Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Reexamination Certificate
1999-05-25
2001-01-23
Brunsman, David (Department: 1755)
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
C127S012000, C127S050000
Reexamination Certificate
active
06176935
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the field of sugar refining, and provides a system and method which improves the efficiency of the refining process.
Raw sugar is obtained by extracting the juice from sugar cane, and processing the juice to produce sugar crystals. The raw sugar is light brown in color, due to the presence of color bodies in the crystals. The color of the crystals is determined by the content of organic chemicals in the sugar. A primary object of the refining process is to convert the raw, brown sugar into white sugar.
A major component of the sugar refining process is known as carbonation. In the carbonation step, carbon dioxide is added to raw sugar which has been dissolved to form a clarified liquor. The carbon dioxide reacts with calcium in the sugar to form calcium carbonate (CaCO
3
). The calcium carbonate precipitates out of the sugar, and takes with it a large proportion of the color bodies. In fact, in a single carbonation step, more than 60% of the coloring matter may be removed. The precipitate can then be removed by filtration. The carbonation step may be repeated, or it may be followed by additional refining steps, such as treatment with activated carbon. These further steps can remove most or all of the remaining color bodies.
The carbonation step may be enhanced by adding lime (CaO) to the reactor which contains the raw sugar. The lime provides more calcium than that which is naturally found in raw sugar or sugar cane. The lime thereby enhances the production of calcium carbonate by providing more calcium atoms to react with the applied carbon dioxide, according to the reaction
CaO+C
0
2
→CaCO
3
.
Because carbonation is the major step in removing coloring matter from raw sugar, it is important to maintain a reliable source of carbon dioxide in a sugar refinery. The reliability of the source of carbon dioxide is a major determinant of the productivity of a sugar refining plant. If the supply of carbon dioxide is curtailed, the entire operation of the plant is correspondingly limited.
Various methods of providing carbon dioxide have been used in the sugar refining industry. A typical approach is to derive carbon dioxide from the effluent of the exhaust of a boiler. A sugar refinery includes a boiler which provides steam which heats the contents of the reactor, thereby increasing the rate of the sugar-refining reactions. The boiler exhaust is itself a source of carbon dioxide. It has therefore been known to recover the boiler exhaust, to purify it (such as by use of a gas scrubber), and to use the purified stream in the above-described sugar-refining reactions. If the fuel for the boiler is natural gas, which is the usual fuel in such applications, the boiler exhaust will contain about 6-9% carbon dioxide, by volume. If some other fuel is used (such as coke, propane, heavy oil, or fuel oil), the percentage of carbon dioxide could be outside of the above range.
The major disadvantage of using the boiler exhaust as a source of carbon dioxide is that if a problem with the boiler develops, it may be necessary to reduce the boiler output. In the latter case, the supply of carbon dioxide is thereby reduced, thus affecting the operation of the entire plant. Similarly, if the purity of the fuel decreases, less carbon would be available for combustion, and the amount of carbon dioxide produced would be correspondingly reduced. The latter occurrence is quite possible where the boiler is fueled by natural gas, because the purity of a natural gas stream may vary continuously over time.
The risk of an interruption in the carbon dioxide supply, due to a problem with the boiler, or due to fluctuations in the purity of the fuel, can be offset by providing a backup source of carbon dioxide on the premises. But providing such backup, which could require storage of large tanks of compressed gas or liquefied gas, is inconvenient and expensive. For this reason, the usual approach is to reduce production when there is an interruption in the source of carbon dioxide.
Another solution, proposed in an article entitled “The use of pure CO
2
in the sugar industry”, Sakharnaya Promyshlennost (1973), is to treat chemically the flue gases from the boiler so as to produce pure carbon dioxide for use in the refining process. The above-cited article suggests treating the flue gas with monoethanolamine, which absorbs carbon dioxide, and later desorbs it, thereby providing pure C
0
2
for use in carbonation. While the latter system works, it is expensive, as it requires the additional steps of handling chemicals. Moreover, most existing installations do not have the capability of processing sugar rapidly enough to justify the use of pure carbon dioxide. Thus, for most sugar refineries, the use of pure carbon dioxide would be unduly expensive relative to the benefit conferred.
The present invention provides a system and method which substantially increases the efficiency of a sugar refining plant. The present invention requires no special chemicals, and can be conveniently used with existing refining plants to increase their productivity.
SUMMARY OF THE INVENTION
In the system of the present invention, flue gases from a boiler are first scrubbed, and then passed through a gas separation membrane module. The membrane module contains a plurality of gas-permeable polymeric membranes which are chosen for their ability to separate carbon dioxide from other gases. After the gas has passed through the membrane module, the concentration of carbon dioxide in the stream is increased to about
20
% by volume. This stream is then injected into a reactor containing raw sugar, to perform the step of carbonation, and thus to remove most of the coloring matter from the raw sugar.
In the preferred embodiment, the boiler used as the source of carbon dioxide is the same boiler used to produce steam which drives the reaction. Thus, the present invention uses exhaust from an already existing boiler, and efficiently converts that exhaust into a usable source of carbon dioxide.
The present invention therefore has the primary object of improving the process of sugar refining.
The invention has the further object of providing a sugar refining process which includes a reliable means of supplying carbon dioxide for use in a carbonation step.
The invention has the further object of providing an improvement to a sugar refining system, wherein the improvement can be easily incorporated into existing refineries.
The invention has the further object of reducing or eliminating the need for an auxiliary supply of pure carbon dioxide, in a sugar refining plant.
The invention has the further object of improving the efficiency and throughput of a sugar refining process.
The invention has the further object of minimizing interruptions to production in a sugar refining plant, by providing a steady and reliable source of carbon dioxide.
The invention has the further object of providing a stream of carbon dioxide, for use in a sugar refining process, wherein the carbon dioxide is provided without using special chemicals.
The reader skilled in the art will recognize other objects and ad- vantages of the present invention, from a reading of the following brief description of the drawings, the detailed description of the invention, and the appended claims.
REFERENCES:
patent: 5480490 (1996-02-01), Toth et al.
patent: 6085549 (2000-11-01), Daus et al.
Abstract of article “The use of pure CO2in the sugar industry”, Sakharnaya Promyshlennost Journal, (1973) No Month Provided VNIISP, USSR.
Brunsman David
Eilberg William H.
MG Industries
LandOfFree
System and method for refining sugar does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for refining sugar, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for refining sugar will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2555732