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Membrane distillation for the concentration of raw cane-sugar syrup and membrane clarified sugarcane juice
DESALINATION Desalination
ELSEVIER
147 (2002) 157-160 www.elsevier.com/locate/desal
Membrane distillation for the concentration of raw cane-sugar syrup and membrane clarified sugarcane juice Sanjay Nene”*, Suhkvinder Kaurb, K. Sumodb, Bhagyashree Joshib, K.S.M.S. Raghavarao” “Chemical Engineering Division, National Chemical Laboratory, Pune 411008.India Tel. i-91 (20) 5893041; Fax +91 (20) 5893355; email: [email protected] “University Department ofchemical Technology (UDCT), Mumbai 400 019. India ‘Food Engineering Division, Central Food Technology Research Institute, Mysore 570 013, India
Received 7 February 2002; accepted 2 April 2002
Abstract Membrane Distillation (MD) is a process being investigated the world over as a low cost energy saving alternative to conventional separation processes such as distillation and reverse osmosis. MD has a wide range of benefits such as a 100% (theoretical) rejection of ionic species, macromolecules, colloids, cells and other non-volatiles, lower operating pressures, reduced chemical interaction between membrane and process solutions, less demanding membrane mechanical properties and reduced vapour spaces. This process is ideally suited for the concentration of aqueous streams such as fruit juice and sugar solutions. Clarified cane sugar solution (20”Brix) obtained from the sugar mill, immediately after the Dorr filtration was subjected to membrane distillation, whereby the sensible heat from this stream was used to remove water as vapour through a hydrophobic polypropylene membrane. The influence of cross-flow rate and continuous water addition on flux was evaluated. Keywords: Membrane
distillation;
Cane sugar solutions; Polypropylene
1. Introduction
erature
In a conventional cane sugar manufacturing process [ 11, the clarified juice (17-20”Brix) which comes as an overflow from the Dot-r at a temp*Corresponding
author.
Presented at the International July 7-12, 2002.
0011-9 164/02/$-
Congress
on Membranes
membranes
of lOO-102°C
either to a rising
film evaporator (Kestner) or a falling film evaporator of the vertical/horizontal type (Fig. l).The falling film calandria is operated with steam (135°C. and 2.1 kg/cm*).From here the juice goes to a multieffect evaporator. The consumption of steam for and Membrane
Processes
See front matter 0 2002 Elsevier Science B.V. All rights reserved
PII: SO0 Ii -9 164(02)00604-5
proceeds
(ICOM),
Toulouse, France,
158
S. Nene et al. /Desalination
147 (2002) 157-160
I
El
HOT
SUMP
Fig. 1. Membrane distillation plate and frame module assembly. Membrane area 75 cm*, temperatures of cold (TC) and hot (TH) fluids are measuredjust before they enter the membrane module. Pumps have variable flow rates between 250-1500 lpm. Initial volume of both fluid sumps is 1000 ml.
the removal of water from this juice is considerable. If one were to put a membrane distillation step before the juice goes to the evaporators, it is technically feasible to increase the solids in juice from 17” to 30”Brix. The experiments were designed to simulate this step.
gain in the distilled water sump. This was correlated with the corresponding loss in weight by the sugar solution. The DNSA assay was periodically performed on cold water side to check for sugar breakthrough. Similarly the Silver nitrate test was performed to check for NaCl breakthrough.
