Title of Invention


Abstract A vacuum pan for sugar industry and other applications is disclosed wherein the central downtake is supplemented by a circular ring-shaped downtake that reduces the travel distances involved in the massecuite recirculation. This reduces strike times and enhances pan productivity by about 15-25% and gives a more uniform crystal size and better mixing of the massecuite. The placing of the additional downtake is such as to, ful1hermore, equalise said travel distances between different regions A, Band C of the calandria faces and the downtakes. Region A covers about 10-15% of the calandria face area round the central downtake while B and C, which are circular ring-shaped cover the remainder. The additional downtake is located symmetrically between B and C. A new solution feed system is described.
Full Text This invention relates to vacuum pans and more particularly to batch type vacuum pans.
Vacuum pans are used for evaporation and crystallisation of sugar solutions in the manufacture of sugar. The solution is introduced into the pan and concentrated by evaporation, the necessary heat being supplied through steam or other heating medium. The evaporation is carried out under vacuum the effect of which is to reduce the boiling point of the solution and prevent/minimise the inversion of the sugar contained in the solution.
A vacuum pan of the sugar industry, therefore, comprises a vertical cylindrical vessel which holds the sugar solution to be concentrated and houses a calandria of tubes which constitutes the heat transfer surface. Heat flows from the steam introduced around the tubes, through the tube walls into the solution flowing in the tubes. Adequate space above the sugar solution level is provided in the vessel to ensure effective separation of the vapour generated and the entrained solution. The vapour exits from the vessel through an outlet at or near the top thereof and goes to a barometric condenser that provides the vacuum.
The sugar solution flows upward through the vertical tubes and across the upper tube-sheet of the calandria- The solution then flows down through a downtake to the region of the vessel below the said tubes and subsequently enters the tubes through their lower mouths, thus completing th^ circulation. The driving force for this natural circulation is the density differences arising from the heating of the solution and the buoyancy provided by the vapour formation in the solution The vessel further comprises connections for the various streams including steam and condensate and a suitable save-all. Other desired/necessary fittings and accessories are also pro\ ided. The vessel also comprises the required instrumentation and control accessories for the control and regulation of the various streams and for monitoring the operation of the pan

Described hereinabove is the basic construction of the vacuum pan of prior art and of the invention. The vacuum pan of prior artand the invention isgeneralh similar to a natural circulation short-tube vertical (STV) type of e\aporator in construction and is therefore also usable solely as an evaporator. The mam difference between said STV evaporators and the vacuum pans for evaporation and crystallisation is that the tubes and downtakes of the latter have greater diameters suitable for handling supersaturated solutions having high viscosities and containing crystals in suspension.
The vacuum pan of the invention is primarily for evaporation and crystallisation of sugar solutions but is simply and easily adapted for concentration and crystallisation in case of other solutions. It is also easily adapted, as mentioned above, for use solely as an evaporator. Such abovedescribed applications and other applications of the vacuum pan of the invention are within the scope of the invention.
However, in the further description hercinbelow. reference is made only to the application thereof in the sugar industry, that is, in the evaporation and concentration of sugar solutions. This has been done in the interests of conciseness.
The sugar solution charged to a vacuum pan is also referred to as the "massecuite"or mass" for short and furthermore, also as the "mother liquor" or "syrup". These terms are used interchangeably in tins specification unless otherwise required by the context. Said sugar solution charge is also referred to as the "strike" by some workers in the industry particularly during and at the completion of the process of evaporation and crystallisation of said charge. The level of the cliarge in the pan is referred to as the "strike level" and the time from the charging of the solution to the completion of evaporation and crystallisation thereof is referred to as the "strike time".

Said charging of the pan is done in stages. In the first stage, the sugar solution is charged into the pan to a level slightly above the top tube plate, that is, above the upper mouths of said tubes of the calandria bundle. This is the graining charge and is concentrated to suitable supersaturation for graining to occur. During the graining operation and subsequently, controlled addition of solution is done to maintain the charge level at the desired point above the mouths of the tubes Following the graining, the crystals grow and when they reach the desired size and quantity the charging is discontinued and the massecuite containing the grown crystals is discharged from the pan. In an alternative arrangement, said graining is done outside the pan and the seeded solution introduced into the vacuum pan. To encourage seeding/graining seeding agents are also optionally employed.
It is important to maintain the rate of boiling in the vacuum pans at an adequately high level as otherwise problems arise in pan operation. For this, an essential requirement is that the rapid circulation of the massecuite through the tubes, across the upper tube-sheet, down the downtake and back into the tubes is maintained.
An important element of this circulation is the generally horizontal movement of the massecuite across said top tube-sheet. This movement does not appear to have been studied in the prior art. in particular the question of reducing the travel distance during the said horizontal movement This invention has studied said horizontal movement and provides solutions to reduce said travel distances This is novel.
The massecuite flows out from the tops of said tubes and moves along generally horizontal paths to the downtake of the pan. Two types of downtakes are known in the prior art; the central downtake and the peripheral downtake. A central downtake is circular in section and is

