FIELD OF INVENTION:
The present invention relates to the field of mechanical engineering. More specifically, it relates to processing machinery for the concentration of sugar syrups and the like. In particular, it pertains to mechanical circulators in vacuum pans. The present application is a divisional application of our application no. 879/DEL/2006 titled "Improved Vertical Continuous Vacuum Pan".
BACKGROUND AND PRIOR ART OF THE INVENTION:
Definition of important Terms:
1. Massecuite: (Pronounced = Mess-kit)
It is a mixture of crystals and mother liquor discharged from a vacuum pan.
2. Calandria: Equipment consisting of closely spaced metal tubes for heat
exchange.
In sugar factories, evaporation and crystallization of the sugar syrup is carried out in specially designed machinery called vacuum pans.
Vacuum Pans are of two types - Batch Vacuum Pans & Continuous Vacuum Pan.
Batch vacuum pan (Batch evaporating crystallizer): It consists of a vertical cylindrical shell and a calandria in the lower part. The shell is surmounted by a dome with an entranment separator juice droplet catcher) to prevent organic contamination of the condenser water. The design of batch vacuum pans has evolved to a practically uniform basic geometry and consists of:
- a central downtake
- straight side walls
- fixed calandria
- calandria tubes of diameter 100mm and length 800-1300 mm
- bottom angle 18-25 deg. and
- means to improve circulation.
In case of calandria pans, W-shaped bottom is preferred over the conical bottom, since W-bottom is efficient in distributing the massecuite. (Circulation in Vacuum Pans - Rein, P.W., Echeverri, L.F. and Acharya, Sumanta - Journal American Society of Sugar Cane Technologists, Vol.24, 2004)
Continuous vacuum pan: These are of two types viz. vertical and
horizontal.
Vertical continuous vacuum pan consists of several stirred crystallization
compartments or chambers with calandria (similar to a batch evaporation
crystallizer), which are mounted on top of each other. The principal layout
of each compartment resembles a batch evaporating crystallizer.
Importance of circulation in syrup processing using vacuum pans
The importance of massecuite circulation in vacuum pans is well established. It has impact on energy, massecuite exhaustion and on sugar quality. As a result considerable efforts have been made worldwide in designing better, improved or novel means for improving circulation in vacuum pans. Mechanical circulators are one of the most commonly used means and these have been well-described in the prior art. (Patent Nos. US387388, US1133821, US1476331, US1785530, US458882, US2355397, GB1061708, US3622387, US3636753, DE2922265, EP0065775, FR2695837).
Mechanical circulation is associated with various advantages at the level of industry viz.
i. Quality improvement of product Better quality of sugar crystals. This is a consequence of the better circulation leading to more homogeneous crystallization conditions within the pan. The crystals grow more evenly and there are fewer mother liquor inclusions (van der poel 1980, Rieger et al. 1989: Zukerindustrie, 105, 237-240). There is less colour in sugar and reduced risk of sugar losses by local overheating.
ii. Reduction in water consumption: In addition stirring also reduces centrifugal wash water consumption by 50% (van der poel 1980: Zukerindustrie, 105, 237-240).
iii. Height of Massecuite: The height of massecuite above the calandria may be pushed considerably above what is reasonable with natural circulation. Hence a gain in capacity and a decrease in graining volume.
iv. Capacity improvement: The mechanical circulation improves heat transfer and so shortens the duration of the batch boiling, thus improving capacity.
v. Better heat economics: Small temperature differences (<12 K) between heating steam and massecuite are only possible with the use of stirrers. A reliable operation without stirrers (mechanical circulation) is not possible and may lead to sedimentation of the crystals (Austmeyer, K.E.; Schliephake, D.; Ekelhof, B.; Sittel, G. (1989): Zukerindustrie 114, 875-878). The use of lower pressure vapours becomes possible (e.g. coming from the 2nd or 3rd evaporator effect), allowing reduction in the factory steam requirements.
vi. Less deposition on calandria tubes: There is less deposit on the tubes, due to the abrasion effect by friction of the circulating crystals.
