MECHANICAL STIRRING IN A CONTINUOUS EVAPORATING CRYSTALLIZER

THE NEW FeB CONTINUOUS VACUUM PAN

by

Gerard Joumet FeB Sugar Division Bd de Iusine 59015 Lille Cedex France Otto Bultas Swenson Process Equipment Inc 15700 Lathrop Ave Harvey IL 60426

Fran~is Rousset Applexion Inc 15700 Lathrop Ave Harvey IL 60426

Presented at the 29th Biennial Meeting of the ASSBT in Phoenix AZ

-PPLIIIOI SWENSON

~ Te lephone 708 bull 331-5500 Fax 708middot 331-5559bull -

shy193 Telephone 708-210-5054 FAX 708middot331-6713

MECHANICAL STIRRING IN A CONTINUOUS EVAPORATING CRYSTALLIZER THE NEW FCB CONTINUOUS VACUUM PAN

by Gerard Journet FCB Sugar Division Bd de Iusine 5901 5 Li lle Cedex France Otto Bultas Swenson Process Equipment Inc 15700 Lathrop Ave Harvey IL 60426 Francois Rousset Applexion Inc 15700 Lathrop Ave Harvey IL 60426

ABSTRACT In an FCB continuous evaporating crystallizer (vacuum pan) the massecuite is stirred only by natural convection due to evaporation Energy savings can be achieved by reducing the quantity of water evaporated during the crystallization operation by feeding such crystallizers with syrups of higher dry substance content As a consequence agitation in the evaporating crystallizer will be insufficient and have a detrimental effect on the heat exchange coefficients and the crystallization rate as well as increasing the fouling of the calandria One way of solving these problems and always ensuring adequate massecuite agitation is to produce agitation by external means that is mechanical stirring

An experiment conducted on the second half of an FCB continuous evaporating crystallizer at the Colleville sugar factory resulted in a gain of about 2 degC on the total 6t and 1 to 15 points in the crystallization exhaustion

Extrapolations from these results have led to an upgrading of the design of the FCB continuous vacuum pan to one with a new shape of calandria which makes possible the installation of mechanical stirrers The expected thermal gains with this new design are 5 to 6 degC minimum on white beet sugar (total Lit)

1 BACKGROUND

The FCB continuous evaporating crystallizer (vacuum pan) was first installed in 1968 at the Nassandres sugar factory to process white sugar massecuite This first evaporating crystallizer was equipped with a longitudinal plate calandria Commencing in 19761978 FCBs continuous evaporating crystallizers were equipped with calandrias consisting of rows of horizontal steam tubes arranged in vertical layers (see Figure 1) Since then the qualities of this type of calandria have been amply demonstrated good heat exchange coefficients low head pressure loss limited scaling excellent long-term reliability and cost-effectiveness

As with all existing continuous evaporating crystallizers the FCB continuous evaporating crystallizer does have a drawback it is difficult to increase its capacity For this reason the authors sought a simple efficient and inexpensive way of increasing the capacity of the FCB continuous evaporating crystallizer in terms of its massecuite flow rate and evaporating capacity without thereby reducing the obtainable exhaustion

194

Meanwhile an 6Jol~tion tovvards an ever lower evaporatior requirement In an evaporating crystallizer has appeared progressively over the last 101 5 years Indeed for the obvious reasons of energy economy sugar manufacturers want to process an increasingly concentrated feed syrup (SL 1) Dry substance contents (OS) were on the order of 70-73 some 1015 years ago whereas they now range more commonly between 74 and 78 Similarly syrup run-offs 1 and 2 are far less dilute than in the past and the dry substance feed syrups are more on the order of 80-82 than 77-79 The reduction in the water evaporation requirement is on the order of 20-35

2 BASIC IDEA

In a continuous evaporating crystallizer the agitation and movement in the massecuite are directly dependent on the quantity of water evaporated in the evaporating crystallizer If less water is evaporated both the movement and the agitation are reduced

Consequently we were quite naturally led to consider fitting the continuous evaporating crystallizers with mechanical stirring

3 REALIZATION OF THE IDEA

After examining several possible arrangements for mechanical stirrers in a continuous evaporating crystallizer the layout shown in Figure 2 was chosen This allows a stirrer to be installed with sufficient room on the feed side and it does not require the removal of any tubes On the other hand the diameter of the stirrer is necessarily limited and the flow from it has little effect on the lowest part of the calandria As a matter of fact this installation seems to be the best compromise sol~tion

Thanks to the prior agreement and kind cooperation of the Colleville sugar factory the mechanical stirring system was tested in an FeB continuous evaporating crystallizer during the 1995 sugar campaign (see Figure 3)

The main specifications of the Colleville CCTR continuous evaporating crystallizer for B sugar were as follows

Volume Heating Surface

64 61 7

m 3

m 2 (2260 fe) (6640 tf)

~iameter 3500 mm (1 1-6) Length 11870 mm (38-11 ) Compartments 13

195

The second half of the evaporating crystalizer (compartments 9 to 13) was et9d with siv

stirrers This was a logical choice because the last compartments are those where the least water is evaporated the dry substance content is the highest and natural agitation is the least

Compartments 9 to 12 were each provided with one stirrer and compartment 13 whose volume was twice as large as the previous ones was provided with two stirrers Obviously steam agitation was eliminated from the compartments fitted with stirrers Moreover the usual feed syrup introduction device is replaced by a feed pipe directed toward the axis of each stirrer

4 Results

The stirrers were started at the beginning of the campaign at the same time as was the evaporating crystallizer and they worked satisfactorily through the last day of the campaign without causing any particular mechanical or electrical problems

Qualitatively speaking the stirring has an unquestionable effect Viewed from above the swirl of the massecuite mass was plain to see Observing the surface of the massecuite in a compartment during a change in the operating conditions of the stirrer from full stop or vice versa a significant change in the behaviour of the massecuite could be noted

As a rule the Colleville sugar factory cleans the crystallizer twice during a campaign For safety reasons this frequency was observed during the 1995 campaign The crystallizer showed less encrustation however on both occasions

In order to demonstrate the quantitative impact of mechanical stirring a series of measurements and analyses was made during the 1994 campaign in order to determine the representative operational parameters of the FCB evaporating crystallizer when it was functioning without stirrers During the 1995 campaign the same measurements and analyses were carried out and the relevant operational parameters determined Of course every effort was made to keep the operating conditions as close as possible to those of the 1994 campaign In particular it was the aim insofar as possible to work with the same massecuite flow rate the same water evaporation rate and the same massecuite dry substance content The measurements were even made approximately 10 days after cleaning the crystallizer just as was done irt 1994 The comparison between the 1994 and 1995 operational parameters is given in Table 1

196

Operational balances in 1994 and 1995

(In customary US units of measurement)

1994 1995

balance 1 (68 h)

balance 2 (16 h)

balance (48 h)

Condensed water flow rate cufth 1257 1406 1353 B feed syrup flow rate cufth 5792 6427 5686 B massecuite flow rate stlh 322 354 316 OS content of B feed syrup 805 805 790 OS content of B massecuite 930 930 926 B massecuite purity 871 871 875 B mother liquor purity 760 760 750 Exhaustion abs ~Pty 111 111 125 Calandria pressure psi 123 127 113 Vapor space vacuum psi 41 41 39 Calandria steam temperature of 2032 2046 1990 Vapor space vacuum temp of 1537 1535 1522

Total t1t of 495 511 468

Operational balances in 1994 and 1995 (In metric units of measurement)

1994 1995

balance 1 (68 h)

balance 2 (16 h)

balance 48 h

Condensed water flow rate m 3h 356 398 383 B feed syrup flow rate mlh 164 182 161 B massecuite flow rate tIh 292 321 287 OS content of B feed syrup 805 805 790 OS content of B massecuite 930 930 26 B massecuite purity 871 871

875

B mother liquor purity 760 760 750 Exhaustion abs ~Pty 111 111 125 Calandria pressure abs bar 0847 0874 0779 Vapor space vacuum abs bar 0281 0280 0271 Calandria steam temperature degC 951 959 928 Vapor space vacuum temp degC 676 675 668

Total t1t OK 275 284 260

197

A gain of about 2 degC on the total ~t of the crystallizer should be noted as well as a rather marked gain of about 1 to 15 pOints of purity in crystallization exhaustion

Tests were made to determine whether this gain in exhaustion might be attributable to a difference in sucrose solubility between 1994 and 1995 Figure 4 illustrates the 1994 and 1995 Colleville solubility curves (Ksat as a function of the NSNI ratio) a difference in solubility was found but it does not affect the B sugar zone in which NSNI ranges between 08 and 16 Therefore there can be no doubt that the increase in exhaustion was due to the mechanical stirring

The 1994 and 1995 operational conditions were simulated using FCBs continuous evaporating crystallizer simulation software CRISCONT Figure 5 illustrates the good correlation between the massecuite OS content measurements and the calculated values This simulation software uses modulation coefficients for heat exchange and mass exchange which make it possible to adjust the simulation to particular operational conditions In the present case with regard to the 1995 balance we distinguished between compartments 1 to 8 without stirrers and compartments 9 to 13 with stirrers

Table 2 gives the coefficients used for the simulation

1994 1995 gain in

modulation

cpts 1 to 13 cpts 1 to 8 cpts 9 to 13 coefficient

modulation coefficient

heat exchange 0864 0866 1137 + 31

modulation coefficient

mass exchange 0518 0505 1150 + 128

- Table 2shy

Table 2 shows a quite marked gain in favor of compartments equipped with stirrers in comparison with those which were not so equipped

The effect of the stirring was also demonstrated by the transient reaction upon stopping or restarting all of the stirrers This transient reaction effects in a reproducible and appreciable way both the instantaneous pressure in the calandria (at constant pressure above the massecuite) and the condensate flow rate (Table 3)

198

Stopping the stirrers Starting the stirrers

Relative time pressure condensate pressure condensate in calandria flow rate in calandria flow rate

(seconds) (psi) (cuftlh) (psi) (cu ftlh)

30 before 883 862 928 798 30 after 898 770 925 809 90 after 917 71 3 909 826 150 after 930 682 895 851 210 after 935 675 873 946

Variation +052 - 187 - 055 + 148

(-22) (+19)

Equivalent tt + 27 OF - 28 OF

- Table 3shy

The electrical power consumption was on the order of 030 to 035 kWm3 which are low

values This depends on the compartments and on the state (viscosity) of the massecuite

Because of lack of reference measurements in 1994 it is not possible to show directJy the contribution of stirring on the quality of grain size However two positive indications should be noted

bull IRIS made crystal size measurements during the 1995 campaign while the evaporating crystallizer was running at a low tightening value (massecuite OS content about 89) These measurements show that stirring improved the coefficient of variation (CV) of the seed magma (remixed C sugar) which was reduced from 39 to 33 at the exit of the crystallizer

bull The centrifugation performance of the B sugar massec~ite was better than usual during the 1995 campaign

We are convinced of the positive effect of mechanical stirring on the crystal quality both in terms of crystal size distribution (CV) and in terms of twins and agglomerates (crystal regularity according to Hill mark)

199

5 CONCLUSIONS

51 IMPROVEMENT OF EXISTING VACUUM PANS

The performance gains measured on Collevilles B sugar evaporating crystallizer were significant even though only the second half of this crystallizer was equipped with stirrers

The overall improvement in performance is directly related to the increase in massecuite circulation through the calandria which is induced by the stirrer This results in an increase in heat exchange coefficients an increase in the crystallization rate and a better massecuite mixing in the compartments which consequently reduces the residence time distribution thereby improving crystal size quality

It is therefore possible to boost an existing crystallizer to the point of gaining a lower ~t by several degrees with an unchanged capacity or of obtaining a 20 to 40 increase in production as the case may be

