Massecuite conditioning, how to improve low raw massecuite curing.

Massecuite conditioning, 

how to improve low raw massecuite curing. 

Rob Sanders 1, Christophe Pelletan 2 

Abstract 

Low-grade massecuite centrifugation operation is a critical step in the process of sugar 

production. Indeed many factors affect the performance of the continuous centrifugals. 

Among them physical characteristics of the product to be treated (such as non-sugar 

content, temperature. viscosity, crystal content, size of the sugar crystal) are of the 

foremost importance. On the other hand, the sugar industry permanently challenges 

ways to reach higher throughput, lower losses and reduced costs. To answer both of 

those general requirements, a range of equipment is on the market with the aim of 

conditioning the massecuite before centrifugation. A review and a comparison of the 

equipment (massecuite dilution and reheater) are undertaken from a theoretical and 

practical point of view. 

Introduction 

The purpose of the crystallisation process being carried out in vacuum pans and 

crystallisers. is to maximise sugar exhaustion from the massecuite mother liquor. In 

low-grade massecuites in particular. resultant high brix. high viscosity massecuite 

creates difficulty to efficiently and economical separate the sugar crystals from the 

mother liquor during centrifuging. It is therefore normal to provide some form of 

"massecuite conditioning" immediately prior to centrifuging to improve the separation 

process. 

Ideally conditioning should be done without or minimal re-dissolution of already 

crystallised sugar. At the same time aid the separation to acquire a desired sugar 

quality and maximise centrifugal capacity. 

There are two basic approaches used for massecuite conditioning 'namely dilution and 

heating. This evaluation is to compare the merits of the different systems. 

Numerous authors have discussed the different methods of massecuite conditioning, 

so we will not go into great detail on the individual systems. 

Dilution by the addition of water direct to massecuites is no longer practised due to the 

negative effects it has on the molasses purity, as reported by McGinnis (S Jour 37, 

1974/75). 

Dilution system using are available today that mix molasses and massecuite, similar to 

technique of SMA. and Fives Cail. 

Heating system like the Stevens Coil (A.H.Stuhlreyer Seet Sugar Jour 2 nd 

Edit). 

Crystalliser heating (E.Hugot series 7). direct heating (Reinhold Hemplelmann 2002 

ISSCT workshop) and finned tube re-heaters (Kirby et al) 

, Fletcher Smith, Norm an House. Fria r Gate, England. 

2 Fives Cail. 22 rue du Caroussel 59600 Villeneuve d'Ascq. France. 

305

The Evaluation of Modern Conditioning Methods 

Basis for Evaluation 

For purpose of this evaluation we have considered a case for a factory slicing 6,000 

tons of beets per day and producing 20 tonnes per hour of low grade massecuite. Also 

used as an example what we regard as a reasonably typical beet low grade 

massecuite having a refractometer brix of 94 degrees and an apparent purity of 76. For 

determination of mother liquor supersaturation the formulae from Z. Budnik et al Sugar 

Tech Manual has been used arid it has been assumed that the molasses has the 

following coefficient a=0.230; b=0.770; c=1.S00. 

It is also assumed that the total massecuite and mother liquor obeys the viscosity 

relationship detailed in the formulae of Z. Budnik et al Sugar Tech Manual. An 

illustration of this relationship and of the effect that temperature has on massecuite and 

mother liquor viscosity during the crystalliser cooling stage is shown in Figure 1. It can 

be seen that there is a steep viscosity increase when the cooling massecuite drops 

below 50°C 

Effect of temperature on MIL viscosity 

5,000 66.00 

64.00 

Q) 4,000 

§ 

:> 

(; 58.00 a. 

:J 2, 000 

g 

Qj 56.00 

.c 

0 1,000 

:2 

54.00 

0 52.00 

40 50 60 70 

80 

Temp (' C) 

1- 94.5 deg Bx - 95.5 deg Bx -+- ML. Purity 1 

Figure 1 - Effect of Crystalliser cooling on massecuite viscosity 

306

Examples of modem conditioners: 

Although Stevens coil re-heaters are still common in a lot of existing factories, they are 

not generally the choice for new installations. When new more modern installations are 

considered there are alternatives choices: 

Alternative Methods for C-massecuite Conditioning 

1) Re heating in the last section of a vertical crystalliser. 

2) Re heating in a dedicated finned tube re heater. 