Those claiming rational circulation without the use of stirrers (mechanical circulators) do so at the cost of simplicity of design and heat economy. (Indian Patent Nos. IN145885, IN169913 and International Patent Nos., US4120745, EP0201629, DE3839182, FR2695837 and Patent Application No. IN/PCT/2002/02149/CHE).
It is, therefore, evident that the installation of mechanical circulators gives all the advantages associated with good circulation.
Mechanical circulator assembly in general consists of the following elements:
- a circulator carrying vanes or other propelling means
- a vertical shaft and
- a driving system connected with the shaft
The driving system usually consists of the shaft, coupling, bearings, gearing, pulleys & belts. The power is supplied by an electric motor.
The circulators mounted in the pans can be top-mounted or bottom mounted.
In case of top-mounted mechanical circulators, the circulator shaft extends through the height of the pan (between 5-8 metres) and projects at its upper end through the top cover of the pan (Patent Nos. US387388, US1133821, US247542, US1785530, GB458882, GB1061708, EP0065775). In other cases, the circulator shaft projects into the pan through its bottom wall (Patent Nos. US1476331, US2355397, FR2695837).
Bottom mounted pans offer a distinct advantage that in comparison to top-mounted mechanical circulators, the shaft length is reduced to 1.7- 2.5 metres as compared to 5-8 meters.
However, despite the advantages of bottom mounted circulators, still top
mounted circulators are popular in Industry because of practical
advantages as follows:
i. No need for elaborate support structure: Top mounted circulators can easily be fitted onto the top of the vacuum pan. In contrast, bottom-mounted mechanical circulators require an elaborate support structure including the foundation for resting the large & heavy gear drive and/or the gear box and for mounting the bearings because the pan is at considerable height from the floor of the plant.
ii. Free availability of space: In top mounted pans, space for mounting the circulator is not a limitation. However, in case of bottom mounted circulators, it can pose practical problems. In case of conventional pans, which are installed at considerable height, with other processing equipments installed below them e.g. cooling crystallizer, space becomes a constraint.
Irrespective of whether the existing mechanical circulators are bottom mounted or top mounted, still they pose certain disadvantages viz.
a. High capital investmentb. High maintenance costs
c. Leakages- air and/or syrup leakages
d. Increase energy load i.e. higher power consumption
Main contributing reasons for these disadvantages are:
1. Long circulator shaft length: Increased length of the shaft is associated with several drawbacks viz.
a. Load: Increased axial as well as radial loads requiring additional means to counter these loads.
b. Vibrations: More Bending vibrations, which in turn have adverse
affect on seals, prove particularly troublesome, and require additional
and supplemental sealing means (Patent Nos. US5078506).
c. Bearings: Bearing life is reduced;
d. Accessories: An auxiliary bearing used at the free end of longer
shaft to reduce vibrations (Patent Nos. US1133821, GB247542,
US1785530) has been found to create problems of alignment,
lubrication, corrosion and maintenance.
e. Supports: Additional support is required to keep the long shaft
aligned like a flange coupling or other means (Patent Nos.
GB458882, US1133821).
f. Shaft diameter: Also with the increase in the shaft length, in order to
transfer the required torque to the circulator, the diameter of the shaft
has to be increased. This necessitates the use of higher power and
larger accompanying/supporting components like gears, bearings,
seals, rings, etc. and also an elaborate housing/foundation there for.
2. Conventional sealing means: used in pan circulator assemblies installed in vacuum pans for sealing purposes consist of packing rings (gland packing) packed tightly around the circulator shaft and compressed by an adjustable component called gland pusher, provided with a threaded nut and spacer. It is mounted in the wall of the pan. The disadvantages of above are as follows:
a. Periodic adjustments: In order to compensate for the f fictional
wear, periodic adjustments are required to be made. If the operator
fails to detect such wear, it causes loss of vacuum and leakage
b. Additional wean Also attempts to adjust the stuffing box in a way to
provide satisfactory seal for extended periods causes additional
wear.
c. Periodic replacement: of the packing rings (glands) is also required.

d. Contamination: Danger of contamination of contents of the vacuum
pan (syrup) by the gland in case of bottom-mounted mechanical
circulators.
e. Power loss: in packing rings (glands) varies from 0.5 hp for smaller
circulator shafts, and up to 5.0 hp for larger shafts (Joshi, M.V.:
Process Equipment Design, 2nd Edition, Reprint 1987, page 399).
Mechanical Seals are also used in vacuum pans for the same purpose i.e. sealing. However, unlike in the present invention, where the sealing means is disposed entirely inside the vacuum pan in a special housing, these are disposed entirely outside the vacuum pan. They are exposed to high radial and axial movements due to long circulator shaft length and have proved troublesome requiring additional and supplemental sealing arrangements such as those described in Patent No. US5078506.
3. Bearings: The bearings used in pan circulator assembly are disposed
entirely outside the pan to give additional support to long circulator shaft.
The bearings are large in size and capacity due to bigger shaft diameter
and greater axial and radial loads.
4. The gearboxes: used in conventional pan circulator assemblies
are of bevel, worm or helical type (Patent Nos. US387388, US1133821,
US1476331, US2355397, DE2922265, EP0065775). The power is
supplied by an electric motor. The disadvantages of these gearboxes are
as follows:
a. High power consumption - High co-efficient of friction requires
higher drive energy;
b. Heavy weight - require elaborate support structure;
c. Large size - require more installation space;
d. High Speed Reduction Ratio achieved only at the cost of efficiency
and size;
e. Radial loads within the gearbox add to that of the circulator shaft;

f. Comparative Lower torque transmission capacity as compared to
the one used in the present invention;
g. Initial assembly and installation cost and time are much more;
h. Maintenance requirements are high;
i. Time & labour involved in ensuring correct alignment of gearbox
and driven member are high; j. Gearbox is not in line with the shaft which is also one of the
reasons for requirement for additional support structure, k. cost and complexity of couplings; I. Low reliability; m. Higher noise levels; n. Inferior efficiency - mechanical efficiency varies between 40-90%.
The present invention has been able to overcome the disadvantages associated with the prior art mechanical circulators installed in vacuum pans in a simple but novel manner. The innovation involved in the present invention lies in the novel features of construction and, combination and relation of readily available, off-the-shelf components making the bottom-mounted pan circulator assembly compact, reduced in size & weight, cost-effective, maintenance-free and energy efficient.
A search of Indian Patent databases reveals that no patent as for the present invention has been described in the prior art.
OBJECTS OF INVENTION:
The principal object of the invention is to provide a bottom-mounted mechanical circulator assembly for a vacuum pan which is of compact construction, reduced in weight & size and energy efficient.
Another object is that it to provide a mechanical circulator assembly in which maintenance requirements are negligible and if at all required, the

time for disassembly and reassembly for repairs is short and the need to realign the drive shaft every time is avoided.
Still another object of the invention is that it can also be readily combined with or installed on existing vacuum pans used for concentration of sugar syrups or the like, in the upwardly tapering cone of the W-shaped bottom of the existing vacuum pans, whether batch or continuous.
Other objects reside in the novel combinations and arrangements of parts and novel details of construction, all of which will be fully described in the course of following description.
SUMMARY OF THE INVENTION:
The invention involves certain novel features of construction, combination, relation and arrangement of components, of which a typical embodiment is disclosed in the description and accompanying drawings making the mechanical circulator assembly compact and reduced in size.
In the present invention, the circulator shaft length has been reduced considerably to only 0.50 - 0.56m as compared to conventional shaft length of 5.0 - 8.0m (in case of top-mounted mechanical circulator) and 1.7- 2.5 m (in case of bottom-mounted mechanical circulators).
This has been achieved by two factors:
a. Positioning: Positioning of the sealing means & bearing assembly in a special sealing and bearing housing disposed entirely within the vacuum pan; and
b. Use of improved gear-box: Use of compact & light weight gearbox of inline planetary type having a hollow spline output and hollow input with key arrangement for direct inline flange mounting of the drive.
