]

2.303 (n' + n + c' u:N) ..

(16)

(17)

THE DIFFUSION PROCESS

153

The increase in sugar loss in a Robert battery, as compared with the hypothetical continuous diffuser, is nearly proportional to the value of (j'

feN,

which is set equal to B. Then the total loss, in pulp and pulp water will be,

(18) where Y is a function of KP and

n,

and can be calculated from Equation (18) by substituting experimentally determined values of X,

CN,

^{and B,} and its relation to KP plotted for various drafts.

Rodgers1G further deduces a relation which it is claimed can be used for calculating the losses when pulp press water is returned to the diffuser :

_n _ Iog n ^�

1

₊

CN - nj"

= KP

n -

1 n(cN jN) ⁽¹⁹⁾

where

CN

is the weight concentration of sugar in exhausted pulp per unit of sugar in fresh cassettes, andjN is the weight concentration of sugar in the diffuser supply water per unit of sugar in fresh cossettes.

Other mathematical treatments of diffusion have been published by KoUman1a Mehrle1u Sorgato,l3 Dorfeldt,BB Slavicek,69. 72 and Oplatka.74.,7&

DESCRIP'TION OF DIFFUSERS IN CURRENT _USE Robert Battery. This batch-type battery is usually made up of four­

teen identical cells, '-w;t.ch fitted with a thermometer, calorizator, water valve, circulation va1:-ve, and juice valve, which are arranged in a straight ' line or a. circle. Each cell

has

a capacity of from 3 to 6t tons of sliced beets, depending upon actual size and degree of packing. For identification purposes, the cells are physically numbered from

1

to 14 ; operationally, in the circulation series, the la.st cell filled with cossettes, and from which the diffusion juice is drawn is considered to be the :first or head cell. Juice circulates through the cell from top to bottom, the cassettes being retained by the screens at the bottom. Chains are hung within the cell to bear part of the weight of the cassettes, and to prevent them from packing too tightly in the bottom and plugging the screen, or preventing free cir�

culation of juice. There is actually a basket of chains at the bottQm,

just

above the screen,

as

shown in Figure 6-8.

The cells are oonnected together in series, so that water pumped into the tail cell will pass through the circulating cells in turn, to be dra.wn off from the hea.d cell. Eleven of the fourteen cells usually are in active dif­

fusion, for one of them is either Itdrawing

off""

or "juicing up," another is lIwasbing/'

'and'

^{the third} is "filling". "Washing" means that the cell is being hosed out with high pressure water in preparation to being filled

154 BEET-SUGAR

TECHNOLOGY

with fresh cassettes. "Juicing up," "coming up," 01' "diffusing" means that the cell filled with fresh cassettes is being also filled with juice from the previous Hfirst" cell. A cell freshly filled with cassettes is filled with j uice from the bottom up to expel air. When this cell is full of juice, the direction of juice flow through it is reversed, so that the already enriched juice retraverses the cassettes it has just passed through. This reversal of direction represents both a loss in time and extraction, since a richer juice

(JQU'r�lI, Utah-Idaho Sugar Co.) Figure 6-6. Robert Battery, West Jordan, Utah . .

comes in contact with the CDssettes in the bottom of the cell, and thus gives up some of its sugar by reverse diffusion.

Normal circulation is from top to bottom, chiefly for mechanical reasons, since a large top-door with adequate screen area would be very difficult to handle. It has also been noted that small pieces of cossettes tend to float, and would tend to plug upper screens if flow were from bottom to top.

The

advantages of this batch type of diffuser come from the fact that the cells are sealed off from air, thus lowering juice oxidation, and that the periodic emptying and cleaning reduce bacterial activity. Its chief dis­

adva.ntages are the high labor requirements, and the pulp water loss.

THE DIFFUSION PROCESS 155

The cells in a circular battery are filled ·with cassettes from a revolvable chute that can be swung from cell to cell, and in a straight�in-line battery, from a belt. :!;requently a mechanical cassette distributor, as shown in Figure

6-10 is included. Close attention must be paid to the filling of the

t>-Wo.P<:I'" "1I.",'1tR 1!- <;:UICU ... '!lOH "AI..lo't;

F - ... "" .. V",'-'II!

,,- STOP 1I ... "'e,�

"_';I,He .. - v",I."'"