52 NEW PAN DESIGN

The excellent performances registered at the Colleville sugar plant led us to go further and to redesign our continuous evaporating crystallizer in order to obtain a better adaptation for mechanical stirrers

Thus after 20 years of operation the FCB continuous evaporating crystallizer CCTR type (Cuite Continue aTubes Ronde = Round Continuous Vacuum Pan with horizontal Tubes) is replaced by a new design an evolution of the first one CCTW type (Cuite Continue aTubes en W =W Shape Continuous Vacuum Pan with horizontal Tubes)

The specifications imposed for the new pan were evident

bull possibility of installation of mechanical stirring under the calandria that speeds up the massecuite flow across the tube nest

To which we added

bull decreasing the hydrostatiC head above the calandria and improving homogeneity of the tube nest

bull increasing section of lateral channel for massecuite recirculation

We kept the principle of a calandria with horizontal tubes fitted in vertical rows We showed by simulation that this type of tube nest presents the best compromise between head loss and heat exchange coefficients (2 opposite characteristics)

200

------

In order to optimize the efficiency of the mechanical stirring and to minimize the maximal hydrostatic head the bottom shape of the tube nest is horizontal

In order to optimize the heat exchange surface to improve the lateral recirculation of massecuite and to increase the lateral overilow height (that is linked to the recirculation f1owrate) the upper shape of the tube nest is sloped towards the lateral channel

Consequently the shell shape is naturally placed around the tube nest This creates a large lateral width of recirculation channel that is progressively reduced downwards (head increasing) and is progressively closed centerwards under the tube nest for avoiding dead zones (see Figure 6)

Figure 7 shows the gain versus a CCTR continuous vacuum pan

The new pan like the former one can operate for all products in a raw sugar plant as well as refinery cane and beet

Mechanical stirring is an option that makes it possible to achieve very substantial improvement in ~t and exhaustion as was proven at the Colleville sugar plant

Like the former design the CCTW continuous evaporating crystallizer range includes 5 diameters and 9 len~ths (see Table 4) The nominal volume doubles every 5 pans The SN ratio is 10 m2m (305 sqftlcuft)

CCTW Continuous Vacuum Pan bull RANGE

Length

of Pan

(mm)

5000 5680 25 33

6620 29 38 50 7500 57 75 8620 87 115 9840 130 11300 12980 14560

- Table 4shy(In metric units of measurement)

201

I

MECHANICAL STIRRING IN A CONTINUOUS EVAPORATING CRYSTALLIZER THE NEW FCB CONTINUOUS VACUUM PAN

by Gerard Journet FCB Sugar Division Bd de Iusine 5901 5 Li lle Cedex France Otto Bultas Swenson Process Equipment Inc 15700 Lathrop Ave Harvey IL 60426 Francois Rousset Applexion Inc 15700 Lathrop Ave Harvey IL 60426

ABSTRACT In an FCB continuous evaporating crystallizer (vacuum pan) the massecuite is stirred only by natural convection due to evaporation Energy savings can be achieved by reducing the quantity of water evaporated during the crystallization operation by feeding such crystallizers with syrups of higher dry substance content As a consequence agitation in the evaporating crystallizer will be insufficient and have a detrimental effect on the heat exchange coefficients and the crystallization rate as well as increasing the fouling of the calandria One way of solving these problems and always ensuring adequate massecuite agitation is to produce agitation by external means that is mechanical stirring

An experiment conducted on the second half of an FCB continuous evaporating crystallizer at the Colleville sugar factory resulted in a gain of about 2 degC on the total 6t and 1 to 15 points in the crystallization exhaustion

Extrapolations from these results have led to an upgrading of the design of the FCB continuous vacuum pan to one with a new shape of calandria which makes possible the installation of mechanical stirrers The expected thermal gains with this new design are 5 to 6 degC minimum on white beet sugar (total Lit)

1 BACKGROUND

The FCB continuous evaporating crystallizer (vacuum pan) was first installed in 1968 at the Nassandres sugar factory to process white sugar massecuite This first evaporating crystallizer was equipped with a longitudinal plate calandria Commencing in 19761978 FCBs continuous evaporating crystallizers were equipped with calandrias consisting of rows of horizontal steam tubes arranged in vertical layers (see Figure 1) Since then the qualities of this type of calandria have been amply demonstrated good heat exchange coefficients low head pressure loss limited scaling excellent long-term reliability and cost-effectiveness

As with all existing continuous evaporating crystallizers the FCB continuous evaporating crystallizer does have a drawback it is difficult to increase its capacity For this reason the authors sought a simple efficient and inexpensive way of increasing the capacity of the FCB continuous evaporating crystallizer in terms of its massecuite flow rate and evaporating capacity without thereby reducing the obtainable exhaustion

194

Meanwhile an 6Jol~tion tovvards an ever lower evaporatior requirement In an evaporating crystallizer has appeared progressively over the last 101 5 years Indeed for the obvious reasons of energy economy sugar manufacturers want to process an increasingly concentrated feed syrup (SL 1) Dry substance contents (OS) were on the order of 70-73 some 1015 years ago whereas they now range more commonly between 74 and 78 Similarly syrup run-offs 1 and 2 are far less dilute than in the past and the dry substance feed syrups are more on the order of 80-82 than 77-79 The reduction in the water evaporation requirement is on the order of 20-35

2 BASIC IDEA

In a continuous evaporating crystallizer the agitation and movement in the massecuite are directly dependent on the quantity of water evaporated in the evaporating crystallizer If less water is evaporated both the movement and the agitation are reduced

Consequently we were quite naturally led to consider fitting the continuous evaporating crystallizers with mechanical stirring

3 REALIZATION OF THE IDEA

After examining several possible arrangements for mechanical stirrers in a continuous evaporating crystallizer the layout shown in Figure 2 was chosen This allows a stirrer to be installed with sufficient room on the feed side and it does not require the removal of any tubes On the other hand the diameter of the stirrer is necessarily limited and the flow from it has little effect on the lowest part of the calandria As a matter of fact this installation seems to be the best compromise sol~tion

Thanks to the prior agreement and kind cooperation of the Colleville sugar factory the mechanical stirring system was tested in an FeB continuous evaporating crystallizer during the 1995 sugar campaign (see Figure 3)

The main specifications of the Colleville CCTR continuous evaporating crystallizer for B sugar were as follows

Volume Heating Surface

64 61 7

m 3

m 2 (2260 fe) (6640 tf)

~iameter 3500 mm (1 1-6) Length 11870 mm (38-11 ) Compartments 13

195

The second half of the evaporating crystalizer (compartments 9 to 13) was et9d with siv

stirrers This was a logical choice because the last compartments are those where the least water is evaporated the dry substance content is the highest and natural agitation is the least

Compartments 9 to 12 were each provided with one stirrer and compartment 13 whose volume was twice as large as the previous ones was provided with two stirrers Obviously steam agitation was eliminated from the compartments fitted with stirrers Moreover the usual feed syrup introduction device is replaced by a feed pipe directed toward the axis of each stirrer

4 Results

The stirrers were started at the beginning of the campaign at the same time as was the evaporating crystallizer and they worked satisfactorily through the last day of the campaign without causing any particular mechanical or electrical problems

Qualitatively speaking the stirring has an unquestionable effect Viewed from above the swirl of the massecuite mass was plain to see Observing the surface of the massecuite in a compartment during a change in the operating conditions of the stirrer from full stop or vice versa a significant change in the behaviour of the massecuite could be noted

As a rule the Colleville sugar factory cleans the crystallizer twice during a campaign For safety reasons this frequency was observed during the 1995 campaign The crystallizer showed less encrustation however on both occasions

In order to demonstrate the quantitative impact of mechanical stirring a series of measurements and analyses was made during the 1994 campaign in order to determine the representative operational parameters of the FCB evaporating crystallizer when it was functioning without stirrers During the 1995 campaign the same measurements and analyses were carried out and the relevant operational parameters determined Of course every effort was made to keep the operating conditions as close as possible to those of the 1994 campaign In particular it was the aim insofar as possible to work with the same massecuite flow rate the same water evaporation rate and the same massecuite dry substance content The measurements were even made approximately 10 days after cleaning the crystallizer just as was done irt 1994 The comparison between the 1994 and 1995 operational parameters is given in Table 1

196

Operational balances in 1994 and 1995

(In customary US units of measurement)

1994 1995

balance 1 (68 h)

balance 2 (16 h)

balance (48 h)

Condensed water flow rate cufth 1257 1406 1353 B feed syrup flow rate cufth 5792 6427 5686 B massecuite flow rate stlh 322 354 316 OS content of B feed syrup 805 805 790 OS content of B massecuite 930 930 926 B massecuite purity 871 871 875 B mother liquor purity 760 760 750 Exhaustion abs ~Pty 111 111 125 Calandria pressure psi 123 127 113 Vapor space vacuum psi 41 41 39 Calandria steam temperature of 2032 2046 1990 Vapor space vacuum temp of 1537 1535 1522

Total t1t of 495 511 468

Operational balances in 1994 and 1995 (In metric units of measurement)

1994 1995

balance 1 (68 h)

balance 2 (16 h)

balance 48 h

Condensed water flow rate m 3h 356 398 383 B feed syrup flow rate mlh 164 182 161 B massecuite flow rate tIh 292 321 287 OS content of B feed syrup 805 805 790 OS content of B massecuite 930 930 26 B massecuite purity 871 871

875

B mother liquor purity 760 760 750 Exhaustion abs ~Pty 111 111 125 Calandria pressure abs bar 0847 0874 0779 Vapor space vacuum abs bar 0281 0280 0271 Calandria steam temperature degC 951 959 928 Vapor space vacuum temp degC 676 675 668

Total t1t OK 275 284 260

197

A gain of about 2 degC on the total ~t of the crystallizer should be noted as well as a rather marked gain of about 1 to 15 pOints of purity in crystallization exhaustion

Tests were made to determine whether this gain in exhaustion might be attributable to a difference in sucrose solubility between 1994 and 1995 Figure 4 illustrates the 1994 and 1995 Colleville solubility curves (Ksat as a function of the NSNI ratio) a difference in solubility was found but it does not affect the B sugar zone in which NSNI ranges between 08 and 16 Therefore there can be no doubt that the increase in exhaustion was due to the mechanical stirring

The 1994 and 1995 operational conditions were simulated using FCBs continuous evaporating crystallizer simulation software CRISCONT Figure 5 illustrates the good correlation between the massecuite OS content measurements and the calculated values This simulation software uses modulation coefficients for heat exchange and mass exchange which make it possible to adjust the simulation to particular operational conditions In the present case with regard to the 1995 balance we distinguished between compartments 1 to 8 without stirrers and compartments 9 to 13 with stirrers

Table 2 gives the coefficients used for the simulation

1994 1995 gain in

modulation

cpts 1 to 13 cpts 1 to 8 cpts 9 to 13 coefficient

modulation coefficient

heat exchange 0864 0866 1137 + 31

modulation coefficient

mass exchange 0518 0505 1150 + 128

- Table 2shy

Table 2 shows a quite marked gain in favor of compartments equipped with stirrers in comparison with those which were not so equipped

The effect of the stirring was also demonstrated by the transient reaction upon stopping or restarting all of the stirrers This transient reaction effects in a reproducible and appreciable way both the instantaneous pressure in the calandria (at constant pressure above the massecuite) and the condensate flow rate (Table 3)

198

Stopping the stirrers Starting the stirrers

Relative time pressure condensate pressure condensate in calandria flow rate in calandria flow rate

(seconds) (psi) (cuftlh) (psi) (cu ftlh)

30 before 883 862 928 798 30 after 898 770 925 809 90 after 917 71 3 909 826 150 after 930 682 895 851 210 after 935 675 873 946

Variation +052 - 187 - 055 + 148

(-22) (+19)

Equivalent tt + 27 OF - 28 OF

- Table 3shy

The electrical power consumption was on the order of 030 to 035 kWm3 which are low

values This depends on the compartments and on the state (viscosity) of the massecuite

Because of lack of reference measurements in 1994 it is not possible to show directJy the contribution of stirring on the quality of grain size However two positive indications should be noted

bull IRIS made crystal size measurements during the 1995 campaign while the evaporating crystallizer was running at a low tightening value (massecuite OS content about 89) These measurements show that stirring improved the coefficient of variation (CV) of the seed magma (remixed C sugar) which was reduced from 39 to 33 at the exit of the crystallizer

bull The centrifugation performance of the B sugar massec~ite was better than usual during the 1995 campaign

We are convinced of the positive effect of mechanical stirring on the crystal quality both in terms of crystal size distribution (CV) and in terms of twins and agglomerates (crystal regularity according to Hill mark)

199

5 CONCLUSIONS

51 IMPROVEMENT OF EXISTING VACUUM PANS

The performance gains measured on Collevilles B sugar evaporating crystallizer were significant even though only the second half of this crystallizer was equipped with stirrers

The overall improvement in performance is directly related to the increase in massecuite circulation through the calandria which is induced by the stirrer This results in an increase in heat exchange coefficients an increase in the crystallization rate and a better massecuite mixing in the compartments which consequently reduces the residence time distribution thereby improving crystal size quality

It is therefore possible to boost an existing crystallizer to the point of gaining a lower ~t by several degrees with an unchanged capacity or of obtaining a 20 to 40 increase in production as the case may be

52 NEW PAN DESIGN

The excellent performances registered at the Colleville sugar plant led us to go further and to redesign our continuous evaporating crystallizer in order to obtain a better adaptation for mechanical stirrers

Thus after 20 years of operation the FCB continuous evaporating crystallizer CCTR type (Cuite Continue aTubes Ronde = Round Continuous Vacuum Pan with horizontal Tubes) is replaced by a new design an evolution of the first one CCTW type (Cuite Continue aTubes en W =W Shape Continuous Vacuum Pan with horizontal Tubes)

The specifications imposed for the new pan were evident

bull possibility of installation of mechanical stirring under the calandria that speeds up the massecuite flow across the tube nest

To which we added

bull decreasing the hydrostatiC head above the calandria and improving homogeneity of the tube nest

bull increasing section of lateral channel for massecuite recirculation

We kept the principle of a calandria with horizontal tubes fitted in vertical rows We showed by simulation that this type of tube nest presents the best compromise between head loss and heat exchange coefficients (2 opposite characteristics)

200

------

In order to optimize the efficiency of the mechanical stirring and to minimize the maximal hydrostatic head the bottom shape of the tube nest is horizontal

In order to optimize the heat exchange surface to improve the lateral recirculation of massecuite and to increase the lateral overilow height (that is linked to the recirculation f1owrate) the upper shape of the tube nest is sloped towards the lateral channel

Consequently the shell shape is naturally placed around the tube nest This creates a large lateral width of recirculation channel that is progressively reduced downwards (head increasing) and is progressively closed centerwards under the tube nest for avoiding dead zones (see Figure 6)

Figure 7 shows the gain versus a CCTR continuous vacuum pan

The new pan like the former one can operate for all products in a raw sugar plant as well as refinery cane and beet

Mechanical stirring is an option that makes it possible to achieve very substantial improvement in ~t and exhaustion as was proven at the Colleville sugar plant

Like the former design the CCTW continuous evaporating crystallizer range includes 5 diameters and 9 len~ths (see Table 4) The nominal volume doubles every 5 pans The SN ratio is 10 m2m (305 sqftlcuft)

CCTW Continuous Vacuum Pan bull RANGE

Length

of Pan

(mm)

5000 5680 25 33

6620 29 38 50 7500 57 75 8620 87 115 9840 130 11300 12980 14560

- Table 4shy(In metric units of measurement)

201

I

Meanwhile an 6Jol~tion tovvards an ever lower evaporatior requirement In an evaporating crystallizer has appeared progressively over the last 101 5 years Indeed for the obvious reasons of energy economy sugar manufacturers want to process an increasingly concentrated feed syrup (SL 1) Dry substance contents (OS) were on the order of 70-73 some 1015 years ago whereas they now range more commonly between 74 and 78 Similarly syrup run-offs 1 and 2 are far less dilute than in the past and the dry substance feed syrups are more on the order of 80-82 than 77-79 The reduction in the water evaporation requirement is on the order of 20-35

2 BASIC IDEA

In a continuous evaporating crystallizer the agitation and movement in the massecuite are directly dependent on the quantity of water evaporated in the evaporating crystallizer If less water is evaporated both the movement and the agitation are reduced

Consequently we were quite naturally led to consider fitting the continuous evaporating crystallizers with mechanical stirring

3 REALIZATION OF THE IDEA

After examining several possible arrangements for mechanical stirrers in a continuous evaporating crystallizer the layout shown in Figure 2 was chosen This allows a stirrer to be installed with sufficient room on the feed side and it does not require the removal of any tubes On the other hand the diameter of the stirrer is necessarily limited and the flow from it has little effect on the lowest part of the calandria As a matter of fact this installation seems to be the best compromise sol~tion

Thanks to the prior agreement and kind cooperation of the Colleville sugar factory the mechanical stirring system was tested in an FeB continuous evaporating crystallizer during the 1995 sugar campaign (see Figure 3)

The main specifications of the Colleville CCTR continuous evaporating crystallizer for B sugar were as follows

Volume Heating Surface

64 61 7

m 3

m 2 (2260 fe) (6640 tf)

~iameter 3500 mm (1 1-6) Length 11870 mm (38-11 ) Compartments 13

195

The second half of the evaporating crystalizer (compartments 9 to 13) was et9d with siv

stirrers This was a logical choice because the last compartments are those where the least water is evaporated the dry substance content is the highest and natural agitation is the least

Compartments 9 to 12 were each provided with one stirrer and compartment 13 whose volume was twice as large as the previous ones was provided with two stirrers Obviously steam agitation was eliminated from the compartments fitted with stirrers Moreover the usual feed syrup introduction device is replaced by a feed pipe directed toward the axis of each stirrer

4 Results

The stirrers were started at the beginning of the campaign at the same time as was the evaporating crystallizer and they worked satisfactorily through the last day of the campaign without causing any particular mechanical or electrical problems

Qualitatively speaking the stirring has an unquestionable effect Viewed from above the swirl of the massecuite mass was plain to see Observing the surface of the massecuite in a compartment during a change in the operating conditions of the stirrer from full stop or vice versa a significant change in the behaviour of the massecuite could be noted

As a rule the Colleville sugar factory cleans the crystallizer twice during a campaign For safety reasons this frequency was observed during the 1995 campaign The crystallizer showed less encrustation however on both occasions

In order to demonstrate the quantitative impact of mechanical stirring a series of measurements and analyses was made during the 1994 campaign in order to determine the representative operational parameters of the FCB evaporating crystallizer when it was functioning without stirrers During the 1995 campaign the same measurements and analyses were carried out and the relevant operational parameters determined Of course every effort was made to keep the operating conditions as close as possible to those of the 1994 campaign In particular it was the aim insofar as possible to work with the same massecuite flow rate the same water evaporation rate and the same massecuite dry substance content The measurements were even made approximately 10 days after cleaning the crystallizer just as was done irt 1994 The comparison between the 1994 and 1995 operational parameters is given in Table 1

196

Operational balances in 1994 and 1995

(In customary US units of measurement)

1994 1995

balance 1 (68 h)

balance 2 (16 h)

balance (48 h)

Condensed water flow rate cufth 1257 1406 1353 B feed syrup flow rate cufth 5792 6427 5686 B massecuite flow rate stlh 322 354 316 OS content of B feed syrup 805 805 790 OS content of B massecuite 930 930 926 B massecuite purity 871 871 875 B mother liquor purity 760 760 750 Exhaustion abs ~Pty 111 111 125 Calandria pressure psi 123 127 113 Vapor space vacuum psi 41 41 39 Calandria steam temperature of 2032 2046 1990 Vapor space vacuum temp of 1537 1535 1522

Total t1t of 495 511 468

Operational balances in 1994 and 1995 (In metric units of measurement)

1994 1995

balance 1 (68 h)

balance 2 (16 h)

balance 48 h

Condensed water flow rate m 3h 356 398 383 B feed syrup flow rate mlh 164 182 161 B massecuite flow rate tIh 292 321 287 OS content of B feed syrup 805 805 790 OS content of B massecuite 930 930 26 B massecuite purity 871 871

875

B mother liquor purity 760 760 750 Exhaustion abs ~Pty 111 111 125 Calandria pressure abs bar 0847 0874 0779 Vapor space vacuum abs bar 0281 0280 0271 Calandria steam temperature degC 951 959 928 Vapor space vacuum temp degC 676 675 668

Total t1t OK 275 284 260

197

A gain of about 2 degC on the total ~t of the crystallizer should be noted as well as a rather marked gain of about 1 to 15 pOints of purity in crystallization exhaustion

Tests were made to determine whether this gain in exhaustion might be attributable to a difference in sucrose solubility between 1994 and 1995 Figure 4 illustrates the 1994 and 1995 Colleville solubility curves (Ksat as a function of the NSNI ratio) a difference in solubility was found but it does not affect the B sugar zone in which NSNI ranges between 08 and 16 Therefore there can be no doubt that the increase in exhaustion was due to the mechanical stirring

The 1994 and 1995 operational conditions were simulated using FCBs continuous evaporating crystallizer simulation software CRISCONT Figure 5 illustrates the good correlation between the massecuite OS content measurements and the calculated values This simulation software uses modulation coefficients for heat exchange and mass exchange which make it possible to adjust the simulation to particular operational conditions In the present case with regard to the 1995 balance we distinguished between compartments 1 to 8 without stirrers and compartments 9 to 13 with stirrers

Table 2 gives the coefficients used for the simulation

1994 1995 gain in

modulation

cpts 1 to 13 cpts 1 to 8 cpts 9 to 13 coefficient

modulation coefficient

heat exchange 0864 0866 1137 + 31

modulation coefficient

mass exchange 0518 0505 1150 + 128

- Table 2shy

Table 2 shows a quite marked gain in favor of compartments equipped with stirrers in comparison with those which were not so equipped

The effect of the stirring was also demonstrated by the transient reaction upon stopping or restarting all of the stirrers This transient reaction effects in a reproducible and appreciable way both the instantaneous pressure in the calandria (at constant pressure above the massecuite) and the condensate flow rate (Table 3)

198

Stopping the stirrers Starting the stirrers

Relative time pressure condensate pressure condensate in calandria flow rate in calandria flow rate

(seconds) (psi) (cuftlh) (psi) (cu ftlh)

30 before 883 862 928 798 30 after 898 770 925 809 90 after 917 71 3 909 826 150 after 930 682 895 851 210 after 935 675 873 946

Variation +052 - 187 - 055 + 148

(-22) (+19)

Equivalent tt + 27 OF - 28 OF

- Table 3shy

The electrical power consumption was on the order of 030 to 035 kWm3 which are low

values This depends on the compartments and on the state (viscosity) of the massecuite

Because of lack of reference measurements in 1994 it is not possible to show directJy the contribution of stirring on the quality of grain size However two positive indications should be noted

bull IRIS made crystal size measurements during the 1995 campaign while the evaporating crystallizer was running at a low tightening value (massecuite OS content about 89) These measurements show that stirring improved the coefficient of variation (CV) of the seed magma (remixed C sugar) which was reduced from 39 to 33 at the exit of the crystallizer

bull The centrifugation performance of the B sugar massec~ite was better than usual during the 1995 campaign