STATEMENT OF INVENTION:
Accordingly, the present invention, provides a vacuum pan assembly (1)
for evaporating-crystallizing a sugar solution equipped with comprising,
a mechanical circulator assembly;
a circulator shaft with vanes or other propelling elements fixed to a hub
mounted on its inner end;
a gearbox driven by an electric motor at its other (outer) end;
sealing means;
a bearing; and
a split retaining ring disposed below the said bearing;
the said mechanical circulator assembly mounted in the upwardly tapering
cone of W-shaped bottom of the vacuum pan along its axis;
wherein the said mechanical circulator assembly is of compact
construction with considerably reduced circulator shaft length
BRIEF DESCRIPTION OF THE DRAWINGS:
The structural arrangements of the present invention will be best
understood by reference to the accompanying drawings.
Flg.1 is the elevation view of a vacuum pan in which the mechanical
circulator assembly of the invention has been installed.
Flg.2 is the enlarged view of the mechanical circulator assembly shown in
Fig.1.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE DRAWINGS:
A search of the prior art has revealed that though it is highly desirable to install a bottom-mounted mechanical circulator in the upwardly tapering cone of W-shaped bottom of the vacuum pan used as an evaporator-crystallizer for sugar solutions, yet there are number of factors which work against their use as already discussed above.
Accordingly, the present invention provides a vacuum pan assembly for
evaporating-crystallizing a sugar solution comprising:
a mechanical circulator assembly;
a circulator shaft with vanes or other propelling elements fixed to a hub
mounted on its inner end;
a gearbox driven by an electric motor at its other (outer) end;
sealing means;
a bearing; and
a split retaining ring disposed below the said bearing,
the said mechanical circulator assembly mounted in the upwardly tapering
cone of the substantially W-shaped bottom of the vacuum pan along its
axis;
wherein the said mechanical circulator assembly is of compact
construction with circulator shaft length.
In an embodiment of the present invention the sealing means and the bearing of the mechanical circulator assembly are disposed entirely inside the vacuum pan in a special housing.
In another embodiment of the present invention the sealing & bearing housing is provided with an inverted cone.
In still another embodiment of the present invention the sealing means is having a mechanical seal made of Silicon Carbide.
In yet another embodiment of the present invention the bearing is mounted in the sealing and bearing housing is a shielded deep groove ball bearing.
In a further embodiment of the present invention the gearbox and gear drive are co-axial (inline) and are mounted directly on to the bottom of the vacuum pan without any coupling and support structure.
In one more embodiment of the present invention the mechanical circulator assembly has an inline gear box which is of planetary type having a hollow spline output and a hollow input with a key arrangement for direct inline flange mounting of the drive.
In the present invention, the circulator shaft length has been reduced considerably to only 0.50 - 0.56 m as compared to conventional shaft length of 5.0 - 8.0m (in case of top-mounted mechanical circulator) and 1.7 - 2.5 m (in case of bottom-mounted mechanical circulators). This has been achieved by two factors -
positioning of the sealing means & bearing assembly in a special sealing and bearing housing within the vacuum pan; and

use of compact & light weight gearbox of inline planetary type having a hollow spline output and a hollow input for direct inline flange mounting of the drive.
Fig.1 shows the elevation view of a vacuum pan assembly (1) in which mechanical circulator assembly (2) of the invention has been installed in the upwardly tapering cone of the W-shaped bottom (3). The vacuum pan is supported by means not shown in the drawings from the floor of the plant.
Fig.2 is the enlarged view of the mechanical circulator assembly (2). According to a feature of the present invention there is provided a novel sealing and bearing housing (4) disposed entirely inside the vacuum pan between the base of the upwardly tapering cone of W-shaped bottom (3) and the bottom level of the calandria (5).