3) Diluting with an inline dilutor/conditioner. 

4) Re heating by direct steam injection of steam into the massecuite. 

1) Re-heating in a crystalliser. 

Alternative evaluations 

Consider a low grade crystalliser is divided up into two sections one for cooling 

and the other section for heating. The cooling section is sized for a thirty-six 

hour cooling time 0.81 deg C per hour. (480 cu M). 

The heating volume is sized adequately to heat the massecuite to saturation 

point while maintaining the same heating surface to volume ratio of 1.3 as per 

. the cooling section. Giving it a 12-hour retention, (160 cu M). 

For the purpose of the evaluation the cooling volume has been divided into two 

sections, both cooling and heating waters are counter current to massecuite 

flows. 

Using a model with the parameters shown in Figure 3 the mother liquor film is 

reduced to a level of saturation acceptable for easy centrifugal separation. 

Massecuite in 74°C 

Cooling water 61 °C out 

Section 1 cooling 57°C 

Section 2 cooling 57°C 

Massecuite 45°C 

M assecu ite out 56°C • • Heating •• 

section • • 

• • • • 

......_----....... 

Cooling water in 31·C 

Heating water out 59"C 

Heating water in 70"C 

Figure 2 - Model of crystal/iser cooling and heating scenario . 

307

Inlet area 1 Oulet area 1 Inlet area 2 Oulet area 2 Inlet area 3 Oulet area 3 

Massecuite Flow Vh 20.0 20.0 20.0 20.0 20.0 20.0 

Brix % 94 94 94 94 94 94 

Purity % 76 76.0 76.0 76.0 76.0 76.0 

Crystal content % 30.0 36 .0 36.0 39.5 39.5 41.0 

Nutch brix % 91.4 90.6 90.6 90.1 90.1 89.8 

Nutch purity % 64.8 61.1 61..1 58.6 58.6 57.4 

Temperature 'c 74.0 57.0 57.0 45.0 45.0 56.0 

Supersaturation 1.24 1.29 1.29 1.32 1.32 1.12 

Film Surpersaturation 1.45 1.48 1.48 1.49 1.14 0.95 

Enthalpy kJl1

A disadvantage of this type of installation is the size and cost of the equipment 

required. 

The thermal balance is optimised in order to maintain the difference of 

temperature between the water and the massecuite so it is kept as constant as 

possible during the phase of cooling and heating. As can be noticed from 

figures 3 and 4, during the cooling phase, the supersaturation of the 

massecuite in close contact with the cooling tubes is higher than 1.45. This 

leads to a potential risk of fine crystal sugar formation or local encrustation on 

the cooling tube surface . On an other hand, during ,the heating phase, the 

temperature of the water in the tubes is such that the massecuite could be 

locally under saturated, in particular just before leaving the crystalliser. 

In conclusion it appears from this review that large vertical crystalliser with 

classical surface/volume ratio (SN

U 

60 

.. .. .. .. 

55 

.. 

1.3 

... 

:J 

~ ... 50 

1.1 ~ ... 

Q) 

.a 

~ 

c 

Q) 0 

0 

E 

Q) 

I 

45 

1.2 

1.0 

ro 

CI) 

40 +------;-------r------~----_+------+ 0.9 

o 5 10 15 20 25 

Residence time (min) 

I~MC Temperature - 

- - MC Saturation I 

Figure 6 - Re-heater temperature & saturation profile 

Figure 6 assumes that the flow of massecuite through a conventional finned 

heater is linear, as it has a high heating surface with narrow massecuite voids. 

It is considered that a correctly designed heater does not channel as it is self 

regulating, with high massecuite flow passing over the heating elements less 

heat is absorbed. This tending to slow the rate of throughput, due to its change 

in its saturation/viscosity. When the rate slows additional heat is taken in, 

again altering the massecuite allowing the flow to increase. 

A Typical massecuite reheater 

310

Inlet 

Quiet 

Massecuite Flow tIh 20.0 20.0 

Brix % 94 94 

Purity % 76.0 76.0 

Crystal content % 41.0 41.0 

Nutch brix % 89.8 89.8 

Nutch purity % 57.4 57.4 

Temperature DC 45.0 55.0 

Supersaturation 1.26 1.14 

Film Surpersaturation 1.14 1.02 

Enthalpy kJlkg 72 90 

Water Flow tIh 23 23 

Temperature DC 54.6 64.6 

Enthalpy kJlkg 229 271 

DT MC-water DC 9.6 9.6 

DTof DT 0.0 

Volume m3 3.5 

SN m·l 114 

Thermal Surface m 2 400 

Exchange DTlog DC 13.19 

HTC w/m2.0 C 20.0 

Residence 

time 

hrs 0.3 

Figure 7 - Balance of finned tube reheater. 