I - Cu"T-OuT Vi'J..V&

J ... ".o.POQ. "" .... VIO.

===::"�,�i·�tu.

�_-"r""_' CI"""

____ "euT_ O<IT' CI!LL __ "'-TI!IlNAn · ... u .. ,,·

Figure 6-7. Cross-sectional elevation of a Robert cell, showing valves and juice flows.

cell, for a well filled cell with evenly distributed cassettes means increa.sed slicing capacity, and less channeling of juice.

After a cell Aas become successively first, second, etc., and essentially all the sugar

has

been extractW from its cassettes, it is cut off from the series, and its contents dumped into a pit common to all the cells. The pulp water it-contains is dumped with the pulp,

SQ

that with this type of battery.there are losses of sugar in pulp water as well as pulp.

Various operational factors will be mentioned briefly.

In

operating the

battery, the cell temperatures are carefully controlled. The juice is heated

156 BEBT-SUGAR TEOHNOLOGY

between cells by the eruorizators, or by direct steam injection. Equally important is uniformity of draw, with high losses as the penalty for ir­

regularity.

Gas

formation frequently occurs with dirty beets, due to microorganisms carried in with the soil. In California, this gaB seems to be mostly methane, which, if not bled off, can bring the battery circulation

Figure

Q...8. Looking down into an empty Robert battery eell.

to

& standstill.

Defective valves

cause _

battery trouhies.

Les.king water v&lves dilute the

luicee,

while

le&king�

doors """

frequently re­

spoDSlble for many

so-called "unknown"

batterY losses, and increase the

diffuBion I""" in factories returning pulp water to the

batteries.

Typiool � of juice samples

taken from the individual cens of an

operating battery

_{shaw that} the purity of the

juice

in the first six cells

is f&irly COIlStant,

but

may drop

to 'V&Iuee bel"", fifty in the last cell. How­

ever, the net effect of inoluding this low purity juice is

quite

8IDll.Il, einoe

THE DIFFUSION PROCESS 157

Figure 6·9. Simplified ftow diagram of a Robert battery, with typical analytical figures.

158 BEET-SUGAR TECHNOLOGY

its solids content is so low. Table 6-3 lists these data. Note that about half the sugar is extracted in the first cell.

Design problems in Robert diffusers have been studied by Porkorny,15 J askolsly 16 Buroni 17 Schecker18 and others. Important papers on opera­

tional su

b

^{jects hav}

�

been written by Leonis19 and Troje.2t1 Best utilization Table 6-3

Juice Characteristics within Individual Robert Battery Cells

�I Temp., °C. GI"llm;sJ:;r.r per

Grams Solids

per Purity Cumulative

%

100 mL

Extracted

��-

I 81 13.92 1 6 . 55 84 . 1 49 . 6

2 85 7 .01 8 . 32 84.3 63.0

3 85 5.15 6 . 16 83 . 6 7 2 . 3

4 83 3 . 85 4 . 62 83 . 3 80 .7

5 79 2 . 69 _" 3 .28 82 .0 87 . 9

6 69 1 . 69 2 _ 07 81 . 6 92.5

7 70 1 . 04 1 . 34 77 .6 9 5 . 7

8 54 0 . 60 0 . 78 76 .9 98.9

9 55 0.16 0 . 29 55 . 2 9 9 . 8

1 0 54

I

^{0 . 03 0 . 14 23 . 6 100 .0}

( a)

( b) COSS

._:t,

Figure 6-1 1 . (a) Flow of cossettes (solid line) and juice (dotted line) through a cell-type continuous diffuser. (b) A plan for using two streams of juice against one of cossettes.

of cell space has occupied Schiebel,21 Vondrak and Pokorny,22 Lasse,23 and V ondrak.24

The

Berg� Continuous

Diffuser.

The continuous d.iffuser designed by Julien Berge, and used at the Raffinerie Tirlemontoise, Belgium, is one of the ea.rlier successful types of continuous diffusers. It is a large revolving drum, separated into "cells" by a helix attached to the interior surface.

As the drum with its helix revolves, the juice, which stays at the bottom, is transported along from the tail end to the head end. Thus the cell actually moves, but it is more convenient to consider the cell as the location

THE DIFFUSION PROCESS 159