The said sealing means comprise a gun metal bushing (6), lip seal (7) and a mechanical seal (8) made preferably of Silicon Carbide instead of the conventional method of packed stuffing box and gland. The stationary and rotary seal rings of the mechanical seal are held in place by flexible O-rings (9). Silicon Carbide is preferred over other materials because of low heat generation eliminating the need for cooling means and its self lubrication property. In materials like Tungsten Carbide due to high generation of heat the small quantity of juice coming in contact with the seal gets burnt creating carbon resulting in wear. The advantages of mechanical seal in comparison to the conventional sealing means are well known viz.
a) Efficient in leakage plugging
b) Self-lubricated- No periodic lubrication required
c) Self-adjusting - No periodic adjustments to compensate for
frictional wear needed
d) Suitable for high temperature and pressure conditions
e) Has extended life - has very low coefficient of friction
f) Very low maintenance requirements
g) There is no risk of contamination of contents of the vacuum pan
due to degradation of lubricants and/or leakage.
The bearing (10) is housed in a bearing receptacle plate (11) attached to the sealing and bearing housing (4) and held in place by a bearing retainer plate (12). A shielded deep groove ball bearing (10) is used which is well adapted to counter both the axial and radial loads of the circulator shaft. It also has reduced noise levels. The size of the bearing (10) used is also small due to reduced diameter of the circulator shaft (13) owing to its shortened length and decreased axial and radial loads. Another advantage of the bearing (10) used is that it does not require periodic lubrication and operates with negligible maintenance.
Decreased axial and radial loads of the circulator shaft (13) resulting in much decreased vibrations and practically nil alignment problems add to the life of both the sealing means and the bearing (10).
The sealing and bearing housing (4) is provided on its outside by an inverted cone (14). The advantage of the said inverted cone (14) is that it avoids stagnation areas adjacent to the housing (4) and assists in the circulation of the massecuite in the vacuum pan. Further advantage of the inverted cone (14) is that it provides reinforcement to the sealing and bearing housing (4).
At the lower (outer) end of the circulator shaft (13) is mounted an inline hollow spline planetary gear box (15) eliminating the use of coupling. The gearbox (15) has a hollow input with key arrangement for direct inline flange mounting of the drive (16) without coupling. The use of such a
gearbox (15) has many advantages over the conventionally used gearboxes in vacuum pans as follows:
a) Inline: The Planetary System is co-axial (inline) and is particularly
suitable for high torque, low speed applications.
b) Efficiency: It is extremely price competitive against other gear
systems and offers high efficiency with minimum dimensions. The
planetary drive can be up to 98% efficient and, critically, is able to
provide extremely low speeds without much loss of efficiency. The
efficiency losses for most gearboxes (excepting planetary types) are
anywhere between 5% (Helical and Spur) and 30% (Worm) per
stage. This is not the case with planetary gearboxes, which minimise
efficiency losses to just 1% per stage (Planetary gearboxes are the
energy saving choice - Website:
http/www.engineeringtalkcom/newsybrv/brvl 04.html)
c) Energy efficient: Ranet gears have a very low coefficient of friction.
Less energy is required to turn them and so more of the driving force
is converted into useful turning force after being geared down. One
major benefit is that the power consumption is much lower than the
conventional gear box and so saves a lot of money.
d) Higher reduction ratios: Planetary gear trains are able to deliver
high reduction ratios in small packages, and to transmit several times
the torque of similarly sized, conventional gear units.
e) Compactness: Planetary gearbox is smaller and lighter, up to half
the size and 60% lighter than conventional heavy engineered
gearboxes. They require little installation space. These features of
the inline planetary drive system eliminate the requirement of
enlarged space and elaborate support structure to mount them.
f) Technical Advancement: Compared with a parallel shaft
arrangement, a planetary gearbox in high torque/intermittent
operations can often achieve the same ratio with one fewer reduction stage, with cost and dimension savings.
g) Reduced Maintenance: Other than routine oil changes, no maintenance is required through the design life, not even replacement of bearings.
h) Coupling elimination: The elimination of the cost and complexity of couplings.
i) Easy Alignment: Elimination of the time and labour involved in ensuring correct alignment of the gearbox and the equipment it is driving make it especially suitable for circulator shaft mounting.
j) Reduced radial loads: Direct drive through shaft mounting also avoids radial loads imposed by belt drives. The planetary gearbox also has tolerance to handle radial loads from the equipment it is driving.
k) Reliability: Finally, high levels of reliability are a feature of the planetary design due to the distribution of stress among several load-bearing components.
