1270
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 15, No. 12
Automatic Char-Filtration Apparatus' By W. D. Horne and E. W. Rice NATIONAL SUGAR REFINERY,YONKERS, N. Y.
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N COMPARIKG the values of samples of bone black for sugar filtration it is customary to run comparative filtration tests. Similar filtration experiments are of great practical value in comparing some of the properties of sugars themselves, as well as varying methods of treatment. Thus, the effects of the reaction of the solution, its time of contact, concentration, temperature, the ratio of char to sugar solids, the shape and proportions of the filter, the depth of char, and other factors are all occasionally to be considered. I n applying these tests it is desirable that the conditions be such that results obtained experimentally on a small scale shall be interpretable as far as possible into refinery practice on a working scale. Among the house conditions required to be simulated in the laboratory, that of length of time of contact has been one of the most inconvenient ones to arrange, as the bone black in refinery practice is usually in contact with flowing sugar solution for many hours, and a laboratory test, to be most accurate, should provide this feature as well as others. Hence the need of some automatic device to feed a sugar solution steadily upon the char, to draw it off with sufficient regularity, and t o segregate the successive portions of the filtrate in individual containers. It is the purpose of this paper to describe such a device, as briefly as possible, omitting details of the various trials leading up to the satisfactory accomplishment. The apparatus devised consists of three main divisions. The central feature is a set of copper tubes properly held in a vertical position in a water bath, the temperature of which is regulated by a thermostat. The filter tubes for containing char have smaller bottom tubes passing through the bottom of the bath which are provided with cocks. There is a wire gauze in the bottom of each filter, overlaid by a disk of cloth. The determined amount of char (a few hundred grams) having been placed in the filter, the determined number of grams of sugar solids in solution are run through the char in the required time. If the size of the filter is to be kept within convenient dimensions, a rate of flow which is so slow as t o be difficult to provide in any ordinary manner is sometimes necessary. This difficulty is met by the second part of the apparatus, the feeding device. The feed is accomplished by a cylindrical container in the top of which is an inverted bottle containing the sugar solution to be used. This provides a reasonably constant head of the liquid in the cylinder, for the solution flows out of the bottle into the cylinder until it rises high enough to close the end of the feed tube, after which the level is automatically controlled to within about 1.5 mm. while the bottle is nearly full, and to within about 5 mm. when it is nearly empty. These slight variations of head are negligible, for, while they may cause a very small variation in rate of flow as between the moments before and after any individual de1 Presented before the Division of Sugar Chemistry a t t h e 66th Meeting of t h e American Chemical Society, Milwaukee, Wis., September 10 t o 14, 1923.
livery of solution from the bottle to the cylinder, the rate of flow considered as a whole remains constant. From the bottom of the cylinder runs a small, rubber feed pipe connected with a fine copper tube 35 cm. long and of 1.5 mm. internal diameter, forming a gooseneck, the top level of which is carefully set in reference to the level of the liquid in the cylinder so as to give the required hydrostatic head and rate of flow. The long, narrow tube is essential to produce enough frictional resistance to allow an appreciable head for the solution in the cylinder. From the gooseneck the solution drips very slowly into a glass tube leading into the filter. It would be simpler, were it practicable, to feed from an inverted bottle directly into the char filter, and regulate the rate of flow by adjusting the level of the gooseneck tube leading to the distributing device, but it has been found that, owing to the disengagement of air from the char or other causes, a very slow constant rate of flow through the char could not be maintained. By having the independent feed described above, the level of the liquid will rise in the filter, if the flow ceases, until the increased head sets the flow into operation again. The third part of the apparatus is the distributor which properly cares for the char filtrate. After the dripping liquid has gradually filled up the filter to a point a little above the char level, the filtered solution begins to overflow through an external tube and gooseneck into the distributing device. The distributor is a brass tube about 30 cm. long and of 6 mm. inside diameter attached vertically by a clamp to the outside of the water bath that holds the filters, and has a t its lower end a series of 1.5-mm., short metal tubes radiating from it a t differences in height of about 1 cm. The filtrate dripping into the brass tube flows slowly out of the lowest of these radiating tubes into a 100-cc. bottle. The neck of this bottle is closed by a stopper through which passes a fine brass tube that connects very closely end to end with the lowest radiant tube by means of rubber tubing. Through the collecting stopper passes vertically a second brass tube 10 cm. long, the lower end of which stands a t the level where the filtrate is to be stopped. When the first collecting bottle becomes full, the filtered solution from the char collects in the vertical brass distributing tube until its level rises 1 cm. when it begins to flow into the second collecting bottle. This operation continues through the cycle of as many bottles as desired. I n order to insure certain passage of the filtered liquor through these fine tubes leading to the bottles, it is well a t the assembling of this part of the apparatus to moisten 'the inside of the various single tubes with water to decrease resistance to the first flow of sugar solution. Care should be taken, however, that the air outlet tubes from the bottles contain no drops of water to cause back pressure.
Effect of Sea Water on Glass The Bureau of Standards has conducted an investigation on the effect of sea water on various types of glass to determine the best kind to use for the lenses of signal lights on ship board. From the data secured, the damage which these lenses oftensuffer appears to be caused by the evaporation of sea spray, which leaves a deposit of salt on the surface of the lens. This e.ventually etches the glass. Three types of glass-borosilicate, lead glass, and ordinary soda-lime glass-have been investigated. Under the conditions of the test, lead glass etched considerably, while the other two did not.