concentric with the axis of the said vessel while a said peripheral downtake is generally annular circular and also concentric with the vessel. A said peripheral downtake extends all round between the calandria bundle and the inside wall of said vessel. In the peripheral downtake arrangement, arms are provided by which the calandria is attached to the vessel wall, said arms extending across the downtake gap. The calandria bundle in this case is, therefore, often referred to as the floating calandria.
Consider a small volume of the massecuite at the top of one of the said tubes. The shortest path for said small volume to the downtake is along the calandria radius extending from the position thereof to the peripheral or central downtake as the case may be. This shortest path is referred to herein as the minimum path. The path a said small volume would actually follow would depend on several hydrodynamic factors but the average of possible paths followed by said small volume could be expected to be related to, that is proportional to said minimum path. Said average is also referred to as the travel distance. This invention provides for reduction of said minimum paths, and therefore of said travel distances from various positions on said upper tube-sheet. This is achieved in the vacuum pan of the invention by the provision of one or more additional downtakes, that is, by provision of a plurality of downtakes in the vacuum pan. This is novel. As mentioned, the vacuum pan of prior art comprises just a single downtake, either of the peripheral or the central type.
The abovementioned analysis of the said horizontal movement, travel distances and the minimum paths has apparently not been done in the prior art and is novel. It suggests that any and each said additional downtake would contribute in speeding up said horizontal movement and increase the speed of said circulation. However, this analysis is presented without commitment as the basic premise of this invention has been established by the experimental investigations carried out by this inventor during which it was found that addition of every extra downtake resulted in better

circulation and in the reduction of strike times. Reduced strike times as would be expected lead to increased pan productivity.
The movement of the massecuite from the bottom of the singular downtake of the prior art to the bottom mouths of the said tubes can be expected to be analogous to the flow phenomena observed above the calandna. For each point on the face of the bottom tube-sheet there would be a said minimum path, and the said average path, that is, said travel distance. However, there is usually greater agitation in this region particularly if the pan comprises a stirrer/agitator. This space is usually referred to as the graining or seeding volume. Many more possible paths can be expected here for each point on the bottom tube-sheet and this could lead to greater deviation of the said average paths(travel distances) for the various points from their respective minimum paths. Nevertheless, the proportionality between said minimum paths and travel distances can be expected to hold here too. The experiments carried out by the inventor seemed to confirm this. In view of the analogous nature thereof, said region below the calandria is not discussed in detail herein in the interests of conciseness. But it will be observed that each reduction in said minimum paths and travel distances above the calandna by means of said additional downtakes has a similar and complementary effect below the calandna.
It will be observed from the above, that the downtake of prior art is a recirculationary downtake the purpose whereof is to provide a recirculationary path for the massecuite. In contrast, the purpose of the additional downtakes of the invention is to cut down said travel distances and to preferably equalise said travel distances for various regions of the top and bottom surfaces of the calandria by suitable location of said additional downtakes.
Thus, the object of this invention is to provide one or more additional downtakes in the pan in addition to the central downtake of prior art or the said annular peripheral downtake of prior art. Said additional downtakes reduce said minimum paths and travel distances both above and below

the calandria and speed-up circulation. They increase boiling rates and improve the heat transfer across the tubes. When a downtake is provided in addition to a central downtake(or a peripheral downtake). it provides scope for reduction of the diameter of the latter. This offers reduction in the size and cost of the vessel and also provides other cost benefits. It increases fluid velocity through the tubes giving better heat transfer leading to increased pan productivity.
Another object of the invention is to generally equalise said travel paths from and to the various positions on said upper and lower tube-sheets. For this, this invention provides for the break¬down of the upper tube-sheet into different regions, the said minimum paths(travel distances) from said regions being reduced by provision of said additional downtake(s) of the invention and preferably equalised by provision of suitable locations therefor.
According to the invention, therefore, there is provided a vacuum pan for evaporation and crystallisation, comprising a vessel for holding the solution to be evaporated(concentrated), or to be evaporated(concentrated) and crystallised, and a calandria for heat transfer from steam or other heating medium to said solution through the tubes thereof, and wherein, during operation, said solution recirculates, moving down a recirculationary downtake and up through said tubes, said pan being characterised in having one or more additional downtakes provided for the purpose of reducing the travel distances involved in said recirculation.
Said vessel in the vacuum pan of the invention is generally cylindrical with dished top and dished or conical bottom. It is usually of carbon steel in the sugar industry and is of welded construction. The vessel is usually in four parts: the bottom dishedfor conical) part, the heater part that houses the calandria. the middle or{separation) part that provides space for said vapour-liquid separation and the top dished part. Flanged joints are provided between the parts or welded construction is used. Sugar industry pans are often as large as five metres diameter or