The gearbox (15) and the drive (16) are directly mounted on to the bottom of the vacuum pan housing giving the mechanical circulator assembly (2) compactness along with all the advantages of short circulator shaft length.
With such a short shaft (13) length of only 0.50-0.56m, there is a drastic reduction in both the radial and the axial loads. This scales down the need to counter these loads and correspondingly lesser number and lower capacity components or parts can be used e.g. neither there is need for additional/auxiliary support means or bearings nor there is requirement of additional/supplemental sealing means or bearings with higher load tolerance capacities.
Benefits of reduced loads and vibration include extended bearing and seal life respectively, a critical component of machinery reliability.
The shaft (13) is also of lesser diameter enabling the use of smaller accompanying/supporting components or parts like seals, bearings, gears, rings, etc.
After aligning the shaft during initial installation, there is practically nil necessity to realign it after every disassembly and reassembly for repair or maintenance of gear box or motor. The reduction in circulator shaft length by using the novel means as described has not only made the mechanical circulator assembly (2) compact and energy efficient but has also reduced the capital and maintenance costs in comparison to the existing mechanical circulators.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the spirit and scope of the present invention as described.
For easy reference, a comparative table showing the novel features of the present invention over the existing prior art is given in Table 1 below:
(Table Removed)

LIST OF REFERENCE NUMBERS:
1. Vacuum Pan Assembly
2. Mechanical Circulator Assembly
3. W-shaped bottom
4. Sealing & Bearing Housing
5. Calandria
6. Gun Metal Bushing
7. Lip Seal
8. Mechanical Seal
9. O-Rings
10. Bearing
11. Bearing Receptacle Plate
12. Bearing Retainer Plate
13. Circulator Shaft
14. Inverted Cone
15. Planetary Gear Box
16. Drive/Motor

CLAIMS: We Claim:
1. A vacuum pan assembly (1) for evaporating-crystallizing a sugar
solution comprising:
a mechanical circulator assembly (2);
a circulator shaft (13) with vanes or other propelling elements fixed to a
hub mounted on its inner end;
a gearbox (15) driven by an electric motor (16) mounted at its other (outer)
end;
sealing means;
a bearing (10); and
a split retaining ring disposed below the said bearing (10),
the said mechanical circulator assembly (2) mounted in the upwardly
tapering cone of the substantially W-shaped bottom (3) of the vacuum pan
along its axis,
wherein the said mechanical circulator assembly (2) is of a compact
construction with a considerably reduced circulator shaft (13) length.
2. The assembly (1) as claimed in daim 1, wherein the sealing means and
the bearing (10) of the mechanical circulator assembly (2) are disposed
entirely inside the vacuum pan in a spedal sealing & bearing housing (4).
3. The assembly (1) as claimed in Claim 1 & 2 wherein sealing & bearing
housing (4) is provided with an inverted cone (14).
4. The assembly (1) as claimed in Claims 1 to 3, wherein the sealing
means have a mechanical seal (8) made of Silicon Carbide.

5. The assembly (1) as claimed in Claims 1 to 4, wherein the bearing (10)
is mounted in the sealing and bearing housing (4) is a shielded deep
groove ball bearing.
6. The assembly (1) as claimed in Claims 1 to 5, wherein the gearbox (15)
and gear drive (16) are coaxial and the gearbox (15) is mounted directly
onto the bottom (3) of the vacuum pan without any coupling and support
structure.
7. The assembly (1) as claimed in any of the preceding daim 1 to 6,
wherein the gearbox (15) is an inline direct mounted planetary gearbox
(15) with hollow spline output and hollow input with key arrangement for
direct inline flange mounting of the drive.
8. The assembly (1) as substantially as herein described with reference to
the accompanying drawings.