Nov., 1921
T H E J O U R N A L OF INDUSTRIAL A N D ENGIA’EERISG C H E M I S T R Y
Oliver Continuous Filters By H. A. Morrison OLIVER CONTINUOUS
FILTER CO , 33
WEST 4
2 S T~ , K ~E W
YORK,
h-.Y .
Different types of Oliver Continuous FiIters are manufactured for various purposes: ST.%NDARD-For materials that do not attack wood, iron or steel. The tank is usually of steel, though redwood, pineor cypress may be substituted. Iron vacuum pipe, copper, steel or wood screen and cotton or wool filter cloth are used. CAusTrc-For all concentrations of caustic solutions. Cast iron arid steel are employed throughout, but the latter is to be preferred by reason of lighter weight. Cotton cloth is used on very weak caustic ( 2 per cent or less), but woven monel metal cloth is entirely satisfactory and remarkably resistant to any strength of caustic, and is in general use in the stronger solutions. Caustic filters are provided with wash apparatus and are arranged to separate the filtrate into either two or three fractions as desired. The separation is made entirely automatic without unduly complicating the unit. CAST IRON-For products such as sodium bicarbonate and ammonium nitrate, which attack steel. They are built with oscillating agitator only and the filter tanks may be jacketed for steam heating. ACID RESISTING-POT handling acid or corrosive solutions, built t o secure maximum resistance to corrosion compatible with mechanical strength. The tanks are built of redwood, lead, copper, monel or rubber-lined steel, reinforced with lead covered rods. All parts of drum in contact with sludge are of wood and have ends enclosed in wood, lead or monel. Vacuum pipes are of lead, copper, monel or hard rubber. Screens of wood, lead, copper, bronze, monel or rubber coated metal support the filter medium, which may be cotton, wool, woven monel, spun glass or asbestos. Copper, phosphor bronze, silicon bronze or monel wire winding is used. Automatic filter valves are of bronze, antimonial lead, monel, aluminium or rubber. Special machines, such as an all-monel type, are built to meet unusual conditions.
PRINCIPLES IWOLVED The underlying principle upon which the success of this filter rests is that of forming a comparatively thin cake (averaging 0.5 in.), followed by rapid washing and drying; and automatically effecting a complete discharge of this cake with a thorough cleansing of the filter medium after each cycle. Careful regard must be given the following points, if the drum filter is to take its rightful place in technical operations: 1-Maximum capacity is secured by building a cake that is just sufficiently thick to be discharged easily. However, dryness of cake or thoroughness of wash are frequently the determining factors as to speed. 2-The sludge to be filtered must be kept homogeneous by suitable agitation so that solids will not settle. 3-Pulp level must be maintained constant in the filter tank. $-Excessive cracking of cake due to shrinkage must be prevented by even distribution of wash water, or by use of canvas drag or flapper, regulation of vacuum, etc. &Vacuum best suited to material being handled must be maintained. Frequently lower vacuum is maintained on the submerged portion of the drum than is carried on the washing and drying portions of the cycle, or vice versa, in order to secure proper ratio between thickness of cake and quantity of wash water or drying time. &Uniform conditions of concentration, temperature, and rate of flow must be maintained to secure maximum efficiency. 7-Automatic discharge of cake by means of low pressure air or steam or both will perfectly clean the filter medium each time a section is discharged. If patches are allowed to remain on the doth, capacity will decrease, washing efficiency will fall, and cake rnoistures will increase. The success of the continuous wire wound drum filter has hinged largely upon this feature. USES
Granular, finely divided solids suspended in cold water with c&e-forming solids amounting to 15 t o 25 per cent of the weight of the mixtures constitute ideal feed for this filter. Cornstarch is an excellent example, and finely ground, clean quartz ore is another.
100.3
The filtjer is in no sense restricted to ideal conditions. Among the more important commercial uses may be mentioned ores and ore concentrates, pulverized coal, foodstuffs including beet sugar, cornstarch and glucose, heavy chemicals such as phosphoric acid and caustic soda, wood pulp in paper manufacture, aniline and other dyes and intermediates, notably P-naphthol and H-acid, edible oils such as cottonseed and coconut, lubricating and fuel oils, explosives including guncotton, and many others. Pineapple and other fruit juices are being clarified. No one can decide by superficial examination whether or not a given filtration can be successfully made on this machine, unless identical material is already being satisfactorily handled. Careful and comprehensive testing is essential with particular attention to temperature, proportion of suspended or cake-forming solids, permeability of cake, chemical composition of solution, specific gravity of both solids and liquid, and extent of cake cracking while drying under vacuum. The use of two filters in tandem for recovery of cawtic from lime mud is coming to be regarded as standard practice. Double filtration takes advantage of countercurrent washing as effecting marked economy in wash water volume, with consequent increased concentration in the resulting filtrate. Clarification of glucose sirup is interesting because in this case a very slight percentage (about 0.35 per cent) of cooked gluten is removed from 18’ BB. glucose a t a temperature only slightly below the boiling point (190’ F.). An inert material, possessing good filtration characteristics, is automatically added to the glucose as it enters the filter. This increases the permeability of the gluten cake enormousIy. Repulping and constant return of all but 1 per cent of the cake being discharged, maintain8 the proper density in the filter tank a t all times and permits high capacity in terms of filtrate. Special filters having 60 to 70 per cent of the cloth constantly submerged have been developed for glucose filtration. Vegetable carbons are gaining ground against bone-black for decolorizing sugar juices, and the necessary agitation and contact are best secured on a series of continuous filters. Countercurrent methods are used here and the carbon travels through the system in a direction opposite to that taken by the juice. This results in enormous reduction in the amount of carbon locked up in process and greatly reduces floor space required. Washing of wood pulp for recovery of cook liquor has only recently