Cane Sugar Technology: 32. HISTORY OF EQUIPMENT AND PROCESS DEVELOPMENT

HISTORY OF EQUIPMENT AND PROCESS DEVELOPMENT

Mills:

Before mechanization vertical three-roller mill was commonly used up to start of 19^th century. The mills were driven by animal, wind or water power.

Fig.11.1 cane unloading by crane in1910

Fig 11.2 revolving cane equalizer in 1910

Collinge in 1794 first made a design of mill with three horizontal rollers arranged in triangle. In 1871, Rousselot, a French engineer, of Martinique made some improvement in the design. All the modern mills are based on this design. At the same time hydraulic loading of mill roller was also employed.

Fig 11.3 Mill with hydraulic pressure

Cranes were used for unloading the cane in 1910. Rotating knives to work as equalizer or leveler were introduced in 1870-72. The crushers and shredders were introduced in 1883 – 1887. However before 1920 there were many factories which were not having proper cane preparatory devices like cutters or shredder. Some factories were having crusher in place of cutter or shredder.

Fig.11.4 Mill design by Rousselot

The introduction of steam as motive power was implemented at the end of the 18^th century. Due to this fabrication of large size mills made possible. Three mill trains with use of imbibition water were installed in Louisiana and Australia in1892. Slow speed horizontal steam engine was standard method of driving the mills. Small steam turbines were used to drive the mills from 1947, which is now general in modern plants.

Noel Deerr in his book (1916) gives mill capacities as follows:

Diffusers:

The diffusion process as applied to the cane sugar industry first came into prominence about 1884, several of plants remain in successful operation. . In 1910 there were many plant working with diffuser. However some factories in Mauritius and Hawaiian Islands have reverted to milling because of faulty designs of difffuser, difficulty in constant even supply of cane, excess fuel consumption.

Fig.11.5 Diffuser

Juice clarification:

Use of phosphate for juice clarification was started in 1862 in USA. Mr Beans has teken the patent of it. Use of sulphur dioxide gas for cane juice clarification was first tried in the year 1865 in Mauritius. In 1905 Prinsen Geerling describes sulphitation process for clarification of cane juice.

Scientist Horlof first followed the process of hot liming and sulphitation at 70-75°C. It improved the precipitation of calcium sulphite and reduced the scaling problem in juice heaters. Hence this process is called as Horloff’s process.

Fig.11.6 Batch type defecators

Hundreds of different chemicals/substances have been tried as clarifying agents. Lime is being used for almost 2000 years. The other common substances phosphate/phosphoric acid and sulphur are being used in last about150 years.

The defecation process has been established in the mid of 19^th century. It was batch operation The juice was being treated with milk of lime being heated in open tanks to boil and allowed to settle. The supernatant clear juice was run off to evaporators. Continuous process started first in Australia in 1890.

Fig. 11.7 Defecation process

The above figure gives the defecation equipment and process followed. There are two horizontal juice heaters, one liming tank and a continuous clarifier.

Fig. 11.8 Hatton's automatic clarifier

The clear juice obtained was send to evaporator and the scum containing suspended solids was send to scum received in tanks where it was limed and allowed to settle, the clear supernatant liquor being decanted and added to the main juice. The scum then passed through the filter presses, the clear filtered liquor being passed to the evaporator.

Multi-tray subsiders or clarifiers of the Dorr type were introduced in West Indies in 1918.

Peter Honig started the use of pH measurement for better control over the process.

The modern continuous process has achieved a great reduction in the total capacity of settlers required as well as a vast reduction in labour requirement. Prototype SRI trayless clarifier was installed at Gin Gin sugar mill in 1969 designed for a crushing rate of 120t/hr. Now trayless clarifiers are commonly installed in mills.

Filtration of scum or muddy juice was carried out by filter presses or Taylor filter or sand filtration.

Rotary vacuum drum filter (RVDF), patented in 1872, is one of the oldest filters used in the industrial liquid-solids separation. It offers a wide range of industrial processing flow sheets and provides a flexible application of dewatering, washing and/or clarification. However use of rotary vacuum filter in sugar industry has started much late, in the mid of 20^th century.

Carbonation process:

The carbonation process, which is quite generally adopted in beet sugar factories, has only been applied to the manufacture of cane sugar in a few few factories in Java and India. This process gave bad results when first introduced into cane sugar factories owing to the presence of glucose in cane juice. However the efforts of Geerligs and Winter made the process practicable. By this process its direct consumption was manufactured.

However, Noel Deerr remarks that the best white sugars of Mauritius made by a defecation process combined with the use of sulphur and phosphoric acid are equal to any that he has seen prepared by the carbonation process. The single carbonation process was adapted to factories having inferior quality cane and is not adapted for making white sugars.

Evaporator:

In the original method of concentrating juice to form crystals was by boiling in shallow open pans with direct heating, either from an open fire or by means of fire enclosed in brickwork (Dutch oven). Use of steam was introduced at about 1800.