We are convinced of the positive effect of mechanical stirring on the crystal quality both in terms of crystal size distribution (CV) and in terms of twins and agglomerates (crystal regularity according to Hill mark)

199

5 CONCLUSIONS

51 IMPROVEMENT OF EXISTING VACUUM PANS

The performance gains measured on Collevilles B sugar evaporating crystallizer were significant even though only the second half of this crystallizer was equipped with stirrers

The overall improvement in performance is directly related to the increase in massecuite circulation through the calandria which is induced by the stirrer This results in an increase in heat exchange coefficients an increase in the crystallization rate and a better massecuite mixing in the compartments which consequently reduces the residence time distribution thereby improving crystal size quality

It is therefore possible to boost an existing crystallizer to the point of gaining a lower ~t by several degrees with an unchanged capacity or of obtaining a 20 to 40 increase in production as the case may be

52 NEW PAN DESIGN

The excellent performances registered at the Colleville sugar plant led us to go further and to redesign our continuous evaporating crystallizer in order to obtain a better adaptation for mechanical stirrers

Thus after 20 years of operation the FCB continuous evaporating crystallizer CCTR type (Cuite Continue aTubes Ronde = Round Continuous Vacuum Pan with horizontal Tubes) is replaced by a new design an evolution of the first one CCTW type (Cuite Continue aTubes en W =W Shape Continuous Vacuum Pan with horizontal Tubes)

The specifications imposed for the new pan were evident

bull possibility of installation of mechanical stirring under the calandria that speeds up the massecuite flow across the tube nest

To which we added

bull decreasing the hydrostatiC head above the calandria and improving homogeneity of the tube nest

bull increasing section of lateral channel for massecuite recirculation

We kept the principle of a calandria with horizontal tubes fitted in vertical rows We showed by simulation that this type of tube nest presents the best compromise between head loss and heat exchange coefficients (2 opposite characteristics)

200

------

In order to optimize the efficiency of the mechanical stirring and to minimize the maximal hydrostatic head the bottom shape of the tube nest is horizontal

In order to optimize the heat exchange surface to improve the lateral recirculation of massecuite and to increase the lateral overilow height (that is linked to the recirculation f1owrate) the upper shape of the tube nest is sloped towards the lateral channel

Consequently the shell shape is naturally placed around the tube nest This creates a large lateral width of recirculation channel that is progressively reduced downwards (head increasing) and is progressively closed centerwards under the tube nest for avoiding dead zones (see Figure 6)

Figure 7 shows the gain versus a CCTR continuous vacuum pan

The new pan like the former one can operate for all products in a raw sugar plant as well as refinery cane and beet

Mechanical stirring is an option that makes it possible to achieve very substantial improvement in ~t and exhaustion as was proven at the Colleville sugar plant

Like the former design the CCTW continuous evaporating crystallizer range includes 5 diameters and 9 len~ths (see Table 4) The nominal volume doubles every 5 pans The SN ratio is 10 m2m (305 sqftlcuft)

CCTW Continuous Vacuum Pan bull RANGE

Length

of Pan

(mm)

5000 5680 25 33

6620 29 38 50 7500 57 75 8620 87 115 9840 130 11300 12980 14560

- Table 4shy(In metric units of measurement)

201

I

The second half of the evaporating crystalizer (compartments 9 to 13) was et9d with siv

stirrers This was a logical choice because the last compartments are those where the least water is evaporated the dry substance content is the highest and natural agitation is the least

Compartments 9 to 12 were each provided with one stirrer and compartment 13 whose volume was twice as large as the previous ones was provided with two stirrers Obviously steam agitation was eliminated from the compartments fitted with stirrers Moreover the usual feed syrup introduction device is replaced by a feed pipe directed toward the axis of each stirrer

4 Results

The stirrers were started at the beginning of the campaign at the same time as was the evaporating crystallizer and they worked satisfactorily through the last day of the campaign without causing any particular mechanical or electrical problems

Qualitatively speaking the stirring has an unquestionable effect Viewed from above the swirl of the massecuite mass was plain to see Observing the surface of the massecuite in a compartment during a change in the operating conditions of the stirrer from full stop or vice versa a significant change in the behaviour of the massecuite could be noted

As a rule the Colleville sugar factory cleans the crystallizer twice during a campaign For safety reasons this frequency was observed during the 1995 campaign The crystallizer showed less encrustation however on both occasions

In order to demonstrate the quantitative impact of mechanical stirring a series of measurements and analyses was made during the 1994 campaign in order to determine the representative operational parameters of the FCB evaporating crystallizer when it was functioning without stirrers During the 1995 campaign the same measurements and analyses were carried out and the relevant operational parameters determined Of course every effort was made to keep the operating conditions as close as possible to those of the 1994 campaign In particular it was the aim insofar as possible to work with the same massecuite flow rate the same water evaporation rate and the same massecuite dry substance content The measurements were even made approximately 10 days after cleaning the crystallizer just as was done irt 1994 The comparison between the 1994 and 1995 operational parameters is given in Table 1

196

Operational balances in 1994 and 1995

(In customary US units of measurement)

1994 1995

balance 1 (68 h)

balance 2 (16 h)

balance (48 h)

Condensed water flow rate cufth 1257 1406 1353 B feed syrup flow rate cufth 5792 6427 5686 B massecuite flow rate stlh 322 354 316 OS content of B feed syrup 805 805 790 OS content of B massecuite 930 930 926 B massecuite purity 871 871 875 B mother liquor purity 760 760 750 Exhaustion abs ~Pty 111 111 125 Calandria pressure psi 123 127 113 Vapor space vacuum psi 41 41 39 Calandria steam temperature of 2032 2046 1990 Vapor space vacuum temp of 1537 1535 1522

Total t1t of 495 511 468

Operational balances in 1994 and 1995 (In metric units of measurement)

1994 1995

balance 1 (68 h)

balance 2 (16 h)

balance 48 h

Condensed water flow rate m 3h 356 398 383 B feed syrup flow rate mlh 164 182 161 B massecuite flow rate tIh 292 321 287 OS content of B feed syrup 805 805 790 OS content of B massecuite 930 930 26 B massecuite purity 871 871

875

B mother liquor purity 760 760 750 Exhaustion abs ~Pty 111 111 125 Calandria pressure abs bar 0847 0874 0779 Vapor space vacuum abs bar 0281 0280 0271 Calandria steam temperature degC 951 959 928 Vapor space vacuum temp degC 676 675 668

Total t1t OK 275 284 260

197

A gain of about 2 degC on the total ~t of the crystallizer should be noted as well as a rather marked gain of about 1 to 15 pOints of purity in crystallization exhaustion

Tests were made to determine whether this gain in exhaustion might be attributable to a difference in sucrose solubility between 1994 and 1995 Figure 4 illustrates the 1994 and 1995 Colleville solubility curves (Ksat as a function of the NSNI ratio) a difference in solubility was found but it does not affect the B sugar zone in which NSNI ranges between 08 and 16 Therefore there can be no doubt that the increase in exhaustion was due to the mechanical stirring

The 1994 and 1995 operational conditions were simulated using FCBs continuous evaporating crystallizer simulation software CRISCONT Figure 5 illustrates the good correlation between the massecuite OS content measurements and the calculated values This simulation software uses modulation coefficients for heat exchange and mass exchange which make it possible to adjust the simulation to particular operational conditions In the present case with regard to the 1995 balance we distinguished between compartments 1 to 8 without stirrers and compartments 9 to 13 with stirrers

Table 2 gives the coefficients used for the simulation

1994 1995 gain in

modulation

cpts 1 to 13 cpts 1 to 8 cpts 9 to 13 coefficient

modulation coefficient

heat exchange 0864 0866 1137 + 31

modulation coefficient

mass exchange 0518 0505 1150 + 128

- Table 2shy

Table 2 shows a quite marked gain in favor of compartments equipped with stirrers in comparison with those which were not so equipped

The effect of the stirring was also demonstrated by the transient reaction upon stopping or restarting all of the stirrers This transient reaction effects in a reproducible and appreciable way both the instantaneous pressure in the calandria (at constant pressure above the massecuite) and the condensate flow rate (Table 3)

198

Stopping the stirrers Starting the stirrers

Relative time pressure condensate pressure condensate in calandria flow rate in calandria flow rate

(seconds) (psi) (cuftlh) (psi) (cu ftlh)

30 before 883 862 928 798 30 after 898 770 925 809 90 after 917 71 3 909 826 150 after 930 682 895 851 210 after 935 675 873 946

Variation +052 - 187 - 055 + 148

(-22) (+19)

Equivalent tt + 27 OF - 28 OF

- Table 3shy

The electrical power consumption was on the order of 030 to 035 kWm3 which are low

values This depends on the compartments and on the state (viscosity) of the massecuite

Because of lack of reference measurements in 1994 it is not possible to show directJy the contribution of stirring on the quality of grain size However two positive indications should be noted

bull IRIS made crystal size measurements during the 1995 campaign while the evaporating crystallizer was running at a low tightening value (massecuite OS content about 89) These measurements show that stirring improved the coefficient of variation (CV) of the seed magma (remixed C sugar) which was reduced from 39 to 33 at the exit of the crystallizer

bull The centrifugation performance of the B sugar massec~ite was better than usual during the 1995 campaign

We are convinced of the positive effect of mechanical stirring on the crystal quality both in terms of crystal size distribution (CV) and in terms of twins and agglomerates (crystal regularity according to Hill mark)

199

5 CONCLUSIONS

51 IMPROVEMENT OF EXISTING VACUUM PANS

The performance gains measured on Collevilles B sugar evaporating crystallizer were significant even though only the second half of this crystallizer was equipped with stirrers

The overall improvement in performance is directly related to the increase in massecuite circulation through the calandria which is induced by the stirrer This results in an increase in heat exchange coefficients an increase in the crystallization rate and a better massecuite mixing in the compartments which consequently reduces the residence time distribution thereby improving crystal size quality

It is therefore possible to boost an existing crystallizer to the point of gaining a lower ~t by several degrees with an unchanged capacity or of obtaining a 20 to 40 increase in production as the case may be

52 NEW PAN DESIGN

The excellent performances registered at the Colleville sugar plant led us to go further and to redesign our continuous evaporating crystallizer in order to obtain a better adaptation for mechanical stirrers

Thus after 20 years of operation the FCB continuous evaporating crystallizer CCTR type (Cuite Continue aTubes Ronde = Round Continuous Vacuum Pan with horizontal Tubes) is replaced by a new design an evolution of the first one CCTW type (Cuite Continue aTubes en W =W Shape Continuous Vacuum Pan with horizontal Tubes)

The specifications imposed for the new pan were evident

bull possibility of installation of mechanical stirring under the calandria that speeds up the massecuite flow across the tube nest

To which we added

bull decreasing the hydrostatiC head above the calandria and improving homogeneity of the tube nest

bull increasing section of lateral channel for massecuite recirculation

We kept the principle of a calandria with horizontal tubes fitted in vertical rows We showed by simulation that this type of tube nest presents the best compromise between head loss and heat exchange coefficients (2 opposite characteristics)

200

------

In order to optimize the efficiency of the mechanical stirring and to minimize the maximal hydrostatic head the bottom shape of the tube nest is horizontal

In order to optimize the heat exchange surface to improve the lateral recirculation of massecuite and to increase the lateral overilow height (that is linked to the recirculation f1owrate) the upper shape of the tube nest is sloped towards the lateral channel

Consequently the shell shape is naturally placed around the tube nest This creates a large lateral width of recirculation channel that is progressively reduced downwards (head increasing) and is progressively closed centerwards under the tube nest for avoiding dead zones (see Figure 6)

Figure 7 shows the gain versus a CCTR continuous vacuum pan

The new pan like the former one can operate for all products in a raw sugar plant as well as refinery cane and beet