more. The calandria is housed in said heater part and comprises a bundle of short, large diameter tubes in the manner of a shell and tube heat exchanger. Steam is introduced outside the tubes while the solution to be concentrated flows within. A central recirculationary downtake is provided in the calandria. It is concentric with the vessel and is usually of circular cross-section. Said downtake cross-sectiort may be upto about 40% of the total cross-sectional area of the tubes.
The solution feed is generally at the bottom but may be positioned above the top tube-sheet of the calandria. In case of the latter, suitable distributors are provided to distribute the solution over the tube-sheet area. Distributors are also used sometimes in the case of bottom feed. However, if the feed is at the bottom stagnation occurs. The vapour leaves the vessel from the top and goes to a barometric condenser. A save-all is provided at the top in the vapour path. The vessel further comprises desired and/or necessary accessories such as lighting arrangement for the vessel interior, sight glasses for observation, sampling arrangements such as a proof stick and others. Necessary instrumentation and control accessories are also provided such as for control and regulation of the various feed streams including steam and condensate, for pressure, temperature and vacuum measurement. The vacuum is provided by a barometric condenser but other systems are within the scope of the invention.
In another construction, the said recirculationary downtake is provided around the calandria, that is, between the calandria and the vessel wall. This annular, circular gap constitutes the said recirculationary downtake. The calandria is mounted on the inside wall of the vessel by means of arms extending from the calandria across said gap. This is the floating calandria arrangement. Ouier calandria arrangements are within the scope of the invention as die additional downtakes of the inventions arc easily adapted to any of the herein mentioned and other constructions.

Other configurations and shapes of the vessel and its components and parts, other materials of constructions, other sizes, dimensions and proportions, other configurations for the calandria and the mounting thereof, other joining arrangements between said parts are within the scope of the invention.
Said additional downtakes of the invention may be circular in shape or linear or curved. They may be annular in configuration with a circular orientation or other. The cross-section of the additional downtake(s) of the invention may be circular, elliptical, cross-shaped or any one of the other possible shapes/configurations. Said cross-section may be uniform along the downtake or may be convergent or divergent. The axes of said additional downtake(s) may be straight and parallel to the vessel axis or inclined thereto. Said axes may also be curved. The edges of said additional downtakes of the invention may be regular or otherwise and the downtake surfaces may be plain or comprise grooves or may be of other patterned construction, for example, having spiral or helical ridges or channels.
The invention provides for substantial equalisation of said travel distances from various
parts(regions) of the calandria tube-sheets(calandria faces). The notional division of said
faces into regions may be sectoral, segmental(by means of chords), through concentric rings or by a non-regular method or another or may be a combination of said methods of division.
Pans of upto five metres diameter or more are found in the industry. The calandria comprises tubes of diameter ranging from about 90 to 150 mm and length from about 900 to 1300mm. The diameter of said central recirculationary downtake ranges from about 25% to 30% of the vessel diameter. When said additional downlakes of the invention are provided it becomes feasible to reduce the size of the recircuJationary downtake. This results in a smaller pan vessel and saving in capital and other costs.

This invention also provides for a novel solution feed distribution system that is of particular relevance to vacuum pans incorporating one or more of the additional downtakcs of the invention. Said system comprises a header wherefrom a supply line extends across the pan in a generally diametrical orientation. A plurality of feed pipes extend, at first, radially and then downwards from said supply line. Said feed pipes extend down through the annular circular additional downtake of the invention and reach out into the graining region below the calandria.
In order to provide a clearer understanding of the invention and without limitation to the scope thereof an embodiment thereof is described hereinbelow with reference to the accompanying drawings wherein like numerals represent like parts and wherein:
Fig, 1 shows a cross-section of the vacuum pan of the invention,
Fig. 2 is a schematic diagram showing the additional downtake of the invention:
Fig, 3 shows the top view of the calandria showing the additional downtake of the invention.
Fig. 4 is a schematic showing the elevation of the solution feed distribution system of the
invention; and
Fig. 5 is a schematic of the plan of the solution feed distribution system of the invention
Reference numeral 4 of Fig. 1 denotes the pan vessel comprising the dished bottom part (2). the separation part(the middle part) (15) and the top dished part (16). Calandria (3) constitutes the said heater part and comprises tubes(17). the top tube-sheet(IR) and the bottom tube-sheet^ 19) The centra! hole(20) in the calandria(3) is the recircuiationary downtake of the pan through which solution flows down from the top to below the ca!andria(3). Central hole(downtake)(20) is circular in cross-section.