been perfected on a working scale. This application now bids fair to become the most notable improvement in the paper industry during recent years. It is frequently contended that continuous filters sometimes fail to make a clean filtrate. Proper choice of filter medium, reduction of vacuum during the early stage of cake building, and careful regulation of air or steam pressure while discharging cake, all assist toward producing clean filtrates. Regulation of vacuum on different portions of the cycle provides flexibility and ease of adjustment to suit changing conditions. Both gypsum in acid solutions and lime carbonate in caustic solutions build cake rapidly, and thickness of cake must be regulated by decreasing vacuum on the cake-forming portion of the cycle in order that washing and drying may proceed under the high vacuum essential to best results. From a cake-forming standpoint, the filtration of gluten presents the reverse case since high vacuum on the submerged portion of the cloth makes the first portion of cake extremely compact, thus reducing capacity. The filtration,of cold saccharate of lime is in strong contrast also, since high vacuum (24 in.) is used on “pick up”
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THE JOURNAL OF IRiDUSTRIAL A N D ENGIhTEERING CHEMISTRY
1006
or cake-forming period in order to form cake of maximum thickness, whereas vacuum is reduced on portion of drum above pulp level in order to prevent cracking of the extremely delicate cake of trisaccharate of lime which washes rapidly under low vacuum. ADVA~L'TAGES 1-Continuous and aut,omatic-no break in the cycle of formation, washing, drying, and discharge of cake. 2-All stages under constant observation. 3-Flexibility of adjustment permits handling products of widely divergent nature by changes in ( a ) cloth, (b) drum speed, [c) percentage of submergence, ( d ) regulation of vacuum, (e) position of blow, (f) temperature of feed. &-Results uniform under any given conditions. %-Less wash water needed to secure high purity in niaterial being washed. 6-Personal factor largely eliminated. 7-Economy of floor space. 8-Power input is small per unit of work accomplished. %-Savnig in filter cloth. 10-Reduction in labor.
Vel. 13, No. 11
Power is applied through appropriate gear trains to the plow shaft for actuating the plows, to the hubs for actunting these parts as a function of thed umping operation and for the regulated feed of the plows through the cake. OPERATION The material to be filtered is delivered to the press by pump, monte-jus, or gravity, until a full cake is formed. The cake is washed or blown by switching the connection to the medium to be used for this purpose. The valve controlling the delivery of the cake from the press is nom opened and power is applied to the hubs and plow shaft.
LIMITATIONS I-Will not remove liquid contained or absorbed inside the individual particles of solids being filtered. Such materials cannot be filtered but must be pressed or squeezed to remove the contained liquid. 2-Finely divided solids of colloidal nature, especially when contained in relatively large volumes of liquor, must be thickened before filtration. 3-Cannot handle products that form explosive or inflammable gases under vacuum. 4-Structurally unsuited to handle the stronger acidshydrochloric, nitric, hydrofluoric, etc. &Cannot operate a t temperatures above 200' F. 6-Unsuited for dewatering products that form an extremely impervious cake, except when admixture of inert filter aids, such as silica, sawdust, fine coal, calcined clay, etc., is permissible.
The Atkins-Shriver Automatic Filter Press By H. D. Atkins T.SHRIVER
&
CO.,HAMILTON ST.,
HBRRISON,
N. J.
The automatic filter press is a modified form of the circular center feed press. The automatic feature lies in the method provided for removing the cake. This consists of a number of plows corresponding to the number of filtering chambers, fastened to a shaft passing through the center opening in the plates. This shaft is carried in bearings mounted near the outer edge of hubs which are fitted into bearings in the head and follower. The center openings in the plates are large enough to receive the plows and shaft assembled as a unit, and a t the same time to permit the cake to drop through the same opening by gravity as it is removed from the chambers by the plows. The hub that is mounted in the follower has an opening through its center to permit the passage of the cake from the press. The filtering unit is arranged to swing on trunions having bearings in the leg supports. This permits swinging the unit to horizontal position for dressing, cleanihg, and making repairs, nnd to vertical position while the press is in operation. The press is fed a t the bottom and the cake is delivered through the opening in the hub mounted, in the follower. These openings are controlled by valves.
ATKINS-SHRIVER PLATE
AND
P L O W ARRANGEMENT
Inasmuch as the bearings for the plow s h d t are located near the outer circumference of the hubs, the shaft is carried bodily around the opening in the plates while the plows are moved in an expanding spiral. The points of the plows move gradually into the chambers, cutting a uniformly thick slice from the cake until the entire chamber is cleared, except for a thin layer that is left on the cloths. The leading faces of the plows direct the layers of cake removed to the center opening through which if falls out of the press. During the pumping operation the plows travel through an arc of about 100" from their starting position within the center opening until they are returned to this position. Upon completion of the dumping operation, the cycle of filtering and dumping is repeated without opening the plates and frames. If the thin layer of cake left on the cloths by the clearance given the plows interferes with efficient filtering, this residue may be cleared off by water, air or steam, applied to the back of the cloths through appropriately arranged connections and parts. During this operation the plows may be moved into the chambers while the cloths are held away from the plates by the pressure. The cake thus removed may be directed back to the material being filtered. The length of a cycle of operations depends upon whether the material being handled is free filtering, but this time may also be varied in the original design of the press by varying the depth of cut made by the plows and by regdating the thickness of the frames. APPLICATION The design and operation of the press are favorable to any free-filtering material that may be handled by any metal press. On account of the first cost of the press it &odd be employed in large units handling large tonnage.
