Sugarcane juice extraction
JUICE EXTRACTION
After weighing, sugarcane is loaded by hand or crane onto a moving table. The table carries the cane into one or two sets of revolving knives, which chop the cane into chips in order to expose the tissue and open the cell structure, thus readying the material for efficient extraction of the juice. Frequently, knives are followed by a shredder, which breaks the chips into shreds for finer cane preparation. The chipped (and shredded) cane then goes through the crusher, a set of roller mills in which the cane cells are crushed and juice extracted. As the crushed cane proceeds through a series of up to eight four-roll mills, it is forced against a countercurrent of water known as water of maceration or imbibition. Streams of juice extracted from the cane, mixed with maceration water from all mills, are combined into a mixed juice called dilute juice. Juice from the last mill in the series (which does not receive a current of maceration water) is called residual juice.
The alternative to extraction by milling is extraction by diffusion. In this process, cane prepared by rotating knives and a shredder is moved through a multicell, countercurrent diffuser. Extraction of sugar is higher by diffusion (an average rate of 93 percent, compared with 85–90 percent by milling), but extraction of nonsugars is also higher. Diffusion, therefore, is most used where cane quality is highest—e.g., in South Africa, Australia, and Hawaii. Occasionally a smaller “bagasse diffuser” is used in order to increase extraction from partially milled cane after two or three mills. (Residual cane fibre, after juice is removed, is called bagasse.)
Disposal of the large amounts of water used by diffusers is a costly environmental problem, as cane factories that practice diffusion must operate their own primary, secondary, and tertiary water-treatment systems.
After weighing, sugarcane is loaded by hand or crane onto a moving table. The table carries the cane into one or two sets of revolving knives, which chop the cane into chips in order to expose the tissue and open the cell structure, thus readying the material for efficient extraction of the juice. Frequently, knives are followed by a shredder, which breaks the chips into shreds for finer cane preparation. The chipped (and shredded) cane then goes through the crusher, a set of roller mills in which the cane cells are crushed and juice extracted. As the crushed cane proceeds through a series of up to eight four-roll mills, it is forced against a countercurrent of water known as water of maceration or imbibition. Streams of juice extracted from the cane, mixed with maceration water from all mills, are combined into a mixed juice called dilute juice. Juice from the last mill in the series (which does not receive a current of maceration water) is called residual juice.
The alternative to extraction by milling is extraction by diffusion. In this process, cane prepared by rotating knives and a shredder is moved through a multicell, countercurrent diffuser. Extraction of sugar is higher by diffusion (an average rate of 93 percent, compared with 85–90 percent by milling), but extraction of nonsugars is also higher. Diffusion, therefore, is most used where cane quality is highest—e.g., in South Africa, Australia, and Hawaii. Occasionally a smaller “bagasse diffuser” is used in order to increase extraction from partially milled cane after two or three mills. (Residual cane fibre, after juice is removed, is called bagasse.)
Disposal of the large amounts of water used by diffusers is a costly environmental problem, as cane factories that practice diffusion must operate their own primary, secondary, and tertiary water-treatment systems.