2. Experimental
3. Results and discussions
Experiments were performed in a laboratory module consisting of a 75 cm2 polypropylene membrane (Akzo, Wuppertal), polyester mesh and Viton gaskets supported between two stainless steel frames. A provision was made for circulating two solutions on either side of the membrane in a co-current or counter current mode. Both solutions were in direct contact with the membrane. 2.5 M and 5 M NaCl followed by a 20” Brix clarified sugarcane solution (equilibrated at 75°C) were circulated at flows ranging between 2501250 ml/min using identical Micropump@ gear pumps. Distilled water (equilibrated at 25°C) was passed on the other side of the membrane in a counter current mode. The flow rate for distilled water was maintained constant at 500 ml/min. Passage of vapour through the membrane was estimated by periodic measurements of weight
When a 2.5 M NaCl solution was subjected to membrane distillation at various values of AT using a PP membrane have a nominal pore size of 0.2 p, an almost linear relation was obtained between flux and AT (Fig. 2). The temperature difference creates a vapour pressure difference, which leads to water vapour diffusion through the membrane. As the temperature difference increases, so does the vapour pressure difference and thus the membrane distillation flux rises. On the basis of the data an operating temperature of 75°C on the (hot) sugar side and a temperature of 25°C on the (cold) water side. With the 20”Brix raw sugar solutions a total of five runs was performed with different flow rates while maintaining a constant temperature difference across the membrane (Fig. 3). Very similar results were obtained with membrane
S. Nene et al. /Desalination
159
147 (2002) 157-160
26
-+
250mllmin 500mllmin 750mllmin
-b\
-*--
%
24
-A-
\
20-
16-
14
00 25
1
121 30
35
40
Temperature
45
50
22-
15
+\\
\ A
14" 1211
s-
lo:_:&
i! LL
F
d t
)
I,,
250
300
\.
n-+--a.,-.
10 i
2
-•---+--. ----.
6-
25. -.-. -=-~--I-~
3 LL 5
64-
-.-
2O-
,I 200
1\ \
16-
E TTl
150
Fig. 3. Membrane distillation of 20”Brix raw sugar solution. Effect of cross-flow rate on permeate flux (at constant AT = 55°C).
247
E‘ d
100
Time (min)
26-
.'-‘-\
q
50
difference AT (OC)
Fig. 2. Membrane distillation of 2.5M NaCl-flux (after 150 min.) for various values of AT (at constant cold side temperature of 25°C).
1620-
I,!,,,
0
55
-*-A-
,
-21,
*, 50
., 100
, 150
, 200
500mVmin 750mVmin 1000ml/min .,
, 250
1
,
*
300
Time (min)
Fig. 4. Flux vs. time at various cross-flow rates for 20”Brix MF juice.
0’
, 50
.
, 100
.
,
.
150
, 200
,
, 250
.
, 300
Time (min)
Fig. 5. Membrane distillation of 20”Brix permeate with constant water addition - permeate flux with time at AT = 50°C and flow rate = 1000 mUmin.
160
S. Nene et al. /Desalination
microfiltered (0.14 p. Carbosep membrane, Orelis) 20”Brix cane juice or permeate. (Fig. 4). However microfiltered cane juice had a lower flux than raw sugar. This could be explained by the observation that the total polysaccharides of MF juice were higher than those in raw sugar, thereby decreasing the flux due to concentration polarization. The higher crossflow rate appeared to improve flux indicating that the influence of increasing shear rate on concentration and temperature polarization was evident. Similar results have been reported by Izquierdo-Gil et al. [2]. In addition to the above experiments, another experiment was performed with permeate at a flow rate of 1000 ml/min with constant water addition thus maintaining a uniform concentration throughout the run. The aim of this experiment was to study the flux decay in membrane distillation when the run conditions were similar to those in the sugar industry. The results (Fig. 5) indicate that it was possible to consistently remove
147 (2002) 157-160
water from the cane sugar solution at a steady state value approximating 10.0 kg/mYh. The results indicate that membrane distillation can create an energy saving niche for itself in removing water from clarified cane juice, using its sensible heat.
Acknowledgement The authors are indebted to the Indo-French Centre, New Delhi (IFCPAR) for financial support for this work.
References [I] [2]
D.P.Kulkami, Cane Sugar Manufacture in India, The Sugar Technologist’s Association of India, 1984. M.A. Izquierdo-Gil, M.C. Garciaand J.C. FemandezPineda, Direct contact membrane distillation of sugar aqueous solutions, Separ. Sci. Technol., 34(9) (1999) 1773-1801.
