Benefits/ Evaluation of Pan
Circulator
By
Javed Hasan
(Senior Manager Process)
Shakarganj Mills Limited, Jhang
Introduction
Circulation of Massecuite in the pan while boiling play a
prime role in proper growth of crystals and exhaustion of
molasses.
The benefits associated with good circulation are:
 Quality: Improved crystal size distribution and low
sugar colour due to uniformity of fluid conditions
within the vacuum pan
 Recovery: A high massecuite dry substance
concentration is possible, leading to a higher crystal
yield and a lower purity of molasses.
 Capacity: Improved heat transfer leads to a higher
crystallization rate and increased throughput.
 Energy Efficiency: Use of vapor from later evaporator
effects becomes possible
Mechanical Circulation
Pan Stirrers if properly designed can significantly:
 Improve the performance of a batch pan.
 The assisted circulation improves heat transfer and shortens
the duration of Batch boiling, thus improving capacity.
Stirrers improves the quality of the high grade sugar produced.
Pan stirrers provide the option of achieving an acceptable heat
transfer with temperature difference as low as 20oC, compare to
at least 45-50oC in the absence of stirrer.
The use of low pressure vapor become possible, allowing
reductions in the factory steam requirements.
Mechanical Circulator Assembly
Mechanical circulator assembly consists of
the following elements
 a circulator carrying vanes or other
propelling means
 A vertical shaft
 A driving system connected with the shaft
The driving system usually consists of the
shaft, coupling, bearings, gearing, pulleys
and belts. The power is supplied by an
electric motor.
Top Mounted Mechanical Circulator
Advantages of Mechanical Circulation
 Quality improvement of product
 Reduction in water consumption
 Height of massecuite
 Capacity improvement
 Better heat economics
 Less deposition on calandria tubes
VACUUM PAN MECHANICAL CIRCULATOR
Design Specification
 The stirrer itself is located in the down take if it is an axial flow
impeller, or just below the down take in the case of a radial flow
impeller.
 Installed power should be in the range of 1-1.7 kW/m3
 Tip speed has to be kept below 7 m/s
 The impeller blade tip clearance shall be no less than 5% of
the impeller diameter.
 The stirrers shall be supplied with either
• A two speed motor
• Direct torque conrtol variable speed drive
Benefits
 Saving in strike time of up to 30%
 Good circulation maintained through the strike
 Provide more uniform grain
 Increased pan capacity by 20-30%
 Increase in crystal yield up to 5%
 The color removal has improved from 88% without
circulator to 92% with circulator
 Sugar conglomerates counts have been reduced by
about 80%
 Strike level in pans can be raised by 30-40 cm with the
use of stirrer
 Increase in heat transfer coefficients from 0.78
kW/m2/oC to 0.87 kW/m2/oC with stirrer
Effects of stirrer on
 Refine sugar colour
 Conglomerate count
 Sugar Quality
 Boiling Times
 Evaporation Rates and Heat Transfer Co-efficient
 Sugar production (T/Hr)
 Boiling time (Hr)
Comparison of Results
Description
No Stirrer With Stirrer
55.2
57.0
77
72
Color Removal %
89.9
91.3
Evaporation Rate
(kg/m2/Hr)
55.6
66.4
Sugar Production (T/Hr)
31.1
33
HTC (kW/m2/oC)
0.78
0.87
Pan Yield %
Conglomerate count %
Refined Sugar colour
No
Stirrers
Stirrers
1st Boiling Sugar
30
20
2nd Boiling Sugar
72
48
3rd Boiling Sugar
98
91
Description
Colours
Effect of the Stirrers on Boiling Times
Stirred Pan
Unstirred Pan
Boiling Time (h)
4.9
7.9
Strike Volume
(m3)
42.8
40.4
Massecuite Brix
94.67
94.73
Massecuite
Purity
54.47
55.30
14
8
Description
No. of Strikes
Quality of crystals
Types of Circulator
Mechanical Circulator
Mechanical Circulator
More than 249 Nos. bottom mounted
and 19 Nos. top mounted Mechanical
circulators are installed world wide
Comparison
 In top mounted mechanical circulators, the
circulator shaft extends through the height
of the pan. (between 5-8 meters)
 Bottom mounted mechanical circulators
offer a distinct advantage that in
comparison to top mounted mechanical
circulators, the shaft length is reduced to
1.7-2.5 meters as compared to 5-8 meters
Novel Mechanical circulator Assembly
Bottom Mounted Mechanical Circulator
Feature of Mechanical circulator Assembly
Description
Prior Art
Present Invention
Shaft Length (Bottom
mounted)
1.7 - 2.5 m requiring
additional support
Shaft Diameter
More, requiring large size Much less, resulting in use of
components
compact components
Compactness
Large and Bulky
Small and concise totally
requiring needs support eliminating the need for any
structure and couplings support structure and couplings
Weight
More weight
60% less weight
Power Consumption
High
Low
Radial and axial loads
on shaft
Very high
Very Low
0.5 - 0.56 m eliminating additional
support
Feature of Mechanical circulator Assembly
Positioning of
sealing means and External to Vacuum pan
bearing
Internal (in a special housing)
Gear Box
worm, Bevel or Helical
Inline, output hollow spline,
plenetary gear box
Bearings
Unshielded requiring
periodic greasing
Shielded, does not require
periodic greasing
Maintenance Cost High
Mechanical
Efficiency
Negligible
Varies between 40-90% 98% efficient
Mechanical Circulator
Speed and Power Requirements
PAN SIZE
DOWNTAKE
3
(ft )
DIAMETER
PROPELLER
DIAMETER
H.P
RPM
CIR.
RATE
(ft3/Min)
1000
39 ¾''
38''
60
100
2500
1500
69 ½''
68''
60
68
4500
2000
81''
72''
75
68
5000
2400
72''
70''
75
73
5090
Comparison of Pan
Capacity Vs Installed Power
Pan Capacity
Installed Power
25T – 30T
22kW
30T – 40T
30kW
40T – 60T
45kW
60T – 80T
55kW
80T – 100T
75kW
100T – 120T
90kW
120T – 150T
110kW
• Operating at 33/48/63 RPM with VFD depending upon pan
duty,design and operation on various viscosities
Conclusions
The installation of mechanical stirrers to pan has to a no. of
improvements in the performance of pan both in respect of
sugar quality, exhaustion efficiency, reduction in strike times
and increase in sugar production rate
The most consistent improvement in terms of sugar quality has
been in lower colors, reduced color formation in the pan, and
more homogeneous crystallization conditions have lowered the
color in the crystal
The color removal has improved from 88% without circulator to
92% with circulator
Pan yields and heat transfer co-efficients have been improved
and taken together are worth approximately 10% additional pan
capacity
Less deposit on the tubes due to friction of the faster circulating
massecuite
Sugar conglomerates counts have been reduced by about 80%
Thanks