Advantages of a finned re-heater are that it has a large heating surface area in 

a very compact area. For this particular model of 400sq m heating surface it 

has a massecuite volume of 3.5 cu M. Giving a heating surface to volume ratio 

of 114 m2/m3, with a massecuite average retention time of 20 minutes within 

the heating section, therefore eliminating the risk of crystals dissolution. 

Another advantage is that they are completely sealed with no moving parts 

and require little maintenance. 

3) Massecuite diluter 

Principle of the process 

A conditioner is normally positioned in the main massecuite pipeline between a 

crystalliser and centrifugal installation. This type of conditioner is normally 

designed to work under extreme pressures. Ideally they would be installed 

close to a cooling crystalliser outlet reducing the pressure loses in the pipe to 

the continuous centrifugals. In modern sugar factories with high capacity 

vertical crystallizers high pressures are exerted on sealing arrangements. With 

the latest development in seals Fives Cail I Fletcher Smith massecuite diluters 

are now designed to work with 8 bar as a nominal pressure. 

Dilutors requires that the mixing molasses used for dilution be diluted and 

temperature adjusted prior to it being mixed into the massecuite. 

311

Cold and viscous 

Ma ssecuite 

MC DILUTER 

Diluted Massecuite 

Diluted and reheated Mola sses 

(10% maxof MC flaw) 

Figure 8 - G. A. of a massecuffe diluter 

High-pressure massecuite diluters are made up of a cylinder shell that can be 

installed horizontally or vertically. It is a self-setting device that can be installed 

in line with an existing massecuite pipeline. The principal of operation is to 

highly shear the massecuite and the molasses, in order to achieve a perfect 

homogenization of the product within a very small volume. A cantilever shaft is 

connected to a motor-reducer on one end, on the rotating shaft there are 

several rows of four 90· oriented cross blades. In normal operation the 

rotational speed of the shaft averages 100 rpm. The counter blades connected 

to the internal shell enhance the mixing of the 2 products. A custom seal 

allows the conditioner to work under high-pressure massecuite without any 

leak of mother liquor. 

Nominal 

Diameter 

(mm) 

500 

350 

250 

200 

Installed 

power 

(kW) 

30 

7.5 

5.5 

2.2 

Rotation 

speed 

(rpm) 

98 

139 

178 

225 

Massecuite 

Flow 

Tm/h 

60 

30 

15 

10 

Number of 

blades 1 

counter blades 

12/16 

6/12 

6/4 

4/3 

Shear 

Number 1 

revolution 

96 

36 

12 

8 

Figure 9 - Characteristic of Fives Cail / Fletcher Smith high pressure massecuite dilute 

312

VERTICAL SEITINGS 

'"':::: \ 

MASSEcurre 

jFEED 

M~ 

FEE \ 

\ 

OUTLET 

MASSECurrE 

DILUTED 

\ 

OOTLET 

MASSECUfTE 

DILUTED 

Figure 10 - General arrangement drawing of a Fives Gail diluter 

The advantages of mixing/conditioning are the following: 

2 actions simultaneously, one dilution, one reheating 

Gontrol of the final supersaturation of the final massecuite 

Lower massecuite viscosity. Indeed for the same final mother liquor viscosity, as 

shown in the comparison table, the massecuite viscosity is much lower than with 

reheating systems (surface heaters or direct steam injection). The massecuite 

viscosity can be decreased up to 30%. 

The massecuite temperature (at 50 0 G max) and the molasses temperature (at 

60 0 G max) remain low, which can be an advantage in relation with the storage of 

this by-product. 

Some specific disadvantages remain: 

Necessity of a powerful and efficient mixer, which absorbs electrical power. 

A control system is necessary. The control system is based on the following 2 

principles: 

1. The molasses temperature and dry matter shall be 

maintained constant. 

2. The flow of molasses shall be adjusted according to the 

intensity absorbed by the diluter motor. 

The quantity of final massecuite to be treated is increased by 7 to 8 %. 

313

4) Re-heatinq with direct contact steam. 

Steam heating is undertaken by introducing steam directly into the flow of 

massecuite entering the centrifugal. The most critical step of this operation is 

the efficiency of the mixing between the steam and the massecuite. Because 

of the high massecuite viscosity it is not easy to mix with any product, and in 

particular with steam. A specific mechanical device is . generally needed in 

order to insure a homogeneous mixing. Figure 11 shows the effect of steam 

mixing with massecuite. There will be thermal losses attributed to this method, 

as often experienced as indicated on Figure 11 . 

Incidence thennal Losses 

2.00% 55.0 

1.75% 

I---- -::---.. 

~1 . 50% / 

1-----,______. /" 

;>< 

,.,.---:' ~ 

0.75% 

o.SO% ~--------- ~-- 

C> 

-'" 

~ 

~1 . 25% 

E 

co 

3; H XJ% 

~ 

~ 

~ 

r- 

0% 5% 10% 15% 20% 25% 30% 35% 40% 

I-u- Steam RON -(}- terrpErnttre I>IC I 

V 

/ 

52.5 

sooE 

.. 

~ 

::J 

0. 

Ẹ. 

47.5 :. 

... 

45.0 u 

::li: 

42 5 

40.0 

Figure 11 - In.cidence ofthe thermal losses on the performance of thfJ direct steam 

injection system 

314

Cooled 

Massecuite 

Massecurte 

Massecurte Massecuile a~er 

a~er 

before a~er Molasses Dilution Steam direct 

Condrtionnin healing injection 

g 

Flowrate mTIh 20.00 20.00 2.18 22.18 0.15 20.15 

'. 

Brix % 94.00 94.00 77.00 92.33 93.30 

Purity % 

Brix of molher liquor % 

Purity of mother liquor % 

Crystal content % 

Temperature 

Pressure 

'C 

bar A 

76.00 76.00 59.00 74.61 76.00 

89.83 89.83 87.83 88.71 

57.43 57.43 57.65 57.43 

41.00 41.00 36.97 40.70 

45.0 60.6 80.0 49.7 115.0 54.3 

Cp kJJ1

Advantages 

Disadvantages 

Crystalliser Possible phased factory Small heating surfaces to volume 

Re-heating upgrades. ratio. 

Need high input levels of 

management, long lag times for a 

control system. Good instrumentation 

control required. Risk of localised 

over heatinf). 

Finned tube No moving parts, totally Instrumentation to control water 

Re-heating sealed. Large heating surface 

to volume ratio. 

temperatures. 

Inline Can be installed into confined Moving parts. 

conditioning spaces. Additional 7 - 8% loading on the 

centrifugal. Conditioning of mixing 

molasses. High degree of 

instru mentation. 

Direct 

heating 

Simple to install. Often 

provided by the centrifugal 

supplier. 

High risk of crystal losses and purity 

rise. Difficult to control, when mass 

flows vary. 

An interesting feature with centrifugal should also to be considered before conditioning 

massecuite. This feature is basket angle to suit different grades of massecuite. Even though 

most of the centrifugal suppliers propose only one basket angle for standardisation of their 

production, it is not hard to understand that if a basket angle is well adapted to treat a given 

massecuite (say B massecuite for a 30° angle basket) with specific characteristics (temperature, 

purity, crystal size, etc), it will be much harder to work with the same basket on a massecuite 

with smaller crystal, lower temperature, and higher viscosity such as low grade massecuite. In 

this case, a massecuite conditioning will be required to achieve good crystal separation 

-;0' , 

.J 

\ . 

Figure 14 - Relative geometry of continuous centrifugal basket 

316

Conclusion 

All of the systems achieve the desired result of reducing the mother liquor 

supersaturation and they all have their merits and disadvantages. One would have to 

decide what would be the most suitable for there partic\Jlar installation. 

References 

Kirby, L.K, Ness J.N, and Stewart, E.J. Massecuite reheating by finned tubes. Proc. Qd 

Soc. Sugar Cane Techno!., 43'd Conf., 255-262. 

Z. Bubnik, P. Kadlec, D. Urban, M. Bruhns. Sugar Technologist Manual 8 th edition. 

317 

..---_ ...

Massecuite conditioning, how to improve low raw massecuite curing.

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?