ELSEVIER
147 (2002) 157-160 www.elsevier.com/locate/desal
Membrane distillation for the concentration of raw cane-sugar syrup and membrane clarified sugarcane juice Sanjay Nene”*, Suhkvinder Kaurb, K. Sumodb, Bhagyashree Joshib, K.S.M.S. Raghavarao” “Chemical Engineering Division, National Chemical Laboratory, Pune 411008.India Tel. i-91 (20) 5893041; Fax +91 (20) 5893355; email: [email protected] “University Department ofchemical Technology (UDCT), Mumbai 400 019. India ‘Food Engineering Division, Central Food Technology Research Institute, Mysore 570 013, India
Received 7 February 2002; accepted 2 April 2002
Abstract Membrane Distillation (MD) is a process being investigated the world over as a low cost energy saving alternative to conventional separation processes such as distillation and reverse osmosis. MD has a wide range of benefits such as a 100% (theoretical) rejection of ionic species, macromolecules, colloids, cells and other non-volatiles, lower operating pressures, reduced chemical interaction between membrane and process solutions, less demanding membrane mechanical properties and reduced vapour spaces. This process is ideally suited for the concentration of aqueous streams such as fruit juice and sugar solutions. Clarified cane sugar solution (20”Brix) obtained from the sugar mill, immediately after the Dorr filtration was subjected to membrane distillation, whereby the sensible heat from this stream was used to remove water as vapour through a hydrophobic polypropylene membrane. The influence of cross-flow rate and continuous water addition on flux was evaluated. Keywords: Membrane
distillation;
Cane sugar solutions; Polypropylene
1. Introduction
erature
In a conventional cane sugar manufacturing process [ 11, the clarified juice (17-20”Brix) which comes as an overflow from the Dot-r at a temp*Corresponding
author.
Presented at the International July 7-12, 2002.
0011-9 164/02/$-
Congress
on Membranes
membranes
of lOO-102°C
either to a rising
film evaporator (Kestner) or a falling film evaporator of the vertical/horizontal type (Fig. l).The falling film calandria is operated with steam (135°C. and 2.1 kg/cm*).From here the juice goes to a multieffect evaporator. The consumption of steam for and Membrane
Processes
See front matter 0 2002 Elsevier Science B.V. All rights reserved
PII: SO0 Ii -9 164(02)00604-5
proceeds
(ICOM),
Toulouse, France,
158
S. Nene et al. /Desalination
147 (2002) 157-160
I
El
HOT
SUMP
Fig. 1. Membrane distillation plate and frame module assembly. Membrane area 75 cm*, temperatures of cold (TC) and hot (TH) fluids are measuredjust before they enter the membrane module. Pumps have variable flow rates between 250-1500 lpm. Initial volume of both fluid sumps is 1000 ml.
the removal of water from this juice is considerable. If one were to put a membrane distillation step before the juice goes to the evaporators, it is technically feasible to increase the solids in juice from 17” to 30”Brix. The experiments were designed to simulate this step.
gain in the distilled water sump. This was correlated with the corresponding loss in weight by the sugar solution. The DNSA assay was periodically performed on cold water side to check for sugar breakthrough. Similarly the Silver nitrate test was performed to check for NaCl breakthrough.
2. Experimental
3. Results and discussions
Experiments were performed in a laboratory module consisting of a 75 cm2 polypropylene membrane (Akzo, Wuppertal), polyester mesh and Viton gaskets supported between two stainless steel frames. A provision was made for circulating two solutions on either side of the membrane in a co-current or counter current mode. Both solutions were in direct contact with the membrane. 2.5 M and 5 M NaCl followed by a 20” Brix clarified sugarcane solution (equilibrated at 75°C) were circulated at flows ranging between 2501250 ml/min using identical Micropump@ gear pumps. Distilled water (equilibrated at 25°C) was passed on the other side of the membrane in a counter current mode. The flow rate for distilled water was maintained constant at 500 ml/min. Passage of vapour through the membrane was estimated by periodic measurements of weight
When a 2.5 M NaCl solution was subjected to membrane distillation at various values of AT using a PP membrane have a nominal pore size of 0.2 p, an almost linear relation was obtained between flux and AT (Fig. 2). The temperature difference creates a vapour pressure difference, which leads to water vapour diffusion through the membrane. As the temperature difference increases, so does the vapour pressure difference and thus the membrane distillation flux rises. On the basis of the data an operating temperature of 75°C on the (hot) sugar side and a temperature of 25°C on the (cold) water side. With the 20”Brix raw sugar solutions a total of five runs was performed with different flow rates while maintaining a constant temperature difference across the membrane (Fig. 3). Very similar results were obtained with membrane
S. Nene et al. /Desalination
159
147 (2002) 157-160
26
-+
250mllmin 500mllmin 750mllmin
-b\
-*--
%
24
-A-
\
20-
16-
14
00 25
1
121 30
35
40
Temperature
45
50
22-
15
+\\
\ A
14" 1211
s-
lo:_:&
i! LL
F
d t
)
I,,
250
300
\.
n-+--a.,-.
10 i
2
-•---+--. ----.
6-
25. -.-. -=-~--I-~
3 LL 5
64-
-.-
2O-
,I 200
1\ \
16-
E TTl
150
Fig. 3. Membrane distillation of 20”Brix raw sugar solution. Effect of cross-flow rate on permeate flux (at constant AT = 55°C).
247
E‘ d
100
Time (min)
26-
.'-‘-\
q
50
difference AT (OC)
Fig. 2. Membrane distillation of 2.5M NaCl-flux (after 150 min.) for various values of AT (at constant cold side temperature of 25°C).
1620-
I,!,,,
0
55
-*-A-
,
-21,
*, 50
., 100
, 150
, 200
500mVmin 750mVmin 1000ml/min .,
, 250
1
,
*
300
Time (min)
Fig. 4. Flux vs. time at various cross-flow rates for 20”Brix MF juice.
0’
, 50
.
, 100
.
,
.
150
, 200
,
, 250
.
, 300
Time (min)
Fig. 5. Membrane distillation of 20”Brix permeate with constant water addition - permeate flux with time at AT = 50°C and flow rate = 1000 mUmin.
160
S. Nene et al. /Desalination
microfiltered (0.14 p. Carbosep membrane, Orelis) 20”Brix cane juice or permeate. (Fig. 4). However microfiltered cane juice had a lower flux than raw sugar. This could be explained by the observation that the total polysaccharides of MF juice were higher than those in raw sugar, thereby decreasing the flux due to concentration polarization. The higher crossflow rate appeared to improve flux indicating that the influence of increasing shear rate on concentration and temperature polarization was evident. Similar results have been reported by Izquierdo-Gil et al. [2]. In addition to the above experiments, another experiment was performed with permeate at a flow rate of 1000 ml/min with constant water addition thus maintaining a uniform concentration throughout the run. The aim of this experiment was to study the flux decay in membrane distillation when the run conditions were similar to those in the sugar industry. The results (Fig. 5) indicate that it was possible to consistently remove
147 (2002) 157-160
water from the cane sugar solution at a steady state value approximating 10.0 kg/mYh. The results indicate that membrane distillation can create an energy saving niche for itself in removing water from clarified cane juice, using its sensible heat.
Acknowledgement The authors are indebted to the Indo-French Centre, New Delhi (IFCPAR) for financial support for this work.
References [I] [2]
D.P.Kulkami, Cane Sugar Manufacture in India, The Sugar Technologist’s Association of India, 1984. M.A. Izquierdo-Gil, M.C. Garciaand J.C. FemandezPineda, Direct contact membrane distillation of sugar aqueous solutions, Separ. Sci. Technol., 34(9) (1999) 1773-1801.