Sugar production and the
multiple effect evaporator


Sugar cane had been planted as early as 1750 near New Orleans, but with only limited success. Throughout most of the eighteenth century indigo, a blue dye, was Louisiana’s cash crop, but the ravages of disease and insects forced planters to look for alternatives. By the 1790s, interest in sugar revived. Production rose steadily thereafter, and by 1830 Louisiana was producing over 33,000 tons of sugar annually.

Sugar cane is normally harvested in the fall. After cutting, the cane is milled to produce sugar cane juice. Originally animal power was used to grind the cane; by the 1830s, steam power began to replace animal power. In either case, the cane juice was boiled in four large open kettles arranged in a kettle train. Each kettle was of different size, and the kettles were arranged from the largest, which held up to five hundred gallons, to the smallest. The first kettle, the largest one, was called the grande, the next the flambeau, then the sirop, and finally, the smallest, the batterie.

In the first kettle, the grande, the juice was brought close to the boiling point, and, as water boiled off, teams of slaves ladled the resulting concentrated sugar syrup to the next kettle. The process was repeated from the flambeau to the sirop kettles. When the syrup thickened and reached the proper quality and density, it was transferred to the batterie. Additional manpower was needed at each step in the process, which was repeated over and over. As soon as one kettle was emptied, its contents were replenished with juice from the kettle that preceded it in the train.

The sugar maker oversaw the syrup boiling in the batterie. When it reached the proper temperature and the right consistency, he would make a "strike." At that moment, when the boiling mass began to produce sugar crystals, the sugar maker ladled the syrup into vats to cool. If the strike occurred at the right time, the syrup would crystallize; if not at the right time, the syrup would cool into a mass of worthless molasses.

This process, the Jamaica train, was primitive because it required the constant attention of teams of slaves performing tedious, backbreaking, and dangerous manual labor; wasteful because much sugar was lost in the process; and inefficient because each kettle required its own source of heat, usually wood, and because the heat could not be regulated. Various attempts, with only partial success, had been made to harness the energy of the steam rising from the boiling juice to heat the liquid in the next step in the refining process.

Norbert Rillieux’s great innovation was his understanding of how latent heat could be used repeatedly in processing sugar. The result was his Multiple Effect Evaporator under Vacuum, which one expert, John Heitman in The Modernization of the Louisiana Sugar Industry, 1830-1910, called "the premier engineering achievement in nineteenth-century sugar technology." Others have described Rillieux’s design as revolutionizing the sugar industry much as Eli Whitney’s gin revolutionized the processing of cotton.

Rillieux utilized the latent heat produced from evaporating sugar cane juice by employing a series of three or four closed evaporating pans in which vapor was piped out of each pan to heat the juice in the next, with the vapors in the end going to a condenser. At the same time, pressure in the system was reduced by pumps, which created partial vacuums and lowered the boiling point of the liquid. A description of the invention’s design is given in Rillieux’s 1846 patent:

A series of vacuum pans, or partial vacuum pans, have been so combined together as to make use of the vapor of the evaporation of the juice in the first, to heat the juice in the second and the vapor from this to heat the juice in the third, which latter is in connection with a condenser, the degree of pressure in each successive one being less… The number of sirup-pans may be increased or decreased at pleasure so long as the last of the series is in conjunction with the condenser.

 


Rillieux’s invention allowed for the production of better quality sugar with less manpower and at reduced cost. One of the major economies was the conservation of fuel, because wood was needed to heat only the first chamber. Each successive chamber used the latent heat released by steam from the preceding chamber. But even though the Rillieux evaporator marked a significant advance in sugar technology, some antebellum Louisiana planters were reluctant to install the devices.

The reasons had to do with the inherent contradictions in slavery. Many planters thought slaves incapable of operating sophisticated equipment. Other planters believed that teaching slaves new skills might lead to their questioning authority, which in turn could lead to rebellion. One slaveholder, Andrew Durnford, himself a free black, refused to install a Rillieux evaporator because he did not want to "give up control of his people."

In the end, however, sugar manufacturers around the world in Cuba, Mexico, France, and Egypt, as well as the United States, adopted Rillieux’s evaporator. Moreover, the device was not limited to sugar production but came to be recognized as the best method for lowering the temperature of all industrial evaporation and for saving large quantities of fuel. Multiple effect evaporation under vacuum is still used in sugar production as well as in the manufacture of condensed milk, soap, glue, and many other products.

The Rillieux evaporator was one of the earliest innovations in chemical engineering and remains the basis of all modern forms of industrial evaporation. It is perhaps most extraordinary that Rillieux invented his device before the Civil War, at a time when the vast majority of African Americans were enslaved. He was successful because he understood the principles of thermodynamics and latent heat and applied that knowledge to the technical needs of the sugar industry.

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A revolution in sugar processing | Norbert Rillieux: chemist and engineer | Sugar production and the multiple effect evaporator | Neither slave nor free | The Degas connection | Landmark designation | Further reading

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