Mechanical stirring is an option that makes it possible to achieve very substantial improvement in ~t and exhaustion as was proven at the Colleville sugar plant

Like the former design the CCTW continuous evaporating crystallizer range includes 5 diameters and 9 len~ths (see Table 4) The nominal volume doubles every 5 pans The SN ratio is 10 m2m (305 sqftlcuft)

CCTW Continuous Vacuum Pan bull RANGE

Length

of Pan

(mm)

5000 5680 25 33

6620 29 38 50 7500 57 75 8620 87 115 9840 130 11300 12980 14560

- Table 4shy(In metric units of measurement)

201

I

Operational balances in 1994 and 1995

(In customary US units of measurement)

1994 1995

balance 1 (68 h)

balance 2 (16 h)

balance (48 h)

Condensed water flow rate cufth 1257 1406 1353 B feed syrup flow rate cufth 5792 6427 5686 B massecuite flow rate stlh 322 354 316 OS content of B feed syrup 805 805 790 OS content of B massecuite 930 930 926 B massecuite purity 871 871 875 B mother liquor purity 760 760 750 Exhaustion abs ~Pty 111 111 125 Calandria pressure psi 123 127 113 Vapor space vacuum psi 41 41 39 Calandria steam temperature of 2032 2046 1990 Vapor space vacuum temp of 1537 1535 1522

Total t1t of 495 511 468

Operational balances in 1994 and 1995 (In metric units of measurement)

1994 1995

balance 1 (68 h)

balance 2 (16 h)

balance 48 h

Condensed water flow rate m 3h 356 398 383 B feed syrup flow rate mlh 164 182 161 B massecuite flow rate tIh 292 321 287 OS content of B feed syrup 805 805 790 OS content of B massecuite 930 930 26 B massecuite purity 871 871

875

B mother liquor purity 760 760 750 Exhaustion abs ~Pty 111 111 125 Calandria pressure abs bar 0847 0874 0779 Vapor space vacuum abs bar 0281 0280 0271 Calandria steam temperature degC 951 959 928 Vapor space vacuum temp degC 676 675 668

Total t1t OK 275 284 260

197

A gain of about 2 degC on the total ~t of the crystallizer should be noted as well as a rather marked gain of about 1 to 15 pOints of purity in crystallization exhaustion

Tests were made to determine whether this gain in exhaustion might be attributable to a difference in sucrose solubility between 1994 and 1995 Figure 4 illustrates the 1994 and 1995 Colleville solubility curves (Ksat as a function of the NSNI ratio) a difference in solubility was found but it does not affect the B sugar zone in which NSNI ranges between 08 and 16 Therefore there can be no doubt that the increase in exhaustion was due to the mechanical stirring

The 1994 and 1995 operational conditions were simulated using FCBs continuous evaporating crystallizer simulation software CRISCONT Figure 5 illustrates the good correlation between the massecuite OS content measurements and the calculated values This simulation software uses modulation coefficients for heat exchange and mass exchange which make it possible to adjust the simulation to particular operational conditions In the present case with regard to the 1995 balance we distinguished between compartments 1 to 8 without stirrers and compartments 9 to 13 with stirrers

Table 2 gives the coefficients used for the simulation

1994 1995 gain in

modulation

cpts 1 to 13 cpts 1 to 8 cpts 9 to 13 coefficient

modulation coefficient

heat exchange 0864 0866 1137 + 31

modulation coefficient

mass exchange 0518 0505 1150 + 128

- Table 2shy

Table 2 shows a quite marked gain in favor of compartments equipped with stirrers in comparison with those which were not so equipped

The effect of the stirring was also demonstrated by the transient reaction upon stopping or restarting all of the stirrers This transient reaction effects in a reproducible and appreciable way both the instantaneous pressure in the calandria (at constant pressure above the massecuite) and the condensate flow rate (Table 3)

198

Stopping the stirrers Starting the stirrers

Relative time pressure condensate pressure condensate in calandria flow rate in calandria flow rate

(seconds) (psi) (cuftlh) (psi) (cu ftlh)

30 before 883 862 928 798 30 after 898 770 925 809 90 after 917 71 3 909 826 150 after 930 682 895 851 210 after 935 675 873 946

Variation +052 - 187 - 055 + 148

(-22) (+19)

Equivalent tt + 27 OF - 28 OF

- Table 3shy

The electrical power consumption was on the order of 030 to 035 kWm3 which are low

values This depends on the compartments and on the state (viscosity) of the massecuite

Because of lack of reference measurements in 1994 it is not possible to show directJy the contribution of stirring on the quality of grain size However two positive indications should be noted

bull IRIS made crystal size measurements during the 1995 campaign while the evaporating crystallizer was running at a low tightening value (massecuite OS content about 89) These measurements show that stirring improved the coefficient of variation (CV) of the seed magma (remixed C sugar) which was reduced from 39 to 33 at the exit of the crystallizer

bull The centrifugation performance of the B sugar massec~ite was better than usual during the 1995 campaign

We are convinced of the positive effect of mechanical stirring on the crystal quality both in terms of crystal size distribution (CV) and in terms of twins and agglomerates (crystal regularity according to Hill mark)

199

5 CONCLUSIONS

51 IMPROVEMENT OF EXISTING VACUUM PANS

The performance gains measured on Collevilles B sugar evaporating crystallizer were significant even though only the second half of this crystallizer was equipped with stirrers

The overall improvement in performance is directly related to the increase in massecuite circulation through the calandria which is induced by the stirrer This results in an increase in heat exchange coefficients an increase in the crystallization rate and a better massecuite mixing in the compartments which consequently reduces the residence time distribution thereby improving crystal size quality

It is therefore possible to boost an existing crystallizer to the point of gaining a lower ~t by several degrees with an unchanged capacity or of obtaining a 20 to 40 increase in production as the case may be

52 NEW PAN DESIGN

The excellent performances registered at the Colleville sugar plant led us to go further and to redesign our continuous evaporating crystallizer in order to obtain a better adaptation for mechanical stirrers

Thus after 20 years of operation the FCB continuous evaporating crystallizer CCTR type (Cuite Continue aTubes Ronde = Round Continuous Vacuum Pan with horizontal Tubes) is replaced by a new design an evolution of the first one CCTW type (Cuite Continue aTubes en W =W Shape Continuous Vacuum Pan with horizontal Tubes)

The specifications imposed for the new pan were evident

bull possibility of installation of mechanical stirring under the calandria that speeds up the massecuite flow across the tube nest

To which we added

bull decreasing the hydrostatiC head above the calandria and improving homogeneity of the tube nest

bull increasing section of lateral channel for massecuite recirculation

We kept the principle of a calandria with horizontal tubes fitted in vertical rows We showed by simulation that this type of tube nest presents the best compromise between head loss and heat exchange coefficients (2 opposite characteristics)

200

------

In order to optimize the efficiency of the mechanical stirring and to minimize the maximal hydrostatic head the bottom shape of the tube nest is horizontal

In order to optimize the heat exchange surface to improve the lateral recirculation of massecuite and to increase the lateral overilow height (that is linked to the recirculation f1owrate) the upper shape of the tube nest is sloped towards the lateral channel

Consequently the shell shape is naturally placed around the tube nest This creates a large lateral width of recirculation channel that is progressively reduced downwards (head increasing) and is progressively closed centerwards under the tube nest for avoiding dead zones (see Figure 6)

Figure 7 shows the gain versus a CCTR continuous vacuum pan

The new pan like the former one can operate for all products in a raw sugar plant as well as refinery cane and beet

Mechanical stirring is an option that makes it possible to achieve very substantial improvement in ~t and exhaustion as was proven at the Colleville sugar plant

Like the former design the CCTW continuous evaporating crystallizer range includes 5 diameters and 9 len~ths (see Table 4) The nominal volume doubles every 5 pans The SN ratio is 10 m2m (305 sqftlcuft)

CCTW Continuous Vacuum Pan bull RANGE

Length

of Pan

(mm)

5000 5680 25 33

6620 29 38 50 7500 57 75 8620 87 115 9840 130 11300 12980 14560

- Table 4shy(In metric units of measurement)

201

I

A gain of about 2 degC on the total ~t of the crystallizer should be noted as well as a rather marked gain of about 1 to 15 pOints of purity in crystallization exhaustion

Tests were made to determine whether this gain in exhaustion might be attributable to a difference in sucrose solubility between 1994 and 1995 Figure 4 illustrates the 1994 and 1995 Colleville solubility curves (Ksat as a function of the NSNI ratio) a difference in solubility was found but it does not affect the B sugar zone in which NSNI ranges between 08 and 16 Therefore there can be no doubt that the increase in exhaustion was due to the mechanical stirring

The 1994 and 1995 operational conditions were simulated using FCBs continuous evaporating crystallizer simulation software CRISCONT Figure 5 illustrates the good correlation between the massecuite OS content measurements and the calculated values This simulation software uses modulation coefficients for heat exchange and mass exchange which make it possible to adjust the simulation to particular operational conditions In the present case with regard to the 1995 balance we distinguished between compartments 1 to 8 without stirrers and compartments 9 to 13 with stirrers

Table 2 gives the coefficients used for the simulation

1994 1995 gain in

modulation

cpts 1 to 13 cpts 1 to 8 cpts 9 to 13 coefficient

modulation coefficient

heat exchange 0864 0866 1137 + 31

modulation coefficient

mass exchange 0518 0505 1150 + 128

- Table 2shy

Table 2 shows a quite marked gain in favor of compartments equipped with stirrers in comparison with those which were not so equipped

The effect of the stirring was also demonstrated by the transient reaction upon stopping or restarting all of the stirrers This transient reaction effects in a reproducible and appreciable way both the instantaneous pressure in the calandria (at constant pressure above the massecuite) and the condensate flow rate (Table 3)

198

Stopping the stirrers Starting the stirrers

Relative time pressure condensate pressure condensate in calandria flow rate in calandria flow rate

(seconds) (psi) (cuftlh) (psi) (cu ftlh)

30 before 883 862 928 798 30 after 898 770 925 809 90 after 917 71 3 909 826 150 after 930 682 895 851 210 after 935 675 873 946

Variation +052 - 187 - 055 + 148

(-22) (+19)

Equivalent tt + 27 OF - 28 OF

- Table 3shy

The electrical power consumption was on the order of 030 to 035 kWm3 which are low

values This depends on the compartments and on the state (viscosity) of the massecuite

Because of lack of reference measurements in 1994 it is not possible to show directJy the contribution of stirring on the quality of grain size However two positive indications should be noted

bull IRIS made crystal size measurements during the 1995 campaign while the evaporating crystallizer was running at a low tightening value (massecuite OS content about 89) These measurements show that stirring improved the coefficient of variation (CV) of the seed magma (remixed C sugar) which was reduced from 39 to 33 at the exit of the crystallizer

bull The centrifugation performance of the B sugar massec~ite was better than usual during the 1995 campaign

We are convinced of the positive effect of mechanical stirring on the crystal quality both in terms of crystal size distribution (CV) and in terms of twins and agglomerates (crystal regularity according to Hill mark)

199

5 CONCLUSIONS

51 IMPROVEMENT OF EXISTING VACUUM PANS

The performance gains measured on Collevilles B sugar evaporating crystallizer were significant even though only the second half of this crystallizer was equipped with stirrers

The overall improvement in performance is directly related to the increase in massecuite circulation through the calandria which is induced by the stirrer This results in an increase in heat exchange coefficients an increase in the crystallization rate and a better massecuite mixing in the compartments which consequently reduces the residence time distribution thereby improving crystal size quality

It is therefore possible to boost an existing crystallizer to the point of gaining a lower ~t by several degrees with an unchanged capacity or of obtaining a 20 to 40 increase in production as the case may be

52 NEW PAN DESIGN

The excellent performances registered at the Colleville sugar plant led us to go further and to redesign our continuous evaporating crystallizer in order to obtain a better adaptation for mechanical stirrers

Thus after 20 years of operation the FCB continuous evaporating crystallizer CCTR type (Cuite Continue aTubes Ronde = Round Continuous Vacuum Pan with horizontal Tubes) is replaced by a new design an evolution of the first one CCTW type (Cuite Continue aTubes en W =W Shape Continuous Vacuum Pan with horizontal Tubes)

The specifications imposed for the new pan were evident

bull possibility of installation of mechanical stirring under the calandria that speeds up the massecuite flow across the tube nest

To which we added

bull decreasing the hydrostatiC head above the calandria and improving homogeneity of the tube nest

bull increasing section of lateral channel for massecuite recirculation

We kept the principle of a calandria with horizontal tubes fitted in vertical rows We showed by simulation that this type of tube nest presents the best compromise between head loss and heat exchange coefficients (2 opposite characteristics)

200

------

In order to optimize the efficiency of the mechanical stirring and to minimize the maximal hydrostatic head the bottom shape of the tube nest is horizontal

In order to optimize the heat exchange surface to improve the lateral recirculation of massecuite and to increase the lateral overilow height (that is linked to the recirculation f1owrate) the upper shape of the tube nest is sloped towards the lateral channel

Consequently the shell shape is naturally placed around the tube nest This creates a large lateral width of recirculation channel that is progressively reduced downwards (head increasing) and is progressively closed centerwards under the tube nest for avoiding dead zones (see Figure 6)

Figure 7 shows the gain versus a CCTR continuous vacuum pan

The new pan like the former one can operate for all products in a raw sugar plant as well as refinery cane and beet

Mechanical stirring is an option that makes it possible to achieve very substantial improvement in ~t and exhaustion as was proven at the Colleville sugar plant

Like the former design the CCTW continuous evaporating crystallizer range includes 5 diameters and 9 len~ths (see Table 4) The nominal volume doubles every 5 pans The SN ratio is 10 m2m (305 sqftlcuft)

CCTW Continuous Vacuum Pan bull RANGE

Length

of Pan

(mm)

5000 5680 25 33

6620 29 38 50 7500 57 75 8620 87 115 9840 130 11300 12980 14560

- Table 4shy(In metric units of measurement)

201

I

Stopping the stirrers Starting the stirrers

Relative time pressure condensate pressure condensate in calandria flow rate in calandria flow rate

(seconds) (psi) (cuftlh) (psi) (cu ftlh)

30 before 883 862 928 798 30 after 898 770 925 809 90 after 917 71 3 909 826 150 after 930 682 895 851 210 after 935 675 873 946

Variation +052 - 187 - 055 + 148

(-22) (+19)

Equivalent tt + 27 OF - 28 OF

- Table 3shy

The electrical power consumption was on the order of 030 to 035 kWm3 which are low

values This depends on the compartments and on the state (viscosity) of the massecuite

Because of lack of reference measurements in 1994 it is not possible to show directJy the contribution of stirring on the quality of grain size However two positive indications should be noted

bull IRIS made crystal size measurements during the 1995 campaign while the evaporating crystallizer was running at a low tightening value (massecuite OS content about 89) These measurements show that stirring improved the coefficient of variation (CV) of the seed magma (remixed C sugar) which was reduced from 39 to 33 at the exit of the crystallizer

bull The centrifugation performance of the B sugar massec~ite was better than usual during the 1995 campaign

We are convinced of the positive effect of mechanical stirring on the crystal quality both in terms of crystal size distribution (CV) and in terms of twins and agglomerates (crystal regularity according to Hill mark)

199

5 CONCLUSIONS

51 IMPROVEMENT OF EXISTING VACUUM PANS

The performance gains measured on Collevilles B sugar evaporating crystallizer were significant even though only the second half of this crystallizer was equipped with stirrers

The overall improvement in performance is directly related to the increase in massecuite circulation through the calandria which is induced by the stirrer This results in an increase in heat exchange coefficients an increase in the crystallization rate and a better massecuite mixing in the compartments which consequently reduces the residence time distribution thereby improving crystal size quality

It is therefore possible to boost an existing crystallizer to the point of gaining a lower ~t by several degrees with an unchanged capacity or of obtaining a 20 to 40 increase in production as the case may be

52 NEW PAN DESIGN

The excellent performances registered at the Colleville sugar plant led us to go further and to redesign our continuous evaporating crystallizer in order to obtain a better adaptation for mechanical stirrers

Thus after 20 years of operation the FCB continuous evaporating crystallizer CCTR type (Cuite Continue aTubes Ronde = Round Continuous Vacuum Pan with horizontal Tubes) is replaced by a new design an evolution of the first one CCTW type (Cuite Continue aTubes en W =W Shape Continuous Vacuum Pan with horizontal Tubes)

The specifications imposed for the new pan were evident

bull possibility of installation of mechanical stirring under the calandria that speeds up the massecuite flow across the tube nest

To which we added

bull decreasing the hydrostatiC head above the calandria and improving homogeneity of the tube nest

bull increasing section of lateral channel for massecuite recirculation

We kept the principle of a calandria with horizontal tubes fitted in vertical rows We showed by simulation that this type of tube nest presents the best compromise between head loss and heat exchange coefficients (2 opposite characteristics)

200

------

In order to optimize the efficiency of the mechanical stirring and to minimize the maximal hydrostatic head the bottom shape of the tube nest is horizontal

In order to optimize the heat exchange surface to improve the lateral recirculation of massecuite and to increase the lateral overilow height (that is linked to the recirculation f1owrate) the upper shape of the tube nest is sloped towards the lateral channel

Consequently the shell shape is naturally placed around the tube nest This creates a large lateral width of recirculation channel that is progressively reduced downwards (head increasing) and is progressively closed centerwards under the tube nest for avoiding dead zones (see Figure 6)

Figure 7 shows the gain versus a CCTR continuous vacuum pan

The new pan like the former one can operate for all products in a raw sugar plant as well as refinery cane and beet

Mechanical stirring is an option that makes it possible to achieve very substantial improvement in ~t and exhaustion as was proven at the Colleville sugar plant

Like the former design the CCTW continuous evaporating crystallizer range includes 5 diameters and 9 len~ths (see Table 4) The nominal volume doubles every 5 pans The SN ratio is 10 m2m (305 sqftlcuft)

CCTW Continuous Vacuum Pan bull RANGE

Length

of Pan

(mm)

5000 5680 25 33

6620 29 38 50 7500 57 75 8620 87 115 9840 130 11300 12980 14560

- Table 4shy(In metric units of measurement)

201

I

5 CONCLUSIONS

51 IMPROVEMENT OF EXISTING VACUUM PANS

The performance gains measured on Collevilles B sugar evaporating crystallizer were significant even though only the second half of this crystallizer was equipped with stirrers

The overall improvement in performance is directly related to the increase in massecuite circulation through the calandria which is induced by the stirrer This results in an increase in heat exchange coefficients an increase in the crystallization rate and a better massecuite mixing in the compartments which consequently reduces the residence time distribution thereby improving crystal size quality

It is therefore possible to boost an existing crystallizer to the point of gaining a lower ~t by several degrees with an unchanged capacity or of obtaining a 20 to 40 increase in production as the case may be

52 NEW PAN DESIGN

The excellent performances registered at the Colleville sugar plant led us to go further and to redesign our continuous evaporating crystallizer in order to obtain a better adaptation for mechanical stirrers

Thus after 20 years of operation the FCB continuous evaporating crystallizer CCTR type (Cuite Continue aTubes Ronde = Round Continuous Vacuum Pan with horizontal Tubes) is replaced by a new design an evolution of the first one CCTW type (Cuite Continue aTubes en W =W Shape Continuous Vacuum Pan with horizontal Tubes)

The specifications imposed for the new pan were evident

bull possibility of installation of mechanical stirring under the calandria that speeds up the massecuite flow across the tube nest

To which we added

bull decreasing the hydrostatiC head above the calandria and improving homogeneity of the tube nest

bull increasing section of lateral channel for massecuite recirculation

We kept the principle of a calandria with horizontal tubes fitted in vertical rows We showed by simulation that this type of tube nest presents the best compromise between head loss and heat exchange coefficients (2 opposite characteristics)

200

------

In order to optimize the efficiency of the mechanical stirring and to minimize the maximal hydrostatic head the bottom shape of the tube nest is horizontal

In order to optimize the heat exchange surface to improve the lateral recirculation of massecuite and to increase the lateral overilow height (that is linked to the recirculation f1owrate) the upper shape of the tube nest is sloped towards the lateral channel

Consequently the shell shape is naturally placed around the tube nest This creates a large lateral width of recirculation channel that is progressively reduced downwards (head increasing) and is progressively closed centerwards under the tube nest for avoiding dead zones (see Figure 6)

Figure 7 shows the gain versus a CCTR continuous vacuum pan

The new pan like the former one can operate for all products in a raw sugar plant as well as refinery cane and beet

Mechanical stirring is an option that makes it possible to achieve very substantial improvement in ~t and exhaustion as was proven at the Colleville sugar plant

Like the former design the CCTW continuous evaporating crystallizer range includes 5 diameters and 9 len~ths (see Table 4) The nominal volume doubles every 5 pans The SN ratio is 10 m2m (305 sqftlcuft)

CCTW Continuous Vacuum Pan bull RANGE

Length

of Pan

(mm)

5000 5680 25 33

6620 29 38 50 7500 57 75 8620 87 115 9840 130 11300 12980 14560

- Table 4shy(In metric units of measurement)

201

I

------

In order to optimize the efficiency of the mechanical stirring and to minimize the maximal hydrostatic head the bottom shape of the tube nest is horizontal

In order to optimize the heat exchange surface to improve the lateral recirculation of massecuite and to increase the lateral overilow height (that is linked to the recirculation f1owrate) the upper shape of the tube nest is sloped towards the lateral channel

Consequently the shell shape is naturally placed around the tube nest This creates a large lateral width of recirculation channel that is progressively reduced downwards (head increasing) and is progressively closed centerwards under the tube nest for avoiding dead zones (see Figure 6)

Figure 7 shows the gain versus a CCTR continuous vacuum pan

The new pan like the former one can operate for all products in a raw sugar plant as well as refinery cane and beet

Mechanical stirring is an option that makes it possible to achieve very substantial improvement in ~t and exhaustion as was proven at the Colleville sugar plant

Like the former design the CCTW continuous evaporating crystallizer range includes 5 diameters and 9 len~ths (see Table 4) The nominal volume doubles every 5 pans The SN ratio is 10 m2m (305 sqftlcuft)

CCTW Continuous Vacuum Pan bull RANGE

Length

of Pan

(mm)

5000 5680 25 33

6620 29 38 50 7500 57 75 8620 87 115 9840 130 11300 12980 14560

- Table 4shy(In metric units of measurement)

201

I

CCTW Continuous Vacuum Pan - RANGE

Nominal Diameter (ft)

1739 984 1132 1283 1509 Length

Number of Tubes

(ft)

of Pan

616 792 468 1096 1454 Nominal Volume (cuft)

1640 m 1864 883 1165

middot13422172 1024 1766 2461 2828 3228 3707 4259 47n

2013 2649 3072 061

- Table 4shy(In customary US units of measurement)

The massecuite circulation through the pan always follows a U shape There are 13 compartments without mechanical stirring and 11 middot with mechanical stirring (see Figure 8)

With 11 compartments the number of stirrers is 12 The impeller diameters vary from 400 to 900 mm (1 31 to 295 ft) For example a pan of 100 m (3531 cuft) will be fitted with impellers of 750 mm diameter (246 ft)

The enhancements of the CCTW when compared with the CCTR are the following

bull easy installation of mechanical stirring

bull larger section of recirculation (+ 25 in average)

bull lower maximal and mean hydrostatic head

bull lower massecuite height

bull better homogeneity of the tube nest

bull less space requirement shorter and lower pan

202

These enhancements make possible the following gains

bull Dt decrease of about 1 to 2 degC without mechanical stirring

bull Dt decrease at a minimum of 4 a 6 degC with mechanical stirring (white and high raw massecuite)

bull improved rate of exhaustion

bull improved grain size quality bull complete replacement of the jigger steam by the mechanical stirring

bull decreased encrustation

Needless to say all these advantages fully justify the decision of FeB to upgrade the continuous vacuum pan to the new design with mechanical stirring a feature now being offered to the sugar industry in their new standard pan

2 03

11- ZI-

_IS

Z

Shell ~

longitudinal partlllon 5 Transversal partitions 6 Calandrla Shields 7

~ to CN

o nJ ~

8 Steam boxes and doors 9 Steam Inlet

1 Catchall 10 Condensed water oullet 2 Masseculte extracllon pIpe 11 Non-condensable gas outlet

2 Oulck-dralnage pipes 12 Tube nest 3 Reinforced ends 13 Magma Inlet

c ~ shymiddot Figure 2 middot CI)

~ I CD l o 5c () CD lJ

~CIt ()en

c0 -~ ~ 0-

CDc gt0 000000000 00000-

CD 000000000 0000000t 0 000000000I

u 000000000 000000000CD15 CIt 000000000 000000000 enC 000000000 0000000000 -0 ~l 000000000 000000000 0 0 00 000000000 000000000 00000

t 000000000 000000000 0000000

-J 000000000 000000000 0000000 000000000 000000000 00000000 000000000 000000000 000000000 000000000 000000000 000000000

- Figure 3 shy

205

-------------- ---------- -----

Figure 4

COMPARISON OF SOLUBILITIES

-

19

18

17

16

-15 ~ til 14 ~

13 2

11

10 --~-0 9 +-1-----+----+-1shy - -t-----j-ishy -+-shy middot middot 1 --1-- 1

00 05 10 15 20 25 30 35 40

1 NSIVV 1 bull

Figure 5

2nd strike zone --1995

SIMULATIONS 93

92

91 o ~ 90 CD

89

88

o shy- - ~

A ~

87 +-~--~-----r-----+----_+----~--~~

1 3 5 7 9 11 compartments

206

13

bull Figure 6middot wllhoul

mechanical stirrer

~ ~ bullbull ~ 0middotmiddot I

I ~ amp1 0 I0 I bull 0 I bullbullbullbullbull 0

~ Imiddotmiddotmiddotmiddotmiddotmiddotilmiddotmiddotmiddotmiddotmiddotol --__-shy - ~ 00 000 -i-oo-bullbullbull--

(

10000deg1deg0000 g o bull 0 0

goo 0 0 0 0 0 0 0 0 0 ~ 0000000000 0 000 0 0 0 0 o g 0 0 bullo 0 0 0 ooooooooeoooooo

with mechanical stirrers

masseculte level

OOl r ~ deg1 bullbull shy ~ amp degISoo ~ 1000000 I bullbull 0 0000 bullbullbullbullbullbullbull

I q ~o ~-o--o1-imiddot bullbullbull i shy-----shy-shybullbullbullbull 00000000000 )o 0 0 0 bull 0 0 0

~ bullbullbull 00 00 000 ) 6 0 bull 0 o 0 0 0

o bullbullbullbullbullbullbullbull 0000 amp o 0 0 0 o 0 0 0 o 0 0 0 o 0 bull 0 ~ bull 0 0t 0 0 0 0 0 bull

- shy C

i

- Figure 7shy

CCTR o 4000

masseculte level

goooo oo o bull bullbullbullbull 0000

0 bullbullbull 00 I

bullbull bull00 bullbullbull 0

Smiddotmiddot o bullbullbull bullbull 00 obullbull

00000000

bull 0o 0 o 0 o 0middot bull 00000 0 00 0

0000 bullbullbullbullmiddot o 0

bull 0 bull 0o 0

bull 00 000000

00000000

bull 0 bull 0bullbullbullbullbullbullbull 0

f bullbullbull bull 01

0 0O bull 00 0

CCTW o 3910

mossecuite level

000 o 0 00 o 000 o 00 0 bull 0 00 0 o 0 0 000 00000 00000000

goooo ooZ 0000001

amp g --------- - - - - - - I0 0000 000000000Q0

0 0000 000 o bull o

00 000000 o bull bull 0

o 0 00000 000

o 0bull bullo 0 000000000 00

Ii i II ~----4-----I~0 bullbullbullbullbullbullbullbullbull 0 bullbullbullbull

3 o )(

3 c 3 ~

0

6 [ n J

bull

207

I

8

- Figure 8 shy

CCTW WITHOUT MECHANICAL STIRRING

BUB Upper Bottom U B

12345 6 7

J

- --

- ~

-

massecuite MaSseculte - draln~ge

u

yOlltput

- 13 12 11 10 9

U B U B

CCTW WITH MECHANICAL STIRRING

B u B U B

1 2 3 4 5 6 --shy ~

i I I

- ~--

_ _ f

i ~ - tmiddot I

I - shy - ~ I

1 1

~

shy --

i j J --shy _ 6shy

shy

I i _-_

- 1 1 10 9 8 7

U B U B

U

B

Upper passage between compartments

Bottom passage between compartment

208

I

COLLEVILLE SUGAR FACTORY CONTINUOUS EVAPORATING CRYSTALLIZER

(Continuous Vacuum Pan)

tv 0 U)

Strike Volume Surface Diameter Length Compartments

2nd 364 m2617 m

3500 mm 11870 mm

13

2260 cUft 6641 sqft 1148 ft 3894 ft

These enhancements make possible the following gains

bull Dt decrease of about 1 to 2 degC without mechanical stirring

bull Dt decrease at a minimum of 4 a 6 degC with mechanical stirring (white and high raw massecuite)

bull improved rate of exhaustion

bull improved grain size quality bull complete replacement of the jigger steam by the mechanical stirring

bull decreased encrustation

Needless to say all these advantages fully justify the decision of FeB to upgrade the continuous vacuum pan to the new design with mechanical stirring a feature now being offered to the sugar industry in their new standard pan

2 03

11- ZI-

_IS

Z

Shell ~

longitudinal partlllon 5 Transversal partitions 6 Calandrla Shields 7

~ to CN

o nJ ~

8 Steam boxes and doors 9 Steam Inlet

1 Catchall 10 Condensed water oullet 2 Masseculte extracllon pIpe 11 Non-condensable gas outlet

2 Oulck-dralnage pipes 12 Tube nest 3 Reinforced ends 13 Magma Inlet

c ~ shymiddot Figure 2 middot CI)

~ I CD l o 5c () CD lJ

~CIt ()en

c0 -~ ~ 0-

CDc gt0 000000000 00000-

CD 000000000 0000000t 0 000000000I

u 000000000 000000000CD15 CIt 000000000 000000000 enC 000000000 0000000000 -0 ~l 000000000 000000000 0 0 00 000000000 000000000 00000

t 000000000 000000000 0000000

-J 000000000 000000000 0000000 000000000 000000000 00000000 000000000 000000000 000000000 000000000 000000000 000000000

- Figure 3 shy

205

-------------- ---------- -----

Figure 4

COMPARISON OF SOLUBILITIES

-

19

18

17

16

-15 ~ til 14 ~

13 2

11

10 --~-0 9 +-1-----+----+-1shy - -t-----j-ishy -+-shy middot middot 1 --1-- 1

00 05 10 15 20 25 30 35 40

1 NSIVV 1 bull

Figure 5

2nd strike zone --1995

SIMULATIONS 93

92

91 o ~ 90 CD

89

88

o shy- - ~

A ~

87 +-~--~-----r-----+----_+----~--~~

1 3 5 7 9 11 compartments

206

13

bull Figure 6middot wllhoul

mechanical stirrer

~ ~ bullbull ~ 0middotmiddot I

I ~ amp1 0 I0 I bull 0 I bullbullbullbullbull 0

~ Imiddotmiddotmiddotmiddotmiddotmiddotilmiddotmiddotmiddotmiddotmiddotol --__-shy - ~ 00 000 -i-oo-bullbullbull--

(

10000deg1deg0000 g o bull 0 0

goo 0 0 0 0 0 0 0 0 0 ~ 0000000000 0 000 0 0 0 0 o g 0 0 bullo 0 0 0 ooooooooeoooooo

with mechanical stirrers

masseculte level

OOl r ~ deg1 bullbull shy ~ amp degISoo ~ 1000000 I bullbull 0 0000 bullbullbullbullbullbullbull

I q ~o ~-o--o1-imiddot bullbullbull i shy-----shy-shybullbullbullbull 00000000000 )o 0 0 0 bull 0 0 0

~ bullbullbull 00 00 000 ) 6 0 bull 0 o 0 0 0

o bullbullbullbullbullbullbullbull 0000 amp o 0 0 0 o 0 0 0 o 0 0 0 o 0 bull 0 ~ bull 0 0t 0 0 0 0 0 bull

- shy C

i

- Figure 7shy

CCTR o 4000

masseculte level

goooo oo o bull bullbullbullbull 0000

0 bullbullbull 00 I

bullbull bull00 bullbullbull 0

Smiddotmiddot o bullbullbull bullbull 00 obullbull

00000000

bull 0o 0 o 0 o 0middot bull 00000 0 00 0

0000 bullbullbullbullmiddot o 0

bull 0 bull 0o 0

bull 00 000000

00000000

bull 0 bull 0bullbullbullbullbullbullbull 0

f bullbullbull bull 01

0 0O bull 00 0

CCTW o 3910

mossecuite level

000 o 0 00 o 000 o 00 0 bull 0 00 0 o 0 0 000 00000 00000000

goooo ooZ 0000001

amp g --------- - - - - - - I0 0000 000000000Q0

0 0000 000 o bull o

00 000000 o bull bull 0

o 0 00000 000

o 0bull bullo 0 000000000 00

Ii i II ~----4-----I~0 bullbullbullbullbullbullbullbullbull 0 bullbullbullbull

3 o )(

3 c 3 ~

0

6 [ n J

bull

207

I

8

- Figure 8 shy

CCTW WITHOUT MECHANICAL STIRRING

BUB Upper Bottom U B

12345 6 7

J

- --

- ~

-

massecuite MaSseculte - draln~ge

u

yOlltput

- 13 12 11 10 9

U B U B

CCTW WITH MECHANICAL STIRRING

B u B U B

1 2 3 4 5 6 --shy ~

i I I

- ~--

_ _ f

i ~ - tmiddot I

I - shy - ~ I

1 1

~

shy --

i j J --shy _ 6shy

shy

I i _-_

- 1 1 10 9 8 7

U B U B

U

B

Upper passage between compartments

Bottom passage between compartment

208

I

COLLEVILLE SUGAR FACTORY CONTINUOUS EVAPORATING CRYSTALLIZER

(Continuous Vacuum Pan)

tv 0 U)

Strike Volume Surface Diameter Length Compartments

2nd 364 m2617 m

3500 mm 11870 mm

13

2260 cUft 6641 sqft 1148 ft 3894 ft

11- ZI-

_IS

Z

Shell ~

longitudinal partlllon 5 Transversal partitions 6 Calandrla Shields 7

~ to CN

o nJ ~

8 Steam boxes and doors 9 Steam Inlet

1 Catchall 10 Condensed water oullet 2 Masseculte extracllon pIpe 11 Non-condensable gas outlet

2 Oulck-dralnage pipes 12 Tube nest 3 Reinforced ends 13 Magma Inlet

c ~ shymiddot Figure 2 middot CI)

~ I CD l o 5c () CD lJ

~CIt ()en

c0 -~ ~ 0-

CDc gt0 000000000 00000-

CD 000000000 0000000t 0 000000000I

u 000000000 000000000CD15 CIt 000000000 000000000 enC 000000000 0000000000 -0 ~l 000000000 000000000 0 0 00 000000000 000000000 00000

t 000000000 000000000 0000000

-J 000000000 000000000 0000000 000000000 000000000 00000000 000000000 000000000 000000000 000000000 000000000 000000000

- Figure 3 shy

205

-------------- ---------- -----

Figure 4

COMPARISON OF SOLUBILITIES

-

19

18

17

16

-15 ~ til 14 ~

13 2

11

10 --~-0 9 +-1-----+----+-1shy - -t-----j-ishy -+-shy middot middot 1 --1-- 1

00 05 10 15 20 25 30 35 40

1 NSIVV 1 bull

Figure 5

2nd strike zone --1995

SIMULATIONS 93

92

91 o ~ 90 CD

89

88

o shy- - ~

A ~

87 +-~--~-----r-----+----_+----~--~~

1 3 5 7 9 11 compartments

206

13

bull Figure 6middot wllhoul

mechanical stirrer

~ ~ bullbull ~ 0middotmiddot I

I ~ amp1 0 I0 I bull 0 I bullbullbullbullbull 0

~ Imiddotmiddotmiddotmiddotmiddotmiddotilmiddotmiddotmiddotmiddotmiddotol --__-shy - ~ 00 000 -i-oo-bullbullbull--

(

10000deg1deg0000 g o bull 0 0

goo 0 0 0 0 0 0 0 0 0 ~ 0000000000 0 000 0 0 0 0 o g 0 0 bullo 0 0 0 ooooooooeoooooo

with mechanical stirrers

masseculte level

OOl r ~ deg1 bullbull shy ~ amp degISoo ~ 1000000 I bullbull 0 0000 bullbullbullbullbullbullbull

I q ~o ~-o--o1-imiddot bullbullbull i shy-----shy-shybullbullbullbull 00000000000 )o 0 0 0 bull 0 0 0

~ bullbullbull 00 00 000 ) 6 0 bull 0 o 0 0 0

o bullbullbullbullbullbullbullbull 0000 amp o 0 0 0 o 0 0 0 o 0 0 0 o 0 bull 0 ~ bull 0 0t 0 0 0 0 0 bull

- shy C

i

- Figure 7shy

CCTR o 4000

masseculte level

goooo oo o bull bullbullbullbull 0000

0 bullbullbull 00 I

bullbull bull00 bullbullbull 0

Smiddotmiddot o bullbullbull bullbull 00 obullbull

00000000

bull 0o 0 o 0 o 0middot bull 00000 0 00 0

0000 bullbullbullbullmiddot o 0

bull 0 bull 0o 0

bull 00 000000

00000000

bull 0 bull 0bullbullbullbullbullbullbull 0

f bullbullbull bull 01

0 0O bull 00 0

CCTW o 3910

mossecuite level

000 o 0 00 o 000 o 00 0 bull 0 00 0 o 0 0 000 00000 00000000

goooo ooZ 0000001

amp g --------- - - - - - - I0 0000 000000000Q0

0 0000 000 o bull o

00 000000 o bull bull 0

o 0 00000 000

o 0bull bullo 0 000000000 00

Ii i II ~----4-----I~0 bullbullbullbullbullbullbullbullbull 0 bullbullbullbull

3 o )(

3 c 3 ~

0

6 [ n J

bull

207

I

8

- Figure 8 shy

CCTW WITHOUT MECHANICAL STIRRING

BUB Upper Bottom U B

12345 6 7

J

- --

- ~

-

massecuite MaSseculte - draln~ge

u

yOlltput

- 13 12 11 10 9

U B U B

CCTW WITH MECHANICAL STIRRING

B u B U B

1 2 3 4 5 6 --shy ~

i I I

- ~--

_ _ f

i ~ - tmiddot I

I - shy - ~ I

1 1

~

shy --

i j J --shy _ 6shy

shy

I i _-_

- 1 1 10 9 8 7

U B U B

U

B

Upper passage between compartments

Bottom passage between compartment

208

I

COLLEVILLE SUGAR FACTORY CONTINUOUS EVAPORATING CRYSTALLIZER

(Continuous Vacuum Pan)

tv 0 U)

Strike Volume Surface Diameter Length Compartments

2nd 364 m2617 m

3500 mm 11870 mm

13

2260 cUft 6641 sqft 1148 ft 3894 ft

c ~ shymiddot Figure 2 middot CI)

~ I CD l o 5c () CD lJ

~CIt ()en

c0 -~ ~ 0-

CDc gt0 000000000 00000-

CD 000000000 0000000t 0 000000000I

u 000000000 000000000CD15 CIt 000000000 000000000 enC 000000000 0000000000 -0 ~l 000000000 000000000 0 0 00 000000000 000000000 00000

t 000000000 000000000 0000000

-J 000000000 000000000 0000000 000000000 000000000 00000000 000000000 000000000 000000000 000000000 000000000 000000000

- Figure 3 shy

205

-------------- ---------- -----

Figure 4

COMPARISON OF SOLUBILITIES

-

19

18

17

16

-15 ~ til 14 ~

13 2

11

10 --~-0 9 +-1-----+----+-1shy - -t-----j-ishy -+-shy middot middot 1 --1-- 1

00 05 10 15 20 25 30 35 40

1 NSIVV 1 bull

Figure 5

2nd strike zone --1995

SIMULATIONS 93

92

91 o ~ 90 CD

89

88

o shy- - ~

A ~

87 +-~--~-----r-----+----_+----~--~~

1 3 5 7 9 11 compartments

206

13

bull Figure 6middot wllhoul

mechanical stirrer

~ ~ bullbull ~ 0middotmiddot I

I ~ amp1 0 I0 I bull 0 I bullbullbullbullbull 0

~ Imiddotmiddotmiddotmiddotmiddotmiddotilmiddotmiddotmiddotmiddotmiddotol --__-shy - ~ 00 000 -i-oo-bullbullbull--

(

10000deg1deg0000 g o bull 0 0

goo 0 0 0 0 0 0 0 0 0 ~ 0000000000 0 000 0 0 0 0 o g 0 0 bullo 0 0 0 ooooooooeoooooo

with mechanical stirrers

masseculte level

OOl r ~ deg1 bullbull shy ~ amp degISoo ~ 1000000 I bullbull 0 0000 bullbullbullbullbullbullbull

I q ~o ~-o--o1-imiddot bullbullbull i shy-----shy-shybullbullbullbull 00000000000 )o 0 0 0 bull 0 0 0

~ bullbullbull 00 00 000 ) 6 0 bull 0 o 0 0 0

o bullbullbullbullbullbullbullbull 0000 amp o 0 0 0 o 0 0 0 o 0 0 0 o 0 bull 0 ~ bull 0 0t 0 0 0 0 0 bull

- shy C

i

- Figure 7shy

CCTR o 4000

masseculte level

goooo oo o bull bullbullbullbull 0000

0 bullbullbull 00 I

bullbull bull00 bullbullbull 0

Smiddotmiddot o bullbullbull bullbull 00 obullbull

00000000

bull 0o 0 o 0 o 0middot bull 00000 0 00 0

0000 bullbullbullbullmiddot o 0

bull 0 bull 0o 0

bull 00 000000

00000000

bull 0 bull 0bullbullbullbullbullbullbull 0

f bullbullbull bull 01

0 0O bull 00 0

CCTW o 3910

mossecuite level

000 o 0 00 o 000 o 00 0 bull 0 00 0 o 0 0 000 00000 00000000

goooo ooZ 0000001

amp g --------- - - - - - - I0 0000 000000000Q0

0 0000 000 o bull o

00 000000 o bull bull 0

o 0 00000 000

o 0bull bullo 0 000000000 00

Ii i II ~----4-----I~0 bullbullbullbullbullbullbullbullbull 0 bullbullbullbull

3 o )(

3 c 3 ~

0

6 [ n J

bull

207

I

8

- Figure 8 shy

CCTW WITHOUT MECHANICAL STIRRING

BUB Upper Bottom U B

12345 6 7

J

- --

- ~

-

massecuite MaSseculte - draln~ge

u

yOlltput

- 13 12 11 10 9

U B U B

CCTW WITH MECHANICAL STIRRING

B u B U B

1 2 3 4 5 6 --shy ~

i I I

- ~--

_ _ f

i ~ - tmiddot I

I - shy - ~ I

1 1

~

shy --

i j J --shy _ 6shy

shy

I i _-_

- 1 1 10 9 8 7

U B U B

U

B

Upper passage between compartments

Bottom passage between compartment

208

I

COLLEVILLE SUGAR FACTORY CONTINUOUS EVAPORATING CRYSTALLIZER

(Continuous Vacuum Pan)

tv 0 U)

Strike Volume Surface Diameter Length Compartments

2nd 364 m2617 m

3500 mm 11870 mm

13

2260 cUft 6641 sqft 1148 ft 3894 ft

-------------- ---------- -----

Figure 4

COMPARISON OF SOLUBILITIES

-

19

18

17

16

-15 ~ til 14 ~

13 2

11

10 --~-0 9 +-1-----+----+-1shy - -t-----j-ishy -+-shy middot middot 1 --1-- 1

00 05 10 15 20 25 30 35 40

1 NSIVV 1 bull

Figure 5

2nd strike zone --1995

SIMULATIONS 93

92

91 o ~ 90 CD

89

88

o shy- - ~

A ~

87 +-~--~-----r-----+----_+----~--~~

1 3 5 7 9 11 compartments

206

13

bull Figure 6middot wllhoul

mechanical stirrer

~ ~ bullbull ~ 0middotmiddot I

I ~ amp1 0 I0 I bull 0 I bullbullbullbullbull 0

~ Imiddotmiddotmiddotmiddotmiddotmiddotilmiddotmiddotmiddotmiddotmiddotol --__-shy - ~ 00 000 -i-oo-bullbullbull--

(

10000deg1deg0000 g o bull 0 0

goo 0 0 0 0 0 0 0 0 0 ~ 0000000000 0 000 0 0 0 0 o g 0 0 bullo 0 0 0 ooooooooeoooooo

with mechanical stirrers

masseculte level

OOl r ~ deg1 bullbull shy ~ amp degISoo ~ 1000000 I bullbull 0 0000 bullbullbullbullbullbullbull

I q ~o ~-o--o1-imiddot bullbullbull i shy-----shy-shybullbullbullbull 00000000000 )o 0 0 0 bull 0 0 0

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COLLEVILLE SUGAR FACTORY CONTINUOUS EVAPORATING CRYSTALLIZER

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Strike Volume Surface Diameter Length Compartments

2nd 364 m2617 m

3500 mm 11870 mm

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2260 cUft 6641 sqft 1148 ft 3894 ft

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Strike Volume Surface Diameter Length Compartments

2nd 364 m2617 m

3500 mm 11870 mm

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COLLEVILLE SUGAR FACTORY CONTINUOUS EVAPORATING CRYSTALLIZER

(Continuous Vacuum Pan)

tv 0 U)

Strike Volume Surface Diameter Length Compartments

2nd 364 m2617 m

3500 mm 11870 mm

13

2260 cUft 6641 sqft 1148 ft 3894 ft

COLLEVILLE SUGAR FACTORY CONTINUOUS EVAPORATING CRYSTALLIZER

(Continuous Vacuum Pan)

tv 0 U)

Strike Volume Surface Diameter Length Compartments

2nd 364 m2617 m

3500 mm 11870 mm

13

2260 cUft 6641 sqft 1148 ft 3894 ft