Multiple effect evaporation was invented by NORBERT RILLIEUX in Louisiana in 1844. Rillieux’s first patent showed two jacketed vacuum pans (Howard’s original pan) coupled together in double effect, i.e. the vapour from the first acting as heating medium to the second. The jacketed pans were soon replaced by evaporators with horizontal steam tubes. In 1851 the first vertical tube evaporator was introduced, from which modern designs have been developed. The principle was extended in turn from double to triple, quadruple and quintuple effect. In 1880 Rillieux announced the idea of bleeding vapours from the evaporators to replace steam at the vacuum pans. This practice is now extensively adopted.

The first multiple evaporator was invented in 1834 by Norbert Rillieux, of Louisiana, and was a double effect horizontal submerged tube apparatus. Evaporator sets conforming to his original design with some differences were in use. Noel Deerr has described seven different evaporator set in his book. Some of which were of horizontal tubes.Noel Deer has also described 'Long Tube Vertical Rising Film' what we now call as semikestner or kestner.

Fig.11.9 Triple effect evaporator

Kestener

Van Trooyen has given particulars of a Kestner quadruple at ‘Pasto-Viejo’ Porto Rico. Each body is a vertical cylinder 24 feet high and 3 feet 6 inches in diameter, made in two pieces with an expansion joint ; the separating chamber is 7 feet in diameter and 6 feet high, except in the last body where it is seven feet high. The heating surface of the first three vessels was consisting of 250 tubes, 23 feet long and 1½ inches outside diameter. The fourth vessel there were 130 tubes, also 23 feet long and 2¾ inches diameter.

Vacuum pans

Howard in 1813 has invented vacuum pan. this was really beginning of a new era. His name is also associated with the invention of the filter-press. Howard’s original vacuum pan was essentially the shallow pan with a cover, that make the pan airtight. The cover from the top was provided with vapour pipe condenser and vacuum pump. Vacuum was obtained by condensing the vapour given off by a jet of water allowed to gravitate down from an overhead tank. A steam jacket below the lower portion of the pan itself was for heating. Necessary accessories such as proof stick and sight glasses were also provided.

The heating surface provided by the jacket was found insufficient and coil pans with internal heating surface by providing spiral coils working on high pressure steam were developed.

In earlry years of 20^th century mostly were coil pans. The heating surface consists of a number of helical copper coils, reaching from the bottom to a little above the centre of the pan, and so arranged as to divide the heating surface as uniformly as possible. The coils were generally 4½ inches in diameter. They are supported by stay rods fixed to the side of the pan. Now coil pans are obsolete and not used in industry except for manufacture of bold sugar (खडीसाखर) in mini plants.

Fig. 11.10 Coil type pan

Latter on calandria pans also have been developed with modifications in vertical tube evaporator. Since 1930, systematic study of pan operation and performance has confirmed the importance maximum massecuite height in the pan to avoid excessive hydrostatic head. Attention has also been given on minimizing resistance to circulation of the massecuite, therefore modern low head pans are designed that give good performance with low pressure vapours.

Fig.11.11 vacuum pan

Crystallizers:

The receivers in which the massecuites were received in order to be cooled in motion are either U shaped or horizontal cylindrical vessels were called as crystallizing tanks. Crystallisation in motion was first described in a patent by WULFF in Germany in 1884. A shaft fitted at both ends passing horizontally through the centre of the vessels is attached the stirring arrangement with worm gears. The crystallizing tanks are made either plain or provided with a jacket, into which hot /cold water can be admitted. So that massecuite cooing rate can be controlled. The use of crystallizers provided with stirring equipment has gradually become general. However the development was slow. With modifications in the old designs various types of crystallisers using water cooling elements have been introduced since 1930.

Fig. 11.12 crystallizer

Centrifugals:

In old days, the separation of massecuite into sugar crystals and mother liquor was carried out by pouring the massecuite into perforated cast-iron vessels. The molasses dripping conducted with holes while sugar crystals were washed by pouring sugar solution. Mother liquor / molasses was separated by force of gravity. The centrifugal machines that were being used in textile industry was tried in sugar industry. Noel Deerr has described the centrifugals as one of the world’s great inventions. He mentioned that centrifugals were perhaps introduced into the sugar industry in 1849, by Dubrunfaut. David Mecolley Westton a Scottish engineer working in Hawaii in 1852 patented a design of centrifugal with flexible suspension. This design then became standard. There were two different type - fixed bearing and suspended pattern ; again they were divided into under and over-driven machines, or according to the method of driving, direct coupled, friction cones, belt, electric, or water drive.

Fig.11.13 A battery of centrifugals

The sugar hoppers and elevators were in use in the industry from the end of 19^th century.

Since beginning of the sugar industry bagasse is being used as fuel in sugar industry, both for sugar boiling and power generation. Originally bagasse was burned after air / sun drying. The first boiler furnaces designed for burning bagasse straight from the mills were introduced in Cuba in about 1880.