Pulping operations washing

In a chlorine bleach operation, the unbleached pulp is mixed with gaseous chlorine at 3% to 5% air dry pulp. After about 1 hour, sodium hydroxide is added to extract the dark colored material the chlorine has liberated. The extracted pulp is washed and dewatered, and then bleached with either chlorine dioxide or sodium hypochlorite. Extractions with sodium hydroxide alternate with the chlorine dioxide or hypochlorite until the pulp achieves the desired brightness without sacrificing too much strength. The pulp is washed, cleaned, screened and sent to storage or the paper mill. 

Up to 0.4 g/L of the iodine stays in solution and the rest precipitates as crystallized iodine, which is removed by flotation (qv). This operation does not require a flotation agent, owing to the hydrophobic character of the crystallized element. From the flotation cell a heavy pulp, which is water-washed and submitted to a second flotation step, is obtained. The washed pulp is introduced into a heat exchanger where it is heated under pressure up to 120°C to melt the iodine that flows into a first reactor for decantation. From there the melt flows into a second reactor for sulfuric acid drying. The refined iodine is either flaked or prilled, and packed in 50- and 25-kg plastic-lined fiber dmms. 

In the wet method, as practiced in Colombia, freshly picked ripe coffee cherries are fed into a tank for initial washing. Stones and other foreign material are removed. The cherries are then transferred to depulping machines which remove the outer skin and most of the pulp. However, some pulp mucilage clings to the parchment shells that encase the coffee beans. Fermentation tanks, usually containing water, remove the last portions of the pulp. Fermentation may last from twelve hours to several days. Because prolonged fermentation may cause development of undesirable flavors and odors in the beans, some operators use enzymes to accelerate the process. 

The pulp recovered during screening may be transferred to a pulp-wash operation to yield further soluble solids by counter-current extraction with water. The washed pulp may be held for further processing or included with the bulk of ejected peel material from the extractors. This is milled, treated with lime (calcium hydroxide or calcium oxide) to break down pectin and reduce water retention, pressed, dried to c.10-12% moisture content and finally converted to pellets. Being high in carbohydrates these are used as filler in livestock feed blends. 

The FMC In-Line Extractor is widely used in the domestic industry, most particularly in Florida, because it can effect simultaneous recovery of both juice and oil. A five-headed extractor can process from 325 to 500 fruit/minute. The extractor consists of a bottom cup, into which the fruit is fed, and an upper cup that meshes with the bottom as circular plugs are cut from the top and bottom of the fruit. The fruit in the bottom cup is compressed as the upper cup descends and juice and other fruit components are forced through the bottom plug into a strainer tube. The contents of the strainer tube, rag, seeds, and cell sacs, are squeezed between the top and bottom plugs resulting in almost complete extraction of juice and, in essence, a first-finishing operation since the plug (seeds, pulp, and peel) is separated from the juice. As the fruit is squeezed in the cup, peel oil expressed from the flavedo and small pieces of peel are washed into a conveyer by a water spray that surrounds the extractor cup. The valuable oil is recovered from the oil/water slurry. 

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