The solution feed inlet (21) is at the side of the vessel. It connects to feed header (7) from where the solution flows to a set of radial pipes, by means of which it is distributed uniformly over the vessel cross-section. The vapour outlet (9) is at the top. It connects to condenser (10) which may be a barometric condenser or a multi-jet condenser. Alternatively other means of providing vacuum may be used.
Save-all (8) is used to separate entrained liquid from the vapour stream and return it back the vessel. The vessel also comprises sight glasses(5) and light glasses(13) for illuminating the vessel interior for observation. Sampling of the massecuite in the pan is periodically done by means of proof-stick (6).
A bottom inlet (1) is provided at the bottom of the vessel for charging miscellaneous liquids into the pan. The steam enters the calandria (3) through steam inlet (11) and the condensate leaves through outlet (12). A pressure gauge (14) is provided for monitoring the steam pressure.
The pan of this embodiment described in detail herein comprises the additional downtake (22) of the invention. Downtake (22) is shaped like a circular hng and is in four parts, that is, it is provided with four breaks constituting the cross-overs (23) for free flow of the heating medium and condensate in the calandria interior. It will be noted that the said additional downtake (22) is a substantially complete nng as the said breaks are of quite small dimentsioiis. Another uay of looking at it is that the said pan comprises four arcuate additional dovvntakes of the invention.
In arriving at the location of said additional downtake the tube sheets were notionally divided into three regions A. B and C. The region A is circular in shape and is concentric with the calandria and the vessel. The area covered by A is about 12-13% of the total upper face area of the calandria. Regions B and C are circular ring-shaped and together they constitute about 86-88%

of the said total face area. Regions B and C are serviced by the concentric additional downtake (22)while the region A is serviced by the central downtake (20). When talking about servicing it may be noted that the intention is to convey that the indicated downtake provides the shortest path for the solution in the indicated region.
In the embodiment described in detail herein, the provision of the additional downtake (22) enhanced the circulation by between 25% and 35% and resulted in increase in pan throughput over a day by about 15% to 25%. Other benefits were a more uniform product crystal size and a better mixing of the massecuite in the pan.
Embodiments and variations other than the those described hereinabove are feasible by persons skilled in the art and the same are within the scope and spirit of the invention.

1 claim.
A vacuum pan for evaporation and crystallisation, comprising a vessel for holding the solution to be evaporated(concentrated), or to be evaporated(concentrated) and crystallised, and a calandria for heat transfer from steam or other heating medium to said solution through the tubes thereof, and wherein, during operation, said solution recirculates, moving down a recirculationary downtake and up through said tubes, said pan being characterised in having one or more additional downtakes provided for the purpose of reducing the travel distances involved in said recirculation.
The vacuum pan as claimed in the preceding Claim 1, wherein said one or more additional downtakes are located such as to substantially equalise the said travel distances for said solution from different regions of the calandria face.
The vacuum pan as claimed in the preceding Claim 2, wherein said face is considered to comprise three said regions, a central circular region covering about 10% to 15% of area of said face around the central recirculationary downtake thereof and two circular ring regions covering the remainder, that is, about 85% to 90% of said face area, said three regions being concentric with the said calandria.
The vacuum pan as claimed in the preceding claim 3, and comprising one said additional downtake that is in the form of a circular ring and is located substantially symmetrically between said two circular ring regions.
The vacuum pan as claimed in the preceding claim 4, wherein breaks arc provided along said circular ring-shaped additional downtake.

The vacuum pan as claimed in any of the preceding claims 1 to 5, wherein the feed system for said solution comprises a plurality of pipes/tubes that first extend radially and then downwards from substantially the centre of said pan.
A vacuum pan for evaporation(concentration) of solutions, or for evaporation(concentration) and crystallisation thereof, substantially as herein described with reference to and as illustrated in the accompanying drawings.


239-mas-2001 abstract duplicate.pdf

239-mas-2001 abstract.pdf

239-mas-2001 claims duplicate.pdf

239-mas-2001 claims.pdf

239-mas-2001 correspondence others.pdf

239-mas-2001 correspondence po.pdf

239-mas-2001 description (complete) duplicate.pdf

239-mas-2001 description (complete).pdf

239-mas-2001 drawings duplicate.pdf

239-mas-2001 drawings.pdf

239-mas-2001 form-1.pdf

239-mas-2001 form-13.pdf

239-mas-2001 form-19.pdf

239-mas-2001 form-26.pdf

239-mas-2001 form-4.pdf

239-mas-2001 form-5.pdf

Patent Number 211909
Indian Patent Application Number 239/MAS/2001
PG Journal Number 02/2008
Publication Date 11-Jan-2008
Grant Date 13-Nov-2007
Date of Filing 16-Mar-2001
Applicant Address H.NO. 31-3-17, MARUTHI NAGAR, VIJAYAWADA, KRISHNA DISTRICT - 520 004,
# Inventor's Name Inventor's Address
PCT International Classification Number C13G 1/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA